Science.gov

Sample records for fast ion diffusion

  1. Electronic diffusion coefficient for fast-ion dechanneling

    NASA Astrophysics Data System (ADS)

    Nitta, H.; Ohtsuki, Y. H.; Kubo, K.

    1986-12-01

    A new local electronic diffusion coefficient for fast-ion dechanneling is derived on the basis of the fundamental method. To reveal detailed effects of electron states, numerical calculations are performed with use of the Roothaan-Hartree-Fock atomic wave functions. It is found that the Lindhard's formula of the electronic diffusion coefficient, which is proportional to the local electron density, is only a simple approximation of our rigorous formula and that this ``local-density approximation'' is not always sufficient, especially for metal targets.

  2. Electronic diffusion coefficient for fast-ion dechanneling

    SciTech Connect

    Nitta, H.; Ohtsuki, Y.H.; Kubo, K.

    1986-12-01

    A new local electronic diffusion coefficient for fast-ion dechanneling is derived on the basis of the fundamental method. To reveal detailed effects of electron states, numerical calculations are performed with use of the Roothaan-Hartree-Fock atomic wave functions. It is found that the Lindhard's formula of the electronic diffusion coefficient, which is proportional to the local electron density, is only a simple approximation of our rigorous formula and that this ''local-density approximation'' is not always sufficient, especially for metal targets.

  3. On The Anomalous Fast Ion Energy Diffusion in Toroidal Plasmas Due to Cavity Modes

    SciTech Connect

    N.N. Gorelenkov, N.J. Fisch and E. Fredrickson

    2010-03-09

    An enormous wave-particle diffusion coefficient along paths suitable for alpha channeling had been deduced in mode converted ion Bernstein wave experiments on Tokamak Fusion Test Reactor (TFTR) the only plausible explanation advanced for such a large diffusion coefficient was the excitation of internal cavity modes which induce particle diffusion along identical diffusion paths, but at much higher rates. Although such a mode was conjectured, it was never observed. However, recent detailed observations of high frequency compressional Alfven eigenmodes (CAEs) on the National Spherical torus Experiment (NSTX) indirectly support the existence of the related conjectured modes on TFTR. The eigenmodes responsible for the high frequency magnetic activity can be identified as CAEs through the polarization of the observed magnetic field oscillations in NSTX and through a comparison with the theoretically derived freuency dispersion relation. Here, we show how these recent observations of high frequency CAEs lend support to this explanation of the long-standing puzzle of anomalous fast ion energy diffusion on TFTR. The support of the conjecure that these internal modes could have caused the remarkable ion energy diffusion on TFTR carries significant and favorable implications for the possibilities in achieving the alpha channeling effect with small injected power in a tokamak reactor.

  4. Fast-ion diffusion measurements from radial triton burn up studies

    SciTech Connect

    McCauley, J.S.; Budny, R.; McCune, D.; Strachan, J.D.

    1993-08-01

    A fast-ion diffusion coefficient of 0.1 {plus_minus} 0.1 m{sup 2}s{sup {minus}1} has been deduced from the triton burnup neutron emission profile measured by a collimated array of helium-4 spectrometers. The experiment was performed with high-power deuterium discharges produced by Princeton University`s Tokamak Fusion Test Reactor (TFTR). The fast ions monitored were the 1.0 MeV tritons produced from the d(d,t)p. These tritons ``burn up`` with deuterons and emit a 14 MeV neutron by the d(t,{alpha})n reaction. The ratio of the measured to calculated DT yield is typically 70%. The measured DT profile width is comparable to that predicted by the TRANSP transport code during neutral beam heating and narrower after the beam heating ended.

  5. Fast and slow ion diffusion processes in lithium ion pouch cells during cycling observed with fiber optic strain sensors

    NASA Astrophysics Data System (ADS)

    Sommer, Lars Wilko; Kiesel, Peter; Ganguli, Anurag; Lochbaum, Alexander; Saha, Bhaskar; Schwartz, Julian; Bae, Chang-Jun; Alamgir, Mohamed; Raghavan, Ajay

    2015-11-01

    Cell monitoring for safe capacity utilization while maximizing pack life and performance is a key requirement for effective battery management and encouraging their adoption for clean-energy technologies. A key cell failure mode is the build-up of residual electrode strain over time, which affects both cell performance and life. Our team has been exploring the use of fiber optic (FO) sensors as a new alternative for cell state monitoring. In this present study, various charge-cycling experiments were performed on Lithium-ion pouch cells with a particular class of FO sensors, fiber Bragg gratings (FBGs), that were externally attached to the cells. An overshooting of the volume change at high SOC that recovers during rest can be observed. This phenomenon originates from the interplay between a fast and a slow Li ion diffusion process, which leads to non-homogeneous intercalation of Li ions. This paper focuses on the strain relaxation processes that occur after switching from charge to no-load phases. The correlation of the excess volume and subsequent relaxation to SOC as well as temperature is discussed. The implications of being able to monitor this phenomenon to control battery utilization for long life are also discussed.

  6. Fast-ion radial diffusivity evaluated from vertical neutral particle measurements following short pulse beam injection into a TFTR ohmic plasma

    SciTech Connect

    Kusama, Y. . Naka Fusion Research Establishment); Heidbrink, W.W. ); Barnes, C.W. ); Beer, M.; Hammett, G.W.; McCune, D.C.; Medley, S.S.; Scott, S.D.; Zarnstorff, M.C. . Plasma Physics Lab.)

    1992-01-01

    The radial diffusivity of fast ions was evaluated from vertical neutral particle measurements in experiments where a short pulse of neutral deuterium beams was injected into a TFTR ohmic deuterium plasma. A comparison between the temporal evolution of the measured neutral particle flux and theoretical calculations showed that the spatially-averaged diffusion coefficient of fast ions is {le} 0.1 m{sup 2}/sec. This value is approximately an order of magnitude less than the diffusion coefficient for thermal ions and is consistent with results obtained previously on TFTR from other diagnostics.

  7. Model for collisional fast ion diffusion into Tokamak Fusion Test Reactor loss cone

    SciTech Connect

    Chang, C.S. |; Zweben, S.J.; Schivell, J.; Budny, R.; Scott, S.

    1994-08-01

    An analytic model is developed to estimate the classical pitch angle scattering loss of energetic fusion product ions into prompt loss orbits in a tokamak geometry. The result is applied to alpha particles produced by deutrium-tritium fusion reactions in a plasma condition relevant to Tokamak Fusion Test Reactor (TFTR). A poloidal angular distribution of collisional fast ion loss at the first wall is obtained and the numerical result from the TRANSP code is discussed. The present model includes the effect that the prompt loss boundary moves away from the slowing-down path due to reduction in banana thickness, which enables us to understand, for the first time. the dependence of the collisional loss rate on Z{sub eff}.

  8. Evidence for fast-ion transport by microturbulence.

    PubMed

    Heidbrink, W W; Park, J M; Murakami, M; Petty, C C; Holcomb, C; Van Zeeland, M A

    2009-10-23

    Cross-field diffusion of energetic ions by microturbulence is measured during neutral-beam injection into the DIII-D tokamak. Fast-ion D(alpha), neutron, and motional Stark effect measurements diagnose the fast-ion distribution function. As expected for transport by plasma turbulence, anomalies relative to the classical prediction are greatest in high temperature plasmas, at low fast-ion energy, and at larger minor radius. Theoretical estimates of fast-ion diffusion are comparable to experimental levels.

  9. Global Confinement, Sawtooth Mixing, and Stochastic Diffusion Ripple Loss of Fast ICRF-driven H+ Minority Ions in TFTR

    SciTech Connect

    Petrov, M.P.; Bell, R.; Budny, R.V.; Gorelenkov, N.N.; Medley, S.S.; Zweben, S.J., PPPL

    1998-07-01

    This paper presents studies of ICRF-driven H+ minority ions in TFTR (Tokamak Fusion Test Reator) deuterium plasmas using primarily passive Ho flux detection in the energy range of 0.2-1.0 MeV with some corroborating active (lithium pellet charge exchange) measurements. It is shown that in the passive mode the main donors for the neutralization of H+ ions in this energy range are C5+ ions. The measured effective H+ tail temperatures range from 0.15 MeV at an ICRF power of 2 MW to 0.35 MeV at 6 MW. Analysis of the ICRF-driven H+ ion energy balance has been performed on the basis of the dependence of effective H+ temperatures on the plasma parameters. The analysis showed that H+ confinement times are comparable with their slowing-down times and tended to decrease with increasing ICRF power. Radial redistribution of ICRF-driven H+ ions was detected when giant sawtooth crashes occurred during the ICRF heating. The redistribution affected ions with energy below 0.7-0.8 MeV. The sawtooth crashes displace H+ ions outward along the plasma major radius into the stochastic ripple diffusion domain were those ions are lost in about 10 milliseconds. These observations are consistent with the model of the redistribution of energetic particles developed previously to explain the results of deuterium-tritium alpha-particle redistribution due to sawteeth observed in TFTR. The experimental data are also consistent with ORBIT code simulations of H+ stochastic ripple diffusion losses.

  10. Fast Ion Conductors

    NASA Astrophysics Data System (ADS)

    Chadwick, Alan V.

    Fast ion conductors, sometimes referred to as superionic conductors or solid electrolytes, are solids with ionic conductivities that are comparable to those found in molten salts and aqueous solutions of strong electrolytes, i.e., 10-2-10 S cm-1. Such materials have been known of for a very long time and some typical examples of the conductivity are shown in Fig. 1, along with sodium chloride as the archetypal normal ionic solid. Faraday [1] first noted the high conductivity of solid lead fluoride (PbF2) and silver sulphide (Ag2S) in the 1830s and silver iodide was known to be unusually high ionic conductor to the German physicists early in the 1900s. However, the materials were regarded as anomalous until the mid 1960s when they became the focus of intense interest to academics and technologists and they have remained at the forefront of materials research [2-4]. The academic aim is to understand the fundamental origin of fast ion behaviour and the technological goal is to utilize the properties in applications, particularly in energy applications such as the electrolyte membranes in solid-state batteries and fuel cells, and in electrochemical sensors. The last four decades has seen an expansion of the types of material that exhibit fast ion behaviour that now extends beyond simple binary ionic crystals to complex solids and even polymeric materials. Over this same period computer simulations of solids has also developed (in fact these methods and the interest in fast ion conductors were almost coincidental in their time of origin) and the techniques have played a key role in this area of research.

  11. Evidence for Fast-Ion Transport by Microturbulence

    SciTech Connect

    Heidbrink, W. W.; Park, Jin Myung; Murakami, Masanori; Petty, C C.; Holcomb, C T; Van Zeeland, Michael

    2009-01-01

    Cross-field diffusion of energetic ions by microturbulence is measured during neutral-beam injection into the DIII-D tokamak. Fast-ion D-alpha, neutron, and motional Stark effect measurements diagnose the fastion distribution function. As expected for transport by plasma turbulence, anomalies relative to the classical prediction are greatest in high temperature plasmas, at low fast-ion energy, and at larger minor radius. Theoretical estimates of fast-ion diffusion are comparable to experimental levels.

  12. Modeling of pickup ion distributions in the Halley cometosheath: Empirical limits on rates of ionization, diffusion, loss and creation of fast neutral atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Neugebauer, M.; Goldstein, B. E.

    1994-01-01

    The shape of the velocity distribution of water group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates of ionization, energy diffusion, and loss in the midcometosheath. The model includes the effect of rapid pitch angle scattering into a bispherical shell distribution as well as the effect of the magnetization of the plasma on the charge exchange loss rate. It is found that the average rate of ionization of cometary neutrals in this region of the cometosheath appears to be of the order of a factor 3 faster than the `standard' rates approx. 1 x 10(exp -6)/s that are generally assumed to model the observations in most regions of the comet environment. For the region of the coma studied in the present work (approx. 1 - 2 x 10(exp 5) km from the nucleus), the inferred energy diffusion coefficient is D(sub 0) approx. equals 0.0002 to 0.0005 sq km/cu s, which is generally lower than values used in other models. The empirically obtained loss rate appears to be about an order of magnitude greater than can be explained by charge exchange with the `standard' cross section of approx. 2 x 10(exp -15)sq cm. However such cross sections are not well known and for water group ion/water group neutral interactions, rates as high as 8 x 10(exp -15) sq cm have previously been suggested in the literature. Assuming the entire loss rate is due to charge exchange yields a rate of creation of fast neutral atoms of the order of approx. 10(exp -4)/s or higher, depending on the level of velocity diffusion. The fast neutrals may, in turn, be partly responsible for the higher-than-expected ionization rate.

  13. Evidence for Fast-Ion Transport by Microturbulence

    SciTech Connect

    Heidbrink, W. W.; Park, J. M.; Murakami, M.; Petty, C. C.; Van Zeeland, M. A.; Holcomb, C.

    2009-10-23

    Cross-field diffusion of energetic ions by microturbulence is measured during neutral-beam injection into the DIII-D tokamak. Fast-ion D{sub {alpha}}, neutron, and motional Stark effect measurements diagnose the fast-ion distribution function. As expected for transport by plasma turbulence, anomalies relative to the classical prediction are greatest in high temperature plasmas, at low fast-ion energy, and at larger minor radius. Theoretical estimates of fast-ion diffusion are comparable to experimental levels.

  14. Turbulent transport of fast ions in the Large Plasma Device

    SciTech Connect

    Zhou Shu; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T.; Vincena, S.; Tripathi, S. K. P.; Popovich, P.; Friedman, B.; Jenko, F.

    2010-09-15

    Strong drift wave turbulence is observed in the Large Plasma Device [H. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] on density gradients produced by a plate limiter. Energetic lithium ions orbit through the turbulent region. Scans with a collimated ion analyzer and with Langmuir probes give detailed profiles of the fast ion spatial distribution and the fluctuating fields. The fast ion transport decreases rapidly with increasing fast ion gyroradius. Unlike the diffusive transport caused by Coulomb collisions, in this case the turbulent transport is nondiffusive. Analysis and simulation suggest that such nondiffusive transport is due to the interaction of the fast ions with stationary two-dimensional electrostatic turbulence.

  15. Modeling of Pickup Ion Distributions in the Halley Cometo-Sheath: Empirical Rates of Ionization, Diffusion, Loss and Creation of Fast Neutral Atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D.; Neugebauer, M.; Goldstein, B.

    1994-01-01

    The shape of the velocity distribution of water-group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates on ionization, energy diffusion, and loss in the mid-cometosheath.

  16. Cytoplasmic hydrogen ion diffusion coefficient.

    PubMed Central

    al-Baldawi, N F; Abercrombie, R F

    1992-01-01

    The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient. PMID:1617134

  17. Fast diffusion of water nanodroplets on graphene.

    PubMed

    Ma, Ming; Tocci, Gabriele; Michaelides, Angelos; Aeppli, Gabriel

    2016-01-01

    Diffusion across surfaces generally involves motion on a vibrating but otherwise stationary substrate. Here, using molecular dynamics, we show that a layered material such as graphene opens up a new mechanism for surface diffusion whereby adsorbates are carried by propagating ripples in a motion similar to surfing. For water nanodroplets, we demonstrate that the mechanism leads to exceedingly fast diffusion that is 2-3 orders of magnitude faster than the self-diffusion of water molecules in liquid water. We also reveal the underlying principles that regulate this new mechanism for diffusion and show how it also applies to adsorbates other than water, thus opening up the prospect of achieving fast and controllable motion of adsorbates across material surfaces more generally.

  18. Fast diffusion of water nanodroplets on graphene

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Tocci, Gabriele; Michaelides, Angelos; Aeppli, Gabriel

    2016-01-01

    Diffusion across surfaces generally involves motion on a vibrating but otherwise stationary substrate. Here, using molecular dynamics, we show that a layered material such as graphene opens up a new mechanism for surface diffusion whereby adsorbates are carried by propagating ripples in a motion similar to surfing. For water nanodroplets, we demonstrate that the mechanism leads to exceedingly fast diffusion that is 2-3 orders of magnitude faster than the self-diffusion of water molecules in liquid water. We also reveal the underlying principles that regulate this new mechanism for diffusion and show how it also applies to adsorbates other than water, thus opening up the prospect of achieving fast and controllable motion of adsorbates across material surfaces more generally.

  19. A TEST FOR DIFFUSIBLE IONS

    PubMed Central

    Northrop, John H.

    1924-01-01

    1. The Donnan equilibrium furnishes a test for the ionic nature of any diffusible substance, since the ratio of the concentration of any ion on the two sides of a membrane must be equal to the ratio of the concentrations of any other ion of the same sign and valence, whereas a non-ionic substance would be equally distributed on both sides. 2. The distribution of trypsin inside and outside of gelatin particles has been compared to the distribution of hydrogen and chloride ions under the same conditions. 3. The ratio of the trypsin concentration in the gelatin to the concentration in the outside liquid is equal to the ratio of the hydrogen ion under the same conditions and to the reciprocal of the chloride ion ratio. 4. This result was obtained between pH 2.0 and 10.2. At pH 10.2 the trypsin is equally distributed and on the akaline side of 10.2 the ratio is directly equal to the chloride ratio. 5. Trypsin is therefore a positive monovalent ion in solutions of pH 10 to 2. It is probably isoelectric at 10.2 and a monovalent negative ion on the alkaline side of 10.2 6. Trypsin must also be a strong base since there is no evidence of any undissociated form on the acid side of pH 10.2. PMID:19872075

  20. Very fast bulk Li ion diffusivity in crystalline Li(1.5)Al(0.5)Ti(1.5)(PO4)3 as seen using NMR relaxometry.

    PubMed

    Epp, Viktor; Ma, Qianli; Hammer, Eva-Maria; Tietz, Frank; Wilkening, Martin

    2015-12-28

    The realization of large powerful all-solid-state batteries is still hampered by the availability of environmentally friendly and low-cost Li ion conductors that can easily be produced on a large scale and with high reproducibility. Advanced solid electrolytes benefit from fast ion-selective transport and non-flammability, but they may have low electrochemical stability with respect to Li metal. Sol-gel-synthesized lithium titanium aluminum phosphate Li(1.5)Al(0.5)Ti(1.5)(PO4)3 (LATP), which was prepared via a new synthesis route taking advantage of an annealing step at relatively low temperatures, has the potential to become one of the major players in this field although it may suffer from reduction upon direct contact with metallic lithium. Its ion dynamics is, however, as yet poorly understood. In the present study, (7)Li nuclear magnetic resonance (NMR) spectroscopy was used to monitor the key Li jump processes on the atomic scale. NMR relaxation clearly reveals heterogeneous dynamics comprising distinct ultra-fast and slower diffusion processes. The high Li ion self-diffusion coefficients deduced originate from a rapid Li exchange with activation energies as low as 0.16 eV which means that sol-gel synthesized LATP is superior to other solid electrolytes. Our NMR results fully support recent theoretical investigations on the underlying diffusion mechanism, indicating that to rapidly jump from site to site, the ions use interstitial sites connected by low-energy barriers in LATP. PMID:26580669

  1. Very fast bulk Li ion diffusivity in crystalline Li(1.5)Al(0.5)Ti(1.5)(PO4)3 as seen using NMR relaxometry.

    PubMed

    Epp, Viktor; Ma, Qianli; Hammer, Eva-Maria; Tietz, Frank; Wilkening, Martin

    2015-12-28

    The realization of large powerful all-solid-state batteries is still hampered by the availability of environmentally friendly and low-cost Li ion conductors that can easily be produced on a large scale and with high reproducibility. Advanced solid electrolytes benefit from fast ion-selective transport and non-flammability, but they may have low electrochemical stability with respect to Li metal. Sol-gel-synthesized lithium titanium aluminum phosphate Li(1.5)Al(0.5)Ti(1.5)(PO4)3 (LATP), which was prepared via a new synthesis route taking advantage of an annealing step at relatively low temperatures, has the potential to become one of the major players in this field although it may suffer from reduction upon direct contact with metallic lithium. Its ion dynamics is, however, as yet poorly understood. In the present study, (7)Li nuclear magnetic resonance (NMR) spectroscopy was used to monitor the key Li jump processes on the atomic scale. NMR relaxation clearly reveals heterogeneous dynamics comprising distinct ultra-fast and slower diffusion processes. The high Li ion self-diffusion coefficients deduced originate from a rapid Li exchange with activation energies as low as 0.16 eV which means that sol-gel synthesized LATP is superior to other solid electrolytes. Our NMR results fully support recent theoretical investigations on the underlying diffusion mechanism, indicating that to rapidly jump from site to site, the ions use interstitial sites connected by low-energy barriers in LATP.

  2. The diffusion of ions in unconsolidated sediments

    USGS Publications Warehouse

    Manheim, F. T.

    1970-01-01

    Diffusion in unconsolidated sediments generally proceeds at rates ranging from half to one twentieth of those applying to diffusion of ions and molecules in free solution. Diffusion rates are predictable with respect to porosity and path tortuosity in host sediments, and can be conveniently measured by determinations of electrical resistivity on bulk sediment samples. Net ion flux is further influenced by reactions of diffusing species with enclosing sediments, but such influences should not be confused with or lumped with diffusion processes. ?? 1970.

  3. KOH etched graphite for fast chargeable lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Cheng, Qian; Yuge, Ryota; Nakahara, Kentaro; Tamura, Noriyuki; Miyamoto, Shigeyuki

    2015-06-01

    Graphite is the most widely used anode material for lithium ion (Li-ion) batteries, although it has limited power performance at high charging rates (Li-ion input). Alternative materials such as silicon and tin alloys, however, have an even more inferior rate capability. We describe here a multi-channel structure with a graphite surface etched with pores that can greatly increase the number of sites for Li-ion intercalation/de-intercalation and reduce the Li-ion diffusion distance for fast chargeable Li-ion batteries by etching the graphite surface with pores. As a result, the multi-channel structure graphite anode shows better charging and discharging rate capability, cyclability, and higher coulombic efficiency than pristine graphite materials. The multi-channel anode material is proposed for use in fast chargeable Li-ion batteries for electric vehicles and plug-in hybrid vehicles.

  4. Fast ion JET diagnostics: confinement and losses

    SciTech Connect

    Kiptily, V. G.; Pinches, S. D.; Sharapov, S. E.; Syme, D. B.; Cecconello, M.; Darrow, D.; Hill, K.; Goloborod'ko, V.; Yavorskij, V.; Johnson, T.; Murari, A.; Reich, M.; Gorini, G.; Zoita, V.

    2008-03-12

    A study of magnetically confined fast ions in tokamaks plays an important role in burning plasma research. To reach ignition and steady burning of a reactor plasma an adequate confinement of energetic ions produced by NBI heating, accelerated with ICRF and born in fusion reactions is essential to provide efficient heating of the bulk plasma. Thus, investigation of the fast ion behaviour is an immediate task for present-day large machines, such as JET, in order to understand the main mechanisms of slowing down, redistribution and losses, and to develop optimal plasma scenarios. Today's JET has an enhanced suite of fast ion diagnostics both of confined and lost ions that enable to significantly contribute to this important area of research. Fast ion populations of p, d, t, {sup 3}He and {sup 4}He, made with ICRF, NBI, and fusion reactions have been investigated in experiments on JET with sophisticated diagnostics in conventional and shear-reversed plasmas, exploring a wide range of effects. This paper will introduce to the JET fast-ion diagnostic techniques and will give an overview of recent observations. A synergy of the unique diagnostic set was utilised in JET, and studies of the response of fast ions to MHD modes (e.g. tornado modes, sawtooth crashes), fast {sup 3}He-ions behaviour in shear-reversed plasmas are impressive examples of that. Some results on fast ion losses in JET experiments with various levels of the toroidal field ripple will be demonstrated.

  5. Search for selective ion diffusion through membranes

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.

    1983-01-01

    The diffusion rates of several ions through some membranes developed as battery separators were measured. The ions investigated were Li(+), Rb(+), Cl(-), and So4. The members were crosslinked polyvinyl alcohol, crosslinked polyacrylic acid, a copolymer of the two, crosslinked calcium polyacrylate, cellulose, and several microporous polyphenylene oxide based films. No true specificity for diffusion of any of these ions was found for any of the membranes. But the calcium polyacrylate membrane was found to exhibit ion exchange with the diffusing ions giving rise to the leaching of the calcium ion and low reproducibility. These findings contrast earlier work where the calcium polyacrylate membrane did show specificity to the diffusion of the copper ion. In general, Fick's law appeared to be obeyed. Except for the microporous membranes, the coefficients for ion diffusion through the membranes were comparable with their values in water. For the microporous membranes, the values found for the coefficients were much less, due to the tortuosity of the micropores.

  6. Diffusion and ion mixing in amorphous alloys

    SciTech Connect

    Hahn, H.; Averback, R.S.; Ding, F.; Loxton, C.; Baker, J.

    1986-10-01

    Tracer impurity diffusion and ion beam mixing in amorphous (a-)Ni/sub 50/Zr/sub 50/ were measured. A correlation between the metallic radius of an impurity and its tracer diffusivity was observed; it is similar to that found in crystalline ..cap alpha..-Zr and ..cap alpha..-Ti. In addition, the temperature dependence of diffusion in a-NiZr exhibits Arrhenius behavior. Ion beam mixing of different impurities in a-NiZr correlates with tracer diffusivity at both high and low temperatures. At higher temperatures radiation enhanced diffusion (RED) was observed. The activation enthalpy of the RED diffusion coefficient is 0.3 eV/atom.

  7. Fast self-diffusion of ions in CH 3 NH 3 PbI 3 : the interstiticaly mechanism versus vacancy-assisted mechanism

    SciTech Connect

    Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang; Wei, Su-Huai

    2016-01-01

    The stability of organic-inorganic halide perovskites is a major challenge for their applications and has been extensively studied. Among the possible underlying reasons, ion self-diffusion has been inferred to play important roles. While theoretical studies congruously support that iodine is more mobile, experimental studies only observe the direct diffusion of the MA ion and possible diffusion of iodine. The discrepancy may result from the incomplete understanding of ion diffusion mechanisms. With the help of first-principles calculations, we studied ion diffusion in CH3NH3PbI3 (MAPbI3) through not only the vacancy-assisted mechanisms presumed in previous theoretical studies, but also the neglected interstiticaly mechanisms. We found that compared to the diffusion through the vacancy-assisted mechanism, MA ion diffusion through the interstiticaly mechanism has a much smaller barrier which could explain experimental observations. For iodine diffusion, both mechanisms can yield relatively small barriers. Depending on the growth conditions, defect densities of vacancies and interstitials can vary and so do the diffusion species as well as diffusion mechanisms. Our work thus supports that both MA and iodine ion diffusion could contribute to the performance instability of MAPbI3. While being congruous with experimental results, our work fills the research gap by providing a full understanding of ion diffusion in halide perovskites.

  8. Trapped ion scaling with pulsed fast gates

    NASA Astrophysics Data System (ADS)

    Bentley, C. D. B.; Carvalho, A. R. R.; Hope, J. J.

    2015-10-01

    Fast entangling gates for trapped ion pairs offer vastly improved gate operation times relative to implemented gates, as well as approaches to trap scaling. Gates on a neighbouring ion pair only involve local ions when performed sufficiently fast, and we find that even a fast gate between a pair of distant ions with few degrees of freedom restores all the motional modes given more stringent gate speed conditions. We compare pulsed fast gate schemes, defined by a timescale faster than the trap period, and find that our proposed scheme has less stringent requirements on laser repetition rate for achieving arbitrary gate time targets and infidelities well below 10-4. By extending gate schemes to ion crystals, we explore the effect of ion number on gate fidelity for coupling two neighbouring ions in large crystals. Inter-ion distance determines the gate time, and a factor of five increase in repetition rate, or correspondingly the laser power, reduces the infidelity by almost two orders of magnitude. We also apply our fast gate scheme to entangle the first and last ions in a crystal. As the number of ions in the crystal increases, significant increases in the laser power are required to provide the short gate times corresponding to fidelity above 0.99.

  9. Interpretation of fast-ion signals during beam modulation experiments

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Collins, C. S.; Stagner, L.; Zhu, Y. B.; Petty, C. C.; Van Zeeland, M. A.

    2016-11-01

    Fast-ion signals produced by a modulated neutral beam are used to infer fast-ion transport. The measured quantity is the divergence of perturbed fast-ion flux from the phase-space volume measured by the diagnostic, \

  10. Li + ion diffusion in nanoscale alumina coatings

    NASA Astrophysics Data System (ADS)

    Johannes, Michelle; Bernstein, Noam

    Nanoscale coatings of alumina are used to stabilize surfaces for a variety of technologies. Diffusion of ions through these coatings is of primary importance: in some cases, diffusion is unwanted (e.g. corrosion) and in others (e.g. electrode materials), it is necessary. In this work DFT and AIMD calculations are used to investigate Li+ ion diffusion through a nano-layer of alumina, examining the phase (alpha, gamma, and amorphous), ion concentration, and electron count dependence. We look at the role of the surface itself in promoting diffusion. One of our main findings is that as the number of ions or charge increases, the diffusivity rises. We show how our data can explain electrochemical data from coated LiCoO2 cathodes and may point toward better and more efficient coatings for stabilizing electrodes.

  11. Fast-ion D{alpha} measurements of the fast-ion distribution (invited)

    SciTech Connect

    Heidbrink, W. W.

    2010-10-15

    The fast-ion D{alpha} (FIDA) diagnostic is an application of charge-exchange recombination spectroscopy. Fast ions that neutralize in an injected neutral beam emit Balmer-{alpha} light with a large Doppler shift. The spectral shift is exploited to distinguish the FIDA emission from other bright sources of D{alpha} light. Background subtraction is the main technical challenge. A spectroscopic diagnostic typically achieves temporal, energy, and transverse spatial resolution of {approx}1 ms, {approx}10 keV, and {approx}2 cm, respectively. Installations that use narrow-band filters achieve high spatial and temporal resolution at the expense of spectral information. For high temporal resolution, the bandpass-filtered light goes directly to a photomultiplier, allowing detection of {approx}50 kHz oscillations in FIDA signal. For two-dimensional spatial profiles, the bandpass-filtered light goes to a charge-coupled device camera; detailed images of fast-ion redistribution at instabilities are obtained. Qualitative and quantitative models relate the measured FIDA signals to the fast-ion distribution function. The first quantitative comparisons between theory and experiment found excellent agreement in beam-heated magnetohydrodynamics (MHD)-quiescent plasmas. FIDA diagnostics are now in operation at magnetic-fusion facilities worldwide. They are used to study fast-ion acceleration by ion cyclotron heating, to detect fast-ion transport by MHD modes and microturbulence, and to study fast-ion driven instabilities.

  12. Fast-ion Dα measurements of the fast-ion distribution (invited).

    PubMed

    Heidbrink, W W

    2010-10-01

    The fast-ion Dα (FIDA) diagnostic is an application of charge-exchange recombination spectroscopy. Fast ions that neutralize in an injected neutral beam emit Balmer-α light with a large Doppler shift. The spectral shift is exploited to distinguish the FIDA emission from other bright sources of Dα light. Background subtraction is the main technical challenge. A spectroscopic diagnostic typically achieves temporal, energy, and transverse spatial resolution of ∼1 ms, ∼10 keV, and ∼2 cm, respectively. Installations that use narrow-band filters achieve high spatial and temporal resolution at the expense of spectral information. For high temporal resolution, the bandpass-filtered light goes directly to a photomultiplier, allowing detection of ∼50 kHz oscillations in FIDA signal. For two-dimensional spatial profiles, the bandpass-filtered light goes to a charge-coupled device camera; detailed images of fast-ion redistribution at instabilities are obtained. Qualitative and quantitative models relate the measured FIDA signals to the fast-ion distribution function. The first quantitative comparisons between theory and experiment found excellent agreement in beam-heated magnetohydrodynamics (MHD)-quiescent plasmas. FIDA diagnostics are now in operation at magnetic-fusion facilities worldwide. They are used to study fast-ion acceleration by ion cyclotron heating, to detect fast-ion transport by MHD modes and microturbulence, and to study fast-ion driven instabilities.

  13. Altitude Dependent Auroral Ion Diffusion Coefficients

    NASA Astrophysics Data System (ADS)

    Ludlow, G. R.

    2011-12-01

    Simultaneous upgoing auroral H+ and O+ ion beams generate ion acoustic waves which have both parallel and oblique wave vectors with respect to the ambient magnetic field. A parallel mode is investigated with phase velocity UO + CO in the direction of beam propagation, where UO is the oxygen beam velocity and CO is the oxygen ion sound speed. Due to the mass difference, this mode preferentially resonates with the oxygen beam through the n = 1 cyclotron resonance, causing O+ ions to diffuse in a direction that is primarily perpendicular to the background magnetic field. The Landau resonance (n = 0) is very narrow in parallel velocity and does not interact with either ion beam. In one case study the parallel acoustic mode begins to resonate with O+ ions within the auroral acceleration region and this resonant region in velocity space sweeps through the entire O+ beam as it moves into weaker magnetic field regions. The O+ quasilinear diffusion coefficients are examined during this process. Perpendicular diffusion becomes significant when the parallel resonant velocity is close to the parallel group velocity of the waves. This selects regions of velocity space where perpendicular diffusion is maximum which occurs at the leading edge of the resonant region as it sweeps through the O+ beam. In k - space these resonant velocities correspond to the regions of peak growth rate. The relevance of this work to the selective energization of heavy auroral ion beams will be discussed.

  14. Physics with fast molecular-ion beams

    SciTech Connect

    Kanter, E.P.

    1980-01-01

    Fast (MeV) molecular-ion beams provide a unique source of energetic projectile nuclei which are correlated in space and time. The recognition of this property has prompted several recent investigations of various aspects of the interactions of these ions with matter. High-resolution measurements on the fragments resulting from these interactions have already yielded a wealth of new information on such diverse topics as plasma oscillations in solids and stereochemical structures of molecular ions as well as a variety of atomic collision phenomena. The general features of several such experiments will be discussed and recent results will be presented.

  15. Sodium ion diffusion in Al2O3: a distinct perspective compared with lithium ion diffusion.

    PubMed

    Jung, Sung Chul; Kim, Hyung-Jin; Choi, Jang Wook; Han, Young-Kyu

    2014-11-12

    Surface coating of active materials has been one of the most effective strategies to mitigate undesirable side reactions and thereby improve the overall battery performance. In this direction, aluminum oxide (Al2O3) is one of the most widely adopted coating materials due to its easy synthesis and low material cost. Nevertheless, the effect of Al2O3 coating on carrier ion diffusion has been investigated mainly for Li ion batteries, and the corresponding understanding for emerging Na ion batteries is currently missing. Using ab initio molecular dynamics calculations, herein, we first find that, unlike lithiation, sodiation of Al2O3 is thermodynamically unfavorable. Nonetheless, there can still exist a threshold in the Na ion content in Al2O3 before further diffusion into the adjacent active material, delivering a new insight that both thermodynamics and kinetics should be taken into account to describe ionic diffusion in any material media. Furthermore, Na ion diffusivity in NaxAl2O3 turns out to be much higher than Li ion diffusivity in LixAl2O3, a result opposite to the conventional stereotype based on the atomic radius consideration. While hopping between the O-rich trapping sites via an Na-O bond breaking/making process is identified as the main Na ion diffusion mechanism, the weaker Na-O bond strength than the Li-O counterpart turns out to be the origin of the superior diffusivity of Na ions.

  16. The Effect of Different Fast-ion Instabilities on the Fast-ion Profile

    NASA Astrophysics Data System (ADS)

    Ruskov, E.; Heidbrink, W.; Liu, D.; Fredrickson, E.; Bortolon, A.

    2014-10-01

    Fast-ion driven instabilities in NSTX take many forms, including steady, bursting, and avalanching toroidal Alfven eigenmodes (TAE), avalanching global AEs, energetic particle modes (EPM), long-lived modes (LLM) and abrupt large-amplitude events (ALE). The occurrence or absence of these modes on Mirnov signals correlates with the ratio of fast-ion to Alfven speed and the ratio of fast-ion to thermal pressure. The drop in neutron rate at these events correlates differently with mode amplitude for the different types of events. In this study, we expand this database to investigate the correlation of vertical fast-ion D-alpha (FIDA) data with the different types of MHD. The measured profiles are compared with classically-predicted profiles. Work supported by US DOE Grant DE-FG02-06ER54867.

  17. Measurements of hohlraum-produced fast ions

    NASA Astrophysics Data System (ADS)

    Zylstra, A. B.; Li, C. K.; Séguin, F. H.; Rosenberg, M. J.; Rinderknecht, H. G.; Sinenian, N.; Frenje, J. A.; Petrasso, R. D.; Izumi, N.; Amendt, P. A.; Landen, O. L.; Koch, J. A.

    2012-04-01

    We report the first fast ion measurements in indirect-drive experiments, which were taken on OMEGA hohlraum and halfraum shots using simple filtered CR-39, a nuclear track detector, and a charged-particle spectrometer. Protons are observed in two energy regimes that are associated with different fast ion production mechanisms. In the first, resonance absorption at the hohlraum wall early in the laser pulse accelerates runaway electrons. In the second, fast electrons are produced with high energy from the two-plasmon decay instability in the exploding laser entrance hole, or from stimulated Raman scattering in the underdense gas fill. In both cases, the runaway electrons set up a strong electrostatic field that accelerates the measured ions. The former mechanism is observed to have an energy conversion efficiency ˜(0.6-4)×10-4 into fast protons depending on the hohlraum and drive. The latter mechanism has an estimated conversion efficiency from the main drive of ˜(0.5-2)×10-5 depending on the assumptions made.

  18. Spectroscopy of ions using fast beams and ion traps

    SciTech Connect

    Pinnington, E H; Trabert, E

    2004-10-01

    A knowledge of the spectra of ionized atoms is of importance in many fields. They can be studied in a wide variety of light sources. In recent years techniques coming under the broad heatings of fast beams and ion traps have been used extensively for such investigations. This article considers the advantages that various techniques have for particular applications.

  19. Thermal plasma and fast ion transport in electrostatic turbulence in the large plasma device

    SciTech Connect

    Zhou Shu; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Tripathi, S. K. P.; Van Compernolle, B.

    2012-05-15

    The transport of thermal plasma and fast ions in electrostatic microturbulence is studied. Strong density and potential fluctuations ({delta}n/n{approx}{delta}{phi}/kT{sub e}{approx} 0.5, f {approx} 5-50 kHz) are observed in the large plasma device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky et al., Rev. Sci. Instrum. 62, 2875 (1991)] in density gradient regions produced by obstacles with slab or cylindrical geometry. Wave characteristics and the associated plasma transport are modified by driving sheared E Multiplication-Sign B drift through biasing the obstacle and by modification of the axial magnetic fields (B{sub z}) and the plasma species. Cross-field plasma transport is suppressed with small bias and large B{sub z} and is enhanced with large bias and small B{sub z}. The transition in thermal plasma confinement is well explained by the cross-phase between density and potential fluctuations. Large gyroradius lithium fast ion beam ({rho}{sub fast}/{rho}{sub s} {approx} 10) orbits through the turbulent region. Scans with a collimated analyzer give detailed profiles of the fast ion spatial-temporal distribution. Fast-ion transport decreases rapidly with increasing fast-ion energy and gyroradius. Background waves with different scale lengths also alter the fast ion transport. Experimental results agree well with gyro-averaging theory. When the fast ion interacts with the wave for most of a wave period, a transition from super-diffusive to sub-diffusive transport is observed, as predicted by diffusion theory. Besides turbulent-wave-induced fast-ion transport, the static radial electric field (E{sub r}) from biasing the obstacle leads to drift of the fast-ion beam centroid. The drift and broadening of the beam due to static E{sub r} are evaluated both analytically and numerically. Simulation results indicate that the E{sub r} induced transport is predominately convective.

  20. Photochronographic registration of fast light ions

    NASA Astrophysics Data System (ADS)

    Litvin, Dmitri N.; Lazarchuk, Valeri P.; Murugov, Vasili M.; Petrov, Sergei I.; Senik, Alexei V.

    1999-06-01

    A possibility of registration of fast ions (protons, alpha- particles) with the help of an X-ray streak camera is demonstrated. The spatial resolution of the device is 50 micrometer, the physical time resolution with the use of a CsJ-cathode is 7 ps. From (alpha) -emission a secondary electrons yield is determined of (eta) equals 8 el../part. The device sensitivity makes it possible to register separate (alpha) -particles and protons. On the basis of the device there have been elaborated techniques of spatial-spectral registering of radiation of fast ions emitted by laser thermonuclear targets. The techniques are destined to study processes of interaction of high-intensive laser radiation with an appliance Iskra-5 target.

  1. Fast ion orbits in spherical tokamaks

    SciTech Connect

    Solano, E.R.

    1995-07-20

    In a spherical tokamak, the 1/R variation of the toroidal field is extreme, and for a given value of the safety factor a relatively low average toroidal field can be used, together with large plasma current and large plasma minor radius and elongation. The poloidal and toroidal fields are then of similar size. In consequence, the orbits of fast ions depart considerably from the guiding center orbits because of gyromotion in the small magnetic fields in the low field side.

  2. Controlling chloride ions diffusion in concrete.

    PubMed

    Zeng, Lunwu; Song, Runxia

    2013-11-28

    The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle.

  3. Controlling chloride ions diffusion in concrete

    PubMed Central

    Zeng, Lunwu; Song, Runxia

    2013-01-01

    The corrosion of steel in concrete is mainly due to the chemical reaction between the chloride ions and iron ions. Indeed, this is a serious threaten for reinforced concrete structure, especially for the reinforced concrete structure in the sea. So it is urgent and important to protect concrete against chloride ions corrosion. In this work, we report multilayer concrete can cloak chloride ions. We formulated five kinds of concrete A, B, C, D and E, which are made of different proportion of cement, sand and glue, and fabricated six-layer (ABACAD) cylinder diffusion cloak and background media E. The simulation results show that the six-layer mass diffusion cloak can protect concrete against chloride ions penetration, while the experiment results show that the concentration gradients are parallel and equal outside the outer circle in the diffusion flux lines, the iso-concentration lines are parallel outside the outer circle, and the concentration gradients in the inner circle are smaller than those outside the outer circle. PMID:24285220

  4. Resolving Fast, Confined Diffusion in Bacteria with Image Correlation Spectroscopy.

    PubMed

    Rowland, David J; Tuson, Hannah H; Biteen, Julie S

    2016-05-24

    By following single fluorescent molecules in a microscope, single-particle tracking (SPT) can measure diffusion and binding on the nanometer and millisecond scales. Still, although SPT can at its limits characterize the fastest biomolecules as they interact with subcellular environments, this measurement may require advanced illumination techniques such as stroboscopic illumination. Here, we address the challenge of measuring fast subcellular motion by instead analyzing single-molecule data with spatiotemporal image correlation spectroscopy (STICS) with a focus on measurements of confined motion. Our SPT and STICS analysis of simulations of the fast diffusion of confined molecules shows that image blur affects both STICS and SPT, and we find biased diffusion rate measurements for STICS analysis in the limits of fast diffusion and tight confinement due to fitting STICS correlation functions to a Gaussian approximation. However, we determine that with STICS, it is possible to correctly interpret the motion that blurs single-molecule images without advanced illumination techniques or fast cameras. In particular, we present a method to overcome the bias due to image blur by properly estimating the width of the correlation function by directly calculating the correlation function variance instead of using the typical Gaussian fitting procedure. Our simulation results are validated by applying the STICS method to experimental measurements of fast, confined motion: we measure the diffusion of cytosolic mMaple3 in living Escherichia coli cells at 25 frames/s under continuous illumination to illustrate the utility of STICS in an experimental parameter regime for which in-frame motion prevents SPT and tight confinement of fast diffusion precludes stroboscopic illumination. Overall, our application of STICS to freely diffusing cytosolic protein in small cells extends the utility of single-molecule experiments to the regime of fast confined diffusion without requiring advanced

  5. Measurements of classical transport of fast ions

    SciTech Connect

    Zhao, L.; Heidbrink, W.W.; Boehmer, H.; McWilliams, R.; Leneman, D.; Vincena, S.

    2005-05-15

    To study the fast-ion transport in a well controlled background plasma, a 3-cm diameter rf ion gun launches a pulsed, {approx}300 eV ribbon shaped argon ion beam parallel to or at 15 deg. to the magnetic field in the Large Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA. The parallel energy of the beam is measured by a two-grid energy analyzer at two axial locations (z=0.32 m and z=6.4 m) from the ion gun in LAPD. The calculated ion beam slowing-down time is consistent to within 10% with the prediction of classical Coulomb collision theory using the LAPD plasma parameters measured by a Langmuir probe. To measure cross-field transport, the beam is launched at 15 deg. to the magnetic field. The beam then is focused periodically by the magnetic field to avoid geometrical spreading. The radial beam profile measurements are performed at different axial locations where the ion beam is periodically focused. The measured cross-field transport is in agreement to within 15% with the analytical classical collision theory and the solution to the Fokker-Planck kinetic equation. Collisions with neutrals have a negligible effect on the beam transport measurement but do attenuate the beam current.

  6. Lithium ion diffusion through glassy carbon plate

    SciTech Connect

    Inaba, M.; Nohmi, S.; Funabiki, A.; Abe, T.; Ogumi, Z.

    1998-07-01

    The electrochemical permeation method was applied to the determination of the diffusion coefficient of Li{sup +} ion (D{sub Li{sup +}}) in a glassy carbon (GC) plate. The cell was composed of two compartments, which were separated by the GC plate. Li{sup +} ions were inserted electrochemically from one face, and extracted from the other. The flux of the permeated Li{sup +} ions was monitored as an oxidation current at the latter face. The diffusion coefficient was determined by fitting the transient current curve with a theoretical one derived from Fick's law. When the potential was stepped between two potentials in the range of 0 to 0.5 V, transient curves were well fitted with the theoretical one, which gave D{sub Li{sup +}} values on the order of 10{sup {minus}8} cm{sup {minus}2} s{sup {minus}1}. In contrast, when the potential was stepped between two potentials across 0.5 V, significant deviation was observed. The deviation indicated the presence of trap sites as well as diffusion sites for Li{sup +} ions, the former of which is the origin of the irreversible capacity of GC.

  7. Investigation of the fast ion beta limit in MST

    NASA Astrophysics Data System (ADS)

    Capecchi, William; Eilerman, Scott; Reusch, Joshua; Koliner, Jonathan; Anderson, Jay; Lin, Liang; Clark, Jerry; Liu, Deyong

    2013-10-01

    Fast ion orbits in the reversed field pinch (RFP) magnetic configuration are well ordered and have low orbit loss, even considering the stochasticity of the magnetic field generated by multiple tearing modes. Purely classical TRANSP modeling of a 1MW tangentially injected hydrogen neutral beam in MST deuterium plasmas predicts a core-localized fast ion density that can be up to 25% of the electron density and a fast ion beta of many times the local thermal beta. However, neutral particle analysis (NPA) of an NBI-driven mode (presumably driven by a fast ion pressure gradient) clearly shows transport of core-localized fast ions and a saturated fast ion density. The TRANSP modeling is presumed valid until the onset of the beam driven mode and gives an initial estimate of the volume-averaged fast ion beta in the range of 1-2% (local core value up to 10%). Distinguishing between an experimental fast ion number limit or fast ion beta limit is performed by scanning both the magnetic field strength and the NBI energy while observing conditions at the onset of the beam driven mode. Upcoming experiments will further investigate the empirical fast ion beta limit through the use of a deuterium beam into deuterium plasma which will allow for the NPA and neutron flux signals to provide a local and global fast ion beta measurement respectively. Work supported by US DoE.

  8. Inference of Fast-Ion Density Profile from Tomographic Reconstructions of Fast-Ion Dα Measurements

    NASA Astrophysics Data System (ADS)

    Stagner, L.; Heidbrink, W. W.; Collins, C.; Grierson, B. A.

    2014-10-01

    The fast-ion Dα (FIDA) diagnostic measures light that energetic particles emit in fusion plasmas. The diagnostic is sensitive to different velocity space regions depending on the viewing angle relative to the magnetic field. Consequently, viewing chords that share a radial location give different, yet still valid, results. Velocity space tomography allows for these viewing chords to be combined to infer the complete fast-ion distribution function from the different partial views. If this is done at many radial locations the fast-ion density profile is measured. We demonstrate this method for the case of a classically described, low power, MHD-quiescent plasma from actual FIDA measurements. FIDA measurements were taken at four radial positions, each with four different viewing angles. Simulation results are also shown. Work supported by the US Department of Energy under SC-G903402, DE-FC02-04ER54698 and DE-AC02-09CH11466.

  9. Importance of diffuse metal ion binding to RNA.

    PubMed

    Tan, Zhi-Jie; Chen, Shi-Jie

    2011-01-01

    RNAs are highly charged polyanionic molecules. RNA structure and function are strongly correlated with the ionic condition of the solution. The primary focus of this article is on the role of diffusive ions in RNA folding. Due to the long-range nature of electrostatic interactions, the diffuse ions can contribute significantly to RNA structural stability and folding kinetics. We present an overview of the experimental findings as well as the theoretical developments on the diffuse ion effects in RNA folding. This review places heavy emphasis on the effect of magnesium ions. Magnesium ions play a highly efficient role in stabilizing RNA tertiary structures and promoting tertiary structural folding. The highly efficient role goes beyond the mean-field effect such as the ionic strength. In addition to the effects of specific ion binding and ion dehydration, ion-ion correlation for the diffuse ions can contribute to the efficient role of the multivalent ions such as the magnesium ions in RNA folding.

  10. Optical properties of fast-diffusing solid-state plasmas

    SciTech Connect

    Forchel, A.; Schweizer, H.; Mahler, G.

    1983-08-08

    Transmission and emission spectra of fast-diffusing nonequilibrium electron-hole plasmas in semiconductors are calculated with use of displaced Fermi distributions. The carrier drift significantly alters the plasma spectra and removes previously reported incomprehensible discrepancies between experimental and theoretical plasma parameters, indicating the necessity to reinterpret entirely the spectroscopic data from nonequilibrium plasmas.

  11. An Ion Diffusion Model in Semi-Permeable Clay Materials

    SciTech Connect

    Liu, Chongxuan

    2007-08-01

    Ion diffusion in semi-impermeable clay materials dynamically interacts with electrostatic fields (or diffuse double layers) associated with clay particles. Current theory of ion transport in porous media containing fixed charges on solid materials, however, cannot explicitly account for the dynamic interactions. Here we proposed a model by coupling electrodynamics and nonequilibrium thermodynamics to describe ion diffusion in the clay materials. The developed model was validated by comparing the calculated and measured apparent ion diffusion coefficients in clay materials as a function of ionic strength, which affects the overlap extent of the electrostatic double layers associated with adjacent clay particles. The model shows that ion diffusion in clay materials is a complex function of factors including surface charge density, tortuosity, porosity, chemico-osmotic coefficient, and ion self-diffusivity. At transitional states, ion diffusive fluxes are dynamically related to the electrostatic fields, which shrink or expand as ion diffusion. At steady states, the electrostatic fields are time-invariant and ion diffusive fluxes conform to flux and concentration gradient relationships; and apparent diffusivity can be expressed by the ion diffusivity in bulk electrolytes corrected by a tortuosity factor and concentration gradient variations at the interfaces between clay materials and bulk solutions.

  12. Development of ultra-fast 2D ion Doppler tomography using image intensified CMOS fast camera

    NASA Astrophysics Data System (ADS)

    Tanabe, Hiroshi; Kuwahata, Akihiro; Yamanaka, Haruki; Inomoto, Michiaki; Ono, Yasushi; TS-group Team

    2015-11-01

    The world fastest novel time-resolved 2D ion Doppler tomography diagnostics has been developed using fast camera with high-speed gated image intensifier (frame rate: 200kfps. phosphor decay time: ~ 1 μ s). Time evolution of line-integrated spectra are diffracted from a f=1m, F/8.3 and g=2400L/mm Czerny-Turner polychromator, whose output is intensified and recorded to a high-speed camera with spectral resolution of ~0.005nm/pixel. The system can accommodate up to 36 (9 ×4) spatial points recorded at 5 μs time resolution, tomographic reconstruction is applied for the line-integrated spectra, time-resolved (5 μs/frame) local 2D ion temperature measurement has been achieved without any assumption of shot repeatability. Ion heating during intermittent reconnection event which tends to happen during high guide field merging tokamak was measured around diffusion region in UTST. The measured 2D profile shows ion heating inside the acceleration channel of reconnection outflow jet, stagnation point and downstream region where reconnected field forms thick closed flux surface as in MAST. Achieved maximum ion temperature increases as a function of Brec2 and shows good fit with MAST experiment, demonstrating promising CS-less startup scenario for spherical tokamak. This work is supported by JSPS KAKENHI Grant Number 15H05750 and 15K20921.

  13. Modeling Diffusion Induced Stresses for Lithium-Ion Battery Materials

    NASA Astrophysics Data System (ADS)

    Chiu Huang, Cheng-Kai

    Advancing lithium-ion battery technology is of paramount importance for satisfying the energy storage needs in the U.S., especially for the application in the electric vehicle industry. To provide a better acceleration for electric vehicles, a fast and repeatable discharging rate is required. However, particle fractures and capacity loss have been reported under high current rate (C-rate) during charging/discharging and after a period of cycling. During charging and discharging, lithium ions extract from and intercalate into electrode materials accompanied with the volume change and phase transition between Li-rich phase and Li-poor phase. It is suggested that the diffusion-induced-stress is one of the main reasons causing capacity loss due to the mechanical degradation of electrode particles. Therefore, there is a fundamental need to provide a mechanistic understanding by considering the structure-mechanics-property interactions in lithium-ion battery materials. Among many cathode materials, the olivine-based lithium-iron-phosphate (LiFePO4) with an orthorhombic crystal structure is one of the promising cathode materials for the application in electric vehicles. In this research we first use a multiphysic approach to investigate the stress evolution, especially on the phase boundary during lithiation in single LiFePO4 particles. A diffusion-controlled finite element model accompanied with the experimentally observed phase boundary propagation is developed via a finite element package, ANSYS, in which lithium ion concentration-dependent anisotropic material properties and volume misfits are incorporated. The stress components on the phase boundary are used to explain the Mode I, Mode II, and Mode III fracture propensities in LiFePO4 particles. The elastic strain energy evolution is also discussed to explain why a layer-by-layer lithium insertion mechanism (i.e. first-order phase transformation) is energetically preferred. Another importation issue is how current

  14. Ion diffusion at interfaces in hot plasmas

    SciTech Connect

    Boercker, D.B.; Warren, K.; Haggin, G.

    1986-04-01

    There are many laboratory applications in which it is important to know how fast two hot, ionized materials mix across an initially sharp interface. The speed of this process is regulated by the interdiffusion coefficient for the species involved. In a previous work, a theoretical method for calculating the interdiffusion coefficient in a Binary Ionic Mixture (classical ions in a uniform, neutralizing background) was described and found to give excellent agreement with Molecular Dynamics estimates. The purpose of this report is to show how these results may be applied to a model of the plasma interface, including electric field effects, to give a good description of the mixing across it.

  15. Measuring Fast Ion Losses in a Reversed Field Pinch Plasma

    NASA Astrophysics Data System (ADS)

    Bonofiglo, P. J.; Anderson, J. K.; Almagri, A. F.; Kim, J.; Clark, J.; Capecchi, W.; Sears, S. H.

    2015-11-01

    The reversed field pinch (RFP) provides a unique environment to study fast ion confinement and transport. The RFP's weak toroidal field, strong magnetic shear, and ability to enter a 3D state provide a wide range of dynamics to study fast ions. Core-localized, 25 keV fast ions are sourced into MST by a tangentially injected hydrogen/deuterium neutral beam. Neutral particle analysis and measured fusion neutron flux indicate enhanced fast ion transport in the plasma core. Past experiments point to a dynamic loss of fast ions associated with the RFP's transition to a 3D state and with beam-driven, bursting magnetic modes. Consequently, fast ion transport and losses in the RFP have garnered recent attention. Valuable information on fast-ion loss, such as energy and pitch distributions, are sought to provide a better understanding of the transport mechanisms at hand. We have constructed and implemented two fast ion loss detectors (FILDs) for use on MST. The FILDs have two, independent, design concepts: collecting particles as a function of v⊥ or with pitch greater than 0.8. In this work, we present our preliminary findings and results from our FILDs on MST. This research is supported by US DOE.

  16. Fast Ion Redistribution and Implications for the Hybrid Regime

    SciTech Connect

    Nazikian, R; Austin, M E; Budny, R V; Chu, M S; Heidbrink, W W; Makowski, M A; Petty, C C; Politzer, P A; Solomon, W M; Van Zeeland, M A

    2007-06-26

    Time dependent TRANSP analysis indicates that radial redistribution of fast ions is unlikely to affect the central current density in hybrid plasmas sufficient to raise q(0) above unity. The results suggest that some other mechanism other than fast ion transport must be involved in raising q(0) and preventing sawteeth in hybrid plasmas.

  17. Improved Hanle effect measurement technique for fast ions.

    NASA Technical Reports Server (NTRS)

    Liu, C. H.; Gardiner, R. B.; Church, D. A.

    1973-01-01

    An improved averaging technique for use with foil-excited fast ions is applied to a Hanle-effect measurement of the mean life of some fast ions. With improved data analysis, the employed technique is expected to be more precise, as well as experimentally simpler than previously used techniques.

  18. Observations of Ag diffusion in ion implanted SiC

    NASA Astrophysics Data System (ADS)

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Hunter, Jerry L.; Giordani, Andrew J.; Allen, Todd R.

    2015-06-01

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500-1625 °C, were investigated by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated, including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.

  19. Observations of Ag diffusion in ion implanted SiC

    SciTech Connect

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Jerry L. Hunter, Jr.; Giordani, Andrew J.; Allen, Todd R.

    2015-03-17

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500–1625°C, were investigated in this study by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated, including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Lastly, estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.

  20. Confinement, Desolvation, And Electrosorption Effects on the Diffusion of Ions in Nanoporous Carbon Electrodes

    PubMed Central

    2015-01-01

    Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption. PMID:26369420

  1. Confinement, Desolvation, And Electrosorption Effects on the Diffusion of Ions in Nanoporous Carbon Electrodes.

    PubMed

    Pean, Clarisse; Daffos, Barbara; Rotenberg, Benjamin; Levitz, Pierre; Haefele, Matthieu; Taberna, Pierre-Louis; Simon, Patrice; Salanne, Mathieu

    2015-10-01

    Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption.

  2. Confinement, Desolvation, And Electrosorption Effects on the Diffusion of Ions in Nanoporous Carbon Electrodes.

    PubMed

    Pean, Clarisse; Daffos, Barbara; Rotenberg, Benjamin; Levitz, Pierre; Haefele, Matthieu; Taberna, Pierre-Louis; Simon, Patrice; Salanne, Mathieu

    2015-10-01

    Supercapacitors are electrochemical devices which store energy by ion adsorption on the surface of a porous carbon. They are characterized by high power delivery. The use of nanoporous carbon to increase their energy density should not hinder their fast charging. However, the mechanisms for ion transport inside electrified nanopores remain largely unknown. Here we show that the diffusion is characterized by a hierarchy of time scales arising from ion confinement, solvation, and electrosorption effects. By combining electrochemistry experiments with molecular dynamics simulations, we determine the in-pore conductivities and diffusion coefficients and their variations with the applied potential. We show that the diffusion of the ions is slower by 1 order of magnitude compared to the bulk electrolyte. The desolvation of the ions occurs on much faster time scales than electrosorption. PMID:26369420

  3. Assessment of Potential for Ion Driven Fast Ignition

    SciTech Connect

    Logan, B. Grant; Bangerter, Roger O.; Callahan, Debra A.; Tabak,Max; Roth, Markus; Perkins, L. John; Caporaso, George

    2005-05-01

    Critical issues and ion beam requirements are explored for fast ignition using ion beams to provide fuel compression using indirect drive and to provide separate short pulse ignition heating using direct drive. Several ion species with different hohlraum geometries are considered for both accelerator-produced and laser-produced ion ignition beams. Ion-driven fast ignition targets are projected to have modestly higher gains than with conventional heavy-ion fusion, and may offer some other advantages for target fabrication and for use of advanced fuels. However, much more analysis and experiments are needed before conclusions can be drawn regarding the feasibility for meeting the ion beam transverse and longitudinal emittances, focal spots, pulse lengths, and target stand-off distances required for ion-driven fast ignition.

  4. Assessment of Potential for Ion Driven Fast Ignition

    SciTech Connect

    Logan, B. Grant; Bangerter, Roger O.; Callahan, Debra A.; Tabak, Max; Roth, Markus; Perkins, L. John; Caporaso, George

    2004-12-01

    Critical issues and ion beam requirements are explored for fast ignition using ion beams to provide fuel compression using indirect drive and to provide separate short pulse ignition heating using direct drive. Several ion species with different hohlraum geometries are considered for both accelerator-produced and laser-produced ion ignition beams. Ion-driven fast ignition targets are projected to have modestly higher gains than with conventional heavy-ion fusion, and may offer some other advantages for target fabrication and for use of advanced fuels. However, much more analysis and experiments are needed before conclusions can be drawn regarding the feasibility for meeting the ion beam transverse and longitudinal emittances, focal spots, pulse lengths, and target standoff distances required for ion-driven fast ignition.

  5. Diffusion cannot govern the discharge of neurotransmitter in fast synapses.

    PubMed Central

    Khanin, R; Parnas, H; Segel, L

    1994-01-01

    In the present work we show that diffusion cannot provide the observed fast discharge of neurotransmitter from a synaptic vesicle during neurotransmitter release, mainly because it is not sufficiently rapid nor is it sufficiently temperature-dependent. Modeling the discharge from the vesicle into the cleft as a continuous point source, we have determined that discharge should occur in 50-75 microseconds, to provide the observed high concentrations of transmitter at the critical zone. Images FIGURE 5 PMID:7811953

  6. Diffusion and Coulomb separation of ions in dense matter.

    PubMed

    Beznogov, M V; Yakovlev, D G

    2013-10-18

    We analyze diffusion equations in strongly coupled Coulomb mixtures of ions in dense stellar matter. Strong coupling of ions in the presence of gravitational forces and electric fields (induced by plasma polarization in the presence of gravity) produces a specific diffusion current which can separate ions with the same A/Z (mass to charge number) ratios but different Z. This Coulomb separation of ions can be important for the evolution of white dwarfs and neutron stars. PMID:24182248

  7. Scaling of Kinetic Instability Induced Fast Ion Losses in NSTX

    SciTech Connect

    E.D. Fredrickson; D. Darrow; S. Medley; J. Menard; H. Park; L. Roquemore; D. Stutman; K. Tritz; S. Kubota; K.C. Lee

    2005-06-24

    During neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX), a wide variety of fast ion driven instabilities is excited by the large ratio of fast ion velocity to Alfven velocity, together with the relatively high fast ion beta, beta(sub)f. The fast ion instabilities have frequencies ranging from a few kilohertz to the ion cyclotron frequency. The modes can be divided roughly into three categories, starting with Energetic Particle Modes (EPM) in the lowest frequency range (0 to 120 kHz), the Toroidal Alfven Eigenmodes (TAE) in the intermediate frequency range (50 to 200 kHz) and the Compressional and Global Alfven Eigenmodes (CAE and GAE, respectively) from approximately equal to 300 kHz up to the ion cyclotron frequency. Each of these categories of modes exhibits a wide range of behavior, including quasi-continuous oscillation, bursting, chirping and, except for the lower frequency range, turbulence.

  8. Anomalously Fast Diffusion of Targeted Carbon Nanotubes in Cellular Spheroids.

    PubMed

    Wang, Yichun; Bahng, Joong Hwan; Che, Quantong; Han, Jishu; Kotov, Nicholas A

    2015-08-25

    Understanding transport of carbon nanotubes (CNTs) and other nanocarriers within tissues is essential for biomedical imaging and drug delivery using these carriers. Compared to traditional cell cultures in animal studies, three-dimensional tissue replicas approach the complexity of the actual organs and enable high temporal and spatial resolution of the carrier permeation. We investigated diffusional transport of CNTs in highly uniform spheroids of hepatocellular carcinoma and found that apparent diffusion coefficients of CNTs in these tissue replicas are anomalously high and comparable to diffusion rates of similarly charged molecules with molecular weights 10000× lower. Moreover, diffusivity of CNTs in tissues is enhanced after functionalization with transforming growth factor β1. This unexpected trend contradicts predictions of the Stokes-Einstein equation and previously obtained empirical dependences of diffusivity on molecular mass for permeants in gas, liquid, solid or gel. It is attributed to the planar diffusion (gliding) of CNTs along cellular membranes reducing effective dimensionality of diffusional space. These findings indicate that nanotubes and potentially similar nanostructures are capable of fast and deep permeation into the tissue, which is often difficult to realize with anticancer agents.

  9. Scintillator-based fast ion loss measurements in the EAST

    NASA Astrophysics Data System (ADS)

    Chang, J. F.; Isobe, M.; Ogawa, K.; Huang, J.; Wu, C. R.; Xu, Z.; Jin, Z.; Lin, S. Y.; Hu, L. Q.

    2016-11-01

    A new scintillator-based fast ion loss detector (FILD) has been installed on Experimental Advanced Superconducting Tokamak (EAST) to investigate the fast ion loss behavior in high performance plasma with neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). A two dimensional 40 mm × 40 mm scintillator-coated (ZnS:Ag) stainless plate is mounted in the front of the detector, capturing the escaping fast ions. Photons from the scintillator plate are imaged with a Phantom V2010 CCD camera. The lost fast ions can be measured with the pitch angle from 60° to 120° and the gyroradius from 10 mm to 180 mm. This paper will describe the details of FILD diagnostic on EAST and describe preliminary measurements during NBI and ICRH heating.

  10. Alfvén Eigenmode Induced Fast Ion Transport in DIII-D Resulting From Finite Larmor Radius Effects

    NASA Astrophysics Data System (ADS)

    Kramer, G. J.; Fu, G. Y.; Nazikian, R.; van Zeeland, M. A.; Fisher, R. K.; Pace, D. C.; Chen, L.; Chen, X.; Heidbrink, W. W.

    2013-10-01

    Alfvén Eigenmode (AE) induced fast-ion redistribution and loss are commonly observed in DIII-D. In those experiments the perpendicular wave vector times the fast-ion Larmor radius is of order unity (k⊥ρi ~ 1), which allows fast ion orbits to traverse the AE mode structures asymmetrically causing a significant change in magnetic moment. Full-orbit simulations of the expected transport in DIII-D plasmas show that this effect can lead to fast-ion radial diffusion constants of 5 m2/s at the measured mode amplitudes. This level of diffusion is not captured with a guiding center approximation and is in agreement with that deduced in DIII-D experiments when AE activity was present. Work supported by the US Department of Energy under DE-AC02-09CH11466, DE-FC02-04ER54698, and SC-G903402.

  11. Electro-diffusion in a plasma with two ion species

    NASA Astrophysics Data System (ADS)

    Kagan, Grigory; Tang, Xian-Zhu

    2012-08-01

    Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.

  12. Electro-diffusion in a plasma with two ion species

    SciTech Connect

    Kagan, Grigory; Tang Xianzhu

    2012-08-15

    Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.

  13. "Fast excitation" CID in a quadrupole ion trap mass spectrometer.

    PubMed

    Murrell, J; Despeyroux, D; Lammert, S A; Stephenson, J L; Goeringer, D E

    2003-07-01

    Collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer is usually performed by applying a small amplitude excitation voltage at the same secular frequency as the ion of interest. Here we disclose studies examining the use of large amplitude voltage excitations (applied for short periods of time) to cause fragmentation of the ions of interest. This process has been examined using leucine enkephalin as the model compound and the motion of the ions within the ion trap simulated using ITSIM. The resulting fragmentation information obtained is identical with that observed by conventional resonance excitation CID. "Fast excitation" CID deposits (as determined by the intensity ratio of the a(4)/b(4) ion of leucine enkephalin) approximately the same amount of internal energy into an ion as conventional resonance excitation CID where the excitation signal is applied for much longer periods of time. The major difference between the two excitation techniques is the higher rate of excitation (gain in kinetic energy) between successive collisions with helium atoms with "fast excitation" CID as opposed to the conventional resonance excitation CID. With conventional resonance excitation CID ions fragment while the excitation voltage is still being applied whereas for "fast excitation" CID a higher proportion of the ions fragment in the ion cooling time following the excitation pulse. The fragmentation of the (M + 17H)(17+) of horse heart myoglobin is also shown to illustrate the application of "fast excitation" CID to proteins.

  14. "Fast Excitation" CID in Quadrupole Ion Trap Mass Spectrometer

    SciTech Connect

    Murrell, J.; Despeyroux, D.; Lammert, Stephen {Steve} A; Stephenson Jr, James {Jim} L; Goeringer, Doug

    2003-01-01

    Collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer is usually performed by applying a small amplitude excitation voltage at the same secular frequency as the ion of interest. Here we disclose studies examining the use of large amplitude voltage excitations (applied for short periods of time) to cause fragmentation of the ions of interest. This process has been examined using leucine enkephalin as the model compound and the motion of the ions within the ion trap simulated using ITSIM. The resulting fragmentation information obtained is identical with that observed by conventional resonance excitation CID. ''Fast excitation'' CID deposits (as determined by the intensity ratio of the a{sub 4}/b{sub 4} ion of leucine enkephalin) approximately the same amount of internal energy into an ion as conventional resonance excitation CID where the excitation signal is applied for much longer periods of time. The major difference between the two excitation techniques is the higher rate of excitation (gain in kinetic energy) between successive collisions with helium atoms with ''fast excitation'' CID as opposed to the conventional resonance excitation CID. With conventional resonance excitation CID ions fragment while the excitation voltage is still being applied whereas for ''fast excitation'' CID a higher proportion of the ions fragment in the ion cooling time following the excitation pulse. The fragmentation of the (M + 17H){sup 17+} of horse heart myoglobin is also shown to illustrate the application of ''fast excitation'' CID to proteins.

  15. Measurements of classical fast ion confinement with fusion product diagnostics

    NASA Astrophysics Data System (ADS)

    Magee, Richard; Clary, Ryan; Korepanov, Sergey; Smirnov, Artem; Garate, Eusebio; Allfrey, Ian; Valentine, Travis; the TAE Team

    2014-10-01

    Neutral beam injected fast ions play a critical role in the C-2 field reversed configuration plasma, helping to sustain magnetic flux against resistive decay and heating the plasma via Coulomb collisions. The fast ions are well confined; due to the relatively low magnetic field strength the fast ions have large, machine-size orbits that permit them to average over otherwise deleterious fluctuations. These same orbits however, have large radial excursions that result in greater interaction of fast ions with edge neutrals and a greater potential for charge exchange losses. In this presentation, the fast ion slowing down time is determined from the decay in neutron flux following beam termination. It is found that the slowing down scaling is close to classical (i.e., τ ~Te3/2/ne) and that charge exchange losses are only significant for ions with 1.5× the nominal injection energy. We will also present initial data from a newly installed proton detector, which complements the temporal resolution of the neutron detector with spatial resolution. The detector will be used to diagnose the axial profile of confined fast ions.

  16. FAST Mapping of Diffuse HI Gas in the Local Universe

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Pisano, D. J.; Ai, M.; Jiao, Q.

    2016-02-01

    We propose to use the Five hundred meter Aperture Spherical radio Telescope (FAST) to map the diffuse intergalactic HI gas in the local universe at column densities of NHI=1018 cm-2 and below. The major science goal is to study gas accretion during galaxy evolution, and trace cosmic web features in the local universe. We disuss the technical feasibilty of such a deep survey, and have conducted test observations with the Arecibo 305 m telescope. Our preliminary results shows that, with about a few thousand hours of observing time, FAST will be able to map several hundred square degree regions at 1 σ of NHI=2×1017 cm-2 level out to a distance of 5-10 Mpc, and with a volume 1000 larger than that of the Local Group.

  17. Strong Pitch-Angle Diffusion of the Ring Current Ions Induced by Electromagnetic ion Cyclotron Waves

    NASA Astrophysics Data System (ADS)

    Gamayunov, K. V.; Khazanov, G. V.

    2005-12-01

    Deep and intense circulation of the magnetospheric plasma during geomagnetic storm is building up an energy content of the terrestrial ring current (RC) to an unusually high level, and the RC intensity strongly influence the storm-time space weather. The recovery of Dst index takes place hours or days after Dst minimum, and is caused by the decay of magnetopause and magnetotail current systems, and removal of the RC ions due to charge exchange, convection through the dayside magnetopause, Coulomb scattering, RC interaction with electromagnetic ion cyclotron (EMIC) waves, and scattering by field-line curvature. During the early recovery phase, the RC loss rate is about one hour or less, and it is more rapid than charge exchange can support. Ion scattering into the loss cone by EMIC waves is believed to be responsible for such fast RC decay during this storm stage. However, most RC-EMIC wave interaction models do not predict the strong pitch-angle diffusion that is theoretically discussed and observed in the Earth magnetosphere (particularly by SEPS detectors on board of the POLAR satellite). In present work, we employ our self-consistent RC-EMIC wave model in order to study systematically the occurrence of the RC strong pitch-angle diffusion caused by interaction with waves during the May 1998 storm. Most of cases of the strong diffusion and of the intense EMIC waves are located in the afternoon-premidnight MLT sector at 3 < L < 6, and exhibit significant linear correlation. During the early recovery phase (at about 08 UT on May 4), the entire RC energy range (less than 450 keV) is subject to strong pitch-angle diffusion. Although the flux transitions between trapped zone and loss cone are steeper for higher energy RC protons than for main body of the distribution function, the pitch-angle distributions are highly isotropic for all energies both inside and outside of the loss cone.

  18. Simulation analysis for ion assisted fast ignition using structured targets

    NASA Astrophysics Data System (ADS)

    Sakagami, H.; Johzaki, T.; Sunahara, A.; Nagatomo, H.

    2016-05-01

    As the heating efficiency by fast electrons in the fast ignition scheme is estimated to be very low due to their large divergence angle and high energy. To mitigate this problem, low-density plastic foam, which can generate not only proton (H+) but also carbon (C6+) beams, can be introduced to currently used cone-guided targets and additional core heating by ions is expected. According to 2D PIC simulations, it is found that the ion beams also diverge by the static electric field and concave surface deformation. Thus structured targets are suggested to optimize ion beam characteristics, and their improvement and core heating enhancement by ion beams are confirmed.

  19. Fast Through-Bond Diffusion of Nitrogen in Silicon

    SciTech Connect

    SCHULTZ,PETER A.; NELSON,JEFFREY S.

    2000-07-12

    The authors report first principles total energy calculations of interaction of nitrogen in silicon with silicon self-interstitials. Substitutional nitrogen captures a silicon interstitial with 3.5 eV binding energy forming a {l_angle}001{r_angle} split interstitial ground state geometry, with the nitrogen forming three bonds. The low energy migration path is through a bond bridge state having two bonds. Fast diffusion of nitrogen occurs through a pure interstitialcy mechanism; the nitrogen never has less than two bonds. Near-zero formation energy of the nitrogen interstitialcy with respect to the substitutional rationalizes the low solubility of substitutional nitrogen in silicon.

  20. Fast ion behavior during neutral beam injection in ATF

    NASA Astrophysics Data System (ADS)

    Wade, M. R.; Thomas, C. E.; Colchin, R. J.; Rome, J. A.; England, A. C.; Fowler, R. H.; Aceto, S. C.

    In stellarators, single-particle confinement properties can be more complex than in their tokamak counterparts. Fast-ion behavior in tokamaks has been well characterized through an abundance of measurements on various devices and in general has been shown to be consistent with classical slowing-down theory, although anomalous ion behavior has been observed during intense beam injection in ISX-B, during fishbone instabilities in PDX, and in experiments on TFR. In contrast, fast ion behavior in stellarators is not as well established experimentally with the primary experiments to date focusing on near-perpendicular or perpendicular neutral beam injection (NBI) on the Wendelstein 7-A stellarator and Heliotron-E. This paper addresses fast-ion confinement properties in a large aspect ratio, moderate shear stellarator, the Advanced Toroidal Facility, during tangential NBI. The primary data used in this study are the experimentally measured energy spectra of charge-exchange neutrals escaping from the plasma, using a two-dimensional scanning neutral particle analyzer. This diagnostic method is well established, having been used on several devices since the early 1970's. Various aspects of fast-ion behavior are investigated by comparing these data with computed theoretical spectra based on energetic ion distributions derived from the fast ion Fokker-Planck equation. Ion orbits are studied by computer orbit following, by the computation of J(sup *) surfaces, and by Monte Carlo calculations.

  1. Investigation of interaction between fast ions and tearing modes in MST plasmas using full orbit tracing

    NASA Astrophysics Data System (ADS)

    Kim, Jungha; Anderson, Jay; Capecchi, William; Bonofiglo, Phillip; Sears, Stephanie; Tsidulko, Yuri

    2015-11-01

    Under proper conditions, global reconnection events generate an anisotropic runaway ion distribution in MST plasmas. Full orbit tracing with time-dependent fluctuating fields, calculated by the nonlinear resistive MHD code DEBS, is used to inform a refined model of ion heating to explain this phenomenon, where tearing modes and ions interact on two distinct scales. There is anisotropic heating of thermal ions (T⊥>T∥), likely through a stochastic heating mechanism that requires high diffusivity and a tearing mode induced radial electric field with correlation length of a few cm. This process does not, however, continuously energize ions into the runaway regime. At sufficient energy, the ion guiding center deviates from the background magnetic field, which reduces the effective diffusivity to classical levels even in a stochastic magnetic field. These ``fast'' ions are accelerated by a parallel electric field (length scale of meters) induced by the equilibrium change accompanying tearing modes. This process relies on multiple global tearing modes; here we focus on a single tearing mode. This is compared to an experimental state where a transition to a single, dominant tearing mode is observed to accelerate fast ions and alter their confinement properties. Work supported by US DOE.

  2. Importance of diffuse metal ion binding to RNA.

    PubMed

    Tan, Zhi-Jie; Chen, Shi-Jie

    2011-01-01

    RNAs are highly charged polyanionic molecules. RNA structure and function are strongly correlated with the ionic condition of the solution. The primary focus of this article is on the role of diffusive ions in RNA folding. Due to the long-range nature of electrostatic interactions, the diffuse ions can contribute significantly to RNA structural stability and folding kinetics. We present an overview of the experimental findings as well as the theoretical developments on the diffuse ion effects in RNA folding. This review places heavy emphasis on the effect of magnesium ions. Magnesium ions play a highly efficient role in stabilizing RNA tertiary structures and promoting tertiary structural folding. The highly efficient role goes beyond the mean-field effect such as the ionic strength. In addition to the effects of specific ion binding and ion dehydration, ion-ion correlation for the diffuse ions can contribute to the efficient role of the multivalent ions such as the magnesium ions in RNA folding. PMID:22010269

  3. Measurements of Fast Ion Distribution in ICRF Heated Plasmas

    SciTech Connect

    Bader, A.; Sears, J.; Bonoli, P.; Granetz, R.; Parker, R.; Wukitch, S.

    2009-11-26

    Alcator C-Mod uses ICRF for the bulk auxiliary heating and relies primarily on hydrogen minority heating scenarios. Measuring the resulting hydrogen ion distribution provides an opportunity to validate upgraded ICRF simulation capability that includes non-Maxwellian ions. The Compact Neutral Particle Analyzer (CNPA) is a diagnostic employed on Alcator C-Mod to measure this fast ion distribution function. The diagnostic can measure the energy distribution of the fast ion tail, serving as a benchmark for simulation results and allowing for an assessment of the simulation algorithm and physics kernel. In this poster, we will present results from the detector in the most recent campaigns. We will discuss the calculation of the fast ion distribution from the measured CNPA distribution and the resulting effective temperature from applying a Stix fit to this distribution.

  4. Experiment to measure fast ion transport by magnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Preiwisch, Adam; Heidbrink, William; Boehmer, Heinz; McWilliams, Roger; Carter, Troy; Gekelman, Walter; Tripathi, Shreekrishna; van Compernolle, Bart; Vincena, Steve

    2013-10-01

    Fast ion transport in a linear magnetic field is studied at the upgraded Large Plasma Device. Recent developments allow for the generation of turbulent magnetic flux ropes, produced by a hot LaB6 cathode situated in the main chamber.1 A large-gyroradius, energetic lithium ion beam (300 <= Efast /Ti <= 1000) is passed through the turbulent region and collected by a collimated analyzer downstream, yielding a detailed plane profile of the fast ion distribution.2 Magnetic fluctuations, density, and temperature profiles are also obtained via probes. Enhanced fast-ion transport is clearly observed in the form of beam broadening. Early analysis shows broadband ion saturation current and magnetic fluctuations attributed to the flux ropes. A follow up experiment is currently under way to address whether the increased transport is primarily attributed to magnetic fields, associated electric fields, or increased Coulomb scattering.

  5. Application of anomalous diffusion in production of negative ions

    SciTech Connect

    Jimbo, K.

    1984-11-01

    The production of negative hydrogen ions is investigated in the reflex-type negative ion sources. When anomalous diffusion in the positive column was found by Hoh and Lehnert (Phys. Fluids 3, 600 (1960)), it was pointed out that the large particle loss produced by anomalous diffusion is compensated for by the larger particle production inside the plasma. In the present experiments anomalous diffusion was artificially encouraged by changing the radial electric field inside the reflex discharge. Apparent encouragement of negative ion current by the increase of the density fluctuation amplitude is observed. Twice as much negative ion current was obtained with the artificial encouragement as without. On the other hand, the larger extracted negative ion current was observed with a lower electron temperature, which is calculated from the anomalous diffusion coefficient derived from a simple nonlinear theory. This result is consistent with Wadehra's calculated results (Appl. Phys. Lett. 35, 917 (1979)).

  6. Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere

    NASA Astrophysics Data System (ADS)

    Paonessa, M.; Cheng, A. F.

    1986-02-01

    Voyager low energy charged particle (LECP) ion phase space densities at constant first and second adiabatic invariants have been used to place limits on the rate of radial diffusion of energetic ions (30 keV to 1 MeV) in Saturn's inner magnetosphere. Upper and lower limits to the radial diffusion coefficient, DLL, are deduced from physical requirements on the rates of diffusion and loss. If DLL is near the lower limit found in this work, then satellite sweeping accounts for a large fraction of the total ion losses. If DLL is near the upper limit, then ion losses can approach 10% of the strong diffusion rate. In this case, ion losses are dominated by wave-particle interactions, and sweeping losses are relatively unimportant.

  7. Fast-ion D-alpha diagnostic for NSTX

    SciTech Connect

    Heidbrink, W. W.; Bell, R. E.; Luo, Y.; Solomon, W.

    2006-10-15

    A fast-ion D-alpha (FIDA) diagnostic is under development for the National Spherical Torus Experiment (NSTX). The FIDA technique is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha light from energetic hydrogenic atoms to infer the fast-ion density. The principal objective of the NSTX installation is to measure the transport of beam ions caused by fast-ion driven instabilities; detection of perpendicular acceleration of fast ions during high harmonic fast wave heating is another important goal. Recent data from a DIII-D FIDA diagnostic guide the design. The planned NSTX diagnostic consists of two separate instruments focusing on different aspects of the measurement. One instrument uses a transmission grating spectrometer to measure the perpendicular energy spectrum and the spatial profile every 10 ms; the anticipated resolution is {approx}10 keV in energy and {approx}5 cm in radius. A second instrument employs bandpass filters to detect fast-ion redistribution events with millisecond temporal resolution.

  8. Effect of fast positive ions incident on caesiated plasma grid of negative ion source

    SciTech Connect

    Bacal, M.

    2012-02-15

    This paper describes the effect on negative ion formation on a caesiated surface of the backscattering of positive ions approaching it with energy of a few tens of eV. For a positive ion energy of 45 eV, the surface produced negative ion current density due to these fast positive ions is 12 times larger than that due to thermal atoms, thus dominating the negative ion surface production instead of the thermal atoms, as considered until now.

  9. Collective effects in electronic sputtering of organic molecular ions by fast incident cluster ions

    SciTech Connect

    Salehpour, M.; Fishel, D.L.; Hunt, J.E.

    1988-07-15

    The collective sputtering effect of fast primary cluster ions on the yield of secondary molecular ions has been demonstrated for the first time. Results show that the sputtering yield of valine negative molecular ions per incident carbon atom, in a C/sup +//sub n/ incident cluster ion, increases with increasing n. The yield results are interpreted as a direct effect of the enhancement in the electronic stopping power per atom in cluster ions compared to atomic ions.

  10. Existence domains of slow and fast ion-acoustic solitons in two-ion space plasmas

    SciTech Connect

    Maharaj, S. K.; Bharuthram, R.; Singh, S. V. Lakhina, G. S.

    2015-03-15

    A study of large amplitude ion-acoustic solitons is conducted for a model composed of cool and hot ions and cool and hot electrons. Using the Sagdeev pseudo-potential formalism, the scope of earlier studies is extended to consider why upper Mach number limitations arise for slow and fast ion-acoustic solitons. Treating all plasma constituents as adiabatic fluids, slow ion-acoustic solitons are limited in the order of increasing cool ion concentrations by the number densities of the cool, and then the hot ions becoming complex valued, followed by positive and then negative potential double layer regions. Only positive potentials are found for fast ion-acoustic solitons which are limited only by the hot ion number density having to remain real valued. The effect of neglecting as opposed to including inertial effects of the hot electrons is found to induce only minor quantitative changes in the existence regions of slow and fast ion-acoustic solitons.

  11. Aggregate influence on chloride ion diffusion into concrete

    SciTech Connect

    Hobbs, D.W.

    1999-12-01

    An attempt is made to predict the probable effect of the aggregate on chloride ion diffusion into saturated concrete. It is shown that if the chloride ion diffusion coefficient of an aggregate ranges from 0.2 to 10 times that of the cement past matrix, then this could result in variations in the concrete chloride ion diffusion coefficient of up to 10:1. Such a variation is equivalent to a change in free water-cement ration from 0.77 to 0.45.

  12. Theory of ion transport with fast acid-base equilibrations in bioelectrochemical systems

    NASA Astrophysics Data System (ADS)

    Dykstra, J. E.; Biesheuvel, P. M.; Bruning, H.; Ter Heijne, A.

    2014-07-01

    Bioelectrochemical systems recover valuable components and energy in the form of hydrogen or electricity from aqueous organic streams. We derive a one-dimensional steady-state model for ion transport in a bioelectrochemical system, with the ions subject to diffusional and electrical forces. Since most of the ionic species can undergo acid-base reactions, ion transport is combined in our model with infinitely fast ion acid-base equilibrations. The model describes the current-induced ammonia evaporation and recovery at the cathode side of a bioelectrochemical system that runs on an organic stream containing ammonium ions. We identify that the rate of ammonia evaporation depends not only on the current but also on the flow rate of gas in the cathode chamber, the diffusion of ammonia from the cathode back into the anode chamber, through the ion exchange membrane placed in between, and the membrane charge density.

  13. Theory of ion transport with fast acid-base equilibrations in bioelectrochemical systems.

    PubMed

    Dykstra, J E; Biesheuvel, P M; Bruning, H; Ter Heijne, A

    2014-07-01

    Bioelectrochemical systems recover valuable components and energy in the form of hydrogen or electricity from aqueous organic streams. We derive a one-dimensional steady-state model for ion transport in a bioelectrochemical system, with the ions subject to diffusional and electrical forces. Since most of the ionic species can undergo acid-base reactions, ion transport is combined in our model with infinitely fast ion acid-base equilibrations. The model describes the current-induced ammonia evaporation and recovery at the cathode side of a bioelectrochemical system that runs on an organic stream containing ammonium ions. We identify that the rate of ammonia evaporation depends not only on the current but also on the flow rate of gas in the cathode chamber, the diffusion of ammonia from the cathode back into the anode chamber, through the ion exchange membrane placed in between, and the membrane charge density. PMID:25122405

  14. Charge exchange spectroscopy as a fast ion diagnostic on TEXTORa)

    NASA Astrophysics Data System (ADS)

    Delabie, E.; Jaspers, R. J. E.; von Hellermann, M. G.; Nielsen, S. K.; Marchuk, O.

    2008-10-01

    An upgraded charge exchange spectroscopy diagnostic has been taken into operation at the TEXTOR tokamak. The angles of the viewing lines with the toroidal magnetic field are close to the pitch angles at birth of fast ions injected by one of the neutral beam injectors. Using another neutral beam for active spectroscopy, injected counter the direction in which fast ions injected by the first beam are circulating, we can simultaneously measure a fast ion tail on the blue wing of the Dα spectrum while the beam emission spectrum is Doppler shifted to the red wing. An analysis combining the two parts of the spectrum offers possibilities to improve the accuracy of the absolute (fast) ion density profiles. Fast beam modulation or passive viewing lines cannot be used for background subtraction on this diagnostic setup and therefore the background has to be modeled and fitted to the data together with a spectral model for the slowing down feature. The analysis of the fast ion Dα spectrum obtained with the new diagnostic is discussed.

  15. Calibration techniques for fast-ion Dα diagnosticsa)

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Bortolon, A.; Muscatello, C. M.; Ruskov, E.; Grierson, B. A.; Podestá, M.

    2012-10-01

    Fast-ion Dα measurements are an application of visible charge-exchange recombination (CER) spectroscopy that provide information about the energetic ion population. Like other CER diagnostics, the standard intensity calibration is obtained with an integrating sphere during a vacuum vessel opening. An alternative approach is to create plasmas where the fast-ion population is known, then calculate the expected signals with a synthetic diagnostic code. The two methods sometimes agree well but are discrepant in other cases. Different background subtraction techniques and simultaneous measurements of visible bremsstrahlung and of beam emission provide useful checks on the calibrations and calculations.

  16. Calibration techniques for fast-ion Dα diagnostics.

    PubMed

    Heidbrink, W W; Bortolon, A; Muscatello, C M; Ruskov, E; Grierson, B A; Podestá, M

    2012-10-01

    Fast-ion D(α) measurements are an application of visible charge-exchange recombination (CER) spectroscopy that provide information about the energetic ion population. Like other CER diagnostics, the standard intensity calibration is obtained with an integrating sphere during a vacuum vessel opening. An alternative approach is to create plasmas where the fast-ion population is known, then calculate the expected signals with a synthetic diagnostic code. The two methods sometimes agree well but are discrepant in other cases. Different background subtraction techniques and simultaneous measurements of visible bremsstrahlung and of beam emission provide useful checks on the calibrations and calculations.

  17. Interaction of fast waves with ions

    SciTech Connect

    Chiu, S.C.; deGrassie, J.S.; Harvey, R.W.; Chan, V.S.; Lin-Liu, Y.R.; Stambaugh, R.D.; Ikezi, H.; Mau, T.K.; Heidbrink, W.W.

    1996-02-01

    To fully utilize the available power sources in DIII{endash}D (FW, NBI, ECH), understanding of the synergism between the heating mechanisms is important. In this paper the ion distribution, under simultaneous application of NBI and FW, is calculated from Fokker-Planck code CQL3D coupled to ray-tracing code CURRAY. It is found that interaction between energetic ions and FW can be minimized or maximized by adjusting various parameters such as magnetic field, density, beam energy, and FW frequency. Specifically, in DIII{endash}D, we find negligible interactions above 1.8 T and above 80 MHz, while the interaction increases at lower fields and frequencies. The results are compared with experiments in DIII{endash}D including the calculated neutron rate. Energetic ion orbit losses may play an important role in the ion distribution, and this effect is being investigated. {copyright} {ital 1996 American Institute of Physics.}

  18. Limits on ion radial diffusion coefficients in Saturn's inner magnetosphere

    NASA Technical Reports Server (NTRS)

    Paonessa, M.; Cheng, A. F.

    1986-01-01

    The development of upper and lower limits for the rate of radial diffusion of energetic ions in Saturn's inner magnetosphere is discussed. Improved calculations of the satellite-sweeping rate and phase space density profiles for a wide range of ion invariants are utilized to determine the limits. The lower limit for the radial diffusion coefficient is established by requiring the rate of inward diffusion to be large enough to balance satellite sweeping losses; the upper limit is obtained by requiring the rate of inward diffusion to be less than the observable ultraviolet aurora on plasma torus L shell. It is concluded that the radial diffusion coefficient for ions in Saturn's inner magnetosphere is calculated to about two orders of magnitude.

  19. Venus ionosphere - Photochemical and thermal diffusion control of ion composition

    NASA Technical Reports Server (NTRS)

    Bauer, S. J.; Hartle, R. E.; Taylor, H. A., Jr.; Donahue, T. M.

    1979-01-01

    The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft are identified. The neutral gas temperature (as a function of solar zenith angle) derived from measured ion distributions in photochemical equilibrium is given. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.

  20. Diffusion coefficients for three major ions in the topside ionosphere

    NASA Astrophysics Data System (ADS)

    Quegan, S.; Bailey, G. J.; Moffett, R. J.

    1981-08-01

    Published experimental data on ion composition in the topside ionosphere are examined. For certain features (the light ion trough, the high-latitude trough, the high-latitude hole and the mid-latitude total ion concentration trough) it is pointed out that the number of major ions present may be three or more. Transport equations derived by Schunk et al. (1975, 1977, 1979) are extended to include the case of the three major ions in the topside ionosphere. Specific calculations are made for the O(+), H(+) and He(+) ions and the behavior of the diffusion coefficients is discussed. From a model of the high-latitude ionization hole, described by Heelis et al. (1981), representative concentration and temperature profiles are obtained. These profiles are used to demonstrate further the behavior of the ion diffusion coefficients.

  1. Radial diffusion and ion partitioning in the Io torus

    NASA Technical Reports Server (NTRS)

    Cheng, A. F.

    1986-01-01

    A model is presented for radial diffusion and charge state partitioning of sulfur and oxygen ions in the Io torus, including effects of electron impact and charge exchange. When applied to Voyager 1 radial profiles of total ion flux tube content, the model shows that the ion residence time in the torus, tau(D), as defined in spectroscopic studies of ion partitioning, is related to the radial diffusion coefficient, D(LL), at L = 7 by tau(D) approximately 8/D(LL)(7). This result appears to bring spectroscopic estimates of the ion residence time (tau/D/ greater than about 60 to 100 days) into reasonable agreement with estimates of D(LL) from magnetospheric diffusion studies, D(LL) equals approximately 10 to the -6th/s.

  2. Experimental investigation of fast electron diffusion during ECRH

    SciTech Connect

    Steimle, R.F.; Roberts, D.R.; Giruzzi, G.

    1995-06-07

    The spatial diffusion of fast electrons created by electron cyclotron resonant heating (ECRH) is examined using electron cyclotron emissions viewed along a nearly vertical chord in the TEXT-U tokamak. Enhanced emission at frequencies downshifted from the cold cyclotron frequency is attributed to non-thermal electrons. The emission spectra during ECRH are consistent with the presence of low density suprathermal electrons. Comparison of the spectra measured during ECRH with a bounce averaged Fokker-Planck code which incorporates the effects of magnetic and/or electrostatic turbulence on the distribution function, shows that the level of magnetic fluctuations in the center of TEXT-U is between 3 and 5 {times} 10{sup {minus}5}. This level of magnetic fluctuation is a factor of 2 to 5 too small to explain the transport of thermal electrons (E {approximately} 1 keV) in TEXT. Thus, magnetic fluctuations are an unlikely major cause of the transport of thermal electrons in TEXT.

  3. Stability of Non-Isolated Asymptotic Profiles for Fast Diffusion

    NASA Astrophysics Data System (ADS)

    Akagi, Goro

    2016-07-01

    The stability of asymptotic profiles of solutions to the Cauchy-Dirichlet problem for fast diffusion equation (FDE, for short) is discussed. The main result of the present paper is the stability of any asymptotic profiles of least energy. It is noteworthy that this result can cover non-isolated profiles, e.g., those for thin annular domain cases. The method of proof is based on the Łojasiewicz-Simon inequality, which is usually used to prove the convergence of solutions to prescribed limits, as well as a uniform extinction estimate for solutions to FDE. Besides, local minimizers of an energy functional associated with this issue are characterized. Furthermore, the instability of positive radial asymptotic profiles in thin annular domains is also proved by applying the Łojasiewicz-Simon inequality in a different way.

  4. Ion diffusion coefficient measurements in nanochannels at various concentrations.

    PubMed

    Wang, Junrong; Zhang, Li; Xue, Jianming; Hu, Guoqing

    2014-03-01

    Diffusion is one of the most fundamental properties of ionic transport in solutions. Here, we present experimental studies and theoretical analysis on the ion diffusion in nanochannels. Based on Fick's second law, we develop a current monitoring method to measure ion diffusion coefficient of high solution concentrations in nanochannels. This method is further extended to the cases at medium and low concentrations. Through monitoring ionic current during diffusion, we obtain diffusion coefficients of potassium chloride solution at different concentrations in nanochannels. These diffusion coefficients within the confined space are close to theirs bulk values. It is also found that the apparent ion diffusion equilibrium in the present experiments is very slow at low concentration, which we attribute to the slow equilibrium of the nanochannel surface charge. Finally, we get a primary acknowledge of the equilibrium rate between the nanochannel surface charge and electrolyte solution. The results in this work have improved the understanding of nanoscale diffusion and nanochannel surface charge and may be useful in nanofluidic applications such as ion-selective transport, energy conversion, and nanopore biosensors. PMID:24803967

  5. Ion diffusion coefficient measurements in nanochannels at various concentrations

    PubMed Central

    Wang, Junrong; Zhang, Li; Xue, Jianming; Hu, Guoqing

    2014-01-01

    Diffusion is one of the most fundamental properties of ionic transport in solutions. Here, we present experimental studies and theoretical analysis on the ion diffusion in nanochannels. Based on Fick's second law, we develop a current monitoring method to measure ion diffusion coefficient of high solution concentrations in nanochannels. This method is further extended to the cases at medium and low concentrations. Through monitoring ionic current during diffusion, we obtain diffusion coefficients of potassium chloride solution at different concentrations in nanochannels. These diffusion coefficients within the confined space are close to theirs bulk values. It is also found that the apparent ion diffusion equilibrium in the present experiments is very slow at low concentration, which we attribute to the slow equilibrium of the nanochannel surface charge. Finally, we get a primary acknowledge of the equilibrium rate between the nanochannel surface charge and electrolyte solution. The results in this work have improved the understanding of nanoscale diffusion and nanochannel surface charge and may be useful in nanofluidic applications such as ion-selective transport, energy conversion, and nanopore biosensors. PMID:24803967

  6. Ion beam analysis of diffusion in heterogeneous materials

    NASA Astrophysics Data System (ADS)

    Clough, A. S.; Jenneson, P. M.

    1998-04-01

    Ion-beam analysis has been applied to a variety of problems involving diffusion in heterogeneous materials. An energy loss technique has been used to study both the diffusion of water and the surface segregation of fluoropolymers in polymeric matrices. A scanning micro-beam technique has been developed to allow water concentrations in hydrophilic polymers and cements to be measured together with associated solute elements. It has also been applied to the diffusion of shampoo into hair.

  7. Ion diffusion at the bonding interface of undoped YAG/Yb:YAG composite ceramics

    NASA Astrophysics Data System (ADS)

    Fujioka, Kana; Sugiyama, Akira; Fujimoto, Yasushi; Kawanaka, Junji; Miyanaga, Noriaki

    2015-08-01

    Cation diffusion across a boundary between ytterbium (Yb)-doped and undoped yttrium aluminum garnet (YAG) ceramics was examined by electron microprobe analysis (EPMA). Polished Yb:YAG and undoped YAG ceramics were bonded by surface treatment with argon fast atom beam, and then heat-treated at 1400 or 1600 °C for 50 h or at 1400 °C for 10 h under vacuum. We obtained EPMA mapping images of the bonded samples that clearly showed the bulk and grain-boundary diffusion of Y and Yb ions. The number density profiles showed that the total diffusion distances of Yb and Y ions were almost equal and approximately 2 and 15 μm at 1400 and 1600 °C, respectively, and the dependence of diffusion distance on heating time was weak. The diffusion curves were well modeled by Harrison type B kinetics including bulk and grain-boundary diffusion. In addition, it was found that Si ions added to the samples as a sintering aid might be segregated at the grain boundary by heat treatment, and diffused only along grain boundaries.

  8. Fast Ion Transport by Magnetic Flux Ropes

    NASA Astrophysics Data System (ADS)

    Preiwisch, Adam; Heidbrink, William; Boehmer, Heinrich; McWilliams, Roger; Carter, Troy; Gekelman, Walter; Tripathi, Shreekrishna; Compernolle, Bart; Vincena, Steven

    2014-10-01

    Energetic Lithium test ions (500 <= Efast/Ti <= 1000) are launched in a Helium plasma in the presence of current-produced magnetic flux ropes at the upgraded Large Plasma Device (LAPD) at UCLA. Perturbing flux ropes are introduced via a hot, biased LaB6 cathode in the main chamber. Ion beam broadening up to fifty percent above background levels is observed in the radial direction after passing through the flux rope region (Te,max = 7 eV, Bperp = 7G, ΔV = 160 V). Density, temperature, and magnetic fluctuation profiles are also obtained. A noise model has been developed to assess the quality of ion signals during the flux rope discharge period. The enhancement to transport may be a result of increased Coulomb scattering, magnetic fluctuations, or electric fields. Further analysis to determine the primary mechanism is ongoing.

  9. Predictive models for fast ion profiles relaxation in burning plasmas

    NASA Astrophysics Data System (ADS)

    Gorelenkov, Nikolai; Heidbrink, W. W.; Lestz, J.; Podesta, M.; van Zeeland, M.; White, R. B.

    2014-10-01

    The performance of the burning plasmas is limited by the confinement of superalfvenic fusion products, alpha particles, which are capable to resonate with the Alfvénic eigenmodes (AEs). Two techniques based on linear AE stability theory are developed to evaluate the AE induced fast ion relaxation. The first is the reduced quasilinear technique or critical gradient model (CGM) where marginally unstable (or critical) gradient of fast ion pressure is due to unstable AEs. It allows the reconstruction of fast ion pressure profile and compute their losses. The second technique is called hybrid that is also based on NOVA-K linear stability computations of TAE (or RSAE) mode structures and growth rates. AE amplitudes are computed from the nonlinear theory perturbatively and used in numerical runs. With the help of the guiding center code ORBIT the hybrid model predicts the relaxation of the fast particle profiles. We apply these models for NSTX and DIII-D plasmas with the neutral beam injections in order to validate the models. Both methods are relatively fast ways to predict the fast ion profiles in burning plasmas and can be used for plasma modeling prior to building experimental devices such as ITER. Partially supported by US DOE Contract DE-AC02-09CH11466.

  10. Fast-ion Dα spectrum diagnostic in the EAST

    NASA Astrophysics Data System (ADS)

    Hou, Y. M.; Wu, C. R.; Huang, J.; Heidbrink, W. W.; von Hellermann, M. G.; Xu, Z.; Jin, Z.; Chang, J. F.; Zhu, Y. B.; Gao, W.; Chen, Y. J.; Lyu, B.; Hu, R. J.; Zhang, P. F.; Zhang, L.; Gao, W.; Wu, Z. W.; Yu, Y.; Ye, M. Y.

    2016-11-01

    In toroidal magnetic fusion devices, fast-ion D-alpha diagnostic (FIDA) is a powerful method to study the fast-ion feature. The fast-ion characteristics can be inferred from the Doppler shifted spectrum of Dα light according to charge exchange recombination process between fast ions and probe beam. Since conceptual design presented in the last HTPD conference, significant progress has been made to apply FIDA systems on the Experimental Advanced Superconducting Tokamak (EAST). Both co-current and counter-current neutral beam injectors are available, and each can deliver 2-4 MW beam power with 50-80 keV beam energy. Presently, two sets of high throughput spectrometer systems have been installed on EAST, allowing to capture passing and trapped fast-ion characteristics simultaneously, using Kaiser HoloSpec transmission grating spectrometer and Bunkoukeiki FLP-200 volume phase holographic spectrometer coupled with Princeton Instruments ProEM 1024B eXcelon and Andor DU-888 iXon3 1024 CCD camera, respectively. This paper will present the details of the hardware descriptions and experimental spectrum.

  11. The NSTX fast-ion D-alpha diagnostic.

    PubMed

    Podestà, M; Heidbrink, W W; Bell, R E; Feder, R

    2008-10-01

    A new diagnostic, aimed at energy-resolved measurements of the spatial and temporal dynamics of fast ions in NSTX plasmas, is described. It is based on active charge-exchange recombination spectroscopy. The fast-ion signal is inferred from light emitted in the wavelength range of the D(alpha) line by fast ions recombining with an injected neutral beam. Two complementary systems are operational. The first system, based on a spectrometer coupled to a charge coupled device detector, has 16 channels with space, time, and energy resolution of 5 cm, 10 ms, and 10 keV, respectively. The second system monitors the energy-integrated fast-ion signal on time scales of approximately 20 micros at three different radii. Signals are measured by a multianode photomultiplier tube. For both systems, each channel includes two paired views, intercepting and missing the neutral beam for a direct subtraction of the background signal not associated with fast ions. Examples of signals from the 2008 NSTX run are presented.

  12. The NSTX fast-ion D-alpha diagnostic

    SciTech Connect

    Podesta, M.; Heidbrink, W. W.; Bell, R. E.; Feder, R.

    2008-10-15

    A new diagnostic, aimed at energy-resolved measurements of the spatial and temporal dynamics of fast ions in NSTX plasmas, is described. It is based on active charge-exchange recombination spectroscopy. The fast-ion signal is inferred from light emitted in the wavelength range of the D{sub {alpha}} line by fast ions recombining with an injected neutral beam. Two complementary systems are operational. The first system, based on a spectrometer coupled to a charge coupled device detector, has 16 channels with space, time, and energy resolution of 5 cm, 10 ms, and 10 keV, respectively. The second system monitors the energy-integrated fast-ion signal on time scales of {approx}20 {mu}s at three different radii. Signals are measured by a multianode photomultiplier tube. For both systems, each channel includes two paired views, intercepting and missing the neutral beam for a direct subtraction of the background signal not associated with fast ions. Examples of signals from the 2008 NSTX run are presented.

  13. Observations of Ag diffusion in ion implanted SiC

    DOE PAGESBeta

    Gerczak, Tyler J.; Leng, Bin; Sridharan, Kumar; Jerry L. Hunter, Jr.; Giordani, Andrew J.; Allen, Todd R.

    2015-03-17

    The nature and magnitude of Ag diffusion in SiC has been a topic of interest in connection with the performance of tristructural isotropic (TRISO) coated particle fuel for high temperature gas-cooled nuclear reactors. Ion implantation diffusion couples have been revisited to continue developing a more complete understanding of Ag fission product diffusion in SiC. Ion implantation diffusion couples fabricated from single crystal 4H-SiC and polycrystalline 3C-SiC substrates and exposed to 1500–1625°C, were investigated in this study by transmission electron microscopy and secondary ion mass spectrometry (SIMS). The high dynamic range of SIMS allowed for multiple diffusion régimes to be investigated,more » including enhanced diffusion by implantation-induced defects and grain boundary (GB) diffusion in undamaged SiC. Lastly, estimated diffusion coefficients suggest GB diffusion in bulk SiC does not properly describe the release observed from TRISO fuel.« less

  14. Ion beam microtexturing and enhanced surface diffusion

    NASA Technical Reports Server (NTRS)

    Robinson, R. S.

    1982-01-01

    Ion beam interactions with solid surfaces are discussed with particular emphasis on microtexturing induced by the deliberate deposition of controllable amounts of an impurity material onto a solid surface while simultaneously sputtering the surface with an ion beam. Experimental study of the optical properties of microtextured surfaces is described. Measurements of both absorptance as a function of wavelength and emissivity are presented. A computer code is described that models the sputtering and ion reflection processes involved in microtexture formation.

  15. Analytical estimates of electron quasi-linear diffusion by fast magnetosonic waves

    NASA Astrophysics Data System (ADS)

    Mourenas, D.; Artemyev, A. V.; Agapitov, O. V.; Krasnoselskikh, V.

    2013-06-01

    Quantifying the loss of relativistic electrons from the Earth's radiation belts requires to estimate the effects of many kinds of observed waves, ranging from ULF to VLF. Analytical estimates of electron quasi-linear diffusion coefficients for whistler-mode chorus and hiss waves of arbitrary obliquity have been recently derived, allowing useful analytical approximations for lifetimes. We examine here the influence of much lower frequency and highly oblique, fast magnetosonic waves (also called ELF equatorial noise) by means of both approximate analytical formulations of the corresponding diffusion coefficients and full numerical simulations. Further analytical developments allow us to identify the most critical wave and plasma parameters necessary for a strong impact of fast magnetosonic waves on electron lifetimes and acceleration in the simultaneous presence of chorus, hiss, or lightning-generated waves, both inside and outside the plasmasphere. In this respect, a relatively small frequency over ion gyrofrequency ratio appears more favorable, and other propitious circumstances are characterized. This study should be useful for a comprehensive appraisal of the potential effect of fast magnetosonic waves throughout the magnetosphere.

  16. Ion beam requirements for fast ignition of inertial fusion targets

    SciTech Connect

    Honrubia, J. J.; Murakami, M.

    2015-01-15

    Ion beam requirements for fast ignition are investigated by numerical simulation taking into account new effects, such as ion beam divergence, not included before. We assume that ions are generated by the TNSA scheme in a curved foil placed inside a re-entrant cone and focused on the cone apex or beyond. From the focusing point to the compressed core, ions propagate with a given divergence angle. Ignition energies are obtained for two compressed fuel configurations heated by proton and carbon ion beams. The dependence of the ignition energies on the beam divergence angle and on the position of the ion beam focusing point has been analyzed. Comparison between TNSA and quasi-monoenergetic ions is also shown.

  17. Diffusion mechanism and the thermal stability of fluorine ions in GaN after ion implantation

    SciTech Connect

    Wang, M. J.; Yuan, L.; Chen, K. J.; Xu, F. J.; Shen, B.

    2009-04-15

    The diffusion mechanisms of fluorine ions in GaN are investigated by means of time-of-flight secondary ion mass spectrometry. Instead of incorporating fluorine ions close to the sample surface by fluorine plasma treatment, fluorine ion implantation with an energy of 180 keV is utilized to implant fluorine ions deep into the GaN bulk, preventing the surface effects from affecting the data analysis. It is found that the diffusion of fluorine ions in GaN is a dynamic process featuring an initial out-diffusion followed by in- diffusion and the final stabilization. A vacancy-assisted diffusion model is proposed to account for the experimental observations, which is also consistent with results on molecular dynamic simulation. Fluorine ions tend to occupy Ga vacancies induced by ion implantation and diffuse to vacancy rich regions. The number of continuous vacancy chains can be significantly reduced by a dynamic thermal annealing process. As a result, strong local confinement and stabilization of fluorine ions can be obtained in GaN crystal, suggesting excellent thermal stability of fluorine ions for device applications.

  18. Mechanisms of Stochastic Diffusion of Energetic Ions in Spherical Tori

    SciTech Connect

    Ya.I. Kolesnichenko; R.B. White; Yu.V. Yakovenko

    2001-01-18

    Stochastic diffusion of the energetic ions in spherical tori is considered. The following issues are addressed: (I) Goldston-White-Boozer diffusion in a rippled field; (ii) cyclotron-resonance-induced diffusion caused by the ripple; (iii) effects of non-conservation of the magnetic moment in an axisymmetric field. It is found that the stochastic diffusion in spherical tori with a weak magnetic field has a number of peculiarities in comparison with conventional tokamaks; in particular, it is characterized by an increased role of mechanisms associated with non-conservation of the particle magnetic moment. It is concluded that in current experiments on National Spherical Torus eXperiment (NSTX) the stochastic diffusion does not have a considerable influence on the confinement of energetic ions.

  19. Stress enhanced diffusion of krypton ions in polycrystalline titanium

    SciTech Connect

    Nsengiyumva, S.; Raji, A. T.; Rivière, J. P.; Britton, D. T.; Härting, M.

    2014-07-14

    An experimental investigation on the mutual influence of pre-existing residual stress and point defect following ion implantation is presented. The study has been carried out using polycrystalline titanium samples energetically implanted with krypton ions at different fluences. Ion beam analysis was used to determine the concentration profile of the injected krypton ions, while synchrotron X-ray diffraction has been used for stress determination. Ion beam analysis and synchrotron X-ray diffraction stress profile measurements of the implanted titanium samples show a clear evidence of stress-enhanced diffusion of krypton ions in titanium. It is further observed that for the titanium samples implanted at low fluence, ion implantation modifies the pre-existing residual stress through the introduction of point and open volume defects. The stress fields resulting from the ion implantation act to drift the krypton inclusions towards the surface of titanium.

  20. Electronic excitations in fast ion-solid collisions

    SciTech Connect

    Burgdoerfer, J. . Dept. of Physics and Astronomy Oak Ridge National Lab., TN )

    1990-01-01

    We review recent developments in the study of electronic excitation of projectiles in fast ion-solid collisions. Our focus will be primarily on theory but experimental advances will also be discussed. Topics include the evidence for velocity-dependent thresholds for the existence of bound states, wake-field effects on excited states, the electronic excitation of channeled projectiles, transport phenomena, and the interaction of highly charged ions with surfaces. 44 refs., 14 figs.

  1. Faraday-cup-type lost fast ion detector on Heliotron J

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Ogawa, K.; Isobe, M.; Darrow, D. S.; Kobayashi, S.; Nagasaki, K.; Okada, H.; Minami, T.; Kado, S.; Ohshima, S.; Weir, G. M.; Nakamura, Y.; Konoshima, S.; Kemmochi, N.; Ohtani, Y.; Mizuuchi, T.

    2016-11-01

    A Faraday-cup type lost-fast ion probe (FLIP) has been designed and installed in Heliotron J for the purpose of the studies of interaction between fast ions and MHD instabilities. The FLIP can measure the co-going fast ions whose energy is in the range of 1.7-42.5 keV (proton) and pitch angle of 90∘-140∘, especially for fast ions having the injection energy of neutral beam injection (NBI). The FLIP successfully measured the re-entering passing ions and trapped lost-fast ions caused by fast-ion-driven energetic particle modes in NBI heated plasmas.

  2. Dependence of fast-ion transport on the nature of the turbulence in the Large Plasma Device

    SciTech Connect

    Zhou Shu; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Tripathi, S. K. P.

    2011-08-15

    Strong turbulent waves ({delta}n/n {approx}0.5, f {approx}5-40 kHz) are observed in the upgraded Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)] on density gradients produced by an annular obstacle. Energetic lithium ions (E{sub fast}/T{sub i}{>=}300, {rho}{sub fast}/{rho}{sub s}{approx}10) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating wave fields. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon and by modifying the bias on the obstacle. Different spatial structure sizes (L{sub s}) and correlation lengths (L{sub corr}) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions.

  3. Polarization Studies in Fast-Ion Beam Spectroscopy

    SciTech Connect

    Trabert, E

    2001-12-20

    In a historical review, the observations and the insight gained from polarization studies of fast ions interacting with solid targets are presented. These began with J. Macek's recognition of zero-field quantum beats in beam-foil spectroscopy as indicating alignment, and D.G. Ellis' density operator analysis that suggested the observability of orientation when using tilted foils. Lastly H. Winter's studies of the ion-beam surface interaction at grazing incidence yielded the means to produce a high degree of nuclear orientation in ion beams.

  4. Near threshold conditions justify critical gradient model for Alvenic mode driven relaxation of fast ions

    NASA Astrophysics Data System (ADS)

    Gorelenkov, Nikolai; Ghantous, Katy; Heidbrink, William; van Zeeland, Michael

    2013-10-01

    Future burning plasma performance will be limited by the constraints to confine energetic superalfvenic fusion products, which can drive several low frequency Alfvénic instabilities. Expected multiple resonances help to justify the model developed recently, called critical gradient or 1.5D reduced quasilinear diffusion model. Similar conditions are expected in burning plasmas with TAE instabilities in a non virulent nonlinear regime. The 1.5D model make use of TAE/RSAEs linear theory. One critical element of the presented model is that it requires averaging over the time comparable to the fast ion slowing down. Another element is that the fast ion diffusion near the resonance does not flatten the distribution function whose gradient is maintained by the collision scattering. Further validations of this model justify its use in case of relatively high collisions. With the parametric plasma dependencies embedded in the model and with the quantitative normalization to NOVA-K growth rates the 1.5D model application to DIII-D experiments is well positioned for validations. Good agreement is summarized here for absolute values of the deduced neutron rate and for the time behavior of fast ion losses near the AE activity thresholds. 1.5D model is applicable for ITER and other BPs. Supported in part by the U.S. Department of Energy under the contract DE-AC02-09CH11466.

  5. Ion-beam-induced topography and surface diffusion

    NASA Technical Reports Server (NTRS)

    Robinson, R. S.; Rossnagel, S. M.

    1982-01-01

    It is pointed out that the development of surface topography along with enhanced surface and bulk diffusion processes accompanying ion bombardment have generated growing interest among users of ion beams and plasmas for thin film or material processing. Interest in these processes stems both from attempts to generate topographic changes for specific studies or applications and from the need to suppress or control undesirable changes. The present investigation provides a summary of the current status of impurity-induced texturing, with emphasis on recent developments. Particular attention is given to the texturing accompanying deposition of an impurity material onto a solid surface while simultaneously etching the surface with an ion beam. A description of experimental considerations is provided, and a thermal-diffusion model is discussed along with the development of sputter cones, and aspects of impact-enhanced surface diffusion.

  6. An ion-beam technique for measuring surface diffusion coefficients

    NASA Astrophysics Data System (ADS)

    DeLuca, P. M.; Labanda, J. G. C.; Barnett, S. A.

    1999-03-01

    The effective surface diffusion coefficient of Ga along the [110] direction on vicinal GaAs(001)2×4 surfaces during molecular-beam epitaxy was measured using specular ion current measurements. In this technique, 3 keV Ar ions were impinged upon the surface at a glancing angle (typically 3°), and the specularly scattered ion current was measured. Since specular reflections require a locally flat surface, adatoms cause a decrease in the measured current, allowing an average adatom density measurement. The time dependence of the Ga adatom population was measured during and after Ga deposition. Diffusion coefficients, obtained from the adatom lifetimes using a simple model of diffusion to the step edges, were fit well by the expression D=2×10-9 exp(-0.73 eV/kT)cm2/s from 400 to 600 °C.

  7. Pyrrole copolymers with enhanced ion diffusion rates for lithium batteries

    SciTech Connect

    Calvert, P.; Gardlund, Z.; Huntoon, T.; Hall, H.K.; Padias, A.

    1998-07-01

    Copolymers of pyrrole with a polyether-substituted pyrrole were tested as cathodes for lithium batteries. The charge and discharge characteristics showed that anion transport was much faster in the copolymer than in polypyrrole. As a result these electrodes store and release much more charge at higher current densities but are similar to polypyrrole at low currents. Pulse and relaxation measurements of the ion diffusion showed that this difference was due to a ten-fold increase in the anion diffusion coefficient.

  8. Fast ion beam chopping system for neutron generators

    NASA Astrophysics Data System (ADS)

    Hahto, S. K.; Hahto, S. T.; Leung, K. N.; Reijonen, J.; Miller, T. G.; Van Staagen, P. K.

    2005-02-01

    Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120keV D+ ion beams hitting a titanium target at the center of the source.

  9. Fast ion beam chopping system for neutron generators

    SciTech Connect

    Hahto, S.K.; Hahto, S.T.; Leung, K.N.; Reijonen, J.; Miller, T.G.; Van Staagen, P.K.

    2005-02-01

    Fast deuterium (D{sup +}) and tritium (T{sup +}) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15 ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120 keV D{sup +} ion beams hitting a titanium target at the center of the source.

  10. Hydrogen ion diffusion coefficient of silicon nitride thin films

    NASA Astrophysics Data System (ADS)

    Yu, George T.; Yen, S. K.

    2002-12-01

    Hydrogen ion diffusion in silicon nitride thin film is of significant interest because of its importance in barrier, sensor and catalytic coating applications. In this study, a novel method based on potential-pH response measurement was used to determine hydrogen ion diffusion in silicon nitride thin films. Hydrogen ion diffusion coefficient in silicon nitride films obtained from this method was 1×10 -19 cm 2/s. A potential-pH response drift was observed and is believed to be due to the presence of a hydrated layer affecting the hydrogen ion diffusion onto the nitride film of the Si 3N 4-gate hydrogen ion-sensitive field effect transistors (ISFETs). The unique feature of the potential-pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface-related effects and/or presence of hydrogen traps in membrane, such as those found in the conventional permeation method. The method also offers a considerable test time reduction, with the experiment being completed in 10 h as compared to the conventional electrochemical permeation method which takes as long as 5 days.

  11. Fast neutral beam ion source coupled to a Fourier transform ion cyclotron resonance mass spectrometer

    SciTech Connect

    Hill, N.C.; Limbach, P.A.; Shomo, R.E. II; Marshall, A.G. ); Appelhans, A.D.; Delmore, J.E. )

    1991-11-01

    The coupling of an autoneutralizing SF{sup {minus}}{sub 6} fast ion-beam gun to a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer is described. The fast neutral beam provides for secondary-ion-type FT/ICR mass analysis (e.g., production of abundant pseudomolecular (M+H){sup +} ions) of involatile samples without the need for external ion injection, since ions are formed at the entrance to the ICR ion trap. The design, construction, and testing of the hybrid instrument are described. The feasibility of the experiment (for both broadband and high-resolution FT/ICR positive-ion mass spectra) is demonstrated with {ital tetra}-butylammonium bromide and a Tylenol{sup ( )} sample. The ability to analyze high molecular weight polymers with high mass resolution is demonstrated for Teflon{sup ( )}. All of the advantages of the fast neutral beam ion source previously demonstrated with quadrupole mass analysis are preserved, and the additional advantages of FT/ICR mass analysis (e.g., high mass resolving power, ion trapping) are retained.

  12. Fast neutral beam ion source coupled to a Fourier transform ion cyclotron resonance mass spectrometer

    NASA Astrophysics Data System (ADS)

    Hill, Nicholas C.; Limbach, Patrick A.; Shomo, Ronald E., II; Marshall, Alan G.; Appelhans, Anthony D.; Delmore, James E.

    1991-11-01

    The coupling of an autoneutralizing SF-6 fast ion-beam gun to a Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometer is described. The fast neutral beam provides for secondary-ion-type FT/ICR mass analysis [e.g., production of abundant pseudomolecular (M+H)+ ions] of involatile samples without the need for external ion injection, since ions are formed at the entrance to the ICR ion trap. The design, construction, and testing of the hybrid instrument are described. The feasibility of the experiment (for both broadband and high-resolution FT/ICR positive-ion mass spectra) is demonstrated with tetra-butylammonium bromide and a Tylenol■ sample. The ability to analyze high molecular weight polymers with high mass resolution is demonstrated for Teflon■. All of the advantages of the fast neutral beam ion source previously demonstrated with quadrupole mass analysis are preserved, and the additional advantages of FT/ICR mass analysis (e.g., high mass resolving power, ion trapping) are retained.

  13. Diffusion of ion implanted aluminum in silicon carbide

    SciTech Connect

    Tajima, Y.; Kijima, K.; Kingery, W.D.

    1982-09-01

    Diffusion of aluminum in silicon carbide was studied by Al implantation into single crystal SiC and subsequent profile analyses by secondary ion mass spectrometry (SIMS). The bulk diffusion coefficient of Al at temperatures between 1350 and 1800 /sup 0/C was determined to be D(cm/sup 2//s) = 1.3 x 10/sup -8/ exp (-231 kJ/mol/RT). The results were characterized by a low activation energy and a low pre-exponential constant compared with previously reported results. Dislocation enhanced diffusion was suggested from the appearance of the tails observed in the annealed concentration profiles.

  14. Wave Driven Fast Ion Loss in the National Spherical Torus Experiment

    SciTech Connect

    E.D. Fredrickson; C.Z. Cheng; D. Darrow; G. Fu; N.N. Gorelenkov; G. Kramer; S.S. Medley; J. Menard; L. Roquemore; D. Stutman; R.B. White

    2003-01-28

    Spherical tokamaks, with their relatively low toroidal field, extend fast-ion-driven instability physics to parameter ranges not normally accessed in conventional tokamaks. The low field means that both the fast-ion Larmor radius normalized to the plasma minor radius and the ratio of the fast-ion velocity to the Alfven speed are relatively large. The large Larmor radius of the ions enhances their interaction with instability modes, influencing the structure of the unstable mode spectrum. The relatively large fast-ion velocity allows for a larger population of fast ions to be in resonance with the mode, increasing the drive. It is therefore an important goal of the present proof-of-principle spherical tokamaks to evaluate the role of fast-ion-driven instabilities in fast-ion confinement. This paper presents the first observations of fast-ion losses resulting from toroidal Alfven eigenmodes and a new, fishbone-like, energetic particle mode.

  15. Coincidence ion imaging with a fast frame camera

    SciTech Connect

    Lee, Suk Kyoung; Cudry, Fadia; Lin, Yun Fei; Lingenfelter, Steven; Winney, Alexander H.; Fan, Lin; Li, Wen

    2014-12-15

    A new time- and position-sensitive particle detection system based on a fast frame CMOS (complementary metal-oxide semiconductors) camera is developed for coincidence ion imaging. The system is composed of four major components: a conventional microchannel plate/phosphor screen ion imager, a fast frame CMOS camera, a single anode photomultiplier tube (PMT), and a high-speed digitizer. The system collects the positional information of ions from a fast frame camera through real-time centroiding while the arrival times are obtained from the timing signal of a PMT processed by a high-speed digitizer. Multi-hit capability is achieved by correlating the intensity of ion spots on each camera frame with the peak heights on the corresponding time-of-flight spectrum of a PMT. Efficient computer algorithms are developed to process camera frames and digitizer traces in real-time at 1 kHz laser repetition rate. We demonstrate the capability of this system by detecting a momentum-matched co-fragments pair (methyl and iodine cations) produced from strong field dissociative double ionization of methyl iodide.

  16. Coincidence ion imaging with a fast frame camera

    NASA Astrophysics Data System (ADS)

    Lee, Suk Kyoung; Cudry, Fadia; Lin, Yun Fei; Lingenfelter, Steven; Winney, Alexander H.; Fan, Lin; Li, Wen

    2014-12-01

    A new time- and position-sensitive particle detection system based on a fast frame CMOS (complementary metal-oxide semiconductors) camera is developed for coincidence ion imaging. The system is composed of four major components: a conventional microchannel plate/phosphor screen ion imager, a fast frame CMOS camera, a single anode photomultiplier tube (PMT), and a high-speed digitizer. The system collects the positional information of ions from a fast frame camera through real-time centroiding while the arrival times are obtained from the timing signal of a PMT processed by a high-speed digitizer. Multi-hit capability is achieved by correlating the intensity of ion spots on each camera frame with the peak heights on the corresponding time-of-flight spectrum of a PMT. Efficient computer algorithms are developed to process camera frames and digitizer traces in real-time at 1 kHz laser repetition rate. We demonstrate the capability of this system by detecting a momentum-matched co-fragments pair (methyl and iodine cations) produced from strong field dissociative double ionization of methyl iodide.

  17. Coincidence electron/ion imaging with a fast frame camera

    NASA Astrophysics Data System (ADS)

    Li, Wen; Lee, Suk Kyoung; Lin, Yun Fei; Lingenfelter, Steven; Winney, Alexander; Fan, Lin

    2015-05-01

    A new time- and position- sensitive particle detection system based on a fast frame CMOS camera is developed for coincidence electron/ion imaging. The system is composed of three major components: a conventional microchannel plate (MCP)/phosphor screen electron/ion imager, a fast frame CMOS camera and a high-speed digitizer. The system collects the positional information of ions/electrons from a fast frame camera through real-time centroiding while the arrival times are obtained from the timing signal of MCPs processed by a high-speed digitizer. Multi-hit capability is achieved by correlating the intensity of electron/ion spots on each camera frame with the peak heights on the corresponding time-of-flight spectrum. Efficient computer algorithms are developed to process camera frames and digitizer traces in real-time at 1 kHz laser repetition rate. We demonstrate the capability of this system by detecting a momentum-matched co-fragments pair (methyl and iodine cations) produced from strong field dissociative double ionization of methyl iodide. We further show that a time resolution of 30 ps can be achieved when measuring electron TOF spectrum and this enables the new system to achieve a good energy resolution along the TOF axis.

  18. Fast and efficient transport of large ion clouds

    NASA Astrophysics Data System (ADS)

    Kamsap, M. R.; Pedregosa-Gutierrez, J.; Champenois, C.; Guyomarc'h, D.; Houssin, M.; Knoop, M.

    2015-10-01

    The manipulation of trapped charged particles by electric fields is an accurate, robust, and reliable technique for many applications or experiments in high-precision spectroscopy. The transfer of an ion sample between multiple traps allows the use of a tailored environment in quantum information, cold chemistry, or frequency metrology experiments. In this article, we experimentally study the transport of ion clouds of up to 80 000 ions over a distance of 20 mm inside a linear radio-frequency trap. Ion transport is controlled by a transfer function, which is designed taking into account the local electric potentials. We observe that the ion response is very sensitive to the details of the description of the electric potential. Nevertheless, we show that fast transport—with a total duration of 100 μ s —results in transport efficiencies attaining values higher than 90% of the ion number, even with large ion clouds. For clouds smaller than 2000 ions, a 100% transfer efficiency is observed. Transport induced heating, which depends on the transport duration, is also analyzed.

  19. Design and development of a fast ion mass spectrometer

    NASA Technical Reports Server (NTRS)

    Burch, J. L.

    1983-01-01

    Two Fast Ion Mass Spectrometers (FIMS A and FIMS B) were developed. The design, development, construction, calibration, integration, and flight of these instruments, along with early results from the data analysis efforts are summarized. A medium energy ion mass spectrometer that covers mass velocity space with significantly higher time resolution, improved mass resolution, (particularly for heavier ions), and wider energy range than existing instruments had achieved was completed. The initial design consisted of a dual channel cylindrical electrostatic analyzer followed by a dual channel cylindrical velocity filter. The gain versus count rate characteristics of the high current channel electron multipliers (CEM's), which were chosen for ion detection, revealed a systematic behavior that can be used as a criterion for selection of CEM's for long counting lifetimes.

  20. Nanoscale mapping of ion diffusion in a lithium-ion battery cathode

    SciTech Connect

    Balke, N.; Jesse, S.; Morozovska, A.; Eliseev, E.; Chung, D.; Kim, Y.; Adamczyk, L.; Garcia, R.

    2010-08-29

    The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO{sub 2} at a resolution of ~100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

  1. The rapid inward diffusion of cold ions in tokamaks and their effect on ion transport

    NASA Astrophysics Data System (ADS)

    Ware, A. A.

    1990-06-01

    The observed increase with density of the density asymmetry caused by the centrifugal force of toroidal motion in the PDX tokamak [Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1981), Vol. 1, p. 665], which is contrary to conventional theory, is explained by the presence of an excess of low-energy ions with 10%-15% concentration. The prime source being recycling, it is shown that low-energy ions undergo rapid inward diffusion (too rapid to thermalize with the outward diffusing energetic ions) because of the combined effects of large νPA, electrostatic diffusion, and negative Er and ∂Ti/∂r. The presence of the low-energy ions alters dramatically the predictions of neoclassical theory and many hydrogen and impurity ion transport phenomena now have simple explanations.

  2. The rapid inward diffusion of cold ions in tokamaks and their effect on ion transport

    SciTech Connect

    Ware, A.A. )

    1990-06-01

    The observed increase with density of the density asymmetry caused by the centrifugal force of toroidal motion in the PDX tokamak ({ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion} {ital Research} (IAEA, Vienna, 1981), Vol. 1, p. 665), which is contrary to conventional theory, is explained by the presence of an excess of low-energy ions with 10%--15% concentration. The prime source being recycling, it is shown that low-energy ions undergo rapid inward diffusion (too rapid to thermalize with the outward diffusing energetic ions) because of the combined effects of large {nu}{sub PA}, electrostatic diffusion, and negative {ital E}{sub {ital r}} and {partial derivative}{ital T}{sub {ital i}}/{partial derivative}{ital r}. The presence of the low-energy ions alters dramatically the predictions of neoclassical theory and many hydrogen and impurity ion transport phenomena now have simple explanations.

  3. The rapid inward diffusion of cold ions in tokamaks and their effect on ion transport

    NASA Astrophysics Data System (ADS)

    Ware, A. A.

    1989-10-01

    The observed increase with density of the density asymmetry caused by the centrifugal force of toroidal motion in PDX, which is contrary to conventional theory, is explained by the presence of an excess of low energy ions with 10 to 15 percent concentration. The prime source being recycling, it is shown that low energy ions undergo rapid inward diffusion (too rapid to thermalize with the outward diffusion energetic ions) due to the combined effects of large nu (sub PA), electrostatic diffusion, and negative E(sub r) and partial derivative of T(sub i)/(partial derivative) of r. The presence of the low energy ions alters dramatically the predictions of neoclassical theory and many hydrogen and impurity ion transport phenomena now have simple explanations.

  4. Self-consistent pitch angle diffusion of newborn ions

    SciTech Connect

    Yoon, P.H.; Ziebell, L.F.; Wu, C.S. )

    1991-04-01

    It is well known from the study of ion pickup process by the solar wind that hydromagnetic turbulence can cause the newborn ions to undergo rapid pitch angle diffusion or scattering, thus forming a partial or complete velocity shell distribution. In most of the recent discussions based on quasi-linear theory it is assumed that the spectral wave energy density associated with the hydromagnetic turbulence is constant in time, implying a saturated turbulence level. In contrast, in this work the effect of self-consistently generated waves on the ion dynamics is discussed on the basis of a simple theoretical model, and it is shown both analytically and numerically that the self-consistent diffusion process leads to a time-asymptotic partial shell distribution which extends approximately from the initial pitch angle cos{sup {minus}1}{mu}{sub 0} to {approximately}{pi}/2 in pitch angle space. Particularly, the role of resonant versus nonresonant diffusion processes is discussed in detail. In addition, the effect of continuous ion source term is also incorporated in the numerical analysis since in cometary environment the ions are continuously created.

  5. Diffusion of ion-exchanging electrolytes in montmorillonite gels

    SciTech Connect

    Jahnke, F.M.

    1987-01-01

    The primary contributions of this work are: (1) Development of a unique radially perfused diffusion cell suitable for measuring transient diffusion rates in compacted, highly adsorbing and swelling porous media such as montmorillonite clay gels; (2) examination of the effective diffusion coefficient (D{sub 6}) of electrolytes in montmorillonite clay gels; and (3) Measurement of the transient diffusion rates of cesium, chloride and tritium in 15 w/o montmorillonite clay gels at pH 9 and sodium chloride backgrounds of 10{sup {minus}1} to 10{sup {minus}3} kmol/m{sup 3}. Results are interpreted by using the dilute limit of the multicomponent transport equations derived for species migration in a single clay pore after macroscopic averaging. The tortuosity of the clay gel is found by tritium diffusion. Transient chloride diffusion rates are found to be at molecular rates. Negative adsorption of anions from the clay gel, required for an a priori prediction of chloride profiles, are calculated from site-binding theory. Surface diffusion is the primary mode of cesium transport in montmorillonite clay gels. Migration of cesium is primarily along the inner Helmholtz plane of clay particles. The primary implication for the montmorillonite clay-based packing as a nuclear waste migration barrier is that surface diffusion must be included to describe properly diffusion rates of either anions or cations. Currently surface diffusion is neglected and cesium penetration into the packing is drastically underestimated. Penetration depths of anions is grossly overestimated. In either case, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations.

  6. Conceptual design of the ITER fast-ion loss detector

    NASA Astrophysics Data System (ADS)

    Garcia-Munoz, M.; Kocan, M.; Ayllon-Guerola, J.; Bertalot, L.; Bonnet, Y.; Casal, N.; Galdon, J.; Garcia Lopez, J.; Giacomin, T.; Gonzalez-Martin, J.; Gunn, J. P.; Jimenez-Ramos, M. C.; Kiptily, V.; Pinches, S. D.; Rodriguez-Ramos, M.; Reichle, R.; Rivero-Rodriguez, J. F.; Sanchis-Sanchez, L.; Snicker, A.; Vayakis, G.; Veshchev, E.; Vorpahl, Ch.; Walsh, M.; Walton, R.

    2016-11-01

    A conceptual design of a reciprocating fast-ion loss detector for ITER has been developed and is presented here. Fast-ion orbit simulations in a 3D magnetic equilibrium and up-to-date first wall have been carried out to revise the measurement requirements for the lost alpha monitor in ITER. In agreement with recent observations, the simulations presented here suggest that a pitch-angle resolution of ˜5° might be necessary to identify the loss mechanisms. Synthetic measurements including realistic lost alpha-particle as well as neutron and gamma fluxes predict scintillator signal-to-noise levels measurable with standard light acquisition systems with the detector aperture at ˜11 cm outside of the diagnostic first wall. At measurement position, heat load on detector head is comparable to that in present devices.

  7. Semianalytical method of solution for solid phase diffusion in lithium ion battery electrodes: Variable diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Renganathan, Sindhuja; White, Ralph E.

    A semianalytical methodology based on the integral transform technique is proposed to solve the diffusion equation with concentration dependent diffusion coefficient in a spherical intercalation electrode particle. The method makes use of an integral transform pair to transform the nonlinear partial differential equation into a set of ordinary differential equations, which is solved with less computational efforts. A general solution procedure is presented and two illustrative examples are used to demonstrate the usefulness of this method for modeling of diffusion process in lithium ion battery electrode. The solutions obtained using the method presented in this study are compared to the numerical solutions.

  8. Pulsed ion beam technique for measuring diffusion coefficient of a slow diffusant in polymers

    NASA Astrophysics Data System (ADS)

    Venkatesan, T.; Edelson, D.; Brown, W. L.

    1983-08-01

    The determination of diffusion coefficients (D) of small molecules in a polymer for D below 10-10 cm2 s-1 is a difficult measurement using conventional self-supporting polymer membrane techniques. We propose a new method for obtaining similar information by irradiating a polymer with a pulsed ion beam and studying the evolving gaseous products. Product molecules that are not limited by the rate of their production in the film tend to exhibit diffusion limited dynamical characteristics in their transient evolution from the surface. By numerically modeling the diffusion problem we can extract diffusion coefficients from the data. Since thin films (<1 μm) can be used in these experiments, diffusion coefficients less than 10-10 cm2 s-1, typical of many molecules in polymers, can be measured with ease.

  9. CALCULATION OF STOPPING POWER VALUES AND RANGES OF FAST IONS.

    2003-03-18

    STOPOW calculates a set of stopping power values and ranges of fast ions in matter for any materials. Furthermore STOPOW can calculate a set of values for one special auxiliary function (e.g. kinematic factors, track structure parameters, time of flight or correction factors in the stopping function) . The user chooses the physical units for stopping powers and ranges and the energy range for calculations.

  10. Fast ion profiles during neutral beam and lower hybrid heating

    SciTech Connect

    Heidbrink, W.W.; Strachan, J.D.; Bell, R.E.; Cavallo, A.; Motley, R.; Schilling, G.; Stevens, J.; Wilson, J.R.

    1985-07-01

    Profiles of the d(d,p)t fusion reaction are measured in the PLT tokamak using an array of collimated 3 MeV proton detectors. During deuterium neutral beam injection, the emission profile indicates that the beam deposition is at least as narrow as predicted by a bounce-averaged Fokker-Planck code. The fast ion tail formed by lower hybrid waves (at densities above the critical density for current drive) also peaks strongly near the magnetic axis.

  11. Estimating The Sodium Ion Diffusion Coefficient in Rat Brain

    NASA Astrophysics Data System (ADS)

    Goodman, James A.; Bretthorst, G. Larry; Kroenke, Christopher D.; Ackerman, Joseph J. H.; Neil, Jeffrey J.

    2004-04-01

    Quantifying sodium ion diffusion in the extra- and intracellular compartments will provide mechanistic insight into the as yet unexplained marked decrease in water diffusion resulting from central nervous system injury. As a first step, the apparent diffusion coefficient (ADC) of bulk brain Na+ has been determined in vivo in rat. A surface coil transmit/receive adiabatic-pulse scheme is used to provide two dimensions of volume localization, thus minimizing echo time. The third dimension is determined by slice selection gradients on the axis perpendicular to the coil plane. Signal decay in the presence of diffusion sensitizing pulsed field gradients was modeled by Bayesian Probability Theory. Preliminary findings indicate a bulk Na+ ADC of (1.16 ± .07) × 10-3 mm2/s.

  12. Electrical studies on silver based fast ion conducting glassy materials

    SciTech Connect

    Rao, B. Appa Kumar, E. Ramesh Kumari, K. Rajani Bhikshamaiah, G.

    2014-04-24

    Among all the available fast ion conductors, silver based glasses exhibit high conductivity. Further, glasses containing silver iodide enhances fast ion conducting behavior at room temperature. Glasses of various compositions of silver based fast ion conductors in the AgI−Ag{sub 2}O−[(1−x)B{sub 2}O{sub 3}−xTeO{sub 2}] (x=0 to1 mol% in steps of 0.2) glassy system have been prepared by melt quenching method. The glassy nature of the compounds has been confirmed by X-ray diffraction. The electrical conductivity (AC) measurements have been carried out in the frequency range of 1 KHz–3MHz by Impedance Analyzer in the temperature range 303–423K. The DC conductivity measurements were also carried out in the temperature range 300–523K. From both AC and DC conductivity studies, it is found that the conductivity increases and activation energy decreases with increasing the concentration of TeO{sub 2} as well as with temperature. The conductivity of the present glass system is found to be of the order of 10{sup −2} S/cm at room temperature. The ionic transport number of these glasses is found to be 0.999 indicating that these glasses can be used as electrolyte in batteries.

  13. Fast ion generation and bulk plasma heating with three-ion ICRF scenarios

    SciTech Connect

    Kazakov, Ye. O. Van Eester, D.; Ongena, J.; Lerche, E.; Messiaen, A.

    2015-12-10

    Launching electromagnetic waves in the ion cyclotron range of frequencies (ICRF) is an efficient method of plasma heating, actively employed in most of fusion machines. ICRF has a number of important supplementary applications, including the generation of high-energy ions. In this paper, we discuss a new set of three-ion ICRF scenarios and the prospect of their use as a dedicated tool for fast ion generation in tokamaks and stellarators. A distinct feature of these scenarios is a strong absorption efficiency possible at very low concentrations of resonant minority ions (∼ 1% or even below). Such concentration levels are typical for impurities contaminating fusion plasmas. An alternative ICRF scenario for maximizing the efficiency of bulk D-T ion heating is suggested for JET and ITER tokamaks, which is based on three-ion ICRF heating of intrinsic Beryllium impurities.

  14. Fast ion generation and bulk plasma heating with three-ion ICRF scenarios

    NASA Astrophysics Data System (ADS)

    Kazakov, Ye. O.; Van Eester, D.; Dumont, R.; Ongena, J.; Lerche, E.; Messiaen, A.

    2015-12-01

    Launching electromagnetic waves in the ion cyclotron range of frequencies (ICRF) is an efficient method of plasma heating, actively employed in most of fusion machines. ICRF has a number of important supplementary applications, including the generation of high-energy ions. In this paper, we discuss a new set of three-ion ICRF scenarios and the prospect of their use as a dedicated tool for fast ion generation in tokamaks and stellarators. A distinct feature of these scenarios is a strong absorption efficiency possible at very low concentrations of resonant minority ions (˜ 1% or even below). Such concentration levels are typical for impurities contaminating fusion plasmas. An alternative ICRF scenario for maximizing the efficiency of bulk D-T ion heating is suggested for JET and ITER tokamaks, which is based on three-ion ICRF heating of intrinsic Beryllium impurities.

  15. Fast ion transport induced by saturated infernal mode

    SciTech Connect

    Marchenko, V. S.

    2014-05-15

    Tokamak discharges with extended weak-shear central core are known to suffer from infernal modes when the core safety factor approaches the mode ratio. These modes can cause an outward convection of the well-passing energetic ions deposited in the core by fusion reactions and/or neutral beam injection. Convection mechanism consists in collisional slowing down of energetic ions trapped in the Doppler-precession resonance with a finite-amplitude infernal mode. Convection velocity can reach a few m/s in modern spherical tori. Possible relation of this transport with the enhanced fast ion losses in the presence of “long lived modes” in the MAST tokamak [I. T. Chapman et al., Nucl. Fusion 50, 045007 (2010)] is discussed.

  16. A New Contraction Family for Porous Medium and Fast Diffusion Equations

    NASA Astrophysics Data System (ADS)

    Chmaycem, G.; Jazar, M.; Monneau, R.

    2016-08-01

    In this paper, we present a surprising two-dimensional contraction family for porous medium and fast diffusion equations. This approach provides new a priori estimates on the solutions, even for the standard heat equation.

  17. Effect of the formation of EDTA complexes on the diffusion of metal ions in water

    NASA Astrophysics Data System (ADS)

    Furukawa, Kenji; Takahashi, Yoshio; Sato, Haruo

    2007-09-01

    The diffusion coefficients of aquo metal ions (M z+ ) and their EDTA complexes (M-EDTA ( z-4)+ ) were compared to understand the effect of EDTA complexation on the diffusion of metal ions by the diffusion cell method for Co 2+, Ga 3+, Rb +, Sr 2+, Ag +, Cd 2+, Cs +, Th 4+, UO22+, and trivalent lanthanides. Most studies about ionic diffusion in water have dealt with free ion (hydrated ion). In many cases, however, polyvalent ions are dissolved as complexed species in natural waters. Hence, we need to study the diffusion behavior of complexes in order to understand the diffusion phenomenon in natural aquifer and to measure speciation by diffusive gradient in thin films (DGT), which requires the diffusion coefficients of the species examined. For many ions, the diffusion coefficients of M-EDTA ( z-4)+ are smaller than those of hydrated ions, but the diffusion coefficients of M-EDTA ( z-4)+ are larger than those of hydrated ions for ions with high ionic potentials (Ga 3+ and Th 4+). As a result, the diffusion coefficients of EDTA complexes are similar among various metal ions. In other words, the diffusion of each ion loses its characteristics by the complexation with EDTA. Although the difference is subtle, it was also found that the diffusion coefficients of EDTA complexes increase as the ionic potential increases, which can be explained by the size of the EDTA complex of each metal ion.

  18. Diffuse plasma effects on the ion-hose instability

    SciTech Connect

    Welch, D.R.; Hughes, T.P. )

    1993-02-01

    The transverse stability of a relativistic electron beam focused by an ion channel in the presence of a diffuse background plasma is investigated. The linear behavior of the ion-hose and electron two-stream instabilities is treated analytically using a spread-mass model for the beam and ion channel and a cold-fluid model for the plasma. The electron two-stream instability is found to be quite weak. As the plasma neutralization radius approaches the beam radius, the ion-hose growth rate is reduced up to 50% before the model's assumptions break down. Particle-in-cell simulations confirm the linear analytic theory and show that the electron two-stream instability can saturate nonlinearly with little beam emittance growth.

  19. The influence of ion/molecule reactions on the evaluation of ion mobility and diffusion coefficients

    NASA Astrophysics Data System (ADS)

    de Urquijo, J.; Alvarez, I.; Cisneros, C.; Martinez, H.

    1996-05-01

    This paper deals with the evaluation of the mean and the variance of the ion flux at the exit of a drift tube, from which the drift velocity, [nu]d, and the longitudinal diffusion coefficient, DL, can be derived. Besides drift and diffusion, the presence of a primary ion conversion process through reactions with the gas is fully considered from the outset. Full expressions for the mean and variance of the ion flux are then approximated by resorting to experimental conditions in which low ionic reactivity, adequate drift tube geometry, and other experimental conditions are met, thus arriving at very simple expressions from which [nu]d and DL are derived. These simple expressions have been obtained previously from analyses ignoring ion/molecule reactions from the outset. The full expressions derived here and their approximations are used to provide a means of evaluating the errors incurred when very simple expressions are used in highly reacting ion/neutral systems.

  20. Association and Diffusion of Li(+) in Carboxymethylcellulose Solutions for Environmentally Friendly Li-ion Batteries.

    PubMed

    Casalegno, Mosè; Castiglione, Franca; Passarello, Marco; Mele, Andrea; Passerini, Stefano; Raos, Guido

    2016-07-21

    Carboxymethylcellulose (CMC) has been proposed as a polymeric binder for electrodes in environmentally friendly Li-ion batteries. Its physical properties and interaction with Li(+) ions in water are interesting not only from the point of view of electrode preparation-processability in water is one of the main reasons for its environmental friendliness-but also for its possible application in aqueous Li-ion batteries. We combine molecular dynamics simulations and variable-time pulsed field gradient spin-echo (PFGSE) NMR spectroscopy to investigate Li(+) transport in CMC-based solutions. Both the simulations and experimental results show that, at concentrations at which Li-CMC has a gel-like consistency, the Li(+) diffusion coefficient is still very close to that in water. These Li(+) ions interact preferentially with the carboxylate groups of CMC, giving rise to a rich variety of coordination patterns. However, the diffusion of Li(+) in these systems is essentially unrestricted, with a fast, nanosecond-scale exchange of the ions between CMC and the aqueous environment. PMID:27253620

  1. Association and Diffusion of Li(+) in Carboxymethylcellulose Solutions for Environmentally Friendly Li-ion Batteries.

    PubMed

    Casalegno, Mosè; Castiglione, Franca; Passarello, Marco; Mele, Andrea; Passerini, Stefano; Raos, Guido

    2016-07-21

    Carboxymethylcellulose (CMC) has been proposed as a polymeric binder for electrodes in environmentally friendly Li-ion batteries. Its physical properties and interaction with Li(+) ions in water are interesting not only from the point of view of electrode preparation-processability in water is one of the main reasons for its environmental friendliness-but also for its possible application in aqueous Li-ion batteries. We combine molecular dynamics simulations and variable-time pulsed field gradient spin-echo (PFGSE) NMR spectroscopy to investigate Li(+) transport in CMC-based solutions. Both the simulations and experimental results show that, at concentrations at which Li-CMC has a gel-like consistency, the Li(+) diffusion coefficient is still very close to that in water. These Li(+) ions interact preferentially with the carboxylate groups of CMC, giving rise to a rich variety of coordination patterns. However, the diffusion of Li(+) in these systems is essentially unrestricted, with a fast, nanosecond-scale exchange of the ions between CMC and the aqueous environment.

  2. The role of diffusion in ISOL targets for the production of radioactive ion beams

    NASA Astrophysics Data System (ADS)

    Beyer, G. J.; Hagebø, E.; Novgorodov, A. F.; Ravn, H. L.; Isolde Collaboration

    2003-05-01

    On-line isotope separation techniques (ISOL) for production of ion beams of short-lived radionuclides require fast separation of nuclear reaction products from irradiated target materials followed by a transfer into an ion source. As a first step in this transport chain the release of nuclear reaction products from refractory metals has been studied systematically and will be reviewed. High-energy protons (500-1000 MeV) produce a large number of radionuclides in irradiated materials via the nuclear reactions spallation, fission and fragmentation. Foils and powders of Re, W, Ta, Hf, Mo, Nb, Zr, Y, Ti and C were irradiated with protons (600-1000 MeV) at the Dubna synchrocyclotron, the CERN synchrocyclotron and at the CERN PS-booster to produce different nuclear reaction products. The main topic of the paper is the determination of diffusion coefficients of the nuclear reaction products in the target matrix, data evaluation and a systematic interpretation of the data. The influence of the ionic radius of the diffusing species and the lattice type of the host material used as matrix or target on the diffusion will be evaluated from these systematics. Special attention was directed to the release of group I-, II- and III-elements. Arrhenius plots lead to activation energies of the diffusion process. Results:A strong radius determined diffusion behaviour was found: DIIIB> DIIA> DIA> DVIIIA, ( DY> DSr> DRb> DKr). Rare earth elements diffuse as Me 3+-species. Within the host elements of one period of the periodic table the diffusion of the trace elements changes in the following order: DIIIB> DIVB≫ DVB> DVIB. In a given target trace elements of group I and II of a lower period diffuse faster than the corresponding elements of the higher period of the periodic table. D2ndperiod> D5thperiod> D6thperiod, ( DBe≫ DSr> DBa). The diffusion determined transport rate of nuclear reaction products in solid target materials is often satisfactory, and consequently several

  3. Donnan dialysis with ion-exchange membranes. 3: Diffusion coefficients using ions of different valence

    SciTech Connect

    Miyoshi, Hirofumi

    1999-01-01

    Donnan dialysis with ion-exchange membranes was studied under various kinds of experimental conditions using ions of different valences. The diffusion coefficients (D{sub d}) of various kinds of ions in the ion-exchange membrane were obtained by curve fitting an equation derived from the mass balance to three kinds of Donnan dialytic experiments. It was found that the value of D{sub d}/D{sub s} using D{sub d} of monovalent ions in Donnan dialysis with a set of monovalent feed ions and bivalent driving ions was 1/175, where D{sub s} represents a diffusion coefficient in solution. D{sub s} was calculated from the Nernst-Einstein equation substituted by the ionic conductance of ions at infinite dilution in water. Using D{sub d} of bivalent ions in Donnan dialysis with the same set led to a D{sub d}/D{sub s} value of 1/438. Moreover, using D{sub d} in Donnan dialysis with the same set, the value of D{sub d}/D{sub e} was kept constant at 0.4 (D{sub e} expresses the diffusion coefficient in the membrane when the valences of the feed and driving ions are equal). On the other hand, both D{sub d}/D{sub s} and D{sub d}/D{sub e} using D{sub d} in Donnan dialysis with a set of bivalent feed ions and monovalent driving ions were not constant.

  4. Temperature Activated Diffusion of Radicals through Ion Implanted Polymers.

    PubMed

    Wakelin, Edgar A; Davies, Michael J; Bilek, Marcela M M; McKenzie, David R

    2015-12-01

    Plasma immersion ion implantation (PIII) is a promising technique for immobilizing biomolecules on the surface of polymers. Radicals generated in a subsurface layer by PIII treatment diffuse throughout the substrate, forming covalent bonds to molecules when they reach the surface. Understanding and controlling the diffusion of radicals through this layer will enable efficient optimization of this technique. We develop a model based on site to site diffusion according to Fick's second law with temperature activation according to the Arrhenius relation. Using our model, the Arrhenius exponential prefactor (for barrierless diffusion), D0, and activation energy, EA, for a radical to diffuse from one position to another are found to be 3.11 × 10(-17) m(2) s(-1) and 0.31 eV, respectively. The model fits experimental data with a high degree of accuracy and allows for accurate prediction of radical diffusion to the surface. The model makes useful predictions for the lifetime over which the surface is sufficiently active to covalently immobilize biomolecules and it can be used to determine radical fluence during biomolecule incubation for a range of storage and incubation temperatures so facilitating selection of the most appropriate parameters.

  5. Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

    NASA Astrophysics Data System (ADS)

    Al'tshuler, O. G.; Shkurenko, G. Yu.; Gorlov, A. A.; Al'tshuler, G. N.

    2016-06-01

    The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10-12 m2/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10-13 m2/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10-14 m2/s in sulfonated polycalixarene.

  6. Fast ion beta limit measurements by collimated neutron detection in MST plasmas

    NASA Astrophysics Data System (ADS)

    Capecchi, William; Anderson, Jay; Bonofiglo, Phillip; Kim, Jungha; Sears, Stephanie

    2015-11-01

    Fast ion orbits in the reversed field pinch (RFP) are well ordered and classically confined despite magnetic field stochasticity generated by multiple tearing modes. Classical TRANSP modeling of a 1MW tangentially injected hydrogen neutral beam in MST deuterium plasmas predicts a core-localized fast ion density that can be up to 25% of the electron density and a fast ion beta of many times the local thermal beta. However, neutral particle analysis of an NBI-driven mode (presumably driven by a fast ion pressure gradient) shows mode-induced transport of core-localized fast ions and a saturated fast ion density. The TRANSP modeling is presumed valid until the onset of the beam-driven mode and gives an initial estimate of the volume-averaged fast ion beta of 1-2% (local core value up to 10%). A collimated neutron detector for fusion product profile measurements will be used to determine the spatial distribution of fast ions, allowing for a first measurement of the critical fast-ion pressure gradient required for mode destabilization. Testing/calibration data and initial fast-ion profiles will be presented. Characterization of both the local and global fast ion beta will be done for deuterium beam injection into deuterium plasmas for comparison to TRANSP predictions. Work supported by US DOE.

  7. Fast fall-time ion beam in neutron generators

    SciTech Connect

    Ji, Q.; Kwan, J.; Regis, M.; Wu, Y.; Wilde, S.B.; Wallig, J.

    2008-08-10

    Ion beam with a fast fall time is useful in building neutron generators for the application of detecting hidden, gamma-shielded SNM using differential die-away (DDA) technique. Typically a fall time of less than 1 {micro}s can't be achieved by just turning off the power to the ion source due to the slow decay of plasma density (partly determined by the fall time of the RF power in the circuit). In this paper, we discuss the method of using an array of mini-apertures (instead of one large aperture beam) such that gating the beamlets can be done with low voltage and a small gap. This geometry minimizes the problem of voltage breakdown as well as reducing the time of flight to produce fast gating. We have designed and fabricated an array of 16 apertures (4 x 4) for a beam extraction experiment. Using a gating voltage of 1400 V and a gap distance of 1 mm, the fall time of extracted ion beam pulses is less than 1 {micro}s at various beam energies ranging between 400 eV to 800 eV. Usually merging an array of beamlets suffers the loss of beam brightness, i.e., emittance growth, but that is not an important issue for neutron source applications.

  8. Mutual diffusion coefficients in systems containing the nickel ion

    NASA Astrophysics Data System (ADS)

    Ribeiro, Ana C. F.; Veríssimo, Luis V. M. M.; Gomes, Joselaine C. S.; Santos, Cecilia I. A. V.; Barros, Marisa C. F.; Lobo, Victor M. M.; Sobral, Abílio J. F. N.; Esteso, Miguel A.; Leaist, Derek G.

    2013-04-01

    Mutual diffusion coefficients of nickel chloride in water have been measured at 293.15 K and 303.15 K and at concentrations between 0.020 mol dm-3 and 0.100 mol dm-3, using a conductimetric cell. The experimental mutual diffusion coefficients are discussed on the basis of the Onsager-Fuoss model. The equivalent conductances at infinitesimal concentration of the nickel ion in these solutions at those temperatures have been estimated using these results. In addition, from these data, we have estimated some transport and structural parameters, such as limiting diffusion coefficient, ionic conductance at infinitesimal concentration, hydrodynamic radii and activation energy, contributing this way to a better understanding of the structure of these systems and of their thermodynamic behavior in aqueous solution at different concentrations.

  9. Measurements of Prompt and MHD-Induced Fast Ion Loss from National Spherical Torus Experiment Plasmas

    SciTech Connect

    D.S. Darrow; S.S. Medley; A.L. Roquemore; W.W. Heidbrink; A. Alekseyev; F.E. Cecil; J. Egedal; V.Ya. Goloborod'ko; N.N. Gorelenkov; M. Isobe; S. Kaye; M. Miah; F. Paoletti; M.H. Redi; S.N. Reznik; A. Rosenberg; R. White; D. Wyatt; V.A. Yavorskij

    2002-10-15

    A range of effects may make fast ion confinement in spherical tokamaks worse than in conventional aspect ratio tokamaks. Data from neutron detectors, a neutral particle analyzer, and a fast ion loss diagnostic on the National Spherical Torus Experiment (NSTX) indicate that neutral beam ion confinement is consistent with classical expectations in quiescent plasmas, within the {approx}25% errors of measurement. However, fast ion confinement in NSTX is frequently affected by magnetohydrodynamic (MHD) activity, and the effect of MHD can be quite strong.

  10. Thermal diffusivity study of aged Li-ion batteries using flash method

    NASA Astrophysics Data System (ADS)

    Nagpure, Shrikant C.; Dinwiddie, Ralph; Babu, S. S.; Rizzoni, Giorgio; Bhushan, Bharat; Frech, Tim

    Advanced Li-ion batteries with high energy and power density are fast approaching compatibility with automotive demands. While the mechanism of operation of these batteries is well understood, the aging mechanisms are still under investigation. Investigation of aging mechanisms in Li-ion batteries becomes very challenging, as aging does not occur due to a single process, but because of multiple physical processes occurring at the same time in a cascading manner. As the current characterization techniques such as Raman spectroscopy, X-ray diffraction, and atomic force microscopy are used independent of each other they do not provide a comprehensive understanding of material degradation at different length (nm 2 to m 2) scales. Thus to relate the damage mechanisms of the cathode at mm length scale to micro/nanoscale, data at an intermediate length scale is needed. As such, we demonstrate here the use of thermal diffusivity analysis by flash method to bridge the gap between different length scales. In this paper we present the thermal diffusivity analysis of an unaged and aged cell. Thermal diffusivity analysis maps the damage to the cathode samples at millimeter scale lengths. Based on these maps we also propose a mechanism leading to the increase of the thermal diffusivity as the cells are aged.

  11. Doping-Enhanced Lithium Diffusion in Lithium-Ion Batteries

    NASA Astrophysics Data System (ADS)

    Wu, Gang; Wu, Shunnian; Wu, Ping

    2011-09-01

    We disclose a distortion-assisted diffusion mechanism in Li3N and Li2.5Co0.5N by first-principles simulations. A B2g soft mode at the Γ point is found in α-Li3N, and a more stable α'-Li3N (P3¯m1) structure, which is 0.71 meV lower in energy, is further derived. The same soft mode is inherited into Li2.5Co0.5N and is enhanced due to Co doping. Consequently, unlike the usual Peierls spin instability along Co-N chains, large lithium-ion displacements on the Li-N plane are induced by a set of soft modes. Such a distortion is expected to offer Li atoms a route to bypass the high diffusion barrier and promote Li-ion conductivity. In addition, we further illustrate abnormal Born effective charges along Co-N chains which result from the competition between the motions of electrons and ion cores. Our results provide future opportunities in both fundamental understanding and structural modifications of Li-ion battery materials.

  12. Fast Ion Effects on Magnetic Instabilities in the Pdx Tokamak

    NASA Astrophysics Data System (ADS)

    Buchenauer, Dean Alan James

    A study of the modification and excitation of nondisruptive magnetic instabilities due to near perpendicular neutral beam injection on the PDX tokamak has been made to determine the importance of these instabilities at low q. The instabilities consisted of resistive MHD modes, beam driven ideal MHD modes, and beam driven ion cyclotron modes. Evidence of enhanced transport (beyond the anamolous transport associated with auxiliary heating) is presented for several of these instabilities as well as comparison of the experimental results with theory. The main results can be summarized as follows: (1) The loss of electron thermal energy due to sawteeth oscillations, although small, increases with increasing auxiliary power and decreasing q, but it was suppressed with high power perpendicular injection due to a loss of the beam ions. (2) m = 2 resistive modes have a disastrous effect on the achieved density, but at present power levels, they can be controlled. (3) Evidence from Mirnov coils, soft x-ray emission, neutron emission, and fast charge-exchange flux indicates that a degradation of the global energy confinement above (beta)(,T)q (DBLTURN) 0.045 is due to a rapid loss of beam ions from the bulk plasma ("fishbone instability"). Scalings of the data indicate that this loss occurs due to a destabilizing resonance between an internal kink mode and the precessing beam ions. The flux of escaping ions was studied using a charged particle detector calibrated for the fast deuterons injected by the beam and an array of high frequency electromagnetic coils. Bursts in the beam ion flux and the rf emission were found to be correlated with drops in the neutron emission and bursts of 20 kHz magnetic oscillations (fishbones). (4) A quiescent level of rf emission was observed to be correlated with increases in the density of trapped beam ions at the outer edge of the plasma. The harmonic structure of this instability was the same as that during fishbones (harmonics of (OMEGA

  13. Fast algorithms for classical X-->0 diffusion-reaction processes.

    PubMed

    Thalmann, Fabrice; Lee, Nam-Kyung

    2009-02-21

    The Doi formalism treats a reaction-diffusion process as a quantum many-body problem. We use this second-quantized formulation as a starting point to derive a numerical scheme for simulating X-->0 reaction-diffusion processes, following a well-established time discretization procedure. In the case of a reaction zone localized in the configuration space, this formulation provides also a systematic way of designing an optimized, multiple time step algorithm, spending most of the computation time to sample the configurations where the reaction is likely to occur.

  14. Secondary ion emission from ethanol microdroplets induced by fast heavy ions

    NASA Astrophysics Data System (ADS)

    Majima, T.; Kitajima, K.; Nishio, T.; Tsuchida, H.; Itoh, A.

    2015-09-01

    We have developed a new experimental setup that allowed us to study collision interactions between fast ions and liquid microdroplets under a high vacuum condition. Microdroplets of ethanol are irradiated with 1.0-MeV H+ and 2.0-MeV C2+ ions. The size distribution of the droplets is evaluated from energy-loss measurements of projectile ions penetrating through the microdroplets. We obtain time-of-flight mass spectra of secondary ions from ethanol droplets. It is demonstrated that coincidence measurements with secondary electrons can distinguish specific ions produced in collisions with the droplets. Production mechanisms of H3O+, C4H9O+, (C2H5)2OH+ in the liquid ethanol are discussed.

  15. The sputtering of insulating materials by fast heavy ions

    NASA Technical Reports Server (NTRS)

    Seiberling, L. E.; Meins, C. K.; Cooper, B. H.; Griffith, J. E.; Mendenhall, M. H.; Tombrello, T. A.

    1982-01-01

    In this paper recent experimental results on sputtering of UF4 and H2O (ice) by fast heavy ions are reviewed. Measurements have been made of the dependence of the sputtering yield on the incident ion type, charge state, and energy. In the case of UF4, the energy spectra of neutral sputtered particles have been obtained as well. There is a clear dependence of the sputtering yield on the electronic part of the stopping power, and the yield is strongly affected by the charge state of the incident ion, which shows that in the near-surface region from which sputtered particles arise, the charge state of the incident ion has not reached equilibrium. The shape of the energy spectra observed for UF4 targets is that expected from a thermal distribution rather than that of the collision cascade form typical of ordinary sputtering. A model of the sputtering-track registration process that has arisen from these data is shown to provide a framework of understanding the close relationship of these observations to the 'plasma desorption' of marcromolecules.

  16. Selection of the material and the temperature conditions of the pickup plate of a fast-ion injector

    SciTech Connect

    Tel'kovskii, V.G.; Igritskii, A.N.; Pisarev, A.A.; Tsyplakov, V.N.

    1986-03-01

    In plasma units with injection of fast particles the authors address the problem of absorbing that part of the injected beam which was not captured by the plasma. In the selection of the material of injector pickup plates for fast ions, metals with a high negative thermal dissolution of hydrogen, a surface activation barrier, and a large coefficient of hydrogen diffusion must be tried. Niobium is the most suitable material as far as the coincidence of these parameters is concerned. The temperature of the pickup plate is chosen on the basis of a compromise between attempts to increase the temperature for obtaining rapid diffusion over the entire thickness of the plate and the need for reducing the temperature to avoid thermal liberation of gas and decomposition of the oxide film. Experiments have shown that a high efficiency of deuterium-ion capture in niobium can be maintained up to high fluxes and high irradiation temperatures.

  17. Fast ion profile stiffness due to the resonance overlap of multiple Alfvén eigenmodes

    NASA Astrophysics Data System (ADS)

    Todo, Y.; Van Zeeland, M. A.; Heidbrink, W. W.

    2016-11-01

    Fast ion pressure profiles flattened by multiple Alfvén eigenmodes (AEs) are investigated for various neutral beam deposition powers in a multi-phase simulation, which is a combination of classical simulation and hybrid simulation for energetic particles interacting with a magnetohydrodynamic fluid. Monotonic degradation of fast ion confinement and fast ion profile stiffness is found with increasing beam deposition power. The confinement degradation and profile stiffness are caused by a sudden increase in fast ion transport flux brought about by AEs for fast ion pressure gradients above a critical value. The critical pressure gradient and the corresponding beam deposition power depend on the radial location. The fast ion pressure gradient stays moderately above the critical value, and the profiles of the fast ion pressure and fast ion transport flux spread radially outward from the inner region, where the beam is injected. It is found that the square root of the MHD fluctuation energy is proportional to the beam deposition power. Analysis of the time evolutions of the fast ion energy flux profiles reveals that intermittent avalanches take place with contributions from the multiple eigenmodes. Surface of section plots demonstrate that the resonance overlap of multiple eigenmodes accounts for the sudden increase in fast ion transport with increasing beam power. The critical gradient and critical beam power for the profile stiffness are substantially higher than the marginal stability threshold.

  18. Modeling Fast Ion Transport in TAE Avalanches in NSTX

    SciTech Connect

    Fredrickson, E D; Bell, R E; Darrow, D; Gorelenkov, N N; Kramer, G; Kubota, S; Levinton, F M; Liu, D; Medley, S S; Podesta, M; Tritz, K

    2009-08-17

    Experiments on the National Spherical Torus Experiment [M. Ono, et al., Nucl. Fusion 40 (2000) 557 ] have found strong bursts of Toroidal Alfven Eigenmode (TAE) activity correlated with abrupt drops in the neutron rate. A fairly complete data set offers the opportunity to benchmark the NOVA [C. Z. Cheng, Phys. Reports 211, 1-51 (1992)] and ORBIT [R. B. White and M. S. Chance, Phys. Fluids 27, 2455 (1984)] codes in the low aspect ratio tokamak (ST) geometry. The internal structure of TAE were modeled with NOVA and good agreement is found with measurements made with an array of five fixed-frequency reflectometers. The fast-ion transport resulting from these bursts of multiple TAE were then modeled with the ORBIT code. The simulations are reasonably consistent with the observed drop in neutron rate. While these results represent our best attempts to find agreement, we believe that further refinements in both the simulation of the TAE structure and in the modeling of the fast ion transport are needed. Benchmarking stability codes against present experiments is an important step in developing the predictive capability needed to plan future experiments.

  19. Concentration dependent nitrogen diffusion coefficient in expanded austenite formed by ion implantation

    NASA Astrophysics Data System (ADS)

    Mandl, S.; Rauschenbach, B.

    2002-06-01

    Expanded austenite, formed after nitrogen plasma immersion ion implantation or low energy nitriding of austenitic stainless, is characterized by a high nitrogen content CN of up to 20 at. % and an unusual fast diffusion, which in general cannot be described using a single diffusion coefficient. Here, the concentration dependent diffusivity is calculated for several experimental parameters and steel alloys. Two mathematical simplifications of the general diffusion theory, well justified for physical reasons, helped in solving the equations. First, a constant surface concentration was assumed, despite a constant nitrogen flux into the surface, and, second, only mobile nitrogen atoms in a stationary steel matrix were considered. Thus, it was possible to solve the Boltzmann-Matano equation and obtain the concentration dependent diffusion coefficient D(CN). In all cases, a step-like behavior, with a high value for high nitrogen contents and a low value for low ones, is found, with the transition point between a nitrogen concentration of 5 and 17 at. %, depending on the sample.

  20. Diffusion of fast rising strong magnetic fields into conductors

    NASA Astrophysics Data System (ADS)

    Labetskaya, N. A.; Oreshkin, V. I.; Chaikovsky, S. A.; Datsko, I. M.; Kuskova, N. I.; Rud, A. D.

    2014-11-01

    The basic processes occurring in a conductor exploding in a current skinning mode are the propagation of a nonlinear magnetic diffusion wave in the conductor and the formation of low-temperature plasma at its surface. An experimental study of the phenomenon of nonlinear magnetic diffusion into conductors in magnetic fields of induction rising at a rate up to 3·109 T/s was carried out on the MIG generator capable of producing a peak current up to 2.5 MA within a rise time of 100 ns. It has been found experimentally that the average velocity of a nonlinear magnetic diffusion wave in an aluminum conductor placed in a strong magnetic field (up to 300 T) rising at a high rate (on average, 3·109 T/s) is (2.7÷3.3)·105 cm/s. This is comparable to the velocity of sound in aluminum under normal conditions and reasonably agrees with predictions of numerical simulations.

  1. Fast Dictionary-Based Reconstruction for Diffusion Spectrum Imaging

    PubMed Central

    Bilgic, Berkin; Chatnuntawech, Itthi; Setsompop, Kawin; Cauley, Stephen F.; Yendiki, Anastasia; Wald, Lawrence L.; Adalsteinsson, Elfar

    2015-01-01

    Diffusion Spectrum Imaging (DSI) reveals detailed local diffusion properties at the expense of substantially long imaging times. It is possible to accelerate acquisition by undersampling in q-space, followed by image reconstruction that exploits prior knowledge on the diffusion probability density functions (pdfs). Previously proposed methods impose this prior in the form of sparsity under wavelet and total variation (TV) transforms, or under adaptive dictionaries that are trained on example datasets to maximize the sparsity of the representation. These compressed sensing (CS) methods require full-brain processing times on the order of hours using Matlab running on a workstation. This work presents two dictionary-based reconstruction techniques that use analytical solutions, and are two orders of magnitude faster than the previously proposed dictionary-based CS approach. The first method generates a dictionary from the training data using Principal Component Analysis (PCA), and performs the reconstruction in the PCA space. The second proposed method applies reconstruction using pseudoinverse with Tikhonov regularization with respect to a dictionary. This dictionary can either be obtained using the K-SVD algorithm, or it can simply be the training dataset of pdfs without any training. All of the proposed methods achieve reconstruction times on the order of seconds per imaging slice, and have reconstruction quality comparable to that of dictionary-based CS algorithm. PMID:23846466

  2. A fast feedback controlled magnetic drive for the ASDEX Upgrade fast-ion loss detectors

    NASA Astrophysics Data System (ADS)

    Ayllon-Guerola, J.; Gonzalez-Martin, J.; Garcia-Munoz, M.; Rivero-Rodriguez, J.; Herrmann, A.; Vorbrugg, S.; Leitenstern, P.; Zoletnik, S.; Galdon, J.; Garcia Lopez, J.; Rodriguez-Ramos, M.; Sanchis-Sanchez, L.; Dominguez, A. D.; Kocan, M.; Gunn, J. P.; Garcia-Vallejo, D.; Dominguez, J.

    2016-11-01

    A magnetically driven fast-ion loss detector system for the ASDEX Upgrade tokamak has been designed and will be presented here. The device is feedback controlled to adapt the detector head position to the heat load and physics requirements. Dynamic simulations have been performed taking into account effects such as friction, coil self-induction, and eddy currents. A real time positioning control algorithm to maximize the detector operational window has been developed. This algorithm considers dynamical behavior and mechanical resistance as well as measured and predicted thermal loads. The mechanical design and real time predictive algorithm presented here may be used for other reciprocating systems.

  3. Apparent electrostatic ion cyclotron waves in the diffuse aurora

    NASA Technical Reports Server (NTRS)

    Bering, E. A.

    1983-01-01

    Emissions that have properties consistent with electrostatic ion cyclotron (EIC) waves have been observed at low altitude in the diffuse aurora by a sounding rocket payload. Peaks were observed in the power spectrum of the electric field near the hydrogen and oxygen ion cyclotron frequencies. Doppler shift and polarization analyses have been performed using EIC wave parameters derived from linear theory. Both analyses indicated that these emissions had properties consistent with those expected for H(+) and O(+) EIC waves. The two analyses indicated that both emission bands were due to waves propagating eastward parallel to the poleward boundary of the diffuse aurora. The large local cold plasma density and resulting Landau damping require that the source be local. Magnetometer data indicated the presence of a downward parallel current density of 5 microamps/sq m. Sufficient free energy for the waves was available from this current, although the waves were observed frequently at altitudes where the ion-neutral collision frequency exceeded the oxygen cyclotron frequency.

  4. Transient enhanced diffusion in ion-implanted silicon

    SciTech Connect

    Pennycook, S.J.; Culbertson, R.J.

    1987-03-01

    We discuss the transient-enhanced diffusion of Sb, As, P, In, Ga, and B in ion-implanted Si, where the near-surface region has been amorphized by the dopant or by a self-implantation process. With Sb, a large transient diffusion enhancement is observed proportional to dopant concentration. For Sb, As, P, and In, the enhancement follows the relative interstitialcy diffusion coefficient. We believe this behavior is caused by stable implantation-induced point defects present in the amorphous surface layer, which decay during thermal processing to release high concentrations of self-interstitials. This process occurs in competition with the solid phase epitaxial (SPE) growth process, and for high dopant concentrations can occur in the amorphous phase ahead of the crystallization front. We believe this may be the origin of the dopant redistribution which can occur during SPE growth, which sets the upper limit to the dopant concentration which can be incorporated in the lattice by SPE growth. These effects are reduced for Ga and are absent for B, although transient enhanced diffusion of these species can still occur from defects emitted from the damaged crystal underlying the original amorphous/crystalline interface.

  5. Electrochemical evidences and consequences of significant differences in ions diffusion rate in polyacrylate-based ion-selective membranes.

    PubMed

    Woźnica, Emilia; Mieczkowski, Józef; Michalska, Agata

    2011-11-21

    The origin and effect of surface accumulation of primary ions within the ion-selective poly(n-butyl acrylate)-based membrane, obtained by thermal polymerization, is discussed. Using a new method, based on the relation between the shape of a potentiometric plot and preconditioning time, the diffusion of copper ions in the membrane was found to be slow (the diffusion coefficient estimated to be close to 10(-11) cm(2) s(-1)), especially when compared to ion-exchanger counter ions--sodium cations diffusion (a diffusion coefficient above 10(-9) cm(2) s(-1)). The higher mobility of sodium ions than those of the copper-ionophore complex results in exposed ion-exchanger role leading to undesirably exposed sensitivity to sodium or potassium ions. PMID:21957488

  6. Fast ion effects on magnetic instabilities in the PDX tokamak

    SciTech Connect

    Buchenauer, D.A.J.

    1985-01-01

    A study of the modification and excitation of nondisruptive magnetic instabilities due to near perpendicular neutral beam injection on the PDX tokamak was made to determine the importance of these instabilities at low q. The instabilities consisted of resistive MHD modes, beam driven ideal MHD modes, and beam driven ion cyclotron modes. Evidence of enhanced transport (beyond the anomalous transport associated with auxiliary heating) is presented for several of these instabilities as well as comparison of the experimental results with theory. The main results can be summarized as follows: (1) The loss of electron thermal energy due to sawteeth oscillations, although small, increases with increasing auxiliary power and decreasing q, but it was suppressed with high power perpendicular injection due to a loss of the beam ions. (2) m = 2 resistive modes have a disastrous effect on the achieved density, but at present power levels, they can be controlled. (3) Evidence from Mirnov coils, soft x-ray emission, neutron emission, and fast charge-exchange flux indicates that a degradation of the global energy confinement above ..beta../sub T/q approx. = 0.045 is due to a rapid loss of beam ions from the bulk plasma (fishbone instability).

  7. Fast-ion D{sub {alpha}} measurements and simulations in quiet plasmas

    SciTech Connect

    Luo, Y.; Heidbrink, W. W.; Burrell, K. H.; Ruskov, E.; Solomon, W. M.

    2007-11-15

    The D{sub {alpha}} light emitted by neutralized deuterium fast ions is measured in magnetohydrodynamics (MHD)-quiescent, magnetically confined plasmas during neutral beam injection. A weighted Monte Carlo simulation code models the fast-ion D{sub {alpha}} spectra based on the fast-ion distribution function calculated classically by TRANSP [R. V. Budny, Nucl. Fusion 34, 1247 (1994)]. The spectral shape is in excellent agreement and the magnitude also has reasonable agreement. The fast-ion D{sub {alpha}} signal has the expected dependencies on various parameters including injection energy, injection angle, viewing angle, beam power, electron temperature, and electron density. The neutral particle diagnostic and measured neutron rate corroborate the fast-ion D{sub {alpha}} measurements. The relative spatial profile agrees with TRANSP and is corroborated by the fast-ion pressure profile inferred from the equilibrium.

  8. Determination of the lithium ion diffusion coefficient in graphite

    SciTech Connect

    Yu, P.; Popov, B.N.; Ritter, J.A.; White, R.E.

    1999-01-01

    A complex impedance model for spherical particles was used to determine the lithium ion diffusion coefficient in graphite as a function of the state of charge (SOC) and temperature. The values obtained range from 1.12 {times} 10{sup {minus}10} to 6.51 {times} 10{sup {minus}11} cm{sup 2}/s at 25 C for 0 and 30% SOC, respectively, and for 0% SOC, the value at 55 C was 1.35 {times} 10{sup {minus}10} cm{sup 2}/s. The conventional potentiostatic intermittent titration technique (PITT) and Warburg impedance approaches were also evaluated, and the advantages and disadvantages of these techniques were exposed.

  9. Effect of lithium-ion diffusibility on interfacial resistance of LiCoO2 thin film electrode modified with lithium tungsten oxides

    NASA Astrophysics Data System (ADS)

    Hayashi, Tetsutaro; Miyazaki, Takamichi; Matsuda, Yasutaka; Kuwata, Naoaki; Saruwatari, Motoaki; Furuichi, Yuki; Kurihara, Koji; Kuzuo, Ryuichi; Kawamura, Junichi

    2016-02-01

    To investigate the contribution of lithium-ion diffusibility of lithium tungsten oxides (LWOs) to low interfacial resistance, we fabricate thin-film electrodes of 6Li-enriched LiCoO2 (6LCO) modified with various structure-types of 6Li-enriched LWOs by pulsed laser deposition. The electrodes are subjected to X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and secondary-ion mass spectrometry (SIMS) analyses. XRD reveals that the LWO layers have Li2WO4 structure with rhombohedral and tetragonal symmetries and amorphous states. EIS shows that the lowest interfacial resistance of the positive electrodes is given by the amorphous state, followed in order by the tetragonal and the rhombohedral symmetry, and that the diffusion coefficients of lithium-ions in the electrodes increase in the same order. SIMS demonstrates that the fastest lithium-ion self-diffusibility into the LWOs is found in the amorphous state, followed in order by tetragonal and rhombohedral symmetry. Furthermore, the amorphous state LWO modification shows smooth lithium-ion diffusion between the LWO and LCO layers after the electrochemical test. Conversely, the rhombohedral LWO modification demonstrates congested lithium-ion diffusion between the LWO and LCO layers after the test. Thus, fast lithium-ion self-diffusibility into the LWO-modified LCO contributes to enhancing the diffusion of lithium-ions, resulting in the reduction of interfacial resistance.

  10. Ion-induced gamma-ray detection of fast ions escaping from fusion plasmas

    SciTech Connect

    Nishiura, M. Mushiake, T.; Doi, K.; Wada, M.; Taniike, A.; Matsuki, T.; Shimazoe, K.; Yoshino, M.; Nagasaka, T.; Tanaka, T.; Kisaki, M.; Fujimoto, Y.; Fujioka, K.; Yamaoka, H.; Matsumoto, Y.

    2014-11-15

    A 12 × 12 pixel detector has been developed and used in a laboratory experiment for lost fast-ion diagnostics. With gamma rays in the MeV range originating from nuclear reactions {sup 9}Be(α, nγ){sup 12}C, {sup 9}Be(d, nγ){sup 12}C, and {sup 12}C(d, pγ){sup 13}C, a high purity germanium (HPGe) detector measured a fine-energy-resolved spectrum of gamma rays. The HPGe detector enables the survey of background-gamma rays and Doppler-shifted photo peak shapes. In the experiments, the pixel detector produces a gamma-ray image reconstructed from the energy spectrum obtained from total photon counts of irradiation passing through the detector's lead collimator. From gamma-ray image, diagnostics are able to produce an analysis of the fast ion loss onto the first wall in principle.

  11. Fast electron current density profile and diffusion studies during LHCD in PBX-M

    SciTech Connect

    Jones, S.E.; Kesner, J.; Luckhardt, S.; Paoletti, F.; von Goeler, S.; Bernabei, S.; Kaita, R.; Rimini, F.

    1993-08-01

    Successful current profile control experiments using lower hybrid current drive (LCHD) clearly require knowledge of (1) the location of the driven fast electrons and (2) the ability to maintain that location from spreading due to radial diffusion. These issues can be addressed by examining the data from the hard x-ray camera on PBX-M, a unique diagnostic producing two-dimensional, time resolved tangential images of fast electron bremsstrahlung. Using modeling, these line-of-sight images are inverted to extract a radial fast electron current density profile. We note that ``hollow`` profiles have been observed, indicative of off-axis current drive. These profiles can then be used to calculate an upper bound for an effective fast electron diffusion constant: assuming an extremely radially narrow lower hybrid absorption profile and a transport model based on Rax and Moreau, a model fast electron current density profile is calculated and compared to the experimentally derived profile. The model diffusion constant is adjusted until a good match is found. Applied to steady-state quiescent modes on PBX-M, we obtain an upper limit for an effective diffusion constant of about D*=1.1 m{sup 2}/sec.

  12. Assessing cognitive processes with diffusion model analyses: a tutorial based on fast-dm-30

    PubMed Central

    Voss, Andreas; Voss, Jochen; Lerche, Veronika

    2015-01-01

    Diffusion models can be used to infer cognitive processes involved in fast binary decision tasks. The model assumes that information is accumulated continuously until one of two thresholds is hit. In the analysis, response time distributions from numerous trials of the decision task are used to estimate a set of parameters mapping distinct cognitive processes. In recent years, diffusion model analyses have become more and more popular in different fields of psychology. This increased popularity is based on the recent development of several software solutions for the parameter estimation. Although these programs make the application of the model relatively easy, there is a shortage of knowledge about different steps of a state-of-the-art diffusion model study. In this paper, we give a concise tutorial on diffusion modeling, and we present fast-dm-30, a thoroughly revised and extended version of the fast-dm software (Voss and Voss, 2007) for diffusion model data analysis. The most important improvement of the fast-dm version is the possibility to choose between different optimization criteria (i.e., Maximum Likelihood, Chi-Square, and Kolmogorov-Smirnov), which differ in applicability for different data sets. PMID:25870575

  13. Anomalous Flattening of the Fast-Ion Profile during Alfvén-Eigenmode Activity

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Gorelenkov, N. N.; Luo, Y.; van Zeeland, M. A.; White, R. B.; Austin, M. E.; Burrell, K. H.; Kramer, G. J.; Makowski, M. A.; McKee, G. R.; Nazikian, R.

    2007-12-01

    Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The first application of fast-ion Dα (FIDA) spectroscopy to Alfvén-eigenmode physics shows that the central fast-ion profile is anomalously flat in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The current density driven by fast ions is also strongly modified. Calculations based on the measured mode amplitudes do not explain the observed fast-ion transport.

  14. Anomalous flattening of the fast-ion profile during Alfvén-Eigenmode activity.

    PubMed

    Heidbrink, W W; Gorelenkov, N N; Luo, Y; Van Zeeland, M A; White, R B; Austin, M E; Burrell, K H; Kramer, G J; Makowski, M A; McKee, G R; Nazikian, R

    2007-12-14

    Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfvén eigenmodes in the DIII-D tokamak. The first application of fast-ion D_{alpha} (FIDA) spectroscopy to Alfvén-eigenmode physics shows that the central fast-ion profile is anomalously flat in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The current density driven by fast ions is also strongly modified. Calculations based on the measured mode amplitudes do not explain the observed fast-ion transport.

  15. Anomalous Flattening of the Fast-Ion Profile during Alfven-Eigenmode Activity

    SciTech Connect

    Heidbrink, W. W.; Luo, Y.; Gorelenkov, N. N.; White, R. B.; Kramer, G. J.; Nazikian, R.; Van Zeeland, M. A.; Burrell, K. H.; Austin, M. E.; Makowski, M. A.; McKee, G. R.

    2007-12-14

    Neutral-beam injection into plasmas with negative central shear produces a rich spectrum of toroidicity-induced and reversed-shear Alfven eigenmodes in the DIII-D tokamak. The first application of fast-ion D{sub {alpha}} (FIDA) spectroscopy to Alfven-eigenmode physics shows that the central fast-ion profile is anomalously flat in the inner half of the discharge. Neutron and equilibrium measurements corroborate the FIDA data. The current density driven by fast ions is also strongly modified. Calculations based on the measured mode amplitudes do not explain the observed fast-ion transport.

  16. Developments of fast emittance monitors for ion sources at RCNP.

    PubMed

    Yorita, T; Hatanaka, K; Fukuda, M; Shimada, K; Yasuda, Y; Saito, T; Tamura, H; Kamakura, K

    2016-02-01

    Recently, several developments of low energy beam transport line and its beam diagnostic systems have been performed to improve the injection efficiency of ion beam to azimuthally varying field cyclotron at Research Center for Nuclear Physics, Osaka University. One of those is the fast emittance monitor which can measure within several seconds for the efficient beam development and a Pepper-Pot Emittance Monitor (PPEM) has been developed. The PPEM consists of pepper-pot mask, multichannel plate, fluorescent screen, mirror, and CCD camera. The CCD image is taken via IEEE1394b to a personal computer and analyzed immediately and frequently, and then real time measurement with about 2 Hz has been achieved.

  17. Developments of fast emittance monitors for ion sources at RCNP

    NASA Astrophysics Data System (ADS)

    Yorita, T.; Hatanaka, K.; Fukuda, M.; Shimada, K.; Yasuda, Y.; Saito, T.; Tamura, H.; Kamakura, K.

    2016-02-01

    Recently, several developments of low energy beam transport line and its beam diagnostic systems have been performed to improve the injection efficiency of ion beam to azimuthally varying field cyclotron at Research Center for Nuclear Physics, Osaka University. One of those is the fast emittance monitor which can measure within several seconds for the efficient beam development and a Pepper-Pot Emittance Monitor (PPEM) has been developed. The PPEM consists of pepper-pot mask, multichannel plate, fluorescent screen, mirror, and CCD camera. The CCD image is taken via IEEE1394b to a personal computer and analyzed immediately and frequently, and then real time measurement with about 2 Hz has been achieved.

  18. Fast control of trapped ion qubits using shaped optical pulses

    NASA Astrophysics Data System (ADS)

    Rangan, Chitra; Monroe, C. R.; Bucksbaum, P. H.; Bloch, A. M.

    2003-05-01

    We present a fast control scheme for producing arbitrary states of trapped ion qubits via shaped optical pulses. When the atomic wavepacket is not localized to under a wavelength (beyond the Lamb-Dicke limit), we show that, we show that the Hilbert space of the qubit-harmonic oscillator can be made finite, and the Schrödinger equation controllable. We then implement an optimal control formalism to determine the pulse shapes that can drive the system to any desired state. This process is faster than using sequential single-frequency laser fields to achieve the same final state. We discuss control schemes for producing entangled states of two qubits. We show progress towards achieving decoherence-free subspaces that could be used in error correction schemes.

  19. Fusion product measurements of the local ion thermal diffusivity in the PLT tokamak

    SciTech Connect

    Heidbrink, W.W.; Lovberg, J.; Strachan, J.D.; Bell, R.E.

    1986-03-01

    Measurement of the gradient of the d-d fusion rate profile in an ohmic PLT plasma is used to deduce the gradient of the ion temperature and, thus, the local ion thermal diffusivity through an energy balance analysis. The inferred ion diffusivity is consistent with neoclassical theory.

  20. Monte-Carlo Orbit/Full Wave Simulation of Fast Alfven Wave (FW) Damping on Resonant Ions in Tokamaks

    SciTech Connect

    Choi, M.; Chan, V.S.; Pinsker, R.I.; Tang, V.; Bonoli, P.; Wright, J.

    2005-09-26

    To simulate the resonant interaction of fast Alfven wave (FW) heating and Coulomb collisions on energetic ions, including finite orbit effects, a Monte-Carlo code ORBIT-RF has been coupled with a 2D full wave code TORIC4. ORBIT-RF solves Hamiltonian guiding center drift equations to follow trajectories of test ions in 2D axisymmetric numerical magnetic equilibrium under Coulomb collisions and ion cyclotron radio frequency quasi-linear heating. Monte-Carlo operators for pitch-angle scattering and drag calculate the changes of test ions in velocity and pitch angle due to Coulomb collisions. A rf-induced random walk model describing fast ion stochastic interaction with FW reproduces quasi-linear diffusion in velocity space. FW fields and its wave numbers from TORIC are passed on to ORBIT-RF to calculate perpendicular rf kicks of resonant ions valid for arbitrary cyclotron harmonics. ORBIT-RF coupled with TORIC using a single dominant toroidal and poloidal wave number has demonstrated consistency of simulations with recent DIII-D FW experimental results for interaction between injected neutral-beam ions and FW, including measured neutron enhancement and enhanced high energy tail. Comparison with C-Mod fundamental heating discharges also yielded reasonable agreement.

  1. Collective Diffusion Model for Ion Conduction through Microscopic Channels

    PubMed Central

    Liu, Yingting; Zhu, Fangqiang

    2013-01-01

    Ion conduction through microscopic channels is of central importance in both biology and nanotechnology. To better understand the current-voltage (I-V) dependence of ion channels, here we describe and prove a collective diffusion model that quantitatively relates the spontaneous ion permeation at equilibrium to the stationary ionic fluxes driven by small voltages. The model makes it possible to determine the channel conductance in the linear I-V range from equilibrium simulations without the application of a voltage. To validate the theory, we perform molecular-dynamics simulations on two channels—a conical-shaped nanopore and the transmembrane pore of an α-hemolysin—under both equilibrium and nonequilibrium conditions. The simulations reveal substantial couplings between the motions of cations and anions, which are effectively captured by the collective coordinate in the model. Although the two channels exhibit very different linear ranges in the I-V curves, in both cases the channel conductance at small voltages is in reasonable agreement with the prediction from the equilibrium simulation. The simulations also suggest that channel charges, rather than geometric asymmetry, play a more prominent role in current rectification. PMID:23442858

  2. Fast diffusion of silver in TiO2 nanotube arrays.

    PubMed

    Zhang, Wanggang; Liu, Yiming; Zhou, Diaoyu; Wang, Hui; Liang, Wei; Yang, Fuqian

    2016-01-01

    Using magnetron sputtering and heat treatment, Ag@TiO2 nanotubes are prepared. The effects of heat-treatment temperature and heating time on the evolution of Ag nanofilms on the surface of TiO2 nanotubes and microstructure of Ag nanofilms are investigated by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Ag atoms migrate mainly on the outmost surface of the TiO2 nanotubes, and fast diffusion of Ag atoms is observed. The diffusivity for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes at 400 °C is 6.87 × 10(-18) m(2)/s, which is three orders of magnitude larger than the diffusivities for the diffusion of Ag through amorphous TiO2 films. The activation energy for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes in the temperature range of 300 to 500 °C is 157 kJ/mol, which is less than that for the lattice diffusion of Ag and larger than that for the grain boundary diffusion. The diffusion of Ag atoms leads to the formation of Ag nanocrystals on the outmost surface of TiO2 nanotubes. Probably there are hardly any Ag nanocrystals formed inside the TiO2 nanotubes through the migration of Ag. PMID:27547630

  3. Fast diffusion of silver in TiO2 nanotube arrays

    PubMed Central

    Zhang, Wanggang; Liu, Yiming; Zhou, Diaoyu; Wang, Hui

    2016-01-01

    Summary Using magnetron sputtering and heat treatment, Ag@TiO2 nanotubes are prepared. The effects of heat-treatment temperature and heating time on the evolution of Ag nanofilms on the surface of TiO2 nanotubes and microstructure of Ag nanofilms are investigated by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Ag atoms migrate mainly on the outmost surface of the TiO2 nanotubes, and fast diffusion of Ag atoms is observed. The diffusivity for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes at 400 °C is 6.87 × 10−18 m2/s, which is three orders of magnitude larger than the diffusivities for the diffusion of Ag through amorphous TiO2 films. The activation energy for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes in the temperature range of 300 to 500 °C is 157 kJ/mol, which is less than that for the lattice diffusion of Ag and larger than that for the grain boundary diffusion. The diffusion of Ag atoms leads to the formation of Ag nanocrystals on the outmost surface of TiO2 nanotubes. Probably there are hardly any Ag nanocrystals formed inside the TiO2 nanotubes through the migration of Ag. PMID:27547630

  4. Dynamical tunneling versus fast diffusion for a non-convex Hamiltonian

    NASA Astrophysics Data System (ADS)

    Pittman, S. M.; Tannenbaum, E.; Heller, E. J.

    2016-08-01

    This paper attempts to resolve the issue of the nature of the 0.01-0.1 cm-1 peak splittings observed in high-resolution IR spectra of polyatomic molecules. One hypothesis is that these splittings are caused by dynamical tunneling, a quantum-mechanical phenomenon whereby energy flows between two disconnected regions of phase-space across dynamical barriers. However, a competing classical mechanism for energy flow is Arnol'd diffusion, which connects different regions of phase-space by a resonance network known as the Arnol'd web. The speed of diffusion is bounded by the Nekhoroshev theorem, which guarantees stability on exponentially long time scales if the Hamiltonian is steep. Here we consider a non-convex Hamiltonian that contains the characteristics of a molecular Hamiltonian, but does not satisfy the Nekhoroshev theorem. The diffusion along the Arnol'd web is expected to be fast for a non-convex Hamiltonian. While fast diffusion is an unlikely competitor for longtime energy flow in molecules, we show how dynamical tunneling dominates compared to fast diffusion in the nearly integrable regime for a non-convex Hamiltonian, as well as present a new kind of dynamical tunneling.

  5. Influence of fast alpha diffusion and thermal alpha buildup on tokamak reactor performance

    SciTech Connect

    Uckan, N.A.; Tolliver, J.S.; Houlberg, W.A.; Attenberger, S.E.

    1987-11-01

    The effect of fast alpha diffusion and thermal alpha accumulation on the confinement capability of a candidate Engineering Test Reactor (ETR) plasma (Tokamak Ignition/Burn Experimental Reactor (TIBER-II)) in achieving ignition and steady-state driven operation has been assessed using both global and 1-1/2-D transport models. Estimates are made of the threshold for radial diffusion of fast alphas and thermal alpha buildup. It is shown that a relatively low level of radial transport, when combined with large gradients in the fast alpha density, leads to a significant radial flow with a deleterious effect on plasma performance. Similarly, modest levels of thermal alpha concentration significantly influence the ignition and steady-state burn capability. 23 refs., 9 figs., 4 tabs.

  6. Collective Thomson scattering measurements of fast-ion transport due to sawtooth crashes in ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Rasmussen, J.; Nielsen, S. K.; Stejner, M.; Galdon-Quiroga, J.; Garcia-Munoz, M.; Geiger, B.; Jacobsen, A. S.; Jaulmes, F.; Korsholm, S. B.; Lazanyi, N.; Leipold, F.; Ryter, F.; Salewski, M.; Schubert, M.; Stober, J.; Wagner, D.; the ASDEX Upgrade Team; the EUROFusion MST1 Team

    2016-11-01

    Sawtooth instabilities can modify heating and current-drive profiles and potentially increase fast-ion losses. Understanding how sawteeth redistribute fast ions as a function of sawtooth parameters and of fast-ion energy and pitch is hence a subject of particular interest for future fusion devices. Here we present the first collective Thomson scattering (CTS) measurements of sawtooth-induced redistribution of fast ions at ASDEX Upgrade. These also represent the first localized fast-ion measurements on the high-field side of this device. The results indicate fast-ion losses in the phase-space measurement volume of about 50% across sawtooth crashes, in good agreement with values predicted with the Kadomtsev sawtooth model implemented in TRANSP and with the sawtooth model in the EBdyna_go code. In contrast to the case of sawteeth, we observe no fast-ion redistribution in the presence of fishbone modes. We highlight how CTS measurements can discriminate between different sawtooth models, in particular when aided by multi-diagnostic velocity-space tomography, and briefly discuss our results in light of existing measurements from other fast-ion diagnostics.

  7. Fast optimization and dose calculation in scanned ion beam therapy

    SciTech Connect

    Hild, S.; Graeff, C.; Trautmann, J.; Kraemer, M.; Zink, K.; Durante, M.; Bert, C.

    2014-07-15

    Purpose: Particle therapy (PT) has advantages over photon irradiation on static tumors. An increased biological effectiveness and active target conformal dose shaping are strong arguments for PT. However, the sensitivity to changes of internal geometry complicates the use of PT for moving organs. In case of interfractionally moving objects adaptive radiotherapy (ART) concepts known from intensity modulated radiotherapy (IMRT) can be adopted for PT treatments. One ART strategy is to optimize a new treatment plan based on daily image data directly before a radiation fraction is delivered [treatment replanning (TRP)]. Optimizing treatment plans for PT using a scanned beam is a time consuming problem especially for particles other than protons where the biological effective dose has to be calculated. For the purpose of TRP, fast optimization and fast dose calculation have been implemented into the GSI in-house treatment planning system (TPS) TRiP98. Methods: This work reports about the outcome of a code analysis that resulted in optimization of the calculation processes as well as implementation of routines supporting parallel execution of the code. To benchmark the new features, the calculation time for therapy treatment planning has been studied. Results: Compared to the original version of the TPS, calculation times for treatment planning (optimization and dose calculation) have been improved by a factor of 10 with code optimization. The parallelization of the TPS resulted in a speedup factor of 12 and 5.5 for the original version and the code optimized version, respectively. Hence the total speedup of the new implementation of the authors' TPS yielded speedup factors up to 55. Conclusions: The improved TPS is capable of completing treatment planning for ion beam therapy of a prostate irradiation considering organs at risk in this has been overseen in the review process. Also see below 6 min.

  8. Nd3+ ion diffusion during sintering of Nd:YAG transparent ceramics

    SciTech Connect

    Hollingsworth, J P; Kuntz, J D; Soules, T F

    2008-10-24

    Using an electron microprobe, we measured and characterized the Nd{sup 3+} ion diffusion across a boundary between Nd doped and undoped ceramic yttrium aluminum garnet (YAG) for different temperature ramps and hold times and temperatures. The results show significant Nd ion diffusion on the order of micrometers to tens of micrometers depending on the time and temperature of sintering. The data fit well a model including bulk diffusion, grain boundary diffusion and grain growth. Grain boundary diffusion dominates and grain growth limits grain boundary diffusion by reducing the total cross sectional area of grain boundaries.

  9. Fast diffusion along defects and corrugations in phospholipid P beta, liquid crystals.

    PubMed Central

    Schneider, M B; Chan, W K; Webb, W W

    1983-01-01

    The diffusion of a fluorescent lipid analogue in liquid crystals of the anisotropic P beta, phase of dimyristoylphosphatidylcholine (DMPC) had been found to be highly variable, suggesting structural defect pathways. Fluorescence photobleaching recovery (FPR) experiments imply two effective diffusion pathways with coefficients differing by at least 100. This is consistent with fast diffusion along submicroscopic bands of disordered material ("defects") in the bilayer corrugations characteristic of this phase. Due to strains during transformation from the L alpha phase, the axis of the corrugations is ordinarily disrupted by mosaic patches rotationally disoriented within the mean plane of the molecular bilayers, although larger oriented domains are sometimes adventitiously aligned into microscopically visible striped textures. The corrugations are also systematically aligned along positive disclinations pairs or "oily streaks." Thus, fast diffusion occurs parallel to the disclination lines and along the textured stripes. FPR results yield an upper limit on the effective diffusion in the ordered material of D less than or equal to 2 X 10(-16) cm2/s at 22 degrees C, D less than or equal to 3 X 10(-17) cm2/s at 13 degrees C. In contrast the diffusion coefficient along defect pathways where disordered ribbons are aligned is D approximately 4 X 10(-11) cm2/s at 16 degrees C. Images FIGURE 4 FIGURE 6 FIGURE 7 PMID:6616004

  10. Sensitivity of the interpretation of the experimental ion thermal diffusivity to the determination of the ion conductive heat flux

    SciTech Connect

    Stacey, W. M.

    2014-04-15

    A moments equation formalism for the interpretation of the experimental ion thermal diffusivity from experimental data is used to determine the radial ion thermal conduction flux that must be used to interpret the measured data. It is shown that the total ion energy flux must be corrected for thermal and rotational energy convection, for the work done by the flowing plasma against the pressure and viscosity, and for ion orbit loss of particles and energy, and expressions are presented for these corrections. Each of these factors is shown to have a significant effect on the interpreted ion thermal diffusivity in a representative DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharge.

  11. Calculation of the fast ion tail distribution for a spherically symmetric hot spot

    SciTech Connect

    McDevitt, C. J.; Tang, X.-Z.; Guo, Z.; Berk, H. L.

    2014-10-15

    The fast ion tail for a spherically symmetric hot spot is computed via the solution of a simplified Fokker-Planck collision operator. Emphasis is placed on describing the energy scaling of the fast ion distribution function in the hot spot as well as the surrounding cold plasma throughout a broad range of collisionalities and temperatures. It is found that while the fast ion tail inside the hot spot is significantly depleted, leading to a reduction of the fusion yield in this region, a surplus of fast ions is observed in the neighboring cold plasma region. The presence of this surplus of fast ions in the neighboring cold region is shown to result in a partial recovery of the fusion yield lost in the hot spot.

  12. Calculation of the fast ion tail distribution for a spherically symmetric hot spot

    NASA Astrophysics Data System (ADS)

    McDevitt, C. J.; Tang, X.-Z.; Guo, Z.; Berk, H. L.

    2014-10-01

    The fast ion tail for a spherically symmetric hot spot is computed via the solution of a simplified Fokker-Planck collision operator. Emphasis is placed on describing the energy scaling of the fast ion distribution function in the hot spot as well as the surrounding cold plasma throughout a broad range of collisionalities and temperatures. It is found that while the fast ion tail inside the hot spot is significantly depleted, leading to a reduction of the fusion yield in this region, a surplus of fast ions is observed in the neighboring cold plasma region. The presence of this surplus of fast ions in the neighboring cold region is shown to result in a partial recovery of the fusion yield lost in the hot spot.

  13. Doppler-shifted cyclotron resonance of fast ions with circularly polarized shear Alfven waves

    SciTech Connect

    Zhang Yang; Heidbrink, W. W.; Zhou Shu; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Lilley, M. K.

    2009-05-15

    The Doppler-shifted cyclotron resonance between fast ions and shear Alfven waves (SAWs) has been experimentally investigated with a test-particle fast-ion (Li{sup +}) beam launched in the helium plasma of the Large Plasma Device [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)]. Left- or right-hand circularly polarized SAWs are launched by an antenna with four current channels. A collimated fast-ion energy analyzer characterizes the resonance by measuring the nonclassical spreading of the averaged beam signal. Left-hand circularly polarized SAWs resonate with the fast ions but right-hand circularly polarized SAWs do not. The measured fast-ion profiles are compared with simulations by a Monte Carlo Lorentz code that uses the measured wave field data.

  14. Fast Ion Confinement in High Beta, Steady-State Scenario Plasmas

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Chen, X.; Ferron, J. R.; van Zeeland, M. A.; Grierson, B. A.; Holcomb, C. T.

    2013-10-01

    Fast-ion confinement is studied for qmin between 1.2-2.8 in plasmas with normalized β > 2 . 6 . Fast-ion D-alpha (FIDA), neutron, and neutral-particle diagnostics measure the confined fast ions. Tearing modes and a ``sea'' of unstable Alfvén eigenmodes (AE) are observed. In preliminary analysis, the degradation in fast-ion confinement increases with qmin ; increased AE activity appears responsible. Predictions of a model that assumes that AE-induced fast-ion transport is stiff are compared with the data. Work supported by the US Department of Energy under SC-G903402, DE-FC-02-04ER54698, DE-AC02-09CH11466, and DE-AC52-07NA27344.

  15. Approximation of super-ions for single-file diffusion of multiple ions through narrow pores.

    PubMed

    Kharkyanen, Valery N; Yesylevskyy, Semen O; Berezetskaya, Natalia M

    2010-11-01

    The general theory of the single-file multiparticle diffusion in the narrow pores could be greatly simplified in the case of inverted bell-like shape of the single-particle energy profile, which is often observed in biological ion channels. There is a narrow and deep groove in the energy landscape of multiple interacting ions in such profiles, which corresponds to the pre-defined optimal conduction pathway in the configurational space. If such groove exists, the motion of multiple ions can be reduced to the motion of single quasiparticle, called the superion, which moves in one-dimensional effective potential. The concept of the superions dramatically reduces the computational complexity of the problem and provides very clear physical interpretation of conduction phenomena in the narrow pores.

  16. Measurement of local ion diffusion coefficients in the Tokamak Fusion Test Reactor

    NASA Astrophysics Data System (ADS)

    Evensen, H. T.; Fonck, R. J.; Paul, S. F.; Scott, S. D.

    1999-01-01

    The perturbations in ion temperature, density and parallel velocity resulting from sawtooth disruptions in TFTR are measured with a novel diagnostic. The local ion thermal diffusivity, particle diffusivity and parallel momentum diffusivity are determined in a high power discharge at r/a = 0.64 by fitting the observed pulses to a simple model of the radial diffusive propagation of heat, particles and momentum caused by the crash. The incremental ion thermal diffusivity, χiinc, is found to be similar in amplitude to the ion and electron thermal diffusivities obtained from a steady state 1-D power balance analysis, and the particle and parallel momentum diffusivities are found to be an order of magnitude smaller than χiinc.

  17. Fokker-Planck model for collisional loss of fast ions in tokamaks

    NASA Astrophysics Data System (ADS)

    Yavorskij, V.; Goloborod'ko, V.; Schoepf, K.

    2016-11-01

    Modelling of the collisional loss of fast ions from tokamak plasmas is important from the point of view of the impact of fusion alphas and neutral beam injection ions on plasma facing components as well as for the development of diagnostics of fast ion losses [1-3]. This paper develops a Fokker-Planck (FP) method for the assessment of distributions of collisional loss of fast ions as depending on the coordinates of the first wall surface and on the velocities of lost ions. It is shown that the complete 4D drift FP approach for description of fast ions in axisymmetric tokamak plasmas can be reduced to a 2D FP problem for lost ions with a boundary condition delivered by the solution of a 3D boundary value problem for confined ions. Based on this newly developed FP approach the poloidal distribution of neoclassical loss, depending on pitch-angle and energy, of fast ions from tokamak plasma may be examined as well as the contribution of this loss to the signal detected by the scintillator probe may be evaluated. It is pointed out that the loss distributions obtained with the novel FP treatment may serve as an alternative approach with respect to Monte-Carlo models [4, 5] commonly used for simulating fast ion loss from toroidal plasmas.

  18. Ion-scale structure in Mercury's magnetopause reconnection diffusion region

    NASA Astrophysics Data System (ADS)

    Gershman, Daniel J.; Dorelli, John C.; DiBraccio, Gina A.; Raines, Jim M.; Slavin, James A.; Poh, Gangkai; Zurbuchen, Thomas H.

    2016-06-01

    The strength and time dependence of the electric field in a magnetopause diffusion region relate to the rate of magnetic reconnection between the solar wind and a planetary magnetic field. Here we use ~150 ms measurements of energetic electrons from the Mercury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft observed over Mercury's dayside polar cap boundary (PCB) to infer such small-scale changes in magnetic topology and reconnection rates. We provide the first direct measurement of open magnetic topology in flux transfer events at Mercury, structures thought to account for a significant portion of the open magnetic flux transport throughout the magnetosphere. In addition, variations in PCB latitude likely correspond to intermittent bursts of ~0.3-3 mV/m reconnection electric fields separated by ~5-10 s, resulting in average and peak normalized dayside reconnection rates of ~0.02 and ~0.2, respectively. These data demonstrate that structure in the magnetopause diffusion region at Mercury occurs at the smallest ion scales relevant to reconnection physics.

  19. Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands

    NASA Technical Reports Server (NTRS)

    Salama, F.; Allamandola, L. J.

    1995-01-01

    Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these Polycyclic Aromatic Hydrocarbons (PAHs) absorb in the visible. C10H8(+) has 12 discrete absorption bands which fall between 6800 and 5000 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBS at 6520, 6151, and 5965 A, other moderately strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 A. If C16H10(+), or a closely related pyrene-like ion is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.

  20. Influence of circulating fast ions on nonlinear kink-tearing modes in tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Xian-Qu

    2016-08-01

    Nonlinear radial displacement modified by the kinetic effect of circulating fast ions is derived. It is found that circulating fast ions play a crucial role in the nonlinear dynamics of m = 1 kink-tearing modes. For a large fraction of fast ions, resonant fast ions can destabilize the mode by wave-particle interaction and enhance the mode saturation level significantly, meanwhile, fast-ion current has a modification on the mode amplitude depending on the plasma pressure gradient. A relation of mode amplitude to linear growth rate is explored by this model, which is valid to study the effects of circulating or trapped fast particles on the mode. The calculation results for the ITER-like parameters suggest that the kink-tearing mode with a global structure is dominated by the wave-particle interaction rather than the fast-ion current, particularly for the small island in which the fraction of fast ions is ignorable in comparison with the ideal region. The dependence of radial displacement on the mode frequency is discussed for different stabilities of the MHD modes.

  1. Progress on Bayesian Inference of the Fast Ion Distribution Function

    NASA Astrophysics Data System (ADS)

    Stagner, L.; Heidbrink, W. W.; Chen, X.; Salewski, W.; Grierson, B. A.

    2013-10-01

    The fast-ion distribution function (DF) has a complicated dependence on several phase-space variables. The standard analysis procedure in energetic particle research is to compute the DF theoretically, use that DF in forward modeling to predict diagnostic signals, then compare with measured data. However, when theory and experiment disagree (for one or more diagnostics), it is unclear how to proceed. Bayesian statistics provides a framework to infer the DF, quantify errors, and reconcile discrepant diagnostic measurements. Diagnostic errors and weight functions that describe the phase space sensitivity of the measurements are incorporated into Bayesian likelihood probabilities. Prior probabilities describe physical constraints. This poster will show reconstructions of classically described, low-power, MHD-quiescent distribution functions from actual FIDA measurements. A description of the full weight functions will also be shown. This work is supported in part by the US Department of Energy under SC-G903402, DE-FC02-04ER54698 and DE-AC02-09CH11466.

  2. Fusion reaction spectra produced by anisotropic fast ions in the PLT tokamak

    SciTech Connect

    Heidbrink, W.W.

    1984-02-01

    For beam-target fusion reactions, collimated measurements of the energy spectrum of one of the reaction products can provide information on the degree of anisotropy of the reacting beam ions. Measurements of the spectrum of 15 MeV protons produced by reactions between energetic /sup 3/He ions and relatively cold deuterons during fast wave minority heating in the PLT tokamak indicate that the velocity distribution of fast /sup 3/He ions is peaked perpendicular to the tokamak magnetic field.

  3. Self-similar fast-reaction limits for reaction-diffusion systems on unbounded domains

    NASA Astrophysics Data System (ADS)

    Crooks, E. C. M.; Hilhorst, D.

    2016-08-01

    We present a unified approach to characterising fast-reaction limits of systems of either two reaction-diffusion equations, or one reaction-diffusion equation and one ordinary differential equation, on unbounded domains, motivated by models of fast chemical reactions where either one or both reactant(s) is/are mobile. For appropriate initial data, solutions of four classes of problems each converge in the fast-reaction limit k → ∞ to a self-similar limit profile that has one of four forms, depending on how many components diffuse and whether the spatial domain is a half or whole line. For fixed k, long-time convergence to these same self-similar profiles is also established, thanks to a scaling argument of Kamin. Our results generalise earlier work of Hilhorst, van der Hout and Peletier to a much wider class of problems, and provide a quantitative description of the penetration of one substance into another in both the fast-reaction and long-time regimes.

  4. Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain.

    PubMed

    Mulkern, Robert V; Vajapeyam, Sridhar; Haker, Steven J; Maier, Stephan E

    2005-05-01

    Magnetization transfer (MT) properties of the fast and slow diffusion components recently observed in the human brain were assessed experimentally. One set of experiments, performed at 1.5 T in healthy volunteers, was designed to determine whether the amplitudes of fast and slow diffusion components, differentiated on the basis of biexponential fits to signal decays over a wide range of b-factors, demonstrated a different or similar magnetization transfer ratio (MTR). Another set of experiments, performed at 3 T in healthy volunteers, was designed to determine whether MTRs differed when measured from high signal-to-noise images acquired with b-factor weightings of 350 vs 3500 s/mm2. The 3 T studies included measurements of MTR as a function of off-resonance frequency for the MT pulse at both low and high b-factors. The primary conclusion drawn from all the studies is that there appears to be no significant difference between the magnetization transfer properties of the fast and slow tissue water diffusion components. The conclusions do not lend support to a direct interpretation of the 'components' of the biexponential diffusion decay in terms of the 'compartments' associated with intra- and extracellular water. PMID:15578729

  5. Diffusion of Rubidium Ion and Potassium Ion in Silver-Bromide and Silver-Chloride

    NASA Astrophysics Data System (ADS)

    Cardegna, Peter Anthony

    The diffusion of Rb('+) in AgBr and AgCl was performed using the standard tracer and serial sectioning technique. For AgBr in the temperature range 184-420(DEGREES)C and AgCl in the temperature range 184-447(DEGREES)C, the temperature dependence of the diffusivity follows the normal, linear relationship D = D(,0) e('-H/kT). The pre-exponential factor for AgBr is. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). and for. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). The diffusion activation energy for AgBr is H = (1.33 (+OR-) 0.02) eV and for AgCl is H = (1.20 (+OR -) 0.02) eV. It is argued that the lack of curvature in these Arrhenius plots, which is predicted on the basis of a temperature dependent defect formation enthalpy, is intimately associated with the elastic strain field set up in the vicinity of the oversized Rb('+) ion. The diffusion of the smaller K('+) ion was also studied in AgBr and AgCl using the same technique. The temperature range investigated for AgBr was 248-418(DEGREES)C and for AgCl was 264-448(DEGREES)C. In this case, the Arrhenius plots describing the temperature dependence of the diffusion coefficient do show a continuous positive curvature as you approach the melting point. However, it is shown that the curvature is not completely accounted for by the the temperature dependent defect enthalpy model. Again, it is argued that small, but nevertheless temperature dependent, elastic binding does exist which affects the degree of curvature in the Arrhenius graphs.

  6. Experimental Evidence for Fast Lithium Diffusion and Isotope Fractionation in Water-bearing Rhyolitic Melts at Magmatic Conditions

    NASA Astrophysics Data System (ADS)

    Cichy, S. B.; Till, C. B.; Roggensack, K.; Hervig, R. L.; Clarke, A. B.

    2015-12-01

    The aim of this work is to extend the existing database of experimentally-determined lithium diffusion coefficients to more natural cases of water-bearing melts at the pressure-temperature range of the upper crust. In particular, we are investigating Li intra-melt and melt-vapor diffusion and Li isotope fractionation, which have the potential to record short-lived magmatic processes (seconds to hours) in the shallow crust, especially during decompression-induced magma degassing. Hydrated intra-melt Li diffusion-couple experiments on Los Posos rhyolite glass [1] were performed in a piston cylinder at 300 MPa and 1050 °C. The polished interfaces between the diffusion couples were marked by addition of Pt powder for post-run detection. Secondary ion mass spectrometry analyses indicate that lithium diffuses extremely fast in the presence of water. Re-equilibration of a hydrated ~2.5 mm long diffusion-couple experiment was observed during the heating period from room temperature to the final temperature of 1050 °C at a rate of ~32 °C/min. Fractionation of ~40‰ δ7Li was also detected in this zero-time experiment. The 0.5h and 3h runs show progressively higher degrees of re-equilibration, while the isotope fractionation becomes imperceptible. Li contamination was observed in some experiments when flakes filed off Pt tubing were used to mark the diffusion couple boundary, while the use of high purity Pt powder produced better results and allowed easier detection of the diffusion-couple boundary. The preliminary lithium isotope fractionation results (δ7Li vs. distance) support findings from [2] that 6Li diffuses substantially faster than 7Li. Further experimental sets are in progress, including lower run temperatures (e.g. 900 °C), faster heating procedure (~100 °C/min), shorter run durations and the extension to mafic systems. [1] Stanton (1990) Ph.D. thesis, Arizona State Univ., [2] Richter et al. (2003) GCA 67, 3905-3923.

  7. Determination of the copper diffusion coefficient in silicon from transient ion-drift

    NASA Astrophysics Data System (ADS)

    Heiser, T.; Mesli, A.

    1993-10-01

    We use the transient ion drift in a depletion region of a Schottky barrier to determine ion diffusivities at moderate temperatures. The pulsed reverse bias leads to temperature dependent capacitance transients similar to deep level carrier emission transients. A simple theoretical model together with classical transient signal analysis provide the means to extract the ion diffusion constant. When applied to copper in silicon, diffusion data are obtained in a not yet investigated temperature range (280 400 K) which agree well with both low and high temperature diffusion data.

  8. Fast-ion Energy Loss During TAE Avalanches in the National Spherical Torus Experiment

    SciTech Connect

    Fredrickson, E D; Darrow, D S; Gorelenkov, N N; Kramer, G J; Kubota, S; Podesta, M; White, R B; Bortolon, A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M

    2012-07-11

    Strong TAE avalanches on NSTX, the National Spherical Torus Experiment [M. Ono, et al., Nucl. Fusion 40 (2000) 557] are typically correlated with drops in the neutron rate in the range of 5% - 15%. In previous studies of avalanches in L-mode plasmas, these neutron drops were found to be consistent with modeled losses of fast ions. Here we expand the study to TAE avalanches in NSTX H-mode plasmas with improved analysis techniques. At the measured TAE mode amplitudes, simulations with the ORBIT code predict that fast ion losses are negligible. However, the simulations predict that the TAE scatter the fast ions in energy, resulting in a small (≈ 6%) drop in fast ion β. The net decrease in energy of the fast ions is sufficient to account for the bulk of the drop in neutron rate, even in the absence of fast ion losses. This loss of energy from the fast ion population is comparable to the estimated energy lost by damping from the Alfven wave during the burst. The previously studied TAE avalanches in L-mode are re-evaluated using an improved calculation of the potential fluctuations in the ORBIT code.

  9. Characterizing Critical Gradient Threshold for Alfvén Eigenmode Induced Fast-Ion Transport

    NASA Astrophysics Data System (ADS)

    Collins, C. S.; Heidbrink, W. W.; Stagner, L.; van Zeeland, M. A.; Pace, D. C.; Petty, C. C.

    2015-11-01

    Recent experiments on DIII-D indicate a sudden increase in fast-ion transport in the presence of many simultaneous Alfvén eigenmodes (AEs) at a threshold in neutral beam power. The threshold is beyond the AE linear stability limit and appears to differ between various fast-ion diagnostics, indicating phase-space dependent transport. Above threshold, transport becomes stiff, resulting in virtually unchanged fast-ion density profiles despite increased beam drive. In the experiment, a beam power scan (2-9 MW) varies AE activity, while the fast-ion pressure profile is modulated using an off-axis neutral beam. Measurements of the fast-ion density evolution are used to infer flux. Fast-ion D α (FIDA) spectroscopy indicates the peak of the modulated fast-ion flux is localized to mid-core radii, corresponding to the radial location of AEs. These measurements facilitate numerical model validation studies, giving greater confidence in predicting the fusion alpha density profiles and losses in future burning plasma devices. Work supported by the US DOE under SC-G903402 & DE-FC02-04ER54698.

  10. Measurements of fast-ion transport by mode-particle resonances on DIII-D

    NASA Astrophysics Data System (ADS)

    Muscatello, C. M.; Grierson, B. A.; Harvey, R. W.; Heidbrink, W. W.; Pace, D. C.; Van Zeeland, M. A.

    2012-10-01

    Magnetohydrodynamic (MHD) instabilities in tokamak plasmas manifest in a variety of ways, characterized by different scale lengths and mode frequencies. MHD activity can cause significant degradation of plasma performance due to transport of particles, energy and current. Among the many different types of MHD, arguably fishbones, sawteeth and Alfvén eigenmodes (AEs) are observed to cause the largest fluxes of superthermal ions. DIII-D's expansive suite of diagnostics makes it possible to rigorously characterize these instabilities and study their interaction with fast ions. This review paper first presents an overview of the recent additions to DIII-D's collection of fast-ion diagnostics. The extended diagnostic capabilities are employed in a series of experiments to investigate fast-ion dynamics in the presence of fishbones, sawteeth and AEs. Results from these seemingly unrelated studies are highlighted, and they reveal that mode-particle resonances play the central role in the observed deterioration of fast-ion confinement.

  11. Does a Critical Gradient Exist for Alfvén Eigenmode Induced Fast-Ion Transport?

    NASA Astrophysics Data System (ADS)

    Collins, C. S.; Heidbrink, W. W.; van Zeeland, M. A.; Petty, C. C.; Pace, D. C.; Grierson, B. A.

    2014-10-01

    In the critical gradient model, if local energetic particle (EP) drive exceeds the Alfvén eigenmode (AE) stability limit, particles diffuse to flatten the pressure profile until marginal stability is maintained. A key signature is a sudden increase in transport above the critical gradient. In DIII-D, the onset of AE-induced EP transport is examined by modulating the EP pressure profile using an off-axis neutral beam while AE activity gradually diminishes during the current ramp. The time evolution of the EP density profile is measured with fast-ion Dα (FIDA) spectroscopy. During quiescent periods, the FIDA intensity rises and decays approximately linearly during and after the beam pulse, whereas during strong AE activity, the modulated FIDA intensity amplitude and decay rate decrease, suggesting additional AE-induced radial diffusion. Hardware upgrades are underway to increase spatial resolution and accommodate the full Dα spectrum, providing better constraints when comparing to predictive models. Work supported by the US Department of Energy under SC-G903402, DE-FC02-04ER54698, and DE-AC02-09CH11466.

  12. Measurement of the D alpha spectrum produced by fast ions in DIII-D.

    PubMed

    Luo, Y; Heidbrink, W W; Burrell, K H; Kaplan, D H; Gohil, P

    2007-03-01

    Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit D(alpha) light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of approximately 1 ms, spatial resolution of approximately 5 cm, and energy resolution of approximately 10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the D(alpha) measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.

  13. Measurement of the D{sub {alpha}} spectrum produced by fast ions in DIII-D

    SciTech Connect

    Luo, Y.; Heidbrink, W. W.; Burrell, K. H.; Kaplan, D. H.; Gohil, P.

    2007-03-15

    Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit D{sub {alpha}} light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of {approx}1 ms, spatial resolution of {approx}5 cm, and energy resolution of {approx}10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the D{sub {alpha}} measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.

  14. Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Coates, A. J.; Johnstone, A. D.; Neubauer, Fritz M.

    1993-01-01

    We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possible explanations for this are discussed. We present also a preliminary investigation of the quasilinear velocity-space diffusion of the implanted heavy ion population at G-S using a transport equation including souce, convection, adiabatic compression, and velocity diffusion terms. Resulting distributions are anisotropic, in agreement with observations. We consider theoretically the waves that may be generated by the diffusion process for the observed solar wind conditions. At initial ion injections, waves are generated at omega approximately Omega(sub i) the ion gyrofrequency, and lower frequencies are predicted for diffusion toward a bispherical shell.

  15. Oxygen self-diffusionfast-paths” in titanite single crystals and a general method for deconvolving self-diffusion profiles with “tails”

    NASA Astrophysics Data System (ADS)

    Zhang, X. Y.; Watson, E. B.; Cherniak, D. J.

    2007-03-01

    Like most other minerals, titanite rarely if ever forms perfect crystals. In addition to the point defects that might affect lattice diffusion, there may be extended line- or planar defects along which fast diffusion could occur. During the course of an experimental study of oxygen lattice diffusion in titanite, we found that almost all of the 18O uptake profiles produced in natural titanite crystals departed from the complementary error function solution expected for simple lattice diffusion with a constant surface concentration. Instead, they exhibited "tails" extending deeper into the samples than expected for simple lattice diffusion. The purpose of this contribution is to report on these features—described as "fast-paths" for oxygen diffusion—and outline a method for coping with them in extracting information from diffusion profiles. For both dry and hydrothermal experiments in which the "fast paths" are observed, 18O was used as the diffusant. In dry experiments, the source material was 18O-enriched SiO 2 powder, while 18O-enriched water was used for the hydrothermal experiments. Diffusive uptake profiles of 18O were measured in all cases by nuclear reaction analysis (NRA) using the 18O (p,α) 15N reaction [see Zhang X. Y., Cherniak D. J., and Watson E. B. (2006) Oxygen diffusion in titanite: lattice and fast-path diffusion in single crystals. Chem. Geol.235 105-123]. In our experiments, different sizes of "tails" (with varying 18O concentrations) were observed. Theoretically, under the same temperature and pressure conditions, the sizes of tails should be affected by two factors: the diffusion duration and the defect density. For the same experiment duration, the higher the defect density, the larger the "tail"; for the same defect densities, the longer the diffusion duration, the larger the "tail." The diffusion "tails" could be a result of either planar defects or one-dimensional "pipe" diffusion. AFM imaging of HF etched titanite surfaces confirmed

  16. Investigating the performance of an ion luminescence probe as a multichannel fast-ion energy spectrometer using pulse height analysis

    SciTech Connect

    Zurro, B.; Baciero, A.; Jimenez-Rey, D.; Rodriguez-Barquero, L.; Crespo, M. T.

    2012-10-15

    We investigate the capability of a fast-ion luminescent probe to operate as a pulse height ion energy analyzer. An existing high sensitivity system has been reconfigured as a single channel ion detector with an amplifier to give a bandwidth comparable to the phosphor response time. A digital pulse processing method has been developed to determine pulse heights from the detector signal so as to obtain time-resolved information on the ion energy distribution of the plasma ions lost to the wall of the TJ-II stellarator. Finally, the potential of this approach for magnetic confined fusion plasmas is evaluated by studying representative TJ-II discharges.

  17. Generation of plasma rotation in a tokamak by ion-cyclotron absorption of fast Alfven waves

    SciTech Connect

    F.W. Perkins; R.B. White; P. Bonoli

    2000-06-13

    Control of rotation in tokamak plasmas provides a method for suppressing fine-scale turbulent transport by velocity shear and for stabilizing large-scale magnetohydrodynamic instabilities via a close-fitting conducting shell. The experimental discovery of rotation in a plasma heated by the fast-wave minority ion cyclotron process is important both as a potential control method for a fusion reactor and as a fundamental issue, because rotation arises even though this heating process introduces negligible angular momentum. This paper proposes and evaluates a mechanism which resolves this apparent conflict. First, it is assumed that angular momentum transport in a tokamak is governed by a diffusion equation with a no-slip boundary condition at the plasma surface and with a torque-density source that is a function of radius. When the torque density source consists of two separated regions of positive and negative torque density, a non-zero central rotation velocity results, even when the total angular momentum input vanishes. Secondly, the authors show that localized ion-cyclotron heating can generate regions of positive and negative torque density and consequently central plasma rotation.

  18. An initial measurement of a fast neutral spectrum for ion cyclotron range of frequency heated plasma using two-channel compact neutral particle analyzers in KSTAR

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Wang, S. J.; Park, M.; Kim, S. K.

    2013-11-01

    The accurate measurement of fast neutral particles from high energy ion tails is very important since it is a measure of ion cyclotron range of frequency (ICRF) or neutral beam (NB) ion heating. In KSTAR, fast neutral measurements have been carried out using a compact neutral particle analyzer based on the silicon photo diode since 2010. As a result, the fast neutral spectrum was observed consistent with the ion temperature, diamagnetic energy, and neutron flux in 2011. However, there was fast neutral count beyond the injected neutral beam energy in NB-only heating. Since it is difficult to expect the count unless the temperature is high enough to diffuse the fast ions beyond the beam energy it was required to identify what it is. During the 2012 campaign, the two-channel diode detectors with and without a particle stopper were used to distinguish fast neutral counts and other counts by a hard X-ray or neutrons. As a result, it was confirmed that the high energy component beyond the beam energy originated from a hard X-ray or neutrons. Finally, it was observed that faster neutrals are generated by ICRF heating and enhanced by electron cyclotron heating compared to NB-only heating.

  19. An initial measurement of a fast neutral spectrum for ion cyclotron range of frequency heated plasma using two-channel compact neutral particle analyzers in KSTAR

    SciTech Connect

    Kim, S. H.; Park, M.; Kim, S. K.; Wang, S. J.

    2013-11-15

    The accurate measurement of fast neutral particles from high energy ion tails is very important since it is a measure of ion cyclotron range of frequency (ICRF) or neutral beam (NB) ion heating. In KSTAR, fast neutral measurements have been carried out using a compact neutral particle analyzer based on the silicon photo diode since 2010. As a result, the fast neutral spectrum was observed consistent with the ion temperature, diamagnetic energy, and neutron flux in 2011. However, there was fast neutral count beyond the injected neutral beam energy in NB-only heating. Since it is difficult to expect the count unless the temperature is high enough to diffuse the fast ions beyond the beam energy it was required to identify what it is. During the 2012 campaign, the two-channel diode detectors with and without a particle stopper were used to distinguish fast neutral counts and other counts by a hard X-ray or neutrons. As a result, it was confirmed that the high energy component beyond the beam energy originated from a hard X-ray or neutrons. Finally, it was observed that faster neutrals are generated by ICRF heating and enhanced by electron cyclotron heating compared to NB-only heating.

  20. Strong Pitch-Angle Diffusion of Ring Current Ions in Geomagnetic Storm-Associated Conditions

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Gamayunov, K. V.; Gallagher, D. L.; Spann, J. F.

    2005-01-01

    Do electromagnetic ion cyclotron (EMIC) waves cause strong pitch-angle diffusion of RC ions? This question is the primary motivation of this paper and has been affirmatively answered from the theoretical point of view. The materials that are presented in the Results section show clear evidence that strong pitch-angle diffusion takes place in the inner magnetosphere indicating an important role for the wave-particle interaction mechanism in the formation of RC ions and EMIC waves.

  1. Parametric Dependence Of Fast-ion Transport Events On The National Spherical Torus Experiment

    SciTech Connect

    Fredrickson, Erik; Gorelenkov, N. N.; Podesta, M.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B.; Bortolon, A.

    2014-03-31

    Neutral-beam heated tokamak plasmas commonly have more than one third of the plasma kinetic energy in the non-thermal energetic beam ion population. This population of fast ions heats the plasma, provides some of the current drive, and can affect the stability (positively or negatively) of magnetohydrodynamic instabilities. This population of energetic ions is not in thermodynamic equilibrium, thus there is free-energy available to drive instabilities, which may lead to redistribution of the fast ion population. Understanding under what conditions beam-driven instabilities arise, and the extent of the resulting perturbation to the fast ion population, is important for predicting and eventually demonstrating non-inductive current ramp-up and sustainment in NSTX-U, as well as the performance of future fusion plasma experiments such as ITER. This paper presents an empirical approach towards characterizing the stability boundaries for some common energetic-ion-driven instabilities seen on NSTX.

  2. First results and analysis of collective Thomson scattering (CTS) fast ion distribution measurements on ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Meo, F.; Stejner, M.; Salewski, M.; Bindslev, H.; Eich, T.; Furtula, V.; Korsholm, S. B.; Leuterer, F.; Leipold, F.; Michelsen, P. K.; Moseev, D.; Nielsen, S. K.; Reiter, B.; Stober, J.; Wagner, D.; Woskov, P.; ASDEX Upgrade Team

    2010-05-01

    Experimental knowledge of the fast ion physics in magnetically confined plasmas is essential. The collective Thomson scattering (CTS) diagnostic is capable of measuring localized 1D ion velocity distributions and anisotropies dependent on the angle to the magnetic field. The CTS installed at ASDEX-Upgrade (AUG) uses mm-waves generated by the 1 MW dual frequency gyrotron. The successful commissioning the CTS at AUG enabled first scattering experiments and the consequent milestone of first fast ion distribution measurements on AUG presented in this paper. The first fast ion distribution results have already uncovered some physics of confined fast ions at the plasma centre with off-axis neutral beam heating. However, CTS experiments on AUG H-mode plasmas have also uncovered some unexpected signals not related to scattering that required additional analysis and treatment of the data. These secondary emission signals are generated from the plasma-gyrotron interaction therefore contain additional physics. Despite their existence that complicate the fast ion analysis, they do not prevent the diagnostic's capability to infer the fast ion distribution function on AUG.

  3. Fast ion loss associated with perturbed field by resonant magnetic perturbation coils in KSTAR

    NASA Astrophysics Data System (ADS)

    Kim, Jun Young; Kim, Junghee; Rhee, Tongnyeol; Yoon, S. W.; Park, G. Y.; Jeon, Y. M.; Isobe, M.; Shimizu, A.; Ogawa, K.; Park, J.-K.; Garcia-Munoz, M.

    2013-10-01

    Resonant magnetic perturbation (RMP) is the most promising strategies for ELM mitigation/suppression. However, it has been found through the modeling and the experiments that RMP for the ELM mitigation can enhance the toroidally localized fast ion loss. During KSTAR experimental campaigns in 2011 and 2012, sudden increase or decrease of the fast ion loss has been observed by the scintillator-based fast ion loss detector (FILD) when the RMP is applied. Three-dimensional perturbed magnetic field by RMP coil in vacuum is calculated by Biot-Savart's law embedded in the Lorentz orbit code (LORBIT). The LORBIT code which is based on gyro-orbit following motion has been used for the simulation of the three-dimensional fast ion trajectories in presence of non-axisymmetric magnetic perturbation. It seems the measured fast ion loss rate at the localized position depends on not only the RMP field configuration but also the plasma profile such as safety factor and so on, varying the ratio between radial drift and stochastization of the fat-ion orbits. The simulation results of fast ion orbit under magnetic perturbation w/ and w/o plasma responses will be presented and compared with KSTAR FILD measurement results in various cases.

  4. Secondary Ion Mass Spectrometry for Mg Tracer Diffusion: Issues and Solutions

    SciTech Connect

    Tuggle, Jay; Giordani, Andrew; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Coffey, Kevin; Sohn, Yong Ho; HunterJr., Jerry

    2014-01-01

    A Secondary Ion Mass Spectrometry (SIMS) method has been developed to measure stable Mg isotope tracer diffusion. This SIMS method was then used to calculate Mg self- diffusivities and the data was verified against historical data measured using radio tracers. The SIMS method has been validated as a reliable alternative to the radio-tracer technique for the measurement of Mg self-diffusion coefficients and can be used as a routine method for determining diffusion coefficients.

  5. Effects of heavy ions on the quasi-linear diffusion coefficients from resonant interactions with electromagnetic ion cyclotron waves

    NASA Astrophysics Data System (ADS)

    Jordanova, V. K.; Kozyra, J. U.; Nagy, A. F.

    1996-09-01

    Ion composition measurements provided by recent satellite missions have confirmed the presence of heavy ions in the terrestrial magnetosphere. In order to describe the resonance of energetic ring current particles with electromagnetic ion cyclotron (EMIC) waves in a more realistic terrestrial environment, general expressions are derived that provide quasi-linear diffusion coefficients in a cold plasma containing heavy ions. Cold plasma theory is used as a first approximation. In such plasma, EMIC waves do not propagate in the frequency range between the ion gyrofrequency and the cutoff frequency for each ion component but form multiple stop bands. No interactions occur within the stop bands and the diffusion coefficients are zero over the corresponding frequency intervals. For most of the wave frequencies of interest, the particles in a multicomponent plasma resonate at lower parallel energies than particles in an electron-proton plasma for a given harmonic value. Therefore resonance with a fixed frequency wave occurs at larger pitch angles (lower parallel energies) in a multi-ion than in a proton-electron plasma. As a direct consequence, pitch angle diffusion coefficients for a given energy decrease at small pitch angles and increase at large pitch angles as heavy ions are added to the plasma. The energy and mixed diffusion coefficients change correspondingly. Also, higher harmonics need to be included in the calculations for resonances at higher energies. The pitch angle diffusion lifetimes are calculated for given plasmaspheric and wave parameters corresponding to conditions at a radial distance L=4. The values of the diffusion lifetimes decrease at low energies and increase at high energies in a multi-ion as compared to an electron-proton plasma. As a result, the resonances at lower energies (~ approximately tens of keV) will contribute to the ion precipitation losses from the ring current during geomagnetic storms.

  6. Diffusion Coefficient Values Obtained at Individual Diffuse Ion Events Based on Cluster Observations: What Do We Know About the Physical Process?

    NASA Astrophysics Data System (ADS)

    Kis, Arpad; Scholer, Manfred; Klecker, Berndt; Lucek, Elisabeth; Reme, Henry

    2010-05-01

    We present simultaneous multipoint observations of diffuse ions in front of the Earth's quasi-parallel bow shock. For the analysis we use data provided by the Cluster CIS-HIA particle instrument and data from FGM magnetic field instrument. Several individual diffuse ion events during various solar wind conditions are presented and analysed. The diffusion coefficients at each analysed upstream ion event present unique characteristics especially at lower diffuse ion energies (around 10 keV). We analyse in detail the reasons for the observed differences in the value of the diffusion coefficient; results are also compared with predictions of the theory and the reason for the eventual difference is explained.

  7. Near midplane scintillator-based fast ion loss detector on DIII-D

    SciTech Connect

    Chen, X.; Heidbrink, W. W.; Fisher, R. K.; Pace, D. C.; Chavez, J. A.; Van Zeeland, M. A.; Garcia-Munoz, M.

    2012-10-15

    A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities ({<=}500 kHz). Combined with the first FILD at {approx}45 Degree-Sign below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010)], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius r{sub L}{approx}[1.5-8] cm and pitch angle {alpha}{approx}[35 Degree-Sign -85 Degree-Sign ]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.

  8. Wave Driven Fast Ion Loss in the National Spherical Torus Experiment

    SciTech Connect

    E.D. Fredrickson; C.Z. Cheng; D. Darrow; G. Fu; N.N. Gorelenkov; G. Kramer; S.S. Medley; J. Menard; L. Roquemore; D. Stutman; R.B. White

    2003-08-05

    The study of fast ion instabilities in conventional aspect ratio tokamaks is motivated in large part by their potential to negatively impact the ignition threshold in fusion reactors by causing fast ion losses. Spherical tokamak's (ST), with intrinsically low magnetic fields, are particularly susceptible to fast ion driven instabilities. The 3.5 MeV alpha's from the D-T [deuterium-tritium] fusion reaction in proposed ST reactors will have velocities much higher than the Alfven speed. The Larmor radius of the fusion alphas, normalized to the plasma size, will also be larger than for conventional aspect ratio tokamak reactors. The resulting longer wavelengths of the *AE instabilities will be more effective in driving fast ion loss. The change in magnetic topology also influences the mode structure, as in the case of the Compressional Alfven Eigenmodes (CAE) seen on NSTX.

  9. Near midplane scintillator-based fast ion loss detector on DIII-D.

    PubMed

    Chen, X; Fisher, R K; Pace, D C; García-Muñoz, M; Chavez, J A; Heidbrink, W W; Van Zeeland, M A

    2012-10-01

    A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities (≤500 kHz). Combined with the first FILD at ∼45° below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010)], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius r(L) ∼ [1.5-8] cm and pitch angle α ∼ [35°-85°]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.

  10. Near midplane scintillator-based fast ion loss detector on DIII-Da)

    NASA Astrophysics Data System (ADS)

    Chen, X.; Fisher, R. K.; Pace, D. C.; García-Muñoz, M.; Chavez, J. A.; Heidbrink, W. W.; Van Zeeland, M. A.

    2012-10-01

    A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities (≤500 kHz). Combined with the first FILD at ˜45° below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010), 10.1063/1.3490020], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius rL ˜ [1.5-8] cm and pitch angle α ˜ [35°-85°]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.

  11. Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

    SciTech Connect

    Lin, L.; Brower, D. L.; Ding, W. X.; Anderson, J. K.; Capecchi, W.; Eilerman, S.; Forest, C. B.; Koliner, J. J.; Nornberg, M. D.; Reusch, J.; Sarff, J. S.; Liu, D.

    2014-05-15

    Multiple bursty energetic-particle (EP) driven modes with fishbone-like structure are observed during 1 MW tangential neutral-beam injection in a reversed field pinch (RFP) device. The distinguishing features of the RFP, including large magnetic shear (tending to add stability) and weak toroidal magnetic field (leading to stronger drive), provide a complementary environment to tokamak and stellarator configurations for exploring basic understanding of EP instabilities. Detailed measurements of the EP mode characteristics and temporal-spatial dynamics reveal their influence on fast ion transport. Density fluctuations exhibit a dynamically evolving, inboard-outboard asymmetric spatial structure that peaks in the core where fast ions reside. The measured mode frequencies are close to the computed shear Alfvén frequency, a feature consistent with continuum modes destabilized by strong drive. The frequency pattern of the dominant mode depends on the fast-ion species. Multiple frequencies occur with deuterium fast ions compared to single frequency for hydrogen fast ions. Furthermore, as the safety factor (q) decreases, the toroidal mode number of the dominant EP mode transits from n=5 to n=6 while retaining the same poloidal mode number m=1. The transition occurs when the m=1, n=5 wave-particle resonance condition cannot be satisfied as the fast-ion safety factor (q{sub fi}) decreases. The fast-ion temporal dynamics, measured by a neutral particle analyzer, resemble a classical predator-prey relaxation oscillation. It contains a slow-growth phase arising from the beam fueling followed by a rapid drop when the EP modes peak, indicating that the fluctuation-induced transport maintains a stiff fast-ion density profile. The inferred transport rate is strongly enhanced with the onset of multiple EP modes.

  12. Numerical studies of anomalous fast diffusion in metallic alloys and semiconductors

    NASA Astrophysics Data System (ADS)

    Hasnaoui, A.; Benmakhlouf, A.; Hoummada, A.; Naciri, J. K.; Menai, A.

    2000-08-01

    The so-called anomalous fast diffusion in metallic alloys and semi-conductors is often analysed within an interstitial-substitutional model. The equations used for modelling these mechanisms are reaction-diffusion type whose analytical solutions are available only under drastic simplifications. The dissociative variety of this model is simulated using both finite difference (FD) and Monte Carlo (MC) methods. In MC simulation, diffusion of different species (interstitial impurities B i, substitutional B s, and vacancies V) and reaction jumps occur according to the suitable probabilities which are jump frequencies-dependent. Whereas in FD method, an implicit scheme is used to solve the system of non-linear partial differential equations. In both cases, the finite source conditions have been considered. A good agreement between results obtained by the two methods is found. On the other hand, the double-stages of simulated profiles are found to have similar shapes to those obtained experimentally in Nb(Co) and in GaAs(Zn). The first stage is well analysed by a Gaussian function, whereas the second one is well represented by an erfc type function. Furthermore, a detailed study of the two stages leads to a qualitative agreement with Stolwijk's analysis in two limited cases where the diffusion is vacancy- or foreign interstitial-controlled. However, the effective diffusion coefficients present a quantitative departure from those obtained by Stolwijk's expressions.

  13. Fast and simplified mapping of mean axon diameter using temporal diffusion spectroscopy.

    PubMed

    Xu, Junzhong; Li, Hua; Li, Ke; Harkins, Kevin D; Jiang, Xiaoyu; Xie, Jingping; Kang, Hakmook; Dortch, Richard D; Anderson, Adam W; Does, Mark D; Gore, John C

    2016-04-01

    Mapping axon diameter is of interest for the potential diagnosis and monitoring of various neuronal pathologies. Advanced diffusion-weighted MRI methods have been developed to measure mean axon diameters non-invasively, but suffer major drawbacks that prevent their direct translation into clinical practice, such as complex non-linear data fitting and, more importantly, long scanning times that are usually not tolerable for most human subjects. In the current study, temporal diffusion spectroscopy using oscillating diffusion gradients was used to measure mean axon diameters with high sensitivity to small axons in the central nervous system. Axon diameters have been found to be correlated with a novel metric, DDR⊥ (the rate of dispersion of the perpendicular diffusion coefficient with gradient frequency), which is a model-free quantity that does not require complex data analyses and can be obtained from two diffusion coefficient measurements in clinically relevant times with conventional MRI machines. A comprehensive investigation including computer simulations and animal experiments ex vivo showed that measurements of DDR⊥ agree closely with histological data. In humans in vivo, DDR⊥ was also found to correlate well with reported mean axon diameters in human corpus callosum, and the total scan time was only about 8 min. In conclusion, DDR⊥ may have potential to serve as a fast, simple and model-free approach to map the mean axon diameter of white matter in clinics for assessing axon diameter changes. PMID:27077155

  14. Fast and simplified mapping of mean axon diameter using temporal diffusion spectroscopy.

    PubMed

    Xu, Junzhong; Li, Hua; Li, Ke; Harkins, Kevin D; Jiang, Xiaoyu; Xie, Jingping; Kang, Hakmook; Dortch, Richard D; Anderson, Adam W; Does, Mark D; Gore, John C

    2016-04-01

    Mapping axon diameter is of interest for the potential diagnosis and monitoring of various neuronal pathologies. Advanced diffusion-weighted MRI methods have been developed to measure mean axon diameters non-invasively, but suffer major drawbacks that prevent their direct translation into clinical practice, such as complex non-linear data fitting and, more importantly, long scanning times that are usually not tolerable for most human subjects. In the current study, temporal diffusion spectroscopy using oscillating diffusion gradients was used to measure mean axon diameters with high sensitivity to small axons in the central nervous system. Axon diameters have been found to be correlated with a novel metric, DDR⊥ (the rate of dispersion of the perpendicular diffusion coefficient with gradient frequency), which is a model-free quantity that does not require complex data analyses and can be obtained from two diffusion coefficient measurements in clinically relevant times with conventional MRI machines. A comprehensive investigation including computer simulations and animal experiments ex vivo showed that measurements of DDR⊥ agree closely with histological data. In humans in vivo, DDR⊥ was also found to correlate well with reported mean axon diameters in human corpus callosum, and the total scan time was only about 8 min. In conclusion, DDR⊥ may have potential to serve as a fast, simple and model-free approach to map the mean axon diameter of white matter in clinics for assessing axon diameter changes.

  15. Ion-plasma processes of the production of diffusion aluminide coatings

    NASA Astrophysics Data System (ADS)

    Muboyadzhyan, S. A.

    2010-03-01

    A novel ion-plasma process for ecologically safe formation of diffusion aluminide coatings on a substrate made of a superalloy, which has advantages as compared to the well-known thermodiffusion processes of their production, is described. The ion-plasma process is shown to provide the formation of diffusion aluminide coatings on the surface of a superalloy substrate according to various technologies. Owing to alloying with one or several elements from the series Y, Si, Cr, Hf, B, Co, etc., ion-plasma diffusion coatings have higher protective properties than analogous coatings produced by the traditional methods of powder, slip, and gas-circulating aluminizing.

  16. Effect of low frequency MHD instability on fast ion distribution in NSTX

    NASA Astrophysics Data System (ADS)

    Hao, G.; Liu, D.; Heidbrink, W. W.; Podesta, M.; Fredrickson, E. D.; Bortolon, A.; White, R.; Darrow, D.; Fu, G. Y.; Wang, Z. R.; Kramer, G. J.; Liu, Y. Q.; Tritz, K.

    2015-11-01

    In NSTX spherical tokamak plasmas, the onset of low-frequency MHD modes cause a rapid ~ 25% reduction in the fast-ion D-alpha (FIDA) signal. These, 5-20 kHz instabilities are commonly observed in the early phase of neutral beam heated plasmas that often have reversed magnetic shear in the plasma core. The collapse of the core fast ion density is measured by the vertical FIDA diagnostic. Although the profile flattens, changes in spectral shape are modest, suggesting that much of the distribution function is affected. Meanwhile, a modest increase of fast-ion losses is indicated by the measurements from neutron and fast-ion loss detectors. Moreover, this mode is always accompanied by Compressional Alfven Eigenmode (CAE). This suggests that low-f MHD instabilities can cause the redistribution of fast ions in both real and velocity space. Preliminary simulation results from the MARS-F code suggest that the low-f instability is a coupled infernal-peeling mode. The dependence of the mode's onset on the equilibrium parameters and its effect on the fast ion distribution will be computed, and compared with experimental measurements. Work supported by U.S. DOE DE-AC0209CH11466, DE-FG02-06ER54867, and DE-FG03-02ER54681.

  17. Observation of fast-ion Doppler-shifted cyclotron resonance with shear Alfven waves

    SciTech Connect

    Zhang Yang; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Vincena, S.; Carter, T. A.; Gekelman, W.; Leneman, D.; Pribyl, P.

    2008-10-15

    The Doppler-shifted cyclotron resonance ({omega}-k{sub z}v{sub z}={omega}{sub f}) between fast ions and shear Alfven waves is experimentally investigated ({omega}, wave frequency; k{sub z}, axial wavenumber; v{sub z}, fast-ion axial speed; {omega}{sub f}, fast-ion cyclotron frequency). A test particle beam of fast ions is launched by a Li{sup +} source in the helium plasma of the LArge Plasma Device (LAPD) [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)], with shear Alfven waves (SAW) (amplitude {delta} B/B up to 1%) launched by a loop antenna. A collimated fast-ion energy analyzer measures the nonclassical spreading of the beam, which is proportional to the resonance with the wave. A resonance spectrum is observed by launching SAWs at 0.3-0.8{omega}{sub ci}. Both the magnitude and frequency dependence of the beam-spreading are in agreement with the theoretical prediction using a Monte Carlo Lorentz code that launches fast ions with an initial spread in real/velocity space and random phases relative to the wave. Measured wave magnetic field data are used in the simulation.

  18. Calculation of diffusion coefficients of defects and ions in UO2

    NASA Astrophysics Data System (ADS)

    Kuksin, A. Yu.; Smirnova, D. E.

    2014-06-01

    This paper has presented molecular dynamics calculations of the diffusion coefficients of interstitials, vacancies, and vacancy complexes of oxygen and uranium in UO2, as well as the coefficients of ion diffusion provided by these defects. The interatomic potentials have been chosen by comparing the defect formation energies with data of the DFT + U calculations. The results of the calculations have been compared with experimental data on the annealing of defects and the measurements of self-diffusion coefficients of ions. The limitations of the model of point defects for the description of the self-diffusion in nominally stoichiometric UO2 have been discussed.

  19. Combined energy and pitch angle diffusion of pickup ions at Comet Halley

    NASA Astrophysics Data System (ADS)

    Ye, G.; Cravens, T. E.

    1991-04-01

    It is well known that cometary pickup ions, e.g., H2O(+), OH(+), O(+), CO(+), H(+), initially form a ring-beam distribution in the solar wind reference frame, which is highly unstable to the growth of MHD waves (such as ion-cyclotron waves). The low-frequency magnetic fluctuations (or waves), which were observed upstream of Comet Halley, cannot only pitch-angle-scatter the pickup ions so that the distribution becomes at least partially isotropized, but also stochastically accelerate the ions, resulting in the energetic ion populations observed in the vicinity of Comet Halley. Here, numerical solutions of the quasi-linear diffusion equation were used to investigate the cometary ion pickup process at Comet Halley. Both pitch angle and energy diffusion are taken into account. Many quasi-linear models of cometary pickup ions exist which involve one type of diffusion or the other but not both types at once. It is found that the pitch angle scattering occurs faster than the energy diffusion, as expected. Moreover, the results demonstrate that the distribution of accelerated energetic ions is more isotropic than that of ions which have just been picked up. In fact, the ion distribution function on the initial pickup shell is quite anisotropic, even close to the Comet-Halley bow shock.

  20. Combined energy and pitch angle diffusion of pickup ions at Comet Halley

    NASA Technical Reports Server (NTRS)

    Ye, Gang; Cravens, T. E.

    1991-01-01

    It is well known that cometary pickup ions, e.g., H2O(+), OH(+), O(+), CO(+), H(+), initially form a ring-beam distribution in the solar wind reference frame, which is highly unstable to the growth of MHD waves (such as ion-cyclotron waves). The low-frequency magnetic fluctuations (or waves), which were observed upstream of Comet Halley, cannot only pitch-angle-scatter the pickup ions so that the distribution becomes at least partially isotropized, but also stochastically accelerate the ions, resulting in the energetic ion populations observed in the vicinity of Comet Halley. Here, numerical solutions of the quasi-linear diffusion equation were used to investigate the cometary ion pickup process at Comet Halley. Both pitch angle and energy diffusion are taken into account. Many quasi-linear models of cometary pickup ions exist which involve one type of diffusion or the other but not both types at once. It is found that the pitch angle scattering occurs faster than the energy diffusion, as expected. Moreover, the results demonstrate that the distribution of accelerated energetic ions is more isotropic than that of ions which have just been picked up. In fact, the ion distribution function on the initial pickup shell is quite anisotropic, even close to the Comet-Halley bow shock.

  1. Third-order transport properties of ion-swarms from mobility and diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Koutselos, Andreas D.

    2005-08-01

    A method is presented for the calculation of third order transport properties of ions drifting in gases under the action of an electrostatic field with the use of mobility and ion-diffusion coefficients. The approach is based on a three-temperature treatment of the Boltzmann equation for the ion transport and follows the development of generalized Einstein relations (GER), between diffusion coefficients and mobility. The whole procedure is tested by comparison with numerical and molecular dynamics simulation results for three available alkali ion-noble gas systems. Extension to systems involving internal degrees of freedom and inelastic collisions is shown to follow the development of molecular GER.

  2. Measurement of the positron diffusion constants in polycrystalline molybdenum by the observation of positronium negative ions

    NASA Astrophysics Data System (ADS)

    Suzuki, Takuji; Iida, Simpei; Yamashita, Takashi; Nagashima, Yasuyuki

    2015-06-01

    We have measured the positron diffusion constants in polycrystalline molybdenum by the observation of positronium negative ions (Ps-). The Ps- ions emitted from the sample surface coated with Na were accelerated. The γ-rays from the accelerated Ps- ions were Doppler- shifted and thus the signals of self-annihilation of the Ps- ions were isolated from those of self-annihilation of para-positronium (p-Ps) or pair-annihilation of positrons in the bulk. Clear and reliable values of the diffusion constants have been obtained.

  3. Scintillator-based diagnostic for fast ion loss measurements on DIII-D.

    PubMed

    Fisher, R K; Pace, D C; García-Muñoz, M; Heidbrink, W W; Muscatello, C M; Van Zeeland, M A; Zhu, Y B

    2010-10-01

    A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response (>100 kHz) needed to study energetic ion losses induced by Alfvén eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed.

  4. Scintillator-based diagnostic for fast ion loss measurements on DIII-D

    SciTech Connect

    Fisher, R. K.; Van Zeeland, M. A.; Pace, D. C.; Heidbrink, W. W.; Muscatello, C. M.; Zhu, Y. B.; Garcia-Munoz, M.

    2010-10-15

    A new scintillator-based fast ion loss detector has been installed on DIII-D with the time response (>100 kHz) needed to study energetic ion losses induced by Alfven eigenmodes and other MHD instabilities. Based on the design used on ASDEX Upgrade, the diagnostic measures the pitch angle and gyroradius of ion losses based on the position of the ions striking the two-dimensional scintillator. For fast time response measurements, a beam splitter and fiberoptics couple a portion of the scintillator light to a photomultiplier. Reverse orbit following techniques trace the lost ions to their possible origin within the plasma. Initial DIII-D results showing prompt losses and energetic ion loss due to MHD instabilities are discussed.

  5. Effects of ion dynamics on kinetic structures of the diffusion region during magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Chen, L. J.; Shuster, J. R.; Bessho, N.; Li, G.; Torbert, R. B.; Daughton, W. S.

    2014-12-01

    Based on results from Particle-in-cell (PIC) simulations, we report how ion dynamics influencethe Hall electric field and electron velocity distributions in the diffusion region of magnetic reconnection.The Hall electric field is due to charge imbalance in the diffusion region. At early times, within a few ion cyclotron oscillations from the peak reconnection,electron orbit dynamics dominate, and the Hall electric field layer assumes the width of the electron current layer.As the pre-existing current sheet ions are accelerated and jetted away, inflowing ions form an ion phase space hole structure.The ion hole structure is self-consistently supported by the Hall electric field. The ion meandering orbit width increasesover the course of about 10 ion cyclotron oscillations from several to approximately 40 electron skin depths (two ion skin depths,where the skin depth is based on the initial current sheet density), and theHall electric field layer widens in the same manner to become much broader than the electron diffusion region.The electron velocity distributions upstream of the electron diffusion region and within the regionof counter streaming ions become fragmented as the ion hole establishes itself.The fragmentation is carried into the electron diffusion region, and through the electron outflow jet, leading to a multitude of arcs in the electron distributions at the end of the jet. The broadening of the Hall electric field layer resolves a longstanding discrepancy concerning whether the narrowest width of the layer is of the electron [Chen et al., 2008] or ion [Mozer et al., 2002] scale. The fragmentation of the electron distributions may be due to an electron-ion instability, and is underinvestigation.

  6. Surface diffusion activation energy determination using ion beam microtexturing

    NASA Technical Reports Server (NTRS)

    Rossnagel, S. M.; Robinson, R. S.

    1982-01-01

    The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.

  7. A novel method to determine the diffusion coefficient of hydrogen ion in ruthenium oxide films

    NASA Astrophysics Data System (ADS)

    Yu, George T.; Yen, S. K.

    2002-10-01

    Hydrogen ion diffusion in ruthenium oxide film is of significant interest because of its importance in capacitor, sensor and catalyst applications. In this study, a method based on potential-pH response measurement was used to determine hydrogen ion diffusion in ruthenium oxide films. The drift in the potential-pH response is believed to be due to the hydrated layer, which affects hydrogen ion diffusion onto the oxide film of the pH sensor. Hydrogen ion diffusion coefficient of ruthenium oxide films obtained from this method was 6×10 -14 cm2/ s. The unique feature of the potential-pH response method is its relatively simple experimental procedure, which eliminates complications arising from surface related effects and/or presence of hydrogen traps in membrane such as those found in the conventional permeation method.

  8. Trapped-ion anomalous diffusion coefficient on the basis of single mode saturation

    NASA Astrophysics Data System (ADS)

    Koshi, Y.; Hatayama, A.; Ogasawara, M.

    1982-03-01

    Expressions of the anomalous diffusion coefficient due to the dissipative trapped ion instability (DTII) are derived for the case with and without the effect of magnetic shear. Derivation is made by taking into account of the single mode saturation of the DTII previously obtained numerically. In the absence of the shear effect, the diffusion coefficient is proportional to the squared effective collision frequency of the trapped ions times the squared minor radius of a torus and is much larger than the neoclassical ion heat conductivity. In the presence of the shear effect, the diffusion coefficient is much smaller than the Kadomtsev and Pogutse's value and is the same order of magnitude as the neoclassical ion heat conductivity. Dependences of the diffusion coefficient on the temperature and on the total particle number density are rather complicated due to the additional spectral cut-off.

  9. Front propagation in cellular flows for fast reaction and small diffusivity.

    PubMed

    Tzella, Alexandra; Vanneste, Jacques

    2014-07-01

    We investigate the influence of fluid flows on the propagation of chemical fronts arising in Fisher-Kolmogorov-Petrovsky-Piskunov (FKPP) type models. We develop an asymptotic theory for the front speed in a cellular flow in the limit of small molecular diffusivity and fast reaction, i.e., large Péclet (Pe) and Damköhler (Da) numbers. The front speed is expressed in terms of a periodic path--an instanton--that minimizes a certain functional. This leads to an efficient procedure to calculate the front speed, and to closed-form expressions for (logPe)(-1) ≪ Da ≪ Pe and for Da ≫ Pe. Our theoretical predictions are compared with (i) numerical solutions of an eigenvalue problem and (ii) simulations of the advection-diffusion-reaction equation. PMID:25122240

  10. Fast dynamics and relaxation of colloidal drops during the drying process using multispeckle diffusing wave spectroscopy.

    PubMed

    Lee, Jeong Yong; Hwang, Ji Won; Jung, Hyun Wook; Kim, Sung Hyun; Lee, Seong Jae; Yoon, Kisun; Weitz, David A

    2013-01-22

    The fast dynamics generated by the Brownian motion of particles in colloidal drops, and the related relaxation during drying, which play key roles in suspension systems, were investigated incorporating multispeckle diffusing wave spectroscopy (MSDWS). MSDWS equipment was implemented to analyze the relaxation properties of suspensions under a nonergodic and nonstationary drying process, which cannot be elucidated by conventional light scattering methods, such as dynamic light scattering and diffusing wave spectroscopy. Rapid particle movement can be identified by the characteristic relaxation time, which is closely related to the Brownian motion due to thermal fluctuations of the particles. In the compacting stage of the drying process, the characteristic relaxation time increased gradually with the drying time because the particles in the colloidal drop were constrained by themselves. Moreover, variations of the initial concentration and particle size considerably affected the complete drying time and characteristic relaxation time, producing a shorter relaxation time for a low concentrated suspension with small particles. PMID:23281633

  11. Open photoacoustic cell for thermal diffusivity measurements of a fast hardening cement used in dental restoring

    NASA Astrophysics Data System (ADS)

    Astrath, F. B. G.; Astrath, N. G. C.; Baesso, M. L.; Bento, A. C.; Moraes, J. C. S.; Santos, A. D.

    2012-01-01

    Thermal diffusivity and conductivity of dental cements have been studied using open photoacoustic cell (OPC). The samples consisted of fast hardening cement named CER, developed to be a root-end filling material. Thermal characterization was performed in samples with different gel/powder ratio and particle sizes and the results were compared to the ones from commercial cements. Complementary measurements of specific heat and mass density were also performed. The results showed that the thermal diffusivity of CER tends to increase smoothly with gel volume and rapidly against particle size. This behavior was linked to the pores size and their distribution in the samples. The OPC method was shown to be a valuable way in deriving thermal properties of porous material.

  12. Hybrid stochastic simulation of reaction-diffusion systems with slow and fast dynamics

    SciTech Connect

    Strehl, Robert; Ilie, Silvana

    2015-12-21

    In this paper, we present a novel hybrid method to simulate discrete stochastic reaction-diffusion models arising in biochemical signaling pathways. We study moderately stiff systems, for which we can partition each reaction or diffusion channel into either a slow or fast subset, based on its propensity. Numerical approaches missing this distinction are often limited with respect to computational run time or approximation quality. We design an approximate scheme that remedies these pitfalls by using a new blending strategy of the well-established inhomogeneous stochastic simulation algorithm and the tau-leaping simulation method. The advantages of our hybrid simulation algorithm are demonstrated on three benchmarking systems, with special focus on approximation accuracy and efficiency.

  13. Finite Time Extinction for Stochastic Sign Fast Diffusion and Self-Organized Criticality

    NASA Astrophysics Data System (ADS)

    Gess, Benjamin

    2015-04-01

    We prove finite time extinction for stochastic sign fast diffusion equations driven by linear multiplicative space-time noise, corresponding to the Bak-Tang-Wiesenfeld model for self-organized criticality. This solves a problem posed and left open in several works: (Barbu, Methods Appl Sci 36:1726-1733, 2013; Röckner and Wang, J Lond Math Soc (2) 87:545-560, 2013; Barbu et al. J Math Anal Appl 389:147-164, 2012; Barbu and Röckner, Comm Math Phys 311:539-555, 2012; Barbu et al., Comm Math Phys 285:901-923, 2009, C R Math Acad Sci Paris 347(1-2):81-84, 2009). The highly singular-degenerate nature of the drift in interplay with the stochastic perturbation causes the need for new methods in the analysis of mass diffusion, and several new estimates and techniques are introduced.

  14. Fast-ion Characteristics in Colliding FRCs with Neutral Beam Injection

    NASA Astrophysics Data System (ADS)

    Clary, Ryan; Smirnov, Artem; Korepanov, Sergey; Dettrick, Sean; TAE Team Team

    2011-10-01

    Tri Alpha Energy's C-2 device aims to explore confinement properties of colliding Field-Reversed Configuration (FRC) plasmas, augmented with neutral beam injection. Naturally, it is desirable to understand the general characteristics of the resulting fast- ion population. For this purpose, several 16 channel silicone-based Neutral Particle Bolometers (NPB) have been designed and installed on the C-2 device, measuring charge-exchanged fast-neutrals originating from the fast-ion population. We present results illustrating the effects on fast-ions from wall recycling and from the n = 2 rotation instability. In addition we find good agreement between NPB measurements and Monte Carlo simulations. The NPB diagnostics are a spatially resolved complement to the energy resolved Neutral Particle Analyzers installed on the C-2 device.

  15. Development towards a fast ion loss detector for the reversed field pinch

    NASA Astrophysics Data System (ADS)

    Bonofiglo, P. J.; Anderson, J. K.; Almagri, A. F.; Kim, J.; Clark, J.; Capecchi, W.; Sears, S. H.; Egedal, J.

    2016-11-01

    A fast ion loss detector has been constructed and implemented on the Madison Symmetric Torus (MST) to investigate energetic ion losses and transport due to energetic particle and MHD instabilities. The detector discriminates particle orbits solely on pitch and consists of two thin-foil, particle collecting plates that are symmetric with respect to the device aperture. One plate collects fast ion signal, while the second aids in the minimization of background and noise effects. Initial measurements are reported along with suggestions for the next design phase of the detector.

  16. Calibration techniques for fast-ion D{sub {alpha}} diagnostics

    SciTech Connect

    Heidbrink, W. W.; Bortolon, A.; Muscatello, C. M.; Ruskov, E.; Grierson, B. A.; Podesta, M.

    2012-10-15

    Fast-ion D{sub {alpha}} measurements are an application of visible charge-exchange recombination (CER) spectroscopy that provide information about the energetic ion population. Like other CER diagnostics, the standard intensity calibration is obtained with an integrating sphere during a vacuum vessel opening. An alternative approach is to create plasmas where the fast-ion population is known, then calculate the expected signals with a synthetic diagnostic code. The two methods sometimes agree well but are discrepant in other cases. Different background subtraction techniques and simultaneous measurements of visible bremsstrahlung and of beam emission provide useful checks on the calibrations and calculations.

  17. Conceptual design of a fast-ion D-alpha diagnostic on experimental advanced superconducting tokamak

    SciTech Connect

    Huang, J. Wan, B.; Hu, L.; Hu, C.; Heidbrink, W. W.; Zhu, Y.; Hellermann, M. G. von; Gao, W.; Wu, C.; Li, Y.; Fu, J.; Lyu, B.; Yu, Y.; Ye, M.; Shi, Y.

    2014-11-15

    To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been planned and is presently under development on Experimental Advanced Superconducting Tokamak. The greatest challenges for the design of a FIDA diagnostic are its extremely low intensity levels, which are usually significantly below the continuum radiation level and several orders of magnitude below the bulk-ion thermal charge-exchange feature. Moreover, an overlaying Motional Stark Effect (MSE) feature in exactly the same wavelength range can interfere. The simulation of spectra code is used here to guide the design and evaluate the diagnostic performance. The details for the parameters of design and hardware are presented.

  18. Conceptual design of a fast-ion D-alpha diagnostic on experimental advanced superconducting tokamak

    NASA Astrophysics Data System (ADS)

    Huang, J.; Heidbrink, W. W.; Wan, B.; von Hellermann, M. G.; Zhu, Y.; Gao, W.; Wu, C.; Li, Y.; Fu, J.; Lyu, B.; Yu, Y.; Shi, Y.; Ye, M.; Hu, L.; Hu, C.

    2014-11-01

    To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been planned and is presently under development on Experimental Advanced Superconducting Tokamak. The greatest challenges for the design of a FIDA diagnostic are its extremely low intensity levels, which are usually significantly below the continuum radiation level and several orders of magnitude below the bulk-ion thermal charge-exchange feature. Moreover, an overlaying Motional Stark Effect (MSE) feature in exactly the same wavelength range can interfere. The simulation of spectra code is used here to guide the design and evaluate the diagnostic performance. The details for the parameters of design and hardware are presented.

  19. Conceptual design of a fast-ion D-alpha diagnostic on experimental advanced superconducting tokamak.

    PubMed

    Huang, J; Heidbrink, W W; Wan, B; von Hellermann, M G; Zhu, Y; Gao, W; Wu, C; Li, Y; Fu, J; Lyu, B; Yu, Y; Shi, Y; Ye, M; Hu, L; Hu, C

    2014-11-01

    To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been planned and is presently under development on Experimental Advanced Superconducting Tokamak. The greatest challenges for the design of a FIDA diagnostic are its extremely low intensity levels, which are usually significantly below the continuum radiation level and several orders of magnitude below the bulk-ion thermal charge-exchange feature. Moreover, an overlaying Motional Stark Effect (MSE) feature in exactly the same wavelength range can interfere. The simulation of spectra code is used here to guide the design and evaluate the diagnostic performance. The details for the parameters of design and hardware are presented.

  20. Effects of ions on the diffusion coefficient of water in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Gao, Xiang; Zhao, Tianshou; Li, Zhigang

    2014-08-01

    In this work, we investigate the ion effects on the diffusion of water in carbon nanotubes through molecular dynamics simulations. The diffusion coefficient of water molecules Dw in the presence of cations (Na+ and K+) and anions (F-, Cl-, and Br-) are calculated by changing the ion concentration. The dependence of Dw on the ion concentration is found highly nonlinear and distinct for different ions. For positively charged systems, as the ion concentration is varied, Dw assumes a maximum under the competition between the number and orientation changes of free OH bonds and the effects of ionic hydration. For negatively charged systems, however, Dw decreases monotonously with increasing ion concentration for F-. For Cl- and Br-, Dw reaches the minima at certain ion concentrations and then gently increases. The different behaviors of Dw in the presence of different anions are caused by the stability change of water hydrogen bonds due to ionic hydration.

  1. Sawtooth control using beam ions accelerated by fast waves in the DIII-D tokamak

    SciTech Connect

    Choi, M.; Turnbull, A. D.; Chan, V. S.; Chu, M. S.; Lao, L. L.; Jeon, Y. M.; Li, G.; Ren, Q.; Pinsker, R. I.

    2007-11-15

    The accuracy of the Porcelli sawtooth model is evaluated using realistic numerical calculations for a DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] experiment with neutral beam injection and fast wave heating. Simulation results confirm that beam ions accelerated by the fast waves play a crucial role in delaying the normal sawtooth crash and inducing giant sawteeth with large amplitude and long period. A single giant sawtooth period was analyzed in detail in an effort to evaluate the efficacy of the Porcelli model in quantitatively predicting a particular sawtooth crash by evaluating the model through the sawtooth period using equilibria reconstructed from the discharge data. The kinetic stabilizing contribution of fast trapped ions is found to depend strongly on both the experimentally reconstructed magnetic shear at the q=1 surface (s{sub 1}) and the calculated poloidal beta of trapped beam ions inside the q=1 surface. To within estimates of the error from the equilibrium reconstructions and the simulation fast ion particle statistics, the results are consistent with the observed sawtooth crash. The calculations indicate that the sawtooth crash is ultimately triggered by the resistive kink in the ion-kinetic regime after the stabilizing contribution from the fast ions is reduced due to an increase in s{sub 1} as the discharge evolves.

  2. Improved Collective Thomson Scattering measurements of fast ions at ASDEX upgrade

    SciTech Connect

    Rasmussen, J.; Nielsen, S. K.; Stejner, M.; Salewski, M.; Jacobsen, A. S.; Korsholm, S. B.; Leipold, F.; Meo, F.; Michelsen, P. K.; Schubert, M.; Stober, J.; Tardini, G.; Wagner, D.; Collaboration: ASDEX Upgrade Team

    2014-08-21

    Understanding the behaviour of the confined fast ions is important in both current and future fusion experiments. These ions play a key role in heating the plasma and will be crucial for achieving conditions for burning plasma in next-step fusion devices. Microwave-based Collective Thomson Scattering (CTS) is well suited for reactor conditions and offers such an opportunity by providing measurements of the confined fast-ion distribution function resolved in space, time and 1D velocity space. We currently operate a CTS system at ASDEX Upgrade using a gyrotron which generates probing radiation at 105 GHz. A new setup using two independent receiver systems has enabled improved subtraction of the background signal, and hence the first accurate characterization of fast-ion properties. Here we review this new dual-receiver CTS setup and present results on fast-ion measurements based on the improved background characterization. These results have been obtained both with and without NBI heating, and with the measurement volume located close to the centre of the plasma. The measurements agree quantitatively with predictions of numerical simulations. Hence, CTS studies of fast-ion dynamics at ASDEX Upgrade are now feasible. The new background subtraction technique could be important for the design of CTS systems in other fusion experiments.

  3. Fusion yield rate recovery by escaping hot-spot fast ions in the neighboring fuel layer

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; McDevitt, C. J.; Guo, Zehua; Berk, H. L.

    2014-02-01

    Free-streaming loss by fast ions can deplete the tail population in the hot spot of an inertial confinement fusion (ICF) target. Escaping fast ions in the neighboring fuel layer of a cryogenic target can produce a surplus of fast ions locally. In contrast to the Knudsen layer effect that reduces hot-spot fusion reactivity due to tail ion depletion, the inverse Knudsen layer effect increases fusion reactivity in the neighboring fuel layer. In the case of a burning ICF target in the presence of significant hydrodynamic mix which aggravates the Knudsen layer effect, the yield recovery largely compensates for the yield reduction. For mix-dominated sub-ignition targets, the yield reduction is the dominant process.

  4. Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

    NASA Astrophysics Data System (ADS)

    Lin, Liang

    2013-10-01

    Multiple bursty energetic-particle (EP) modes with fishbone-like structures are observed during 1 MW tangential neutral-beam injection into MST reversed field pinch (RFP) plasmas. The distinguishing features of the RFP, including large magnetic shear (tending to add stability) and weak toroidal magnetic field (leading to large fast ion beta and stronger drive), provide a complementary environment to tokamak and stellarator configurations for exploring basic understanding of these instabilities. Detailed measurements of the EP mode characteristics and temporal-spatial dynamics reveal their influence on fast ion transport and interaction with global tearing modes. Internal magnetic field fluctuations associated with the EP modes are directly observed for the first time by Faraday-effect polarimetry (frequency ~ 90 kHz and amplitude ~ 2 G). Simultaneously measured density fluctuations exhibit a dynamically evolving and asymmetric spatial structure that peaks near the core where fast ions reside and shifts outward as the instability evolves. Furthermore, the EP mode frequencies appear at ~k∥VA , consistent with continuum modes destabilized by strong drive. The fast-ion temporal dynamics, measured by a neutral particle analyzer, resemble a classical predator-prey relaxation oscillation. It contains a slow-growing phase arising from the beam fueling followed by a rapid drop (~ 15 %) when the EP modes peak, indicating the fluctuation-induced transport maintains a stiff fast-ion density profile. The inferred transport rate is strongly enhanced (× 2) with the onset of multiple nonlinearly-interacting EP modes. The fast ions also impact global tearing modes, reducing their amplitudes by up to 65%. This mode reduction is lessened following the EP-bursts, further evidence for fast ion redistribution that weakens the suppression mechanism. Possible tearing mode suppression mechanisms will be discussed. Work supported by US DoE.

  5. Desorption yield for valine as induced by fast heavy ions

    SciTech Connect

    Beining, P.; Scheer, J.; Nieschler, E.; Nees, B.; Voit, H.

    1988-11-01

    The dependence of the desorption yield for the amino acid valine on the energy of different MeV primary ions has been measured. The primary-ion energies cover a relatively large range with corresponding energy losses between 2 and 55 keV/(..mu..g/cm/sup 2/). The observed energy dependence can be understood in the framework of a simple macroscopic model.

  6. Electron currents and heating in the ion diffusion region of asymmetric reconnection

    NASA Astrophysics Data System (ADS)

    Graham, D. B.; Khotyaintsev, Yu. V.; Norgren, C.; Vaivads, A.; André, M.; Lindqvist, P.-A.; Marklund, G. T.; Ergun, R. E.; Paterson, W. R.; Gershman, D. J.; Giles, B. L.; Pollock, C. J.; Dorelli, J. C.; Avanov, L. A.; Lavraud, B.; Saito, Y.; Magnes, W.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.; Burch, J. L.

    2016-05-01

    In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

  7. Phase space effects on fast ion distribution function modeling in tokamaks

    DOE PAGESBeta

    Podesta, M.; Gorelenkova, M.; Fredrickson, E. D.; Gorelenkov, N. N.; White, R. B.

    2016-04-14

    Here, integrated simulations of tokamak discharges typically rely on classical physics to model energetic particle (EP) dynamics. However, there are numerous cases in which energetic particles can suffer additional transport that is not classical in nature. Examples include transport by applied 3D magnetic perturbations and, more notably, by plasma instabilities. Focusing on the effects of instabilities,ad-hocmodels can empirically reproduce increased transport, but the choice of transport coefficients is usually somehow arbitrary. New approaches based on physics-based reduced models are being developed to address those issues in a simplified way, while retaining a more correct treatment of resonant wave-particle interactions. Themore » kick model implemented in the tokamaktransport code TRANSP is an example of such reduced models. It includes modifications of the EP distribution by instabilities in real and velocity space, retaining correlations between transport in energy and space typical of resonant EP transport. The relevance of EP phase space modifications by instabilities is first discussed in terms of predicted fast ion distribution. Results are compared with those from a simple, ad-hoc diffusive model. It is then shown that the phase-space resolved model can also provide additional insight into important issues such as internal consistency of the simulations and mode stability through the analysis of the power exchanged between energetic particles and the instabilities.« less

  8. Whole-cell imaging at nanometer resolutions using fast and slow focused helium ions.

    PubMed

    Chen, Xiao; Udalagama, Chammika N B; Chen, Ce-Belle; Bettiol, Andrew A; Pickard, Daniel S; Venkatesan, T; Watt, Frank

    2011-10-01

    Observations of the interior structure of cells and subcellular organelles are important steps in unraveling organelle functions. Microscopy using helium ions can play a major role in both surface and subcellular imaging because it can provide subnanometer resolutions at the cell surface for slow helium ions, and fast helium ions can penetrate cells without a significant loss of resolution. Slow (e.g., 10-50 keV) helium ion beams can now be focused to subnanometer dimensions (∼0.25 nm), and keV helium ion microscopy can be used to image the surfaces of cells at high resolutions. Because of the ease of neutralizing the sample charge using a flood electron beam, surface charging effects are minimal and therefore cell surfaces can be imaged without the need for a conducting metallic coating. Fast (MeV) helium ions maintain a straight path as they pass through a cell. Along the ion trajectory, the helium ion undergoes multiple electron collisions, and for each collision a small amount of energy is lost to the scattered electron. By measuring the total energy loss of each MeV helium ion as it passes through the cell, we can construct an energy-loss image that is representative of the mass distribution of the cell. This work paves the way to use ions for whole-cell investigations at nanometer resolutions through structural, elemental (via nuclear elastic backscattering), and fluorescence (via ion induced fluorescence) imaging.

  9. Negative Ion Drift Velocity and Longitudinal Diffusion in Mixtures of Carbon Disulfide and Methane

    NASA Technical Reports Server (NTRS)

    Dion, Michael P.; Son, S.; Hunter, S. D.; deNolfo, G. A.

    2011-01-01

    Negative ion drift velocity and longitudinal diffusion has been measured for gas mixtures of carbon disulfide (CS2) and methane (CH4)' Measurements were made as a function of total pressure, CS2 partial pressure and electric field. Constant mobility and thermal-limit longitudinal diffusion is observed for all gas mixtures tested. Gas gain for some of the mixtures is also included.

  10. Secondary ion mass spectroscopy determination of oxygen diffusion coefficient in heavily Sb doped Si

    NASA Astrophysics Data System (ADS)

    Pagani, M.

    1990-10-01

    The diffusion coefficient of oxygen in heavily antimony doped Czochralski Si was measured in the temperature range 950-1100 °C by using secondary ion mass spectroscopy (SIMS). The diffusion coefficient, obtained from SIMS oxygen concentration profiles in samples submitted to out diffusion, shows no dependence on antimony concentration. The combined data give an activation energy of 2.68 eV, which is in good agreement with published results.

  11. Correlation of Local Structure and Diffusion Pathways in the Modulated Anisotropic Oxide Ion Conductor CeNbO(4.25).

    PubMed

    Pramana, Stevin S; Baikie, Tom; An, Tao; Tucker, Matthew G; Wu, Ji; Schreyer, Martin K; Wei, Fengxia; Bayliss, Ryan D; Kloc, Christian L; White, Timothy J; Horsfield, Andrew P; Skinner, Stephen J

    2016-02-01

    CeNbO4.25 is reported to exhibit fast oxygen ion diffusion at moderate temperatures, making this the prototype of a new class of ion conductor with applications in a range of energy generation and storage devices. To date, the mechanism by which this ion transport is achieved has remained obscure, in part due to the long-range commensurately modulated structural motif. Here we show that CeNbO4.25 forms with a unit cell ∼12 times larger than the stoichiometric tetragonal parent phase of CeNbO4 as a result of the helical ordering of Ce(3+) and Ce(4+) ions along z. Interstitial oxygen ion incorporation leads to a cooperative displacement of the surrounding oxygen species, creating interlayer "NbO6" connectivity by extending the oxygen coordination number to 7 and 8. Molecular dynamic simulations suggest that fast ion migration occurs predominantly within the xz plane. It is concluded that the oxide ion diffuses anisotropically, with the major migration mechanism being intralayer; however, when obstructed, oxygen can readily move to an adjacent layer along y via alternate lower energy barrier pathways. PMID:26771687

  12. Molecular Simulations of Water and Ion Diffusion in Nanosized Mineral Fractures

    SciTech Connect

    Kerisit, Sebastien N.; Liu, Chongxuan

    2009-02-01

    Molecular dynamics simulations were carried out to investigate the effects of confinement and of the presence of the mineral surface on the diffusion of water and electrolyte ions in nano-sized mineral fractures. Feldspar was used as a representative mineral because recent studies found that it is an important mineral that hosts contaminants within its intragrain fractures at US Department of Energy Hanford site (1, 2). Several properties of the mineral-water interface were varied, such as the fracture width, the ionic strength of the contacting solution, and the surface charge, to provide atomic-level insights into the diffusion of ions and contaminants within intragrain regions. In each case, the self-diffusion coefficient of water and that of the electrolyte ions were computed as a function of distance from the mineral surface. Our calculations reveal a 2.0 to 2.5 nm interfacial region within which the self-diffusion coefficient of water and that of the electrolyte ions decrease as the diffusing species approach the surface. As a result of the extent of the interfacial region, water and electrolyte ions are predicted to never reach bulk-like diffusion in fractures narrower than approximately 5 nm. A density weighted, averaged diffusion coefficient was computed as a function of fracture width and indicated that the surface effects only become negligible for fractures several tens of nanometers wide. The calculations also showed that, within 1.2 nm from the surface, the diffusion of electrolyte ions is affected by the presence of the mineral surface to a greater extent than that of water. The molecular dynamics results improve our conceptual models of ion transport in nano-scale pore regions surrounded by mineral surfaces in porous media.

  13. Fast silicon photomultiplier improves signal harvesting and reduces complexity in time-domain diffuse optics.

    PubMed

    Mora, Alberto Dalla; Martinenghi, Edoardo; Contini, Davide; Tosi, Alberto; Boso, Gianluca; Durduran, Turgut; Arridge, Simon; Martelli, Fabrizio; Farina, Andrea; Torricelli, Alessandro; Pifferi, Antonio

    2015-06-01

    We present a proof of concept prototype of a time-domain diffuse optics probe exploiting a fast Silicon PhotoMultiplier (SiPM), featuring a timing resolution better than 80 ps, a fast tail with just 90 ps decay time-constant and a wide active area of 1 mm2. The detector is hosted into the probe and used in direct contact with the sample under investigation, thus providing high harvesting efficiency by exploiting the whole SiPM numerical aperture and also reducing complexity by avoiding the use of cumbersome fiber bundles. Our tests also demonstrate high accuracy and linearity in retrieving the optical properties and suitable contrast and depth sensitivity for detecting localized inhomogeneities. In addition to a strong improvement in both instrumentation cost and size with respect to legacy solutions, the setup performances are comparable to those of state-of-the-art time-domain instrumentation, thus opening a new way to compact, low-cost and high-performance time-resolved devices for diffuse optical imaging and spectroscopy. PMID:26072763

  14. Accelerated ions from pulsed-power-driven fast plasma flow in perpendicular magnetic field

    NASA Astrophysics Data System (ADS)

    Takezaki, Taichi; Takahashi, Kazumasa; Sasaki, Toru; Kikuchi, Takashi; Harada, Nob.

    2016-06-01

    To understand the interaction between fast plasma flow and perpendicular magnetic field, we have investigated the behavior of a one-dimensional fast plasma flow in a perpendicular magnetic field by a laboratory-scale experiment using a pulsed-power discharge. The velocity of the plasma flow generated by a tapered cone plasma focus device is about 30 km/s, and the magnetic Reynolds number is estimated to be 8.8. After flow through the perpendicular magnetic field, the accelerated ions are measured by an ion collector. To clarify the behavior of the accelerated ions and the electromagnetic fields, numerical simulations based on an electromagnetic hybrid particle-in-cell method have been carried out. The results show that the behavior of the accelerated ions corresponds qualitatively to the experimental results. Faster ions in the plasma flow are accelerated by the induced electromagnetic fields modulated with the plasma flow.

  15. Ion movement through gramicidin A channels. Studies on the diffusion-controlled association step.

    PubMed Central

    Andersen, O S

    1983-01-01

    The permeability characteristics of gramicidin A channels are generally considered to reflect accurately the intrinsic properties of the channels themselves; i.e., the aqueous convergence regions are assumed to be negligible barriers for ion movement through the channels. The validity of this assumption has been examined by an analysis of gramicidin A single-channel current-voltage characteristics up to very high potentials (500 mV). At low permeant ion concentrations the currents approach a voltage-independent limiting value, whose magnitude is proportional to the permeant ion concentration. The magnitude of this current is decreased by experimental maneuvers that decrease the aqueous diffusion coefficient of the ions. It is concluded that the magnitude of this limiting current is determined by the diffusive ion movement through the aqueous convergence regions up to the channel entrance. It is further shown that the small-signal (ohmic) permeability properties also reflect the existence of the aqueous diffusion limitation. These results have considerable consequences for the construction of kinetic models for ion movement through gramicidin A channels. It is shown that the simple two-site-three-barrier model commonly used to interpret gramicidin A permeability data may lead to erroneous conclusions, as biionic potentials will be concentration dependent even when the channel is occupied by at most one ion. The aqueous diffusion limitation must be considered explicitly in the analysis of gramicidin A permeability characteristics. Some implications for understanding the properties of ion-conducting channels in biological membranes will be considered. PMID:6188502

  16. Multi-view fast-ion D-alpha spectroscopy diagnostic at ASDEX Upgrade

    SciTech Connect

    Geiger, B.; Dux, R.; McDermott, R. M.; Potzel, S.; Reich, M.; Ryter, F.; Weiland, M.; Wünderlich, D.; Garcia-Munoz, M.; Collaboration: ASDEX Upgrade Team

    2013-11-15

    A novel fast-ion D-alpha (FIDA) diagnostic that is based on charge exchange spectroscopy has been installed at ASDEX Upgrade. The diagnostic uses a newly developed high-photon-throughput spectrometer together with a low-noise EM-CCD camera that allow measurements with 2 ms exposure time. Absolute intensities are obtained by calibrating the system with an integrating sphere and the wavelength dependence is determined to high accuracy using a neon lamp. Additional perturbative contributions to the spectra, such as D{sub 2}-molecular lines, the Stark broadened edge D-alpha emission, and passive FIDA radiation have been identified and can be subtracted or avoided experimentally. The FIDA radiation from fast deuterium ions after charge exchange reactions can therefore be analyzed continuously without superimposed line emissions at large Doppler shifts. Radial information on the fast ions is obtained from radially distributed lines of sight. The investigation of the fast-ion velocity distribution is possible due to three different viewing geometries. The independent viewing geometries access distinct parts of the fast-ion velocity space and make tomographic reconstructions possible.

  17. Velocity-space tomography of the fast-ion distribution function

    NASA Astrophysics Data System (ADS)

    Jacobsen, Asger Schou; Salewski, Mirko; Geiger, Benedikt; García-Muñoz, Manuel; Heidbrink, William; Korsholm, Søren Bang; Leipold, Frank; Madsen, Jens; Michelsen, Poul; Moseev, Dmitry; Nielsen, Stefan Kragh; Rasmussen, Jesper; Stejner, Morten; Tardini, Giovanni; ASDEX Upgrade Team

    2013-10-01

    Fast ions play an important role in heating the plasma in a magnetic confinement fusion device. Fast-ion Dα(FIDA) spectroscopy diagnoses fast ions in small measurement volumes. Spectra measured by a FIDA diagnostic can be related to the 2D fast-ion velocity distribution function. A single FIDA view probes certain regions in velocity-space, determined by the geometry of the set-up. Exploiting this, the fast-ion distribution function can be inferred using a velocity-space tomography method. This poster contains a tomography calculated from measured spectra from three different FIDA views at ASDEX Upgrade. The quality of the tomography improves with the number of FIDA views simultaneously measuring the same volume. To investigate the potential benefits of including additional views (up to 18), tomographies are inferred from synthetic spectra calculated from a simulated distribution function. The number of experimentally available views can be increased by combining different types of diagnostics in a joint velocity-space tomography. Using this, up to 7 views are available at ASDEX Upgrade from 2014.

  18. From Fast Fluorescence Imaging to Molecular Diffusion Law on Live Cell Membranes in a Commercial Microscope

    PubMed Central

    Di Rienzo, Carmine; Gratton, Enrico; Beltram, Fabio; Cardarelli, Francesco

    2014-01-01

    It has become increasingly evident that the spatial distribution and the motion of membrane components like lipids and proteins are key factors in the regulation of many cellular functions. However, due to the fast dynamics and the tiny structures involved, a very high spatio-temporal resolution is required to catch the real behavior of molecules. Here we present the experimental protocol for studying the dynamics of fluorescently-labeled plasma-membrane proteins and lipids in live cells with high spatiotemporal resolution. Notably, this approach doesn’t need to track each molecule, but it calculates population behavior using all molecules in a given region of the membrane. The starting point is a fast imaging of a given region on the membrane. Afterwards, a complete spatio-temporal autocorrelation function is calculated correlating acquired images at increasing time delays, for example each 2, 3, n repetitions. It is possible to demonstrate that the width of the peak of the spatial autocorrelation function increases at increasing time delay as a function of particle movement due to diffusion. Therefore, fitting of the series of autocorrelation functions enables to extract the actual protein mean square displacement from imaging (iMSD), here presented in the form of apparent diffusivity vs average displacement. This yields a quantitative view of the average dynamics of single molecules with nanometer accuracy. By using a GFP-tagged variant of the Transferrin Receptor (TfR) and an ATTO488 labeled 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine (PPE) it is possible to observe the spatiotemporal regulation of protein and lipid diffusion on µm-sized membrane regions in the micro-to-milli-second time range. PMID:25350683

  19. From fast fluorescence imaging to molecular diffusion law on live cell membranes in a commercial microscope.

    PubMed

    Di Rienzo, Carmine; Gratton, Enrico; Beltram, Fabio; Cardarelli, Francesco

    2014-01-01

    It has become increasingly evident that the spatial distribution and the motion of membrane components like lipids and proteins are key factors in the regulation of many cellular functions. However, due to the fast dynamics and the tiny structures involved, a very high spatio-temporal resolution is required to catch the real behavior of molecules. Here we present the experimental protocol for studying the dynamics of fluorescently-labeled plasma-membrane proteins and lipids in live cells with high spatiotemporal resolution. Notably, this approach doesn't need to track each molecule, but it calculates population behavior using all molecules in a given region of the membrane. The starting point is a fast imaging of a given region on the membrane. Afterwards, a complete spatio-temporal autocorrelation function is calculated correlating acquired images at increasing time delays, for example each 2, 3, n repetitions. It is possible to demonstrate that the width of the peak of the spatial autocorrelation function increases at increasing time delay as a function of particle movement due to diffusion. Therefore, fitting of the series of autocorrelation functions enables to extract the actual protein mean square displacement from imaging (iMSD), here presented in the form of apparent diffusivity vs average displacement. This yields a quantitative view of the average dynamics of single molecules with nanometer accuracy. By using a GFP-tagged variant of the Transferrin Receptor (TfR) and an ATTO488 labeled 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine (PPE) it is possible to observe the spatiotemporal regulation of protein and lipid diffusion on µm-sized membrane regions in the micro-to-milli-second time range. PMID:25350683

  20. Finite Larmor radii effects in fast ion measurements with neutron emission spectrometry

    NASA Astrophysics Data System (ADS)

    Eriksson, J.; Hellesen, C.; Andersson Sundén, E.; Cecconello, M.; Conroy, S.; Ericsson, G.; Gatu Johnson, M.; Pinches, S. D.; Sharapov, S. E.; Weiszflog, M.; EFDA contributors, JET

    2013-01-01

    When analysing data from fast ion measurements it is normally assumed that the gyro-phase distribution of the ions is isotropic within the field of view of the measuring instrument. This assumption is not valid if the Larmor radii of the fast ions are comparable to—or larger than—the gradient scale length in the spatial distribution of the ions, and if this scale length is comparable to—or smaller than—the width of the field of view of the measuring instrument. In this paper the effect of such an anisotropy is demonstrated by analysing neutron emission spectrometry data from a JET experiment with deuterium neutral beams together with radiofrequency heating at the third harmonic of the deuterium cyclotron frequency. In the experiment, the neutron time-of-flight spectrometer TOFOR was used to measure the neutrons from the d(d,n)3He-reaction. Comparison of the experimental data with Monte Carlo calculations shows that the finite Larmor radii of the fast ions need to be included in the modelling to get a good description of the data. Similar effects are likely to be important for other fast ion diagnostics, such as γ-ray spectroscopy and neutral particle analysis, as well.

  1. Shear-Limited Diffusion of Test Particles in Pure Ion Plasmas.

    NASA Astrophysics Data System (ADS)

    Anderegg, F.; Driscoll, C. F.; Dubin, D. H. E.

    2001-10-01

    Measurements of test-particle diffusion in pure ion plasmas show 2D enhancements over the 3D rates, limited by shear in the plasma rotation ωE (r). The diffusion is due to ``long-range'' ion-ion collisions in the quiescent, steady-state Mg^+ plasma. For short plasma length Lp and low shear ω_E^' ≡ partial ωE / partial r, thermal ions bounce axially many times before shear separates them in θ, so the ions may move in (r, θ ) as bounce averaged ``rods'' of charge (i.e. 2D point vortices). Experimentally, we vary the number of bounces over the range 0.2 <= Nb ≡ ( barv / 2 Lp ) / r ω_E^' <= 10,000. For long plasmas with Nb <= 1, we observe diffusion in quantitative agreement with the 3D theory of long-range E × B drift collisions.(F. Anderegg et al.), Phys. Rev. Lett. 78, 2128 (1997). For shorter plasmas or lower shear, with Nb > 1, we measure diffusion rates enhanced by approximately N_b. For exceedingly small shear, i.e. Nb >= 1000, we observe diffusion rates consistent with the Taylor-McNamara estimates for a shear-free plasma. Overall, the data shows fair agreement with Dubin's new theory of 2D diffusion in shear.(D.H.E. Dubin and D.Z. Jin, Phys. Lett. A 284), 112-117 (2001).

  2. Fast ion mass spectrometry and charged particle spectrography investigations of transverse ion acceleration and beam-plasma interactions

    NASA Technical Reports Server (NTRS)

    Gibson, W. C.; Tomlinson, W. M.; Marshall, J. A.

    1987-01-01

    Ion acceleration transverse to the magnetic field in the topside ionosphere was investigated. Transverse acceleration is believed to be responsible for the upward-moving conical ion distributions commonly observed along auroral field lines at altitudes from several hundred to several thousand kilometers. Of primary concern in this investigation is the extent of these conic events in space and time. Theoretical predictions indicate very rapid initial heating rates, depending on the ion species. These same theories predict that the events will occur within a narrow vertical region of only a few hundred kilometers. Thus an instrument with very high spatial and temporal resolution was required; further, since different heating rates were predicted for different ions, it was necessary to obtain composition as well as velocity space distributions. The fast ion mass spectrometer (FIMS) was designed to meet these criteria. This instrument and its operation is discussed.

  3. Fast Pyrolysis of Wood for Biofuels: Spatiotemporally Resolved Diffuse Reflectance In situ Spectroscopy of Particles.

    PubMed

    Paulsen, Alex D; Hough, Blake R; Williams, C Luke; Teixeira, Andrew R; Schwartz, Daniel T; Pfaendtner, Jim; Dauenhauer, Paul J

    2014-02-20

    Fast pyrolysis of woody biomass is a promising process capable of producing renewable transportation fuels to replace gasoline, diesel, and chemicals currently derived from nonrenewable sources. However, biomass pyrolysis is not yet economically viable and requires significant optimization before it can contribute to the existing oil-based transportation system. One method of optimization uses detailed kinetic models for predicting the products of biomass fast pyrolysis, which serve as the basis for the design of pyrolysis reactors capable of producing the highest value products. The goal of this work is to improve upon current pyrolysis models, usually derived from experiments with low heating rates and temperatures, by developing models that account for both transport and pyrolysis decomposition kinetics at high heating rates and high temperatures (>400 °C). A new experimental technique is proposed herein: spatiotemporally resolved diffuse reflectance in situ spectroscopy of particles (STR-DRiSP), which is capable of measuring biomass composition during fast pyrolysis with high spatial (10 μm) and temporal (1 ms) resolution. Compositional data were compared with a comprehensive 2D single-particle model, which incorporated a multistep, semiglobal reaction mechanism, prescribed particle shrinkage, and thermophysical properties that varied with temperature, composition, and orientation. The STR-DRiSP technique can be used to determine the transport-limited kinetic parameters of biomass decomposition for a wide variety of biomass feedstocks. PMID:24678023

  4. A fast SPAD-based small animal imager for early-photon diffuse optical tomography.

    PubMed

    Mu, Ying; Niedre, Mark

    2014-01-01

    Photon scatter is the dominant light transport process in biological tissue and is well understood to degrade imaging performance in near-infrared diffuse optical tomography. Measurement of photons arriving at early times following a short laser pulse is considered to be an effective method to improve this limitation, i.e. by systematically selecting photons that have experienced fewer scattering events. Previously, we tested the performance of single photon avalanche photodiode (SPAD) in measurement of early transmitted photons through diffusive media and showed that it outperformed photo-multiplier tube (PMT) systems in similar configurations, principally due to its faster temporal response. In this paper, we extended this work and developed a fast SPAD-based time-resolved diffuse optical tomography system. As a first validation of the instrument, we scanned an optical phantom with multiple absorbing inclusions and measured full time-resolved data at 3240 scan points per axial slice. We performed image reconstruction with very early-arriving photon data and showed significant improvements compared to time-integrated data. Extension of this work to mice in vivo and measurement of time-resolved fluorescence data is the subject of ongoing research.

  5. X-PROP: a fast and robust diffusion-weighted propeller technique.

    PubMed

    Li, Zhiqiang; Pipe, James G; Lee, Chu-Yu; Debbins, Josef P; Karis, John P; Huo, Donglai

    2011-08-01

    Diffusion-weighted imaging (DWI) has shown great benefits in clinical MR exams. However, current DWI techniques have shortcomings of sensitivity to distortion or long scan times or combinations of the two. Diffusion-weighted echo-planar imaging (EPI) is fast but suffers from severe geometric distortion. Periodically rotated overlapping parallel lines with enhanced reconstruction diffusion-weighted imaging (PROPELLER DWI) is free of geometric distortion, but the scan time is usually long and imposes high Specific Absorption Rate (SAR) especially at high fields. TurboPROP was proposed to accelerate the scan by combining signal from gradient echoes, but the off-resonance artifacts from gradient echoes can still degrade the image quality. In this study, a new method called X-PROP is presented. Similar to TurboPROP, it uses gradient echoes to reduce the scan time. By separating the gradient and spin echoes into individual blades and removing the off-resonance phase, the off-resonance artifacts in X-PROP are minimized. Special reconstruction processes are applied on these blades to correct for the motion artifacts. In vivo results show its advantages over EPI, PROPELLER DWI, and TurboPROP techniques.

  6. DIFFUSIVE SHOCK ACCELERATION OF HIGH-ENERGY CHARGED PARTICLES AT FAST INTERPLANETARY SHOCKS: A PARAMETER SURVEY

    SciTech Connect

    Giacalone, Joe

    2015-01-20

    We present results from numerical simulations of the acceleration of solar energetic particles (SEPs) associated with strong, fast, and radially propagating interplanetary shocks. We focus on the phase of the SEP event at the time of the shock passage at 1 AU, which is when the peak intensity at energies below a few MeV is the highest. The shocks in our study start between 2 and 10 solar radii and propagate beyond 1 AU. We study the effect of various shock and particle input parameters, such as the spatial diffusion coefficient, shock speed, solar wind speed, initial location of the shock, and shock deceleration rate, on the total integrated differential intensity, I, of SEPs with kinetic energies > 10 MeV. I is the integral over energy of the differential intensity spectrum at the time of the shock passage at 1 AU. We find that relatively small changes in the parameters can lead to significant event-to-event changes in I. For example, a factor of 2 increase in the diffusion coefficient at a given energy and spatial location, can lead to a decrease in I by as much as a factor of 50. This may help explain why there are fewer large SEP events seen during the current solar maximum compared to previous maxima. It is known that the magnitude of the interplanetary magnetic field is noticeably weaker this solar cycle than it was in the previous cycle and this will naturally lead to a somewhat larger diffusion coefficient of SEPs.

  7. The description of charge transfer in fast negative ions scattering on water covered Si(100) surfaces

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Qiu, Shunli; Liu, Pinyang; Xiong, Feifei; Lu, Jianjie; Liu, Yuefeng; Li, Guopeng; Liu, Yiran; Ren, Fei; Xiao, Yunqing; Gao, Lei; Zhao, Qiushuang; Ding, Bin; Li, Yuan; Guo, Yanling; Chen, Ximeng

    2016-11-01

    Doping has significantly affected the characteristics and performance of semiconductor electronic devices. In this work, we study the charge transfer processes for 8.5-22.5 keV C- and F- ions scattering on H2O-terminated p-type Si(100) surfaces with two different doping concentrations. We find that doping has no influence on negative-ion formation for fast collisions in this relatively high energy range. Moreover, we build a model to calculate negative ion fractions including the contribution from positive ions. The calculations support the nonadiabatic feature of charge transfer.

  8. Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

    SciTech Connect

    Fredrickson, E.D.; Bell, R.E.; Darrow, D.S.; Fu, G.Y.; Gorelenkov, N.N.; LeBlanc, B.P.; Medley, S.S.; Menard, J.E.; Park, H.; Roquemore, A.L.; Heidbrink, W.W.; Sabbagh, S.A.; Stutman, D.; Tritz, K.; Crocker, N.A.; Kubota, S.; Peebles, W.; Lee, K.C.; Levinton, F.M.

    2006-05-15

    A wide variety of fast ion driven instabilities are excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX) [Nucl. Fusion 40, 557 (2000)] due to the large ratio of fast ion velocity to Alfven velocity, V{sub fast}/V{sub Alfven}, and high fast ion beta. The ratio V{sub fast}/V{sub Alfven} in ITER [Nucl. Fusion 39, 2137 (1999)] and NSTX is comparable. The modes can be divided into three categories: chirping energetic particle modes (EPM) in the frequency range 0 to 120 kHz, the toroidal Alfven eigenmodes (TAE) with a frequency range of 50 kHz to 200 kHz, and the compressional and global Alfven eigenmodes (CAE and GAE, respectively) between 300 kHz and the ion cyclotron frequency. Fast ion driven modes are of particular interest because of their potential to cause substantial fast ion losses. In all regimes of NBI heated operation we see transient neutron rate drops, correlated with bursts of TAE or fishbone-like EPMs. The fast ion loss events are predominantly correlated with the EPMs, although losses are also seen with bursts of multiple, large amplitude TAE. The latter is of particular significance for ITER; the transport of fast ions from the expected resonance overlap in phase space of a 'sea' of large amplitude TAE is the kind of physics expected in ITER. The internal structure and amplitude of the TAE and EPMs has been measured with quadrature reflectometry and soft x-ray cameras. The TAE bursts have internal amplitudes of n-tilde/n=1% and toroidal mode numbers 21 and can have a toroidal mode number n>1. The range of the frequency chirp can be quite large and the resonance can be through a fishbone-like precessional drift resonance, or through a bounce resonance.

  9. Shot-to-shot reproducibility in the emission of fast highly charged metal ions from a laser ion source

    SciTech Connect

    Krasa, J.; Velyhan, A.; Margarone, D.; Krousky, E.; Laska, L.; Jungwirth, K.; Rohlena, K.; Ullschmied, J.; Parys, P.; Ryc, L.; Wolowski, J.

    2012-02-15

    The generation of fast highly charged metal ions with the use of the sub-nanosecond Prague Asterix Laser System, operated at a fundamental wavelength of 1315 nm, is reported. Particular attention is paid to shot-to-shot reproducibility in the ion emission. Au and Pd targets were exposed to intensities up to 5 x 10{sup 16} W/cm{sup 2}. Above the laser intensity threshold of {approx}3 x 10{sup 14} W/cm{sup 2} the plasma is generated in a form of irregular bursts. The maximum energy of protons constituting the leading edge of the fastest burst reaches a value up to 1 MeV. The fast ions in the following bursts have energy gradually decreasing with the increasing burst number, namely, from a value of about 0.5 MeV/charge regardless of the atomic number and mass of the ionized species.

  10. Reduced Fast Ion Transport Model For The Tokamak Transport Code TRANSP

    SciTech Connect

    Podesta,, Mario; Gorelenkova, Marina; White, Roscoe

    2014-02-28

    Fast ion transport models presently implemented in the tokamak transport code TRANSP [R. J. Hawryluk, in Physics of Plasmas Close to Thermonuclear Conditions, CEC Brussels, 1 , 19 (1980)] are not capturing important aspects of the physics associated with resonant transport caused by instabilities such as Toroidal Alfv en Eigenmodes (TAEs). This work describes the implementation of a fast ion transport model consistent with the basic mechanisms of resonant mode-particle interaction. The model is formulated in terms of a probability distribution function for the particle's steps in phase space, which is consistent with the MonteCarlo approach used in TRANSP. The proposed model is based on the analysis of fast ion response to TAE modes through the ORBIT code [R. B. White et al., Phys. Fluids 27 , 2455 (1984)], but it can be generalized to higher frequency modes (e.g. Compressional and Global Alfv en Eigenmodes) and to other numerical codes or theories.

  11. 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.

  12. A tangentially viewing fast ion D-alpha diagnostic for NSTX.

    PubMed

    Bortolon, A; Heidbrink, W W; Podestà, M

    2010-10-01

    A second fast ion D-alpha (FIDA) installation is planned at NSTX to complement the present perpendicular viewing FIDA diagnostics. Following the present diagnostic scheme, the new diagnostic will consist of two instruments: a spectroscopic diagnostic that measures fast ion spectra and profiles at 16 radial points with 5-10 ms resolution and a system that uses a band pass filter and photomultiplier to measure changes in FIDA light with 50 kHz sampling rate. The new pair of FIDA instruments will view the heating beams tangentially. The viewing geometry minimizes spectral contamination by beam emission or edge sources of background emission. The improved velocity-space resolution will provide detailed information about neutral-beam current drive and about fast ion acceleration and transport by injected radio frequency waves and plasma instabilities.

  13. A tangentially viewing fast ion D-alpha diagnostic for NSTX

    SciTech Connect

    Bortolon, A.; Heidbrink, W. W.; Podesta, M.

    2010-10-15

    A second fast ion D-alpha (FIDA) installation is planned at NSTX to complement the present perpendicular viewing FIDA diagnostics. Following the present diagnostic scheme, the new diagnostic will consist of two instruments: a spectroscopic diagnostic that measures fast ion spectra and profiles at 16 radial points with 5-10 ms resolution and a system that uses a band pass filter and photomultiplier to measure changes in FIDA light with 50 kHz sampling rate. The new pair of FIDA instruments will view the heating beams tangentially. The viewing geometry minimizes spectral contamination by beam emission or edge sources of background emission. The improved velocity-space resolution will provide detailed information about neutral-beam current drive and about fast ion acceleration and transport by injected radio frequency waves and plasma instabilities.

  14. The effect of the fast-ion profile on Alfvén eigenmode stability

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Van Zeeland, M. A.; Austin, M. E.; Bass, E. M.; Ghantous, K.; Gorelenkov, N. N.; Grierson, B. A.; Spong, D. A.; Tobias, B. J.

    2013-09-01

    Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇βf in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on- and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a ‘critical-gradient’ model of fast-ion transport.

  15. Nonlinear effects in desorption of valine with fast incident molecular ions

    SciTech Connect

    Salehpour, M.; Fishel, D.L.; Hunt, J.E.

    1988-12-15

    Fast molecular ions as primary particles have been used to study secondary-ion desorption from organic layers. The secondary molecular-ion yield of the amino acid valine (molecular weight, 117) has been measured as a function of the velocity of primary atomic and molecular incident ions. The primary ions used were C/sup +/, O/sup +/, Ar/sup +/, C/sub 2//sup +/, O/sub 2//sup +/ , CO/sup +/, CO/sub 2//sup +/, CH/sup +/, CH/sub 3//sup +/, CF/sup +/, CF/sub 3//sup +/, C/sub 3/F/sub 5//sup +/, and C/sub 4/F/sub 7//sup +/ in the energy range 600 keV--3.7 MeV. The secondary molecular-ion yields, when compared to yields for atomic constituents, unambiguously show that collective effects exist in desorption with incident molecular ions. Results are discussed in the framework of enhancement in the electronic stopping power per atom for molecular ions due to the vicinage of the fast-moving charges in the material. The resulting high-yield enhancements, especially with the use of large incident ions such as C/sub 3/F/sub 5//sup +/ and C/sub 4/F/sub 7//sup +/, are very encouraging for the future of mass spectrometry of large organic molecules.

  16. Probing the pseudo-1-D ion diffusion in lithium titanium niobate anode for Li-ion battery.

    PubMed

    Das, Suman; Dutta, Dipak; Araujo, Rafael B; Chakraborty, Sudip; Ahuja, Rajeev; Bhattacharyya, Aninda J

    2016-08-10

    Comprehensive understanding of the charge transport mechanism in the intrinsic structure of an electrode material is essential in accounting for its electrochemical performance. We present here systematic experimental and theoretical investigations of Li(+)-ion diffusion in a novel layered material, viz. lithium titanium niobate. Lithium titanium niobate (exact composition Li0.55K0.45TiNbO5·1.06H2O) is obtained from sol-gel synthesized potassium titanium niobate (KTiNbO5) by an ion-exchange method. The Li(+)-ions are inserted and de-inserted preferentially into the galleries between the octahedral layers formed by edge and corner sharing TiO6 and NbO6 octahedral units and the effective chemical diffusion coefficient, is estimated to be 3.8 × 10(-11) cm(2) s(-1) using the galvanostatic intermittent titration technique (GITT). Calculations based on density functional theory (DFT) strongly confirm the anisotropic Li(+)-ion diffusion in the interlayer galleries and that Li(+)-ions predominantly diffuse along the crystallographic b-direction. The preferential Li(+)-ion diffusion along the b-direction is assisted by line-defects, which are observed to be higher in concentration along the b-direction compared to the a- and c-directions, as revealed by high resolution electron microscopy. The Li-Ti niobate can be cycled to low voltages (≈0.2 V) and show stable and satisfactory battery performance over 100 cycles. Due to the possibility of cycling to low voltages, cyclic voltammetry and X-ray photoelectron spectroscopy convincingly reveal the reversibility of Ti(3+) ↔ Ti(2+) along with Ti(4+) ↔ Ti(3+) and Nb(5+) ↔ Nb(4+). PMID:27459636

  17. Probing the pseudo-1-D ion diffusion in lithium titanium niobate anode for Li-ion battery.

    PubMed

    Das, Suman; Dutta, Dipak; Araujo, Rafael B; Chakraborty, Sudip; Ahuja, Rajeev; Bhattacharyya, Aninda J

    2016-08-10

    Comprehensive understanding of the charge transport mechanism in the intrinsic structure of an electrode material is essential in accounting for its electrochemical performance. We present here systematic experimental and theoretical investigations of Li(+)-ion diffusion in a novel layered material, viz. lithium titanium niobate. Lithium titanium niobate (exact composition Li0.55K0.45TiNbO5·1.06H2O) is obtained from sol-gel synthesized potassium titanium niobate (KTiNbO5) by an ion-exchange method. The Li(+)-ions are inserted and de-inserted preferentially into the galleries between the octahedral layers formed by edge and corner sharing TiO6 and NbO6 octahedral units and the effective chemical diffusion coefficient, is estimated to be 3.8 × 10(-11) cm(2) s(-1) using the galvanostatic intermittent titration technique (GITT). Calculations based on density functional theory (DFT) strongly confirm the anisotropic Li(+)-ion diffusion in the interlayer galleries and that Li(+)-ions predominantly diffuse along the crystallographic b-direction. The preferential Li(+)-ion diffusion along the b-direction is assisted by line-defects, which are observed to be higher in concentration along the b-direction compared to the a- and c-directions, as revealed by high resolution electron microscopy. The Li-Ti niobate can be cycled to low voltages (≈0.2 V) and show stable and satisfactory battery performance over 100 cycles. Due to the possibility of cycling to low voltages, cyclic voltammetry and X-ray photoelectron spectroscopy convincingly reveal the reversibility of Ti(3+) ↔ Ti(2+) along with Ti(4+) ↔ Ti(3+) and Nb(5+) ↔ Nb(4+).

  18. Fast ion effects on magnetic instabilities in the PDX tokamak

    NASA Astrophysics Data System (ADS)

    Buchenauer, D. A.

    Modification and excitation of nondisruptive magnetic instabilities due to near perpendicular neutral beam injection on the PDX tokamak were made to determine the importance of these instabilities at low q. The instabilities consisted of resistive MHD modes, beam driven ideal MHD modes, and beam driven ion cyclotron modes. Evidence of enhanced transport is presented for several of these instabilities as well as comparison of the experimental results with theory. Possible consequences for reactor type tokamaks and high power auxiliary heating systems are discussed.

  19. Comparison of fast ion confinement during on-axis and off-axis neutral beam experiments on NSTX-U

    NASA Astrophysics Data System (ADS)

    Liu, D.; Heidbrink, W. W.; Hao, G. Z.; Podesta, M.; Darrow, D. S.; Fredrickson, E. D.; Medley, S. S.

    2015-11-01

    A second and more tangential neutral beam line is a major upgrade component of the National Spherical Torus Experiment - Upgrade (NSTX-U) with the purpose of improving neutral beam current drive efficiency and providing more flexibility in current/pressure profile control. Good fast ion confinement is essential to achieve the anticipated improvements in performance. In a planed ``sanity check'' experiment, various short and long (relative to fast ion slowing-down time) neutral beam (NB) pulses with different source mixes will be injected into quiescent L-mode plasmas to characterize the fast ion confinement and distribution function produced by the new and the existing NBI lines. The neutron rate decay after the turn-off of short NB pulses will be used to estimate the fast ion confinement time and to investigate its dependence on NB source/geometry, injection energy, and plasma current. The newly installed Solid State Neutral Particle Analyzer (SSNPA) and Fast-Ion D-Alapha (FIDA) diagnostics will be described and will be used to measure fast ion slowing-down distribution function and spatial profile during the injection of relatively long NB pulses. Fast ion prompt losses will be monitored with a scintillator Fast Lost Ion Probe (sFLIP) diagnostic. The experimental techniques, measurements of fast ion confinement time and distribution function, and comparisons with classical predictions from NUBEAM modeling will be presented in detail. Work supported by US DOE.

  20. Use of Fast Ion D-Alpha diagnostics for understanding ICRF effects

    SciTech Connect

    Podesta, M.; Heidbrink, W. W.; Liu, D.; Luo, Y.; Ruskov, E.; Bell, R. E.; Fredrickson, E. D.; Hosea, J. C.; Medley, S. S.; Burrell, K. H.; Choi, M.; Pinsker, R. I.; Harvey, R. W.

    2009-11-26

    Combined neutral beam injection and fast wave heating at cyclotron harmonics accelerate deuterium fast ions in the National Spherical Torus Experiment (NSTX) and in the DIII-D tokamak. Acceleration above the injected energy is evident in fast-ion D-alpha (FIDA) and volume-average neutron data. The FIDA diagnostic measures spatial profiles of the accelerated fast ions. In DIII-D, the acceleration is at a 4th or 5th cyclotron harmonic; the maximum enhancement in the high-energy FIDA signal is 8-10 cm beyond the resonance layer. In NSTX, acceleration is observed at five harmonics (7-11) simultaneously; overall, the profile of accelerated fast ions is much broader than in DIII-D. The energy distribution predicted by the CQL3D Fokker-Planck code agrees fairly well with measurements in DIII-D. However, the predicted profiles differ from experiment, presumably because the current version of CQL3D uses a zero-banana-width model.

  1. Use of Fast Ion D-Alpha diagnostics for understanding ICRF effects

    NASA Astrophysics Data System (ADS)

    Podestà, M.; Heidbrink, W. W.; Liu, D.; Luo, Y.; Ruskov, E.; Bell, R. E.; Fredrickson, E. D.; Hosea, J. C.; Medley, S. S.; Burrell, K. H.; Choi, M.; Pinsker, R. I.; Harvey, R. W.

    2009-11-01

    Combined neutral beam injection and fast wave heating at cyclotron harmonics accelerate deuterium fast ions in the National Spherical Torus Experiment (NSTX) and in the DIII-D tokamak. Acceleration above the injected energy is evident in fast-ion D-alpha (FIDA) and volume-average neutron data. The FIDA diagnostic measures spatial profiles of the accelerated fast ions. In DIII-D, the acceleration is at a 4th or 5th cyclotron harmonic; the maximum enhancement in the high-energy FIDA signal is 8-10 cm beyond the resonance layer. In NSTX, acceleration is observed at five harmonics (7-11) simultaneously; overall, the profile of accelerated fast ions is much broader than in DIII-D. The energy distribution predicted by the CQL3D Fokker-Planck code agrees fairly well with measurements in DIII-D. However, the predicted profiles differ from experiment, presumably because the current version of CQL3D uses a zero-banana-width model.

  2. Fast ion measurement using a hybrid directional probe in the large helical device

    SciTech Connect

    Nagaoka, Kenichi; Watanabe, Kiyomasa Y.; Osakabe, Masaki; Takeiri, Yasuhiko; Minami, Takashi; Toi, Kazuo; Isobe, Mitsutaka; Nishiura, Masaki; Ito, Takafumi; Ogawa, Kunihiro

    2008-10-15

    A hybrid directional probe was newly installed in the large helical device for fast ion measurement. The collector of the probe mounts a thermocouple to estimate local power flux and can be also utilized as a collector of a conventional Langmuir probe; therefore, the hybrid directional probe can simultaneously measure both local power density flux and current flux at the same collector surface. The concept and design of the hybrid directional probe, the calibration of the power density measurement, and preliminary result of the fast ion measurement are presented.

  3. A photodiode-based neutral particle bolometer for characterizing charge-exchanged fast-ion behavior

    SciTech Connect

    Clary, R.; Smirnov, A.; Dettrick, S.; Knapp, K.; Korepanov, S.; Ruskov, E.; Heidbrink, W. W.; Zhu, Y.

    2012-10-15

    A neutral particle bolometer (NPB) has been designed and implemented on Tri Alpha Energy's C-2 device in order to spatially and temporally resolve the charge-exchange losses of fast-ion populations originating from neutral beam injection into field-reversed configuration plasmas. This instrument employs a silicon photodiode as the detection device with an integrated tungsten filter coating to reduce sensitivity to light radiation. Here we discuss the technical aspects and calibration of the NPB, and report typical NPB measurement results of wall recycling effects on fast-ion losses.

  4. A photodiode-based neutral particle bolometer for characterizing charge-exchanged fast-ion behaviora)

    NASA Astrophysics Data System (ADS)

    Clary, R.; Smirnov, A.; Dettrick, S.; Knapp, K.; Korepanov, S.; Ruskov, E.; Heidbrink, W. W.; Zhu, Y.

    2012-10-01

    A neutral particle bolometer (NPB) has been designed and implemented on Tri Alpha Energy's C-2 device in order to spatially and temporally resolve the charge-exchange losses of fast-ion populations originating from neutral beam injection into field-reversed configuration plasmas. This instrument employs a silicon photodiode as the detection device with an integrated tungsten filter coating to reduce sensitivity to light radiation. Here we discuss the technical aspects and calibration of the NPB, and report typical NPB measurement results of wall recycling effects on fast-ion losses.

  5. A photodiode-based neutral particle bolometer for characterizing charge-exchanged fast-ion behavior.

    PubMed

    Clary, R; Smirnov, A; Dettrick, S; Knapp, K; Korepanov, S; Ruskov, E; Heidbrink, W W; Zhu, Y

    2012-10-01

    A neutral particle bolometer (NPB) has been designed and implemented on Tri Alpha Energy's C-2 device in order to spatially and temporally resolve the charge-exchange losses of fast-ion populations originating from neutral beam injection into field-reversed configuration plasmas. This instrument employs a silicon photodiode as the detection device with an integrated tungsten filter coating to reduce sensitivity to light radiation. Here we discuss the technical aspects and calibration of the NPB, and report typical NPB measurement results of wall recycling effects on fast-ion losses.

  6. Deuterium retention after deuterium plasma implantation in tungsten pre-damaged by fast C+ ions

    NASA Astrophysics Data System (ADS)

    Efimov, V. S.; Gasparyan, Yu M.; Pisarev, A. A.; Khripunov, B. I.; Koidan, V. S.; Ryazanov, A. I.; Semenov, E. V.

    2016-09-01

    Thermal desorption of deuterium from W was investigated. Virgin samples and samples damaged by 10 MeV C 3+ ions were implanted from plasma in the LENTA facility at 370 K and 773 K. In comparison with the undamaged sample, deuterium retention in the damaged sample slightly increased in the case of deuterium implantation at RT, but decreased in the case of deuterium implantation at 773 K. At 773 K, deuterium was concluded to diffuse far behind the D ion range in the virgin sample, while C implantation region was concluded to be a barrier for D diffusion in the damaged sample.

  7. A new fast-ion D{sub {alpha}} diagnostic for DIII-D

    SciTech Connect

    Heidbrink, W. W.; Luo, Y.; Muscatello, C. M.; Zhu, Y.; Burrell, K. H.

    2008-10-15

    The fast-ion D{sub {alpha}} (FIDA) technique is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha light from energetic hydrogenic atoms to infer the fast-ion density. Operational experience with the first dedicated FIDA diagnostic on DIII-D is guiding the design of the second-generation instrument. In the first instrument, dynamic changes in background light associated with plasma instabilities usually dominate measurement uncertainties. Accordingly, the design of the new instrument minimizes scattering of cold D{sub {alpha}} light while monitoring its level. The first instrument uses a vertical view to avoid bright interference from the injected-neutral beams. The sightline of the new instrument includes a toroidal component but only measures blueshifted fast-ion light that is Doppler shifted away from the redshifted light of the injected neutrals. The new views are more sensitive to fast ions that circulate in the direction of the plasma current and less sensitive to the trapped-ion and countercirculating populations. Details of the design criteria and solutions are presented.

  8. A new fast-ion D(alpha) diagnostic for DIII-D.

    PubMed

    Heidbrink, W W; Luo, Y; Muscatello, C M; Zhu, Y; Burrell, K H

    2008-10-01

    The fast-ion D(alpha) (FIDA) technique is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha light from energetic hydrogenic atoms to infer the fast-ion density. Operational experience with the first dedicated FIDA diagnostic on DIII-D is guiding the design of the second-generation instrument. In the first instrument, dynamic changes in background light associated with plasma instabilities usually dominate measurement uncertainties. Accordingly, the design of the new instrument minimizes scattering of cold D(alpha) light while monitoring its level. The first instrument uses a vertical view to avoid bright interference from the injected-neutral beams. The sightline of the new instrument includes a toroidal component but only measures blueshifted fast-ion light that is Doppler shifted away from the redshifted light of the injected neutrals. The new views are more sensitive to fast ions that circulate in the direction of the plasma current and less sensitive to the trapped-ion and countercirculating populations. Details of the design criteria and solutions are presented.

  9. Combination of fast-ion diagnostics in velocity-space tomographies

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; García-Muñoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.; Tardini, G.; the ASDEX Upgrade Team

    2013-06-01

    Fast-ion Dα (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fast-ion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods.

  10. Modeling of fast wave absorption by beam ions in DIII-D discharges

    SciTech Connect

    Mau, T. K.; Petty, C. C.; Porkolab, M.; Heidbrink, W. W.

    1999-09-20

    In recent discharges on DIII-D, neutron measurements indicated absorption of the fast wave by energetic deuterium beam ions when the fourth harmonic resonance is on axis, but little or no interaction for the fifth harmonic. In this work, a geometric optics code is used to quantify the beam ion absorption of fast waves as the frequency (or on-axis harmonic resonance) is varied. Isotropic and anisotropic Maxwellians are used to model the beam ion distribution. Wave power flow in this harmonic range has been found to exhibit a strong poloidal and toroidal behavior in its initial transits across the plasma. Absorption along the rays is calculated using the fully thermal and magnetized treatment. Competing with the beam ions for absorption are the minority hydrogen and background electrons. The modeling results are only in partial agreement with experimental observations, indicating that more detailed physics may need to be included. (c) 1999 American Institute of Physics.

  11. Fast ion transport during applied 3D magnetic perturbations on DIII-D

    NASA Astrophysics Data System (ADS)

    Van Zeeland, M. A.; Ferraro, N. M.; Grierson, B. A.; Heidbrink, W. W.; Kramer, G. J.; Lasnier, C. J.; Pace, D. C.; Allen, S. L.; Chen, X.; Evans, T. E.; García-Muñoz, M.; Hanson, J. M.; Lanctot, M. J.; Lao, L. L.; Meyer, W. H.; Moyer, R. A.; Nazikian, R.; Orlov, D. M.; Paz-Soldan, C.; Wingen, A.

    2015-07-01

    Measurements show fast ion losses correlated with applied three-dimensional (3D) fields in a variety of plasmas ranging from L-mode to resonant magnetic perturbation (RMP) edge localized mode (ELM) suppressed H-mode discharges. In DIII-D L-mode discharges with a slowly rotating n=2 magnetic perturbation, scintillator detector loss signals synchronized with the applied fields are observed to decay within one poloidal transit time after beam turn-off indicating they arise predominantly from prompt loss orbits. Full orbit following using M3D-C1 calculations of the perturbed fields and kinetic profiles reproduce many features of the measured losses and points to the importance of the applied 3D field phase with respect to the beam injection location in determining the overall impact on prompt beam ion loss. Modeling of these results includes a self-consistent calculation of the 3D perturbed beam ion birth profiles and scrape-off-layer ionization, a factor found to be essential to reproducing the experimental measurements. Extension of the simulations to full slowing down timescales, including fueling and the effects of drag and pitch angle scattering, show the applied n=3 RMPs in ELM suppressed H-mode plasmas can induce a significant loss of energetic particles from the core. With the applied n=3 fields, up to 8.4% of the injected beam power is predicted to be lost, compared to 2.7% with axisymmetric fields only. These fast ions, originating from minor radii ρ >0.7 , are predicted to be primarily passing particles lost to the divertor region, consistent with wide field-of-view infrared periscope measurements of wall heating in n=3 RMP ELM suppressed plasmas. Edge fast ion {{\\text{D}}α} (FIDA) measurements also confirm a large change in edge fast ion profile due to the n=3 fields, where the effect was isolated by using short 50 ms RMP-off periods during which ELM suppression was maintained yet the fast ion profile was allowed to recover. The role of resonances

  12. Monte Carlo calculations of drift velocities and diffusion coefficients of Ar + ions in helium

    NASA Astrophysics Data System (ADS)

    Barata, J. A. S.; Conde, C. A. N.

    2007-09-01

    Results are presented for the calculated drift velocities and diffusion coefficients for Ar + ions in helium at atmospheric pressure, temperature T=300 K and for reduced electric fields E/ N from about 1 Td up to about 150 Td, using Monte Carlo techniques. The drift velocities range from 5.94×10 3 to 559.0×10 3 cm s -1 for the Ar + ions in the ground state 2P 3/2 and from 5.85×10 3 to 545.0×10 3 cm s -1 for the Ar + ions in the metastable excited state 2P 1/2. These values are in good agreement (within about 5%) with the few experimental values available. The mobilities and diffusion coefficients for atomic Ar + ions in helium gas show no significant dependence on the spin state of the ion.

  13. The Heavy-Ion Approximation for Ambipolar Diffusion Calcuations for Weakly Ionized Plasmas

    SciTech Connect

    Li, P; McKee, C; Klein, R

    2006-07-27

    Ambipolar diffusion redistributes magnetic flux in weakly ionized plasmas and plays a critical role in star formation. Simulations of ambipolar diffusion using explicit MHD codes are prohibitively expensive for the level of ionization observed in molecular clouds ({approx}< 10{sup -6}) since an enormous number of time steps is required to represent the dynamics of the dominant neutral component with a time step determined by the trace ion component. Here we show that ambipolar diffusion calculations can be significantly accelerated by the 'heavy-ion approximation', in which the mass density of the ions is increased and the collisional coupling constant with the neutrals decreased such that the product remains constant. In this approximation, the ambipolar diffusion time and the ambipolar magnetic Reynolds number remain unchanged. We present three tests of the heavy-ion approximation: C-type shocks, the Wardle instability, and the 1D collapse of a magnetized slab. We show that this approximation is quite accurate provided that (1) the square of the Alfven Mach number is small compared to the ambipolar diffusion Reynolds number for dynamical problems, and that (2) the ion mass density is negligible for quasi-static problems; a specific criterion is given for the magnetized slab problem. The first condition can be very stringent for turbulent flows with large density fluctuations.

  14. Positive and negative cluster ions from liquid ethanol by fast ion bombardment.

    PubMed

    Kaneda, M; Shimizu, M; Hayakawa, T; Iriki, Y; Tsuchida, H; Itoh, A

    2010-04-14

    Secondary ion mass spectra have been measured for the first time for a liquid ethanol target bombarded by 2.0 MeV He(+) ions. Positive and negative ion spectra exhibit evidently a series of cluster ions of the forms [(EtOH)(n)H](+) and [(EtOH)(n)-H](-), respectively, in addition to light fragment ions from intact parent molecules. It was found that these cluster ions are produced only from liquid phase ethanol. Both positive and negative secondary ion spectra show similar cluster size distributions with almost the same decay slope. We also present for the first time the cluster ion distribution emitted from the liquid at different liquid temperatures.

  15. Modification of diffusion coefficients in MgO(100) through the chemical properties of implanted ions

    NASA Astrophysics Data System (ADS)

    Lu, M.; Lupu, C.; Lee, S. M.; Rabalais, J. W.

    2001-07-01

    Ti bulk diffusion coefficients have been determined for Ti in single crystal MgO(100) for four types of samples: Ti evaporated onto MgO and Ti evaporated onto MgO that was pre-bombarded with 7 keV Cl+, Ar+, and Cr+, respectively. Diffusion was induced by annealing to 1000 °C following the evaporation or pre-bombardment. Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. A model that includes a depth-dependent bulk diffusion coefficient was used to analyze the observed radiation enhanced diffusion (RED) effects. The bulk diffusion coefficients are of the order of 10-20 m2/s and are enhanced due to the defect structure inflected by the ion pre-bombardment. Different RED effects for the samples pre-bombarded with Cl+, Ar+, and Cr+ were observed despite their very similar ballistic implantation parameters. The diffusion model was extended to include the effects of lattice deformation, requirement of electrical neutrality, and chemical effects such as volatile compound formation. This extended model satisfactorily explains the RED differences observed for Cl+, Ar+, and Cr+ implantation. Our results show that RED is strongly influenced by the chemical properties of implanted ions.

  16. Nonlinear excitation of subcritical fast ion-driven modes

    NASA Astrophysics Data System (ADS)

    Lesur, M.; Itoh, K.; Ido, T.; Itoh, S.-I.; Kosuga, Y.; Sasaki, M.; Inagaki, S.; Osakabe, M.; Ogawa, K.; Shimizu, A.; Ida, K.; the LHD experiment group

    2016-05-01

    In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave–wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave–wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.

  17. Absorption of Fast Waves at Moderate to High Ion Cyclotron Harmonics on DIII-D

    NASA Astrophysics Data System (ADS)

    Pinsker, R. I.; Porkolab, M.; Heidbrink, W. W.; Luo, Y.; Petty, C. C.; Prater, R.; Choi, M.; Baity, F. W.; Fredd, E.; Hosea, J. C.; Harvey, R. W.; Smirnov, A. P.; Murakami, M.; Van Zeeland, M. A.

    2005-09-01

    The absorption of fast Alfvén waves (FW) by ion cyclotron harmonic damping in the range of harmonics from fourth to eighth is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on Maxwellian ion species is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the eighth harmonic if the fast ion beta and the background plasma density are both high enough. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. Possible explanations of the discrepancy are discussed.

  18. Absorption of fast waves at moderate to high ion cyclotron harmonics on DIII-D

    NASA Astrophysics Data System (ADS)

    Pinsker, R. I.; Porkolab, M.; Heidbrink, W. W.; Luo, Y.; Petty, C. C.; Prater, R.; Choi, M.; Schaffner, D. A.; Baity, F. W.; Fredd, E.; Hosea, J. C.; Harvey, R. W.; Smirnov, A. P.; Murakami, M.; Van Zeeland, M. A.

    2006-07-01

    The absorption of fast Alfvén waves (FW) by ion cyclotron harmonic damping in the range of harmonics from 4th to 8th is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on ions with an arbitrary distribution function which is symmetric about the magnetic field is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the 8th harmonic if the fast ion beta, the beam injection energy and the background plasma density are high enough and the beam injection geometry is appropriate. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. The linear modelling predicts a strong dependence of the 8th harmonic absorption on the initial pitch-angle of the injected beam, which is not observed in the experiment. Possible explanations of the discrepancy are discussed.

  19. Absorption of Fast Waves at Moderate to High Ion Cyclotron Harmonics on DIII-D

    SciTech Connect

    Pinsker, R.I.; Petty, C.C.; Prater, R.; Choi, M.; Porkolab, M.; Heidbrink, W.W.; Luo, Y.; Baity, F.W.; Murakami, M.; Fredd, E.; Hosea, J.C.; Harvey, R.W.; Smirnov, A.P.; Van Zeeland, M.A.

    2005-09-26

    The absorption of fast Alfven waves (FW) by ion cyclotron harmonic damping in the range of harmonics from fourth to eighth is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on Maxwellian ion species is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the eighth harmonic if the fast ion beta and the background plasma density are both high enough. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. Possible explanations of the discrepancy are discussed.

  20. Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport.

    PubMed

    Collins, C S; Heidbrink, W W; Austin, M E; Kramer, G J; Pace, D C; Petty, C C; Stagner, L; Van Zeeland, M A; White, R B; Zhu, Y B

    2016-03-01

    Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold in the presence of many overlapping small-amplitude Alfvén eigenmodes (AEs). The threshold is phase-space dependent and occurs when particle orbits become stochastic due to resonances with AEs. Above threshold, equilibrium fast-ion density profiles are unchanged despite increased drive, and intermittent fast-ion losses are observed. Fast-ion Dα spectroscopy indicates radially localized transport of the copassing population at radii that correspond to the location of midcore AEs. The observation of stiff fast-ion transport suggests that reduced models can be used to effectively predict alpha profiles, beam ion profiles, and losses to aid in the design of optimized scenarios for future burning plasma devices.

  1. Observation of Critical-Gradient Behavior in Alfvén-Eigenmode-Induced Fast-Ion Transport

    NASA Astrophysics Data System (ADS)

    Collins, C. S.; Heidbrink, W. W.; Austin, M. E.; Kramer, G. J.; Pace, D. C.; Petty, C. C.; Stagner, L.; Van Zeeland, M. A.; White, R. B.; Zhu, Y. B.

    2016-03-01

    Experiments in the DIII-D tokamak show that fast-ion transport suddenly becomes stiff above a critical threshold in the presence of many overlapping small-amplitude Alfvén eigenmodes (AEs). The threshold is phase-space dependent and occurs when particle orbits become stochastic due to resonances with AEs. Above threshold, equilibrium fast-ion density profiles are unchanged despite increased drive, and intermittent fast-ion losses are observed. Fast-ion D α spectroscopy indicates radially localized transport of the copassing population at radii that correspond to the location of midcore AEs. The observation of stiff fast-ion transport suggests that reduced models can be used to effectively predict alpha profiles, beam ion profiles, and losses to aid in the design of optimized scenarios for future burning plasma devices.

  2. Fast single photon avalanche photodiode-based time-resolved diffuse optical tomography scanner

    PubMed Central

    Mu, Ying; Niedre, Mark

    2015-01-01

    Resolution in diffuse optical tomography (DOT) is a persistent problem and is primarily limited by high degree of light scatter in biological tissue. We showed previously that the reduction in photon scatter between a source and detector pair at early time points following a laser pulse in time-resolved DOT is highly dependent on the temporal response of the instrument. To this end, we developed a new single-photon avalanche photodiode (SPAD) based time-resolved DOT scanner. This instrument uses an array of fast SPADs, a femto-second Titanium Sapphire laser and single photon counting electronics. In combination, the overall instrument temporal impulse response function width was 59 ps. In this paper, we report the design of this instrument and validate its operation in symmetrical and irregularly shaped optical phantoms of approximately small animal size. We were able to accurately reconstruct the size and position of up to 4 absorbing inclusions, with increasing image quality at earlier time windows. We attribute these results primarily to the rapid response time of our instrument. These data illustrate the potential utility of fast SPAD detectors in time-resolved DOT. PMID:26417526

  3. Fast single photon avalanche photodiode-based time-resolved diffuse optical tomography scanner.

    PubMed

    Mu, Ying; Niedre, Mark

    2015-09-01

    Resolution in diffuse optical tomography (DOT) is a persistent problem and is primarily limited by high degree of light scatter in biological tissue. We showed previously that the reduction in photon scatter between a source and detector pair at early time points following a laser pulse in time-resolved DOT is highly dependent on the temporal response of the instrument. To this end, we developed a new single-photon avalanche photodiode (SPAD) based time-resolved DOT scanner. This instrument uses an array of fast SPADs, a femto-second Titanium Sapphire laser and single photon counting electronics. In combination, the overall instrument temporal impulse response function width was 59 ps. In this paper, we report the design of this instrument and validate its operation in symmetrical and irregularly shaped optical phantoms of approximately small animal size. We were able to accurately reconstruct the size and position of up to 4 absorbing inclusions, with increasing image quality at earlier time windows. We attribute these results primarily to the rapid response time of our instrument. These data illustrate the potential utility of fast SPAD detectors in time-resolved DOT.

  4. Fast Diffusion to Self-Similarity: Complete Spectrum, Long-Time Asymptotics, and Numerology

    NASA Astrophysics Data System (ADS)

    Denzler, Jochen; McCann, Robert J.

    2005-03-01

    The complete spectrum is determined for the operator on the Sobolev space W1,2ρ(Rn) formed by closing the smooth functions of compact support with respect to the norm Here the Barenblatt profile ρ is the stationary attractor of the rescaled diffusion equation in the fast, supercritical regime m the same diffusion dynamics represent the steepest descent down an entropy E(u) on probability measures with respect to the Wasserstein distance d2. Formally, the operator H=HessρE is the Hessian of this entropy at its minimum ρ, so the spectral gap H≧α:=2-n(1-m) found below suggests the sharp rate of asymptotic convergence: from any centered initial data 0≦u(0,x) ∈ L1(Rn) with second moments. This bound improves various results in the literature, and suggests the conjecture that the self-similar solution u(t,x)=R(t)-nρ(x/R(t)) is always slowest to converge. The higher eigenfunctions which are polynomials with hypergeometric radial parts and the presence of continuous spectrum yield additional insight into the relations between symmetries of Rn and the flow. Thus the rate of convergence can be improved if we are willing to replace the distance to ρ with the distance to its nearest mass-preserving dilation (or still better, affine image). The strange numerology of the spectrum is explained in terms of the number of moments of ρ.

  5. Diffuse correlation spectroscopy with a fast Fourier transform-based software autocorrelator

    NASA Astrophysics Data System (ADS)

    Dong, Jing; Bi, Renzhe; Ho, Jun Hui; Thong, Patricia S. P.; Soo, Khee-Chee; Lee, Kijoon

    2012-09-01

    Diffuse correlation spectroscopy (DCS) is an emerging noninvasive technique that probes the deep tissue blood flow, by using the time-averaged intensity autocorrelation function of the fluctuating diffuse reflectance signal. We present a fast Fourier transform (FFT)-based software autocorrelator that utilizes the graphical programming language LabVIEW (National Instruments) to complete data acquisition, recording, and processing tasks. The validation and evaluation experiments were conducted on an in-house flow phantom, human forearm, and photodynamic therapy (PDT) on mouse tumors under the acquisition rate of ˜400 kHz. The software autocorrelator in general has certain advantages, such as flexibility in raw photon count data preprocessing and low cost. In addition to that, our FFT-based software autocorrelator offers smoother starting and ending plateaus when compared to a hardware correlator, which could directly benefit the fitting results without too much sacrifice in speed. We show that the blood flow index (BFI) obtained by using a software autocorrelator exhibits better linear behavior in a phantom control experiment when compared to a hardware one. The results indicate that an FFT-based software autocorrelator can be an alternative solution to the conventional hardware ones in DCS systems with considerable benefits.

  6. Ion beam technique for the measurement of deuterium diffusion coefficients

    SciTech Connect

    Lewis, M.B.; Farrell, K.

    1980-05-15

    This letter describes how a combination of the techniques of nuclear microanalysis and cathodic hydrogenation has been used to determine the diffusion coefficient of dueterium in austenitic stainless steel at room temperature. Samples charged in deuterated acid solutions to levels of about 20 at. % deuterium were quickly transferred to a scattering chamber where a depth profile of the near-surface deuterium was measured. For charging times much longer than the transfer plus anlyzing time, the deuterium profile could be described by an error function at the specimen surface. A diffusion coefficient was determined by a chi-squared test fitting procedure and shown to be consistent with values reported for other methods measured at higher temperatures.

  7. Application of the pH-Imaging Sensor to Determining the Diffusion Coefficients of Ions in Electrolytic Solutions

    NASA Astrophysics Data System (ADS)

    Yoshinobu, Tatsuo; Harada, Tetsuro; Iwasaki, Hiroshi

    2000-04-01

    The pH-imaging sensor is applied to visualization of ionic diffusion in an electrochemical system. Redistribution of the pH value due to diffusion of ions after electrolysis is measured to determine the diffusion coefficients of anions and cations. Dependence of the diffusion coefficient on the molecular weight of ions is investigated. Applicability of the pH-imaging sensor to quantitative analysis of dynamics in a chemical system is demonstrated.

  8. Effect of carbon ion irradiation on Ag diffusion in SiC

    NASA Astrophysics Data System (ADS)

    Leng, Bin; Ko, Hyunseok; Gerczak, Tyler J.; Deng, Jie; Giordani, Andrew J.; Hunter, Jerry L.; Morgan, Dane; Szlufarska, Izabela; Sridharan, Kumar

    2016-04-01

    Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C-SiC, as well as Ag and single crystalline 4H-SiC samples before and after irradiation with C2+ ions. The diffusion couple samples were exposed to temperatures of 1500 °C, 1535 °C, and 1569 °C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). Diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.

  9. Effect of carbon ion irradiation on Ag diffusion in SiC

    SciTech Connect

    Leng, Bin; Ko, Hyunseok; Gerczak, Tyler J.; Deng, Jie; Giordani, Andrew J.; Hunter, Jerry L.; Morgan, Dane; Szlufarska, Izabela; Sridharan, Kumar

    2015-11-14

    Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C–SiC, as well as Ag and single crystalline 4H–SiC samples before and after irradiation with C2+ ions. The diffusion couple samples were exposed to temperatures of 1500 °C, 1535 °C, and 1569 °C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). We found that diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.

  10. Effect of carbon ion irradiation on Ag diffusion in SiC

    DOE PAGESBeta

    Leng, Bin; Ko, Hyunseok; Gerczak, Tyler J.; Deng, Jie; Giordani, Andrew J.; Hunter, Jerry L.; Morgan, Dane; Szlufarska, Izabela; Sridharan, Kumar

    2015-11-14

    Transport of Ag fission product through the silicon-carbide (SiC) diffusion barrier layer in TRISO fuel particles is of considerable interest given the application of this fuel type in high temperature gas-cooled reactor (HTGR) and other future reactor concepts. The reactor experiments indicate that radiation may play an important role in release of Ag; however so far the isolated effect of radiation on Ag diffusion has not been investigated in controlled laboratory experiments. In this study, we investigate the diffusion couples of Ag and polycrystalline 3C–SiC, as well as Ag and single crystalline 4H–SiC samples before and after irradiation with C2+more » ions. The diffusion couple samples were exposed to temperatures of 1500 °C, 1535 °C, and 1569 °C, and the ensuing diffusion profiles were analyzed by secondary ion mass spectrometry (SIMS). We found that diffusion coefficients calculated from these measurements indicate that Ag diffusion was greatly enhanced by carbon irradiation due to a combined effect of radiation damage on diffusion and the presence of grain boundaries in polycrystalline SiC samples.« less

  11. Diffusion coefficient for ions in the presence of a coherent lower hybrid wave

    NASA Astrophysics Data System (ADS)

    Antonsen, T. M., Jr.; Ott, J.

    1981-09-01

    The diffusion coefficient resulting from ergodic ion motion when the amplitude of a coherent lower hybrid wave exceeds a certain stochasticity threshold is considered. A previously developed method by Rechester et al. (1981) is adopted to obtain an analytical result for the diffusion coefficient of an ion in a lower hybrid wave, and results are in good agreement with those of Karney (1979). The problem is formulated in terms of a recursion relation for the Fourier transformed distribution function, and results show a sharp resonance behavior in the diffusion coefficient. For large amplitude waves, the diffusion coefficient oscillates with decreasing amplitude about the quasi-linear value as the wave amplitude increases, and the coefficient is shown to be subject to narrow resonances at wave amplitudes corresponding to fixed points in the map.

  12. Stripline fast faraday cup for measuring GHz structure of ion beams

    DOEpatents

    Bogaty, John M.

    1992-01-01

    The Stripline Fast Faraday Cup is a device which is used to quantitatively and qualitatively measure gigahertz time structure characteristics of ion beams with energies up to at least 30 Mev per nucleon. A stripline geometry is employed in conjunction with an electrostatic screen and a Faraday cup to provide for analysis of the structural characteristics of an ion beam. The stripline geometry allows for a large reduction in the size of the instrument while the electrostatic screen permits measurements of the properties associated with low speed ion beams.

  13. Fast Correction Optics to Reduce Chromatic Aberrations in Longitudinally Compressed Ion Beams

    SciTech Connect

    Lidia, S.M.; Lee, E.P.; Ogata, D.; Seidl, P.A.; Waldron, W.L.; Lund, S.M.

    2009-04-30

    Longitudinally compressed ion beam pulses are currently employed in ion-beam based warm dense matter studies [1]. Compression arises from an imposed time-dependent longitudinal velocity ramp followed by drift in a neutralized channel. Chromatic aberrations in the final focusing system arising from this chirp increase the attainable beam spot and reduce the effective fluence on target. We report recent work on fast correction optics that remove the time-dependent beam envelope divergence and minimizes the beam spot on target. We present models of the optical element design and predicted ion beam fluence.

  14. Diffusion and possible freezing phases of Li-ions in LiFePO4

    NASA Astrophysics Data System (ADS)

    Yiu, Yuen; Toft-Petersen, Rasmus; Ehlers, Georg; Vaknin, David

    Elastic and inelastic neutron scattering studies of LiFePO4 single crystal reveal new Li-ion diffusion properties relevant to its function as Li-battery materials. In the past decade there has been broad interest in LiFePO4 and its related compounds, largely due to the applications of these materials as cathodes in Li- batteries. This is owing to these materials' high charge-discharge ability and conductivity, both of which are by virtue of the Li-ions' high mobility. In this talk, we present our findings on the temperature and directional dependence of Li-ions' diffusion in LiFePO4. LiFePO4 adopts the olivine structure at room temperature (Space group: Pnma), which contains channels along principal crystalline directions that allow Li-ion motion. Elastic neutron scattering reveals lowering of symmetry from the Pnma structure below room temperature, which can be interpreted as the freezing of Li-ions, and can be subsequently linked to the reported decrease in Li-ion conductivity. Inelastic neutron scattering, in the 35K to 720K temperature range, shows temperature dependence, as well as anisotropy (i.e. along 0K0 versus 00L) of Li-ion diffusion. Ames Laboratory is supported by U.S. DOE, BES, DMSE, under Contract #DE-AC02-07CH11358. Spallation Neutron Source of Oak Ridge National Laboratory is sponsored by U.S. DOE, BES, SUFD.

  15. Single electron capture in fast ion-atom collisions

    NASA Astrophysics Data System (ADS)

    Milojević, Nenad

    2014-12-01

    Single-electron capture cross sections in collisions between fast bare projectiles and heliumlike atomic systems are investigated by means of the four-body boundary-corrected first Born (CB1-4B) approximation. The prior and post transition amplitudes for single charge exchange encompassing symmetric and asymmetric collisions are derived in terms of twodimensional real integrals in the case of the prior form and five-dimensional quadratures for the post form. The dielectronic interaction V12 = 1/r12 = 1/|r1 - r2| explicitly appears in the complete perturbation potential Vf of the post transition probability amplitude T+if. An illustrative computation is performed involving state-selective and total single capture cross sections for the p - He (prior and post form) and He2+, Li3+Be4+B5+C6+ - He (prior form) collisions at intermediate and high impact energies. We have also studied differential cross sections in prior and post form for single electron transfer from helium by protons. The role of dynamic correlations is examined as a function of increased projectile energy. Detailed comparisons with the measurements are carried out and the obtained theoretical cross sections are in reasonable agreement with the available experimental data.

  16. Preface: Photon and fast Ion induced Processes in Atoms, MOlecules and Nanostructures (PIPAMON)

    NASA Astrophysics Data System (ADS)

    Kövér, László

    2016-02-01

    This Special Issue contains selected papers of contributions presented in the International Workshop on Photon and fast Ion induced Processes in Atoms, MOlecules and Nanostructures (PIPAMON), held between March 24 and 26, 2015 in Debrecen, Hungary. The venue, the Aquaticum Thermal and Wellness Hotel provided a pleasant "all-under-one-roof" environment for the event.

  17. Interaction of Fast Ions with Global Plasma Modes in the C-2 Field Reversed Configuration Experiment

    NASA Astrophysics Data System (ADS)

    Smirnov, Artem; Dettrick, Sean; Clary, Ryan; Korepanov, Sergey; Thompson, Matthew; Trask, Erik; Tuszewski, Michel

    2012-10-01

    A high-confinement operating regime [1] with plasma lifetimes significantly exceeding past empirical scaling laws was recently obtained by combining plasma gun edge biasing and tangential Neutral Beam Injection (NBI) in the C-2 field-reversed configuration (FRC) experiment [2, 3]. We present experimental and computational results on the interaction of fast ions with the n=2 rotational and n=1 wobble modes in the C-2 FRC. It is found that the n=2 mode is similar to quadrupole magnetic fields in its detrimental effect on the fast ion transport due to symmetry breaking. The plasma gun generates an inward radial electric field, thus stabilizing the n=2 rotational instability without applying the quadrupole magnetic fields. The resultant FRCs are nearly axisymmetric, which enables fast ion confinement. The NBI further suppresses the n=2 mode, improves the plasma confinement characteristics, and increases the plasma configuration lifetime [4]. The n=1 wobble mode has relatively little effect on the fast ion transport, likely due to the approximate axisymmetry about the displaced plasma column. [4pt] [1] M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012).[0pt] [2] M. Binderbauer et al., Phys. Rev. Lett. 105, 045003 (2010).[0pt] [3] H.Y. Guo et al., Phys. Plasmas 18, 056110 (2011).[0pt] [4] M. Tuszewski et al., Phys. Plasmas 19, 056108 (2012)

  18. Diffusion permeability of yttrium-based heat-resistant ion-plasma coatings

    NASA Astrophysics Data System (ADS)

    Goncharov, V. S.; Goncharov, M. V.; Vasil'ev, E. V.

    2016-09-01

    The diffusion permeability of yttrium-containing ion-plasma coatings on substrates made of the low-alloy chromium-based Cr-0.7V-0.17La alloy has been studied. It has been found that protective coatings of this type have a strong barrier effect on diffusion fluxes in the substrate-coating-environment system and that YCr + YCrO3 coatings ensure the best protection of the substrates against gas saturation.

  19. Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Bolte, Nathan G.; Heidbrink, William W.; Pace, David; Van Zeeland, Michael; Chen, Xi

    2016-11-01

    Spectra of passive fast-ion D-alpha (FIDA) light from beam ions that charge exchange with background neutrals are measured and simulated. The fast ions come from three sources: ions that pass through the diagnostic sightlines on their first full orbit, an axisymmetric confined population, and ions that are expelled into the edge region by instabilities. A passive FIDA simulation (P-FIDASIM) is developed as a forward model for the spectra of the first-orbit fast ions and consists of an experimentally-validated beam deposition model, an ion orbit-following code, a collisional-radiative model, and a synthetic spectrometer. Model validation consists of the simulation of 86 experimental spectra that are obtained using 6 different neutral beam fast-ion sources and 13 different lines of sight. Calibrated spectra are used to estimate the neutral density throughout the cross-section of the tokamak. The resulting 2D neutral density shows the expected increase toward each X-point with average neutral densities of 8× {{10}9}~\\text{c}{{\\text{m}}-3} at the plasma boundary and 1× {{10}11}~\\text{c}{{\\text{m}}-3} near the wall. Fast ions that are on passing orbits are expelled by the sawtooth instability more readily than trapped ions. In a sample discharge, approximately 1% of the fast-ion population is ejected into the high neutral density region per sawtooth crash.

  20. Influence of ion induced amorphicity on the diffusion of gold into silicon

    SciTech Connect

    Ehrhardt, J.; Klimmer, A.; Eisenmenger, J.; Mueller, Th.; Boyen, H.-G.; Ziemann, P.; Biskupek, J.; Kaiser, U.

    2006-09-15

    It is experimentally demonstrated that, after ion irradiating 60 nm thick Au films on Si substrates with 230 keV Ar{sup +} ions, annealing conditions can be found leading to strong diffusional contrasts between bombarded and unbombarded areas. While Au readily diffuses into the bombarded part of the sample at 310 deg. C, its diffusion is still completely blocked under identical conditions in the unbombarded parts. Clear evidence is provided that this diffusional contrast is due to bombardment induced amorphization of the underlying Si substrate. The amorphous Silicon (a-Si), however, has to extend right to the Au/Si interface, since any intermediate crystalline layer will suppress the diffusional contrast. An example for this latter situation is realized by performing the ion bombardment prior to the evaporation of the top Au layer leading to a still crystalline Si surface layer, which is found to act as a barrier against Au diffusion at 310 deg. C. In accordance with the idea that a-Si, independent of its specific preparation, causes the observed Au diffusion enhancement, the effect is also found for a-Si prepared by evaporation at ambient temperature. In that case an even higher Au diffusion coefficient is obtained than for Si amorphized by ion bombardment pointing to subtle structural differences between both types of amorphous Si.

  1. Specific Ions Modulate Diffusion Dynamics of Hydration Water on Lipid Membrane Surfaces

    PubMed Central

    2015-01-01

    Effects of specific ions on the local translational diffusion of water near large hydrophilic lipid vesicle surfaces were measured by Overhauser dynamic nuclear polarization (ODNP). ODNP relies on an unpaired electron spin-containing probe located at molecular or surface sites to report on the dynamics of water protons within ∼10 Å from the spin probe, which give rise to spectral densities for electron–proton cross-relaxation processes in the 10 GHz regime. This pushes nuclear magnetic resonance relaxometry to more than an order of magnitude higher frequencies than conventionally feasible, permitting the measurement of water moving with picosecond to subnanosecond correlation times. Diffusion of water within ∼10 Å of, i.e., up to ∼3 water layers around the spin probes located on hydrophilic lipid vesicle surfaces is ∼5 times retarded compared to the bulk water translational diffusion. This directly reflects on the activation barrier for surface water diffusion, i.e., how tightly water is bound to the hydrophilic surface and surrounding waters. We find this value to be modulated by the presence of specific ions in solution, with its order following the known Hofmeister series. While a molecular description of how ions affect the hydration structure at the hydrophilic surface remains to be answered, the finding that Hofmeister ions directly modulate the surface water diffusivity implies that the strength of the hydrogen bond network of surface hydration water is directly modulated on hydrophilic surfaces. PMID:24456096

  2. Measurement of CO2 diffusivity in synthetic and saline aquifer solutions at reservoir conditions: the role of ion interactions

    NASA Astrophysics Data System (ADS)

    Jafari Raad, Seyed Mostafa; Azin, Reza; Osfouri, Shahriar

    2015-11-01

    Storage and disposal of CO2 as the main component of greenhouse gases in saline aquifers require careful measurement of diffusivity for predicting rate of transfer and cumulative amount of trapped gas. Little information is available on diffusion of CO2 in highly concentrated saline aquifers at reservoir conditions. In this study, diffusivity of CO2 was measured into different solutions, including saline aquifer taken from oil field, distilled water and synthetic solutions prepared from four most common ions, Mg2+, Ca2+, K+, Na+. The roles of salvation effect and hydration phenomenon were studied on diffusivity of dissolved CO2. Synthetic solutions were prepared at concentration ranges of 83-200 g/l. Experimental measurements were reported at temperature and pressure ranges of 30-40 °C and 5,880-6,265 kPa, respectively. Results show that both type and concentration of ion affect CO2 diffusivity. Diffusion coefficient was found dependent on effective radius of hydrated ions. Also, CO2 diffusivity increase by increasing strength of bonds between ion and neighbor water molecules. Also, presence of ions in water solution creates hydration competition between solution metal ions and aqua ions from diffusive gas. The Mg2+ cation, which has strongest hydration competition among other ions, has an increasing effect on gas diffusivity into saline aquifer. However, increasing ion concentration in solution decreases diffusivity of CO2 due to growth in fraction of contact ion pairs. Results of this study provide unique measures of CO2 diffusion coefficient in saline aquifer at high pressure and temperature conditions and conceptual information about effect of each common saline formation ion on gas diffusivity.

  3. Analysis and Numerical Solution for Multi-Physics Coupling of Neutron Diffusion and Thermomechanics in Spherical Fast Burst Reactors

    SciTech Connect

    Samet Y. Kadioglu; Dana A. Knoll; Cassiano de Oliveira

    2009-05-01

    Coupling neutronics to thermomechanics is important for the analysis of fast burst reactors, because the criticality and safety study of fast burst reactors heavily depends on the thermomechanical behavior of fuel materials. For instance, the shut down mechanism or the transition between super and sub-critical states are driven by the fuel material expansion or contraction. The material expansion or contraction is due to temperature gradient which results from fission power. In this paper, we introduce a numerical model for coupling of neutron diffusion and thermomechanics in fast burst reactors. We also provide some analysis of the coupled system. We studied material behaviors corresponding to different levels of power pulses.

  4. Fast ignition of an inertial fusion target with a solid noncryogenic fuel by an ion beam

    SciTech Connect

    Gus’kov, S. Yu.; Zmitrenko, N. V.; Il’in, D. V.; Sherman, V. E.

    2015-09-15

    The burning efficiency of a preliminarily compressed inertial confinement fusion (ICF) target with a solid noncryogenic fuel (deuterium-tritium beryllium hydride) upon fast central ignition by a fast ion beam is studied. The main aim of the study was to determine the extent to which the spatial temperature distribution formed under the heating of an ICF target by ion beams with different particle energy spectra affects the thermonuclear gain. The study is based on a complex numerical modeling including computer simulations of (i) the heating of a compressed target with a spatially nonuniform density and temperature distributions by a fast ion beam and (ii) the burning of the target with the initial spatial density distribution formed at the instant of maximum compression of the target and the initial spatial temperature distribution formed as a result of heating of the compressed target by the ion beam. The threshold energy of the igniting ion beam and the dependence of the thermonuclear gain on the energy deposited in the target are determined.

  5. Alfv?nic Instabilities and Fast Ion Transport in the DIII-D Tokamak

    SciTech Connect

    Van Zeeland, M; Heidbrink, W; Nazikian, R; Austin, M; Berk, H; Gorelenkov, N; Holcomb, C; Kramer, G; Lohr, J; Luo, Y; Makowski, M; McKee, G; Petty, C; Prater, R; Solomon, W; White, R

    2008-10-14

    Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including Toroidicity and Ellipticity induced Alfven Eigenmodes (TAE/EAE, respectively) and Reversed Shear Alfven Eigenmodes (RSAE) as well as their spatial coupling. These modes are typically studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. During this same time period Fast-Ion D{sub {alpha}} (FIDA) spectroscopy shows that the central fast ion profile is flattened, the degree of which depends on the Alfven eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. To simulate the observed neutral beam ion redistribution, NOVA calculations of the 3D eigenmode structures are matched with experimental measurements and used in combination with the ORBIT guiding center following code. For fixed frequency eigenmodes, it is found that ORBIT calculations cannot explain the observed beam ion transport with experimentally measured mode amplitudes. Possible explanations are considered including recent simulation results incorporating eigenmodes with time dependent frequencies.

  6. A statistical mechanical theory of the self-diffusion coefficient of simple ions in electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Yuan Mou, Chung; Thacher, Thomas S.; Lin, Jeong-long

    1983-07-01

    A statistical mechanical theory of the self-diffusion coefficient of ions in solutions of simple electrolytes has been developed. Beginning with a generalized Langevin equation the self-diffusion coefficients of ions may be evaluated at the zero-frequency limit of the Laplace transform of the random force correlation function. We assume that the random force acting on the tagged ion may be separated into contributions from the solvent part, due to the surrounding solvent molecules and an ionic part due to all the other ions. Further, we assume that the evolution of the ionic random force is governed by the Smoluchowski operator. With these assumptions and using the Debye-Hückel pair correlation function, the Onsager limiting law may be derived. Numerical calculations using the HNC pair correlation function shows that our theory can describe experimental data of moderately concentrated solutions adequately.

  7. Self-diffusion coefficients of ions in electrolyte solutions by nonequilibrium Brownian dynamics

    NASA Astrophysics Data System (ADS)

    Raineri, Fernando O.; Wood, Mark D.; Friedman, Harold L.

    1990-01-01

    The self-diffusion coefficients of the ions in a model electrolyte solution are calculated with a novel implementation of the nonequilibrium Brownian dynamics technique. The ions are coupled to an external color field E by color charges in such a way that each ionic species as a whole is electrically neutral to E. The ion-ion forces are not directly affected by the color charges or E. The method is tested on a model of a 1 M NaCl aqueous solution without hydrodynamic interactions and the results are compared with those of a previous equilibrium simulation for the same model system. The self-diffusion coefficients of Na+ and Cl- are determined with 2%-3% accuracy and, within this margin, agree with the results of the equilibrium simulation obtained with more than twice the computational effort. Furthermore, within the range of field strengths studied, the average color flows depend linearly on E.

  8. First fast-ion D-alpha (FIDA) measurements and simulations on C-2U

    NASA Astrophysics Data System (ADS)

    Bolte, N. G.; Gupta, D.; Stagner, L.; Onofri, M.; Dettrick, S.; Granstedt, E. M.; Petrov, P.

    2016-11-01

    The first measurements of fast-ion D-alpha (FIDA) radiation have been acquired on C-2U, Tri Alpha Energy's advanced, beam-driven field-reversed configuration (FRC). These measurements are also forward modeled by FIDASIM. This is the first measurement and simulation of FIDA carried out on an FRC topology. FIDA measurements are made of Doppler-shifted Balmer-alpha light from neutralized fast ions using a bandpass filter and photomultiplier tube. One adjustable line-of-sight measured signals at eight locations and eight times during the FRC lifetime over 26 discharges. Filtered signals include only the highest energy ions (>6 keV) and share some salient features with the FIDASIM result. Highly Doppler-shifted beam radiation is also measured with a high-speed camera and is spatially well-correlated with FIDASIM.

  9. Absorption of Fast Waves at Moderate to High Ion Cyclotron Harmonics: Experimental Results and Theoretical Models

    NASA Astrophysics Data System (ADS)

    Pinsker, R. I.; Choi, M.; Prater, R.; Heidbrink, W. W.; Luo, Y.; Baity, F. W.; Murakami, M.; Porkolab, M.

    2006-10-01

    Strong absorption of fast Alfvén waves (FW) by ion cyclotron damping has been observed in DIII-D at the 4th and 5th harmonic of an injected beam while only weak absorption is observed at the 8th harmonic. The experimental results are compared with three different theoretical models; differences between the predictions of the models suggest the possible importance of finite-width orbit effects at high harmonics. In a linear model, it is found that damping on fast ions from neutral beam injection can be significant even at the 8th harmonic under experimentally relevant conditions. This is tested in experiments in DIII-D with FW power at 60 MHz and at 116 MHz. A novel Dα charge exchange recombination diagnostic is used to observe interaction of the FW power with beam ions. The results are compared with modeling with quasilinear and with orbit-following codes.

  10. Validation of fast-ion D-alpha spectrum measurements during EAST neutral-beam heated plasmas

    NASA Astrophysics Data System (ADS)

    Huang, J.; Heidbrink, W. W.; von Hellermann, M. G.; Stagner, L.; Wu, C. R.; Hou, Y. M.; Chang, J. F.; Ding, S. Y.; Chen, Y. J.; Zhu, Y. B.; Jin, Z.; Xu, Z.; Gao, W.; Wang, J. F.; Lyu, B.; Zang, Q.; Zhong, G. Q.; Hu, L.; Wan, B.

    2016-11-01

    To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been installed on EAST. Fast ion features can be inferred from the Doppler shifted spectrum of Balmer-alpha light from energetic hydrogenic atoms. This paper will focus on the validation of FIDA measurements performed using MHD-quiescent discharges in 2015 campaign. Two codes have been applied to calculate the Dα spectrum: one is a Monte Carlo code, Fortran 90 version FIDASIM, and the other is an analytical code, Simulation of Spectra (SOS). The predicted SOS fast-ion spectrum agrees well with the measurement; however, the level of fast-ion part from FIDASIM is lower. The discrepancy is possibly due to the difference between FIDASIM and SOS velocity distribution function. The details will be presented in the paper to primarily address comparisons of predicted and observed spectrum shapes/amplitudes.

  11. Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel

    SciTech Connect

    Martinavicius, A.; Abrasonis, G.; Moeller, W.

    2011-10-01

    The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3-0.7 mA cm{sup -2}), ion energy (0.5-1.2 keV), and temperature (370-430 deg. C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

  12. Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Martinavičius, A.; Abrasonis, G.; Möller, W.

    2011-10-01

    The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3-0.7 mA cm-2), ion energy (0.5-1.2 keV), and temperature (370-430 °C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

  13. Stability thresholds and calculation techniques for fast entangling gates on trapped ions

    NASA Astrophysics Data System (ADS)

    Bentley, C. D. B.; Taylor, R. L.; Carvalho, A. R. R.; Hope, J. J.

    2016-04-01

    Fast entangling gates have been proposed for trapped ions that are orders of magnitude faster than current implementations. We present here a detailed analysis of the challenges involved in performing a successful fast gate. We show that the rotating wave approximation is stable with respect to pulse numbers: the time scale on which we can neglect terms rotating at the atomic frequency is negligibly affected by the number of pulses in the fast gate. In contrast, we show that the laser pulse instability does give rise to a pulse-number-dependent effect; the fast gate infidelity is compounded with the number of applied imperfect pulses. Using the dimensional reduction method presented here, we find bounds on the pulse stability required to achieve two-qubit gate fidelity thresholds.

  14. Benchmark and combined velocity-space tomography of fast-ion D-alpha spectroscopy and collective Thomson scattering measurements

    NASA Astrophysics Data System (ADS)

    Jacobsen, A. S.; Salewski, M.; Geiger, B.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

    2016-04-01

    We demonstrate the combination of fast-ion D-alpha spectroscopy (FIDA) and collective Thomson scattering (CTS) measurements to determine a common best estimate of the fast-ion velocity distribution function by velocity-space tomography. We further demonstrate a benchmark of FIDA tomography and CTS measurements without using a numerical simulation as common reference. Combined velocity-space tomographies from FIDA and CTS measurements confirm that sawtooth crashes reduce the fast-ion phase-space densities in the plasma center and affect ions with pitches close to one more strongly than those with pitches close to zero.

  15. Investigating the possibility of a monitoring fast ion diagnostic for ITER.

    PubMed

    De Angelis, R; von Hellermann, M G; Orsitto, F P; Tugarinov, S

    2008-10-01

    In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information for safe and reliable plasma operations. In this paper, we examine the feasibility of a monitoring system based on active charge exchange recombination spectroscopy making use of the 0.5 MeV/amu ITER heating neutral beams for detecting fast (4)He(+2) (alphas) particles in ITER plasmas. There are two time scales relevant to fast ion dynamics: the first is the slowing down time of the distribution function which is of the order of 1 s, and the second is the time scale of burstlike transport events such as collective Alfven mode excitations, which--for typical ITER plasma parameters--can be as low as 0.2-1 ms. To detect such fast events a broadband high-throughput spectrometer is needed, while for the reconstruction of the alpha velocity distribution function a higher resolution spectrometer and longer integration time are necessary. To monitor a spatial redistribution of fast particles due to the propagation of the instability, it is proposed to use a limited number of spatial channels, looking at the charge exchange He II spectra induced by the heating beams, whose energy matches the slowing down energies of fast particles. The proposal is to share the motional stark effect periscope on equatorial port 3 [A. Malaquias et al., Rev. Sci. Instrum. 75, 3393 (2004)] adding additional fibers and suitable instruments. A signal to noise ratio of 5 could be achieved with a spatial resolution of a/15 and a time resolution of 5 ms, in a broad spectral band of 100 A, corresponding to the spectral broadening of the line emitted by alpha particles with energies DeltaE < or = 1.5 MeV. Fast H and D ion populations created by heating neutral beam or ion cyclotron resonance heating are

  16. Statistical analysis of diffuse ion events upstream of the Earth's bow shock

    NASA Technical Reports Server (NTRS)

    Trattner, K. J.; Mobius, E.; Scholer, M.; Klecker, B.; Hilchenbach, M.; Luehr, H.

    1994-01-01

    A statistical study of diffuse energetic ion events and their related waves upstream of the Earth's bow shock was performed using data from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM) satellite over two 5-month periods in 1984 and 1985. The data set was used to test the assumption in the self-consistent model of the upstream wave and particle populations by Lee (1982) that the particle acceleration through hydromagnetic waves and the wave generation are directly coupled. The comparison between the observed wave power and the wave power predicted on the observed energetic particle energy density and solar wind parameters results in a high correlation coefficient of about 0.89. The intensity of diffuse ions falls off approximately exponentially with the distance upstream from the bow shock parallel to the magnetic field with e-folding distances which vary from approximately 3.3 R(sub E) to approximately 11.7 R(sub E) over the energy range from 10 keV/e to 67.3 keV/e for both protons and alpha particles. After normalizing the upstream particle densities to zero bow shock distance by using these exponential variations, a good correlation (0.7) of the density of the diffuse ions with the solar wind density was found. This supports the suggestion that the solar wind is the source of the diffuse ions. Furthermore, the spectral slope of the diffuse ions correlates well with the solar wind velocity component in the direction of the interplanetary magnetic field (0.68 and 0.66 for protons and alpha particles) which concurs with the notion that the solar wind plays an important role in the acceleration of the upstream particles.

  17. An analysis of the influence of impurities on fast particle attenuation and on fast ion spectral shape in LHD

    SciTech Connect

    Veshchev, Evgeny A.; Goncharov, Pavel R.; Ozaki, Tetsuo; Sudo, Shigeru

    2008-10-15

    Neutral particle fluxes measured by neutral particle analyzers can provide information about the ion temperature as well as the non-Maxwellian anisotropic ion distribution tails from neutral beam injection and ion cyclotron radio frequency heating. In the case of multidirectional diagnostics employing high resolution atomic energy spectrometers, the neutral atomic flux source is not localized in contrast to pellet charge exchange or diagnostic neutral beam methods. The correct interpretation of such measurements from plasma in a complex toroidally asymmetric geometry, like that of LHD, requires careful numerical modeling of the neutral flux formation. Previously a measured neutral flux calculation scheme was developed and was used for the LHD geometry and a suitable analytic expression for ionization cross sections {sigma}{sub s}{sup (z)}(E,n{sub e},T{sub e},Z{sub eff}) of impurities was formulated by Janev et al. [Nucl. Fusion 29, 2125 (1989)]. In this paper, the attenuation of fast particles by impurities is incorporated into the neutral flux calculation scheme and the influence of impurities on the calculated neutral flux spectra is shown. Finally, the behavior of the calculated and experimental suprathermal particle distributions is compared for pure hydrogen and for argon impurity seeded plasmas.

  18. An analysis of the influence of impurities on fast particle attenuation and on fast ion spectral shape in LHD.

    PubMed

    Veshchev, Evgeny A; Goncharov, Pavel R; Ozaki, Tetsuo; Sudo, Shigeru

    2008-10-01

    Neutral particle fluxes measured by neutral particle analyzers can provide information about the ion temperature as well as the non-Maxwellian anisotropic ion distribution tails from neutral beam injection and ion cyclotron radio frequency heating. In the case of multidirectional diagnostics employing high resolution atomic energy spectrometers, the neutral atomic flux source is not localized in contrast to pellet charge exchange or diagnostic neutral beam methods. The correct interpretation of such measurements from plasma in a complex toroidally asymmetric geometry, like that of LHD, requires careful numerical modeling of the neutral flux formation. Previously a measured neutral flux calculation scheme was developed and was used for the LHD geometry and a suitable analytic expression for ionization cross sections sigma(s)(z)(E,n(e),T(e),Z(eff)) of impurities was formulated by Janev et al. [Nucl. Fusion 29, 2125 (1989)]. In this paper, the attenuation of fast particles by impurities is incorporated into the neutral flux calculation scheme and the influence of impurities on the calculated neutral flux spectra is shown. Finally, the behavior of the calculated and experimental suprathermal particle distributions is compared for pure hydrogen and for argon impurity seeded plasmas.

  19. Edge Ion Heating by Launched High Harmonic Fast Waves in NSTX

    SciTech Connect

    T.M. Biewer; R.E. Bell; S.J. Diem; C.K. Phillips; J.R. Wilson; P.M. Ryan

    2004-12-01

    A new spectroscopic diagnostic on the National Spherical Torus Experiment (NSTX) measures the velocity distribution of ions in the plasma edge simultaneously along both poloidal and toroidal views. An anisotropic ion temperature is measured during high-power high harmonic fast wave (HHFW) radio-frequency (rf) heating in helium plasmas, with the poloidal ion temperature roughly twice the toroidal ion temperature. Moreover, the measured spectral distribution suggests that two populations of ions are present and have temperatures of typically 500 eV and 50 eV with rotation velocities of -50 km/s and -10 km/s, respectively (predominantly perpendicular to the local magnetic field). This bi-modal distribution is observed in both the toroidal and poloidal views (for both He{sup +} and C{sup 2+} ions), and is well correlated with the period of rf power application to the plasma. The temperature of the hot component is observed to increase with the applied rf power, which was scanned between 0 and 4.3 MW . The 30 MHz HHFW launched by the NSTX antenna is expected and observed to heat core electrons, but plasma ions do not resonate with the launched wave, which is typically at >10th harmonic of the ion cyclotron frequency in the region of observation. A likely ion heating mechanism is parametric decay of the launched HHFW into an Ion Bernstein Wave (IBW). The presence of the IBW in NSTX plasmas during HHFW application has been directly confirmed with probe measurements. IBW heating occurs in the perpendicular ion distribution, consistent with the toroidal and poloidal observations. Calculations of IBW propagation indicate that multiple waves could be created in the parametric decay process, and that most of the IBW power would be absorbed in the outer 10 to 20 cm of the plasma, predominantly on fully stripped ions. These predictions are in qualitative agreement with the observations, and must be accounted for when calculating the energy budget of the plasma.

  20. Extended fast-ion D-alpha diagnostic on DIII-D

    SciTech Connect

    Muscatello, C. M.; Heidbrink, W. W.; Taussig, D.; Burrell, K. H.

    2010-10-15

    A fast-ion deuterium-alpha (FIDA) diagnostic, first commissioned on DIII-D in 2005, relies on Doppler-shifted light from charge-exchange between beam neutrals and energetic ions. The second generation (2G) system was installed on DIII-D in 2009. Its most obvious improvement is the spatial coverage with 11 active in-beam and three passive off-beam views; the latter allows for simultaneous monitoring of the background signal. Providing extended coverage in fast-ion velocity space, the new views possess a more tangential component with respect to the toroidal field compared to their first generation counterparts. Each viewing chord consists of a bundle of three 1.5 mm core fibers to maximize light gathering. For greater throughput, fast f/1.8 optical components are used throughout. The signal is transmitted via fiber optics to a patch panel, so the user is able to choose the detector. FIDA was originally installed with a spectrometer and charge-coupled device (CCD) camera to monitor the full D{sub {alpha}} spectrum for two spatial views. 2G adds another spectrometer and CCD that monitor the blue-shifted wing for six spatial views at 1 kHz. In addition, a photomultiplier tube and fast digitizer provide wavelength-integrated signals at 1 MHz for eight spatial views.

  1. Extended fast-ion D-alpha diagnostic on DIII-D.

    PubMed

    Muscatello, C M; Heidbrink, W W; Taussig, D; Burrell, K H

    2010-10-01

    A fast-ion deuterium-alpha (FIDA) diagnostic, first commissioned on DIII-D in 2005, relies on Doppler-shifted light from charge-exchange between beam neutrals and energetic ions. The second generation (2G) system was installed on DIII-D in 2009. Its most obvious improvement is the spatial coverage with 11 active in-beam and three passive off-beam views; the latter allows for simultaneous monitoring of the background signal. Providing extended coverage in fast-ion velocity space, the new views possess a more tangential component with respect to the toroidal field compared to their first generation counterparts. Each viewing chord consists of a bundle of three 1.5 mm core fibers to maximize light gathering. For greater throughput, fast f/1.8 optical components are used throughout. The signal is transmitted via fiber optics to a patch panel, so the user is able to choose the detector. FIDA was originally installed with a spectrometer and charge-coupled device (CCD) camera to monitor the full D(α) spectrum for two spatial views. 2G adds another spectrometer and CCD that monitor the blue-shifted wing for six spatial views at 1 kHz. In addition, a photomultiplier tube and fast digitizer provide wavelength-integrated signals at 1 MHz for eight spatial views.

  2. Self-diffusion and activity coefficients of ions in charged disordered media

    NASA Astrophysics Data System (ADS)

    Jardat, Marie; Hribar-Lee, Barbara; Dahirel, Vincent; Vlachy, Vojko

    2012-09-01

    Self-diffusion and single ion activity coefficients of ions of size symmetric electrolytes were studied in the presence of a collection of charged obstacles (called matrix) within a "soft" version of the primitive model of electrolyte solutions. The matrix subsystem possesses a net charge, depending on the concentration and charge of obstacles. The Brownian dynamics method was used to calculate the self-diffusion coefficients of mobile species. The replica Ornstein-Zernike theory for the partly quenched systems was used to calculate the individual activity coefficients of mobile ionic species. The results reflect the competition between attractive (obstacle-counterion, co-ion-counterion), and repulsive (obstacle-co-ion) interactions in these model systems. For the simplest possible system of symmetric monovalent ions the latter effect wins: Co-ions are excluded from the area around obstacles, and this slows down their diffusion compared to that of counterions. Introduction of divalent charges into the system changes this result when the concentration of obstacles is low. We compare these results to those obtained for the corresponding fully annealed systems, i.e., where all the species are mobile. In most cases the self-diffusion and activity coefficients of counterions and co-ions in the presence of charged obstacles follow the trends of the fully annealed solution, which are dictated by the composition of the mixture. In few situations, however, the presence of charged obstacles modifies these trends. Our study allows us to clearly identify the effects due to obstacles, and to separate them from those arising from the composition of the solution. In the case of charge and size symmetric systems, the results for the individual activity coefficients fully support the hypothesis of the "electrostatic excluded volume". Thermodynamic and dynamic results are consistent in explaining the behavior of the systems studied.

  3. A new type of MHD activity in JET ICRF-only discharges with high fast-ion energy contents

    NASA Astrophysics Data System (ADS)

    Mantsinen, M. J.; Sharapov, S.; Alper, B.; Gondhalekar, A.; McDonald, D. C.

    2000-12-01

    The question of sawtooth stabilization at very high fast-ion energy contents has been addressed in discharges carried out in the JET tokamak with ion cyclotron resonance frequency (ICRF) heating and varying plasma density, controlled by deuterium gas puffs. In these experiments dramatic differences in the sawtooth behaviour have been observed. When the plasma density ne decreases below a certain threshold, the sawtooth frequency and the crash duration time increase by a factor of five. Since the fast-ion energy content increases with decreasing ne due to the inverse proportionality of the fast-ion slowing-down time on ne, the threshold in ne corresponds to a threshold in the fast-ion energy content. In the present experiments, this threshold is reached when the fast-ion energy contribution to the total plasma diamagnetic energy content becomes larger than 45%. The sawtooth activity with short sawtooth free period is accompanied by MHD activity, with a toroidal mode number n = 1 at frequencies between 55 and 65 kHz. This activity is interpreted as an energetic particle fishbone mode that is resonant with the ICRF-driven fast ions. The experimental results appear to be consistent with the stability diagram for sawtooth and fishbone modes (White 1989 Theory of Tokamak Plasmas (Amsterdam: North-Holland)), exploring the part of the diagram with a very large fast-ion population.

  4. Modification of Sawteeth Periods By Trapped Fast Ions in DIII-D

    NASA Astrophysics Data System (ADS)

    Choi, M.; Chan, V. S.; Chu, M. S.; Lao, L. L.; Turnbull, A. D.

    2006-10-01

    The main auxiliary heating methods for ITER are neutral beam and ion cyclotron wave heating. Sawtooth physics is very important in optimizing the heating efficiency for ITER. This requires understanding of the interaction between fast ions and fast Alfvén wave (FW) on MHD stability. Experimentally, the DIII-D discharges have demonstrated strong acceleration of deuterium beam ions above the injected beam energy from measurements of enhanced neutron emissions during FW heating. Theory predicts that high pressure from fast ions in the center of plasma may act as a stabilizing kinetic effect on ideal internal kink mode. However, the DIII-D experimental results showed that sawteeth characteristics strongly depend on a combination of plasma and wave conditions. We apply a Monte-Carlo orbit code (ORBIT-RF) and ideal MHD code (GATO) to model existing DIII-D experiments and explore the triggering and stabilization mechanisms for sawteeth. The analytical model by Bussac and Porcelli will be compared with NOVA-K calculations.

  5. Inferring DIII-D Edge Neutral Density from Fast-Ion D-Alpha Emission

    NASA Astrophysics Data System (ADS)

    Bolte, N. G.; Heidbrink, W. W.; Pace, D.; van Zeeland, M.

    2014-10-01

    Promptly-lost beam ions produce Doppler-shifted Balmer-Alpha light after charge exchanging with edge neutrals. Spectra of this edge-localized fast-ion D-alpha (FIDA) emission have been measured at DIII-D using six chords that view the edge region. A new simulation P-FIDASim has been developed that models prompt-loss radiation. P-FIDASim uses modules from the active FIDA code, FIDASIM but uses fast-ion orbits from a single beam in place of FIDASIM's use of a theoretical fast-ion distribution function and considers CX with edge, not beam or halo neutrals. Initial results show good correlation between experiment and simulation in spectral shape. Intensity variations between chords show that empirical results are inconsistent with neutral density being a pure flux function. Modeling a neutral source term at the wall gives the z-dependence of the neutral density by inversion. Results will be presented of 2D (R,z) cross-sectional values of neutral density found by this method. Work supported in part by the US DOE under SC-G903402 and DE-FC02-04ER54698.

  6. Investigation of Inter-Ion Species Diffusion in Inertial Confinement Fusion Implosions

    NASA Astrophysics Data System (ADS)

    Herrmann, Hans W.; Kim, Yongho; Hoffman, Nelson M.; Schmitt, Mark J.; Kagan, Grigory; Batha, Steven H.; Garbett, Warren J.; Horsfield, Colin J.; Rubery, Michael S.; Gales, Steven

    2014-10-01

    Anomalous fusion yield degradation has been observed for gas fill mixtures in inertial confinement fusion (ICF) implosions. These mixtures have included D/3He [Rygg et al., Phys Plasmas 13, 052702 (2006)], D/T/3He [Herrmann et al., Phys Plasmas 16, 056312 (2009)], D/Ar [Lindl et al., Phys Plasmas 11, 339 (2004)] and even D/T [Casey et al., PRL 108, 075005 (2012)]. Fuel ion segregation has been suggested as a possible cause [Amendt et al., PRL 18, 056308 (2011); Kagan et al., Phys Lett. A 10.1016 (2014)]. Segregation may be caused by inter-ion species diffusion driven by gradients in plasma pressure, temperature and electric field, either across a relatively narrow shock boundary or across the entire interior of the compressed capsule. It is expected that lower Z &/or A ions will diffuse outward while higher Z &/or A diffuse inward. In the case of D/T/3He, the 3He diffuses inward to the hotter core, reducing the DT reactivity. A D/T/H mixture should result in H diffusing outward, leaving the hotter core D & T rich and hence enhance reactivity over the simulated expectation. Past results will be reviewed and plans for a hydro-equivalent comparison D/T/3He and D/T/H will be presented. Research conducted under the auspices of the U.S. Department of Energy under Contract DE-AC52-06NA25396.

  7. Comparison of ICRF-Induced Ion Diffusion Coefficients Calculated with the DC and AORSA Codes

    SciTech Connect

    Harvey, R. W.; Petrov, Yu.; Jaeger, E. F.; Berry, L. A.; Batchelor, D. B.; Bonoli, P. T.; Wright, J. C.

    2009-11-26

    The DC (Diffusion Coefficient) code obtains RF diffusion coefficients by direct numerical integration of the Lorentz force equation for ion motion in the combined equilibrium fields and the RF full wave EM fields from the AORSA full-wave code. Suitable averaging over initial gyro- and toroidal-angle of coordinate 'kicks' after a bounce-period, gives noise-free bounce-averaged diffusion coefficients. For direct comparison with zero-banana-width coefficients from AORSA, perpendicular-drift terms in the Lorentz equation are subtracted off the integration. The DC code has been coupled to the CQL3D Fokker-Planck code. For a C-Mod minority ion ICRF heating test case, the total power absorption using the diffusion coefficients agree well, and the profiles are similarly close. This supports the DC calculation and the Kennel-Engelmann-based, no-correlations, coefficient calculation in AORSA. However, resonance correlations cause large differences in the pitch angle variations of the diffusion coefficients, and in the resulting evolution of the ion distribution functions.

  8. Comparison of ICRF-Induced Ion Diffusion Coefficients Calculated with the DC and AORSA Codes

    NASA Astrophysics Data System (ADS)

    Harvey, R. W.; Petrov, Yu.; Jaeger, E. F.; Berry, L. A.; Batchelor, D. B.; Bonoli, P. T.; Wright, J. C.

    2009-11-01

    The DC (Diffusion Coefficient) code obtains RF diffusion coefficients by direct numerical integration of the Lorentz force equation for ion motion in the combined equilibrium fields and the RF full wave EM fields from the AORSA full-wave code. Suitable averaging over initial gyro- and toroidal-angle of coordinate "kicks" after a bounce-period, gives noise-free bounce-averaged diffusion coefficients. For direct comparison with zero-banana-width coefficients from AORSA, perpendicular-drift terms in the Lorentz equation are subtracted off the integration. The DC code has been coupled to the CQL3D Fokker-Planck code. For a C-Mod minority ion ICRF heating test case, the total power absorption using the diffusion coefficients agree well, and the profiles are similarly close. This supports the DC calculation and the Kennel-Engelmann-based, no-correlations, coefficient calculation in AORSA. However, resonance correlations cause large differences in the pitch angle variations of the diffusion coefficients, and in the resulting evolution of the ion distribution functions.

  9. Gaussian energy distribution of fast ions emitted by laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Krása, J.

    2013-05-01

    The analysis of ion collector signals with the use of a time-of-fight signal function derived from a shifted Maxwell-Boltzmann velocity distribution is used to quantify the ion characteristics as the ion temperature and velocity of centre-of-mass motion of groups of ionized species constituting the ablated plasma. The analysis is also focused on velocity and energy distributions derived from the signal of a time-of-flight detector taking into account the underlying principle of sensor operation. The energy Maxwell spectra of ions are compared with the Gauss distribution with respect to the ratio of the centre-of-mass energy of ions to their temperature. The difference threshold between the Gauss and energy Maxwell spectra is determined via the limited validity of the basic relationship between spreads in energy and time-of-flight spectra ½ΔE/E = Δt/t. The analysis of velocity spectrum of fast ions emitted by Ti plasma produced with 300 ps, kJ-class iodine laser operating at PALS facility shows that ion bursts consist of almost monoenergetic ion beams.

  10. ITER Plasma at Ion Cyclotron Frequency Domain: The Fusion Alpha Particles Diagnostics Based on the Stimulated Raman Scattering of Fast Magnetosonic Wave off High Harmonic Ion Bernstein Modes

    NASA Astrophysics Data System (ADS)

    Stefan, V. Alexander

    2014-10-01

    A novel method for alpha particle diagnostics is proposed. The theory of stimulated Raman scattering, SRS, of the fast wave and ion Bernstein mode, IBM, turbulence in multi-ion species plasmas, (Stefan University Press, La Jolla, CA, 2008). is utilized for the diagnostics of fast ions, (4)He (+2), in ITER plasmas. Nonlinear Landau damping of the IBM on fast ions near the plasma edge leads to the space-time changes in the turbulence level, (inverse alpha particle channeling). The space-time monitoring of the IBM turbulence via the SRS techniques may prove efficient for the real time study of the fast ion velocity distribution function, spatial distribution, and transport. Supported by Nikola Tesla Labs., La Jolla, CA 92037.

  11. Lithium ion sources for investigations of fast ion transport in magnetized plasmas

    SciTech Connect

    Zhang, Y.; Boehmer, H.; Heidbrink, W. W.; McWilliams, R.; Leneman, D.; Vincena, S.

    2007-01-15

    In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters (Li aluminosilicate) were developed. Compared to discharge based ion sources, they are compact, have zero gas load, small energy dispersion, and can be operated at any angle with respect to an ambient magnetic field of up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mA/cm{sup 2} range. Because of the low ion mass, beam velocities of 100-300 km/s are in the range of Alfven speeds in typical helium plasmas in the large plasma device.

  12. Lithium ion sources for investigations of fast ion transport in magnetized plasmas.

    PubMed

    Zhang, Y; Boehmer, H; Heidbrink, W W; McWilliams, R; Leneman, D; Vincena, S

    2007-01-01

    In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters (Li aluminosilicate) were developed. Compared to discharge based ion sources, they are compact, have zero gas load, small energy dispersion, and can be operated at any angle with respect to an ambient magnetic field of up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mAcm(2) range. Because of the low ion mass, beam velocities of 100-300 kms are in the range of Alfven speeds in typical helium plasmas in the large plasma device.

  13. Measurement of a 2D fast-ion velocity distribution function by tomographic inversion of fast-ion D-alpha spectra

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Jacobsen, A. S.; García-Muñoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Tardini, G.; Weiland, M.; the ASDEX Upgrade Team

    2014-02-01

    We present the first measurement of a local fast-ion 2D velocity distribution function f(v‖, v⊥). To this end, we heated a plasma in ASDEX Upgrade by neutral beam injection and measured spectra of fast-ion Dα (FIDA) light from the plasma centre in three views simultaneously. The measured spectra agree very well with synthetic spectra calculated from a TRANSP/NUBEAM simulation. Based on the measured FIDA spectra alone, we infer f(v‖, v⊥) by tomographic inversion. Salient features of our measurement of f(v‖, v⊥) agree reasonably well with the simulation: the measured as well as the simulated f(v‖, v⊥) are lopsided towards negative velocities parallel to the magnetic field, and they have similar shapes. Further, the peaks in the simulation of f(v‖, v⊥) at full and half injection energies of the neutral beam also appear in the measurement at similar velocity-space locations. We expect that we can measure spectra in up to seven views simultaneously in the next ASDEX Upgrade campaign which would further improve measurements of f(v‖, v⊥) by tomographic inversion.

  14. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

    DOE PAGESBeta

    Bayu Aji, L. B.; Wallace, J. B.; Shao, L.; Kucheyev, S. O.

    2016-04-14

    Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ~10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. Lastly, these results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

  15. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

    NASA Astrophysics Data System (ADS)

    Bayu Aji, L. B.; Wallace, J. B.; Shao, L.; Kucheyev, S. O.

    2016-05-01

    Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of  ∼10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. These results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

  16. Investigation of Ion Absorption of the High Harmonic Fast Wave in NSTX using HPRT

    SciTech Connect

    Rosenberg, A.; Menard, J.E.; and LeBlanc, B.P.

    2001-05-18

    Understanding high harmonic fast wave (HHFW) power absorption by ions in a spherical torus (ST) is of critical importance to assessing the wave's viability as a means of heating and especially driving current. In this work, the HPRT code is used to calculate absorption for helium and deuterium, with and without minority hydrogen in National Spherical Torus Experiment (NSTX) plasmas using experimental EFIT code equilibria and kinetic profiles. HPRT is a two-dimensional ray-tracing code which uses the full hot plasma dielectric to compute the perpendicular wave number along the hot electron and cold ion plasma ray path. Ion and electron absorption dependence on antenna phasing, ion temperature, beta (subscript t), and minority temperature and concentration is analyzed. These results form the basis for comparisons with other codes, such as CURRAY, METS, TORIC, and AORSA.

  17. Mobile ion distribution and anharmonic thermal motion in fast ion conducting Cu/sub 2/S

    SciTech Connect

    Cava, R.J.; Reidinger, F.; Wuensch, B.J.

    1981-01-01

    A unique model was determined for the mobile copper ion disorder in hexagonal Cu/sub 2/S between 120/sup 0/ and 325/sup 0/C via single crystal neutron diffraction. The copper ions partially occupy two sets of three-coordinated sites within the HCP sulfur array and display anharmonic thermal motion. The results suggest that the conductivity is two dimensional in nature.

  18. Competition between diffusion and electroconvection at an ion-selective surface in intensive current regimes.

    PubMed

    Nikonenko, V V; Vasil'eva, V I; Akberova, E M; Uzdenova, A M; Urtenov, M K; Kovalenko, A V; Pismenskaya, N P; Mareev, S A; Pourcelly, G

    2016-09-01

    Considering diffusion near a solid surface and simplifying the shape of concentration profile in diffusion-dominated layer allowed Nernst and Brunner to propose their famous equation for calculating the solute diffusion flux. Intensive (overlimiting) currents generate electroconvection (EC), which is a recently discovered interfacial phenomenon produced by the action of an external electric field on the electric space charge formed near an ion-selective interface. EC microscale vortices effectively mix the depleted solution layer that allows the reduction of diffusion transport limitations. Enhancement of ion transport by EC is important in membrane separation, nano-microfluidics, analytical chemistry, electrode kinetics and some other fields. This paper presents a review of the actual understanding of the transport mechanisms in intensive current regimes, where the role of diffusion declines in the profit of EC. We analyse recent publications devoted to explore the properties of different zones of the diffusion layer. Visualization of concentration profile and fluid current lines are considered as well as mathematical modelling of the overlimiting transfer. PMID:27457287

  19. Metal ions diffusion through polymeric matrices: A total reflection X-ray fluorescence study

    NASA Astrophysics Data System (ADS)

    Boeykens, S.; Caracciolo, N.; D'Angelo, M. V.; Vázquez, C.

    2006-11-01

    This work proposes the use of X-ray fluorescence with total reflection geometry to explore the metal ions transport in aqueous hydrophilic polymer solutions. It is centered in the study of polymer concentration influence on ion diffusion. This subject is relevant to various and diverse applications, such as drug controlled release, microbiologic corrosion protection and enhanced oil recovery. It is anticipated that diffusion is influenced by various factors in these systems, including those specific to the diffusing species, such as charge, shape, molecular size, and those related to the structural complexity of the matrix as well as any specific interaction between the diffusing species and the matrix. The diffusion of nitrate salts of Ba and Mn (same charge, different hydrodynamic radii) through water-swollen polymeric solutions and gels in the 0.01% to 1% concentration ranges was investigated. The measurements of the metal concentration were performed by TXRF analysis using the scattered radiation by the sample as internal standard. Results are discussed according to different physical models for solute diffusion in polymeric solutions.

  20. Cloride ion diffusion in low water-to-solid cement pastes

    SciTech Connect

    Clifton, J.R.; Knab, L.I.; Garboczi, E.J. ); Xiong, L.X. )

    1991-06-01

    Diffusion coefficients of 0.3 water to solids ratio (w/s) hydrated portland cement paste specimens were measured using a conventional diffusion cell. Specimens were made from both ASTM Type 1 and Type 2 portland cements and blends containing mineral admixtures (fly ash, granulated blastfurnace slag, or silica fume). The average diffusion coefficient for the portland cement paste specimens was 14 {times} 10{sup {minus}13} m{sup 2}/s. The diffusion coefficients for the specimens containing mineral admixtures were such more variable than those for the portland cement paste specimens. A probable cause of the variability in the test results was the presence of cracks observed in the test specimens. The effects of the depth of concrete cover over reinforcing steel and of the chloride ion diffusion coefficient on the service life of reinforced concrete exposed to chloride ions were predicted based on a diffusion model. Based on the model, the effect of the cover was shown to be proportional to the square of the cover depth. 18 refs., 5 figs., 6 tabs.

  1. Measurement and Simulation of First-Orbit Fast-Ion D-Alpha Emission and the Application to Fast-Ion Loss Detection in the DIII-D Tokamak

    NASA Astrophysics Data System (ADS)

    Bolte, Nathan; Heidbrink, W. W.; Pace, D. C.; van Zeeland, M. A.; Chen, X.

    2015-11-01

    A new fast-ion diagnostic method uses passive emission of D-alpha radiation to determine fast-ion losses quantitatively. The passive fast-ion D-alpha simulation (P-FIDAsim) forward models the Doppler-shifted spectra of first-orbit fast ions that charge exchange with edge neutrals. Simulated spectra are up to 80 % correlated with experimental spectra. Calibrated spectra are used to estimate the 2D neutral density profile by inverting simulated spectra. The inferred neutral density shows the expected increase toward each x-point and an average value of 8 × 10 9 cm-3 at the plasma boundary and 1 × 10 11 cm-3 near the wall. Measuring and simulating first-orbit spectra effectively ``calibrates'' the system, allowing for the quantification of more general fast-ion losses. Sawtooth crashes are estimated to eject 1.2 % of the fast-ion inventory, in good agreement with a 1.7 % loss estimate made by TRANSP. Sightlines sensitive to passing ions observe larger sawtooth losses than sightlines sensitive to trapped ions. Supported by US DOE under SC-G903402, DE-FC02-04ER54698.

  2. Point defect sinks in self-ion-irradiated nickel: A self-diffusion investigation

    SciTech Connect

    Mueller, A.; Naundorf, V.; Macht, M.

    1988-10-01

    The diffusion coefficient of /sup 63/Ni in pure nickel after irradiation with 300 keV Ni ions has been measured directly using a secondary ion mass spectrometer. The calculated displacement rate for this irradiation ranged from 1.2 x 10/sup -5/ to 3.1 x 10/sup -2/ dpa/s, the dose from 0.2 to 102 dpa, and the temperatures from 293 to 950 K. Between 293 and 650 K the irradiation-induced diffusion coefficient is temperature independent for a displacement rate of 1.2 x 10/sup -2/ dpa/s. In this temperature range mass transport by atomic mixing prevails over diffusion via point defects (radiation-enhanced diffusion). Normalized to the displacement rate K' the diffusion coefficient describing atomic mixing attains a value of D/sub mix/ /K' = 1.3 x 10/sup -18/ m/sup 2/ /dpa. The temperature and displacement rate dependence of the radiation-enhanced diffusion coefficient is discussed in the framework of a rate equation model. The analysis yields a production rate of freely migrating defects of about 1.5% of the calculated displacement rate. The effective concentration of point defect sinks was derived for nickel under heavy ion irradiation. This effective sink concentration C/sub s/ showed no dependence on displacement rate but a considerable temperature dependence, e.g., C/sub s/ = 2 x 10/sup -6/ at 850 K and C/sub s/ = 2.5 x 10/sup -7/ at 950 K. The conditions for a stationary effective sink concentration in self-ion irradiated nickel are discussed.

  3. The diffusion properties of ion implanted species in selected target materials

    SciTech Connect

    Alton, G.D.; Dellwo, J.; Carter, H.K.; Kormicki, J.; Bartolo, G. di; Batchelder, J.C.; Breitenbach, J.; Chediak, J.A.; Jentoff-Nilsen, K.; Ichikawa, S.

    1995-02-01

    Experiments important to the future success of the Holifield Radioactive Ion Beam Facility (HRIBF) are in progress at the Oak Ridge National Laboratory which are designed to select the most appropriate target material for generating a particular radioactive ion beam (RIB). The 25-MV HHIRF tandem accelerator is used to implant stable complements of interesting radioactive elements into refractory targets mounted in a high-temperature FEBIAD ion source which is {open_quotes}on-line{close_quotes} at the UNISOR facility. The intensity versus time of implanted species, which diffuse from the high-temperature target material ({approximately}1700{degrees}C) and are ionized in the FEBIAD ion source, is used to determine release times for a particular projectile/target material combination. From such release data, diffusion coefficients can be derived by fitting the theoretical results obtained by computational solution of Fick`s second equation to experimental data. The diffusion coefficient can be used subsequently to predict the release properties of the particular element from the same material in other target geometries and at other temperatures, provided that the activation energy is also known. Diffusion coefficients for Cl implanted into and diffused from CeS and Zr{sub 5}Si{sub 3} and As, Br, and Se implanted into and diffused from Zr{sub 5}Ge{sub 3} have been derived from the resulting intensity versus time profiles. Brief descriptions of the experimental apparatus and procedures utilized in the present experiments and plans for future related experiments are presented.

  4. Melting Point Depression and Fast Diffusion in Nanostructured Brazing Fillers Confined Between Barrier Nanolayers

    NASA Astrophysics Data System (ADS)

    Kaptay, G.; Janczak-Rusch, J.; Jeurgens, L. P. H.

    2016-08-01

    Successful brazing using Cu-based nanostructured brazing fillers at temperatures much below the bulk melting temperature of Cu was recently demonstrated (Lehmert et al. in, Mater Trans 56:1015-1018, 2015). The Cu-based nano-fillers are composed of alternating nanolayers of Cu and a permeable, non-wetted AlN barrier. In this study, a thermodynamic model is derived to estimate the melting point depression (MPD) in such Cu/AlN nano-multilayers (NMLs) as function of the Cu nanolayer thickness. Depending on the melting route, the model predicts a MPD range of 238-609 K for Cu10nm/AlN10nm NMLs, which suggests a heterogeneous pre-melting temperature range of 750-1147 K (476-874 °C), which is consistent with experimental observations. As suggested by basic kinetic considerations, the observed Cu outflow to the NML surface at the temperatures of 723-1023 K (450-750 °C) can also be partially rationalized by fast solid-state diffusion of Cu along internal interfaces, especially for the higher temperatures.

  5. Pitch angle diffusion of newborn ions due to intrinsic turbulence in the solar wind

    NASA Technical Reports Server (NTRS)

    Ziebell, L. F.; Yoon, Peter H.; Wu, C. S.; Winske, D.

    1990-01-01

    The objective of the present study is to understand the interaction of the solar wind with newborn ions in far upstream regions of a comet where the level of intrinsic turbulence is moderately low. Based on the assumption that quasi-linear theory is adequate and applicable, the pitch angle diffusion process and the time evolution of the newborn ion distribution function are investigated. Numerical solutions to the quasi-linear diffusion equation, including the effect of resonance broadening and that of continuous creation of newborn ions due to the ionization process, are obtained under several assumptions and approximations. It is found that theoretical results are consistent with the Giotto observations recently reported by Neugebauer et al. (1989).

  6. Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

    SciTech Connect

    Hofmann, F.; Mason, D. R.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Dudarev, S. L.

    2015-11-03

    Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.

  7. Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

    DOE PAGESBeta

    Hofmann, F.; Mason, D. R.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Dudarev, S. L.

    2015-11-03

    Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying withmore » transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.« less

  8. Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials

    PubMed Central

    Hofmann, F.; Mason, D. R.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Dudarev, S. L.

    2015-01-01

    Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants. PMID:26527099

  9. Tracer diffusion coefficient of oxide ions in LaCoO 3 single crystal

    NASA Astrophysics Data System (ADS)

    Ishigaki, Takamasa; Yamauchi, Shigeru; Mizusaki, Junichiro; Fueki, Kazuo; Tamura, Hifumi

    1984-08-01

    The tracer diffusion coefficient, D∗ O, of oxide ions in LaCoO 3 single crystal was determined over the temperature range of 700-1000°C by a gas-solid isotopic exchange technique using 18O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of D∗ O in LaCoO 3 was expressed by D∗ O( cm2· sec-1) = 3.63 × 10 4exp- {(74 ± 5) kcal · mole-1}/{RT} D∗ O at 950°C was found to be proportional to P-0.35O 2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole -1.

  10. Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials.

    PubMed

    Hofmann, F; Mason, D R; Eliason, J K; Maznev, A A; Nelson, K A; Dudarev, S L

    2015-01-01

    Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants. PMID:26527099

  11. Pitch angle diffusion of newborn ions due to intrinsic turbulence in the solar wind

    NASA Astrophysics Data System (ADS)

    Ziebell, L. F.; Yoon, Peter H.; Wu, C. S.; Winske, D.

    1990-10-01

    The objective of the present study is to understand the interaction of the solar wind with newborn ions in far upstream regions of a comet where the level of intrinsic turbulence is moderately low. Based on the assumption that quasi-linear theory is adequate and applicable, the pitch angle diffusion process and the time evolution of the newborn ion distribution function are investigated. Numerical solutions to the quasi-linear diffusion equation, including the effect of resonance broadening and that of continuous creation of newborn ions due to the ionization process, are obtained under several assumptions and approximations. It is found that theoretical results are consistent with the Giotto observations recently reported by Neugebauer et al. (1989).

  12. Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials.

    PubMed

    Hofmann, F; Mason, D R; Eliason, J K; Maznev, A A; Nelson, K A; Dudarev, S L

    2015-11-03

    Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.

  13. On resonant ICRF absorption in three-ion component plasmas: a new promising tool for fast ion generation

    NASA Astrophysics Data System (ADS)

    Kazakov, Ye. O.; Van Eester, D.; Dumont, R.; Ongena, J.

    2015-03-01

    We report on a very efficient ion-cyclotron-resonance-frequency (ICRF) absorption scheme (Z)-Y-X, which hinges on the presence of three ion species residing in the plasma. A mode conversion (cutoff-resonance) layer is well known to appear in two-ion species plasmas. If the location of the L-cutoff in Y-X plasmas, which can be controlled by varying the Y : X density ratio, almost coincides with the fundamental cyclotron resonance of the third ion species Z (resonant absorber), the latter—albeit present only in trace quantities—is shown to absorb almost all the incoming RF power. A quantitative criterion for the resonant Y : X plasma composition is derived and a few numerical examples are given. Since the absorbed power per resonant particle is much larger than for any other ICRF scheme, the here discussed scenarios are particularly promising for fast particle generation. Their possible application as a source of high-energy ions for the stellarator W7-X and to mimic alpha particles during the non-activated phase of ITER tokamak is briefly discussed.

  14. Inversion methods for fast-ion velocity-space tomography in fusion plasmas

    NASA Astrophysics Data System (ADS)

    Jacobsen, A. S.; Stagner, L.; Salewski, M.; Geiger, B.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Thomsen, H.; Weiland, M.; the ASDEX Upgrade Team

    2016-04-01

    Velocity-space tomography has been used to infer 2D fast-ion velocity distribution functions. Here we compare the performance of five different tomographic inversion methods: truncated singular value decomposition, maximum entropy, minimum Fisher information and zeroth- and first-order Tikhonov regularization. The inversion methods are applied to fast-ion {{\\text{D}}α} measurements taken just before and just after a sawtooth crash in the ASDEX Upgrade tokamak as well as to synthetic measurements from different test distributions. We find that the methods regularizing by penalizing steep gradients or maximizing entropy perform best. We assess the uncertainty of the calculated inversions taking into account photon noise, uncertainties in the forward model as well as uncertainties introduced by the regularization which allows us to distinguish regions of high and low confidence in the tomographies. In high confidence regions, all methods agree that ions with pitch values close to zero, as well as ions with large pitch values, are ejected from the plasma center by the sawtooth crash, and that this ejection depletes the ion population with large pitch values more strongly.

  15. Simulations of ion acceleration at non-relativistic shocks. III. Particle diffusion

    SciTech Connect

    Caprioli, D.; Spitkovsky, A.

    2014-10-10

    We use large hybrid (kinetic-protons-fluid-electrons) simulations to investigate the transport of energetic particles in self-consistent electromagnetic configurations of collisionless shocks. In previous papers of this series, we showed that ion acceleration may be very efficient (up to 10%-20% in energy), and outlined how the streaming of energetic particles amplifies the upstream magnetic field. Here, we measure particle diffusion around shocks with different strengths, finding that the mean free path for pitch-angle scattering of energetic ions is comparable with their gyroradii calculated in the self-generated turbulence. For moderately strong shocks, magnetic field amplification proceeds in the quasi-linear regime, and particles diffuse according to the self-generated diffusion coefficient, i.e., the scattering rate depends only on the amount of energy in modes with wavelengths comparable with the particle gyroradius. For very strong shocks, instead, the magnetic field is amplified up to non-linear levels, with most of the energy in modes with wavelengths comparable to the gyroradii of highest-energy ions, and energetic particles experience Bohm-like diffusion in the amplified field. We also show how enhanced diffusion facilitates the return of energetic particles to the shock, thereby determining the maximum energy that can be achieved in a given time via diffusive shock acceleration. The parameterization of the diffusion coefficient that we derive can be used to introduce self-consistent microphysics into large-scale models of cosmic ray acceleration in astrophysical sources, such as supernova remnants and clusters of galaxies.

  16. Design and calibration of the fast ion diagnostic experiment detector on the poloidal divertor experiment

    SciTech Connect

    Kaita, R.; Goldston, R.J.; Meyerhofer, D.; Eridon, J.

    1981-12-01

    A special purpose charge-exchange analyzer was constructed to measure the spatial distribution of hot-plasma ions, as a function of energy and time, in the poloidal divertor experiment (PDX). The fast neutrals produced by charge exchange within the tokamak are reionized as they pass through a helium stripping cell in the detector. The energies of these ions are determined by the trajectories they follow between cylindrical deflection plates which are set at known electrostatic potentials. We describe the technique used to calibrate the response of this system as it depends on the energies and the masses of the particles which are being detected.

  17. Fast solute diffusivity in ionic liquids with silyl or siloxane groups studied by the transient grating method

    NASA Astrophysics Data System (ADS)

    Endo, Takatsugu; Nemugaki, Shinya; Matsushita, Yuki; Sakai, Yasuhiro; Ozaki, Hiroaki; Hiejima, Yusuke; Kimura, Yoshifumi; Takahashi, Kenji

    2016-06-01

    To achieve ionic liquids (ILs) that show fast solute diffusivity independent of viscosity domination, sixteen ILs containing Si or Si-O-Si groups (SiILs) were synthesized. Diffusion coefficients of three solute molecules with different molecular sizes, i.e., CO, diphenylacetylene, and diphenylcyclopropenone, were determined in SiILs using the transient grating method and the results were compared to other solvent system. SiILs showed distinguishably faster diffusivity for the smallest solute, CO, than conventional ILs at the same viscosity, particularly in the high viscosity region. Based on previous results and our estimation, three plausible factors exists that contribute to the faster solute diffusivity in SiILs, i.e., the flexibility of the Si or Si-O-Si group, decreased interaction between the cation and the solute, and increased free volume because of the bulky structure.

  18. A 3D computer simulation of negative ion extraction influenced by electron diffusion and weak magnetic field

    SciTech Connect

    Turek, M.; Sielanko, J.

    2008-03-19

    The numerical model of negative ion beam extraction from the RF ion source by different kinds of large extraction grid systems is considered. The model takes into account the influence of the transversal magnetic field and the electron diffusion. The magnetic filter field increases H{sup -} yields significantly. The random-walk electron diffusion model enables electrons to travel through magnetic field. The H{sup -} currents obtained from simulations with or without the diffusion are compared.

  19. Fast-ion energy resolution by one-step reaction gamma-ray spectrometry

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Nocente, M.; Gorini, G.; Jacobsen, A. S.; Kiptily, V. G.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Tardocchi, M.; Contributors, JET

    2016-04-01

    The spectral broadening of γ-rays from fusion plasmas can be measured in high-resolution gamma-ray spectrometry (GRS). We derive weight functions that determine the observable velocity space and quantify the velocity-space sensitivity of one-step reaction high-resolution GRS measurements in magnetized fusion plasmas. The weight functions suggest that GRS resolves the energies of fast ions directly without the need for tomographic inversion for selected one-step reactions at moderate plasma temperatures. The D(p,γ)3He reaction allows the best direct fast-ion energy resolution. We illustrate our general formalism using reactions with and without intrinsic broadening of the γ-rays for the GRS diagnostic at JET.

  20. Studies of the fast ion energy spectra in TJ-II

    SciTech Connect

    Bustos, A.; Fontdecaba, J. M.; Arevalo, J.; Castejon, F.; Velasco, J. L.; Tereshchenko, M.

    2013-02-15

    The dynamics of the neutral beam injection fast ions in the TJ-II stellarator is studied in this paper from both the theoretical and experimental points of view. The code Integrator of Stochastic Differential Equations for Plasmas (ISDEP) is used to estimate the fast ion distribution function in 3D:1D in real space and 2D in velocity space, considering the 3D structure of TJ-II, the electrostatic potential, non turbulent collisional transport, and charge exchange losses. The results of ISDEP are compared with the experimental data from the compact neutral particle analyzer, which measures the outgoing neutral flux spectra in the energy range E Element-Of (1-45) keV.

  1. A compact high resolution ion mobility spectrometer for fast trace gas analysis.

    PubMed

    Kirk, Ansgar T; Allers, Maria; Cochems, Philipp; Langejuergen, Jens; Zimmermann, Stefan

    2013-09-21

    Drift tube ion mobility spectrometers (IMS) are widely used for fast trace gas detection in air, but portable compact systems are typically very limited in their resolving power. Decreasing the initial ion packet width improves the resolution, but is generally associated with a reduced signal-to-noise-ratio (SNR) due to the lower number of ions injected into the drift region. In this paper, we present a refined theory of IMS operation which employs a combined approach for the analysis of the ion drift and the subsequent amplification to predict both the resolution and the SNR of the measured ion current peak. This theoretical analysis shows that the SNR is not a function of the initial ion packet width, meaning that compact drift tube IMS with both very high resolution and extremely low limits of detection can be designed. Based on these implications, an optimized combination of a compact drift tube with a length of just 10 cm and a transimpedance amplifier has been constructed with a resolution of 183 measured for the positive reactant ion peak (RIP(+)), which is sufficient to e.g. separate the RIP(+) from the protonated acetone monomer, even though their drift times only differ by a factor of 1.007. Furthermore, the limits of detection (LODs) for acetone are 180 pptv within 1 s of averaging time and 580 pptv within only 100 ms.

  2. Ion cyclotron diffusion of velocity distributions in the extended solar corona

    NASA Astrophysics Data System (ADS)

    Cranmer, Steven R.

    2001-11-01

    The Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory has revealed strong kinetic anisotropies and extremely large perpendicular temperatures of heavy ions in the extended solar corona. These observations have revived interest in the idea that the high-speed solar wind is heated and accelerated by the dissipation of ion cyclotron resonant Alfvén waves. This process naturally produces departures from Maxwellian and bi-Maxwellian velocity distributions. Here it is argued that these departures must be taken into account in order to understand the resonant velocity space diffusion, the wave damping, and the formation of ultraviolet emission lines. Time-dependent ion velocity distributions are computed for a fixed spectrum of waves in a homogeneous plasma, and the moments of the distributions are compared with simple bi-Maxwellian models. The existence of a boundary, in parallel velocity space, between resonance and nonresonance produces an effective saturation of the velocity space diffusion that bi-Maxwellian models could not predict. The damping of an input wave spectrum is computed for a coronal population of 1000 ion species with the above saturation effect included. For realistic levels of fluctuation power, it is concluded that waves propagating solely from the coronal base would not be able to heat and accelerate the ions that have been observed to exhibit strong energization and that local wave generation is required. Ultraviolet emission line profiles are computed for the derived non-Maxwellian distributions, and possible unique identifiers of the ion cyclotron resonance mechanism are noted.

  3. Modeling ion exchange in glass with concentration-dependent diffusion coefficients and mobilities

    NASA Astrophysics Data System (ADS)

    Lupascu, Alexandru I.; Kevorkian, Antoine P.; Boudet, Thierry; Saint-Andre, Francoise; Persegol, Dominique; Levy, Michel

    1996-06-01

    Multimode buried waveguides made in silicate glass by field-assisted ion exchange present very asymmetric profiles. We show how this phenomenon originates in the large dependence of the kinetics on the local ion concentrations. For this purpose, we derive an interdiffusion equation that includes the effects of concentration-dependent diffusion coefficients and mobilities. We show how to deduce this dependence from measurements on ion- diffused samples. The maximum concentration of the incoming ions is computed from surface equilibrium conditions and is used in the interdiffusion equation as a limiting parameter for coefficient variations. To control the model accuracy for surface as well as buried waveguides, we measure ion profiles with three independent methods: M-lines, scanning electron microscopy, and near-field refractometry. When applied to Ag+-Na+ exchange in silicate glass, the model yields theoretical estimations in good agreement with experiments. This approach underlines the fundamentally nonlinear process that takes place during ion exchange and is also valuable to properly model singlemode waveguide fabrication.

  4. Phase angle diffusion of newborn ions in the self-consistently generated fields in solar wind plasmas

    NASA Astrophysics Data System (ADS)

    Cao, J. B.; Mazelle, C.; Zhou, G. C.

    2000-02-01

    The phase angle diffusion, pitch angle diffusion, and energy diffusion of newborn ions in the self-consistently generated fields in solar wind plasmas are studied by means of a one-dimensional electromagnetic hybrid code. For newborn ions, the time for phase angle diffusing to 2π is a little shorter than the time for pitch angle scattering to a relatively thin complete shell, and it is much shorter than the energy scattering time for broadening of the shell toward a thermal distribution. The speed of phase angle diffusion increases monotonously with the injection velocity, but it does not change in the same way with the injection rate. The phase angle diffusion of heavier injected ions is slower than that of lighter injected ions. The complete pickup process of newborn ions should consist of four stages: (1) the creation of the newborn ions and macroperpendicular pickup due to the motional electric field; (2) phase angle diffusion; (3) pitch angle diffusion; and (4) energy diffusion.

  5. High-definition velocity-space tomography of fast-ion dynamics

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Jacobsen, A. S.; Hansen, P. C.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S. K.; Nocente, M.; Odstrčil, T.; Rasmussen, J.; Stagner, L.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

    2016-10-01

    Velocity-space tomography of the fast-ion distribution function in a fusion plasma is usually a photon-starved tomography method due to limited optical access and signal-to-noise ratio of fast-ion D α (FIDA) spectroscopy as well as the strive for high-resolution images. In high-definition tomography, prior information makes up for this lack of data. We restrict the target velocity space through the measured absence of FIDA light, impose phase-space densities to be non-negative, and encode the known geometry of neutral beam injection (NBI) sources. We further use a numerical simulation as prior information to reconstruct where in velocity space the measurements and the simulation disagree. This alternative approach is demonstrated for four-view as well as for two-view FIDA measurements. The high-definition tomography tools allow us to study fast ions in sawtoothing plasmas and the formation of NBI peaks at full, half and one-third energy by time-resolved tomographic movies.

  6. Interstitial and interlayer ion diffusion geometry extraction in graphitic nanosphere battery materials

    DOE PAGESBeta

    Gyulassy, Attila; Knoll, Aaron; Lau, Kah Chun; Wang, Bei; Bremer, Peer -Timo; Papka, Michael E.; Curtiss, Larry A.; Pascucci, Valerio

    2016-01-31

    Large-scale molecular dynamics (MD) simulations are commonly used for simulating the synthesis and ion diffusion of battery materials. A good battery anode material is determined by its capacity to store ion or other diffusers. However, modeling of ion diffusion dynamics and transport properties at large length and long time scales would be impossible with current MD codes. To analyze the fundamental properties of these materials, therefore, we turn to geometric and topological analysis of their structure. In this paper, we apply a novel technique inspired by discrete Morse theory to the Delaunay triangulation of the simulated geometry of a thermallymore » annealed carbon nanosphere. We utilize our computed structures to drive further geometric analysis to extract the interstitial diffusion structure as a single mesh. Lastly, our results provide a new approach to analyze the geometry of the simulated carbon nanosphere, and new insights into the role of carbon defect size and distribution in determining the charge capacity and charge dynamics of these carbon based battery materials.« less

  7. The dissociative single and double ionization of some simple molecules by fast ions and VUV photons

    NASA Astrophysics Data System (ADS)

    Browne, Clive Ronald Harold

    The partial cross sections for the production of energetic fragment protons/deuterons in the dissociative photoionization of HCl/DCl and H2S/D2 S have been determined using vacuum ultraviolet (VUV) photons in the 20-50eV photon energy range. Thresholds in the gross structure of the partial photoionization. cross sections were visible and these values were found to agree well with previous experimental and theoretical data corresponding to Franck-Condon excitations. The kinetic energy spectra of the fragment protons/deuterons produced in the dissociative single and double photoionization of HCl/DCl and H 2S/D2S by 20-50eV photons have been obtained for the first time. The nature of the fragment ions shown in the energy spectra confirm the important role played by indirect fragmentation mechanisms, especially in the double ionization processes. Complementary mass and kinetic energy spectra of the molecular fragment ions formed in the dissociative ionization of the CH4, C2 H2, C2H4, C2H6, and C3H8 group of hydrocarbons have been measured using fast (3-30keV) H+ and He+ ions. The observed differences, between projectiles, in the mass and energy spectra indicate that in contrast to H+, fragmentation of the molecules by He + ions is not governed by the Born approximation. An investigation has also been carried out into the energy distribution of the fragment ion-pairs produced in the dissociative double ionization of H2, D2, H2O and N2 by fast (3-30keV) ion impact. The kinetic energy spectra show ample evidence of low energy (2-7eV) ions and ion-pairs, in agreement with previous reports, supporting the suggestion that they are formed through two-electron excited autoionizing states. The energy distributions of N+N+ ion-pairs produced from the dissociative ionization of N2 by He+ ions shows considerable structure and some interesting contrasts with those produced by H+ ions.

  8. Radon (222Rn) in ground water of fractured rocks: A diffusion/ion exchange model

    USGS Publications Warehouse

    Wood, W.W.; Kraemer, T.F.; Shapiro, A.

    2004-01-01

    Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion- exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42??56???N, 71??43???W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model.

  9. Radon (222Rn) in ground water of fractured rocks: a diffusion/ion exchange model.

    PubMed

    Wood, Warren W; Kraemer, Thomas F; Shapiro, Allen

    2004-01-01

    Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion-exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42 degrees 56'N, 71 degrees 43'W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model. PMID:15318778

  10. Radon (222Rn) in ground water of fractured rocks: a diffusion/ion exchange model.

    PubMed

    Wood, Warren W; Kraemer, Thomas F; Shapiro, Allen

    2004-01-01

    Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion-exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42 degrees 56'N, 71 degrees 43'W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model.

  11. The influence of collisional and anomalous radial diffusion on parallel ion transport in edge plasmas

    SciTech Connect

    Helander, P.; Hazeltine, R.D.; Catto, P.J.

    1996-12-31

    The orderings in the kinetic equations commonly used to study the plasma core of a tokamak do not allow a balance between parallel ion streaming and radial diffusion, and are, therefore, inappropriate in the plasma edge. Different orderings are required in the edge region where radial transport across the steep gradients associated with the scrape-off layer is large enough to balance the rapid parallel flow caused by conditions close to collecting surfaces (such as the Bohm sheath condition). In the present work, we derive and solve novel kinetic equations, allowing for such a balance, and construct distinctive transport laws for impure, collisional, edge plasmas in which the perpendicular transport is (i) due to Coulomb collisions of ions with heavy impurities, or (ii) governed by anomalous diffusion driven by electrostatic turbulence. In both the collisional and anomalous radial transport cases, we find that one single diffusion coefficient determines the radial transport of particles, momentum and heat. The parallel transport laws and parallel thermal force in the scrape-off layer assume an unconventional form, in which the relative ion-impurity flow is driven by a combination of the conventional parallel gradients, and new (i) collisional or (ii) anomalous terms involving products of radial derivatives of the temperature and density with the radial shear of the parallel velocity. Thus, in the presence of anomalous radial diffusion, the parallel ion transport cannot be entirely classical, as usually assumed in numerical edge computations. The underlying physical reason is the appearance of a novel type of parallel thermal force resulting from the combined action of anomalous diffusion and radial temperature and velocity gradients. In highly sheared flows the new terms can modify impurity penetration into the core plasma.

  12. Modification of water in a nanosecond diffuse discharge with fast electron preionization at a short voltage rise time

    NASA Astrophysics Data System (ADS)

    Orlovskii, Victor M.; Panarin, Victor A.; Shulepov, Mikhail A.

    2015-12-01

    The paper studies the dynamics of a nanosecond diffuse discharge with no additional preionization at a voltage rise time of less than 1 ns and its effect on drinking and distilled water. It is shown that the diffuse discharge is formed due to avalanche charge multiplication initiated by fast electrons and is sustained by secondary breakdown waves through ionized gas channels. Fourier transform infrared spectroscopy reveals that repeated exposure to the discharge changes the absorption spectra of drinking and distilled water such that the stretching vibration band of OH groups broadens and lacks clearly defined peaks. The water conductivity after irradiation increases. Probably, this is due to cluster rearrangement of water molecules.

  13. Relation between Longitudinal and Transverse Diffusion Coefficients of Alkali Ions in Noble Gases

    NASA Astrophysics Data System (ADS)

    Hogan, M. J.

    1997-10-01

    The relation between longitudinal and transverse diffusion coefficients of ions drifting in a neutral gas under the influence of an electric field has been investigated for alkali ions in noble gases. The 125 combinations of ions of Li, Na, K, Rb, and Cs in the neutral gases He, Ne, Ar, Kr, and Xe at gas temperatures of 100, 200, 300, 400 and 500 K were included in this study. Plots of the ratio of the longitudinal-to-transverse diffusion coefficients versus E/N exhibited similar variation in the values of the ratios. As the value of E/N increased from zero, the value of the ratio increased rapidly from one for all ion/neutral/temperature combinations. The ratio peaked at values mostly in the range of 1.2 to 2.5 at E/N values in the range of 20 to 120 Td. As E/N increased further, the ratio values decreased, at an ever lower rate, to values ranging from 0.8 to 1.2. These results suggest the existence of a single function relating the longitudinal and transverse diffusion coefficients.

  14. Diffusion coefficients of ions in lighter gases in an electric field

    NASA Astrophysics Data System (ADS)

    Ferrari, Leonardo

    1996-05-01

    The diffusion theory for ions in single lighter gases (and in mixtures of lighter gases), in moderately low electrostatic fields, is formulated in the so-called quasi-Rayleigh limit, starting from a proper approximate kinetic equation previously derived by the author. In this way new simple approximate expressions for transverse and longitudinal ion temperatures and diffusion coefficients are obtained. Their dependence on the ion-neutral interaction law is investigated in the simple case of an inverse-power force law. Moreover, the results are compared with the previous ones of the literature. In particular, agreement is found with Wannier's results in the Maxwell model and with the results of the first Chapman-Enskog approximation. On the contrary, some discrepancies with the one-temperature formulation of the moment method are encountered as regards the transverse ion temperature and the transverse diffusion coefficient, but this appears to be due to the questionable computational criteria used in the above method. Finally, the limits of validity of the present formulas are discussed.

  15. Quasi-linear pitch angle and energy diffusion of pickup ions near Comet Halley

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Johnstone, A. D.; Coates, A. J.; Neubauer, F. M.

    1991-01-01

    The process of ion pickup in the environment of Halley's comet is studied in order to see if velocity diffusion driven by the observed level of turbulence can explain the observed development of the implanted ion distribution. The theoretical description used is based on a quasi-linear approach and considers the implantation and transport of cometary ions along solar wind flow lines. To make such a study requires some way of extrapolating the measurements on the Giotto trajectory into the upstream region; models for mass loading and turbulence are used. A simplified kinetic equation describing the source, convection, and quasi-linear velocity diffusion of the heavy cometary ions is solved numerically along flow lines parallel to the sun-comet line. Full two-dimensional (pitch angle and velocity) distributions are obtained at positions along the Giotto trajectory, which are compared with measurements. This study finds that quasi-linear theory, with the empirical model for the observed turbulence level, produces the right order of pitch angle diffusion.

  16. Ultrafast and directional diffusion of lithium in phosphorene for high-performance lithium-ion battery.

    PubMed

    Li, Weifeng; Yang, Yanmei; Zhang, Gang; Zhang, Yong-Wei

    2015-03-11

    Density functional theory calculations have been performed to investigate the binding and diffusion behavior of Li in phosphorene. Our studies reveal the following findings: (1) Li atom forms strong binding with phosphorus atoms and exists in the cationic state; (2) the shallow energy barrier (0.08 eV) of Li diffusion on monolayer phosphorene along zigzag direction leads to an ultrahigh diffusivity, which is estimated to be 10(2) (10(4)) times faster than that on MoS2 (graphene) at room temperature; (3) the large energy barrier (0.68 eV) along armchair direction results in a nearly forbidden diffusion, and such strong diffusion anisotropy is absent in graphene and MoS2; (4) a remarkably large average voltage of 2.9 V is predicted in the phosphorene-based Li-ion battery; and (5) a semiconducting to metallic transition induced by Li intercalation of phosphorene gives rise to a good electrical conductivity, ideal for use as an electrode. Given these advantages, it is expected that phosphorene will present abundant opportunities for applications in novel electronic device and lithium-ion battery with a high rate capability and high charging voltage.

  17. Ultrafast and directional diffusion of lithium in phosphorene for high-performance lithium-ion battery.

    PubMed

    Li, Weifeng; Yang, Yanmei; Zhang, Gang; Zhang, Yong-Wei

    2015-03-11

    Density functional theory calculations have been performed to investigate the binding and diffusion behavior of Li in phosphorene. Our studies reveal the following findings: (1) Li atom forms strong binding with phosphorus atoms and exists in the cationic state; (2) the shallow energy barrier (0.08 eV) of Li diffusion on monolayer phosphorene along zigzag direction leads to an ultrahigh diffusivity, which is estimated to be 10(2) (10(4)) times faster than that on MoS2 (graphene) at room temperature; (3) the large energy barrier (0.68 eV) along armchair direction results in a nearly forbidden diffusion, and such strong diffusion anisotropy is absent in graphene and MoS2; (4) a remarkably large average voltage of 2.9 V is predicted in the phosphorene-based Li-ion battery; and (5) a semiconducting to metallic transition induced by Li intercalation of phosphorene gives rise to a good electrical conductivity, ideal for use as an electrode. Given these advantages, it is expected that phosphorene will present abundant opportunities for applications in novel electronic device and lithium-ion battery with a high rate capability and high charging voltage. PMID:25664808

  18. Study of Cu diffusion in porous dielectrics using secondary-ion-mass spectrometry

    SciTech Connect

    Rodriguez, Oscar R.; Gill, William N.; Plawsky, Joel L.; Tsui Ting, Y.; Grunow, Stephan

    2005-12-15

    Secondary-ion-mass spectrometry measurements were used to study Cu diffusion in porous silica. The total concentration of Cu{sup +} decreases with increasing porosity of the dielectric. This behavior is the combined result of both the chemistry and the morphology of the dielectric. The injection of Cu is triggered by outgassing of hydroxyl and water-related species from the dielectric; furthermore, the reduced available cross-sectional area of solid for diffusion, due to porosity, leads to reduced diffusion through the porous film. This suggests that surface diffusion does not play an important role in this process. The Cu{sup +} concentration at the Cu/dielectric interface is on the order of 10{sup 23} at./m{sup 3}, but decreases with time and exponentially with porosity, which suggests the occurrence of a chemical reaction at the interface. A model of molecular diffusion and ion drift that considers the porosity of the film is developed and the results are consistent with the experimental data.

  19. Distribution of energetic positive ion species above a diffuse midnight aurora

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Evans, D. S.

    1979-01-01

    The present paper deals with species-identifying distribution function measurements of auroral primary particles, made during a magnetically quiet presubstorm period above a hydrogen-associated diffuse aurora. Only ions identified as H(+) and He(++) were detected. In the mass spectrum data, the He(++) was not clearly above background. At energies between 2.5 and 12 keV, the He(++)/H(+) intensity ratio had an upper limit of 2 to 4 percent. The same upper limit applies to all other ions, such as He(+) and O(+). Though this would suggest a solar wind source for these ions, an admixture including an appreciable fraction of polar wind protons is not precluded. This situation contrasts sharply with a number of recently reported observations of large intensities of precipitating O(+) ions during magnetic storms, and may be characteristic of undisturbed periods.

  20. Ultra-low vanadium ion diffusion amphoteric ion-exchange membranes for all-vanadium redox flow batteries

    NASA Astrophysics Data System (ADS)

    Liao, J. B.; Lu, M. Z.; Chu, Y. Q.; Wang, J. L.

    2015-05-01

    An amphoteric ion-exchange membrane (AIEM) from fluoro-methyl sulfonated poly(arylene ether ketone) bearing content-controlled benzimidazole moiety, was firstly fabricated for vanadium redox flow battery (VRB). The AIEM and its covalently cross-linked membrane (AIEM-c) behave the highly suppressed vanadium-ion crossover and their tested VO2+ permeability are about 638 and 1117 times lower than that of Nafion117, respectively. This is further typically verified by the lower VO2+ concentration inside AIEM that is less than half of that inside Nafion117 detected by energy dispersive X-ray spectrometry, in addition of the nearly 3 times longer battery self-discharge time. The ultra-low vanadium ion diffusion could be ascribed to the narrower ion transporting channel originated from the acid-base interactions and the rebelling effect between the positively-charged benzimidazole structure and VO2+ ions. It is found that, VRB assembled with AIEM exhibits the equal or higher Coulombic efficiency (99.0% vs. 96.4%), voltage efficiency (90.7% vs. 90.7%) and energy efficiency (89.8% vs. 87.4%) than that with Nafion117 and keeps continuous 220 charge-discharge cycles for over 25 days, confirming that the AIEM of this type is a potentially suitable separator for VRB application.

  1. Coherent Events and Spectral Shape at Ion Kinetic Scales in the Fast Solar Wind Turbulence

    NASA Astrophysics Data System (ADS)

    Lion, Sonny; Alexandrova, Olga; Zaslavsky, Arnaud

    2016-06-01

    In this paper we investigate spectral and phase coherence properties of magnetic fluctuations in the vicinity of the spectral transition from large, magnetohydrodynamic to sub-ion scales using in situ measurements of the Wind spacecraft in a fast stream. For the time interval investigated by Leamon et al. (1998) the phase coherence analysis shows the presence of sporadic quasi-parallel Alfvén ion cyclotron (AIC) waves as well as coherent structures in the form of large-amplitude, quasi-perpendicular Alfvén vortex-like structures and current sheets. These waves and structures importantly contribute to the observed power spectrum of magnetic fluctuations around ion scales; AIC waves contribute to the spectrum in a narrow frequency range whereas the coherent structures contribute to the spectrum over a wide frequency band from the inertial range to the sub-ion frequency range. We conclude that a particular combination of waves and coherent structures determines the spectral shape of the magnetic field spectrum around ion scales. This phenomenon provides a possible explanation for a high variability of the magnetic power spectra around ion scales observed in the solar wind.

  2. Diffusivity of ions in agarose gels and intervertebral disc: effect of porosity.

    PubMed

    Gu, Wei Yong; Yao, Hai; Vega, Adriana L; Flagler, Daniel

    2004-12-01

    The effect of tissue porosity on ion (sodium, potassium, and chloride) diffusivity in agarose gels and porcine intervertebral disc tissues was investigated using an electrical conductivity method. An empirical, constitutive model for diffusivity (D) of solutes in porous fibrous media was proposed: D/Do = exp[-alpha(r(s)/k(1/2))beta] where r(s) is the Stokes radius of a solute, kappa is the Darcy permeability of the porous medium, Do is the diffusivity in free solution, alpha and beta are two positive parameters whose values depend on material structure. It is found that alpha = 1.25 +/- 0.138, beta = 0.681 +/- 0.059 (95% confidence interval, R2 = 0.92, n = 72) for agarose gels and alpha = 1.29 +/- 0.171 and beta = 0.372 +/- 0.088 (95% confidence interval, R2 = 0.88, n = 86) for porcine annulus fibrosus. The functional relationship between solute diffusivity and tissue deformation was derived. Comparisons of our model prediction with experimental data on diffusion coefficients of macromolecules (proteins, dextrans, polymer beads) in agarose gels in the literature were made. Our results were also compared to the data on ion diffusivity in charged gels and in cartilaginous tissues reported in the literature. There was a good agreement between our model prediction and the data in the literature. The present study provides additional information on solute diffusivity in uncharged gels and charged tissues, and is important for understanding nutritional transport in avascular cartilaginous tissues under different mechanical loading conditions.

  3. Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind

    SciTech Connect

    Ziebell, L.F.; Yoon, P.H. )

    1990-12-01

    The present study is dedicated to the analysis of dynamical processes relevant to the interaction of newborn ions with turbulence in the solar wind, when the level of turbulence is moderately low so that quasi-linear theory is applicable. It is assumed that the low-frequency turbulence is at saturation level and not affected by the newborn ions. In order to follow the time evolution of the ion distribution, the quasi-linear diffusion equation is derived and numerically solved, starting from a ring-beam initial distribution. A simplified treatment of the resonance broadening effect is included in the diffusion equation, and its role in the pickup process is discussed. Two different configurations of wave polarization and direction of propagation are considered, using model turbulence spectra. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as well as the conditions leading to significant acceleration of the ions.

  4. Experience With Carbon Ion Radiotherapy for WHO Grade 2 Diffuse Astrocytomas

    SciTech Connect

    Hasegawa, Azusa; Mizoe, Jun-Etsu; Tsujii, Hirohiko; Kamada, Tadashi; Jingu, Keiichi; Iwadate, Yasuo; Nakazato, Youichi; Matsutani, Masao; Takakura, Kintomo

    2012-05-01

    Purpose: To assess outcomes of carbon ion radiotherapy for diffuse astrocytomas in adults. Methods and Materials: Between October 1994 and February 2002, 14 patients with diffuse astrocytoma, identified as eligible for carbon ion radiotherapy, were enrolled in a phase I/II clinical trial. Carbon ion radiotherapy was administered in 24 fractions over 6 weeks. The normal tissue morbidity was monitored carefully, and the carbon ion dose was escalated from 50.4 Gy equivalent (GyE) to 55.2 GyE. Patients were divided into two groups according to their carbon ion doses: a low-dose group in which 2 patients were irradiated with 46.2 GyE and 7 patients were irradiated with 50.4 GyE, and a high-dose group in which 5 patients were irradiated with 55.2 GyE. Results: Toxicities were within acceptable limits, and none of the patients developed Grade 3 or higher acute or late reactions. The median progression-free survival (PFS) time was 18 months for the low-dose group and 91 months for the high-dose group (p = 0.0030). The median overall survival (OS) time was 28 months for the low-dose group and not reached for the high-dose group (p = 0.0208). Conclusion: High-dose group patients showed significant improvement in PFS and OS rates compared to those in the low-dose group, and both dose groups showed acceptable toxicity.

  5. Validity of the second Fick's law for modeling ion-exchange diffusion in non-crystalline viscoelastic media (glasses)

    NASA Astrophysics Data System (ADS)

    Tagantsev, D. K.; Ivanenko, D. V.

    2016-04-01

    It is shown that, in general case, the diffusion equation (or the second Fick's law) does not provide an adequate description of ion-exchange transport phenomena in viscoelastic media, including glassy or any other non-crystalline media. In this connection the general phenomenological model of ion-exchange diffusion in viscoelastic media has been developed. A theoretical analysis of the model shows that, in the case of a linear dependence of medium density on the concentration of diffusing ions, the necessary and sufficient condition of the absolute validity of the diffusion equation in viscoelastic media is Φ ≫ 1, where Φ = τD/τR is the dimensionless value (or criterion of similarity), with τD = L2/D being the characteristic time of diffusion and τR = η/G being the characteristic time of stress relaxation, where L, D, η, and G are the characteristic length of diffusion, the diffusivity, the viscosity, and the shear modulus, respectively. The value of 1/Φ characterizes the accuracy which is provided if the second Fick's law is used in the simulation of ion-exchange diffusion in viscoelastic media. We have demonstrated the applicability of this criterion experimentally. Our experimental studies on ion-exchange diffusion in an oxide glass (typical viscoelastic media) have shown that under the condition the Φ > 105 the experimental concentration profiles are close to those predicted by the second Fick's law to within an accuracy of 1%.

  6. Na0.44MnO2 with very fast sodium diffusion and stable cycling synthesized via polyvinylpyrrolidone-combustion method

    NASA Astrophysics Data System (ADS)

    Dai, Kehua; Mao, Jing; Song, Xiangyun; Battaglia, Vince; Liu, Gao

    2015-07-01

    Na0.44MnO2 is a very promising cathode material in sodium-ion batteries for large-scale application. Na0.44MnO2 with very fast sodium diffusion and stable cycling is prepared by polyvinylpyrrolidone (PVP)-combustion method. X-ray diffraction, scanning electron microscope and high-resolution transmission electron microscopy are conducted to explore the morphology and structure. Electrochemical performance of the samples is examined in coin cells with sodium foil anode and nonaqueous electrolyte. The Na0.44MnO2 sample synthesized at 900 °C (NMO-900) discharges the highest capacity of 122.9 mAh g-1 at C/5. A fast-rate-test technique developed by Newman et al. is adopted for quick determination of the rate capability. All the samples exhibit good rate capability while the NMO-900 shows the best. Normal rate test result supports the reliability of the fast rate test. Even at 20C charge and discharge rate, the NMO-900 delivers 99 mAh g-1 capacity. The chemical diffusion coefficient of sodium is measured to be around 3 × 10-12 cm2 s-1 by potential intermittent titration technique (PITT). The cycling stability is also very good. The capacity retention after 100 cycles at 1C is 87.9% and the capacity still remains 82.9% even after 700 cycles at 10C. During cycling the coulombic efficiency keeps near 99.8%.

  7. Experimental studies on fast-ion transport by Alfven wave avalanches on the National Spherical Torus Experiment

    SciTech Connect

    Podesta, M.; Heidbrink, W. W.; Liu, D.; Ruskov, E.; Bell, R. E.; Darrow, D. S.; Fredrickson, E. D.; Gorelenkov, N. N.; Kramer, G. J.; LeBlanc, B. P.; Medley, S. S.; Roquemore, A. L.; Crocker, N. A.; Kubota, S.; Yuh, H.

    2009-05-15

    Fast-ion transport induced by Alfven eigenmodes (AEs) is studied in beam-heated plasmas on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)] through space, time, and energy resolved measurements of the fast-ion population. Fast-ion losses associated with multiple toroidicity-induced AEs (TAEs), which interact nonlinearly and terminate in avalanches, are characterized. A depletion of the energy range >20 keV, leading to sudden drops of up to 40% in the neutron rate over 1 ms, is observed over a broad spatial range. It is shown that avalanches lead to a relaxation of the fast-ion profile, which in turn reduces the drive for the instabilities. The measured radial eigenmode structure and frequency of TAEs are compared with the predictions from a linear magnetohydrodynamics stability code. The partial disagreement suggests that nonlinearities may compromise a direct comparison between experiment and linear theory.

  8. Confinement degradation by Alfvén-eigenmode induced fast-ion transport in steady-state scenario discharges

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Ferron, J. R.; Holcomb, C. T.; Van Zeeland, M. A.; Chen, Xi; Collins, C. M.; Garofalo, A.; Gong, X.; Grierson, B. A.; Podestà, M.; Stagner, L.; Zhu, Y.

    2014-09-01

    Analysis of neutron and fast-ion Dα data from the DIII-D tokamak shows that Alfvén eigenmode activity degrades fast-ion confinement in many high βN, high qmin, steady-state scenario discharges. (βN is the normalized plasma pressure and qmin is the minimum value of the plasma safety factor.) Fast-ion diagnostics that are sensitive to the co-passing population exhibit the largest reduction relative to classical predictions. The increased fast-ion transport in discharges with strong AE activity accounts for the previously observed reduction in global confinement with increasing qmin; however, not all high qmin discharges show appreciable degradation. Two relatively simple empirical quantities provide convenient monitors of these effects: (1) an ‘AE amplitude’ signal based on interferometer measurements and (2) the ratio of the neutron rate to a zero-dimensional classical prediction.

  9. Effects of size and concentration on diffusion-induced stress in lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Ma, Zengsheng; Gao, Xiang; Wang, Yan; Lu, Chunsheng

    2016-07-01

    Capacity fade of lithium-ion batteries induced by chemo-mechanical degradation during charge-discharge cycles is the bottleneck in design of high-performance batteries, especially high-capacity electrode materials. Stress generated due to diffusion-mechanical coupling in lithium-ion intercalation and deintercalation is accompanied by swelling, shrinking, and even micro-cracking. In this paper, we propose a theoretical model for a cylindrical nanowire electrode by combining the bond-order-length-strength and diffusion theories. It is shown that size and concentration have a significant influence on the stress fields in radial, hoop, and axial directions. This can explain why a smaller electrode with a huge volume change survives in the lithiation/delithiation process.

  10. Effect of exposure environment on surface decomposition of SiC-silver ion implantation diffusion couples

    NASA Astrophysics Data System (ADS)

    Gerczak, Tyler J.; Zheng, Guiqiu; Field, Kevin G.; Allen, Todd R.

    2015-01-01

    SiC is a promising material for nuclear applications and is a critical component in the construction of tristructural isotropic (TRISO) fuel. A primary issue with TRISO fuel operation is the observed release of 110mAg from intact fuel particles. The release of Ag has prompted research efforts to directly measure the transport mechanism of Ag in bulk SiC. Recent experimental efforts have focused primarily on Ag ion implantation designs. The effect of the thermal exposure system on the ion implantation surface has been investigated. Results indicate the utilization of a mated sample geometry and the establishment of a static thermal exposure environment is critical to maintaining an intact surface for diffusion analysis. The nature of the implantation surface and its potential role in Ag diffusion analysis are discussed.

  11. Effect of exposure environment on surface decomposition of SiC-silver ion implantation diffusion couples

    SciTech Connect

    Gerczak, Tyler J.; Zheng, Guiqui; Field, Kevin G.; Allen, Todd R.

    2014-10-05

    SiC is a promising material for nuclear applications and is a critical component in the construction of tristructural isotropic (TRISO) fuel. A primary issue with TRISO fuel operation is the observed release of 110m Ag from intact fuel particles. The release of Ag has prompted research efforts to directly measure the transport mechanism of Ag in bulk SiC. Recent research efforts have focused primarily on Ag ion implantation designs. The effect of the thermal exposure system on the ion implantation surface has been investigated. Results indicate the utilization of a mated sample geometry and the establishment of a static thermal exposure environment is critical to maintaining an intact surface for diffusion analysis. In conclusion, the nature of the implantation surface and its potential role in Ag diffusion analysis are discussed.

  12. Effect of exposure environment on surface decomposition of SiC-silver ion implantation diffusion couples

    DOE PAGESBeta

    Gerczak, Tyler J.; Zheng, Guiqui; Field, Kevin G.; Allen, Todd R.

    2014-10-05

    SiC is a promising material for nuclear applications and is a critical component in the construction of tristructural isotropic (TRISO) fuel. A primary issue with TRISO fuel operation is the observed release of 110m Ag from intact fuel particles. The release of Ag has prompted research efforts to directly measure the transport mechanism of Ag in bulk SiC. Recent research efforts have focused primarily on Ag ion implantation designs. The effect of the thermal exposure system on the ion implantation surface has been investigated. Results indicate the utilization of a mated sample geometry and the establishment of a static thermalmore » exposure environment is critical to maintaining an intact surface for diffusion analysis. In conclusion, the nature of the implantation surface and its potential role in Ag diffusion analysis are discussed.« less

  13. Diffusion coefficients of energetic water group ions near Comet Giacobini-Zinner

    NASA Technical Reports Server (NTRS)

    Tan, L. C.; Mason, G. M.; Richardson, I. G.; Ipavich, F. M.

    1993-01-01

    Data from the ultralow-energy charge analyzer and energetic particle anisotropy spectrometer sensors, acquired when the ICE spacecraft flew past Comet Giacobini-Zinner on September 11, 1985, are combined, and a single, self-consistent analysis technique is applied to derive a single-particle spectrum from about 200 to 1600 km/s. This information, together with the deduced bulk flow speed of the ions, is used to calculate a parallel diffusion coefficient in the transition region downstream of the bow wave (2.3 +/- 0.5) x 10 exp 17 sq cm/s; the corresponding scattering mean free path is (6 +/- 1) x 10 exp 4 km. The parallel diffusion coefficient is found to depend on the collision frequency of water group ions with Alfven waves, which are assumed to be propagating parallel (antiparallel) to the magnetic field.

  14. Diffusion coefficients of energetic water group ions near Comet Giacobini-Zinner

    NASA Astrophysics Data System (ADS)

    Tan, L. C.; Mason, G. M.; Richardson, I. G.; Ipavich, F. M.

    1993-03-01

    Data from the ultralow-energy charge analyzer and energetic particle anisotropy spectrometer sensors, acquired when the ICE spacecraft flew past Comet Giacobini-Zinner on September 11, 1985, are combined, and a single, self-consistent analysis technique is applied to derive a single-particle spectrum from about 200 to 1600 km/s. This information, together with the deduced bulk flow speed of the ions, is used to calculate a parallel diffusion coefficient in the transition region downstream of the bow wave (2.3 +/- 0.5) x 10 exp 17 sq cm/s; the corresponding scattering mean free path is (6 +/- 1) x 10 exp 4 km. The parallel diffusion coefficient is found to depend on the collision frequency of water group ions with Alfven waves, which are assumed to be propagating parallel (antiparallel) to the magnetic field.

  15. Lithium ion diffusion in Li β-alumina single crystals measured by pulsed field gradient NMR spectroscopy

    SciTech Connect

    Chowdhury, Mohammed Tareque Takekawa, Reiji; Iwai, Yoshiki; Kuwata, Naoaki; Kawamura, Junichi

    2014-03-28

    The lithium ion diffusion coefficient of a 93% Li β-alumina single crystal was measured for the first time using pulsed field gradient (PFG) NMR spectroscopy with two different crystal orientations. The diffusion coefficient was found to be 1.2 × 10{sup −11} m{sup 2}/s in the direction perpendicular to the c axis at room temperature. The Li ion diffusion coefficient along the c axis direction was found to be very small (6.4 × 10{sup −13} m{sup 2}/s at 333 K), which suggests that the macroscopic diffusion of the Li ion in the β-alumina crystal is mainly two-dimensional. The diffusion coefficient for the same sample was also estimated using NMR line narrowing data and impedance measurements. The impedance data show reasonable agreement with PFG-NMR data, while the line narrowing measurements provided a lower value for the diffusion coefficient. Line narrowing measurements also provided a relatively low value for the activation energy and pre-exponential factor. The temperature dependent diffusion coefficient was obtained in the temperature range 297–333 K by PFG-NMR, from which the activation energy for diffusion of the Li ion was estimated. The activation energy obtained by PFG-NMR was smaller than that obtained by impedance measurements, which suggests that thermally activated defect formation energy exists for 93% Li β-alumina single crystals. The diffusion time dependence of the diffusion coefficient was observed for the Li ion in the 93% Li β-alumina single crystal by means of PFG-NMR experiments. Motion of Li ion in fractal dimension might be a possible explanation for the observed diffusion time dependence of the diffusion coefficient in the 93% Li β–alumina system.

  16. Ultra-sensitive high-precision spectroscopy of a fast molecular ion beam.

    PubMed

    Mills, Andrew A; Siller, Brian M; Porambo, Michael W; Perera, Manori; Kreckel, Holger; McCall, Benjamin J

    2011-12-14

    Direct spectroscopy of a fast molecular ion beam offers many advantages over competing techniques, including the generality of the approach to any molecular ion, the complete elimination of spectral confusion due to neutral molecules, and the mass identification of individual spectral lines. The major challenge is the intrinsic weakness of absorption or dispersion signals resulting from the relatively low number density of ions in the beam. Direct spectroscopy of an ion beam was pioneered by Saykally and co-workers in the late 1980s, but has not been attempted since that time. Here, we present the design and construction of an ion beam spectrometer with several improvements over the Saykally design. The ion beam and its characterization have been improved by adopting recent advances in electrostatic optics, along with a time-of-flight mass spectrometer that can be used simultaneously with optical spectroscopy. As a proof of concept, a noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) setup with a noise equivalent absorption of ~2 × 10(-11) cm(-1) Hz(-1/2) has been used to observe several transitions of the Meinel 1-0 band of N(2) (+) with linewidths of ~120 MHz. An optical frequency comb has been used for absolute frequency calibration of transition frequencies to within ~8 MHz. This work represents the first direct spectroscopy of an electronic transition in an ion beam, and also represents a major step toward the development of routine infrared spectroscopy of rotationally cooled molecular ions. PMID:22168687

  17. Ultra-sensitive high-precision spectroscopy of a fast molecular ion beam

    SciTech Connect

    Mills, Andrew A.; Siller, Brian M.; Porambo, Michael W.; Perera, Manori; Kreckel, Holger; McCall, Benjamin J.

    2011-12-14

    Direct spectroscopy of a fast molecular ion beam offers many advantages over competing techniques, including the generality of the approach to any molecular ion, the complete elimination of spectral confusion due to neutral molecules, and the mass identification of individual spectral lines. The major challenge is the intrinsic weakness of absorption or dispersion signals resulting from the relatively low number density of ions in the beam. Direct spectroscopy of an ion beam was pioneered by Saykally and co-workers in the late 1980s, but has not been attempted since that time. Here, we present the design and construction of an ion beam spectrometer with several improvements over the Saykally design. The ion beam and its characterization have been improved by adopting recent advances in electrostatic optics, along with a time-of-flight mass spectrometer that can be used simultaneously with optical spectroscopy. As a proof of concept, a noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) setup with a noise equivalent absorption of {approx}2 x 10{sup -11} cm{sup -1} Hz{sup -1/2} has been used to observe several transitions of the Meinel 1-0 band of N{sub 2}{sup +} with linewidths of {approx}120 MHz. An optical frequency comb has been used for absolute frequency calibration of transition frequencies to within {approx}8 MHz. This work represents the first direct spectroscopy of an electronic transition in an ion beam, and also represents a major step toward the development of routine infrared spectroscopy of rotationally cooled molecular ions.

  18. Theory of dust and dust-void structures in the presence of the ion diffusion.

    PubMed

    Tsytovich, V N; Vladimirov, S V; Morfill, G E

    2004-12-01

    A dust void is a dust-free region inside the dust cloud that often develops for conditions relevant to plasma processing discharges and complex plasma experiments. A distinctive feature of the void is a sharp boundary between the dust and dust-free regions; this is manifested especially clear when dissipation in the plasma is small and discontinuity of the dust number density appear. Here, the structure of the dust void boundary and the distribution of the dust and plasma parameters in the dust structure bordering the void is analyzed taking into account effects of dissipation due to the ion diffusion on plasma neutrals. The sharp boundary between the dust and void regions exists also in the presence of the ion diffusion; however, only derivatives of the dust density, dust charge, electron density and electric field are discontinuous at the void boundaries, while the functions themselves as well as derivatives of the ion drift velocity and the ion density are continuous. Numerical calculations demonstrate various sorts of diffusive dust void structures; the possibility of singularities in the balance equations caused by the diffusion process inside the dust structures is investigated. These singularities can be responsible for a new type of shocklike structures. Other structures are typically self-organized to eliminate the singularities. Numerical computations in this case demonstrate a set of thin dust layers separated by high density thin dust clouds similar to the multiple-layer dust structures observed in the laboratory and in the upper ionosphere. The possibility for existence of a few equilibrium positions of the void boundary is discussed.

  19. Role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions

    NASA Astrophysics Data System (ADS)

    Dutt, Ishwar; Puri, Rajeev K.

    2010-04-01

    We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.

  20. Dynamic properties and third order diffusion coefficients of ions in electrostatic fields

    NASA Astrophysics Data System (ADS)

    Koutselos, Andreas D.

    1997-05-01

    Velocity correlation functions and third order diffusion coefficients of ions moving in a buffer gas under the influence of an electrostatic field are determined via molecular dynamics simulation. For the closed shell system of K+ in Ar using a universal interaction model potential, the general form of the third order correlation functions is found to be monotonically decaying in time except in the cases of <ΔvZ(0)ΔvX(t)2>, <ΔvZ(0)ΔvY(t)2>, and <ΔvZ(0)ΔvZ(t)2>, with Δv(t)=v(t) - and the field in the z direction. These functions acquire positive slope at short times showing enhancement of correlations between instantaneous vz components of the ions and their future kinetic energies or velocity measures. This feature is shown to quantify the dynamics of correlations between velocity components suggested in the past by Ong, Hogan, Lam and Viehland [Phys. Rev. A 45, 3997 (1992)] in order to explain the form of an ion velocity distribution function calculated through a Monte Carlo simulation method. In addition, within a stochastic analysis which establishes a relation between velocity correlation functions and third order diffusion coefficients, only two independent components of the diffusion tensor, Q∥ and Q⊥, are predicted. We thereby calculate the Q⊥ component, which has not been determined so far, over a wide field range. The magnitudes of the resulting third order diffusion coefficients indicate that their contribution to the ion transport in usual drift-tube measurements should be very small.

  1. Data for evaluation of fast kurtosis strategies, b-value optimization and exploration of diffusion MRI contrast.

    PubMed

    Hansen, Brian; Jespersen, Sune Nørhøj

    2016-01-01

    Here we describe and provide diffusion magnetic resonance imaging (dMRI) data that was acquired in neural tissue and a physical phantom. Data acquired in biological tissue includes: fixed rat brain (acquired at 9.4 T) and spinal cord (acquired at 16.4 T) and in normal human brain (acquired at 3 T). This data was recently used for evaluation of diffusion kurtosis imaging (DKI) contrasts and for comparison to diffusion tensor imaging (DTI) parameter contrast. The data has also been used to optimize b-values for ex vivo and in vivo fast kurtosis imaging. The remaining data was obtained in a physical phantom with three orthogonal fiber orientations (fresh asparagus stems) for exploration of the kurtosis fractional anisotropy. However, the data may have broader interest and, collectively, may form the basis for image contrast exploration and simulations based on a wide range of dMRI analysis strategies. PMID:27576023

  2. Data for evaluation of fast kurtosis strategies, b-value optimization and exploration of diffusion MRI contrast

    PubMed Central

    Hansen, Brian; Jespersen, Sune Nørhøj

    2016-01-01

    Here we describe and provide diffusion magnetic resonance imaging (dMRI) data that was acquired in neural tissue and a physical phantom. Data acquired in biological tissue includes: fixed rat brain (acquired at 9.4 T) and spinal cord (acquired at 16.4 T) and in normal human brain (acquired at 3 T). This data was recently used for evaluation of diffusion kurtosis imaging (DKI) contrasts and for comparison to diffusion tensor imaging (DTI) parameter contrast. The data has also been used to optimize b-values for ex vivo and in vivo fast kurtosis imaging. The remaining data was obtained in a physical phantom with three orthogonal fiber orientations (fresh asparagus stems) for exploration of the kurtosis fractional anisotropy. However, the data may have broader interest and, collectively, may form the basis for image contrast exploration and simulations based on a wide range of dMRI analysis strategies. PMID:27576023

  3. Velocity space diffusion and nongyrotropy of pickup water group ions at comet Grigg-Skjellerup

    NASA Technical Reports Server (NTRS)

    Coates, A. J.; Johnstone, A. D.; Wilken, B.; Neubauer, Fritz M.

    1993-01-01

    The diffusion of water group cometary ions in velocity space at comet Grigg-Skjellerup was measured during the Giotto spacecraft encounter. The evolution of the collapsed pitch angle and energy distributions during the inbound and outbound passes shows that the timescale for energy diffusion may be similar to that for pitch angle diffusion. Fully isotropic pitch angle distributions were never seen. Also the bulk parameters of the three-dimensional distributions are examined. Transformation of these parameters into a field-aligned solar wind frame allows us to test the gyrotropy of the distributions. These observations imply that there were deviations from gyrotropy throughout the encounter becoming most important near to closest approach.

  4. Charge collected by diffusion from an ion track under mixed boundary conditions

    SciTech Connect

    Edmonds, L.D. )

    1991-04-01

    This paper analyzes charge-carrier diffusion from an ion track in a silicon substrate, at least a few hundred {mu}m thick. The substrate upper surface is treated as reflective except for a small section, intended to represent a reverse-biased junction, which is treated as a sink. Total charge collected by the sink is calculated by assuming transport to be governed by an ambipolar diffusion equation with temporally constant and spatially uniform carrier lifetime and diffusion coefficient. Present results apply to a normally incident track but could easily be generalized to arbitrary track direction. The collected charge is found to depend on track length and on the electrostatic capacitance, rather than the area, of the sink. Theoretical prediction are compared to the results of a numerical simulation called the Poisson and Continuity Equation Solver (PISCES) for three cases and are found to agree within a factor of two in the worst case.

  5. Ion diffusion coefficients model and molar conductivities of ionic salts in aprotic solvents.

    PubMed

    Garrido, Leoncio; Mejía, Alberto; García, Nuria; Tiemblo, Pilar; Guzmán, Julio

    2015-02-19

    In the study of the electric properties of electrolytes, the determination of the diffusion coefficients of the species that intervene in the charge transport process is of great importance, particularly that of the free ions (D(+) and D(-)), the only species that contribute to the conductivity. In this work we propose a model that allows, with reasonable assumptions, determination of D(+) and D(-), and the degree of dissociation of the salt, α, at different concentrations, using the diffusion coefficients experimentally obtained with NMR. Also, it is shown that the NMR data suffice to estimate the conductivity of the electrolytes. The model was checked by means of experimental results of conductivity and NMR diffusion coefficients obtained with solutions of lithium triflate in ethylene and propylene carbonates, as well as with other results taken from the literature. PMID:25603311

  6. A Description of the Full Particle Orbit Following SPIRAL Code for Simulating Fast-ion Experiments in Tokamaks

    SciTech Connect

    Kramer, G.J.; Budny, R.V.; Bortolon, A.; Fredrickson, E.D.; Fu, G.Y.; Heidbrink, W.W.; Nazikian, R.; Valeo, E.; Van Zeeland, M.A.

    2012-07-27

    The numerical methods used in the full particle-orbit following SPIRAL code are described and a number of physics studies performed with the code are presented to illustrate its capabilities. The SPIRAL code is a test-particle code and is a powerful numerical tool to interpret and plan fast-ion experiments in Tokamaks. Gyro-orbit effects are important for fast ions in low-field machines such as NSTX and to a lesser extent in DIII-D. A number of physics studies are interlaced between the description of the code to illustrate its capabilities. Results on heat loads generated by a localized error-field on the DIII-D wall are compared to measurements. The enhanced Triton losses caused by the same localized error-field are calculated and compared to measured neutron signals. MHD activity such as tearing modes and Toroidicity-induced Alfven Eigenmodes (TAEs) have a profound effect on the fast-ion content of Tokamak plasmas and SPIRAL can calculate the effects of MHD activity on the confined and lost fast-ion population as illustrated for a burst of TAE activity in NSTX. The interaction between Ion Cyclotron Range of Frequency (ICRF) heating and fast ions depends solely on the gyro-motion of the fast ions and is captured exactly in the SPIRAL code. A calculation of ICRF absorption on beam ions in ITER is presented. The effects of high harmonic fast wave heating on the beam-ion slowing-down distribution in NSTX is also studied.

  7. A description of the full-particle-orbit-following SPIRAL code for simulating fast-ion experiments in tokamaks

    NASA Astrophysics Data System (ADS)

    Kramer, G. J.; Budny, R. V.; Bortolon, A.; Fredrickson, E. D.; Fu, G. Y.; Heidbrink, W. W.; Nazikian, R.; Valeo, E.; Van Zeeland, M. A.

    2013-02-01

    The numerical methods used in the full particle-orbit following SPIRAL code are described and a number of physics studies performed with the code are presented to illustrate its capabilities. The SPIRAL code is a test-particle code and is a powerful numerical tool to interpret and plan fast-ion experiments in tokamaks. Gyro-orbit effects are important for fast ions in low-field machines such as NSTX and to a lesser extent in DIII-D. A number of physics studies are interlaced between the description of the code to illustrate its capabilities. Results on heat loads generated by a localized error-field on the DIII-D wall are compared with measurements. The enhanced Triton losses caused by the same localized error-field are calculated and compared with measured neutron signals. Magnetohydrodynamic (MHD) activity such as tearing modes and toroidicity-induced Alfvén eigenmodes (TAEs) have a profound effect on the fast-ion content of tokamak plasmas and SPIRAL can calculate the effects of MHD activity on the confined and lost fast-ion population as illustrated for a burst of TAE activity in NSTX. The interaction between ion cyclotron range of frequency (ICRF) heating and fast ions depends solely on the gyro-motion of the fast ions and is captured exactly in the SPIRAL code. A calculation of ICRF absorption on beam ions in ITER is presented. The effects of high harmonic fast wave heating on the beam-ion slowing-down distribution in NSTX is also studied.

  8. Pitch angle diffusion of newborn ions due to intrinsic turbulence in the solar wind

    SciTech Connect

    Ziebell, L.F.; Yoon, P.H.; Wu, C.S. ); Winske, D. )

    1990-10-01

    The objective of the present study is to understand the interaction of the solar wind with newborn ions in far upstream regions of a comet where the level of intrinsic turbulence is moderately low. Based on the assumption that quasi-linear theory is adequate and applicable, the authors investigate the pitch angle diffusion process and the time evolution of the newborn ion distribution function. Numerical solutions to the quasilinear diffusion equation, including the effect of resonance broadening and that of continuous creation of newborn ions due to ionization process, are obtained under several assumptions and approximations. It is found that theoretical results are consistent with the Giotto observations recently reported by Neugebauer et al. (1989) which enable them to understand the formation of partial shells which were frequently observed in far upstream regions. The pitch angle diffusion process is also examined by the hybrid simulation. The results of the simulation are in qualitative agreement with those obtained from the quasi-linear analysis.

  9. Estimation of diffusion coefficient by photoemission electron microscopy in ion-implanted nanostructures

    NASA Astrophysics Data System (ADS)

    Batabyal, R.; Patra, S.; Roy, A.; Roy, S.; Bischoff, L.; Dev, B. N.

    2009-10-01

    We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga + ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm × 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ˜1.3 × 10 -15 m 2/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.

  10. LSP simulations of fast ions slowing down in cool magnetized plasma

    NASA Astrophysics Data System (ADS)

    Evans, Eugene S.; Cohen, Samuel A.

    2015-11-01

    In MFE devices, rapid transport of fusion products, e.g., tritons and alpha particles, from the plasma core into the scrape-off layer (SOL) could perform the dual roles of energy and ash removal. Through these two processes in the SOL, the fast particle slowing-down time will have a major effect on the energy balance of a fusion reactor and its neutron emissions, topics of great importance. In small field-reversed configuration (FRC) devices, the first-orbit trajectories of most fusion products will traverse the SOL, potentially allowing those particles to deposit their energy in the SOL and eventually be exhausted along the open field lines. However, the dynamics of the fast-ion energy loss processes under conditions expected in the FRC SOL, where the Debye length is greater than the electron gyroradius, are not fully understood. What modifications to the classical slowing down rate are necessary? Will instabilities accelerate the energy loss? We use LSP, a 3D PIC code, to examine the effects of SOL plasma parameters (density, temperature and background magnetic field strength) on the slowing down time of fast ions in a cool plasma with parameters similar to those expected in the SOL of small FRC reactors. This work supported by DOE contract DE-AC02-09CH11466.

  11. Antenna design for fast ion collective Thomson scattering diagnostic for the international thermonuclear experimental reactor.

    PubMed

    Leipold, F; Furtula, V; Salewski, M; Bindslev, H; Korsholm, S B; Meo, F; Michelsen, P K; Moseev, D; Nielsen, S K; Stejner, M

    2009-09-01

    Fast ion physics will play an important role for the international thermonuclear experimental reactor (ITER), where confined alpha particles will affect and be affected by plasma dynamics and thereby have impacts on the overall confinement. A fast ion collective Thomson scattering (CTS) diagnostic using gyrotrons operated at 60 GHz will meet the requirements for spatially and temporally resolved measurements of the velocity distributions of confined fast alphas in ITER by evaluating the scattered radiation (CTS signal). While a receiver antenna on the low field side of the tokamak, resolving near perpendicular (to the magnetic field) velocity components, has been enabled, an additional antenna on the high field side (HFS) would enable measurements of near parallel (to the magnetic field) velocity components. A compact design solution for the proposed mirror system on the HFS is presented. The HFS CTS antenna is located behind the blankets and views the plasma through the gap between two blanket modules. The viewing gap has been modified to dimensions 30x500 mm(2) to optimize the CTS signal. A 1:1 mock-up of the HFS mirror system was built. Measurements of the beam characteristics for millimeter-waves at 60 GHz used in the mock-up agree well with the modeling.

  12. Diffusion of dissolved ions from wet silica sol-gel monoliths: implications for biological encapsulation.

    PubMed

    Dickson, David J; Lassetter, Bethany; Glassy, Benjamin; Page, Catherine J; Yokochi, Alexandre F T; Ely, Roger L

    2013-02-01

    Divalent nickel (Ni(2+)), Cu(II)EDTA, methyl orange, and dichromate were used to investigate diffusion from hydrated silica sol-gel monoliths. The objective was to examine diffusion of compounds on a size regime relevant to supporting biological components encapsulated within silica gel prepared in a biologically compatible process space with no post-gelation treatments. With an initial sample set, gels prepared from tetraethoxysilane were explored in a factorial design with Ni(2+) as the tracer, varying water content during hydrolysis, acid catalyst present during hydrolysis, and the final concentration of silica. A second sample set explored diffusion of all four tracers in gels prepared with aqueous silica precursors and a variety of organically modified siloxanes. Excluding six outliers which displayed significant syneresis, the mean diffusion constant (D(gel)) across the entire process space of sample set 1 was 2.42×10(-10) m(2) s(-1); approximately 24% of the diffusion coefficient of Ni(2+) in unconfined aqueous solution. In sample set 2, the tracer size and not gel hydrophobicity was the primary determinant of changes in diffusion rates. A strong linear inverse correlation was found between tracer size and the magnitude of D(gel). Based on correlation with the tracers used in this investigation, the characteristic 1-h diffusion distance for carbonate species relevant to supporting active phototrophic organisms was approximately 1.5mm. These results support the notion that silica sol-gel formulations may be optimized for a given biological entity of interest with manageable impact to the diffusion of small ions and molecules.

  13. Structure and ionic diffusion of alkaline-earth ions in mixed cation glasses

    SciTech Connect

    Konstantinou, Konstantinos; Sushko, Petr; Duffy, Dorothy M.

    2015-08-15

    A series of mixed cation silicate glasses of the composition A2O – 2MO – 4SiO2, with A=Li,Na,K and M=Ca,Sr,Ba has been investigated by means of molecular dynamics simulations in order to understand the effect of the nature of the cations on the mobility of the alkaline-earth ions within the glass network. The size of the alkaline-earth cation was found to affect the inter-atomic distances, the coordination number distributions and the bond angle distributions , whereas the medium-range order was almost unaffected by the type of the cation. All the alkaline-earth cations contribute to lower vibrational frequencies but it is observed that that there is a shift to smaller frequencies and the vibrational density of states distribution gets narrower as the size of the alkaline-earth increases. The results from our modeling for the ionic diffusion of the alkaline-earth cations are in a qualitative agreement with the experimental observations in that there is a distinct correlation between the activation energy for diffusion of alkaline earth-ions and the cation radii ratio. An asymmetrical linear behavior in the diffusion activation energy with increasing size difference is observed. The results can be described on the basis of a theoretical model that relates the diffusion activation energy to the electrostatic interactions of the cations with the oxygens and the elastic deformation of the silicate network.

  14. Fast removal of copper ions from aqueous solution using an eco-friendly fibrous adsorbent.

    PubMed

    Niu, Yaolan; Ying, Diwen; Li, Kan; Wang, Yalin; Jia, Jinping

    2016-10-01

    Functional PET fiber (PET-AA-CS) was prepared by oxygen-plasma pretreatment and grafting of acrylic acid (AA) and low-molecular-weight chitosan (LMCS) on the polyethylene glycol terephthalate (PET) substrate. This adsorbent was targeted for quick removal of metal ion in river pollutions with an easy recycling of the fiber after emergency processing. The fabricated PET-AA-CS was characterized by the scanning electron microscope (SEM), contact angle, fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) to look into its morphology, surface functional groups, and adsorption mechanism of copper ions from the aqueous solution. The overall adsorption process of copper ions on the PET-AA-CS was pH-dependent with an optimal pH value of 5.0, at which a maximum capacity of 68.97 mg g(-1) was obtained. The result of fitting also shows that adsorption process follows the Langmuir isotherm and pseudo-second-order model. Moreover, the material shows good stability during 5 cycles of adsorption and desorption, and also shows no significant effect of co-existing ions including Ca(2+), Mg(2+), K(+), Cl(-), and et al. In general, PET-AA-CS developed in this study shows significant benefit of eco-friend and cost-efficiency for fast removal of copper ions in potential river metal pollutions comparing with traditional adsorbents.

  15. Fast vacancy-mediated oxygen ion incorporation across the ceria-gas electrochemical interface.

    PubMed

    Feng, Zhuoluo A; El Gabaly, Farid; Ye, Xiaofei; Shen, Zhi-Xun; Chueh, William C

    2014-07-09

    Electrochemical incorporation reactions are ubiquitous in energy storage and conversion devices based on mixed ionic and electronic conductors, such as lithium-ion batteries, solid-oxide fuel cells and water-splitting membranes. The two-way traffic of ions and electrons across the electrochemical interface, coupled with the bulk transport of mass and charge, has been challenging to understand. Here we report an investigation of the oxygen-ion incorporation pathway in CeO2-δ (ceria), one of the most recognized oxygen-deficient compounds, during hydrogen oxidation and water splitting. We probe the response of surface oxygen vacancies, electrons and adsorbates to the electrochemical polarization at the ceria-gas interface. We show that surface oxygen-ion transfer, mediated by oxygen vacancies, is fast. Furthermore, we infer that the electron transfer between cerium cations and hydroxyl ions is the rate-determining step. Our in operando observations reveal the precise roles of surface oxygen vacancy and electron defects in determining the rate of surface incorporation reactions.

  16. Fast removal of copper ions from aqueous solution using an eco-friendly fibrous adsorbent.

    PubMed

    Niu, Yaolan; Ying, Diwen; Li, Kan; Wang, Yalin; Jia, Jinping

    2016-10-01

    Functional PET fiber (PET-AA-CS) was prepared by oxygen-plasma pretreatment and grafting of acrylic acid (AA) and low-molecular-weight chitosan (LMCS) on the polyethylene glycol terephthalate (PET) substrate. This adsorbent was targeted for quick removal of metal ion in river pollutions with an easy recycling of the fiber after emergency processing. The fabricated PET-AA-CS was characterized by the scanning electron microscope (SEM), contact angle, fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) to look into its morphology, surface functional groups, and adsorption mechanism of copper ions from the aqueous solution. The overall adsorption process of copper ions on the PET-AA-CS was pH-dependent with an optimal pH value of 5.0, at which a maximum capacity of 68.97 mg g(-1) was obtained. The result of fitting also shows that adsorption process follows the Langmuir isotherm and pseudo-second-order model. Moreover, the material shows good stability during 5 cycles of adsorption and desorption, and also shows no significant effect of co-existing ions including Ca(2+), Mg(2+), K(+), Cl(-), and et al. In general, PET-AA-CS developed in this study shows significant benefit of eco-friend and cost-efficiency for fast removal of copper ions in potential river metal pollutions comparing with traditional adsorbents. PMID:27470942

  17. Fast-ion effects during test blanket module simulation experiments in DIII-D

    SciTech Connect

    Kramer, G.; Budny, R. V.; Ellis, R.; Gorelenkova, M.; Heidbrink, W.; Kurki-Suonio, T.; Nazikian, Raffi; Saimi, A.; Schaffer, M. J.; Shinohara, K.; Snipes, J. A.; Spong, Donald A; Koskela, T.; Van Zeeland, Michael

    2011-01-01

    Fast beam-ion losses were studied in DIII-D in the presence of a scaled mock-up of two test blanket modules (TBM) for ITER. Heating of the protective tiles on the front of the TBM surface was found when neutral beams were injected and the TBM fields were engaged. The fast-ion core confinement was not significantly affected. Different orbit-following codes predict the formation of a hot spot on the TBM surface arising from beam ions deposited near the edge of the plasma. The codes are in good agreement with each other on the total power deposited at the hot spot, predicting an increase in power with decreasing separation between the plasma edge and the TBM surface. A thermal analysis of the heat flow through the tiles shows that the simulated power can account for the measured tile temperature rise. The thermal analysis, however, is very sensitive to the details of the localization of the hot spot, which is predicted to be different among the various codes.

  18. Fast ion diagnostic's neutral beam injector on the poloidal divertor experiment

    SciTech Connect

    Nudelman, A.; Goldston, R.; Kaita, R.

    1982-04-01

    Neutral beams, in conjunction with charge-exchange analyzers, have proved to be valuable diagnostic tools for studying high temperature tokamak plasmas. The PDX Fast Ion Diagnostic Experiment (FIDE) consists of a Diagnostic Neutral Beam (DNB) and spatially imaging charge-exchange analyzer. The DNB is built around a Lawrence--Berkeley Laboratory 40-kV, 10-A, 4-grid ion source. The power requirements are 0.5 MW in up to 10-ms-long pulse bursts. The accelerating grid is supplied from a 125-kJ, 50-kV capacitor bank with a hard-tube modulator for switching and pulse burst generation at up to 3 kHz. The filament and arc power is drawn directly from a 480-V ac line through multiphase controlled rectifiers, which provide a soft start for the filament and fast switching for the arc. Special attention was paid to the H--V transmission line, since the power supplies could not be located close to the ion source. The DNB has been tested under actual operating conditions and is now being used in experiments with the charge-exchange analyzer.

  19. Fast Ion Effects During Test Blanket Module Simulation Experiments in DIII-D

    SciTech Connect

    Kramer, G J; Ellis, R; Gorelenkova, M; Heidbrink, W W; Kurki-Suonio, T; Nazikian, R; Salmi, A; Schaffer, M J; Shinohara, K; Snipes, J A; Spong, D A; Koskela, T

    2011-06-03

    Fast beam-ion losses were studied in DIII-D in the presence of a scaled mockup of two Test Blanket Modules (TBM) for ITER. Heating of the protective tiles on the front of the TBM surface was found when neutral beams were injected and the TBM fields were engaged. The fast-ion core confinement was not significantly affected. Different orbit-following codes predict the formation of a hot spot on the TBM surface arising from beam-ions deposited near the edge of the plasma. The codes are in good agreement with each other on the total power deposited at the hot spot predicting an increase in power with decreasing separation between the plasma edge and the TBM surface. A thermal analysis of the heat flow through the tiles shows that the simulated power can account for the measured tile temperature rise. The thermal analysis, however, is very sensitive to the details of the localization of the hot spot which is predicted to be different among the various codes.

  20. Effect of exchangeable cations on apparent diffusion of Ca 2+ ions in Na- and Ca-montmorillonite mixtures

    NASA Astrophysics Data System (ADS)

    Kozaki, T.; Sawaguchi, T.; Fujishima, A.; Sato, S.

    Compacted Na-bentonite, of which the major mineral is montmorillonite, is a candidate buffer material for the geological disposal of high-level radioactive waste. A potential alteration of the bentonite in a repository is the partial replacement of the exchangeable cations of Na + with Ca 2+. The Ca 2+ cations could be released from cementitious materials and diffuse into the buffer material in the repository. In this study, to evaluate the alteration that could reduce the performance of the bentonite buffer, the apparent diffusion coefficients of HTO and Ca 2+ ions were determined from non-steady, one-dimensional diffusion experiments using Na- and Ca-montmorillonite mixtures with different ionic equivalent fractions of Ca 2+ ions. The apparent diffusion coefficient of HTO at a dry density of 1.0 Mg m -3 slightly increased with an increase in the ionic equivalent fraction of Ca 2+ ions. However, the apparent diffusion coefficient of Ca 2+ and the activation energy for diffusion at the same dry density were independent of the ionic equivalent fraction of Ca 2+ ions. These findings suggest that unlike HTO, which can be postulated to diffuse mainly in pore water, Ca 2+ ion diffusion could occur predominantly in interlayer spaces, of which the basal spacing was determined to be constant by the XRD technique.

  1. Diffusion-weighted Magnetic Resonance Imaging: What Makes Water Run Fast or Slow?

    PubMed Central

    Fornasa, Francesca

    2011-01-01

    Diffusion-Weighted Magnetic Resonance Imaging (DWI) obtains information useful in diagnosing several diseases through the measurement of random, Brownian diffusion of water molecules in tissues. This pictorial essay illustrates the main factors, i.e., ratio between the volume occupied by cells and the extracellular space, composition of the extracellular space, and temperature, that determine the rate of the water diffusion. The mechanism through which these influencing factors affect water diffusion is explained. Clinical and experimental examples, derived both from physiology and from non-human models, are described. PMID:21966624

  2. Improved technique for studying ion channels expressed in Xenopus oocytes, including fast superfusion.

    PubMed Central

    Costa, A C; Patrick, J W; Dani, J A

    1994-01-01

    The study of whole-cell currents from ion channels expressed in Xenopus oocytes with conventional two-electrode voltage clamp has two major limitations. First, the large diameter and spherical geometry of oocytes prevent extremely fast solution changes. Second, the internal medium is not controlled, which limits the experimental versatility of the oocyte expression system. For example, because the internal medium is not controlled, endogenous calcium-activated chloride conductances can contaminate currents measured with channels that are permeable to calcium. We describe a new technique that combines vaseline-gap voltage clamp for oocytes with a fast superfusion system. The vaseline-gap procedure is simplified by having the micropipette that monitors voltage serve a dual role as a perfusion micropipette that controls the internal solution. In addition, the technique provides fast external solution changes that are complete in 30-50 ms. We applied the approach to measure the calcium permeability of a muscle and a neuronal nicotinic acetylcholine receptor. Very fast agonist induced currents were measured without contamination by the secondary activation of calcium-dependent chloride channels. Images FIGURE 1 FIGURE 2 PMID:7522597

  3. Diffusion enhancement due to low-energy ion bombardment during sputter etching and deposition

    SciTech Connect

    Eltoukhy, A.H.; Greene, J.E.

    1980-08-01

    The effects of low-energy ion bombardment on enhancing elemental diffusion rates at both heterojunction interfaces during film deposition and over the compositionally altered layer created during sputter etching alloy targets have been considered. Depth dependent enhanced interdiffusion coefficients, expressed as D*(x)=D*(0) exp(-x/L/sub d/), where D*(0) is more than five orders of magnitude greater than thermal diffusion values, were measured in InSb/GaSb multilayer structures deposited by multitarget bias sputering. D*(0) was determined from the amplitude u of the compositional modulation in the multilayered films (layer thicknesses between 20 and 45 A) as measured by superlattice x-ray diffraction techniques. The value of D*(0) was found to increase from 3 x 10/sup -17/ to 1 x 10/sup -16/ cm/sup 2//sec as the applied substrate bias was increased from 0 to -75 V. However even at V/sub a/=0, the diffusion coefficient was enhanced owing to an induced substrate potential with respect to the positive space-charge region in the Ar discharge. The diffusion length of L/sub d/ of the ion bombardment created defects was approx.1000 A. Enhanced diffusion also has a significiant effect on the altered layer thickness x/sub e/ and the total sputtering time t/sub e/ (or ion dose) required to reach steady state during ion etching of multielement targets. The effects of using an exponentially depth dependent versus a constant value of the enhanced diffusion coefficient on calculated values of x/sub e/ and t/sub e/ in single-phase binary alloys were considered. The results show that both x/sub e/ and t/sub e/ are considerably larger using a depth dependent D*(x), when L/sub d/D*(0)/v, the usual case for most sputtering applications, the two solutions approach each other.

  4. Diffusion, trapping, and isotope exchange of plasma implanted deuterium in ion beam damaged tungsten

    NASA Astrophysics Data System (ADS)

    Barton, Joseph Lincoln

    Tritium accumulation in nuclear fusion reactor materials is a major concern for practical and safe fusion energy. This work examines hydrogen isotope exchange as a tritium removal technique, analyzes the effects of neutron damage using high energy copper ion beams, and introduces a diffusion coefficient that is a function of the concentration of trapped atoms. Tungsten samples were irradiated with high energy (0.5 - 5 MeV) copper ions for controlled levels of damage - 10-3 to 10-1 displacements per atom (dpa) - at room temperature. Samples were then exposed to deuterium plasma at constant temperature (˜ 380 K) to a high fluence of 1024 ions/m2, where retention is at is maximized (i.e. saturated). By then subsequently exposing these samples to fractions of this fluence with hydrogen plasma, isotope exchange rates were observed. The resulting deuterium still trapped in the tungsten is then measured post mortem. Nuclear reaction analysis (NRA) gives the depth resolved deuterium retention profile with the 3He(D,p) 4He reaction, and thermal desorption spectroscopy (TDS) gives the total amount of deuterium trapped in the tungsten by heating a sample in vacuum up to 1200 K and measuring the evaporated gas molecules with a residual gas analyzer. Isotope exchange data show that hydrogen atoms can displace trapped deuterium atoms efficiently only up to the first few microns, but does not affect the atoms trapped at greater depths. In ion damaged tungsten, measurements showed a significant increase in retention in the damage region proportional to dpa 0.66, which results in a significant spike in total retention, and isotope exchange in damaged samples is still ineffective at depths greater than a few microns. Thus, isotope exchange is not an affective tritium removal technique; however, these experiments have shown that trapping in material defects greatly affects diffusion. These experiments lead to a simplified diffusion model with defect densities as the only free

  5. Nanometer-scale electrochemical intercalation and diffusion mapping of Li-ion battery materials

    SciTech Connect

    Balke, Nina; Jesse, Stephen; Morozovska, A. N.; Eliseev, E. A.; Chung, Ding-wen; Garcia, R. Edwin; Dudney, Nancy J; Kalinin, Sergei V

    2010-01-01

    The electrochemical energy storage systems based on Li-based insertion and reconstitution chemistries are a vital component of future energy technologies. Development of high energy and power density materials demands detailed understanding of the nanoscale mechanisms involved in Li-battery operation, including the interplay between the interfacial electrochemical reactions, electron and Li-ion diffusion, and structural defects. We demonstrate that strong coupling between Li-ion concentration and lattice parameters can be used as an efficient basis for real-space imaging of Li-ion currents and electrochemical reactivity on the nanometer length scales, providing what until now has been an elusive view of the electrochemical reactivity on a level of single structural element.

  6. Fast calculations of the spectral diffuse-to-global ratios for approximating spectral irradiance at the street canyon level

    NASA Astrophysics Data System (ADS)

    Carrasco-Hernandez, Roberto; Smedley, Andrew R. D.; Webb, Ann R.

    2016-05-01

    Two radiative transfer models are presented that simplify calculations of street canyon spectral irradiances with minimum data input requirements, allowing better assessment of urban exposures than can be provided by standard unobstructed radiation measurements alone. Fast calculations improve the computational performance of radiation models, when numerous repetitions are required in time and location. The core of the models is the calculation of the spectral diffuse-to-global ratios (DGR) from an unobstructed global spectral measurement. The models are based on, and have been tested against, outcomes of the SMARTS2 algorithm (i.e. Simple Model of the Atmospheric Radiative Transfer of Sunshine). The modelled DGRs can then be used to partition global spectral irradiance values into their direct and diffuse components for different solar zenith angles. Finally, the effects of canyon obstructions can be evaluated independently on the direct and diffuse components, which are then recombined to give the total canyon irradiance. The first model allows ozone and aerosol inputs, while the second provides a further simplification, restricted to average ozone and aerosol contents but specifically designed for faster calculations. To assess the effect of obstructions and validate the calculations, a set of experiments with simulated obstructions (simulated canyons) were performed. The greatest source of uncertainty in the simplified calculations is in the treatment of diffuse radiation. The measurement-model agreement is therefore dependent on the region of the sky obscured and ranges from <5 % at all wavelengths to 20-40 % (wavelength dependent) when diffuse sky only is visible from the canyon.

  7. Examination of methods to determine free-ion diffusivity and number density from analysis of electrode polarization.

    PubMed

    Wang, Yangyang; Sun, Che-Nan; Fan, Fei; Sangoro, Joshua R; Berman, Marc B; Greenbaum, Steve G; Zawodzinski, Thomas A; Sokolov, Alexei P

    2013-04-01

    Electrode polarization analysis is frequently used to determine free-ion diffusivity and number density in ionic conductors. In the present study, this approach is critically examined in a wide variety of electrolytes, including aqueous and nonaqueous solutions, polymer electrolytes, and ionic liquids. It is shown that the electrode polarization analysis based on the Macdonald-Trukhan model [J. Chem. Phys. 124, 144903 (2006); J. Non-Cryst. Solids 357, 3064 (2011)] progressively fails to give reasonable values of free-ion diffusivity and number density with increasing salt concentration. This should be expected because the original model of electrode polarization is designed for dilute electrolytes. An empirical correction method which yields ion diffusivities in reasonable agreement with pulsed-field gradient nuclear magnetic resonance measurements is proposed. However, the analysis of free-ion diffusivity and number density from electrode polarization should still be exercised with great caution because there is no solid theoretical justification for the proposed corrections. PMID:23679415

  8. Examination of methods to determine free-ion diffusivity and number density from analysis of electrode polarization

    SciTech Connect

    Wang, Yangyang; Sun, Che-Nan; Fan, Fei; Sangoro, Joshua R; Berman, Marc; Greenbaum, Steve; Zawodzinski, Thomas; Sokolov, Alexei P

    2013-01-01

    Electrode polarization analysis is frequently used to determine free-ion diffusivity and number density in ionic conductors. In the present study, this approach is critically examined in a wide variety of electrolytes, including aqueous and nonaqueous solutions, polymer electrolytes, and ionic liquids. It is shown that the electrode polarization analysis based on theMacdonald-Trukhan model [J. Chem. Phys. 124, 144903 (2006); J. Non-Cryst. Solids 357, 3064 (2011)] progressively fails to give reasonable values of free-ion diffusivity and number density with increasing salt concentration. This should be expected because the original model of electrode polarization is designed for dilute electrolytes. An empirical correction method which yields ion diffusivities in reasonable agreement with pulsed-field gradient nuclear magnetic resonance measurements is proposed. However, the analysis of free-ion diffusivity and number density from electrode polarization should still be exercised with great caution because there is no solid theoretical justification for the proposed corrections.

  9. On velocity-space sensitivity of fast-ion D-alpha spectroscopy

    NASA Astrophysics Data System (ADS)

    Salewski, M.; Geiger, B.; Moseev, D.; Heidbrink, W. W.; Jacobsen, A. S.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

    2014-10-01

    The velocity-space observation regions and sensitivities in fast-ion Dα (FIDA) spectroscopy measurements are often described by so-called weight functions. Here we derive expressions for FIDA weight functions accounting for the Doppler shift, Stark splitting, and the charge-exchange reaction and electron transition probabilities. Our approach yields an efficient way to calculate correctly scaled FIDA weight functions and implies simple analytic expressions for their boundaries that separate the triangular observable regions in (v‖, v⊥)-space from the unobservable regions. These boundaries are determined by the Doppler shift and Stark splitting and could until now only be found by numeric simulation.

  10. Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging

    SciTech Connect

    Tobias, Ben; Classen, I.G.J.; Domier, C. W.; Heidbrink, W.; Luhmann, N.C.; Nazikian, Raffi; Park, H.K.; Spong, Donald A; Van Zeeland, Michael

    2011-01-01

    Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.

  11. Analysis of fast-ion D α data from the National Spherical Torus Experiment

    NASA Astrophysics Data System (ADS)

    Heidbrink, W. W.; Ruskov, E.; Liu, D.; Stagner, L.; Fredrickson, E. D.; Podestà, M.; Bortolon, A.

    2016-05-01

    Measured fast-ion {{D}α} (FIDA) data from an extensive NSTX database are compared to ‘classical’ predictions that neglect transport by instabilities. Even in the absence of appreciable MHD, in many cases, the profile peaks at smaller major radius and the profile is broader than the predictions. Abrupt large-amplitude MHD events flatten the FIDA profile, as do most toroidal Alfvén eigenmode (TAE) avalanche events. Generally, the onset of a long-lived mode also flattens the FIDA profile.

  12. Study of high-beta magnetohydrodynamic modes and fast-ion losses in PDX

    SciTech Connect

    McGuire, K.; Goldston, R.; Bell, M.

    1983-03-21

    Strong magnetohydrodynamic activity has been observed in PDX neutral-beam--heated discharges. It occurs for ..beta../sub T/q> or =0.045 and is associated with a significant loss of fast ions and a drop in neutron emission. As much as 20%--40% of the beam heating power may be lost. The instability occurs in repetitive bursts of oscillations of < or =1 msec duration at 1--6 msec intervals. The magnetohydrodynamic activity has been dubbed the ''fishbone instability'' from its characteristic signature on the Mirnov coils.

  13. Study of High-Beta Magnetohydrodynamic Modes and Fast-Ion Losses in PDX

    NASA Astrophysics Data System (ADS)

    McGuire, K.; Goldston, R.; Bell, M.; Bitter, M.; Bol, K.; Brau, K.; Buchenauer, D.; Crowley, T.; Davis, S.; Dylla, F.; Eubank, H.; Fishman, H.; Fonck, R.; Grek, B.; Grimm, R.; Hawryluk, R.; Hsuan, H.; Hulse, R.; Izzo, R.; Kaita, R.; Kaye, S.; Kugel, H.; Johnson, D.; Manickam, J.; Manos, D.; Mansfield, D.; Mazzucato, E.; McCann, R.; McCune, D.; Monticello, D.; Motley, R.; Mueller, D.; Oasa, K.; Okabayashi, M.; Owens, K.; Park, W.; Reusch, M.; Sauthoff, N.; Schmidt, G.; Sesnic, S.; Strachan, J.; Surko, C.; Slusher, R.; Takahashi, H.; Tenney, F.; Thomas, P.; Towner, H.; Valley, J.; White, R.

    1983-03-01

    Strong magnetohydrodynamic activity has been observed in PDX neutral-beam-heated discharges. It occurs for βTq>=0.045 and is associated with a significant loss of fast ions and a drop in neutron emission. As much as 20%-40% of the beam heating power may be lost. The instability occurs in repetitive bursts of oscillations of <= 1 msec duration at 1-6-msec intervals. The magnetohydrodynamic activity has been dubbed the "fishbone instability" from its characteristic signature on the Mirnov coils.

  14. National Diffusion Network's Evaluation of the Fast Track Music System 1992-93.

    ERIC Educational Resources Information Center

    Szymczuk, Michael

    This document reports on an evaluation project to determine the effectiveness of the Fast Track method of instrumental music instruction as applied to beginning band instruction. The Fast Track music system is unique because it simultaneously aids both visual and aural learning by using a book and cassette tape approach to instruction. Traditional…

  15. An arbitrary amplitude fast magnetosonic soliton in quantum electron-positron-ion plasmas

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Mushtaq, A.; Mahmood, S.

    2013-02-01

    Nonlinear fast magnetosonic waves are studied in a collisionless homogenous, magnetized electron-positron-ion (e-p-i) plasma. The multi-component quantum magneto-hydrodynamic model is used in which ions are assumed to be dynamic whereas electron and positron quantum fluids are taken to be inertialess. The Sagdeev potential approach is used to obtain arbitrary amplitude magnetosonic structures in dense e-p-i plasmas. It is found that the wave amplitude as well as the width of the magnetosonic structure depends on different plasma parameters such as the electron to positron density ratio, plasma beta, quantum parameter and the Alfvénic Mach number. The numerical results have also been obtained for illustration.

  16. Extended π-conjugated system for fast-charge and -discharge sodium-ion batteries.

    PubMed

    Wang, Chengliang; Xu, Yang; Fang, Yaoguo; Zhou, Min; Liang, Liying; Singh, Sukhdeep; Zhao, Huaping; Schober, Andreas; Lei, Yong

    2015-03-01

    Organic sodium-ion batteries (SIBs) are potential alternatives of current commercial inorganic lithium-ion batteries for portable electronics (especially wearable electronics) because of their low cost and flexibility, making them possible to meet the future flexible and large-scale requirements. However, only a few organic SIBs have been reported so far, and most of them either were tested in a very slow rate or suffered significant performance degradation when cycled under high rate. Here, we are focusing on the molecular design for improving the battery performance and addressing the current challenge of fast-charge and -discharge. Through reasonable molecular design strategy, we demonstrate that the extension of the π-conjugated system is an efficient way to improve the high rate performance, leading to much enhanced capacity and cyclability with full recovery even after cycled under current density as high as 10 A g(-1).

  17. Analysis of fast-ion D-alpha data from NSTX

    NASA Astrophysics Data System (ADS)

    Ruskov, E.; Heidbrink, W.; Liu, D.; Bortolon, A.; Fredrickson, E.; Podesta, M.

    2015-11-01

    Measured fast-ion D-alpha (FIDA) data from an extensive NSTX database are compared to ``classical'' predictions that neglect transport by instabilities. Even in the absence of detectable MHD, in virtually all cases, the measured radiance is lower, the profile peaks at smaller major radius, and the profile is broader than the predictions. Abrupt large-amplitude MHD events flatten the FIDA profile, as do most toroidal Alfven eigenmode (TAE) avalanche events. Generally, the onset of a long-lived mode also flattens the FIDA profile. There is a shortfall of high-energy ions at large major radius in discharges with repetitive TAE bursts. Work supported by DE-FG03-02ER54681 and DE-AC02-09CH11466.

  18. Tunable proton stopping power of deuterium-tritium by mixing heavy ion dopants for fast ignition

    NASA Astrophysics Data System (ADS)

    Zou, D. B.; Hu, L. X.; Wang, W. Q.; Yang, X. H.; Yu, T. P.; Zhang, G. B.; Ouyang, J. M.; Shao, F. Q.; Zhuo, H. B.

    2016-03-01

    The theoretical model of charged-particle stopping power for the Coulomb logarithm lnΛb ≥ 2 plasma [Phys. Rev. Lett., 20, 3059 (1993)] is extended to investigate the transport of the energetic protons in a compressed deuterium-tritium (DT) pellet mixed with heavy ion dopants. It shows that an increase of mixed-ion charge state and density ratio results in the substantial enhancement of the proton stopping power, which leads to a shorter penetration distance and an earlier appearance of the Bragg peak with a higher magnitude. The effect of hot-spot mix on the proton-driven fast ignition model is discussed. It is found that ignition time required for a small mixed hot-spot can be significantly reduced with slightly increased beam energy. Nevertheless, the ignition cannot maintain for a long time due to increasing alpha-particle penetration distance and energy loss from mechanical work and thermal conduction at high temperatures.

  19. Diffusion of hydroxyl ions from calcium hydroxide and Aloe vera pastes.

    PubMed

    Batista, Victor Eduardo de Souza; Olian, Douglas Dáquila; Mori, Graziela Garrido

    2014-01-01

    This study evaluated the diffusion through the dentinal tubules of hydroxyl ions from different calcium hydroxide (CH) pastes containing Aloe vera. Sixty single-rooted bovine teeth were used. The tooth crowns were removed, the root canals were instrumented and the specimens were assigned to 4 groups (n=15) according to the intracanal medication: Group CH/S - CH powder and saline paste; Group CH/P - CH powder and propylene glycol paste; Group CH/A - calcium hydroxide powder and Aloe vera gel paste; Group CH/A/P - CH powder, Aloe vera powder and propylene glycol paste. After placement of the root canal dressings, the teeth were sealed coronally and apically with a two-step epoxy adhesive. The teeth were placed in identified flasks containing deionized water and stored in an oven with 100% humidity at 37 °C. After 3 h, 24 h, 72 h, 7 days, 15 days and 30 days, the deionized water in the flasks was collected and its pH was measured by a pH meter. The obtained data were subjected to statistical analysis at a significance level of 5%. The results demonstrated that all pastes provided diffusion of hydroxyl ions through the dentinal tubules. The combination of Aloe vera and CH (group CH/A) provided a constant release of calcium ions. Group CH/A/P showed the highest pH at 24 and 72 h. In conclusion, the experimental pastes containing Aloe vera were able to enable the diffusion of hydroxyl ions through the dentinal tubules.

  20. Fast detection of narcotics by single photon ionization mass spectrometry and laser ion mobility spectrometry

    NASA Astrophysics Data System (ADS)

    Laudien, Robert; Schultze, Rainer; Wieser, Jochen

    2010-10-01

    In this contribution two analytical devices for the fast detection of security-relevant substances like narcotics and explosives are presented. One system is based on an ion trap mass spectrometer (ITMS) with single photon ionization (SPI). This soft ionization technique, unlike electron impact ionization (EI), reduces unwanted fragment ions in the mass spectra allowing the clear determination of characteristic (usually molecular) ions. Their enrichment in the ion trap and identification by tandem MS investigations (MS/MS) enables the detection of the target substances in complex matrices at low concentrations without time-consuming sample preparation. For SPI an electron beam pumped excimer light source of own fabrication (E-Lux) is used. The SPI-ITMS system was characterized by the analytical study of different drugs like cannabis, heroin, cocaine, amphetamines, and some precursors. Additionally, it was successfully tested on-site in a closed illegal drug laboratory, where low quantities of MDMA could be directly detected in samples from floors, walls and lab equipments. The second analytical system is based on an ion mobility (IM) spectrometer with resonant multiphoton ionization (REMPI). With the frequency quadrupled Nd:YAG laser (266 nm), used for ionization, a selective and sensitive detection of aromatic compounds is possible. By application of suited aromatic dopants, in addition, also non-aromatic polar compounds are accessible by ion molecule reactions like proton transfer or complex formation. Selected drug precursors could be successfully detected with this device as well, qualifying it to a lower-priced alternative or useful supplement of the SPI-ITMS system for security analysis.