Analysis of performance degradation in an electron heating dominant H-mode plasma after ECRH termination in EAST

NASA Astrophysics Data System (ADS)

Du, Hongfei; Ding, Siye; Chen, Jiale; Wang, Yifeng; Lian, Hui; Xu, Guosheng; Zhai, Xuemei; Liu, Haiqing; Zang, Qing; Lyu, Bo; Duan, Yanmin; Qian, Jinping; Gong, Xianzu

2018-06-01

In recent EAST experiments, significant performance degradation accompanied by a decrease of internal inductance is observed in an electron heating dominant H-mode plasma after the electron cyclotron resonance heating termination. The lower hybrid wave (LHW) deposition and effective electron heat diffusivity are calculated to explain this phenomenon. Analysis shows that the changes of LHW heating deposition rather than the increase of transport are responsible for the significant decrease in energy confinement (). The reason why the confinement degradation occurred on a long time scale could be attributed to both good local energy confinement in the core and also the dependence of LHW deposition on the magnetic shear. The electron temperature profile shows weaker stiffness in near axis region where electron heating is dominant, compared to that in large radius region. Unstable electron modes from low to high k in the core plasma have been calculated in the linear GYRO simulations, which qualitatively agree with the experimental observation. This understanding of the plasma performance degradation mechanism will help to find ways of improving the global confinement in the radio-frequency dominant scenario in EAST.

Physics and potentials of fissioning plasmas for space power and propulsion

NASA Technical Reports Server (NTRS)

Thom, K.; Schwenk, F. C.; Schneider, R. T.

1976-01-01

Fissioning uranium plasmas are the nuclear fuel in conceptual high-temperature gaseous-core reactors for advanced rocket propulsion in space. A gaseous-core nuclear rocket would be a thermal reactor in which an enriched uranium plasma at about 10,000 K is confined in a reflector-moderator cavity where it is nuclear critical and transfers its fission power to a confining propellant flow for the production of thrust at a specific impulse up to 5000 sec. With a thrust-to-engine weight ratio approaching unity, the gaseous-core nuclear rocket could provide for propulsion capabilities needed for manned missions to the nearby planets and for economical cislunar ferry services. Fueled with enriched uranium hexafluoride and operated at temperatures lower than needed for propulsion, the gaseous-core reactor scheme also offers significant benefits in applications for space and terrestrial power. They include high-efficiency power generation at low specific mass, the burnup of certain fission products and actinides, the breeding of U-233 from thorium with short doubling times, and improved convenience of fuel handling and processing in the gaseous phase.

Feedback controlled, reactor relevant, high-density, high-confinement scenarios at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Lang, P. T.; Blanken, T. C.; Dunne, M.; McDermott, R. M.; Wolfrum, E.; Bobkov, V.; Felici, F.; Fischer, R.; Janky, F.; Kallenbach, A.; Kardaun, O.; Kudlacek, O.; Mertens, V.; Mlynek, A.; Ploeckl, B.; Stober, J. K.; Treutterer, W.; Zohm, H.; ASDEX Upgrade Team

2018-03-01

One main programme topic at the ASDEX Upgrade all-metal-wall tokamak is development of a high-density regime with central densities at reactor grade level while retaining high-confinement properties. This required development of appropriate control techniques capable of coping with the pellet tool, a powerful means of fuelling but one which presented challenges to the control system for handling of related perturbations. Real-time density profile control was demonstrated, raising the core density well above the Greenwald density while retaining the edge density in order to avoid confinement losses. Recently, a new model-based approach was implemented that allows direct control of the central density. Investigations focussed first on the N-seeding scenario owing to its proven potential to yield confinement enhancements. Combining pellets and N seeding was found to improve the divertor buffering further and enhance the operational range accessible. For core densities up to about the Greenwald density, a clear improvement with respect to the non-seeding reference was achieved; however, at higher densities this benefit is reduced. This behaviour is attributed to recurrence of an outward shift of the edge density profile, resulting in a reduced peeling-ballooning stability. This is similar to the shift seen during strong gas puffing, which is required to prevent impurity influx in ASDEX Upgrade. First tests indicate that highly-shaped plasma configurations like the ITER base-line scenario, respond very well to pellet injection, showing efficient fuelling with no measurable impact on the edge density profile.

Geochemical changes and fracture development in Woodford Shale cores following hydrous pyrolysis under uniaxial confinement

USGS Publications Warehouse

Birdwell, Justin E.; Lewan, Michael D.; Miller, Michael; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

A uniaxial confinement clamp was used on Woodford Shale cores in hydrous pyrolysis experiments to study fracture development during thermal maturation. The clamp simulates overburden in that it prevents cores from expanding perpendicular to bedding fabric during the volume-increasing reactions associated with petroleum generation. Cores were cut from a slab of immature Woodford Shale and subjected to hydrous pyrolysis under confinement at 300, 330, and 365 °C for 72 hours to induce thermal maturities ranging from early bitumen to maximum expelled-oil generation. Two additional cores were used as experimental controls: (1) a confined core was saturated with water by heating it to 100 °C under hydrous pyrolysis conditions for 72 hours to use for characterization of the original rock, and (2) an unconfined core was heated at 365 °C for 72 hours to evaluate the effects of confinement on petroleum generation and expulsion. X-ray computed tomography (X-CT) imaging and other analyses identified five distinct beds within the cored interval. Using a tentative classification system, beds 1, 2, and 3 are described as dolomitic marlstone (DM) with total organic carbon (TOC) contents of 7.7, 5.8, and 7.7 wt. %, respectively; bed 4 is a cherty quartzose claystone (CQC) with TOC content of 5.5 wt. %; and bed 5 is a quartzose claystone with TOC content of 10.9 wt. %. Bed samples all had similar Rock-Eval hydrogen indices (600 ± 46 mg S2/g-TOC) and Tmax values (433 ± 2 °C), demonstrating organic matter uniformity and low thermal maturity. The X-CT scan of the core heated to 100 °C showed preexisting fractures that were nearly perpendicular to the bedding fabric primarily in the low-TOC DM bed 2 and CQC bed 4. Heating led to enhancement of preexisting fractures in the confined cores with the greatest enhancement occurring in CQC bed 4. The fractures increased in size and intensity with temperature. This is attributed to the internal pressure generated by volume-increasing reactions during the conversion of kerogen to bitumen and bitumen to oil and gas. The unconfined core heated to 365 °C showed no enhanced fracturing and its X-CT-scan resembled that of the 100 °C confined core. Comparison of the oil and gas yields from the confined and unconfined cores heated to 365 °C showed no significant differences, indicating that product expulsion is not inhibited by the procedure used in this study. These results also indicate that fracturing during thermal maturation is driven primarily by the enhancement of existing fractures.

Comparative analysis of core heat transport of JET high density H-mode plasmas in carbon wall and ITER-like wall

NASA Astrophysics Data System (ADS)

Kim, Hyun-Tae; Romanelli, M.; Voitsekhovitch, I.; Koskela, T.; Conboy, J.; Giroud, C.; Maddison, G.; Joffrin, E.; contributors, JET

2015-06-01

A consistent deterioration of global confinement in H-mode experiments has been observed in JET [1] following the replacement of all carbon plasma facing components (PFCs) with an all metal (‘ITER-like’) wall (ILW). This has been correlated to the observed degradation of the pedestal confinement, as lower electron temperature (Te) values are routinely measured at the top of the edge barrier region. A comparative investigation of core heat transport in JET-ILW and JET-CW (carbon wall) discharges has been performed, to assess whether core confinement has also been affected by the wall change. The results presented here have been obtained by analysing a set of discharges consisting of high density JET-ILW H-mode plasmas and comparing them against their counterpart discharges in JET-CW having similar global operational parameters. The set contains 10 baseline ({βN}=1.5∼ 2 ) discharge-pairs with 2.7 T toroidal magnetic field, 2.5 MA plasma current, and 14 to 17 MW of neutral beam injection (NBI) heating. Based on a Te profile analysis using high resolution Thomson scattering (HRTS) data, the Te profile peaking (i.e. core Te (ρ = 0.3) / edge Te (ρ = 0.7)) is found to be similar, and weakly dependent on edge Te, for both JET-ILW and JET-CW discharges. When ILW discharges are seeded with N2, core and edge Te both increase to maintain a similar peaking factor. The change in core confinement is addressed with interpretative TRANSP simulations. It is found that JET-ILW H-mode plasmas have higher NBI power deposition to electrons and lower NBI power deposition to ions as compared to the JET-CW counterparts. This is an effect of the lower electron temperature at the top of the pedestal. As a result, the core electron energy confinement time is reduced in JET-ILW discharges, but the core ion energy confinement time is not decreased. Overall, the core energy confinement is found to be the same in the JET-ILW discharges compared to the JET-CW counterparts.

Comparative Analysis of Hexagonal Solid Silica and Nitro-benzene Filled Hollow Core Photonic Crystal Fiber

NASA Astrophysics Data System (ADS)

Shahiruddin; Singh, Dharmendra K.; Hassan, M. A.

2018-02-01

A comparative study of five ring solid core and nitrobenzene filled hollow core liquid filled photonic crystal fiber (PCF) are presented. Considering the same structure, one is used as solid silica and another one is filled with nitrobenzene in the core. Here the paper elaborates the confinement loss, dispersion properties and birefringence of an index-guiding PCF with asymmetric cladding designed and analyzed by the finite-element method. The proposed structure shows the low confinement loss in case of solid silica, negative dispersion in nitrobenzene filled hollow core PCF and high birefringence in both the cases. The calculated values shows flat zero confinement loss in 0.7 µm to 1.54 µm range, flat zero dispersion is achieved in solid core and -2000 ps/km-nm in nitrobenzene filled hollow core PCF and high birefringence in the range of 10-3 in nitrobenzene filled hollow core PCF. Results show the relative analysis at different air fill fraction.

Transport simulation of EAST long-pulse H-mode discharge with integrated modeling

NASA Astrophysics Data System (ADS)

Wu, M. Q.; Li, G. Q.; Chen, J. L.; Du, H. F.; Gao, X.; Ren, Q. L.; Li, K.; Chan, Vincent; Pan, C. K.; Ding, S. Y.; Jian, X.; Zhu, X.; Lian, H.; Qian, J. P.; Gong, X. Z.; Zang, Q.; Duan, Y. M.; Liu, H. Q.; Lyu, B.

2018-04-01

In the 2017 EAST experimental campaign, a steady-state long-pulse H-mode discharge lasting longer than 100 s has been obtained using only radio frequency heating and current drive, and the confinement quality is slightly better than standard H-mode, H98y2 ~ 1.1, with stationary peaked electron temperature profiles. Integrated modeling of one long-pulse H-mode discharge in the 2016 EAST experimental campaign has been performed with equilibrium code EFIT, and transport codes TGYRO and ONETWO under integrated modeling framework OMFIT. The plasma current is fully-noninductively driven with a combination of ~2.2 MW LHW, ~0.3 MW ECH and ~1.1 MW ICRF. Time evolution of the predicted electron and ion temperature profiles through integrated modeling agree closely with that from measurements. The plasma current (I p ~ 0.45 MA) and electron density are kept constantly. A steady-state is achieved using integrated modeling, and the bootstrap current fraction is ~28%, the RF drive current fraction is ~72%. The predicted current density profile matches the experimental one well. Analysis shows that electron cyclotron heating (ECH) makes large contribution to the plasma confinement when heating in the core region while heating in large radius does smaller improvement, also a more peaked LHW driven current profile is got when heating in the core. Linear analysis shows that the high-k modes instability (electron temperature gradient driven modes) is suppressed in the core region where exists weak electron internal transport barriers. The trapped electron modes dominates in the low-k region, which is mainly responsible for driving the electron energy flux. It is found that the ECH heating effect is very local and not the main cause to sustained the good confinement, the peaked current density profile has the most important effect on plasma confinement improvement. Transport analysis of the long-pulse H-mode experiments on EAST will be helpful to build future experiments.

Enhancement of the sensitivity of gas sensor based on microstructure optical fiber

NASA Astrophysics Data System (ADS)

Morshed, Monir; Hasan, Md. Imran; Razzak, S. M. Abdur

2015-12-01

This paper proposes the design and characterization of microstructure optical fiber for gas sensing applications. The aim is to detect toxic and colorless gases over a wide transmission band covering 0.80 µm to 2.00 µm wavelength. Numerical investigation is carried out by using the finite element method (FEM). The numerical study shows that sensitivity of the proposed sensor is moderately increased by introducing four non-circular holes around the defected core of photonic crystal fiber and the confinement loss is also reduced. Furthermore, we confirm that increasing the diameter of central air core and size of the non-circular holes can improve the relative sensitivity and the confinement loss is reduced by increasing the diameter of air holes in the cladding. The enhancement of the relative sensitivity is more than 27.58% (0.1323 to 0.1688) at the wavelength λ=1.33µm that is the absorption line of methane (CH4) and hydrogen fluoride (HF) gases. The confinement loss of the fiber is 1.765×10-8 dB/m.

Single mode, broad-waveguide ARROW-type semiconductor diode lasers

NASA Astrophysics Data System (ADS)

Al-Muhanna, Abdulrahman Ali

A broad transverse waveguide (low confinement) concept is used to achieve a record-high spatially incoherent cw output power of 11W for InGaAs active devices (λ = 0.97 μm) from 100μm wide-stripe and 2mm-long devices with low internal loss, α1 = 1cm-1, and high characteristic temperatures, T0 = 210K, and T1 = 1800K. A detailed above-threshold analysis reveals that reduction in gain spatial hole burning (GSHB) is possible in ARROW-type structures by using a low transverse confinement factor; consequently, a wider ARROW-core can be utilized. By incorporating both a broad-waveguide concept as well as an asymmetric structure in the transverse direction, and an ARROW-type structure in the lateral direction, a novel single-spatial mode diode laser with improved performance is obtained. Devices with low transverse confinement factor (Γ ~ 1%) and a core-region width of 7.8 μm achieved 510mW single-spatial mode pulsed output power (λ = 0.946 μm) with a full- width at half-maximum (FWHM) of the lateral far-field pattern of 4.7°.

Extension of the XGC code for global gyrokinetic simulations in stellarator geometry

NASA Astrophysics Data System (ADS)

Cole, Michael; Moritaka, Toseo; White, Roscoe; Hager, Robert; Ku, Seung-Hoe; Chang, Choong-Seock

2017-10-01

In this work, the total-f, gyrokinetic particle-in-cell code XGC is extended to treat stellarator geometries. Improvements to meshing tools and the code itself have enabled the first physics studies, including single particle tracing and flux surface mapping in the magnetic geometry of the heliotron LHD and quasi-isodynamic stellarator Wendelstein 7-X. These have provided the first successful test cases for our approach. XGC is uniquely placed to model the complex edge physics of stellarators. A roadmap to such a global confinement modeling capability will be presented. Single particle studies will include the physics of energetic particles' global stochastic motions and their effect on confinement. Good confinement of energetic particles is vital for a successful stellarator reactor design. These results can be compared in the core region with those of other codes, such as ORBIT3d. In subsequent work, neoclassical transport and turbulence can then be considered and compared to results from codes such as EUTERPE and GENE. After sufficient verification in the core region, XGC will move into the stellarator edge region including the material wall and neutral particle recycling.

Photonic bandgap of inverse opals prepared from core-shell spheres

PubMed Central

2012-01-01

In this study, we synthesized monodispersed polystyrene (PS)-silica core-shell spheres with various shell thicknesses for the fabrication of photonic crystals. The shell thickness of the spheres was controlled by various additions of tetraethyl orthosilicate during the shell growth process. The shrinkage ratio of the inverse opal photonic crystals prepared from the core-shell spheres was significantly reduced from 14.7% to within 3%. We suspected that the improvement resulted from the confinement of silica shell to the contraction of PS space during calcination. Due to the shell effect, the inverse opals prepared from the core-shell spheres have higher filling fraction and larger wavelength of stop band maximum. PMID:22894600

Experimental Research of FRP Composite Tube Confined Steel-reinforced Concrete Stub Columns Under Axial Compression

NASA Astrophysics Data System (ADS)

Wang, Ji Zhong; Cheng, Lu; Wang, Xin Pei

2018-06-01

A new column of FRP composite tube confined steel-reinforced concrete (FTCSRC) column was proposed. This paper elaborates on laboratorial and analytical studies on the behavior of FCTSRC columns subjected to axial compressive load. Eight circular FTCSRC stub columns and one circular steel tube confined concrete (STCC) stub column were tested to investigate the failure mode and axial compression performance of circular FTCRSC columns. Parametric analysis was implemented to inquire the influence of confinement material (CFRP-steel tube or CFRP-GFRP tube), internal steel and CFRP layers on the ultimate load capacity. CFRP-steel composite tube was composed of steel tube and CFRP layer which was wrapped outside the steel tube, while CFRP-GFRP composite tube was composite of GFRP tube and CFRP layer. The test results indicate that the confinement effect of CFRP-steel tube is greatly superior to CFRP-GFRP tube. The ductility performance of steel tube confined high-strength concrete column can be improved obviously by encasing steel in the core concrete. Furthermore, with the increase in the layers of FRP wraps, the axial load capacity increases greatly.

Extrapolation of the DIII-D high poloidal beta scenario to ITER steady-state using transport modeling

NASA Astrophysics Data System (ADS)

McClenaghan, J.; Garofalo, A. M.; Meneghini, O.; Smith, S. P.

2016-10-01

Transport modeling of a proposed ITER steady-state scenario based on DIII-D high βP discharges finds that the core confinement may be improved with either sufficient rotation or a negative central shear q-profile. The high poloidal beta scenario is characterized by a large bootstrap current fraction( 80%) which reduces the demands on the external current drive, and a large radius internal transport barrier which is associated with improved normalized confinement. Typical temperature and density profiles from the non-inductive high poloidal beta scenario on DIII-D are scaled according to 0D modeling predictions of the requirements for achieving Q=5 steady state performance in ITER with ``day one'' H&CD capabilities. Then, TGLF turbulence modeling is carried out under systematic variations of the toroidal rotation and the core q-profile. Either strong negative central magnetic shear or rotation are found to successfully provide the turbulence suppression required to maintain the temperature and density profiles. This work supported by the US Department of Energy under DE-FC02-04ER54698.

Ion heat transport in improved confinement MST plasmas

NASA Astrophysics Data System (ADS)

Xing, Zichuan; Nornberg, Mark; den Hartog, Daniel J.; Kumar, Santhosh; Anderson, Jay K.

2016-10-01

Ion power balance in improved confinement (PPCD) plasmas in MST is dominated by electron collisional heating balanced by charge exchange transport. Neoclassical effects on ions in the RFP are inherently small and PPCD plasmas have reduced turbulence and stochasticity. Thus PPCD plasmas provide a good starting point for a transport model developed to account for collisional equilibration between species, classical conductive energy transport, and energy loss due to charge exchange collisions. This model also allows a possible noncollisional anomalous term to be isolated for study, and correlations between residual magnetic fluctuations during PPCD plasmas and anomalous heating and transport will be investigated. Recent modeling with DEGAS2 Monte Carlo neutral simulation suggests higher core neutral temperature than previously estimated with more simplistic assumptions. However, the working model does not fully account for the electron density increase in the core during PPCD, which is higher than expected from classical particle transport, and neutral and impurity ionization. Other possible mechanisms are considered and analyzed, including more complex impurity charge-state balance and pinch effects. Work supported by the US DOE. DEGAS2 is provided by PPPL.

Power Radiated from ITER and CIT by Impurities

DOE R&D Accomplishments Database

Cummings, J.; Cohen, S. A.; Hulse, R.; Post, D. E.; Redi, M. H.; Perkins, J.

1990-07-01

The MIST code has been used to model impurity radiation from the edge and core plasmas in ITER and CIT. A broad range of parameters have been varied, including Z{sub eff}, impurity species, impurity transport coefficients, and plasma temperature and density profiles, especially at the edge. For a set of these parameters representative of the baseline ITER ignition scenario, it is seen that impurity radiation, which is produced in roughly equal amounts by the edge and core regions, can make a major improvement in divertor operation without compromising core energy confinement. Scalings of impurity radiation with atomic number and machine size are also discussed.

Radical re-appraisal of water structure in hydrophilic confinement.

PubMed

Soper, Alan K

2013-12-18

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298 K to 210 K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around -100 MPa, inside the pore.

Strain distribution of confined Ge/GeO2 core/shell nanoparticles engineered by growth environments

NASA Astrophysics Data System (ADS)

Wei, Wenyan; Yuan, Cailei; Luo, Xingfang; Yu, Ting; Wang, Gongping

2016-02-01

The strain distributions of Ge/GeO2 core/shell nanoparticles confined in different host matrix grown by surface oxidation are investigated. The simulated results by finite element method demonstrated that the strains of the Ge core and the GeO2 shell strongly depend on the growth environments of the nanoparticles. Moreover, it can be found that there is a transformation of the strain on Ge core from tensile to compressive strain during the growth of Ge/GeO2 core/shell nanoparticles. And, the transformation of the strain is closely related with the Young's modulus of surrounding materials of Ge/GeO2 core/shell nanoparticles.

Rational-q Triggered Transport Changes With Varying Toroidal Rotation in DIII-D

NASA Astrophysics Data System (ADS)

Austin, M. E.; Burrell, K. H.; Waltz, R. E.; van Zeeland, M. A.; McKee, G. R.; Shafer, M. W.; Rhodes, T. L.

2007-11-01

Comparison of rational-q triggered ITBs in discharges with varying toroidal torque injection was carried out. Experiments were conducted in negative central shear discharges with different mixes of co/counter neutral beam injection (NBI) that altered the equilibrium ExB shear in conditions where transient improvements in transport occur near integer qmin values. The transport changes were seen in high and low rotation cases; however, the latter discharges did not transition to improved core confinement. Observations support the model that sufficient background ExB shear is required for barrier formation and zonal flow effects at integer qmin act as trigger in this case. The lack of TAE modes in the balanced injection cases indicates they are not linked to the transient confinement improvement. Fluctuation data obtained in co and balanced NBI show similar reductions in turbulence near integer qmin as well as poloidal velocity excursions that may be further evidence of zonal flow.

Effects of Salinity and Confining Pressure on Hydration-Induced Fracture Propagation and Permeability of Mancos Shale

NASA Astrophysics Data System (ADS)

Zhang, Shifeng; Sheng, James J.

2017-11-01

Low-salinity water imbibition was considered an enhanced recovery method in shale oil/gas reservoirs due to the resulting hydration-induced fractures, as observed at ambient conditions. To study the effect of confining pressure and salinity on hydration-induced fractures, time-elapsed computerized tomography (CT) was used to obtain cross-sectional images of shale cores. Based on the CT data of these cross-sectional images, cut faces parallel to the core axial in the middle of the core and 3D fracture images were also reconstructed. To study the effects of confining pressure and salinity on shale pore fluid flowing, shale permeability was measured with Nitrogen (N2), distilled water, 4% KCl solution, and 8% KCl solution. With confining pressures increased to 2 MPa or more, either in distilled water or in KCl solutions of different salinities, fractures were observed to close instead to propagate at the end of the tests. The intrinsic permeabilities of #1 and #2 Mancos shale cores were 60.0 and 7000 nD, respectively. When tested with distilled water, the permeability of #1 shale sample with 20.0 MPa confining pressure loaded, and #2 shale sample with 2.5 MPa confining pressure loaded, decreased to 0.45 and 15 nD, respectively. Using KCl can partly mitigate shale permeability degradation. Compared to 4% KCl, 8% KCl can decrease more permeability damage. From this point of view, high salinity KCl solution should be required for the water-based fracturing fluid.

Application of uniaxial confining-core clamp with hydrous pyrolysis in petrophysical and geochemical studies of source rocks at various thermal maturities

USGS Publications Warehouse

Lewan, Michael D.; Birdwell, Justin E.; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

Understanding changes in petrophysical and geochemical parameters during source rock thermal maturation is a critical component in evaluating source-rock petroleum accumulations. Natural core data are preferred, but obtaining cores that represent the same facies of a source rock at different thermal maturities is seldom possible. An alternative approach is to induce thermal maturity changes by laboratory pyrolysis on aliquots of a source-rock sample of a given facies of interest. Hydrous pyrolysis is an effective way to induce thermal maturity on source-rock cores and provide expelled oils that are similar in composition to natural crude oils. However, net-volume increases during bitumen and oil generation result in expanded cores due to opening of bedding-plane partings. Although meaningful geochemical measurements on expanded, recovered cores are possible, the utility of the core for measuring petrophysical properties relevant to natural subsurface cores is not suitable. This problem created during hydrous pyrolysis is alleviated by using a stainless steel uniaxial confinement clamp on rock cores cut perpendicular to bedding fabric. The clamp prevents expansion just as overburden does during natural petroleum formation in the subsurface. As a result, intact cores can be recovered at various thermal maturities for the measurement of petrophysical properties as well as for geochemical analyses. This approach has been applied to 1.7-inch diameter cores taken perpendicular to the bedding fabric of a 2.3- to 2.4-inch thick slab of Mahogany oil shale from the Eocene Green River Formation. Cores were subjected to hydrous pyrolysis at 360 °C for 72 h, which represents near maximum oil generation. One core was heated unconfined and the other was heated in the uniaxial confinement clamp. The unconfined core developed open tensile fractures parallel to the bedding fabric that result in a 38 % vertical expansion of the core. These open fractures did not occur in the confined core, but short, discontinuous vertical fractures on the core periphery occurred as a result of lateral expansion.

Luminescence properties of In(Zn)P alloy core/ZnS shell quantum dots

NASA Astrophysics Data System (ADS)

Thuy, Ung Thi Dieu; Reiss, Peter; Liem, Nguyen Quang

2010-11-01

Chemically synthesized InP/ZnS core/shell quantum dots (QDs) are studied using time-resolved photoluminescence spectroscopy and x-ray diffraction. Zinc stearate, which is added during the synthesis of the InP core, significantly improves the optical characteristics of the QDs. The luminescence quantum yield (QY) reaches 60%-70% and the emission is tunable from 485 to 586 nm by varying the Zn2+:In3+ molar ratio and growth temperature. The observed increased Stokes shift, luminescence decay time, and QY in the presence of Zn are rationalized by the formation of an In(Zn)P alloy structure that causes band-edge fluctuation to enhance the confinement of the excited carriers.

Advancing flexible volatile compound sensors using liquid crystals encapsulated in polymer fibers

NASA Astrophysics Data System (ADS)

Reyes, Catherine G.; Lagerwall, Jan P. F.

2018-02-01

Until recently, organic vapor sensors using liquid crystals (LCs) have employed rigid glass substrates for confining the LC, and bulky equipment for vapor detection. Previously, we demonstrated that coaxially electrospinning nematic LC within the core of polymer fibers provides an alternative and improved form factor for confinement. This enables ppm level sensitivity to harmful industrial organics, such as toluene, while giving the flexibility of textile-like sheets (imparted by polymer encapsulation). Moreover, toluene vapor responses of the LC-core fiber mats were visible macroscopically with the naked eye depending on the morphology of the fibers produced, and whether they were oriented in specific geometries (aligned, or random). We identified two types of responses: one corresponds to the LC transition from nematic to isotropic, and the other we suggest is due to an anchoring change at the LC-polymer interface that influences the alignment. While we need to study the presence that defects can have in more detail, we noted that fiber mat thickness is crucial in attempting to understand how and why we are able to visualize two responses in aligned LC-fiber mats. Ultimately, we noted that the response of the polymer sheath itself (softening) to organic vapor exposure affects the liquid crystal confinement in the core. From the microscopic point of view, this will influence the threshold concentration that fibers in a mat will overall respond to. In this paper we will discuss three findings the morphologies enabling LC-core fiber mat response to vapor seen both micro- and macroscopically, how thickness of the fiber mat can play a role in the visualization of the responses, and the effect that the polymer structure has in the mat's sensitivity threshold.

Changes in transport and confinement in the EXTRAP-T2 reversed field pinch

NASA Astrophysics Data System (ADS)

Sallander, E.; Sallander, J.; Hedqvist, A.

1999-09-01

At the EXTRAP-T2 reversed field pinch a non-intrusive approach has been undertaken to monitor transport driven by magnetic fluctuations. Correlations are presented between fluctuations observed in the core and at the edge of the plasma. The fluctuations are characterized and their effect on the confinement of core electron energy is estimated.

Physics and performance of the I-mode regime over an expanded operating space on Alcator C-Mod

NASA Astrophysics Data System (ADS)

Hubbard, A. E.; Baek, S.-G.; Brunner, D.; Creely, A. J.; Cziegler, I.; Edlund, E.; Hughes, J. W.; LaBombard, B.; Lin, Y.; Liu, Z.; Marmar, E. S.; Reinke, M. L.; Rice, J. E.; Sorbom, B.; Sung, C.; Terry, J.; Theiler, C.; Tolman, E. A.; Walk, J. R.; White, A. E.; Whyte, D.; Wolfe, S. M.; Wukitch, S.; Xu, X. Q.; the Alcator C-Mod Team

2017-12-01

New results on the I-mode regime of operation on the Alcator C-Mod tokamak are reported. This ELM-free regime features high energy confinement and a steep temperature pedestal, while particle confinement remains at L-mode levels, giving stationary density and avoiding impurity accumulation. I-mode has now been obtained over nearly all of the magnetic fields and currents possible in this high field tokamak (I p 0.55-1.7 MA, B T 2.8-8 T) using a configuration with B  ×  ∇ B drift away from the X-point. Results at 8 T confirm that the L-I power threshold varies only weakly with B T, and that the power range for I-mode increases with B T; no 8 T discharges transitioned to H-mode. Parameter dependences of energy confinement are investigated. Core transport simulations are giving insight into the observed turbulence reduction, profile stiffness and confinement improvement. Pedestal models explain the observed stability to ELMs, and can simulate the observed weakly coherent mode. Conditions for I-H transitions have complex dependences on density as well as power. I-modes have now been maintained in near-DN configurations, leading to improved divertor power flux sharing. Prospects for I-mode on future fusion devices such as ITER and ARC are encouraging. Further experiments on other tokamaks are needed to improve confidence in extrapolation.

Effects of quantum confinement and shape on band gap of core/shell quantum dots and nanowires

NASA Astrophysics Data System (ADS)

Gao, Faming

2011-05-01

A quantum confinement model for nanocrystals developed is extended to study for the optical gap shifts in core/shell quantum dots and nanowires. The chemical bond properties and gap shifts in the InP/ZnS, CdSe/CdS, CdSe/ZnS, and CdTe/ZnS core/shell quantum dots are calculated in detail. The calculated band gaps are in excellent agreement with experimental values. The effects of structural taping and twinning on quantum confinement of InP and Si nanowires are elucidated. It is found theoretically that a competition between the positive Kubo energy-gap shift and the negative surface energy shift plays the crucial role in the optical gaps of these nanosystems.

Atomistic Design of CdSe/CdS Core-Shell Quantum Dots with Suppressed Auger Recombination.

PubMed

Jain, Ankit; Voznyy, Oleksandr; Hoogland, Sjoerd; Korkusinski, Marek; Hawrylak, Pawel; Sargent, Edward H

2016-10-12

We design quasi-type-II CdSe/CdS core-shell colloidal quantum dots (CQDs) exhibiting a suppressed Auger recombination rate. We do so using fully atomistic tight-binding wave functions and microscopic Coulomb interactions. The recombination rate as a function of the core and shell size and shape is tested against experiments. Because of a higher density of deep hole states and stronger hole confinement, Auger recombination is found to be up to six times faster for positive trions compared to negative ones in 4 nm core/10 nm shell CQDs. Soft-confinement at the interface results in weak suppression of Auger recombination compared to same-bandgap sharp-interface CQDs. We find that the suppression is due to increased volume of the core resulting in delocalization of the wave functions, rather than due to soft-confinement itself. We show that our results are consistent with previous effective mass models with the same system parameters. Increasing the dot volume remains the most efficient way to suppress Auger recombination. We predict that a 4-fold suppression of Auger recombination can be achieved in 10 nm CQDs by increasing the core volume by using rodlike cores embedded in thick shells.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

2017-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs < 0.14 , and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

Effect of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal solar cells

NASA Astrophysics Data System (ADS)

Sahin, Mehmet

2018-05-01

In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p–n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy () of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same . The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same , become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.

Response of plasma rotation to resonant magnetic perturbations in J-TEXT tokamak

NASA Astrophysics Data System (ADS)

Yan, W.; Chen, Z. Y.; Huang, D. W.; Hu, Q. M.; Shi, Y. J.; Ding, Y. H.; Cheng, Z. F.; Yang, Z. J.; Pan, X. M.; Lee, S. G.; Tong, R. H.; Wei, Y. N.; Dong, Y. B.; J-TEXT Team

2018-03-01

The response of plasma toroidal rotation to the external resonant magnetic perturbations (RMP) has been investigated in Joint Texas Experimental Tokamak (J-TEXT) ohmic heating plasmas. For the J-TEXT’s plasmas without the application of RMP, the core toroidal rotation is in the counter-current direction while the edge rotation is near zero or slightly in the co-current direction. Both static RMP experiments and rotating RMP experiments have been applied to investigate the plasma toroidal rotation. The core toroidal rotation decreases to lower level with static RMP. At the same time, the edge rotation can spin to more than 20 km s-1 in co-current direction. On the other hand, the core plasma rotation can be slowed down or be accelerated with the rotating RMP. When the rotating RMP frequency is higher than mode frequency, the plasma rotation can be accelerated to the rotating RMP frequency. The plasma confinement is improved with high frequency rotating RMP. The plasma rotation is decelerated to the rotating RMP frequency when the rotating RMP frequency is lower than the mode frequency. The plasma confinement also degrades with low frequency rotating RMP.

Control of ion gyroscale fluctuations via electrostatic biasing and sheared E×B flow in the C-2 field reversed configuration

NASA Astrophysics Data System (ADS)

Schmitz, L.; Ruskov, E.; Deng, B. H.; Binderbauer, M.; Tajima, T.; Gota, H.; Tuszewski, M.

2016-03-01

Control of radial particle and thermal transport is instrumental for achieving and sustaining well-confined high-β plasma in a Field-Reversed Configuration (FRC). Radial profiles of low frequency ion gyro-scale density fluctuations (0.5≤kρs≤40), consistent with drift- or drift-interchange modes, have been measured in the scrape-off layer (SOL) and core of the C-2 Field-Reversed Configuration (FRC), together with the toroidal E×B velocity. It is shown here that axial electrostatic SOL biasing controls and reduces gyro-scale density fluctuations, resulting in very low FRC core fluctuation levels. When the radial E×B flow shearing rate decreases below the turbulence decorrelation rate, fluctuation levels increase substantially, concomitantly with onset of the n=2 instability and rapid loss of diamagnetism. Low turbulence levels, improved energy/particle confinement and substantially increased FRC life times are achieved when E×B shear near the separatrix is maintained via axial SOL biasing using an annular washer gun.

Design and Synthesis of Antiblinking and Antibleaching Quantum Dots in Multiple Colors via Wave Function Confinement.

PubMed

Cao, Hujia; Ma, Junliang; Huang, Lin; Qin, Haiyan; Meng, Renyang; Li, Yang; Peng, Xiaogang

2016-12-07

Single-molecular spectroscopy reveals that photoluminescence (PL) of a single quantum dot blinks, randomly switching between bright and dim/dark states under constant photoexcitation, and quantum dots photobleach readily. These facts cast great doubts on potential applications of these promising emitters. After ∼20 years of efforts, synthesis of nonblinking quantum dots is still challenging, with nonblinking quantum dots only available in red-emitting window. Here we report synthesis of nonblinking quantum dots covering most part of the visible window using a new synthetic strategy, i.e., confining the excited-state wave functions of the core/shell quantum dots within the core quantum dot and its inner shells (≤ ∼5 monolayers). For the red-emitting ones, the new synthetic strategy yields nonblinking quantum dots with small sizes (∼8 nm in diameter) and improved nonblinking properties. These new nonblinking quantum dots are found to be antibleaching. Results further imply that the PL blinking and photobleaching of quantum dots are likely related to each other.

Crystallization in Micellar Cores: confinement effects and dynamics

NASA Astrophysics Data System (ADS)

Lund, Reidar; Zinn, Thomas; Willner, Lutz; Department of Chemistry, University of Oslo Team; Forschungszentrum Jülich Collaboration

It is well known that liquids confined to small nanoscopic pores and droplets exhibit thermal behavior very different from bulk samples. Here we demonstrate that n-alkanes forming 2-3 nm small micellar cores are considerably affected by confinement in analogue with hard confined systems. We study micelles form by self-assembly of a series of well-defined n-Alkyl-PEO polymers in aqueous solutions. By using small-angle X-ray scattering (SAXS), densiometry and differential scanning calorimetry (DSC), we show that n-alkane exhibit a first-order phase transition i.e. melting. Correlating the structural and thermodynamic data, we find that a melting depression can be accurately described by the Gibbs-Thomson equation. ∖f1 The effect of core crystallinity on the molecular exchange kinetics is investigated using time-resolved small-angle neutron scattering (TR-SANS). We show that there are considerable entropic and enthalpic contributions from the chain packing that affect the kinetic stability of micelles. ∖pard

Nuclear reactor

DOEpatents

Yant, Howard W.; Stinebiser, Karl W.; Anzur, Gregory C.

1977-01-01

A nuclear reactor, particularly a liquid-metal breeder reactor, whose upper internals include outlet modules for channeling the liquid-metal coolant from selected areas of the outlet of the core vertically to the outlet plenum. The modules are composed of a highly-refractory, high corrosion-resistant alloy, for example, INCONEL-718. Each module is disposed to confine and channel generally vertically the coolant emitted from a subplurality of core-component assemblies. Each module has a grid with openings, each opening disposed to receive the coolant from an assembly of the subplurality. The grid in addition serves as a holdown for the assemblies of the corresponding subplurality preventing their excessive ejection upwardly from the core. In the region directly over the core the outlet modules are of such peripheral form that they nest forming a continuum over the core-component assemblies whose outlet coolant they confine. Each subassembly includes a chimney which confines the coolant emitted by its corresponding subassemblies to generally vertical flow between the outlet of the core and the outlet plenum. Each subplurality of assemblies whose emitted coolant is confined by an outlet module includes assemblies which emit lower-temperature coolant, for example, a control-rod assembly, or fertile assemblies, and assemblies which emit coolant of substantially higher temperature, for example, fuel-rod assemblies. The coolants of different temperatures are mixed in the chimneys reducing the effect of stripping (hot-cold temperature fluctuations) on the remainder of the upper internals which are composed typically of AISI-304 or AISI-316 stainless steel.

Effects of microchannel confinement on acoustic vaporisation of ultrasound phase change contrast agents

NASA Astrophysics Data System (ADS)

Lin, Shengtao; Zhang, Ge; Hau Leow, Chee; Tang, Meng-Xing

2017-09-01

The sub-micron phase change contrast agent (PCCA) composed of a perfluorocarbon liquid core can be activated into gaseous state and form stable echogenic microbubbles for contrast-enhanced ultrasound imaging. It has shown great promise in imaging microvasculature, tumour microenvironment, and cancer cells. Although PCCAs have been extensively studied for different diagnostic and therapeutic applications, the effect of biologically geometrical confinement on the acoustic vaporisation of PCCAs is still not clear. We have investigated the difference in PCCA-produced ultrasound contrast enhancement after acoustic activation with and without a microvessel confinement on a microchannel phantom. The experimental results indicated more than one-order of magnitude less acoustic vaporisation in a microchannel than that in a free environment taking into account the attenuation effect of the vessel on the microbubble scattering. This may provide an improved understanding in the applications of PCCAs in vivo.

Highly non-linear solid core photonic crystal fiber with one nano hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangwar, Rahul Kumar, E-mail: rahul0889@gmail.com; Bhardwaj, Vanita, E-mail: bhardwajphy12@gmail.com; Singh, Vinod Kumar, E-mail: singh.vk.ap@ismdhanbad.co.in

2015-08-28

The numerical study of newly designed solid core photonic crystal fiber (SCPCF) having three hexagonal air hole rings in cladding region and one small nano hole at the center are presented. By using full vectorial finite element method (FV-FEM), we analyses the optical properties like effective area, nonlinearity and confinement loss of the proposed PCF. Results show that the change in core diameter controls the effective area, nonlinearity and confinement loss. A low effective area (3.34 µm{sup 2}), high nonlinearity (36.34 W{sup −1}km{sup −1}) and low confinement loss (0.00106 dB/km) are achieved at the communication wavelength 1.55 µm for themore » SCPCF having core air hole diameter 0.10 µm, cladding air holes diameter 1.00 µm and pitch 2.50 µm. This type of PCF is very useful in non-linear applications such as supercontinuum generation, four wave mixing, second harmonic generation etc.« less

Effect of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal solar cells.

PubMed

Sahin, Mehmet

2018-05-23

In this study, the effects of the shell material and confinement type on the conversion efficiency of core/shell quantum dot nanocrystal (QDNC) solar cells have been investigated in detail. For this purpose, the conventional, i.e. original, detailed balance model, developed by Shockley and Queisser to calculate an upper limit for the conversion efficiency of silicon p-n junction solar cells, is modified in a simple and effective way to calculate the conversion efficiency of core/shell QDNC solar cells. Since the existing model relies on the gap energy ([Formula: see text]) of the solar cell, it does not make an estimation about the effect of QDNC materials on the efficiency of the solar cells, and gives the same efficiency values for several QDNC solar cells with the same [Formula: see text]. The proposed modification, however, estimates a conversion efficiency in relation to the material properties and also the confinement type of the QDNCs. The results of the modified model show that, in contrast to the original one, the conversion efficiencies of different QDNC solar cells, even if they have the same [Formula: see text], become different depending upon the confinement type and shell material of the core/shell QDNCs, and this is crucial in the design and fabrication of the new generation solar cells to predict the confinement type and also appropriate QDNC materials for better efficiency.

Linear complexions: Confined chemical and structural states at dislocations

NASA Astrophysics Data System (ADS)

Kuzmina, M.; Herbig, M.; Ponge, D.; Sandlöbes, S.; Raabe, D.

2015-09-01

For 5000 years, metals have been mankind’s most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states.

Magnetic induction spectroscopy (MIS)-probe design for cervical tissue measurements.

PubMed

Wang, Jau-Yi; Healey, Timothy; Barker, Anthony; Brown, Brian; Monk, Chris; Anumba, Dilly

2017-05-01

Gradiometers have the advantage of increasing measuring sensitivity, which is particularly useful in magnetic induction spectroscopy (MIS) for bio-impedance measurements. Traditional gradiometers use a pair of field sensing coils equally distant and on opposite sides of a drive coil, which provides high immunity to interference. In this paper, a ferrite-cored coaxial gradiometer probe of 29 mm diameter has been developed for measuring the impedance spectra of cervical tissues in vivo. It consists of a ferrite rod with outer ferrite confinement screening in order to eliminate the signals from surrounding tissue. The magnetic screening efficiency was compared with an air-cored gradiometer probe. For both gradiometer probes, a drive coil and two sensing coils were wound on a borosilicate glass former aligned coaxially with two sensing coils equidistant from the drive coil. The signal sensitivity of those two MIS gradiometers has been measured using saline samples with a conductivity range between 0.1 and 1.1 S m -1 . Finite element methods using COMSOL Multiphysics have been used to simulate the distribution of sensitivity to conductivity over the face of each probe and with depth. The ferrite-cored probe has a sensitivity confined to the volume defined by the gap between the ferrite core and outer tube of ferrite while the air-cored probe without any magnetic shielding had a wide sensitivity over the face and the side of the probe. Four saline samples and one of distilled water with conductivities from 0.1 to 1.1 S m -1 have been used to make conductivity measurements at frequencies of 50 kHz, 100 kHz, and 300 kHz. The measurement accuracy of the air-cored MIS probe was 0.09 S m -1 at 50 kHz, improving to 0.05 S m -1 at 300 kHz. For the ferrite-cored MIS probe, the measurement accuracy was 0.28 S m -1 at 50 kHz, improving to 0.04 S m -1 at 300 kHz. In vivo measurements on human hand have been performed using both types of gradiometers and the conductivity is consistent with reported data.

Plasma confinement at JET

NASA Astrophysics Data System (ADS)

Nunes, I.; JET Contributors

2016-01-01

Operation with a Be/W wall at JET (JET-ILW) has an impact on scenario development and energy confinement with respect to the carbon wall (JET-C). The main differences observed were (1) strong accumulation of W in the plasma core and (2) the need to mitigate the divertor target temperature to avoid W sputtering by Be and other low Z impurities and (3) a decrease of plasma energy confinement. A major difference is observed on the pedestal pressure, namely a reduction of the pedestal temperature which, due to profile stiffness the plasma core temperature is also reduced leading to a degradation of the global confinement. This effect is more pronounced in low β N scenarios. At high β N, the impact of the wall on the plasma energy confinement is mitigated by the weaker plasma energy degradation with power relative to the IPB98(y, 2) scaling calculated empirically for a CFC first wall. The smaller tolerable impurity concentration for tungsten (<10-5) compared to that of carbon requires the use of electron heating methods to prevent W accumulation in the plasma core region as well as gas puffing to avoid W entering the plasma core by ELM flushing and reduction of the W source by decreasing the target temperature. W source and the target temperature can also be controlled by impurity seeding. Nitrogen and Neon have been used and with both gases the reduction of the W source and the target temperature is observed. Whilst more experiments with Neon are necessary to assess its impact on energy confinement, a partial increase of plasma energy confinement is observed with Nitrogen, through the increase of edge temperature. The challenge for scenario development at JET is to extend the pulse length curtailed by its transient behavior (W accumulation or MHD), but more importantly by the divertor target temperature limits. Re-optimisation of the scenarios to mitigate the effect of the change of wall materials maintaining high global energy confinement similar to JET-C is underway and JET has successfully achieved H 98(y,2)  =  1 for plasma currents up to 2.5 MA at moderate β N.

Intrinsic Flow Behavior During Improved Confinement in MST Reversed-field Pinch

NASA Astrophysics Data System (ADS)

Tan, E.; Craig, D.; Schott, B.; Boguski, J.; Xing, Z. A.; Nornberg, M. D.; Anderson, J. K.

2017-10-01

We used active charge exchange recombination spectroscopy to measure impurity ion flow velocity in high-current plasmas during periods of improved confinement. Velocity measurements througout the core reveal that ion flow parallel to the magnetic field is dominant compared to the perpendicular flow. The poloidal flow profile reverses at r/a = 0.6, and the flow near the core is larger on outboard positions compared to the inboard positions. A strong shear in the toroidal flow develops near the axis as PPCD proceeds. In the past, the mode velocity has been used to infer the toroidal flow based on the `no-slip' assumption that the mode and local plasma co-rotate. We tested this assumption with direct measurements near the m = 1, n = 6 resonant surface. Inboard flow measurements are consistent with the no-slip condition and exhibit a time dependence where the flow decreases together with the n = 6 mode velocity. The outboard flow is consistent in magnitude with the no-slip condition but the variations in time and across shots do not correlate well with the n = 6 mode velocity. Possible reasons why the inboard and outboard flow exhibit different behavior are discussed. This work has been supported by the US DOE and the Wheaton College summer research program.

Linear complexions: Confined chemical and structural states at dislocations.

PubMed

Kuzmina, M; Herbig, M; Ponge, D; Sandlöbes, S; Raabe, D

2015-09-04

For 5000 years, metals have been mankind's most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states. Copyright © 2015, American Association for the Advancement of Science.

Confinement in Wendelstein 7-X Limiter Plasmas

DOE PAGES

Hirsch, M.; Dinklage, A.; Alonso, A.; ...

2017-06-14

Observations on confinement in the first experimental campaign on the optimized Stellarator Wendelstein 7-X are summarized. In this phase W7-X was equipped with five inboard limiters only and thus the discharge length restricted to avoid local overheating. Stationary plasmas are limited to low densities <2–3 centerdot 10 19 m -3. With the available 4.3 MW ECR Heating core T e ~ 8 keV, T i ~ 1–2 keV are achieved routinely resulting in energy confinement time τ E between 80 ms to 150 ms. For these conditions the plasmas show characteristics of core electron root confinement with peaked T e-profilesmore » and positive E r up to about half of the minor radius. Lastly, profiles and plasma currents respond to on- and off-axis heating and co- and counter ECCD respectively.« less

Laboratory-scale uranium RF plasma confinement experiments

NASA Technical Reports Server (NTRS)

Roman, W. C.

1976-01-01

An experimental investigation was conducted using 80 kW and 1.2 MW RF induction heater facilities to aid in developing the technology necessary for designing a self-critical fissioning uranium plasma core reactor. Pure uranium hexafluoride (UF6) was injected into argon-confined, steady-state, RF-heated plasmas in different uranium plasma confinement tests to investigate the characteristics of plamas core nuclear reactors. The objectives were: (1) to confine as high a density of uranium vapor as possible within the plasma while simultaneously minimizing the uranium compound wall deposition; (2) to develop and test materials and handling techniques suitable for use with high-temperature, high-pressure gaseous UF6; and (3) to develop complementary diagnostic instrumentation and measurement techniques to characterize the uranium plasma and residue deposited on the test chamber components. In all tests, the plasma was a fluid-mechanically-confined vortex-type contained within a fused-silica cylindrical test chamber. The test chamber peripheral wall was 5.7 cm ID by 10 cm long.

ON THE COAGULATION AND SIZE DISTRIBUTION OF PRESSURE CONFINED CORES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang Xu; Zhou Tingtao; Lin, D. N. C., E-mail: xuhuang@princeton.edu

2013-05-20

Observations of the Pipe Nebula have led to the discovery of dense starless cores. The mass of most cores is too small for their self-gravity to hold them together. Instead, they are thought to be pressure confined. The observed dense cores' mass function (CMF) matches well with the initial mass function of stars in young clusters. Similar CMFs are observed in other star forming regions such as the Aquila Nebula, albeit with some dispersion. The shape of these CMF provides important clues to the competing physical processes which lead to star formation and its feedback on the interstellar media. Inmore » this paper, we investigate the dynamical origin of the mass function of starless cores which are confined by a warm, less dense medium. In order to follow the evolution of the CMF, we construct a numerical method to consider the coagulation between the cold cores and their ablation due to Kelvin-Helmholtz instability induced by their relative motion through the warm medium. We are able to reproduce the observed CMF among the starless cores in the Pipe Nebula. Our results indicate that in environment similar to the Pipe Nebula: (1) before the onset of their gravitational collapse, the mass distribution of the progenitor cores is similar to that of the young stars, (2) the observed CMF is a robust consequence of dynamical equilibrium between the coagulation and ablation of cores, and (3) a break in the slope of the CMF is due to the enhancement of collisional cross section and suppression of ablation for cores with masses larger than the cores' Bonnor-Ebert mass.« less

Photoluminescence Intermittency and Photo-Bleaching of Single Colloidal Quantum Dot.

PubMed

Qin, Haiyan; Meng, Renyang; Wang, Na; Peng, Xiaogang

2017-04-01

Photoluminescence (PL) blinking of single colloidal quantum dot (QD)-PL intensity switching between different brightness states under constant excitation-and photo-bleaching are roadblocks for most applications of QDs. This progress report shall treat PL blinking and photo-bleaching both as photochemical events, namely, PL blinking as reversible and photo-bleaching being irreversible ones. Most studies on single-molecule spectroscopy of QDs in literature are related to PL blinking, which invites us to concentrate our discussions on the PL blinking, including its brief history in 20 years, analysis methods, competitive mechanisms and different strategies to battle it. In terms of suppression of the PL blinking, wavefunction confinement-confining photo-generated electron and hole within the core and inner portion of the shell of a core/shell QD-demonstrates significant advantages. This strategy yields nearly non-blinking QDs with their emission peaks covering most part of the visible window. As expected, the resulting QDs from this new strategy also show substantially improved anti-bleaching features. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cui, L.; Nazikian, Raffi; Grierson, B. A.

Here, Resonant Magnetic Perturbations (RMPs) are a leading method for edge localized modes (ELMs) Control in fusion plasmas. However they can also cause a rapid degradation in energy confinement. In this paper we show that the energy confinement in low collisionality (v* e < 0.3) DIII-D ITER Similar Shape (ISS) plasmas often recovers after several energy confinement times for RMP amplitudes up to the threshold for ELM suppression. Immediately following the application of the RMP, the plasma stored energy decreases in proportion to the decrease in the line-averaged density during density "pump-out". Later in the discharge confinement recovery is observedmore » in the thermal ion channel and is correlated with the increase in the ion temperature at the top of the H-mode pedestal. A correlation between the inverse scale length of the ion temperature (α/L Ti) and the E x B shearing rate at the top of the pedestal is seen during the confinement recovery phase. Transport analysis reveals that the confinement improvement in the ion channel results from the self-similarity in the ion temperature profiles in the plasma core combined with the observed increase in α/L Ti in the plasma edge following density pump-out. In contrast the electron temperature scale length (α/L Ti) remains essentially unchanged in response to the application of the RMP. At significantly higher RMP levels the edge EXB shearing rate and α/L Ti does not increase and the confinement does not recover following density pump-out.« less

Exciton and core-level electron confinement effects in transparent ZnO thin films

PubMed Central

Mosquera, Adolfo A.; Horwat, David; Rashkovskiy, Alexandr; Kovalev, Anatoly; Miska, Patrice; Wainstein, Dmitry; Albella, Jose M.; Endrino, Jose L.

2013-01-01

The excitonic light emission of ZnO films have been investigated by means of photoluminescence measurements in ultraviolet-visible region. Exciton confinement effects have been observed in thin ZnO coatings with thickness below 20 nm. This is enhanced by a rise of the intensity and a blue shift of the photoluminescence peak after extraction of the adsorbed species upon annealing in air. It is found experimentally that the free exciton energy (determined by the photoluminescence peak) is inversely proportional to the square of the thickness while core-level binding energy is inversely proportional to the thickness. These findings correlate very well with the theory of kinetic and potential confinements.

The energy confinement response of DIII-D plasmas to Resonant Magnetic Perturbations

DOE PAGES

Cui, L.; Nazikian, Raffi; Grierson, B. A.; ...

2017-07-11

Here, Resonant Magnetic Perturbations (RMPs) are a leading method for edge localized modes (ELMs) Control in fusion plasmas. However they can also cause a rapid degradation in energy confinement. In this paper we show that the energy confinement in low collisionality (v* e < 0.3) DIII-D ITER Similar Shape (ISS) plasmas often recovers after several energy confinement times for RMP amplitudes up to the threshold for ELM suppression. Immediately following the application of the RMP, the plasma stored energy decreases in proportion to the decrease in the line-averaged density during density "pump-out". Later in the discharge confinement recovery is observedmore » in the thermal ion channel and is correlated with the increase in the ion temperature at the top of the H-mode pedestal. A correlation between the inverse scale length of the ion temperature (α/L Ti) and the E x B shearing rate at the top of the pedestal is seen during the confinement recovery phase. Transport analysis reveals that the confinement improvement in the ion channel results from the self-similarity in the ion temperature profiles in the plasma core combined with the observed increase in α/L Ti in the plasma edge following density pump-out. In contrast the electron temperature scale length (α/L Ti) remains essentially unchanged in response to the application of the RMP. At significantly higher RMP levels the edge EXB shearing rate and α/L Ti does not increase and the confinement does not recover following density pump-out.« less

Generation and confinement of microwave gas-plasma in photonic dielectric microstructure.

PubMed

Debord, B; Jamier, R; Gérôme, F; Leroy, O; Boisse-Laporte, C; Leprince, P; Alves, L L; Benabid, F

2013-10-21

We report on a self-guided microwave surface-wave induced generation of ~60 μm diameter and 6 cm-long column of argon-plasma confined in the core of a hollow-core photonic crystal fiber. At gas pressure of 1 mbar, the micro-confined plasma exhibits a stable transverse profile with a maximum gas-temperature as high as 1300 ± 200 K, and a wall-temperature as low as 500 K, and an electron density level of 10¹⁴ cm⁻³. The fiber guided fluorescence emission presents strong Ar⁺ spectral lines in the visible and near UV. Theory shows that the observed combination of relatively low wall-temperature and high ionisation rate in this strongly confined configuration is due to an unprecedentedly wide electrostatic space-charge field and the subsequent ion acceleration dominance in the plasma-to-gas power transfer.

Energy Confinement Recovery in Low Collisionality ITER Shape Plasmas with Applied Resonant Magnetic Perturbations (RMPs)

NASA Astrophysics Data System (ADS)

Cui, L.; Grierson, B.; Logan, N.; Nazikian, R.

2016-10-01

Application of RMPs to low collisionality (ν*e < 0.4) ITER shape plasmas on DIII-D leads to a rapid reduction in stored energy due to density pumpout that is sometimes followed by a gradual recovery in the plasma stored energy. Understanding this confinement recovery is essential to optimize the confinement of RMP plasmas in present and future devices such as ITER. Transport modeling using TRANSP+TGLF indicates that the core a/LTi is stiff in these plasmas while the ion temperature gradient is much less stiff in the pedestal region. The reduction in the edge density during pumpout leads to an increase in the core ion temperature predicted by TGLF based on experimental data. This is correlated to the increase in the normalized ion heat flux. Transport stiffness in the core combined with an increase in the edge a/LTi results in an increase of the plasma stored energy, consistent with experimental observations. For plasmas where the edge density is controlled using deuterium gas puffs, the effect of the RMP on ion thermal confinement is significantly reduced. Work supported by US DOE Grant DE-FC02-04ER54698 and DE-AC02-09CH11466.

Photochemistry on soft-glass hollow-core photonic crystal fibre

NASA Astrophysics Data System (ADS)

Cubillas, Ana M.; Jiang, Xin; Euser, Tijmen G.; Taccardi, Nicola; Etzold, Bastian J. M.; Wasserscheid, Peter; Russell, Philip St. J.

2014-05-01

Hollow-core photonic crystal fibre (HC-PCF) offers strong light confinement and long interaction lengths in an optofluidic channel. These unique advantages have motivated its recent use as a highly efficient and versatile microreactor for liquid-phase photochemistry and catalysis. In this work, we use a soft-glass HC-PCF to carry out photochemical experiments in a high-index solvent such as toluene. The high-intensity and strong confinement in the fibre is demonstrated to enhance the performance of a proof-of-principle photolysis reaction.

Linear and nonlinear magneto-optical properties of an off-center single dopant in a spherical core/shell quantum dot

NASA Astrophysics Data System (ADS)

Feddi, E.; Talbi, A.; Mora-Ramos, M. E.; El Haouari, M.; Dujardin, F.; Duque, C. A.

2017-11-01

Using the effective mass approximation and a variational procedure, we have investigated the nonlinear optical absorption coefficient and the relative refractive index changes associated to a single dopant confined in core/shell quantum dots considering the influences of the core/shell dimensions, externally applied magnetic field, and dielectric mismatch. The results show that the optical absorption coefficient and the coefficients of relative refractive index change depend strongly on the core/shell sizes and they are blue shifted when the spatial confinement increases so this effect is magnified by higher structural dimensions. Additionally, it is obtained that both studied optical properties are sensitive to the dielectric environment in such a way that their amplitudes are very affected by the local field corrections.

A Full Virial Analysis of the Prestellar Cores in the Ophiuchus Molecular Cloud

NASA Astrophysics Data System (ADS)

Pattle, Kate; Ward-Thompson, Derek

We use SCUBA-2, HARP C18O J= 3 -> 2, Herschel and IRAM N2H+ J= 1 -> 0 observations of the Ophiuchus molecular cloud to identify and characterise the properties of the starless cores in the region. The SCUBA-2, HARP and Herschel data were taken as part of the JCMT and Herschel Gould Belt Surveys. We determine masses and temperatures and perform a full virial analysis on our cores, and find that our cores are all either bound or virialised, with gravitational energy and external pressure energy on average of similar importance in confining the cores. There is wide variation from region to region, with cores in the region influenced by B stars (Oph A) being substantially gravitationally bound, and cores in the most quiescent region (Oph C) being pressure-confined. We observe dissipation of turbulence in all our cores, and find that this dissipation is more effective in regions which do not contain outflow-driving protostars. Full details of this analysis are presented by Pattle et al. (2015).

Overview of MST Research

NASA Astrophysics Data System (ADS)

Sarff, J. S.; MST Team

2011-10-01

MST progress in advancing the RFP for (1) fusion plasma confinement with minimal external magnetization, (2) toroidal confinement physics, and (3) basic plasma physics is summarized. New tools and diagnostics are accessing physics barely studied in the RFP. Several diagnostic advances are important for ITER/burning plasma. A 1 MW neutral beam injector operates routinely for fast ion, heating, and transport investigations. Energetic ions are also created spontaneously by tearing mode reconnection, reminiscent of astrophysical plasmas. Classical confinement of impurity ions is measured in reduced-tearing plasmas. Fast ion slowing-down is also classical. Alfven-eigenmode-like activity occurs with NBI, but apparently not TAE. Stellarator-like helical structure appears in the core of high current plasmas, with improved confinement characteristics. FIR interferometry, Thomson scattering, and HIBP diagnostics are beginning to explore microturbulence scales, an opportunity to exploit the RFP's high beta and strong magnetic shear parameter space. A programmable power supply for the toroidal field flexibly explores scenarios from advanced inductive profile control to low current tokamak operation. A 1 MW 5.5 GHz source for electron Bernstein wave injection is nearly complete to investigate heating and current drive in over-dense plasmas. Supported by DOE and NSF.

Probing RFP Density Limits and the Interaction of Pellet Fueling and NBI Heating on MST

NASA Astrophysics Data System (ADS)

Caspary, K. J.; Chapman, B. E.; Anderson, J. K.; Limbach, S. T.; Oliva, S. P.; Sarff, J. S.; Waksman, J.; Combs, S. K.; Foust, C. R.

2013-10-01

Pellet fueling on MST has previously achieved Greenwald fractions of up to 1.5 in 200 kA improved confinement discharges. Additionally, pellet fueling to densities above the Greenwald limit in 200 kA standard discharges resulted in early termination of the plasma, but pellet size was insufficient to exceed the limit for higher current discharges. To this end, the pellet injector on MST has been upgraded to increase the maximum fueling capability by increasing the size of the pellet guide tubes, which constrain the lateral motion of the pellet in flight, to accommodate pellets of up to 4.0 mm in diameter. These 4.0 mm pellets are capable of triggering density limit terminations for MST's peak current of 600 kA. An unexpected improvement in the pellet speed and mass control was also observed compared to the smaller diameter pellets. Exploring the effect of increased density on NBI particle and heat deposition shows that for MST's 1 MW tangential NBI, core deposition of 25 keV neutrals is optimized for densities of 2-3 × 1019 m-3. This is key for beta limit studies in pellet fueled discharges with improved confinement where maximum NBI heating is desired. An observed toroidal deflection of pellets injected into NBI heated discharges is consistent with asymmetric ablation due to the fast ion population. In 200 kA improved confinement plasmas with NBI heating, pellet fueling has achieved a Greenwald fraction of 2.0. Work supported by US DoE.

Kinetic turbulence simulations at extreme scale on leadership-class systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Bei; Ethier, Stephane; Tang, William

2013-01-01

Reliable predictive simulation capability addressing confinement properties in magnetically confined fusion plasmas is critically-important for ITER, a 20 billion dollar international burning plasma device under construction in France. The complex study of kinetic turbulence, which can severely limit the energy confinement and impact the economic viability of fusion systems, requires simulations at extreme scale for such an unprecedented device size. Our newly optimized, global, ab initio particle-in-cell code solving the nonlinear equations underlying gyrokinetic theory achieves excellent performance with respect to "time to solution" at the full capacity of the IBM Blue Gene/Q on 786,432 cores of Mira at ALCFmore » and recently of the 1,572,864 cores of Sequoia at LLNL. Recent multithreading and domain decomposition optimizations in the new GTC-P code represent critically important software advances for modern, low memory per core systems by enabling routine simulations at unprecedented size (130 million grid points ITER-scale) and resolution (65 billion particles).« less

Stress dependence of permeability of intact and fractured shale cores.

NASA Astrophysics Data System (ADS)

van Noort, Reinier; Yarushina, Viktoriya

2016-04-01

Whether a shale acts as a caprock, source rock, or reservoir, understanding fluid flow through shale is of major importance for understanding fluid flow in geological systems. Because of the low permeability of shale, flow is thought to be largely confined to fractures and similar features. In fracking operations, fractures are induced specifically to allow for hydrocarbon exploration. We have constructed an experimental setup to measure core permeabilities, using constant flow or a transient pulse. In this setup, we have measured the permeability of intact and fractured shale core samples, using either water or supercritical CO2 as the transporting fluid. Our measurements show decreasing permeability with increasing confining pressure, mainly due to time-dependent creep. Furthermore, our measurements show that for a simple splitting fracture, time-dependent creep will also eliminate any significant effect of this fracture on permeability. This effect of confinement on fracture permeability can have important implications regarding the effects of fracturing on shale permeability, and hence for operations depending on that.

Active core profile and transport modification by application of ion Bernstein wave power in the Princeton Beta Experiment-Modification

NASA Astrophysics Data System (ADS)

LeBlanc, B.; Batha, S.; Bell, R.; Bernabei, S.; Blush, L.; de la Luna, E.; Doerner, R.; Dunlap, J.; England, A.; Garcia, I.; Ignat, D.; Isler, R.; Jones, S.; Kaita, R.; Kaye, S.; Kugel, H.; Levinton, F.; Luckhardt, S.; Mutoh, T.; Okabayashi, M.; Ono, M.; Paoletti, F.; Paul, S.; Petravich, G.; Post-Zwicker, A.; Sauthoff, N.; Schmitz, L.; Sesnic, S.; Takahashi, H.; Talvard, M.; Tighe, W.; Tynan, G.; von Goeler, S.; Woskov, P.; Zolfaghari, A.

1995-03-01

Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇ne, ∇Te, ∇νφ, and ∇Ti, delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central Ti results from χi reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32-0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma.

Multiple cores of Gleason score 6 correlate with favourable findings at radical prostatectomy

PubMed Central

Ellis, Carla L.; Walsh, Patrick C.; Partin, Alan W.; Epstein, Jonathan I.

2014-01-01

Objective To establish whether the good prognosis of Gleason score 6 (GS6) is maintained in the setting of multiple involved cores. Patients and Methods In total, 6156 men (from 1 April 2000 to 30 April 2007) with GS6 on biopsy underwent radical prostatectomy (RP) at our institution. The number of positive cores was correlated with the outcome at RP. Results More positive cores correlated with less organ-confined disease (P < 0.001), positive margins (P < 0.012), increasing RP grade (P < 0.001) and increased seminal vesicles/lymph node involvement (P = 0.012). For men with data available, the actuarial risk of being biochemically free of disease at 5 years was 93.2% when ≤6 cores were positive (812 men followed to 5 years) vs 89.1% if >6 cores were positive (41 men followed to 2 years) (P = 0.6). Although the predicted ‘cure rate’ of >75% probability of a tumour showing no evidence of biochemical recurrence at 10 years after RP was statistically different between cases with ≤6 vs >6 positive cores (P < 0.0001), the outcome in both groups was still favourable (90.5% vs 84%). Partin-like tables were generated factoring in the number of positive cores to predict organ-confined disease as a guide for urologists to perform nerve-sparing surgery. For example, with T1c disease, there was a ≥75% probability of organ-confined disease with one to three positive cores regardless of prostate-specific antigen (PSA) level, and the same probability was present with four to six positive cores and a PSA level of 0–4 ng/mL. Conclusion A low Gleason score on biopsy is a powerful prognostic finding, such that this favourable outcome is maintained even in the setting of multiple positive cores with GS6. PMID:23350787

Multiple cores of Gleason score 6 correlate with favourable findings at radical prostatectomy.

PubMed

Ellis, Carla L; Walsh, Patrick C; Partin, Alan W; Epstein, Jonathan I

2013-06-01

To establish whether the good prognosis of Gleason score 6 (GS6) is maintained in the setting of multiple involved cores. In total, 6156 men (from 1 April 2000 to 30 April 2007) with GS6 on biopsy underwent radical prostatectomy (RP) at our institution. The number of positive cores was correlated with the outcome at RP. More positive cores correlated with less organ-confined disease (P < 0.001), positive margins (P < 0.012), increasing RP grade (P < 0.001) and increased seminal vesicles/lymph node involvement (P = 0.012). For men with data available, the actuarial risk of being biochemically free of disease at 5 years was 93.2% when ≤6 cores were positive (812 men followed to 5 years) vs 89.1% if >6 cores were positive (41 men followed to 2 years) (P = 0.6). Although the predicted 'cure rate' of >75% probability of a tumour showing no evidence of biochemical recurrence at 10 years after RP was statistically different between cases with ≤6 vs >6 positive cores (P < 0.0001), the outcome in both groups was still favourable (90.5% vs 84%). Partin-like tables were generated factoring in the number of positive cores to predict organ-confined disease as a guide for urologists to perform nerve-sparing surgery. For example, with T1c disease, there was a ≥75% probability of organ-confined disease with one to three positive cores regardless of prostate-specific antigen (PSA) level, and the same probability was present with four to six positive cores and a PSA level of 0-4 ng/mL. A low Gleason score on biopsy is a powerful prognostic finding, such that this favourable outcome is maintained even in the setting of multiple positive cores with GS6. © 2013 BJU International.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James

2016-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when transport associated with MHD tearing is reduced. Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking. Using inductive control, the tearing modes are reduced and global confinement is increased to values expected for a comparable tokamak plasma. The improved confinement is associated with a large increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have frequencies >50 kHz, wavenumbers k_phi*rho_s<0.14, and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in fluctuations associated with global tearing modes. Their amplitude increases with the local density gradient, and they exhibit a density-gradient threshold at R/L_n 15, higher than in tokamak plasmas by R/a. the GENE code, modified for RFP equilibria, predicts the onset of microinstability for these strong-gradient plasma conditions. The density-gradient-driven TEM is the dominant instability in the region where the measured density fluctuations are largest, and the experimental threshold-gradient is close to the predicted critical gradient for linear stability. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Similar circumstances could occur in the edge region of tokamak plasmas when resonant magnetic perturbations are applied for the control of ELMs. Work supported by US DOE.

Direct observation of terahertz surface modes in nanometer-sized liquid water pools.

PubMed

Boyd, J E; Briskman, A; Colvin, V L; Mittleman, D M

2001-10-01

The far-infrared absorption spectrum of nanometer-sized water pools at the core of AOT micelles exhibits a pronounced resonance which is absent in bulk water. The amplitude and spectral position of this resonance are sensitive to the size of the confined water core. This resonance results from size-dependent modifications in the vibrational density of states, and thus has far-reaching implications for chemical processes which involve water sequestered within small cavities. These data represent the first study of the terahertz dielectric properties of confined liquids.

ABC Triblock Copolymer Vesicles with Mesh-like Morphology

NASA Astrophysics Data System (ADS)

Zhao, Wei; Russell, Thomas; Grason, Gregory

2010-03-01

Polymer vesicles can be made from poly(isoprene-b-styrene-b-2-vinylpyridene) (PI-b-PS-b-P2VP) triblock copolymer under the confinement of anodic aluminum oxide (AAO) membrane. It was found that these vesicles have well-defined, nanoscopic size and a microphase-separated hydrophobic core, comprised of PS and PI blocks. Vesicle formation was tracked using both transmission and scanning electron microscopy. A mesh-like morphology formed in the core at a well-defined composition of three blocks. Confinement played an important role in generating these vesicles with such an unusual morphology.

Plasma core reactor simulations using RF uranium seeded argon discharges

NASA Technical Reports Server (NTRS)

Roman, W. C.

1976-01-01

Experimental results are described in which pure uranium hexafluoride was injected into an argon-confined, steady-state, RF-heated plasma to investigate characteristics of plasma core nuclear reactors. The 80 kW (13.56 MHz) and 1.2 MW (5.51 MHz) rf induction heater facilities were used to determine a test chamber flow scheme which offered best uranium confinement with minimum wall coating. The cylindrical fused-silica test chamber walls were 5.7-cm-ID by 10-cm-long. Test conditions included RF powers of 2-85 kW, chamber pressures of 1-12 atm, and uranium hexafluoride mass-flow rates of 0.005-0.13 g/s. Successful techniques were developed for fluid-mechanical confinement of RF-heated plasmas with pure uranium hexafluoride injection.

Structural and electronic properties of CdSe/ZnS and ZnS/CdSe core/shell nanowires via first principles study

NASA Astrophysics Data System (ADS)

Rehman, Shafiq Ur; Li, H. M.; Ding, Z. J.

2018-05-01

First principles calculations have been performed to predict the structural stability and electronic structures of hydrogen passivated wurtzite CdSe/ZnS and ZnS/CdSe core/shell nanowires (CSNWs) in the [0001] direction. The calculated binding energy shows that ZnS/CdSe CSNWs are more stable than CdSe/ZnS CSNWs and the stability of ZnS/CdSe CSNWs increases with increasing the thickness of ZnS shell. The modulated electronic band gap demonstrates an increase when the size of both CSNWs is reduced, as a result of the quantum confinement effect. The core-to-shell chemical composition of atoms shows that a strong composition effect also exists in these CSNWs, which in turn affects their electronic properties. Our simulated results show that the photoemission spectra of the CSNWs can be significantly improved by tuning the energy gap of CSNWs.

Effect of Symmetry on Performance of Imploding Capsules using the Big Foot Design

NASA Astrophysics Data System (ADS)

Khan, Shahab; Casey, Daniel; Baker, Kevin; Thomas, Cliff; Nora, Ryan; Spears, Brian; Benedetti, Laura; Izumi, Nobuhiko; Ma, Tammy; Nagel, Sabrina; Pak, Arthur; National Ignition Facility Collaboration

2017-10-01

At the National Ignition Facility, several simultaneous designs are investigated for optimizing Inertial Confinement Fusion (ICF) energy gain of indirectly driven imploding fuel capsules. Relatively high neutron yield has been achieved while exhibiting a non-symmetric central core and/or shell. While developing the ``Big Foot'' design, several tuning steps were undertaken to minimize the asymmetry of both the central hot core as well as the shell. Surrogate capsules (symcaps) were utilized in the 2-D Radiography platform to assess both the shell and central core symmetry. The results of the tuning experiments are presented. In addition, a comparison of performance and shape metrics demonstrates that improving symmetry of the implosion can yield better performance. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-683471.

Fluctuation reduction and enhanced confinement in the MST reversed-field pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chapman, Brett Edward

1997-10-01

Plasmas with a factor of ≥3 improvement in energy confinement have been achieved in the MST reversed-field pinch (RFP). These plasmas occur spontaneously, following sawtooth crashes, subject to constraints on, eg, toroidal magnetic field reversal and wall conditioning. Possible contributors to the improved confinement include a reduction of core-resonant, global magnetic fluctuations and a reduction of electrostatic fluctuations over the entire plasma edge. One feature of these plasmas is a region of strong ExB flow shear in the edge. Never before observed in conjunction with enhanced confinement in the RFP, such shear is common in enhanced confinement discharges in tokamaks and stellarators. Another feature of these plasmas is a new type of discrete dynamo event. Like sawtooth crashes, a common form of discrete dynamo, these events correspond to bursts of edge parallel current. The reduction of electrostatic fluctuations in these plasmas occurs within and beyond the region of strong ExB flow shear, similar to what is observed in tokamaks and stellarators. However, the reductions in the MST include fluctuations whose correlation lengths are larger than the width of the shear region. The reduction of the global magnetic fluctuations is most likely due to flattening of the μ=μ 0more » $$\\vec{J}$$∙$$\\vec{B}$$/B 2 profile. Flattening can occur, eg, due to the new type of discrete dynamo event and reduced edge resistivity. Enhanced confinement plasmas are also achieved in the MST when auxiliary current is applied to flatten the μ profile and reduce magnetic fluctuations. Unexpectedly, these plasmas also exhibit a region (broader than in the case above) of strong ExB flow shear in the edge, an edge-wide reduction of electrostatic fluctuations, and the new type of discrete dynamo event. Auxiliary current drive has historically been viewed as the principal route to fusion reactor viability for the RFP.« less

PDC-bit performance under simulated borehole conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, E.E.; Azar, J.J.

1993-09-01

Laboratory drilling tests were used to investigate the effects of pressure on polycrystalline-diamond-compact (PDC) drill-bit performance. Catoosa shale core samples were drilled with PDC and roller-cone bits at up to 1,750-psi confining pressure. All tests were conducted in a controlled environment with a full-scale laboratory drilling system. Test results indicate, that under similar operating conditions, increases in confining pressure reduce PDC-bit performance as much as or more than conventional-rock-bit performance. Specific energy calculations indicate that a combination of rock strength, chip hold-down, and bit balling may have reduced performance. Quantifying the degree to which pressure reduces PDC-bit performance will helpmore » researchers interpret test results and improve bit designs and will help drilling engineers run PDC bits more effectively in the field.« less

Nonlinear gyrokinetic simulations of the I-mode high confinement regime and comparisons with experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

White, A. E., E-mail: whitea@mit.edu; Howard, N. T.; Creely, A. J.

2015-05-15

For the first time, nonlinear gyrokinetic simulations of I-mode plasmas are performed and compared with experiment. I-mode is a high confinement regime, featuring energy confinement similar to H-mode, but without enhanced particle and impurity particle confinement [D. G. Whyte et al., Nucl. Fusion 50, 105005 (2010)]. As a consequence of the separation between heat and particle transport, I-mode exhibits several favorable characteristics compared to H-mode. The nonlinear gyrokinetic code GYRO [J. Candy and R. E. Waltz, J Comput. Phys. 186, 545 (2003)] is used to explore the effects of E × B shear and profile stiffness in I-mode and comparemore » with L-mode. The nonlinear GYRO simulations show that I-mode core ion temperature and electron temperature profiles are more stiff than L-mode core plasmas. Scans of the input E × B shear in GYRO simulations show that E × B shearing of turbulence is a stronger effect in the core of I-mode than L-mode. The nonlinear simulations match the observed reductions in long wavelength density fluctuation levels across the L-I transition but underestimate the reduction of long wavelength electron temperature fluctuation levels. The comparisons between experiment and gyrokinetic simulations for I-mode suggest that increased E × B shearing of turbulence combined with increased profile stiffness are responsible for the reductions in core turbulence observed in the experiment, and that I-mode resembles H-mode plasmas more than L-mode plasmas with regards to marginal stability and temperature profile stiffness.« less

Rock Deformation at High Confining Pressure and Temperature.

DTIC Science & Technology

debugged, delivered and installed to the contracting agency. Clay specimens of illite, kaolinite and montmorillonite were deformed in tri-axial compression...at 25 and 3000C at a constant confining pressure of 2 kb and a constant strain rate of .0001 sec. The illite and kaolinite are stronger under these...conditions than montmorillonite . Cores from dolomite single crystals were deformed at a confining pressure of 7 kb and temperatures of 300 and 500C

Overview of long pulse H-mode operation on EAST

NASA Astrophysics Data System (ADS)

Gong, X.; Garofalo, A. M.; Wan, B.; Li, J.; Qian, J.; Li, E.; Liu, F.; Zhao, Y.; Wang, M.; Xu, H.; EAST Team

2017-10-01

The EAST research program aims to demonstrate steady-state long-pulse high-performance H-mode operations with ITER-like poloidal configuration and RF-dominated heating schemes. In the recent experimental campaign, a long pulse fully non-inductive H-mode discharge lasting over 100 seconds using the upper ITER-like tungsten divertor has been achieved in EAST. This scenario used only RF heating and current drive, but also benefitted from an integrated control of the wall conditioning, plasma configuration, divertor heat flux, particle exhaust, impurity management and superconducting coils safety. Maintaining effective coupling of multiple RF heating and current drive sources on EAST is a critical ingredient. This long pulse discharge had good energy confinement, H98,y2 1.1-1.2, and all of the plasma parameters reach a true steady-state. Power balance indicates that the confinement improvement is due partly to a significantly reduced core electron transport inside minor radius rho<0.4. This work was supported by the National Magnetic Confinement Fusion Program of China Contract No. 2015GB10200 and the US Department of Energy Contract No. DE-SC0010685.

Conceptual hydrogeologic framework of the shallow aquifer system at Virginia Beach, Virginia

USGS Publications Warehouse

Smith, Barry S.; Harlow, George E.

2002-01-01

The hydrogeologic framework of the shallow aquifer system at Virginia Beach was revised to provide a better understanding of the distribution of fresh ground water, its potential use, and its susceptibility to contamination. The revised conceptual framework is based primarily on analyses of continuous cores and downhole geophysical logs collected at 7 sites to depths of approximately 200 ft.The shallow aquifer system at Virginia Beach is composed of the Columbia aquifer, the Yorktown confining unit, and the Yorktown-East-over aquifer. The shallow aquifer system is separated from deeper units by the continuous St. Marys confining unit.The Columbia aquifer is defined as the predominantly sandy surficial deposits above the Yorktown confining unit. The Yorktown confining unit is composed of a series of very fine sandy to silty clay units of various colors at or near the top of the Yorktown Formation. The Yorktown confining unit varies in thickness and in composition, but on a regional scale is a leaky confining unit. The Yorktown-Eastover aquifer is defined as the predominantly sandy deposits of the Yorktown Formation and the upper part of the Eastover Formation above the confining clays of the St. Marys Formation. The limited areal extent of highly permeable deposits containing freshwater in the Yorktown-Eastover aquifer precludes the installation of highly productive freshwater wells over most of the city. Some deposits of biofragmental sand or shell hashes in the Yorktown-Eastover aquifer can support high-capacity wells.A water sample was collected from each of 10 wells installed at 5 of the 7 core sites to determine the basic chemistry of the aquifer system. One shallow well and one deep well was installed at each site. Concentrations of chloride were higher in the water from the deeper well at each site. Concentrations of dissolved iron in all of the water samples were higher than the U.S. Environmental Protection Agency Secondary Drinking Water Regulations. Concentrations of manganese and chloride were higher than the Secondary Drinking Water Regulations in samples from some wells.In the humid climate of Virginia Beach, the periodic recharge of freshwater through the sand units of the shallow aquifer system occurs often enough to create a dynamic equilibrium whereby freshwater flows continually down and away from the center of the ridges to mix with and sweep brackish water and saltwater back toward the tidal rivers, bays, salt marshes, and the Atlantic Ocean.The aquifers and confining units of the shallow aquifer system at Virginia Beach are heterogeneous, discontinuous, and without exact marker beds, which makes correlations in the study area difficult. Investigations using well cuttings, spot cores, or split-spoon samples with geophysical logs are not as definitive as continuous cores for determining or correlating hydrogeologic units. Future investigations of the shallow aquifer system would benefit by collecting continuous cores.

Quantum confinement-induced tunable exciton states in graphene oxide.

PubMed

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology.

Lithostratigraphy, petrography, biostratigraphy, and strontium-isotope stratigraphy of the surficial aquifer system of western Collier County, Florida

USGS Publications Warehouse

Edwards, L.E.; Weedman, S.D.; Simmons, R.; Scott, T.M.; Brewster-Wingard, G. L.; Ishman, S.E.; Carlin, N.M.

1998-01-01

In 1996, seven cores were recovered in western Collier County, southwestern Florida, to acquire subsurface geologic and hydrologic data to support ground-water modeling efforts. This report presents the lithostratigraphy, X-ray diffraction analyses, petrography, biostratigraphy, and strontium-isotope stratigraphy of these cores. The oldest unit encountered in the study cores is an unnamed formation that is late Miocene. At least four depositional sequences are present within this formation. Calculated age of the formation, based on strontium-isotope stratigraphy, ranges from 9.5 to 5.7 Ma (million years ago). An unconformity within this formation that represents a hiatus of at least 2 million years is indicated in the Old Pump Road core. In two cores, Collier-Seminole and Old Pump Road, the uppermost sediments of the unnamed formation are not dated by strontium isotopes, and, based on the fossils present, these sediments could be as young as Pliocene. In another core (Fakahatchee Strand-Ranger Station), the upper part of the unnamed formation is dated by mollusks as Pliocene. The Tamiami Formation overlies the unnamed formation throughout the study area and is represented by the Ochopee Limestone Member. The unit is Pliocene and probably includes the interval of time near the early/late Pliocene boundary. Strontium-isotope analysis indicates an early Pliocene age (calculated ages range from 5.1 to 3.5 Ma), but the margin of error includes the latest Miocene and the late Pliocene. The dinocyst assemblages in the Ochopee typically are not age-diagnostic, but, near the base of the unit in the Collier-Seminole, Jones Grade, and Fakahatchee Strand State Forest cores, they indicate an age of late Miocene or Pliocene. The molluscan assemblages indicate a Pliocene age for the Ochopee, and a distinctive assemblage of Carditimera arata and Chione cortinaria in several of the cores specifically indicates an age near the early/late Pliocene boundary. Undifferentiated sands overlie the Pliocene limestones in two cores in the southern part of the study area. Artificial fill occurs at the top of most of the cores. The hydrologic confining units penetrated by these cores are different in different parts of the study area. To the west, a hard tightly cemented dolostone forms the first major confining unit below the water table. In the eastern part of the study area, confinement is more difficult to determine. A tightly cemented sandstone, much younger than the dolostones to the west and probably not laterally connected to them, forms a slight confining unit in one core. Thick zones of poorly sorted muddy unconsolidated sands form a slight confining unit in other cores; these probably are not correlative to either the sandstone or the dolostones to the west. The age and sedimentologic observations suggest a complex compartmentalization of the surficial aquifer system in southwestern Florida. The calibrations of dinocyst and molluscan occurrences with strontium-isotope stratigraphy allows us to expand and document the reported ranges of many taxa. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

MST Pellet Injector Upgrades to Probe Beta and Density Limits and Impurity Particle Transport

NASA Astrophysics Data System (ADS)

Caspary, K. J.; Chapman, B. E.; Anderson, J. K.; Kumar, S. T. A.; Limbach, S. T.; Oliva, S. P.; Sarff, J. S.; Waksman, J.; Combs, S. K.; Foust, C. R.

2012-10-01

Upgrades to the pellet injector on MST will allow for significantly increased fueling capability enabling density limit studies for previously unavailable density regimes. Thus far, Greenwald fractions of 1.2 and 1.5 have been achieved in 500 kA and 200 kA improved confinement plasmas, respectively. The size of the pellet guide tubes, which constrain the lateral motion of the pellet in flight, was increased to accommodate pellets of up to 4.0 mm in diameter, capable of fueling to Greenwald fractions > 2.0 for MST's peak current of 600 kA. Exploring the effect of increased density on NBI deposition shows that for MST's NBI, core deposition of 25 keV neutrals is optimized for densities of 2 -- 3 x 10^19 m-3. This is key for beta limit studies in pellet fueled discharges with improved confinement where maximum NBI heating is desired. In addition, a modification to the injector has allowed operation using alternative pellet fuels with triple points significantly higher than that of deuterium (18.7 K). A small flow of helium into the pellet formation vacuum chamber introduces a controllable heat source capable of elevating the operating temperature of the injector. Injection of methane pellets with a triple point of 90.7 K results in a 12-fold increase in the core carbon impurity density. The flow rate is easily adjusted to optimize injector operating temperature for other fuel gases as well. Work supported by US DoE.

Modulation of Core Turbulent Density Fluctuations by Large-Scale Neoclassical Tearing Mode Islands in the DIII-D Tokamak

DOE PAGES

Bardóczi, L.; Rhodes, T. L.; Carter, T. A.; ...

2016-05-26

We report the first observation of localized modulation of turbulent density uctuations en (via Beam Emission Spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that en could be dominantly driven by the ion temperature gradient (ITG) instability.

Polymer optical waveguide with multiple graded-index cores for on-board interconnects fabricated using soft-lithography.

PubMed

Ishigure, Takaaki; Nitta, Yosuke

2010-06-21

We successfully fabricate a polymer optical waveguide with multiple graded-index (GI) cores directly on a substrate utilizing the soft-lithography method. A UV-curable polymer (TPIR-202) supplied from Tokyo Ohka Kogyo Co., Ltd. is used, and the GI cores are formed during the curing process of the core region, which is similar to the preform process we previously reported. We experimentally confirm that near parabolic refractive index profiles are formed in the parallel cores (more than 50 channels) with 40 microm x 40 microm size at 250-microm pitch. Although the loss is still as high as 0.1 approximately 0.3 dB/cm at 850 nm, which is mainly due to scattering loss inherent to the polymer matrix, the scattering loss attributed to the waveguide's structural irregularity could be sufficiently reduced by a graded refractive index profile. For comparison, we fabricate step-index (SI)-core waveguides with the same materials by means of the same process. Then, we evaluate the inter-channel crosstalk in the SI- and GI-core waveguides under almost the same conditions. It is noteworthy that remarkable crosstalk reduction (5 dB and beyond) is confirmed in the GI-core waveguides, since the propagating modes in GI-cores are tightly confined near the core center and less optical power is found near the core cladding boundary. This significant improvement in the inter-channel crosstalk allows the GI-core waveguides to be utilized for extra high-density on-board optical interconnections.

Confined Ultrathin Pd-Ce Nanowires with Outstanding Moisture and SO2 Tolerance in Methane Combustion.

PubMed

Peng, Honggen; Rao, Cheng; Zhang, Ning; Wang, Xiang; Liu, Wenming; Mao, Wenting; Han, Lu; Zhang, Pengfei; Dai, Sheng

2018-05-22

An efficient strategy (enhanced metal oxide interaction and core-shell confinement to inhibit the sintering of noble metal) is presented confined ultrathin Pd-CeO x nanowire (2.4 nm) catalysts for methane combustion, which enable CH 4 total oxidation at a low temperature of 350 °C, much lower than that of a commercial Pd/Al 2 O 3 catalyst (425 °C). Importantly, unexpected stability was observed even under harsh conditions (800 °C, water vapor, and SO 2 ), owing to the confinement and shielding effect of the porous silica shell together with the promotion of CeO 2 . Pd-CeO x solid solution nanowires (Pd-Ce NW) as cores and porous silica as shells (Pd-CeNW@SiO 2 ) were rationally prepared by a facile and direct self-assembly strategy for the first time. This strategy is expected to inspire more active and stable catalysts for use under severe conditions (vehicle emissions control, reforming, and water-gas shift reaction). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Boundary perturbations coupled to core 3/2 tearing modes on the DIII-D tokamak

NASA Astrophysics Data System (ADS)

Tobias, B.; Yu, L.; Domier, C. W.; Luhmann, N. C., Jr.; Austin, M. E.; Paz-Soldan, C.; Turnbull, A. D.; Classen, I. G. J.; the DIII-D Team

2013-09-01

High confinement (H-mode) discharges on the DIII-D tokamak are routinely subject to the formation of long-lived, non-disruptive magnetic islands that degrade confinement and limit fusion performance. Simultaneous, 2D measurement of electron temperature fluctuations in the core and edge regions allows for reconstruction of the radially resolved poloidal mode number spectrum and phase of the global plasma response associated with these modes. Coherent, n = 2 excursions of the plasma boundary are found to be the result of coupling to an n = 2, kink-like mode which arises locked in phase to the 3/2 island chain. This coupling dictates the relative phase of the displacement at the boundary with respect to the tearing mode. This unambiguous phase relationship, for which no counter-examples are observed, is presented as a test for modeling of the perturbed fields to be expected outside the confined plasma.

Quantum confinement-induced tunable exciton states in graphene oxide

PubMed Central

Lee, Dongwook; Seo, Jiwon; Zhu, Xi; Lee, Jiyoul; Shin, Hyeon-Jin; Cole, Jacqueline M.; Shin, Taeho; Lee, Jaichan; Lee, Hangil; Su, Haibin

2013-01-01

Graphene oxide has recently been considered to be a potential replacement for cadmium-based quantum dots due to its expected high fluorescence. Although previously reported, the origin of the luminescence in graphene oxide is still controversial. Here, we report the presence of core/valence excitons in graphene-based materials, a basic ingredient for optical devices, induced by quantum confinement. Electron confinement in the unreacted graphitic regions of graphene oxide was probed by high resolution X-ray absorption near edge structure spectroscopy and first-principles calculations. Using experiments and simulations, we were able to tune the core/valence exciton energy by manipulating the size of graphitic regions through the degree of oxidation. The binding energy of an exciton in highly oxidized graphene oxide is similar to that in organic electroluminescent materials. These results open the possibility of graphene oxide-based optoelectronic device technology. PMID:23872608

An MR/MRI compatible core holder with the RF probe immersed in the confining fluid.

PubMed

Shakerian, M; Balcom, B J

2018-01-01

An open frame RF probe for high pressure and high temperature MR/MRI measurements was designed, fabricated, and tested. The open frame RF probe was installed inside an MR/MRI compatible metallic core holder, withstanding a maximum pressure and temperature of 5000 psi and 80 °C. The open frame RF probe was tunable for both 1 H and 19 F resonance frequencies with a 0.2 T static magnetic field. The open frame structure was based on simple pillars of PEEK polymer upon which the RF probe was wound. The RF probe was immersed in the high pressure confining fluid during operation. The open frame structure simplified fabrication of the RF probe and significantly reduced the amount of polymeric materials in the core holder. This minimized the MR background signal detected. Phase encoding MRI methods were employed to map the spin density of a sulfur hexafluoride gas saturating a Berea core plug in the core holder. The SF 6 was imaged as a high pressure gas and as a supercritical fluid. Copyright © 2017 Elsevier Inc. All rights reserved.

An MR/MRI compatible core holder with the RF probe immersed in the confining fluid

NASA Astrophysics Data System (ADS)

Shakerian, M.; Balcom, B. J.

2018-01-01

An open frame RF probe for high pressure and high temperature MR/MRI measurements was designed, fabricated, and tested. The open frame RF probe was installed inside an MR/MRI compatible metallic core holder, withstanding a maximum pressure and temperature of 5000 psi and 80 °C. The open frame RF probe was tunable for both 1H and 19F resonance frequencies with a 0.2 T static magnetic field. The open frame structure was based on simple pillars of PEEK polymer upon which the RF probe was wound. The RF probe was immersed in the high pressure confining fluid during operation. The open frame structure simplified fabrication of the RF probe and significantly reduced the amount of polymeric materials in the core holder. This minimized the MR background signal detected. Phase encoding MRI methods were employed to map the spin density of a sulfur hexafluoride gas saturating a Berea core plug in the core holder. The SF6 was imaged as a high pressure gas and as a supercritical fluid.

Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers.

PubMed

Li, Changyi; Wright, Jeremy B; Liu, Sheng; Lu, Ping; Figiel, Jeffrey J; Leung, Benjamin; Chow, Weng W; Brener, Igal; Koleske, Daniel D; Luk, Ting-Shan; Feezell, Daniel F; Brueck, S R J; Wang, George T

2017-02-08

We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

Diamagnetic susceptibility of a hydrogenic donor in a group IV-VI quantum dot-quantum well heterostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saravanamoorthy, S. N.; Peter, A. John, E-mail: a.john.peter@gmail.com

2016-05-23

Electronic properties of a hydrogenic donor impurity in a CdSe/Pb{sub 0.8}Cd{sub 0.2}Se/CdSe quantum dot quantum well system are investigated for various radii of core with shell materials. Confined energies are obtained taking into account the geometrical size of the system and thereby the donor binding energies are found. The diamagnetic susceptibility is estimated for a confined shallow donor in the well system. The results show that the diamagnetic susceptibility strongly depends on core and shell radii and it is more sensitive to variations of the geometrical size of the well material.

Rydberg atoms in hollow-core photonic crystal fibres.

PubMed

Epple, G; Kleinbach, K S; Euser, T G; Joly, N Y; Pfau, T; Russell, P St J; Löw, R

2014-06-19

The exceptionally large polarizability of highly excited Rydberg atoms-six orders of magnitude higher than ground-state atoms--makes them of great interest in fields such as quantum optics, quantum computing, quantum simulation and metrology. However, if they are to be used routinely in applications, a major requirement is their integration into technically feasible, miniaturized devices. Here we show that a Rydberg medium based on room temperature caesium vapour can be confined in broadband-guiding kagome-style hollow-core photonic crystal fibres. Three-photon spectroscopy performed on a caesium-filled fibre detects Rydberg states up to a principal quantum number of n=40. Besides small energy-level shifts we observe narrow lines confirming the coherence of the Rydberg excitation. Using different Rydberg states and core diameters we study the influence of confinement within the fibre core after different exposure times. Understanding these effects is essential for the successful future development of novel applications based on integrated room temperature Rydberg systems.

Glucose Infusion into Exercising Dogs after Confinement: Rectal and Active Muscle Temperatures

NASA Technical Reports Server (NTRS)

Greenleaf, J. E.; Kruk, B.; Nazar, K.; Falecka-Wieczorek, I.; Kaciuba-Uscilko, H.

1995-01-01

Intravenous glucose infusion into ambulatory dogs results in attenuation of exercise-induced increase of both rectal and thigh muscle temperatures. That glucose (Glu) infusion attenuates excessive increase in body temperature from restricted activity during confinement deconditioning. Intravenous glucose infusion attenuates the rise in exercise core temperature in deconditioned dogs by a yet undefined mechanism.

NEUTRONIC REACTOR CORE

DOEpatents

Thomson, W.B.; Corbin, A. Jr.

1961-07-18

An improved core for a gas-cooled power reactor which admits gas coolant at high temperatures while affording strong integral supporting structure and efficient moderation of neutrons is described. The multiplicities of fuel elements constituting the critical amassment of fissionable material are supported and confined by a matrix of metallic structure which is interspersed therebetween. Thermal insulation is interposed between substantially all of the metallic matrix and the fuel elements; the insulation then defines the principal conduit system for conducting the coolant gas in heat-transfer relationship with the fuel elements. The metallic matrix itseif comprises a system of ducts through which an externally-cooled hydrogeneous liquid, such as water, is circulated to serve as the principal neutron moderant for the core and conjointly as the principal coolant for the insulated metallic structure. In this way, use of substantially neutron transparent metals, such as aluminum, becomes possible for the supporting structure, despite the high temperatures of the proximate gas. The Aircraft Nuclear Propulsion program's "R-1" reactor design is a preferred embodiment.

PARVMEC: An Efficient, Scalable Implementation of the Variational Moments Equilibrium Code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seal, Sudip K; Hirshman, Steven Paul; Wingen, Andreas

The ability to sustain magnetically confined plasma in a state of stable equilibrium is crucial for optimal and cost-effective operations of fusion devices like tokamaks and stellarators. The Variational Moments Equilibrium Code (VMEC) is the de-facto serial application used by fusion scientists to compute magnetohydrodynamics (MHD) equilibria and study the physics of three dimensional plasmas in confined configurations. Modern fusion energy experiments have larger system scales with more interactive experimental workflows, both demanding faster analysis turnaround times on computational workloads that are stressing the capabilities of sequential VMEC. In this paper, we present PARVMEC, an efficient, parallel version of itsmore » sequential counterpart, capable of scaling to thousands of processors on distributed memory machines. PARVMEC is a non-linear code, with multiple numerical physics modules, each with its own computational complexity. A detailed speedup analysis supported by scaling results on 1,024 cores of a Cray XC30 supercomputer is presented. Depending on the mode of PARVMEC execution, speedup improvements of one to two orders of magnitude are reported. PARVMEC equips fusion scientists for the first time with a state-of-theart capability for rapid, high fidelity analyses of magnetically confined plasmas at unprecedented scales.« less

A double-layer based model of ion confinement in electron cyclotron resonance ion source.

PubMed

Mascali, D; Neri, L; Celona, L; Castro, G; Torrisi, G; Gammino, S; Sorbello, G; Ciavola, G

2014-02-01

The paper proposes a new model of ion confinement in ECRIS, which can be easily generalized to any magnetic configuration characterized by closed magnetic surfaces. Traditionally, ion confinement in B-min configurations is ascribed to a negative potential dip due to superhot electrons, adiabatically confined by the magneto-static field. However, kinetic simulations including RF heating affected by cavity modes structures indicate that high energy electrons populate just a thin slab overlapping the ECR layer, while their density drops down of more than one order of magnitude outside. Ions, instead, diffuse across the electron layer due to their high collisionality. This is the proper physical condition to establish a double-layer (DL) configuration which self-consistently originates a potential barrier; this "barrier" confines the ions inside the plasma core surrounded by the ECR surface. The paper will describe a simplified ion confinement model based on plasma density non-homogeneity and DL formation.

Observation of energetic electron confinement in a largely stochastic reversed-field pinch plasma

NASA Astrophysics Data System (ADS)

Clayton, D. J.; Chapman, B. E.; O'Connell, R.; Almagri, A. F.; Burke, D. R.; Forest, C. B.; Goetz, J. A.; Kaufman, M. C.; Bonomo, F.; Franz, P.; Gobbin, M.; Piovesan, P.

2010-01-01

Runaway electrons with energies >100 keV are observed with the appearance of an m =1 magnetic island in the core of otherwise stochastic Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field-pinch plasmas. The island is associated with the innermost resonant tearing mode, which is usually the largest in the m =1 spectrum. The island appears over a range of mode spectra, from those with a weakly dominant mode to those, referred to as quasi single helicity, with a strongly dominant mode. In a stochastic field, the rate of electron loss increases with electron parallel velocity. Hence, high-energy electrons imply a region of reduced stochasticity. The global energy confinement time is about the same as in plasmas without high-energy electrons or an island in the core. Hence, the region of reduced stochasticity must be localized. Within a numerical reconstruction of the magnetic field topology, high-energy electrons are substantially better confined inside the island, relative to the external region. Therefore, it is deduced that the island provides a region of reduced stochasticity and that the high-energy electrons are generated and well confined within this region.

Highly birefringent elliptical core photonic crystal fiber for terahertz application

NASA Astrophysics Data System (ADS)

Sultana, Jakeya; Islam, Md. Saiful; Faisal, Mohammad; Islam, Mohammad Rakibul; Ng, Brian W.-H.; Ebendorff-Heidepriem, Heike; Abbott, Derek

2018-01-01

We present a novel strategy for designing a highly birefringent photonic crystal fiber (PCF) with near zero flattened dispersion properties by applying elliptical air holes in the core area. The elliptical structure of the air holes in the porous-core region introduces asymmetry between x and y polarization modes, which consequently offers ultra-high birefringence. Also the compact geometry of the conventional hexagonal structure in the cladding confines most of the useful power. The optical properties including birefringence, dispersion, confinement loss, effective material loss (EML) and single modeness of the fiber are investigated using a full-vector finite element method. Simulation results show an ultra-high birefringence of 0 . 086 ultra-flattened near zero dispersion of 0 . 53 ± 0 . 07 ps/THz/cm in a broad frequency range. The practical implementation of the proposed fiber is feasible using existing fabrication technology and is applicable to the areas of terahertz sensing and polarization maintaining systems.

Shafranov shift bifurcation of turbulent transport in the high βp scenario on DIII-D

NASA Astrophysics Data System (ADS)

McClenaghan, J.; Garofalo, A. M.; Staebler, G. M.; Qian, J.; Gong, X.; Ding, S. Y.

2017-10-01

The Shafranov shift stabilization of turbulence creates a bifurcation in transport leading to formation of a large radius internal transport barrier (ITB) in the high βp scenario on DIII-D. The high βp scenario exhibits high confinement at high βN and high bootstrap fraction in the absence of rapid rotation or negative central shear. Spontaneous formation of an ITB at fixed βN is examined. The energy confinement improves following formation of the ITB. The improvement is associated with a decrease in the minimum mid-radius characteristic turbulence parameter associated with the Shafranov shift: α - s , where α =q2 Rdβ / dρ is a measure of the Shafranov shift, and s is the magnetic shear. After ITB formation, α - s > 0 within region of ITB and α - s < 0 outside the ITB. Before ITB formation, α - s < 0 throughout the entire core. TGLF transport simulations show a bifurcation of the transport depending on the electron pressure gradient scale length. Before ITB formation, the experimental scale length is on the high-transport side of bifurcation. After ITB formation, experimental scale length is on the low-transport side of the bifurcation in the region of the ITB. Work supported in part by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences DE-FC02-04ER54698 (Cooperative Agreement #DE-SC0010685), and by the National Magnetic Confinement Fusion Program of China (No. 2015GB102002, 2015GB10.

One-dimensional carrier confinement in “Giant” CdS/CdSe excitonic nanoshells

DOE PAGES

Razgoniaeva, Natalia; Moroz, Pavel; Yang, Mingrui; ...

2017-05-23

Here, the emerging generation of quantum dot optoelectronic devices offers an appealing prospect of a size-tunable band gap. The confinement-enabled control over electronic properties, however, requires nanoparticles to be sufficiently small, which leads to a large area of interparticle boundaries in a film. Such interfaces lead to a high density of surface traps which ultimately increase the electrical resistance of a solid. To address this issue, we have developed an inverse energy-gradient core/shell architecture supporting the quantum confinement in nanoparticles larger than the exciton Bohr radius. The assembly of such nanostructures exhibits a relatively low surface-to-volume ratio, which was manifestedmore » in this work through the enhanced conductance of solution-processed films. The reported core/shell geometry was realized by growing a narrow gap semiconductor layer (CdSe) on the surface of a wide-gap core material (CdS) promoting the localization of excitons in the shell domain, as was confirmed by ultrafast transient absorption and emission lifetime measurements. The band gap emission of fabricated nanoshells, ranging from 15 to 30 nm in diameter, has revealed a characteristic size-dependent behavior tunable via the shell thickness with associated quantum yields in the 4.4–16.0% range.« less

A simple structure of all circular-air-holes photonic crystal fiber for achieving high birefringence and low confinement loss

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chou Chau, Yuan-Fong, E-mail: chou.fong@ubd.edu.bn; Lim, Chee Ming; Yoong, Voo Nyuk

2015-12-28

We propose a simple structure of photonic crystal fibers (PCFs) with high birefringence and low confinement loss based on one rectangular centric ring of smaller circular air holes (CAHs) in the fiber core, and three rings of larger CAHs in the fiber cladding. This simple geometry (using all CAHs with two different air hole sizes) is capable of achieving a flexible control of the birefringence, B = 5.501 × 10{sup −3}, and ultra-low confinement loss, 7.30 × 10{sup −5 }dB/km, at an excitation wavelength of λ = 1550 nm. The birefringence value is ∼5.0 times greater than that obtained for conventional CAH PCF. This simple structure has the added advantagemore » from the view point of easy fabrication, robustness, and cost. A full-vector finite element method combined with anisotropic perfectly matched layers was used to analyze the various fiber structures. We have analyzed four cases of CAH PCFs, focusing on the core asymmetry design as opposed to the conventional approach of CAHs or elliptical air holes on the cladding and core. The robustness against manufacturing inaccuracies of the proposed structure has also been further investigated in this work.« less

One-dimensional carrier confinement in “Giant” CdS/CdSe excitonic nanoshells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Razgoniaeva, Natalia; Moroz, Pavel; Yang, Mingrui

Here, the emerging generation of quantum dot optoelectronic devices offers an appealing prospect of a size-tunable band gap. The confinement-enabled control over electronic properties, however, requires nanoparticles to be sufficiently small, which leads to a large area of interparticle boundaries in a film. Such interfaces lead to a high density of surface traps which ultimately increase the electrical resistance of a solid. To address this issue, we have developed an inverse energy-gradient core/shell architecture supporting the quantum confinement in nanoparticles larger than the exciton Bohr radius. The assembly of such nanostructures exhibits a relatively low surface-to-volume ratio, which was manifestedmore » in this work through the enhanced conductance of solution-processed films. The reported core/shell geometry was realized by growing a narrow gap semiconductor layer (CdSe) on the surface of a wide-gap core material (CdS) promoting the localization of excitons in the shell domain, as was confirmed by ultrafast transient absorption and emission lifetime measurements. The band gap emission of fabricated nanoshells, ranging from 15 to 30 nm in diameter, has revealed a characteristic size-dependent behavior tunable via the shell thickness with associated quantum yields in the 4.4–16.0% range.« less

Effectiveness of a confinement strategy in reducing pack stock impacts at campsites in the Selway-Bitterroot Wilderness, Idaho

Treesearch

David R. Spildie; David N. Cole; Sarah C. Walker

2000-01-01

In 1993, a management program was initiated in the Seven Lakes Basin in the Selway-Bitterroot Wilderness to bring high levels of campsite impact into compliance with management standards. The core of the strategy involved confining use, particularly by stock groups, and restoring certain campsites and portions of campsites. In just five years, campsite impacts were...

Advantages and Challenges of Radiative Liquid Lithium Divertor

NASA Astrophysics Data System (ADS)

Ono, Masayuki

2017-10-01

Steady-state fusion power plant designs present major divertor technology challenges, including high divertor heat flux both in steady-state and during transients. In addition to these concerns, there are the unresolved technology issues of long term dust accumulation and associated tritium inventory and safety issues. The application of lithium (Li) in NSTX resulted in improved H-mode confinement, H-mode power threshold reduction, and reduction in the divertor peak heat flux while maintaining essentially Li-free core plasma operation even during H-modes. These promising results in NSTX and related modeling calculations motivated the radiative liquid Li divertor (RLLD) concept and its variant, the active liquid Li divertor concept (ARLLD), taking advantage of the enhanced Li radiation in relatively poorly confined divertor plasmas. It has been suggested that radiation-based liquid lithium (LL) divertor concepts with a modest Li-loop could provide a possible solution for the outstanding fusion reactor technology issues such as divertor heat flux mitigation and real time dust removal, while potentially improving the reactor plasma performance. Laboratory tests are also planned to investigate the Li-T recover efficiency and other relevant research topics of the RLLD. This work supported by DoE Contract No. DE-AC02-09CH11466.

Study of Turbulence and Radial Electric Field Transitions in ASDEX Upgrade using Doppler Reflectometry

NASA Astrophysics Data System (ADS)

Conway, Garrard

2006-10-01

The radial electric field is recognised as an important factor in the performance of magnetically confined fusion plasmas. On ASDEX Upgrade microwave Doppler reflectometry has been developed to directly measure Er profiles, its shear and its fluctuations. Here a poloidally tilted antenna selects via Bragg a specific turbulence wavenumber giving a frequency shift directly proportional to the perpendicular rotation velocity u= vE xB+ vturb of the turbulence moving in the plasma. Turbulence simulations show vE xBvturb allowing simple extraction of Er with good accuracy. In the scrape-off-layer Er is positive, but reverses across the separatrix due to the pedestal pressure gradient to form a negative well. The strength of the well scales directly with confinement, typically -50V/cm for ohmic/L-mode, rising to -300V/cm for H-mode and in excess of -500V/cm for improved H-modes. Without NBI vE xB vturb which allows the turbulence behaviour to be investigated. For example the core rotation reverses from ion to electron direction when plasma collisionality is raised while matched gyro-kinetic turbulence simulations show the dominant turbulence changing from TEM to ITG with corresponding vturb reversal, which implies the core Er reverses sign with the turbulence. Also of major importance to confinement are zonal flows and GAMs - radially localised oscillating E xB flows. Er fluctuations directly measured by Doppler refl. reveal coherent modes in the edge gradient region where turbulence vorticity and Er shear are largest. The mode frequency scales as sound speed over major radius but is sensitive to plasma shape and local q. So far GAMs have not been seen in H-modes, nor in the plasma core. In each topic, the synergetic combination of experiment, theory and numerical simulation aids interpretation shows Er is interlinked with turbulence and the mean plasma profiles. Collaborators: J.Schirmer, W.Suttrop, C.Angioni, R.Dux, F.Jenko, E.Holzhauer, S.Klenge, B.Kurzan, C.Maggi, A.G.Peeters, M.Reich, F.Ryter, B.Scott, C.Tr"oster, E.Wolfrum, H.Zohm and the ASDEX Upgrade Team.

Photonic crystal fiber heat sensors

NASA Astrophysics Data System (ADS)

Twigg, S.; Coompson, J.; Colalillo, A.; Wynne, R.

2011-04-01

A sensing configuration based on commercially available triple-core photonic crystal fiber (PCF) for the image-based collection of thermal information is presented. Detection of thermal phenomena on the micro and nano scale is important for monitoring thermodynamic processes including cooling mechanisms for industry and basic research in both civil and mechanical systems. The thermal characteristics of the PCF combined with coupled-mode theory principles are used to construct a three core PCF with a 1-D core arrangement to simultaneously measure heat flux and temperature. The PCF sensor demonstrated high detection sensitivity (<1°C) and fast response times (<30μs), which is a significant improvement to current commercial standards. PCFs are specialty optical fibers that contain carefully spaced micronsized cavities that provide extraordinary waveguide characteristics not demonstrated by standard optical fiber. The three core PCF has a core diameter of 3.9μm, outer diameter of 132.5μm and varied inter core spacing. A single mode fiber is fusion spliced with the multi-core PCF such that the optical field is confined and launched into the PCF core. The output end of the fiber is inspected and imaged with a CCD camera. A 25mm section of the PCF is surrounded by a guarded hotplate configuration to control the thermal conditions for sensor characterization. Evanescent wave coupling occurs whereby power is transferred from the central core to a neighboring core. Minimum detection sensitivities of 0.2 °C were recorded. Theoretical sensitivities on the order of 10-2 °C are possible. Experimental results were in agreement with coupled-mode theoretical results.

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays

PubMed Central

Choi, Yoon-Young; Yun, Tae Gwang; Qaiser, Nadeem; Paik, Haemin; Roh, Hee Seok; Hong, Jongin; Hong, Seungbum; Han, Seung Min; No, Kwangsoo

2015-01-01

PVDF and P(VDF-TrFE) nano- and micro- structures have been widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use of the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures. PMID:26040539

Vertically aligned P(VDF-TrFE) core-shell structures on flexible pillar arrays

DOE PAGES

Choi, Yoon-Young; Yun, Tae Gwang; Qaiser, Nadeem; ...

2015-06-04

PVDF and P(VDF-TrFE) nano- and micro- structures are widely used due to their potential applications in several fields, including sensors, actuators, vital sign transducers, and energy harvesters. In this study, we developed vertically aligned P(VDF-TrFE) core-shell structures using high modulus polyurethane acrylate (PUA) pillars as the support structure to maintain the structural integrity. In addition, we were able to improve the piezoelectric effect by 1.85 times from 40 ± 2 to 74 ± 2 pm/V when compared to the thin film counterpart, which contributes to the more efficient current generation under a given stress, by making an effective use ofmore » the P(VDF-TrFE) thin top layer as well as the side walls. We attribute the enhancement of piezoelectric effects to the contributions from the shell component and the strain confinement effect, which was supported by our modeling results. We envision that these organic-based P(VDF-TrFE) core-shell structures will be used widely as 3D sensors and power generators because they are optimized for current generations by utilizing all surface areas, including the side walls of core-shell structures.« less

Exercise thermoregulation with bed rest, confinement, and immersion deconditioning

NASA Technical Reports Server (NTRS)

Greenleaf, J. E.

1997-01-01

Altered thermoregulation following exposure to prolonged (12-14 days) of bed rest and 6 hr of head-down thermoneutral water immersion in humans, and cage confinement (8 weeks) in male, mongrel dogs resulted in occasional increased core temperature (Tcore) at rest, but consistent "excessive" increase in Tcore during submaximal exercise. This excessive increase in Tcore in nonexercising and exercising subjects was independent of the mode (isometric or isotonic) of exercise training during bed rest, and was associated with the consistent hypovolemia in men but not in women taking estrogen supplementation (1.25 mg premarin/ day) which restored plasma volume during bed rest to ambulatory control levels. Post-bed rest exercise sweating (evaporative heat loss) was unchanged or higher than control levels; however, calculated tissue heat conductance was significantly lower in men, and forearm venoconstriction was greater (venous volume was reduced) in women during exercise after bed rest. Because sweating appeared proportional to the increased level of Tcore, these findings suggest that one major factor for the excessive hyperthermia is decreased core to periphery heat conduction. Exercising dogs respond like humans with excessive increase in both rectal (Tre) and exercising muscle temperatures (Tmu) after confinement and, after eight weeks of exercise training on a treadmill following confinement, they had an attenuated rate of increase of Tre even below ambulatory control levels. Intravenous infusion of glucose also attenuated not only the rise in Tre during exercise in normal dogs, but also the excessive rise in Tre and exercising Tmu after confinement. Oral glucose also appeared to reduce the rate of increase in excessive Tre in men after immersion deconditioning. There was a greater rate of rise in Tcore in two cosmonauts during supine submaximal exercise (65% VO2 max) on the fifth recovery day after the 115-day Mir 18 mission. Thus, the excessive rise in core temperature after deconditioning appears to be caused by decreased peripheral vasodilation in humans. Factors related to glucose metabolism may influence this mechanism.

Suppression of large edge-localized modes in high-confinement DIII-D plasmas with a stochastic magnetic boundary.

PubMed

Evans, T E; Moyer, R A; Thomas, P R; Watkins, J G; Osborne, T H; Boedo, J A; Doyle, E J; Fenstermacher, M E; Finken, K H; Groebner, R J; Groth, M; Harris, J H; La Haye, R J; Lasnier, C J; Masuzaki, S; Ohyabu, N; Pretty, D G; Rhodes, T L; Reimerdes, H; Rudakov, D L; Schaffer, M J; Wang, G; Zeng, L

2004-06-11

A stochastic magnetic boundary, produced by an applied edge resonant magnetic perturbation, is used to suppress most large edge-localized modes (ELMs) in high confinement (H-mode) plasmas. The resulting H mode displays rapid, small oscillations with a bursty character modulated by a coherent 130 Hz envelope. The H mode transport barrier and core confinement are unaffected by the stochastic boundary, despite a threefold drop in the toroidal rotation. These results demonstrate that stochastic boundaries are compatible with H modes and may be attractive for ELM control in next-step fusion tokamaks.

Geologic, geotechnical, and geophysical properties of core from the Acme Fire-Pit-1 drill hole, Sheridan County, Wyoming

USGS Publications Warehouse

Collins, Donley S.

1983-01-01

A preliminary core study from the Acme Fire-Pit-1 drill hole, Sheridan County, Wyoming, revealed that the upper portion of the core had been baked by a fire confined to the underlying Monarch coal bed. The baked (clinkered) sediment above the Monarch coal bed was determined to have higher point-load strength values (greater than 2 MPa) than the sediment under the burned coal

Joint DIII-D/EAST Experiments Toward Steady State AT Demonstration

NASA Astrophysics Data System (ADS)

Garofalo, A. M.; Meneghini, O.; Staebler, G. M.; van Zeeland, M. A.; Gong, X.; Ding, S.; Qian, J.; Ren, Q.; Xu, G.; Grierson, B. A.; Solomon, W. M.; Holcomb, C. T.

2015-11-01

Joint DIII-D/EAST experiments on fully noninductive operation at high poloidal beta have demonstrated several attractive features of this regime for a steady-state fusion reactor. Very large bootstrap fraction (>80 %) is desirable because it reduces the demands on external noninductive current drive. High bootstrap fraction with an H-mode edge results in a broad current profile and internal transport barriers (ITBs) at large minor radius, leading to high normalized energy confinement and high MHD stability limits. The ITB radius expands with higher normalized beta, further improving both stability and confinement. Electron density ITB and large Shafranov shift lead to low AE activity in the plasma core and low anomalous fast ion losses. Both the ITB and the current profile show remarkable robustness against perturbations, without external control. Supported by US DOE under DE-FC02-04ER54698, DE-AC02-09CH11466 & DE-AC52-07NA27344 & by NMCFSP under contracts 2015GB102000 and 2015GB110001.

Observation of trapped-electron-mode microturbulence in reversed field pinch plasmas

NASA Astrophysics Data System (ADS)

Duff, J. R.; Williams, Z. R.; Brower, D. L.; Chapman, B. E.; Ding, W. X.; Pueschel, M. J.; Sarff, J. S.; Terry, P. W.

2018-01-01

Density fluctuations in the large-density-gradient region of improved confinement Madison Symmetric Torus reversed field pinch (RFP) plasmas exhibit multiple features that are characteristic of the trapped-electron mode (TEM). Core transport in conventional RFP plasmas is governed by magnetic stochasticity stemming from multiple long-wavelength tearing modes. Using inductive current profile control, these tearing modes are reduced, and global confinement is increased to that expected for comparable tokamak plasmas. Under these conditions, new short-wavelength fluctuations distinct from global tearing modes appear in the spectrum at a frequency of f ˜ 50 kHz, which have normalized perpendicular wavenumbers k⊥ρs≲ 0.2 and propagate in the electron diamagnetic drift direction. They exhibit a critical-gradient threshold, and the fluctuation amplitude increases with the local electron density gradient. These characteristics are consistent with predictions from gyrokinetic analysis using the Gene code, including increased TEM turbulence and transport from the interaction of remnant tearing magnetic fluctuations and zonal flow.

Response of impurity particle confinement time to external actuators in QH-mode plasmas on DIII-D

DOE PAGES

Grierson, Brian A.; Burrell, Keith H.; Garofalo, Andrea M.; ...

2014-11-04

A series of quiescent H-mode discharges have been executed with the specific aim of determining the particle confinement time of impurities in the presence of the edge harmonic oscillation. These discharges utilize non-intrinsic, non-recycling fully-stripped fluorine as the diagnostic species monitored by charge-exchange recombination spectroscopy. It is found that the EHO is an efficient means of impurity expulsion from the core plasma, with impurity exhaust rates comparable to or exceeding those in companion ELMing discharges. Furthermore, as the external torque from neutral beam injection is lowered, the global energy confinement time increases while the impurity confinement time does not displaymore » an increase.« less

Access to a New Plasma Edge State with High Density and Pressures using Quiescent H-mode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solomon, Wayne M.; Snyder, P. B.; Burrell, K. H.

2014-07-01

A path to a new high performance regime has been discovered in tokamaks that could improve the attractiveness of a fusion reactor. Experiments on DIII-D using a quiescent H-mode edge have navigated a valley of improved edge peeling-ballooning stability that opens up with strong plasma shaping at high density, leading to a doubling of the edge pressure over standard edge localized mode (ELM)ing H-mode at these parameters. The thermal energy confinement time increases both as a result of the increased pedestal height and improvements in the core transport and reduced low-k turbulence. Calculations of the pedestal height and width asmore » a function of density using constraints imposed by peeling-ballooning and kinetic-ballooning theory are in quantitative agreement with the measurements.« less

Magnetic bucket for rotating unmagnetized plasma.

PubMed

Katz, Noam; Collins, Cami; Wallace, John; Clark, Mike; Weisberg, David; Jara-Almonte, Jon; Reese, Ingrid; Wahl, Carl; Forest, Cary

2012-06-01

A new experiment is described which generates flow in unmagnetized plasma. Confinement is provided by a cage of permanent magnets, arranged to form an axisymmetric, high-order, multipolar magnetic field. This field configuration-sometimes called a "magnetic bucket"-has a vanishingly small field in the core of the experiment. Toroidal rotation is driven by J × B forces applied in the magnetized edge. The cross-field current that is required for this forcing flows from anodes to thermionic cathodes, which are inserted between the magnet rings. The rotation at the edge reaches 3 km/s and is viscously coupled to the unmagnetized core plasma. We describe the conditions necessary for rotation, as well as a 0-dimensional power balance used to understand plasma confinement in the experiment.

Yb-doped large mode area tapered fiber with depressed cladding and dopant confinement

NASA Astrophysics Data System (ADS)

Roy, V.; Paré, C.; Labranche, B.; Laperle, P.; Desbiens, L.; Boivin, M.; Taillon, Y.

2017-02-01

A polarization-maintaining Yb-doped large mode area fiber with depressed-index inner cladding layer and confinement of rare-earth dopants has been drawn as a long tapered fiber. The larger end features a core/clad diameter of 56/400 μm and core NA 0.07, thus leading to an effective mode area over 1000 μm2. The fiber was tested up to 100 W average power, with near diffraction-limited output as the beam quality M2 was measured < 1.2. As effective single-mode guidance is enforced in the first section due to enhanced bending loss, subsequent adiabatic transition of the mode field in the taper section preserves single-mode amplification towards the larger end of the fiber.

Beyond Yolk–Shell Nanoparticles: Fe 3 O 4 @Fe 3 C Core@Shell Nanoparticles as Yolks and Carbon Nanospindles as Shells for Efficient Lithium Ion Storage

DOE PAGES

Zhang, Jianan; Wang, Kaixi; Xu, Qun; ...

2015-02-25

In order to well address the problems of large volume change and dissolution of Fe 3O 4 nanomaterials during Li + intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk–shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe 3O 4@Fe 3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This structure can not only introduce VSIVS to accommodate volume change of Fe 3O 4 but also afford a dual shell of Fe 3C and carbon to restrict Femore » 3O 4 dissolution, thus providing dual roles for greatly improving the capacity retention. Consequently, Fe 3O 4@Fe 3C–C yolk–shell nanospindles deliver a high reversible capacity of 1128.3 mAh g –1 at even 500 mA g –1, excellent high rate capacity (604.8 mAh g –1 at 2000 mA g –1), and prolonged cycling life (maintaining 1120.2 mAh g –1 at 500 mA g –1 for 100 cycles) for LIBs, which are much better than those of Fe 3O 4@C core@shell nanospindles and Fe 3O 4 nanoparticles. The present Fe 3O 4@Fe 3C–C yolk–shell nanospindles are the most efficient Fe 3O 4-based anode materials ever reported for LIBs.« less

Biasing experiments on the Advanced Toroidal Facility

NASA Astrophysics Data System (ADS)

Uckan, T.; Isler, R. C.; Jernigan, T. C.; Lyon, J. F.; Mioduszewski, P. K.; Murakami, M.; Rasmussen, D. A.; Wilgen, J. B.; Aceto, S. C.; Zielinski, J. J.

1992-09-01

Biasing experiments have been carried out in 1 T plasmas with approximately 200 kW of electron cyclotron heating (ECH) in the current-fire Advanced Toroidal Facility (ATF) torsatron. Two rail limiters, one at the top and one at the bottom of the device, located at the last closed flux surface (LCFS), are, biased at positive and negative potentials with respect to the vacuum vessel. When the limiters are positively biased at up to 300 V and the plasma density is controlled with a significantly reduced gas feed, the H(sub alpha) radiation from both the limiter and the wall drops, indicating reduced particle recycling as a result of improved particle confinement. For bias voltages around +100 V, there is almost no change of plasma stored energy W(sub p), but W(sub p) then drops with the higher biasing voltages. Positive biasing has caused the core plasma density profile to become peaked and the electric field to become more negative inside the LCFS. At the same time, edge plasma fluctuations are reduced significantly and their power spectrum becomes less broad. The propagation direction of these electrostatic fluctuations reverses to the ion diamagnetic direction, and their wavelengths become longer. The resulting fluctuation-induced particle flux is also reduced. Power deposition on the limiters is lower as a result of reduced edge plasma density and temperature. Negative biasing yields somewhat less improvement in the particle confinement while having almost no apparent effect on W(sub p) or on the core and the edge plasma density and temperature profiles. Simultaneous measurements of the plasma potential profile indicate almost no significant change. Biasing has almost no effect on the intrinsic impurity levels in the plasma.

Surface Chemistry in Cobalt Phosphide-Stabilized Lithium-Sulfur Batteries.

PubMed

Zhong, Yiren; Yin, Lichang; He, Peng; Liu, Wen; Wu, Zishan; Wang, Hailiang

2018-01-31

Chemistry at the cathode/electrolyte interface plays an important role for lithium-sulfur batteries in which stable cycling of the sulfur cathode requires confinement of the lithium polysulfide intermediates and their fast electrochemical conversion on the electrode surface. While many materials have been found to be effective for confining polysulfides, the underlying chemical interactions remain poorly understood. We report a new and general lithium polysulfide-binding mechanism enabled by surface oxidation layers of transition-metal phosphide and chalcogenide materials. We for the first time find that CoP nanoparticles strongly adsorb polysulfides because their natural oxidation (forming Co-O-P-like species) activates the surface Co sites for binding polysulfides via strong Co-S bonding. With a surface oxidation layer capable of confining polysulfides and an inner core suitable for conducting electrons, the CoP nanoparticles are thus a desirable candidate for stabilizing and improving the performance of sulfur cathodes in lithium-sulfur batteries. We demonstrate that sulfur electrodes that hold a high mass loading of 7 mg cm -2 and a high areal capacity of 5.6 mAh cm -2 can be stably cycled for 200 cycles. We further reveal that this new surface oxidation-induced polysulfide-binding scheme applies to a series of transition-metal phosphide and chalcogenide materials and can explain their stabilizing effects for lithium-sulfur batteries.

Characteristics of gradient-interface-structured ZnCdSSe quantum dots with modified interface and its application to quantum-dot-sensitized solar cells

NASA Astrophysics Data System (ADS)

Jeong, Da-Woon; Kim, Jae-Yup; Seo, Han Wook; Lim, Kyoung-Mook; Ko, Min Jae; Seong, Tae-Yeon; Kim, Bum Sung

2018-01-01

Colloidal quantum dots (QDs) are attractive materials for application in photovoltaics, LEDs, displays, and bio devices owing to their unique properties. In this study, we synthesized gradient-interface-structured ZnCdSSe QDs and modified the interface based on a thermodynamic simulation to investigate its optical and physical properties. In addition, the interface was modified by increasing the molar concentration of Se. QDs at the modified interface were applied to QD-sensitized solar cells, which showed a 25.5% increase in photoelectric conversion efficiency owing to the reduced electron confinement effect. The increase seems to be caused by the excited electrons being relatively easily transferred to the level of TiO2 owing to the reduced electron confinement effect. Consequently, the electron confinement effect was observed to be reduced by increasing the ZnSe (or Zn1-xCdxSe)-rich phase at the interface. This means that, based on the thermodynamic simulation, the interface between the core QDs and the surface of the QDs can be controlled. The improvement of optical and electronic properties by controlling interfaces and surfaces during the synthesis of QDs, as reported in this work, can be useful for many applications beyond solar cells.

Hydrogeologic framework and simulation of ground-water flow and travel time in the shallow aquifer system in the area of Naval Support Activity Memphis, Millington, Tennessee

USGS Publications Warehouse

Robinson, James L.; Carmichael, John K.; Halford, Keith J.; Ladd, David E.

1997-01-01

Naval Support Activity (NSA) Memphis is a Department of the Navy facility located at the City of Millington, Tennessee, about 5 miles north of Memphis. Contaminants have been detected in surface-water, sediment, and ground-water samples collected at the facility. As part of the Installation Restoration Program, the Navy is considering remedial-action options to prevent or lessen the effect of ground-water contamination at the facility and to control the movement and discharge of contaminants. A numerical model of the ground-water-flow system in the area of NSA Memphis was constructed and calibrated so that quantifiable estimates could be made of ground-water-flow rates, direction, and time-of-travel. The sediments beneath NSA Memphis, to a depth of about 200 feet, form a shallow aquifer system. From youngest to oldest, the stratigraphic units that form the shallow aquifer system are alluvium, loess, fluvial deposits, and the Cockfield and Cook Mountain Formations. The shallow aquifer system is organized into five hydrogeologic units: (1) a confining unit composed of the relatively low permeability sediments of the upper alluvium and the loess; (2) the A1 aquifer comprising sand and gravel of the lower alluvium and the fluvial deposits, and sand lenses in the upper part of the preserved section of the Cockfield Formation; (3) a confining unit composed of clay and silt within the upper part of the Cockfield Formation; (4) the Cockfield aquifer comprising sand lenses within the lower part of the preserved section of the Cockfield Formation; and (5) a confining unit formed by low permeability sediments of the Cook Mountain Formation that composes the upper confining unit for the Memphis aquifer. Thicknesses of individual units vary considerably across the facility. Structural and depositional features that affect the occurrence of ground water in the shallow aquifer system include faulting, an erosional scarp, and 'windows' in the confining units. Underlying the shallow aquifer system is the Memphis aquifer, the primary source of water for NSA Memphis and the City of Memphis, Tennessee. Analyses of sediment cores, aquifer and well specific-capacity tests, and numerical modeling were used to estimate the hydraulic characteristics of units of the shallow aquifer system. The vertical hydraulic conductivity of core samples of the alluvium-loess confining unit ranged from about 8.5 x 10-5 to 1.6 x 10-2 feet per day, and the total porosity of the samples ranged from about 35 to 48 percent. The results of the aquifer test were used to estimate a horizontal hydraulic conductivity of about 5 feet per day for the alluvial-fluvial deposits aquifer. The total porosity of core samples of the alluvial-fluvial deposits aquifer ranged from about 22 to 39 percent. The vertical hydraulic conductivity of core samples of the Cockfield confining unit ranged from about 4.5 x 10-5 to 2.5 x 10-3 feet per day, and the total porosity ranged from about 41 to 55 percent. Well specific-capacity tests indicate that the horizontal hydraulic conductivity of sand units that compose the Cockfield aquifer range from about 0.5 to 3 feet per day. The vertical hydraulic conductivity of core samples of the Cook Mountain confining unit ranged from about 5.0 x 10-6 to 9.9 x 10-4 feet per day. Total porosity of core samples of the Cook Mountain confining unit ranged from about 30 to 42 percent. Ground-water flow and time-of-travel in the shallow aquifer system were simulated using the MODFLOW finite-difference model and the -particle-tracking program MODPATH. A three-layer, steady-state model of the shallow aquifer system was constructed and calibrated to the potentiometric surface of the A1 aquifer. Results of numerical modeling support the proposed conceptual hydrogeologic model of the shallow aquifer system. Ground-water time-of-travel in the A1 aquifer was simulated using an assumed effective porosity of 25 percent. Typical ground-water-flow velocities were on the or

Experimental Simulations of Methane Gas Migration through Water-Saturated Sediment Cores

NASA Astrophysics Data System (ADS)

Choi, J.; Seol, Y.; Rosenbaum, E. J.

2010-12-01

Previous numerical simulations (Jaines and Juanes, 2009) showed that modes of gas migration would mainly be determined by grain size; capillary invasion preferably occurring in coarse-grained sediments vs. fracturing dominantly in fine-grained sediments. This study was intended to experimentally simulate preferential modes of gas migration in various water-saturated sediment cores. The cores compacted in the laboratory include a silica sand core (mean size of 180 μm), a silica silt core (1.7 μm), and a kaolin clay core (1.0 μm). Methane gas was injected into the core placed within an x-ray-transparent pressure vessel, which was under continuous x-ray computed tomography (CT) scanning with controlled radial (σr), axial (σa), and pore pressures (P). The CT image analysis reveals that, under the radial effective stress (σr') of 0.69 MPa and the axial effective stress (σa') of 1.31 MPa, fracturings by methane gas injection occur in both silt and clay cores. Fracturing initiates at the capillary pressure (Pc) of ~ 0.41 MPa and ~ 2.41 MPa for silt and clay cores, respectively. Fracturing appears as irregular fracture-networks consisting of nearly invisibly-fine multiple fractures, longitudinally-oriented round tube-shape conduits, or fine fractures branching off from the large conduits. However, for the sand core, only capillary invasion was observed at or above 0.034 MPa of capillary pressure under the confining pressure condition of σr' = 1.38 MPa and σa' = 2.62 MPa. Compared to the numerical predictions under similar confining pressure conditions, fracturing occurs with relatively larger grain sizes, which may result from lower grain-contact compression and friction caused by loose compaction and flexible lateral boundary employed in the experiment.

Onset of the Magnetic Explosion in Filament-Eruption Flares and Coronal Mass Ejections: Single-Bipole Events

NASA Technical Reports Server (NTRS)

Moore, Ron L.; Sterling, Alphonse C.

2000-01-01

We present three-dimensional sketches of die magnetic field before and during filament eruptions in flares and coronal mass ejections. Before the eruption, the overall magnetic field is a closed bipole in which the core field (the field rooted along the bipole's neutral line in the photospheric magnetic flux) is strongly sheared and has oppositely curved "elbows" that bulge out from the opposite ends of the neutral line. This core-field sigmoid runs under and is pressed down in the middle by the rest of the field in the bipole, the less-sheared envelope field rooted outside the core field (as in the model of Antiochos, Dahlburg, & Klimchuk. A filament of chromospheric-temperature plasma is often held in the core field over the neutral line. In a filament eruption, the core field undergoes an explosive eruption, the frozen-in filament plasma providing a visible tracer of the erupting field. The core-field explosion may be either confined (as in some flares) or ejective (as in CMEs that begin together with the onset of a long-duration two-ribbon flare). We present examples of each of these two kind of events as observed in sequences of coronal X-ray images from the Yohkoh SXT, and consider (1) how the explosion begins, and (2) whether confined eruptions begin in basically the same way as ejective eruptions.

High temperature UF6 RF plasma experiments applicable to uranium plasma core reactors

NASA Technical Reports Server (NTRS)

Roman, W. C.

1979-01-01

An investigation was conducted using a 1.2 MW RF induction heater facility to aid in developing the technology necessary for designing a self critical fissioning uranium plasma core reactor. Pure, high temperature uranium hexafluoride (UF6) was injected into an argon fluid mechanically confined, steady state, RF heated plasma while employing different exhaust systems and diagnostic techniques to simulate and investigate some potential characteristics of uranium plasma core nuclear reactors. The development of techniques and equipment for fluid mechanical confinement of RF heated uranium plasmas with a high density of uranium vapor within the plasma, while simultaneously minimizing deposition of uranium and uranium compounds on the test chamber peripheral wall, endwall surfaces, and primary exhaust ducts, is discussed. The material tests and handling techniques suitable for use with high temperature, high pressure, gaseous UF6 are described and the development of complementary diagnostic instrumentation and measurement techniques to characterize the uranium plasma, effluent exhaust gases, and residue deposited on the test chamber and exhaust system components is reported.

Faraday spectroscopy of ultracold atoms guided in hollow core optical fibers

NASA Astrophysics Data System (ADS)

Fatemi, Fredrik; Pechkis, Joseph

2013-05-01

We have performed spatially and temporally resolved magnetometry using Faraday spectroscopy of ultracold rubidium atoms confined in hollow core optical fibers. We first guide 105 Rb atoms into a 3-cm-long, 100-micron-core hollow fiber using blue-detuned hollow waveguide modes. Inside the fiber, the atoms are exposed to an optical pumping pulse, and the Larmor precession is monitored by the polarization rotation of a probe laser beam detuned by 50 GHz. The intense guide beams can perturb the detected Larmor precession frequencies, but we show that by confining the atoms to the intensity null of higher order blue-detuned hollow modes, these perturbations are reduced by over 95% compared to red-detuned guides. By adjusting the guide beam detuning and polarization, the deleterious effects of both photon scattering and frequency shifts can be suppressed such that multiple magnetic field measurements with sensitivity of 30 nT per sampling pulse can be obtained throughout the length of the fiber in a single loading cycle. Work supported by ONR and DARPA.

Stationary QH-mode plasmas with high and wide pedestal at low rotation on DIII-D

DOE PAGES

Chen, Xi; Burrell, K. H.; Osborne, T. H.; ...

2016-09-30

A stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D with reactor relevant edge parameters and no ELMs. As the injected neutral beam torque is ramped down and the edge ExB rotation shear reduces, the transition from standard QH to the wide pedestal QH-mode occurs. And at the transition, the coherent edge harmonic oscillations (EHO) that usually regulate the standard QH edge cease and broadband edge MHD modes appear along with a rapid increase in the pedestal pressure height (by ≤60%) and width (by ≤50%). We posit that themore » enhanced edge turbulence-driven transport, enabled by the lower edge ExB flow shear due to lower torque reduces the pedestal gradient and, combined with the high edge instability limit provided by the balanced double-null plasma shape, permits the development of a broader and thus higher pedestal that is turbulence-transport-limited. Even with the significantly enhanced pedestal pressure, the edge operating point is below the peeling ballooning mode stability boundary and thus without ELMs. Improved transport in the outer core region (0.8≤ρ≤0.9) owing to increased ExB flow shear in that region and the enhanced pedestal boost the overall confinement by up to 45%. Our findings advance the physics basis for developing stationary ELM-free high-confinement operation at low rotation for future burning plasma where similar collisionality and rotation levels are expected.« less

Quantum confined stark effect on the binding energy of exciton in type II quantum heterostructure

NASA Astrophysics Data System (ADS)

Suseel, Rahul K.; Mathew, Vincent

2018-05-01

In this work, we have investigated the effect of external electric field on the strongly confined excitonic properties of CdTe/CdSe/CdTe/CdSe type-II quantum dot heterostructures. Within the effective mass approximation, we solved the Poisson-Schrodinger equations of the exciton in nanostructure using relaxation method in a self-consistent iterative manner. We changed both the external electric field and core radius of the quantum dot, to study the behavior of binding energy of exciton. Our studies show that the external electric field destroys the positional flipped state of exciton by modifying the confining potentials of electron and hole.

In-situ sputtering apparatus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erickson, Mark R.; Poole, Henry J.; Custer, III, Arthur W.

A sputtering apparatus that includes at least a target presented as an inner surface of a confinement structure, the inner surface of the confinement structure is preferably an internal wall of a circular tube. A cathode is disposed adjacent the internal wall of the circular tube. The cathode preferably provides a hollow core, within which a magnetron is disposed. Preferably, an actuator is attached to the magnetron, wherein a position of the magnetron within the hollow core is altered upon activation of the actuator. Additionally, a carriage supporting the cathode and communicating with the target is preferably provided, and amore » cable bundle interacting with the cathode and linked to a cable bundle take up mechanism provided power and coolant to the cathode, magnetron, actuator and an anode of the sputtering apparatus.« less

A novel Zeonex based oligoporous-core photonic crystal fiber for polarization preserving terahertz applications

NASA Astrophysics Data System (ADS)

Islam, Md. Saiful; Sultana, Jakeya; Dinovitser, Alex; Ng, Brian W.-H.; Abbott, Derek

2018-04-01

A novel waveguide consisting of oligo-porous core photonic crystal fiber (PCF) with a kagome lattice cladding has been designed for highly birefringent and near zero dispersion flattened applications of terahertz waves. The wave guiding properties of the designed PCF including birefringence, dispersion, effective material loss (EML), core power fraction, confinement loss, and modal effective area are investigated using a full vector Finite Element Method (FEM) with Perfectly Matched Layer (PML) absorbing boundary condition. Simulation results demonstrate that an ultra-high birefringence of 0.079, low EML of 0.05 cm-1, higher core power fraction of 44% and negligible confinement loss of 7 . 24 × 10-7 cm-1 can be achieved at 1 THz. Furthermore, for the y-polarization mode a near zero flattened dispersion of 0 . 49 ± 0 . 05 ps/THz/cm is achieved within a broad frequency range of 0.8-1.7 THz. The fabrication of the proposed fiber is feasible using the existing fabrication technology. Due to favorable wave-guiding properties, the proposed fiber has potential for terahertz imaging, sensing and polarization maintaining applications in the terahertz frequency range.

Mirror-field confined compact plasma source using permanent magnet for plasma processings.

PubMed

Goto, Tetsuya; Sato, Kei-Ichiro; Yabuta, Yuki; Sugawa, Shigetoshi

2016-12-01

A mirror-field confined compact electron cyclotron resonance (ECR) plasma source using permanent magnets was developed, aiming for the realization of high-quality plasma processings where high-density reactive species are supplied to a substrate with minimizing the ion bombardment damages. The ECR position was located between a microwave transmissive window and a quartz limiter, and plasmas were transported from the ECR position to a midplane of the magnetic mirror field through the quartz limiter. Thus, a radius of core plasma could be determined by the limiter, which was 15 mm in this study. Plasma parameters were investigated by the Langmuir probe measurement. High-density plasma larger than 10 11 cm -3 could be produced by applying 5.85-GHz microwave power of 10 W or more. For the outside region of the core plasma where a wafer for plasma processings will be set at, the ion current density was decreased dramatically with distance from the core plasma and became smaller by approximately two orders of magnitude that in the core plasma region for the radial position of 40 mm, suggesting the realization of reduction in ion bombardment damages.

REVIEW ARTICLE: Major results from the stellarator Wendelstein 7-AS

NASA Astrophysics Data System (ADS)

Hirsch, M.; Baldzuhn, J.; Beidler, C.; Brakel, R.; Burhenn, R.; Dinklage, A.; Ehmler, H.; Endler, M.; Erckmann, V.; Feng, Y.; Geiger, J.; Giannone, L.; Grieger, G.; Grigull, P.; Hartfuß, H.-J.; Hartmann, D.; Jaenicke, R.; König, R.; Laqua, H. P.; Maaßberg, H.; McCormick, K.; Sardei, F.; Speth, E.; Stroth, U.; Wagner, F.; Weller, A.; Werner, A.; Wobig, H.; Zoletnik, S.; W7-AS Team

2008-05-01

Wendelstein 7-AS was the first modular stellarator device to test some basic elements of stellarator optimization: a reduced Shafranov shift and improved stability properties resulted in β-values up to 3.4% (at 0.9 T). This operational limit was determined by power balance and impurity radiation without noticeable degradation of stability or a violent collapse. The partial reduction of neoclassical transport could be verified in agreement with calculations indicating the feasibility of the concept of drift optimization. A full neoclassical optimization, in particular a minimization of the bootstrap current was beyond the scope of this project. A variety of non-ohmic heating and current drive scenarios by ICRH, NBI and in particular, ECRH were tested and compared successfully with their theoretical predictions. Besides, new heating schemes of overdense plasmas were developed such as RF mode conversion heating—Ordinary mode, Extraordinary mode, Bernstein-wave (OXB) heating—or 2nd harmonic O-mode (O2) heating. The energy confinement was about a factor of 2 above ISS95 without degradation near operational boundaries. A number of improved confinement regimes such as core electron-root confinement with central Te <= 7 keV and regimes with strongly sheared radial electric field at the plasma edge resulting in Ti <= 1.7 keV were obtained. As the first non-tokamak device, W7-AS achieved the H-mode and moreover developed a high density H-mode regime (HDH) with strongly reduced impurity confinement that allowed quasi-steady-state operation (τ ≈ 65 · τE) at densities \\bar {n}_{\\rme} \\cong 4 \\times 10^{20}\\,\\mbox{m}^{-3} (at 2.5 T). The first island divertor was tested successfully and operated with stable partial detachment in agreement with numerical simulations. With these results W7-AS laid the physics background for operation of an optimized low-shear steady-state stellarator.

Recent progress of RF-dominated experiments on EAST

NASA Astrophysics Data System (ADS)

Liu, F. K.; Zhao, Y. P.; Shan, J. F.; Zhang, X. J.; Ding, B. J.; Wang, X. J.; Wang, M.; Xu, H. D.; Qin, C. M.; Li, M. H.; Gong, X. Z.; Hu, L. Q.; Wan, B. N.; Song, Y. T.; Li, J. G.

2017-10-01

The research of EAST program is mostly focused on the development of high performance steady state scenario with ITER-like poloidal configuration and RF-dominated heating schemes. With the enhanced ITER-relevant auxiliary heating and current drive systems, the plasma profile control by coupling/integration of various combinations has been investigated, including lower hybrid current drive (LHCD), electron cyclotron resonance heating (ECRH) and ion cyclotron resonance heating (ICRH). The 12 MW ICRH system has been installed on EAST. Heating and confinement studies using the Hydrogen Minority Heating scheme have been investigated. One of the importance challenges for EAST is coupling higher power into the core plasma, experiments including changing plasma position, electron density, local gas puffing and antenna phasing scanning were performed to improve ICRF coupling efficiency on EAST. Results show that local gas injection and reducing the k|| can improve the coupling efficiency directly. By means of the 4.6 GHz and 2.45 GHz LHCD systems, H-mode can be obtained and sustained at relatively high density, even up to ne ˜ 4.5 × 1019 m-3, where a current drive effect is still observed. Meanwhile, effect of source frequency (2.45GHz and 4.6GHz) on LHCD characteristic has been studied on EAST, showing that higher frequency improves penetration of the coupled LH (lower hybrid) power into the plasma core and leads to a better effect on plasma characteristics. Studies demonstrate the role of parasitic effects of edge plasma in LHCD and the mitigation by increasing source frequency. Experiments of effect of LH spectrum and plasma density on plasma characteristics are performed, suggesting the possibility of plasma control for high performance. The development of a 4MW ECRH system is in progress for the purpose of plasma heating and MHD control. The built ECRH system with 1MW source power has been successfully put into use on EAST in 2015. H-mode discharges with L-H transition triggered by ECRH injection were obtained and its effects on the electron temperature, particle confinement and the core MHD stabilities were observed. By further exploring and optimizing the RF combination for the sole RF heating and current drive regime, fully non-inductive H-mode discharges with Vloop˜0V has progressed steadily in the 2016 campaign. The overview of the significant progress of RF dominated experiments is presented in this paper.

Access to a new plasma edge state with high density and pressures using the quiescent H mode

DOE PAGES

Solomon, Wayne M.; Snyder, Philip B.; Burrell, Keith H.; ...

2014-09-24

A path to a new high performance regime has been discovered in tokamaks that could improve the attractiveness of a fusion reactor. Experiments on DIII-D using a quiescent H-mode edge have navigated a valley of improved edge peeling-ballooning stability that opens up with strong plasma shaping at high density, leading to a doubling of the edge pressure over the standard H mode with edge localized modes at these parameters. The thermal energy confinement time increases as a result of both the increased pedestal height and improvements in the core transport and reduced low-k turbulence. As a result, calculations of themore » pedestal height and width as a function of density using constraints imposed by peeling-ballooning and kinetic-ballooning theory are in quantitative agreement with the measurements.« less

Large-pitch kagome-structured hollow-core photonic crystal fiber

NASA Astrophysics Data System (ADS)

Couny, F.; Benabid, F.; Light, P. S.

2006-12-01

We report the fabrication and characterization of a new type of hollow-core photonic crystal fiber based on large-pitch (˜12μm) kagome lattice cladding. The optical characteristics of the 19-cell, 7-cell, and single-cell core defect fibers include broad optical transmission bands covering the visible and near-IR parts of the spectrum with relatively low loss and low chromatic dispersion, no detectable surface modes and high confinement of light in the core. Various applications of such a novel fiber are also discussed, including gas sensing, quantum optics, and high harmonic generation.

Pore-water extraction from unsaturated tuff by triaxial and one-dimensional compression methods, Nevada Test Site, Nevada

USGS Publications Warehouse

Mower, Timothy E.; Higgins, Jerry D.; Yang, In C.; Peters, Charles A.

1994-01-01

Study of the hydrologic system at Yucca Mountain, Nevada, requires the extraction of pore-water samples from welded and nonwelded, unsaturated tuffs. Two compression methods (triaxial compression and one-dimensional compression) were examined to develop a repeatable extraction technique and to investigate the effects of the extraction method on the original pore-fluid composition. A commercially available triaxial cell was modified to collect pore water expelled from tuff cores. The triaxial cell applied a maximum axial stress of 193 MPa and a maximum confining stress of 68 MPa. Results obtained from triaxial compression testing indicated that pore-water samples could be obtained from nonwelded tuff cores that had initial moisture contents as small as 13 percent (by weight of dry soil). Injection of nitrogen gas while the test core was held at the maximum axial stress caused expulsion of additional pore water and reduced the required initial moisture content from 13 to 11 percent. Experimental calculations, together with experience gained from testing moderately welded tuff cores, indicated that the triaxial cell used in this study could not apply adequate axial or confining stress to expel pore water from cores of densely welded tuffs. This concern led to the design, fabrication, and testing of a one-dimensional compression cell. The one-dimensional compression cell used in this study was constructed from hardened 4340-alloy and nickel-alloy steels and could apply a maximum axial stress of 552 MPa. The major components of the device include a corpus ring and sample sleeve to confine the sample, a piston and base platen to apply axial load, and drainage plates to transmit expelled water from the test core out of the cell. One-dimensional compression extracted pore water from nonwelded tuff cores that had initial moisture contents as small as 7.6 percent; pore water was expelled from densely welded tuff cores that had initial moisture contents as small as 7.7 percent. Injection of nitrogen gas at the maximum axial stress did not produce additional pore water from nonwelded tuff cores, but was critical to recovery of pore water from densely welded tuff cores. Gas injection reduced the required initial moisture content in welded tuff cores from 7.7 to 6.5 percent. Based on the mechanical ability of a pore-water extraction method to remove water from welded and nonwelded tuff cores, one-dimensional compression is a more effective extraction method than triaxial compression. However, because the effects that one-dimensional compression has on pore-water chemistry are not completely understood, additional testing will be needed to verify that this method is suitable for pore-water extraction from Yucca Mountain tuffs.

Controllable Synthesis of Ordered Mesoporous Mo2C@Graphitic Carbon Core-Shell Nanowire Arrays for Efficient Electrocatalytic Hydrogen Evolution.

PubMed

Zhu, Jiahui; Yao, Yan; Chen, Zhi; Zhang, Aijian; Zhou, Mengyuan; Guo, Jun; Wu, Winston Duo; Chen, Xiao Dong; Li, Yanguang; Wu, Zhangxiong

2018-06-06

Mo 2 C is a possible substitute to Pt-group metals for electrocatalytic hydrogen evolution reaction (HER). Both support-free and carbon-supported Mo 2 C nanomaterials with improved HER performance have been developed. Herein, distinct from prior research, novel ordered mesoporous core-shell nanowires with Mo 2 C cores and ultrathin graphitic carbon (GC) shells are rationally synthesized and demonstrated to be excellent for HER. The synthesis is fulfilled via a hard-templating approach combining in situ carburization and localized carbon deposition. Phosphomolybdic acid confined in the SBA-15 template is first converted to MoO 2 , which is then in situ carburized to Mo 2 C nanowires with abundant surface defects. Simultaneously, GC layer (the thickness is down to ∼1.0 nm in most areas) is controlled to be locally deposited on the Mo 2 C surface because of its strong affinity with carbon and catalytic effect on graphitization. Removal of the template results in the Mo 2 C@GC core-shell nanowire arrays with the structural properties well-characterized. They exhibit excellent performance for HER with a low overpotential of 125 mV at 10 mA cm -2 , a small Tafel slope of 66 mV dec -1 , and an excellent stability in acidic electrolytes. The influences of several factors, especially the spatial configuration and relative contents of the GC and Mo 2 C components, on HER performance are elucidated with control experiments. The excellent HER performance of the mesoporous Mo 2 C@GC core-shell nanowire arrays originates from the rough Mo 2 C nanowires with diverse active sites and short charge-transfer paths and the ultrathin GC shells with improved surface area, electronic conductivity, and stabilizing effect on Mo 2 C.

Collisionality dependence and ion species effects on heat transport in He and H plasma, and the role of ion scale turbulence in LHD

NASA Astrophysics Data System (ADS)

Tanaka, K.; Nagaoka, K.; Murakami, S.; Takahashi, H.; Osakabe, M.; Yokoyama, M.; Seki, R.; Michael, C. A.; Yamaguchi, H.; Suzuki, C.; Shimizu, A.; Tokuzawa, T.; Yoshinuma, M.; Akiyama, T.; Ida, K.; Yamada, I.; Yasuhara, R.; Funaba, H.; Kobayashi, T.; Yamada, H.; Du, X. D.; Vyacheslavov, L. N.; Mikkelsen, D. R.; Yun, G. S.; the LHD Experimental Group

2017-11-01

Surveys of the ion and electron heat transports of neutral beam (NB) heating plasma were carried out by power balance analysis in He and H rich plasma at LHD. Collisionality was scanned by changing density and heating power. The characteristics of the transport vary depending on collisionality. In low collisionality, with low density and high heating power, an ion internal transport barrier (ITB) was formed. The ion heat conductivity (χ i) is lower than electron heat conductivity (χ e) in the core region at ρ  <  0.7. On the other hand, in high collisionality, with high density and low heating power, χ i is higher than χ e across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at ρ  =  0.7, and in normal confinement, fluctuation has a peak at ρ  =  1.0. The two confinement modes change gradually depending on the collisionality. Scans of concentration ratio between He and H were also performed. The ion confinement improvements were investigated using gyro-Bohm normalization, taking account of the effective mass and charge. The concentration ratio affected the normalized χ i only in the edge region (ρ ~ 1.0). This indicates ion species effects vary depending on collisionality. Turbulence was modulated by the fast ion loss instability. The modulation of turbulence is higher in H rich than in He rich plasma.

Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

NASA Astrophysics Data System (ADS)

Sukkabot, Worasak

2018-05-01

A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron-hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron-hole interactions is observed with increasing external ZnS shell size. The strong electron-hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.

Nanoparticle (star polymer) delivery of nitric oxide effectively negates Pseudomonas aeruginosa biofilm formation.

PubMed

Duong, Hien T T; Jung, Kenward; Kutty, Samuel K; Agustina, Sri; Adnan, Nik Nik M; Basuki, Johan S; Kumar, Naresh; Davis, Thomas P; Barraud, Nicolas; Boyer, Cyrille

2014-07-14

Biofilms are increasingly recognized as playing a major role in human infectious diseases, as they can form on both living tissues and abiotic surfaces, with serious implications for applications that rely on prolonged exposure to the body such as implantable biomedical devices or catheters. Therefore, there is an urgent need to develop improved therapeutics to effectively eradicate unwanted biofilms. Recently, the biological signaling molecule nitric oxide (NO) was identified as a key regulator of dispersal events in biofilms. In this paper, we report a new class of core cross-linked star polymers designed to store and release nitric oxide, in a controlled way, for the dispersion of biofilms. First, core cross-linked star polymers were prepared by reversible addition-fragmentation chain transfer polymerization (RAFT) via an arm first approach. Poly(oligoethylene methoxy acrylate) chains were synthesized by RAFT polymerization, and then chain extended in the presence of 2-vinyl-4,4-dimethyl-5-oxazolone monomer (VDM) with N,N-methylenebis(acrylamide) employed as a cross-linker to yield functional core cross-linked star polymers. Spermine was successfully attached to the star core by reaction with VDM. Finally, the secondary amine groups were reacted with NO gas to yield NO-core cross-linked star polymers. The core cross-linked star polymers were found to release NO in a controlled, slow delivery in bacterial cultures showing great efficacy in preventing both cell attachment and biofilm formation in Pseudomonas aeruginosa over time via a nontoxic mechanism, confining bacterial growth to the suspended liquid.

Thomson scattering for core plasma on DEMO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukhin, E. E.; Kurskiev, G. S.; Tolstyakov, S. Yu.

2014-08-21

This paper describes the challenges of Thomson scattering implementation for core plasma on DEMO and evaluates the capability to measure extremely high electron temperature range 0.5-40keV. A number of solutions to be developed for ITER diagnostics are suggested in consideration of their realization for DEMO. New approaches suggested for DEMO may also be of interest to ITER and currently operating magnetic confinement devices.

The Green Bank Ammonia Survey: Dense Cores under Pressure in Orion A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Helen; Di Francesco, James; Friesen, Rachel K.

We use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests thatmore » most of the dense cores are pressure-confined.« less

Flow characteristics of Korea multi-purpose research reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heonil Kim; Hee Taek Chae; Byung Jin Jun

1995-09-01

The construction of Korea Multi-purpose Research Reactor (KMRR), a 30 MW{sub th} open-tank-in-pool type, is completed. Various thermal-hydraulic experiments have been conducted to verify the design characteristics of the KMRR. This paper describes the commissioning experiments to determine the flow distribution of KMRR core and the flow characteristics inside the chimney which stands on top of the core. The core flow is distributed to within {+-}6% of the average values, which is sufficiently flat in the sense that the design velocity in the fueled region is satisfied. The role of core bypass flow to confine the activated core coolant inmore » the chimney structure is confirmed.« less

The Green Bank Ammonia Survey: Dense Cores under Pressure in Orion A

NASA Astrophysics Data System (ADS)

Kirk, Helen; Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Offner, Stella S. R.; Matzner, Christopher D.; Myers, Philip C.; Di Francesco, James; Caselli, Paola; Alves, Felipe O.; Chacón-Tanarro, Ana; Chen, How-Huan; Chun-Yuan Chen, Michael; Keown, Jared; Punanova, Anna; Seo, Young Min; Shirley, Yancy; Ginsburg, Adam; Hall, Christine; Singh, Ayushi; Arce, Héctor G.; Goodman, Alyssa A.; Martin, Peter; Redaelli, Elena

2017-09-01

We use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests that most of the dense cores are pressure-confined.

Electron temperature structures associated with magnetic tearing modes in the Madison Symmetric Torus

NASA Astrophysics Data System (ADS)

Stephens, Hillary Dianne

Tearing mode induced magnetic islands have a significant impact on the thermal characteristics of magnetically confined plasmas such as those in the reversed-field-pinch. Using a state-of-the-art Thomson scattering (TS) diagnostic, electron temperature fluctuations correlated with magnetic tearing modes have been observed on the Madison Symmetric Torus reversed-field-pinch. The TS diagnostic consists of two independently triggerable Nd:YAG lasers that can each pulse up to 15 times each plasma discharge and 21 General Atomics polchromators equipped with avalanche photodiode modules. Detailed calibrations focusing on accuracy, ease of use and repeatability and in-situ measurements have been performed on the system. Electron temperature (Te) profiles are acquired at 25 kHz with 2 cm or less resolution along the minor radius, sufficient to measure the effect of an island on the profile as the island rotates by the measurement point. Bayesian data analysis techniques are developed and used to detect fluctuations over an ensemble of shots. Four cases are studied; standard plasmas in quiescent periods, through sawteeth, through core reconnection events and in plasmas where the tearing mode activity is decreased. With a spectrum of unstable tearing modes, remnant islands that tend to flatten the temperature profile are present in the core between sawtooth-like reconnection events. This flattening is characteristic of rapid parallel heat conduction along helical magnetic field lines. The spatial structure of the temperature fluctuations show that the location of the rational surface of the m/n = 1/6 tearing mode is significantly further in than equilibrium suggestions predict. The fluctuations also provide a measurement of the remnant island width which is significantly smaller than the predicted full island width. These correlated fluctuations disappear during both global and core reconnection events. In striking contrast to temperature flattening, a temperature gradient within an m/m = 1/5 island is observed just after a global reconnection event. This suggests local heating and relatively good confinement within the island. Local power balance calculations suggest reduced thermal transport within this island. During improved confinement plasmas with reduced stochasticity, brought about by a reduction in tearing instability temperature fluctuations correlated with magnetic modes are small with characteristic fluctuation amplitudes of T˜e/Te ˜ 2%.

NIMROD Simulations of Spheromak Formation, Magnetic Reconnection and Energy Confinement in SSPX

NASA Astrophysics Data System (ADS)

Hooper, E. B.; Sovinec, C. R.

2005-10-01

The SSPX spheromak is formed and driven by a coaxial electrostatic gun that injects current and magnetic flux. Magnetic fluctuations are associated with the conversion of toroidal to poloidal magnetic flux during formation. After formation, fluctuations that break axisymmetry degrade magnetic surfaces, and are anti-correlated with the core temperature and energy confinement time. We report NIMROD simulations extending earlier work^1 supporting the SSPX experiment through predictions of performance and providing insight. The simulations are in fairly good agreement with features observed in SSPX and underscore the importance of current profile control in mitigating magnetic fluctuation amplitudes and improving confinement. The simulations yield insight into magnetic reconnection and the relationship of fluctuations to field line stochasticity. We have added external circuit equations for the new 32 module capacitor bank in SSPX that will add flexibility in shaping the injector current pulses and substantially increase the injected currents and the magnetic energy. New NIMROD simulations of SSPX lead to higher temperature plasmas than in previous simulations. *Work supported by U.S. DOE, under Contr. No. W-7405-ENG-48 at U. Cal. LLNL and under grant FG02-01ER54661 at U. Wisc Madison. ^1C. R. Sovinec, B. I. Cohen, et al., Phys. Rev. Lett. 94, 035003 (2005); B. I. Cohen, E. B. Hooper, et al., Phys. Plasmas 12, 056106 (2005).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bardóczi, L.; Rhodes, T. L.; Carter, T. A.

We report the first observation of localized modulation of turbulent density uctuations en (via Beam Emission Spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that en could be dominantly driven by the ion temperature gradient (ITG) instability.

Elliptical As2Se3 filled core ultra-high-nonlinearity and polarization-maintaining photonic crystal fiber with double hexagonal lattice cladding

NASA Astrophysics Data System (ADS)

Li, Feng; He, Menghui; Zhang, Xuedian; Chang, Min; Wu, Zhizheng; Liu, Zheng; Chen, Hua

2018-05-01

A high birefringence and ultra-high nonlinearity photonic crystal fiber (PCF) is proposed, which is composed of an elliptical As2Se3-doped core and an inner cladding with hexagonal lattice. Optical properties of the PCF are simulated by the full-vector finite element method. The simulation results show that the high birefringence of ∼0.33, ultra-high-nonlinearity coefficient of 300757 W-1km-1 and the low confinement loss can be achieved in the proposed PCF simultaneously at the wavelength of 1.55 μm. Furthermore, by comparison with the other two materials (80PbO•20Ga2O3, As2S3) filled in the core, the As2Se3-doped PCF is found to have the highest birefringence and nonlinearity due to its higher refractive index and nonlinear refractive index. The flattened dispersion feature, as well as the low confinement loss of the proposed PCF structure make it suitable as a wide range of applications, such as the coherent optical communications, polarization-maintaining and nonlinear optics, etc.

Stationary QH-mode plasmas with high and wide pedestal at low rotation on DIII-D

NASA Astrophysics Data System (ADS)

Chen, Xi; Burrell, K. H.; Osborne, T. H.; Solomon, W. M.; Barada, K.; Garofalo, A. M.; Groebner, R. J.; Luhmann, N. C.; McKee, G. R.; Muscatello, C. M.; Ono, M.; Petty, C. C.; Porkolab, M.; Rhodes, T. L.; Rost, J. C.; Snyder, P. B.; Staebler, G. M.; Tobias, B. J.; Yan, Z.; the DIII-D Team

2017-02-01

A stationary, quiescent H-mode (QH-mode) regime with a wide pedestal and improved confinement at low rotation has been discovered on DIII-D with reactor relevant edge parameters and no ELMs. As the injected neutral beam torque is ramped down and the edge E  ×  B rotation shear reduces, the transition from standard QH to the wide pedestal QH-mode occurs. At the transition, the coherent edge harmonic oscillations (EHO) that usually regulate the standard QH edge cease and broadband edge MHD modes appear along with a rapid increase in the pedestal pressure height (by  ⩽60%) and width (by  ⩽50%). We posit that the enhanced edge turbulence-driven transport, enabled by the lower edge E  ×  B flow shear due to lower torque reduces the pedestal gradient and, combined with the high edge instability limit provided by the balanced double-null plasma shape, permits the development of a broader and thus higher pedestal that is turbulence-transport-limited. Even with the significantly enhanced pedestal pressure, the edge operating point is below the peeling ballooning mode stability boundary and thus without ELMs. Improved transport in the outer core region (0.8  ⩽  ρ  ⩽0.9) owing to increased E  ×  B flow shear in that region and the enhanced pedestal boost the overall confinement by up to 45%. These findings advance the physics basis for developing stationary ELM-free high-confinement operation at low rotation for future burning plasma where similar collisionality and rotation levels are expected.

Uranium droplet core nuclear rocket

NASA Technical Reports Server (NTRS)

Anghaie, Samim

1991-01-01

Uranium droplet nuclear rocket is conceptually designed to utilize the broad temperature range ofthe liquid phase of metallic uranium in droplet configuration which maximizes the energy transfer area per unit fuel volume. In a baseline system dissociated hydrogen at 100 bar is heated to 6000 K, providing 2000 second of Isp. Fission fragments and intense radian field enhance the dissociation of molecular hydrogen beyond the equilibrium thermodynamic level. Uranium droplets in the core are confined and separated by an axisymmetric vortex flow generated by high velocity tangential injection of hydrogen in the mid-core regions. Droplet uranium flow to the core is controlled and adjusted by a twin flow nozzle injection system.

How thermal stress alters the confinement of polymers vitrificated in nanopores

NASA Astrophysics Data System (ADS)

Teng, Chao; Li, Linling; Wang, Yong; Wang, Rong; Chen, Wei; Wang, Xiaoliang; Xue, Gi

2017-05-01

Understanding and controlling the glass transition temperature (Tg) and dynamics of polymers in confined geometries are of significance in both academia and industry. Here, we investigate how the thermal stress induced by a mismatch in the coefficient of thermal expansion affects the Tg behavior of polystyrene (PS) nanorods located inside cylindrical alumina nanopores. The size effects and molecular weight dependence of the Tg are also studied. A multi-step relaxation process was employed to study the relationship between thermal stress and cooling rate. At fast cooling rates, the imparted thermal stress would overcome the yield stress of PS and peel chains off the pore walls, while at slow cooling rates, chains are kept in contact with the pore walls due to timely dissipation of the produced thermal stress during vitrification. In smaller nanopores, more PS chains closely contact with pore walls, then stronger internal thermal stress would be generated between core and shell of PS nanorod, which results in a larger deviation between two Tgs. The core part of PS shows lower Tg than bulk value, which can induce faster dynamics in the center region. A complex and important role stress plays is supposed in complex confinement condition, e.g., in nanopores, during vitrification.

CT scanning and flow measurements of shale fractures after multiple shearing events

DOE PAGES

Crandall, Dustin; Moore, Johnathan; Gill, Magdalena; ...

2017-11-05

A shearing apparatus was used in conjunction with a Hassler-style core holder to incrementally shear fractured shale cores while maintaining various confining pressures. Computed tomography scans were performed after each shearing event, and were used to obtain information on evolving fracture geometry. Fracture transmissivity was measured after each shearing event to understand the hydrodynamic response to the evolving fracture structure. The digital fracture volumes were used to perform laminar single phase flow simulations (local cubic law with a tapered plate correction model) to qualitatively examine small scale flow path variations within the altered fractures. Fractures were found to generally increasemore » in aperture after several shear slip events, with corresponding transmissivity increases. Lower confining pressure resulted in a fracture more prone to episodic mechanical failure and sudden changes in transmissivity. Conversely, higher confining pressures resulted in a system where, after an initial setting of the fracture surfaces, changes to the fracture geometry and transmissivity occurred gradually. Flow paths within the fractures are largely controlled by the location and evolution of zero aperture locations. Lastly, a reduction in the number of primary flow pathways through the fracture, and an increase in their width, was observed during all shearing tests.« less

CT scanning and flow measurements of shale fractures after multiple shearing events

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crandall, Dustin; Moore, Johnathan; Gill, Magdalena

A shearing apparatus was used in conjunction with a Hassler-style core holder to incrementally shear fractured shale cores while maintaining various confining pressures. Computed tomography scans were performed after each shearing event, and were used to obtain information on evolving fracture geometry. Fracture transmissivity was measured after each shearing event to understand the hydrodynamic response to the evolving fracture structure. The digital fracture volumes were used to perform laminar single phase flow simulations (local cubic law with a tapered plate correction model) to qualitatively examine small scale flow path variations within the altered fractures. Fractures were found to generally increasemore » in aperture after several shear slip events, with corresponding transmissivity increases. Lower confining pressure resulted in a fracture more prone to episodic mechanical failure and sudden changes in transmissivity. Conversely, higher confining pressures resulted in a system where, after an initial setting of the fracture surfaces, changes to the fracture geometry and transmissivity occurred gradually. Flow paths within the fractures are largely controlled by the location and evolution of zero aperture locations. Lastly, a reduction in the number of primary flow pathways through the fracture, and an increase in their width, was observed during all shearing tests.« less

X-ray and Neutron Scattering Study of the Formation of Core–Shell-Type Polyoxometalates

DOE PAGES

Yin, Panchao; Wu, Bin; Mamontov, Eugene; ...

2016-02-05

A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo 72Fe 30}. Small angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Time-resolved small angle X-ray scattering is applied to monitor the synthetic reactions and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures and two different types ofmore » water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures. A typical type of core shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo 72Fe 30}. Small-angle X-ray scattering is used to study the structural features and stability of the core shell structures in aqueous solutions. Time-resolved small-angle X-ray scattering is applied to monitor the synthetic reactions, and a three-stage formation mechanism is proposed to describe the synthesis of the core shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with custom physical models, which provide more convincing, objective, and completed data interpretation. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core shell structures, and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures.« less

High-pressure Phase Ge nanoparticles and Si-ZnS nanocomposites: New Paradigms to Improve the Efficiency of MEG Solar Cells

NASA Astrophysics Data System (ADS)

Wippermann, Stefan; Voros, Marton; Somogyi, Balint; Gali, Adam; Rocca, Dario; Gygi, Francois; Zimanyi, Gergely; Galli, Giulia

2014-03-01

The efficiency of nanoparticle (NP) solar cells may substantially exceed the Shockley-Queisser limit by exploiting multi-exciton generation. However, (i) quantum confinement tends to increase the electronic gap and thus the MEG threshold beyond the solar spectrum and (ii) charge extraction through NP networks may be hindered by facile recombination. Using ab initio calculations we found that (i) Ge NPs with exotic core structures such as BC8 exhibit significantly lower gaps and MEG thresholds than particles with diamond cores, and an order of magnitude higher MEG rates. (ii) We also investigated Si NPs embedded in a ZnS host matrix and observed complementary charge transport networks, where electron transport occurs by hopping between NPs and hole transport through the ZnS-matrix. Such complementary pathways may substantially reduce recombination, as was indeed observed in recent experiments. We employed several levels of theory, including DFT with hybrid functionals and GW calculations.

Suppressed ion-scale turbulence in a hot high-β plasma

NASA Astrophysics Data System (ADS)

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-12-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements.

Suppressed ion-scale turbulence in a hot high-β plasma

PubMed Central

Schmitz, L.; Fulton, D. P.; Ruskov, E.; Lau, C.; Deng, B. H.; Tajima, T.; Binderbauer, M. W.; Holod, I.; Lin, Z.; Gota, H.; Tuszewski, M.; Dettrick, S. A.; Steinhauer, L. C.

2016-01-01

An economic magnetic fusion reactor favours a high ratio of plasma kinetic pressure to magnetic pressure in a well-confined, hot plasma with low thermal losses across the confining magnetic field. Field-reversed configuration (FRC) plasmas are potentially attractive as a reactor concept, achieving high plasma pressure in a simple axisymmetric geometry. Here, we show that FRC plasmas have unique, beneficial microstability properties that differ from typical regimes in toroidal confinement devices. Ion-scale fluctuations are found to be absent or strongly suppressed in the plasma core, mainly due to the large FRC ion orbits, resulting in near-classical thermal ion confinement. In the surrounding boundary layer plasma, ion- and electron-scale turbulence is observed once a critical pressure gradient is exceeded. The critical gradient increases in the presence of sheared plasma flow induced via electrostatic biasing, opening the prospect of active boundary and transport control in view of reactor requirements. PMID:28000675

Generation of a strong core centering force in a submillimeter compound droplet system

NASA Technical Reports Server (NTRS)

Lee, M. C.; Feng, I. A.; Elleman, D. D.; Wang, T. G.; Young, A. T.

1982-01-01

By amplitude-modulating the driving voltage of an acoustic levitating apparatus, a strong core centering force was generated in a submillimeter compound droplet system suspended by the radiation pressure in a gaseous medium. Depending on the acoustic characteristics of the droplet system, it was found that the technique can be utilized advantageously in the multiple-layer coating of an inertial confinement fusion pellet.

Results from core-edge experiments in high Power, high performance plasmas on DIII-D

DOE PAGES

Petrie, T. W.; Fenstermacher, M. E.; Holcomb, C. T.; ...

2016-12-24

Here, significant challenges to reducing divertor heat flux in highly powered near-double null divertor (DND) hybrid plasmas, while still maintaining both high performance metrics and low enough density for application of RF heating, are identified. For these DNDs on DIII-D, the scaling of the peak heat flux at the outer target (q ⊥ P) ∝ [P SOL x I P] 0.92 for P SOL = 8-19 MW and I P = 1.0–1.4 MA, and is consistent with standard ITPA scaling for single-null H-mode plasmas. Two divertor heat flux reduction methods were tested. First, applying the puff-and-pump radiating divertor to DIII-Dmore » plasmas may be problematical at high power and H98 (≥ 1.5) due to improvement in confinement time with deuterium gas puffing which can lead to unacceptably high core density under certain conditions. Second, q ⊥ P for these high performance DNDs was reduced by ≈35% when an open divertor is closed on the common flux side of the outer divertor target (“semi-slot”) but also that heating near the slot opening is a significant source for impurity contamination of the core.« less

Electron mobility limited by optical phonons in wurtzite InGaN/GaN core-shell nanowires

NASA Astrophysics Data System (ADS)

Liu, W. H.; Qu, Y.; Ban, S. L.

2017-09-01

Based on the force-balance and energy-balance equations, the optical phonon-limited electron mobility in InxGa1-xN/GaN core-shell nanowires (CSNWs) is discussed. It is found that the electrons tend to distribute in the core of the CSNWs due to the strong quantum confinement. Thus, the scattering from first kind of the quasi-confined optical (CO) phonons is more important than that from the interface (IF) and propagating (PR) optical phonons. Ternary mixed crystal and size effects on the electron mobility are also investigated. The results show that the PR phonons exist while the IF phonons disappear when the indium composition x < 0.047, and vice versa. Accordingly, the total electron mobility μ first increases and then decreases with indium composition x, and reaches a peak value of approximately 3700 cm2/(V.s) when x = 0.047. The results also show that the mobility μ increases as increasing the core radius of CSNWs due to the weakened interaction between the electrons and CO phonons. The total electron mobility limited by the optical phonons exhibits an obvious enhancement as decreasing temperature or increasing line electron density. Our theoretical results are expected to be helpful to develop electronic devices based on CSNWs.

On Heat Loading, Novel Divertors, and Fusion Reactors

NASA Astrophysics Data System (ADS)

Kotschenreuther, Mike

2006-10-01

A new magnetic divertor geometry has been proposed to solve reactor heat exhaust problems, which are far more severe for a reactor than for ITER. Using reactor-compatible coils to generate an extra X-point downstream from the main X-point, the new X-divertor (XD) is shown to greatly expand magnetic flux at the divertor plates. As a result, the heat is distributed over a larger area and the line length is greatly increased. The heat-flux limitations of a standard divertor (SD) force a high core radiation fraction (fRad) in most reactor designs that necessarily have a several times higher ratio of heating power to radius (P/R) than ITER. It is argued that such high values of fRad will probably have serious deleterious consequences on the core confinement and stability of a burning plasma. Operation with internal transport barriers (ITBs) does not appear to overcome this problem. By reducing the core fRad within an acceptable range, the X-divertor is shown to substantially lower the core confinement requirement for a fusion reactor. As a bonus, the XD also enables the use of liquid metals by reducing the MHD drag. A possible series of experiments for an efficient and attractive path to practical fusion power is suggested.

Hierarchically structured nanowires on and nanosticks in ZnO microtubes

PubMed Central

Rivaldo-Gómez, C. M.; Cabrera-Pasca, G. A.; Zúñiga, A.; Carbonari, A. W.; Souza, J. A.

2015-01-01

We report both coaxial core-shell structured microwires and ZnO microtubes with growth of nanosticks in the inner and nanowires on the outer surface as a novel hierarchical micro/nanoarchitecture. First, a core-shell structure is obtained—the core is formed by metallic Zn and the semiconducting shell is comprised by a thin oxide layer covered with a high density of nanowires. Such Zn/ZnO core-shell array showed magnetoresistance effect. It is suggested that magnetic moments in the nanostructured shell superimposes to the external magnetic field enhancing the MR effect. Second, microtubes decorated with nanowires on the external surface are obtained. In an intermediate stage, a hierarchical morphology comprised of discrete nanosticks in the inner surface of the microtube has been found. Hyperfine interaction measurements disclosed the presence of confined metallic Zn regions at the interface between linked ZnO grains forming a chain and a ZnO thicker layer. Surprisingly, the metallic clusters form highly textured thin flat regions oriented parallel to the surface of the microtube as revealed by the electrical field gradient direction. The driving force to grow the internal nanosticks has been ascribed to stress-induced migration of Zn ions due to compressive stress caused by the presence of these confined regions. PMID:26456527

Breaking the glass ceiling: hollow OmniGuide fibers

NASA Astrophysics Data System (ADS)

Johnson, Steven G.; Ibanescu, Mihai; Skorobogatiy, Maksim A.; Weisberg, Ori; Engeness, Torkel D.; Soljacic, Marin; Jacobs, Steven A.; Joannopoulos, John D.; Fink, Yoel

2002-04-01

We argue that OmniGuide fibers, which guide light within a hollow core by concentric multilayer films having the property of omnidirectional reflection, have the potential to lift several physical limitations of silica fibers. We show how the strong confinement in OmniGuide fibers greatly suppresses the properties of the cladding materials: even if highly lossy and nonlinear materials are employed, both the intrinsic losses and nonlinearities of silica fibers can be surpassed by orders of magnitude. This feat, impossible to duplicate in an index-guided fiber with existing materials, would open up new regimes for long-distance propagation and dense wavelength-division multiplexing (DWDM). The OmniGuide-fiber modes bear a strong analogy to those of hollow metallic waveguides; from this analogy, we are able to derive several general scaling laws with core radius. Moreover, there is strong loss discrimination between guided modes, depending upon their degree of confinement in the hollow core: this allows large, ostensibly multi-mode cores to be used, with the lowest-loss TE01 mode propagating in an effectively single-mode fashion. Finally, because this TE01 mode is a cylindrically symmetrical ('azimuthally' polarized) singlet state, it is immune to polarization-mode dispersion (PMD), unlike the doubly-degenerate linearly-polarized modes in silica fibers that are vulnerable to birefringence.

Progress Towards a Rad-Hydro Code for Modern Computing Architectures LA-UR-10-02825

NASA Astrophysics Data System (ADS)

Wohlbier, J. G.; Lowrie, R. B.; Bergen, B.; Calef, M.

2010-11-01

We are entering an era of high performance computing where data movement is the overwhelming bottleneck to scalable performance, as opposed to the speed of floating-point operations per processor. All multi-core hardware paradigms, whether heterogeneous or homogeneous, be it the Cell processor, GPGPU, or multi-core x86, share this common trait. In multi-physics applications such as inertial confinement fusion or astrophysics, one may be solving multi-material hydrodynamics with tabular equation of state data lookups, radiation transport, nuclear reactions, and charged particle transport in a single time cycle. The algorithms are intensely data dependent, e.g., EOS, opacity, nuclear data, and multi-core hardware memory restrictions are forcing code developers to rethink code and algorithm design. For the past two years LANL has been funding a small effort referred to as Multi-Physics on Multi-Core to explore ideas for code design as pertaining to inertial confinement fusion and astrophysics applications. The near term goals of this project are to have a multi-material radiation hydrodynamics capability, with tabular equation of state lookups, on cartesian and curvilinear block structured meshes. In the longer term we plan to add fully implicit multi-group radiation diffusion and material heat conduction, and block structured AMR. We will report on our progress to date.

Integrated modelling of H-mode pedestal and confinement in JET-ILW

NASA Astrophysics Data System (ADS)

Saarelma, S.; Challis, C. D.; Garzotti, L.; Frassinetti, L.; Maggi, C. F.; Romanelli, M.; Stokes, C.; Contributors, JET

2018-01-01

A pedestal prediction model Europed is built on the existing EPED1 model by coupling it with core transport simulation using a Bohm-gyroBohm transport model to self-consistently predict JET-ILW power scan for hybrid plasmas that display weaker power degradation than the IPB98(y, 2) scaling of the energy confinement time. The weak power degradation is reproduced in the coupled core-pedestal simulation. The coupled core-pedestal model is further tested for a 3.0 MA plasma with the highest stored energy achieved in JET-ILW so far, giving a prediction of the stored plasma energy within the error margins of the measured experimental value. A pedestal density prediction model based on the neutral penetration is tested on a JET-ILW database giving a prediction with an average error of 17% from the experimental data when a parameter taking into account the fuelling rate is added into the model. However the model fails to reproduce the power dependence of the pedestal density implying missing transport physics in the model. The future JET-ILW deuterium campaign with increased heating power is predicted to reach plasma energy of 11 MJ, which would correspond to 11-13 MW of fusion power in equivalent deuterium-tritium plasma but with isotope effects on pedestal stability and core transport ignored.

Probing the relationship between magnetic and temperature structures with soft x-rays on the Madison Symmetric Torus

NASA Astrophysics Data System (ADS)

McGarry, Meghan B.

An innovative new soft x-ray (SXR) diagnostic has been developed for the Madison Symmetric Torus that provides measurements of tomographic emissivity and electron temperature (Te) via the double-foil technique. Two measurements of electron temperature from SXR emission are available, one from the ratio of the emissivities through thin and thick filters as mapped onto magnetic flux surfaces, and the other directly from the ratio of two foils sharing a single line-of-sight. The SXR measurements have been benchmarked against Thomson Scattering electron temperature during high current, improved confinement discharges, and show excellent agreement. The SXR diagnostic has been used to investigate the source of emissive structures seen during high-current improved confinement discharges. Although the emissivity structures are correlated to the magnetic configuration of the discharges, direct-brightness Te measurements do not typically show a clear Te structure, indicating a general upper limit of ˜ 15--20% on any possible localized increase in Te. In most shots, the flux-surface reconstructed Te shows no indication of Te structure. However, in one discharge with a very large tearing mode amplitude (15 Gauss), measurements and modeling indicate that the structure has a localized increase of 20-180 eV in Te. The structure cannot be explained by a localized enhancement of electron density. A second case study with a multiple-helicity magnetic spectrum indicates that a ring of enhanced SXR emission at 0.4 normalized radius is caused by an impurity accumulation of up to 58% that of the core region. For the first time, the SXR diagnostic has also been combined with Al11+ impurity measurements to normalize the aluminum contribution to the SXR emission spectrum and demonstrate that the filter thicknesses used for the diagnostic do not pass aluminum line radiation. The new SXR Te and tomography diagnostic will continue to provide insight into the relationship between magnetic structures and electron temperature in improved confinement plasmas.

Enhanced propagation for relativistic laser pulses in inhomogeneous plasmas using hollow channels.

PubMed

Fuchs, J; d'Humières, E; Sentoku, Y; Antici, P; Atzeni, S; Bandulet, H; Depierreux, S; Labaune, C; Schiavi, A

2010-11-26

The influence of long (several millimeters) and hollow channels, bored in inhomogeneous ionized plasma by using a long pulse laser beam, on the propagation of short, ultraintense laser pulses has been studied. Compared to the case without a channel, propagation in channels significantly improves beam transmission and maintains a beam quality close to propagation in vacuum. In addition, the growth of the forward-Raman instability is strongly reduced. These results are beneficial for the direct scheme of the fast ignitor concept of inertial confinement fusion as we demonstrate, in fast-ignition-relevant conditions, that with such channels laser energy can be carried through increasingly dense plasmas close to the fuel core with minimal losses.

Formation and sustainment of internal transport barriers in the International Thermonuclear Experimental Reactor with the baseline heating mixa)

NASA Astrophysics Data System (ADS)

Poli, Francesca M.; Kessel, Charles E.

2013-05-01

Plasmas with internal transport barriers (ITBs) are a potential and attractive route to steady-state operation in ITER. These plasmas exhibit radially localized regions of improved confinement with steep pressure gradients in the plasma core, which drive large bootstrap current and generate hollow current profiles and negative magnetic shear. This work examines the formation and sustainment of ITBs in ITER with electron cyclotron heating and current drive. The time-dependent transport simulations indicate that, with a trade-off of the power delivered to the equatorial and to the upper launcher, the sustainment of steady-state ITBs can be demonstrated in ITER with the baseline heating configuration.

The effect of a metal wall on confinement in JET and ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Beurskens, M. N. A.; Schweinzer, J.; Angioni, C.; Burckhart, A.; Challis, C. D.; Chapman, I.; Fischer, R.; Flanagan, J.; Frassinetti, L.; Giroud, C.; Hobirk, J.; Joffrin, E.; Kallenbach, A.; Kempenaars, M.; Leyland, M.; Lomas, P.; Maddison, G.; Maslov, M.; McDermott, R.; Neu, R.; Nunes, I.; Osborne, T.; Ryter, F.; Saarelma, S.; Schneider, P. A.; Snyder, P.; Tardini, G.; Viezzer, E.; Wolfrum, E.; the ASDEX Upgrade Team; Contributors, JET-EFDA

2013-12-01

In both JET and ASDEX Upgrade (AUG) the plasma energy confinement has been affected by the presence of a metal wall by the requirement of increased gas fuelling to avoid tungsten pollution of the plasma. In JET with a beryllium/tungsten wall the high triangularity baseline H-mode scenario (i.e. similar to the ITER reference scenario) has been the strongest affected and the benefit of high shaping to give good normalized confinement of H98 ˜ 1 at high Greenwald density fraction of fGW ˜ 0.8 has not been recovered to date. In AUG with a full tungsten wall, a good normalized confinement H98 ˜ 1 could be achieved in the high triangularity baseline plasmas, albeit at elevated normalized pressure βN > 2. The confinement lost with respect to the carbon devices can be largely recovered by the seeding of nitrogen in both JET and AUG. This suggests that the absence of carbon in JET and AUG with a metal wall may have affected the achievable confinement. Three mechanisms have been tested that could explain the effect of carbon or nitrogen (and the absence thereof) on the plasma confinement. First it has been seen in experiments and by means of nonlinear gyrokinetic simulations (with the GENE code), that nitrogen seeding does not significantly change the core temperature profile peaking and does not affect the critical ion temperature gradient. Secondly, the dilution of the edge ion density by the injection of nitrogen is not sufficient to explain the plasma temperature and pressure rise. For this latter mechanism to explain the confinement improvement with nitrogen seeding, strongly hollow Zeff profiles would be required which is not supported by experimental observations. The confinement improvement with nitrogen seeding cannot be explained with these two mechanisms. Thirdly, detailed pedestal structure analysis in JET high triangularity baseline plasmas have shown that the fuelling of either deuterium or nitrogen widens the pressure pedestal. However, in JET-ILW this only leads to a confinement benefit in the case of nitrogen seeding where, as the pedestal widens, the obtained pedestal pressure gradient is conserved. In the case of deuterium fuelling in JET-ILW the pressure gradient is strongly degraded in the fuelling scan leading to no net confinement gain due to the pedestal widening. The pedestal code EPED correctly predicts the pedestal pressure of the unseeded plasmas in JET-ILW within ±5%, however it does not capture the complex variation of pedestal width and gradient with fuelling and impurity seeding. Also it does not predict the observed increase of pedestal pressure by nitrogen seeding in JET-ILW. Ideal peeling ballooning MHD stability analysis shows that the widening of the pedestal leads to a down shift of the marginal stability boundary by only 10-20%. However, the variations in the pressure gradient observed in the JET-ILW fuelling experiment is much larger and spans a factor of more than two. As a result the experimental points move from deeply unstable to deeply stable on the stability diagram in a deuterium fuelling scan. In AUG-W nitrogen seeded plasmas, a widening of the pedestal has also been observed, consistent with the JET observations. The absence of carbon can thus affect the pedestal structure, and mainly the achieved pedestal gradient, which can be recovered by seeding nitrogen. The underlying physics mechanism is still under investigation and requires further understanding of the role of impurities on the pedestal stability and pedestal structure formation.

Fuel handling system for a nuclear reactor

DOEpatents

Saiveau, James G.; Kann, William J.; Burelbach, James P.

1986-01-01

A pool type nuclear fission reactor has a core, with a plurality of core elements and a redan which confines coolant as a hot pool at a first end of the core separated from a cold pool at a second end of the core by the redan. A fuel handling system for use with such reactors comprises a core element storage basket located outside of the redan in the cold pool. An access passage is formed in the redan with a gate for opening and closing the passage to maintain the temperature differential between the hot pool and the cold pool. A mechanism is provided for opening and closing the gate. A lifting arm is also provided for manipulating the fuel core elements through the access passage between the storage basket and the core when the redan gate is open.

Fuel handling system for a nuclear reactor

DOEpatents

Saiveau, James G.; Kann, William J.; Burelbach, James P.

1986-12-02

A pool type nuclear fission reactor has a core, with a plurality of core elements and a redan which confines coolant as a hot pool at a first end of the core separated from a cold pool at a second end of the core by the redan. A fuel handling system for use with such reactors comprises a core element storage basket located outside of the redan in the cold pool. An access passage is formed in the redan with a gate for opening and closing the passage to maintain the temperature differential between the hot pool and the cold pool. A mechanism is provided for opening and closing the gate. A lifting arm is also provided for manipulating the fuel core elements through the access passage between the storage basket and the core when the redan gate is open.

Generation of surface-wave microwave microplasmas in hollow-core photonic crystal fiber based on a split-ring resonator.

PubMed

Vial, Florian; Gadonna, Katell; Debord, Benoît; Delahaye, Frédéric; Amrani, Foued; Leroy, Olivier; Gérôme, Frédéric; Benabid, Fetah

2016-05-15

We report on a new and highly compact scheme for the generation and sustainment of microwave-driven plasmas inside the core of an inhibited coupling Kagome hollow-core photonic crystal fiber. The microwave plasma generator consists of a split-ring resonator that efficiently couples the microwave field into the gas-filled fiber. This coupling induces the concomitant generation of a microwave surface wave at the fiber core surround and a stable plasma column confined in the fiber core. The scheme allowed the generation of several centimeters long argon microplasma columns with a very low excitation power threshold. This result represents an important step toward highly compact plasma lasers or plasma-based photonic components.

Plasma core reactor simulations using RF uranium seeded argon discharges

NASA Technical Reports Server (NTRS)

Roman, W. C.

1975-01-01

An experimental investigation was conducted using the United Technologies Research Center (UTRC) 80 kW and 1.2 MW RF induction heater systems to aid in developing the technology necessary for designing a self-critical fissioning uranium plasma core reactor (PCR). A nonfissioning, steady-state RF-heated argon plasma seeded with pure uranium hexafluoride (UF6) was used. An overall objective was to achieve maximum confinement of uranium vapor within the plasma while simultaneously minimizing the uranium compound wall deposition. Exploratory tests were conducted using the 80 kW RF induction heater with the test chamber at approximately atmospheric pressure and discharge power levels on the order of 10 kW. Four different test chamber flow configurations were tested to permit selection of the configuration offering the best confinement characteristics for subsequent tests at higher pressure and power in the 1.2 MW RF induction heater facility.

Projecting High Beta Steady-State Scenarios from DIII-D Advanced Tokamk Discharges

NASA Astrophysics Data System (ADS)

Park, J. M.

2013-10-01

Fusion power plant studies based on steady-state tokamak operation suggest that normalized beta in the range of 4-6 is needed for economic viability. DIII-D is exploring a range of candidate high beta scenarios guided by FASTRAN modeling in a repeated cycle of experiment and modeling validation. FASTRAN is a new iterative numerical procedure coupled to the Integrated Plasma Simulator (IPS) that integrates models of core transport, heating and current drive, equilibrium and stability self-consistently to find steady state (d / dt = 0) solutions, and reproduces most features of DIII-D high beta discharges with a stationary current profile. Separately, modeling components such as core transport (TGLF) and off-axis neutral beam current drive (NUBEAM) show reasonable agreement with experiment. Projecting forward to scenarios possible on DIII-D with future upgrades, two self-consistent noninductive scenarios at βN > 4 are found: high qmin and high internal inductance li. Both have bootstrap current fraction fBS > 0 . 5 and rely on the planned addition of a second off-axis neutral beamline and increased electron cyclotron heating. The high qmin > 2 scenario achieves stable operation at βN as high as 5 by a very broad current density profile to improve the ideal-wall stabilization of low-n instabilities along with confinement enhancement from low magnetic shear. The li near 1 scenario does not depend on ideal-wall stabilization. Improved confinement from strong magnetic shear makes up for the lower pedestal needed to maintain li high. The tradeoff between increasing li and reduced edge pedestal determines the achievable βN (near 4) and fBS (near 0.5). This modeling identifies the necessary upgrades to achieve target scenarios and clarifies the pros and cons of particular scenarios to better inform the development of steady-state fusion. Supported by the US Department of Energy under DE-AC05-00OR22725 & DE-FC02-04ER54698.

Demonstration of Ignition Radiation Temperatures in Indirect-Drive Inertial Confinement Fusion Hohlraums

NASA Astrophysics Data System (ADS)

Glenzer, S. H.; MacGowan, B. J.; Meezan, N. B.; Adams, P. A.; Alfonso, J. B.; Alger, E. T.; Alherz, Z.; Alvarez, L. F.; Alvarez, S. S.; Amick, P. V.; Andersson, K. S.; Andrews, S. D.; Antonini, G. J.; Arnold, P. A.; Atkinson, D. P.; Auyang, L.; Azevedo, S. G.; Balaoing, B. N. M.; Baltz, J. A.; Barbosa, F.; Bardsley, G. W.; Barker, D. A.; Barnes, A. I.; Baron, A.; Beeler, R. G.; Beeman, B. V.; Belk, L. R.; Bell, J. C.; Bell, P. M.; Berger, R. L.; Bergonia, M. A.; Bernardez, L. J.; Berzins, L. V.; Bettenhausen, R. C.; Bezerides, L.; Bhandarkar, S. D.; Bishop, C. L.; Bond, E. J.; Bopp, D. R.; Borgman, J. A.; Bower, J. R.; Bowers, G. A.; Bowers, M. W.; Boyle, D. T.; Bradley, D. K.; Bragg, J. L.; Braucht, J.; Brinkerhoff, D. L.; Browning, D. F.; Brunton, G. K.; Burkhart, S. C.; Burns, S. R.; Burns, K. E.; Burr, B.; Burrows, L. M.; Butlin, R. K.; Cahayag, N. J.; Callahan, D. A.; Cardinale, P. S.; Carey, R. W.; Carlson, J. W.; Casey, A. D.; Castro, C.; Celeste, J. R.; Chakicherla, A. Y.; Chambers, F. W.; Chan, C.; Chandrasekaran, H.; Chang, C.; Chapman, R. F.; Charron, K.; Chen, Y.; Christensen, M. J.; Churby, A. J.; Clancy, T. J.; Cline, B. D.; Clowdus, L. C.; Cocherell, D. G.; Coffield, F. E.; Cohen, S. J.; Costa, R. L.; Cox, J. R.; Curnow, G. M.; Dailey, M. J.; Danforth, P. M.; Darbee, R.; Datte, P. S.; Davis, J. A.; Deis, G. A.; Demaret, R. D.; Dewald, E. L.; di Nicola, P.; di Nicola, J. M.; Divol, L.; Dixit, S.; Dobson, D. B.; Doppner, T.; Driscoll, J. D.; Dugorepec, J.; Duncan, J. J.; Dupuy, P. C.; Dzenitis, E. G.; Eckart, M. J.; Edson, S. L.; Edwards, G. J.; Edwards, M. J.; Edwards, O. D.; Edwards, P. W.; Ellefson, J. C.; Ellerbee, C. H.; Erbert, G. V.; Estes, C. M.; Fabyan, W. J.; Fallejo, R. N.; Fedorov, M.; Felker, B.; Fink, J. T.; Finney, M. D.; Finnie, L. F.; Fischer, M. J.; Fisher, J. M.; Fishler, B. T.; Florio, J. W.; Forsman, A.; Foxworthy, C. B.; Franks, R. M.; Frazier, T.; Frieder, G.; Fung, T.; Gawinski, G. N.; Gibson, C. R.; Giraldez, E.; Glenn, S. M.; Golick, B. P.; Gonzales, H.; Gonzales, S. A.; Gonzalez, M. J.; Griffin, K. L.; Grippen, J.; Gross, S. M.; Gschweng, P. H.; Gururangan, G.; Gu, K.; Haan, S. W.; Hahn, S. R.; Haid, B. J.; Hamblen, J. E.; Hammel, B. A.; Hamza, A. V.; Hardy, D. L.; Hart, D. R.; Hartley, R. G.; Haynam, C. A.; Heestand, G. M.; Hermann, M. R.; Hermes, G. L.; Hey, D. S.; Hibbard, R. L.; Hicks, D. G.; Hinkel, D. E.; Hipple, D. L.; Hitchcock, J. D.; Hodtwalker, D. L.; Holder, J. P.; Hollis, J. D.; Holtmeier, G. M.; Huber, S. R.; Huey, A. W.; Hulsey, D. N.; Hunter, S. L.; Huppler, T. R.; Hutton, M. S.; Izumi, N.; Jackson, J. L.; Jackson, M. A.; Jancaitis, K. S.; Jedlovec, D. R.; Johnson, B.; Johnson, M. C.; Johnson, T.; Johnston, M. P.; Jones, O. S.; Kalantar, D. H.; Kamperschroer, J. H.; Kauffman, R. L.; Keating, G. A.; Kegelmeyer, L. M.; Kenitzer, S. L.; Kimbrough, J. R.; King, K.; Kirkwood, R. K.; Klingmann, J. L.; Knittel, K. M.; Kohut, T. R.; Koka, K. G.; Kramer, S. W.; Krammen, J. E.; Krauter, K. G.; Krauter, G. W.; Krieger, E. K.; Kroll, J. J.; La Fortune, K. N.; Lagin, L. J.; Lakamsani, V. K.; Landen, O. L.; Lane, S. W.; Langdon, A. B.; Langer, S. H.; Lao, N.; Larson, D. W.; Latray, D.; Lau, G. T.; Le Pape, S.; Lechleiter, B. L.; Lee, Y.; Lee, T. L.; Li, J.; Liebman, J. A.; Lindl, J. D.; Locke, S. F.; Loey, H. K.; London, R. A.; Lopez, F. J.; Lord, D. M.; Lowe-Webb, R. R.; Lown, J. G.; Ludwigsen, A. P.; Lum, N. W.; Lyons, R. R.; Ma, T.; MacKinnon, A. J.; Magat, M. D.; Maloy, D. T.; Malsbury, T. N.; Markham, G.; Marquez, R. M.; Marsh, A. A.; Marshall, C. D.; Marshall, S. R.; Maslennikov, I. L.; Mathisen, D. G.; Mauger, G. J.; Mauvais, M.-Y.; McBride, J. A.; McCarville, T.; McCloud, J. B.; McGrew, A.; McHale, B.; Macphee, A. G.; Meeker, J. F.; Merill, J. S.; Mertens, E. P.; Michel, P. A.; Miller, M. G.; Mills, T.; Milovich, J. L.; Miramontes, R.; Montesanti, R. C.; Montoya, M. M.; Moody, J.; Moody, J. D.; Moreno, K. A.; Morris, J.; Morriston, K. M.; Nelson, J. R.; Neto, M.; Neumann, J. D.; Ng, E.; Ngo, Q. M.; Olejniczak, B. L.; Olson, R. E.; Orsi, N. L.; Owens, M. W.; Padilla, E. H.; Pannell, T. M.; Parham, T. G.; Patterson, R. W., Jr.; Pavel, G.; Prasad, R. R.; Pendlton, D.; Penko, F. A.; Pepmeier, B. L.; Petersen, D. E.; Phillips, T. W.; Pigg, D.; Piston, K. W.; Pletcher, K. D.; Powell, C. L.; Radousky, H. B.; Raimondi, B. S.; Ralph, J. E.; Rampke, R. L.; Reed, R. K.; Reid, W. A.; Rekow, V. V.; Reynolds, J. L.; Rhodes, J. J.; Richardson, M. J.; Rinnert, R. J.; Riordan, B. P.; Rivenes, A. S.; Rivera, A. T.; Roberts, C. J.; Robinson, J. A.; Robinson, R. B.; Robison, S. R.; Rodriguez, O. R.; Rogers, S. P.; Rosen, M. D.; Ross, G. F.; Runkel, M.; Runtal, A. S.; Sacks, R. A.; Sailors, S. F.; Salmon, J. T.; Salmonson, J. D.; Saunders, R. L.; Schaffer, J. R.; Schindler, T. M.; Schmitt, M. J.; Schneider, M. B.; Segraves, K. S.; Shaw, M. J.; Sheldrick, M. E.; Shelton, R. T.; Shiflett, M. K.; Shiromizu, S. J.; Shor, M.; Silva, L. L.; Silva, S. A.; Skulina, K. M.; Smauley, D. A.; Smith, B. E.; Smith, L. K.; Solomon, A. L.; Sommer, S.; Soto, J. G.; Spafford, N. I.; Speck, D. E.; Springer, P. T.; Stadermann, M.; Stanley, F.; Stone, T. G.; Stout, E. A.; Stratton, P. L.; Strausser, R. J.; Suter, L. J.; Sweet, W.; Swisher, M. F.; Tappero, J. D.; Tassano, J. B.; Taylor, J. S.; Tekle, E. A.; Thai, C.; Thomas, C. A.; Thomas, A.; Throop, A. L.; Tietbohl, G. L.; Tillman, J. M.; Town, R. P. J.; Townsend, S. L.; Tribbey, K. L.; Trummer, D.; Truong, J.; Vaher, J.; Valadez, M.; van Arsdall, P.; van Prooyen, A. J.; Vergel de Dios, E. O.; Vergino, M. D.; Vernon, S. P.; Vickers, J. L.; Villanueva, G. T.; Vitalich, M. A.; Vonhof, S. A.; Wade, F. E.; Wallace, R. J.; Warren, C. T.; Warrick, A. L.; Watkins, J.; Weaver, S.; Wegner, P. J.; Weingart, M. A.; Wen, J.; White, K. S.; Whitman, P. K.; Widmann, K.; Widmayer, C. C.; Wilhelmsen, K.; Williams, E. A.; Williams, W. H.; Willis, L.; Wilson, E. F.; Wilson, B. A.; Witte, M. C.; Work, K.; Yang, P. S.; Young, B. K.; Youngblood, K. P.; Zacharias, R. A.; Zaleski, T.; Zapata, P. G.; Zhang, H.; Zielinski, J. S.; Kline, J. L.; Kyrala, G. A.; Niemann, C.; Kilkenny, J. D.; Nikroo, A.; van Wonterghem, B. M.; Atherton, L. J.; Moses, E. I.

2011-02-01

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of TRAD=300eV and a symmetric implosion to a 100μm diameter hot core.

A Neutral Beam for the Lithium Tokamak eXperiment Upgrade (LTX-U)

NASA Astrophysics Data System (ADS)

Merino, Enrique; Majeski, Richard; Kaita, Robert; Kozub, Thomas; Boyle, Dennis; Schmitt, John; Smirnov, Artem

2015-11-01

Neutral beam injection into tokamaks is a proven method of plasma heating and fueling. In LTX, high confinement discharges have been achieved with low-recycling lithium walls. To further improve plasma performance, a neutral beam (NB) will be installed as part of an upgrade to LTX (LTX-U). The NB will provide core plasma fueling with up to 700 kW of injected power. Requirements for accommodating the NB include the addition of injection and beam-dump ports onto the vessel and enhancement of the vacuum vessel pumping capability. Because the NB can also serve as a source of neutrals for charge-exchange recombination spectroscopy, ``active'' spectroscopic diagnostics will also be developed. An overview of these plans and other improvements for upgrading LTX to LTX-U will be presented. Supported by US DOE contracts DE-AC02-09CH11466 and DE-AC52-07NA27344.

Performance improvement of magnetized coaxial plasma gun by magnetic circuit on a bias coil

NASA Astrophysics Data System (ADS)

Edo, Takahiro; Matsumoto, Tadafumi; Asai, Tomohiko; Kamino, Yasuhiro; Inomoto, Michiaki; Gota, Hiroshi

2016-10-01

A magnetized coaxial plasmoid accelerator has been utilized for compact torus (CT) injection to refuel into fusion reactor core plasma. Recently, CT injection experiments have been conducted on the C-2/C-2U facility at Tri Alpha Energy. In the series of experiments successful refueling, i.e. increased particle inventory of field-reversed configuration (FRC) plasma, has been observed. In order to improve the performance of CT injector and to refuel in the upgraded FRC device, called C-2W, with higher confinement magnetic field, magnetic circuit consisting of magnetic material onto a bias magnetic coil is currently being tested at Nihon University. Numerical work suggests that the optimized bias magnetic field distribution realizes the increased injection velocity because of higher conversion efficiency of Lorenz self force to kinetic energy. Details of the magnetic circuit design as well as results of the test experiment and field calculations will be presented and discussed.

X-ray penumbral imaging diagnostic developments at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Bachmann, B.; Abu-Shawareb, H.; Alexander, N.; Ayers, J.; Bailey, C. G.; Bell, P.; Benedetti, L. R.; Bradley, D.; Collins, G.; Divol, L.; Döppner, T.; Felker, S.; Field, J.; Forsman, A.; Galbraith, J. D.; Hardy, C. M.; Hilsabeck, T.; Izumi, N.; Jarrot, C.; Kilkenny, J.; Kramer, S.; Landen, O. L.; Ma, T.; MacPhee, A.; Masters, N.; Nagel, S. R.; Pak, A.; Patel, P.; Pickworth, L. A.; Ralph, J. E.; Reed, C.; Rygg, J. R.; Thorn, D. B.

2017-08-01

X-ray penumbral imaging has been successfully fielded on a variety of inertial confinement fusion (ICF) capsule implosion experiments on the National Ignition Facility (NIF). We have demonstrated sub-5 μm resolution imaging of stagnated plasma cores (hot spots) at x-ray energies from 6 to 30 keV. These measurements are crucial for improving our understanding of the hot deuterium-tritium fuel assembly, which can be affected by various mechanisms, including complex 3-D perturbations caused by the support tent, fill tube or capsule surface roughness. Here we present the progress on several approaches to improve x-ray penumbral imaging experiments on the NIF. We will discuss experimental setups that include penumbral imaging from multiple lines-of-sight, target mounted penumbral apertures and variably filtered penumbral images. Such setups will improve the signal-to-noise ratio and the spatial imaging resolution, with the goal of enabling spatially resolved measurements of the hot spot electron temperature and material mix in ICF implosions.

Experimental study of dynamic effective stress coefficient for ultrasonic velocities of Bakken cores

NASA Astrophysics Data System (ADS)

Ma, X.; Zoback, M. D.

2016-12-01

We have performed a series of exhaustive experiments to measure the effective stress coefficient (α) of the tight cores from the Bakken shale oil play. Five distinct, bedding-normal cores from a vertical well were tested, covering the sequences of Lodgepole, Middle Bakken, and Three Forks. The scope of this laboratory study is two-fold: (1) to obtain the dynamic effective stress coefficient for ultrasonic velocities; (2) to characterize the poromechanical properties in relation to rock's mineral composition and microstructure. The experiments were carried out as follows: Argon-saturated specimen (1-inch length, 1-inch diameter) was subjected to hydrostatic confining pressure under drained conditions. Pore pressure was regulated as Argon was injected into both ends of the specimen. We drilled multiple non-through-going boreholes (1-mm diameter) in the specimen to facilitate pore pressure equilibrium, without compromising its integrity. The specimen was put through a loading path to experience confining pressure and pore pressure up to 70 and 60 MPa, respectively. P- and S- wave velocities were measured and used to calculate the rock's dynamic effective stress coefficient. Results of all five cores unanimously show that the dynamic a is a function of both confining and pore pressures, regardless of the wave type and loading path. When the simple effective stress is low, α is close to unity; however, α consistently increases as the simple effective stress rises and can reach as much as 3 when the latter reaches 60 MPa. This trend is rather surprising as it is diametrically the opposite of what was observed for the static α. A possible explanation is that high-frequency wave-induced pore pressure increment may have not remained equilibrated throughout the pore space, especially in very thin cracks, according to the squirt model. This phenomenon can be enhanced when the bulk modulus of pore fluid (gas typically considered to be `soft' and `non-viscous') increases with pore pressure and becomes comparable to the crack stiffness.

Electronic state and photoionization cross section of a single dopant in GaN/InGaN core/shell quantum dot under magnetic field and hydrostatic pressure

NASA Astrophysics Data System (ADS)

Aouami, A. El; Feddi, E.; Talbi, A.; Dujardin, F.; Duque, C. A.

2018-06-01

In this study, we have investigated the simultaneous influence of magnetic field combined to the hydrostatic pressure and the geometrical confinement on the behavior of a single dopant confined in GaN/InGaN core/shell quantum dots. Within the scheme of the effective-mass approximation, the eigenvalues equation has solved by using the variational method with one-parameter trial wavefunctions. Variation of the ground state binding energy of the single dopant is determined according to the magnetic field and hydrostatic pressure for several dimensions of the heterostructure. The results show that the binding energy is strongly dependent on the core/shell sizes, the magnetic field, and the hydrostatic pressure. The analysis of the photoionization cross section, corresponding to optical transitions associated to the first donor energy level and the conduction band, shows clearly that the reduction of the dot dimensions and/or the simultaneous influences of applied magnetic field, combined to the hydrostatic pressure strength, cause a shift in resonance peaks towards the higher energies with important variations in the magnitude of the resonant peaks.

Demonstration of Confined Electron Gas and Steep-Slope Behavior in Delta-Doped GaAs-AlGaAs Core-Shell Nanowire Transistors.

PubMed

Morkötter, S; Jeon, N; Rudolph, D; Loitsch, B; Spirkoska, D; Hoffmann, E; Döblinger, M; Matich, S; Finley, J J; Lauhon, L J; Abstreiter, G; Koblmüller, G

2015-05-13

Strong surface and impurity scattering in III-V semiconductor-based nanowires (NW) degrade the performance of electronic devices, requiring refined concepts for controlling charge carrier conductivity. Here, we demonstrate remote Si delta (δ)-doping of radial GaAs-AlGaAs core-shell NWs that unambiguously exhibit a strongly confined electron gas with enhanced low-temperature field-effect mobilities up to 5 × 10(3) cm(2) V(-1) s(-1). The spatial separation between the high-mobility free electron gas at the NW core-shell interface and the Si dopants in the shell is directly verified by atom probe tomographic (APT) analysis, band-profile calculations, and transport characterization in advanced field-effect transistor (FET) geometries, demonstrating powerful control over the free electron gas density and conductivity. Multigated NW-FETs allow us to spatially resolve channel width- and crystal phase-dependent variations in electron gas density and mobility along single NW-FETs. Notably, dc output and transfer characteristics of these n-type depletion mode NW-FETs reveal excellent drain current saturation and record low subthreshold slopes of 70 mV/dec at on/off ratios >10(4)-10(5) at room temperature.

N-Doped Dual Carbon-Confined 3D Architecture rGO/Fe3O4/AC Nanocomposite for High-Performance Lithium-Ion Batteries.

PubMed

Ding, Ranran; Zhang, Jie; Qi, Jie; Li, Zhenhua; Wang, Chengyang; Chen, Mingming

2018-04-25

To address the issues of low electrical conductivity, sluggish lithiation kinetics and dramatic volume variation in Fe 3 O 4 anodes of lithium ion battery, herein, a double carbon-confined three-dimensional (3D) nanocomposite architecture was synthesized by an electrostatically assisted self-assembly strategy. In the constructed architecture, the ultrafine Fe 3 O 4 subunits (∼10 nm) self-organize to form nanospheres (NSs) that are fully coated by amorphous carbon (AC), formatting core-shell structural Fe 3 O 4 /AC NSs. By further encapsulation by reduced graphene oxide (rGO) layers, a constructed 3D architecture was built as dual carbon-confined rGO/Fe 3 O 4 /AC. Such structure restrains the adverse reaction of the electrolyte, improves the electronic conductivity and buffers the mechanical stress of the entire electrode, thus performing excellent long-term cycling stability (99.4% capacity retention after 465 cycles relevant to the second cycle at 5 A g -1 ). Kinetic analysis reveals that a dual lithium storage mechanism including a diffusion reaction mechanism and a surface capacitive behavior mechanism coexists in the composites. Consequently, the resulting rGO/Fe 3 O 4 /AC nanocomposite delivers a high reversible capacity (835.8 mA h g -1 for 300 cycles at 1 A g -1 ), as well as remarkable rate capability (436.7 mA h g -1 at 10 A g -1 ).

Measurements of confined alphas and tritons in the MHD quiescent core of TFTR plasmas using the pellet charge exchange diagnostic

NASA Astrophysics Data System (ADS)

Medley, S. S.; Budny, R. V.; Mansfield, D. K.; Redi, M. H.; Roquemore, A. L.; Fisher, R. K.; Duong, H. H.; McChesney, J. M.; Parks, P. B.; Petrov, M. P.; Gorelenkov, N. N.

1996-10-01

The energy distributions and radial density profiles of the fast confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5 - 3.5 MeV using the pellet charge exchange (PCX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MHD quiescent TFTR discharges where the expected classical slowing-down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. In particular, the first measurement of the alpha slowing-down distribution up to the birth energy, obtained using boron pellet injection, is presented. The measurements are compared with predictions using either the TRANSP Monte Carlo code and/or a Fokker - Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations. We can conclude that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons.

Signal quality improvement using cylindrical confinement for laser induced breakdown spectroscopy.

PubMed

Hou, Zongyu; Wang, Zhe; Liu, Jianmin; Ni, Weidou; Li, Zheng

2013-07-01

In our previous work, we found that there was great potential to improve the pulse-to-pulse signal repeatability using a moderate cylindrical cavity confinement. However, the improvement was achieved only with certain experimental parameters; while under other conditions, there was no improvement or even worse repeatability. In the present work, the experimental configuration was redesigned and unexpected uncertainty from the variation of the laser and cavity alignment and the laser ablated aerosols were avoided. With these two improvements, we demonstrated that the cavity can always increase the signal repeatability. In addition, image taken by ICCD verified that the confinement improved the stability of the plasma morphology as expected.

Influence of dimensionality and interface type on optical and electronic properties of CdS/ZnS core-shell nanocrystals—A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocevski, V., E-mail: vancho.vk@gmail.com, E-mail: vancho.kocevski@physics.uu.se; Eriksson, O.; Gerard, C.

2015-10-28

Semiconducting nanocrystals (NCs) have become one of the leading materials in a variety of applications, mainly due to their size tunable band gap and high intensity emission. Their photoluminescence (PL) properties can be notably improved by capping the nanocrystals with a shell of another semiconductor, making core-shell structures. We focus our study on the CdS/ZnS core-shell nanocrystals that are closely related to extensively studied CdSe/CdS NCs, albeit exhibiting rather different photoluminescence properties. We employ density functional theory to investigate the changes in the electronic and optical properties of these nanocrystals with size, core/shell ratio, and interface structure between the coremore » and the shell. We have found that both the lowest unoccupied eigenstate (LUES) and the highest occupied eigenstate (HOES) wavefunction (WF) are localized in the core of the NCs, with the distribution of the LUES WF being more sensitive to the size and the core/shell ratio. We show that the radiative lifetimes are increasing, and the Coulomb interaction energies decrease with increasing NC size. Furthermore, we investigated the electronic and optical properties of the NCs with different interfaces between the core and the shell and different core types. We find that the different interfaces and core types have rather small influence on the band gaps and the absorption indexes, as well as on the confinement of the HOES and LUES WFs. Also the radiative lifetimes are found to be only slightly influenced by the different structural models. In addition, we compare these results with the previous results for CdSe/CdS NCs, reflecting the different PL properties of these two types of NCs. We argue that the difference in their Coulomb interaction energies is one of the main reasons for their distinct PL properties.« less

Advances towards high performance low-torque qmin > 2 operations with large-radius ITB on DIII-D

NASA Astrophysics Data System (ADS)

Xu, G. S.; Solomon, W. M.; Garofalo, A. M.; Ferron, J. R.; Hyatt, A. W.; Wang, Q.; Yan, Z.; McKee, G. R.; Holcomb, C. T.; EAST Team

2015-11-01

A joint DIII-D/EAST experiment was performed aimed at extending a fully noninductive scenario with high βP and qmin > 2 to inductive operation at lower torque and higher Ip (0.6 --> 0.8 MA) for better performance. Extremely high confinement was obtained, i.e., H98y2 ~ 2.1 at βN ~ 3, which was associated with a strong ITB at large minor radius (ρ ~ 0.7). Alfvén Eigenmodes and broadband turbulence were significantly suppressed in the core, and fast-ion confinement was improved. ITB collapses at 0.8 MA were induced by ELM-triggered n = 1 MHD modes at the ITB location, which is different from the ``relaxation oscillations'' associated with the steady-state plasmas at lower current (0.6 MA). This successful joint experiment may open up a new avenue towards high performance low-torque qmin > 2 plasmas with large-radius ITBs, which will be demonstrated on EAST in the near future. Work supported by NMCFSP 2015GB102000, 2015GB110001 and the US DOE under DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-89ER53296 and DE-AC52-07NA27344.

Development of high poloidal beta, steady-state scenario with ITER-like tungsten divertor on EAST

NASA Astrophysics Data System (ADS)

Garofalo, A. M.; Gong, X. Z.; Qian, J.; Chen, J.; Li, G.; Li, K.; Li, M. H.; Zhai, X.; Bonoli, P.; Brower, D.; Cao, L.; Cui, L.; Ding, S.; Ding, W. X.; Guo, W.; Holcomb, C.; Huang, J.; Hyatt, A.; Lanctot, M.; Lao, L. L.; Liu, H.; Lyu, B.; McClenaghan, J.; Peysson, Y.; Ren, Q.; Shiraiwa, S.; Solomon, W.; Zang, Q.; Wan, B.

2017-07-01

Recent experiments on EAST have achieved the first long pulse H-mode (61 s) with zero loop voltage and an ITER-like tungsten divertor, and have demonstrated access to broad plasma current profiles by increasing the density in fully-noninductive lower hybrid current-driven discharges. These long pulse discharges reach wall thermal and particle balance, exhibit stationary good confinement (H 98y2 ~ 1.1) with low core electron transport, and are only possible with optimal active cooling of the tungsten armors. In separate experiments, the electron density was systematically varied in order to study its effect on the deposition profile of the external lower hybrid current drive (LHCD), while keeping the plasma in fully-noninductive conditions and with divertor strike points on the tungsten divertor. A broadening of the current profile is found, as indicated by lower values of the internal inductance at higher density. A broad current profile is attractive because, among other reasons, it enables internal transport barriers at large minor radius, leading to improved confinement as shown in companion DIII-D experiments. These experiments strengthen the physics basis for achieving high performance, steady state discharges in future burning plasmas.

In situ assembly in confined spaces of coated particle scaffolds as thermal underfills with extraordinary thermal conductivity.

PubMed

Hong, Guo; Schutzius, Thomas M; Zimmermann, Severin; Burg, Brian R; Zürcher, Jonas; Brunschwiler, Thomas; Tagliabue, Giulia; Michel, Bruno; Poulikakos, Dimos

2015-01-14

In situ assembly of high thermal conductivity materials in severely confined spaces is an important problem bringing with it scientific challenges but also significant application relevance. Here we present a simple, affordable, and reproducible methodology for synthesizing such materials, composed of hierarchical diamond micro/nanoparticle scaffolds and an ethylenediamine coating. An important feature of the assembly process is the utilization of ethylenediamine as an immobilizing agent to secure the integrity of the microparticle scaffolds during and after each processing step. After other liquid components employed in the scaffolds assembly dry out, the immobilization agent solidifies forming a stable coated particle scaffold structure. Nanoparticles tend to concentrate in the shell and neck regions between adjacent microparticles. The interface between core and shell, along with the concentrated neck regions of nanoparticles, significantly enhance the thermal conductivity, making such materials an excellent candidate as thermal underfills in the electronics industry, where efficient heat removal is a major stumbling block toward increasing packing density. We show that the presented structures exhibit nearly 1 order of magnitude improvement in thermal conductivity, enhanced temperature uniformity, and reduced processing time compared to commercially available products for electronics cooling, which underpins their potential utility.

Development of high poloidal beta, steady-state scenario with ITER-like tungsten divertor on EAST

DOE PAGES

Garofalo, Andrea M.; Gong, X. Z.; Qian, J.; ...

2017-06-07

Recent experiments on EAST have achieved the first long pulse H-mode (61 s) with zero loop voltage and an ITER-like tungsten divertor, and have demonstrated access to broad plasma current profiles by increasing the density in fully-noninductive lower hybrid current-driven discharges. These long pulse discharges reach wall thermal and particle balance, exhibit stationary good confinement (H 98y2~1.1) with low core electron transport, and are only possible with optimal active cooling of the tungsten armors. In separate experiments, the electron density was systematically varied in order to study its effect on the deposition profile of the external lower hybrid current drivemore » (LHCD), while keeping the plasma in fully-noninductive conditions and with divertor strike points on the tungsten divertor. A broadening of the current profile is found, as indicated by lower values of the internal inductance at higher density. A broad current profile is attractive because, among other reasons, it enables internal transport barriers at large minor radius, leading to improved confinement as shown in companion DIII-D experiments. These experiments strengthen the physics basis for achieving high performance, steady state discharges in future burning plasmas.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaita, Robert; Boyle, Dennis; Gray, Timothy

Liquid metal walls have been proposed to address the first wall challenge for fusion reactors. The Lithium Tokamak Experiment (LTX) at the Princeton Plasma Physics Laboratory (PPPL) is the first magnetic confinement device to have liquid metal plasma-facing components (PFC's) that encloses virtually the entire plasma. In the Current Drive Experiment-Upgrade (CDX-U), a predecessor to LTX at PPPL, the highest improvement in energy confinement ever observed in Ohmically-heated tokamak plasmas was achieved with a toroidal liquid lithium limiter. The LTX extends this liquid lithium PFC by using a conducting conformal shell that almost completely surrounds the plasma. By heating themore » shell, a lithium coating on the plasma-facing side can be kept liquefied. A consequence of the low-recycling conditions from liquid lithium walls is the need for efficient plasma fueling. For this purpose, a molecular cluster injector is being developed. Future plans include the installation of a neutral beam for core plasma fueling, and also ion temperature measurements using charge-exchange recombination spectroscopy. Low edge recycling is also predicted to reduce temperature gradients that drive drift wave turbulence. Gyrokinetic simulations are in progress to calculate fluctuation levels and transport for LTX plasmas, and new fluctuation diagnostics are under development to test these predictions. __________________________________________________« less

Microstructured optical fibers for gas sensing systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Challener, William Albert; Choudhury, Niloy; Palit, Sabarni

2017-10-17

Microstructured optical fiber (MOF) includes a cladding extending a length between first and second ends. The cladding includes an inner porous microstructure that at least partially surrounds a hollow core. A perimeter contour of the hollow core has a non-uniform radial distance from a center axis of the cladding such that first segments of the cladding along the perimeter contour have a shorter radial distance from the center axis relative to second segments of the cladding along the perimeter contour. The cladding receives and propagates light energy through the hollow core, and the inner porous microstructure substantially confines the lightmore » energy within the hollow core. The cladding defines at least one port hole that extends radially from an exterior surface of the cladding to the hollow core. Each port hole penetrates the perimeter contour of the hollow core through one of the second segments of the cladding.« less

MERCHANT MARINE SHIP REACTOR

DOEpatents

Mumm, J.F.; North, D.C. Jr.; Rock, H.R.; Geston, D.K.

1961-05-01

A nuclear reactor is described for use in a merchant marine ship. The reactor is of pressurized light water cooled and moderated design in which three passes of the water through the core in successive regions of low, intermediate, and high heat generation and downflow in a fuel region are made. The foregoing design makes a compact reactor construction with extended core life. The core has an egg-crate lattice containing the fuel elements confined between a lower flow baffle and upper grid plate, with the latter serving also as part of a turn- around manifold from which the entire coolant is distributed into the outer fuel elements for the second pass through the core. The inner fuel elements are cooled in the third pass.

Merchant Marine Ship Reactor

DOEpatents

Sankovich, M. F.; Mumm, J. F.; North, Jr, D. C.; Rock, H. R.; Gestson, D. K.

1961-05-01

A nuclear reactor for use in a merchant marine ship is described. The reactor is of pressurized, light water cooled and moderated design in which three passes of the water through the core in successive regions of low, intermediate, and high heat generation and downflow in a fuel region are made. The design makes a compact reactor construction with extended core life. The core has an egg-crate lattice containing the fuel elements that are confined between a lower flow baffle and upper grid plate, with the latter serving also as part of a turn- around manifold from which the entire coolant is distributed into the outer fuel elements for the second pass through the core. The inner fuel elements are cooled in the third pass. (AEC)

Continuous resistivity profiling data from Great South Bay, Long Island, New York

USGS Publications Warehouse

Cross, V.A.; Bratton, J.F.; Kroeger, K.D.; Crusius, John; Worley, C.R.

2013-01-01

An investigation of submarine aquifers adjacent to the Fire Island National Seashore and Long Island, New York was conducted to assess the importance of submarine groundwater discharge as a potential nonpoint source of nitrogen delivery to Great South Bay. Over 200 kilometers of continuous resistivity profiling data were collected to image the fresh-saline groundwater interface in sediments beneath the bay. In addition, groundwater sampling was performed at sites (1) along the north shore of Great South Bay, particularly in Patchogue Bay, that were representative of the developed Long Island shoreline, and (2) at sites on and adjacent to Fire Island, a 50-kilometer-long barrier island on the south side of Great South Bay. Other field activities included sediment coring, stationary electrical resistivity profiling, and surveys of in situ pore water conductivity. Results of continuous resistivity profiling surveys are described in this report. The onshore and offshore shallow hydrostratigraphy of the Great South Bay shorelines, particularly the presence and nature of submarine confining units, appears to exert primary control on the dimensions and chemistry of the submarine groundwater flow and discharge zones. Sediment coring has shown that the confining units commonly consist of drowned and buried peat layers likely deposited in salt marshes. Low-salinity groundwater extends from 10 to 100 meters offshore along much of the north and south shores of Great South Bay based on continuous resistivity profiling data, especially off the mouths of tidal creeks and beneath shallow flats to the north of Fire Island adjacent to modern salt marshes. Human modifications of much of the shoreline and nearshore areas along the north shore of the bay, including filling of salt marshes, construction of bulkheads and piers, and dredging of navigation channels, has substantially altered the natural hydrogeology of the bay's shorelines by truncating confining units and increasing recharge near the shore in filled areas. Better understanding of the nature of submarine groundwater discharge along developed and undeveloped shorelines of embayments such as this could lead to improved models and mitigation strategies for nutrient overenrichment of estuaries.

Behavior of plastic sand confinement grids

DOT National Transportation Integrated Search

1986-01-01

The concept of improving the load carrying ability of unbound aggregates, particularly sand, by lateral confinement has been investigated for some time. Extensive full-scale testing of the trafficability of confined beach sand pavement layers has bee...

Divertor detachment

NASA Astrophysics Data System (ADS)

Krasheninnikov, Sergei

2015-11-01

The heat exhaust is one of the main conceptual issues of magnetic fusion reactor. In a standard operational regime the large heat flux onto divertor target reaches unacceptable level in any foreseeable reactor design. However, about two decades ago so-called ``detached divertor'' regimes were found. They are characterized by reduced power and plasma flux on divertor targets and look as a promising solution for heat exhaust in future reactors. In particular, it is envisioned that ITER will operate in a partly detached divertor regime. However, even though divertor detachment was studied extensively for two decades, still there are some issues requiring a new look. Among them is the compatibility of detached divertor regime with a good core confinement. For example, ELMy H-mode exhibits a very good core confinement, but large ELMs can ``burn through'' detached divertor and release large amounts of energy on the targets. In addition, detached divertor regimes can be subject to thermal instabilities resulting in the MARFE formation, which, potentially, can cause disruption of the discharge. Finally, often inner and outer divertors detach at different plasma conditions, which can lead to core confinement degradation. Here we discuss basic physics of divertor detachment including different mechanisms of power and momentum loss (ionization, impurity and hydrogen radiation loss, ion-neutral collisions, recombination, and their synergistic effects) and evaluate the roles of different plasma processes in the reduction of the plasma flux; detachment stability; and an impact of ELMs on detachment. We also evaluate an impact of different magnetic and divertor geometries on detachment onset, stability, in- out- asymmetry, and tolerance to the ELMs. Supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences under Award Number DE-DE-FG02-04ER54739 at UCSD.

Extremely low-loss, dispersion flattened porous-core photonic crystal fiber for terahertz regime

NASA Astrophysics Data System (ADS)

Islam, Saiful; Islam, Mohammad Rakibul; Faisal, Mohammad; Arefin, Abu Sayeed Muhammad Shamsul; Rahman, Hasan; Sultana, Jakeya; Rana, Sohel

2016-07-01

A porous-core octagonal photonic crystal fiber (PC-OPCF) with ultralow effective material loss (EML), high core power fraction, and ultra flattened dispersion is proposed for terahertz (THz) wave propagation. At an operating frequency of 1 THz and core diameter of 345 μm, simulation results display an extremely low EML of 0.047 cm-1, 49.1% power transmission through core air holes, decreased confinement loss with the increase of frequency, and dispersion variation of 0.15 ps/THz/cm. In addition, the proposed PCF can successfully operate in single-mode condition. All the simulations are performed with finite-element modeling package, COMSOL v4.2. The design can be fabricated using a stacking and drilling method. Thus, the proposed fiber has the potential of being an effective transmission medium of broadband THz waves.

Simulation of the Plasma Density Evolution during Electron Cyclotron Resonance Heating at the T-10 Tokamak

NASA Astrophysics Data System (ADS)

Dnestrovskij, Yu. N.; Vershkov, V. A.; Danilov, A. V.; Dnestrovskij, A. Yu.; Zenin, V. N.; Lysenko, S. E.; Melnikov, A. V.; Shelukhin, D. A.; Subbotin, G. F.; Cherkasov, S. V.

2018-01-01

In ohmically heated (OH) plasma with low recycling, an improved particle confinement (IPC) mode is established during gas puffing. However, after gas puffing is switched off, this mode is retained only for about 100 ms, after which an abrupt phase transition into the low particle confinement (LPC) mode occurs in the entire plasma cross section. During such a transition, energy transport due to heat conduction does not change. The phase transition in OH plasma is similar to the effect of density pump-out from the plasma core, which occurs after electron cyclotron heating (ECH) is switched on. Analysis of the measured plasma pressure profiles in the T-10 tokamak shows that, after gas puffing in the OH mode is switched off, the plasma pressure profile in the IPC stage becomes more peaked and, after the peakedness exceeds a certain critical value, the IPC-LPC transition occurs. Similar processes are also observed during ECH. If the pressure profile is insufficiently peaked during ECH, then the density pump-out effect comes into play only after the critical peakedness of the pressure profile is reached. In the plasma core, the density and pressure profiles are close to the corresponding canonical profiles. This allows one to derive an expression for the particle flux within the canonical profile model and formulate a criterion for the IPC-LPC transition. The time evolution of the plasma density profile during phase transitions was simulated for a number of T-10 shots with ECH and high recycling. The particle transport coefficients in the IPC and LPC phases, as well as the dependences of these coefficients on the ECH power, are determined.

CONFERENCE REPORT: Summary of the 16th IAEA Technical Meeting on 'Research using Small Fusion Devices'

NASA Astrophysics Data System (ADS)

Gribkov, V.; Van Oost, G.; Malaquias, A.; Herrera, J.

2006-10-01

Common research topics that are being studied in small, medium and large devices such as H-mode like or improved confinement, turbulence and transport are reported. These included modelling and diagnostic developments for edge and core, to characterize plasma density, temperature, electric potential, plasma flows, turbulence scale, etc. Innovative diagnostic methods were designed and implemented which could be used to develop experiments in small devices (in some cases not possible in large devices due to higher power deposition) to allow a better understanding of plasma edge and core properties. Reports are given addressing research in linear devices that can be used to study particular plasma physics topics relevant for other magnetic confinement devices such as the radial transport and the modelling of self-organized plasma jets involved in spheromak-like plasma formation. Some aspects of the work presented are of interest to the astrophysics community since they are believed to shed light on the basis of the physics of stellar jets. On the dense magnetized plasmas (DMP) topic, the present status of research, operation of new devices, plasma dynamics modelling and diagnostic developments is reported. The main devices presented belong to the class of Z-pinches, mostly plasma foci, and several papers were presented under this topic. The physics of DMP is important both for the main-stream fusion investigations as well as for providing the basis for elaboration of new concepts. New high-current technology introduced in the DMP devices design and construction make these devices nowadays more reliably fitted to various applications and give the possibility to widen the energy range used by them in both directions—to the multi-MJ level facilities and down to miniature plasma focus devices with energy of just a few J.

Improvement in dehydrogenation of MXH4 where M = Na, Li and X = Al, B confined in CNTs: a DFT investigation

NASA Astrophysics Data System (ADS)

Meenakshi; Agnihotri, Deepak; Jeet, Kiran; Sharma, Hitesh

2016-11-01

Nanoconfinement improves dehydrogenation kinetics of complex metal hydrides. The present paper reports effect of confinement of MXH4, where M = Na, Li and X = Al, B inside carbon nanotubes (CNTs) (n, 0) n = 9-11 chirality and diameter of 7.47 Å, 7.87 Å, 8.73 Å, respectively, using Density Functional calculations. The MXH4 interacts strongly with the surface atoms of CNT (11, 0) and is found to be the smallest stable system for confinement of MXH4 clusters. The Hydrogen release energy (E Hre) of NaAlH4 decreases sharply by 68.3 % , w.r.t. pure NaAlH4 cluster when confined inside CNT(11, 0). Similarly, in CNT (11, 0) E Hre decreases by 38.1 % for LiAlH4, 12.7 % for NaBH4 and 19.1 % for LiBH4. Thus, resulting confinement had a profound effect in improving the energetics of complex metal hydride nanoparticles without catalyst.

Band bending at the heterointerface of GaAs/InAs core/shell nanowires monitored by synchrotron X-ray photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Khanbabaee, B.; Bussone, G.; Knutsson, J. V.; Geijselaers, I.; Pryor, C. E.; Rieger, T.; Demarina, N.; Grützmacher, D.; Lepsa, M. I.; Timm, R.; Pietsch, U.

2016-10-01

Unique electronic properties of semiconductor heterostructured nanowires make them useful for future nano-electronic devices. Here, we present a study of the band bending effect at the heterointerface of GaAs/InAs core/shell nanowires by means of synchrotron based X-ray photoelectron spectroscopy. Different Ga, In, and As core-levels of the nanowire constituents have been monitored prior to and after cleaning from native oxides. The cleaning process mainly affected the As-oxides and was accompanied by an energy shift of the core-level spectra towards lower binding energy, suggesting that the As-oxides turn the nanowire surfaces to n-type. After cleaning, both As and Ga core-levels revealed an energy shift of about -0.3 eV for core/shell compared to core reference nanowires. With respect to depth dependence and in agreement with calculated strain distribution and electron quantum confinement, the observed energy shift is interpreted by band bending of core-levels at the heterointerface between the GaAs nanowire core and the InAs shell.

Coherently Strained Si-SixGe1-x Core-Shell Nanowire Heterostructures.

PubMed

Dillen, David C; Wen, Feng; Kim, Kyounghwan; Tutuc, Emanuel

2016-01-13

Coherently strained Si-SixGe1-x core-shell nanowire heterostructures are expected to possess a positive shell-to-core conduction band offset, allowing for quantum confinement of electrons in the Si core. We report the growth of epitaxial, coherently strained Si-SixGe1-x core-shell heterostructures through the vapor-liquid-solid mechanism for the Si core, followed in situ by the epitaxial SixGe1-x shell growth using ultrahigh vacuum chemical vapor deposition. The Raman spectra of individual nanowires reveal peaks associated with the Si-Si optical phonon mode in the Si core and the Si-Si, Si-Ge, and Ge-Ge vibrational modes of the SixGe1-x shell. The core Si-Si mode displays a clear red-shift compared to unstrained, bare Si nanowires thanks to the lattice mismatch-induced tensile strain, in agreement with calculated values using a finite-element continuum elasticity model combined with lattice dynamic theory. N-type field-effect transistors using Si-SixGe1-x core-shell nanowires as channel are demonstrated.

Combination of cylindrical confinement and spark discharge for signal improvement using laser induced breakdown spectroscopy.

PubMed

Hou, Zongyu; Wang, Zhe; Liu, Jianmin; Ni, Weidou; Li, Zheng

2014-06-02

Spark discharge has been proved to be an effective way to enhance the LIBS signal while moderate cylindrical confinement is able to increase the signal repeatability with limited signal enhancement effects. In the present work, these two methods were combined together not only to improve the pulse-to-pulse signal repeatability but also to simultaneously and significantly enhance the signal as well as SNR. Plasma images showed that the confinement stabilized the morphology of the plasma, especially for the discharge assisted process, which explained the improvement of the signal repeatability.

The effect of deformation on two-phase flow through proppant-packed fractured shale samples: A micro-scale experimental investigation

NASA Astrophysics Data System (ADS)

Arshadi, Maziar; Zolfaghari, Arsalan; Piri, Mohammad; Al-Muntasheri, Ghaithan A.; Sayed, Mohammed

2017-07-01

We present the results of an extensive micro-scale experimental investigation of two-phase flow through miniature, fractured reservoir shale samples that contained different packings of proppant grains. We investigated permeability reduction in the samples by conducting experiments under a wide range of net confining pressures. Three different proppant grain distributions in three individual fractured shale samples were studied: i) multi-layer, ii) uniform mono-layer, and iii) non-uniform mono-layer. We performed oil-displacing-brine (drainage) and brine-displacing-oil (imbibition) flow experiments in the proppant packs under net confining pressures ranging from 200 to 6000 psi. The flow experiments were performed using a state-of-the-art miniature core-flooding apparatus integrated with a high-resolution, X-ray microtomography system. We visualized fluid occupancies, proppant embedment, and shale deformation under different flow and stress conditions. We examined deformation of pore space within the proppant packs and its impact on permeability and residual trapping, proppant embedment due to changes in net confining stress, shale surface deformation, and disintegration of proppant grains at high stress conditions. In particular, geometrical deformation and two-phase flow effects within the proppant pack impacting hydraulic conductivity of the medium were probed. A significant reduction in effective oil permeability at irreducible water saturation was observed due to increase in confining pressure. We propose different mechanisms responsible for the observed permeability reduction in different fracture packings. Samples with dissimilar proppant grain distributions showed significantly different proppant embedment behavior. Thinner proppant layer increased embedment significantly and lowered the onset confining pressure of embedment. As confining stress was increased, small embedments caused the surface of the shale to fracture. The produced shale fragments were then entrained by the flow and partially blocked pore-throat connections within the proppant pack. Deformation of proppant packs resulted in significant changes in waterflood residual oil saturation. In-situ contact angles measured using micro-CT images showed that proppant grains had experienced a drastic alteration of wettability (from strong water-wet to weakly oil-wet) after the medium had been subjected to flow of oil and brine for multiple weeks. Nanometer resolution SEM images captured nano-fractures induced in the shale surfaces during the experiments with mono-layer proppant packing. These fractures improved the effective permeability of the medium and shale/fracture interactions.

Self-assembled morphologies of an amphiphilic Y-shaped weak polyelectrolyte in a thin film.

PubMed

Mu, Dan; Li, Jian-Quan; Feng, Sheng-Yu

2017-11-29

Different from the self-assembly of neutral polymers, polyelectrolytes self-assemble into smaller aggregates with a more loosely assembled structure, which results from the repulsive forces acting between similar electrical compositions with the introduction of ions. The Y-shaped weak polyelectrolytes self-assemble into a core-shell type cylindrical structure with a hexagonal arrangement in a thin film, whose thickness is smaller than the gyration radius of the polymer chain. The corresponding formation mechanism consists of enrichment of the same components, adjustment of the shape of the aggregate, and the subsequent separation into individual aggregates. With the increase in the thickness of the thin film until it exceeds the gyration radius of the polymer chain, combined with the greater freedom of movement along the direction of thin film thickness, the self-assembled structure changes into a micellar structure. Under confinement, the repulsive force to the polymeric components is weakened by the repulsive forces among polyelectrolyte components with like charges, and this helps in generating aggregates with more uniform size and density distribution. In particular, when the repulsive force between the walls and the core forming components is greater than that between the walls and the shell forming components, such asymmetric confinement produces a crossed-cylindrical structure with nearly perpendicular arrangement of two cylinder arrays. Similarly, a novel three-crossed cylinder morphology is self-assembled upon removal of confinement.

Strings with a confining core in a quark-gluon plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Layek, Biswanath; Mishra, Ananta P.; Srivastava, Ajit M.

2005-04-01

We consider the intersection of N different interfaces interpolating between different Z{sub N} vacua of an SU(N) gauge theory using the Polyakov loop order parameter. Topological arguments show that at such a stringlike junction, the order parameter should vanish, implying that the core of this string (i.e. the junction region of all the interfaces) is in the confining phase. Using the effective potential for the Polyakov loop proposed by Pisarski for QCD, we use numerical minimization technique and estimate the energy per unit length of the core of this string to be about 2.7 GeV/fm at a temperature about twicemore » the critical temperature. For the parameters used, the interface tension is obtained to be about 7 GeV/fm{sup 2}. Lattice simulation of pure gauge theories should be able to investigate properties of these strings. For QCD with quarks, it has been discussed in the literature that this Z{sub N} symmetry may still be meaningful, with quark contributions leading to explicit breaking of this Z{sub N} symmetry. With this interpretation, such quark-gluon plasma strings may play important role in the evolution of the quark-gluon plasma phase and in the dynamics of quark-hadron transition.« less

Optimizing accuracy of determinations of CO₂ storage capacity and permanence, and designing more efficient storage operations: An example from the Rock Springs Uplift, Wyoming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bentley, Ramsey; Dahl, Shanna; Deiss, Allory

At a potential injection site on the Rock Springs Uplift in southwest Wyoming, an investigation of confining layers was undertaken to develop and test methodology, identify key data requirements, assess previous injection scenarios relative to detailed confining layer properties, and integrate all findings in order to reduce the uncertainty of CO₂ storage permanence. The assurance of safe and permanent storage of CO₂ at a storage site involves a detailed evaluation of the confining layers. Four suites of field data were recognized as crucial for determining storage permanence relative to the confining layers; seismic, core and petrophysical data from a wellbore,more » formation fluid samples, and in-situ formation tests. Core and petrophysical data were used to create a vertical heterogenic property model that defined porosity, permeability, displacement pressure, geomechanical strengths, and diagenetic history. These analyses identified four primary confining layers and multiple redundant confining layers. In-situ formation tests were used to evaluate fracture gradients, regional stress fields, baseline microseismic data, step-rate injection tests, and formation perforation responses. Seismic attributes, correlated with the vertical heterogenic property models, were calculated and used to create a 3-D volume model over the entire site. The seismic data provided the vehicle to transform the vertical heterogenic property model into a horizontal heterogenic property model, which allowed for the evaluation of confining layers across the entire study site without risking additional wellbore perforations. Lastly, formation fluids were collected and analyzed for geochemical and isotopic compositions from stacked reservoir systems. These data further tested primary confining layers, by evaluating the evidence of mixing between target reservoirs (mixing would imply an existing breach of primary confining layers). All data were propagated into a dynamic, heterogenic geologic property model used to test various injection scenarios. These tests showed that the study site could retain 25MT of injected CO₂ over an injection lifespan of 50 years. Major findings indicate that active reservoir pressure management through reservoir fluid production (minimum of three production wells) greatly reduces the risk of breaching a confining layer. To address brine production, a well completion and engineering study was incorporated to reduce the risks of scaling and erosion during injection and production. These scenarios suggest that the dolostone within the Mississippian Madison Limestone is the site’s best injection/production target by two orders of magnitude, and that commercial well equipment would meet all performance requirements. This confirms that there are multiple confining layers in southwest Wyoming that are capable of retaining commercial volumes of CO₃, making Wyoming’s Paleozoic reservoirs ideal storage targets for low-risk injection and long-term storage. This study also indicates that column height retention calculations are reduced in a CO₂-brine system relative to a hydrocarbon-brine system, which is an observation that affects all potential CCS sites. Likewise, this study identified the impacts that downhole testing imparts on reservoir fluids, and the likelihood of introducing uncertainty in baseline site assumptions and later modeling.« less

Zero-mode clad waveguides for performing spectroscopy with confined effective observation volumes

DOEpatents

Levene, Michael J.; Korlach, Jonas; Turner, Stephen W.; Craighead, Harold G.; Webb, Watt W.

2005-07-12

The present invention is directed to a method and an apparatus for analysis of an analyte. The method involves providing a zero-mode waveguide which includes a cladding surrounding a core where the cladding is configured to preclude propagation of electromagnetic energy of a frequency less than a cutoff frequency longitudinally through the core of the zero-mode waveguide. The analyte is positioned in the core of the zero-mode waveguide and is then subjected, in the core of the zero-mode waveguide, to activating electromagnetic radiation of a frequency less than the cut-off frequency under conditions effective to permit analysis of the analyte in an effective observation volume which is more compact than if the analysis were carried out in the absence of the zero-mode waveguide.

Waveguides for performing spectroscopy with confined effective observation volumes

DOEpatents

Levene, Michael J.; Korlach, Jonas; Turner, Stephen W.; Craighead, Harold G.; Webb, Watt W.

2006-03-14

The present invention is directed to a method and an apparatus for analysis of an analyte. The method involves providing a zero-mode waveguide which includes a cladding surrounding a core where the cladding is configured to preclude propagation of electromagnetic energy of a frequency less than a cutoff frequency longitudinally through the core of the zero-mode waveguide. The analyte is positioned in the core of the zero-mode waveguide and is then subjected, in the core of the zero-mode waveguide, to activating electromagnetic radiation of a frequency less than the cut-off frequency under conditions effective to permit analysis of the analyte in an effective observation volume which is more compact than if the analysis were carried out in the absence of the zero-mode waveguide.

Centralised 3D printing in the NHS: a radiological review.

PubMed

Eley, K A

2017-04-01

In recent years, three-dimensional (3D) printing has seen an explosion of interest fuelled by improvements in technology and associated reduction in costs. The literature is replete with novel medical applications of custom anatomical models, prostheses, and surgical guides. Although the fundamental core of 3D printing lies in image manipulation, the driving force in many National Health Service (NHS) trusts has come from individual surgical specialties with 3D printers independently run and confined to respective departments. In this review of 3D printing, experience of establishing a new centralised 3D-printing service within an NHS hospital trust is reported, focusing on the requirements and challenges of such an endeavour. Copyright © 2017 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Ultra low-loss hybrid core porous fiber for broadband applications.

PubMed

Islam, Md Saiful; Sultana, Jakeya; Atai, Javid; Abbott, Derek; Rana, Sohel; Islam, Mohammad Rakibul

2017-02-01

In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04  cm^-1 at an operating frequency of 1 THz with a core porosity of 81%. Moreover, the proposed photonic crystal fiber also exhibits comparatively higher core power fraction, lower confinement loss, higher effective mode area, and an ultra-flattened dispersion profile with single mode propagation. This fiber can be readily fabricated using capillary stacking and sol-gel techniques, and it can be used for broadband terahertz applications.

Hanging core support system for a nuclear reactor. [LMFBR

DOEpatents

Burelbach, J.P.; Kann, W.J.; Pan, Y.C.; Saiveau, J.G.; Seidensticker, R.W.

1984-04-26

For holding the reactor core in the confining reactor vessel, a support is disclosed that is structurally independent of the vessel, that is dimensionally accurate and stable, and that comprises tandem tension linkages that act redundantly of one another to maintain stabilized core support even in the unlikely event of the complete failure of one of the linkages. The core support has a mounting platform for the reactor core, and unitary structure including a flange overlying the top edge of the reactor vessels, and a skirt and box beams between the flange and platform for establishing one of the linkages. A plurality of tension rods connect between the deck closing the reactor vessel and the platform for establishing the redundant linkage. Loaded Belleville springs flexibly hold the tension rods at the deck and separable bayonet-type connections hold the tension rods at the platform.

Coaxial microreactor for particle synthesis

DOEpatents

Bartsch, Michael; Kanouff, Michael P; Ferko, Scott M; Crocker, Robert W; Wally, Karl

2013-10-22

A coaxial fluid flow microreactor system disposed on a microfluidic chip utilizing laminar flow for synthesizing particles from solution. Flow geometries produced by the mixing system make use of hydrodynamic focusing to confine a core flow to a small axially-symmetric, centrally positioned and spatially well-defined portion of a flow channel cross-section to provide highly uniform diffusional mixing between a reactant core and sheath flow streams. The microreactor is fabricated in such a way that a substantially planar two-dimensional arrangement of microfluidic channels will produce a three-dimensional core/sheath flow geometry. The microreactor system can comprise one or more coaxial mixing stages that can be arranged singly, in series, in parallel or nested concentrically in parallel.

Amorphization and Directional Crystallization of Metals Confined in Carbon Nanotubes Investigated by in Situ Transmission Electron Microscopy.

PubMed

Tang, Dai-Ming; Ren, Cui-Lan; Lv, Ruitao; Yu, Wan-Jing; Hou, Peng-Xiang; Wang, Ming-Sheng; Wei, Xianlong; Xu, Zhi; Kawamoto, Naoyuki; Bando, Yoshio; Mitome, Masanori; Liu, Chang; Cheng, Hui-Ming; Golberg, Dmitri

2015-08-12

The hollow core of a carbon nanotube (CNT) provides a unique opportunity to explore the physics, chemistry, biology, and metallurgy of different materials confined in such nanospace. Here, we investigate the nonequilibrium metallurgical processes taking place inside CNTs by in situ transmission electron microscopy using CNTs as nanoscale resistively heated crucibles having encapsulated metal nanowires/crystals in their channels. Because of nanometer size of the system and intimate contact between the CNTs and confined metals, an efficient heat transfer and high cooling rates (∼10(13) K/s) were achieved as a result of a flash bias pulse followed by system natural quenching, leading to the formation of disordered amorphous-like structures in iron, cobalt, and gold. An intermediate state between crystalline and amorphous phases was discovered, revealing a memory effect of local short-to-medium range order during these phase transitions. Furthermore, subsequent directional crystallization of an amorphous iron nanowire formed by this method was realized under controlled Joule heating. High-density crystalline defects were generated during crystallization due to a confinement effect from the CNT and severe plastic deformation involved.

Creating deep soil core monoliths: Beyond the solum

USDA-ARS?s Scientific Manuscript database

Soil monoliths serve as useful teaching aids in the study of the Earth’s critical zone where rock, soil, water, air, and organisms interact. Typical monolith preparation has so far been confined to the 1 to 2-m depth of the solum. Critical ecosystem services provided by soils include materials from ...

Solitary Confinement in Education

ERIC Educational Resources Information Center

Goldberg, Merryl

2009-01-01

Arts Education is, technically, core to the school curriculum according to federal mandates and certain state mandates. However, it is rarely made accessible to all students despite earnest advocating on the part of dedicated organizations and individuals. In order for a democratic society to function successfully, its members must be invested and…

Pore-Water Quality in the Clay-Silt Confining Units of the Lower Miocene Kirkwood Formation and Hypothetical Effects on Water Quality in the Atlantic City 800-Foot Sand, Northeastern Cape May County, New Jersey, 2001

USGS Publications Warehouse

Szabo, Zoltan; Keller, Elizabeth A.; Defawe, Rose M.

2006-01-01

Pore water was extracted from clay-silt core samples collected from a borehole at Ocean View, west of Sea Isle City, in northeastern Cape May County, New Jersey. The borehole intersects the lower Miocene Kirkwood Formation, which includes a thick sand and gravel unit between two clay-silt units. The sand and gravel unit forms a major confined aquifer in the region, known as the Atlantic City 800-foot sand, the major source of potable water along the Atlantic Coast of southern New Jersey. The pore water from the core is of interest because the borehole intersects the aquifer in an area where the ground water is sodium-rich and sulfidic. Locally in the aquifer in central and southern Cape May County, sodium concentrations are near the New Jersey secondary drinking-water standard of 50 mg/L (milligrams per liter), and typically are greater than 30 mg/L, but chloride and sulfate do not approach their respective secondary drinking-water standards except in southernmost Cape May County. Pore waters from the confining units are suspected to be a source of sodium, sulfur, and chloride to the aquifer. Constituent concentrations in filtered pore-water samples were determined using the inductively coupled plasma-mass spectrometry analytical technique to facilitate the determination of low-level concentrations of many trace constituents. Calcium-sodium-sulfate-bicarbonate, calcium-chloride-sulfate, calcium-sulfate, and sodium-sulfate-chloride-bicarbonate type waters characterize samples from the deepest part of the confining unit directly overlying the aquifer (termed the 'lower' confining unit). A sodium-chloride-sulfate type water is dominant in the composite confining unit below the aquifer. Sodium, chloride, and sulfate became increasingly dominant with depth. Pore water from the deepest sample recovered (1,390 ft (feet) below land surface) was brackish, with concentrations of sodium, chloride, and sulfate of 5,930, 8,400, and 5,070 mg/L, respectively. Pore-water samples from 900 ft or less below land surface, although mineralized, were fresh, not brackish. Sodium concentrations ranged from 51.3 to 513 mg/L, with the maximum concentration found at 882 ft below land surface in the composite confining unit below the aquifer. Chloride concentrations ranged from 46.4 to 757 mg/L, with the maximum concentration found at 596 ft below land surface in the 'lower' confining unit, and were higher than those in pore water from the same units at Atlantic City, N.J. Concentrations of chloride in the composite confining unit below the aquifer were consistently greater than 250 mg/L, indicating that the confining unit can be a source of chloride at depth. Of the major anions, sulfate was the constituent whose concentration varied most, ranging from 42 to 799 mg/L. The maximum concentration was found at 406 ft below land surface, in the upper part of the confining unit overlying the aquifer and the Rio Grande water-bearing zone (termed the 'upper' confining unit). Sulfide was not detected in any pore-water sample despite the presence of abundant quantities of sulfate and sulfide in the aquifer. The absence of sulfide in the pore waters is consistent with the hypothesis that sulfate is reduced in the aquifer. The presence of arsenic, at concentrations ranging from 0.0062 to 0.0374 mg/L, is consistent with the absence of sulfide and the possible presence of iron in the pore water.

Low index contrast heterostructure photonic crystal cavities with high quality factors and vertical radiation coupling

NASA Astrophysics Data System (ADS)

Ge, Xiaochen; Minkov, Momchil; Fan, Shanhui; Li, Xiuling; Zhou, Weidong

2018-04-01

We report here design and experimental demonstration of heterostructure photonic crystal cavities resonating near the Γ point with simultaneous strong lateral confinement and highly directional vertical radiation patterns. The lateral confinement is provided by a mode gap originating from a gradual modulation of the hole radii. High quality factor resonance is realized with a low index contrast between silicon nitride and quartz. The near surface-normal directional emission is preserved when the size of the core region is scaled down. The influence of the cavity size parameters on the resonant modes is also investigated theoretically and experimentally.

Region-confined restoration method for motion-blurred star image of the star sensor under dynamic conditions.

PubMed

Ma, Liheng; Bernelli-Zazzera, Franco; Jiang, Guangwen; Wang, Xingshu; Huang, Zongsheng; Qin, Shiqiao

2016-06-10

Under dynamic conditions, the centroiding accuracy of the motion-blurred star image decreases and the number of identified stars reduces, which leads to the degradation of the attitude accuracy of the star sensor. To improve the attitude accuracy, a region-confined restoration method, which concentrates on the noise removal and signal to noise ratio (SNR) improvement of the motion-blurred star images, is proposed for the star sensor under dynamic conditions. A multi-seed-region growing technique with the kinematic recursive model for star image motion is given to find the star image regions and to remove the noise. Subsequently, a restoration strategy is employed in the extracted regions, taking the time consumption and SNR improvement into consideration simultaneously. Simulation results indicate that the region-confined restoration method is effective in removing noise and improving the centroiding accuracy. The identification rate and the average number of identified stars in the experiments verify the advantages of the region-confined restoration method.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yanagawa, T.; Sakagami, H.; Nagatomo, H.

In inertial confinement fusion, the implosion process is important in forming a high-density plasma core. In the case of a fast ignition scheme using a cone-guided target, the fuel target is imploded with a cone inserted. This scheme is advantageous for efficiently heating the imploded fuel core; however, asymmetric implosion is essentially inevitable. Moreover, the effect of cone position and opening angle on implosion also becomes critical. Focusing on these problems, the effect of the asymmetric implosion, the initial position, and the opening angle on the compression rate of the fuel is investigated using a three-dimensional pure hydrodynamic code.

Baby Skyrme model and fermionic zero modes

NASA Astrophysics Data System (ADS)

Queiruga, J. M.

2016-09-01

In this work we investigate some features of the fermionic sector of the supersymmetric version of the baby Skyrme model. We find that, in the background of Bogomol'nyi-Prasad-Sommerfield compact baby Skyrmions, fermionic zero modes are confined to the defect core. Further, we show that, while three Supersymmetry (SUSY) generators are broken in the defect core, SUSY is completely restored outside. We study also the effect of a D-term deformation of the model. Such a deformation allows for the existence of fermionic zero modes and broken SUSY outside the compact defect.

Spin Vortex Resonance in Non-planar Ferromagnetic Dots

DOE PAGES

Ding, Junjia; Lapa, Pavel; Jain, Shikha; ...

2016-05-04

In planar structures, the vortex resonance frequency changes little as a function of an in-plane magnetic field as long as the vortex state persists. Altering the topography of the element leads to a vastly different dynamic response that arises due to the local vortex core confinement effect. In this work, we studied the magnetic excitations in non-planar ferromagnetic dots using a broadband microwave spectroscopy technique. Two distinct regimes of vortex gyration were detected depending on the vortex core position. The experimental results are in qualitative agreement with micromagnetic simulations.

Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.

PubMed

Tuszewski, M; Smirnov, A; Thompson, M C; Korepanov, S; Akhmetov, T; Ivanov, A; Voskoboynikov, R; Schmitz, L; Barnes, D; Binderbauer, M W; Brown, R; Bui, D Q; Clary, R; Conroy, K D; Deng, B H; Dettrick, S A; Douglass, J D; Garate, E; Glass, F J; Gota, H; Guo, H Y; Gupta, D; Gupta, S; Kinley, J S; Knapp, K; Longman, A; Hollins, M; Li, X L; Luo, Y; Mendoza, R; Mok, Y; Necas, A; Primavera, S; Ruskov, E; Schroeder, J H; Sevier, L; Sibley, A; Song, Y; Sun, X; Trask, E; Van Drie, A D; Walters, J K; Wyman, M D

2012-06-22

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

Compact Fast Ignition experiments using Joule-class tailored drive pulses under counterbeam configuration

NASA Astrophysics Data System (ADS)

Mori, Yoshitaka; Hanayama, Ryohei; Ishii, Katsuhiro; Kitagawa, Yoneyoshi; Sekine, Takashi; Takeuchi, Yasuki; Kurita, Takashi; Katoh, Yoshinori; Satoh, Nakahiro; Kurita, Norio; Kawashima, Toshiyuki; Komeda, Osamu; Hioki, Tatsumi; Motohiro, Tomoyoshi; Sunahara, Atsushi; Sentoku, Yasuhiko; Miura, Eisuke; Iwamoto, Akifumi; Sakagami, Hitoshi

2017-10-01

Fast ignition (FI) is a form of inertial confinement fusion in which the ignition step and the compression step are separate processes resulting in a reduction of the symmetry requirement for hot spot generation. One of the problems of FI so far are the accessibility of an ignition laser pulse into the assembled core in which the driver energy is converted into relativistic electrons produced in the laser-plasma interaction. We have experimentally demonstrated that a tailored-pulse-assembled core with a diameter of 70 μ m, originally a deuterated polystyrene spherical shell of 500 μ m diameter, is flashed by directly counter irradiating 0.8 J/110 fs laser pulses [Y. MORI et al., PRL 2016]. This result indicates that once the assembled core is squeezed into the target center, the heating lasers can access the core's; edges and deposit their energy into the core. In this talk, we will discuss the heating effects in relation to formation of the assembled core.

Structural and electronic properties of CdS/ZnS core/shell nanowires: A first-principles study

NASA Astrophysics Data System (ADS)

Kim, Hyo Seok; Kim, Yong-Hoon

2015-03-01

Carrying out density functional theory (DFT) calculation, we studied the relative effects of quantum confinement and strain on the electronic structures of II-IV semiconductor compounds with a large lattice-mismatch, CdS and ZnS, in the core/shell nanowire geometry. We considered different core radii and shell thickness of the CdS/ZnS core/shell nanowire, different surface facets, and various defects in the core/shell interface and surface regions. To properly describe the band level alignment at the core/shell boundary, we adopted the self-interaction correction (SIC)-DFT scheme. Implications of our findings in the context of device applications will be also discussed. This work was supported by the Basic Science Research Grant (No. 2012R1A1A2044793), Global Frontier Program (No. 2013-073298), and Nano-Material Technology Development Program (2012M3A7B4049888) of the National Research Foundation funded by the Ministry of Education, Science and Technology of Korea. Corresponding author

Hanging core support system for a nuclear reactor

DOEpatents

Burelbach, James P.; Kann, William J.; Pan, Yen-Cheng; Saiveau, James G.; Seidensticker, Ralph W.

1987-01-01

For holding the reactor core in the confining reactor vessel, a support is disclosed that is structurally independent of the vessel, that is dimensionally accurate and stable, and that comprises tandem tension linkages that act redundantly of one another to maintain stabilized core support even in the unlikely event of the complete failure of one of the linkages. The core support has a mounting platform for the reactor core, and unitary structure including a flange overlying the top edge of the reactor vessels, and a skirt and box beams between the flange and platform for establishing one of the linkages. A plurality of tension rods connect between the deck closing the reactor vessel and the platform for establishing the redundant linkage. Loaded Belleville springs flexibly hold the tension rods at the deck and separable bayonet-type connections hold the tension rods at the platform. Motion or radiation sensing detectors can be provide at the lower ends of the tension rods for obtaining pertinent readings proximate the core.

Hollow-Core Photonic Band Gap Fibers for Particle Acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Noble, Robert J.; Spencer, James E.; /SLAC

Photonic band gap (PBG) dielectric fibers with hollow cores are being studied both theoretically and experimentally for use as laser driven accelerator structures. The hollow core functions as both a longitudinal waveguide for the transverse-magnetic (TM) accelerating fields and a channel for the charged particles. The dielectric surrounding the core is permeated by a periodic array of smaller holes to confine the mode, forming a photonic crystal fiber in which modes exist in frequency pass-bands, separated by band gaps. The hollow core acts as a defect which breaks the crystal symmetry, and so-called defect, or trapped modes having frequencies inmore » the band gap will only propagate near the defect. We describe the design of 2-D hollow-core PBG fibers to support TM defect modes with high longitudinal fields and high characteristic impedance. Using as-built dimensions of industrially-made fibers, we perform a simulation analysis of the first prototype PBG fibers specifically designed to support speed-of-light TM modes.« less

Effect of bright light at night on core temperature, subjective alertness and performance as a function of exposure time.

PubMed

Foret, J; Daurat, A; Tirilly, G

1998-01-01

This simulated night shift study measured the effects of moderate bright light (a 4-hour pulse starting at 2000 or 0400) during the exposure night and subsequent night (dim light). Eight young males remained confined with little physical activity to a laboratory in groups of 4. After a night of reference, they were active for 24 hours; then after a morning recovery sleep, they were active again for 16 hours. Continuously measured rectal temperature proved to be immediately sensitive to 4 hours of bright light, particularly when given at the end of the night. Self-assessed alertness and also performance on a task with a high requirement for short-term memory were improved by the exposure to bright light. During the subsequent night the subjects were exposed only to dim light. Core temperature, subjective alertness and performance continued to show a time course depending on the preceding bright light exposure. Probably because evening exposure to bright light and morning sleep both had a phase-delaying effect, the effects on the circadian pacemaker were more pronounced. Thus, for practical applications in long night shifts, bright light can be considered to improve mood and alertness immediately but the possibility of modifying the circadian "clock" during subsequent nights should be taken into consideration, in particular after exposure to bright light in the evening.

High Field Side MHD Activity During Local Helicity Injection

NASA Astrophysics Data System (ADS)

Pachicano, J. L.; Bongard, M. W.; Fonck, R. J.; Perry, J. M.; Reusch, J. A.; Richner, N. J.

2017-10-01

MHD is an essential part of understanding the mechanism for local helicity injection (LHI) current drive. The new high field side (HFS) LHI system on the Pegasus ST permits new tests of recent NIMROD simulations. In that model, LHI current streams in the plasma edge undergo large-scale reconnection events, leading to current drive. This produces bursty n = 1 activity around 30 kHz on low field side (LFS) Mirnov coils, consistent with experiment. The simulations also feature coherent injector streams winding down the center column. Improvements to the core high-resolution poloidal Mirnov array with Cat7A Ethernet cabling and differentially driven signal processing eliminated EMI-driven switching noise, enabling detailed spectral analysis. Preliminary results from the recovered HFS poloidal Mirnov coils suggest n = 1 activity is present at the top of the vessel core, but does not persist down the centerstack. HFS LHI experiments can exhibit an operating regime where the high amplitude MHD is abruptly reduced by more than an order of magnitude on LFS Mirnov coils, leading to higher plasma current and improved particle confinement. This reduction is not observed on the HFS midplane magnetics. Instead, they show broadband turbulence-like magnetic features with near consistent amplitude in a frequency range of 90-200 kHz. Work supported by US DOE Grant DE-FG02-96ER54375.

Confined compressive strength analysis can improve PDC bit selection. [Polycrystalline Diamond Compact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fabain, R.T.

1994-05-16

A rock strength analysis program, through intensive log analysis, can quantify rock hardness in terms of confined compressive strength to identify intervals suited for drilling with polycrystalline diamond compact (PDC) bits. Additionally, knowing the confined compressive strength helps determine the optimum PDC bit for the intervals. Computing rock strength as confined compressive strength can more accurately characterize a rock's actual hardness downhole than other methods. the information can be used to improve bit selections and to help adjust drilling parameters to reduce drilling costs. Empirical data compiled from numerous field strength analyses have provided a guide to selecting PDC drillmore » bits. A computer analysis program has been developed to aid in PDC bit selection. The program more accurately defines rock hardness in terms of confined strength, which approximates the in situ rock hardness downhole. Unconfined compressive strength is rock hardness at atmospheric pressure. The program uses sonic and gamma ray logs as well as numerous input data from mud logs. Within the range of lithologies for which the program is valid, rock hardness can be determine with improved accuracy. The program's output is typically graphed in a log format displaying raw data traces from well logs, computer-interpreted lithology, the calculated values of confined compressive strength, and various optional rock mechanic outputs.« less

Equilibrium drives of the low and high field side n = 2 plasma response and impact on global confinement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paz-Soldan, C.; Logan, N. C.; Haskey, S. R.

The nature of the multi-modal n=2 plasma response and its impact on global confinement is studied as a function of the axisymmetric equilibrium pressure, edge safety factor, collisionality, and L-versus H-mode conditions. Varying the relative phase (ΔΦ UL) between upper and lower in-vessel coils demonstrates that different n=2 poloidal spectra preferentially excite different plasma responses. These different plasma response modes are preferentially detected on the tokamak high-field side (HFS) or low-field side (LFS) midplanes, have different radial extents, couple differently to the resonant surfaces, and have variable impacts on edge stability and global confinement. In all equilibrium conditions studied, themore » observed confinement degradation shares the same ΔΦ UL dependence as the coupling to the resonant surfaces given by both ideal (IPEC) and resistive (MARS-F) MHD computation. Varying the edge safety factor shifts the equilibrium field-line pitch and thus the ΔΦ UL dependence of both the global confinement and the n=2 magnetic response. As edge safety factor is varied, modeling finds that the HFS response (but not the LFS response), the resonant surface coupling, and the edge displacements near the X-point all share the same ΔΦ UL dependence. The LFS response magnitude is strongly sensitive to the core pressure and is insensitive to the collisionality and edge safety factor. This indicates that the LFS measurements are primarily sensitive to a pressure-driven kink-ballooning mode that couples to the core plasma. MHD modeling accurately reproduces these (and indeed all) LFS experimental trends and supports this interpretation. In contrast to the LFS, the HFS magnetic response and correlated global confinement impact is unchanged with plasma pressure, but is strongly reduced in high collisionality conditions in both H- and L-mode. This experimentally suggests the bootstrap current drives the HFS response through the kink-peeling mode drive, though surprisingly weak or no dependence on the bootstrap current is seen in modeling. Instead, modeling is revealed to be very sensitive to the details of the edge current profile and equilibrium truncation. Furthermore, holding truncation fixed, most HFS experimental trends are not captured, thus demonstrating a stark contrast between the robustness of the HFS experimental results and the sensitivity of its computation.« less

Equilibrium drives of the low and high field side n  =  2 plasma response and impact on global confinement

NASA Astrophysics Data System (ADS)

Paz-Soldan, C.; Logan, N. C.; Haskey, S. R.; Nazikian, R.; Strait, E. J.; Chen, X.; Ferraro, N. M.; King, J. D.; Lyons, B. C.; Park, J.-K.

2016-05-01

The nature of the multi-modal n  =  2 plasma response and its impact on global confinement is studied as a function of the axisymmetric equilibrium pressure, edge safety factor, collisionality, and L-versus H-mode conditions. Varying the relative phase (Δ {φ\\text{UL}} ) between upper and lower in-vessel coils demonstrates that different n  =  2 poloidal spectra preferentially excite different plasma responses. These different plasma response modes are preferentially detected on the tokamak high-field side (HFS) or low-field side (LFS) midplanes, have different radial extents, couple differently to the resonant surfaces, and have variable impacts on edge stability and global confinement. In all equilibrium conditions studied, the observed confinement degradation shares the same Δ {φ\\text{UL}} dependence as the coupling to the resonant surfaces given by both ideal (IPEC) and resistive (MARS-F) MHD computation. Varying the edge safety factor shifts the equilibrium field-line pitch and thus the Δ {φ\\text{UL}} dependence of both the global confinement and the n  =  2 magnetic response. As edge safety factor is varied, modeling finds that the HFS response (but not the LFS response), the resonant surface coupling, and the edge displacements near the X-point all share the same Δ {φ\\text{UL}} dependence. The LFS response magnitude is strongly sensitive to the core pressure and is insensitive to the collisionality and edge safety factor. This indicates that the LFS measurements are primarily sensitive to a pressure-driven kink-ballooning mode that couples to the core plasma. MHD modeling accurately reproduces these (and indeed all) LFS experimental trends and supports this interpretation. In contrast to the LFS, the HFS magnetic response and correlated global confinement impact is unchanged with plasma pressure, but is strongly reduced in high collisionality conditions in both H- and L-mode. This experimentally suggests the bootstrap current drives the HFS response through the kink-peeling mode drive, though surprisingly weak or no dependence on the bootstrap current is seen in modeling. Instead, modeling is revealed to be very sensitive to the details of the edge current profile and equilibrium truncation. Holding truncation fixed, most HFS experimental trends are not captured, thus demonstrating a stark contrast between the robustness of the HFS experimental results and the sensitivity of its computation.

Equilibrium drives of the low and high field side n = 2 plasma response and impact on global confinement

DOE PAGES

Paz-Soldan, C.; Logan, N. C.; Haskey, S. R.; ...

2016-03-31

The nature of the multi-modal n=2 plasma response and its impact on global confinement is studied as a function of the axisymmetric equilibrium pressure, edge safety factor, collisionality, and L-versus H-mode conditions. Varying the relative phase (ΔΦ UL) between upper and lower in-vessel coils demonstrates that different n=2 poloidal spectra preferentially excite different plasma responses. These different plasma response modes are preferentially detected on the tokamak high-field side (HFS) or low-field side (LFS) midplanes, have different radial extents, couple differently to the resonant surfaces, and have variable impacts on edge stability and global confinement. In all equilibrium conditions studied, themore » observed confinement degradation shares the same ΔΦ UL dependence as the coupling to the resonant surfaces given by both ideal (IPEC) and resistive (MARS-F) MHD computation. Varying the edge safety factor shifts the equilibrium field-line pitch and thus the ΔΦ UL dependence of both the global confinement and the n=2 magnetic response. As edge safety factor is varied, modeling finds that the HFS response (but not the LFS response), the resonant surface coupling, and the edge displacements near the X-point all share the same ΔΦ UL dependence. The LFS response magnitude is strongly sensitive to the core pressure and is insensitive to the collisionality and edge safety factor. This indicates that the LFS measurements are primarily sensitive to a pressure-driven kink-ballooning mode that couples to the core plasma. MHD modeling accurately reproduces these (and indeed all) LFS experimental trends and supports this interpretation. In contrast to the LFS, the HFS magnetic response and correlated global confinement impact is unchanged with plasma pressure, but is strongly reduced in high collisionality conditions in both H- and L-mode. This experimentally suggests the bootstrap current drives the HFS response through the kink-peeling mode drive, though surprisingly weak or no dependence on the bootstrap current is seen in modeling. Instead, modeling is revealed to be very sensitive to the details of the edge current profile and equilibrium truncation. Furthermore, holding truncation fixed, most HFS experimental trends are not captured, thus demonstrating a stark contrast between the robustness of the HFS experimental results and the sensitivity of its computation.« less

Conservation of prehistoric caves and stability of their inner climate: lessons from Chauvet and other French caves.

PubMed

Bourges, F; Genthon, P; Genty, D; Lorblanchet, M; Mauduit, E; D'Hulst, D

2014-09-15

In the last 150 years, some prehistoric painted caves suffered irreversible degradations due to misperception of conservation issues and subsequent mismanagement. These sites presented naturally an exceptional stability of their internal climate allowing conservation in situ of outstanding fragile remains, some for nearly 40,000 years. This is for a large part due to exchanges of air, CO2, heat and water with the karstic system in which these caves are included. We introduce the concept of underground confinement, based on the stability of the inner cave climate parameters, especially its temperature. Confined caves present the best conservative properties. It is emphasized that this confined state implies slow exchanges with the surrounding karst and that a stable cave cannot be viewed as a closed system. This is illustrated on four case studies of French caves of various confinement states evidenced by long term continuous monitoring and on strategies to improve their conservation properties. The Chauvet cave presents optimal conservation properties. It is wholly confined as shown by the stability of its internal parameters since its discovery in 1994. In Marsoulas cave, archeological works removed the entrance scree and let a strong opening situation of the decorated zone. Remediation is expected by adding a buffer structure at the entrance. In Pech Merle tourist cave, recurrent painting fading was related to natural seasonal drying of walls. Improvement of the cave closure system restored a confined state insuring optimal visibility of the paintings. In Gargas tourist cave, optimization of closures, lighting system and number of visitors, allowed it to gradually reach a semi-confined state that improved the conservation properties. Conclusions are drawn on the characterization of confinement state of caves and on the ways to improve their conservation properties by restoring their initial regulation mechanisms and to avoid threats to their stability. Copyright © 2013 Elsevier B.V. All rights reserved.

Effects of the current boundary conditions at the plasma-gun gap on density in SSPX

NASA Astrophysics Data System (ADS)

Kolesnikov, Roman; Lodestro, L. L.; Meyer, W. H.

2012-10-01

The Sustained Spheromak Physics Experiment (SSPX) was a toroidal magnetic-confinement device without toroidal magnetic-field coils or a central transformer but which generated core-plasma currents by dynamo processes driven by coaxial plasma-gun injection into a flux-conserving vessel. Record electron temperatures in a spheromak (Te˜500eV) were achieved, and final results of the SSPX program were reported in [1]. Plasma density, which depended strongly on wall conditions, was an important parameter in SSPX. It was observed that density rises with Igun and that confinement improved as the density was lowered. Shortly after the last experiments, a new feature was added to the Corsica code's solver used to reconstruct SSPX equilibria. Motivated by n=0 fields observed in NIMROD simulations of SSPX, an insulating boundary condition was implemented at the plasma-gun gap. Using this option we will perform new reconstructions of SSPX equilibria and look for correlations between the location of the separatrix (which moves up the gun wall and onto the insulating gap as Igun increases) and plasma density and magnetic-flux amplification [2].[4pt] [1] H. S. McLean, APS, DPP, Dallas, TX, 2008.[0pt] [2] E. B. Hooper et al., Nucl. Fusion 47, 1064 (2007).

On the Development of Hydrogen Isotope Extraction Technologies for a Full LiMIT-Style PFC Liquid Lithium Loop

NASA Astrophysics Data System (ADS)

Christenson, Michael; Szott, Matthew; Stemmley, Steven; Mettler, Jeremy; Wendeborn, John; Moynihan, Cody; Ahn, Chisung; Andruczyk, Daniel; Ruzic, David

2017-10-01

Lithium has proven over numerous studies to improve core confinement, allowing access to operational regimes previously unattainable when using solid, high-Z divertor and limiter modules in magnetic confinement devices. Lithium readily absorbs fuel species, and while this is advantageous, it is also detrimental with regards to tritium inventory and safety concerns. As such, extraction technologies for the recovery of hydrogenic isotopes captured by lithium require development and testing in the context of a larger lithium loop recycling system. Proposed reclamation technologies at the University of Illinois at Urbana-Champaign (UIUC) will take advantage of the thermophysical properties of the lithium-hydrogen-lithium hydride system as the driving force for recovery. Previous work done at UIUC indicates that hydrogen release from pure lithium hydride reaches a maximum of 7 x 1018 s-1 at 665 °C. While this recovery rate is appreciable, reactor-scale scenarios will require isotope recycling to happen on an even faster timescale. The ratio of isotope dissolution to hydride precipitate formation must therefore be determined, along with the energy needed to recoup trapped hydrogen isotopes. Extraction technologies for use with a LiMIT-style loop system will be discussed and results will be presented. DOE/ALPS DE-FG02-99ER54515.

On stress-state optimization in steel-concrete composite structures

NASA Astrophysics Data System (ADS)

Brauns, J.; Skadins, U.

2017-10-01

The plastic resistance of a concrete-filled column commonly is given as a sum of the components and taking into account the effect of confinement. The stress state in a composite column is determined by taking into account the non-linear relationship of modulus of elasticity and Poisson’s ratio on the stress level in the concrete core. The effect of confinement occurs at a high stress level when structural steel acts in tension and concrete in lateral compression. The stress state of a composite beam is determined taking into account non-linear dependence on the position of neutral axis. In order to improve the stress state of a composite element and increase the safety of the construction the appropriate strength of steel and concrete has to be applied. The safety of high-stressed composite structures can be achieved by using high-performance concrete (HPC). In this study stress analysis of the composite column and beam is performed with the purpose of obtaining the maximum load-bearing capacity and enhance the safety of the structure by using components with the appropriate strength and by taking into account the composite action. The effect of HPC on the stress state and load carrying capacity of composite elements is analysed.

Analysis of trends in experimental observables: Reconstruction of the implosion dynamics and implications for fusion yield extrapolation for direct-drive cryogenic targets on OMEGA

NASA Astrophysics Data System (ADS)

Bose, A.; Betti, R.; Mangino, D.; Woo, K. M.; Patel, D.; Christopherson, A. R.; Gopalaswamy, V.; Mannion, O. M.; Regan, S. P.; Goncharov, V. N.; Edgell, D. H.; Forrest, C. J.; Frenje, J. A.; Gatu Johnson, M.; Yu Glebov, V.; Igumenshchev, I. V.; Knauer, J. P.; Marshall, F. J.; Radha, P. B.; Shah, R.; Stoeckl, C.; Theobald, W.; Sangster, T. C.; Shvarts, D.; Campbell, E. M.

2018-06-01

This paper describes a technique for identifying trends in performance degradation for inertial confinement fusion implosion experiments. It is based on reconstruction of the implosion core with a combination of low- and mid-mode asymmetries. This technique was applied to an ensemble of hydro-equivalent deuterium-tritium implosions on OMEGA which achieved inferred hot-spot pressures ≈56 ± 7 Gbar [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)]. All the experimental observables pertaining to the core could be reconstructed simultaneously with the same combination of low and mid-modes. This suggests that in addition to low modes, which can cause a degradation of the stagnation pressure, mid-modes are present which reduce the size of the neutron and x-ray producing volume. The systematic analysis shows that asymmetries can cause an overestimation of the total areal density in these implosions. It is also found that an improvement in implosion symmetry resulting from correction of either the systematic mid or low modes would result in an increase in the hot-spot pressure from 56 Gbar to ≈ 80 Gbar and could produce a burning plasma when the implosion core is extrapolated to an equivalent 1.9 MJ symmetric direct illumination [Bose et al., Phys. Rev. E 94, 011201(R) (2016)].

Phase locking of multi-helicity neoclassical tearing modes in tokamak plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fitzpatrick, Richard

2015-04-15

The attractive “hybrid” tokamak scenario combines comparatively high q{sub 95} operation with improved confinement compared with the conventional H{sub 98,y2} scaling law. Somewhat unusually, hybrid discharges often exhibit multiple neoclassical tearing modes (NTMs) possessing different mode numbers. The various NTMs are eventually observed to phase lock to one another, giving rise to a significant flattening, or even an inversion, of the core toroidal plasma rotation profile. This behavior is highly undesirable because the loss of core plasma rotation is known to have a deleterious effect on plasma stability. This paper presents a simple, single-fluid, cylindrical model of the phase lockingmore » of two NTMs with different poloidal and toroidal mode numbers in a tokamak plasma. Such locking takes place via a combination of nonlinear three-wave coupling and conventional toroidal coupling. In accordance with experimental observations, the model predicts that there is a bifurcation to a phase-locked state when the frequency mismatch between the modes is reduced to one half of its original value. In further accordance, the phase-locked state is characterized by the permanent alignment of one of the X-points of NTM island chains on the outboard mid-plane of the plasma, and a modified toroidal angular velocity profile, interior to the outermost coupled rational surface, which is such that the core rotation is flattened, or even inverted.« less

Polarization characteristics of double-clad elliptical fibers.

PubMed

Zhang, F; Lit, J W

1990-12-20

A scalar variational analysis based on a Gaussian approximation of the fundamental mode of a double-clad elliptical fiber with a depressed inner cladding is studied. The polarization properties and graphic results are presented; they are given in terms of three parameters: the ratio of the major axis to the minor axis of the core, the ratio of the inner cladding major axis to the core major axis, and the difference between the core index and the inner cladding index. The variations of both the spot size and the field intensity with core ellipticity are examined. It is shown that high birefringence and dispersion-free orthogonal polarization modes can be obtained within the single-mode region and that the field intensity distribution may be more confined to the fiber center than in a single-clad elliptical fiber.

Fast particle confinement with optimized coil currents in the W7-X stellarator

NASA Astrophysics Data System (ADS)

Drevlak, M.; Geiger, J.; Helander, P.; Turkin, Y.

2014-07-01

One of the principal goals of the W7-X stellarator is to demonstrate good confinement of energetic ions at finite β. This confinement, however, is sensitive to the magnetic field configuration and is thus vulnerable to design modifications of the coil geometry. The collisionless drift orbit losses for 60 keV protons in W7-X are studied using the ANTS code. Particles in this energy range will be produced by the neutral beam injection (NBI) system being constructed for W7-X, and are particularly important because protons at this energy accurately mimick the behaviour of 3.5 MeV α-particles in a HELIAS reactor. To investigate the possibility of improved fast particle confinement, several approaches to adjust the coil currents (5 main field coil currents +2 auxiliary coil currents) were explored. These strategies include simple rules of thumb as well as computational optimization of various properties of the magnetic field. It is shown that significant improvement of collisionless fast particle confinement can be achieved in W7-X for particle populations similar to α particles produced in fusion reactions. Nevertheless, the experimental goal of demonstrating confinement improvement with rising plasma pressure using an NBI-generated population appears to be difficult based on optimization of the coil currents only. The principal reason for this difficulty is that the NBI deposition profile is broader than the region of good fast-ion confinement around the magnetic axis.

Topology of polymer chains under nanoscale confinement.

PubMed

Satarifard, Vahid; Heidari, Maziar; Mashaghi, Samaneh; Tans, Sander J; Ejtehadi, Mohammad Reza; Mashaghi, Alireza

2017-08-24

Spatial confinement limits the conformational space accessible to biomolecules but the implications for bimolecular topology are not yet known. Folded linear biopolymers can be seen as molecular circuits formed by intramolecular contacts. The pairwise arrangement of intra-chain contacts can be categorized as parallel, series or cross, and has been identified as a topological property. Using molecular dynamics simulations, we determine the contact order distributions and topological circuits of short semi-flexible linear and ring polymer chains with a persistence length of l p under a spherical confinement of radius R c . At low values of l p /R c , the entropy of the linear chain leads to the formation of independent contacts along the chain and accordingly, increases the fraction of series topology with respect to other topologies. However, at high l p /R c , the fraction of cross and parallel topologies are enhanced in the chain topological circuits with cross becoming predominant. At an intermediate confining regime, we identify a critical value of l p /R c , at which all topological states have equal probability. Confinement thus equalizes the probability of more complex cross and parallel topologies to the level of the more simple, non-cooperative series topology. Moreover, our topology analysis reveals distinct behaviours for ring- and linear polymers under weak confinement; however, we find no difference between ring- and linear polymers under strong confinement. Under weak confinement, ring polymers adopt parallel and series topologies with equal likelihood, while linear polymers show a higher tendency for series arrangement. The radial distribution analysis of the topology reveals a non-uniform effect of confinement on the topology of polymer chains, thereby imposing more pronounced effects on the core region than on the confinement surface. Additionally, our results reveal that over a wide range of confining radii, loops arranged in parallel and cross topologies have nearly the same contact orders. Such degeneracy implies that the kinetics and transition rates between the topological states cannot be solely explained by contact order. We expect these findings to be of general importance in understanding chaperone assisted protein folding, chromosome architecture, and the evolution of molecular folds.

Edge Ohmic Heating Experiment on HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Gao, Xiang; Fan, Shuping; Li, Jian'gang; Meng, Yuedong; Luo, Jiarong; Yin, Fuxian; Zeng, Lei; Ding, Liancheng; Lin, Bili; Zhang, Wei; Han, Yuqing; Tong, Xingde; Luo, Lanchang; Gong, Xianzu; Jiang, Jiaguang; Wu, Mingjun; Yin, Fei

1994-03-01

An improved ohmic confinement has been achieved on HT-6M tokamak after application of edge ohmic heating pulse which makes plasma current rapidly ramp up (0.4 ms) in a ramp rate of 12 Ma/s. The improved ohmic confinement phase is characterized by (a) energy and particle confinement time increase, (b) non-symmetric increased density ne, (c) reduced Hα radiation, (d) increased Te and steeper Te, ne profile at the edge. The results from soft x-ray sawteeth inversion radius and βp + li/2 implied the anomalous current penetration.

High pressure gas flow, storage, and displacement in fractured rock—Experimental setup development and application

NASA Astrophysics Data System (ADS)

Hadi Mosleh, M.; Turner, M.; Sedighi, M.; Vardon, P. J.

2017-01-01

This paper presents the design, development, and application of a laboratory setup for the experimental investigations of gas flow and reactions in a fractured rock. The laboratory facility comprises (i) a high pressure manometric sorption apparatus, where equilibrium and kinetic phenomena of adsorption and desorption can be examined, (ii) a high pressure triaxial core flooding system where the chemical reactive transport properties or processes can be explored, and (iii) an ancillary system including pure and mixed gas supply and analysis units. Underground conditions, in terms of pore pressure, confining pressure, and temperature, can be replicated using the triaxial core flooding system developed for depths up to 2 km. Core flooding experiments can be conducted under a range of gas injection pressures up to 20 MPa and temperatures up to 338 K. Details of the design considerations and the specification for the critical measuring instruments are described. The newly developed laboratory facility has been applied to study the adsorption of N2, CH4, and CO2 relevant to applications in carbon sequestration in coal and enhanced coalbed methane recovery. Under a wide range of pressures, the flow of helium in a core sample was studied and the evolution of absolute permeability at different effective stress conditions has been investigated. A comprehensive set of high resolution data has been produced on anthracite coal samples from the South Wales coalfield, using the developed apparatus. The results of the applications provide improved insight into the high pressure flow and reaction of various gas species in the coal samples from the South Wales coalfield.

Improved Confinement by Edge Multi-pulse Turbulent Heating on HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Mao, Jian-shan; Luo, Jia-rong; Li, Jian-gang; Pan, Yuan; Wang, Mao-quan; Liu, Bao-hua; Wan, Yuan-xi; Li, Qiang; Wu, Xin-chao; Liang, Yun-feng; Xu, Yu-hong; Yu, Chang-xuan

1997-10-01

In the recent experiment on HT-6M tokamak, an improved ohmic confinement phase has been observed after application of the edge multi-pulse turbulent heating, and variance of plasma current ΔIp/Ip is about 14-20%. The improved edge plasma confinement phase is characterized by (a) increased average electron density bar Ne and electron temperature Te; (b) reduced Hα radiation from the edge; (c) steeper density and temperature profiles at the edge; (d) a more negative radial electric field over a region of ~ 5 mm deep inside the limiter; (e) a deeper electrostatic potential well at the edge; (f) reduced magnetic fluctuations at the edge.

Rigorous simulations of a helical core fiber by the use of transformation optics formalism.

PubMed

Napiorkowski, Maciej; Urbanczyk, Waclaw

2014-09-22

We report for the first time on rigorous numerical simulations of a helical-core fiber by using a full vectorial method based on the transformation optics formalism. We modeled the dependence of circular birefringence of the fundamental mode on the helix pitch and analyzed the effect of a birefringence increase caused by the mode displacement induced by a core twist. Furthermore, we analyzed the complex field evolution versus the helix pitch in the first order modes, including polarization and intensity distribution. Finally, we show that the use of the rigorous vectorial method allows to better predict the confinement loss of the guided modes compared to approximate methods based on equivalent in-plane bending models.

Laboratory Seismic Monitoring and X-ray CT imaging of Supercritical CO2 Injection in Reservoir Sand: WESTCAB King Island Project

NASA Astrophysics Data System (ADS)

Nakashima, S.; Kneafsey, T. J.; Nakagawa, S.; Harper, E. J.

2013-12-01

The Central Valley of California contains promising locations for on-shore geologic CO2 storage. DOE's WESTCARB (West Coast Regional Carbon Sequestration Partnership) project drilled and cored a borehole (Citizen Green Well) at King Island (near Stockton, CA) to study the CO2 storage capability of saline and gas-bearing formations in the southwestern Sacramento Basin. Potential reservoirs encountered in the borehole include Domengine, Mokelumne River (primary target), and Top Starkey formations. In anticipation of geophysical monitoring of possible CO2 injection into this particular borehole and of the long-term migration of the CO2, we conducted small-scale CO2 injection experiments on three core samples retrieved from the well (Mokelumne River sand A and B) and from a mine outcrop (Domengine sandstone). During the experiment, a jacketed core sample (diameter 1.5 inches, length 4.0-6.0 inches) saturated with brine- (1% NaCl aq.) was confined within a pressure vessel via compressed nitrogen to 3,500-4,000psi, and supercritical CO2 was injected into the core at 2,000-2,500psi and 45-60 degrees C. The CO2 pressure and temperature were adjusted so that the bulk elastic modulus of the CO2 was close to the expected in-situ modulus--which affects the seismic properties most--while keeping the confining stress within our experimental capabilities. After the CO2 broke through the core, fresh brine was re-injected to remove the CO2 by both displacement and dissolution. Throughout the experiment, seismic velocity and attenuation of the core sample were measured using the Split Hopkinson Resonant Bar method (Nakagawa, 2012, Rev. Sci. Instr.) at near 1 kHz (500Hz--1.5 kHz), and the CO2 distribution determined via x-ray CT imaging. In contrast to relatively isotropic Mokelumne sand A, Domengine sandstone and Mokelumne sand B cores exhibited CO2 distributions strongly controlled by the bedding planes. During the CO2 injection, P-wave velocity and attenuation of the layered samples changed irregularly, roughly corresponding to the sequential invasion of the compliant fluid in the sedimentary layers revealed by the CT images. The overall behavior the seismic waves and the final CO2 saturation of the cores, however, were similar for all three cores used in this experiment.

Nomograms to predict the pathological stage of clinically localized prostate cancer in Korean men: comparison with western predictive tools using decision curve analysis.

PubMed

Jeong, Chang Wook; Jeong, Seong Jin; Hong, Sung Kyu; Lee, Seung Bae; Ku, Ja Hyeon; Byun, Seok-Soo; Jeong, Hyeon; Kwak, Cheol; Kim, Hyeon Hoe; Lee, Eunsik; Lee, Sang Eun

2012-09-01

To develop and evaluate nomograms to predict the pathological stage of clinically localized prostate cancer after radical prostatectomy in Korean men. We reviewed the medical records of 2041 patients who had clinical stages T1c-T3a prostate cancer and were treated solely with radical prostatectomy at two hospitals. Logistic regressions were carried out to predict organ-confined disease, extraprostatic extension, seminal vesicle invasion, and lymph node metastasis using preoperative variables and resulting nomograms. Internal validations were assessed using the area under the receiver operating characteristic curve and calibration plot, and then external validations were carried out on 129 patients from another hospital. Head-to-head comparisons with 2007 Partin tables and Cancer of the Prostate Risk Assessment score were carried out using the area under the curve and decision curve analysis. The significant predictors for organ-confined disease and extraprostatic extension were clinical stage, prostate-specific antigen, Gleason score and a percent positive core of biopsy. Significant predictors for seminal vesicle invasion were prostate-specific antigen, Gleason score and percent positive core, and those for lymph node metastasis were prostate-specific antigen and percent positive core. The area under the curve of established nomograms for organ-confined disease, extraprostatic extension, seminal vesicle invasion and lymph node metastasis were 0.809, 0.804, 0.889 and 0.838, respectively. The nomograms were well calibrated and externally validated. These nomograms showed significantly higher accuracies and net benefits than two Western tools in Korean men. This is the first study to have developed and fully validated nomograms to predict the pathological stage of prostate cancer in an Asian population. These nomograms might be more accurate and useful for Korean men than other predictive models developed using Western populations. © 2012 The Japanese Urological Association.

Improved mechanical stability of HKUST-1 in confined nanospace.

PubMed

Casco, M E; Fernández-Catalá, J; Martínez-Escandell, M; Rodríguez-Reinoso, F; Ramos-Fernández, E V; Silvestre-Albero, J

2015-09-28

One of the main concerns in the technological application of several metal-organic frameworks (MOFs) relates to their structural instability under pressure (after a conforming step). Here we report for the first time that mechanical instability can be highly improved via nucleation and growth of MOF nanocrystals in the confined nanospace of activated carbons.

Characterization of the core poloidal flow at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Lebschy, Alexander

2017-10-01

An essential result from neoclassical (NC) theory is that the fluid poloidal rotation (upol) of the main ions is strongly damped by magnetic pumping and, therefore, expected to be small (< 2 km / s). Despite many previous investigations, the nature of the core upol remains an open question: studies at DIII-D show that at low collisionalities, upol is significantly higher in the plasma core than expected. At higher collisionalities, however, a rather good agreement between experiment and theory has been found at both DIII-D and TCV. This is qualitatively consistent with the edge results from both Alcator C-Mod and ASDEX Upgrade (AUG). At AUG thanks to an upgrade of the core charge exchange recombination spectroscopy (CXRS) diagnostics, the core upol can be evaluated through the inboard-outboard asymmetry of the toroidal rotation with an accuracy of 0.5 - 1 km / s . This measurement also provides the missing ingredient to evaluate the core (E-> × B->) velocity (uE-> × B->) via the radial force balance equation. At AUG the core upol (0.35 <ρtor < 0.65) is found to be ion-diamagnetic directed in contradiction to NC predictions. However, the edge rotation is always found to be electron-directed and in good quantitative agreement with NC codes. Additionally, the intrinsic rotation has been measured in Ohmic L-mode plasmas. From the observed data, it is clear that the gradient of the toroidal rotation is flat to slightly negative at the critical density defining the transition from the linear to the saturated Ohmic confinement regime. Furthermore, the non-neoclassical upol observed in these plasma leads to a good agreement between the uE-> × B-> determined from CXRS and the perpendicular velocity measured from turbulence propagation. The difference between these two quantities is the turbulent phase velocity. The gathered dataset indicates that the transition in the turbulence regime occurs after the saturation of the energy confinement time. The author thankfully acknowledges the financial support from the Helmholtz Association of German Research Centers through the Helmholtz Young Investigators Group program.

A mechanism for large divertor plasma energy loss via lithium radiation in tokamaks

NASA Astrophysics Data System (ADS)

Rognlien, T. D.; Meier, E. T.; Soukhanovskii, V. A.

2012-10-01

Lithium has been used as a wall-conditioning element in a number of tokamaks over the years, including TFTR, FTU, and NSTX, where core plasma energy confinement and particle control are often found to improve following such conditioning. Here the possible role of Li in providing substantial energy loss for divertor plasmas via line radiation is reported. A multi-charge-state 2D UEDGE fluid model is used where the hydrogenic and Li ions and neutrals are each evolved as separate species and separate equations are solved for the electron and ion temperatures. It is shown that a sufficient level of Li neutrals evolving from the divertor surface via sputtering or evaporation can induce energy detachment of the divertor plasma, yielding a strongly radiating zone near the divertor where ionization and recombination from/to neutral Li can radiate most of the power flowing into the scrape-off layer while maintaining low core contamination. A local peaking of Li emissivity for electron temperatures near 1 eV appears to play an important role in the detachment of the mixed deuterium/Li plasma. Evidence of such behavior from NSTX discharges will be discussed.

Simulations of inertial confinement fusion driven by a novel synchrotron-radiation-based x-ray igniter

NASA Astrophysics Data System (ADS)

Shlyaptsev, Vyacheslav N.; Tatchyn, Roman O.

2004-01-01

The advantages and challenges of using a powerful x-ray source for the fast ignition of compressed Inertial Confinement Fusion (ICF) targets have been considered. The requirements for such a source together with the optics to focus the x-rays onto compressed DT cores lead to a conceptual design based on Energy Recovery Linacs (ERLs) and long wigglers to produce x-ray pulses with the appropriate phase space properties. A comparative assessment of the parameters of the igniter system indicates that the technologies for building it, although expensive, are physically achievable. Our x-ray fast ignition (XFI) scheme requires substantially smaller energy for the initiation of nuclear fusion reactions than other methods.

Summary of hydraulic properties of the Floridan Aquifer system in coastal Georgia and adjacent parts of South Carolina and Florida

USGS Publications Warehouse

Clarke, John S.; Leeth, David C.; Taylor-Harris, DaVette; Painter, Jaime A.; Labowski, James L.

2005-01-01

Hydraulic-property data for the Floridan aquifer system and equivalent clastic sediments in a 67-county area of coastal Georgia and adjacent parts of South Carolina and Florida were evaluated to provide data necessary for development of ground-water flow and solute-transport models. Data include transmissivity at 324 wells, storage coefficient at 115 wells, and vertical hydraulic conductivity of 72 core samples from 27 sites. Hydraulic properties of the Upper Floridan aquifer vary greatly in the study area due to the heterogeneity (and locally to anisotropy) of the aquifer and to variations in the degree of confinement provided by confining units. Prominent structural features in the areathe Southeast Georgia Embayment, the Beaufort Arch, and the Gulf Troughinfluence the thickness and hydraulic properties of the sediments comprising the Floridan aquifer system. Transmissivity of the Upper Floridan aquifer and equivalent updip units was compiled for 239 wells and ranges from 530 feet squared per day (ft2/d) at Beaufort County, South Carolina, to 600,000 ft2/d in Coffee County, Georgia. In carbonate rock settings of the lower Coastal Plain, transmissivity of the Upper Floridan aquifer generally is greater than 20,000 ft2/d, with values exceeding 100,000 ft2/d in the southeastern and southwestern parts of the study area (generally coinciding with the area of greatest aquifer thickness). Transmissivity of the Upper Floridan aquifer generally is less than 10,000 ft2/d in and near the upper Coastal Plain, where the aquifer is thin and consists largely of clastic sediments, and in the vicinity of the Gulf Trough, where the aquifer consists of low permeability rocks and sediments. Large variability in the range of transmissivity in Camden and Glynn Counties, Georgia, and Nassau County, Florida, demonstrates the anisotropic distribution of hydraulic properties that may result from fractures or solution openings in the carbonate rocks. Storage coefficient of the Upper Floridan aquifer was compiled for 106 wells and ranges from about 0.00004 at Beaufort County, South Carolina, to 0.04 in Baker County, Florida. Transmissivity of the Lower Floridan aquifer and equivalent updip clastic units was compiled for 53 wells and ranges from about 170 ft2/d in Barnwell County, South Carolina, to about 43,000 ft2/d in Camden County, Georgia. Transmissivity of the Lower Floridan aquifer is greatest where the aquifer is thickest in southeastern Georgia and northeastern Floridawhere estimates are greater than 10,000 ft2/d; at one well in southeastern Georgia transmissivity was estimated to be as high as 200,000 ft2/d. Storage-coefficient data for the Lower Floridan aquifer are limited to three estimates in Barnwell and Allendale Counties, South Carolina, and to estimates determined from six multi-aquifer tests in Duval County, Florida. In the South Carolina tests, storage coefficient ranges from 0.0003 to 0.0004; this range is indicative of a confined aquifer. The storage coefficient for the combined Upper and Lower Floridan wells in Duval County, Florida, ranges from 0.00002 to 0.02. Vertical hydraulic conductivity was compiled from core samples collected at 27 sites. For the Upper Floridan confining unit, values from 39 core samples at 17 sites range from 0.0002 to 3 feet per day (ft/d). For the Lower Floridan confining unit, values from 10 core samples at 9 sites range from about 0.000004 to 0.16 ft/d. Vertical hydraulic conductivity of the Upper Floridan aquifer was compiled from 16 core samples at five sites, mostly in the Brunswick, Georgia, area and values range from 0.00134 to 160.4 ft/d. Vertical hydraulic conductivity for the semiconfining unit separating the upper and lower water-bearing zones of the Upper Floridan at Brunswick, Georgia, compiled from 6 core samples at three sites ranges from 0.000008 to 0.000134 ft/d. The vertical hydraulic conductivity of the Lower Floridan aquifer in a core sample from a well at Brunswick, G

Multitude of core-localized shear Alfvén waves in a high-temperature fusion plasma.

PubMed

Nazikian, R; Berk, H L; Budny, R V; Burrell, K H; Doyle, E J; Fonck, R J; Gorelenkov, N N; Holcomb, C; Kramer, G J; Jayakumar, R J; La Haye, R J; McKee, G R; Makowski, M A; Peebles, W A; Rhodes, T L; Solomon, W M; Strait, E J; Vanzeeland, M A; Zeng, L

2006-03-17

Evidence is presented for a multitude of discrete frequency Alfvén waves in the core of magnetically confined high-temperature fusion plasmas. Multiple diagnostic instruments confirm wave excitation over a wide spatial range from the device size at the longest wavelengths down to the thermal ion Larmor radius. At the shortest scales, the poloidal wavelengths are comparable to the scale length of electrostatic drift wave turbulence. Theoretical analysis confirms a dominant interaction of the modes with particles in the thermal ion distribution traveling well below the Alfvén velocity.

Accuracy enhancement of laser induced breakdown spectra using permittivity and size optimized plasma confinement rings.

PubMed

Li, An; Guo, Shuai; Wazir, Nasrullah; Chai, Ke; Liang, Liang; Zhang, Min; Hao, Yan; Nan, Pengfei; Liu, Ruibin

2017-10-30

The inevitable problems in laser induced breakdown spectroscopy are matrix effect and statistical fluctuation of the spectral signal, which can be partly avoided by utilizing a proper confined unit. The dependences of spectral signal enhancement on relative permittivity were studied by varying materials to confine the plasma, which include polytetrafluoroethylene(PTFE), nylon/dacron, silicagel, and nitrile-butadiene rubber (NBR) with the relative permittivity 2.2, ~3.3, 3.6, 8~13, 15~22. We found that higher relative permittivity rings induce stronger enhancement ability, which restricts the energy dissipation of plasma better and due to the reflected electromagnetic wave from the wall of different materials, the electromagnetic field of plasma can be well confined and makes the distribution of plasma more orderly. The spectral intensities of the characteristic lines Si I 243.5 nm and Si I 263.1 nm increased approximately 2 times with relative permittivity values from 2.2 to ~20. The size dependent enhancement of PTFE was further checked and the maximum gain was realized by using a confinement ring with a diameter size of 5 mm and a height of 3 mm (D5mmH3mm), and the rings with D2mmH1mm and D3mmH2mm also show higher enhancement factor. In view of peak shift, peak lost and accidental peaks in the obtained spectra were properly treated in data progressing; the spectral fluctuation decreased drastically for various materials with different relative permittivities as confined units, which means the core of plasma is stabilized, attributing to the confinement effect. Furthermore, the quantitative analysis in coal shows wonderful results-the prediction fitting coefficient R 2 reaches 0.98 for ash and 0.99 for both volatile and carbon.

Improved confinement in highly powered high performance scenarios on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrie, Thomas W.; Osborne, Thomas; Fenstermacher, Max E.

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4–1.8, and β N = 2.5–4.0. The ion B xmore » $$\\triangledown$$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $$\\tau$$ E and β N in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $$\\tau$$ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.« less

Improved confinement in highly powered high performance scenarios on DIII-D

DOE PAGES

Petrie, Thomas W.; Osborne, Thomas; Fenstermacher, Max E.; ...

2017-06-09

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95 = 6, P IN up to 15 MW, H 98 = 1.4–1.8, and β N = 2.5–4.0. The ion B xmore » $$\\triangledown$$B direction is away from the primary X-point. While plasma conditions at lower to moderate power input (e.g., 11 MW) are shown to be favorable to successful puff-and-pump radiating divertor applications, particularly when using argon seeds, plasma behavior at higher powers (e.g., ≥14 MW) may make successful puff-and-pump operation more problematic. In contrast to lower powered high performance plasmas, both $$\\tau$$ E and β N in the high power cases (≥14 MW) increased and ELM frequency decreased, as density was raised by deuterium gas injection. Improved performance in the higher power plasmas was tied to higher pedestal pressure, which according to peeling-ballooning mode stability analysis using the ELITE code could increase with density along the kink/peeling stability threshold, while the pedestal pressure gradient in the lower power discharges were limited by the ballooning threshold. This resulted in improved fueling efficiency and ≈10% higher $$\\tau$$ E and β N than is normally observed in comparable high performance plasmas on DIII-D. Applying the puff-and-pump radiating divertor approach at moderate versus high power input is shown to result in a much different evolution in core and pedestal plasma behavior. In conclusion, we find that injecting deuterium gas into these highly powered DND plasmas may open up a new avenue for achieving elevated plasma performance, including better fueling, but the resulting higher density may also complicate application of a radiating divertor approach to heat flux reduction in present-day tokamaks, if scenarios involving second-harmonic electron cyclotron heating are used.« less

Pressure sensitivity of low permeability sandstones

USGS Publications Warehouse

Kilmer, N.H.; Morrow, N.R.; Pitman, Janet K.

1987-01-01

Detailed core analysis has been carried out on 32 tight sandstones with permeabilities ranging over four orders of magnitude (0.0002 to 4.8 mD at 5000 psi confining pressure). Relationships between gas permeability and net confining pressure were measured for cycles of loading and unloading. For some samples, permeabilities were measured both along and across bedding planes. Large variations in stress sensitivity of permeability were observed from one sample to another. The ratio of permeability at a nominal confining pressure of 500 psi to that at 5000 psi was used to define a stress sensitivity ratio. For a given sample, confining pressure vs permeability followed a linear log-log relationship, the slope of which provided an index of pressure sensitivity. This index, as obtained for first unloading data, was used in testing relationships between stress sensitivity and other measured rock properties. Pressure sensitivity tended to increase with increase in carbonate content and depth, and with decrease in porosity, permeability and sodium feldspar. However, scatter in these relationships increased as permeability decreased. Tests for correlations between pressure sensitivity and various linear combinations of variables are reported. Details of pore structure related to diagenetic changes appears to be of much greater significance to pressure sensitivity than mineral composition. ?? 1987.

Heating efficiency evaluation with mimicking plasma conditions of integrated fast-ignition experiment.

PubMed

Fujioka, Shinsuke; Johzaki, Tomoyuki; Arikawa, Yasunobu; Zhang, Zhe; Morace, Alessio; Ikenouchi, Takahito; Ozaki, Tetsuo; Nagai, Takahiro; Abe, Yuki; Kojima, Sadaoki; Sakata, Shohei; Inoue, Hiroaki; Utsugi, Masaru; Hattori, Shoji; Hosoda, Tatsuya; Lee, Seung Ho; Shigemori, Keisuke; Hironaka, Youichiro; Sunahara, Atsushi; Sakagami, Hitoshi; Mima, Kunioki; Fujimoto, Yasushi; Yamanoi, Kohei; Norimatsu, Takayoshi; Tokita, Shigeki; Nakata, Yoshiki; Kawanaka, Junji; Jitsuno, Takahisa; Miyanaga, Noriaki; Nakai, Mitsuo; Nishimura, Hiroaki; Shiraga, Hiroyuki; Nagatomo, Hideo; Azechi, Hiroshi

2015-06-01

A series of experiments were carried out to evaluate the energy-coupling efficiency from heating laser to a fuel core in the fast-ignition scheme of laser-driven inertial confinement fusion. Although the efficiency is determined by a wide variety of complex physics, from intense laser plasma interactions to the properties of high-energy density plasmas and the transport of relativistic electron beams (REB), here we simplify the physics by breaking down the efficiency into three measurable parameters: (i) energy conversion ratio from laser to REB, (ii) probability of collision between the REB and the fusion fuel core, and (iii) fraction of energy deposited in the fuel core from the REB. These three parameters were measured with the newly developed experimental platform designed for mimicking the plasma conditions of a realistic integrated fast-ignition experiment. The experimental results indicate that the high-energy tail of REB must be suppressed to heat the fuel core efficiently.

Exciton dynamics in GaAs/(Al,Ga)As core-shell nanowires with shell quantum dots

NASA Astrophysics Data System (ADS)

Corfdir, Pierre; Küpers, Hanno; Lewis, Ryan B.; Flissikowski, Timur; Grahn, Holger T.; Geelhaar, Lutz; Brandt, Oliver

2016-10-01

We study the dynamics of excitons in GaAs/(Al,Ga)As core-shell nanowires by continuous-wave and time-resolved photoluminescence and photoluminescence excitation spectroscopy. Strong Al segregation in the shell of the nanowires leads to the formation of Ga-rich inclusions acting as quantum dots. At 10 K, intense light emission associated with these shell quantum dots is observed. The average radiative lifetime of excitons confined in the shell quantum dots is 1.7 ns. We show that excitons may tunnel toward adjacent shell quantum dots and nonradiative point defects. We investigate the changes in the dynamics of charge carriers in the shell with increasing temperature, with particular emphasis on the transfer of carriers from the shell to the core of the nanowires. We finally discuss the implications of carrier localization in the (Al,Ga)As shell for fundamental studies and optoelectronic applications based on core-shell III-As nanowires.

Vortex dynamics and frequency splitting in vertically coupled nanomagnets

DOE PAGES

Stebliy, M. E.; Jain, S.; Kolesnikov, A. G.; ...

2017-04-25

Here, we explored the dynamic response of a vortex core in a circular nanomagnet by manipulating its dipole-dipole interaction with another vortex core confined locally on top of the nanomagnet. A clear frequency splitting is observed corresponding to the gyrofrequencies of the two vortex cores. The peak positions of the two resonance frequencies can be engineered by controlling the magnitude and direction of the external magnetic field. Both experimental and micromagnetic simulations show that the frequency spectra for the combined system is significantly dependent on the chirality of the circular nanomagnet and is asymmetric with respect to the external biasmore » field. We attribute this result to the strong dynamic dipole-dipole interaction between the two vortex cores, which varies with the distance between them. The possibility of having multiple states in a single nanomagnet with vertical coupling could be of interest for magnetoresistive memories.« less

ELMO Bumpy Square proposal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dory, R.A.; Uckan, N.A.; Ard, W.B.

The ELMO Bumpy Square (EBS) concept consists of four straight magnetic mirror arrays linked by four high-field corner coils. Extensive calculations show that this configuration offers major improvements over the ELMO Bumpy Torus (EBT) in particle confinement, heating, transport, ring production, and stability. The components of the EBT device at Oak Ridge National Laboratory can be reconfigured into a square arrangement having straight sides composed of EBT coils, with new microwave cavities and high-field corners designed and built for this application. The elimination of neoclassical convection, identified as the dominant mechanism for the limited confinement in EBT, will give themore » EBS device substantially improved confinement and the flexibility to explore the concepts that produce this improvement. The primary goals of the EBS program are twofold: first, to improve the physics of confinement in toroidal systems by developing the concepts of plasma stabilization using the effects of energetic electrons and confinement optimization using magnetic field shaping and electrostatic potential control to limit particle drift, and second, to develop bumpy toroid devices as attractive candidates for fusion reactors. This report presents a brief review of the physics analyses that support the EBS concept, discussions of the design and expected performance of the EBS device, a description of the EBS experimental program, and a review of the reactor potential of bumpy toroid configurations. Detailed information is presented in the appendices.« less

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments.

PubMed

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-07-14

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China's HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress-strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure.

Coupled transport in field-reversed configurations

NASA Astrophysics Data System (ADS)

Steinhauer, L. C.; Berk, H. L.; TAE Team

2018-02-01

Coupled transport is the close interconnection between the cross-field and parallel fluxes in different regions due to topological changes in the magnetic field. This occurs because perpendicular transport is necessary for particles or energy to leave closed field-line regions, while parallel transport strongly affects evolution of open field-line regions. In most toroidal confinement systems, the periphery, namely, the portion with open magnetic surfaces, is small in thickness and volume compared to the core plasma, the portion with closed surfaces. In field-reversed configurations (FRCs), the periphery plays an outsized role in overall confinement. This effect is addressed by an FRC-relevant model of coupled particle transport that is well suited for immediate interpretation of experiments. The focus here is particle confinement rather than energy confinement since the two track together in FRCs. The interpretive tool yields both the particle transport rate χn and the end-loss time τǁ. The results indicate that particle confinement depends on both χn across magnetic surfaces throughout the plasma and τǁ along open surfaces and that they provide roughly equal transport barriers, inhibiting particle loss. The interpretation of traditional FRCs shows Bohm-like χn and inertial (free-streaming) τǁ. However, in recent advanced beam-driven FRC experiments, χn approaches the classical rate and τǁ is comparable to classic empty-loss-cone mirrors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fenstermacher, M. E.; Garofalo, A. M.; Gerhardt, S. P.

The H-mode confinement regime is characterized by a region of good thermal and particle confinement at the edge of the confined plasma, and has generally been envisioned as the operating regime for ITER and other next step devices. This good confinement is often interrupted, however, by edge-localized instabilities, known as ELMs. On the one hand, these ELMs provide particle and impurity flushing from the plasma core, a beneficial effect facilitating density control and stationary operation. On the other hand, the ELMs result in a substantial fraction of the edge stored energy flowing in bursts to the divertor and first wall;more » this impulsive thermal loading would result in unacceptable erosion of these material surfaces if it is not arrested. Hence, developing and understanding operating regimes that have the energy confinement of standard H-mode and the stationarity that is provided by ELMs, while at the same time eliminating the impulsive thermal loading of large ELMs, is the focus of the 2013 FES Joint Research Target (JRT): Annual Target: Conduct experiments and analysis on major fusion facilities, to evaluate stationary enhanced confinement regimes without large Edge Localized Modes (ELMs), and to improve understanding of the underlying physical mechanisms that allow acceptable edge particle transport while maintaining a strong thermal transport barrier. Mechanisms to be investigated can include intrinsic continuous edge plasma modes and externally applied 3D fields. Candidate regimes and techniques have been pioneered by each of the three major US facilities (C-Mod, D3D and NSTX). Coordinated experiments, measurements, and analysis will be carried out to assess and understand the operational space for the regimes. Exploiting the complementary parameters and tools of the devices, joint teams will aim to more closely approach key dimensionless parameters of ITER, and to identify correlations between edge fluctuations and transport. The role of rotation will be investigated. The research will strengthen the basis for extrapolation of stationary regimes which combine high energy confinement with good particle and impurity control, to ITER and other future fusion facilities for which avoidance of large ELMs is a critical issue. Data from the Alcator C-Mod tokamak (MIT), DIII-D tokamak (General Atomics), and NSTX spherical tokamak (PPPL) contribute to this report. Experiments specifically motivated by this research target were conducted on DIII-D, with a national team of researchers from GA, LLNL, PPPL, MIT and ORNL contributing. Both the Alcator C-Mod and NSTX-U teams contributed analysis of previously collected data, as those two facilities did not operate in FY2013. Within each of the three research groups, members from both the host institutions and collaborating institutions made critical contributions. Highlights from these research activities are provided, with additional details.« less

Comparison and analysis of theoretical models for diffusion-controlled dissolution.

PubMed

Wang, Yanxing; Abrahamsson, Bertil; Lindfors, Lennart; Brasseur, James G

2012-05-07

Dissolution models require, at their core, an accurate diffusion model. The accuracy of the model for diffusion-dominated dissolution is particularly important with the trend toward micro- and nanoscale drug particles. Often such models are based on the concept of a "diffusion layer." Here a framework is developed for diffusion-dominated dissolution models, and we discuss the inadequacy of classical models that are based on an unphysical constant diffusion layer thickness assumption, or do not correctly modify dissolution rate due to "confinement effects": (1) the increase in bulk concentration from confinement of the dissolution process, (2) the modification of the flux model (the Sherwood number) by confinement. We derive the exact mathematical solution for a spherical particle in a confined fluid with impermeable boundaries. Using this solution, we analyze the accuracy of a time-dependent "infinite domain model" (IDM) and "quasi steady-state model" (QSM), both formally derived for infinite domains but which can be applied in approximate fashion to confined dissolution with proper adjustment of a concentration parameter. We show that dissolution rate is sensitive to the degree of confinement or, equivalently, to the total concentration C(tot). The most practical model, the QSM, is shown to be very accurate for most applications and, consequently, can be used with confidence in design-level dissolution models so long as confinement is accurately treated. The QSM predicts the ratio of diffusion layer thickness to particle radius (the Sherwood number) as a constant plus a correction that depends on the degree of confinement. The QSM also predicts that the time required for complete saturation or dissolution in diffusion-controlled dissolution experiments is singular (i.e., infinite) when total concentration equals the solubility. Using the QSM, we show that measured differences in dissolution rate in a diffusion-controlled dissolution experiment are a result of differences in the degree of confinement on the increase in bulk concentration independent of container geometry and polydisperse vs single particle dissolution. We conclude that the constant diffusion-layer thickness assumption is incorrect in principle and should be replaced by the QSM with accurate treatment of confinement in models of diffusion-controlled dissolution.

Radio Frequency (RF) Trap for Confinement of Antimatter Plasmas Using Rotating Wall Electric Fields

NASA Technical Reports Server (NTRS)

Sims, William Herbert, III; Pearson, J. Boise

2004-01-01

Perturbations associated with a rotating wall electric field enable the confinement of ions for periods approaching weeks. This steady state confinement is a result of a radio frequency manipulation of the ions. Using state-of-the-art techniques it is shown that radio frequency energy can produce useable manipulation of the ion cloud (matter or antimatter) for use in containment experiments. The current research focuses on the improvement of confinement systems capable of containing and transporting antimatter.

Understanding "The Other" through Art: Fostering Narrative Imagination in Elementary Students

ERIC Educational Resources Information Center

Kim, Jeong-Hee; Wiehe-Beck, Anna

2016-01-01

Teachers in many countries live the language of standards although it is confined to uniformity and standardization. In the United States, for example, teachers teach to what is now called the Common Core State Standards that focus on students' college and career readiness while falling short of developing good judgment and wisdom. In this…

Tuning and Switching a Plasmonic Quantum Dot "Sandwich" in a Nematic Line Defect.

PubMed

Mundoor, Haridas; Sheetah, Ghadah H; Park, Sungoh; Ackerman, Paul J; Smalyukh, Ivan I; van de Lagemaat, Jao

2018-03-27

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the "sandwich" confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that "push" the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter when nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic "sandwich". These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.

Tuning and Switching a Plasmonic Quantum Dot “Sandwich” in a Nematic Line Defect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mundoor, Haridas; Sheetah, Ghadah H.; Park, Sungoh

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the 'sandwich' confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that 'push' the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter whenmore » nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic 'sandwich'. These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.« less

Tuning and Switching a Plasmonic Quantum Dot “Sandwich” in a Nematic Line Defect

DOE PAGES

Mundoor, Haridas; Sheetah, Ghadah H.; Park, Sungoh; ...

2018-02-28

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot (QD) controllably sandwiched between two plasmonic nanorods. Control over the position and the 'sandwich' confinement structure is achieved by the use of a linear-trap liquid crystal (LC) line defect and laser tweezers that 'push' the sandwich together. This arrangement allows for the study of exciton-plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon antibunching behavior of the QD and its luminescence lifetime. The QD behaves as a single emitter whenmore » nanorods are far away from the QD but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic 'sandwich'. These findings demonstrate that LC defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.« less

Beyond the single-file fluid limit using transfer matrix method: Exact results for confined parallel hard squares

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gurin, Péter; Varga, Szabolcs

2015-06-14

We extend the transfer matrix method of one-dimensional hard core fluids placed between confining walls for that case where the particles can pass each other and at most two layers can form. We derive an eigenvalue equation for a quasi-one-dimensional system of hard squares confined between two parallel walls, where the pore width is between σ and 3σ (σ is the side length of the square). The exact equation of state and the nearest neighbor distribution functions show three different structures: a fluid phase with one layer, a fluid phase with two layers, and a solid-like structure where the fluidmore » layers are strongly correlated. The structural transition between differently ordered fluids develops continuously with increasing density, i.e., no thermodynamic phase transition occurs. The high density structure of the system consists of clusters with two layers which are broken with particles staying in the middle of the pore.« less

Geometry of the Nojima fault at Nojima-Hirabayashi, Japan - I. A simple damage structure inferred from borehole core permeability

USGS Publications Warehouse

Lockner, David A.; Tanaka, Hidemi; Ito, Hisao; Ikeda, Ryuji; Omura, Kentaro; Naka, Hisanobu

2009-01-01

The 1995 Kobe (Hyogo-ken Nanbu) earthquake, M = 7.2, ruptured the Nojima fault in southwest Japan. We have studied core samples taken from two scientific drillholes that crossed the fault zone SW of the epicentral region on Awaji Island. The shallower hole, drilled by the Geological Survey of Japan (GSJ), was started 75 m to the SE of the surface trace of the Nojima fault and crossed the fault at a depth of 624 m. A deeper hole, drilled by the National Research Institute for Earth Science and Disaster Prevention (NIED) was started 302 m to the SE of the fault and crossed fault strands below a depth of 1140 m. We have measured strength and matrix permeability of core samples taken from these two drillholes. We find a strong correlation between permeability and proximity to the fault zone shear axes. The half-width of the high permeability zone (approximately 15 to 25 m) is in good agreement with the fault zone width inferred from trapped seismic wave analysis and other evidence. The fault zone core or shear axis contains clays with permeabilities of approximately 0.1 to 1 microdarcy at 50 MPa effective confining pressure (10 to 30 microdarcy at in situ pressures). Within a few meters of the fault zone core, the rock is highly fractured but has sustained little net shear. Matrix permeability of this zone is approximately 30 to 60 microdarcy at 50 MPa effective confining pressure (300 to 1000 microdarcy at in situ pressures). Outside this damage zone, matrix permeability drops below 0.01 microdarcy. The clay-rich core material has the lowest strength with a coefficient of friction of approximately 0.55. Shear strength increases with distance from the shear axis. These permeability and strength observations reveal a simple fault zone structure with a relatively weak fine-grained core surrounded by a damage zone of fractured rock. In this case, the damage zone will act as a high-permeability conduit for vertical and horizontal flow in the plane of the fault. The fine-grained core region, however, will impede fluid flow across the fault.

Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas

NASA Astrophysics Data System (ADS)

Dinklage, A.; Yokoyama, M.; Tanaka, K.; Velasco, J. L.; López-Bruna, D.; Beidler, C. D.; Satake, S.; Ascasíbar, E.; Arévalo, J.; Baldzuhn, J.; Feng, Y.; Gates, D.; Geiger, J.; Ida, K.; Isaev, M.; Jakubowski, M.; López-Fraguas, A.; Maaßberg, H.; Miyazawa, J.; Morisaki, T.; Murakami, S.; Pablant, N.; Kobayashi, S.; Seki, R.; Suzuki, C.; Suzuki, Y.; Turkin, Yu.; Wakasa, A.; Wolf, R.; Yamada, H.; Yoshinuma, M.; LHD Exp. Group; TJ-II Team; W7-AS Team

2013-06-01

A comparative study of energy transport for medium- to high-density discharges in the stellarator-heliotrons TJ-II, W7-AS and LHD is carried out. The specific discharge parameters are chosen to apply a recently concluded benchmarking study of neoclassical (NC) transport coefficients (Beidler et al 2011 Nucl. Fusion 51 076001) to perform this validation study. In contrast to previous experiments at low densities for which electron transport was predominant (Yokoyama et al 2007 Nucl. Fusion 47 1213), the current discharges also exhibit significant ion energy transport. As it affects the energy transport in 3D devices, the ambipolar radial electric field is addressed as well. For the discharges described, ion-root conditions, i.e. a small negative radial electric field were found. The energy transport in the peripheral region cannot be explained by NC theory. Within a ‘core region’(r/a < 1/2 ˜ 2/3), the predicted NC energy fluxes comply with experimental findings for W7-AS. For TJ-II, compliance in the core region is found for the particle transport and the electron energy transport. For the specific LHD discharges, the core energy transport complied with NC theory except for the electron energy transport in the inward-shifted magnetic configuration. The NC radial electric field tends to agree with experimental results for all devices but is measured to be more negative in the core of both LHD and TJ-II. As a general observation, the energy confinement time approaches the gyro-Bohm-type confinement scaling ISS04 (Yamada et al 2005 Nucl. Fusion 45 1684). This work is carried out within the International Stellarator-Heliotron Profile Database (www.ipp.mpg.de/ISS and http://ishpdb.nifs.ac.jp/index.html).

Emergence of a High-Temperature Superconductivity in Hydrogen Cycled pd Compounds as AN Evidence for Superstoihiometric H/d Sites

NASA Astrophysics Data System (ADS)

Lipson, Andrei; Castano, Carlos; Miley, George; Lipson, Andrei; Lyakhov, Boris; Mitin, Alexander

2006-02-01

Transport and magnetic properties of hydrogen cycled PdHx and Pd/PdO:Hx (x ~ (4/6) × 10-4) nano-composite consisting of a Pd matrix with hydrogen trapped inside dislocation cores have been studied. The results suggest emergence of a high-temperature superconductivity state of a condensed hydrogen phase confined inside deep dislocation cores in the Pd matrix. The possible role of hydrogen/deuterium filled dislocation nano-tubes is discussed. These dislocation cores could be considered as active centers of LENR triggering due to (i) short D-D separation distance (~Bohr radius); (ii) high-local D-loading in the Pd and the corresponding effective lattice compression; (iii) a large optic phonon energy resulting in a most effective lattice-nuclei energy transfer.

Ultrafast light matter interaction in CdSe/ZnS core-shell quantum dots

NASA Astrophysics Data System (ADS)

Yadav, Rajesh Kumar; Sharma, Rituraj; Mondal, Anirban; Adarsh, K. V.

2018-04-01

Core-shell quantum dot are imperative for carrier (electron and holes) confinement in core/shell, which provides a stage to explore the linear and nonlinear optical phenomena at the nanoscalelimit. Here we present a comprehensive study of ultrafast excitation dynamics and nonlinear optical absorption of CdSe/ZnS core shell quantum dot with the help of ultrafast spectroscopy. Pump-probe and time-resolved measurements revealed the drop of trapping at CdSe surface due to the presence of the ZnS shell, which makes more efficient photoluminescence. We have carried out femtosecond transient absorption studies of the CdSe/ZnS core-shell quantum dot by irradiation with 400 nm laser light, monitoring the transients in the visible region. The optical nonlinearity of the core-shell quantum dot studied by using the Z-scan technique with 120 fs pulses at the wavelengths of 800 nm. The value of two photon absorption coefficients (β) of core-shell QDs extracted as80cm/GW, and it shows excellent benchmark for the optical limiting onset of 2.5GW/cm2 with the low limiting differential transmittance of 0.10, that is an order of magnitude better than graphene based materials.

Heavy ion beam probe operation in time varying equilibria of improved confinement reversed field pinch discharges.

PubMed

Demers, D R; Chen, X; Schoch, P M; Fimognari, P J

2010-10-01

Operation of a heavy ion beam probe (HIBP) on a reversed field pinch is unique from other toroidal applications because the magnetic field is more temporal and largely produced by plasma current. Improved confinement, produced through the transient application of a poloidal electric field which leads to a reduction of dynamo activity, exhibits gradual changes in equilibrium plasma quantities. A consequence of this is sweeping of the HIBP trajectories by the dynamic magnetic field, resulting in motion of the sample volume. In addition, the plasma potential evolves with the magnetic equilibrium. Measurement of the potential as a function of time is thus a combination of temporal changes of the equilibrium and motion of the sample volume. A frequent additional complication is a nonideal balance of ion current on the detectors resulting from changes in the beam trajectory (magnetic field) and energy (plasma potential). This necessitates use of data selection criteria. Nevertheless, the HIBP on the Madison Symmetric Torus has acquired measurements as a function of time throughout improved confinement. A technique developed to infer the potential in the improved confinement reversed field pinch from HIBP data in light of the time varying plasma equilibrium will be discussed.

Acoustic emission of retrofitted fiber-wrapped columns

NASA Astrophysics Data System (ADS)

El Echary, Hazem; Mirmiran, Amir

1998-03-01

In recent years, fiber-wrapping technique has become increasingly popular for retrofitting of existing bridge pier columns in seismic zones. By the way of confinement, the external jacket enhances strength, ductility and shear performance of the column. However, since state of the concrete core is not visible from outside of the jacket, it is of great necessity to develop proper non-destructive methods to evaluate structural integrity of the column. Extensive research on FRP-confined concrete at the University of Central Florida has shown that failure of such hybrid columns is often accompanied by considerable audible and sub-audible noise, making acoustic emission (AE) a viable NDE technique for retrofitted columns. Acoustic emission from fiber-wrapped concrete specimens were monitored. A total of 24 concrete specimens with two types of construction (bonded and unbonded) and four different number of layers (1, 3, 5 and 7) were tested under uniaxial compression. All specimens were made of S-glass fabric and polyester resin with a core diameter of 6' and a length of 12'. Some of the specimens were subjected to cycles of loading and unloading to examine the presence of the Kaiser and the Felicity effects. A 4-channel AEDSP-32/16 (Mistras-2001) machine from Physical Acoustics Corp. was used for the experiments. Results indicate that AE energy and the number of AE counts can both be good representatives for the response of confined concrete. Further, plots of AE energy versus load follows the same bilinear trend that has been observed in the stress-strain response of such specimens. Finally, Felicity effect was observed in all composite specimens.

NMR relaxation dispersion of Miglyol molecules confined inside polymeric micro-capsules.

PubMed

Nechifor, Ruben; Ardelean, Ioan; Mattea, Carlos; Stapf, Siegfried; Bogdan, Mircea

2011-11-01

Frequency dependent NMR relaxation studies have been carried out on Miglyol molecules confined inside core shell polymeric capsules to obtain a correlation between capsule dimension and the measurable parameters. The polymeric capsules were prepared using an interfacial polymerization technique for three different concentrations of Miglyol. It was shown that the variation of Miglyol concentration influences the capsule dimension. Their average size was estimated using the pulsed field gradient diffusometry technique. The relaxation dispersion curves were obtained at room temperature by a combined use of a fast field cycling instrument and a high-field instrument. The frequency dependence of relaxation rate shows a transition from a diffusion-limited to a surface-limited relaxation regime. Copyright © 2011 John Wiley & Sons, Ltd.

Evidence for Stratification of Deuterium-Tritium Fuel in Inertial Confinement Fusion Implosions

NASA Astrophysics Data System (ADS)

Casey, D. T.; Frenje, J. A.; Gatu Johnson, M.; Manuel, M. J.-E.; Rinderknecht, H. G.; Sinenian, N.; Séguin, F. H.; Li, C. K.; Petrasso, R. D.; Radha, P. B.; Delettrez, J. A.; Glebov, V. Yu; Meyerhofer, D. D.; Sangster, T. C.; McNabb, D. P.; Amendt, P. A.; Boyd, R. N.; Rygg, J. R.; Herrmann, H. W.; Kim, Y. H.; Bacher, A. D.

2012-02-01

Measurements of the D(d,p)T (dd) and T(t,2n)He4 (tt) reaction yields have been compared with those of the D(t,n)He4 (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.

Evidence for stratification of deuterium-tritium fuel in inertial confinement fusion implosions.

PubMed

Casey, D T; Frenje, J A; Johnson, M Gatu; Manuel, M J-E; Rinderknecht, H G; Sinenian, N; Séguin, F H; Li, C K; Petrasso, R D; Radha, P B; Delettrez, J A; Glebov, V Yu; Meyerhofer, D D; Sangster, T C; McNabb, D P; Amendt, P A; Boyd, R N; Rygg, J R; Herrmann, H W; Kim, Y H; Bacher, A D

2012-02-17

Measurements of the D(d,p)T (dd) and T(t,2n)(4)He (tt) reaction yields have been compared with those of the D(t,n)(4)He (dt) reaction yield, using deuterium-tritium gas-filled inertial confinement fusion capsule implosions. In these experiments, carried out on the OMEGA laser, absolute spectral measurements of dd protons and tt neutrons were obtained. From these measurements, it was concluded that the dd yield is anomalously low and the tt yield is anomalously high relative to the dt yield, an observation that we conjecture to be caused by a stratification of the fuel in the implosion core. This effect may be present in ignition experiments planned on the National Ignition Facility.

Experimental Study of Damage Evolution in Circular Stirrup-Confined Concrete

PubMed Central

Li, Zuohua; Peng, Zhihan; Teng, Jun; Wang, Ying

2016-01-01

This paper presents an experimental study on circular stirrup-confined concrete specimens under uniaxial and monotonic load. The effects of stirrup volume ratio, stirrup yield strength and concrete strength on damage evolution of stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, the concrete damage evolution can be relatively restrained with the increase of the stirrup volume ratio. Secondly, higher stirrup yield strength usually causes larger confining pressures and slower concrete damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates the concrete damage evolution. A plastic strain expression is obtained through curve fitting, and a damage evolution equation for circular stirrup-confined concrete is proposed by introducing a confinement factor (C) based on the experimental data. The comparison results demonstrate that the proposed damage evolution model can accurately describe the experimental results. PMID:28773402

Experimental Study of Damage Evolution in Circular Stirrup-Confined Concrete.

PubMed

Li, Zuohua; Peng, Zhihan; Teng, Jun; Wang, Ying

2016-04-08

This paper presents an experimental study on circular stirrup-confined concrete specimens under uniaxial and monotonic load. The effects of stirrup volume ratio, stirrup yield strength and concrete strength on damage evolution of stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, the concrete damage evolution can be relatively restrained with the increase of the stirrup volume ratio. Secondly, higher stirrup yield strength usually causes larger confining pressures and slower concrete damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates the concrete damage evolution. A plastic strain expression is obtained through curve fitting, and a damage evolution equation for circular stirrup-confined concrete is proposed by introducing a confinement factor ( C ) based on the experimental data. The comparison results demonstrate that the proposed damage evolution model can accurately describe the experimental results.

Elmo bumpy square plasma confinement device

DOEpatents

Owen, L.W.

1985-01-01

The invention is an Elmo bumpy type plasma confinement device having a polygonal configuration of closed magnet field lines for improved plasma confinement. In the preferred embodiment, the device is of a square configuration which is referred to as an Elmo bumpy square (EBS). The EBS is formed by four linear magnetic mirror sections each comprising a plurality of axisymmetric assemblies connected in series and linked by 90/sup 0/ sections of a high magnetic field toroidal solenoid type field generating coils. These coils provide corner confinement with a minimum of radial dispersion of the confined plasma to minimize the detrimental effects of the toroidal curvature of the magnetic field. Each corner is formed by a plurality of circular or elliptical coils aligned about the corner radius to provide maximum continuity in the closing of the magnetic field lines about the square configuration confining the plasma within a vacuum vessel located within the various coils forming the square configuration confinement geometry.

Lithium As Plasma Facing Component for Magnetic Fusion Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masayuki Ono

The use of lithium in magnetic fusion confinement experiments started in the 1990's in order to improve tokamak plasma performance as a low-recycling plasma-facing component (PFC). Lithium is the lightest alkali metal and it is highly chemically reactive with relevant ion species in fusion plasmas including hydrogen, deuterium, tritium, carbon, and oxygen. Because of the reactive properties, lithium can provide strong pumping for those ions. It was indeed a spectacular success in TFTR where a very small amount (~ 0.02 gram) of lithium coating of the PFCs resulted in the fusion power output to improve by nearly a factor ofmore » two. The plasma confinement also improved by a factor of two. This success was attributed to the reduced recycling of cold gas surrounding the fusion plasma due to highly reactive lithium on the wall. The plasma confinement and performance improvements have since been confirmed in a large number of fusion devices with various magnetic configurations including CDX-U/LTX (US), CPD (Japan), HT-7 (China), EAST (China), FTU (Italy), NSTX (US), T-10, T-11M (Russia), TJ-II (Spain), and RFX (Italy). Additionally, lithium was shown to broaden the plasma pressure profile in NSTX, which is advantageous in achieving high performance H-mode operation for tokamak reactors. It is also noted that even with significant applications (up to 1,000 grams in NSTX) of lithium on PFCs, very little contamination (< 0.1%) of lithium fraction in main fusion plasma core was observed even during high confinement modes. The lithium therefore appears to be a highly desirable material to be used as a plasma PFC material from the magnetic fusion plasma performance and operational point of view. An exciting development in recent years is the growing realization of lithium as a potential solution to solve the exceptionally challenging need to handle the fusion reactor divertor heat flux, which could reach 60 MW/m2 . By placing the liquid lithium (LL) surface in the path of the main divertor heat flux (divertor strike point), the lithium is evaporated from the surface. The evaporated lithium is quickly ionized by the plasma and the ionized lithium ions can provide a strongly radiative layer of plasma ("radiative mantle"), thus could significantly reduce the heat flux to the divertor strike point surfaces, thus protecting the divertor surface. The protective effects of LL have been observed in many experiments and test stands. As a possible reactor divertor candidate, a closed LL divertor system is described. Finally, it is noted that the lithium applications as a PFC can be quite flexible and broad. The lithium application should be quite compatible with various divertor configurations, and it can be also applied to protecting the presently envisioned tungsten based solid PFC surfaces such as the ones for ITER. Lithium based PFCs therefore have the exciting prospect of providing a cost effective flexible means to improve the fusion reactor performance, while providing a practical solution to the highly challenging divertor heat handling issue confronting the steadystate magnetic fusion reactors.« less

Faster vortex core switching with lower current density using three-nanocontact spin-polarized currents in a confined structure

NASA Astrophysics Data System (ADS)

Li, Hua-Nan; Hua, Zhong; Li, Dong-Fei

2017-01-01

Not Available Project supported by the China Postdoctoral Science Foundation (Grant No. 2013M541286), the Science and Technology Planning Project of Jilin Province, China (Grant Nos. 20140520109JH and 20150414003GH), and the “Twelfth Five year” Scientific and Technological Research Project of Department of Education of Jilin Province, China.

Drilling side holes from a borehole

NASA Technical Reports Server (NTRS)

Collins, E. R., Jr.

1980-01-01

Machine takes long horizontal stratum samples from confines of 21 cm bore hole. Stacked interlocking half cylindrical shells mate to form rigid thrust tube. Drive shaft and core storage device is flexible and retractable. Entire machine fits in 10 meter length of steel tube. Machine could drill drainage or ventilation holes in coal mines, or provide important information for geological, oil, and geothermal surveys.

Turbulence in high-beta ASDEX upgrade advanced scenarios

NASA Astrophysics Data System (ADS)

Doerk, H.; Bock, A.; Di Siena, A.; Fable, E.; Görler, T.; Jenko, F.; Stober, J.; The ASDEX Upgrade Team

2018-01-01

Recent experiments at ASDEX Upgrade achieve non-inductive operation in full tungsten wall conditions by applying electron cyclotron and neutral beam current drive. These discharges are characterised by a well-measured safety factor profile, which does not drop below one, and a good energy confinement. By reproducing the experimental heat fluxes, nonlinear gyrokinetic simulations suggest that the observed strong peaking of the ion temperature in the core is caused by the stabilising impact of a significant beam ion content, as well as strong electromagnetic effects on turbulent transport. Quasilinear transport models are not yet applicable in this interesting and reactor relevant parameter regime, but available simulation data may serve as a testbed for improvements. As the present plasma is close to the kinetic ballooning (KBM) threshold, elevating the safety factor profile under otherwise identical conditions is proposed to clarify, whether profiles are ultimately limited by KBM turbulence, or by global stability constraints.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Triaxial testing system for pressure core analysis using image processing technique

NASA Astrophysics Data System (ADS)

Yoneda, J.; Masui, A.; Tenma, N.; Nagao, J.

2013-11-01

In this study, a newly developed innovative triaxial testing system to investigate strength, deformation behavior, and/or permeability of gas hydrate bearing-sediments in deep sea is described. Transport of the pressure core from the storage chamber to the interior of the sealing sleeve of a triaxial cell without depressurization was achieved. An image processing technique was used to capture the motion and local deformation of a specimen in a transparent acrylic triaxial pressure cell and digital photographs were obtained at each strain level during the compression test. The material strength was successfully measured and the failure mode was evaluated under high confining and pore water pressures.

Structurally flexible triethanolamine-core poly(amidoamine) dendrimers as effective nanovectors to deliver RNAi-based therapeutics.

PubMed

Liu, Xiaoxuan; Liu, Cheng; Catapano, Carlo V; Peng, Ling; Zhou, Jiehua; Rocchi, Palma

2014-01-01

RNAi-based nucleic acid molecules have attracted considerable attention as compelling therapeutics providing safe and competent delivery systems are available. Dendrimers are emerging as appealing nanocarriers for nucleic acid delivery thanks to their unique well-defined architecture and the resulting cooperativity and multivalency confined within a nanostructure. The present review offers a brief overview of the structurally flexible triethanolamine-core poly(amidoamine) (PAMAM) dendrimers developed in our group as nanovectors for the delivery of RNAi therapeutics. Their excellent activity for delivering different RNAi therapeutics in various disease models in vitro and in vivo will be highlighted here. © 2013.

Ultralow-power four-wave mixing with Rb in a hollow-core photonic band-gap fiber.

PubMed

Londero, Pablo; Venkataraman, Vivek; Bhagwat, Amar R; Slepkov, Aaron D; Gaeta, Alexander L

2009-07-24

We demonstrate extremely efficient four-wave mixing with gains greater than 100 at microwatt pump powers and signal-to-idler conversion of 50% in Rb vapor confined to a hollow-core photonic band-gap fiber. We present a theoretical model that demonstrates such efficiency is consistent with the dimensions of the fiber and the optical depths attained. This is, to our knowledge, the largest four-wave mixing gain observed at such low total pump powers and the first demonstrated example of four-wave mixing in an alkali-metal vapor system with a large (approximately 30 MHz) ground state decoherence rate.

Manipulation of metal-dielectric core-shell particles in optical fields

NASA Astrophysics Data System (ADS)

Chvátal, Lukáš; Šiler, Martin; Zemánek, Pavel

2014-12-01

Metal-dielectric core-shell particles represent promising tools in nanoplasmonics. In combination with optical tweezers they can be manipulated in a contactless way through fluid and their plasmonic properties can be used to probe or modify the local environment. We perform a numerical parametric study to find the particle geometry and material parameters under which such particle can be stably confined in optical tweezers. We use the theory based on Mie scattering in the focal field of an ideal water immersion objective of numerical aperture NA=1.2. For very thin metal layers we find that strong trapping on the optical axis can be achieved.

Density and beta limits in the Madison Symmetric Torus Reversed-Field Pinch

NASA Astrophysics Data System (ADS)

Caspary, Kyle Jonathan

Operational limits and the underlying physics are explored on the Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP) using deuterium pellet fueling. The injection of a fast pellet provides a large source of fuel in the plasma edge upon impact with the vessel wall, capable of triggering density limit terminations for the full range of plasma current, up to 600 kA. As the pellet size and plasma density increase, approaching the empirical Greenwald limit, plasma degradation is observed in the form of current decay, increased magnetic activity in the edge and core, increased radiation and plasma cooling. The complete termination of the plasma is consistent with the Greenwald limit; however, a slightly smaller maximum density is observed in discharges without toroidal field reversal. The plasma beta is the ratio of the plasma pressure to the confining magnetic pressure. Beta limits are known to constrain other magnetic confinement devices, but no beta limit has yet been established on the RFP. On MST, the highest beta values are obtained in improved confinement discharges with pellet fueling. By using pellet injection to scan the plasma density during PPCD, we also achieve a scan of Ohmic input power due to the increase in plasma resistivity. We observe a factor of 3 or more increase in Ohmic power as we increase the density from 1*1019 to 3*10 19 m-3. Despite this increased Ohmic power, the electron contribution to beta is constant, suggesting a confinement limited beta for the RFP. The electrons and ions are classically well coupled in these cold, dense pellet fueled plasmas, so the increase in total beta at higher density is primarily due to the increased ion contribution. The interaction of pellet fueling and NBI heating is explored. Modeling of MST's neutral heating beam suggests an optimal density for beam power deposition of 2-3*1019 m-3. Low current, NBI heated discharges show evidence of an increased electron beta in this density range. Additionally, the fast ion population can enhance ablation as well as cause pellet deflection. Other exploratory experiments with the pellet injection system explore additional injection scenarios and expand the injector capabilities.

Investigating the source of anomalous PKP travel-times on south-Sandwich to Alaska paths

NASA Astrophysics Data System (ADS)

Frost, D. A.; Romanowicz, B. A.

2017-12-01

Inner core anisotropy was proposed thirty years ago to explain differences in travel times of inner core phases (PKIKP) on polar and equatorial paths (Morelli et al., 1986). Over time, models of inner core anisotropy have become very complex, with evidence for depth dependence, hemispherical variations, and other localised features. Some models propose the strength of anisotropy to be in excess of 4% in the western hemisphere of the inner core. This is difficult to reconcile with predictions from mineral physics and dynamical models of inner core growth. The strong anisotropy is confined to anomalous paths between earthquakes in the south Sandwich Islands and stations in Alaska. In contrast, the strength of inner core anisotropy obtained from measurements of PKPPKP travel times on polar paths does not exceed 1-2% (Bréger et al., 2000; Frost and Romanowicz, 2017). We re-examine the trends of PKIKP travel times on polar paths, in order to reconcile the different measurements and to determine whether discrepancies can be explained by structure in the mantle, the outer core, or localized strong anisotropy in the inner core. For this, we combine existing and new measurements, taking advantage of recent deployments of broadband arrays in Alaska and Antarctica.

Carbon impurities behavior and its impact on ion thermal confinement in high-ion-temperature deuterium discharges on the Large Helical Device

NASA Astrophysics Data System (ADS)

Mukai, K.; Nagaoka, K.; Takahashi, H.; Yokoyama, M.; Murakami, S.; Nakano, H.; Ida, K.; Yoshinuma, M.; Seki, R.; Kamio, S.; Fujiwara, Y.; Oishi, T.; Goto, M.; Morita, S.; Morisaki, T.; Osakabe, M.; LHD Experiment Group1, the

2018-07-01

The behavior of carbon impurities in deuterium plasmas and its impact on thermal confinement were investigated in comparison with hydrogen plasmas in the Large Helical Device (LHD). Deuterium plasma experiments have been started in the LHD and high-ion-temperature plasmas with central ion temperature (T i) of 10 keV were successfully obtained. The thermal confinement improvement could be sustained for a longer time compared with hydrogen plasmas. An isotope effect was observed in the time evolution of the carbon density profiles. A transiently peaked profile was observed in the deuterium plasmas due to the smaller carbon convection velocity and diffusivity in the deuterium plasmas compared with the hydrogen plasmas. The peaked carbon density profile was strongly correlated to the ion thermal confinement improvement. The peaking of the carbon density profile will be one of the clues to clarify the unexplained mechanisms for the formations of ion internal transport barrier and impurity hole on LHD. These results could also lead to a better understanding of the isotope effect in the thermal confinement in torus plasma.

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments

PubMed Central

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-01-01

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China’s HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress–strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure. PMID:28773157

Enhanced field emission properties of carbon nanotube bundles confined in SiO2 pits

NASA Astrophysics Data System (ADS)

Lim, Yu Dian; Grapov, Dmitry; Hu, Liangxing; Kong, Qinyu; Tay, Beng Kang; Labunov, Vladimir; Miao, Jianmin; Coquet, Philippe; Aditya, Sheel

2018-02-01

It has been widely reported that carbon nanotubes (CNTs) exhibit superior field emission (FE) properties due to their high aspect ratios and unique structural properties. Among the various types of CNTs, random growth CNTs exhibit promising FE properties due to their reduced inter-tube screening effect. However, growing random growth CNTs on individual catalyst islands often results in spread out CNT bundles, which reduces overall field enhancement. In this study, significant improvement in FE properties in CNT bundles is demonstrated by confining them in microfabricated SiO2 pits. Growing CNT bundles in narrow (0.5 μm diameter and 2 μm height) SiO2 pits achieves FE current density of 1-1.4 A cm-2, which is much higher than for freestanding CNT bundles (76.9 mA cm-2). From the Fowler Nordheim plots, confined CNT bundles show a higher field enhancement factor. This improvement can be attributed to the reduced bundle diameter by SiO2 pit confinement, which yields bundles with higher aspect ratios. Combining the obtained outcomes, it can be conclusively summarized that confining CNTs in SiO2 pits yields higher FE current density due to the higher field enhancement of confined CNTs.

Acoustic velocity in rift basin mudstones: effects of in situ stress and sample lithology, and its relation to formation strength

NASA Astrophysics Data System (ADS)

Zakharova, N. V.; Goldberg, D.

2017-12-01

Acoustic/sonic velocity (Vp) provides one of the best proxies for formation strength, which is essential for geomechanical modeling and formation evaluation. Vp-strength relations need to be built empirically for specific basins and/or rock types. Since velocity is stress- and frequency-dependent, such relations can be very sensitive to experimental conditions; therefore, it is important to quantify their effect on velocity values. In this study, we present confined velocity and strength measurements for over 70 samples from the Newark Rift basin, a candidate site for carbon sequestration, and one of the largest in a series of the Mesozoic rift basins on the eastern North-American coast. Acoustic velocity measurements were obtained for a range of confining pressures from 0 to 6,000 psi, roughly corresponding to in situ confining pressure range. Although, overall, Vp values tend to increase with increasing pressure, the degree of Vp response to stress varies dramatically from sample to sample, and does not appear to correlate directly to lithology or porosity. Select samples exhibit near-zero change in Vp with increasing confining pressure, while others are characterized by up to 15% Vp change with 3,000 psi increase in confining pressure. Compared to sonic logs, the low-stress Vp values usually underestimate sonic velocities, while high-stress values tend to overestimate them. Therefore, a systematic frequency-dependent core-log difference is not observed in these rift basin formations, but accounting for Vp dependence on confining pressure is important. We quantify the Vp-pressure dependence using laboratory acoustic measurements, and develop depth-dependent Vp-strength relation, which could be used with sonic logs for geomechanical analysis in similar Mesozoic rift basin formations.

Effect of spatial confinement on magnetic hyperthermia via dipolar interactions in Fe3O4 nanoparticles for biomedical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadat, M E; Patel, Ronak; Sookoor, Jason

2014-09-01

In this work, the effect of nanoparticle confinement on the magnetic relaxation of iron oxide (Fe3O4) nanoparticles (NP) was investigated by measuring the hyperthermia heating behavior in high frequency alternating magnetic field. Three different Fe3O4 nanoparticle systems having distinct nanoparticle configurations were studied in terms of magnetic hyperthermia heating rate and DC magnetization. All magnetic nanoparticle (MNP) systems were constructed using equivalent ~10nm diameter NP that were structured differently in terms of configuration, physical confinement, and interparticle spacing. The spatial confinement was achieved by embedding the Fe3O4 nanoparticles in the matrices of the polystyrene spheres of 100 nm, while themore » unconfined was the free Fe3O4 nanoparticles well-dispersed in the liquid via PAA surface coating. Assuming the identical core MNPs in each system, the heating behavior was analyzed in terms of particle freedom (or confinement), interparticle spacing, and magnetic coupling (or dipole-dipole interaction). DC magnetization data were correlated to the heating behavior with different material properties. Analysis of DC magnetization measurements showed deviation from classical Langevin behavior near saturation due to dipole interaction modification of the MNPs resulting in a high magnetic anisotropy. It was found that the Specific Absorption Rate (SAR) of the unconfined nanoparticle systems were significantly higher than those of confined (the MNPs embedded in the polystyrene matrix). This increase of SAR was found to be attributable to high Néel relaxation rate and hysteresis loss of the unconfined MNPs. It was also found that the dipole-dipole interactions can significantly reduce the global magnetic response of the MNPs and thereby decrease the SAR of the nanoparticle systems.« less

The status of Fast Ignition Realization Experiment (FIREX) and prospects for inertial fusion energy

NASA Astrophysics Data System (ADS)

Azechi, H.; FIREX Project Team

2016-05-01

Here we report recent progress for the fast ignition inertial confinement fusion demonstration. The fraction of low energy (< 1 MeV) component of the relativistic electron beam (REB), which efficiently heats the fuel core, increases by a factor of 4 by enhancing pulse contrast of heating laser and removing preformed plasma sources. Kilo-tesla magnetic field is studied to guide the diverging REB to the fuel core. The transport simulation of the REB accelerated by the heating laser in the externally applied and compressed magnetic field indicates that the REB can be guided efficiently to the fuel core. The integrated simulation shows > 4% of the heating efficiency and > 4 keV of ion temperature are achievable by using GEKKO-XII and LFEX, properly designed cone-fuel and an external magnetic field.

Experimental Investigation of the Influence of Confining Stress on Hard Rock Fragmentation Using a Conical Pick

NASA Astrophysics Data System (ADS)

Li, Xibing; Wang, Shaofeng; Wang, Shanyong

2018-01-01

High geostress is a prominent condition in deep excavations and affects the cuttability of deep hard rock. This study aims to determine the influence of confining stress on hard rock fragmentation as applied by a conical pick. Using a true triaxial test apparatus, static and coupled static and dynamic loadings from pick forces were applied to end faces of cubic rock specimens to break them under biaxial, uniaxial and stress-free confining stress conditions. The cuttability indices (peak pick force, insertion depth and disturbance duration), failure patterns and fragment sizes were measured and compared to estimate the effects of confining stress. The results show that the rock cuttabilities decreased in order from rock breakages under stress-free conditions to uniaxial confining stress and then to biaxial confining stress. Under biaxial confining stress, only flake-shaped fragments were stripped from the rock surfaces under the requirements of large pick forces or disturbance durations. As the level of uniaxial confining stress increased, the peak pick force and the insertion depth initially increased and then decreased, and the failure patterns varied from splitting to partial splitting and then to rock bursts with decreasing average fragment sizes. Rock bursts will occur under elastic compression via ultra-high uniaxial confining stresses. There are two critical uniaxial confining stress levels, namely stress values at which peak pick forces begin to decrease and improve rock cuttability, and those at which rock bursts initially occur and cutting safety decreases. In particular, hard rock is easiest to split safely and efficiently under stress-free conditions. Moreover, coupled static preloading and dynamic disturbance can increase the efficiency of rock fragmentation with increasing preloading levels and disturbance amplitudes. The concluding remarks confirm hard rock cuttability using conical pick, which can improve the applicability of mechanical excavation in deep hard rock masses.

Optical phonon modes of III-V nanoparticles and indium phosphide/II-VI core-shell nanoparticles: A Raman and infrared study

NASA Astrophysics Data System (ADS)

Manciu, Felicia Speranta

The prospects for realizing efficient nanoparticle light emitters in the visible/near IR for communications and bio-medical applications have benefited from progress in chemical fabrication of nanoparticles. III-V semiconductor nanopaticles such as GaP and InP are promising materials for the development of "blue" and "green" emitters, respectively, due to their large effective bandgaps. Enhanced emission efficiency has been achieved for core-shell nanoparticles, since inorganic shell materials increase electronic tunability and may decrease surface defects that often occur for nanoparticles capped with organic molecules. Also, the emission wavelength of InP nanoparticle cores can be tuned from green to red by changing the shell material in InP/II-VI core-shell nanoparticles. Investigations of phonon modes in nanocrystals are of both fundamental and applied interest. In the former case the optical phonon modes, such as surface/interface modes, are dependent on the nanoparticle dimensions, and also can provide information about dynamical properties of the nanoparticles and test the validity of various theoretical approaches. In the latter case the vibronic properties of nanoparticle emitters are controlled by confined phonons and modifications of the electron-phonon interaction by the confinement. Thus, the objective of the present thesis is the detailed study of the phonon modes of III-V nanoparticles (GaP and InP) and InP/II-VI core-shell nanoparticles by IR absorption and Raman scattering spectroscopies, and an elucidation of their complex vibrational properties. With the exception of three samples (two GaP and one InP), all samples were synthesized by a novel colloidal chemistry method, which does not requires added surfactant, but rather treatment of the corresponding precursors in octadecene noncoordinative solvent. Sample quality was characterized by ED, TEM and X-ray diffraction. Based on a comparison with a dielectric continuum model, the observed features in the IR and Raman results are assigned to the surface optical (SO) modes of the corresponding nanoparticles (InP and GaP), and to SO/interface modes for InP/II-VI core-shell nanoparticles. For the latter systems, an evaluation of the ratio of the shell material thickness to the core radius is achieved. Reasonable agreement is obtained between the Raman and FIR results, as well as with the calculations. (Abstract shortened by UMI.)

Coronal Heating by Magnetic Explosions

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Falconer, D. A.; Porter, Jason G.; Suess, Steven T.

1998-01-01

We build a case for the persistent strong coronal heating in active regions and the pervasive quasi-steady heating of the corona in quiet regions and coronal holes being driven in basically the same way as the intense transient heating in solar flares: by explosions of sheared magnetic fields in the cores of initially closed bipoles. We begin by summarizing the observational case for exploding sheared core fields being the drivers of a wide variety of flare events, with and without coronal mass ejections. We conclude that the arrangement of an event's flare heating, whether there is a coronal mass ejection, and the time and place of the ejection relative to the flare heating are all largely determined by four elements of the form and action the magnetic field: (1) the arrangement of the impacted, interacting bipoles participating in the event, (2) which of these bipoles are active (have sheared core fields that explode) and which are passive (are heated by injection from impacted active bipoles), (3) which core field explodes first, and (4) which core-field explosions are confined within the closed field of their bipoles and which ejectively open their bipoles.

Hypersonic vibrations of Ag@SiO2 (cubic core)-shell nanospheres.

PubMed

Sun, Jing Ya; Wang, Zhi Kui; Lim, Hock Siah; Ng, Ser Choon; Kuok, Meng Hau; Tran, Toan Trong; Lu, Xianmao

2010-12-28

The intriguing optical and catalytic properties of metal-silica core-shell nanoparticles, inherited from their plasmonic metallic cores together with the rich surface chemistry and increased stability offered by their silica shells, have enabled a wide variety of applications. In this work, we investigate the confined vibrational modes of a series of monodisperse Ag@SiO(2) (cubic core)-shell nanospheres synthesized using a modified Stöber sol-gel method. The particle-size dependence of their mode frequencies has been mapped by Brillouin light scattering, a powerful tool for probing hypersonic vibrations. Unlike the larger particles, the observed spheroidal-like mode frequencies of the smaller ones do not scale with inverse diameter. Interestingly, the onset of the deviation from this linearity occurs at a smaller particle size for higher-energy modes than for lower-energy ones. Finite element simulations show that the mode displacement profiles of the Ag@SiO(2) core-shells closely resemble those of a homogeneous SiO(2) sphere. Simulations have also been performed to ascertain the effects that the core shape and the relative hardness of the core and shell materials have on the vibrations of the core-shell as a whole. As the vibrational modes of a particle have a bearing on its thermal and mechanical properties, the findings would be of value in designing core-shell nanostructures with customized thermal and mechanical characteristics.

Confinement of translated field-reversed configurations

NASA Astrophysics Data System (ADS)

Tuszewski, M.; Armstrong, W. T.; Chrien, R. E.; Klingner, P. L.; McKenna, K. F.; Rej, D. J.; Sherwood, E. G.; Siemon, R. E.

1986-03-01

The confinement properties of translating field-reversed configurations (FRC) in the FRX-C/T device [Phys. Fluids 29, (1986)] are analyzed and compared to previous data without translation and to available theory. Translation dynamics do not appear to appreciably modify the FRC confinement. Some empirical scaling laws with respect to various plasma parameters are extracted from the data. These are qualitatively similar to those obtained in the TRX-1 device [Phys. Fluids 28, 888 (1985)] without translation and with a different formation method. Translation with a static gas fill offers new opportunities such as improved particle confinement or refueling of the FRC particle inventory.

Core barrier formation near integer q surfaces in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Austin, M. E.; Gentle, K. W.; Burrell, K. H.

2006-08-15

Recent DIII-D experiments have significantly improved the understanding of internal transport barriers (ITBs) that are triggered close to the time when an integer value of the minimum in q is crossed. While this phenomenon has been observed on many tokamaks, the extensive transport and fluctuation diagnostics on DIII-D have permitted a detailed study of the generation mechanisms of q-triggered ITBs as pertaining to turbulence suppression dynamics, shear flows, and energetic particle modes. In these discharges, the evolution of the q profile is measured using motional Stark effect polarimetry and the integer q{sub min} crossings are further pinpointed in time bymore » the observation of Alfven cascades. High time resolution measurements of the ion and electron temperatures and the toroidal rotation show that the start of improved confinement is simultaneous in all three channels, and that this event precedes the traversal of integer q{sub min} by 5-20 ms. There is no significant low-frequency magnetohydrodynamic activity prior to or just after the crossing of the integer q{sub min} and hence magnetic reconnection is determined not to be the precipitant of the confinement change. Instead, results from the GYRO code point to the effects of zonal flows near low order rational q values as playing a role in ITB triggering. A reduction in local turbulent fluctuations is observed at the start of the temperature rise and, concurrently, an increase in turbulence poloidal flow velocity and flow shear is measured with the beam emission spectroscopy diagnostic. For the case of a transition to an enduring internal barrier the fluctuation level remains at a reduced amplitude. The timing and nature of the temperature, rotation, and fluctuation changes leading to internal barriers suggests transport improvement due to increased shear flow arising from the zonal flow structures.« less

A Novel Shape Memory Alloy Annuloplasty Ring for Minimally Invasive Surgery: Design, Fabrication, and Evaluation

PubMed Central

Purser, Molly F.; Richards, Andrew L.; Cook, Richard C.; Osborne, Jason A.; Cormier, Denis R.; Buckner, Gregory D.

2013-01-01

A novel annuloplasty ring with a shape memory alloy core has been developed to facilitate minimally invasive mitral valve repair. In its activated (austenitic) phase, this prototype ring has comparable mechanical properties to commercial semi-rigid rings. In its pre-activated (martensitic) phase, this ring is flexible enough to be introduced through an 8-mm trocar and easily manipulated with robotic instruments within the confines of a left atrial model. The core is constructed of 0.50 mm diameter NiTi, which is maintained below its martensitic transition temperature (24 °C) during deployment and suturing. After suturing, the ring is heated above its austenitic transition temperature (37 °C, normal human body temperature) enabling the NiTi core to attain its optimal geometry and stiffness characteristics indefinitely. This article summarizes the design, fabrication, and evaluation of this prototype ring. Experimental results suggest that the NiTi core ring could be a viable alternative to flexible bands in robot-assisted minimally invasive mitral valve repair. PMID:20652747

Time-resolved photoluminescence study of CdSe/CdMnS/CdS core/multi-shell nanoplatelets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, J. R.; Department of Physics, State University of New York, University at Buffalo, Buffalo, New York 14260; Delikanli, S.

2016-06-13

We used photoluminescence spectroscopy to resolve two emission features in CdSe/CdMnS/CdS and CdSe/CdS core/multi-shell nanoplatelet heterostructures. The photoluminescence from the magnetic sample has a positive circular polarization with a maximum centered at the position of the lower energy feature. The higher energy feature has a corresponding signature in the absorption spectrum; this is not the case for the low-energy feature. We have also studied the temporal evolution of these features using a pulsed-excitation/time-resolved photoluminescence technique to investigate their corresponding recombination channels. A model was used to analyze the temporal dynamics of the photoluminescence which yielded two distinct timescales associated withmore » these recombination channels. The above results indicate that the low-energy feature is associated with recombination of electrons with holes localized at the core/shell interfaces; the high-energy feature, on the other hand, is excitonic in nature with the holes confined within the CdSe cores.« less

FORGE Milford Triaxial Test Data and Summary from EGI labs

DOE Data Explorer

Joe Moore

2016-03-01

Six samples were evaluated in unconfined and triaxial compression, their data are included in separate excel spreadsheets, and summarized in the word document. Three samples were plugged along the axis of the core (presumed to be nominally vertical) and three samples were plugged perpendicular to the axis of the core. A designation of "V"indicates vertical or the long axis of the plugged sample is aligned with the axis of the core. Similarly, "H" indicates a sample that is nominally horizontal and cut orthogonal to the axis of the core. Stress-strain curves were made before and after the testing, and are included in the word doc.. The confining pressure for this test was 2800 psi. A series of tests are being carried out on to define a failure envelope, to provide representative hydraulic fracture design parameters and for future geomechanical assessments. The samples are from well 52-21, which reaches a maximum depth of 3581 ft +/- 2 ft into a gneiss complex.

Single-polarization hollow-core square photonic bandgap waveguide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eguchi, Masashi, E-mail: megu@ieee.org; Tsuji, Yasuhide, E-mail: y-tsuji@mmm.muroran-it.ac.jp

Materials with a periodic structure have photonic bandgaps (PBGs), in which light can not be guided within certain wavelength ranges; thus light can be confined within a low-index region by the bandgap effect. In this paper, rectangular-shaped hollow waveguides having waveguide-walls (claddings) using the PBG have been discussed. The design principle for HE modes of hollow-core rectangular PBG waveguides with a Bragg cladding consisting of alternating high- and low-index layers, based on a 1D periodic multilayer approximation for the Bragg cladding, is established and then a novel single-polarization hollow-core square PBG waveguide using the bandgap difference between two polarized wavesmore » is proposed. Our results demonstrated that a single-polarization guiding can be achieved by using the square Bragg cladding structure with different layer thickness ratios in the mutually orthogonal directions and the transmission loss of the guided mode in a designed hollow-core square PBG waveguide is numerically estimated to be 0.04 dB/cm.« less

Novel intercore-cladding lithium niobate thin film coated MOEMS fiber sensor/modulator

NASA Technical Reports Server (NTRS)

Jamlson, Tracee L.; Konreich, Phillip; Yu, Chung

2005-01-01

A MOEMS fiber modulator/sensor is fabricated by depositing a lithium niobate sol-gel thin film between the core and cladding of a fiber preform. The preform is then drawn into 125-micron fibers. Such a MOEMS modulator design is expected to enhance existing lithium niobate undersea acousto-optic sound wave detectors. In our proposed version, the lithium niobate thin film alters the ordinary silica core/cladding boundary conditions such that, when a stress or strain is applied to the fiber, the core light confinement factor changes, leading to modulation of fiber light transmission. Test results of the lithium niobate embedded fiber with a 1550-nm, 4-mW laser source revealed a reduction in light transmission with applied tension. As a comparison, using the same laser source, an ordinary silica core/cladding fiber did not exhibit any reduction in transmitted light when the same strain was applied. Further experimental work and theoretical analysis is ongoing.

A nitrogen-doped 3D hierarchical carbon/sulfur composite for advanced lithium sulfur batteries

NASA Astrophysics Data System (ADS)

Liu, Xiaoyan; Huang, Wenlong; Wang, Dongdong; Tian, Jianhua; Shan, Zhongqiang

2017-07-01

Hybrid nanostructures containing one-dimensional (1D) carbon nanotubes (CNTs) and three-dimensional (3D) mesoporous carbon sphere have many promising applications due to their unique physical chemical properties. In this study, a novel 3D hierarchical carbon material (MCCNT) composed of mesoporous carbon sphere core and nitrogen rich CNTs shell is successfully prepared via an aerosol spray and subsequent chemical vapor deposition (CVD) processes. Owning to its well defined porous structure and favorable conductive framework, MCCNT is used as a potential sulfur host in lithium sulfur batteries through a classic melt-diffusion method. When cycled at a current density of 0.2 C (1 C = 1675 mA h g-1), it delivers an initial capacity as high as 1438.7 mAh g-1. Even if the current density increase to 1 C, the specific capacity still remain up to 534.6 mAh g-1 after 300 cycles. The enhanced electrochemical performance can be attributed to the hybrid structure of MCCNT, in which, the porous core works as a host to confine sulfur and accommodate volume expansion and the external CNTs provide excellent electron and ion conductive frame work. Furthermore, the in-situ doped nitrogen on the surface of CNTs enables effective trapping of lithium polysulfides, leading to a much-improved cycling performance.

Divertor power load feedback with nitrogen seeding in ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Kallenbach, A.; Dux, R.; Fuchs, J. C.; Fischer, R.; Geiger, B.; Giannone, L.; Herrmann, A.; Lunt, T.; Mertens, V.; McDermott, R.; Neu, R.; Pütterich, T.; Rathgeber, S.; Rohde, V.; Schmid, K.; Schweinzer, J.; Treutterer, W.; ASDEX Upgrade Team

2010-05-01

Feedback control of the divertor power load by means of nitrogen seeding has been developed into a routine operational tool in the all-tungsten clad ASDEX Upgrade tokamak. For heating powers above about 12 MW, its use has become inevitable to protect the divertor tungsten coating under boronized conditions. The use of nitrogen seeding is accompanied by improved energy confinement due to higher core plasma temperatures, which more than compensates the negative effect of plasma dilution by nitrogen on the neutron rate. This paper describes the technical details of the feedback controller. A simple model for its underlying physics allows the prediction of its behaviour and the optimization of the feedback gain coefficients used. Storage and release of nitrogen in tungsten surfaces were found to have substantial impact on the behaviour of the seeded plasma, resulting in increased nitrogen consumption with unloaded walls and a latency of nitrogen release over several discharges after its injection. Nitrogen is released from tungsten plasma facing components with moderate surface temperature in a sputtering-like process; therefore no uncontrolled excursions of the nitrogen wall release are observed. Overall, very stable operation of the high-Z tokamak is possible with nitrogen seeding, where core radiative losses are avoided due to its low atomic charge Z and a high ELM frequency is maintained.

[Analysis of Cr in soil by LIBS based on conical spatial confinement of plasma].

PubMed

Lin, Yong-Zeng; Yao, Ming-Yin; Chen, Tian-Bing; Li, Wen-Bing; Zheng, Mei-Lan; Xu, Xue-Hong; Tu, Jian-Ping; Liu, Mu-Hua

2013-11-01

The present study is to improve the sensitivity of detection and reduce the limit of detection in detecting heavy metal of soil by laser induced breakdown spectroscopy (LIBS). The Cr element of national standard soil was regarded as the research object. In the experiment, a conical cavity with small diameter end of 20 mm and large diameter end of 45 mm respectively was installed below the focusing lens near the experiment sample to mainly confine the signal transmitted by plasma and to some extent to confine the plasma itself in the LIBS setup. In detecting Cr I 425.44 nm, the beast delay time gained from experiment is 1.3 micros, and the relative standard deviation is below 10%. Compared with the setup of non-spatial confinement, the spectral intensity of Cr in the soil sample was enhanced more than 7%. Calibration curve was established in the Cr concentration range from 60 to 400 microg x g(-1). Under the condition of spatial confinement, the liner regression coefficient and the limit of detection were 0.997 71 and 18.85 microg x g(-1) respectively, however, the regression coefficient and the limit of detection were 0.991 22 and 36.99 microg x g(-1) without spatial confinement. So, this shows that conical spatial confinement can/improve the sensitivity of detection and enhance the spectral intensity. And it is a good auxiliary function in detecting Cr in the soil by laser induced breakdown spectroscopy.

System of extraction of volatiles from soil using microwave processes

NASA Technical Reports Server (NTRS)

Ethridge, Edwin C. (Inventor); Kaukler, William F. (Inventor)

2013-01-01

A device for the extraction and collection of volatiles from soil or planetary regolith. The device utilizes core drilled holes to gain access to underlying volatiles below the surface. Microwave energy beamed into the holes penetrates through the soil or regolith to heat it, and thereby produces vapor by sublimation. The device confines and transports volatiles to a cold trap for collection.

0-6781 : improved nighttime work zone channelization in confined urban projects.

DOT National Transportation Integrated Search

2014-08-01

Turning into and out of driveways in confined or : dense urban work zones can present significant : challenges to drivers, especially during nighttime : conditions when other visual cues about the : driveways may be masked in the dark. These : challe...

Railgun armature velocity improvement, SBIR phase 2

NASA Astrophysics Data System (ADS)

Thurmond, Leo E.; Bauer, David P.

1992-08-01

Railgun hypervelocity performance has not been repeatably demonstrated at velocities over 6 km/s. A significant performance limiting phenomena is the formation of secondary current paths in parallel with the main projectile accelerating plasma. A confined plasma armature technique was developed to prevent secondary armature formation. Confinement prevents loss of ionized material from the plasma armature and thereby prevents formation of a low rail-to-rail conductance. We controlled pressure in the confined armature via controlled venting through ports in the rails. Railgun tests with the confined armature show that sealing at the rail-confinement vessel interface is critical and difficult to achieve. Our tests show that during low seal leakage operation secondaries are prevented. However, maintaining good seal for the entire launch is very difficult.

Non-covalent synthesis of supermicelles with complex architectures using spatially confined hydrogen-bonding interactions

PubMed Central

Li, Xiaoyu; Gao, Yang; Boott, Charlotte E.; Winnik, Mitchell A.; Manners, Ian

2015-01-01

Nature uses orthogonal interactions over different length scales to construct structures with hierarchical levels of order and provides an important source of inspiration for the creation of synthetic functional materials. Here, we report the programmed assembly of monodisperse cylindrical block comicelle building blocks with crystalline cores to create supermicelles using spatially confined hydrogen-bonding interactions. We also demonstrate that it is possible to further program the self-assembly of these synthetic building blocks into structures of increased complexity by combining hydrogen-bonding interactions with segment solvophobicity. The overall approach offers an efficient, non-covalent synthesis method for the solution-phase fabrication of a range of complex and potentially functional supermicelle architectures in which the crystallization, hydrogen-bonding and solvophobic interactions are combined in an orthogonal manner. PMID:26337527

Modelling of Field-Reversed Configuration Experiment with Large Safety Factor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steinhauer, L; Guo, H; Hoffman, A

2005-11-28

The Translation-Confinement-Sustainment facility has been operated in the 'translation-formation' mode in which a plasma is ejected at high-speed from a {theta}-pinch-like source into a confinement chamber where it settles into a field-reversed-configuration state. Measurements of the poloidal and toroidal field have been the basis of modeling to infer the safety factor. It is found that the edge safety factor exceeds two, and that there is strong forward magnetic shear. The high-q arises because the large elongation compensates for the modest ratio of toroidal-to-poloidal field in the plasma. This is the first known instance of a very high-{beta} plasma with amore » safety factor greater than unity. Two-fluid modeling of the measurements also indicate several other significant features: a broad 'transition layer' at the plasma boundary with probable line-tying effects, complex high-speed flows, and the appearance of a two-fluid minimum-energy state in the plasma core. All these features may contribute to both the stability and good confinement of the plasma.« less

Confinement properties of tokamak plasmas with extended regions of low magnetic shear

NASA Astrophysics Data System (ADS)

Graves, J. P.; Cooper, W. A.; Kleiner, A.; Raghunathan, M.; Neto, E.; Nicolas, T.; Lanthaler, S.; Patten, H.; Pfefferle, D.; Brunetti, D.; Lutjens, H.

2017-10-01

Extended regions of low magnetic shear can be advantageous to tokamak plasmas. But the core and edge can be susceptible to non-resonant ideal fluctuations due to the weakened restoring force associated with magnetic field line bending. This contribution shows how saturated non-linear phenomenology, such as 1 / 1 Long Lived Modes, and Edge Harmonic Oscillations associated with QH-modes, can be modelled accurately using the non-linear stability code XTOR, the free boundary 3D equilibrium code VMEC, and non-linear analytic theory. That the equilibrium approach is valid is particularly valuable because it enables advanced particle confinement studies to be undertaken in the ordinarily difficult environment of strongly 3D magnetic fields. The VENUS-LEVIS code exploits the Fourier description of the VMEC equilibrium fields, such that full Lorenzian and guiding centre approximated differential operators in curvilinear angular coordinates can be evaluated analytically. Consequently, the confinement properties of minority ions such as energetic particles and high Z impurities can be calculated accurately over slowing down timescales in experimentally relevant 3D plasmas.

Lithium-ion battery electrolyte mobility at nano-confined graphene interfaces

PubMed Central

Moeremans, Boaz; Cheng, Hsiu-Wei; Hu, Qingyun; Garces, Hector F.; Padture, Nitin P.; Renner, Frank Uwe; Valtiner, Markus

2016-01-01

Interfaces are essential in electrochemical processes, providing a critical nanoscopic design feature for composite electrodes used in Li-ion batteries. Understanding the structure, wetting and mobility at nano-confined interfaces is important for improving the efficiency and lifetime of electrochemical devices. Here we use a Surface Forces Apparatus to quantify the initial wetting of nanometre-confined graphene, gold and mica surfaces by Li-ion battery electrolytes. Our results indicate preferential wetting of confined graphene in comparison with gold or mica surfaces because of specific interactions of the electrolyte with the graphene surface. In addition, wetting of a confined pore proceeds via a profoundly different mechanism compared with wetting of a macroscopic surface. We further reveal the existence of molecularly layered structures of the confined electrolyte. Nanoscopic confinement of less than 4–5 nm and the presence of water decrease the mobility of the electrolyte. These results suggest a lower limit for the pore diameter in nanostructured electrodes. PMID:27562148

Core-shell designed scaffolds for drug delivery and tissue engineering.

PubMed

Perez, Roman A; Kim, Hae-Won

2015-07-01

Scaffolds that secure and deliver therapeutic ingredients like signaling molecules and stem cells hold great promise for drug delivery and tissue engineering. Employing a core-shell design for scaffolds provides a promising solution. Some unique methods, such as co-concentric nozzle extrusion, microfluidics generation, and chemical confinement reactions, have been successful in producing core-shelled nano/microfibers and nano/microspheres. Signaling molecules and drugs, spatially allocated to the core and/or shell part, can be delivered in a controllable and sequential manner for optimal therapeutic effects. Stem cells can be loaded within the core part on-demand, safely protected from the environments, which ultimately affords ex vivo culture and in vivo tissue engineering. The encapsulated cells experience three-dimensional tissue-mimic microenvironments in which therapeutic molecules are secreted to the surrounding tissues through the semi-permeable shell. Tuning the material properties of the core and shell, changing the geometrical parameters, and shaping them into proper forms significantly influence the release behaviors of biomolecules and the fate of the cells. This topical issue highlights the immense usefulness of core-shell designs for the therapeutic actions of scaffolds in the delivery of signaling molecules and stem cells for tissue regeneration and disease treatment. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Remediation of hydrophobic, persistent pollutants using a magnetic permanently confined micelle array (Mag-PCMA)

NASA Astrophysics Data System (ADS)

Clark, K. K.; Keller, A. A.

2009-12-01

Natural and anthropogenic factors have resulted in the deposition of hydrophobic organic contaminants (HOCs) like PAHs and PCBs in elevated levels in soils and sediments. Currently there are 150 Superfund sites in the United States with contaminated sediments. Dredging is the most common practice for restoring Superfund sites to their preexisting conditions; this requires the transport of large volumes of material off-site for additional storage or processing. Our lab has designed a nano-hybrid material that can be used on-site; it combines a magnetic nanoscale iron oxide core coated with a cationic surfactant and is encased in a mesoporous silica matrix, called magnetic permanently confined micelle arrays, (Mag-PCMAs). This sorbent has been designed to remove HOCs from such scenarios. Surfactants are important in the enhancement of transport from binding sites in nature, such as organic matter, onto sorbents and other recoverable materials. The sorbent’s magnetic core allows for rapid separation by applying a magnetic field. It has also been shown to be reusable and maintain a removal efficiency of 95% over five cycles of reuse. Preliminary sorption studies show that the sorbent is capable of removing up to 98% of hydrophobic compounds from aqueous media. Current sorption studies are being done to test the efficiency of removing PAHs and PCBs from sediments, soils, and suspended sediments. Physicochemical properties that will influence the desorption/sorption hysteresis are being characterized to determine which properties enhance desorption from the contaminated media onto the Mag-PCMAs. Relevant applications are diverse as this material has the potential to recover a variety of HOCs in both ex situ and in situ remediation scenarios. Magnetic Permanently Confined Micelle Arrays

Anomalous current diffusion and improved confinement in the HT-6M tohamak

NASA Astrophysics Data System (ADS)

Gao, X.; Li, J. G.; Wan, Y. X.; Huo, Y. P.; Guo, W. K.; Fan, S. P.; Yu, C. X.; Luo, J. R.; Yin, F. X.; Meng, Y. D.; Zheng, L.; Yin, F.; Lin, B. L.; Zhang, S. Y.; Wang, S. Y.; Lu, H. J.; Liu, S. X.; Tong, X. D.; Ding, L. C.; Wu, Z. Y.; Yin, X. J.; Guo, Q. L.; Gong, X. Z.; Wu, X. C.; Zhao, J. Y.; Xi, J. S.

1994-10-01

Current diffusion was studied during edge ohmic heating (EOH) experiments in the HT-6M tokamak. The EOH power system makes the plasma current linearly ramp up from an initial steady state ( Ip=55kA) to a second steady state ( Ip=60kA) at a fast ramp rate of 12 MA/s. A stable discharge of an improved confinement was observed experimentally in the HT-6M tokamak after the plasma current was ramped to rise rapidly to a second steady state. The plasma current is ramped up much faster than both the classical skin time and neoclassical skin time. Fast current ramp up increases the anomalous current diffusion. The measured values of {β P+l i}/{2} and the soft X-ray sawtooth inversion radius imply the anomalous current penetration. The mechanism of anomalous penetration and improved confinement is discussed.

A full virial analysis of the prestellar cores in the Ophiuchus molecular cloud

NASA Astrophysics Data System (ADS)

Pattle, Kate; Ward-Thompson, Derek

2015-08-01

We present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell (JCMT) Gould Belt Survey with the SCUBA-2 instrument. We demonstrate methods for combining these data with HARP CO, Herschel and IRAM N2H+ observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus.We perform a full virial analysis on the starless cores in Ophiuchus, including external pressure. We find that the majority of our cores are either bound or virialised, and that gravity and external pressure are typically of similar importance in confining cores. We find that the critical Bonnor-Ebert stability criterion is not a good indicator of the boundedness of our cores. We determine that N2H+ is a good tracer of the bound material of prestellar cores, and find that non-thermal linewidths decrease substantially between the intermediate-density gas traced by C18O and the high-density gas traced by N2H+, indicating the dissipation of turbulence within cores.We find variation from region to region in the virial balance of cores and the relative contributions of pressure and gravity to core support, as well as variation in the degree to which turbulence is dissipated within cores and in the relative numbers of protostellar and starless sources. We find further support for our previous hypothesis of a global evolutionary gradient from southwest to northeast across Ophiuchus, indicating sequential star formation across the region.

Improved confinement region without large magnetohydrodynamic activity in TPE-RX reversed-field pinch plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yambe, Kiyoyuki; Hirano, Yoichi; Sakakita, Hajime

2014-11-15

We found that spontaneous improved confinement was brought about depending on the operating region in the Toroidal Pinch Experiment-Reversed eXperiment (TPE-RX) reversed-field pinch plasma [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. Gradual decay of the toroidal magnetic field at plasma surface B{sub tw} reversal makes it possible to realize a prolonged discharge, and the poloidal beta value and energy confinement time increase in the latter half of the discharge, where reversal and pinch parameters become shallow and low, respectively. In the latter half of the discharge, the plasma current and volume-averaged toroidal magnetic field 〈B{sub t}〉 increasemore » again, the electron density slowly decays, the electron temperature and soft X-ray radiation intensity increase, and the magnetic fluctuations are markedly reduced. In this period of improved confinement, the value of (〈B{sub t}〉-B{sub tw})/B{sub pw}, where B{sub pw} is the poloidal magnetic field at the plasma surface, stays almost constant, which indicates that the dynamo action occurs without large magnetohydrodynamic activities.« less

Use of a bilayer lattice-matched AlInGaN barrier for improving the channel carrier confinement of enhancement-mode AlInGaN/GaN hetero-structure field-effect transistors

NASA Astrophysics Data System (ADS)

Rahbardar Mojaver, Hassan; Gosselin, Jean-Lou; Valizadeh, Pouya

2017-06-01

A quaternary lattice-matched layer structure based on employing a bilayer barrier for improving the carrier confinement in the channel of enhancement-mode metal-face c-plane wurtzite AlInGaN/GaN hetero-structure field effect transistors (HFETs) is for the first time proposed. Using the commercial self-consistent Poisson-Schrödinger solver Nextnano, electronic properties of the proposed hetero-structure, including the sheet charge density and carrier confinement on the GaN side of the hetero-interface, are evaluated. Based on these evaluations, it is shown that while the proposed layer structure substantially improves the carrier confinement in the GaN channel layer, it also upholds the merits of employing a lattice-matched barrier towards achieving an enhancement-mode operation (i.e., in the absence of the piezoelectric effect). According to these simulations, in terms of maintaining the required positive threshold-voltage for the enhancement-mode operation, it is also shown that the proposed layer structure substantially outperforms the quaternary AlInGaN/GaN HFETs employing a thin AlN spacer layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, C G; Denison, A B; Weber, M H

We employed the two detector coincident Doppler Broadening Technique (coPAS) to investigate Ag, Au and Ag/Au alloy quantum dots of varying sizes which were deposited in thin layers on glass slides. The Ag quantum dots range from 2 to 3 nm in diameter, while the Ag/Au alloy quantum dots exhibit Ag cores of 2 nm and 3 nm and Au shells of varying thickness. We investigate the possibility of positron confinement in the Ag core due to positron affinity differences between Ag and Au. We describe the results and their significance to resolving the issue of whether positrons annihilate withinmore » the quantum dot itself or whether surface and positron escape effects play an important role.« less

Low-loss polarization-maintaining terahertz fiber based on central air hole movements

NASA Astrophysics Data System (ADS)

Wu, Zhiqing; Li, Qingzhi; Xia, Handing; Shi, Zhaohua; Zhou, Xiaoyan; Deng, Qinghua; Wu, Weidong

2018-04-01

We report a type of single-hole core photonic crystal fiber for low-loss polarization-maintaining terahertz (THz) wave guidance. Simulation results show that high birefringence at a level of 10 - 2 can be obtained by a design of minor position adjustment of the central air hole. Low effective material loss can be achieved because of the introduced central air hole. The strategy of the central air hole movements is also applicable for the three-hole core THz photonic crystal fibers. Other transmission characteristics including single-mode condition, power fraction, confinement loss, and dispersion were discussed in detail. It is quite clear that the proposal facilitates the fabrication process due to the simple structure.

Porous silicon omnidirectional mirrors and distributed Bragg reflectors for planar waveguide applications

NASA Astrophysics Data System (ADS)

Xifré-Pérez, E.; Marsal, L. F.; Ferré-Borrull, J.; Pallarès, J.

2007-09-01

The use of omnidirectional mirrors (an special case of distributed Bragg reflectors) as cladding for planar waveguides is proposed and analyzed. The proposed structure is an all-porous silicon multilayer consisting of a core layer inserted between two omnidirectional mirrors. The transfer matrix method is applied for the modal analysis. The influence of the parameters of the waveguide structure on the guided modes is analyzed. These parameters are the layer thickness and number of periods of the omnidirectional mirror, and the refractive index and thickness of the core layer. Finally, the confinement of the omnidirectional mirror cladding is analyzed with respect to two other different distributed Bragg reflector claddings.

A New Analysis of the Two Classical ZZ Ceti White Dwarfs GD 165 and Ross 548. II. Seismic Modeling

NASA Astrophysics Data System (ADS)

Giammichele, N.; Fontaine, G.; Brassard, P.; Charpinet, S.

2016-03-01

We present the second of a two-part seismic analysis of the bright, hot ZZ Ceti stars GD 165 and Ross 548. In this second part, we report the results of detailed searches in parameter space for identifying an optimal model for each star that can account well for the observed periods, while being consistent with the spectroscopic constraints derived in our first paper. We find optimal models for each target that reproduce the six observed periods well within ∼0.3% on the average. We also find that there is a sensitivity on the core composition for Ross 548, while there is practically none for GD 165. Our optimal model of Ross 548, with its thin envelope, indeed shows weight functions for some confined modes that extend relatively deep into the interior, thus explaining the sensitivity of the period spectrum on the core composition in that star. In contrast, our optimal seismic model of its spectroscopic sibling, GD 165 with its thick envelope, does not trap/confine modes very efficiently, and we find weight functions for all six observed modes that do not extend into the deep core, hence accounting for the lack of sensitivity in that case. Furthermore, we exploit after the fact the observed multiplet structure that we ascribe to rotation. We are able to map the rotation profile in GD 165 (Ross 548) over the outermost ∼20% (∼5%) of its radius, and we find that the profile is consistent with solid-body rotation.

Changes in porosity and organic matter phase distribution monitored by NMR relaxometry following hydrous pyrolysis under uniaxial confinement

USGS Publications Warehouse

Washburn, Kathryn E.; Birdwell, Justin E.; Lewan, Michael D.; Miller, Michael; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

2013-01-01

Artificial maturation methods are used to induce changes in source rock thermal maturity without the uncertainties that arise when comparing natural samples from a particular basin that often represent different levels of maturation and different lithofacies. A novel uniaxial confinement clamp was used on Woodford Shale cores in hydrous pyrolysis experiments to limit sample expansion by simulating the effect of overburden present during thermal maturation in natural systems. These samples were then subjected to X-ray computed tomography (X-CT) imaging and low-field nuclear magnetic resonance (LF-NMR) relaxometry measurements. LF-NMR relaxometry is a noninvasive technique commonly used to measure porosity and pore-size distributions in fluid-filled porous media, but may also measure hydrogen present in hydrogen-bearing organic solids. Standard T1 and T2 relaxation distributions were determined and two dimensional T1-T2 correlation measurements were performed on the Woodford Shale cores. The T1-T2 correlations facilitate resolution of organic phases in the system. The changes observed in NMR-relaxation times correspond to bitumen and lighter hydrocarbon production that occur as source rock organic matter matures. The LF-NMR porosities of the core samples at maximum oil generation are significantly higher than porosities measured by other methods. This discrepancy likely arises from the measurement of highly viscous organic constituents in addition to fluid-filled porosity. An unconfined sample showed shorter relaxation times and lower porosity. This difference is attributed to the lack of fractures observed in the unconfined sample by X-CT.

Improved Performance of an Optically Pumped Mid-Infrared Acetylene-Filled Hollow-Core Fiber Laser

NASA Astrophysics Data System (ADS)

Dadashzadeh, Neda

The focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 mum and 3.17 mum lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 mum using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 microm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 muJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M2 measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M2 was investigated at several input pump powers in addition to the reproducibility checks. M 2 of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 muJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers.

First identification and characterization of Borrobol‐type tephra in the Greenland ice cores: new deposits and improved age estimates

PubMed Central

Davies, Siwan M.; Guðmundsdóttir, Esther R.; Abbott, Peter M.; Pearce, Nicholas J. G.

2018-01-01

ABSTRACT Contiguous sampling of ice spanning key intervals of the deglaciation from the Greenland ice cores of NGRIP, GRIP and NEEM has revealed three new silicic cryptotephra deposits that are geochemically similar to the well‐known Borrobol Tephra (BT). The BT is complex and confounded by the younger closely timed and compositionally similar Penifiler Tephra (PT). Two of the deposits found in the ice are in Greenland Interstadial 1e (GI‐1e) and an older deposit is found in Greenland Stadial 2.1 (GS‐2.1). Until now, the BT was confined to GI‐1‐equivalent lacustrine sequences in the British Isles, Sweden and Germany, and our discovery in Greenland ice extends its distribution and geochemical composition. However, the two cryptotephras that fall within GI‐1e ice cannot be separated on the basis of geochemistry and are dated to 14358 ± 177 a b2k and 14252 ± 173 a b2k, just 106 ± 3 years apart. The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI‐1e events identified in the ice‐cores or that it relates to just one of the ice‐core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice‐cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine sediment cores from the North Iceland Shelf (ca. 17179‐16754 cal a BP). Despite showing similarities to the BT, this deposit can be distinguished on the basis of lower CaO and TiO2 and is a valuable new tie‐point that could eventually be used in high‐resolution marine records to compare the climate signals from the ocean and atmosphere. PMID:29576671

Edge Plasma behavior during Improved Confinement by Lower Hybrid Wave Heating in HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Li, Jian-gang; Bao, Yi; Luo, Jia-rong; Wan, Bao-nian; Liu, Yue-xiu; Gong, Xian-zu; Chen, Jun-ling; Liang, Yun-feng

2002-10-01

Lower hybrid heating (LHH) has been successfully carried out in the HT-6M tokamak. The H-mode has been obtained with a power threshold of 50 kW under a boronized wall condition. Both energy and particle confinements have been improved along with a dropped edge plasma density and an increase electron temperature during the LHH phase. A negative Er well plays a key role of triggering and sustaining the good confinement. Both electrostatic fluctuation of the plasma potential and the density fluctuations dropped to an ultra-low level. The observation of an enhanced Er shear before the reduction in turbulence level is consistent with an increased Er shear as the cause of turbulence suppression.

Superwettability-Induced Confined Reaction toward High-Performance Flexible Electrodes.

PubMed

Xiong, Weiwei; Liu, Hongliang; Zhou, Yahong; Ding, Yi; Zhang, Xiqi; Jiang, Lei

2016-05-18

To find a general strategy to realize confinement of the conductive layer for high-performance flexible electrodes, with improved interfacial adhesion and high conductivity, is of important scientific significance. In this work, superwettability-induced confined reaction is used to fabricate high-performance flexible Ag/polymer electrodes, showing significantly improved silver conversion efficiency and interfacial adhesion. The as-prepared flexible electrodes by superhydrophilic polymeric surface under oil are highly conductive with an order of magnitude higher than the Ag/polymer electrodes obtained from original polymeric surface. The high conductivity achieved via superhydrophilic confinement is ascribed to the fact that the superhydrophilic polymeric surface can enhance the reaction rate of silver deposition and reduce the size of silver nanoparticles to achieve the densest packing. This new approach will provide a simple method to fabricate flexible and highly conductive Ag/polymer electrodes with excellent adhesion between the conductive layer and the substrate, and can be extended to other metal/polymeric electrodes or alloy/polymeric electrodes.

Laboratory Investigation of Coal Deformation Behavior and Its Influence on Permeability Evolution During Methane Displacement by CO2

NASA Astrophysics Data System (ADS)

Fan, Jingjing; Feng, Ruimin; Wang, Jin; Wang, Yanbin

2017-07-01

Geological sequestration of CO2 in coal seams is of significant interest to both academia and industry. A thorough laboratory investigation of mechanical and flow behaviors is crucial for understanding the complex response of coalbeds to CO2 injection-enhanced coalbed methane recovery (CO2-ECBM) operation. In this work, systematic experiments were carried out on cylindrical coal core specimens under different uniform confining stresses. The coal deformation caused by variations in effective stress as well as the sorption-induced matrix swelling/shrinkage was monitored. The competitive gas sorption characteristics and permeability evolution during the process of methane displacement by CO2 were also investigated. The measured volumetric strain results indicate that sorption-induced strain is the dominant factor in the coal deformation. The relationship between the volumetric strain and the adsorbed gas volume has been revealed to be a linear function. Experimental results obtained under different stress conditions suggest that higher confining stress suppresses the increase in both volumetric strain and the adsorbed gas volume. Furthermore, both methane displacement and CO2 injection are reduced when applying higher confining stresses. In addition, the permeability enhancement is heavily suppressed at higher confining stress. At a certain confining stress, a characteristic "U-shaped" trend of permeability is presented as a function of decreasing pore pressure. This study contributes to the understanding of coal deformation and its impact on permeability evolution under uniformly stressed condition, which has practical significance for CO2 sequestration and CO2-ECBM operation in the Qinshui basin.

Core conditions for alpha heating attained in direct-drive inertial confinement fusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, A.; Woo, K. M.; Betti, R.

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117,more » 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.« less

Core conditions for alpha heating attained in direct-drive inertial confinement fusion

DOE PAGES

Bose, A.; Woo, K. M.; Betti, R.; ...

2016-07-07

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117,more » 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.« less

To Demonstrate an Integrated Solution for Plasma-Material Interfaces Compatible with an Optimized Core Plasma

NASA Astrophysics Data System (ADS)

Goldston, Robert; Brooks, Jeffrey; Hubbard, Amanda; Leonard, Anthony; Lipschultz, Bruce; Maingi, Rajesh; Ulrickson, Michael; Whyte, Dennis

2009-11-01

The plasma facing components in a Demo reactor will face much more extreme boundary plasma conditions and operating requirements than any present or planned experiment. These include 1) Power density a factor of four or more greater than in ITER, 2) Continuous operation resulting in annual energy and particle throughput 100-200 times larger than ITER, 3) Elevated surface operating temperature for efficient electricity production, 4) Tritium fuel cycle control for safety and breeding requirements, and 5) Steady state plasma confinement and control. Consistent with ReNeW Thrust 12, design options are being explored for a new moderate-scale facility to assess core-edge interaction issues and solutions. Key desired features include high power density, sufficient pulse length and duty cycle, elevated wall temperature, steady-state control of an optimized core plasma, and flexibility in changing boundary components as well as access for comprehensive measurements.

Tokamak reactor for treating fertile material or waste nuclear by-products

DOEpatents

Kotschenreuther, Michael T.; Mahajan, Swadesh M.; Valanju, Prashant M.

2012-10-02

Disclosed is a tokamak reactor. The reactor includes a first toroidal chamber, current carrying conductors, at least one divertor plate within the first toroidal chamber and a second chamber adjacent to the first toroidal chamber surrounded by a section that insulates the reactor from neutrons. The current carrying conductors are configured to confine a core plasma within enclosed walls of the first toroidal chamber such that the core plasma has an elongation of 1.5 to 4 and produce within the first toroidal chamber at least one stagnation point at a perpendicular distance from an equatorial plane through the core plasma that is greater than the plasma minor radius. The at least one divertor plate and current carrying conductors are configured relative to one another such that the current carrying conductors expand the open magnetic field lines at the divertor plate.

Optical imagery and spectrophotometry of CTB 80

NASA Technical Reports Server (NTRS)

Hester, J. Jeff; Kulkarni, Shrinivas R.

1989-01-01

Narrow-band imagery and spectrophotometry of the central region of CTB 80 are presented. The images show weak forbidden O III and ubiquitous filamentary forbidden S II and H-alpha emission from the extended radio lobes in which the core is embedded. The data indicate that the extended component is shock heated. Balmer line-dominated emission is observed around the perimeter of the core. Assuming that the volume of the radio shell is similar to the volume of the thermal shell, it is found that a magnetic field of about 600 microG and a cosmic-ray proton-to-electron ratio of about 200 are required to explain the pressure and synchrotron volume emissivity in the radio shell. It is suggested that the optical emission form the core of CTB 80 arises behind shocks which are being driven into a magnetized thermal plasma by the confined relativistic wind from PSR 1951+32.

Core conditions for alpha heating attained in direct-drive inertial confinement fusion.

PubMed

Bose, A; Woo, K M; Betti, R; Campbell, E M; Mangino, D; Christopherson, A R; McCrory, R L; Nora, R; Regan, S P; Goncharov, V N; Sangster, T C; Forrest, C J; Frenje, J; Gatu Johnson, M; Glebov, V Yu; Knauer, J P; Marshall, F J; Stoeckl, C; Theobald, W

2016-07-01

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)10.1103/PhysRevLett.117.025001] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.

Ground water chlorinated ethenes in tree trunks: case studies, influence of recharge, and potential degradation mechanism

Treesearch

Don A. Vroblesky; Barton D. Clinton; James M. Vose; Clifton C. Casey; Gregory J. Harvey; Paul M. Bradley

2004-01-01

Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ~3 m of clay. Additional ground...

Kinetic studies of ICF implosions

DOE PAGES

Kagan, Grigory; Herrmann, H. W.; Kim, Y. -H.; ...

2016-05-26

Here, kinetic effects on inertial confinement fusion have been investigated. In particular, inter-ion-species diffusion and suprathermal ion distribution have been analyzed. The former drives separation of the fuel constituents in the hot reacting core and governs mix at the shell/fuel interface. The latter underlie measurements obtained with nuclear diagnostics, including the fusion yield and inferred ion burn temperatures. Basic mechanisms behind and practical consequences from these effects are discussed.

Performance analysis of vortex based mixers for confined flows

NASA Astrophysics Data System (ADS)

Buschhagen, Timo

The hybrid rocket is still sparsely employed within major space or defense projects due to their relatively poor combustion efficiency and low fuel grain regression rate. Although hybrid rockets can claim advantages in safety, environmental and performance aspects against established solid and liquid propellant systems, the boundary layer combustion process and the diffusion based mixing within a hybrid rocket grain port leaves the core flow unmixed and limits the system performance. One principle used to enhance the mixing of gaseous flows is to induce streamwise vorticity. The counter-rotating vortex pair (CVP) mixer utilizes this principle and introduces two vortices into a confined flow, generating a stirring motion in order to transport near wall media towards the core and vice versa. Recent studies investigated the velocity field introduced by this type of swirler. The current work is evaluating the mixing performance of the CVP concept, by using an experimental setup to simulate an axial primary pipe flow with a radially entering secondary flow. Hereby the primary flow is altered by the CVP swirler unit. The resulting setup therefore emulates a hybrid rocket motor with a cylindrical single port grain. In order to evaluate the mixing performance the secondary flow concentration at the pipe assembly exit is measured, utilizing a pressure-sensitive paint based procedure.

Temperature and hydrostatic pressure effects on single dopant states in hollow cylindrical core-shell quantum dot

NASA Astrophysics Data System (ADS)

El-Yadri, M.; Aghoutane, N.; El Aouami, A.; Feddi, E.; Dujardin, F.; Duque, C. A.

2018-05-01

This work reports on theoretical investigation of the temperature and hydrostatic pressure effects on the confined donor impurity in a AlGaAs-GaAs hollow cylindrical core-shell quantum dot. The charges are assumed to be completely confined to the interior of the shell with approximately rigid walls. Within the framework of the effective-mass approximation and by using a variational approach, we have computed the donor binding energies as a function of the shell size in order to study the behavior of the electron-impurity attraction for a very small thickness under the influence of both temperature and hydrostatic pressure. Our results show that the temperature and hydrostatic pressure have a significant influence on the impurity binding energy for large shell quantum dots. It will be shown that the binding energy is more pronounced with increasing pressure and decreasing temperature for any impurity position and quantum dot size. The photoionization cross section is also analyzed by considering only the in-plane incident radiation polarization. Its behavior is investigated as a function of photon energy for different values of pressure and temperature. The opposite effects caused by temperature and hydrostatic pressure reveal a big practical interest and offer an alternative way to tuning of correlated electron-impurity transitions in optoelectronic devices.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chrystal, C.; Grierson, B. A.; Staebler, G. M.

Here, experiments at the DIII-D tokamak have used dimensionless parameter scans to investigate the dependencies of intrinsic torque and momentum transport in order to inform a prediction of the rotation profile in ITER. Measurements of intrinsic torque profiles and momentum confinement time in dimensionless parameter scans of normalized gyroradius and collisionality are used to predict the amount of intrinsic rotation in the pedestal of ITER. Additional scans of T e/T i and safety factor are used to determine the accuracy of momentum flux predictions of the quasi-linear gyrokinetic code TGLF. In these scans, applications of modulated torque are used tomore » measure the incremental momentum diffusivity, and results are consistent with the E x B shear suppression of turbulent transport. These incremental transport measurements are also compared with the TGLF results. In order to form a prediction of the rotation profile for ITER, the pedestal prediction is used as a boundary condition to a simulation that uses TGLF to determine the transport in the core of the plasma. The predicted rotation is ≈20 krad/s in the core, lower than in many current tokamak operating scenarios. TGLF predictions show that this rotation is still significant enough to have a strong effect on confinement via E x B shear.« less

Predicting rotation for ITER via studies of intrinsic torque and momentum transport in DIII-D

DOE PAGES

Chrystal, C.; Grierson, B. A.; Staebler, G. M.; ...

2017-03-30

Here, experiments at the DIII-D tokamak have used dimensionless parameter scans to investigate the dependencies of intrinsic torque and momentum transport in order to inform a prediction of the rotation profile in ITER. Measurements of intrinsic torque profiles and momentum confinement time in dimensionless parameter scans of normalized gyroradius and collisionality are used to predict the amount of intrinsic rotation in the pedestal of ITER. Additional scans of T e/T i and safety factor are used to determine the accuracy of momentum flux predictions of the quasi-linear gyrokinetic code TGLF. In these scans, applications of modulated torque are used tomore » measure the incremental momentum diffusivity, and results are consistent with the E x B shear suppression of turbulent transport. These incremental transport measurements are also compared with the TGLF results. In order to form a prediction of the rotation profile for ITER, the pedestal prediction is used as a boundary condition to a simulation that uses TGLF to determine the transport in the core of the plasma. The predicted rotation is ≈20 krad/s in the core, lower than in many current tokamak operating scenarios. TGLF predictions show that this rotation is still significant enough to have a strong effect on confinement via E x B shear.« less

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

DOE PAGES

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.; ...

2018-03-07

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Synthesis of Ordered Mesoporous Phenanthrenequinone-Carbon via π-π Interaction-Dependent Vapor Pressure for Rechargeable Batteries

PubMed Central

Kwon, Mi-Sook; Choi, Aram; Park, Yuwon; Cheon, Jae Yeong; Kang, Hyojin; Jo, Yong Nam; Kim, Young-Jun; Hong, Sung You; Joo, Sang Hoon; Yang, Changduk; Lee, Kyu Tae

2014-01-01

The π-π interaction-dependent vapour pressure of phenanthrenequinone can be used to synthesize a phenanthrenequinone-confined ordered mesoporous carbon. Intimate contact between the insulating phenanthrenequinone and the conductive carbon framework improves the electrical conductivity. This enables a more complete redox reaction take place. The confinement of the phenanthrenequinone in the mesoporous carbon mitigates the diffusion of the dissolved phenanthrenequinone out of the mesoporous carbon, and improves cycling performance. PMID:25490893

Improved confinement in highly powered high performance scenarios on DIII-D

NASA Astrophysics Data System (ADS)

Petrie, T. W.; Osborne, T.; Fenstermacher, M. E.; Ferron, J.; Groebner, R.; Grierson, B.; Holcomb, C.; Lasnier, C.; Leonard, A.; Luce, T.; Makowski, M.; Turco, F.; Solomon, W.; Victor, B.; Watkins, J.

2017-08-01

DIII-D has recently demonstrated improved energy confinement by injecting neutral deuterium gas into high performance near-double null divertor (DND) plasmas during high power operation. Representative parameters for these plasmas are: q 95  =  6, P IN up to 15 MW, H 98  =  1.4-1.8, and β N  =  2.5-4.0. The ion B   ×  \

On Heating the Sun's Corona by Magnetic Explosions: Feasibility in Active Regions and prospects for Quiet Regions and Coronal Holes

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Falconer, D. A.; Porter, Jason G.; Suess, Steven T.

1999-01-01

We build a case for the persistent strong coronal heating in active regions and the pervasive quasi-steady heating of the corona in quiet regions and coronal holes being driven in basically the same way as the intense transient heating in solar flares: by explosions of sheared magnetic fields in the cores of initially closed bipoles. We begin by summarizing the observational case for exploding sheared core fields being the drivers of a wide variety of flare events, with and without coronal mass ejections. We conclude that the arrangement of an event's flare heating, whether there is a coronal mass ejection, and the time and place of the ejection relative to the flare heating are all largely determined by four elements of the form and action of the magnetic field: (1) the arrangement of the impacted, interacting bipoles participating in the event, (2) which of these bipoles are active (have sheared core fields that explode) and which are passive (are heated by injection from impacted active bipoles), (3) which core field explodes first, and (4) which core-field explosions are confined within the closed field of their bipoles and which ejectively open their bipoles. We then apply this magnetic-configuration framework for flare heating to the strong coronal heating observed by the Yohkoh Soft X-ray Telescope in an active region with strongly sheared core fields observed by the MSFC vector magnetograph. All of the strong coronal heating is in continually microflaring sheared core fields or in extended loops rooted against the active core fields. Thus, the strong heating occurs in field configurations consistent with the heating being driven by frequent core-field explosions that are smaller but similar to those in confined flares and flaring arches. From analysis of the thermal and magnetic energetics of two selected core-field microflares and a bright extended loop, we find that (1) it is energetically feasible for the sheared core fields to drive all of the coronal heating in the active region via a staccato of magnetic microexplosions, (2) the microflares at the feet of the extended loop behave as the flares at the feet of flaring arches in that more coronal heating is driven within the active bipole than in the extended loop, (3) the filling factor of the X-ray plasma in the core field microflares and in the extended loop is approximately 0.1, and (4) to release enough magnetic energy for a typical microflare (10^27 - 10^28 erg), a microflaring strand of sheared core field need expand and/or untwist by only a few percent at most. Finally, we point out that (1) the field configurations for strong coronal heating in our example active region (i.e., neutral-line core fields, many embedded in the feet of extended loops) are present in abundance in the magnetic network in quiet regions and coronal holes, and (2) it is known that many network bipoles do microflare and that many produce detectable coronal heating. We therefore propose that exploding sheared core fields are the drivers of most of the heating and dynamics of the solar atmosphere, ranging from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in active regions, to the multitude of fine-scale explosive events in the magnetic network. The low-lysing exploding core fields in the network drive microflares, spicules, global coronal heating, and ,consequently, the solar wind.

Three dimensional fracture aperture and porosity distribution using computerized tomography

NASA Astrophysics Data System (ADS)

Wenning, Q.; Madonna, C.; Joss, L.; Pini, R.

2017-12-01

A wide range of geologic processes and geo-engineered applications are governed by coupled hydromechanical properties in the subsurface. In geothermal energy reservoirs, quantifying the rate of heat transfer is directly linked with the transport properties of fractures, underscoring the importance of fracture aperture characterization for achieving optimal heat production. In this context, coupled core-flooding experiments with non-invasive imaging techniques (e.g., X-Ray Computed Tomography - X-Ray CT) provide a powerful method to make observations of these properties under representative geologic conditions. This study focuses on quantifying fracture aperture distribution in a fractured westerly granite core by using a recently developed calibration-free method [Huo et al., 2016]. Porosity is also estimated with the X-ray saturation technique using helium and krypton gases as saturating fluids, chosen for their high transmissibility and high CT contrast [e.g., Vega et al., 2014]. The westerly granite sample (diameter: 5 cm, length: 10 cm) with a single through-going rough-walled fracture was mounted in a high-pressure aluminum core-holder and placed inside a medical CT scanner for imaging. During scanning the pore fluid pressure was undrained and constant, and the confining pressure was regulated to have the desired effective pressure (0.5, 5, 7 and 10 MPa) under loading and unloading conditions. 3D reconstructions of the sample have been prepared in terms of fracture aperture and porosity at a maximum resolution of (0.24×0.24×1) mm3. Fracture aperture maps obtained independently using helium and krypton for the whole core depict a similar heterogeneous aperture field, which is also dependent on confining pressure. Estimates of the average hydraulic aperture from CT scans are in quantitative agreement with results from fluid flow experiments. However, the latter lack of the level of observational detail achieved through imaging, which further evidence the presence of strong heterogeneities in fracture aperture at the mm-scale. These results exemplify the use of non-destructive imaging to determine fracture aperture maps, which can be used to address flow channelization and heat transfer that cannot be obtained from core-flooding experiments alone.

Detecting alkali-silica reaction in thick concrete structures using linear array ultrasound

NASA Astrophysics Data System (ADS)

Bull Ezell, N. Dianne; Albright, Austin; Clayton, Dwight; Santos-Villalobos, Hector

2018-03-01

Commercial nuclear power plants (NPPs) depend heavily on concrete structures, making the long-term performance of these structures crucial for safe operation, especially with license period extensions to 60 years and possibly beyond. Alkali-silica reaction (ASR) is a reaction that occurs over time in concrete between alkaline cement paste and reactive, noncrystalline silica (aggregates). In the presence of water, an expansive gel is formed within the aggregates, which results in microcracks in aggregates and adjacent cement paste. ASR can potentially affect concrete properties and performance characteristics such as compressive strength, modulus of elasticity, flexural stiffness, shear strength, and tensile strength. Currently, no nondestructive evaluation methods have proven effective in identifying ASR before surface cracks form. ASR is identified visibly or by petrographic analysis. Although ASR definitely impacts concrete material properties, the performance of concrete structures exhibiting ASR depends on whether or not the concrete is unconfined or confined with reinforcing bars. Confinement by reinforcing bars restrainsthe expansion of ASR-affected concrete, similar to prestressing, thus improving the performance of a structure. Additionally, there is no direct correlation between the mechanical properties of concrete sample cores and the in-situ properties of the concrete. The University of Tennessee-Knoxville, Oak Ridge National Laboratory, and a consortium of universities have developed an accelerated ASR experiment. Three large concrete specimens, representative of NPP infrastructure, were constructed containing both embedded and surface instruments. This paper presents preliminary analysis of these specimens using a frequency-banded synthetic aperture focusing technique.

Formation of the internal transport barrier in KSTAR

NASA Astrophysics Data System (ADS)

Chung, J.; Kim, H. S.; Jeon, Y. M.; Kim, J.; Choi, M. J.; Ko, J.; Lee, K. D.; Lee, H. H.; Yi, S.; Kwon, J. M.; Hahn, S.-H.; Ko, W. H.; Lee, J. H.; Yoon, S. W.

2018-01-01

One of key objectives of tokamak experiments is the exploration of enhanced confinement regimes, and the access of the internal transport barrier (ITB) formation is dealt with an important physics issue in the most of major tokamaks. Also, the advanced tokamak scenario with ITB is expected to lead to a continuous reactor with high fusion power density. From that point of view, the formation of the ITB in KSTAR which is designed for long pulse operation capability is very important although its heating and current drive systems are not fully equipped yet. We have therefore assumed that an early injection of the full NBI power (∼5.5 MW) during the current ramp-up would give a chance to form an internal barrier if the plasma could stay in the L-mode. To avoid the H-mode transition, we have produced inboard limited plasmas with detaching from the both upper and lower divertors. Using this approach, an ITB formation during L-mode has been observed which shows improved core confinement. Ion and electron temperature profiles show the barrier clearly in the temperature, and it was sustained for about 7 s in the dedicated experiment. This is the first stationary ITB observed in a full superconducting tokamak. This operation scenario with the ITB could be an alternative way to achieve a high performance regime in KSTAR, and the length of the ITB discharge could be extended even longer. In this paper, we present the formation of the ITB using measured and simulated characteristic profiles.

Roothaan's approach to solve the Hartree-Fock equations for atoms confined by soft walls: Basis set with correct asymptotic behavior.

PubMed

Rodriguez-Bautista, Mariano; Díaz-García, Cecilia; Navarrete-López, Alejandra M; Vargas, Rubicelia; Garza, Jorge

2015-07-21

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energies always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.

Roothaan’s approach to solve the Hartree-Fock equations for atoms confined by soft walls: Basis set with correct asymptotic behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez-Bautista, Mariano; Díaz-García, Cecilia; Navarrete-López, Alejandra M.

2015-07-21

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energiesmore » always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.« less

Improved Density Control in the Pegasus Toroidal Experiment using Internal Fueling

NASA Astrophysics Data System (ADS)

Thome, K. E.; Bongard, M. W.; Cole, J. A.; Fonck, R. J.; Redd, A. J.; Winz, G. R.

2012-10-01

Routine density control up to and exceeding the Greenwald limit is critical to key Pegasus operational scenarios, including non-solenoidal startup plasmas created using single-point helicity injection and high β Ohmic plasmas. Confinement scalings suggest it is possible to achieve very high β plasmas in Pegasus by lowering the toroidal field and increasing ne/ng. In the past, Pegasus achieved β ˜ 20% in high recycling Ohmic plasmas without running into any operational boundaries.footnotetext Garstka, G.D. et al., Phys. Plasmas 10, 1705 (2003) However, recent Ohmic experiments have demonstrated that Pegasus currently operates in an extremely low-recycling regime with R < 0.8 and Zeff ˜ 1 using improved vacuum conditioning techniques, such as Ti gettering and cryogenic pumping. Hence, it is difficult to achieve ne/ng> 0.3 with these improved wall conditions. Presently, gas is injected using low-field side (LFS) modified PV-10 valves. To attain high ne/ng operation and coincidentally separate core plasma and local current source fueling two new gas fueling capabilities are under development. A centerstack capillary injection system has been commissioned and is undergoing initial tests. A LFS movable midplane needle gas injection system is currently under design and will reach r/a ˜ 0.25. Initial results from both systems will be presented.

Long-term bioavailability of redox nanoparticles effectively reduces organ dysfunctions and death in whole-body irradiated mice.

PubMed

Feliciano, Chitho P; Tsuboi, Koji; Suzuki, Kenshi; Kimura, Hiroyuki; Nagasaki, Yukio

2017-06-01

Radioprotective agents have been developed to protect patients against the damaging and lethal effects of ionizing radiation. However, in addition to the intrinsic ability to target reactive oxygen species (ROS), the ability to retain a significant level of bioavailability is desirable in radioprotective agents because that would increase and prolong their radioprotective efficacy and improve its safety. Here, we report the development of a novel nanoparticle-based radioprotective agent with improved bioavailability, which suppressed the adverse effects typically associated with low-molecular-weight (LMW) antioxidants. We developed biocompatible and colloidally stable nanoparticles in which nitroxide radicals that were covalently conjugated (redox nanoparticles, RNP N ) effectively scavenged radiation-induced ROS with a characteristically prolonged bioavailability and tissue-residence time compared with that of conventional LMW antioxidants. The confinement of the nitroxide radicals in the RNP N core prevented its rapid metabolism and excretion out of the body. The nano-sized formulation prevented internalization of RNP N in healthy cells, thereby preserving the normal function of the redox reactions in the cell. This improved pharmacological performance dramatically reduced the radiation-induced organ dysfunctions and increased the survival time of the lethally irradiated mice when the nanoparticles were administered 3-24 h before whole-body irradiation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Core Radial Electric Field and Transport in Wendelstein 7-X Plasmas

NASA Astrophysics Data System (ADS)

Pablant, Novimir

2016-10-01

Results from the investigation of core transport and the role of the radial electric field profile (Er) in the first operational phase of the Wendelstein 7-X (W7-X) stellarator are presented. In stellarator plasmas, the details of the Er profile are expected to have a strong effect on both the particle and heat fluxes. Neoclassical particle fluxes are not intrinsically ambipolar, which leads to the formation of a radial electric field that enforces ambipolarity. The radial electric field is closely related to the perpendicular plasma flow (u⊥) through the force balance equation. This allows the radial electric field to be inferred from measurements of the perpendicular flow velocity from the x-ray imaging crystal spectrometer (XICS) and correlation reflectometry diagnostics. Large changes in the perpendicular rotation, on the order of Δu⊥ 5km /s (ΔEr 12kV / m), have been observed within a set of experiments where the heating power was stepped down from 2 MW to 0.6 MW . These experiments are examined in detail to explore the relationship between, heating power, response of the temperature and density profiles and the response of the radial electric field. Estimations of the core transport are based on power balance and utilize electron temperature (Te) profiles from the ECE and Thomson scattering, electron density profiles (ne) from interferometry and Thomson scattering, ion temperature (Ti) profiles from XICS, along with measurements of the total stored energy and radiated power. Also described are a set core impurity confinement experiments and results. Impurity confinement has been investigated through the injection of trace amount of argon impurity gas at the plasma edge in conjunction with measurements of the density of various ionization states of argon from the XICS and High Efficiency eXtreme-UV Overview Spectrometer (HEXOS) diagnostics. Finally the inferred Er and heat flux profiles are compared to initial neoclassical calculations using measured plasma profiles. On behalf of the W7-X Team.

Hydro-mechanical properties of pressure core sediments recovered from the Krishna-Godavari Basin during India's National Gas Hydrate Program Expedition NGHP-02

NASA Astrophysics Data System (ADS)

Yoneda, J.; Oshima, M.; Kida, M.; Kato, A.; Konno, Y.; Jin, Y.; Waite, W. F.; Jang, J.; Kumar, P.; Tenma, N.

2017-12-01

Pressure coring and analysis technology allows for gas hydrate to be recovered from the deep seabed, transferred to the laboratory and characterized while continuously maintaining gas hydrate stability. For this study, dozens of hydrate-bearing pressure core sediment subsections recovered from the Krishna-Godavari Basin during India's National Gas Hydrate Program Expedition NGHP-02 were tested with Pressure Core Non-destructive Analysis Tools (PNATs) through a collaboration between Japan and India. PNATs, originally developed by AIST as a part of the Japanese National hydrate research program (MH21, funded by METI) conducted permeability, compression and consolidation tests under various effective stress conditions, including the in situ stress state estimated from downhole bulk density measurements. At the in situ effective stress, gas hydrate-bearing sediments had an effective permeability range of 0.01-10mD even at pore-space hydrate saturations above 60%. Permeability increased by 10 to 100 times after hydrate dissociation at the same effective stress, but these post-dissociation gains were erased when effective stress was increased from in situ values ( 1 MPa) to 10MPa in a simulation of the depressurization method for methane extraction from hydrate. Vertical-to-horizontal permeability anisotropy was also investigated. First-ever multi-stage loading tests and strain-rate alternation compression tests were successfully conducted for evaluating sediment strengthening dependence on the rate and magnitude of effective confining stress changes. In addition, oedometer tests were performed up to 40MPa of consolidation stress to simulate the depressurization method in ultra-deep sea environments. Consolidation curves measured with and without gas hydrate were investigated over a wide range of effective confining stresses. Compression curves for gas hydrate-bearing sediments were convex downward due to high hydrate saturations. Consolidation tests show that, regardless of the consolidation history with hydrate in place, the consolidation behavior after dissociation will first return to, then follow, the original normal consolidation curve for the hydrate-free host sediment.

Surface sediment remobilization triggered by earthquakes in the Nankai forearc region

NASA Astrophysics Data System (ADS)

Okutsu, N.; Ashi, J.; Yamaguchi, A.; Irino, T.; Ikehara, K.; Kanamatsu, T.; Suganuma, Y.; Murayama, M.

2017-12-01

Submarine landslides triggered by earthquakes generate turbidity currents (e.g. Piper et al., 1988; 1999). Recently several studies report that the remobilization of the surface sediment triggered by earthquakes can also generate turbidity currents. However, studies that proposed such process are still limited (e.g. Ikehara et al., 2016; Mchugh et al., 2016; Moernaut et al., 2017). The purpose of this study is to examine those sedimentary processes in the Nankai forearc region, SW Japan using sedimentary records. We collected 46 cm-long multiple core (MC01) and a 6.7 m-long piston core (PC03) from the small basin during the R/V Shinsei Maru KS-14-8 cruise. The small confined basin, which is our study site, block the paths of direct sediment supply from river-submarine canyon system. The sampling site is located at the ENE-WSW elongated basin between the accretionary prism and the forearc basin off Kumano without direct sediment supply from river-submarine canyon system. The basin exhibits a confined basin that captures almost of sediments supplied from outside. Core samples are mainly composed of silty clay or very fine sand. Cs-137 measurement conducted on a MC01 core shows constantly high value at the upper 17 cm section and no detection below it. Moreover, the sedimentary structure is similar to fine-grained turbidite described by Stow and Shanmgam (1980), we interpret the upper 17 cm of MC01 as muddy turbidite. Grain size distribution and magnetic susceptibility also agree to this interpretation. Rapid sediment deposition after 1950 is assumed and the most likely event is the 2004 off Kii peninsula earthquakes (Mw=6.6-7.4). By calculation from extent of provenance area, which are estimated by paleocurrent analysis and bathymetric map, and thickness of turbidite layer we conclude that surface 1 cm of slope sediments may be remobilized by the 2004 earthquakes. Muddy turbidites are also identified in a PC03 core. The radiocarbon age gap of 170 years obtained around 2 mbsf of PC03 core also indicates similar sedimentary process. However, we also obtained large age gap in a thick turbidite layer, indicating remobilization of deeper sediments by landslide. Our results revealed that the studied basin recorded various scales and styles of sediment remobilizations by earthquake shakings.

Reflux physics and an operational scenario for the spheromak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hooper, E. B.

2010-07-20

The spheromak [1] is a toroidal magnetic confinement geometry for plasma with most of the magnetic field generated by internal currents. It has been demonstrated to have excellent energy confinement properties: A peak electron temperature of 0.4 keV was achieved in the Compact Torus Experiment (CTX) experiment [2] and of 0.5 keV in the Sustained Spheromak Physics Experiment (SSPX) [3]. In both cases the plasmas were decaying slowly following formation and (in SSPX) sustainment by coaxial helicity injection (CHI) [4]. In SSPX, power balance analysis during this operational phase yielded electron thermal conductivities in the core plasma in the rangemore » of 1-10 m 2/s [5, 6], comparable to the tokamak L-mode. These results motivate the consideration of possible operating scenarios for future fusion experiments or even reactors.« less

Influence of confinement layers in the emitting layer of the blue phosphorescent organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Ji, Chang-Yan; Gu, Zheng-Tian; Kou, Zhi-Qi

2016-10-01

The electrical and optical properties of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be affected by the various structure of confinement layer in the emitting layer (EML). A series of devices with different electron or hole confinement layer (TCTA or Bphen) are fabricated, it is more effective to balance charge carriers injection for the device with the double electron confinement layers structure, the power efficiency and luminance can reach 17.7 lm/W (at 103 cd/m2) and 3536 cd/m2 (at 8 V). In case of the same double electron confinement layers, another series of devices with different profile of EML are fabricated by changing the confinement layers position, the power efficiency and luminance can be improved to 21.7 lm/W (at 103 cd/m2) and 7674 cd/m2 (at 8 V) when the thickness of EML separated by confinement layers increases gradually from the hole injection side to the electron injection side, the driving voltage can also be reduced.

Physical stratigraphy and hydrostratigraphy of Upper Cretaceous and Paleocene sediments, Burke and Screven Counties, Georgia

USGS Publications Warehouse

Falls, W.F.; Baum, J.S.; Prowell, D.C.

1997-01-01

Six geologic units are recognized in the Cretaceous and the Paleocene sediments of eastern Burke and Screven Counties in Georgia on the basis of lithologic, geophysical, and paleontologic data collected from three continuously cored testholes in Georgia and one testhole in South Carolina. The six geologic units are separated by regional unconformities and are designated from oldest to youngest as the Cape Fear Formation, the Middendorf Formation, the Black Creek Group (undivided), and the Steel Creek Formation in the Upper Cretaceous section, and the Ellenton and the Snapp Formations in the Paleocene section. The geologic units provide a spatial and temporal framework for the identification and correlation of a basal confining unit beneath the Midville aquifer system and five aquifers and five confining units in the Dublin and the Midville aquifer systems. The Dublin aquifer system is divided hydrostratigraphically into the Millers Pond, the upper Dublin, and the lower Dublin aquifers. The Midville aquifer system is divided hydrostratigraphically into the upper and the lower Midville aquifers. The fine-grained sediments of the Millers Pond, the lower Dublin, and the lower Midville confining units are nonmarine deposits and are present in the upper part of the Snapp Formation, the Black Creek Group (undivided), and the Middendorf Formation, respectively. Hydrologic data for specific sets of monitoring wells at the Savannah River Site in South Carolina and the Millers Pond site in Georgia confirm that these three units are leaky confining units and locally impede vertical ground-water flow between adjacent aquifers. The fine-grained sediments of the upper Dublin and the upper Midville confining units are marine-deltaic deposits of the Ellenton Formation and the Black Creek Group (undivided), respectively. Hydrologic data confirm that the upper Dublin confining unit regionally impedes vertical ground-water flow on both sides of the Savannah River. The upper Midville confining unit impedes vertical ground-water flow in the middle and downdip parts of the study area and is a leaky confining unit in the updip part of the study area. Recognition of the upper Dublin confining unit as a regional confining unit between the Millers Pond and the upper Dublin aquifers also confirms that the Millers Pond aquifer is a separate hydrologic unit from the rest of the Dublin aquifer system. This multi-aquifer framework increases the vertical hydrostratigraphic resolution of hydraulic properties and gradients in the Dublin and Midville aquifer systems for the investigation of ground-water flow beneath the Savannah River in the vicinity of the U.S. Department of Energy Savannah River Site.

Ground water chlorinated ethenes in tree trunks: Case studies, influence of recharge, and potential degradation mechanism

USGS Publications Warehouse

Vroblesky, D.A.; Clinton, B.D.; Vose, J.M.; Casey, C.C.; Harvey, G.J.; Bradley, P.M.

2004-01-01

Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ???3 m of clay. Additional ground water contaminants detected in the tree cores were cis-1,2-dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differing TCE concentrations around the trunk of some trees appear to be related to the roots deriving water from differing areas. Opportunistic uptake of infiltrating rainfall can dilute prerain TCE concentrations in the trunk. TCE concentrations in core headspace may differ among some tree species. In some trees, infestation of bacteria in decaying heartwood may provide a TCE dechlorination mechanism within the trunk.

Experimental evidence of body centered cubic iron in Earth's core

NASA Astrophysics Data System (ADS)

Hrubiak, R.; Meng, Y.; Shen, G.

2017-12-01

The Earth's core is mainly composed of iron. While seismic evidence has shown a liquid outer core and a solid inner core, the crystalline nature of the solid iron at the core condition remains debated, largely due to the difficulties in experimental determination of exact polymorphs at corresponding pressure-temperature conditions. We have examined crystal structures of iron up to 220 GPa and 6000 K with x-ray diffraction using a double-sided laser heating system at HPCAT, Advanced Photon Source. The iron sample is confined in a small chamber surrounded by single crystal MgO. The laser power can be modulated together with temperature measurements. The modulated heating of iron in an MgO single crystal matrix allows for microstructure analysis during heating and after the sample is quenched. We present experimental evidence of a body-centered-cubic (BCC) iron from about 100 GPa and 3000 K to at least 220 GPa and 4000 K. The observed BCC phase may be consistent with a theoretically predicted BCC phase that is dynamically stable in similar pressure-temperature conditions [1]. We will discuss the stability region of the BCC phase and the melting curve of iron and their implications in the nature of the Earth's inner core. References: A. B. Belonoshko et al., Nat. Geosci., 1-6 (2017).

Enhanced Electron Mobility in Nonplanar Tensile Strained Si Epitaxially Grown on SixGe1-x Nanowires.

PubMed

Wen, Feng; Tutuc, Emanuel

2018-01-10

We report the growth and characterization of epitaxial, coherently strained Si x Ge 1-x -Si core-shell nanowire heterostructure through vapor-liquid-solid growth mechanism for the Si x Ge 1-x core, followed by an in situ ultrahigh-vacuum chemical vapor deposition for the Si shell. Raman spectra acquired from individual nanowire reveal the Si-Si, Si-Ge, and Ge-Ge modes of the Si x Ge 1-x core and the Si-Si mode of the shell. Because of the compressive (tensile) strain induced by lattice mismatch, the core (shell) Raman modes are blue (red) shifted compared to those of unstrained bare Si x Ge 1-x (Si) nanowires, in good agreement with values calculated using continuum elasticity model coupled with lattice dynamic theory. A large tensile strain of up to 2.3% is achieved in the Si shell, which is expected to provide quantum confinement for electrons due to a positive core-to-shell conduction band offset. We demonstrate n-type metal-oxide-semiconductor field-effect transistors using Si x Ge 1-x -Si core-shell nanowires as channel and observe a 40% enhancement of the average electron mobility compared to control devices using Si nanowires due to an increased electron mobility in the tensile-strained Si shell.

INSTALLATION OF A POST-ACCIDENT CONFINEMENT HIGH-LEVEL RADIATION MONITORING SYSTEM IN THE KOLA NUCLEAR POWER STATION (UNIT 2) IN RUSSIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

GREENE,G.A.; GUPPY,J.G.

1998-09-01

This is the final report on the INSP project entitled, ``Post-Accident Confinement High-Level Radiation Monitoring System'' conducted by BNL under the authorization of Project Work Plan WBS 1.2.2.6 (Attachment 1). This project was initiated in February 1993 to assist the Russians in reducing risks associated with the continued operation of older Soviet-designed nuclear power plants, specifically the Kola VVER-440/230 Unit 2, through improved accident detection capability, specifically by the installation of a dual train high-level radiation detection system in the confinement of Unit 2 of the Kola NPP. The major technical objective of this project was to provide, install andmore » make operational the necessary hardware inside the confinement of the Kola NPP Unit 2 to provide early and reliable warning of the release of radionuclides from the reactor into the confinement air space as an indication of the occurrence of a severe accident at the plant. In addition, it was intended to provide hands-on experience and training to the Russian plant workers in the installation, operation, calibration and maintenance of the equipment in order that they may use the equipment without continued US assistance as an effective measure to improve reactor safety at the plant.« less

Fast ion motion in the plasma part of a stellarator-mirror fission-fusion hybrid

NASA Astrophysics Data System (ADS)

Moiseenko, V. E.; Nemov, V. V.; Ågren, O.; Kasilov, S. V.; Garkusha, I. E.

2016-06-01

Recent developments of a stellarator-mirror (SM) fission-fusion hybrid concept are reviewed. The hybrid consists of a fusion neutron source and a powerful sub-critical fast fission reactor core. The aim is transmutation of spent nuclear fuel and safe fission energy production. In its fusion part, a stellarator-type system with an embedded magnetic mirror is used. The stellarator confines deuterium plasma with moderate temperature, 1-2 keV. In the magnetic mirror, a hot component of sloshing tritium ions is trapped. There, the fusion neutrons are generated. A candidate for a combined SM system is a DRACON magnetic trap. A basic idea behind an SM device is to maintain local neutron production in a mirror part, but at the same time eliminate the end losses by using a toroidal device. A possible drawback is that the stellarator part can introduce collision-free radial drift losses, which is the main topic for this study. For high energy ions of tritium with an energy of 70 keV, comparative computations of collisionless losses in the rectilinear part of a specific design of the DRACON type trap are carried out. Two versions of the trap are considered with different lengths of the rectilinear sections. Also the total number of current-carrying rings in the magnetic system is varied. The results predict that high energy ions from neutral beam injection can be satisfactorily confined in the mirror part during 0.1-1 s. The Uragan-2M experimental device is used to check key points of the SM concept. The magnetic configuration of a stellarator with an embedded magnetic mirror is arranged in this device by switching off one toroidal coil. The motion of particles magnetically trapped in the embedded mirror is analyzed numerically with use of motional invariants. It is found that without radial electric field particles quickly drift out of the SM, even if the particles initially are located on a nested magnetic surface. We will show that a weak radial electric field, which would be spontaneously created by the ambipolar radial particle losses, can make drift trajectories closed, which substantially improves particle confinement. It is remarkable that the improvement acts both for positive and negative charges.

Single-mode tunable laser emission in the single-exciton regime from colloidal nanocrystals

PubMed Central

Grivas, Christos; Li, Chunyong; Andreakou, Peristera; Wang, Pengfei; Ding, Ming; Brambilla, Gilberto; Manna, Liberato; Lagoudakis, Pavlos

2013-01-01

Whispering-gallery-mode resonators have been extensively used in conjunction with different materials for the development of a variety of photonic devices. Among the latter, hybrid structures, consisting of dielectric microspheres and colloidal core/shell semiconductor nanocrystals as gain media, have attracted interest for the development of microlasers and studies of cavity quantum electrodynamic effects. Here we demonstrate single-exciton, single-mode, spectrally tuned lasing from ensembles of optical antenna-designed, colloidal core/shell CdSe/CdS quantum rods deposited on silica microspheres. We obtain single-exciton emission by capitalizing on the band structure of the specific core/shell architecture that strongly localizes holes in the core, and the two-dimensional quantum confinement of electrons across the elongated shell. This creates a type-II conduction band alignment driven by coulombic repulsion that eliminates non-radiative multi-exciton Auger recombination processes, thereby inducing a large exciton–bi-exciton energy shift. Their ultra-low thresholds and single-mode, single-exciton emission make these hybrid lasers appealing for various applications, including quantum information processing. PMID:23974520

Temperature dependence Infrared and Raman studies of III-V/II-VI core-shell nanostructures

NASA Astrophysics Data System (ADS)

Manciu, Felicia S.; McCombe, Bruce D.; Lucey, Derrick

2005-03-01

The temperature dependence (8 K < T < 300 K) of optical phonon modes confined in InP/II-VI core-shell nanostructures have been investigated by far-infrared (FIR) and Raman scattering spectroscopies. The core-shell nanostructures were fabricated by colloidal chemistry and characterized by transmission electron microscopy and X-ray diffraction prior to being embedded in a polycrystalline CsI matrix for the present studies. The FIR measurements of InP/ZnSe sample exhibits three absorption features, one clearly due to the Froelich mode of the InP cores, and the others related to modes associated with the shell layer and its coupling to the matrix. Strong mixing of the characteristic vibrations of each constituent material was observed for InP/ZnS sample. Raman scattering (457.9 nm excitation) features were determined without polarization selection in the backscattering geometry. Interesting T-dependent resonant Raman effect of the surface optical phonon modes has been discovered in InP/ZnSe sample. Reasonable agreement is obtained between the Raman and FIR results, as well as with theoretical calculations.

In-gap corner states in core-shell polygonal quantum rings.

PubMed

Sitek, Anna; Ţolea, Mugurel; Niţă, Marian; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2017-01-10

We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states.

In-gap corner states in core-shell polygonal quantum rings

NASA Astrophysics Data System (ADS)

Sitek, Anna; Ţolea, Mugurel; Niţă, Marian; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2017-01-01

We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states.

Leakage of the fundamental mode in photonic crystal fiber tapers.

PubMed

Nguyen, Hong C; Kuhlmey, Boris T; Steel, Michael J; Smith, Cameron L; Mägi, Eric C; McPhedran, Ross C; Eggleton, Benjamin J

2005-05-15

We report detailed measurements of the optical properties of tapered photonic crystal fibers (PCFs). We observe a striking long-wavelength loss as the fiber diameter is reduced, despite the minimal airhole collapse along the taper. We associate this loss with a transition of the fundamental core mode as the fiber dimensions contract: At wavelengths shorter than this transition wavelength, the core mode is strongly confined in the fiber microstructure, whereas at longer wavelengths the mode expands beyond the microstructure and couples out to higher-order modes. These experimental results are discussed in the context of the so-called fundamental mode cutoff described by Kuhlmey et al. [Opt. Express 10, 1285 (2002)], which apply to PCFs with a finite microstructure.

Structure and Barrier Properties of Multinanolayered Biodegradable PLA/PBSA Films: Confinement Effect via Forced Assembly Coextrusion.

PubMed

Messin, Tiphaine; Follain, Nadège; Guinault, Alain; Sollogoub, Cyrille; Gaucher, Valérie; Delpouve, Nicolas; Marais, Stéphane

2017-08-30

Multilayer coextrusion processing was applied to produce 2049-layer film of poly(butylene succinate-co-butylene adipate) (PBSA) confined against poly(lactic acid) (PLA) using forced assembly, where the PBSA layer thickness was about 60 nm. This unique technology allowed to process semicrystalline PBSA as confined polymer and amorphous PLA as confining polymer in a continuous manner. The continuity of PBSA layers within the 80/20 wt % PLA/PBSA layered films was clearly evidenced by atomic force microscopy (AFM). Similar thermal events to the reference films were revealed by thermal studies; indicating no diffusion of polymers during the melt-processing. Mechanical properties were measured for the multilayer film and the obtained results were those expected considering the fraction of each polymer, revealing the absence of delamination in the PLA/PBSA multinanolayer film. The confinement effect induced by PLA led to a slight orientation of the crystals, an increase of the rigid amorphous fraction (RAF) in PBSA with a densification of this fraction without changing film crystallinity. These structural changes allowed to strongly improve the water vapor and gas barrier properties of the PBSA layer into the multilayer film up to two decades in the case of CO 2 gas. By confining the PBSA structure in very thin and continuous layers, it was then possible to improve the barrier performances of a biodegradable system and the resulting barrier properties were successfully correlated to the effect of confinement on the microstructure and the chain segment mobility of the amorphous phase. Such investigation on these multinanolayers of PLA/PBSA with the aim of evidencing relationships between microstructure implying RAF and barrier performances has never been performed yet. Besides, gas and water permeation results have shown that the barrier improvement obtained from the multilayer was mainly due to the reduction of solubility linked to the reduction of the free volume while the tortuosity effect, as usually expected, was not really observed. This work brings new insights in the field of physicochemical behaviors of new multilayer films made of biodegradable polyesters but also in interfacial processes due to the confinement effect induced in these multinanolayer structures obtained by the forced assembly coextrusion. This original coextrusion process was a very advantageous technique to produce eco-friendly materials with functional properties without the help of tie layer, additives, solvents, surface treatments, or inorganic fillers.

Influence of confining layers' heterogeneity on the barometric response functions in semi-confined aquifers

NASA Astrophysics Data System (ADS)

Redaelli, Marco; Perulero Serrano, Raul

2017-04-01

It has been shown that Barometric Response Functions (BRFs) can provide a useful tool for detecting the occurrence of highly conducive bodies which span across aquifer confining layers and can potentially give rise to pathways for pollutant migration (Hussein et al 2013, Odling et al 2015). Analytical models employed to estimate BRFs from geological system properties assume homogeneity within the aquifer and its confining layer. These assumptions are rarely satisfied in practice. Our study focusses on the impact on predicted BRFs of heterogeneous distribution of high conductivity geomaterials within the confining layer. The work is grounded on a suite of three-dimensional, transient numerical computations of groundwater flow in a confining layer-aquifer system for i) a perfectly homogeneous two-layer setting where a single highly conducive block is fully penetrating the confining layer and ii) a heterogeneous two-layer system where hydraulic conductivity in the confining layer is modelled as a stochastic process. Our numerical results are interpreted through a comparison against those associated with an analytical model which assumes system homogeneity. Monitoring points located in the middle of the modelled aquifer domain, mimicking screened boreholes in field conditions, are used to extract water level records. The output is used to obtain the corresponding BRFs (in terms of gain and phase components) and compared vis-a-vis the selected analytical solution. The results show a wide variety of BRF responses, especially in the gain component, which vary from almost confined to unconfined scenarios. Our simulations show that the BRFs are a viable tool to improve understanding of the degree of spatial continuity within low permeability heterogeneous geological materials such as glacial till which is frequently found overlying water bearing units across the UK and other localities worldwide. As such, it has the potential to improve groundwater vulnerability assessment protocols. The results are promising and support the merit of additional developments through, e.g., numerical Monte Carlo simulations which can be performed to extract meaningful statistical information on the nature of BRFs as a function of randomly heterogeneous confining layers. Keywords: groundwater vulnerability, numerical modeling, barometric response functions, semi-confined aquifers References Hussein M.E.A., Odling N.E. & Clark R.A. (2013). Borehole water level response to barometric pressure as an indicator of aquifer vulnerability, Water Resources Research, 49: 7102-7119. Odling N.E, Perulero Serrano R., Hussein M.E.A, Riva M. & Guadagnini A. (2015). Detecting the vulnerability of groundwater in semi-confined aquifers using barometric response functions, Journal of Hydrology, 520: 143-156.

Integrated modeling of high βN steady state scenario on DIII-D

DOE PAGES

Park, Jin Myung; Ferron, J. R.; Holcomb, Christopher T.; ...

2018-01-10

Theory-based integrated modeling validated against DIII-D experiments predicts that fully non-inductive DIII-D operation with β N > 4.5 is possible with certain upgrades. IPS-FASTRAN is a new iterative numerical procedure that integrates models of core transport, edge pedestal, equilibrium, stability, heating, and current drive self-consistently to find steady-state ( d/dt = 0) solutions and reproduces most features of DIII-D high β N discharges with a stationary current profile. Projecting forward to scenarios possible on DIII-D with future upgrades, the high q min > 2 scenario achieves stable operation at β N as high as 5 by using a very broadmore » current density profile to improve the ideal-wall stabilization of low- n instabilities along with confinement enhancement from low magnetic shear. This modeling guides the necessary upgrades of the heating and current drive system to realize reactor-relevant high β N steady-state scenarios on DIII-D by simultaneous optimization of the current and pressure profiles.« less

Identifying and modeling the structural discontinuities of human interactions

NASA Astrophysics Data System (ADS)

Grauwin, Sebastian; Szell, Michael; Sobolevsky, Stanislav; Hövel, Philipp; Simini, Filippo; Vanhoof, Maarten; Smoreda, Zbigniew; Barabási, Albert-László; Ratti, Carlo

2017-04-01

The idea of a hierarchical spatial organization of society lies at the core of seminal theories in human geography that have strongly influenced our understanding of social organization. Along the same line, the recent availability of large-scale human mobility and communication data has offered novel quantitative insights hinting at a strong geographical confinement of human interactions within neighboring regions, extending to local levels within countries. However, models of human interaction largely ignore this effect. Here, we analyze several country-wide networks of telephone calls - both, mobile and landline - and in either case uncover a systematic decrease of communication induced by borders which we identify as the missing variable in state-of-the-art models. Using this empirical evidence, we propose an alternative modeling framework that naturally stylizes the damping effect of borders. We show that this new notion substantially improves the predictive power of widely used interaction models. This increases our ability to understand, model and predict social activities and to plan the development of infrastructures across multiple scales.

Integrated modeling of high βN steady state scenario on DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jin Myung; Ferron, J. R.; Holcomb, Christopher T.

Theory-based integrated modeling validated against DIII-D experiments predicts that fully non-inductive DIII-D operation with β N > 4.5 is possible with certain upgrades. IPS-FASTRAN is a new iterative numerical procedure that integrates models of core transport, edge pedestal, equilibrium, stability, heating, and current drive self-consistently to find steady-state ( d/dt = 0) solutions and reproduces most features of DIII-D high β N discharges with a stationary current profile. Projecting forward to scenarios possible on DIII-D with future upgrades, the high q min > 2 scenario achieves stable operation at β N as high as 5 by using a very broadmore » current density profile to improve the ideal-wall stabilization of low- n instabilities along with confinement enhancement from low magnetic shear. This modeling guides the necessary upgrades of the heating and current drive system to realize reactor-relevant high β N steady-state scenarios on DIII-D by simultaneous optimization of the current and pressure profiles.« less

Identifying and modeling the structural discontinuities of human interactions

PubMed Central

Grauwin, Sebastian; Szell, Michael; Sobolevsky, Stanislav; Hövel, Philipp; Simini, Filippo; Vanhoof, Maarten; Smoreda, Zbigniew; Barabási, Albert-László; Ratti, Carlo

2017-01-01

The idea of a hierarchical spatial organization of society lies at the core of seminal theories in human geography that have strongly influenced our understanding of social organization. Along the same line, the recent availability of large-scale human mobility and communication data has offered novel quantitative insights hinting at a strong geographical confinement of human interactions within neighboring regions, extending to local levels within countries. However, models of human interaction largely ignore this effect. Here, we analyze several country-wide networks of telephone calls - both, mobile and landline - and in either case uncover a systematic decrease of communication induced by borders which we identify as the missing variable in state-of-the-art models. Using this empirical evidence, we propose an alternative modeling framework that naturally stylizes the damping effect of borders. We show that this new notion substantially improves the predictive power of widely used interaction models. This increases our ability to understand, model and predict social activities and to plan the development of infrastructures across multiple scales. PMID:28443647

Lithofacies and sequence stratigraphic description of the upper part of the Avon Park Formation and the Arcadia Formation in U.S. Geological Survey G–2984 test corehole, Broward County, Florida

USGS Publications Warehouse

Cunningham, Kevin J.; Robinson, Edward

2017-07-18

Rock core and sediment from U.S. Geological Survey test corehole G–2984 completed in 2011 in Broward County, Florida, provide an opportunity to improve the understanding of the lithostratigraphic, sequence stratigraphic, and hydrogeologic framework of the intermediate confining unit and Floridan aquifer system in southeastern Florida. A multidisciplinary approach including characterization of sequence stratigraphy, lithofacies, ichnology, foraminiferal paleontology, depositional environments, porosity, and permeability was used to describe the geologic samples from this test corehole. This information has produced a detailed characterization of the lithofacies and sequence stratigraphy of the upper part of the middle Eocene Avon Park Formation and Oligocene to middle Miocene Arcadia Formation. This enhancement of the knowledge of the sequence stratigraphic framework is especially important, because subaerial karst unconformities at the upper boundary of depositional cycles at various hierarchical scales are commonly associated with secondary porosity and enhanced permeability in the Floridan aquifer system.

Identifying and modeling the structural discontinuities of human interactions.

PubMed

Grauwin, Sebastian; Szell, Michael; Sobolevsky, Stanislav; Hövel, Philipp; Simini, Filippo; Vanhoof, Maarten; Smoreda, Zbigniew; Barabási, Albert-László; Ratti, Carlo

2017-04-26

The idea of a hierarchical spatial organization of society lies at the core of seminal theories in human geography that have strongly influenced our understanding of social organization. Along the same line, the recent availability of large-scale human mobility and communication data has offered novel quantitative insights hinting at a strong geographical confinement of human interactions within neighboring regions, extending to local levels within countries. However, models of human interaction largely ignore this effect. Here, we analyze several country-wide networks of telephone calls - both, mobile and landline - and in either case uncover a systematic decrease of communication induced by borders which we identify as the missing variable in state-of-the-art models. Using this empirical evidence, we propose an alternative modeling framework that naturally stylizes the damping effect of borders. We show that this new notion substantially improves the predictive power of widely used interaction models. This increases our ability to understand, model and predict social activities and to plan the development of infrastructures across multiple scales.

Integrated modeling of high βN steady state scenario on DIII-D

NASA Astrophysics Data System (ADS)

Park, J. M.; Ferron, J. R.; Holcomb, C. T.; Buttery, R. J.; Solomon, W. M.; Batchelor, D. B.; Elwasif, W.; Green, D. L.; Kim, K.; Meneghini, O.; Murakami, M.; Snyder, P. B.

2018-01-01

Theory-based integrated modeling validated against DIII-D experiments predicts that fully non-inductive DIII-D operation with βN > 4.5 is possible with certain upgrades. IPS-FASTRAN is a new iterative numerical procedure that integrates models of core transport, edge pedestal, equilibrium, stability, heating, and current drive self-consistently to find steady-state (d/dt = 0) solutions and reproduces most features of DIII-D high βN discharges with a stationary current profile. Projecting forward to scenarios possible on DIII-D with future upgrades, the high qmin > 2 scenario achieves stable operation at βN as high as 5 by using a very broad current density profile to improve the ideal-wall stabilization of low-n instabilities along with confinement enhancement from low magnetic shear. This modeling guides the necessary upgrades of the heating and current drive system to realize reactor-relevant high βN steady-state scenarios on DIII-D by simultaneous optimization of the current and pressure profiles.

Donor impurity binding energies of coaxial GaAs / Alx Ga1 - x As cylindrical quantum wires in a parallel applied magnetic field

NASA Astrophysics Data System (ADS)

Tshipa, M.; Winkoun, D. P.; Nijegorodov, N.; Masale, M.

2018-04-01

Theoretical investigations are carried out of binding energies of a donor charge assumed to be located exactly at the center of symmetry of two concentric cylindrical quantum wires. The intrinsic confinement potential in the region of the inner cylinder is modeled in any one of the three profiles: simple parabolic, shifted parabolic or the polynomial potential. The potential inside the shell is taken to be a potential step or potential barrier of a finite height. Additional confinement of the charge carriers is due to the vector potential of the axial applied magnetic field. It is found that the binding energies attain maxima in their variations with the radius of the inner cylinder irrespective of the particular intrinsic confinement of the inner cylinder. As the radius of the inner cylinder is increased further, the binding energies corresponding to either the parabolic or the polynomial potentials attain minima at some critical core-radius. Finally, as anticipated, the binding energies increase with the increase of the parallel applied magnetic field. This behaviour of the binding energies is irrespective of the particular electric potential of the nanostructure or its specific dimensions.

Experimental Studies of Compact Toroidal Plasma on BCTX

NASA Astrophysics Data System (ADS)

Morse, Edward C.; Coomer, Eric D.; Hartman, Charles W.

1998-11-01

The Berkeley Compact Toroid Experiment (BCTX) is a spheromak-type magnetically confined fusion confinement experiment. The plasma is formed using a Marshall gun and injected into a 70 cm diameter copper flux conserver. The BCTX device has an RF heating sy stem which can deliver twenty megawatts of RF power for 100 μs pulse length. The RF system operates at 450 MHz, and energy is coupled into the plasma by lower hybrid waves. The purpose of the experiment is to assess the energy-confining capability of the spheromak plasma configuration by using the RF power as a heat pulse and determining the decay rate of the plasma temperature following the heat pulse. Electron temperatures up to 150 eV have been measured in BCTX using Thomson scattering. Core dens ities have been measured with the Raman-calibrated Thomson system in the 2 arrow 5 × 10^14 per cc range. Other diagnostics include magnetic probes, a laser interferometer electron density measurement, three UV spectrometers for impurity l ine radiation, and an ion Doppler temperature measurement. Some data will be presented which shows the effects of an axial pinch being present in the device, giving the device a nonzero q at the wall.

Quantized Self-Assembly of Discotic Rings in a Liquid Crystal Confined in Nanopores

NASA Astrophysics Data System (ADS)

Sentker, Kathrin; Zantop, Arne W.; Lippmann, Milena; Hofmann, Tommy; Seeck, Oliver H.; Kityk, Andriy V.; Yildirim, Arda; Schönhals, Andreas; Mazza, Marco G.; Huber, Patrick

2018-02-01

Disklike molecules with aromatic cores spontaneously stack up in linear columns with high, one-dimensional charge carrier mobilities along the columnar axes, making them prominent model systems for functional, self-organized matter. We show by high-resolution optical birefringence and synchrotron-based x-ray diffraction that confining a thermotropic discotic liquid crystal in cylindrical nanopores induces a quantized formation of annular layers consisting of concentric circular bent columns, unknown in the bulk state. Starting from the walls this ring self-assembly propagates layer by layer towards the pore center in the supercooled domain of the bulk isotropic-columnar transition and thus allows one to switch on and off reversibly single, nanosized rings through small temperature variations. By establishing a Gibbs free energy phase diagram we trace the phase transition quantization to the discreteness of the layers' excess bend deformation energies in comparison to the thermal energy, even for this near room-temperature system. Monte Carlo simulations yielding spatially resolved nematic order parameters, density maps, and bond-orientational order parameters corroborate the universality and robustness of the confinement-induced columnar ring formation as well as its quantized nature.

Alcohol sensing over O+E+S+C+L+U transmission band based on porous cored octagonal photonic crystal fiber

NASA Astrophysics Data System (ADS)

Paul, Bikash Kumar; Islam, Md. Shadidul; Ahmed, Kawsar; Asaduzzaman, Sayed

2017-06-01

A micro structure porous cored octagonal photonic crystal fiber (P-OPCF) has been proposed to sense aqueous analysts (alcohol series) over a wavelength range of 0.80 μm to 2.0 μm. By implementing a full vectorial finite element method (FEM), the numerical simulation on the proposed O-PCF has been analyzed. Numerical investigation shows that high sensitivity can be gained by changing the structural parameters. The obtained result shows the sensitivities of 66.78%, 67.66%, 68.34%, 68.72%, and 69.09%, and the confinement losses of 2.42×10-10 dB/m, 3.28×10-11 dB/m, 1.21×10-6 dB/m, 4.79×10-10 dB/m, and 4.99×10-9 dB/m at the 1.33 μm wavelength for methanol, ethanol, propanol, butanol, and pentanol, respectively can satisfy the condition of much legibility to install an optical system. The effects of the varying core and cladding diameters, pitch distance, operating wavelength, and effective refractive index are also reported here. It reflects that a significant sensitivity and low confinement loss can be achieved by the proposed P-OPCF. The proposed P-OPCF also covers the wavelength band (O+E+S+C+L+U). The investigation also exhibits that the sensitivity increases when the wavelength increases like S O-band< S E-band < S S-band < S C-band < S L-band < S U-band. This research observation has much pellucidity which has remarkable impact on the field of optical fiber sensor.

Synthesis characterisation series of newly fabricated type II CdSe CdSe/CdTe nanocrystals and their optical properties

NASA Astrophysics Data System (ADS)

Ahmed, A. S.; Christopher, W.

2018-03-01

Nanocrystalline semiconductors exhibit different properties due to two basic factors. They possess high surface to volume ratio and the actual size of particle can determine the electronic and physical properties of the material. The small size results in an observable quantum confinement effect, defined by the increasing bandgap accompanied by the quantization of the energy levels to discrete values. In present work we have synthesized the series of cadmium selenide/cadmium telluride (CdSe/CdTe) core/shell and CdSe/CdTe/CdS core/shell/shell to investigate the biexciton energy through transient absorption measurements. These structures are type II nanocrystals are with a hole in the shell and the electron confined to the core. We specifically investigate the effect of nanoparticle shape on the electronic structure and ultrafast electronic dynamics in the band-edge exciton states of CdSe quantum dots, nanorods, and nanoplatelets. Particle size was chosen to enable straightforward comparisons of the effects of particle shape on the spectra and dynamics without retuning the laser source. In our results the Uv-vis showed only a mild redshift in the first excitonic an elongated tail with increasing shell thickness. High resolution Transmission Electron Microscopy (HRTEM) shows the slight agglomeration of the nanocrystals but still the size distribution was calculate able. Spherical small crystals ranging from 5.9 nm to 10 nm are observed. CdTe/CdSe structures were quasi spherical with a rough diameter 6 nm with some little agglomerated structure. . The spherical nanocrystals could be peanut shaped oriented along the c axis or the spherical only, which could explain the two peak emission. p-XRD results indicate the predominant wurtzite structure throughout.

["Tied down"--the process of becoming bedridden through gradual local confinement].

PubMed

Zegelin, Angelika

2005-10-01

To be bedridden is a common phenomenon in nursing. However, there is no solid base of knowledge on reasons, types, development of and coping with this situation. The concept of being bedridden is applied in an arbitrary manner and the state of being bedridden is far from being clearly defined. A literature review revealed that only pathophysiological effects of this state are sufficiently explained. The aim of this study was to gain knowledge of the development of being confined to bed. Thirty-two interviews with elderly, bedridden people (nineteen women, thirteen men) were conducted. They were asked about their perspective on and their experience of the development of being confined to bed. Half of the interviewees lived in a nursing home, the others were cared for at home. Data collection and analysis were performed by using a Grounded Theory approach as developed by Strauss and Corbin. "Gradual local fixation" was identified as the core category. Becoming bedridden is a slow process by which the person is increasingly confined to one location. This development is related to an increasing need for support and to negative consequences such as a pathology of immobility, narrowing of interests, and loss of time. These consequences again are responsible for a downward spiral development. This study reveals phases of development and a range of factors influencing them. Many of these factors arise from the person and his/her interactional behaviour in the circumstances, other influences are structural factors such as external pressure caused by time constraints of professional nursing services or unfavourable arrangements of furniture. A lot of factors of being confined to bed are changeable. Long periods of being bedridden can be prevented in many cases, if early warning signs are being recognized and preventive measures are taken in time.

Simple agarose micro-confinement array and machine-learning-based classification for analyzing the patterned differentiation of mesenchymal stem cells

PubMed Central

Sato, Asako; Vogel, Viola; Tanaka, Yo

2017-01-01

The geometrical confinement of small cell colonies gives differential cues to cells sitting at the periphery versus the core. To utilize this effect, for example to create spatially graded differentiation patterns of human mesenchymal stem cells (hMSCs) in vitro or to investigate underpinning mechanisms, the confinement needs to be robust for extended time periods. To create highly repeatable micro-fabricated structures for cellular patterning and high-throughput data mining, we employed here a simple casting method to fabricate more than 800 adhesive patches confined by agarose micro-walls. In addition, a machine learning based image processing software was developed (open code) to detect the differentiation patterns of the population of hMSCs automatically. Utilizing the agarose walls, the circular patterns of hMSCs were successfully maintained throughout 15 days of cell culture. After staining lipid droplets and alkaline phosphatase as the markers of adipogenic and osteogenic differentiation, respectively, the mega-pixels of RGB color images of hMSCs were processed by the software on a laptop PC within several minutes. The image analysis successfully showed that hMSCs sitting on the more central versus peripheral sections of the adhesive circles showed adipogenic versus osteogenic differentiation as reported previously, indicating the compatibility of patterned agarose walls to conventional microcontact printing. In addition, we found a considerable fraction of undifferentiated cells which are preferentially located at the peripheral part of the adhesive circles, even in differentiation-inducing culture media. In this study, we thus successfully demonstrated a simple framework for analyzing the patterned differentiation of hMSCs in confined microenvironments, which has a range of applications in biology, including stem cell biology. PMID:28380036

Impact of water temperature and stressor controllability on swim stress-induced changes in body temperature, serum corticosterone, and immobility in rats.

PubMed

Drugan, Robert C; Eren, Senem; Hazi, Agnes; Silva, Jennifer; Christianson, John P; Kent, Stephen

2005-10-01

The present study compared the effects of three different water temperatures (20, 25, and 30 degrees C) and stressor controllability on several physiological and behavioral endpoints in an intermittent swim stress paradigm. The escape latency of rats in the 20 and 25 degrees C water was less than that observed for the 30 degrees C group. Both escape and yoked groups at 20 and 25 degrees C exhibited moderate to severe hypothermia following the swim stress session that returned to prestress levels 30-40 min post-stress. At 30 degrees C core body temperature (Tb) only decreased by 1 degree C for either swim group. Following swim, serum corticosterone (CORT) levels were significantly elevated in both escape and yoked groups in comparison to confined and home cage controls. The confined control group showed a significant elevation that was approximately halfway between the home cage control and the swim stress groups. At 30 degrees C, there was still a significant elevation of serum CORT in both swim groups in comparison to confined and home cage controls. Therefore, 30 degrees C appears to be the optimal water temperature to evaluate stress controllability effects in the current paradigm. In a final experiment, swim stressor controllability effects were examined in a 5 min forced swim test (FST) 24 h following the initial stress exposure. Rats exposed to yoked-inescapable swim stress at 30 degrees C exhibited more immobility than their escapable swim stress and confined counterparts, while the escape and confined controls did not differ. These results demonstrate that the behavioral deficits observed in the FST are attributable to the stress of inescapable swim and not swim stress per se.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, Stephanie

2017-10-01

The burning core of an inertial confinement fusion (ICF) plasma at stagnation is surrounded by a shell of warm, dense matter whose properties are difficult both to model (due to a complex interplay of thermal, degeneracy, and strong coupling effects) and to diagnose (due to low emissivity and high opacity). We demonstrate a promising technique to study the warm dense shells of ICF plasmas based on the fluorescence emission of dopants or impurities in the shell material. This emission, which is driven by x-rays produced in the hot core, exhibits signature changes in response to compression and heating. High-resolution measurements of absorption and fluorescence features can refine our understanding of the electronic structure of material under high compression, improve our models of density-driven phenomena such as ionization potential depression and plasma polarization shifts, and help diagnose shell density, temperature, mass distribution, and residual motion in ICF plasmas at stagnation. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. This work was supported by the U.S. Department of Energy, Office of Science Early Career Research Program, Office of Fusion Energy Sciences under FWP-14-017426.

Overview of Recent Alcator C-Mod Highlights

NASA Astrophysics Data System (ADS)

Marmar, Earl; C-Mod Team

2013-10-01

Analysis and modeling of recent C-Mod experiments has yielded significant results across multiple research topics. I-mode provides routine access to high confinement plasma (H98 up to 1.2) in quasi-steady state, without large ELMs; pedestal pressure and impurity transport are regulated by short-wavelength EM waves, and core turbulence is reduced. Multi-channel transport is being investigated in Ohmic and RF-heated plasmas, using advanced diagnostics to validate non-linear gyrokinetic simulations. Results from the new field-aligned ICRF antenna, including significantly reduced high-Z metal impurity contamination, and greatly improved load-tolerance, are being understood through antenna-plasma modeling. Reduced LHCD efficiency at high density correlates with parametric decay and enhanced edge absorption. Strong flow drive and edge turbulence suppression are seen from LHRF, providing new approaches for plasma control. Plasma density profiles directly in front of the LH coupler show non-linear modifications, with important consequences for wave coupling. Disruption-mitigation experiments using massive gas injection at multiple toroidal locations show unexpected results, with potentially significant implications for ITER. First results from a novel accelerator-based PMI diagnostic are presented. What would be the world's first actively-heated high-temperature advanced tungsten divertor is designed and ready for construction. Conceptual designs are being developed for an ultra-advanced divertor facility, Alcator DX, to attack key FNSF and DEMO heat-flux challenges integrated with a high-performance core. Supported by USDOE.

Single-layer graphdiyne-covered Pt(111) surface: improved catalysis confined under two-dimensional overlayer

NASA Astrophysics Data System (ADS)

Chen, Xi; Lin, Zheng-Zhe

2018-05-01

In recent years, two-dimensional confined catalysis, i.e., the enhanced catalytic reactions in confined space between metal surface and two-dimensional overlayer, makes a hit and opens up a new way to enhance the performance of catalysts. In this work, graphdiyne overlayer was proposed as a more excellent material than graphene or hexagonal boron nitride for two-dimensional confined catalysis on Pt(111) surface. Density functional theory calculations revealed the superiority of graphdiyne overlayer originates from the steric hindrance effect which increases the catalytic ability and lowers the reaction barriers. Moreover, with the big triangle holes as natural gas tunnels, graphdiyne possesses higher efficiency for the transit of gaseous reactants and products than graphene or hexagonal boron nitride. The results in this work would benefit future development of two-dimensional confined catalysis. [Figure not available: see fulltext.

Generation of highly confined photonic nanojet using crescent-shape refractive index profile in microsphere

NASA Astrophysics Data System (ADS)

Patel, H. S.; Kushwaha, P. K.; Swami, M. K.

2018-05-01

Photonic nanojets (PNJs) owing to their sub-wavelength near-field features have found many interesting applications like nanoscopy, nano photolithography, high density optical storage, enhancement of Raman signal and single molecule spectroscopy etc. More recently, the focus of research has been on tailoring of PNJs either for better confinement and thus higher peak intensity or for elongation of nanojet for high resolution far field applications. In this paper, we show that crescent-shape refractive index profile (CSRP) of microspheres can be used to generate highly confined PNJ. By optimizing the refractive index of different layers in CSRP microsphere, we show a free space confinement down to ∼ λ / 4 . 5 (FWHM ∼ 110 nm for excitation with 500 nm wavelength). Further, it was observed that the optical properties of substrates also modulate the PNJ characteristics and lead to a further improvement in the transverse confinement to ∼ λ / 6 . 7.

Permeability Evolution of Fractured Anhydrite Caused by Chemical and Mechanical Alteration

NASA Astrophysics Data System (ADS)

Detwiler, R. L.; Elkhoury, J. E.; Ameli, P.

2011-12-01

Geologic carbon sequestration requires competent structural seals (caprock) to prevent leakage over decadal time scales. Injection of large volumes of CO2 perturbs the target formation from chemical and mechanical equilibrium leading to the possible creation or enhancement of leakage pathways. We investigate the potential for leakage pathways (fractures) to grow over time under reservoir conditions in a series of anhydrite (Ca2SO4) cores. To simulate a potential leakage event in the laboratory, we fractured and jacketed the cores, and placed them in a flow-through reactor vessel. A high-pressure syringe pump applied confining stresses ranging from 7 to 17 MPa and another syringe pump pushed water through the sample at a constant flow rate with pressure control at the outlet. Effluent was sampled periodically and analyzed for Ca2+ and SO42- using an ion chromatograph. Before and after each experiment, we characterized the surfaces of the fractures using a high-resolution optical profilometer and a scanning electron microscope. Careful alignment of the surfaces during optical profiling allowed reproduction of the fracture aperture before and after each experiment. We present results from several experiments each carried out under different conditions in similar fractured anhydrite cores. One involved a well-mated pre-existing fracture and results showed that the permeability of the fractured core was similar to the intact rock matrix (O(10-18 m2); chemical alteration of the core was largely limited to the inflow face of the core and the fracture surfaces remained largely unaltered. To enhance permeability during subsequent experiments, we imposed a small (380 μm) shear displacement between the fracture surfaces resulting in a four-order-of-magnitude increase in initial permeability. The first of these was run at a constant flow rate of 0.6 ml/min for a period of 7 days. The measured pressure gradient within the core increased slowly for a period of 4 days followed by a rapid increase in differential pressure corresponding to a two-order-of-magnitude decrease in permeability. During the experiment, the diameter of the core decreased by ~300 μm at the inlet and a skin of gypsum (Ca2SO42H2O) was created along the length of the fracture. Dissolution of anhydrite and transition to gypsum of additional anhydrite weakened the fracture surfaces leading to closure of the fracture with a corresponding reduction in aperture and permeability. Additional experiments explore the influence of flow at a lower flow rate, which, in the absence of a large confining stress, has been shown to lead to the development of dissolution channels or wormholes.

Effect of prepartum exercise, pasture turnout, or total confinement on hoof health.

PubMed

Black, R A; van Amstel, S R; Krawczel, P D

2017-10-01

Lameness is a major welfare concern in the dairy industry, and access to physical activity during the dry period may improve hoof health. The objective of this study was to determine the effects of forced exercise, pasture turnout, or total confinement of dry cows on horn growth and wear and sole thickness. Twenty-nine primiparous and 31 multiparous, pregnant, nonlactating Holstein (n = 58) and Jersey-Holstein crossbred (n = 2) dairy cows were assigned to either total confinement (n = 20), exercise (n = 20), or pasture (n = 20) treatments at dry-off using rolling enrollment from January to November 2015. Cows were managed with a 60-d dry period (58.5 ± 5.4 d) divided into far-off (dry-off to 2 wk before parturition) and close-up periods (2 wk before projected parturition). Cows were housed in a naturally ventilated, 4-row freestall barn at the University of Tennessee's Little River Animal and Environmental Unit (Walland, TN) with concrete flooring and deep-bedded sand freestalls. Cows assigned to confinement remained in the housing pen. Exercise cows were walked for a targeted 1.5 h at 3.25 km/h, 5 times/wk until calving. Pasture cows were turned out for a targeted 1.5 h, 5 times/wk until calving. Hoof growth and wear and sole thickness of the rear hooves were measured on d 2 and 44, relative to dry-off. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). Cranial and caudal horn wear was greater for exercise cows than confinement and pasture cows. Exercise cows experienced more equal rates of horn growth and wear cranially. Confined cows tended to increase sole thickness from d 2 to 44, relative to dry-off. Frequent, short duration exercise on concrete did not impair the hoof health of late-gestation dry cows. Further, exercise may improve overall hoof health, potentially improving cow welfare. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Progress in the Development of a Global Quasi-3-D Multiscale Modeling Framework

NASA Astrophysics Data System (ADS)

Jung, J.; Konor, C. S.; Randall, D. A.

2017-12-01

The Quasi-3-D Multiscale Modeling Framework (Q3D MMF) is a second-generation MMF, which has following advances over the first-generation MMF: 1) The cloud-resolving models (CRMs) that replace conventional parameterizations are not confined to the large-scale dynamical-core grid cells, and are seamlessly connected to each other, 2) The CRMs sense the three-dimensional large- and cloud-scale environment, 3) Two perpendicular sets of CRM channels are used, and 4) The CRMs can resolve the steep surface topography along the channel direction. The basic design of the Q3D MMF has been developed and successfully tested in a limited-area modeling framework. Currently, global versions of the Q3D MMF are being developed for both weather and climate applications. The dynamical cores governing the large-scale circulation in the global Q3D MMF are selected from two cube-based global atmospheric models. The CRM used in the model is the 3-D nonhydrostatic anelastic Vector-Vorticity Model (VVM), which has been tested with the limited-area version for its suitability for this framework. As a first step of the development, the VVM has been reconstructed on the cubed-sphere grid so that it can be applied to global channel domains and also easily fitted to the large-scale dynamical cores. We have successfully tested the new VVM by advecting a bell-shaped passive tracer and simulating the evolutions of waves resulted from idealized barotropic and baroclinic instabilities. For improvement of the model, we also modified the tracer advection scheme to yield positive-definite results and plan to implement a new physics package that includes a double-moment microphysics and an aerosol physics. The interface for coupling the large-scale dynamical core and the VVM is under development. In this presentation, we shall describe the recent progress in the development and show some test results.

H-Mode Behavior Induced by Modulated Toroidal Current on HT-7 and HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Mao, J. S.; Luo, J. R.; Xu, Y. H.; Zhao, J. Y.; Zhang, X. M.; Li, J. G.; Zhang, X. M.; Gao, X.; Li, Y. D.; Jie, Y. X.; Wu, Z. W.; Hu, L. Q.; Liu, S. X.; Zhang, X. D.; Bao, Y.; Yang, K.; Wang, G. X.; Chen, L.; Shi, Y. J.; Qin, P. J.; Gu, X. M.; Cui, N. Z.; Fan, H. Y.; Chen, Y. F.; Xia, C. Y.; Ruan, H. L.; Tong, X. D.; Phillips, P. E.

2001-10-01

An improved Ohmic confinement phase (similar to H-mode) has been observed during Modulating Toroidal Current on the Hefei Tokamak-6M (HT-6M) and Hefei super-conducting Tokamak-7 (HT-7). This improved plasma confinement phase is characterized by: (a) an increase in ne and T_e(0); (b) reduced H_α radiation from the edge; (c) steeper density and temperature profiles at the edge; (d) a more negative radial electric field inside the limiter; (e) a deeper electrostatic potential well at the edge; (f) reduced magnetic fluctuations at the edge; (g) MHD suppressing; (h) and by an increase in global energy confinement time, τ _e, by 27%-45%. The well-like structure of the radial electric field E_r, appears at an L-H like transition.

Use of /sup 3/He/sup + +/ ICRF minority heating to simulate alpha particle heating

DOEpatents

Post, D.E. Jr.; Hwang, D.Q.; Hovey, J.

1983-11-16

It is an object of the present invention to provide a better understanding of alpha particle behavior in a magnetically confined, energetic plasma. Another object of the present invention is to provide an improved means and method for studying and measuring the energy distribution of heated alpha particles in a confined plasma. Yet another object of the present invention is to permit detailed analysis of energetic alpha particle behavior in a magnetically confined plasma for use in near term fusion reactor experiments. A still further object of the present invention is to simulate energetic alpha particle behavior in a deuterium-tritium plasma confined in a fusion reactor without producing the neutron activation associated with the thus produced alpha particles.

Geomorphic expression of strike-slip faults: field observations vs. analog experiments: preliminary results

NASA Astrophysics Data System (ADS)

Hsieh, S. Y.; Neubauer, F.; Genser, J.

2012-04-01

The aim of this project is to study the surface expression of strike-slip faults with main aim to find rules how these structures can be extrapolated to depth. In the first step, several basic properties of the fault architecture are in focus: (1) Is it possible to define the fault architecture by studying surface structures of the damage zone vs. the fault core, particularly the width of the damage zone? (2) Which second order structures define the damage zone of strike-slip faults, and how relate these to such reported in basement fault strike-slip analog experiments? (3) Beside classical fault bend structures, is there a systematic along-strike variation of the damage zone width and to which properties relates the variation of the damage zone width. We study the above mentioned properties on the dextral Altyn fault, which is one of the largest strike-slip on Earth with the advantage to have developed in a fully arid climate. The Altyn fault includes a ca. 250 to 600 m wide fault valley, usually with the trace of actual fault in its center. The fault valley is confined by basement highs, from which alluvial fans develop towards the center of the fault valley. The active fault trace is marked by small scale pressure ridges and offset of alluvial fans. The fault valley confining basement highs are several kilometer long and ca. 0.5 to 1 km wide and confined by rotated dextral anti-Riedel faults and internally structured by a regular fracture pattern. Dextral anti-Riedel faults are often cut by Riedel faults. Consequently, the Altyn fault comprises a several km wide damage zone. The fault core zone is a barrier to fluid flow, and the few springs of the region are located on the margin of the fault valley implying the fractured basement highs as the reservoir. Consequently, the southern Silk Road was using the Altyn fault valley. The preliminary data show that two or more orders of structures exist. Small-scale develop during a single earthquake. These finally accumulate to a several 100 m wide fault core, which is in part exposed at surface to arid climate and a km wide damage zone. The basic structures of analog experiments can be well transferred to nature, although along strike changes are common due to fault bending and fracture failure of country rocks.

The JCMT Gould Belt Survey: first results from SCUBA-2 observations of the Cepheus Flare region

NASA Astrophysics Data System (ADS)

Pattle, K.; Ward-Thompson, D.; Kirk, J. M.; Di Francesco, J.; Kirk, H.; Mottram, J. C.; Keown, J.; Buckle, J.; Beaulieu, S. F.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Hatchell, J.; Jenness, T.; Johnstone, D.; Nutter, D.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Walker-Smith, S.; Hogerheijde, M. R.; Bastien, P.; Bresnahan, D.; Butner, H.; Chen, M.; Chrysostomou, A.; Coudé, S.; Davis, C. J.; Drabek-Maunder, E.; Duarte-Cabral, A.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Sadavoy, S.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

2017-02-01

We present observations of the Cepheus Flare obtained as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Legacy Survey (GBLS) with the SCUBA-2 instrument. We produce a catalogue of sources found by SCUBA-2, and separate these into starless cores and protostars. We determine masses and densities for each of our sources, using source temperatures determined by the Herschel Gould Belt Survey. We compare the properties of starless cores in four different molecular clouds: L1147/58, L1172/74, L1251 and L1228. We find that the core mass functions for each region typically show shallower-than-Salpeter behaviour. We find that L1147/58 and L1228 have a high ratio of starless cores to Class II protostars, while L1251 and L1174 have a low ratio, consistent with the latter regions being more active sites of current star formation, while the former are forming stars less actively. We determine that if modelled as thermally supported Bonnor-Ebert spheres, most of our cores have stable configurations accessible to them. We estimate the external pressures on our cores using archival 13CO velocity dispersion measurements and find that our cores are typically pressure confined, rather than gravitationally bound. We perform a virial analysis on our cores, and find that they typically cannot be supported against collapse by internal thermal energy alone, due primarily to the measured external pressures. This suggests that the dominant mode of internal support in starless cores in the Cepheus Flare is either non-thermal motions or internal magnetic fields.

On the seat of the solar cycle

NASA Technical Reports Server (NTRS)

Gough, D.

1981-01-01

A discussion of some of the issues raised in connection with the seat of the solar cycle are presented. Is the cycle controlled by a strictly periodic oscillator that operates in the core, or is it a turbulent dynamo confined to the convection zone and possibly a thin boundary layer beneath it? Sunspot statistics are discussed, with a view to ascertaining the length of the memory of the cycle, without drawing a definitive conclusion. Also discussed are some of the processes that might bring about variations delta L and delta R in the luminosity and the radius of the photosphere. It appears that the ratio W = delta lnR/delta lnL increases with the depth of the disturbance that produces the variations, so that imminent observations might determine whether or not the principal dynamical processes are confined to only the outer layers of the Sun.

Parametric analyses of planned flowing uranium hexafluoride critical experiments

NASA Technical Reports Server (NTRS)

Rodgers, R. J.; Latham, T. S.

1976-01-01

Analytical investigations were conducted to determine preliminary design and operating characteristics of flowing uranium hexafluoride (UF6) gaseous nuclear reactor experiments in which a hybrid core configuration comprised of UF6 gas and a region of solid fuel will be employed. The investigations are part of a planned program to perform a series of experiments of increasing performance, culminating in an approximately 5 MW fissioning uranium plasma experiment. A preliminary design is described for an argon buffer gas confined, UF6 flow loop system for future use in flowing critical experiments. Initial calculations to estimate the operating characteristics of the gaseous fissioning UF6 in a confined flow test at a pressure of 4 atm, indicate temperature increases of approximately 100 and 1000 K in the UF6 may be obtained for total test power levels of 100 kW and 1 MW for test times of 320 and 32 sec, respectively.

Stability properties and fast ion confinement of hybrid tokamak plasma configurations

NASA Astrophysics Data System (ADS)

Graves, J. P.; Brunetti, D.; Pfefferle, D.; Faustin, J. M. P.; Cooper, W. A.; Kleiner, A.; Lanthaler, S.; Patten, H. W.; Raghunathan, M.

2015-11-01

In hybrid scenarios with flat q just above unity, extremely fast growing tearing modes are born from toroidal sidebands of the near resonant ideal internal kink mode. New scalings of the growth rate with the magnetic Reynolds number arise from two fluid effects and sheared toroidal flow. Non-linear saturated 1/1 dominant modes obtained from initial value stability calculation agree with the amplitude of the 1/1 component of a 3D VMEC equilibrium calculation. Viable and realistic equilibrium representation of such internal kink modes allow fast ion studies to be accurately established. Calculations of MAST neutral beam ion distributions using the VENUS-LEVIS code show very good agreement of observed impaired core fast ion confinement when long lived modes occur. The 3D ICRH code SCENIC also enables the establishment of minority RF distributions in hybrid plasmas susceptible to saturated near resonant internal kink modes.

Fast Ion Effects During Test Blanket Module Simulation Experiments in DIII-D

NASA Astrophysics Data System (ADS)

Kramer, G. J.; Budny, R.; Nazikian, R.; Heidbrink, W. W.; Kurki-Suonio, T.; Salmi, A.; Schaffer, M. J.; van Zeeland, M. A.; Shinohara, K.; Snipes, J. A.; Spong, D.

2010-11-01

The fast beam-ion confinement in the presence of a scaled mock-up of two Test Blanket Modules (TBM) for ITER was studied in DIII-D. The TBM on DIII-D has four vertically arranged protective carbon tiles with thermocouples placed at the back of each tile. Temperature increases of up to 200^oC were measured for the two tiles closest to the midplane when the TBM fields were present. These measurements agree qualitatively with results from the full orbit-following beam-ion code, SPIRAL, that predict beam-ion losses to be localized on the central two carbon tiles when the TBM fields present. Within the experimental uncertainties no significant change in the fast-ion population was found in the core of these plasmas which is consistent with SPIRAL analysis. These experiments indicate that the TBM fields do not affect the fast-ion confinement in a harmful way which is good news for ITER.

Realizing steady-state tokamak operation for fusion energy

NASA Astrophysics Data System (ADS)

Luce, T. C.

2011-03-01

Continuous operation of a tokamak for fusion energy has clear engineering advantages but requires conditions beyond those sufficient for a burning plasma. The fusion reactions and external sources must support both the pressure and the current equilibrium without inductive current drive, leading to demands on stability, confinement, current drive, and plasma-wall interactions that exceed those for pulsed tokamaks. These conditions have been met individually, and significant progress has been made in the past decade to realize scenarios where the required conditions are obtained simultaneously. Tokamaks are operated routinely without disruptions near pressure limits, as needed for steady-state operation. Fully noninductive sustainment with more than half of the current from intrinsic currents has been obtained for a resistive time with normalized pressure and confinement approaching those needed for steady-state conditions. One remaining challenge is handling the heat and particle fluxes expected in a steady-state tokamak without compromising the core plasma performance.

Au10(SG)10: A Chiral Gold Catenane Nanocluster with Zero Confined Electrons. Optical Properties and First-Principles Theoretical Analysis.

PubMed

Bertorelle, Franck; Russier-Antoine, Isabelle; Calin, Nathalie; Comby-Zerbino, Clothilde; Bensalah-Ledoux, Amina; Guy, Stephan; Dugourd, Philippe; Brevet, Pierre-François; Sanader, Željka; Krstić, Marjan; Bonačić-Koutecký, Vlasta; Antoine, Rodolphe

2017-05-04

We report facile synthesis of the Au 10 (SG) 10 nanoclusters, where SG stands for glutathione, found to be promising as a new class of radiosensitizers for cancer radiotherapy. The homoleptic catenane structure with two Au 5 SG 5 interconnected rings, among different isomer structures, gives the best agreement between theoretical and experimental optical spectra and XRD patterns. This catenane structure exhibits a centrosymmetry-broken structure, resulting in enhanced second harmonic response and new characteristic circular dichroism signals in the spectral region of 250-400 nm. This is the first determination of the nonlinear optical properties of a ligated cluster with an equal Au-to-ligand ratio, thus without a metallic core and therefore zero confined electrons. Insight into the nonlinear and chiroptical efficiencies arising from interplay between structural and electronic properties is provided by the TD-DFT approach.

Optimisation of confinement in a fusion reactor using a nonlinear turbulence model

NASA Astrophysics Data System (ADS)

Highcock, E. G.; Mandell, N. R.; Barnes, M.

2018-04-01

The confinement of heat in the core of a magnetic fusion reactor is optimised using a multidimensional optimisation algorithm. For the first time in such a study, the loss of heat due to turbulence is modelled at every stage using first-principles nonlinear simulations which accurately capture the turbulent cascade and large-scale zonal flows. The simulations utilise a novel approach, with gyrofluid treatment of the small-scale drift waves and gyrokinetic treatment of the large-scale zonal flows. A simple near-circular equilibrium with standard parameters is chosen as the initial condition. The figure of merit, fusion power per unit volume, is calculated, and then two control parameters, the elongation and triangularity of the outer flux surface, are varied, with the algorithm seeking to optimise the chosen figure of merit. A twofold increase in the plasma power per unit volume is achieved by moving to higher elongation and strongly negative triangularity.

Radio frequency discharge with control of plasma potential distribution.

PubMed

Dudnikov, Vadim; Dudnikov, A

2012-02-01

A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.

Theoretical and experimental study of bent fully aperiodic large-pitch fibers for enhancing the high-order modes delocalization

NASA Astrophysics Data System (ADS)

du Jeu, Rémi; Dauliat, Romain; Darwich, Dia; Auguste, Jean-Louis; Benoît, Aurélien; Leconte, Baptiste; Malleville, Marie-Alicia; Jamier, Raphaël.; Schuster, Kay; Roy, Philippe

2018-02-01

The power scaling of fiber lasers and amplifiers has triggered an extensive development of large-mode area fibers among which the most promising are the distributed mode filtering fibers and the large-pitch fibers. These structures enable for an effective higher-order modes delocalization and subsequently a singlemode emission. An interesting alternative consists in using the fully-aperiodic large-pitch fibers, into which the standard air-silica photonic crystal cladding is replaced by an aperiodic pattern made of solid low-index inclusions cladding. However, in such a structure, the core and the background cladding material surrounding it must have rigorously the same refractive index. Current synthesis processes and measurement techniques offer respectively a maximum resolution of 5×10-4 and 1×10-4 while the indexmatching must be as precise as 1×10-5 . Lately a gain material with a refractive index 1.5×10-4 higher than that of the background cladding material was fabricated, thus re-confining the first higher-order modes in the core. A numerical study is carried out on the benefit of bending such fully-aperiodic fiber to counteract this phenomenon. Optimized bending axis and radius have been determined. Experiments are done in a laser cavity operating at 1030 nm using an 88cm-long 51μm core diameter ytterbium-doped fiber. Results demonstrate an improvement of the M2 from 1.7 when the fiber is kept straight to 1.2 when it is bent with a 100 to 60 cm bend radius. These primary results are promising for future power scaling.

Automatic Between-Pulse Analysis of DIII-D Experimental Data Performed Remotely on a Supercomputer at Argonne Leadership Computing Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostuk, M.; Uram, T. D.; Evans, T.

For the first time, an automatically triggered, between-pulse fusion science analysis code was run on-demand at a remotely located supercomputer at Argonne Leadership Computing Facility (ALCF, Lemont, IL) in support of in-process experiments being performed at DIII-D (San Diego, CA). This represents a new paradigm for combining geographically distant experimental and high performance computing (HPC) facilities to provide enhanced data analysis that is quickly available to researchers. Enhanced analysis improves the understanding of the current pulse, translating into a more efficient use of experimental resources, and to the quality of the resultant science. The analysis code used here, called SURFMN,more » calculates the magnetic structure of the plasma using Fourier transform. Increasing the number of Fourier components provides a more accurate determination of the stochastic boundary layer near the plasma edge by better resolving magnetic islands, but requires 26 minutes to complete using local DIII-D resources, putting it well outside the useful time range for between pulse analysis. These islands relate to confinement and edge localized mode (ELM) suppression, and may be controlled by adjusting coil currents for the next pulse. Argonne has ensured on-demand execution of SURFMN by providing a reserved queue, a specialized service that launches the code after receiving an automatic trigger, and with network access from the worker nodes for data transfer. Runs are executed on 252 cores of ALCF’s Cooley cluster and the data is available locally at DIII-D within three minutes of triggering. The original SURFMN design limits additional improvements with more cores, however our work shows a path forward where codes that benefit from thousands of processors can run between pulses.« less

Automatic Between-Pulse Analysis of DIII-D Experimental Data Performed Remotely on a Supercomputer at Argonne Leadership Computing Facility

DOE PAGES

Kostuk, M.; Uram, T. D.; Evans, T.; ...

2018-02-01

For the first time, an automatically triggered, between-pulse fusion science analysis code was run on-demand at a remotely located supercomputer at Argonne Leadership Computing Facility (ALCF, Lemont, IL) in support of in-process experiments being performed at DIII-D (San Diego, CA). This represents a new paradigm for combining geographically distant experimental and high performance computing (HPC) facilities to provide enhanced data analysis that is quickly available to researchers. Enhanced analysis improves the understanding of the current pulse, translating into a more efficient use of experimental resources, and to the quality of the resultant science. The analysis code used here, called SURFMN,more » calculates the magnetic structure of the plasma using Fourier transform. Increasing the number of Fourier components provides a more accurate determination of the stochastic boundary layer near the plasma edge by better resolving magnetic islands, but requires 26 minutes to complete using local DIII-D resources, putting it well outside the useful time range for between pulse analysis. These islands relate to confinement and edge localized mode (ELM) suppression, and may be controlled by adjusting coil currents for the next pulse. Argonne has ensured on-demand execution of SURFMN by providing a reserved queue, a specialized service that launches the code after receiving an automatic trigger, and with network access from the worker nodes for data transfer. Runs are executed on 252 cores of ALCF’s Cooley cluster and the data is available locally at DIII-D within three minutes of triggering. The original SURFMN design limits additional improvements with more cores, however our work shows a path forward where codes that benefit from thousands of processors can run between pulses.« less

Suppression of MHD fluctuations leading to improved confinement in a gun-driven spheromak.

PubMed

McLean, H S; Woodruff, S; Hooper, E B; Bulmer, R H; Hill, D N; Holcomb, C; Moller, J; Stallard, B W; Wood, R D; Wang, Z

2002-03-25

Magnetic fluctuations have been reduced to approximately 1% during discharges on the Sustained Spheromak Physics Experiment by shaping the spatial distribution of the bias magnetic flux in the device. In the resulting quiescent regime, the safety factor profile is nearly flat in the plasma and the dominant ideal and resistive MHD modes are greatly reduced. During this period, the temperature profile is peaked at the magnetic axis and maps onto magnetic flux contours. Energy confinement time is improved over previous reports in a driven spheromak.

In-gap corner states in core-shell polygonal quantum rings

PubMed Central

Sitek, Anna; Ţolea, Mugurel; Niţă, Marian; Serra, Llorenç; Gudmundsson, Vidar; Manolescu, Andrei

2017-01-01

We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states. PMID:28071750

Combined effect of cortical cytoskeleton and transmembrane proteins on domain formation in biomembranes

PubMed Central

Sikder, Md. Kabir Uddin; Stone, Kyle A.; Kumar, P. B. Sunil; Laradji, Mohamed

2014-01-01

We investigate the combined effects of transmembrane proteins and the subjacent cytoskeleton on the dynamics of phase separation in multicomponent lipid bilayers using computer simulations of a particle-based implicit solvent model for lipid membranes with soft-core interactions. We find that microphase separation can be achieved by the protein confinement by the cytoskeleton. Our results have relevance to the finite size of lipid rafts in the plasma membrane of mammalian cells. PMID:25106608

Imaging of high-energy x-ray emission from cryogenic thermonuclear fuel implosions on the NIF.

PubMed

Ma, T; Izumi, N; Tommasini, R; Bradley, D K; Bell, P; Cerjan, C J; Dixit, S; Döppner, T; Jones, O; Kline, J L; Kyrala, G; Landen, O L; LePape, S; Mackinnon, A J; Park, H-S; Patel, P K; Prasad, R R; Ralph, J; Regan, S P; Smalyuk, V A; Springer, P T; Suter, L; Town, R P J; Weber, S V; Glenzer, S H

2012-10-01

Accurately assessing and optimizing the implosion performance of inertial confinement fusion capsules is a crucial step to achieving ignition on the NIF. We have applied differential filtering (matched Ross filter pairs) to provide broadband time-integrated absolute x-ray self-emission images of the imploded core of cryogenic layered implosions. This diagnostic measures the temperature- and density-sensitive bremsstrahlung emission and provides estimates of hot spot mass, mix mass, and pressure.

Development And Testing Of The Inertial Electrostatic Confinement Diffusion Thruster

NASA Technical Reports Server (NTRS)

Becnel, Mark D.; Polzin, Kurt A.

2013-01-01

The Inertial Electrostatic Confinement (IEC) diffusion thruster is an experiment in active development that takes advantage of physical phenomenon that occurs during operation of an IEC device. The IEC device has been proposed as a fusion reactor design that relies on traditional electrostatic ion acceleration and is typically arranged in a spherical geometry. The design incorporates two radially-symmetric spherical electrodes. Often the inner electrode utilizes a grid of wire shaped in a sphere with a radius 15 to 50 percent of the radius of the outer electrode. The inner electrode traditionally has 90 percent or more transparency to allow particles (ions) to pass to the center of the spheres and collide/recombine in the dense plasma core at r=0. When operating the IEC, an unsteady plasma leak is typically observed passing out one of the gaps in the lattice grid of the inner electrode. The IED diffusion thruster is based upon the idea that this plasma leak can be used for propulsive purposes. The IEC diffusion thruster utilizes the radial symmetry found in the IEC device. A cylindrical configuration is employed here as it will produce a dense core of plasma the length of the cylindrical grid while promoting the plasma leak to exhaust through an electromagnetic nozzle at one end of the apparatus. A proof-of-concept IEC diffusion thruster is operational and under testing using argon as propellant (Figure 1).

Ultra-confined surface phonon polaritons in molecular layers of van der Waals dielectrics.

PubMed

Dubrovkin, Alexander M; Qiang, Bo; Krishnamoorthy, Harish N S; Zheludev, Nikolay I; Wang, Qi Jie

2018-05-02

Improvements in device density in photonic circuits can only be achieved with interconnects exploiting highly confined states of light. Recently this has brought interest to highly confined plasmon and phonon polaritons. While plasmonic structures have been extensively studied, the ultimate limits of phonon polariton squeezing, in particular enabling the confinement (the ratio between the excitation and polariton wavelengths) exceeding 10 2 , is yet to be explored. Here, exploiting unique structure of 2D materials, we report for the first time that atomically thin van der Waals dielectrics (e.g., transition-metal dichalcogenides) on silicon carbide substrate demonstrate experimentally record-breaking propagating phonon polaritons confinement resulting in 190-times squeezed surface waves. The strongly dispersive confinement can be potentially tuned to greater than 10 3 near the phonon resonance of the substrate, and it scales with number of van der Waals layers. We argue that our findings are a substantial step towards infrared ultra-compact phonon polaritonic circuits and resonators, and would stimulate further investigations on nanophotonics in non-plasmonic atomically thin interface platforms.

Confined wormlike chains in external fields

NASA Astrophysics Data System (ADS)

Morrison, Greg

The confinement of biomolecules is ubiquitous in nature, such as the spatial constraints of viral encapsulation, histone binding, and chromosomal packing. Advances in microfluidics and nanopore fabrication have permitted powerful new tools in single molecule manipulation and gene sequencing through molecular confinement as well. In order to fully understand and exploit these systems, the ability to predict the structure of spatially confined molecules is essential. In this talk, I describe a mean field approach to determine the properties of stiff polymers confined to cylinders and slits, which is relevant for a variety of biological and experimental conditions. I show that this approach is able to not only reproduce known scaling laws for confined wormlike chains, but also provides an improvement over existing weakly bending rod approximations in determining the detailed chain properties (such as correlation functions). Using this approach, we also show that it is possible to study the effect of an externally applied tension or static electric field in a natural and analytically tractable way. These external perturbations can alter the scaling laws and introduce important new length scales into the system, relevant for histone unbinding and single-molecule analysis of DNA.

MEASUREMENTS OF THE CONFINEMENT LEAKTIGHTNESS AT THE KOLA NUCLEAR POWER STATION (UNIT 2) IN RUSSIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

GREENE,G.A.; GUPPY,J.G.

1998-08-01

This is the final report on the INSP project entitled, ``Kola Confinement Leaktightness'' conducted by BNL under the authorization of Project Work Plan WBS 1.2.2.1. This project was initiated in February 1993 to assist the Russians to reduce risks associated with the continued operation of older Soviet-designed nuclear power plants, specifically the Kola VVER-440/230 Units 1 and 2, through upgrades in the confinement performance to reduce the uncontrolled leakage rate. The major technical objective of this-project was to improve the leaktightness of the Kola NPP VVER confinement boundaries, through the application of a variety of sealants to penetrations, doors andmore » hatches, seams and surfaces, to the extent that current technology permitted. A related objective was the transfer, through training of Russian staff, of the materials application procedures to the staff of the Kola NPP. This project was part of an overall approach to minimizing uncontrolled releases from the Kola NPP VVER440/230s in the event of a serious accident, and to thereby significantly mitigate the consequences of such an accident. The US provided materials, application technology, and applications equipment for application of sealant materials, surface coatings, potting materials and gaskets, to improve the confinement leaktightness of the Kola VVER-440/23Os. The US provided for training of Russian personnel in the applications technology.« less

Heavy impurity confinement in hybrid operation scenario plasmas with a rotating 1/1 continuous mode

NASA Astrophysics Data System (ADS)

Raghunathan, M.; Graves, J. P.; Nicolas, T.; Cooper, W. A.; Garbet, X.; Pfefferlé, D.

2017-12-01

In future tokamaks like ITER with tungsten walls, it is imperative to control tungsten accumulation in the core of operational plasmas, especially since tungsten accumulation can lead to radiative collapse and disruption. We investigate the behavior of tungsten trace impurities in a JET-like hybrid scenario with both axisymmetric and saturated 1/1 ideal helical core in the presence of strong plasma rotation. For this purpose, we obtain the equilibria from VMEC and use VENUS-LEVIS, a guiding-center orbit-following code, to follow heavy impurity particles. In this work, VENUS-LEVIS has been modified to account for strong plasma flows with associated neoclassical effects arising from such flows. We find that the combination of helical core and plasma rotation augments the standard neoclassical inward pinch compared to axisymmetry, and leads to a strong inward pinch of impurities towards the magnetic axis despite the strong outward diffusion provided by the centrifugal force, as frequently observed in experiments.

Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

DOE PAGES

Wang, Xue; Choi, Sang-Il; Roling, Luke T.; ...

2015-07-02

Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can bemore » attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.« less

Bifurcated helical core equilibrium states in tokamaks

NASA Astrophysics Data System (ADS)

Cooper, W. A.; Chapman, I. T.; Schmitz, O.; Turnbull, A. D.; Tobias, B. J.; Lazarus, E. A.; Turco, F.; Lanctot, M. J.; Evans, T. E.; Graves, J. P.; Brunetti, D.; Pfefferlé, D.; Reimerdes, H.; Sauter, O.; Halpern, F. D.; Tran, T. M.; Coda, S.; Duval, B. P.; Labit, B.; Pochelon, A.; Turnyanskiy, M. R.; Lao, L.; Luce, T. C.; Buttery, R.; Ferron, J. R.; Hollmann, E. M.; Petty, C. C.; van Zeeland, M.; Fenstermacher, M. E.; Hanson, J. M.; Lütjens, H.

2013-07-01

Tokamaks with weak to moderate reversed central shear in which the minimum inverse rotational transform (safety factor) qmin is in the neighbourhood of unity can trigger bifurcated magnetohydrodynamic equilibrium states, one of which is similar to a saturated ideal internal kink mode. Peaked prescribed pressure profiles reproduce the ‘snake’ structures observed in many tokamaks which has led to a novel explanation of the snake as a bifurcated equilibrium state. Snake equilibrium structures are computed in simulations of the tokamak à configuration variable (TCV), DIII-D and mega amp spherical torus (MAST) tokamaks. The internal helical deformations only weakly modulate the plasma-vacuum interface which is more sensitive to ripple and resonant magnetic perturbations. On the other hand, the external perturbations do not alter the helical core deformation in a significant manner. The confinement of fast particles in MAST simulations deteriorate with the amplitude of the helical core distortion. These three-dimensional bifurcated solutions constitute a paradigm shift that motivates the applications of tools developed for stellarator research in tokamak physics investigations.

A preliminary examination of differential decomposition patterns in mass graves.

PubMed

Troutman, Lauren; Moffatt, Colin; Simmons, Tal

2014-05-01

Five pairs of mass graves, each containing carcasses of 21 rabbits, were used to examine differential decomposition at four locations within the burial: surface, deep, mid-outer, and core. Every 100 accumulated degree days (ADD), a pair of graves was exhumed, and total body score (TBS) and internal carcass temperature of each rabbit were recorded. Decomposition did not differ for core- and deep-positioned carcasses (p = 0.13); differences were significant (p < 0.001) for all other location comparisons. Decomposition occurred fastest in shallow carcasses, followed by mid-outer carcasses; deep and core carcasses decomposed slowest and at rates not significantly different from one another. Adipocere formation was minimal and confined to deep carcasses. Carcass location within the mass grave significantly influenced internal carcass temperature (p < 0.001); a mean internal temperature difference of ca. 1°C existed between deep and shallow carcasses (30 cm apart). Effects of mass compactness and oxygenation require further investigation. © 2013 American Academy of Forensic Sciences.

Accuracy improvement of quantitative analysis by spatial confinement in laser-induced breakdown spectroscopy.

PubMed

Guo, L B; Hao, Z Q; Shen, M; Xiong, W; He, X N; Xie, Z Q; Gao, M; Li, X Y; Zeng, X Y; Lu, Y F

2013-07-29

To improve the accuracy of quantitative analysis in laser-induced breakdown spectroscopy, the plasma produced by a Nd:YAG laser from steel targets was confined by a cavity. A number of elements with low concentrations, such as vanadium (V), chromium (Cr), and manganese (Mn), in the steel samples were investigated. After the optimization of the cavity dimension and laser fluence, significant enhancement factors of 4.2, 3.1, and 2.87 in the emission intensity of V, Cr, and Mn lines, respectively, were achieved at a laser fluence of 42.9 J/cm(2) using a hemispherical cavity (diameter: 5 mm). More importantly, the correlation coefficient of the V I 440.85/Fe I 438.35 nm was increased from 0.946 (without the cavity) to 0.981 (with the cavity); and similar results for Cr I 425.43/Fe I 425.08 nm and Mn I 476.64/Fe I 492.05 nm were also obtained. Therefore, it was demonstrated that the accuracy of quantitative analysis with low concentration elements in steel samples was improved, because the plasma became uniform with spatial confinement. The results of this study provide a new pathway for improving the accuracy of quantitative analysis of LIBS.

Fault zone structure and fluid-rock interaction of a high angle normal fault in Carrara marble (NW Tuscany, Italy)

NASA Astrophysics Data System (ADS)

Molli, G.; Cortecci, G.; Vaselli, L.; Ottria, G.; Cortopassi, A.; Dinelli, E.; Mussi, M.; Barbieri, M.

2010-09-01

We studied the geometry, intensity of deformation and fluid-rock interaction of a high angle normal fault within Carrara marble in the Alpi Apuane NW Tuscany, Italy. The fault is comprised of a core bounded by two major, non-parallel slip surfaces. The fault core, marked by crush breccia and cataclasites, asymmetrically grades to the host protolith through a damage zone, which is well developed only in the footwall block. On the contrary, the transition from the fault core to the hangingwall protolith is sharply defined by the upper main slip surface. Faulting was associated with fluid-rock interaction, as evidenced by kinematically related veins observable in the damage zone and fluid channelling within the fault core, where an orange-brownish cataclasite matrix can be observed. A chemical and isotopic study of veins and different structural elements of the fault zone (protolith, damage zone and fault core), including a mathematical model, was performed to document type, role, and activity of fluid-rock interactions during deformation. The results of our studies suggested that deformation pattern was mainly controlled by processes associated with a linking-damage zone at a fault tip, development of a fault core, localization and channelling of fluids within the fault zone. Syn-kinematic microstructural modification of calcite microfabric possibly played a role in confining fluid percolation.

Electronic, Optical, and Thermal Properties of Reduced-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Huang, Shouting

Reduced-dimensional materials have attracted tremendous attention because of their new physics and exotic properties, which are of great interests for fundamental science. More importantly, the manipulation and engineering of matter on an atomic scale yield promising applications for many fields including nanoelectronics, nanobiotechnology, environments, and renewable energy. Because of the unusual quantum confinement and enhanced surface effect of reduced-dimensional materials, traditional empirical models suffer from necessary but unreliable parameters extracted from previously-studied bulk materials. In this sense, quantitative, parameter-free approaches are highly useful for understanding properties of reduced-dimensional materials and, furthermore, predicting their novel applications. The first-principles density functional theory (DFT) is proven to be a reliable and convenient tool. In particular, recent progress in many-body perturbation theory (MBPT) makes it possible to calculate excited-state properties, e.g., quasiparticle (QP) band gap and optical excitations, by the first-principles approach based on DFT. Therefore, during my PhD study, I employed first-principles calculations based on DFT and MBPT to systematically study fundamental properties of typical reduced-dimensional semiconductors, i.e., the electronic structure, phonons, and optical excitations of core-shell nanowires (NWs) and graphene-like two-dimensional (2D) structures of current interests. First, I present first-principles studies on how to engineer band alignments of nano-sized radial heterojunctions, Si/Ge core-shell NWs. Our calculation reveals that band offsets in these one-dimensional (1D) nanostructures can be tailored by applying axial strain or varying core-shell sizes. In particular, the valence band offset can be efficiently tuned across a wide range and even be diminished via applied strain. Two mechanisms contribute to this tuning of band offsets. Furthermore, varying the size of Si/Ge core-shell NWs and corresponding quantum confinement is shown to be efficient for modifying both valence and conduction band offsets simultaneously. Our proposed approaches to control band offsets in nano-sized heterojunctions may be of practical interest for nanoelectronic and photovoltaic applications. Additionally, I also studied the lattice vibrational modes of Si/Ge core-shell N-Ws. Our calculations show that the internal strain induced by the lattice mismatch between core and shell plays an important role in significantly shifting the frequency of characteristic optical modes of core-shell NWs. In particular, our simulation demonstrates that these frequency shifts can be detected by Raman-scattering experiments, giving rise to a convenient and nondestructive way to obtain structural information of core-shell materials. Meanwhile, another type of collective modes, the radial breathing modes (RBM), is identified in Si-core/Ge-shell NWs and their frequency dependence is explained by an elastic media model. Our studied vibrational modes and their frequency evolution are useful for thermoelectric applications based on core-shell nanostructures. Then I studied optical properties and exciton spectra of 2D semiconducting carbon structures. The energy spectra and wavefunctions of excitons in the 2D graphene derivatives, i.e., graphyne and graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity and optical selection rules are preserved. Thus a one-parameter hydrogenic model is applied to quantitatively explain the ab initio exciton spectra, and allows one to extrapolate the electron-hole binding energy from optical spectroscopies of 2D semiconductors without costly simulations. Meanwhile, our calculated optical absorption spectrum and enhanced spin singlet-triplet splitting project graphyne, an allotrope of graphene, as a good candidate for intriguing energy and biomedical applications. Lastly, we report first-principles results on electronic structures of 2D graphene-like system, i.e., silicene. For planar and simply buckled silicene structures, we confirm their zero-gap nature and show a significant renormalization of their Fermi velocity by including many-electron effects. However, the other two recently proposed silicene structures exhibit a finite band gap, indicating that they are gapped semiconductors instead of expected Dirac-fermion semimetals. This finite band gap of the latter two structures is preserved even with the Ag substrate included. The gap opening is explained by the symmetry breaking of the buckled structures. Moreover, our GW calculation reveals enhanced many-electron effects in these 2D structures. Finally the band gap of the latter two structures can be tuned in a wide range by applying strain.

Wormhole at the core of an infinite cosmic string

NASA Astrophysics Data System (ADS)

Aros, Rodrigo O.; Zamorano, Nelson

1997-11-01

We study a solution of Einstein's equations that describes a straight cosmic string with a variable angular deficit, starting with a 2π deficit at the core. We show that the coordinate singularity associated with this defect can be interpreted as a traversable wormhole lodging at the core of the string. A negative energy density gradually decreases the angular deficit as the distance from the core increases, ending, at radial infinity, in a Minkowski spacetime. The negative energy density can be confined to a small transversal section of the string by gluing to it an exterior Gott-like solution that freezes the angular deficit existing at the matching border. The equation of state of the string is such that any massive particle may stay at rest anywhere in this spacetime. In this sense this is a 2+1 spacetime solution. A generalization that includes the existence of two interacting parallel wormholes is displayed. These wormholes are not traversable. Finally, we point out that a similar result, flat at infinity and with a 2π defect (or excess) at the core, has been recently published by Dyer and Marleau. Even though theirs is a local string fully coupled to gravity, our toy model captures important aspects of this solution.

The effect of macro-bending on power confinement factor in single mode fibers

NASA Astrophysics Data System (ADS)

Waluyo, T. B.; Bayuwati, D.; Mulyanto, I.

2018-03-01

One of the methods to determine the macro-bending effect in a single mode fiber is by calculating its power loss coefficient. We describe an alternative method by using the equation of fractional power in the fiber core. Knowing the fiber parameters such as its core radius, refractive indexes, and operating wavelength; we can calculate the V-number and the fractional power in the core. Because the value of the fiber refractive indexes and the propagation constant are affected by bending, we can calculate the value of the fractional power in the core as a function of the bending radius. We calculate the fractional power in the core of an SMF28 and SM600 fiber and, to verify our calculation, we measure its transmission loss using an optical spectrum analyzer. Our calculations and experimental results showed that for SMF28 fiber, there is about 4% power loss due to bending at 633 nm, about 8% at 1310 nm, about 20% at 1550 nm, and about 60% at 1064 nm. For SM600 fiber, there is about 6% power loss due to bending at 633 nm, about 11% at 850 nm, and this fiber is not suitable for operating wavelength beyond 1000 nm.

Dynamo Tests for Stratification Below the Core-Mantle Boundary

NASA Astrophysics Data System (ADS)

Olson, P.; Landeau, M.

2017-12-01

Evidence from seismology, mineral physics, and core dynamics points to a layer with an overall stable stratification in the Earth's outer core, possibly thermal in origin, extending below the core-mantle boundary (CMB) for several hundred kilometers. In contrast, energetic deep mantle convection with elevated heat flux implies locally unstable thermal stratification below the CMB in places, consistent with interpretations of non-dipole geomagnetic field behavior that favor upwelling flows below the CMB. Here, we model the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux in order to rationalize this conflicting evidence. Strongly heterogeneous boundary heat flux generates localized convection beneath the CMB that coexists with an overall stable stratification there. Partially stratified dynamos have distinctive time average magnetic field structures. Without stratification or with stratification confined to a thin layer, the octupole component is small and the CMB magnetic field structure includes polar intensity minima. With more extensive stratification, the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions. Comparisons with the time-averaged geomagnetic field are generally favorable for partial stratification in a thin layer but unfavorable for stratification in a thick layer beneath the CMB.

Tellurite microstructure fibers with small hexagonal core for supercontinuum generation.

PubMed

Liao, Meisong; Chaudhari, Chitrarekha; Qin, Guanshi; Yan, Xin; Suzuki, Takenobu; Ohishi, Yasutake

2009-07-06

Tellurite glass microstructure fibers with a 1 microm hexagonal core were fabricated successfully by accurately controlling the temperature field in the fiber-drawing process. The diameter ratio of holey region to core (DRHC) for the fiber can be adjusted freely in the range of 1-20 by pumping a positive pressure into the holes when drawing fiber, which provides much freedom in engineering the chromatic dispersion. With the increase of DRHC from 3.5 to 20, the zero dispersion wavelengths were shifted several hundred nanometers, the cutoff wavelength due to confinement loss was increased from 1600 nm to 3800 nm, and the nonlinear coefficient gamma was increased from 3.9 to 5.7 W(-1)/m. Efficient visible emissions due to third harmonic generation were found for fibers with a DRHC of 10 and 20 under the 1557 nm pump of a femtosecond fiber laser. One octave flattened supercontinuum spectrum was generated from fibers with a DRHC of 3.5, 10 and 20 by the 1064 nm pump of a picosecond fiber laser. To the best of our knowledge, we have for the first time fabricated a hexagonal core fiber by soft glass with such a small core size, and have demonstrated a large influence of the holey region on the dispersion, nonlinear coefficient and supercontinuum generation for such fiber.

Range of earth structure nonuniqueness implied by body wave observations.

NASA Technical Reports Server (NTRS)

Wiggins, R. A.; Mcmechan, G. A.; Toksoz, M. N.

1973-01-01

The Herglotz-Wiechert integral for the direct inversion of ray parameter versus distance curves can be manipulated to find the envelope of all possible models consistent with geometrical body wave observations (travel time and ray parameter versus distance). Such an extremal inversion approach has been used to find the uncertainty bounds for the velocity structure in the mantle and core. It is found, for example, that there is an uncertainty of plus or minus 40 km in the radius of the inner core boundary, plus or minus 18 km at the core-mantle boundary, and plus or minus 35 km at the 435-km transition zone. The velocity uncertainty is about plus or minus 0.08 km/sec for P and S waves in the lower mantle and about plus or minus 0.20 km/sec in the core. Experiments with various combinations of ray types in the core indicate that rather crude observations of SKKS-SKS travel times confine the range of possible models far more dramatically than do the most precise estimates of PmKP travel times. Comparisons of results from extremal inversion and linearized perturbation inversions indicate that body wave behavior is too strongly nonlinear for linearized schemes to be effective for predicting uncertainty.

Detecting the transition to failure: wavelet analysis of multi-scale crack patterns at different confining pressures

NASA Astrophysics Data System (ADS)

Rizzo, R. E.; Healy, D.; Farrell, N. J.

2017-12-01

Numerous laboratory brittle deformation experiments have shown that a rapid transition exists in the behaviour of porous materials under stress: at a certain point, early formed tensile cracks interact and coalesce into a `single' narrow zone, the shear plane, rather than remaining distributed throughout the material. In this work, we present and apply a novel image processing tool which is able to quantify this transition between distributed (`stable') damage accumulation and localised (`unstable') deformation, in terms of size, density, and orientation of cracks at the point of failure. Our technique, based on a two-dimensional (2D) continuous Morlet wavelet analysis, can recognise, extract and visually separate the multi-scale changes occurring in the fracture network during the deformation process. We have analysed high-resolution SEM-BSE images of thin sections of Hopeman Sandstone (Scotland, UK) taken from core plugs deformed under triaxial conditions, with increasing confining pressure. Through this analysis, we can determine the relationship between the initial orientation of tensile microcracks and the final geometry of the through-going shear fault, exploiting the total areal coverage of the analysed image. In addition, by comparing patterns of fractures in thin sections derived from triaxial (σ1>σ2=σ3=Pc) laboratory experiments conducted at different confining pressures (Pc), we can quantitatively explore the relationship between the observed geometry and the inferred mechanical processes. The methodology presented here can have important implications for larger-scale mechanical problems related to major fault propagation. Just as a core plug scale fault localises through extension and coalescence of microcracks, larger faults also grow by extension and coalescence of segments in a multi-scale process by which microscopic cracks can ultimately lead to macroscopic faulting. Consequently, wavelet analysis represents a useful tool for fracture pattern recognition, applicable to the detection of the transitions occurring at the time of catastrophic rupture.

Reducing and measuring fluctuations in the MST RFP: Enhancement of energy confinement and measurement of the MHD dynamo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Den Hartog, D.J.; Almagri, A.F.; Cekic, M.

1996-09-01

A three- to five-fold enhancement of the energy confinement time in a reversed-field pinch (RFP) has been achieved in the Madison Symmetric Torus (MST) by reducing the amplitude of tearing mode fluctuations responsible for anomalous transport in the core of the RFP. By applying a transient poloidal inductive electric field to flatten the current density profile, the fluctuation amplitude {tilde b}/B decreases from 1.5% to 0.8%, the electron temperature T{sub e0} increases from 250 eV to 370 eV, the ohmic input power decreases from 4.5 MW to approximately 1.5 MW, the poloidal beta {beta}{sub 0} increases from 6% to 9%,more » and the energy confinement time {tau}{sub E} increases from 1 ms to {approximately}5 ms in I{sub {phi}} = 340 kA plasmas with density {tilde n} = 1 {times} 10{sup 19} m{sup -3}. Current profile control methods are being developed for the RFP in a program to eliminate transport associated with these current-gradient-driven fluctuations. In addition to controlling the amplitude of the tearing modes, we are vigorously pursuing an understanding of the physics of these fluctuations. In particular, plasma flow, both equilibrium and fluctuating, plays a critical role in a diversity of physical phenomena in MST. The key results: 1) Edge probe measurements show that the MHD dynamo is active in low collisionality plasmas, while at high collisionality a new mechanism, the `electron diamagnetic dynamo,` is observed. 2) Core spectroscopic measurements show that the toroidal velocity fluctuations of the plasma are coherent with the large-scale magnetic tearing modes; the scalar product of these two fluctuating quantities is similar to that expected for the MHD dynamo electromotive force. 3) Toroidal plasma flow in MST exhibits large radial shear and can be actively controlled, including unlocking locked discharges, by modifying E{sub r} with a robust biased probe. 24 refs.« less

Flow characteristics of bounded self-organized dust vortex in a complex plasma

NASA Astrophysics Data System (ADS)

Laishram, Modhuchandra; Sharma, D.; Chattopdhyay, P. K.; Kaw, P. K.

2018-01-01

Dust clouds are often formed in many dusty plasma experiments, when micron size dust particles introduced in the plasma are confined by spatial non-uniformities of the potential. These formations show self-organized patterns like vortex or circulation flows. Steady-state equilibrium dynamics of such dust clouds is analyzed by 2D hydrodynamics for varying Reynolds number, Re, when the cloud is confined in an azimuthally symmetric cylindrical setup by an effective potential and is in a dynamic equilibrium with an unbounded sheared plasma flow. The nonconservative forcing due to ion flow shear generates finite vorticity in the confined dust clouds. In the linear limit (Re ≪ 1), the collective flow is characterized by a single symmetric and elongated vortex with scales correlating with the driving field and those generated by friction with the boundaries. However in the high Re limit, (Re ≥ 1), the nonlinear inertial transport (u . ∇u) is effective and the vortex structure is characterized by an asymmetric equilibrium and emergence of a circular core region with uniform vorticity, over which the viscous stress is negligible. The core domain is surrounded by a virtual boundary of highly convective flow followed by thin shear layers filled with low-velocity co- and counter-rotating vortices, enabling the smooth matching with external boundary conditions. In linear regime, the effective boundary layer thickness is recovered to scale with the dust kinematic viscosity as Δr ≈ μ1/3 and is modified as Δr ≈ (μL∥/u)1/2 in the nonlinear regime through a critical kinematic viscosity μ∗ that signifies a structural bifurcation of the flow field solutions. The flow characteristics recovered are relevant to many microscopic biological processes at lower Re, as well as gigantic vortex flows such as Jovian great red spot and white ovals at higher Re.

Geophysical Characterization of in situ Serpentinization Processes at the Coast Range Ophiolite Microbial Observatory (CROMO)

NASA Astrophysics Data System (ADS)

Ortiz, E.; Tominaga, M.; Cardace, D.; Schrenk, M. O.; Hoehler, T. M.; Kubo, M. D.

2016-12-01

Electrical and magnetic remote sensing both on land and at sea have emerged as a powerful approach to characterize in situ serpentinization and carbonation processes in time and space. We conducted 2D Electrical Resistivity Tomography (ERT) surveys to investigate in situ geological and hydrogeological architecture within the rock formation of the Jurassic age tectonic mélange portion of the Coast Range Ophiolite Microbiological Observatory (CROMO) where serpentinization processes are thought to facilitate an active deep biosphere. We acquired ERT imagery during both wet and dry seasons, along 9 survey tracks traversing two previously drilled wells, CSW1.1 and QV1.1, at different lateral and horizontal resolutions, yielding imagery with depth of 6.9 - 41m. Integrating ERT inversion models with wire-line and core data, we successfully documented temporal changes in the in situ hydrological properties at CROMO, i.e. the lateral and vertical water table boundaries (unconfined aquifer), non-permeable zones (confining bed), and possible confined aquifers that are juxtaposed within three dominant lithological units of serpentinite top soil, serpentinite gravel with clay, and serpentinite basement formation. We conducted rock magnetic experiments on core samples from drilled sites, including Magnetic Property Measurement System (MPMS) measurements, to better understand the connection between these hydrogeological properties and in situ serpentinization processes. Based on the observed downhole distribution of magnetite in correlation with ERT results and lithostratigraphy, we proposed that, at CROMO: (i) zones enriched in ferromagnetic minerals, correspond to in situ serpentinite formation with both high and low resistivity, suggesting that resistivity zones represent in situ architecture of consolidated serpentinite confining beds and possible fractured serpentinite aquifers, respectively; and (ii) zones (e.g. 14 - 31m at CSW site) enriched in superparamagnetic size magnetites (i.e. "pepper flake" magnetites that are observed in serpentine veins) are present in permeable serpentinite gravel aquifer formations (i.e. low resistivity, possible fractured serpentinite aquifers) suggesting groundwater available around the drilled sites is driving present-day serpentinization.

Structure and dynamics of reverse micelles containing supercooled water investigated by neutron scattering

NASA Astrophysics Data System (ADS)

Spehr, Tinka; Frick, Bernhard; Grillo, Isabelle; Falus, Peter; Müller, Martin; Stühn, Bernd

2009-03-01

We present a detailed neutron scattering study of the structure, shape fluctuations, and translational diffusion of microemulsion droplets at low temperatures. We investigate the ternary microemulsion D2O , AOT [bis(2-ethyl-hexyl) sulfosuccinate], and toluene-d8 (or heptane-d16) which forms spherical water droplets surrounded by a monolayer of AOT dispersed in oil around room temperature. At T=290K , varying the molar ratio ω of water to AOT between 3 and 12, we find using small angle neutron scattering water core radii Rc between 7 and 18Å , respectively. We characterize the structure at low temperatures down to T=220K . Upon cooling the droplet structure is maintained and Rc stays roughly constant down to temperatures where the confined water is deeply supercooled. At an ω -dependent temperature Ts we observe for all compositions a shrinking of the droplets, which depends on the initial droplet size: the smaller the initial radii, the lower the Ts is. At the lowest investigated temperature T=220K we find an ω -independent remaining water core corresponding to a number of about 2 water molecules per AOT molecule. Neutron spin-echo spectroscopy is used to monitor shape fluctuations and translational diffusion for one microemulsion ( ω=8 , Rw=12Å ) from T=300K down to temperatures below the corresponding shrinking temperature Ts . Thereby we determine the bending elasticity to be κ=0.3kBT over the whole investigated temperature range where the droplets are stable. From these results we cannot establish a link between surfactant membrane elasticity and low temperature structural instability of the droplets. Moreover, our results show that reverse AOT micelles are an excellent tool for the study of soft confined water over a broad range of confining sizes and temperatures down to the supercooled state.

Slow light generation in single-mode rectangular core photonic crystal fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yadav, Sandeep; Saini, Than Singh; Kumar, Ajeet, E-mail: ajeetdph@gmail.com

2016-05-06

In this paper, we have designed and analyzed a rectangular core photonic crystal fiber (PCF) in Tellurite material. For the designed photonics crystal fiber, we have calculated the values of confinement loss and effective mode area for different values of air filling fraction (d/Λ). For single mode operation of the designed photonic crystal fiber, we have taken d/Λ= 0.4 for the further calculation of stimulated Brillouin scattering based time delay. A maximum time delay of 158 ns has been achieved for input pump power of 39 mW. We feel the detailed theoretical investigations and simulations carried out in the study have themore » potential impact on the design and development of slow light-based photonic devices.« less

Dual-hole unit-based kagome lattice microstructure fiber for low-loss and highly birefringent terahertz guidance

NASA Astrophysics Data System (ADS)

Hasan, Md. Rabiul; Akter, Sanjida; Khatun, Tania; Rifat, Ahmmed A.; Anower, Md. Shamim

2017-04-01

A low-loss microstructure fiber is numerically investigated for convenient transmission of polarization maintaining terahertz (THz) waves. The dual-hole units (DHUs) are used inside the core of the kagome lattice microstructure to achieve high birefringence and low effective material loss (EML). It is demonstrated that by rotating the axis of orientation of the DHUs, it is possible to obtain low EML of 0.052 cm-1, low confinement loss of 0.01 cm-1, and high birefringence of 0.0354 at 0.85 THz. It is also reported that the transmission properties of the proposed microstructure fiber are varied with rotation angle, core diameter, and operating frequencies. Other guiding characteristics, such as single-mode propagation, power fraction, and dispersion, are also discussed thoroughly.

Fiber-Type Random Laser Based on a Cylindrical Waveguide with a Disordered Cladding Layer.

PubMed

Zhang, Wei Li; Zheng, Meng Ya; Ma, Rui; Gong, Chao Yang; Yang, Zhao Ji; Peng, Gang Ding; Rao, Yun Jiang

2016-05-25

This letter reports a fiber-type random laser (RL) which is made from a capillary coated with a disordered layer at its internal surface and filled with a gain (laser dye) solution in the core region. This fiber-type optical structure, with the disordered layer providing randomly scattered light into the gain region and the cylindrical waveguide providing confinement of light, assists the formation of random lasing modes and enables a flexible and efficient way of making random lasers. We found that the RL is sensitive to laser dye concentration in the core region and there exists a fine exponential relationship between the lasing intensity and particle concentration in the gain solution. The proposed structure could be a fine platform of realizing random lasing and random lasing based sensing.

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

PubMed

Fang, Xinzuo; Shang, Qichao; Wang, Yu; Jiao, Long; Yao, Tao; Li, Yafei; Zhang, Qun; Luo, Yi; Jiang, Hai-Long

2018-02-01

It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h -1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H 2 production activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fivefold confinement time increase in the Madison Symmetric Torus using inductive poloidal current drive

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoneking, M.R.; Lanier, N.E.; Prager, S.C.

1996-12-01

Current profile control is employed in the Madison Symmetric Torus reversed field pinch to reduce the magnetic fluctuations responsible for anomalous transport. An inductive poloidal electric field pulse is applied in the sense to flatten the parallel current profile, reducing the dynamo fluctuation amplitude required to sustain the equilibrium. This technique demonstrates a substantial reduction in fluctuation amplitude (as much as 50%), and improvement in energy confinement (from 1 ms to 5 ms); a record low fluctuation (0.8%) and record high temperature (615 eV) for this device were observed simultaneously during current drive experiments. Plasma beta increases by 50% andmore » the Ohmic input power is three times lower. Particle confinement improves and plasma impurity contamination is reduced. The results of the transient current drive experiments provide motivation for continuing development of steady-state current profile control strategies for the reversed field pinch.« less

Comparison of confinement in resistive-shell reversed-field pinch devices with two different magnetic shell penetration times

NASA Astrophysics Data System (ADS)

Gravestijn, R. M.; Drake, J. R.; Hedqvist, A.; Rachlew, E.

2004-01-01

A loop voltage is required to sustain the reversed-field pinch (RFP) equilibrium. The configuration is characterized by redistribution of magnetic helicity but with the condition that the total helicity is maintained constant. The magnetic field shell penetration time, tgrs, has a critical role in the stability and performance of the RFP. Confinement in the EXTRAP device has been studied with two values of tgrs, first (EXTRAP-T2) with tgrs of the order of the typical relaxation cycle timescale and then (EXTRAP-T2R) with tgrs much longer than the relaxation cycle timescale, but still much shorter than the pulse length. Plasma parameters show significant improvements in confinement in EXTRAP-T2R. The typical loop voltage required to sustain comparable electron poloidal beta values is a factor of 3 lower in the EXTRAP-T2R device. The improvement is attributed to reduced magnetic turbulence.

Characteristics of hybrid scenarios in KSTAR

NASA Astrophysics Data System (ADS)

Lee, Youngho; Byun, Cheol-Sik; Na, Yong-Su; Kstar Team

2017-10-01

We report the characteristics of hybrid scenarios under development in KSTAR. Firstly, detailed definition of the hybrid scenario in KSTAR is described and categorized according to the MHD activities. The discharges exhibiting H89 >1.9, betaN >2.2 sustained more than 5*tauE at q95 <6.5 without or mild sawtooth are classified into the hybrid regime. Fishbones and neoclassical tearing modes are usually observed in this regime. Improved confinement in this regime is also confirmed with comparing general H-mode in KSTAR. Secondly, several experimental approaches are presented to access the hybrid regime. Here, four different recipes are described. Thirdly, the origin of the confinement enhancement is discussed. The role of the plasma rotation is found to be small in experiments where electron cyclotron heating is applied to reduce the toroidal rotation. The pedestal enhancement is thought to be the main reason for the confinement improvement in KSTAR hybrid scenarios.

Non-inductive improved H-mode operation at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Bock, A.; Fable, E.; Fischer, R.; Reich, M.; Rittich, D.; Stober, J.; Bernert, M.; Burckhart, A.; Doerk, H.; Dunne, M.; Geiger, B.; Giannone, L.; Igochine, V.; Kappatou, A.; McDermott, R.; Mlynek, A.; Odstrčil, T.; Tardini, G.; Zohm, H.; The ASDEX Upgrade Team

2017-12-01

Recent improvements to the heating and diagnostic systems on the ASDEX Upgrade tokamak allow renewed investigations into non-inductive operation scenarios with improved confinement in a full-metal device. Motivated by this, a scenario with \

Passive and active mid-infrared semiconductor nanostructures: Three-dimensional metamaterials and high wall plug efficiency quantum cascade lasers

NASA Astrophysics Data System (ADS)

Hoffman, Anthony J.

Every instant, light and matter are interacting in ways that shape the world around us. This dissertation examines the interaction of mid-infrared light with stacks of thin semiconductor layers. The work is divided into two parts: mid-infrared metamaterials and high wall plug efficiency (WPE) Quantum Cascade (QC) lasers. The mid-infrared metamaterials represent an entirely new class of material and have great potential for enabling highly-desired applications such as sub-diffraction imaging, confinement, and waveguiding. High WPE QC lasers greatly enhance the commercial feasibility of sensing, infrared countermeasures and free-space infrared communications. The first part of this dissertation describes the first three-dimensional, optical metamaterial. The all-semiconductor metamaterial is based on a strongly anisotropic dielectric function and exhibits negative refraction for a large bandwidth in the mid-infrared. The underlying theory of strongly anisotropic metamaterials is discussed, detailed characterization of several metamaterials is presented, and a macroscopic beam experiment is employed to demonstrate negative refraction. A detailed study of waveguides with strongly anisotropic cores is also presented and the low-order mode cutoff for such left-handed waveguides is observed. The second part of this dissertation discusses improvements in QC laser WPE through improved processing, packaging, and design. Devices using conventional QC design strategies processed as buried heterostructures operate with 5% WPE at room temperature in continuous wave mode, a significant improvement over previous generation devices. To further improve WPE, QC lasers based on ultra-strong coupling between the injector and upper-laser levels are designed and characterized. These devices operate with nearly 50% pulsed WPE---a true milestone for QC technology. A new type of QC laser design incorporating heterogeneous injector regions to reduce the voltage defect and thus improve WPE is also presented. Optimized devices exhibit efficiencies in excess of 30% at cryogenic temperatures. Finally, a new measurement technique to characterize lasers in continuous wave operation is described in detail. The technique is used to measure the instantaneous threshold, active core heating, device thermal resistance, and laser current efficiency as well as determine the cause of light power roll-over. This new characterization technique allows for improved understanding of QC lasers and further improvements in device performance.

Recent breakthroughs on C-2U: Norman’s legacy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binderbauer, M. W.; Tajima, T.; Tuszewski, M.

Conventional field-reversed configurations (FRC) face notable stability and confinement concerns, which can be ameliorated by introducing and maintaining a significant fast ion population in the system. This is the conjecture first introduced by Norman Rostoker multiple decades ago and adopted as the central design tenet in Tri Alpha Energy’s advanced beam driven FRC concept. In fact, studying the physics of such neutral beam (NB) driven FRCs over the past decade, considerable improvements were made in confinement and stability. Next to NB injection, the addition of axially streaming plasma guns, magnetic end plugs, as well as advanced surface conditioning lead tomore » dramatic reductions in turbulence driven losses and greatly improved stability. In turn, fast ion confinement improved significantly and allowed for the build-up of a dominant fast particle population. This recently led to the breakthrough of sustaining an advanced beam driven FRC, thereby demonstrating successful maintenance of trapped magnetic flux, plasma dimensions and total pressure inventory for times much longer than all characteristic system time scales and only limited by hardware and electric supply constraints.« less

Correlation of TEM data with confined phonons to determine strain and size of Ge nanocrystals embedded in SixNy matrix

NASA Astrophysics Data System (ADS)

Bahariqushchi, Rahim; Gündoğdu, Sinan; Aydinli, Atilla

2017-11-01

Models that use phonon confinement fail to provide consistent results for nanocrystal sizes in differing dielectric matrices due to varying stress experienced by nanocrystals in different dielectric environments. In cases where direct measurement of stress is difficult, the possibility of stress saturation as a function of size opens up a window for the use of phonon confinement to determine size. We report on a test of this possibility in Ge: SixNy system. Ge nanocrystals (NCs) embedded in silicon nitride matrix have been fabricated using plasma enhanced chemical vapor deposition (PECVD) followed by post annealing in Ar ambient. Nanocrystal size dependence of Raman spectra was studied taking into account associated stress and an improved phonon confinement approach. Our analysis show same stress for NCs which have sizes below 7.0 nm allowing the use of phonon confinement to determine the nanocrystal size. The results are compared with TEM data and good agreement is observed.

Tuning quadratic nonlinear photonic crystal fibers for zero group-velocity mismatch.

PubMed

Bache, Morten; Nielsen, Hanne; Laegsgaard, Jesper; Bang, Ole

2006-06-01

We consider an index-guiding silica photonic crystal fiber with a triangular hole pattern and a periodically poled quadratic nonlinearity. By tuning the pitch and the relative hole size, second-harmonic generation with zero group-velocity mismatch is found for any fundamental wavelength above 780 nm. The nonlinear strength is optimized when the fundamental has maximum confinement in the core. The conversion bandwidth allows for femtosecond-pulse conversion, and 4%-180%W(-1)cm(-2) relative efficiencies were found.

Exercise performance, core temperature, and metabolism after prolonged restricted activity and retraining in dogs

NASA Technical Reports Server (NTRS)

Nazar, K.; Greenleaf, J. E.; Pohoska, E.; Turlejska, E.; Kaciuba-Uscilko, H.; Kozlowski, S.

1992-01-01

Physiological effects of restricted activity (RA) and subsequent retraining have been studied. Ten male mongrel dogs performed a submaximal exercise endurance test on a treadmill during kennel control, after 8 weeks of cage confinement and after eight weeks of retraining using the same treadmill protocol 1 h/d for 6 d/week. Data obtained show that RA reduces exercise endurance, the effectiveness of exercise thermoregulation, muscle glycogen stores, and the lipolytic response to exercise and to noradrenaline stimulation.

Manipulation of polarization anisotropy in bare InAs and InAs/GaSb core-shell nanowires

NASA Astrophysics Data System (ADS)

Patra, Atanu; Roy, Anushree; Gomes, Umesh Prasad; Zannier, Valentina; Ercolani, Daniele; Sorba, Lucia

2018-04-01

In this article, we compare the excitation wavelength dependence of the polarization anisotropy (ρ) of an internal field induced Raman scattering signal in individual bare InAs and InAs/GaSb core-shell nanowires. The measured value of ρ of the Raman scattering intensity for InAs/GaSb core-shell nanowires has a minimum at ˜500 nm, while for the bare InAs nanowire, the value of ρ monotonically increases over the same range of wavelengths. We have modeled the scattering intensities of both systems by considering the joint role of Raman tensor components and confinement of electromagnetic radiation inside the nanowire at two orthogonal polarization configurations of the electromagnetic radiation. The theoretical results allow us to understand that the observed behavior of ρ is related to the nanowire geometry and to the difference in the wavelength dependence of the dielectric constants of InAs and GaSb. This work shows the possibility of manipulating the polarization anisotropy by selecting suitable diameters and materials for the core and the shell of the nanowire. We also report a six-fold increase in Raman scattering intensity due to the GaSb shell on InAs nanowires.

Regulation of the X-ray luminosity of clusters of galaxies by cooling and supernova feedback.

PubMed

Voit, G M; Bryan, G L

2001-11-22

Clusters of galaxies are thought to contain about ten times as much dark matter as baryonic matter. The dark component therefore dominates the gravitational potential of a cluster, and the baryons confined by this potential radiate X-rays with a luminosity that depends mainly on the gas density in the cluster's core. Predictions of the X-rays' properties based on models of cluster formation do not, however, agree with the observations. If the models ignore the condensation of cooling gas into stars and feedback from the associated supernovae, they overestimate the X-ray luminosity because the density of the core gas is too high. An early episode of uniformly distributed supernova feedback could rectify this by heating the uncondensed gas and therefore making it harder to compress into the core, but such a process seems to require an implausibly large number of supernovae. Here we show how radiative cooling of intergalactic gas and subsequent supernova heating conspire to eliminate highly compressible low-entropy gas from the intracluster medium. This brings the core entropy and X-ray luminosities of clusters into agreement with the observations, in a way that depends little on the efficiency of supernova heating in the early Universe.

Geomagnetic spikes on the core-mantle boundary

NASA Astrophysics Data System (ADS)

Davies, C. J.; Constable, C.

2017-12-01

Extreme variations of Earth's magnetic field occurred in the Levantine region around 1000 BC, where the field intensity rose and fell by a factor of 2-3 over a short time and confined spatial region. There is presently no coherent link between this intensity spike and the generating processes in Earth's liquid core. Here we test the attribution of a surface spike to a flux patch visible on the core-mantle boundary (CMB), calculating geometric and energetic bounds on resulting surface geomagnetic features. We show that the Levantine intensity high must span at least 60 degrees in longitude. Models providing the best trade-off between matching surface spike intensity, minimizing L1 and L2 misfit to the available data and satisfying core energy constraints produce CMB spikes 8-22 degrees wide with peak values of O(100) mT. We propose that the Levantine spike grew in place before migrating northward and westward, contributing to the growth of the axial dipole field seen in Holocene field models. Estimates of Ohmic dissipation suggest that diffusive processes, which are often neglected, likely govern the ultimate decay of geomagnetic spikes. Using these results, we search for the presence of spike-like features in geodynamo simulations.

Migration: a core public health ethics issue.

PubMed

Wild, V; Dawson, A

2018-05-01

In this article, we outline the link between migration, public health and ethics. Discussing relevant arguments about migration from the perspective of public health and public health ethics. Critical review of theories and frameworks, case-based analysis and systematic identification and discussion of challenges. Migration is a core issue of public health ethics and must take a case-based approach: seeking to identify the specific ethical dimensions and vulnerabilities in each particular context. Public health as a practice, built upon the core value of justice, requires the protection and promotion of migrants' well-being (even if this produces tension with immigration services). Ethical analysis should take all phases of migration into account: before, during and after transit. We argue that migration policies, at least as they relate to migrants' well-being, should be founded upon a shared humanity, respect for human rights and on the idea that effective public health cannot and should not be confined within the borders and to the citizens of any host country. We make the case for migration to be seen as a core issue of public health ethics. Copyright © 2018 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.

Multiple patterns of diblock copolymer confined in irregular geometries with soft surface

NASA Astrophysics Data System (ADS)

Li, Ying; Sun, Min-Na; Zhang, Jin-Jun; Pan, Jun-Xing; Guo, Yu-Qi; Wang, Bao-Feng; Wu, Hai-Shun

2015-12-01

The different confinement shapes can induce the formation of various interesting and novel morphologies, which might inspire potential applications of materials. In this paper, we study the directed self-assembly of diblock copolymer confined in irregular geometries with a soft surface by using self-consistent field theory. Two types of confinement geometries are considered, namely, one is the concave pore with one groove and the other is the concave pore with two grooves. We obtain more novel and different structures which could not be produced in other two-dimensional (2D) confinements. Comparing these new structures with those obtained in regular square confinement, we find that the range of ordered lamellae is enlarged and the range of disordered structure is narrowed down under the concave pore confinement. We also compare the different structures obtained under the two types of confinement geometries, the results show that the effect of confinement would increase, which might induce the diblock copolymer to form novel structures. We construct the phase diagram as a function of the fraction of B block and the ratio of h/L of the groove. The simulation reveals that the wetting effect of brushes and the shape of confinement geometries play important roles in determining the morphologies of the system. Our results improve the applications in the directed self-assembly of diblock copolymer for fabricating the irregular structures. Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20121404110004), the Research Foundation for Excellent Talents of Shanxi Provincial Department of Human Resources and Social Security, China, and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province, China.

Role of Reynolds Stress-Induced Poloidal Flow in Triggering the Transition to Improved Ohmic Confinement on the HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Xu, Y. H.; Yu, C. X.; Luo, J. R.; Mao, J. S.; Liu, B. H.; Li, J. G.; Wan, B. N.; Wan, Y. X.

2000-04-01

Time and space resolved measurements of electrostatic Reynolds stress, radial electric field Er, and plasma rotations have been performed across the transition to improved Ohmic confinement in the Hefei Tokamak-6M (HT-6M). The first experimental evidence of the correlation between the enhanced Reynolds stress gradient and the poloidal flow acceleration in the edge plasma is presented. The results indicate that the turbulence-induced Reynolds stress might be the dominant mechanism to create the sheared poloidal flow and Er, which may further trigger the transition.

Role of reynolds stress-induced poloidal flow in triggering the transition to improved ohmic confinement on the HT-6M tokamak

PubMed

Xu; Yu; Luo; Mao; Liu; Li; Wan; Wan

2000-04-24

Time and space resolved measurements of electrostatic Reynolds stress, radial electric field E(r), and plasma rotations have been performed across the transition to improved Ohmic confinement in the Hefei Tokamak-6M (HT-6M). The first experimental evidence of the correlation between the enhanced Reynolds stress gradient and the poloidal flow acceleration in the edge plasma is presented. The results indicate that the turbulence-induced Reynolds stress might be the dominant mechanism to create the sheared poloidal flow and E(r), which may further trigger the transition.

Improved particle confinement in transition from multiple-helicity to quasi-single-helicity regimes of a reversed-field pinch.

PubMed

Frassinetti, L; Predebon, I; Koguchi, H; Yagi, Y; Hirano, Y; Sakakita, H; Spizzo, G; White, R B

2006-10-27

The quasi-single-helicity (QSH) state of a reversed-field pinch (RFP) plasma is a regime in which the RFP configuration can be sustained by a dynamo produced mainly by a single tearing mode and in which a helical structure with well-defined magnetic flux surfaces arises. In this Letter, we show that spontaneous transitions to the QSH regime enhance the particle confinement. This improvement is originated by the simultaneous and cooperative action of the increase of the magnetic island and the reduction of the magnetic stochasticity.

Measurements of impurity concentrations and transport in the Lithium Tokamak Experiment

NASA Astrophysics Data System (ADS)

Boyle, Dennis Patrick

This thesis presents new measurements of core impurity concentrations and transport in plasmas with lithium coatings on all-metal plasma facing components (PFCs) in the Lithium Tokamak Experiment (LTX). LTX is a modest-sized spherical tokamak uniquely capable of operating with large area solid and/or liquid lithium coatings essentially surrounding the entire plasma (as opposed to just the divertor or limiter region in other devices). Lithium (Li) wall-coatings have improved plasma performance and confinement in several tokamaks with carbon (C) PFCs, including the National Spherical Torus Experiment (NSTX). In NSTX, contamination of the core plasma with Li impurities was very low (<0.1%) despite extensive divertor coatings. Low Li levels in NSTX were found to be largely due to neoclassical forces from the high level of C impurities. Studying impurity levels and transport with Li coatings on stainless steel surfaces in LTX is relevant to future devices (including future enhancements to NSTX-Upgrade) with all-metal PFCs. The new measurements in this thesis were enabled by a refurbished Thomson scattering system and improved impurity spectroscopy, primarily using a novel visible spectrometer monitoring several Li, C, and oxygen (O) emission lines. A simple model was used to account for impurities in unmeasured charge states, assuming constant density in the plasma core and constant concentration in the edge. In discharges with solid Li coatings, volume averaged impurity concentrations were low but non-negligible, with 2-4% Li, 0.6-2% C, 0.4-0.7% O, and Z eff<1.2. Transport was assessed using the TRANSP, NCLASS, and MIST codes. Collisions with the main H ions dominated the neoclassical impurity transport, unlike in NSTX, where collisions with C dominated. Furthermore, neoclassical transport coefficients calculated with NCLASS were similar across all impurity species and differed no more than a factor of two, in contrast to NSTX where they differed by an order of magnitude. However, time-independent simulations with MIST indicated that unlike NSTX, neoclassical theory did not fully capture the impurity transport and anomalous transport likely played a significant role in determining impurity profiles.

Measurements of impurity concentrations and transport in the Lithium Tokamak Experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyle, Dennis Patrick

This thesis presents new measurements of core impurity concentrations and transport in plasmas with lithium coatings on all-metal plasma facing components (PFCs) in the Lithium Tokamak Experiment (LTX). LTX is a modest-sized spherical tokamak uniquely capable of operating with large area solid and/or liquid lithium coatings essentially surrounding the entire plasma (as opposed to just the divertor or limiter region in other devices). Lithium (Li) wall-coatings have improved plasma performance and confinement in several tokamaks with carbon (C) PFCs, including the National Spherical Torus Experiment (NSTX). In NSTX, contamination of the core plasma with Li impurities was very low (<0.1%)more » despite extensive divertor coatings. Low Li levels in NSTX were found to be largely due to neoclassical forces from the high level of C impurities. Studying impurity levels and transport with Li coatings on stainless steel surfaces in LTX is relevant to future devices (including future enhancements to NSTX-Upgrade) with all-metal PFCs. The new measurements in this thesis were enabled by a refurbished Thomson scattering system and improved impurity spectroscopy, primarily using a novel visible spectrometer monitoring several Li, C, and oxygen (O) emission lines. A simple model was used to account for impurities in unmeasured charge states, assuming constant density in the plasma core and constant concentration in the edge. In discharges with solid Li coatings, volume averaged impurity concentrations were low but non-negligible, with~2-4% Li, ~0.6-2% C, ~0.4-0.7% O, and Z_eff<1.2. Transport was assessed using the TRANSP, NCLASS, and MIST codes. Collisions with the main H ions dominated the neoclassical impurity transport, unlike in NSTX, where collisions with C dominated. Furthermore, neoclassical transport coefficients calculated with NCLASS were similar across all impurity species and differed no more than a factor of two, in contrast to NSTX where they differed by an order of magnitude. However, time-independent simulations with MIST indicated that unlike NSTX, neoclassical theory did not fully capture the impurity transport and anomalous transport likely played a significant role in determining impurity profiles.« less

Expanding Non-solenoidal Startup with Local Helicity Injection to Increased Toroidal Field and Helicity Injection Rate

NASA Astrophysics Data System (ADS)

Perry, J. M.; Barr, J. L.; Bodner, G. M.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Hinson, E. T.; Lewicki, B. T.; Reusch, J. A.; Schlossberg, D. J.; Winz, G. R.

2015-11-01

Local helicity injection (LHI) is a non-solenoidal startup technique under development on the Pegasus ST. Plasma currents up to 0.18 MA have been initiated by LHI in conjunction with poloidal field induction. A 0-D power balance model has been developed to predict plasma current evolution by balancing helicity input against resistive dissipation. The model is being validated against a set of experimental measurements and magnetic reconstructions with radically varied plasma geometric evolutions. Outstanding physics issues with LHI startup are the scalings of confinement and MHD activity with helicity injection rate and toroidal field strength, as well as injector behavior at high field. Preliminary results from the newly-installed Thomson scattering system suggest core temperatures of a few hundred eV during LHI startup. Measurements are being expanded to multiple spatial points for ongoing confinement studies. A set of larger-area injectors is being installed in the lower divertor region, where increased toroidal field will provide a helicity injection rate over 3 times that of outboard injectors. In this regime helicity injection will be the dominant current drive. Experiments with divertor injectors will permit experimental differentiation of several possible confinement models, and demonstrate the feasibility of LHI startup at high field. Work supported by US DOE grant DE-FG02-96ER54375.

High-resolution hydro- and geo-stratigraphy at Atlantic Coastal Plain drillhole CR-622 (Strat 8)

USGS Publications Warehouse

Wrege, B.M.; Isely, J.J.

2009-01-01

We interpret borehole geophysical logs in conjunction with lithology developed from continuous core to produce high-resolution hydro- and geo-stratigraphic profiles for the drillhole CR-622 (Strat 8) in the Atlantic Coastal Plain of North Carolina. The resulting hydrologic and stratigraphic columns show a generalized relation between hydrologic and geologic units. Fresh-water aquifers encountered are the surficial, Yorktown, Pungo River and Castle Hayne. Geologic units present are of the middle and upper Tertiary and Quaternary periods, these are the Castle Hayne (Eocene), Pungo River (Miocene), Yorktown (Pliocene), James City and Flanner Beach (Pleistocene), and the topsoil (Holocene). The River Bend Formation (Oligocene) is missing as a distinct unit between the Pungo River Formation and the Castle Hayne Formation. The confining unit underlying the Yorktown Aquifer corresponds to the Yorktown Geologic Unit. The remaining hydrologic units and geologic units are hydrologically transitional and non-coincident. The lower Pungo River Formation serves as the confining unit for the Castle Hayne Aquifer, rather than the River Bend Aquifer, and separates the Pungo River Aquifer from the upper Castle Hayne Aquifer. All geologic formations were bound by unconformities. All aquifers were confined by the anticipated hydrologic units. We conclude that CR-622 (Strat 8) represents a normal sequence in the Atlantic Coastal Plain.

Hydrostratigraphic characterization of intergranular and secondary porosity in part of the Cambrian sandstone aquifer system of the cratonic interior of North America: Improving predictability of hydrogeologic properties

USGS Publications Warehouse

Runkel, Anthony C.; Tipping, R.G.; Alexander, E.C.; Alexander, S.C.

2006-01-01

The Upper Cambrian interval of strata in the cratonic interior of North America has a long history of inconsistent hydrogeologic classification and a reputation for marked and unpredictable variability in hydraulic properties. We employed a hydrostratigraphic approach that requires hydraulic data to be interpreted within the context of a detailed characterization of the distribution of porosity and permeability to arrive at a better understanding of these rocks. As a first step, we constructed a framework of hydrostratigraphic attributes that is a depiction of the spatial distribution of both rock matrix and secondary porosity, independent of hydraulic data such as pumping-test results. The locations of hundreds of borehole geophysical logs and laboratory measurements of rock sample matrix porosity and permeability were mapped on detailed (mostly 1:100,000 or greater), conventional, lithostratigraphic maps. Stratigraphic cross-sections, based on hundreds of natural gamma logs and thousands of water-well records, have provided a markedly improved depiction of the regional distribution of rock matrix hydrostratigraphic components. Borehole, core and outcrop observations of secondary porosity were also tied to detailed stratigraphic sections and interpolated regionally. As a second step, we compiled and conducted a large number of hydraulic tests (e.g., packer tests and borehole flowmeter logs) and analyzed thousands of specific capacity tests (converted to hydraulic conductivity). Interpretation of these data within the context of the hydrostratigraphic attributes allowed us to produce a new hydrogeologic characterization for this stratigraphic interval and gain important insights into geologic controls on hydraulic variability. There are a number of assumptions in herent in most previous hydrogeologic investigations of these strata, such as equivalency of lithostratigraphic and hydrogeologic units and the dominance of intergranular flow in sandstone, that are not consistent with our results. A particularly important outcome of our study is recognition of regionally extensive bedding-plane fracture clusters. Such exceptionally high hydraulic conductivity features dominate the hydraulics of aquifers and confining units in these siliciclastic-dominated strata, including within intervals consisting largely of friable sandstone with high intergranular conductivity. Furthermore, our results provide some measure of fracture predictability, by correlating their abundance and hydraulic importance to specific stratigraphic positions and particular depths of burial beneath younger bedrock. A discrete, consistent stratigraphic interval of fine-grained siliciclastic beds also is apparently resistant to the development of vertically interconnected fractures, making the location of this regionally extensive confining unit predictable. Our more rigorous approach of interpreting typical hydraulic tests as well as relatively new techniques of borehole flowmeter logging, within the context of a hydrostratigraphic framework, results in improved definition of individual aquifers and confining units. It also enables quantification of their hydraulic properties, which leads to improved prediction of groundwater flow paths and time-of-travel. ?? 2005 Elsevier B.V. All rights reserved.

A Vision-Based Relative Navigation Approach for Autonomous Multirotor Aircraft

NASA Astrophysics Data System (ADS)

Leishman, Robert C.

Autonomous flight in unstructured, confined, and unknown GPS-denied environments is a challenging problem. Solutions could be tremendously beneficial for scenarios that require information about areas that are difficult to access and that present a great amount of risk. The goal of this research is to develop a new framework that enables improved solutions to this problem and to validate the approach with experiments using a hardware prototype. In Chapter 2 we examine the consequences and practical aspects of using an improved dynamic model for multirotor state estimation, using only IMU measurements. The improved model correctly explains the measurements available from the accelerometers on a multirotor. We provide hardware results demonstrating the improved attitude, velocity and even position estimates that can be achieved through the use of this model. We propose a new architecture to simplify some of the challenges that constrain GPS-denied aerial flight in Chapter 3. At the core, the approach combines visual graph-SLAM with a multiplicative extended Kalman filter (MEKF). More importantly, we depart from the common practice of estimating global states and instead keep the position and yaw states of the MEKF relative to the current node in the map. This relative navigation approach provides a tremendous benefit compared to maintaining estimates with respect to a single global coordinate frame. We discuss the architecture of this new system and provide important details for each component. We verify the approach with goal-directed autonomous flight-test results. The MEKF is the basis of the new relative navigation approach and is detailed in Chapter 4. We derive the relative filter and show how the states must be augmented and marginalized each time a new node is declared. The relative estimation approach is verified using hardware flight test results accompanied by comparisons to motion capture truth. Additionally, flight results with estimates in the control loop are provided. We believe that the relative, vision-based framework described in this work is an important step in furthering the capabilities of indoor aerial navigation in confined, unknown environments. Current approaches incur challenging problems by requiring globally referenced states. Utilizing a relative approach allows more flexibility as the critical, real-time processes of localization and control do not depend on computationally-demanding optimization and loop-closure processes.

CFCC: A Covert Flows Confinement Mechanism for Virtual Machine Coalitions

NASA Astrophysics Data System (ADS)

Cheng, Ge; Jin, Hai; Zou, Deqing; Shi, Lei; Ohoussou, Alex K.

Normally, virtualization technology is adopted to construct the infrastructure of cloud computing environment. Resources are managed and organized dynamically through virtual machine (VM) coalitions in accordance with the requirements of applications. Enforcing mandatory access control (MAC) on the VM coalitions will greatly improve the security of VM-based cloud computing. However, the existing MAC models lack the mechanism to confine the covert flows and are hard to eliminate the convert channels. In this paper, we propose a covert flows confinement mechanism for virtual machine coalitions (CFCC), which introduces dynamic conflicts of interest based on the activity history of VMs, each of which is attached with a label. The proposed mechanism can be used to confine the covert flows between VMs in different coalitions. We implement a prototype system, evaluate its performance, and show that our mechanism is practical.

The Conformations of Confined Polymers in an External Potential

NASA Astrophysics Data System (ADS)

Morrison, Greg

The confinement of biomolecules is ubiquitous in nature, such as the spatial constraints of viral encapsulation, histone binding, and chromosomal packing. Advances in microfluidics and nanopore fabrication have permitted powerful new tools in single molecule manipulation and gene sequencing through molecular confinement as well. In order to fully understand and exploit these systems, the ability to predict the structure of spatially confined molecules is essential. In this talk, I describe a mean field approach to determine the properties of stiff polymers confined to cylinders and slits, which is relevant for a variety of biological and experimental conditions. I show that this approach is able to not only reproduce known scaling laws for confined wormlike chains, but also provides an improvement over existing weakly bending rod approximations in determining the detailed chain properties (such as correlation functions). Using this approach, we also show that it is possible to study the effect of an externally applied tension or static electric field in a natural and analytically tractable way. These external perturbations can alter the scaling laws and introduce important new length scales into the system, relevant for histone unbinding and single-molecule analysis of DNA.

Core-to-core uniformity improvement in multi-core fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Lindley, Emma; Min, Seong-Sik; Leon-Saval, Sergio; Cvetojevic, Nick; Jovanovic, Nemanja; Bland-Hawthorn, Joss; Lawrence, Jon; Gris-Sanchez, Itandehui; Birks, Tim; Haynes, Roger; Haynes, Dionne

2014-07-01

Multi-core fiber Bragg gratings (MCFBGs) will be a valuable tool not only in communications but also various astronomical, sensing and industry applications. In this paper we address some of the technical challenges of fabricating effective multi-core gratings by simulating improvements to the writing method. These methods allow a system designed for inscribing single-core fibers to cope with MCFBG fabrication with only minor, passive changes to the writing process. Using a capillary tube that was polished on one side, the field entering the fiber was flattened which improved the coverage and uniformity of all cores.

Preparation of nanocrystals and nanocomposites of nanocrystal-conjugated polymer, and their photophysical properties in confined geometries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Jun

2007-01-01

Semiconductors nanocrystals (NCs), also called quantum dots (QDs), have attracted tremendous interest over the past decade in the fields of physics, chemistry, and engineering. Due to the quantum-confined nature of QDs, the variation of particle size provides continuous and predictable changes in fluorescence emission. On the other hand, conjugated polymers (CPs) have been extensively studied for two decades due to their semiconductor-like optical and electronic properties. The electron and energy transfer between NCs and CPs occur in solar cells and light emitting diodes (LEDs), respectively. Placing CPs in direct contact with a NC (i.e., preparing NC-CP nanocomposites) carries advantage overmore » cases where NC aggregation dominates. Such NC-CP nanocomposites possess a well-defined interface that significantly promotes the charge or energy transfer between these two components. However, very few studies have centered on such direct integration. We prepared NCs and NC-CP nanocomposites based on heck coupling and investigated the energy and charge transfer between semiconductor NCs (i.e., CdSe QDs), CPs (i.e., poly(3-hexyl thiophene) (P3HT)) in the nanocomposites in confined geometries. Two novel strategies were used to confine NC and/or NC-CP nanocomposites: (a) directly immobilizing nanohybrids, QDs and nanorods in nanoscopic porous alumina membrane (PAM) , and (b) confining the QDs and CPs in sphere-on-flat geometry to induce self-assembly. While investigating the confinement effect, gradient concentric ring patterns of high regularity form spontaneously simply by allowing a droplet of solution containing either conjugated polymer or semiconductor nanocrystal in a consecutive stick-slip mothion in a confined geometry. Such constrained evaporation can be utilized as a simple, cheap, and robust strategy for self-assembling various materials with easily tailored optical and electronic properties into spatially ordered, two-dimensional patterns. These self-organized patterns of functional nanoscale materials over large areas offer a tremendous potential for applications in optoelectronic devices, LEDs, solar cells, and biosensors. Meanwhile, spherical nanocrystals (i.e. CdSe/ZnS core/shell QDs) were placed in a hexagonal array of highly ordered cylindrical nanopores of PAMs by a simple dip-coating method and vacuum suction process, respectively. The fluorescence of CdSe/ZnS QD was retained after being filled inside PAMs and the filling contents were obtained via transmission UV-vis measurements.« less

Experimental Studies on Permeability of Intact and Singly Jointed Meta-Sedimentary Rocks Under Confining Pressure

NASA Astrophysics Data System (ADS)

Wong, Louis Ngai Yuen; Li, Diyuan; Liu, Gang

2013-01-01

Three different types of permeability tests were conducted on 23 intact and singly jointed rock specimens, which were cored from rock blocks collected from a rock cavern under construction in Singapore. The studied rock types belong to inter-bedded meta-sandstone and meta-siltstone with very low porosity and high uniaxial compressive strength. The transient pulse water flow method was employed to measure the permeability of intact meta-sandstone under a confining pressure up to 30 MPa. It showed that the magnitude order of meta-sandstone's intrinsic permeability is about 10-18 m2. The steady-state gas flow method was used to measure the permeability of both intact meta-siltstone and meta-sandstone in a triaxial cell under different confining pressures spanning from 2.5 to 10 MPa. The measured permeability of both rock types ranged from 10-21 to 10-20 m2. The influence of a single natural joint on the permeability of both rock types was studied by using the steady-state water flow method under different confining pressures spanning from 1.25 to 5.0 MPa, including loading and unloading phases. The measured permeability of both jointed rocks ranged from 10-13 to 10-11 m2, where the permeability of jointed meta-siltstone was usually slightly lower than that of jointed meta-sandstone. The permeability of jointed rocks decreases with increasing confining pressure, which can be well fitted by an empirical power law relationship between the permeability and confining pressure or effective pressure. The permeability of partly open cracked specimens is lower than that of open cracked specimens, but it is higher than that of the specimen with a dominant vein for the meta-sandstone under the same confining pressure. The permeability of open cracked rock specimens will partially recover during the unloading confining pressure process. The equivalent crack (joint) aperture is as narrow as a magnitude order of 10-6 m (1 μm) in the rock specimens under confining pressures spanning from 1.25 to 5.0 MPa, which represent the typical ground stress conditions in the cavern. The in situ hydraulic conductivity measurements conducted in six boreholes by the injection test showed that the in situ permeability of rock mass varies between 10-18 and 10-11 m2. The lower bound of the in situ permeability is larger than that of the present laboratory-tested intact rock specimens, while the upper bound of the in situ permeability is less than that of the present laboratory-tested jointed rock specimens. The in situ permeability test results were thus compatible with our present laboratory permeability results of both intact and jointed rock specimens.

Inter-aquifer Dynamics in and Near a Confining Unit Window in Shelby County, Tennessee, USA

NASA Astrophysics Data System (ADS)

Gentry, R. W.; McKay, L. D.; Larsen, D.; Carmichael, J. K.; Solomon, D. K.; Thonnard, N.; Anderson, J. L.

2003-12-01

An interdisplinary research team is investigating the interaction between the surficial alluvial aquifer and the deeper confined Memphis aquifer in the Memphis area, Shelby County, Tennessee. Previous research has identified a window in the clay-rich, upper Claiborne confining unit that separates the two aquifers near a closed municipal landfill in east-central Shelby County, an area undergoing rapid urbanization. For this investigation, a combination of environmental tracers (tritium/helium-3), major and trace ion geochemistry, hydraulic response testing, measurement of hydraulic gradients, and groundwater flow modeling is being used to quantify recharge of young water from the alluvial aquifer through the window to the Memphis aquifer. The research will provide results to better understand how windows were formed and how they influence recharge and water quality in otherwise confined parts of the Memphis aquifer downdip of its outcrop/subcrop area. Examination of continuous core samples and geophysical logs from wells installed for the study using Rotasonic drilling methods confirmed the existence of a sand-dominated window that may be as much as 1 km in diameter in the upper Claiborne confining unit. The upper Claiborne confining unit is 15 to 20 m thick in most of the study area and is overlain by a 10 to 12 m thick alluvial aquifer. The window is interpreted to have formed as a result of depositional and incisional processes in an Eocene-age deltaic system. Hydraulic gradients of several feet exist vertically between the alluvial and Memphis aquifers within the window, indicating downward flow. Groundwater age-dates from tritium/helium-3 analyses indicate that groundwater in the window at the depth of the base of the surrounding confining unit (approximately 30 m) has an apparent age of 19.8 years, which confirms the occurrence of downward flow. Young groundwater age dates (less than 32 years) also were obtained from wells in the Memphis aquifer at confined sites downgradient of the window, suggesting that a plume of young water is spreading outwards from the window and mixing with the older Memphis aquifer water. Preliminary inverse modeling of the site using a genetic algorithm coupled with a central finite difference flow model indicates a probable steady-state downward flux of about 12,000 m3/d through the window. Collection and analysis of additional groundwater samples are planned to examine geochemical conditions in the confining unit and in the Memphis aquifer upgradient of the window. These analyses will aid in developing a final conceptual model and in subsequent numerical modeling of mixing of the young recharge water with the older Memphis aquifer water.

Innovative diagnostics for ITER physics addressed in JET

NASA Astrophysics Data System (ADS)

Murari, A.; Edlington, T.; Alfier, A.; Alonso, A.; Andrew, Y.; Arnoux, G.; Beurskens, M.; Coad, P.; Crombe, C.; Gauthier, E.; Giroud, C.; Hidalgo, C.; Hong, S.; Kempenaars, M.; Kiptily, V.; Loarer, T.; Meigs, A.; Pasqualotto, R.; Tala, T.; Contributors, JET-EFDA

2008-12-01

In recent years, JET diagnostic capability has been significantly improved to widen the range of physical phenomena that can be studied and thus contribute to the understanding of some ITER relevant issues. The most significant results reported in this paper refer to the plasma wall interactions, the interplay between core and edge physics and fast particles. A synergy between new infrared cameras, visible cameras and spectroscopy diagnostics has allowed investigating a series of new aspects of the plasma wall interactions. The power loads on the plasma facing components of JET main chambers have been assessed at steady state and during transient events like ELMs and disruptions. Evidence of filaments in the edge region of the plasma has been collected with a new fast visible camera and high resolution Thomson scattering. The physics of detached plasmas and some new aspects of dust formation have also been devoted particular attention. The influence of the edge plasma on the core has been investigated with upgraded active spectroscopy, providing new information on momentum transport and the effects of impurity injection on ELMs and ITBs and their interdependence. Given the fact that JET is the only machine with a plasma volume big enough to confine the alphas, a coherent programme of diagnostic developments for the energetic particles has been undertaken. With upgraded γ-ray spectroscopy and a new scintillator probe, it is now possible to study both the redistribution and the losses of the fast particles in various plasma conditions.

In situ transmission electron microscopy observation of pulverization of aluminum nanowires and evolution of the thin surface Al2O3 layers during lithiation-delithiation cycles.

PubMed

Liu, Yang; Hudak, Nicholas S; Huber, Dale L; Limmer, Steven J; Sullivan, John P; Huang, Jian Yu

2011-10-12

Lithiation-delithiation cycles of individual aluminum nanowires (NWs) with naturally oxidized Al(2)O(3) surface layers (thickness 4-5 nm) were conducted in situ in a transmission electron microscope. Surprisingly, the lithiation was always initiated from the surface Al(2)O(3) layer, forming a stable Li-Al-O glass tube with a thickness of about 6-10 nm wrapping around the NW core. After lithiation of the surface Al(2)O(3) layer, lithiation of the inner Al core took place, which converted the single crystal Al to a polycrystalline LiAl alloy, with a volume expansion of about 100%. The Li-Al-O glass tube survived the 100% volume expansion, by enlarging through elastic and plastic deformation, acting as a solid electrolyte with exceptional mechanical robustness and ion conduction. Voids were formed in the Al NWs during the initial delithiation step and grew continuously with each subsequent delithiation, leading to pulverization of the Al NWs to isolated nanoparticles confined inside the Li-Al-O tube. There was a corresponding loss of capacity with each delithiation step when arrays of NWs were galvonostatically cycled. The results provide important insight into the degradation mechanism of lithium-alloy electrodes and into recent reports about the performance improvement of lithium ion batteries by atomic layer deposition of Al(2)O(3) onto the active materials or electrodes.

Self-Generated Magnetic Fields in the Stagnation Phase of Indirect-Drive Implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Walsh, C. A.; Chittenden, J. P.; McGlinchey, K.; Niasse, N. P. L.; Appelbe, B. D.

2017-04-01

Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing self-generated magnetic fields over 104 T . Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.

Self-Generated Magnetic Fields in the Stagnation Phase of Indirect-Drive Implosions on the National Ignition Facility.

PubMed

Walsh, C A; Chittenden, J P; McGlinchey, K; Niasse, N P L; Appelbe, B D

2017-04-14

Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing self-generated magnetic fields over 10^{4}  T. Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.

Compact and low power operation optical switch using silicon-germanium/silicon hetero-structure waveguide.

PubMed

Sekiguchi, Shigeaki; Kurahashi, Teruo; Zhu, Lei; Kawaguchi, Kenichi; Morito, Ken

2012-04-09

We proposed a silicon-based optical switch with a carrier-plasma-induced phase shifter which employs a silicon-germanium (SiGe) / silicon (Si) hetero-structure in the waveguide core. A type-I hetero-interface formed by SiGe and Si is expected to confine carriers effectively in the SiGe waveguide core. The fabricated Mach-Zehnder optical switch shows a low switching power of only 1.53 mW with a compact phase shifter length of 250 μm. The switching time of the optical switch is less than 4.6 ns for the case of a square waveform driving condition, and 1 ns for the case of a pre-emphasis electric driving condition. These results show that our proposed SiGe/Si waveguide structure holds promise for active devices with compact size and low operation power.

Elastic anisotropy of core samples from the Taiwan Chelungpu Fault Drilling Project (TCDP): direct 3-D measurements and weak anisotropy approximations

NASA Astrophysics Data System (ADS)

Louis, Laurent; David, Christian; Špaček, Petr; Wong, Teng-Fong; Fortin, Jérôme; Song, Sheng Rong

2012-01-01

The study of seismic anisotropy has become a powerful tool to decipher rock physics attributes in reservoirs or in complex tectonic settings. We compare direct 3-D measurements of P-wave velocity in 132 different directions on spherical rock samples to the prediction of the approximate model proposed by Louis et al. based on a tensorial approach. The data set includes measurements on dry spheres under confining pressure ranging from 5 to 200 MPa for three sandstones retrieved at a depth of 850, 1365 and 1394 metres in TCDP hole A (Taiwan Chelungpu Fault Drilling Project). As long as the P-wave velocity anisotropy is weak, we show that the predictions of the approximate model are in good agreement with the measurements. As the tensorial method is designed to work with cylindrical samples cored in three orthogonal directions, a significant gain both in the number of measurements involved and in sample preparation is achieved compared to measurements on spheres. We analysed the pressure dependence of the velocity field and show that as the confining pressure is raised the velocity increases, the anisotropy decreases but remains significant even at high pressure, and the shape of the ellipsoid representing the velocity (or elastic) fabric evolves from elongated to planar. These observations can be accounted for by considering the existence of both isotropic and anisotropic crack distributions and their evolution with applied pressure.

Results from the first operation phase of W7-X

NASA Astrophysics Data System (ADS)

Pedersen, Thomas Sunn

2016-10-01

This talk will give a review of stellarator physics and the mission of Wendelstein 7-X (W7-X), and will summarize the most important results obtained during its first operation phase, OP1.1, which was completed in March 2016. The HELIAS reactor vision and open issues in stellarator research will also be discussed. The stellarator concept dates back to the 1950's. It has several intrinsic advantages, including being free of current-driven disruptions, and not needing current drive. However, the stellarator has been lagging behind the tokamak with respect to energy confinement. Recent advances in plasma theory and computational power have led to renewed interest in stellarators since they allow a complex but effective optimization of the confinement properties, one that should allow for tokamak-like confinement times. W7-X is the largest and most optimized stellarator in the world, and aims to show that the earlier weaknesses of the stellarator concept have been addressed successfully by optimization, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. It is built for steady-state operation, featuring 70 superconducting coils, and a confinement volume of about 30 m3. During OP1.1, it was operated at full field (B = 2.5 T on axis), with ECRH power up to 4.3 MW (later to be extended to 10 MW). Plasma operation was performed with helium and hydrogen, with deuterium planned for later phases. More than 2,000 discharges were created during the 10 operation weeks of OP1.1. Core Te 8 keV and Ti 2 keV were reached in discharge with densities in the low to mid 1019 range, and confinement times were on the order of 100-150 ms, within expectation. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement Number 633053.

Hydrogeologic data from a 2,000-foot deep core hole at Polk City, Green Swamp area, central Florida

USGS Publications Warehouse

Navoy, A.S.

1986-01-01

Two core holes were drilled to depths of 906 and 1,996 feet, respectively, within the Tertiary limestone (Floridan) aquifers, at Polk City, central Florida. Data from the two holes revealed that the bottom of the zone of vigorous groundwater circulation is confined by carbonate rocks at a depth of about 1,000 feet (863 feet below sea level). The zone of circulation is divided into two high-permeability zones. The dissolved solids of the water within the high-permeability zones is approximately 150 milligrams per liter. Within the carbonate rocks, the dissolved solids content of the water reaches about 2,000 milligrams per liter at the bottom of the core hole. Water levels in the core holes declined a total of about 16 feet as the hole was drilled; most of the head loss occurred at depths below 1,800 feet. The porosities of selected cores ranged from 1.6 to 45.3 percent; the hydraulic conductivities ranged from less than 0.000024 to 19.0786 feet per day in the horizontal direction and from less than 0.000024 to 2.99 feet per day in the vertical direction; and the ratio of vertical to horizontal permeability ranged from 0.03 to 1.98. Due to drilling problems, packer tests and geophysical logging could not be accomplished. (USGS)

Age Estimates of Holocene Glacial Retreat in Lapeyrère Bay, Anvers Island, Antarctica

NASA Astrophysics Data System (ADS)

Mead, K. A.; Wellner, J. S.; Rosenheim, B. E.

2011-12-01

Lapeyrère Bay is a fjord on the eastern side of Anvers Island, located off the Western Antarctic Peninsula. Anvers island has a maximum elevation of 2400m (comprised of ice overlaying bedrock), and experiences colder temperatures and more precipitation than the South Shetlands, which are ~230km to the north. Two glaciers enter Lapeyrère Bay, one large and vulnerable to avalanching, the Iliad Glacier, and one smaller glacier confined to a northern unnamed cove. Though several research cruises have visited Lapeyrère Bay, very little has been published on the fjord's glacial retreat history or sediment flux. The primary purpose of this study is to reconstruct the glacial retreat and sediment flux histories of Lapeyrère Bay using a SHALDRIL core and standard piston cores for chronology and sedimentary facies analysis, and multibeam swath bathymetry data for identifying seafloor morphological features. Preliminary core data from the proximal northern flank of Lapeyrère Bay show greenish grey sandy mud with scattered pebble and sand lens lithology. A core taken in the distal-most part of the fjord is largely diatomaceous sediment grading into grey silty mud with thin sandy turbidites. Multibeam data has exposed seafloor features including a grounding zone wedge at the entrance of the unnamed cove of northern Lapeyrère Bay, drumlins, glacial lineations, and a glacial outwash fan near the ocean-termination of the Iliad glacier. Additionally, this study seeks to assess the effectiveness of a novel 14C method of dating sediment lacking sufficient calcareous material for carbonate 14C dating. The method being tested is ramped pyrolysis radiocarbon analysis, which dates individual fractions of organic material. It is hypothesized that ramped pyrolysis will improve upon bulk acid insoluble organic material (AIOM) dating, as AIOM can include both autochthonous syndepositionally aged carbon and allochthonous pre-aged carbon, resulting in 14C ages inherently older than the age of deposition. Performing ramped pyrolysis 14C dating and carbonate 14C dating on the same cores and comparing the resulting ages will address this hypothesis. Carbonate radiocarbon dating has been completed for cores taken in the proximal fjord, from the glacial outwash fan. Four dates from a 20.3m drill core yield an average sedimentation rate of 2.2mm/yr. Four dates from the nearby 293cm gravity core yield a sedimentation rate of 1.4mm/yr. Ramped pyrolysis has been performed on a total of nine samples, six taken from the proximal drill core and three taken from the distal-most gravity core of the fjord. The average proximal sample TOC is 0.22%, and the average distal sample TOC is 0.55%. These values show a trend of increasing TOC values with increasing oceanic influence in the distal fjord.

A high performance field-reversed configuration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binderbauer, M. W.; Tajima, T.; Steinhauer, L. C.

2015-05-15

Conventional field-reversed configurations (FRCs), high-beta, prolate compact toroids embedded in poloidal magnetic fields, face notable stability and confinement concerns. These can be ameliorated by various control techniques, such as introducing a significant fast ion population. Indeed, adding neutral beam injection into the FRC over the past half-decade has contributed to striking improvements in confinement and stability. Further, the addition of electrically biased plasma guns at the ends, magnetic end plugs, and advanced surface conditioning led to dramatic reductions in turbulence-driven losses and greatly improved stability. Together, these enabled the build-up of a well-confined and dominant fast-ion population. Under such conditions,more » highly reproducible, macroscopically stable hot FRCs (with total plasma temperature of ∼1 keV) with record lifetimes were achieved. These accomplishments point to the prospect of advanced, beam-driven FRCs as an intriguing path toward fusion reactors. This paper reviews key results and presents context for further interpretation.« less

Impurity behavior during ion-Bernstein wave heating in PBX-M

NASA Astrophysics Data System (ADS)

Isler, R. C.; Post-Zwicker, A. P.; Paul, S. F.; Tighe, W.; Ono, M.; Leblanc, B. P.; Bell, R.; Kugel, H. W.; Kaita, R.

1994-07-01

Ion-Bernstein-wave heating (IBWH) has been tested in several tokamaks. In some cases the results have been quite positive, producing temperature increases and also improving both energy and particle confinement times, whereas in others, no distinctive changes were observed. Most recently, IBWH has been utilized in the Princeton Beta Experiment-Modified (PBX-M) where the long-range goal is the achievement of operation in the second stable region by current and pressure profile control. Investigations have been performed in this machine using IBWH as the sole source of auxiliary power or using IBWH in conjunction with neutral-beam injection (NBI) or with lower-hybrid current drive (LHCD). Impurity studies seem particularly important for IBWH since not only have influxes often been observed to increase, but the global impurity confinement time has also been shown to lengthen as the confinement of the working gas improved. The authors present here a set of characteristic experimental results regarding the impurity behavior in PBX-M; in general, these are consonant with previous observations in other tokamaks.

Edge ohmic heating and improved confinement on HT-6M Tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, X.

1995-04-01

An improved confinement has been observed on HT-6M tokamak after application of Edge Ohmic Heating (EOH) which makes plasma current rapidly ramp up from an initial steady state (I{sub p}=55 kA) within a small time scale (0.4 ms) to a second steady state (I{sub p}=60 kA) with a ramp rate of 12 MA/sec. The improved confinement is characterized by (a) increased average density n{sub e}; (b) reduced H{sub alpha} radiation; (c) reduced density fluctuations both in the center and at the edge; (d) a steeper n{sub e} and T{sub e} profile at the edge; (e) the changed profiles of plasmamore » parameters n{sub e}(r), q(r) and j(r); (f) transferred the oscillation modes of the soft-X ray signals from Mirnov fluctuation (12 kHz) to sawtooth oscillation (1.7 kHz). The changes of edge fluctuation, radial electric field and bremsstrahlung during EOH were measured and discussed in details. The measured values of {beta}{sub p}+l{sub i}/2 and soft-X ray sawtooth inversion radius implied the anomalous current penetration. 10 refs., 2 figs.« less