Electron density in surface barrier discharge emerging at argon/water interface: quantification for streamers and leaders

NASA Astrophysics Data System (ADS)

Cvetanović, Nikola; Galmiz, Oleksandr; Synek, Petr; Zemánek, Miroslav; Brablec, Antonín; Hoder, Tomáš

2018-02-01

Optical emission spectroscopy, fast intensified CCD imaging and electrical measurements were applied to investigate the basic plasma parameters of surface barrier discharge emerging from a conductive water electrode. The discharge was generated at the triple-line interface of atmospheric pressure argon gas and conductive water solution at the fused silica dielectrics using a sinusoidal high-voltage waveform. The spectroscopic methods of atomic line broadening and molecular spectroscopy were used to determine the electron densities and the gas temperature in the active plasma. These parameters were obtained for both applied voltage polarities and resolved spatially. Two different spectral signatures were identified in the spatially resolved spectra resulting in electron densities differing by two orders of magnitude. It is shown that two discharge mechanisms take a place: the streamer and the leader one, with electron densities of 1014 and 1016 cm-3, respectively. This spectroscopic evidence is supported by the combined diagnostics of electrical current measurements and phase-resolved intensified CCD camera imaging.

Ionospheric tomography by gradient-enhanced kriging with STEC measurements and ionosonde characteristics

NASA Astrophysics Data System (ADS)

Minkwitz, David; van den Boogaart, Karl Gerald; Gerzen, Tatjana; Hoque, Mainul; Hernández-Pajares, Manuel

2016-11-01

The estimation of the ionospheric electron density by kriging is based on the optimization of a parametric measurement covariance model. First, the extension of kriging with slant total electron content (STEC) measurements based on a spatial covariance to kriging with a spatial-temporal covariance model, assimilating STEC data of a sliding window, is presented. Secondly, a novel tomography approach by gradient-enhanced kriging (GEK) is developed. Beyond the ingestion of STEC measurements, GEK assimilates ionosonde characteristics, providing peak electron density measurements as well as gradient information. Both approaches deploy the 3-D electron density model NeQuick as a priori information and estimate the covariance parameter vector within a maximum likelihood estimation for the dedicated tomography time stamp. The methods are validated in the European region for two periods covering quiet and active ionospheric conditions. The kriging with spatial and spatial-temporal covariance model is analysed regarding its capability to reproduce STEC, differential STEC and foF2. Therefore, the estimates are compared to the NeQuick model results, the 2-D TEC maps of the International GNSS Service and the DLR's Ionospheric Monitoring and Prediction Center, and in the case of foF2 to two independent ionosonde stations. Moreover, simulated STEC and ionosonde measurements are used to investigate the electron density profiles estimated by the GEK in comparison to a kriging with STEC only. The results indicate a crucial improvement in the initial guess by the developed methods and point out the potential compensation for a bias in the peak height hmF2 by means of GEK.

An automated system for the study of ionospheric spatial structures

NASA Astrophysics Data System (ADS)

Belinskaya, I. V.; Boitman, O. N.; Vugmeister, B. O.; Vyborova, V. M.; Zakharov, V. N.; Laptev, V. A.; Mamchenko, M. S.; Potemkin, A. A.; Radionov, V. V.

The system is designed for the study of the vertical distribution of electron density and the parameters of medium-scale ionospheric irregularities over the sounding site as well as the reconstruction of the spatial distribution of electron density within the range of up to 300 km from the sounding location. The system comprises an active central station as well as passive companion stations. The central station is equipped with the digital ionosonde ``Basis'', the measuring-and-computing complex IVK-2, and the receiver-recorder PRK-3M. The companion stations are equipped with receivers-recorders PRK-3. The automated comlex software system includes 14 subsystems. Data transfer between them is effected using magnetic disk data sets. The system is operated in both ionogram mode and Doppler shift and angle-of-arrival mode. Using data obtained in these two modes, the reconstruction of the spatial distribution of electron density in the region is carried out. Reconstruction is checked for accuracy using data from companion stations.

Spatially resolved density and ionization measurements of shocked foams using x-ray fluorescence

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

MacDonald, M. J.; Keiter, P. A.; Montgomery, D. S.

2016-09-22

We present experiments at the Trident laser facility demonstrating the use of x-ray fluorescence (XRF) to simultaneously measure density, ionization state populations, and electron temperature in shocked foams. An imaging x-ray spectrometer was used to obtain spatially-resolved measurements of Ti K-more » $$\\alpha$$ emission. Density profiles were measured from K-$$\\alpha$$ intensity. Ti ionization state distributions and electron temperatures were inferred by fitting K-$$\\alpha$$ spectra to spectra from CRETIN simulations. This study shows that XRF provides a powerful tool to complement other diagnostics to make equation of state measurements of shocked materials containing a suitable tracer element.« less

Optical Diagnostics in the Gaseous Electronics Conference Reference Cell

PubMed Central

Hebner, G. A.; Greenberg, K. E.

1995-01-01

A number of laser-induced fluorescence and absorption spectroscopy studies have been conducted using Gaseous Electronics Conference Reference Cells. Laser-induced fluorescence has been used to measure hydrogen atom densities, to measure argon metastable spatial profiles, to determine the sheath electric field, and to infer the electron density and temperature. Absorption spectroscopy, using lamp sources and diode lasers, has been used to measure metastable atom densities in helium and argon discharges and fluorocarbon densities in silicon etching discharges. The experimental techniques and sample results of these investigations are reviewed. PMID:29151748

Time-dependent density functional theory (TD-DFT) coupled with reference interaction site model self-consistent field explicitly including spatial electron density distribution (RISM-SCF-SEDD)

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

Yokogawa, D., E-mail: d.yokogawa@chem.nagoya-u.ac.jp; Institute of Transformative Bio-Molecules

2016-09-07

Theoretical approach to design bright bio-imaging molecules is one of the most progressing ones. However, because of the system size and computational accuracy, the number of theoretical studies is limited to our knowledge. To overcome the difficulties, we developed a new method based on reference interaction site model self-consistent field explicitly including spatial electron density distribution and time-dependent density functional theory. We applied it to the calculation of indole and 5-cyanoindole at ground and excited states in gas and solution phases. The changes in the optimized geometries were clearly explained with resonance structures and the Stokes shift was correctly reproduced.

Normal and abnormal evolution of argon metastable density in high-density plasmas

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

Seo, B. H.; Kim, J. H., E-mail: jhkim86@kriss.re.kr; You, S. J., E-mail: sjyou@cnu.ac.kr

2015-05-15

A controversial problem on the evolution of Ar metastable density as a function of electron density (increasing trend versus decreasing trend) was resolved by discovering the anomalous evolution of the argon metastable density with increasing electron density (discharge power), including both trends of the metastable density [Daltrini et al., Appl. Phys. Lett. 92, 061504 (2008)]. Later, by virtue of an adequate physical explanation based on a simple global model, both evolutions of the metastable density were comprehensively understood as part of the abnormal evolution occurring at low- and high-density regimes, respectively, and thus the physics behind the metastable evolution hasmore » seemed to be clearly disclosed. In this study, however, a remarkable result for the metastable density behavior with increasing electron density was observed: even in the same electron density regime, there are both normal and abnormal evolutions of metastable-state density with electron density depending on the measurement position: The metastable density increases with increasing electron density at a position far from the inductively coupled plasma antenna but decreases at a position close to the antenna. The effect of electron temperature, which is spatially nonuniform in the plasma, on the electron population and depopulation processes of Argon metastable atoms with increasing electron density is a clue to understanding the results. The calculated results of the global model, including multistep ionization for the argon metastable state and measured electron temperature, are in a good agreement with the experimental results.« less

First-principles electron dynamics control simulation of diamond under femtosecond laser pulse train irradiation.

PubMed

Wang, Cong; Jiang, Lan; Wang, Feng; Li, Xin; Yuan, Yanping; Xiao, Hai; Tsai, Hai-Lung; Lu, Yongfeng

2012-07-11

A real-time and real-space time-dependent density functional is applied to simulate the nonlinear electron-photon interactions during shaped femtosecond laser pulse train ablation of diamond. Effects of the key pulse train parameters such as the pulse separation, spatial/temporal pulse energy distribution and pulse number per train on the electron excitation and energy absorption are discussed. The calculations show that photon-electron interactions and transient localized electron dynamics can be controlled including photon absorption, electron excitation, electron density, and free electron distribution by the ultrafast laser pulse train.

Neutral particle dynamics in a high-power RF source

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

Todorov, D., E-mail: dimitar-tdrv@phys.uni-sofia.bg; Paunska, Ts.; Shivarova, A.

2015-04-08

Previous studies on the spatial discharge structure in the SPIDER source of negative hydrogen/deuterium ions carried out at low applied power are extended towards description of the discharge maintenance under the conditions of the actual rf power deposition of 100 kW planned for a single driver of the source. In addition to the expected higher electron density, the results show strong increase of the electron temperature and of the temperatures of the neutral species (hydrogen atoms and molecules). In the discussions, not only the spatial distribution of the plasma parameters but also that of the fluxes in the discharge (particlemore » and energy fluxes) is involved. The obtained results come in confirmation of basic concepts for low-pressure discharge maintenance: (i) mutually related electron density and temperature as a display of the generalized Schottky condition, (ii) discharge behavior governed by the fluxes, i.e. strong nonlocality in the discharge, and (iii) a non-ambipolarity in the discharge regime, which originates from shifted maxima of the electron density and temperature and shows evidence in a vortex electron flux and in a dc current in a rf discharge, the latter resulting from a shift in the positions of the maxima of the electron density and plasma potential.« less

A temporally and spatially resolved electron density diagnostic method for the edge plasma based on Stark broadening

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

Zafar, A., E-mail: zafara@ornl.gov; Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830; Martin, E. H.

2016-11-15

An electron density diagnostic (≥10{sup 10} cm{sup −3}) capable of high temporal (ms) and spatial (mm) resolution is currently under development at Oak Ridge National Laboratory. The diagnostic is based on measuring the Stark broadened, Doppler-free spectral line profile of the n = 6–2 hydrogen Balmer series transition. The profile is then fit to a fully quantum mechanical model including the appropriate electric and magnetic field operators. The quasi-static approach used to calculate the Doppler-free spectral line profile is outlined here and the results from the model are presented for H-δ spectra for electron densities of 10{sup 10}–10{sup 13} cm{supmore » −3}. The profile shows complex behavior due to the interaction between the magnetic substates of the atom.« less

Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium

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

Ostrovskaya, G. V., E-mail: galya-ostr@mail.ru; Markov, V. S.; Frank, A. G., E-mail: annfrank@fpl.gpi.ru

The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.

The resolved layer of a collisionless, high beta, supercritical, quasi-perpendicular shock wave. I - Rankine-Hugoniot geometry, currents, and stationarity

NASA Technical Reports Server (NTRS)

Scudder, J. D.; Aggson, T. L.; Mangeney, A.; Lacombe, C.; Harvey, C. C.

1986-01-01

Data collected by the ISEE dual-spacecraft mission (on November 7, 1977) on a slowly moving, supercritical, high-beta, quasi-perpendicular bow shock are presented, and the local geometry, spatial scales, and stationarity of this shock wave are assessed in a self-consistent Rankine-Hugoniot-constrained frame of reference. Included are spatial profiles of the ac and dc magnetic and electric fields, electron and proton fluid velocities, current densities, electron and proton number densities, temperatures, pressures, and partial densities of the reflected protons. The observed layer profile is shown to be nearly phase standing and one-dimensional in a Rankine-Hugoniot frame, empirically determined by the magnetofluid parameters outside the layer proper.

Relativistic electron plasma oscillations in an inhomogeneous ion background

NASA Astrophysics Data System (ADS)

Karmakar, Mithun; Maity, Chandan; Chakrabarti, Nikhil

2018-06-01

The combined effect of relativistic electron mass variation and background ion inhomogeneity on the phase mixing process of large amplitude electron oscillations in cold plasmas have been analyzed by using Lagrangian coordinates. An inhomogeneity in the ion density is assumed to be time-independent but spatially periodic, and a periodic perturbation in the electron density is considered as well. An approximate space-time dependent solution is obtained in the weakly-relativistic limit by employing the Bogolyubov and Krylov method of averaging. It is shown that the phase mixing process of relativistically corrected electron oscillations is strongly influenced by the presence of a pre-existing ion density ripple in the plasma background.

Multicomponent density functional theory embedding formulation.

PubMed

Culpitt, Tanner; Brorsen, Kurt R; Pak, Michael V; Hammes-Schiffer, Sharon

2016-07-28

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF(-) molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.

Multicomponent density functional theory embedding formulation

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

Culpitt, Tanner; Brorsen, Kurt R.; Pak, Michael V.

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density ismore » separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF{sup −} molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.« less

Comparisons of ionospheric electron density distributions reconstructed by GPS computerized tomography, backscatter ionograms, and vertical ionograms

NASA Astrophysics Data System (ADS)

Zhou, Chen; Lei, Yong; Li, Bofeng; An, Jiachun; Zhu, Peng; Jiang, Chunhua; Zhao, Zhengyu; Zhang, Yuannong; Ni, Binbin; Wang, Zemin; Zhou, Xuhua

2015-12-01

Global Positioning System (GPS) computerized ionosphere tomography (CIT) and ionospheric sky wave ground backscatter radar are both capable of measuring the large-scale, two-dimensional (2-D) distributions of ionospheric electron density (IED). Here we report the spatial and temporal electron density results obtained by GPS CIT and backscatter ionogram (BSI) inversion for three individual experiments. Both the GPS CIT and BSI inversion techniques demonstrate the capability and the consistency of reconstructing large-scale IED distributions. To validate the results, electron density profiles obtained from GPS CIT and BSI inversion are quantitatively compared to the vertical ionosonde data, which clearly manifests that both methods output accurate information of ionopsheric electron density and thereby provide reliable approaches to ionospheric soundings. Our study can improve current understanding of the capability and insufficiency of these two methods on the large-scale IED reconstruction.

Spatial structure and electronic spectrum of TiSi{/n -} clusters ( n = 6-18)

NASA Astrophysics Data System (ADS)

Borshch, N. A.; Pereslavtseva, N. S.; Kurganskii, S. I.

2014-10-01

Results from optimizing the spatial structure and calculated electronic spectra of anion clusters TiSi{/n -} ( n = 6-18) are presented. Calculations are performed within the density functional theory. Spatial structures of clusters detected experimentally are established by comparing the calculated and experimental data. It is shown that prismatic and fullerene-like structures are the ones most energetically favorable for clusters TiSi{/n -}. It is concluded that these structures are basic when building clusters with close numbers of silicon atoms.

Probing the solar corona with very long baseline interferometry.

PubMed

Soja, B; Heinkelmann, R; Schuh, H

2014-06-20

Understanding and monitoring the solar corona and solar wind is important for many applications like telecommunications or geomagnetic studies. Coronal electron density models have been derived by various techniques over the last 45 years, principally by analysing the effect of the corona on spacecraft tracking. Here we show that recent observational data from very long baseline interferometry (VLBI), a radio technique crucial for astrophysics and geodesy, could be used to develop electron density models of the Sun's corona. The VLBI results agree well with previous models from spacecraft measurements. They also show that the simple spherical electron density model is violated by regional density variations and that on average the electron density in active regions is about three times that of low-density regions. Unlike spacecraft tracking, a VLBI campaign would be possible on a regular basis and would provide highly resolved spatial-temporal samplings over a complete solar cycle.

Multi-Point Measurements to Characterize Radiation Belt Electron Precipitation Loss

NASA Astrophysics Data System (ADS)

Blum, L. W.

2017-12-01

Multipoint measurements in the inner magnetosphere allow the spatial and temporal evolution of various particle populations and wave modes to be disentangled. To better characterize and quantify radiation belt precipitation loss, we utilize multi-point measurements both to study precipitating electrons directly as well as the potential drivers of this loss process. Magnetically conjugate CubeSat and balloon measurements are combined to estimate of the temporal and spatial characteristics of dusk-side precipitation features and quantify loss due to these events. To then understand the drivers of precipitation events, and what determines their spatial structure, we utilize measurements from the dual Van Allen Probes to estimate spatial and temporal scales of various wave modes in the inner magnetosphere, and compare these to precipitation characteristics. The structure, timing, and spatial extent of waves are compared to those of MeV electron precipitation during a few individual events to determine when and where EMIC waves cause radiation belt electron precipitation. Magnetically conjugate measurements provide observational support of the theoretical picture of duskside interaction of EMIC waves and MeV electrons leading to radiation belt loss. Finally, understanding the drivers controlling the spatial scales of wave activity in the inner magnetosphere is critical for uncovering the underlying physics behind the wave generation as well as for better predicting where and when waves will be present. Again using multipoint measurements from the Van Allen Probes, we estimate the spatial and temporal extents and evolution of plasma structures and their gradients in the inner magnetosphere, to better understand the drivers of magnetospheric wave characteristic scales. In particular, we focus on EMIC waves and the plasma parameters important for their growth, namely cold plasma density and cool and warm ion density, anisotropy, and composition.

X-ray imaging spectroscopic diagnostics on Nike

NASA Astrophysics Data System (ADS)

Aglitskiy, Y.; Karasik, M.; Serlin, V.; Weaver, J. L.; Oh, J.; Obenschain, S. P.; Ralchenko, Yu.

2017-10-01

Electron temperature and density diagnostics of the laser plasma produced within the focal spot of the NRL's Nike laser are being explored with the help of X-ray imaging spectroscopy. Spectra of He-like and H-like ions were taken by Nike focusing spectrometers in a range of lower (1.8 kev, Si XIV) and higher (6.7 kev, Fe XXV) x-ray energies. Data that were obtained with spatial resolution were translated into the temperature and density as functions of distance from the target. As an example electron density was determined from He-like satellites to Ly-alpha in Si XIV. The dielectronic satellites with intensity ratios that are sensitive to collisional transfer of population between different triplet groups of double-excited states 2l2l' in Si XIII were observed with high spatial and spectral resolution Lineouts taken at different axial distances from the planar Si target show changing spectral shapes due to the different electron densities as determined by supporting non-LTE simulations. These shapes are relatively insensitive to the plasma temperature which was measured using different spectral lines. This work was supported by the US DOE/NNSA.

Variational Optimization of the Second-Order Density Matrix Corresponding to a Seniority-Zero Configuration Interaction Wave Function.

PubMed

Poelmans, Ward; Van Raemdonck, Mario; Verstichel, Brecht; De Baerdemacker, Stijn; Torre, Alicia; Lain, Luis; Massaccesi, Gustavo E; Alcoba, Diego R; Bultinck, Patrick; Van Neck, Dimitri

2015-09-08

We perform a direct variational determination of the second-order (two-particle) density matrix corresponding to a many-electron system, under a restricted set of the two-index N-representability P-, Q-, and G-conditions. In addition, we impose a set of necessary constraints that the two-particle density matrix must be derivable from a doubly occupied many-electron wave function, i.e., a singlet wave function for which the Slater determinant decomposition only contains determinants in which spatial orbitals are doubly occupied. We rederive the two-index N-representability conditions first found by Weinhold and Wilson and apply them to various benchmark systems (linear hydrogen chains, He, N2, and CN(-)). This work is motivated by the fact that a doubly occupied many-electron wave function captures in many cases the bulk of the static correlation. Compared to the general case, the structure of doubly occupied two-particle density matrices causes the associate semidefinite program to have a very favorable scaling as L(3), where L is the number of spatial orbitals. Since the doubly occupied Hilbert space depends on the choice of the orbitals, variational calculation steps of the two-particle density matrix are interspersed with orbital-optimization steps (based on Jacobi rotations in the space of the spatial orbitals). We also point to the importance of symmetry breaking of the orbitals when performing calculations in a doubly occupied framework.

Spatially resolving density-dependent screening around a single charged atom in graphene

NASA Astrophysics Data System (ADS)

Wong, Dillon; Corsetti, Fabiano; Wang, Yang; Brar, Victor W.; Tsai, Hsin-Zon; Wu, Qiong; Kawakami, Roland K.; Zettl, Alex; Mostofi, Arash A.; Lischner, Johannes; Crommie, Michael F.

2017-05-01

Electrons in two-dimensional graphene sheets behave as interacting chiral Dirac fermions and have unique screening properties due to their symmetry and reduced dimensionality. By using a combination of scanning tunneling spectroscopy measurements and theoretical modeling we have characterized how graphene's massless charge carriers screen individual charged calcium atoms. A backgated graphene device configuration has allowed us to directly visualize how the screening length for this system can be tuned with carrier density. Our results provide insight into electron-impurity and electron-electron interactions in a relativistic setting with important consequences for other graphene-based electronic devices.

Mapping low-frequency carbon radio recombination lines towards Cassiopeia A at 340, 148, 54, and 43 MHz

NASA Astrophysics Data System (ADS)

Salas, P.; Oonk, J. B. R.; van Weeren, R. J.; Wolfire, M. G.; Emig, K. L.; Toribio, M. C.; Röttgering, H. J. A.; Tielens, A. G. G. M.

2018-04-01

Quantitative understanding of the interstellar medium requires knowledge of its physical conditions. Low-frequency carbon radio recombination lines (CRRLs) trace cold interstellar gas and can be used to determine its physical conditions (e.g. electron temperature and density). In this work, we present spatially resolved observations of the low-frequency (≤390 MHz) CRRLs centred around C268α, C357α, C494α, and C539α towards Cassiopeia A on scales of ≤1.2 pc. We compare the spatial distribution of CRRLs with other interstellar medium tracers. This comparison reveals a spatial offset between the peak of the CRRLs and other tracers, which is very characteristic for photodissociation regions and that we take as evidence for CRRLs being preferentially detected from the surfaces of molecular clouds. Using the CRRLs, we constrain the gas electron temperature and density. These constraints on the gas conditions suggest variations of less than a factor of 2 in pressure over ˜1 pc scales, and an average hydrogen density of 200-470 cm-3. From the electron temperature and density maps, we also constrain the ionized carbon emission measure, column density, and path length. Based on these, the hydrogen column density is larger than 1022 cm-2, with a peak of ˜4 × 1022 cm-2 towards the south of Cassiopeia A. Towards the southern peak, the line-of-sight length is ˜40 pc over a ˜2 pc wide structure, which implies that the gas is a thin surface layer on a large (molecular) cloud that is only partially intersected by Cassiopeia A. These observations highlight the utility of CRRLs as tracers of low-density extended H I and CO-dark gas halo's around molecular clouds.

Effect of plasma density around Io on local electron heating in the Io plasma torus

NASA Astrophysics Data System (ADS)

Tsuchiya, F.; Yoshioka, K.; Kagitani, M.; Kimura, T.; Murakami, G.; Yamazaki, A.; Misawa, H.; Kasaba, Y.; Yoshikawa, I.; Sakanoi, T.; Koga, R.; Ryo, A.; Suzuki, F.; Hikida, R.

2017-12-01

HISAKI observation of Io plasma torus (IPT) with extreme ultraviolet (EUV) wavelength range is a useful probe to access plasma environment in inner magnetosphere of Jupiter. Emissions from sulfur and oxygen ions in EUV range are caused by electron impact excitation and their intensity is well correlated with the abundance of hot electron in IPT. Previous observation showed that the brightness was enhanced downstream of the satellite Io, indicating that efficient electron heating takes place at Io and/or just downstream of Io. Detailed analysis of the emission intensity shows that the brightness depends on the magnetic longitude at Io and primary and secondary peaks appear in the longitude ranges of 100-130 and 250-340 degrees, respectively. The peak position and amplitude are slightly different between dawn and dusk sides. Here, we introduce inhomogeneous IPT density model in order to investigate relation between the emission intensity and local plasma density around Io in detail. An empirical IPT model is used for spatial distribution of ion and electron densities in the meridional plane. To include longitude and local time asymmetry in IPT, we consider (1)dawnward shift of IPT due to global convection electric field, (2) offset of Jupiter's dipole magnetic field, and (3) tilt of IPT with respect to Io's orbital plane. The modeled electron density at the position of Io as a function of magnetic longitude at Io shows similar profile with the ion emission intensity derived from the observation. This result suggests that energy extracted around Io and/or efficiency of electron heating is closely related to the plasma density around Io and longitude and local time dependences is explained by the spatial inhomogeneity of plasma density in IPT. A part of the energy extracted around Io could be transferred to the Jovian ionosphere along the magnetic field line and cause bright aurora spots and strong radio emissions.

Differential interferometry for measurement of density fluctuations and fluctuation-induced transport (invited)

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

Lin, L.; Ding, W. X.; Brower, D. L.

2010-10-15

Differential interferometry employs two parallel laser beams with a small spatial offset (less than beam width) and frequency difference (1-2 MHz) using common optics and a single mixer for a heterodyne detection. The differential approach allows measurement of the electron density gradient, its fluctuations, as well as the equilibrium density distribution. This novel interferometry technique is immune to fringe skip errors and is particularly useful in harsh plasma environments. Accurate calibration of the beam spatial offset, accomplished by use of a rotating dielectric wedge, is required to enable broad application of this approach. Differential interferometry has been successfully used onmore » the Madison Symmetric Torus reversed-field pinch plasma to directly measure fluctuation-induced transport along with equilibrium density profile evolution during pellet injection. In addition, by combining differential and conventional interferometry, both linear and nonlinear terms of the electron density fluctuation energy equation can be determined, thereby allowing quantitative investigation of the origin of the density fluctuations. The concept, calibration, and application of differential interferometry are presented.« less

The effect of a longitudinal density gradient on electron plasma wake field acceleration

NASA Astrophysics Data System (ADS)

Tsiklauri, David

2016-12-01

Three-dimensional, particle-in-cell, fully electromagnetic simulations of electron plasma wake field acceleration in the blow-out regime are presented. Earlier results are extended by (i) studying the effect of a longitudinal density gradient, (ii) avoiding the use of a co-moving simulation box, (iii) inclusion of ion motion, and (iv) studying fully electromagnetic plasma wake fields. It is established that injecting driving and trailing electron bunches into a positive density gradient of 10-fold increasing density over 10 cm long lithium vapour plasma results in spatially more compact and three times larger, compared with the uniform density case, electric fields (-6.4×1010 V m-1), leading to acceleration of the trailing bunch up to 24.4 GeV (starting from an initial 20.4 GeV), with energy transfer efficiencies from the leading to trailing bunch of 75%. In the uniform density case, a -2.5×1010 V m-1 wake is created leading to acceleration of the trailing bunch up to 22.4 GeV, with energy transfer efficiencies of 65%. It is also established that injecting the electron bunches into a negative density gradient of 10-fold decreasing density over 10 cm long plasma results in spatially more spread and two and a half smaller electric fields (-1.0×1010 V m-1), leading to a weaker acceleration of the trailing bunch up to 21.4 GeV, with energy transfer efficiencies of 45%. Taking ion motions into consideration shows that in the plasma wake ion number density can increase over a few times the background value. It is also shown that transverse electromagnetic fields in a plasma wake are of the same order as the longitudinal (electrostatic) ones.

Reconstruction of the ionospheric electron density by geostatistical inversion

NASA Astrophysics Data System (ADS)

Minkwitz, David; van den Boogaart, Karl Gerald; Hoque, Mainul; Gerzen, Tatjana

2015-04-01

The ionosphere is the upper part of the atmosphere where sufficient free electrons exist to affect the propagation of radio waves. Typically, the ionosphere extends from about 50 - 1000 km and its morphology is mainly driven by solar radiation, particle precipitation and charge exchange. Due to the strong ionospheric impact on many applications dealing with trans-ionospheric signals such as Global Navigation Satellite Systems (GNSS) positioning, navigation and remote sensing, the demand for a highly accurate reconstruction of the electron density is ever increasing. Within the Helmholtz Alliance project "Remote Sensing and Earth System Dynamics" (EDA) the utilization of the upcoming radar mission TanDEM-L and its related products are prepared. The TanDEM-L mission will operate in L-band with a wavelength of approximately 24 cm and aims at an improved understanding of environmental processes and ecosystem change, e.g. earthquakes, volcanos, glaciers, soil moisture and carbon cycle. Since its lower frequency compared to the X-band (3 cm) and C-band (5 cm) radar missions, the influence of the ionosphere will increase and might lead to a significant degradation of the radar image quality if no correction is applied. Consequently, our interest is the reconstruction of the ionospheric electron density in order to mitigate the ionospheric delay. Following the ionosphere's behaviour we establish a non-stationary and anisotropic spatial covariance model of the electron density separated into a vertical and horizontal component. In order to estimate the model's parameters we chose a maximum likelihood approach. This approach incorporates GNSS total electron content measurements, representing integral measurements of the electron density between satellite to receiver ray paths, and the NeQuick model as a non-stationary trend. Based on a multivariate normal distribution the spatial covariance model parameters are optimized and afterwards the 3D electron density can be calculated by kriging for arbitrary points or grids of interest.

2D electron density profile measurement in tokamak by laser-accelerated ion-beam probe.

PubMed

Chen, Y H; Yang, X Y; Lin, C; Wang, L; Xu, M; Wang, X G; Xiao, C J

2014-11-01

A new concept of Heavy Ion Beam Probe (HIBP) diagnostic has been proposed, of which the key is to replace the electrostatic accelerator of traditional HIBP by a laser-driven ion accelerator. Due to the large energy spread of ions, the laser-accelerated HIBP can measure the two-dimensional (2D) electron density profile of tokamak plasma. In a preliminary simulation, a 2D density profile was reconstructed with a spatial resolution of about 2 cm, and with the error below 15% in the core region. Diagnostics of 2D density fluctuation is also discussed.

Nuclear spatial delocalization silences electron density oscillations in 2-phenyl-ethyl-amine (PEA) and 2-phenylethyl-N,N-dimethylamine (PENNA) cations

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

Jenkins, Andrew J.; Vacher, Morgane; Bearpark, Michael J.

2016-03-14

We simulate electron dynamics following ionization in 2-phenyl-ethyl-amine and 2-phenylethyl-N,N-dimethylamine as examples of systems where 3 coupled cationic states are involved. We study two nuclear effects on electron dynamics: (i) coupled electron-nuclear motion and (ii) nuclear spatial delocalization as a result of the zero-point energy in the neutral molecule. Within the Ehrenfest approximation, our calculations show that the coherent electron dynamics in these molecules is not lost as a result of coupled electron-nuclear motion. In contrast, as a result of nuclear spatial delocalization, dephasing of the oscillations occurs on a time scale of only a few fs, long before anymore » significant nuclear motion can occur. The results have been rationalized using a semi-quantitative model based upon the gradients of the potential energy surfaces.« less

An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics.

PubMed

Valdivia, M P; Stutman, D; Stoeckl, C; Theobald, W; Mileham, C; Begishev, I A; Bromage, J; Regan, S P

2016-02-01

X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 10(23) cm(-3) in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. The 50 ± 15 μm spatial resolution achieved across the full field of view was found to be limited by the x-ray source-size, similar to conventional radiography.

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics.

PubMed

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Jaung, Jae Yun; Kim, Yong-Hoon; Park, Sung Kyu

2015-09-28

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics

NASA Astrophysics Data System (ADS)

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Yun Jaung, Jae; Kim, Yong-Hoon; Kyu Park, Sung

2015-09-01

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.

Features of Electron Density Distribution in Delafossite Cualo2

NASA Astrophysics Data System (ADS)

Pogoreltsev, A. I.; Schmidt, S. V.; Gavrilenko, A. N.; Shulgin, D. A.; Korzun, B. V.; Matukhin, V. L.

2015-07-01

We have used pulsed 63,65Cu nuclear quadrupole resonance at room temperature to study the semiconductor compound CuAlO2 with a delafossite crystal structure, and we have determined the quadrupole frequency νQ = 28.12 MHz and the asymmetry parameter η ~ 0, which we used to study the features of the electron density distribution in the vicinity of the quadrupolar nucleus. In order to take into account the influence of correlation effects on the electric field gradient, we carried out ab initio calculations within the density functional theory (DFT) approximation using a set of correlation functionals VWN1RPA, VWN5, PW91LDA, CPW91, and B3LYP1. We mapped the electron density distribution in the vicinity of the quadrupolar copper nucleus for the Cu7Al6o{14/- 1} cluster and we calculated the size of the LUMO-HOMO gap, Δ ~ 3.33 eV. We established the anisotropy of the spatial electron density distribution. Based on analysis of the electron density distribution obtained, we suggest that the bond in CuAlO2 is not purely covalent.

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

NASA Astrophysics Data System (ADS)

Lu, Chao; Jiang, Tao; Liu, Shengguang; Wang, Rui; Zhao, Lingrong; Zhu, Pengfei; Liu, Yaqi; Xu, Jun; Yu, Dapeng; Wan, Weishi; Zhu, Yimei; Xiang, Dao; Zhang, Jie

2018-03-01

An accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ˜3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10-19 s m, about 2 orders of magnitude higher than that achieved with state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.

Quantum coherent switch utilizing commensurate nanoelectrode and charge density periodicities

DOEpatents

Harrison,; Neil, Singleton [Santa Fe, NM; John, Migliori [Los Alamos, NM; Albert, [Santa Fe, NM

2008-08-05

A quantum coherent switch having a substrate formed from a density wave (DW) material capable of having a periodic electron density modulation or spin density modulation, a dielectric layer formed onto a surface of the substrate that is orthogonal to an intrinsic wave vector of the DW material; and structure for applying an external spatially periodic electrostatic potential over the dielectric layer.

Dynamics of electron injection in a laser-wakefield accelerator

NASA Astrophysics Data System (ADS)

Xu, J.; Buck, A.; Chou, S.-W.; Schmid, K.; Shen, B.; Tajima, T.; Kaluza, M. C.; Veisz, L.

2017-08-01

The detailed temporal evolution of the laser-wakefield acceleration process with controlled injection, producing reproducible high-quality electron bunches, has been investigated. The localized injection of electrons into the wakefield has been realized in a simple way—called shock-front injection—utilizing a sharp drop in plasma density. Both experimental and numerical results reveal the electron injection and acceleration process as well as the electron bunch's temporal properties. The possibility to visualize the plasma wave gives invaluable spatially resolved information about the local background electron density, which in turn allows for an efficient suppression of electron self-injection before the controlled process of injection at the sharp density jump. Upper limits for the electron bunch duration of 6.6 fs FWHM, or 2.8 fs (r.m.s.) were found. These results indicate that shock-front injection not only provides stable and tunable, but also few-femtosecond short electron pulses for applications such as ultrashort radiation sources, time-resolved electron diffraction or for the seeding of further acceleration stages.

Behavior of Excited Argon Atoms in Inductively Driven Plasmas

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

HEBNER,GREGORY A.; MILLER,PAUL A.

1999-12-07

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s{sub 5} and 1s{sub 4}, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s{sub 5} level is metastable and the 1s{sub 4} level is radiatively coupled to the ground state but is radiation trapped. The argon data is compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the datamore » suggest that both processes play a major role in determining the excited state density. At lower rfpower and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rfpowers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the 1s{sub 5} and 1s{sub 4} argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong fi.mction of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of two decrease in the fluorescence lifetime while adding Cl{sub 2} or BCl{sub 3} increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When Cl{sub 2} or BCl{sub 3} was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically possible for argon excited states to dissociate some of the molecular species present in this discharge, it does not appear to be a significant source of dissociation. The major source of interaction between the argon and the molecular species BCl{sub 3} and Cl{sub 2} appears to be through modification of the electron density.« less

Proximity-induced magnetism in transition-metal substituted graphene

PubMed Central

Crook, Charles B.; Constantin, Costel; Ahmed, Towfiq; Zhu, Jian-Xin; Balatsky, Alexander V.; Haraldsen, Jason T.

2015-01-01

We investigate the interactions between two identical magnetic impurities substituted into a graphene superlattice. Using a first-principles approach, we calculate the electronic and magnetic properties for transition-metal substituted graphene systems with varying spatial separation. These calculations are compared for three different magnetic impurities, manganese, chromium, and vanadium. We determine the electronic band structure, density of states, and Millikan populations (magnetic moment) for each atom, as well as calculate the exchange parameter between the two magnetic atoms as a function of spatial separation. We find that the presence of magnetic impurities establishes a distinct magnetic moment in the graphene lattice, where the interactions are highly dependent on the spatial and magnetic characteristic between the magnetic and carbon atoms, which leads to either ferromagnetic or antiferromagnetic behavior. Furthermore, through an analysis of the calculated exchange energies and partial density of states, it is determined that interactions between the magnetic atoms can be classified as an RKKY interaction. PMID:26235646

Three Dimensional High-Resolution Reconstruction of the Ionosphere Over the Very Large Array

DTIC Science & Technology

2010-12-15

Watts Progress Report, Dec 10; 1 Final Report: Three Dimensional High-Resolution Reconstruction of the Ionosphere over the Very Large Array...proposed research is reconstruct the three-dimensional regional electron density profile of Earth’s ionosphere with spatial resolution of better than 10 km...10x better sensitivity to total electron content (TEC, or chord integrated density) in the ionosphere that does GPS. The proposal funds the

Dense solar wind cloud geometries deduced from comparisons of radio signal delay and in situ plasma measurements

NASA Technical Reports Server (NTRS)

Landt, J. A.

1974-01-01

The geometries of dense solar wind clouds are estimated by comparing single-location measurements of the solar wind plasma with the average of the electron density obtained by radio signal delay measurements along a radio path between earth and interplanetary spacecraft. Several of these geometries agree with the current theoretical spatial models of flare-induced shock waves. A new class of spatially limited structures that contain regions with densities greater than any observed in the broad clouds is identified. The extent of a cloud was found to be approximately inversely proportional to its density.

The effect of the electric wind on the spatial distribution of chemical species in the positive corona discharge

NASA Astrophysics Data System (ADS)

Yanallah, K.; Pontiga, F.; Bouazza, M. R.; Chen, J. H.

2017-08-01

The electrohydrodynamic air flow generated by a positive corona discharge, and its effect on the spatial distribution of chemical species within a wire-plate corona reactor, have been numerically simulated. The computational model is based on the solutions of the Navier-Stokes equation and the continuity equation of each chemical species generated by the electrical discharge. A simplified analytical expression of the electric force density, which only requires the current density as the input parameter, has been used in the Navier-Stokes equation to obtain the velocity field. For the solution of the continuity equations, a plasma chemistry model that includes the most important reactions between electrons, atoms and molecules in air has been used. Similar to the electric force, the electron density distribution has been approximated by using a semi-analytical expression appropriate for the electrode geometry. The results of the study show that the spatial distribution of chemical species can be very different, and depends on the interplay between the electrohydrodynamic flow, the chemical kinetics of the species and its characteristic lifetime.

Spatial confinement effects on spectroscopic and morphological studies of nanosecond laser-ablated Zirconium

NASA Astrophysics Data System (ADS)

Hayat, Asma; Bashir, Shazia; Rafique, Muhammad Shahid; Ahmad, Riaz; Akram, Mahreen; Mahmood, Khaliq; Zaheer, Ali

2017-12-01

Spatial confinement effects on plasma parameters and surface morphology of laser ablated Zr (Zirconium) are studied by introducing a metallic blocker. Nd:YAG laser at various fluencies ranging from 8 J cm-2 to 32 J cm-2 was employed as an irradiation source. All measurements were performed in the presence of Ar under different pressures. Confinement effects offered by metallic blocker are investigated by placing the blocker at different distances of 6 mm, 8 mm and 10 mm from the target surface. It is revealed from LIBS analysis that both plasma parameters i.e. excitation temperature and electron number density increase with increasing laser fluence due to enhancement in energy deposition. It is also observed that spatial confinement offered by metallic blocker is responsible for the enhancement of both electron temperature and electron number density of Zr plasma. This is true for all laser fluences and pressures of Ar. Maximum values of electron temperature and electron number density without blocker are 12,600 K and 14 × 1017 cm-3 respectively whereas, these values are enhanced to 15,000 K and 21 × 1017 cm-3 in the presence of blocker. The physical mechanisms responsible for the enhancement of Zr plasma parameters are plasma compression, confinement and pronounced collisional excitations due to reflection of shock waves. Scanning Electron Microscope (SEM) analysis was performed to explore the surface morphology of laser ablated Zr. It reveals the formation of cones, cavities and ripples. These features become more distinct and well defined in the presence of blocker due to plasma confinement. The optimum combination of blocker distance, fluence and Ar pressure can identify the suitable conditions for defining the role of plasma parameters for surface structuring.

Relationship between the Geotail spacecraft potential and the magnetospheric electron number density including the distant tail regions

NASA Astrophysics Data System (ADS)

Ishisaka, K.; Okada, T.; Tsuruda, K.; Hayakawa, H.; Mukai, T.; Matsumoto, H.

2001-04-01

The spacecraft potential has been used to derive the electron number density surrounding the spacecraft in the magnetosphere and solar wind. We have investigated the correlation between the spacecraft potential of the Geotail spacecraft and the electron number density derived from the plasma waves in the solar wind and almost all the regions of the magnetosphere, except for the high-density plasmasphere, and obtained an empirical formula to show their relation. The new formula is effective in the range of spacecraft potential from a few volts up to 90 V, corresponding to the electron number density from 0.001 to 50 cm-3. We compared the electron number density obtained by the empirical formula with the density obtained by the plasma wave and plasma particle measurements. On occasions the density determined by plasma wave measurements in the lobe region is different from that calculated by the empirical formula. Using the difference in the densities measured by two methods, we discuss whether or not the lower cutoff frequency of the plasma waves, such as continuum radiation, indicates the local electron density near the spacecraft. Then we applied the new relation to the spacecraft potential measured by the Geotail spacecraft during the period from October 1993 to December 1995, and obtained the electron spatial distribution in the solar wind and magnetosphere, including the distant tail region. Higher electron number density is clearly observed on the dawnside than on the duskside of the magnetosphere in the distant tail beyond 100RE.

Great Lakes Region Morphology and Impacts of March 17, 2015 SED Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Heine, T.; Moldwin, M.; Zou, S.

2015-12-01

Under quiet geomagnetic conditions, the mid-latitude ionosphere is relatively uniform with little spatial variation in electron density. However, during intense geomagnetic storms, density gradients associated with Storm Enhanced Density (SED) plumes and Sub-auroral Polarization Streams (SAPS) can move across the dayside mid-latitude ionosphere producing small spatial scale density structure that may be connected to ionospheric scintillation. The evolution of the SED plume during the March 17, 2015 "St. Patrick's Day Storm" is investigated using aggregated data from high resolution GPS receivers at the University of Michigan and throughout the Great Lakes region. Structural density features in the SED gradient can be observed and compared to GPS scintillation measurements—providing insight into the physical mechanisms behind ionospheric scintillation.

CheckDen, a program to compute quantum molecular properties on spatial grids.

PubMed

Pacios, Luis F; Fernandez, Alberto

2009-09-01

CheckDen, a program to compute quantum molecular properties on a variety of spatial grids is presented. The program reads as unique input wavefunction files written by standard quantum packages and calculates the electron density rho(r), promolecule and density difference function, gradient of rho(r), Laplacian of rho(r), information entropy, electrostatic potential, kinetic energy densities G(r) and K(r), electron localization function (ELF), and localized orbital locator (LOL) function. These properties can be calculated on a wide range of one-, two-, and three-dimensional grids that can be processed by widely used graphics programs to render high-resolution images. CheckDen offers also other options as extracting separate atom contributions to the property computed, converting grid output data into CUBE and OpenDX volumetric data formats, and perform arithmetic combinations with grid files in all the recognized formats.

Ponderomotive force on solitary structures created during radiation pressure acceleration of thin foils

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

Tripathi, Vipin K.; Sharma, Anamika

2013-05-15

We estimate the ponderomotive force on an expanded inhomogeneous electron density profile, created in the later phase of laser irradiated diamond like ultrathin foil. When ions are uniformly distributed along the plasma slab and electron density obeys the Poisson's equation with space charge potential equal to negative of ponderomotive potential, φ=−φ{sub p}=−(mc{sup 2}/e)(γ−1), where γ=(1+|a|{sup 2}){sup 1/2}, and |a| is the normalized local laser amplitude inside the slab; the net ponderomotive force on the slab per unit area is demonstrated analytically to be equal to radiation pressure force for both overdense and underdense plasmas. In case electron density is takenmore » to be frozen as a Gaussian profile with peak density close to relativistic critical density, the ponderomotive force has non-monotonic spatial variation and sums up on all electrons per unit area to equal radiation pressure force at all laser intensities. The same result is obtained for the case of Gaussian ion density profile and self consistent electron density profile, obeying Poisson's equation with φ=−φ{sub p}.« less

Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

NASA Astrophysics Data System (ADS)

Belianinov, Alex; Ganesh, Panchapakesan; Lin, Wenzhi; Sales, Brian C.; Sefat, Athena S.; Jesse, Stephen; Pan, Minghu; Kalinin, Sergei V.

2014-12-01

Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1-xSex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

Control of tunable, monoenergetic laser-plasma-accelerated electron beams using a shock-induced density downramp injector

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

Swanson, K. K.; Tsai, H. -E.; Barber, S. K.

Control of the properties of laser-plasma-accelerated electron beams that were injected along a shock-induced density downramp through precision tailoring of the density profile was demonstrated using a 1.8 J, 45 fs laser interacting with a mm-scale gas jet. The effects on the beam spatial profile, steering, and absolute energy spread of the density region before the shock and tilt of the shock were investigated experimentally and with particle-in-cell simulations. By adjusting these density parameters, the electron beam quality was controlled and improved while the energy (30-180 MeV) and energy spread (2-11 MeV) were independently tuned. Simple models that are inmore » good agreement with the experimental results are proposed to explain these relationships, advancing the understanding of downramp injection. In conclusion, this technique allows for high-quality electron beams with percent-level energy spread to be tailored based on the application.« less

Control of tunable, monoenergetic laser-plasma-accelerated electron beams using a shock-induced density downramp injector

DOE PAGES

Swanson, K. K.; Tsai, H. -E.; Barber, S. K.; ...

2017-05-30

Control of the properties of laser-plasma-accelerated electron beams that were injected along a shock-induced density downramp through precision tailoring of the density profile was demonstrated using a 1.8 J, 45 fs laser interacting with a mm-scale gas jet. The effects on the beam spatial profile, steering, and absolute energy spread of the density region before the shock and tilt of the shock were investigated experimentally and with particle-in-cell simulations. By adjusting these density parameters, the electron beam quality was controlled and improved while the energy (30-180 MeV) and energy spread (2-11 MeV) were independently tuned. Simple models that are inmore » good agreement with the experimental results are proposed to explain these relationships, advancing the understanding of downramp injection. In conclusion, this technique allows for high-quality electron beams with percent-level energy spread to be tailored based on the application.« less

CT image electron density quantification in regions with metal implants: implications for radiotherapy treatment planning

NASA Astrophysics Data System (ADS)

Jechel, Christopher Alexander

In radiotherapy planning, computed tomography (CT) images are used to quantify the electron density of tissues and provide spatial anatomical information. Treatment planning systems use these data to calculate the expected spatial distribution of absorbed dose in a patient. CT imaging is complicated by the presence of metal implants which cause increased image noise, produce artifacts throughout the image and can exceed the available range of CT number values within the implant, perturbing electron density estimates in the image. Furthermore, current dose calculation algorithms do not accurately model radiation transport at metal-tissue interfaces. Combined, these issues adversely affect the accuracy of dose calculations in the vicinity of metal implants. As the number of patients with orthopedic and dental implants grows, so does the need to deliver safe and effective radiotherapy treatments in the presence of implants. The Medical Physics group at the Cancer Centre of Southeastern Ontario and Queen's University has developed a Cobalt-60 CT system that is relatively insensitive to metal artifacts due to the high energy, nearly monoenergetic Cobalt-60 photon beam. Kilovoltage CT (kVCT) images, including images corrected using a commercial metal artifact reduction tool, were compared to Cobalt-60 CT images throughout the treatment planning process, from initial imaging through to dose calculation. An effective metal artifact reduction algorithm was also implemented for the Cobalt-60 CT system. Electron density maps derived from the same kVCT and Cobalt-60 CT images indicated the impact of image artifacts on estimates of photon attenuation for treatment planning applications. Measurements showed that truncation of CT number data in kVCT images produced significant mischaracterization of the electron density of metals. Dose measurements downstream of metal inserts in a water phantom were compared to dose data calculated using CT images from kVCT and Cobalt-60 systems with and without artifact correction. The superior accuracy of electron density data derived from Cobalt-60 images compared to kVCT images produced calculated dose with far better agreement with measured results. These results indicated that dose calculation errors from metal image artifacts are primarily due to misrepresentation of electron density within metals rather than artifacts surrounding the implants.

Interplanetary density models as inferred from solar Type III bursts

NASA Astrophysics Data System (ADS)

Oppeneiger, Lucas; Boudjada, Mohammed Y.; Lammer, Helmut; Lichtenegger, Herbert

2016-04-01

We report on the density models derived from spectral features of solar Type III bursts. They are generated by beams of electrons travelling outward from the Sun along open magnetic field lines. Electrons generate Langmuir waves at the plasma frequency along their ray paths through the corona and the interplanetary medium. A large frequency band is covered by the Type III bursts from several MHz down to few kHz. In this analysis, we consider the previous empirical density models proposed to describe the electron density in the interplanetary medium. We show that those models are mainly based on the analysis of Type III bursts generated in the interplanetary medium and observed by satellites (e.g. RAE, HELIOS, VOYAGER, ULYSSES,WIND). Those models are confronted to stereoscopic observations of Type III bursts recorded by WIND, ULYSSES and CASSINI spacecraft. We discuss the spatial evolution of the electron beam along the interplanetary medium where the trajectory is an Archimedean spiral. We show that the electron beams and the source locations are depending on the choose of the empirical density models.

Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

NASA Astrophysics Data System (ADS)

Nakamura, Takuma; Nakamura, Rumi; Haseagwa, Hiroshi

2016-03-01

Spatial dimensions of the detailed structures of the electron diffusion region in anti-parallel magnetic reconnection were analyzed based on two-dimensional fully kinetic particle-in-cell simulations. The electron diffusion region in this study is defined as the region where the positive reconnection electric field is sustained by the electron inertial and non-gyrotropic pressure components. Past kinetic studies demonstrated that the dimensions of the whole electron diffusion region and the inner non-gyrotropic region are scaled by the electron inertial length de and the width of the electron meandering motion, respectively. In this study, we successfully obtained more precise scalings of the dimensions of these two regions than the previous studies by performing simulations with sufficiently small grid spacing (1/16-1/8 de) and a sufficient number of particles (800 particles cell-1 on average) under different conditions changing the ion-to-electron mass ratio, the background density and the electron βe (temperature). The obtained scalings are adequately supported by some theories considering spatial variations of field and plasma parameters within the diffusion region. In the reconnection inflow direction, the dimensions of both regions are proportional to de based on the background density. Both dimensions also depend on βe based on the background values, but the dependence in the inner region ( ˜ 0.375th power) is larger than the whole region (0.125th power) reflecting the orbits of meandering and accelerated electrons within the inner region. In the outflow direction, almost only the non-gyrotropic component sustains the positive reconnection electric field. The dimension of this single-scale diffusion region is proportional to the ion-electron hybrid inertial length (dide)1/2 based on the background density and weakly depends on the background βe with the 0.25th power. These firm scalings allow us to predict observable dimensions in real space which are indeed in reasonable agreement with past in situ spacecraft observations in the Earth's magnetotail and have important implications for future observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.

Modeling of electron cyclotron resonance discharges

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

Meyyappan, M.; Govindan, T.R.

The current trend in plasma processing is the development of high density plasma sources to achieve high deposition and etch rates, uniformity over large ares, and low wafer damage. Here, is a simple model to predict the spatially-averaged plasma characteristics of electron cyclotron resonance (ECR) reactors is presented. The model consists of global conservation equations for species concentration, electron density and energy. A gas energy balance is used to predict the neutral temperature self-consistently. The model is demonstrated for an ECR argon discharge. The predicted behavior of the discharge as a function of system variables agrees well with experimental observations.

An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics

DOE PAGES

Valdivia, M. P.; Stutman, D.; Stoeckl, C.; ...

2016-02-10

X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 10 23 cm ₋3more » in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. We found the 50 ± 15 μm spatial resolution achieved across the full field of view was limited by the x-ray source-size, similar to conventional radiography.« less

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

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

Lu, Chao; Jiang, Tao; Liu, Shengguang

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

DOE PAGES

Lu, Chao; Jiang, Tao; Liu, Shengguang; ...

2018-03-12

Here, an accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ~3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10 –19 sm, about 2 orders of magnitude higher than that achieved withmore » state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.« less

Detection of an electron beam in a high density plasma via an electrostatic probe

NASA Astrophysics Data System (ADS)

Majeski, Stephen; Yoo, Jongsoo; Zweben, Stewart; Yamada, Masaaki; Ji, Hantao

2017-10-01

The perturbation in floating potential by an electron beam is detected by a 1D floating potential probe array to evaluate the use of an electron beam for magnetic field line mapping in the Magnetic Reconnection Experiment (MRX) plasma. The MRX plasma is relatively high density (1013 cm-3) and low temperature (5 eV). Beam electrons are emitted from a tungsten filament and are accelerated by a 200 V potential across the sheath. They stream along the magnetic field lines towards the probe array. The spatial electron beam density profile is assumed to be a Gaussian along the radial axis of MRX and the effective beam width is determined from the radial profile of the floating potential. The magnitude of the perturbation is in agreement with theoretical predictions and the location of the perturbation is also in agreement with field line mapping. In addition, no significant broadening of the electron beam is observed after propagation for tens of centimeters through the high density plasma. These results demonstrate that this method of field line mapping is, in principle, feasible in high density plasmas. This work is supported by the DOE Contract No. DE-AC0209CH11466.

Scalable Sub-micron Patterning of Organic Materials Toward High Density Soft Electronics

PubMed Central

Kim, Jaekyun; Kim, Myung-Gil; Kim, Jaehyun; Jo, Sangho; Kang, Jingu; Jo, Jeong-Wan; Lee, Woobin; Hwang, Chahwan; Moon, Juhyuk; Yang, Lin; Kim, Yun-Hi; Noh, Yong-Young; Yun Jaung, Jae; Kim, Yong-Hoon; Kyu Park, Sung

2015-01-01

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. In this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. The successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics. PMID:26411932

Scalable sub-micron patterning of organic materials toward high density soft electronics

DOE PAGES

Kim, Jaekyun; Kim, Myung -Gil; Kim, Jaehyun; ...

2015-09-28

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. Inmore » this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. As a result, the successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.« less

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

PubMed

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

2015-05-13

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

Nanoscale femtosecond imaging of transient hot solid density plasmas with elemental and charge state sensitivity using resonant coherent diffraction

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

Kluge, T., E-mail: t.kluge@hzdr.de; Bussmann, M.; Huang, L. G., E-mail: lingen.huang@hzdr.de

Here, we propose to exploit the low energy bandwidth, small wavelength, and penetration power of ultrashort pulses from XFELs for resonant Small Angle Scattering (SAXS) on plasma structures in laser excited plasmas. Small angle scattering allows to detect nanoscale density fluctuations in forward scattering direction. Typically, the SAXS signal from laser excited plasmas is expected to be dominated by the free electron distribution. We propose that the ionic scattering signal becomes visible when the X-ray energy is in resonance with an electron transition between two bound states (resonant coherent X-ray diffraction). In this case, the scattering cross-section dramatically increases somore » that the signal of X-ray scattering from ions silhouettes against the free electron scattering background which allows to measure the opacity and derived quantities with high spatial and temporal resolution, being fundamentally limited only by the X-ray wavelength and timing. Deriving quantities such as ion spatial distribution, charge state distribution, and plasma temperature with such high spatial and temporal resolution will make a vast number of processes in shortpulse laser-solid interaction accessible for direct experimental observation, e.g., hole-boring and shock propagation, filamentation and instability dynamics, electron transport, heating, and ultrafast ionization dynamics.« less

SU-G-JeP2-02: A Unifying Multi-Atlas Approach to Electron Density Mapping Using Multi-Parametric MRI for Radiation Treatment Planning

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

Ren, S; Tianjin University, Tianjin; Hara, W

Purpose: MRI has a number of advantages over CT as a primary modality for radiation treatment planning (RTP). However, one key bottleneck problem still remains, which is the lack of electron density information in MRI. In the work, a reliable method to map electron density is developed by leveraging the differential contrast of multi-parametric MRI. Methods: We propose a probabilistic Bayesian approach for electron density mapping based on T1 and T2-weighted MRI, using multiple patients as atlases. For each voxel, we compute two conditional probabilities: (1) electron density given its image intensity on T1 and T2-weighted MR images, and (2)more » electron density given its geometric location in a reference anatomy. The two sources of information (image intensity and spatial location) are combined into a unifying posterior probability density function using the Bayesian formalism. The mean value of the posterior probability density function provides the estimated electron density. Results: We evaluated the method on 10 head and neck patients and performed leave-one-out cross validation (9 patients as atlases and remaining 1 as test). The proposed method significantly reduced the errors in electron density estimation, with a mean absolute HU error of 138, compared with 193 for the T1-weighted intensity approach and 261 without density correction. For bone detection (HU>200), the proposed method had an accuracy of 84% and a sensitivity of 73% at specificity of 90% (AUC = 87%). In comparison, the AUC for bone detection is 73% and 50% using the intensity approach and without density correction, respectively. Conclusion: The proposed unifying method provides accurate electron density estimation and bone detection based on multi-parametric MRI of the head with highly heterogeneous anatomy. This could allow for accurate dose calculation and reference image generation for patient setup in MRI-based radiation treatment planning.« less

Transverse Space-Charge Field-Induced Plasma Dynamics for Ultraintense Electron-Beam Characterization

NASA Astrophysics Data System (ADS)

Tarkeshian, R.; Vay, J. L.; Lehe, R.; Schroeder, C. B.; Esarey, E. H.; Feurer, T.; Leemans, W. P.

2018-04-01

Similarly to laser or x-ray beams, the interaction of sufficiently intense particle beams with neutral gases will result in the creation of plasma. In contrast to photon-based ionization, the strong unipolar field of a particle beam can generate a plasma where the electron population receives a large initial momentum kick and escapes, leaving behind unshielded ions. Measuring the properties of the ensuing Coulomb exploding ions—such as their kinetic energy distribution, yield, and spatial distribution—can provide information about the peak electric fields that are achieved in the electron beams. Particle-in-cell simulations and analytical models are presented for high-brightness electron beams of a few femtoseconds or even hundreds of attoseconds, and transverse beam sizes on the micron scale, as generated by today's free electron lasers. Different density regimes for the utilization as a potential diagnostics are explored, and the fundamental differences in plasma dynamical behavior for e-beam or photon-based ionization are highlighted. By measuring the dynamics of field-induced ions for different gas and beam densities, a lower bound on the beam charge density can be obtained in a single shot and in a noninvasive way. The exponential dependency of the ionization yield on the beam properties can provide unprecedented spatial and temporal resolution, at the submicrometer and subfemtosecond scales, respectively, offering a practical and powerful approach to characterizing beams from accelerators at the frontiers of performance.

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory.

PubMed

Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J; Lopata, Kenneth

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

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

Sissay, Adonay; Abanador, Paul; Mauger, François

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagatingmore » the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.« less

Two dimensional simulations of triode VHF SiH4 plasma

NASA Astrophysics Data System (ADS)

Su, Li-Wen; Chen, Weiting; Uchino, Kiichiro; Kawai, Yoshinobu

2018-06-01

Two-dimensional simulations of a triode VHF SiH4 plasma (60 MHz) were performed using a fluid model, where the plasma was realized using multirod electrodes. Higher-order silanes that are responsible for the quality of amorphous silicon were included in the simulations. A typical VHF plasma with an electron density higher than 1016 m‑3 and an electron temperature lower than 3 eV was predicted between discharge electrodes while the electron density near the substrate was very low. The SiH3 density was fairly uniform between discharge electrodes and did not decrease rapidly near the substrate, suggesting a high-speed deposition. Higher-order molecules and radicals that play an important role in dust formation had similar spatial profiles and their densities were five to 6 orders of magnitude lower than the SiH3 density. We discussed the effect of the rate constant of reaction, SiH3 + SiH3 → SiH2 + SiH4, on the SiH3 density.

Open-Circuit Voltage Losses in Selenium-Substituted Organic Photovoltaic Devices from Increased Density of Charge-Transfer States

DOE PAGES

Sulas, Dana B.; Yao, Kai; Intemann, Jeremy J.; ...

2015-09-12

Using an analysis based on Marcus theory, we characterize losses in open-circuit voltage (V OC) due to changes in charge-transfer state energy, electronic coupling, and spatial density of charge-transfer states in a series of polymer/fullerene solar cells. Here, we use a series of indacenodithiophene polymers and their selenium-substituted analogs as electron donor materials and fullerenes as the acceptors. By combining device measurements and spectroscopic studies (including subgap photocurrent, electroluminescence, and, importantly, time-resolved photoluminescence of the charge-transfer state) we are able to isolate the values for electronic coupling and the density of charge-transfer states (NCT), rather than the more commonly measuredmore » product of these values. We find values for NCT that are surprisingly large (~4.5 × 10 21–6.2 × 10 22 cm -3), and we find that a significant increase in N CT upon selenium substitution in donor polymers correlates with lower VOC for bulk heterojunction photovoltaic devices. The increase in N CT upon selenium substitution is also consistent with nanoscale morphological characterization. Using transmission electron microscopy, selected area electron diffraction, and grazing incidence wide-angle X-ray scattering, we find evidence of more intermixed polymer and fullerene domains in the selenophene blends, which have higher densities of polymer/fullerene interfacial charge-transfer states. Our results provide an important step toward understanding the spatial nature of charge-transfer states and their effect on the open-circuit voltage of polymer/fullerene solar cells« less

Proximity-induced magnetism in transition-metal substituted graphene

DOE PAGES

Crook, Charles B.; Constantin, Costel; Ahmed, Towfiq; ...

2015-08-03

We investigate the interactions between two identical magnetic impurities substituted into a graphene superlattice. Using a first-principles approach, we calculate the electronic and magnetic properties for transition-metal substituted graphene systems with varying spatial separation. These calculations are compared for three different magnetic impurities, manganese, chromium, and vanadium. We determine the electronic band structure, density of states, and Millikan populations (magnetic moment) for each atom, as well as calculate the exchange parameter between the two magnetic atoms as a function of spatial separation. We find that the presence of magnetic impurities establishes a distinct magnetic moment in the graphene lattice, wheremore » the interactions are highly dependent on the spatial and magnetic characteristic between the magnetic and carbon atoms, which leads to either ferromagnetic or antiferromagnetic behavior. Furthermore, through an analysis of the calculated exchange energies and partial density of states, it is determined that interactions between the magnetic atoms can be classified as an RKKY interaction.« less

Robust Estimation of Electron Density From Anatomic Magnetic Resonance Imaging of the Brain Using a Unifying Multi-Atlas Approach

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

Ren, Shangjie; Department of Radiation Oncology, Stanford University School of Medicine, Palo Alto, California; Hara, Wendy

Purpose: To develop a reliable method to estimate electron density based on anatomic magnetic resonance imaging (MRI) of the brain. Methods and Materials: We proposed a unifying multi-atlas approach for electron density estimation based on standard T1- and T2-weighted MRI. First, a composite atlas was constructed through a voxelwise matching process using multiple atlases, with the goal of mitigating effects of inherent anatomic variations between patients. Next we computed for each voxel 2 kinds of conditional probabilities: (1) electron density given its image intensity on T1- and T2-weighted MR images; and (2) electron density given its spatial location in a referencemore » anatomy, obtained by deformable image registration. These were combined into a unifying posterior probability density function using the Bayesian formalism, which provided the optimal estimates for electron density. We evaluated the method on 10 patients using leave-one-patient-out cross-validation. Receiver operating characteristic analyses for detecting different tissue types were performed. Results: The proposed method significantly reduced the errors in electron density estimation, with a mean absolute Hounsfield unit error of 119, compared with 140 and 144 (P<.0001) using conventional T1-weighted intensity and geometry-based approaches, respectively. For detection of bony anatomy, the proposed method achieved an 89% area under the curve, 86% sensitivity, 88% specificity, and 90% accuracy, which improved upon intensity and geometry-based approaches (area under the curve: 79% and 80%, respectively). Conclusion: The proposed multi-atlas approach provides robust electron density estimation and bone detection based on anatomic MRI. If validated on a larger population, our work could enable the use of MRI as a primary modality for radiation treatment planning.« less

The spatial distribution of two dimensional electron gas at the LaTiO3/KTaO3 interface

NASA Astrophysics Data System (ADS)

Song, Qi; Peng, Rui; Xu, Haichao; Feng, Donglai

2017-08-01

We report the photoemission spectroscopy studies on the newly discovered two dimensional electron gas (2DEG) system LaTiO3/KTaO3, whose interfacial carriers show much higher mobility than that in LaAlO3/SrTiO3 at room temperature, thus raising the application prospect of transition metal oxide-based 2DEG. By measuring the density of states at the Fermi energy (EF), we directly reveal the spatial distribution of the conducting electrons at the interface. The density of states near EF of the topmost LTO reaches the highest when LTO is 2-unit-cell thick, and diminishes at the 5th unit cell of LTO. We discussed the origin of such a spacial distribution of conducting electrons and its relation with 2DEG, and proposed two possible scenarios based on electrostatic relaxations and chemical reconstructions. These results offer experimental clues in understanding the characteristics and origin of the 2DEG, and also shed light on improving the performance of 2DEG.

The spatial distribution of two dimensional electron gas at the LaTiO3/KTaO3 interface.

PubMed

Song, Qi; Peng, Rui; Xu, Haichao; Feng, Donglai

2017-08-09

We report the photoemission spectroscopy studies on the newly discovered two dimensional electron gas (2DEG) system LaTiO 3 /KTaO 3 , whose interfacial carriers show much higher mobility than that in LaAlO 3 /SrTiO 3 at room temperature, thus raising the application prospect of transition metal oxide-based 2DEG. By measuring the density of states at the Fermi energy (E F ), we directly reveal the spatial distribution of the conducting electrons at the interface. The density of states near E F of the topmost LTO reaches the highest when LTO is 2-unit-cell thick, and diminishes at the 5th unit cell of LTO. We discussed the origin of such a spacial distribution of conducting electrons and its relation with 2DEG, and proposed two possible scenarios based on electrostatic relaxations and chemical reconstructions. These results offer experimental clues in understanding the characteristics and origin of the 2DEG, and also shed light on improving the performance of 2DEG.

Investigation of temporal-resolved emission spectra of highly charged Al ions from laser-produced plasmas

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

Su, M. G., E-mail: sumg@nwnu.edu.cn; Sun, D. X.; Dong, C. Z.

2016-03-15

Temporal evolution of extreme ultraviolet emission from laser-produced aluminum (Al) plasma has been experimentally and theoretically investigated. Al plasmas have been measured by using the temporal-spatially resolved laser-produced plasma technique. The emission lines can be identified from 2p-3s, 3d, 4s, 4d, 5d transition lines from Al{sup 3+} to Al{sup 6+} ions. In order to quickly diagnose the plasma, the assumptions of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model are used to estimate the values of electron temperature and electron density in plasma. We succeeded in reproducing the simulated spectra related to the different timemore » delays, which are in good agreement with experiments. Temporal evolution behavior of highly charged Al ions in plasma has been analyzed, and the exponential decay about electron temperature and electron density has been obtained. The results indicate that the temporal-spatially resolved measurement is essential for accurate understanding of evolution behavior of highly charged ions in laser-produced plasmas.« less

Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

DOE PAGES

Belianinov, Alex; Panchapakesan, G.; Lin, Wenzhi; ...

2014-12-02

Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1 x Sex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signaturemore » and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.« less

Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

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

Belianinov, Alex, E-mail: belianinova@ornl.gov; Ganesh, Panchapakesan; Lin, Wenzhi

2014-12-01

Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe{sub 0.55}Se{sub 0.45} (T{sub c} = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe{sub 1−x}Se{sub x} structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified bymore » their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.« less

Fabrication method of two-photon luminescent organic nano-architectures using electron-beam irradiation

NASA Astrophysics Data System (ADS)

Kamura, Yoshio; Imura, Kohei

2018-06-01

Optical recording on organic thin films with a high spatial resolution is promising for high-density optical memories, optical computing, and security systems. The spatial resolution of the optical recording is limited by the diffraction of light. Electrons can be focused to a nanometer-sized spot, providing the potential for achieving better resolution. In conventional electron-beam lithography, however, optical tuning of the fabricated structures is limited mostly to metals and semiconductors rather than organic materials. In this article, we report a fabrication method of luminescent organic architectures using a focused electron beam. We optimized the fabrication conditions of the electron beam to generate chemical species showing visible photoluminescence via two-photon near-infrared excitations. We utilized this fabrication method to draw nanoscale optical architectures on a polystyrene thin film.

Electron density and gas density measurements in a millimeter-wave discharge

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

Schaub, S. C., E-mail: sschaub@mit.edu; Hummelt, J. S.; Guss, W. C.

2016-08-15

Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal tomore » the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.« less

Behavior of collisional sheath in electronegative plasma with q-nonextensive electron distribution

NASA Astrophysics Data System (ADS)

Borgohain, Dima Rani; Saharia, K.

2018-03-01

Electronegative plasma sheath is addressed in a collisional unmagnetized plasma consisting of q-nonextensive electrons, Boltzmann distributed negative ions and cold fluid positive ions. Considering the positive ion-neutral collisions and ignoring the effects of ionization and collisions between negative species and positive ions (neutrals), a modified Bohm sheath criterion and hence floating potential are derived by using multifluid model. Using the modified Bohm sheath criterion, the sheath characteristics such as spatial profiles of density, potential and net space charge density have been numerically investigated. It is found that increasing values of q-nonextensivity, electronegativity and collisionality lead to a decrease of the sheath thickness and an increase of the sheath potential and the net space charge density. With increasing values of the electron temperature to negative ion temperature ratio, the sheath thickness increases and the sheath potential as well as the net space charge density in the sheath region decreases.

Spatially and temporally resolved measurements of a dense copper plasma heated by intense relativistic electrons

NASA Astrophysics Data System (ADS)

Coleman, J. E.; Colgan, J.

2017-08-01

A 100-μm-thick Cu foil is isochorically heated by a ˜100-ns-long electron bunch with an energy of 19.8 MeV and current of 1.7 kA to Te > 1 eV. After 100 ns of heating and 20 ns of expansion, the plasma exhibits a stable, quiescent temperature and density distribution for >200 ns. Several intense Cu-I emission lines are observed after ˜20 J of electron beam energy is deposited. These lines have well known Stark widths providing a direct measurement of ne. The Los Alamos ATOMIC code [Magee et al., AIP Conf. Proc. 2004, 168-179 and Hakel et al., J. Quant. Spectrosc. Radiat. Transfer 99, 265 (2006)] was run in local-thermodynamic-equilibrium mode to estimate Te and ne. Spatially and temporally resolved measurements are presented in both the vertical and horizontal directions adjacent to the foil indicating temperatures >1 eV and densities ranging from 1-3 × 1017 cm-3 after expansion and cooling.

Projected quasiparticle theory for molecular electronic structure

NASA Astrophysics Data System (ADS)

Scuseria, Gustavo E.; Jiménez-Hoyos, Carlos A.; Henderson, Thomas M.; Samanta, Kousik; Ellis, Jason K.

2011-09-01

We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry.

Quasi-monoenergetic multi-GeV electron acceleration by optimizing the spatial and spectral phases of PW laser pulses

NASA Astrophysics Data System (ADS)

Shin, Junghun; Kim, Hyung Taek; Pathak, V. B.; Hojbota, Calin; Lee, Seong Ku; Sung, Jae Hee; Lee, Hwang Woon; Yoon, Jin Woo; Jeon, Cheonha; Nakajima, Kazuhisa; Sylla, F.; Lifschitz, A.; Guillaume, E.; Thaury, C.; Malka, V.; Nam, Chang Hee

2018-06-01

Generation of high-quality electron beams from laser wakefield acceleration requires optimization of initial experimental parameters. We present here the dependence of accelerated electron beams on the temporal profile of a driving PW laser, the density, and length of an interacting medium. We have optimized the initial parameters to obtain 2.8 GeV quasi-monoenergetic electrons which can be applied further to the development of compact electron accelerators and radiations sources.

Axial Structure of High-Vacuum Planar Magnetron Discharge Space

NASA Astrophysics Data System (ADS)

Miura, Tsutomu

1999-09-01

The spatial structure of high-vacuum planar magnetron discharge is theoretically investigated taking into account the electron confinement. The boundary xes of the electron confinement region depends on BA with Ea/BA as the parameter (BA: the magnetic flux density at the anode, Ea: the average electric field strength). The location at which the frequency of ionization events takes the maximum is expressed as CnNxiep (CnN: a factor related to the electron density distribution, xiep: the distance of the location from the cathode at which the ionization is most efficient). With increasing Ea and BA at a fixed Ea/BA, the density of the confined energetic electrons increases. With increasing Ea, the region where ionization is efficient shifts to the cathode side to give a high efficiency of the magnet. The boundary xes as determined by the probe method agreed with the theoretical prediction.

Simulation of Non-Uniform Electron Beams in the Gyrotron Electron-Optical System

NASA Astrophysics Data System (ADS)

Louksha, O. I.; Trofimov, P. A.

2018-04-01

New calculated data on the effect of emission inhomogeneities on the quality of the electron beam, which is formed in an electron-optical system of a gyrotron, have been obtained. The calculations were based on emission current density distributions, which were measured for the different cathodes in the gyrotron of Peter the Great St. Petersburg Polytechnic University. A satisfactory agreement between the experimental and calculated data on the influence of emission nonuniformities on the velocity spread of electrons has been shown. The necessity of considering the real distribution of the emission current density over the cathode surface to determine the main parameters of the electron beam—the velocity and energy spreads of the electrons, spatial structure of the beam, and coefficient of reflection of electrons from the magnetic mirror—has been demonstrated. The maximum level of emission inhomogeneities, which are permissible for effective work of gyrotrons, has been discussed.

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

St Lishev, Stiliyan; Shivarova, Antonia P.

The study combines experiments on probe diagnostics with laser-photodetachment-technique and Faraday-cup measurements directed towards determination of the position of the extraction device and its influence on the discharge structure. The measurements have been carried out in the second chamber of an inductively-driven tandem plasma source performed as small scale arrangements, with a magnetic filter located just after the transition between the two chambers of the source. Results for the axial profiles of the plasma parameters display the correlation of the ratio n lowbar /n{sub e} of the densities of the negative hydrogen ions and of the electrons and of themore » concentration of the negative ions with the electron density and temperature: The maxima of the (n lowbar /n{sub e})-ratio and of the density of the negative ions obtained are located at the position of maximum of the electron density behind the filter, in the region of the low electron temperature. Results from probe diagnostics and laser photodetachment measurements at a given axial position for different positions of the Faraday cup show the changes in the spatial distribution of the electron density and temperature and the reduction of the (n lowbar /n{sub e})-ratio and of the density of the negative ions caused by the extraction device.« less

Magneto-electronic properties of graphene nanoribbons in the spatially modulated electric field

NASA Astrophysics Data System (ADS)

Chen, S. C.; Wang, T. S.; Lee, C. H.; Lin, M. F.

2008-09-01

The Peierls tight-binding model with the nearest-neighbor interactions is used to calculate the magneto-electronic structure of graphene nanoribbons under a spatially modulated electric field along the y-axis. A uniform perpendicular magnetic field could make energy dispersions change into the quasi-Landau levels. Such levels are composed of the dispersionless and parabolic energy bands. A spatially modulated electric field would further induce a lot of oscillating parabolic bands with several band-edge states. It drastically modifies energy dispersions, alters subband spacings, destroys symmetry of energy spectrum about k=0, and changes features of band-edge states (number and energy). The above-mentioned magneto-electronic structures are directly reflected in density of states (DOS). The modulation effect changes shape, number, positions, and intensities of peaks in DOS. The predicted result could be tested by the optical measurements.

Watching excitons move: the time-dependent transition density matrix

NASA Astrophysics Data System (ADS)

Ullrich, Carsten

2012-02-01

Time-dependent density-functional theory allows one to calculate excitation energies and the associated transition densities in principle exactly. The transition density matrix (TDM) provides additional information on electron-hole localization and coherence of specific excitations of the many-body system. We have extended the TDM concept into the real-time domain in order to visualize the excited-state dynamics in conjugated molecules. The time-dependent TDM is defined as an implicit density functional, and can be approximately obtained from the time-dependent Kohn-Sham orbitals. The quality of this approximation is assessed in simple model systems. A computational scheme for real molecular systems is presented: the time-dependent Kohn-Sham equations are solved with the OCTOPUS code and the time-dependent Kohn-Sham TDM is calculated using a spatial partitioning scheme. The method is applied to show in real time how locally created electron-hole pairs spread out over neighboring conjugated molecular chains. The coupling mechanism, electron-hole coherence, and the possibility of charge separation are discussed.

Seismo-electromagnetic anomalies observed by Fomosat-1 and GIM TEC during January 27 1999 to July 2004

NASA Astrophysics Data System (ADS)

Yu, C. Y.; Liu, J. Y. G.

2014-12-01

In this study, we examine the pre-earthquake ionospheric anomalies (PEIAs) by the electron density (Ne) and ion temperature (Ti) observed by FORMOSAT-1 (ROCSAT-1) satellite during magnitude greater than 7.0 worldwide earthquakes during 1999-2004. Meanwhile, PEIAs is also currently investigated to have a better understanding of the spatial distribution of the ROCSAT-1 SIPs. Total electron density (TEC) of the global ionosphere map (GIM) confirm that the anomalous feature appear near the epicenters before the earthquakes.

Transport and spatial energy deposition of relativistic electrons in copper-doped fast ignition plasmas

DOE PAGES

Jarrott, L. C.; McGuffey, C.; Beg, F. N.; ...

2017-10-24

Fast electron transport and spatial energy deposition are investigated in integrated cone-guided Fast Ignition experiments by measuring fast electron induced copper K-shell emission using a copper tracer added to deuterated plastic shells with a geometrically reentrant gold cone. Experiments were carried out at the Laboratory for Laser Energetics on the OMEGA/OMEGA-EP Laser where the plastic shells were imploded using 54 of the 60 OMEGA60 beams (3ω, 20 kJ), while the high intensity OMEGA-EP (BL2) beam (1 ω, 10 ps, 500 J, I peak > 10 19 W/cm 2) was focused onto the inner cone tip. Here, a retrograde analysis usingmore » the hybrid-PIC electron transport code, ZUMA, is performed to examine the sensitivity of the copper Kα spatial profile on the laser-produced fast electrons, facilitating the optimization of new target point designs and laser configurations to improve the compressed core areal density by a factor of 4 and the fast electron energy coupling by a factor of 3.5.« less

Seismo-ionospheric anomalies in total electron content of the GIM and electron density of DEMETER before the 27 February 2010 M8.8 Chile earthquake

NASA Astrophysics Data System (ADS)

Ho, Yi-Ying; Jhuang, Hau-Kun; Su, Yung-Chih; Liu, Jann-Yenq

2013-06-01

In this paper we examine the pre-earthquake ionospheric anomalies by the total electron content (TEC) extracted from GIM (global ionospheric map) and the electron density (Ne) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during the 2010 M8.8 Chile earthquake. Temporal variations show the nighttime TEC and Ne simultaneously increase 9-19 days before the earthquake. A cross-comparison of data recorded during the period of 1 February to 3 March in 2006-2010 confirms the above temporal anomalies specifically appear in 2010. The spatial analyses show that the anomalies tend to appear over the epicenter.

On Spatial Structuring of the F2 Layer Studied by the Satellite Radio Sounding of the Ionosphere Disturbed by High-Power HF Radio Waves

NASA Astrophysics Data System (ADS)

Tereshchenko, E. D.; Turyansky, V. A.; Khudukon, B. Z.; Yurik, R. Yu.; Frolov, V. L.

2018-01-01

We present the results of studying the characteristics of the artificial plasma structures excited in the ionospheric F2 region modified by high-power HF radio waves. The experiments were carried out at the Sura heating facility using satellite radio sounding of the ionosphere. The plasma density profile was reconstructed with the highest possible spatial resolution for today, about 4 km. In a direction close to the magnetic zenith of the pump wave, the following phenomena were observed: the formation of a cavity with a 15% lower plasma density at the altitudes of the F2 layer and below; the formation of an area with plasma density increased by 12% at altitudes greater than 400 km. With a long-term quasiperiodic impact of the pump wave on the ionosphere, wavy large-scale electron-density perturbations (the meridional scale λx ≈ 130 km and the vertical scale λz ≈ 440 km) are also formed above the Sura facility. These perturbations can be due to the plasma density modulation by an artificial acoustic-gravity wave with a period of 10.6 m, which was formed by the heat source inside a large-scale cavity with low plasma density; there is generation of the electron density irregularities for the electrons with ΔNe/Ne ≈ 3% in the form of layers having the sizes 10-12 km along and about 24 km across the geomagnetic field, which are found both below and above the F2-layer maximum. The mechanisms of the formation of these plasma structures are discussed.

Two-resonance probe for measuring electron density in low-pressure plasmas

NASA Astrophysics Data System (ADS)

Kim, D. W.; You, S. J.; Kim, S. J.; Kim, J. H.; Oh, W. Y.

2017-04-01

A technique for measuring double-checked electron density using two types of microwave resonance is presented. Simultaneous measurement of the resonances (plasma and quarter-wavelength resonator resonances), which were used for the cutoff probe (CP) and hairpin probe (HP), was achieved by the proposed microwave resonance probe. The developed two-resonance probe (TRP) consists of parallel separated coaxial cables exposing the radiation and detection tips. The structure resembles that of the CP, except the gapped coaxial cables operate not only as a microwave feeder for the CP but also as a U- shaped quarter-wavelength resonator for the HP. By virtue of this structure, the microwave resonances that have typically been used for measuring the electron density for the CP and HP were clearly identified on the microwave transmission spectrum of the TRP. The two types of resonances were measured experimentally under various power and pressure conditions for the plasma. A three-dimensional full-wave simulation model for the TRP is also presented and used to investigate and reproduce the resonances. The electron densities inferred from the resonances were compared and showed good agreement. Quantitative differences between the densities were attributed to the effects of the sheath width and spatial density gradient on the resonances. This accessible technique of using the TRP to obtain double-checked electron densities may be useful for comparative study and provides complementary uses for the CP and HP.

2D imaging X-ray diagnostic for measuring the current density distribution in a wide-area electron beam produced in a multiaperture diode with plasma cathode

NASA Astrophysics Data System (ADS)

Kurkuchekov, V.; Kandaurov, I.; Trunev, Y.

2018-05-01

A simple and inexpensive X-ray diagnostic tool was designed for measuring the cross-sectional current density distribution in a low-relativistic pulsed electron beam produced in a source based on an arc-discharge plasma cathode and multiaperture diode-type electron optical system. The beam parameters were as follows: Uacc = 50–110 kV, Ibeam = 20–100 A, τbeam = 0.1–0.3 ms. The beam effective diameter was ca. 7 cm. Based on a pinhole camera, the diagnostic allows one to obtain a 2D profile of electron beam flux distribution on a flat metal target in a single shot. The linearity of the diagnostic system response to the electron flux density was established experimentally. Spatial resolution of the diagnostic was also estimated in special test experiments. The optimal choice of the main components of the diagnostic technique is discussed.

Experimentally Determined Plasma Parameters in a 30 cm Ion Engine

NASA Technical Reports Server (NTRS)

Sengupta, Anita; Goebel, Dan; Fitzgerald, Dennis; Owens, Al; Tynan, George; Dorner, Russ

2004-01-01

Single planar Langmuir probes and fiber optic probes are used to concurrently measure the plasma properties and neutral density variation in a 30cm diameter ion engine discharge chamber, from the immediate vicinity of the keeper to the near grid plasma region. The fiber optic probe consists of a collimated optical fiber recessed into a double bore ceramic tube fitted with a stainless steel light-limiting window. The optical fiber probe is used to measure the emission intensity of excited neutral xenon for a small volume of plasma, at various radial and axial locations. The single Langmuir probes, are used to generate current-voltage characteristics at a total of 140 spatial locations inside the discharge chamber. Assuming a maxwellian distribution for the electron population, the Langmuir probe traces provide spatially resolved measurements of plasma potential, electron temperature, and plasma density. Data reduction for the NSTAR TH8 and TH15 throttle points indicates an electron temperature range of 1 to 7.9 eV and an electron density range of 4e10 to le13 cm(sup -3), throughout the discharge chamber, consistent with the results in the literature. Plasma potential estimates, computed from the first derivative of the probe characteristic, indicate potential from 0.5V to 11V above the discharge voltage along the thruster centerline. These values are believed to be excessively high due to the sampling of the primary electron population along the thruster centerline. Relative neutral density profiles are also obtained with a fiber optic probe sampling photon flux from the 823.1 nm excited to ground state transition. Plasma parameter measurements and neutral density profiles will be presented as a function of probe location and engine discharge conditions. A discussion of the measured electron energy distribution function will also be presented, with regards to variation from pure maxwellian. It has been found that there is a distinct primary population found along the thruster centerline, which causes estimates of electron temperature, electron density, and plasma potential, to err on the high side, due this energetic population. Computation of the energy distribution fimction of the plasma clearly indicates the presence of primaries, whose presence become less obvious with radial distance from the main discharge plume.

Streamer properties and associated x-rays in perturbed air

NASA Astrophysics Data System (ADS)

Köhn, C.; Chanrion, O.; Babich, L. P.; Neubert, T.

2018-01-01

Streamers are ionization waves in electric discharges. One of the key ingredients of streamer propagation is an ambient gas that serves as a source of free electrons. Here, we explore the dependence of streamer dynamics on different spatial distributions of ambient air molecules. We vary the spatial profile of air parallel and perpendicular to the ambient electric field. We consider local sinusoidal perturbations of 5%-100%, as induced from discharge shock waves. We use a cylindrically symmetric particle-in-cell code to simulate the evolution of bidirectional streamers and compare the electron density, electric field, streamer velocity and electron energy of streamers in uniform air and in perturbed air. In all considered cases, the motion is driven along in decreasing air density and damped along increasing air density. Perturbations of at most 5%-10% change the velocity differences by up to approximately 40%. Perturbations perpendicular to the electric field additionally squeeze or branch streamers. Air variations can thus partly explain the difference of velocities and morphologies of streamer discharges. In cases with large perturbations, electrons gain energies of up to 30 keV compared to 100 eV in uniformly distributed air. For such perturbations parallel to the ambient electric field, we see the spontaneous initiation of a negative streamer; for perpendicular perturbations, x-rays with energies of up to 20 keV are emitted within 0.17 ns.

High speed FPGA-based Phasemeter for the far-infrared laser interferometers on EAST

NASA Astrophysics Data System (ADS)

Yao, Y.; Liu, H.; Zou, Z.; Li, W.; Lian, H.; Jie, Y.

2017-12-01

The far-infrared laser-based HCN interferometer and POlarimeter/INTerferometer\\break (POINT) system are important diagnostics for plasma density measurement on EAST tokamak. Both HCN and POINT provide high spatial and temporal resolution of electron density measurement and used for plasma density feedback control. The density is calculated by measuring the real-time phase difference between the reference beams and the probe beams. For long-pulse operations on EAST, the calculation of density has to meet the requirements of Real-Time and high precision. In this paper, a Phasemeter for far-infrared laser-based interferometers will be introduced. The FPGA-based Phasemeter leverages fast ADCs to obtain the three-frequency signals from VDI planar-diode Mixers, and realizes digital filters and an FFT algorithm in FPGA to provide real-time, high precision electron density output. Implementation of the Phasemeter will be helpful for the future plasma real-time feedback control in long-pulse discharge.

Characterization of spatially resolved high resolution x-ray spectrometers for HEDP and light-source experiments

NASA Astrophysics Data System (ADS)

Hill, K. W.; Bitter, M.; Delgado-Aparicio, L.; Efthimion, P.; Pablant, N.; Lu, J.; Beiersdorfer, P.; Chen, H.; Magee, E.

2014-10-01

A high resolution 1D imaging x-ray spectrometer concept comprising a spherically bent crystal and a 2D pixelated detector is being optimized for diagnostics of small sources such as high energy density physics (HEDP) and synchrotron radiation or x-ray free electron laser experiments. This instrument is used on tokamak experiments for measurement of spatial profiles of Doppler ion temperature and plasma flow velocity, as well as electron temperature. Laboratory measurements demonstrate a resolving power, E/ ΔE of 10,000 and spatial resolution better than 10 μm. Good performance is obtained for Bragg angles ranging from 23 to 63 degrees. Initial tests of the instrument on HEDP plasmas are being performed with a goal of developing spatially resolved ion and electron temperature diagnostics. This work was performed under the auspices of the US DOE by PPPL under Contract DE-AC02-09CH11466 and by LLNL under Contract DE-AC52-07NA27344.

Monitoring nonadiabatic avoided crossing dynamics in molecules by ultrafast X-ray diffraction

DOE PAGES

Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

2017-05-26

We examine time-resolved X-ray diffraction from molecules in the gas phase which undergo nonadiabatic avoided-crossing dynamics involving strongly coupled electrons and nuclei. Several contributions to the signal are identified, representing (in decreasing strength) elastic scattering, contributions of the electronic coherences created by nonadiabatic couplings in the avoided crossing regime, and inelastic scattering. The former probes the charge density and delivers direct information on the evolving molecular geometry. The latter two contributions are weaker and carry spatial information through the transition charge densities (off-diagonal elements of the charge-density operator). Furthermore, simulations are presented for the nonadiabatic harpooning process in the excitedmore » state of sodium fluoride.« less

NGC 3503 and its molecular environment

NASA Astrophysics Data System (ADS)

Duronea, N. U.; Vasquez, J.; Cappa, C. E.; Corti, M.; Arnal, E. M.

2012-01-01

Aims: We present a study of the molecular gas and interstellar dust distribution in the environs of the Hii region NGC 3503 associated with the open cluster Pis 17 with the aim of investigating the spatial distribution of the molecular gas linked to the nebula and achieving a better understanding of the interaction of the nebula and Pis 17 with their molecular environment. Methods: We based our study on 12CO(1-0) observations of a region of ~0.6° in size obtained with the 4-m NANTEN telescope, unpublished radio continuum data at 4800 and 8640 MHz obtained with the ATCA telescope, radio continuum data at 843 MHz obtained from SUMSS, and available IRAS, MSX, IRAC-GLIMPSE, and MIPSGAL images. Results: We found a molecular cloud (Component 1) having a mean velocity of -24.7 km s-1 ,compatible with the velocity of the ionized gas, which is associated with the nebula and its surroundings. Adopting a distance of 2.9 ± 0.4 kpc, the total molecular mass yields (7.6 ± 2.1) × 103M⊙ and density yields 400 ± 240 cm-3. The radio continuum data confirm the existence of an electron density gradient in NGC 3503. The IR emission shows a PDR bordering the higher density regions of the nebula. The spatial distribution of the CO emission shows that the nebula coincides with a molecular clump, and the strongest CO emission peak is located close to the higher electron density region. The more negative velocities of the molecular gas (about -27 km s-1), are coincident with NGC 3503. Candidate young stellar objects (YSOs) were detected toward the Hii region, suggesting that embedded star formation may be occurring in the neighborhood of the nebula. The clear electron density gradient, along with the spatial distribution of the molecular gas and PAHs in the region indicates that NGC 3503 is a blister-type Hii region that has probably undergone a champagne phase.

A Hydrodynamic Theory for Spatially Inhomogeneous Semiconductor Lasers. 2; Numerical Results

NASA Technical Reports Server (NTRS)

Li, Jianzhong; Ning, C. Z.; Biegel, Bryan A. (Technical Monitor)

2001-01-01

We present numerical results of the diffusion coefficients (DCs) in the coupled diffusion model derived in the preceding paper for a semiconductor quantum well. These include self and mutual DCs in the general two-component case, as well as density- and temperature-related DCs under the single-component approximation. The results are analyzed from the viewpoint of free Fermi gas theory with many-body effects incorporated. We discuss in detail the dependence of these DCs on densities and temperatures in order to identify different roles played by the free carrier contributions including carrier statistics and carrier-LO phonon scattering, and many-body corrections including bandgap renormalization and electron-hole (e-h) scattering. In the general two-component case, it is found that the self- and mutual- diffusion coefficients are determined mainly by the free carrier contributions, but with significant many-body corrections near the critical density. Carrier-LO phonon scattering is dominant at low density, but e-h scattering becomes important in determining their density dependence above the critical electron density. In the single-component case, it is found that many-body effects suppress the density coefficients but enhance the temperature coefficients. The modification is of the order of 10% and reaches a maximum of over 20% for the density coefficients. Overall, temperature elevation enhances the diffusive capability or DCs of carriers linearly, and such an enhancement grows with density. Finally, the complete dataset of various DCs as functions of carrier densities and temperatures provides necessary ingredients for future applications of the model to various spatially inhomogeneous optoelectronic devices.

Schlieren Technique Applied to Magnetohydrodynamic Generator Plasma Torch

NASA Astrophysics Data System (ADS)

Chopra, Nirbhav; Pearcy, Jacob; Jaworski, Michael

2017-10-01

Magnetohydrodynamic (MHD) generators are a promising augmentation to current hydrocarbon based combustion schemes for creating electrical power. In recent years, interest in MHD generators has been revitalized due to advances in a number of technologies such as superconducting magnets, solid-state power electronics and materials science as well as changing economics associated with carbon capture, utilization, and sequestration. We use a multi-wavelength schlieren imaging system to evaluate electron density independently of gas density in a plasma torch under conditions relevant to MHD generators. The sensitivity and resolution of the optical system are evaluated alongside the development of an automated analysis and calibration program in Python. Preliminary analysis shows spatial resolutions less than 1mm and measures an electron density of ne = 1 ×1016 cm-3 in an atmospheric microwave torch. Work supported by DOE contract DE-AC02-09CH11466.

2D laser-collision induced fluorescence in low-pressure argon discharges

DOE PAGES

Barnat, E. V.; Weatherford, B. R.

2015-09-25

Development and application of laser-collision induced fluorescence (LCIF) diagnostic technique is presented for the use of interrogating argon plasma discharges. Key atomic states of argon utilized for the LCIF method are identified. A simplified two-state collisional radiative model is then used to establish scaling relations between the LCIF, electron density, and reduced electric fields ( E/N). The procedure used to generate, detect and calibrate the LCIF in controlled plasma environments is discussed in detail. LCIF emanating from an argon discharge is then presented for electron densities spanning 10 9 e cm –3 to 10 12 e cm –3 and reducedmore » electric fields spanning 0.1 Td to 40 Td. Lastly, application of the LCIF technique for measuring the spatial distribution of both electron densities and reduced electric field is demonstrated.« less

Advanced spectroscopic analysis of 0.8-1.0-MA Mo x pinches and the influence of plasma electron beams on L-shell spectra of Mo ions.

PubMed

Shlyaptseva, A S; Hansen, S B; Kantsyrev, V L; Fedin, D A; Ouart, N; Fournier, K B; Safronova, U I

2003-02-01

This paper presents a detailed investigation of the temporal, spatial, and spectroscopic properties of L-shell radiation from 0.8 to 1.0 MA Mo x pinches. Time-resolved measurements of x-ray radiation and both time-gated and time-integrated spectra and pinhole images are presented and analyzed. High-current x pinches are found to have complex spatial and temporal structures. A collisional-radiative kinetic model has been developed and used to interpret L-shell Mo spectra. The model includes the ground state of every ionization stage of Mo and detailed structure for the O-, F-, Ne-, Na-, and Mg-like ionization stages. Hot electron beams generated by current-carrying electrons in the x pinch are modeled by a non-Maxwellian electron distribution function and have significant influence on L-shell spectra. The results of 20 Mo x-pinch shots with wire diameters from 24 to 62 microm have been modeled. Overall, the modeled spectra fit the experimental spectra well and indicate for time-integrated spectra electron densities between 2 x 10(21) and 2 x 10(22) cm(-3), electron temperatures between 700 and 850 eV, and hot electron fractions between 3% and 7%. Time-gated spectra exhibit wide variations in temperature and density of plasma hot spots during the same discharge.

Monitoring Shuttle Burns and Rocket Launches with GPS

NASA Astrophysics Data System (ADS)

Coster, A. J.; Bhatt, A.; O'Hanlon, B.; Rideout, W.

2009-12-01

We report on different GPS analysis techniques that can be used to examine the effects of rocket exhaust on the upper atmosphere. GPS observations of artificially produced electron density holes created by chemical releases from Space Shuttle Orbital Maneuvering System (OMS) engine burns will be discussed. The percentage drop in total electron content (TEC) and the temporal and spatial scales observed in the electron density hole for different Shuttle burn experiments will be compared. We will also report on observations of TEC depletions associated with Titan rocket launches on 8 April 2003 and on 19 October 2005. Finally we will discuss the use of GPS measurements of precipitable water vapor from time periods before, during, and after Shuttle burns.

Interconnections in ULSI: Correlation and Crosstalk

DTIC Science & Technology

1992-12-31

basic tool is electron beam lithography of poly (methyl methacrylate) (PMMA). The two central issues to creating very dense patterns as described...direct lithographic techniques. Fig. 2: Ti/Au (2 nm/15 nm) grating with 38 nm pitch fabricated by electron beam lithography using our high contrast...G. H. Bernstein, G. Bazan, and D. A. Hill, "Spatial Density of Lines in PMMA by Electron Beam Lithography ," Journal of Vacuum Science and Technology

Simulation of electron energy loss spectra of nanomaterials with linear-scaling density functional theory

DOE PAGES

Tait, E. W.; Ratcliff, L. E.; Payne, M. C.; ...

2016-04-20

Experimental techniques for electron energy loss spectroscopy (EELS) combine high energy resolution with high spatial resolution. They are therefore powerful tools for investigating the local electronic structure of complex systems such as nanostructures, interfaces and even individual defects. Interpretation of experimental electron energy loss spectra is often challenging and can require theoretical modelling of candidate structures, which themselves may be large and complex, beyond the capabilities of traditional cubic-scaling density functional theory. In this work, we present functionality to compute electron energy loss spectra within the onetep linear-scaling density functional theory code. We first demonstrate that simulated spectra agree withmore » those computed using conventional plane wave pseudopotential methods to a high degree of precision. The ability of onetep to tackle large problems is then exploited to investigate convergence of spectra with respect to supercell size. As a result, we apply the novel functionality to a study of the electron energy loss spectra of defects on the (1 0 1) surface of an anatase slab and determine concentrations of defects which might be experimentally detectable.« less

Ion flux enhancements and oscillations in spatially confined laser produced aluminum plasmas

NASA Astrophysics Data System (ADS)

Singh, S. C.; Fallon, C.; Hayden, P.; Mujawar, M.; Yeates, P.; Costello, J. T.

2014-09-01

Ion signals from laser produced plasmas (LPPs) generated inside aluminum rectangular cavities at a fixed depth d = 2 mm and varying width, x = 1.0, 1.6, and 2.75 mm were obtained by spatially varying the position of a negatively biased Langmuir probe. Damped oscillatory features superimposed on Maxwellian distributed ion signals were observed. Depending on the distance of the probe from the target surface, three to twelve fold enhancements in peak ion density were observed via confinement of the LPP, generated within rectangular cavities of varying width which constrained the plasma plume to near one dimensional expansion in the vertical plane. The effects of lateral spatial confinement on the expansion velocity of the LPP plume front, the temperature, density and expansion velocity of ions, enhancement of ion flux, and ion energy distribution were recorded. The periodic behavior of ion signals was analyzed and found to be related to the electron plasma frequency and electron-ion collision frequency. The effects of confinement and enhancement of various ion parameters and expansion velocities of the LPP ion plume are explained on the basis of shock wave theory.

Electron and ion distribution functions in magnetopause reconnection

NASA Astrophysics Data System (ADS)

Wang, S.; Chen, L. J.; Bessho, N.; Hesse, M.; Kistler, L. M.; Torbert, R. B.; Mouikis, C.; Pollock, C. J.

2015-12-01

We investigate electron and ion velocity distribution functions in dayside magnetopause reconnection events observed by the Cluster and MMS spacecraft. The goal is to build a spatial map of electron and ion distribution features to enable the indication of the spacecraft location in the reconnection structure, and to understand plasma energization processes. Distribution functions, together with electromagnetic field structures, plasma densities, and bulk velocities, are organized and compared with particle-in-cell simulation results to indicate the proximities to the reconnection X-line. Anisotropic features in the distributions of magnetospheric- and magnetosheath- origin electrons at different locations in the reconnection inflow and exhaust are identified. In particular, parallel electron heating is observed in both the magnetosheath and magnetosphere inflow regions. Possible effects of the guide field strength, waves, and upstream density and temperature asymmetries on the distribution features will be discussed.

High-current fast electron beam propagation in a dielectric target.

PubMed

Klimo, Ondrej; Tikhonchuk, V T; Debayle, A

2007-01-01

Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.

Density-functional theory based on the electron distribution on the energy coordinate

NASA Astrophysics Data System (ADS)

Takahashi, Hideaki

2018-03-01

We developed an electronic density functional theory utilizing a novel electron distribution n(ɛ) as a basic variable to compute ground state energy of a system. n(ɛ) is obtained by projecting the electron density n({\\boldsymbol{r}}) defined on the space coordinate {\\boldsymbol{r}} onto the energy coordinate ɛ specified with the external potential {\\upsilon }ext}({\\boldsymbol{r}}) of interest. It was demonstrated that the Kohn-Sham equation can also be formulated with the exchange-correlation functional E xc[n(ɛ)] that employs the density n(ɛ) as an argument. It turned out an exchange functional proposed in our preliminary development suffices to describe properly the potential energies of several types of chemical bonds with comparable accuracies to the corresponding functional based on local density approximation. As a remarkable feature of the distribution n(ɛ) it inherently involves the spatially non-local information of the exchange hole at the bond dissociation limit in contrast to conventional approximate functionals. By taking advantage of this property we also developed a prototype of the static correlation functional E sc including no empirical parameters, which showed marked improvements in describing the dissociations of covalent bonds in {{{H}}}2,{{{C}}}2{{{H}}}4 and {CH}}4 molecules.

Electron temperature and heat load measurements in the COMPASS divertor using the new system of probes

NASA Astrophysics Data System (ADS)

Adamek, J.; Seidl, J.; Horacek, J.; Komm, M.; Eich, T.; Panek, R.; Cavalier, J.; Devitre, A.; Peterka, M.; Vondracek, P.; Stöckel, J.; Sestak, D.; Grover, O.; Bilkova, P.; Böhm, P.; Varju, J.; Havranek, A.; Weinzettl, V.; Lovell, J.; Dimitrova, M.; Mitosinkova, K.; Dejarnac, R.; Hron, M.; The COMPASS Team; The EUROfusion MST1 Team

2017-11-01

A new system of probes was recently installed in the divertor of tokamak COMPASS in order to investigate the ELM energy density with high spatial and temporal resolution. The new system consists of two arrays of rooftop-shaped Langmuir probes (LPs) used to measure the floating potential or the ion saturation current density and one array of Ball-pen probes (BPPs) used to measure the plasma potential with a spatial resolution of ~3.5 mm. The combination of floating BPPs and LPs yields the electron temperature with microsecond temporal resolution. We report on the design of the new divertor probe arrays and first results of electron temperature profile measurements in ELMy H-mode and L-mode. We also present comparative measurements of the parallel heat flux using the new probe arrays and fast infrared termography (IR) data during L-mode with excellent agreement between both techniques using a heat power transmission coefficient γ  =  7. The ELM energy density {{\\varepsilon }\\parallel } was measured during a set of NBI assisted ELMy H-mode discharges. The peak values of {{\\varepsilon }\\parallel } were compared with those predicted by model and with experimental data from JET, AUG and MAST with a good agreement.

Electron-acoustic solitons and double layers in the inner magnetosphere: ELECTRON-ACOUSTIC SOLITONS

DOE PAGES

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; ...

2017-05-28

The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV)more » is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron-acoustic waves (existing due to the presence of cold and hot electrons) and follow the Korteweg-de Vries (KdV) dispersion relation derived for the observed plasma conditions (electron energy spectrum is a power law between about 100 eV and 10 keV and Maxwellian above 10 keV). The ESW spatial scales are in general agreement with the KdV theory. We interpret the asymmetric ESW in terms of electron-acoustic solitons and double layers (shocks waves).« less

Electron-acoustic solitons and double layers in the inner magnetosphere: ELECTRON-ACOUSTIC SOLITONS

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

Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.

The Van Allen Probes observe generally two types of electrostatic solitary waves (ESW) contributing to the broadband electrostatic wave activity in the nightside inner magnetosphere. ESW with symmetric bipolar parallel electric field are electron phase space holes. The nature of ESW with asymmetric bipolar (and almost unipolar) parallel electric field has remained puzzling. To address their nature, we consider a particular event observed by Van Allen Probes to argue that during the broadband wave activity electrons with energy above 200 eV provide the dominant contribution to the total electron density, while the density of cold electrons (below a few eV)more » is less than a few tenths of the total electron density. We show that velocities of the asymmetric ESW are close to velocity of electron-acoustic waves (existing due to the presence of cold and hot electrons) and follow the Korteweg-de Vries (KdV) dispersion relation derived for the observed plasma conditions (electron energy spectrum is a power law between about 100 eV and 10 keV and Maxwellian above 10 keV). The ESW spatial scales are in general agreement with the KdV theory. We interpret the asymmetric ESW in terms of electron-acoustic solitons and double layers (shocks waves).« less

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

Fang, Dongfan, E-mail: fangdongfan1208@126.com; Sun, Qizhi; Zhao, Xiaoming

A 633 nm laser interferometer has been designed based on a novel concept, which, without the acousto-optic modulator or the demodulator circuit, adopts the fibers to connect all elements except photodetectors and oscilloscope in this system to make it more compact, portable, and efficient. The noteworthy feature is to mathematically compare the two divided interference signals, which have the same phase-shift caused by the electron density but possess the different initial phase and low angular frequencies. It is possible to read the plasma density directly on the oscilloscope by our original mathematic demodulation method without a camera. Based on themore » Abel inversion algorithm, the radial electron density profiles versus time can be obtained by using the multi-chord system. The designed measurable phase shift ranges from 0 to 2π rad corresponding to the maximum line integral of electron density less than 3.5 × 10{sup 17} cm{sup −2}, and the phase accuracy is about 0.017 rad corresponding to the line integral of electron density accuracy of 1 × 10{sup 15} cm{sup −2}. After the construction of eight-chord interferometer, it will provide the detailed time resolved information of the spatial distribution of the electron density in the field-reversed configuration (FRC) plasma target produced by the “Yingguang-1” programmed-discharge device, which is being constructed in the Key Laboratory of Pulsed Power, China Academy of Engineering Physics.« less

Characteristics of Electronegative Plasma Sheath with q-Nonextensive Electron Distribution

NASA Astrophysics Data System (ADS)

Borgohain, D. R.; Saharia, K.

2018-01-01

The characteristics of sheath in a plasma system containing q-nonextensive electrons, cold fluid ions, and Boltzmann-distributed negative ions are investigated. A modified Bohm sheath criterion is derived by using the Sagdeev pseudopotential technique. It is found that the proposed Bohm velocity depends on the degree of nonextensivity ( q), negative ion temperature to nonextensive electron temperature ratio (σ), and negative ion density ( B). Using the modified Bohm sheath criterion, the sheath characteristics, such as the spatial distribution of the potential, positive ion velocity, and density profile, have been numerically investigated, which clearly shows the effect of negative ions, as well as the nonextensive distribution of electrons. It is found that, as the nonextensivity parameter and the electronegativity increases, the electrostatic sheath potential increases sharply and the sheath width decreases.

Effects of neutral gas releases on electron beam injection from electrically tethered spacecraft

NASA Technical Reports Server (NTRS)

Winglee, R. M.

1990-01-01

The presence of high neutral densities at low altitudes and/or during thruster firings is known to modify the spacecraft potential during active electron beam injection. Two-dimensional (three velocity) particle simulations are used to investigate the ionization processes including the neutral density required, the modification of the spacecraft potential, beam profile and spatial distribution of the return current into the spacecraft. Three processes are identified: (1) beam-induced ionization, (2) vehicle-induced ionization, and (3) beam plasma discharge. Only in the first two cases does the beam propagate away with little distortion.

Capacitive radio frequency discharges with a single ring-shaped narrow trench of various depths to enhance the plasma density and lateral uniformity

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

Ohtsu, Y., E-mail: ohtsuy@cc.saga-u.ac.jp; Matsumoto, N.; Schulze, J.

2016-03-15

Spatial structures of the electron density and temperature in ring-shaped hollow cathode capacitive rf plasma with a single narrow trench of 2 mm width have been investigated at various trench depths of D = 5, 8, 10, 12, and 15 mm. It is found that the plasma density is increased in the presence of the trench and that the radial profile of the plasma density has a peak around the narrow hollow trench near the cathode. The density becomes uniform further away from the cathode at all trench depths, whereas the electron temperature distribution remains almost uniform. The measured radial profiles of the plasmamore » density are in good agreement with a theoretical diffusion model for all the trench depths, which explains the local density increase by a local enhancement of the electron heating. Under the conditions investigated, the trench of 10 mm depth is found to result in the highest plasma density at various axial and radial positions. The results show that the radial uniformity of the plasma density at various axial positions can be improved by using structured electrodes of distinct depths rather than planar electrodes.« less

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Karasik, M.; Chan, L. Y.

2015-08-01

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (˜1 ns FWHM) with the intensity of 1.1 × 1015 W/cm2. The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 1021 cm-3 with the density scale length of 120 μm along the plasma symmetry axis. The resulting ne and Te profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Observation of ultrahigh-energy electrons by resonance absorption of high-power microwaves in a pulsed plasma.

PubMed

Rajyaguru, C; Fuji, T; Ito, H; Yugami, N; Nishida, Y

2001-07-01

The interaction of high power microwave with collisionless unmagnetized plasma is studied. Investigation on the generation of superthermal electrons near the critical layer, by the resonance absorption phenomenon, is extended to very high microwave power levels (eta=E(2)(0)/4 pi n(e)kT(e) approximately 0.3). Here E0, n(e), and T(e) are the vacuum electric field, electron density, and electron temperature, respectively. Successive generation of electron bunches having maximum energy of about 2 keV, due to nonlinear wave breaking, is observed. The electron energy epsilon scales as a function of the incident microwave power P, according to epsilon proportional to P0.5 up to 250 kW. The two-dimensional spatial distribution of high energy electrons reveals that they are generated near the critical layer. However, the lower energy component is again produced in the subcritical density region indicating the possibility of other electron heating mechanisms.

Multi-scale transport in the DIII-D ITER baseline scenario with direct electron heating and projection to ITER

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

Grierson, B. A.; Staebler, G. M.; Solomon, W. M.

Multi-scale fluctuations measured by turbulence diagnostics spanning long and short wavelength spatial scales impact energy confinement and the scale-lengths of plasma kinetic profiles in the DIII-D ITER baseline scenario with direct electron heating. Contrasting discharge phases with ECH + neutral beam injection (NBI) and NBI only at similar rotation reveal higher energy confinement and lower fluctuations when only NBI heating is used. Modeling of the core transport with TGYRO using the TGLF turbulent transport model and NEO neoclassical transport reproduces the experimental profile changes upon application of direct electron heating and indicates that multi-scale transport mechanisms are responsible for changesmore » in the temperature and density profiles. Intermediate and high-k fluctuations appear responsible for the enhanced electron thermal flux, and intermediate-k electron modes produce an inward particle pinch that increases the inverse density scale length. Projection to ITER is performed with TGLF and indicates a density profile that has a finite scale length due to intermediate-k electron modes at low collisionality and increases the fusion gain. Finally, for a range of E×B shear, the dominant mechanism that increases fusion performance is suppression of outward low-k particle flux and increased density peaking.« less

Multi-scale transport in the DIII-D ITER baseline scenario with direct electron heating and projection to ITER

DOE PAGES

Grierson, B. A.; Staebler, G. M.; Solomon, W. M.; ...

2018-02-01

Multi-scale fluctuations measured by turbulence diagnostics spanning long and short wavelength spatial scales impact energy confinement and the scale-lengths of plasma kinetic profiles in the DIII-D ITER baseline scenario with direct electron heating. Contrasting discharge phases with ECH + neutral beam injection (NBI) and NBI only at similar rotation reveal higher energy confinement and lower fluctuations when only NBI heating is used. Modeling of the core transport with TGYRO using the TGLF turbulent transport model and NEO neoclassical transport reproduces the experimental profile changes upon application of direct electron heating and indicates that multi-scale transport mechanisms are responsible for changesmore » in the temperature and density profiles. Intermediate and high-k fluctuations appear responsible for the enhanced electron thermal flux, and intermediate-k electron modes produce an inward particle pinch that increases the inverse density scale length. Projection to ITER is performed with TGLF and indicates a density profile that has a finite scale length due to intermediate-k electron modes at low collisionality and increases the fusion gain. Finally, for a range of E×B shear, the dominant mechanism that increases fusion performance is suppression of outward low-k particle flux and increased density peaking.« less

Multi-scale transport in the DIII-D ITER baseline scenario with direct electron heating and projection to ITER

NASA Astrophysics Data System (ADS)

Grierson, B. A.; Staebler, G. M.; Solomon, W. M.; McKee, G. R.; Holland, C.; Austin, M.; Marinoni, A.; Schmitz, L.; Pinsker, R. I.; DIII-D Team

2018-02-01

Multi-scale fluctuations measured by turbulence diagnostics spanning long and short wavelength spatial scales impact energy confinement and the scale-lengths of plasma kinetic profiles in the DIII-D ITER baseline scenario with direct electron heating. Contrasting discharge phases with ECH + neutral beam injection (NBI) and NBI only at similar rotation reveal higher energy confinement and lower fluctuations when only NBI heating is used. Modeling of the core transport with TGYRO using the TGLF turbulent transport model and NEO neoclassical transport reproduces the experimental profile changes upon application of direct electron heating and indicates that multi-scale transport mechanisms are responsible for changes in the temperature and density profiles. Intermediate and high-k fluctuations appear responsible for the enhanced electron thermal flux, and intermediate-k electron modes produce an inward particle pinch that increases the inverse density scale length. Projection to ITER is performed with TGLF and indicates a density profile that has a finite scale length due to intermediate-k electron modes at low collisionality and increases the fusion gain. For a range of E × B shear, the dominant mechanism that increases fusion performance is suppression of outward low-k particle flux and increased density peaking.

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

Forme, F.R.E.; Fontaine, D.; Wahlund, J.E.

UHF and VHF data for the EISCAT incoherent scatter radar facility in northern Scandinavia is presented. Electron and ion temperatures, electron density, and ion drift velocity were measured from heights of 280 to 1500 km. Enhanced ion acoustic fluctuations are more observable with VHF than UHF radar due to wavelength effects. The fluctuations are usually associated with a large flux of precipitating electrons with energies from 100 ev to 10 kev. The spatial extent of the turbulent regions are determined. 23 refs., 6 figs.

Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe.

PubMed

Pollock, B B; Meinecke, J; Kuschel, S; Ross, J S; Shaw, J L; Stoafer, C; Divol, L; Tynan, G R; Glenzer, S H

2012-10-01

Uniform density and temperature Xe plasmas have been produced over >4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 μm in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 μm at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accurate determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 μm spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 μm, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3-10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20±4 at up to 200 eV electron temperatures.

Evolution of dense spatially modulated electron bunches

NASA Astrophysics Data System (ADS)

Balal, N.; Bratman, V. L.; Friedman, A.

2018-03-01

An analytical theory describing the dynamics of relativistic moving 1D electron pulses (layers) with the density modulation affected by a space charge has been revised and generalized for its application to the formation of dense picosecond bunches from linear accelerators with laser-driven photo injectors, and its good agreement with General Particle Tracer simulations has been demonstrated. Evolution of quasi-one-dimensional bunches (disks), for which the derived formulas predict longitudinal expansion, is compared with that for thin and long electron cylinders (threads), for which the excitation of non-linear waves with density spikes was found earlier by Musumeci et al. [Phys. Rev. Lett. 106(18), 184801 (2011)] and Musumeci et al. [Phys. Rev. Spec. Top. -Accel. Beams 16(10), 100701 (2013)]. Both types of bunches can be used for efficiency enhancement of THz sources based on the Doppler frequency up-shifted coherent spontaneous radiation of electrons. Despite the strong Coulomb repulsion, the periodicity of a preliminary modulation in dense 1D layers persists during their expansion in the most interesting case of a relatively small change in particle energy. However, the period of modulation increases and its amplitude decreases in time. In the case of a large change in electron energy, the uniformity of periodicity is broken due to different relativistic changes in longitudinal scales along the bunch: the "period" of modulation decreases and its amplitude increases from the rear to the front boundary. Nevertheless, the use of relatively long electron bunches with a proper preliminary spatial modulation of density can provide a significantly higher power and a narrower spectrum of coherent spontaneous radiation of dense bunches than in the case of initially short single bunches with the same charge.

The concept of quasi-tissue-equivalent nanodosimeter based on the glow peak 5a/5 in LiF:Mg,Ti (TLD-100).

PubMed

Oster, L; Horowitz, Y S; Biderman, S; Haddad, J

2003-12-01

We demonstrate the viability of the concept of using existing molecular nanostructures in thermoluminescent solid-state materials as solid-state nanodosimeters. The concept is based on mimicking radiobiology (specifically the ionization density dependence of double strand breaks in DNA) by using the similar ionization density dependence of simultaneous electron-hole capture in spatially correlated trapping and luminescent centres pairs in the thermoluminescence of LiF:Mg,Ti. This simultaneous electron-hole capture has been shown to lead to ionization density dependence in the relative intensity of peak 5a to peak 5 similar to the ratio of double-strand breaks to single-strand breaks for low energy He ions.

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J.

PubMed

Kenmochi, N; Minami, T; Takahashi, C; Tei, S; Mizuuchi, T; Kobayashi, S; Nagasaki, K; Nakamura, Y; Okada, H; Kado, S; Yamamoto, S; Ohshima, S; Konoshima, S; Shi, N; Zang, L; Ohtani, Y; Kasajima, K; Sano, F

2014-11-01

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (ne ∼ 0.5 × 10(19) m(-3)). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma may be possible.

Measurement of large parallel and perpendicular electric fields on electron spatial scales in the terrestrial bow shock.

PubMed

Bale, S D; Mozer, F S

2007-05-18

Large parallel (

Spatial correlations and probability density function of the phase difference in a developed speckle-field: numerical and natural experiments

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

Mysina, N Yu; Maksimova, L A; Ryabukho, V P

Investigated are statistical properties of the phase difference of oscillations in speckle-fields at two points in the far-field diffraction region, with different shapes of the scatterer aperture. Statistical and spatial nonuniformity of the probability density function of the field phase difference is established. Numerical experiments show that, for the speckle-fields with an oscillating alternating-sign transverse correlation function, a significant nonuniformity of the probability density function of the phase difference in the correlation region of the field complex amplitude, with the most probable values 0 and p, is observed. A natural statistical interference experiment using Young diagrams has confirmed the resultsmore » of numerical experiments. (laser applications and other topics in quantum electronics)« less

Limits of applicability of a two-temperature model under nonuniform heating of metal by an ultrashort laser pulse

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

Polyakov, D S; Yakovlev, E B

The heating of metals (silver and aluminium) by ultrashort laser pulses is analysed proceeding from a spatially nonuniform kinetic equation for the electron distribution function. The electron subsystem thermalisation is estimated in a wide range of absorbed pulse energy density. The limits of applicability are determined for the two-temperature model. (interaction of laser radiation with matter)

Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

NASA Astrophysics Data System (ADS)

Stange, Torsten; Laqua, Heinrich Peter; Beurskens, Marc; Bosch, Hans-Stephan; Bozhenkov, Sergey; Brakel, Rudolf; Braune, Harald; Brunner, Kai Jakob; Cappa, Alvaro; Dinklage, Andreas; Erckmann, Volker; Fuchert, Golo; Gantenbein, Gerd; Gellert, Florian; Grulke, Olaf; Hartmann, Dirk; Hirsch, Matthias; Höfel, Udo; Kasparek, Walter; Knauer, Jens; Langenberg, Andreas; Marsen, Stefan; Marushchenko, Nikolai; Moseev, Dmitry; Pablant, Novomir; Pasch, Ekkehard; Rahbarnia, Kian; Mora, Humberto Trimino; Tsujimura, Toru; Turkin, Yuriy; Wauters, Tom; Wolf, Robert

2017-10-01

During the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n e > 3·1019 m-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·1020 m-3 after full commissioning of the ECRH system in the next operation phase OP1.2.

Probing 67P/Churyumov-Gerasimenko's Electron Environment Through Ultraviolet Emission by Rosetta Alice Observations

NASA Astrophysics Data System (ADS)

Schindhelm, Eric; Noonan, John; Keeney, Brian A.; Broiles, Thomas; Bieler, Andre; A'Hearn, Michael F.; Bertaux, Jean-Loup; Feaga, Lori M.; Feldman, Paul D.; Parker, Joel Wm.; Steffl, Andrew Joseph; Stern, S. Alan; Weaver, Harold A.

2016-10-01

The Alice Far-Ultraviolet (FUV) Spectrograph onboard ESA's Rosetta spacecraft has observed the coma of comet 67P/Churyumov-Gerasimenko from far approach in summer 2014 until the end of mission in September 2016. We present an overall perspective of the bright FUV emission lines (HI 1026 Å, OI 1302/1305/1306 Å multiplet, OI] 1356 Å, CO 1510 (1-0) Å, and CI 1657 Å) above the sunward hemisphere, detailing their spatial extent and brightness as a function of time and the heliocentric distance of the comet. We compare our observed gas column densities derived using electron temperatures and densities from the Ion Electron Sensor (IES) with those derived using the Inner Coma Environment Simulator (ICES) models in periods when electron-impact excited emission dominates over solar fluorescence emission. The electron population is characterized with 2 three-dimensional kappa functions, one dense and warm, one rarefied and hot.

Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3.

PubMed

Stashans, Arvids; Chamba, Gaston; Pinto, Henry

2008-02-01

The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures. (c) 2007 Wiley Periodicals, Inc.

Plasma density irregularities and Total Electron Content gradients over Europe

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Kotulak, K.; Cherniak, I.; Krankowski, A.; Froń, A.

2017-12-01

Perturbations of the ionospheric plasma density are crucial from the scientific and application points of view, as they can severe affect radio signals used in the Global Navigation Satellite Systems (GNSS) and low frequency radio astronomy. For several decades the ionospheric irregularities have been extensively studied by different techniques, including ground-based GNSS observations. Spatial distribution of ionospheric disturbances can be specified by horizontal gradients of the ionospheric density (total electron content, TEC). Another, widely used tool in irregularities monitoring is the rate of TEC index (ROTI). Recently, the Northern Hemisphere ROTI product has been implemented to the International GNSS Service (IGS) and available for community. In this study, we present climatology of the spatial TEC gradients occurred over European region at high to middle latitudes. We developed the TEC gradient maps based on the high-resolution (0.5 degree in latitude and longitude) regional TEC maps covering Europe. The obtained climatological characteristics of the spatial TEC gradients are superimposed and analyzed with the global and regional ROTI product in order to reveal development of highly intense plasma irregularities occurred at high and middle latitudes. During geomagnetic storm the complex of physical processes at auroal zone leads to development of intnse ionospheric irregularities and travelling ionospheric disturbances (TIDs). We presents results of the geomagnetic storm analysis including the 2013 and 2015 St. Patrick's Day geomagnetic storms.

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

Zuo, Zhiqi

The Full Potential Linear Augmented Plane Wave (FPLAPW or FLAPW) method is used for a spin-polarized band calculation for ordered Fe 3Pt. As major purpose, the momentum distributions of the spin-polarized electrons are calculated and compared with results from a magnetic Compton scattering measurement. To get related information, the electronic behavior is also analyzed by examining the partial densities of states and the spatial electron distributions; the role of alloying effects is then explored by studying the electrons in some related alloys: Fe 3Ni, Fe 3Pd, Ni 3Pt and Co 3Pt.

Hard x-ray (>100 keV) imager to measure hot electron preheat for indirectly driven capsule implosions on the NIF.

PubMed

Döppner, T; Dewald, E L; Divol, L; Thomas, C A; Burns, S; Celliers, P M; Izumi, N; Kline, J L; LaCaille, G; McNaney, J M; Prasad, R R; Robey, H F; Glenzer, S H; Landen, O L

2012-10-01

We have fielded a hard x-ray (>100 keV) imager with high aspect ratio pinholes to measure the spatially resolved bremsstrahlung emission from energetic electrons slowing in a plastic ablator shell during indirectly driven implosions at the National Ignition Facility. These electrons are generated in laser plasma interactions and are a source of preheat to the deuterium-tritium fuel. First measurements show that hot electron preheat does not limit obtaining the fuel areal densities required for ignition and burn.

Estimate of size distribution of charged MSPs measured in situ in winter during the WADIS-2 sounding rocket campaign

NASA Astrophysics Data System (ADS)

Asmus, Heiner; Staszak, Tristan; Strelnikov, Boris; Lübken, Franz-Josef; Friedrich, Martin; Rapp, Markus

2017-08-01

We present results of in situ measurements of mesosphere-lower thermosphere dusty-plasma densities including electrons, positive ions and charged aerosols conducted during the WADIS-2 sounding rocket campaign. The neutral air density was also measured, allowing for robust derivation of turbulence energy dissipation rates. A unique feature of these measurements is that they were done in a true common volume and with high spatial resolution. This allows for a reliable derivation of mean sizes and a size distribution function for the charged meteor smoke particles (MSPs). The mean particle radius derived from Schmidt numbers obtained from electron density fluctuations was ˜ 0.56 nm. We assumed a lognormal size distribution of the charged meteor smoke particles and derived the distribution width of 1.66 based on in situ-measured densities of different plasma constituents. We found that layers of enhanced meteor smoke particles' density measured by the particle detector coincide with enhanced Schmidt numbers obtained from the electron and neutral density fluctuations. Thus, we found that large particles with sizes > 1 nm were stratified in layers of ˜ 1 km thickness and lying some kilometers apart from each other.

Spatial Electron-hole Separation in a One Dimensional Hybrid Organic-Inorganic Lead Iodide

NASA Astrophysics Data System (ADS)

Savory, Christopher N.; Palgrave, Robert G.; Bronstein, Hugo; Scanlon, David O.

2016-02-01

The increasing efficiency of the inorganic-organic hybrid halides has revolutionised photovoltaic research. Despite this rapid progress, the significant issues of poor stability and toxicity have yet to be suitably overcome. In this article, we use Density Functional Theory to examine (Pb2I6) · (H2DPNDI) · (H2O) · (NMP), an alternative lead-based hybrid inorganic-organic solar absorber based on a photoactive organic cation. Our results demonstrate that optical properties suitable for photovoltaic applications, in addition to spatial electron-hole separation, are possible but efficient charge transport may be a limiting factor.

Spatial Electron-hole Separation in a One Dimensional Hybrid Organic–Inorganic Lead Iodide

PubMed Central

Savory, Christopher N.; Palgrave, Robert G.; Bronstein, Hugo; Scanlon, David O.

2016-01-01

The increasing efficiency of the inorganic-organic hybrid halides has revolutionised photovoltaic research. Despite this rapid progress, the significant issues of poor stability and toxicity have yet to be suitably overcome. In this article, we use Density Functional Theory to examine (Pb2I6) · (H2DPNDI) · (H2O) · (NMP), an alternative lead-based hybrid inorganic-organic solar absorber based on a photoactive organic cation. Our results demonstrate that optical properties suitable for photovoltaic applications, in addition to spatial electron-hole separation, are possible but efficient charge transport may be a limiting factor. PMID:26858147

Electronic Structure and Band Gap of Fullerenes on Tungsten Surfaces: Transition from a Semiconductor to a Metal Triggered by Annealing.

PubMed

Monazami, Ehsan; McClimon, John B; Rondinelli, James; Reinke, Petra

2016-12-21

The understanding and control of molecule-metal interfaces is critical to the performance of molecular electronics and photovoltaics devices. We present a study of the interface between C 60 and W, which is a carbide-forming transition metal. The complex solid-state reaction at the interface can be exploited to adjust the electronic properties of the molecule layer. Scanning tunneling microscopy/spectroscopy measurements demonstrate the progression of this reaction from wide band gap (>2.5 eV) to metallic molecular surface during annealing from 300 to 800 K. Differential conduction maps with 10 4 scanning tunneling spectra are used to quantify the transition in the density of states and the reduction of the band gap during annealing with nanometer spatial resolution. The electronic transition is spatially homogeneous, and the surface band gap can therefore be adjusted by a targeted annealing step. The modified molecules, which we call nanospheres, are quite resistant to ripening and coalescence, unlike any other metallic nanoparticle of the same size. Densely packed C 60 and isolated C 60 molecules show the same transition in electronic structure, which confirms that the transformation is controlled by the reaction at the C 60 -W interface. Density functional theory calculations are used to develop possible reaction pathways in agreement with experimentally observed electronic structure modulation. Control of the band gap by the choice of annealing temperature is a unique route to tailoring molecular-layer electronic properties.

Observations Of Planetary Nebula NGC 3242 Using STIS From HST19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Dufour, Reginald J.; Henry, Richard B. C.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2014-06-01

During HST Cycle 19, we obtained long-slit spectra using STIS of the planetary nebula NGC 3242 with higher spatial resolution than previously published. The full wavelength range is around 1100-10200Å, covering many nebular lines for determining numerous ionic abundances and electron densities and temperatures. In this work, we first analyze the low- and moderate-resolution UV emission lines of carbon, nitrogen and oxygen. In particular, the resolved lines of C_III] 1907 and C_III] 1909 have yielded a direct measurement of one of the dominant ionic species for carbon and a determination of the density occupied by doubly-ionized carbon and other similar ions. Next, the spatial emission profile of these lines reveals variations in the inferred density along the line of sight from about 2800-11500 cm-3, compared with a value ~3800 cm-3, when averaged over the entire slit. Similarly, the electron temperature is around 12000K for the entire slit and ranges from about 11400-14000K when the slit is divided into smaller sub-regions. Lastly, these sub-regions of the nebula have been modeled in detail with the photoionization code CLOUDY. This modeling will assess the density profile that produces the observed density variation, reproduce the temperature fluctuations, and constrain the central star temperature. We acknowledge the gracious support from HST and the University of Oklahoma.

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

DOE PAGES

Kapetanakis, Myron; Zhou, Wu; Oxley, Mark P.; ...

2015-09-25

Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. They are a powerful tool for probing the electronic properties of nanostructures, but they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron energy loss spectroscopy (EELS), are now capable of subangstrom spatial resolution. Core-loss EELS, a spatially resolved analog of x-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with amore » theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines density functional theory–based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution.« less

Spatial analyses on seismo-ionospheric precursors observed by GIM TEC and DEMETER during the 2008 M8.0 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Liu, Jann-Yenq; Chen, Yuh-Ing; Huang, Ching-Chi; Parrot, Michel; Pulinets, Sergey; Ouzounov, Dimitar

2015-04-01

This paper examines seismo-ionospheric precursors (SIPs) in the total electron content (TEC) of the global ionosphere map (GIM) and observations in the French satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) during the 12 May 2008 M8.0 Wenchuan earthquake. The temporal and spatial analyses on the GIM TEC are used to search SIPs of the Wenchuan earthquake. Meanwhile, both daytime and nighttime electron density (Ne), electron temperature (Te), ion density (Ni) and ion temperature (Ti) probed by DEMETER are investigated. A statistical analysis of the box-and-whisker method is utilized to see if the four DEMETER data sets 1-6 days before and after the earthquake are significantly different. The analysis is employed to investigate the epicenter and three reference areas along the same magnetic latitude discriminating the SIPs from global effects. Results show that the nighttime Ne and Ni (daytime Ti) over the epicenter significantly decrease (increase) 1-6 days before the earthquake. The intersections of the global distribution of the significant differences (or anomalous changes) in the nighttime Ne, the nighttime Ni, and the daytime Ti 1-6 days before and after the earthquake specifically appear over the epicenter. The spatial analyses confirm that SIPs of GIM TEC and DEMETER observations appearing 2-6 days before are related to the 2008 M8.0 Wenchuan earthquake.

One-dimensional Ar-SF{sub 6} hydromodel at low-pressure in e-beam generated plasmas

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

Petrov, George M., E-mail: george.petrov@nrl.navy.mil; Boris, David R.; Petrova, Tzvetelina B.

2016-03-15

A one-dimensional steady-state hydrodynamic model of electron beam generated plasmas produced in Ar-SF{sub 6} mixtures at low pressure in a constant magnetic field was developed. Simulations were performed for a range of SF{sub 6} partial pressures at constant 30 mTorr total gas pressure to determine the spatial distribution of species densities and fluxes. With the addition of small amount of SF{sub 6} (∼1%), the confining electrostatic field sharply decreases with respect to the pure argon case. This effect is due to the applied magnetic field inhibiting electron diffusion. The hallmark of electronegative discharge plasmas, positive ion—negative ion core and positivemore » ion—electron edge, was not observed. Instead, a plasma with large electronegativity (∼100) is formed throughout the volume, and only a small fraction (≈30%) of the parent SF{sub 6} molecules were dissociated to F{sub 2}, SF{sub 2}, and SF{sub 4}. Importantly, F radical densities were found to be very low, on the order of the ion density. Model predictions for the electron density, ion density, and plasma electronegativity are in good agreement with experimental data over the entire range of SF{sub 6} concentrations investigated.« less

Global 3-D ionospheric electron density reanalysis based on multisource data assimilation

NASA Astrophysics Data System (ADS)

Yue, Xinan; Schreiner, William S.; Kuo, Ying-Hwa; Hunt, Douglas C.; Wang, Wenbin; Solomon, Stanley C.; Burns, Alan G.; Bilitza, Dieter; Liu, Jann-Yenq; Wan, Weixing; Wickert, Jens

2012-09-01

We report preliminary results of a global 3-D ionospheric electron density reanalysis demonstration study during 2002-2011 based on multisource data assimilation. The monthly global ionospheric electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground-based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 h in universal time, 5° in latitude, 10° in longitude, and ˜30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content derived from the international GNSS service global ionospheric maps, the observed electron density profiles from the Poker Flat Incoherent Scatter Radar during 2007-2010, and foF2 observed by the global ionosonde network during 2002-2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.

A real-space stochastic density matrix approach for density functional electronic structure.

PubMed

Beck, Thomas L

2015-12-21

The recent development of real-space grid methods has led to more efficient, accurate, and adaptable approaches for large-scale electrostatics and density functional electronic structure modeling. With the incorporation of multiscale techniques, linear-scaling real-space solvers are possible for density functional problems if localized orbitals are used to represent the Kohn-Sham energy functional. These methods still suffer from high computational and storage overheads, however, due to extensive matrix operations related to the underlying wave function grid representation. In this paper, an alternative stochastic method is outlined that aims to solve directly for the one-electron density matrix in real space. In order to illustrate aspects of the method, model calculations are performed for simple one-dimensional problems that display some features of the more general problem, such as spatial nodes in the density matrix. This orbital-free approach may prove helpful considering a future involving increasingly parallel computing architectures. Its primary advantage is the near-locality of the random walks, allowing for simultaneous updates of the density matrix in different regions of space partitioned across the processors. In addition, it allows for testing and enforcement of the particle number and idempotency constraints through stabilization of a Feynman-Kac functional integral as opposed to the extensive matrix operations in traditional approaches.

Erosion and refilling of the plasmasphere during a geomagnetic storm modeled by a neural network

NASA Astrophysics Data System (ADS)

Chu, X. N.; Bortnik, J.; Li, W.; Ma, Q.; Angelopoulos, V.; Thorne, R. M.

2017-07-01

We present a history-dependent model of the equatorial plasma density of the inner magnetosphere using a feedforward neural network with two hidden layers. As the model inputs, we take locations and time series of SYM-H, AL, and F10.7 indices. By considering not only the instantaneous values but also the past values of geomagnetic and solar indices, the model is history dependent on levels of geomagnetic and solar activity. The modeled electron density is continuous both spatially and temporally so that the evolution of the density can be studied (such as plasmaspheric refilling). The model is trained using the electron density inferred from the spacecraft potential from three THEMIS probes. The equatorial electron density is shown to be accurately reconstructed with a correlation coefficient of r 0.953 between data and model target. Since the model is history dependent, it succeeds in reconstructing various density features and dynamic behaviors, such as the quiet time plasmasphere, erosion and recovery of the plasmasphere, as well as the plume formation during a storm on 4 February 2011. Our model may provide unprecedented insight into the behavior of the equatorial density at any time and location; as an example we show the inferred refilling rate from our model and compare it to previous estimates.

RF attenuation as a dusty plasma diagnostic

NASA Astrophysics Data System (ADS)

Doyle, Brandon; Konopka, Uwe; Thomas, Edward

2017-10-01

When a dusty plasma is formed by adding dust to a plasma environment, the electron density of the background plasma is depleted as the dust particles acquire their negative charge. The magnitude of the electron depletion depends on the dust particle charge, and thus its properties, as well as the dust number density. A direct measurement of the electron density in a dusty plasma therefore contains information about the charging state of the dust particles. This measurement is difficult to obtain without influencing the system. For example, Langmuir probes influence the system by creating voids, or they become unreliable due to their potential contamination with dust. A less invasive diagnostic tool might be realized using plasma chamber electrodes for a plasma impedance measurement as it depends on the excitation frequency: the spatially averaged electron density is derived from the electron plasma frequency, which is related to the radio frequency attenuation characteristic. We present preliminary experiments using two impedance probe designs: probes immersed in a plasma and electrodes located at the edge of the plasma. We evaluate the potential application of this method for ground-based laboratory experiments and future microgravity experiment facilities aboard the ISS. This work was supported by JPL/NASA (JPL-RSA 1571699) the US Dept. of Energy (DE-SC0016330) and NSF (PHY-1613087).

Exploiting the spatial locality of electron correlation within the parametric two-electron reduced-density-matrix method

NASA Astrophysics Data System (ADS)

DePrince, A. Eugene; Mazziotti, David A.

2010-01-01

The parametric variational two-electron reduced-density-matrix (2-RDM) method is applied to computing electronic correlation energies of medium-to-large molecular systems by exploiting the spatial locality of electron correlation within the framework of the cluster-in-molecule (CIM) approximation [S. Li et al., J. Comput. Chem. 23, 238 (2002); J. Chem. Phys. 125, 074109 (2006)]. The 2-RDMs of individual molecular fragments within a molecule are determined, and selected portions of these 2-RDMs are recombined to yield an accurate approximation to the correlation energy of the entire molecule. In addition to extending CIM to the parametric 2-RDM method, we (i) suggest a more systematic selection of atomic-orbital domains than that presented in previous CIM studies and (ii) generalize the CIM method for open-shell quantum systems. The resulting method is tested with a series of polyacetylene molecules, water clusters, and diazobenzene derivatives in minimal and nonminimal basis sets. Calculations show that the computational cost of the method scales linearly with system size. We also compute hydrogen-abstraction energies for a series of hydroxyurea derivatives. Abstraction of hydrogen from hydroxyurea is thought to be a key step in its treatment of sickle cell anemia; the design of hydroxyurea derivatives that oxidize more rapidly is one approach to devising more effective treatments.

Electric field imaging of single atoms

PubMed Central

Shibata, Naoya; Seki, Takehito; Sánchez-Santolino, Gabriel; Findlay, Scott D.; Kohno, Yuji; Matsumoto, Takao; Ishikawa, Ryo; Ikuhara, Yuichi

2017-01-01

In scanning transmission electron microscopy (STEM), single atoms can be imaged by detecting electrons scattered through high angles using post-specimen, annular-type detectors. Recently, it has been shown that the atomic-scale electric field of both the positive atomic nuclei and the surrounding negative electrons within crystalline materials can be probed by atomic-resolution differential phase contrast STEM. Here we demonstrate the real-space imaging of the (projected) atomic electric field distribution inside single Au atoms, using sub-Å spatial resolution STEM combined with a high-speed segmented detector. We directly visualize that the electric field distribution (blurred by the sub-Å size electron probe) drastically changes within the single Au atom in a shape that relates to the spatial variation of total charge density within the atom. Atomic-resolution electric field mapping with single-atom sensitivity enables us to examine their detailed internal and boundary structures. PMID:28555629

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J

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

Kenmochi, N., E-mail: kemmchi.naoki.62r@st.kyoto-u.ac.jp; Tei, S.; Zang, L.

2014-11-15

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (n{sub e} ∼ 0.5 × 10{sup 19} m{sup −3}). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma maymore » be possible.« less

Comment on: Polar Plumes and Fine-scale Coronal Structures - On the Interpretation of Coronal Radio Sounding Data by Patzold and Bird

NASA Technical Reports Server (NTRS)

Woo, R.; Habbal, S. R.

1998-01-01

Radio occultation measurements, which probe electron density over a wide dynamic range with high sensitivity and high spatial and temporal resolution reveal a solar corona permeated by a hierarchy of filamentary structures.

Data-driven sensitivity inference for Thomson scattering electron density measurement systems.

PubMed

Fujii, Keisuke; Yamada, Ichihiro; Hasuo, Masahiro

2017-01-01

We developed a method to infer the calibration parameters of multichannel measurement systems, such as channel variations of sensitivity and noise amplitude, from experimental data. We regard such uncertainties of the calibration parameters as dependent noise. The statistical properties of the dependent noise and that of the latent functions were modeled and implemented in the Gaussian process kernel. Based on their statistical difference, both parameters were inferred from the data. We applied this method to the electron density measurement system by Thomson scattering for the Large Helical Device plasma, which is equipped with 141 spatial channels. Based on the 210 sets of experimental data, we evaluated the correction factor of the sensitivity and noise amplitude for each channel. The correction factor varies by ≈10%, and the random noise amplitude is ≈2%, i.e., the measurement accuracy increases by a factor of 5 after this sensitivity correction. The certainty improvement in the spatial derivative inference was demonstrated.

Observation of large-scale density cavities and parametric-decay instabilities in the high-altitude discrete auroral ionosphere under pulsed electromagnetic radiation.

PubMed

Wong, A Y; Chen, J; Lee, L C; Liu, L Y

2009-03-13

A large density cavity that measured 2000 km across and 500 km in height was observed by DEMETER and Formosat/COSMIC satellites in temporal and spatial relation to a new mode of propagation of electromagnetic (em) pulses between discrete magnetic field-aligned auroral plasmas to high altitudes. Recorded positive plasma potential from satellite probes is consistent with the expulsion of electrons in the creation of density cavities. High-frequency decay spectra support the concept of parametric instabilities fed by free energy sources.

Analysis of Co-spatial UV-Optical STIS Spectra of Planetary Nebulae From HST Cycle 19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Henry, Richard B. C.; Dufour, Reginald J.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2015-01-01

We present an analysis of five spatially resolved planetary nebulae (PNe), NGC 5315, NGC 5882, NGC 7662, IC 2165, and IC 3568, from observations in the Cycle 19 program GO 12600 using HST STIS. Details of the observations and data are presented in the poster by Dufour et al. in this session. These five observations cover the wavelength range 1150-10,270 Å with 0.2 and 0.5 arcsec wide slits, and are co-spatial to 0.1 arcsec along a 25 arcsec length across each nebula. This unprecedented resolution in both wavelength and spatial coverage enabled detailed studies of physical conditions and abundances from UV line ion emissions (compared to optical lines). We first analyzed the low- and moderate-resolution UV emission lines of carbon using the resolved lines of C III] 1906.68 and 1908.73, which yielded a direct measurement of the density within the volume occupied by doubly-ionized carbon and other similar co-spatial ions. Next, each PN spectrum was divided into spatial sub-regions in order to assess inferred density variations among the sub-regions along the entire slit. Variations in electron temperature and chemical abundances were also probed. Lastly, these nebulae were modeled in detail with the photoionization code CLOUDY. This modeling tested different density profiles in order to reproduce the observed density variations and temperature fluctuations, and constrain central star parameters. We gratefully acknowledge generous support from NASA through grants related to the Cycle 19 program GO 12600, as well as from the University of Oklahoma.

Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe

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

Pollock, B. B.; University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093; Meinecke, J.

2012-10-15

Uniform density and temperature Xe plasmas have been produced over >4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 {mu}m in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 {mu}m at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accuratemore » determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 {mu}m spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 {mu}m, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3-10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20{+-}4 at up to 200 eV electron temperatures.« less

Time resolved interferometric study of the plasma plume induced shock wave in confined geometry: Two-dimensional mapping of the ambient and plasma density

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

Choudhury, Kaushik; Singh, R. K.; Kumar, Ajai, E-mail: ajai@ipr.res.in

2016-04-15

An experimental investigation of the laser produced plasma induced shock wave in the presence of confining walls placed along the axial as well as the lateral direction has been performed. A time resolved Mach Zehnder interferometer is set up to track the primary as well as the reflected shock waves and its effect on the evolving plasma plume has been studied. An attempt has been made to discriminate the electronic and medium density contributions towards the changes in the refractive index of the medium. Two dimensional spatial distributions for both ambient medium density and plasma density (electron density) have beenmore » obtained by employing customised inversion technique and algorithm on the recorded interferograms. The observed density pattern of the surrounding medium in the presence of confining walls is correlated with the reflected shock wave propagation in the medium. Further, the shock wave plasma interaction and the subsequent changes in the shape and density of the plasma plume in confined geometry are briefly described.« less

Mass density images from the diffraction enhanced imaging technique.

PubMed

Hasnah, M O; Parham, C; Pisano, E D; Zhong, Z; Oltulu, O; Chapman, D

2005-02-01

Conventional x-ray radiography measures the projected x-ray attenuation of an object. It requires attenuation differences to obtain contrast of embedded features. In general, the best absorption contrast is obtained at x-ray energies where the absorption is high, meaning a high absorbed dose. Diffraction-enhanced imaging (DEI) derives contrast from absorption, refraction, and extinction. The refraction angle image of DEI visualizes the spatial gradient of the projected electron density of the object. The projected electron density often correlates well with the projected mass density and projected absorption in soft-tissue imaging, yet the mass density is not an "energy"-dependent property of the object, as is the case of absorption. This simple difference can lead to imaging with less x-ray exposure or dose. In addition, the mass density image can be directly compared (i.e., a signal-to-noise comparison) with conventional radiography. We present the method of obtaining the mass density image, the results of experiments in which comparisons are made with radiography, and an application of the method to breast cancer imaging.

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research.

PubMed

Oh, Jaechul; Weaver, J L; Karasik, M; Chan, L Y

2015-08-01

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (∼1 ns FWHM) with the intensity of 1.1 × 10(15) W/cm(2). The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 10(21) cm(-3) with the density scale length of 120 μm along the plasma symmetry axis. The resulting n(e) and T(e) profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Ionospheric responses during equinox and solstice periods over Turkey

NASA Astrophysics Data System (ADS)

Karatay, Secil; Cinar, Ali; Arikan, Feza

2017-11-01

Ionospheric electron density is the determining variable for investigation of the spatial and temporal variations in the ionosphere. Total Electron Content (TEC) is the integral of the electron density along a ray path that indicates the total variability through the ionosphere. Global Positioning System (GPS) recordings can be utilized to estimate the TEC, thus GPS proves itself as a useful tool in monitoring the total variability of electron distribution within the ionosphere. This study focuses on the analysis of the variations of ionosphere over Turkey that can be grouped into anomalies during equinox and solstice periods using TEC estimates obtained by a regional GPS network. It is observed that noon time depletions in TEC distributions predominantly occur in winter for minimum Sun Spots Numbers (SSN) in the central regions of Turkey which also exhibit high variability due to midlatitude winter anomaly. TEC values and ionospheric variations at solstice periods demonstrate significant enhancements compared to those at equinox periods.

Millimeter-wave reflectometry for electron density profile and fluctuation measurements on NSTX

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

Kubota, S.; Nguyen, X. V.; Peebles, W. A.

2001-01-01

A millimeter-wave reflectometry system for electron density profile and fluctuation measurements is being developed and installed on the National Spherical Torus Experiment. The initial frequency coverage will be in the bands 12--18, 20--32, and 33--50 GHz, provided by frequency-tunable solid-state sources. These frequencies correspond to O-mode cutoff densities ranging from 1.8x10{sup 12} to 3.1x10{sup 13}cm{sup -3}, which will span both the plasma core ({rho}=r/a<0.8) and edge ({rho}>0.8) regions. Operated as a broadband swept-frequency (frequency-modulated continuous-wave) reflectometer, the diagnostic is expected to provide routine (shot-to-shot) time- ({<=}50 {mu}s) and spatially resolved ({approx}1 cm) density profiles. The previous hardware can be easilymore » reconfigured as a fixed-frequency reflectometer for density fluctuation measurements. The combination of measurements would be valuable for studying phenomena such as possible L- to H-mode transitions and edge-localized modes.« less

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

Jarrott, L. C.; McGuffey, C.; Beg, F. N.

Fast electron transport and spatial energy deposition are investigated in integrated cone-guided Fast Ignition experiments by measuring fast electron induced copper K-shell emission using a copper tracer added to deuterated plastic shells with a geometrically reentrant gold cone. Experiments were carried out at the Laboratory for Laser Energetics on the OMEGA/OMEGA-EP Laser where the plastic shells were imploded using 54 of the 60 OMEGA60 beams (3ω, 20 kJ), while the high intensity OMEGA-EP (BL2) beam (1 ω, 10 ps, 500 J, I peak > 10 19 W/cm 2) was focused onto the inner cone tip. Here, a retrograde analysis usingmore » the hybrid-PIC electron transport code, ZUMA, is performed to examine the sensitivity of the copper Kα spatial profile on the laser-produced fast electrons, facilitating the optimization of new target point designs and laser configurations to improve the compressed core areal density by a factor of 4 and the fast electron energy coupling by a factor of 3.5.« less

An inverted cylindrical sputter magnetron as metal vapor supply for electron cyclotron resonance ion sources.

PubMed

Weichsel, T; Hartung, U; Kopte, T; Zschornack, G; Kreller, M; Silze, A

2014-05-01

An inverted cylindrical sputter magnetron device has been developed. The magnetron is acting as a metal vapor supply for an electron cyclotron resonance (ECR) ion source. FEM simulation of magnetic flux density was used to ensure that there is no critical interaction between both magnetic fields of magnetron and ECR ion source. Spatially resolved double Langmuir probe and optical emission spectroscopy measurements show an increase in electron density by one order of magnitude from 1 × 10(10) cm(-3) to 1 × 10(11) cm(-3), when the magnetron plasma is exposed to the magnetic mirror field of the ECR ion source. Electron density enhancement is also indicated by magnetron plasma emission photography with a CCD camera. Furthermore, photographs visualize the formation of a localized loss-cone - area, when the magnetron is operated at magnetic mirror field conditions. The inverted cylindrical magnetron supplies a metal atom load rate of R > 1 × 10(18) atoms/s for aluminum, which meets the demand for the production of a milliampere Al(+) ion beam.

Global Characteristics of the Correlation and Time Lag Between Solar and Ionospheric Parameters in the 27-day Period

NASA Technical Reports Server (NTRS)

Lee, Choon-Ki; Han, Shin-Chan; Dieter,Bilitza; Ki-Weon,Seo

2012-01-01

The 27-day variations of topside ionosphere are investigated using the in-situ electron density measurements from the CHAMP planar Langmuir probe and GRACE K-band ranging system. As the two satellite systems orbit at the altitudes of approx. 370 km and approx. 480 km, respectively, the satellite data sets are greatly valuable for examining the electron density variations in the vicinity of F2-peak. In a 27-day period, the electron density measurements from the satellites are in good agreements with the solar flux, except during the solar minimum period. The time delays are mostly 1-2 day and represent the hemispherical asymmetry. The globally-estimated spatial patterns of the correlation between solar flux and in-situ satellite measurements show poor correlations in the (magnetic) equatorial region, which are not found from the ground measurements of vertically-integrated electron content. We suggest that the most plausible cause for the poor correlation is the vertical movement of ionization due to atmospheric dynamic processes that is not controlled by the solar extreme ultraviolet radiation.

Arbitrarily shaped high-coherence electron bunches from cold atoms

NASA Astrophysics Data System (ADS)

McCulloch, A. J.; Sheludko, D. V.; Saliba, S. D.; Bell, S. C.; Junker, M.; Nugent, K. A.; Scholten, R. E.

2011-10-01

Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.

Adiabatic electron thermal pressure fluctuations in tokamak plasmas.

PubMed

Meier, M A; Bengtson, R D; Hallock, G A; Wootton, A J

2001-08-20

Electron thermal pressure fluctuations measured in the edge plasma of the Texas Experimental Tokamak Upgrade are a fundamental component of plasma turbulence on both sides of the velocity shear layer. The ratio of specific heats, estimated from fluctuations in electron temperature and electron number density measured simultaneously at the same electrode, indicates that observed fluctuations are adiabatic. The observations are made by means of a novel Langmuir probe technique, the time domain triple-probe method, which concurrently measures multiple plasma properties at each of two electrodes with the temporal and the spatial resolution required to estimate thermodynamic properties in a turbulent plasma.

Manipulation of electron transport in graphene by nanopatterned electrostatic potential on an electret

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Wang, Rui; Wang, Shengnan; Zhang, Dongdong; Jiang, Xingbin; Cheng, Zhihai; Qiu, Xiaohui

2018-01-01

The electron transport characteristics of graphene can be finely tuned using local electrostatic fields. Here, we use a scanning probe technique to construct a statically charged electret gate that enables in-situ fabrication of graphene devices with precisely designed potential landscapes, including p-type and n-type unipolar graphene transistors and p-n junctions. Electron dynamic simulation suggests that electron beam collimation and focusing in graphene can be achieved via periodic charge lines and concentric charge circles. This approach to spatially manipulating carrier density distribution may offer an efficient way to investigate the novel electronic properties of graphene and other low-dimensional materials.

Spatially Resolved Nano-Scale Characterization of Electronic States in SrTiO3(001) Surfaces by STM/STS

NASA Astrophysics Data System (ADS)

Iwaya, Katsuya; Ohsawa, Takeo; Shimizu, Ryota; Hashizume, Tomihiro; Hitosugi, Taro

2012-02-01

We have performed low temperature scanning tunneling microscopy/spectroscopy (STM/STS) measurements on TiO2-terminated SrTiO3(001) thin film surfaces. The conductance map exhibited electronic modulations that were completely different from the surface structure. We also found that the electronic modulations were strongly dependent on temperature and the density of atomic defects associated with oxygen vacancies. These results suggest the existence of strongly correlated two-dimensional electronic states near the SrTiO3 surface, implying the importance of electron correlation at the interfaces of SrTiO3-related heterostructures.

STM on Gate-Tunable Graphene

NASA Astrophysics Data System (ADS)

Zhang, Yuanbo

2009-03-01

We have successfully performed atomically-resolved scanning tunneling microscopy and spectroscopy (STS) on mechanically exfoliated graphene samples having tunable back-gates. We have discovered that the tunneling spectra of graphene flakes display an unexpected gap-like feature that is pinned to the Fermi level for different gate voltages, and which coexists with another depression in density-of-states that moves with gate voltage. Extensive tests and careful analysis show that the gap-feature is due to phonon-assisted inelastic tunneling, and the depression directly marks the location of the graphene Dirac point. Using tunneling spectroscopy as a new tool, we further probe the local energetic variations of the graphene charge neutral point (Dirac point) to map out spatial electron density inhomogeneities in graphene. Such measurements are two orders of magnitude higher in resolution than previous experiments, and they can be directly correlated with nanometer scale topographic features. Based on our observation of energy-dependent periodic electronic interference patterns, our measurements also reveal the nature of impurity scattering of Dirac fermions in graphene. These results are significant for understanding the sources of electron density inhomogeneity and electron scattering in graphene, and the microscopic causes of graphene electron mobility.

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

Migunov, V., E-mail: v.migunov@fz-juelich.de; Dunin-Borkowski, R. E.; London, A.

The one-dimensional charge density distribution along an electrically biased Fe atom probe needle is measured using a model-independent approach based on off-axis electron holography in the transmission electron microscope. Both the mean inner potential and the magnetic contribution to the phase shift are subtracted by taking differences between electron-optical phase images recorded with different voltages applied to the needle. The measured one-dimensional charge density distribution along the needle is compared with a similar result obtained using model-based fitting of the phase shift surrounding the needle. On the assumption of cylindrical symmetry, it is then used to infer the three-dimensional electricmore » field and electrostatic potential around the needle with ∼10 nm spatial resolution, without needing to consider either the influence of the perturbed reference wave or the extension of the projected potential outside the field of view of the electron hologram. The present study illustrates how a model-independent approach can be used to measure local variations in charge density in a material using electron holography in the presence of additional contributions to the phase, such as those arising from changes in mean inner potential and specimen thickness.« less

FUSION++: A New Data Assimilative Model for Electron Density Forecasting

NASA Astrophysics Data System (ADS)

Bust, G. S.; Comberiate, J.; Paxton, L. J.; Kelly, M.; Datta-Barua, S.

2014-12-01

There is a continuing need within the operational space weather community, both civilian and military, for accurate, robust data assimilative specifications and forecasts of the global electron density field, as well as derived RF application product specifications and forecasts obtained from the electron density field. The spatial scales of interest range from a hundred to a few thousand kilometers horizontally (synoptic large scale structuring) and meters to kilometers (small scale structuring that cause scintillations). RF space weather applications affected by electron density variability on these scales include navigation, communication and geo-location of RF frequencies ranging from 100's of Hz to GHz. For many of these applications, the necessary forecast time periods range from nowcasts to 1-3 hours. For more "mission planning" applications, necessary forecast times can range from hours to days. In this paper we present a new ionosphere-thermosphere (IT) specification and forecast model being developed at JHU/APL based upon the well-known data assimilation algorithms Ionospheric Data Assimilation Four Dimensional (IDA4D) and Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE). This new forecast model, "Forward Update Simple IONosphere model Plus IDA4D Plus EMPIRE (FUSION++), ingests data from observations related to electron density, winds, electric fields and neutral composition and provides improved specification and forecast of electron density. In addition, the new model provides improved specification of winds, electric fields and composition. We will present a short overview and derivation of the methodology behind FUSION++, some preliminary results using real observational sources, example derived RF application products such as HF bi-static propagation, and initial comparisons with independent data sources for validation.

Spatial irregularities in Jupiter's upper ionosphere observed by Voyager radio occultations

NASA Technical Reports Server (NTRS)

Hinson, D. P.; Tyler, G. L.

1982-01-01

Radio scintillations (at 3.6 and 13 cm) produced by scattering from ionospheric irregularities during the Voyager occultations are interpreted using a weak-scattering theory. Least squares solutions for ionospheric parameters derived from the observed fluctuation spectra yield estimates of (1) the axial ratio, (2) angular orientation of the anisotropic irregularities, (3) the power law exponent of the spatial spectrum of irregularities, and (4) the magnitude of the spatial variations in electron density. It is shown that the measured angular orientation of the anisotropic irregularities indicates magnetic field direction and may provide a basis for refining Jovian magnetic field models.

Remote Sensing of Ionosphere by IONOLAB Group

NASA Astrophysics Data System (ADS)

Arikan, Feza

2016-07-01

Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. Electron density is a complex function of spatial and temporal variations of solar, geomagnetic, and seismic activities. Ionosphere is the main source of error for navigation and positioning systems and satellite communication. Therefore, characterization and constant monitoring of variability of the ionosphere is of utmost importance for the performance improvement of these systems. Since ionospheric electron density is not a directly measurable quantity, an important derivable parameter is the Total Electron Content (TEC), which is used widely to characterize the ionosphere. TEC is proportional to the total number of electrons on a line crossing the atmosphere. IONOLAB is a research group is formed by Hacettepe University, Bilkent University and Kastamonu University, Turkey gathered to handle the challenges of the ionosphere using state-of-the-art remote sensing and signal processing techniques. IONOLAB group provides unique space weather services of IONOLAB-TEC, International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model based IRI-Plas-MAP, IRI-Plas-STEC and Online IRI-Plas-2015 model at www.ionolab.org. IONOLAB group has been working for imaging and monitoring of ionospheric structure for the last 15 years. TEC is estimated from dual frequency GPS receivers as IONOLAB-TEC using IONOLAB-BIAS. For high spatio-temporal resolution 2-D imaging or mapping, IONOLAB-MAP algorithm is developed that uses automated Universal Kriging or Ordinary Kriging in which the experimental semivariogram is fitted to Matern Function with Particle Swarm Optimization (PSO). For 3-D imaging of ionosphere and 1-D vertical profiles of electron density, state-of-the-art IRI-Plas model based IONOLAB-CIT algorithm is developed for regional reconstruction that employs Kalman Filters for state/temporal transition. IONOLAB group contributes to remote sensing of upper atmosphere, ionosphere and plasmasphere with continuing TUBITAK projects. IONOLAB group is open to joint research and collaboration with researchers from all disciplines that investigate the challenges of ionosphere and space weather. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

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

Barnat, E. V.; Fierro, A.

The implementation and demonstration of laser-collision-induced fluorescence (LCIF) generated in atmospheric pressure helium environments is presented in this communication. As collision times are observed to be fast (~10 ns), ultrashort pulse laser excitation (<100 fs) of the 2 3S to 3 3P (388.9 nm) is utilized to initiate the LCIF process. Both neutral-induced and electron-induced components of the LCIF are observed in the helium afterglow plasma as the reduced electric field (E/N) is tuned from <0.1 Td to over 5 Td. Under the discharge conditions presented in this study (640 Torr He), the lower limit of electron density detection ismore » ~10 12 e cm -3. Lastly, the spatial profiles of the 2 3S helium metastable and electrons are presented as functions of E/N to demonstrate the spatial resolving capabilities of the LCIF method.« less

High-Energy Emissions Induced by Air Density Fluctuations of Discharges

NASA Astrophysics Data System (ADS)

Köhn, C.; Chanrion, O.; Neubert, T.

2018-05-01

Bursts of X-rays and γ-rays are observed from lightning and laboratory sparks. They are bremsstrahlung from energetic electrons interacting with neutral air molecules, but it is still unclear how the electrons achieve the required energies. It has been proposed that the enhanced electric field of streamers, found in the corona of leader tips, may account for the acceleration; however, their efficiency is questioned because of the relatively low production rate found in simulations. Here we emphasize that streamers usually are simulated with the assumption of homogeneous gas, which may not be the case on the small temporal and spatial scales of discharges. Since the streamer properties strongly depend on the reduced electric field E/n, where n is the neutral number density, fluctuations may potentially have a significant effect. To explore what might be expected if the assumption of homogeneity is relaxed, we conducted simple numerical experiments based on simulations of streamers in a neutral gas with a radial gradient in the neutral density, assumed to be created, for instance, by a previous spark. We also studied the effects of background electron density from previous discharges. We find that X-radiation and γ-radiation are enhanced when the on-axis air density is reduced by more than ˜25%. Pre-ionization tends to reduce the streamer field and thereby the production rate of high-energy electrons; however, the reduction is modest. The simulations suggest that fluctuations in the neutral densities, on the temporal and spacial scales of streamers, may be important for electron acceleration and bremsstrahlung radiation.

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Varney, R. H.; Schlatter, N.; Huba, J. D.

2013-12-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at HAARP on March 12, 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert [1968, 1970], we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with significant induced ionization in view of the spatial intermittency of the airglow.

Absolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging

NASA Astrophysics Data System (ADS)

Chérigier, L.; Czarnetzki, U.; Luggenhölscher, D.; Schulz-von der Gathen, V.; Döbele, H. F.

1999-01-01

Absolute atomic hydrogen densities were measured in the gaseous electronics conference reference cell parallel plate reactor by Doppler-free two-photon absorption laser induced fluorescence spectroscopy (TALIF) at λ=205 nm. The capacitively coupled radio frequency discharge was operated at 13.56 MHz in pure hydrogen under various input power and pressure conditions. The Doppler-free excitation technique with an unfocused laser beam together with imaging the fluorescence radiation by an intensified charge coupled device camera allows instantaneous spatial resolution along the radial direction. Absolute density calibration is obtained with the aid of a flow tube reactor and titration with NO2. The influence of spatial intensity inhomogenities along the laser beam and subsequent fluorescence are corrected by TALIF in xenon. A full mapping of the absolute density distribution between the electrodes was obtained. The detection limit for atomic hydrogen amounts to about 2×1018 m-3. The dissociation degree is of the order of a few percent.

Critical thickness for the two-dimensional electron gas in LaTiO3/SrTiO3 superlattices

NASA Astrophysics Data System (ADS)

You, Jeong Ho; Lee, Jun Hee

2013-10-01

Transport dimensionality of Ti d electrons in (LaTiO3)1/(SrTiO3)N superlattices has been investigated using density functional theory with local spin-density approximation + U method. Different spatial distribution patterns have been found between Ti t2g orbital electrons. The dxy orbital electrons are highly localized near interfaces due to the potentials by positively charged LaO layers, while the degenerate dyz and dxz orbital electrons are more distributed inside SrTiO3 insulators. For N ≥ 3 unit cells (u.c.), the Ti dxy densities of state exhibit the staircaselike increments, which appear at the same energy levels as the dxy flat bands along the Γ-Z direction in band structures. The kz-independent discrete energy levels indicate that the electrons in dxy flat bands are two-dimensional electron gases (2DEGs) which can transport along interfaces, but they cannot transport perpendicularly to interfaces due to the confinements in the potential wells by LaO layers. Unlike the dxy orbital electrons, the dyz and dxz orbital electrons have three-dimensional (3D) transport characteristics, regardless of SrTiO3 thicknesses. The 2DEG formation by dxy orbital electrons, when N ≥ 3 u.c., indicates the existence of critical SrTiO3 thickness where the electron transport dimensionality starts to change from 3D to 2D in (LaTiO3)1/(SrTiO3)N superlattices.

Refraction-enhanced backlit imaging of axially symmetric inertial confinement fusion plasmas.

PubMed

Koch, Jeffrey A; Landen, Otto L; Suter, Laurence J; Masse, Laurent P; Clark, Daniel S; Ross, James S; Mackinnon, Andrew J; Meezan, Nathan B; Thomas, Cliff A; Ping, Yuan

2013-05-20

X-ray backlit radiographs of dense plasma shells can be significantly altered by refraction of x rays that would otherwise travel straight-ray paths, and this effect can be a powerful tool for diagnosing the spatial structure of the plasma being radiographed. We explore the conditions under which refraction effects may be observed, and we use analytical and numerical approaches to quantify these effects for one-dimensional radial opacity and density profiles characteristic of inertial-confinement fusion (ICF) implosions. We also show how analytical and numerical approaches allow approximate radial plasma opacity and density profiles to be inferred from point-projection refraction-enhanced radiography data. This imaging technique can provide unique data on electron density profiles in ICF plasmas that cannot be obtained using other techniques, and the uniform illumination provided by point-like x-ray backlighters eliminates a significant source of uncertainty in inferences of plasma opacity profiles from area-backlit pinhole imaging data when the backlight spatial profile cannot be independently characterized. The technique is particularly suited to in-flight radiography of imploding low-opacity shells surrounding hydrogen ice, because refraction is sensitive to the electron density of the hydrogen plasma even when it is invisible to absorption radiography. It may also provide an alternative approach to timing shockwaves created by the implosion drive, that are currently invisible to absorption radiography.

DensToolKit: A comprehensive open-source package for analyzing the electron density and its derivative scalar and vector fields

NASA Astrophysics Data System (ADS)

Solano-Altamirano, J. M.; Hernández-Pérez, Julio M.

2015-11-01

DensToolKit is a suite of cross-platform, optionally parallelized, programs for analyzing the molecular electron density (ρ) and several fields derived from it. Scalar and vector fields, such as the gradient of the electron density (∇ρ), electron localization function (ELF) and its gradient, localized orbital locator (LOL), region of slow electrons (RoSE), reduced density gradient, localized electrons detector (LED), information entropy, molecular electrostatic potential, kinetic energy densities K and G, among others, can be evaluated on zero, one, two, and three dimensional grids. The suite includes a program for searching critical points and bond paths of the electron density, under the framework of Quantum Theory of Atoms in Molecules. DensToolKit also evaluates the momentum space electron density on spatial grids, and the reduced density matrix of order one along lines joining two arbitrary atoms of a molecule. The source code is distributed under the GNU-GPLv3 license, and we release the code with the intent of establishing an open-source collaborative project. The style of DensToolKit's code follows some of the guidelines of an object-oriented program. This allows us to supply the user with a simple manner for easily implement new scalar or vector fields, provided they are derived from any of the fields already implemented in the code. In this paper, we present some of the most salient features of the programs contained in the suite, some examples of how to run them, and the mathematical definitions of the implemented fields along with hints of how we optimized their evaluation. We benchmarked our suite against both a freely-available program and a commercial package. Speed-ups of ˜2×, and up to 12× were obtained using a non-parallel compilation of DensToolKit for the evaluation of fields. DensToolKit takes similar times for finding critical points, compared to a commercial package. Finally, we present some perspectives for the future development and growth of the suite.

MO-F-CAMPUS-J-04: Tissue Segmentation-Based MR Electron Density Mapping Method for MR-Only Radiation Treatment Planning of Brain

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

Yu, H; Lee, Y; Ruschin, M

2015-06-15

Purpose: Automatically derive electron density of tissues using MR images and generate a pseudo-CT for MR-only treatment planning of brain tumours. Methods: 20 stereotactic radiosurgery (SRS) patients’ T1-weighted MR images and CT images were retrospectively acquired. First, a semi-automated tissue segmentation algorithm was developed to differentiate tissues with similar MR intensities and large differences in electron densities. The method started with approximately 12 slices of manually contoured spatial regions containing sinuses and airways, then air, bone, brain, cerebrospinal fluid (CSF) and eyes were automatically segmented using edge detection and anatomical information including location, shape, tissue uniformity and relative intensity distribution.more » Next, soft tissues - muscle and fat were segmented based on their relative intensity histogram. Finally, intensities of voxels in each segmented tissue were mapped into their electron density range to generate pseudo-CT by linearly fitting their relative intensity histograms. Co-registered CT was used as a ground truth. The bone segmentations of pseudo-CT were compared with those of co-registered CT obtained by using a 300HU threshold. The average distances between voxels on external edges of the skull of pseudo-CT and CT in three axial, coronal and sagittal slices with the largest width of skull were calculated. The mean absolute electron density (in Hounsfield unit) difference of voxels in each segmented tissues was calculated. Results: The average of distances between voxels on external skull from pseudo-CT and CT were 0.6±1.1mm (mean±1SD). The mean absolute electron density differences for bone, brain, CSF, muscle and fat are 78±114 HU, and 21±8 HU, 14±29 HU, 57±37 HU, and 31±63 HU, respectively. Conclusion: The semi-automated MR electron density mapping technique was developed using T1-weighted MR images. The generated pseudo-CT is comparable to that of CT in terms of anatomical position of tissues and similarity of electron density assignment. This method can allow MR-only treatment planning.« less

The spatial-temporal ambiguity in auroral modeling

NASA Technical Reports Server (NTRS)

Rees, M. H.; Roble, R. G.; Kopp, J.; Abreu, V. J.; Rusch, D. W.; Brace, L. H.; Brinton, H. C.; Hoffman, R. A.; Heelis, R. A.; Kayser, D. C.

1980-01-01

The paper examines the time-dependent models of the aurora which show that various ionospheric parameters respond to the onset of auroral ionization with different time histories. A pass of the Atmosphere Explorer C satellite over Poker Flat, Alaska, and ground based photometric and photographic observations have been used to resolve the time-space ambiguity of a specific auroral event. The density of the O(+), NO(+), O2(+), and N2(+) ions, the electron density, and the electron temperature observed at 280 km altitude in a 50 km wide segment of an auroral arc are predicted by the model if particle precipitation into the region commenced about 11 min prior to the overpass.

Theory of Tunneling Spectroscopy in a Mn12 Single-Electron Transistor by Density-Functional Theory Methods

NASA Astrophysics Data System (ADS)

Michalak, Ł.; Canali, C. M.; Pederson, M. R.; Paulsson, M.; Benza, V. G.

2010-01-01

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Theory of tunneling spectroscopy in a Mn12 single-electron transistor by density-functional theory methods.

PubMed

Michalak, Ł; Canali, C M; Pederson, M R; Paulsson, M; Benza, V G

2010-01-08

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Theory of hydrodynamic transport in fluctuating electronic charge density wave states

NASA Astrophysics Data System (ADS)

Delacrétaz, Luca V.; Goutéraux, Blaise; Hartnoll, Sean A.; Karlsson, Anna

2017-11-01

We describe the collective hydrodynamic motion of an incommensurate charge density wave state in a clean electronic system. Our description simultaneously incorporates the effects of both pinning due to weak disorder and also phase relaxation due to proliferating dislocations. We show that the interplay between these two phenomena has important consequences for charge and momentum transport. For instance, it can lead to metal-insulator transitions. We furthermore identify signatures of fluctuating density waves in frequency and spatially resolved conductivities. Phase disordering is well known to lead to a large viscosity. We derive a precise formula for the phase relaxation rate in terms of the viscosity in the dislocation cores. We thereby determine the viscosity of the superconducting state of BSCCO from the observed melting dynamics of Abrikosov lattices and show that the result is consistent with dissipation into Bogoliubov quasiparticles.

Spatial and Time Dynamics of Non-Linear Vortices in Plasma Lens for High-Current Ion Beam Focusing

NASA Astrophysics Data System (ADS)

Goncharov, Alexei A.; Maslov, Vasyl I.; Onishchenko, Ivan N.; Tretyakov, Vitalij N.

2002-11-01

It is known from numerical simulation (see, for example, [1]) and from experiments (see, for example, [2]), that an electron density bunches as discrete vortices are long - living structures in vacuum. However, in laboratory experiments [2] it has been shown that the vortices are changed faster, when they are submersed in electrons, distributed around them. The charged plasma lens intended for a focussing of high-current ion beams, has the same crossed configuration of a radial electrical and longitudinal magnetic field [3], as only electron plasma. In this lens the vortical turbulence is excited [3]. The vortex - bunch and vortex - hole are rotated in the inverse directions in system of their rest. The instability development in initially homogeneous plasma causes that the vortices are excited by pairs. Namely, if the vortex - bunch of electrons is generated, near the vortex - hole of electrons is also generated. It is shown, that in nonuniform plasma the vortices behave is various in time. Namely, the vortex - bunch goes to area of larger electron density, and the vortex - hole goes to area of smaller electron density. The speed of the vortex - hole is less than speed of the vortex - bunch. It is shown, that the electron vortices, generated in the plasma lens, can result in to formation of spiral distribution of electron density. The physical mechanism of coalescence of electron vortices - bunches is proposed. 1.Driscoll C.F. et al. Plasma Phys. Contr. Fus. Res. 3 (1989) 507. 2.Kiwamoto Y. et al. Non-neutral plasma physics. Princeton. 1999. P. 99-105. 3.Goncharov A. et al. Plasma Phys. Rep. 20 (1994) 499.

geometric optics and WKB method for electromagnetic wave propagation in an inhomogeneous plasma near cutoff

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

Light, Max Eugene

This report outlines the theory underlying electromagnetic (EM) wave propagation in an unmagnetized, inhomogeneous plasma. The inhomogeneity is given by a spatially nonuniform plasma electron density n e(r), which will modify the wave propagation in the direction of the gradient rn e(r).

Numerical simulation of current-free double layers created in a helicon plasma device

NASA Astrophysics Data System (ADS)

Rao, Sathyanarayan; Singh, Nagendra

2012-09-01

Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E⊥) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E⊥ on the high potential side of the double layer in the CFDL. The accelerated ions are trapped near the conical surface, where E⊥ reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop (φ||o) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.

Electron Mobility in γ -Al2O3/SrTiO3

NASA Astrophysics Data System (ADS)

Christensen, D. V.; Frenkel, Y.; Schütz, P.; Trier, F.; Wissberg, S.; Claessen, R.; Kalisky, B.; Smith, A.; Chen, Y. Z.; Pryds, N.

2018-05-01

One of the key issues in engineering oxide interfaces for electronic devices is achieving high electron mobility. SrTiO3 -based interfaces with high electron mobility have gained a lot of interest due to the possibility of combining quantum phenomena with the many functionalities exhibited by SrTiO3 . To date, the highest electron mobility (140 000 cm2/V s at 2 K) is obtained by interfacing perovskite SrTiO3 with spinel γ -Al2O3 . The origin of the high mobility, however, remains poorly understood. Here, we investigate the scattering mechanisms limiting the mobility in γ -Al2O3/SrTiO3 at temperatures between 2 and 300 K and over a wide range of sheet carrier densities. For T >150 K , we find that the mobility is limited by longitudinal optical phonon scattering. For large sheet carrier densities (>8 ×1013 cm-2 ), the screened electron-phonon coupling leads to room-temperature mobilities up to μ ˜12 cm2/V s . For 5 K

Spatial variations of the local density of states modified by CDWs in 1 T- TaS2- xSex

NASA Astrophysics Data System (ADS)

Hasegawa, T.; Yamaguchi, W.; Kim, J.-J.; Wei, W.; Nantoh, M.; Ikuta, H.; Kitazawa, K.; Manivannan, A.; Fujishima, A.; Uchinokura, K.

1994-07-01

Spatial variations of the local density of states (LDOS) near the Fermi level have been observed on the layered dichalcogenides 1 T- TaS2- xSex ( x = 0, 0.2, 2) for the first time. The tunneling spectra on the cleaved surfaces were measured by atomic-site tunneling (AST) spectroscopy technique at room temperature. In 1T-TaS 2, the LDOS was substantially different among the three inequivalent Ta atomic sites induced by the CDW formation. However, the surface electronic structure became homogeneous, as the Se content was increased. By substituting Se for S, the minimum position of the LDOS was systematically shifted to a higher energy side above the Fermi level.

Negative ion kinetics in RF glow discharges

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

Gottscho, R.A.; Gacbe, C.E.

1986-04-01

Using temporally and spatially resolved laser spectroscopy, the authors have determined the identities, approximate concentrations, effects on the local field, and kinetics of formation and loss of negative ions in RF discharges. CI/sup -/ and BCI/sub 3//sup -/ are the dominant negative ions found in low-frequency discharges through CI/sub 2/ and BCI/sub 3/, respectively. The electron affinity for CI is measured to be 3.6118 +- 0.0005 eV. Negative ion kinetics are strongly affected by application of the RF field. Formation of negative ions by attachment of slow electrons in RF discharges is governed by the extent and duration of electronmore » energy relaxation. Similarly, destruction of negative ions by collisional detachment and field extraction is dependent upon ion energy modulation. Thus, at low frequency, the anion density peaks at the beginning of the anodic and cathodic half-cycles after electrons have attached but before detachment and extraction have had time to occur. At higher frequencies, electrons have insufficient time to attach before they are reheated and the instantaneous anion density in the sheath is greatly reduced. When the negative ion density is comparable to the positive ion density, the plasma potential is observed to lie below the anode potential, double layers form between sheath and plasma, and anions and electrons are accelerated by large sheath fields to electrode surfaces.« less

Analysis of Co-spatial UV-Optical STIS Spectra of Seven Planetary Nebulae From HST Cycle 19 GO 12600

NASA Astrophysics Data System (ADS)

Miller, Timothy R.; Henry, Richard B. C.; Dufour, Reginald J.; Kwitter, Karen B.; Shaw, Richard A.; Balick, Bruce; Corradi, Romano

2016-01-01

We present an analysis of seven spatially resolved planetary nebulae (PNe), NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, IC 2165, and IC 3568, from observations in the Cycle 19 program GO 12600 using HST STIS. These seven observations cover the wavelength range 1150-10,270 Å with 0.2 and 0.5 arcsec wide slits, and are co-spatial to within 0.1 arcsec along a 25 arcsec length across each nebula. The wavelength and spatial coverage enabled a detailed study of physical conditions and abundances from UV and optical line emissions (compared to only optical lines) for these seven PNe. The first UV lines of interest are those of carbon. The resolved lines of C III] 1906.68 and 1908.73 yielded a direct measurement of the density within the volume occupied by doubly-ionized carbon and other similar co-spatial ions as well as contributed to an accurate measurement of the carbon abundance. Each PN spectrum was divided into smaller spatial regions or segments in order to assess inferred density variations among the regions along the entire slit. There is a clear difference in the inferred density for several regions of each PNe. Variations in electron temperature and chemical abundances were also probed and shown to be completely homogeneous within the errors. Lastly, these nebulae were modeled in detail with the photoionization code CLOUDY. This modeling constrained the central star parameters of temperature and luminosity and tested the effects different density profiles have on these parameters. We gratefully acknowledge generous support from NASA through grants related to the Cycle 19 program GO 12600, as well as from the University of Oklahoma.

Ionization asymmetry effects on the properties modulation of atmospheric pressure dielectric barrier discharge sustained by tailored voltage waveforms

NASA Astrophysics Data System (ADS)

Zhang, Z. L.; Nie, Q. Y.; Zhang, X. N.; Wang, Z. B.; Kong, F. R.; Jiang, B. H.; Lim, J. W. M.

2018-04-01

The dielectric barrier discharge (DBD) is a promising technology to generate high density and uniform cold plasmas in atmospheric pressure gases. The effective independent tuning of key plasma parameters is quite important for both application-focused and fundamental studies. In this paper, based on a one-dimensional fluid model with semi-kinetics treatment, numerical studies of ionization asymmetry effects on the properties modulation of atmospheric DBD sustained by tailored voltage waveforms are reported. The driving voltage waveform is characterized by an asymmetric-slope fundamental sinusoidal radio frequency signal superimposing one or more harmonics, and the effects of the number of harmonics, phase shift, as well as the fluctuation of harmonics on the sheath dynamics, impact ionization of electrons and key plasma parameters are investigated. The results have shown that the electron density can exhibit a substantial increase due to the effective electron heating by a spatially asymmetric sheath structure. The strategic modulation of harmonics number and phase shift is capable of raising the electron density significantly (e.g., nearly three times in this case), but without a significant increase in the gas temperature. Moreover, by tailoring the fluctuation of harmonics with a steeper slope, a more profound efficiency in electron impact ionization can be achieved, and thus enhancing the electron density effectively. This method then enables a novel alternative approach to realize the independent control of the key plasma parameters under atmospheric pressure.

Density of states and extent of wave function: two crucial factors for small polaron hopping conductivity in 1D

NASA Astrophysics Data System (ADS)

Dimakogianni, M.; Simserides, C.; Triberis, G. P.

2013-07-01

We introduce a theoretical model to scrutinize the conductivity of small polarons in 1D disordered systems, focusing on two crucial - as will be demonstrated - factors: the density of states and the spatial extent of the electronic wave function. The investigation is performed for any temperature up to 300 K and under electric field of arbitrary strength up to the polaron dissociation limit. To accomplish this task, we combine analytical work with numerical calculations.

Electron-Beam Diagnostic Methods for Hypersonic Flow Diagnostics

NASA Technical Reports Server (NTRS)

1994-01-01

The purpose of this work was the evaluation of the use of electron-bean fluorescence for flow measurements during hypersonic flight. Both analytical and numerical models were developed in this investigation to evaluate quantitatively flow field imaging concepts based upon the electron beam fluorescence technique for use in flight research and wind tunnel applications. Specific models were developed for: (1) fluorescence excitation/emission for nitrogen, (2) rotational fluorescence spectrum for nitrogen, (3) single and multiple scattering of electrons in a variable density medium, (4) spatial and spectral distribution of fluorescence, (5) measurement of rotational temperature and density, (6) optical filter design for fluorescence imaging, and (7) temperature accuracy and signal acquisition time requirements. Application of these models to a typical hypersonic wind tunnel flow is presented. In particular, the capability of simulating the fluorescence resulting from electron impact ionization in a variable density nitrogen or air flow provides the capability to evaluate the design of imaging instruments for flow field mapping. The result of this analysis is a recommendation that quantitative measurements of hypersonic flow fields using electron-bean fluorescence is a tractable method with electron beam energies of 100 keV. With lower electron energies, electron scattering increases with significant beam divergence which makes quantitative imaging difficult. The potential application of the analytical and numerical models developed in this work is in the design of a flow field imaging instrument for use in hypersonic wind tunnels or onboard a flight research vehicle.

Aluminum/vacuum multilayer configuration for spatial high-energy electron shielding via electron return effects induced by magnetic field.

PubMed

Chen, Tuo; Tang, Xiaobin; Chen, Feida; Ni, Minxuan; Huang, Hai; Zhang, Yun; Chen, Da

2017-06-26

Radiation shielding of high-energy electrons is critical for successful space missions. However, conventional passive shielding systems exhibit several limitations, such as heavy configuration, poor shielding ability, and strong secondary bremsstrahlung radiation. In this work, an aluminum/vacuum multilayer structure was proposed based on the electron return effects induced by magnetic field. The shielding property of several configurations was evaluated by using the Monte Carlo method. Results showed that multilayer systems presented improved shielding ability to electrons, and less secondary x-ray transmissions than those of conventional systems. Moreover, the influences of magnetic flux density and number of layers on the shielding property of multilayer systems were investigated using a female Chinese hybrid reference phantom based on cumulative dose. In the case of two aluminum layers, the cumulative dose in a phantom gradually decreased with increasing magnetic flux density. The maximum decline rate was found within 0.4-1 Tesla. With increasing layers of configuration, the cumulative dose decreased and the shielding ability improved. This research provides effective shielding measures for future space radiation protection in high-energy electron environments.

Ultrafast laser-collision-induced fluorescence in atmospheric pressure plasma

DOE PAGES

Barnat, E. V.; Fierro, A.

2017-03-07

The implementation and demonstration of laser-collision-induced fluorescence (LCIF) generated in atmospheric pressure helium environments is presented in this communication. As collision times are observed to be fast (~10 ns), ultrashort pulse laser excitation (<100 fs) of the 2 3S to 3 3P (388.9 nm) is utilized to initiate the LCIF process. Both neutral-induced and electron-induced components of the LCIF are observed in the helium afterglow plasma as the reduced electric field (E/N) is tuned from <0.1 Td to over 5 Td. Under the discharge conditions presented in this study (640 Torr He), the lower limit of electron density detection ismore » ~10 12 e cm -3. Lastly, the spatial profiles of the 2 3S helium metastable and electrons are presented as functions of E/N to demonstrate the spatial resolving capabilities of the LCIF method.« less

Signal acquisition and scale calibration for beam power density distribution of electron beam welding

NASA Astrophysics Data System (ADS)

Peng, Yong; Li, Hongqiang; Shen, Chunlong; Guo, Shun; Zhou, Qi; Wang, Kehong

2017-06-01

The power density distribution of electron beam welding (EBW) is a key factor to reflect the beam quality. The beam quality test system was designed for the actual beam power density distribution of high-voltage EBW. After the analysis of characteristics and phase relationship between the deflection control signal and the acquisition signal, the Post-Trigger mode was proposed for the signal acquisition meanwhile the same external clock source was shared by the control signal and the sampling clock. The power density distribution of beam cross-section was reconstructed using one-dimensional signal that was processed by median filtering, twice signal segmentation and spatial scale calibration. The diameter of beam cross-section was defined by amplitude method and integral method respectively. The measured diameter of integral definition is bigger than that of amplitude definition, but for the ideal distribution the former is smaller than the latter. The measured distribution without symmetrical shape is not concentrated compared to Gaussian distribution.

A Monte Carlo Sensitivity Analysis of CF2 and CF Radical Densities in a c-C4F8 Plasma

NASA Technical Reports Server (NTRS)

Bose, Deepak; Rauf, Shahid; Hash, D. B.; Govindan, T. R.; Meyyappan, M.

2004-01-01

A Monte Carlo sensitivity analysis is used to build a plasma chemistry model for octacyclofluorobutane (c-C4F8) which is commonly used in dielectric etch. Experimental data are used both quantitatively and quantitatively to analyze the gas phase and gas surface reactions for neutral radical chemistry. The sensitivity data of the resulting model identifies a few critical gas phase and surface aided reactions that account for most of the uncertainty in the CF2 and CF radical densities. Electron impact dissociation of small radicals (CF2 and CF) and their surface recombination reactions are found to be the rate-limiting steps in the neutral radical chemistry. The relative rates for these electron impact dissociation and surface recombination reactions are also suggested. The resulting mechanism is able to explain the measurements of CF2 and CF densities available in the literature and also their hollow spatial density profiles.

Progress on FIR interferometry and Thomson Scattering measurements on HIT-SI3

NASA Astrophysics Data System (ADS)

Everson, Christopher; Jarboe, Thomas; Morgan, Kyle

2017-10-01

Spatially resolved measurements of the electron temperature (Te) and density (ne) will be fundamental in assessing the degree to which HIT-SI3 demonstrates closed magnetic flux and energy confinement. Further, electron temperature measurements have not yet been made on an inductively-driven spheromak. Far infrared (FIR) interferometer and Thomson Scattering (TS) systems have been installed on the HIT-SI3 spheromak. The TS system currently implemented on HIT-SI3 was originally designed for other magnetic confinement experiments, and progress continues toward modifying and optimizing for HIT-SI3 plasmas. Initial results suggest that the electron temperature is of order 10 eV. Plans to modify the TS system to provide more sensitivity and accuracy at low temperatures are presented. The line-integrated ne is measured on one chord by the FIR interferometer, with densities near 5x1019 m-3. Four cylindrical volumes have been added to the HIT-SI3 apparatus to enhance passive pumping. It is hoped that this will allow for more control of the density during the 2 ms discharges. Density measurements from before and after the installation of the passive pumping volumes are presented for comparison.

Electron energetics in the inner coma of Comet Halley

NASA Astrophysics Data System (ADS)

Gan, L.; Cravens, T. E.

1990-05-01

A quasi-two-dimensional model of the spatial and energy distribution of electrons in the inner coma of Comet Halley has been constructed from a spherically symmetric ion density profile based on Giotto measurements, using the two-stream electron transport method and the time-dependent electron energy equation. A sharp jump in the electron temperature was found to be present at a cometocentric distance of about 15,000 km. This thermal boundary separates an inner region where cooling processes are dominant from an outer region where heat transport is more important. Both thermal and suprathermal electron populations exist inside the thermal boundary with comparable kinetic pressures. Outside the thermal boundary, a cloud electron population does not exist, and the electrons are almost isothermal along the magnetic field lines.

MO-FG-204-01: Improved Noise Suppression for Dual-Energy CT Through Entropy Minimization

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

Petrongolo, M; Zhu, L

2015-06-15

Purpose: In dual energy CT (DECT), noise amplification during signal decomposition significantly limits the utility of basis material images. Since clinically relevant objects contain a limited number of materials, we propose to suppress noise for DECT based on image entropy minimization. An adaptive weighting scheme is employed during noise suppression to improve decomposition accuracy with limited effect on spatial resolution and image texture preservation. Methods: From decomposed images, we first generate a 2D plot of scattered data points, using basis material densities as coordinates. Data points representing the same material generate a highly asymmetric cluster. We orient an axis bymore » minimizing the entropy in a 1D histogram of these points projected onto the axis. To suppress noise, we replace pixel values of decomposed images with center-of-mass values in the direction perpendicular to the optimal axis. To limit errors due to cluster overlap, we weight each data point’s contribution based on its high and low energy CT values and location within the image. The proposed method’s performance is assessed on physical phantom studies. Electron density is used as the quality metric for decomposition accuracy. Our results are compared to those without noise suppression and with a recently developed iterative method. Results: The proposed method reduces noise standard deviations of the decomposed images by at least one order of magnitude. On the Catphan phantom, this method greatly preserves the spatial resolution and texture of the CT images and limits induced error in measured electron density to below 1.2%. In the head phantom study, the proposed method performs the best in retaining fine, intricate structures. Conclusion: The entropy minimization based algorithm with adaptive weighting substantially reduces DECT noise while preserving image spatial resolution and texture. Future investigations will include extensive investigations on material decomposition accuracy that go beyond the current electron density calculations. This work was supported in part by the National Institutes of Health (NIH) under Grant Number R21 EB012700.« less

A semi-analytical study of positive corona discharge in wire-plane electrode configuration

NASA Astrophysics Data System (ADS)

Yanallah, K.; Pontiga, F.; Chen, J. H.

2013-08-01

Wire-to-plane positive corona discharge in air has been studied using an analytical model of two species (electrons and positive ions). The spatial distributions of electric field and charged species are obtained by integrating Gauss's law and the continuity equations of species along the Laplacian field lines. The experimental values of corona current intensity and applied voltage, together with Warburg's law, have been used to formulate the boundary condition for the electron density on the corona wire. To test the accuracy of the model, the approximate electric field distribution has been compared with the exact numerical solution obtained from a finite element analysis. A parametrical study of wire-to-plane corona discharge has then been undertaken using the approximate semi-analytical solutions. Thus, the spatial distributions of electric field and charged particles have been computed for different values of the gas pressure, wire radius and electrode separation. Also, the two dimensional distribution of ozone density has been obtained using a simplified plasma chemistry model. The approximate semi-analytical solutions can be evaluated in a negligible computational time, yet provide precise estimates of corona discharge variables.

Identification of the spatial location of deep trap states in AlGaN/GaN heterostructures by surface photovoltage spectroscopy

NASA Astrophysics Data System (ADS)

Jana, Dipankar; Porwal, S.; Sharma, T. K.

2017-12-01

Spatial and spectral origin of deep level defects in molecular beam epitaxy grown AlGaN/GaN heterostructures are investigated by using surface photovoltage spectroscopy (SPS) and pump-probe SPS techniques. A deep trap center ∼1 eV above the valence band is observed in SPS measurements which is correlated with the yellow luminescence feature in GaN. Capture of electrons and holes is resolved by performing temperature dependent SPS and pump-probe SPS measurements. It is found that the deep trap states are distributed throughout the sample while their dominance in SPS spectra depends on the density, occupation probability of deep trap states and the background electron density of GaN channel layer. Dynamics of deep trap states associated with GaN channel layer is investigated by performing frequency dependent photoluminescence (PL) and SPS measurements. A time constant of few millisecond is estimated for the deep defects which might limit the dynamic performance of AlGaN/GaN based devices.

Spatial Control of Laser Wakefield Accelerated Electron Beams

NASA Astrophysics Data System (ADS)

Maksimchuk, A.; Behm, K.; Zhao, T.; Joglekar, A. S.; Hussein, A.; Nees, J.; Thomas, A. G. R.; Krushelnick, K.; Elle, J.; Lucero, A.; Samarin, G. M.; Sarry, G.; Warwick, J.

2017-10-01

The laser wakefield experiments to study and control spatial properties of electron beams were performed using HERCULES laser at the University of Michigan at power of 100 TW. In the first experiment multi-electron beam generation was demonstrated using co-propagating, parallel laser beams with a π-phase shift mirror and showing that interaction between the wakefields can cause injection to occur for plasma and laser parameters in which a single wakefield displays no significant injection. In the second experiment a magnetic triplet quadrupole system was used to refocus and stabilize electron beams at the distance of 60 cm from the interaction region. This produced a 10-fold increase in remote gamma-ray activation of 63Cu using a lead converter. In the third experiment measurements of un-trapped electrons with high transverse momentum produce a 500 mrad (FWHM) ring. This ring is formed by electrons that receive a forward momentum boost by traversing behind the bubble and its size is inversely proportional to the plasma density. The characterization of divergence and charge of this electron ring may reveal information about the wakefield structure and trapping potential. Supported by U.S. Department of Energy and the National Nuclear Security Administration and Air Force Office of Scientific Research.

Extending the reanalysis to the ionosphere based on ground and LEO based GNSS observations

NASA Astrophysics Data System (ADS)

Yue, X.; Schreiner, W. S.; Kuo, Y.

2012-12-01

We report preliminary results of a global 3-D ionospheric electron density reanalysis during 2002-2011 based on multi-source data assimilation. The monthly global ionospheric electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 hr in universal time, 5o in latitude, 10o in longitude, and ~ 30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content (GEC) derived from the international GNSS service (IGS) global ionospheric maps (GIM), the observed electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) during 2007-2010, and foF2 observed by the global ionosonde network during 2002-2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F-region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.

Exploring the Spatial and Temporal Organization of a Cell’s Proteome

PubMed Central

Beck, Martin; Topf, Maya; Frazier, Zachary; Tjong, Harianto; Xu, Min; Zhang, Shihua; Alber, Frank

2013-01-01

To increase our current understanding of cellular processes, such as cell signaling and division, knowledge is needed about the spatial and temporal organization of the proteome at different organizational levels. These levels cover a wide range of length and time scales: from the atomic structures of macromolecules for inferring their molecular function, to the quantitative description of their abundance, and distribution in the cell. Emerging new experimental technologies are greatly increasing the availability of such spatial information on the molecular organization in living cells. This review addresses three fields that have significantly contributed to our understanding of the proteome’s spatial and temporal organization: first, methods for the structure determination of individual macromolecular assemblies, specifically the fitting of atomic structures into density maps generated from electron microscopy techniques; second, research that visualizes the spatial distributions of these complexes within the cellular context using cryo electron tomography techniques combined with computational image processing; and third, methods for the spatial modeling of the dynamic organization of the proteome, specifically those methods for simulating reaction and diffusion of proteins and complexes in crowded intracellular fluids. The long-term goal is to integrate the varied data about a proteome’s organization into a spatially explicit, predictive model of cellular processes. PMID:21094684

Atomic-scale distortions and temperature-dependent large pseudogap in thin films of the parent iron-chalcogenide superconductor Fe1+y Te

NASA Astrophysics Data System (ADS)

Gerbi, Andrea; Buzio, Renato; Kawale, Shrikant; Bellingeri, Emilio; Martinelli, Alberto; Bernini, Cristina; Tresca, Cesare; Capone, Massimo; Profeta, Gianni; Ferdeghini, Carlo

2017-12-01

We investigate with scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT) calculations the surface structures and the electronic properties of Fe1+y Te thin films grown by pulsed laser deposition. Contrary to the regular arrangement of antiferromagnetic nanostripes previously reported on cleaved single-crystal samples, the surface of Fe1+y Te thin films displays a peculiar distribution of spatially inhomogeneous nanostripes. Both STM and DFT calculations show the bias-dependent nature of such features and support the interpretation of spin-polarized tunneling between the FeTe surface and an unintentionally magnetized tip. In addition, the spatial inhomogeneity is interpreted as a purely electronic effect related to changes in hybridization and Fe-Fe bond length driven by local variations in the concentration of excess interstitial Fe cations. Unexpectedly, the surface density of states measured by STS strongly evolves with temperature in close proximity to the antiferromagnetic-paramagnetic first-order transition, and reveals a large pseudogap of 180-250 meV at about 50-65 K. We believe that in this temperature range a phase transition takes place, and the system orders and locks into particular combinations of orbitals and spins because of the interplay between excess interstitial magnetic Fe and strongly correlated d-electrons.

Qualification and implementation of line ratio spectroscopy on helium as plasma edge diagnostic at ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Griener, M.; Muñoz Burgos, J. M.; Cavedon, M.; Birkenmeier, G.; Dux, R.; Kurzan, B.; Schmitz, O.; Sieglin, B.; Stroth, U.; Viezzer, E.; Wolfrum, E.; the ASDEX Upgrade Team

2018-02-01

A new thermal helium beam diagnostic has been implemented as plasma edge diagnostic at the ASDEX Upgrade (AUG) tokamak. The helium beam is built to measure the electron density n e and temperature T e simultaneously with high spatial and temporal resolution in order to investigate steady-state as well as fast transport processes in the plasma edge region. For the thermal helium beam emission line ratio spectroscopy, neutral helium is locally injected into the plasma by a piezo valve. This enabled the measurement of the line resolved emission intensities of seven He I lines for different plasma scenarios in AUG. The different line ratios can be used together with a collisional-radiative model (CRM) to reconstruct the underlying electron temperature and density. Ratios from the same spin species are used for the electron density reconstruction, whereas spin mixed ratios are sensitive to electron temperature changes. The different line ratios as well as different CRMs are tested for their suitability for diagnostic applications. Furthermore their consistency in calculating identical parameters is validated and the resulting profiles are compared to other available diagnostics at AUG.

An inverted cylindrical sputter magnetron as metal vapor supply for electron cyclotron resonance ion sources

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

Weichsel, T., E-mail: tim.weichsel@fep.fraunhofer.de; Hartung, U.; Kopte, T.

2014-05-15

An inverted cylindrical sputter magnetron device has been developed. The magnetron is acting as a metal vapor supply for an electron cyclotron resonance (ECR) ion source. FEM simulation of magnetic flux density was used to ensure that there is no critical interaction between both magnetic fields of magnetron and ECR ion source. Spatially resolved double Langmuir probe and optical emission spectroscopy measurements show an increase in electron density by one order of magnitude from 1 × 10{sup 10} cm{sup −3} to 1 × 10{sup 11} cm{sup −3}, when the magnetron plasma is exposed to the magnetic mirror field of themore » ECR ion source. Electron density enhancement is also indicated by magnetron plasma emission photography with a CCD camera. Furthermore, photographs visualize the formation of a localized loss-cone - area, when the magnetron is operated at magnetic mirror field conditions. The inverted cylindrical magnetron supplies a metal atom load rate of R > 1 × 10{sup 18} atoms/s for aluminum, which meets the demand for the production of a milliampere Al{sup +} ion beam.« less

The energy balance and pressure in the solar transition zone for network and active region features

NASA Technical Reports Server (NTRS)

Nicolas, K. R.; Bartoe, J.-D. F.; Brueckner, G. E.; Vanhoosier, M. E.

1979-01-01

The electron pressure and energy balance in the solar transition zone are determined for about 125 network and active region features on the basis of high spectral and spatial resolution extreme ultraviolet spectra. Si III line intensity ratios obtained from the Naval Research Laboratory high-resolution telescope and spectrograph during a rocket flight are used as diagnostics of electron density and pressure for solar features near 3.5 x 10 to the 4th K. Observed ratios are compared with the calculated dependence of the 1301 A/1312 A and 1301 A/1296 A line intensity ratios on electron density, temperature and pressure. Electron densities ranging from 2 x 10 to the 10th/cu cm to 10 to the 12th/cu cm and active region pressures from 3 x 10 to the 15th to 10 to the 16th/cu cm K are obtained. Energy balance calculations reveal the balance of the divergence of the conductive flux and turbulent energy dissipation by radiative energy losses in a plane-parallel homogeneous transition zone (fill factor of 1), and an energy source requirement for a cylindrical zone geometry (fill factor less than 0.04).

Mapping the Physical and Chemical Conditions of the Ring Nebula

NASA Astrophysics Data System (ADS)

Leal-Ferreira, Marcelo L.; Aleman, Isabel; Gaughan, Andrea; Ladjal, Djazia; Ueta, Toshiya; Kerber, Samuel; Conn, Blair; Gardiner, Rhiannon; Tielens, Alexander G. G. M.

2017-10-01

We observed the Planetary Nebula NGC 6720 with the Gemini Telescope and the Gemini Multi-Object Spectrographs. We obtained spatial maps of 36 emission-lines in the wavelength range between 3600 Å and 9400 Å. We derived maps of c(Hβ), electronic densities, electronic temperatures, ionic and elemental abundances, and Ionization Correction Factors (ICFs) in the source and investigated the mass-loss history of the progenitor. The elemental abundance results indicate the need for ICFs based on three-dimensional photoionization models.

Effect of Variation of Silicon Nitride Passivation Layer on Electron Irradiated Aluminum Gallium Nitride/Gallium Nitride HEMT Structures

DTIC Science & Technology

2014-06-19

the AlGaN is unintentionally doped . Figure 2.3. AlGaN/GaN band diagram showing polarization charges. The band diagram in Figure 2.3 shows...intentionally doped as are MESFETS, and the channel gets its electrons from the unintentional doping . There is less Coulomb scattering in the...temperature measurements are often used to provide spatial PL maps of doping and trap densities. Laser excitation (quasi-monochromatic) is

Dissipative transport in superlattices within the Wigner function formalism

DOE PAGES

Jonasson, O.; Knezevic, I.

2015-07-30

Here, we employ the Wigner function formalism to simulate partially coherent, dissipative electron transport in biased semiconductor superlattices. We introduce a model collision integral with terms that describe energy dissipation, momentum relaxation, and the decay of spatial coherences (localization). Based on a particle-based solution to the Wigner transport equation with the model collision integral, we simulate quantum electronic transport at 10 K in a GaAs/AlGaAs superlattice and accurately reproduce its current density vs field characteristics obtained in experiment.

Heater-induced ionization inferred from spectrometric airglow measurements

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Miceli, R. J.; Kendall, E. A.; Schlatter, N. M.; Varney, R. H.; Watkins, B. J.; Pedersen, T. R.; Bernhardt, P. A.; Huba, J. D.

2014-03-01

Spectrographic airglow measurements were made during an ionospheric modification experiment at High Frequency Active Auroral Research Program on 12 March 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert (1968, 1970), we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with heater-induced ionization in view of the spatial intermittency of the airglow.

Tip-induced reduction of the resonant tunneling current on semiconductor surfaces.

PubMed

Jelínek, Pavel; Svec, Martin; Pou, Pablo; Perez, Ruben; Cháb, Vladimír

2008-10-24

We report scanning tunneling microscope measurements showing a substantial decrease of the current, almost to zero, on the Si(111)-(7x7) reconstruction in the near-to-contact region under low bias conditions. First principles simulations for the tip-sample interaction and transport calculations show that this effect is driven by the substantial local modification of the atomic and electronic structure of the surface. The chemical reactivity of the adatom dangling bond states that dominate the electronic density of states close to the Fermi level and their spatial localization result in a strong modification of the electronic current.

Multidimensional Attosecond Resonant X-Ray Spectroscopy of Molecules: Lessons from the Optical Regime

PubMed Central

Mukamel, Shaul; Healion, Daniel; Zhang, Yu; Biggs, Jason D.

2013-01-01

New free-electron laser and high-harmonic generation X-ray light sources are capable of supplying pulses short and intense enough to perform resonant nonlinear time-resolved experiments in molecules. Valence-electron motions can be triggered impulsively by core excitations and monitored with high temporal and spatial resolution. We discuss possible experiments that employ attosecond X-ray pulses to probe the quantum coherence and correlations of valence electrons and holes, rather than the charge density alone, building on the analogy with existing studies of vibrational motions using femtosecond techniques in the visible regime. PMID:23245522

The synchrotron-self-Compton process in spherical geometries. I - Theoretical framework

NASA Technical Reports Server (NTRS)

Band, D. L.; Grindlay, J. E.

1985-01-01

Both spatial and spectral accuracies are stressed in the present method for the calculation of the synchrotron-self-Compton model in spherical geometries, especially in the partially opaque regime of the synchrotron spectrum of inhomogeneous sources that can span a few frequency decades and contribute a significant portion of the scattered flux. A formalism is developed that permits accurate calculation of incident photon density throughout an optically thin sphere. An approximation to the Klein-Nishina cross section is used to model the effects of variable electron and incident photon cutoffs, as well as the decrease in the cross section at high energies. General results are derived for the case of inhomogeneous sources with power law profiles in both electron density and magnetic field.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings

NASA Astrophysics Data System (ADS)

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-01

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter rS is increased, we observe—at a fixed spin magnetic moment—the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing rS. We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical rSc at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing rS the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.

Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings.

PubMed

Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

2011-08-24

We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid. © 2011 IOP Publishing Ltd

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

Kim, Jaekyun; Kim, Myung -Gil; Kim, Jaehyun

The success of silicon based high density integrated circuits ignited explosive expansion of microelectronics. Although the inorganic semiconductors have shown superior carrier mobilities for conventional high speed switching devices, the emergence of unconventional applications, such as flexible electronics, highly sensitive photosensors, large area sensor array, and tailored optoelectronics, brought intensive research on next generation electronic materials. The rationally designed multifunctional soft electronic materials, organic and carbon-based semiconductors, are demonstrated with low-cost solution process, exceptional mechanical stability, and on-demand optoelectronic properties. Unfortunately, the industrial implementation of the soft electronic materials has been hindered due to lack of scalable fine-patterning methods. Inmore » this report, we demonstrated facile general route for high throughput sub-micron patterning of soft materials, using spatially selective deep-ultraviolet irradiation. For organic and carbon-based materials, the highly energetic photons (e.g. deep-ultraviolet rays) enable direct photo-conversion from conducting/semiconducting to insulating state through molecular dissociation and disordering with spatial resolution down to a sub-μm-scale. As a result, the successful demonstration of organic semiconductor circuitry promise our result proliferate industrial adoption of soft materials for next generation electronics.« less

Bound and resonance states of the dipolar anion of hydrogen cyanide: Competition between threshold effects and rotation in an open quantum system

DOE PAGES

Fossez, K.; Michel, N.; Nazarewicz, W.; ...

2015-01-12

In this paper, bound and resonance states of the dipole-bound anion of hydrogen cyanide HCN – are studied using a nonadiabatic pseudopotential method and the Berggren expansion technique involving bound states, decaying resonant states, and nonresonant scattering continuum. We devise an algorithm to identify the resonant states in the complex energy plane. To characterize spatial distributions of electronic wave functions, we introduce the body-fixed density and use it to assign families of resonant states into collective rotational bands. We find that the nonadiabatic coupling of electronic motion to molecular rotation results in a transition from the strong-coupling to weak-coupling regime.more » In the strong-coupling limit, the electron moving in a subthreshold, spatially extended halo state follows the rotational motion of the molecule. Above the ionization threshold, the electron's motion in a resonance state becomes largely decoupled from molecular rotation. Finally, the widths of resonance-band members depend primarily on the electron orbital angular momentum.« less

Design, modeling, and diagnostics of microplasma generation at microwave frequency

NASA Astrophysics Data System (ADS)

Miura, Naoto

Plasmas are partially ionized gases that find wide utility in the processing of materials, especially in integrated circuit fabrication. Most industrial applications of plasma occur in near-vacuum where the electrons are hot (>10,000 K) but the gas remains near room temperature. Typical atmospheric plasmas, such as arcs, are hot and destructive to sensitive materials. Recently the emerging field of microplasmas has demonstrated that atmospheric ionization of cold gases is possible if the plasma is microscopic. This dissertation investigates the fundamental physical properties of two classes of microplasma, both driven by microwave electric fields. The extension of point-source microplasmas into a line-shaped plasma is also described. The line-shape plasma is important for atmospheric processing of materials using roll-coating. Microplasma generators driven near 1 GHz were designed using microstrip transmission lines and characterized using argon near atmospheric pressure. The electrical characteristics of the microplasma including the discharge voltage, current and resistance were estimated by comparing the experimental power reflection coefficient to that of an electromagnetic simulation. The gas temperature, argon metastable density and electron density were obtained by optical absorption and emission spectroscopy. The microscopic internal plasma structure was probed using spatially-resolved diode laser absorption spectroscopy of excited argon states. The spatially resolved diagnostics revealed that argon metastable atoms were depleted within the 200mum core of the microplasma where the electron density was maximum. Two microplasma generators, the split-ring resonator (SRR) and the transmission line (T-line) generator, were compared. The SRR ran efficiently with a high impedance plasma (>1000 O) and was stabilized by the self-limiting of absorbed power (<1W) as a lower impedance plasma caused an impedance mismatch. Gas temperatures were <1000 K and electron densities were ~1020 m-3, conditions which are favorable for treatment of delicate materials. The T-line generator ran most efficiently with an intense, low impedance plasma that matched the impedance of the T-line (35 O). With the T-line generator, the absorbed power could exceed 20W, which created an electron density of 1021 m-3, but the gas temperature exceeded 2000 K. Finally, line-shaped microplasmas based on resonant and non-resonant configurations were developed, tested, and analyzed.

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

NASA Astrophysics Data System (ADS)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III bursts to be more frequently observed. The large instability distances required before Langmuir waves are produced by some electron beams, and the small magnitude of the background density gradients makes closed loops less facilitative for radio emission than loops that extend into interplanetary space.

Density functional with full exact exchange, balanced nonlocality of correlations, and constraint satisfaction

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

Tao, Jianmin; Perdew, John P; Staroverov, Viktor N

2008-01-01

We construct a nonlocal density functional approximation with full exact exchange, while preserving the constraint-satisfaction approach and justified error cancellations of simpler semilocal functionals. This is achieved by interpolating between different approximations suitable for two extreme regions of the electron density. In a 'normal' region, the exact exchange-correlation hole density around an electron is semilocal because its spatial range is reduced by correlation and because it integrates over a narrow range to -1. These regions are well described by popular semilocal approximations (many of which have been constructed nonempirically), because of proper accuracy for a slowly-varying density or because ofmore » error cancellation between exchange and correlation. 'Abnormal' regions, where non locality is unveiled, include those in which exchange can dominate correlation (one-electron, nonuniform high-density, and rapidly-varying limits), and those open subsystems of fluctuating electron number over which the exact exchange-correlation hole integrates to a value greater than -1. Regions between these extremes are described by a hybrid functional mixing exact and semi local exchange energy densities locally (i.e., with a mixing fraction that is a function of position r and a functional of the density). Because our mixing fraction tends to 1 in the high-density limit, we employ full exact exchange according to the rigorous definition of the exchange component of any exchange-correlation energy functional. Use of full exact exchange permits the satisfaction of many exact constraints, but the nonlocality of exchange also requires balanced nonlocality of correlation. We find that this nonlocality can demand at least five empirical parameters (corresponding roughly to the four kinds of abnormal regions). Our local hybrid functional is perhaps the first accurate size-consistent density functional with full exact exchange. It satisfies other known exact constraints, including exactness for all one-electron densities, and provides an excellent, fit 1.0 the 223 molecular enthalpies of formation of the G3/99 set and the 42 reaction barrier heights of the BH42/03 set, improving both (but especially the latter) over most semilocal functionals and global hybrids. Exact constraints, physical insights, and paradigm examples hopefully suppress 'overfitting'.« less

Alkali-metal induced band structure deformation investigated by angle-resolved photoemission spectroscopy and first-principles calculations

NASA Astrophysics Data System (ADS)

Ito, S.; Feng, B.; Arita, M.; Someya, T.; Chen, W.-C.; Takayama, A.; Iimori, T.; Namatame, H.; Taniguchi, M.; Cheng, C.-M.; Tang, S.-J.; Komori, F.; Matsuda, I.

2018-04-01

Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials.

Tracking of an electron beam through the solar corona with LOFAR

NASA Astrophysics Data System (ADS)

Mann, G.; Breitling, F.; Vocks, C.; Aurass, H.; Steinmetz, M.; Strassmeier, K. G.; Bisi, M. M.; Fallows, R. A.; Gallagher, P.; Kerdraon, A.; Mackinnon, A.; Magdalenic, J.; Rucker, H.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Best, P.; Bîrzan, L.; Bonafede, A.; Broderick, J. W.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Gasperin, F. de; Geus, E. de; Deller, A.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Gunst, A. W.; van Haarlem, M.; Hassall, T. E.; Heald, G.; Hessels, J. W. T.; Hoeft, M.; Hörandel, J.; Horneffer, A.; Juette, E.; Karastergiou, A.; Klijn, W. F. A.; Kondratiev, V. I.; Kramer, M.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Markoff, S.; McFadden, R.; McKay-Bukowski, D.; McKean, J. P.; Mulcahy, D. D.; Munk, H.; Nelles, A.; Norden, M. J.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A. G.; Rafferty, D.; Reich, W.; Röttgering, H.; Scaife, A. M. M.; Schwarz, D. J.; Serylak, M.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Tagger, M.; Tang, Y.; Tasse, C.; ter Veen, S.; Thoudam, S.; Toribio, M. C.; Vermeulen, R.; van Weeren, R. J.; Wise, M. W.; Wucknitz, O.; Yatawatta, S.; Zarka, P.; Zensus, J. A.

2018-03-01

The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).

Free-electron-laser coherent diffraction images of individual drug-carrying liposome particles in solution.

PubMed

Huang, Chi-Feng; Liang, Keng S; Hsu, Tsui-Ling; Lee, Tsung-Tse; Chen, Yi-Yun; Yang, Shun-Min; Chen, Hsiang-Hsin; Huang, Shih-Hsin; Chang, Wei-Hau; Lee, Ting-Kuo; Chen, Peilin; Peng, Kuei-En; Chen, Chien-Chun; Shi, Cheng-Zhi; Hu, Yu-Fang; Margaritondo, Giorgio; Ishikawa, Tetsuya; Wong, Chi-Huey; Hwu, Y

2018-02-08

Using the excellent performances of a SACLA (RIKEN/HARIMA, Japan) X-ray free electron laser (X-FEL), coherent diffraction imaging (CDI) was used to detect individual liposome particles in water, with or without inserted doxorubicin nanorods. This was possible because of the electron density differences between the carrier, the liposome, and the drug. The result is important since liposome nanocarriers at present dominate drug delivery systems. In spite of the low cross-section of the original ingredients, the diffracted intensity of drug-free liposomes was sufficient for spatial reconstruction yielding quantitative structural information. For particles containing doxorubicin, the structural parameters of the nanorods could be extracted from CDI. Furthermore, the measurement of the electron density of the solution enclosed in each liposome provides direct evidence of the incorporation of ammonium sulphate into the nanorods. Overall, ours is an important test for extending the X-FEL analysis of individual nanoparticles to low cross-sectional systems in solution, and also for its potential use to optimize the manufacturing of drug nanocarriers.

Negative differential resistance and switch behavior of T-BxNy (x, y = 5, 6, 11) molecular junctions

NASA Astrophysics Data System (ADS)

Wang, Shi-Liang; Yang, Chuan-Lu; Wang, Mei-Shan; Ma, Xiao-Guang; Xin, Jian-Guo

2017-05-01

The electronic transport properties of T-BxNy (x, y = 5, 6, 11) molecular junction are investigated based on first-principle density functional theory and non-equilibrium Green's function method. Strong negative differential resistance (NDR) behavior is observed for T-B5N6 molecule under negative and positive bias voltages, with an obvious switch effect for T-B6N5. However, only small NDR is shown for the complex of the two molecules. The projected device density of states, the spatial distribution of molecular orbitals, and the effect of transmission spectra under various bias voltages on the electronic transport properties are analyzed. The obvious effect of bias voltage on the changes in the electronic distribution of frontier molecular orbitals is responsible for the NDR or switch behavior. Therefore, different functional molecular devices can be obtained with different structures of T-BxNy.

Multiple loss processes of relativistic electrons outside the heart of outer radiation belt during a storm sudden commencement

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

Yu, J.; Li, L. Y.; Cao, J. B.

By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2 MeV) outside the heart of outer radiation belt (L*≥5) undergo multiple losses during a storm sudden commencement. The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α < 30° or >150°), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°–150° increase (decrease) with the decreasingmore » (increasing) geocentric distance (|ΔL|<0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2–10 min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850 km), and magnetic field fluctuations in the Pc5 band. Finally, the intense EMIC waves and whistler mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 h. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient.« less

Multiple loss processes of relativistic electrons outside the heart of outer radiation belt during a storm sudden commencement

DOE PAGES

Yu, J.; Li, L. Y.; Cao, J. B.; ...

2015-11-10

By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2 MeV) outside the heart of outer radiation belt (L*≥5) undergo multiple losses during a storm sudden commencement. The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α < 30° or >150°), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°–150° increase (decrease) with the decreasingmore » (increasing) geocentric distance (|ΔL|<0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2–10 min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850 km), and magnetic field fluctuations in the Pc5 band. Finally, the intense EMIC waves and whistler mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 h. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient.« less

Scale-invariant puddles in graphene: Geometric properties of electron-hole distribution at the Dirac point.

PubMed

Najafi, M N; Nezhadhaghighi, M Ghasemi

2017-03-01

We characterize the carrier density profile of the ground state of graphene in the presence of particle-particle interaction and random charged impurity in zero gate voltage. We provide detailed analysis on the resulting spatially inhomogeneous electron gas, taking into account the particle-particle interaction and the remote Coulomb disorder on an equal footing within the Thomas-Fermi-Dirac theory. We present some general features of the carrier density probability measure of the graphene sheet. We also show that, when viewed as a random surface, the electron-hole puddles at zero chemical potential show peculiar self-similar statistical properties. Although the disorder potential is chosen to be Gaussian, we show that the charge field is non-Gaussian with unusual Kondev relations, which can be regarded as a new class of two-dimensional random-field surfaces. Using Schramm-Loewner (SLE) evolution, we numerically demonstrate that the ungated graphene has conformal invariance and the random zero-charge density contours are SLE_{κ} with κ=1.8±0.2, consistent with c=-3 conformal field theory.

Self-consistent discharge growing model of helicon plasma

NASA Astrophysics Data System (ADS)

Isayama, Shogo; Hada, Tohru; Shinohara, Shunjiro; Tanikawa, Takao

2015-11-01

Helicon plasma is a high-density and low-temperature plasma generated by the electromagnetic (Helicon) wave excited in the plasma. It is thought to be useful for various applications including electric thrusters. Physics of helicon plasma production involves such fundamental processes as the wave propagation (dispersion relation), collisional and non-collisional wave damping, plasma heating, ionization/recombination of neutral particles, and modification of the dispersion relation by newly ionized plasma. There remain a number of unsolved physical issues such as, how the Helicon and the TG modes influence the plasma density, electron temperature and their spatial profiles. While the Helicon mode is absorbed in the bulk plasma, the TG mode is mostly absorbed near the edge of the plasma. The local power deposition in the helicon plasma is mostly balanced by collisional loss. This local power balance can give rise to the inhomogeneous electron temperature profile that leads to time evolution of density profile and dispersion relation. In our study, we construct a self-consistent model of the discharge evolution that includes the wave excitation, electron heat transfer, and diffusion of charged particles.

Precipitating auroral electrons and lower thermospheric nitric oxide densities: SNOE, POLAR, SAMPEX, and NOAA/POES Comparisons for Geomagnetic Storms in 1998-2001

NASA Astrophysics Data System (ADS)

Baker, D. N.; Fisher, T. A.; Barth, C. A.; Mankoff, K. D.; Kanekal, S. G.; Bailey, S. M.; Petrinec, S. M.; Luhmann, J. G.; Mason, G. M.; Mazur, J. E.; Evans, D. S.

2002-05-01

Nitric oxide (NO) densities measured at altitudes between 97 and 150 km have been acquired using the UVS sensor onboard the Student Nitric Oxide Explorer (SNOE) spacecraft during the years 1998-2001. These data are compared with energetic electron fluxes (E>25 keV) measured concurrently using a sensitive sensor system (LICA) onboard the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) spacecraft. Geomagnetic storm intervals are examined to determine altitude and latitude variations of NO density as it compares to energetic electron precipitation. A broader statistical analysis is then carried out using daily averages of peak NO densities (at 106 km altitudes) and electron intensities measured by SAMPEX/LICA and by the TED sensor system onboard the NOAA/Polar Orbiting Environmental Satellite (POES) spacecraft. We also use the PIXIE instrument onboard POLAR to obtain global views of 2-12 keV x-rays emanating from the upper atmosphere. This gives a broad synoptic measure of relatively low-energy electron precipitation into the atmosphere. Latitude versus time displays of the UVS, PIXIE, LICA and TED data show excellent temporal and spatial correlations of the data sets. More detailed comparisons help us to assess spectral and local time relationships between auroral particle inputs and lower thermospheric chemical responses. These results are potentially quite important since past modeling has shown that particle inputs are significant for changing the chemistry and subsequent dynamics of the atmosphere.

Two color interferometric electron density measurement in an axially blown arc

NASA Astrophysics Data System (ADS)

Stoller, Patrick; Carstensen, Jan; Galletti, Bernardo; Doiron, Charles; Sokolov, Alexey; Salzmann, René; Simon, Sandor; Jabs, Philipp

2016-09-01

High voltage circuit breakers protect the power grid by interrupting the current in case of a short circuit. To do so an arc is ignited between two contacts as they separate; transonic gas flow is used to cool and ultimately extinguish the arc at a current-zero crossing of the alternating current. A detailed understanding of the arc interruption process is needed to improve circuit breaker design. The conductivity of the partially ionized gas remaining after the current-zero crossing, a key parameter in determining whether the arc will be interrupted or not, is a function of the electron density. The electron density, in turn, is a function of the detailed dynamics of the arc cooling process, which does not necessarily occur under local thermodynamic equilibrium (LTE) conditions. In this work, we measure the spatially resolved line-integrated index of refraction in a near-current-zero arc stabilized in an axial flow of synthetic air with two nanosecond pulsed lasers at wavelengths of 532 nm and 671 nm. Generating a stable, cylindrically symmetric arc enables us to determine the three-dimensional index of refraction distribution using Abel inversion. Due to the wavelength dependence of the component of the index of refraction related to the free electrons, the information at two different wavelengths can be used to determine the electron density. This information allows us to determine how important it is to take into account non-equilibrium effects for accurate modeling of the physics of decaying arcs.

Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states.

PubMed

Moerland, Robert J; Weppelman, I Gerward C; Garming, Mathijs W H; Kruit, Pieter; Hoogenboom, Jacob P

2016-10-17

We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial hardware in a standard SEM, which allows us to easily switch from pulsed to continuous operation of the SEM. Electron pulses of 80-90 ps duration are generated by conjugate blanking of a high-brightness electron beam, which allows probing emitters within a large range of decay rates. Moreover, we simultaneously attain a resolution better than λ/10, which ensures details at deep-subwavelength scales can be retrieved. As a proof-of-principle, we employ the pulsed electron beam to spatially measure excited-state lifetime modifications in a phosphor material across the edge of an aluminum half-plane, coated on top of the phosphor. The measured emission dynamics can be directly related to the structure of the sample by recording photon arrival histograms together with the secondary-electron signal. Our results show that time-resolved electron cathodoluminescence spectroscopy is a powerful tool of choice for nanophotonics, within reach of a large audience.

Electron Temperature Gradient Scale Measurements in ICRF Heated Plasmas at Alcator C-Mod

NASA Astrophysics Data System (ADS)

Houshmandyar, Saeid; Phillips, Perry E.; Rowan, William L.; Howard, Nathaniel T.; Greenwald, Martin

2016-10-01

It is generally believed that the temperature gradient is a driving mechanism for the turbulent transport in hot and magnetically confined plasmas. A feature of many anomalous transport models is the critical threshold value (LC) for the gradient scale length, above which both the turbulence and the heat transport increases. This threshold is also predicted by the recent multi-scale gyrokinetic simulations, which are focused on addressing the electron (and ion) heat transport in tokamaks. Recently, we have established an accurate technique (BT-jog) to directly measure the electron temperature gradient scale length (LTe =Te / ∇T) profile, using a high-spatial resolution radiometer-based electron cyclotron emission (ECE) diagnostic. For the work presented here, electrons are heated by ion cyclotron range of frequencies (ICRF) through minority heating in L-mode plasmas at different power levels, TRANSP runs determine the electron heat fluxes and the scale lengths are measured through the BT-jog technique. Furthermore, the experiment is extended for different plasma current and electron densities by which the parametric dependence of LC on magnetic shear, safety factor and density will be investigated. This work is supported by U.S. DoE OFES, under Award No. DE-FG03-96ER-54373.

Small-scale plasma irregularities in the nightside Venus ionosphere

NASA Astrophysics Data System (ADS)

Grebowsky, J. M.; Curtis, S. A.; Brace, L. H.

1991-12-01

The individual volt-ampere curves from the Pioneer Venus Orbiter electron temperature probe showed evidence for small-scale density irregularities, or short-period plasma waves, in regions of the nightside ionosphere where the Orbiter electric field detector observed waves in its 100-Hz channel. A survey of the nightside volt-ampere curves has revealed several hundred examples of such irregularities. The I-V structures correspond to plasma density structure with spatial scale sizes in the range of about 100-2000 m, or alternatively they could be viewed as waves having frequencies extending toward 100 Hz. They are often seen as isolated events, with spatial extent along the orbit frequently less than 80 km. The density irregularities or waves occur in or near prominent gradients in the ambient plasma concentrations both at low altitudes where molecular ions are dominant and at higher altitudes in regions of reduced plasma density where O(+) is the major ion. Electric field 100-Hz bursts occur simultaneously, with the majority of the structured I-V curves providing demonstrative evidence that at least some of the E field signals are produced within the ionosphere.

Spatial distribution of CH3 and CH2 radicals in a methane rf discharge

NASA Astrophysics Data System (ADS)

Sugai, H.; Kojima, H.; Ishida, A.; Toyoda, H.

1990-06-01

Spatial distributions of neutral radicals CH3 and CH2 in a capacitively coupled rf glow discharge of methane were measured by threshold ionization mass spectrometry. A strong asymmetry of the density profile was found for the CH2 radical in the high-pressure (˜100 mTorr) discharge. In addition, comprehensive measurements of electron energy distribution, ionic composition, and radical sticking coefficient were made to use as inputs to theoretical modeling of radicals in the methane plasma. The model predictions agree substantially with the measured radical distributions.

Spatial Structure of Large-Scale Plasma Density Perturbations HF-Induced in the Ionospheric F 2 Region

NASA Astrophysics Data System (ADS)

Frolov, V. L.; Komrakov, G. P.; Glukhov, Ya. V.; Andreeva, E. S.; Kunitsyn, V. E.; Kurbatov, G. A.

2016-07-01

We consider the experimental results obtained by studying the large-scale structure of the HF-disturbed ionospheric region. The experiments were performed using the SURA heating facility. The disturbed ionospheric region was sounded by signals radiated by GPS navigation satellite beacons as well as by signals of low-orbit satellites (radio tomography). The results of the experiments show that large-scale plasma density perturbations induced at altitudes higher than the F2 layer maximum can contribute significantly to the measured variations of the total electron density and can, with a certain arrangement of the reception points, be measured by the GPS sounding method.

Spatial mapping and statistical reproducibility of an array of 256 one-dimensional quantum wires

NASA Astrophysics Data System (ADS)

Al-Taie, H.; Smith, L. W.; Lesage, A. A. J.; See, P.; Griffiths, J. P.; Beere, H. E.; Jones, G. A. C.; Ritchie, D. A.; Kelly, M. J.; Smith, C. G.

2015-08-01

We utilize a multiplexing architecture to measure the conductance properties of an array of 256 split gates. We investigate the reproducibility of the pinch off and one-dimensional definition voltage as a function of spatial location on two different cooldowns, and after illuminating the device. The reproducibility of both these properties on the two cooldowns is high, the result of the density of the two-dimensional electron gas returning to a similar state after thermal cycling. The spatial variation of the pinch-off voltage reduces after illumination; however, the variation of the one-dimensional definition voltage increases due to an anomalous feature in the center of the array. A technique which quantifies the homogeneity of split-gate properties across the array is developed which captures the experimentally observed trends. In addition, the one-dimensional definition voltage is used to probe the density of the wafer at each split gate in the array on a micron scale using a capacitive model.

High-resolution imaging of a shock front in plastic by phase contrast imaging at LCLS

NASA Astrophysics Data System (ADS)

Beckwith, M.; Jiang, S.; Zhao, Y.; Schropp, A.; Fernandez-Panella, A.; Rinderknecht, H. G.; Wilks, S.; Fournier, K.; Galtier, E.; Xing, Z.; Granados, E.; Gamboa, E.; Glenzer, S. H.; Heimann, P.; Zastrau, U.; Cho, B. I.; Eggert, J. H.; Collins, G. W.; Ping, Y.

2017-10-01

Understanding the propagation of shock waves is important for many areas of high energy density physics, including inertial confinement fusion (ICF) and shock compression science. In order to probe the shock front structures in detail, a diagnostic capable of detecting both the small spatial and temporal changes in the material is required. Here we show the experiment using hard X-ray phase contrast imaging (PCI) to probe the shock wave propagation in polyimide with submicron spatial resolution. The experiment was performed at the Matter in Extreme Conditions (MEC) endstation of the Linac Coherent Lightsource (LCLS). PCI together with the femtosecond time scales of x-ray free electron lasers enables the imaging of optically opaque materials that undergo rapid temporal and spatial changes. The result reveals the evolution of the density profile with time. Work performed under DOE Contract No. DE-AC52-07NA27344 with support from OFES Early Career and LLNL LDRD program.

Axial- and radial-resolved electron density and excitation temperature of aluminum plasma induced by nanosecond laser: Effect of the ambient gas composition and pressure

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

Dawood, Mahmoud S.; Hamdan, Ahmad, E-mail: ahmad.ba.hamdan@gmail.com, E-mail: Joelle.margot@umontreal.ca; Margot, Joëlle, E-mail: ahmad.ba.hamdan@gmail.com, E-mail: Joelle.margot@umontreal.ca

2015-11-15

The spatial variation of the characteristics of an aluminum plasma induced by a pulsed nanosecond XeCl laser is studied in this paper. The electron density and the excitation temperature are deduced from time- and space- resolved Stark broadening of an ion line and from a Boltzmann diagram, respectively. The influence of the gas pressure (from vacuum up to atmospheric pressure) and compositions (argon, nitrogen and helium) on these characteristics is investigated. It is observed that the highest electron density occurs near the laser spot and decreases by moving away both from the target surface and from the plume center tomore » its edge. The electron density increases with the gas pressure, the highest values being occurred at atmospheric pressure when the ambient gas has the highest mass, i.e. in argon. The excitation temperature is determined from the Boltzmann plot of line intensities of iron impurities present in the aluminum target. The highest temperature is observed close to the laser spot location for argon at atmospheric pressure. It decreases by moving away from the target surface in the axial direction. However, no significant variation of temperature occurs along the radial direction. The differences observed between the axial and radial direction are mainly due to the different plasma kinetics in both directions.« less

High density plasmas and new diagnostics: An overview (invited).

PubMed

Celona, L; Gammino, S; Mascali, D

2016-02-01

One of the limiting factors for the full understanding of Electron Cyclotron Resonance Ion Sources (ECRISs) fundamental mechanisms consists of few types of diagnostic tools so far available for such compact machines. Microwave-to-plasma coupling optimisation, new methods of density overboost provided by plasma wave generation, and magnetostatic field tailoring for generating a proper electron energy distribution function, suitable for optimal ion beams formation, require diagnostic tools spanning across the entire electromagnetic spectrum from microwave interferometry to X-ray spectroscopy; these methods are going to be implemented including high resolution and spatially resolved X-ray spectroscopy made by quasi-optical methods (pin-hole cameras). The ion confinement optimisation also requires a complete control of cold electrons displacement, which can be performed by optical emission spectroscopy. Several diagnostic tools have been recently developed at INFN-LNS, including "volume-integrated" X-ray spectroscopy in low energy domain (2-30 keV, by using silicon drift detectors) or high energy regime (>30 keV, by using high purity germanium detectors). For the direct detection of the spatially resolved spectral distribution of X-rays produced by the electronic motion, a "pin-hole camera" has been developed also taking profit from previous experiences in the ECRIS field. The paper will give an overview of INFN-LNS strategy in terms of new microwave-to-plasma coupling schemes and advanced diagnostics supporting the design of new ion sources and for optimizing the performances of the existing ones, with the goal of a microwave-absorption oriented design of future machines.

Phenomenological theory of laser-plasma interaction in ``bubble'' regime

NASA Astrophysics Data System (ADS)

Kostyukov, I.; Pukhov, A.; Kiselev, S.

2004-11-01

The electron trapping in the "bubble" regime of laser-plasma interaction as proposed by Pukhov and Meyer-ter-Vehn [A. Pukhov and J. Meyer-ter-Vehn, Appl. Phys. B 74, 355 (2002)] is studied. In this regime the laser pulse generates a solitary plasma electron cavity: the bubble. It is free from the cold plasma electrons and runs with nearly light velocity. The present work discusses the form of the bubble and the spatial distribution of electromagnetic fields within the cavity. We extend the one-dimensional electron capture theory to the three-dimensional case. It is shown that the bubble can trap plasma electrons. The trapping condition is derived and the trapping cross section is estimated. Electron motion in the self-generated electron bunch is investigated. Estimates for the maximum of electron bunch energy and the bunch density are provided.

Electron transfer in a virtual quantum state of LiBH4 induced by strong optical fields and mapped by femtosecond x-ray diffraction.

PubMed

Stingl, J; Zamponi, F; Freyer, B; Woerner, M; Elsaesser, T; Borgschulte, A

2012-10-05

Transient polarizations connected with a spatial redistribution of electronic charge in a mixed quantum state are induced by optical fields of high amplitude. We determine for the first time the related transient electron density maps, applying femtosecond x-ray powder diffraction as a structure probe. The prototype ionic material LiBH4 driven nonresonantly by an intense sub-40 fs optical pulse displays a large-amplitude fully reversible electron transfer from the BH4(-) anion to the Li+ cation during excitation. Our results establish this mechanism as the source of the strong optical polarization which agrees quantitatively with theoretical estimates.

Gas-filled capillaries for plasma-based accelerators

NASA Astrophysics Data System (ADS)

Filippi, F.; Anania, M. P.; Brentegani, E.; Biagioni, A.; Cianchi, A.; Chiadroni, E.; Ferrario, M.; Pompili, R.; Romeo, S.; Zigler, A.

2017-07-01

Plasma Wakefield Accelerators are based on the excitation of large amplitude plasma waves excited by either a laser or a particle driver beam. The amplitude of the waves, as well as their spatial dimensions and the consequent accelerating gradient depend strongly on the background electron density along the path of the accelerated particles. The process needs stable and reliable plasma sources, whose density profile must be controlled and properly engineered to ensure the appropriate accelerating mechanism. Plasma confinement inside gas filled capillaries have been studied in the past since this technique allows to control the evolution of the plasma, ensuring a stable and repeatable plasma density distribution during the interaction with the drivers. Moreover, in a gas filled capillary plasma can be pre-ionized by a current discharge to avoid ionization losses. Different capillary geometries have been studied to allow the proper temporal and spatial evolution of the plasma along the acceleration length. Results of this analysis obtained by varying the length and the number of gas inlets will be presented.

Evolution of star formation conditions from high-redshift to low-redshift

NASA Astrophysics Data System (ADS)

Shirazi, Maryam

2015-08-01

There are some hints indicating extreme interstellar medium (ISM) conditions at high redshift e.g., harder ionsing radiation fields and higher electron densities. By analysing the ionisation state of galaxies using their [OIII]5007/[OII]3727 line ratios we recently showed that star-forming galaxies at z~ 1. 5 -- 3. 5 have higher ionisation parameters and higher gas densities relative to that of local galaxies with similar global properties (Shirazi et al. 2014). This means the intrinsic properties e.g., the density of star forming regions at high redshift is different from what we observe in the local Universe. Based on the distribution of galaxies in the BPT diagram, it is proposed that the transition to nearby like conditions happen at 0. 8 < z < 1. 5 (Kewley et al 2013). However, we do not know how star-forming regions of the intermediate redshift galaxies are compared to that of high redshift galaxies that have higher gas fractions and are close to the peak of star formation activity in the Universe. We use the unique capability of the MUSE to indirectly trace the ISM conditions at those redshifts. We measure the spatially-resolved ionisation parameter using [OIII ]5007/ [O II]3727 ratio and we measure the spatially resolved gas density using the [OII] 3727,3729 doublet. We probe the spatial distributions of the ionisation parameter and gas density and search for systematic differences between high, intermediate and low redshift galaxies in terms of their global galaxy properties.

Ionospheric TEC Weather Map Over South America

NASA Astrophysics Data System (ADS)

Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; de Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

2016-11-01

Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

Electron Currents and Heating in the Ion Diffusion Region of Asymmetric Reconnection

NASA Technical Reports Server (NTRS)

Graham, D. B.; Khotyaintsev, Yu. V.; Norgren, C.; Vaivads, A.; Andre, M.; Lindqvist, P. A.; Marklund, G. T.; Ergun, R. E.; Paterson, W. R.; Gershman, D. J.;

Bohm velocity in the presence of a hot cathode

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

Palacio Mizrahi, J. H.; Krasik, Ya. E.

2013-08-15

The spatial distribution of the plasma and beam electrons in a region whose extension from a hot cathode is larger than the Debye length, but smaller than the electron mean free path, is analyzed. In addition, the influence of electrons thermionically emitted from a hot cathode and the ratio of electron-to-ion mass on the Bohm velocity and on the ion and electron densities at the plasma-sheath boundary in a gas discharge are studied. It is shown that thermionic emission has the effect of increasing the Bohm velocity, and this effect is more pronounced for lighter ions. In addition, it ismore » shown that the Bohm velocity cannot be increased to more than 24% above its value when there is no electron emission.« less

A mathematical model for predicting cyclic voltammograms of electronically conductive polypyrrole

NASA Technical Reports Server (NTRS)

Yeu, Taewhan; Nguyen, Trung V.; White, Ralph E.

1988-01-01

Polypyrrole is an attractive polymer for use as a high-energy-density secondary battery because of its potential as an inexpensive, lightweight, and noncorrosive electrode material. A mathematical model to simulate cyclic voltammograms for polypyrrole is presented. The model is for a conductive porous electrode film on a rotating disk electrode (RDE) and is used to predict the spatial and time dependence of concentration, overpotential, and stored charge profiles within a polypyrrole film. The model includes both faradic and capacitance charge components in the total current density expression.

A mathematical model for predicting cyclic voltammograms of electronically conductive polypyrrole

NASA Technical Reports Server (NTRS)

Yeu, Taewhan; Nguyen, Trung V.; White, Ralph E.

1987-01-01

Polypyrrole is an attractive polymer for use as a high-energy-density secondary battery because of its potential as an inexpensive, lightweight, and noncorrosive electrode material. A mathematical model to simulate cyclic voltammograms for polypyrrole is presented. The model is for a conductive porous electrode film on a rotating disk electrode (RDE) and is used to predict the spatial and time dependence of concentration, overpotential, and stored charge profiles within a polypyrrole film. The model includes both faradic and capacitance charge components in the total current density expression.

Ion beam enhancement in magnetically insulated ion diodes for high-intensity pulsed ion beam generation in non-relativistic mode

NASA Astrophysics Data System (ADS)

Zhu, X. P.; Zhang, Z. C.; Pushkarev, A. I.; Lei, M. K.

2016-01-01

High-intensity pulsed ion beam (HIPIB) with ion current density above Child-Langmuir limit is achieved by extracting ion beam from anode plasma of ion diodes with suppressing electron flow under magnetic field insulation. It was theoretically estimated that with increasing the magnetic field, a maximal value of ion current density may reach nearly 3 times that of Child-Langmuir limit in a non-relativistic mode and close to 6 times in a highly relativistic mode. In this study, the behavior of ion beam enhancement by magnetic insulation is systematically investigated in three types of magnetically insulated ion diodes (MIDs) with passive anode, taking into account the anode plasma generation process on the anode surface. A maximal enhancement factor higher than 6 over the Child-Langmuir limit can be obtained in the non-relativistic mode with accelerating voltage of 200-300 kV. The MIDs differ in two anode plasma formation mechanisms, i.e., surface flashover of a dielectric coating on the anode and explosive emission of electrons from the anode, as well as in two insulation modes of external-magnetic field and self-magnetic field with either non-closed or closed drift of electrons in the anode-cathode (A-K) gap, respectively. Combined with ion current density measurement, energy density characterization is employed to resolve the spatial distribution of energy density before focusing for exploring the ion beam generation process. Consistent results are obtained on three types of MIDs concerning control of neutralizing electron flows for the space charge of ions where the high ion beam enhancement is determined by effective electron neutralization in the A-K gap, while the HIPIB composition of different ion species downstream from the diode may be considerably affected by the ion beam neutralization during propagation.

Electron swarm properties under the influence of a very strong attachment in SF6 and CF3I obtained by Monte Carlo rescaling procedures

NASA Astrophysics Data System (ADS)

Mirić, J.; Bošnjaković, D.; Simonović, I.; Petrović, Z. Lj; Dujko, S.

2016-12-01

Electron attachment often imposes practical difficulties in Monte Carlo simulations, particularly under conditions of extensive losses of seed electrons. In this paper, we discuss two rescaling procedures for Monte Carlo simulations of electron transport in strongly attaching gases: (1) discrete rescaling, and (2) continuous rescaling. The two procedures are implemented in our Monte Carlo code with an aim of analyzing electron transport processes and attachment induced phenomena in sulfur-hexafluoride (SF6) and trifluoroiodomethane (CF3I). Though calculations have been performed over the entire range of reduced electric fields E/n 0 (where n 0 is the gas number density) where experimental data are available, the emphasis is placed on the analysis below critical (electric gas breakdown) fields and under conditions when transport properties are greatly affected by electron attachment. The present calculations of electron transport data for SF6 and CF3I at low E/n 0 take into account the full extent of the influence of electron attachment and spatially selective electron losses along the profile of electron swarm and attempts to produce data that may be used to model this range of conditions. The results of Monte Carlo simulations are compared to those predicted by the publicly available two term Boltzmann solver BOLSIG+. A multitude of kinetic phenomena in electron transport has been observed and discussed using physical arguments. In particular, we discuss two important phenomena: (1) the reduction of the mean energy with increasing E/n 0 for electrons in \\text{S}{{\\text{F}}6} and (2) the occurrence of negative differential conductivity (NDC) in the bulk drift velocity only for electrons in both \\text{S}{{\\text{F}}6} and CF3I. The electron energy distribution function, spatial variations of the rate coefficient for electron attachment and average energy as well as spatial profile of the swarm are calculated and used to understand these phenomena.

Thomson scattering diagnostics of steady state and pulsed welding processes without and with metal vapor

NASA Astrophysics Data System (ADS)

Kühn-Kauffeldt, M.; Marqués, J.-L.; Schein, J.

2015-01-01

Thomson scattering is applied to measure temperature and density of electrons in the arc plasma of the direct current gas tungsten arc welding (GTAW) process and pulsed gas metal arc welding (GMAW) process. This diagnostic technique allows to determine these plasma parameters independent from the gas composition and heavy particles temperature. The experimental setup is adapted to perform measurements on stationary as well as transient processes. Spatial and temporal electron temperature and density profiles of a pure argon arc in the case of the GTAW process and argon arc with the presence of aluminum metal vapor in the case of the GMAW process were obtained. Additionally the data is used to estimate the concentration of the metal vapor in the GMAW plasma.

Local representation of the electronic dielectric response function

DOE PAGES

Lu, Deyu; Ge, Xiaochuan

2015-12-11

We present a local representation of the electronic dielectric response function, based on a spatial partition of the dielectric response into contributions from each occupied Wannier orbital using a generalized density functional perturbation theory. This procedure is fully ab initio, and therefore allows us to rigorously define local metrics, such as “bond polarizability,” on Wannier centers. We show that the locality of the bare response function is determined by the locality of three quantities: Wannier functions of the occupied manifold, the density matrix, and the Hamiltonian matrix. Furthermore, in systems with a gap, the bare dielectric response is exponentially localized,more » which supports the physical picture of the dielectric response function as a collection of interacting local responses that can be captured by a tight-binding model.« less

Negative hydrogen ions in a linear helicon plasma device

NASA Astrophysics Data System (ADS)

Corr, Cormac; Santoso, Jesse; Samuell, Cameron; Willett, Hannah; Manoharan, Rounak; O'Byrne, Sean

2015-09-01

Low-pressure negative ion sources are of crucial importance to the development of high-energy (>1 MeV) neutral beam injection systems for the ITER experimental tokamak device. Due to their high power coupling efficiency and high plasma densities, helicon devices may be able to reduce power requirements and potentially remove the need for caesium. In helicon sources, the RF power can be coupled efficiently into the plasma and it has been previously observed that the application of a small magnetic field can lead to a significant increase in the plasma density. In this work, we investigate negative ion dynamics in a high-power (20 kW) helicon plasma source. The negative ion fraction is measured by probe-based laser photodetachment, electron density and temperature are determined by a Langmuir probe and tuneable diode laser absorption spectroscopy is used to determine the density of the H(n = 2) excited atomic state and the gas temperature. The negative ion density and excited atomic hydrogen density display a maximum at a low applied magnetic field of 3 mT, while the electron temperature displays a minimum. The negative ion density can be increased by a factor of 8 with the application of the magnetic field. Spatial and temporal measurements will also be presented. The Australian Research Grants Council is acknowledged for funding.

Variations of ionospheric plasma at different altitudes before the 2005 Sumatra Indonesia Ms 7.2 earthquake

NASA Astrophysics Data System (ADS)

Liu, Jing; Zhang, Xuemin; Novikov, Victor; Shen, Xuhui

2016-09-01

In recent years, many researchers pay more attention to abnormities before earthquake, and in this study, seismo-ionospheric synchronous disturbances at different altitudes by GPS and satellite observations were first studied around one Sumatra Indonesia Ms 7.2 earthquake that occurred on 5 July 2005. By using the same temporal and spatial methods, data of GPS-total electron content (TEC) from Jet Propulsion Laboratory, electron density (Ne) from Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions, and ion density (Ni) from Defense Meteorological Satellite Program were deeply analyzed. The ionospheric plasma disturbances in GPS-TEC and increasement of Ne at 710 km were found on 4 July, and plasma density at the three altitudes has all increased on 7 July after the earthquake. All the disturbances were not just above the epicenter. TEC perturbations have happened at the east of the epicenter for the two days, and electron density enhancement at 710 km has moved to west of the TEC perturbations at the same time on 4 July, which may be caused by E × B drift. The moving direction of upgoing plasma was simulated using SAMI2 model. The results have shown that the plasma will move to higher altitude along the geomagnetic force line, which could exactly account for the plasma density enhancement in the northern direction of the geomagnetic south latitude earthquake.

Numerical investigation of the spatiotemporal distribution of chemical species in an atmospheric surface barrier-discharge

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

Hasan, M. I.; Walsh, J. L., E-mail: jlwalsh@liverpool.ac.uk

Using a one dimensional time dependent convection-reaction-diffusion model, the temporal and spatial distributions of species propagating downstream of an atmospheric pressure air surface barrier discharge was studied. It was found that the distribution of negatively charged species is more spatially spread compared to positive ions species, which is attributed to the diffusion of electrons that cool down and attach to background gas molecules, creating different negative ions downstream of the discharge region. Given the widespread use of such discharges in applications involving the remote microbial decontamination of surfaces and liquids, the transport of plasma generated reactive species away from themore » discharge region was studied by implementing mechanical convection through the discharge region. It was shown that increased convection causes the spatial distribution of species density to become uniform. It was also found that many species have a lower density close to the surface of the discharge as convection prevents their accumulation. While for some species, such as NO{sub 2}, convection causes a general increase in the density due to a reduced residence time close to the discharge region, where it is rapidly lost through reactions with OH. The impact of the applied power was also investigated, and it was found that the densities of most species, whether charged or neutral, are directly proportional to the applied power.« less

High-speed digital holography for neutral gas and electron density imaging

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

Granstedt, E. M., E-mail: egranstedt@gmail.com; Thomas, C. E.; Kaita, R.

2016-05-15

An instrument was developed using digital holographic reconstruction of the wavefront from a CO{sub 2} laser imaged on a high-speed commercial IR camera. An acousto-optic modulator is used to generate 1–25 μs pulses from a continuous-wave CO{sub 2} laser, both to limit the average power at the detector and also to freeze motion from sub-interframe time scales. Extensive effort was made to characterize and eliminate noise from vibrations and second-surface reflections. Mismatch of the reference and object beam curvature initially contributed substantially to vibrational noise, but was mitigated through careful positioning of identical imaging lenses. Vibrational mode amplitudes were successfullymore » reduced to ≲1 nm for frequencies ≳50 Hz, and the inter-frame noise across the 128 × 128 pixel window which is typically used is ≲2.5 nm. To demonstrate the capabilities of the system, a piezo-electric valve and a reducing-expanding nozzle were used to generate a super-sonic gas jet which was imaged with high spatial resolution (better than 0.8 lp/mm) at high speed. Abel inversions were performed on the phase images to produce 2-D images of localized gas density. This system could also be used for high spatial and temporal resolution measurements of plasma electron density or surface deformations.« less

A Kinetics Model for KrF Laser Amplifiers

NASA Astrophysics Data System (ADS)

Giuliani, J. L.; Kepple, P.; Lehmberg, R.; Obenschain, S. P.; Petrov, G.

1999-11-01

A computer kinetics code has been developed to model the temporal and spatial behavior of an e-beam pumped KrF laser amplifier. The deposition of the primary beam electrons is assumed to be spatially uniform and the energy distribution function of the nascent electron population is calculated to be near Maxwellian below 10 eV. For an initial Kr/Ar/F2 composition, the code calculates the densities of 24 species subject to over 100 reactions with 1-D spatial resolution (typically 16 zones) along the longitudinal lasing axis. Enthalpy accounting for each process is performed to partition the energy into internal, thermal, and radiative components. The electron as well as the heavy particle temperatures are followed for energy conservation and excitation rates. Transport of the lasing photons is performed along the axis on a dense subgrid using the method of characteristics. Amplified spontaneous emission is calculated using a discrete ordinates approach and includes contributions to the local intensity from the whole amplifier volume. Specular reflection off side walls and the rear mirror are included. Results of the model will be compared with data from the NRL NIKE laser and other published results.

Single-shot coherent diffraction imaging of microbunched relativistic electron beams for free-electron laser applications.

PubMed

Marinelli, A; Dunning, M; Weathersby, S; Hemsing, E; Xiang, D; Andonian, G; O'Shea, F; Miao, Jianwei; Hast, C; Rosenzweig, J B

2013-03-01

With the advent of coherent x rays provided by the x-ray free-electron laser (FEL), strong interest has been kindled in sophisticated diffraction imaging techniques. In this Letter, we exploit such techniques for the diagnosis of the density distribution of the intense electron beams typically utilized in an x-ray FEL itself. We have implemented this method by analyzing the far-field coherent transition radiation emitted by an inverse-FEL microbunched electron beam. This analysis utilizes an oversampling phase retrieval method on the transition radiation angular spectrum to reconstruct the transverse spatial distribution of the electron beam. This application of diffraction imaging represents a significant advance in electron beam physics, having critical applications to the diagnosis of high-brightness beams, as well as the collective microbunching instabilities afflicting these systems.

Electrostatic properties of graphene edges for electron emission under an external electric field

NASA Astrophysics Data System (ADS)

Gao, Yanlin; Okada, Susumu

2018-04-01

Electronic properties of graphene edges under a lateral electric field were theoretically studied in regard to their edge shapes and terminations to provide a theoretical insight into their field emission properties. The work function and potential barrier for the electron emission from the graphene edges are sensitive to their shape and termination. We also found that the hydrogenated armchair edge shows the largest emission current among all edges studied here. The electric field outside the chiral edges is spatially modulated along the edge because of the inhomogeneous charge density at the atomic sites of the edge arising from the bond alternation.

Excitation of terahertz radiation by an electron beam in a dielectric lined waveguide with rippled dielectric surface

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

Tripathi, Deepak; Uma, R.; Tripathi, V. K.

A relativistic electron beam propagating through a dielectric lined waveguide, with ripple on the dielectric surface, excites a free electron laser type instability where ripple acts as a wiggler. The spatial modulation of permittivity in the ripple region couples a terahertz radiation mode to a driven mode of lower phase velocity, where the beam is in Cerenkov resonance with the slow mode. Both the modes grow at the expanse of beam energy. The terahertz frequency increases as the beam velocity increases. The growth rate of the instability goes as one third power of beam density.

Digital holographic interferometry employing Fresnel transform reconstruction for the study of flow shear stabilized Z-pinch plasmas.

PubMed

Ross, M P; Shumlak, U

2016-10-01

The ZaP-HD flow Z-pinch project provides a platform to explore how shear flow stabilized Z-pinches could scale to high-energy-density plasma (plasma with pressures exceeding 1 Mbar) and fusion reactor conditions. The Z-pinch is a linear plasma confinement geometry in which the plasma carries axial electric current and is confined by its self-induced magnetic field. ZaP-HD generates shear stabilized, axisymmetric Z-pinches with stable lifetimes approaching 60 μs. The goal of the project is to increase the plasma density and temperature compared to the previous ZaP project by compressing the plasma to smaller radii (≈1 mm). Radial and axial plasma electron density structure is measured using digital holographic interferometry (DHI), which provides the necessary fine spatial resolution. ZaP-HD's DHI system uses a 2 ns Nd:YAG laser pulse with a second harmonic generator (λ = 532 nm) to produce holograms recorded by a Nikon D3200 digital camera. The holograms are numerically reconstructed with the Fresnel transform reconstruction method to obtain the phase shift caused by the interaction of the laser beam with the plasma. This provides a two-dimensional map of line-integrated electron density, which can be Abel inverted to determine the local number density. The DHI resolves line-integrated densities down to 3 × 10 20 m -2 with spatial resolution near 10 μm. This paper presents the first application of Fresnel transform reconstruction as an analysis technique for a plasma diagnostic, and it analyzes the method's accuracy through study of synthetic data. It then presents an Abel inversion procedure that utilizes data on both sides of a Z-pinch local number density profile to maximize profile symmetry. Error estimation and Abel inversion are applied to the measured data.

The Electron Density Features Revealed by the GNSS-Based Radio Tomography in the Different Latitudinal and Longitudinal Sectors of the Ionosphere

NASA Astrophysics Data System (ADS)

Andreeva, Elena; Tereshchenko, Evgeniy; Nazarenko, Marina; Nesterov, Ivan; Kozharin, Maksim; Padokhin, Artem; Tumanova, Yulia

2016-04-01

The ionospheric radio tomography is an efficient method for electron density imaging in the different geographical regions of the world under different space weather conditions. The input for the satellite-based ionospheric radio tomography is provided by the signals that are transmitted from the navigational satellites and recorded by the chains or networks of ground receivers. The low-orbiting (LO) radio tomography employs the 150/400 MHz radio transmissions from the Earth's orbiters (like the Russian Tsikada/Parus and American Transit) flying at a height of ~1000 km above the Earth in the nearly polar orbits. The phases of the signals from a moving satellite which are recorded by the chains of ground receivers oriented along the satellite path form the families of linear integrals of electron density along the satellite-receiver rays that are used as the input data for LORT. The LO tomographic inversion of these data by phase difference method yields the 2D distributions of the ionospheric plasma in the vertical plane containing the receiving chain and the satellite path. LORT provides vertical resolution of 20-30 km and horizontal resolution of 30-40 km. The high-orbiting (HO) radio tomography employs the radio transmissions from the GPS/GLONASS satellites and enables 4D imaging of the ionosphere (3 spatial coordinates and time). HORT has a much wider spatial coverage (almost worldwide) and provides continuous time series of the reconstructions. However, the spatial resolution of HORT is lower (~100 km horizontally with a time step 60-20 min). In the regions with dense receiving networks (Europe, USA, Alaska, Japan), the resolution can be increased to 30-50 km with a time interval of 30-10 min. To date, the extensive RT data collected from the existing RT chains and networks enable a thorough analysis of both the regular and sporadic ionospheric features which are observed systematically or appear spontaneously, whose origin is fairly well understood or requires a dedicated study. We present the examples of the both types of the structures. We show a collection of different ionospheric structures under different space weather conditions: the ionization troughs, with their widely varying shapes, depths, positions, and internal distributions of plasma; isolated spots of the increased or decreased electron density, sharp wall-like density gradients, blobs, wavelike disturbances on different spatiotemporal scales etc. We demonstrate the series of the local isolated irregularities which are observed during both the quiet and disturbed days. We show the examples of the ionospheric plasma distributions strikingly varying during the geomagnetic storms. Some of the RT data are compared to the independent observations by the ionosondes. We also present the examples of RT images comparison with the UV spectroscopy data.

High-spatial-resolution electron density measurement by Langmuir probe for multi-point observations using tiny spacecraft

NASA Astrophysics Data System (ADS)

Hoang, H.; Røed, K.; Bekkeng, T. A.; Trondsen, E.; Clausen, L. B. N.; Miloch, W. J.; Moen, J. I.

2017-11-01

A method for evaluating electron density using a single fixed-bias Langmuir probe is presented. The technique allows for high-spatio-temporal resolution electron density measurements, which can be effectively carried out by tiny spacecraft for multi-point observations in the ionosphere. The results are compared with the multi-needle Langmuir probe system, which is a scientific instrument developed at the University of Oslo comprising four fixed-bias cylindrical probes that allow small-scale plasma density structures to be characterized in the ionosphere. The technique proposed in this paper can comply with the requirements of future small-sized spacecraft, where the cost-effectiveness, limited space available on the craft, low power consumption and capacity for data-links need to be addressed. The first experimental results in both the plasma laboratory and space confirm the efficiency of the new approach. Moreover, detailed analyses on two challenging issues when deploying the DC Langmuir probe on a tiny spacecraft, which are the limited conductive area of the spacecraft and probe surface contamination, are presented in the paper. It is demonstrated that the limited conductive area, depending on applications, can either be of no concern for the experiment or can be resolved by mitigation methods. Surface contamination has a small impact on the performance of the developed probe.

WDM production with intense relativistic electrons

NASA Astrophysics Data System (ADS)

Coleman, Josh; Andrews, Heather; Klasky, Mark; Colgan, James; Burris-Mog, Trevor; Creveling, Dan; Miller, Craig; Welch, Dale; Berninger, Mike

2016-10-01

The production of warm dense matter (WDM) through collisional heating with intense relativistic electrons is underway. A 100-ns-long monochromatic bunch of electrons with energies of 19.1-19.8 MeV and currents of 0.2-1.7 kA is used to heat 100- μm-thick foils with Z <29. The principal objective of these experiments is to develop a controlled method of measuring the equation of state with particle beams and benchmark numerical models. Measurements indicate the formation of a warm dense plasma near the end of the pulse, which is on the order of the beam size. These plasmas expand 5 mm in the first microsecond and slow down to <0.5 mm/ μs over the next 10 μs. These plasmas also produce both emitted and absorbed spectra amongst a continuum for Ti, Fe, and Cu. Cu-I spectra is dominated by stark broadening, indicating a cool plasma with ne >1018 cm-3. At these densities our plasma is collisionally dominated making it possible to spectrally model the density and temperature in LTE. Preliminary density gradient measurements will also be presented indicating the spatial extent of the solid density cutoff. This work was supported by the National Nuclear Se- curity Administration of the U.S. Department of Energy under Contract No. DE-AC52-06NA25396.

The cause of spatial structure in solar He I 1083 nm multiplet images

NASA Astrophysics Data System (ADS)

Leenaarts, Jorrit; Golding, Thomas; Carlsson, Mats; Libbrecht, Tine; Joshi, Jayant

2016-10-01

Context. The He I 1083 nm is a powerful diagnostic for inferring properties of the upper solar chromosphere, in particular for the magnetic field. The basic formation of the line in one-dimensional models is well understood, but the influence of the complex three-dimensional structure of the chromosphere and corona has however never been investigated. This structure must play an essential role because images taken in He I 1083 nm show structures with widths down to 100 km. Aims: We aim to understand the effect of the three-dimensional temperature and density structure in the solar atmosphere on the formation of the He I 1083 nm line. Methods: We solved the non-LTE radiative transfer problem assuming statistical equilibrium for a simple nine-level helium atom that nevertheless captures all essential physics. As a model atmosphere we used a snapshot from a 3D radiation-MHD simulation computed with the Bifrost code. Ionising radiation from the corona was self-consistently taken into account. Results: The emergent intensity in the He I 1083 nm is set by the source function and the opacity in the upper chromosphere. The former is dominated by scattering of photospheric radiation and does not vary much with spatial location. The latter is determined by the photonionisation rate in the He I ground state continuum, as well as the electron density in the chromosphere. The spatial variation of the flux of ionising radiation is caused by the spatially-structured emissivity of the ionising photons from material at T ≈ 100 kK in the transition region. The hotter coronal material produces more ionising photons, but the resulting radiation field is smooth and does not lead to small-scale variation of the UV flux. The corrugation of the transition region further increases the spatial variation of the amount of UV radiation in the chromosphere. Finally we find that variations in the chromospheric electron density also cause strong variation in He I 1083 nm opacity. We compare our findings to observations using SST, IRIS and SDO/AIA data. A movie associated to Fig. 4 is available at http://www.aanda.org

Single-particle excitations in periodically modulated two-dimensional electron gas

NASA Astrophysics Data System (ADS)

Kushwaha, Manvir S.

2008-06-01

A theoretical investigation is made of the plasmon excitations in a two-dimensional electron gas subjected to a one-dimensional periodic potential. We embark on the single-particle excitations within a two-subband model in the framework of Bohm-Pines’ random-phase approximation. For such an anisotropic system with spatially modulated charge density, we observe the existence of interesting esthetic necktie gaps that are found to center at the zone boundaries within the intersubband single-particle excitations. We discuss the dependence of the size of necktie gaps on the modulation potential.

Characteristics of a RF-Driven Ion Source for a Neutron Generator Used for Associated Particle Imaging

NASA Astrophysics Data System (ADS)

Wu, Ying; Hurley, John P.; Ji, Qing; Kwan, Joe; Leung, Ka-Ngo

2009-03-01

We present recent work on a prototype compact neutron generator for associated particle imaging (API). API uses alpha particles that are produced simultaneously with neutrons in the deuterium-tritium (2D(3T,n)4α) fusion reaction to determine the direction of the neutrons upon exiting the reaction. This method determines the spatial position of each neutron interaction and requires the neutrons to be generated from a small spot in order to achieve high spatial resolution. The ion source for API is designed to produce a focused ion beam with a beam spot diameter of 1-mm or less on the target. We use an axial type neutron generator with a predicted neutron yield of 108 n/s for a 50 μA D/T ion beam current accelerated to 80 kV. The generator utilizes an RF planar spiral antenna at 13.56 MHz to create a highly efficient inductively coupled plasma at the ion source. Experimental results show that beams with an atomic ion fraction of over 80% can be obtained while utilizing only 100 watts of RF power in the ion source. A single acceleration gap with a secondary electron suppression electrode is used in the tube. Experimental results from ion source testing, such as the current density, atomic ion fraction, electron temperature, and electron density will be discussed.

A study of the Ionospheric electron density profile with FORMOSAT-3/COSMIC observation data

NASA Astrophysics Data System (ADS)

Chou, Min-Yang; Tsai, Ho-Fang; Lin, Chi-Yen; Lee, I.-Te; Lin, Charles; Liu, Jann-Yenq

2015-04-01

The GPS Occultation Experiment payload onboard FORMOSAT-3/COSMIC microsatellite constellation is capable of scanning the ionospheric structure by the radio occultation (RO) technique to retrieve precise electron density profiles since 2006. Due to the success of FORMOSAT-3/COSMIC, the follow-on mission, FORMOSAT-7/COSMIC-2, is to launch 12 microsatellites in 2016 and 2018, respectively, with　the Global Navigation Satellite Systems (GNSS) RO instrument onboard for tracking GPS, Galileo and/or GLONASS satellite signals and to provide more than 8,000 RO soundings per day globally. An overview of the validation of the FORMOSAT-3/COSMIC ionospheric profiling is given by means of the traditional Abel transform through bending angle and total electron content (TEC), while the ionospheric data assimilation is also applied, based on the Gauss-Markov Kalman filter with the International Reference Ionosphere model (IRI-2007) and global ionosphere map (GIM) as background model, to assimilate TEC observations from FORMOSAT-3/COSMIC. The results shows comparison of electron density profiles from Abel inversion and data assimilation. Furthermore, an observing system simulation experiment is also applied to determine the impact of FORMOSAT-7/COSMIC-2 on ionospheric weather monitoring, which reveals an opportunity on advanced study of small spatial and temporal variations in the ionosphere.

Spectral Quadrature method for accurate O ( N ) electronic structure calculations of metals and insulators

DOE PAGES

Pratapa, Phanisri P.; Suryanarayana, Phanish; Pask, John E.

2015-12-02

We present the Clenshaw–Curtis Spectral Quadrature (SQ) method for real-space O(N) Density Functional Theory (DFT) calculations. In this approach, all quantities of interest are expressed as bilinear forms or sums over bilinear forms, which are then approximated by spatially localized Clenshaw–Curtis quadrature rules. This technique is identically applicable to both insulating and metallic systems, and in conjunction with local reformulation of the electrostatics, enables the O(N) evaluation of the electronic density, energy, and atomic forces. The SQ approach also permits infinite-cell calculations without recourse to Brillouin zone integration or large supercells. We employ a finite difference representation in order tomore » exploit the locality of electronic interactions in real space, enable systematic convergence, and facilitate large-scale parallel implementation. In particular, we derive expressions for the electronic density, total energy, and atomic forces that can be evaluated in O(N) operations. We demonstrate the systematic convergence of energies and forces with respect to quadrature order as well as truncation radius to the exact diagonalization result. In addition, we show convergence with respect to mesh size to established O(N 3) planewave results. In conclusion, we establish the efficiency of the proposed approach for high temperature calculations and discuss its particular suitability for large-scale parallel computation.« less

Laser-induced plasmas in air studied using two-color interferometry

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

Yang, Zefeng; Wu, Jian, E-mail: jxjawj@mail.xjtu.edu.cn; Li, Xingwen

2016-08-15

Temporally and spatially resolved density profiles of Cu atoms, electrons, and compressed air, from laser-induced copper plasmas in air, are measured using fast spectral imaging and two-color interferometry. From the intensified CCD images filtered by a narrow-band-pass filter centered at 515.32 nm, the Cu atoms expansion route is estimated and used to determine the position of the fracture surface between the Cu atoms and the air. Results indicate that the Cu atoms density at distances closer to the target (0–0.4 mm) is quite low, with the maximum density appearing at the edge of the plasma's core being ∼4.6 × 10{sup 24 }m{sup −3} at 304 ns.more » The free electrons are mainly located in the internal region of the plume, which is supposed to have a higher temperature. The density of the shock wave is (4–6) × 10{sup 25 }m{sup −3}, corresponding to air compression of a factor of 1.7–2.5.« less

Numerical simulation of current-free double layers created in a helicon plasma device

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

Rao, Sathyanarayan; Singh, Nagendra

2012-09-15

Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E{sub Up-Tack }) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E{sub Up-Tack} on the high potential side of the double layer in the CFDL. Themore » accelerated ions are trapped near the conical surface, where E{sub Up-Tack} reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop ({phi}{sub Double-Vertical-Line Double-Vertical-Line o}) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.« less

Hybrid simulations of solenoidal radio-frequency inductively coupled hydrogen discharges at low pressures

NASA Astrophysics Data System (ADS)

Yang, Wei; Li, Hong; Gao, Fei; Wang, You-Nian

2016-12-01

In this article, we have described a radio-frequency (RF) inductively coupled H2 plasma using a hybrid computational model, incorporating the Maxwell equations and the linear part of the electron Boltzmann equation into global model equations. This report focuses on the effects of RF frequency, gas pressure, and coil current on the spatial profiles of the induced electric field and plasma absorption power density. The plasma parameters, i.e., plasma density, electron temperature, density of negative ion, electronegativity, densities of neutral species, and dissociation degree of H2, as a function of absorption power, are evaluated at different gas pressures. The simulation results show that the utilization efficiency of the RF source characterized by the coupling efficiency of the RF electric field and power to the plasma can be significantly improved at the low RF frequency, gas pressure, and coil current, due to a low plasma density in these cases. The densities of vibrational states of H2 first rapidly increase with increasing absorption power and then tend to saturate. This is because the rapidly increased dissociation degree of H2 with increasing absorption power somewhat suppresses the increase of the vibrational states of H2, thus inhibiting the increase of the H-. The effects of absorption power on the utilization efficiency of the RF source and the production of the vibrational states of H2 should be considered when setting a value of the coil current. To validate the model simulations, the calculated electron density and temperature are compared with experimental measurements, and a reasonable agreement is achieved.

Laser beam coupling with capillary discharge plasma for laser wakefield acceleration applications

NASA Astrophysics Data System (ADS)

Bagdasarov, G. A.; Sasorov, P. V.; Gasilov, V. A.; Boldarev, A. S.; Olkhovskaya, O. G.; Benedetti, C.; Bulanov, S. S.; Gonsalves, A.; Mao, H.-S.; Schroeder, C. B.; van Tilborg, J.; Esarey, E.; Leemans, W. P.; Levato, T.; Margarone, D.; Korn, G.

2017-08-01

One of the most robust methods, demonstrated to date, of accelerating electron beams by laser-plasma sources is the utilization of plasma channels generated by the capillary discharges. Although the spatial structure of the installation is simple in principle, there may be some important effects caused by the open ends of the capillary, by the supplying channels etc., which require a detailed 3D modeling of the processes. In the present work, such simulations are performed using the code MARPLE. First, the process of capillary filling with cold hydrogen before the discharge is fired, through the side supply channels is simulated. Second, the simulation of the capillary discharge is performed with the goal to obtain a time-dependent spatial distribution of the electron density near the open ends of the capillary as well as inside the capillary. Finally, to evaluate the effectiveness of the beam coupling with the channeling plasma wave guide and of the electron acceleration, modeling of the laser-plasma interaction was performed with the code INF&RNO.

Small-scale structure of the midlatitude storm enhanced density plume during the 17 March 2015 St. Patrick's Day storm

NASA Astrophysics Data System (ADS)

Heine, Thomas R. P.; Moldwin, Mark B.; Zou, Shasha

2017-03-01

Kilometer-scale density irregularities in the ionosphere can cause ionospheric scintillation—a phenomenon that degrades space-based navigation and communication signals. During strong geomagnetic storms, the midlatitude ionosphere is primed to produce these ˜1-10 km small-scale irregularities along the steep gradients between midlatitude storm enhanced density (SED) plumes and the adjacent low-density trough. The length scales of irregularities on the order of 1-10 km are determined from a combination of spatial, temporal, and frequency analyses using single-station ground-based Global Positioning System total electron content (TEC) combined with radar plasma velocity measurements. Kilometer-scale irregularities are detected along the boundaries of the SED plume and depleted density trough during the 17 March 2015 geomagnetic storm, but not equatorward of the plume or within the plume itself. Analysis using the fast Fourier transform of high-pass filtered slant TEC suggests that the kilometer-scale irregularities formed near the poleward gradients of SED plumes can have similar intensity and length scales to those typically found in the aurora but are shown to be distinct phenomena in spacecraft electron precipitation measurements.

Study of the operating parameters of a helicon plasma discharge source using PIC-MCC simulation technique

NASA Astrophysics Data System (ADS)

Jaafarian, Rokhsare; Ganjovi, Alireza; Etaati, Gholamreza

2018-01-01

In this work, a Particle in Cell-Monte Carlo Collision simulation technique is used to study the operating parameters of a typical helicon plasma source. These parameters mainly include the gas pressure, externally applied static magnetic field, the length and radius of the helicon antenna, and the frequency and voltage amplitude of the applied RF power on the helicon antenna. It is shown that, while the strong radial gradient of the formed plasma density in the proximity of the plasma surface is substantially proportional to the energy absorption from the existing Trivelpiece-Gould (TG) modes, the observed high electron temperature in the helicon source at lower static magnetic fields is significant evidence for the energy absorption from the helicon modes. Furthermore, it is found that, at higher gas pressures, both the plasma electron density and temperature are reduced. Besides, it is shown that, at higher static magnetic fields, owing to the enhancement of the energy absorption by the plasma charged species, the plasma electron density is linearly increased. Moreover, it is seen that, at the higher spatial dimensions of the antenna, both the plasma electron density and temperature are reduced. Additionally, while, for the applied frequencies of 13.56 MHz and 27.12 MHz on the helicon antenna, the TG modes appear, for the applied frequency of 18.12 MHz on the helicon antenna, the existence of helicon modes is proved. Moreover, by increasing the applied voltage amplitude on the antenna, the generation of mono-energetic electrons is more probable.

Rational design of crystal contact-free space in protein crystals for analyzing spatial distribution of motions within protein molecules.

PubMed

Matsuoka, Rei; Shimada, Atsushi; Komuro, Yasuaki; Sugita, Yuji; Kohda, Daisuke

2016-03-01

Contacts with neighboring molecules in protein crystals inevitably restrict the internal motions of intrinsically flexible proteins. The resultant clear electron densities permit model building, as crystallographic snapshot structures. Although these still images are informative, they could provide biased pictures of the protein motions. If the mobile parts are located at a site lacking direct contacts in rationally designed crystals, then the amplitude of the movements can be experimentally analyzed. We propose a fusion protein method, to create crystal contact-free space (CCFS) in protein crystals and to place the mobile parts in the CCFS. Conventional model building fails when large amplitude motions exist. In this study, the mobile parts appear as smeared electron densities in the CCFS, by suitable processing of the X-ray diffraction data. We applied the CCFS method to a highly mobile presequence peptide bound to the mitochondrial import receptor, Tom20, and a catalytically relevant flexible segment in the oligosaccharyltransferase, AglB. These two examples demonstrated the general applicability of the CCFS method to the analysis of the spatial distribution of motions within protein molecules. © 2016 The Protein Society.

Spatial and temporal dynamics of a pulsed spark microplasma used for aerosol analysis

NASA Astrophysics Data System (ADS)

Zheng, Lina; Kulkarni, Pramod; Diwakar, Prasoon

2018-06-01

The spatial and temporal dynamics of a pulsed, electrical spark microplasma used for spectrochemical analysis of aerosols was investigated. The spark discharge was generated by applying a high voltage pulse between a coaxial anode and cathode. Aerosol particles of black carbon were collected on the cathode for 2 min, following which the pulsed microplasma was introduced, leading to ablation and atomization of the collected particles. The space- and time-resolved emission spectra showed that the atomic emission signal from the carbon species originated from the region close to the cathode surface during the early evolution of the microplasma. The C I and C II atomic emission reached peak intensities at 11 and 6 μs delay time, respectively. Peak emission intensities occurred between 0.5-1.3 mm above the cathode surface. The average excitation temperature and the electron number density of the spark microplasma were estimated to be 23,000 K, and 1.6 × 1017 cm-3, respectively. The effects of pulse energy on the excitation temperature and electron density were also investigated. The results provide insights into the dynamics of the pulsed spark microplasma and are helpful in optimizing elemental analysis of aerosols using this technique.

Determining energy balance in the flaring chromosphere from oxygen V line ratios

NASA Astrophysics Data System (ADS)

Graham, D. R.; Fletcher, L.; Labrosse, N.

2015-12-01

Context. The impulsive phase of solar flares is a time of rapid energy deposition and heating in the lower solar atmosphere, leading to changes in the temperature and density structure of the region. Aims: We use an O v density diagnostic formed from the λ192 /λ248 line ratio, provided by the Hinode/EIS instrument, to determine the density of flare footpoint plasma at O v formation temperatures of ~2.5 × 105 K, giving a constraint on the properties of the heated transition region. Methods: Hinode/EIS rasters from 2 small flare events in December 2007 were used. Raster images were co-aligned to identify and establish the footpoint pixels, multiple-component Gaussian line fitting of the spectra was carried out to isolate the density diagnostic pair, and the density was calculated for several footpoint areas. The assumptions of equilibrium ionisation and optically-thin radiation for the O v lines used were assessed and found to be acceptable. For one of the events, properties of the electron distribution were deduced from earlier RHESSI hard X-ray observations. These were used to calculate the plasma heating rate delivered by an electron beam for 2 semi-empirical atmospheres under collisional thick-target assumptions. The radiative loss rate for this plasma was also calculated for comparison with possible energy input mechanisms. Results: Electron number densities of up to 1011.9 cm-3 were measured during the flare impulsive phase using the O v λ192 /λ248 diagnostic ratio. The heating rate delivered by an electron beam was found to exceed the radiative losses at this density, corresponding to a height of 450 km, and when assuming a completely ionised target atmosphere far exceed the losses but at a height of 1450-1600 km. A chromospheric thickness of 70-700 km was found to be required to balance a conductive input to the O v-emitting region with radiative losses. Conclusions: Electron densities have been observed in footpoint sources at transition region temperatures, comparable to previous results but with improved spatial information. The observed densities can be explained by heating of the chromosphere by collisional electrons, with O v formed at heights of 450-1600 km above the photosphere, depending on the atmospheric ionisation fraction.

Control of Wigner localization and electron cavity effects in near-field emission spectra of In(Ga)P/GaInP quantum-dot structures

NASA Astrophysics Data System (ADS)

Mintairov, A. M.; Kapaldo, J.; Merz, J. L.; Rouvimov, S.; Lebedev, D. V.; Kalyuzhnyy, N. A.; Mintairov, S. A.; Belyaev, K. G.; Rakhlin, M. V.; Toropov, A. A.; Brunkov, P. N.; Vlasov, A. S.; Zadiranov, Yu. M.; Blundell, S. A.; Mozharov, A. M.; Mukhin, I.; Yakimov, M.; Oktyabrsky, S.; Shelaev, A. V.; Bykov, V. A.

2018-05-01

Structural and emission properties of few-electron In(Ga)P/GaInP quantum dots (QDs) representing natural Wigner molecules (WM) and whispering gallery mode (WGM) electron (e ) cavities have been investigated. QD structures were grown using self-organized metal-organic vapor phase epitaxy and deposition from ˜3 to 7 monolayers of InP at 700 °C. Using atomic force microscopy, transmission electron microscopy, near-field scanning optical microscopy (NSOM), and μ -photoluminescence (μ -PL) spectra we obtained In(Ga)P/GaInP QDs having lateral size 80-180 nm, height 5-30 nm, Ga content 0.0-0.4, density 2 -10 μm-2 , and electron population up to 20 and demonstrated control of their density and size distribution. Using high-spatial-resolution low-temperature PL spectra, NSOM imaging, and calculations of charge density distributions we observed Wigner localization and e -cavity effects for a series of dots having quantum confinement ℏ ω0=0.5 -6 meV . We used these data together with time-resolved PL measurements to clarify the effect of Coulomb interaction and WM formation on emission spectra of few-electron QDs. We present direct observation of 2 e , 6 e , and 9 e WMs; 2 e and 4 e WGMs; and Fabry-Perot e modes and establish conditions of e -WGM-cavity formation in these QDs.

Operando observations of solid-state electrochemical reactions in Li-ion batteries by spatially resolved TEM EELS and electron holography.

PubMed

Yamamoto, Kazuo; Iriyama, Yasutoshi; Hirayama, Tsukasa

2017-02-08

All-solid-state Li-ion batteries having incombustible solid electrolytes are promising energy storage devices because they have significant advantages in terms of safety, lifetime and energy density. Electrochemical reactions, namely, Li-ion insertion/extraction reactions, commonly occur around the nanometer-scale interfaces between the electrodes and solid electrolytes. Thus, transmission electron microscopy (TEM) is an appropriate technique to directly observe such reactions, providing important information for understanding the fundamental solid-state electrochemistry and improving battery performance. In this review, we introduce two types of TEM techniques for operando observations of battery reactions, spatially resolved electron energy-loss spectroscopy in a TEM mode for direct detection of the Li concentration profiles and electron holography for observing the electric potential changes due to Li-ion insertion/extraction reactions. We visually show how Li-ion insertion/extractions affect the crystal structures, electronic structures, and local electric potential during the charge-discharge processes in these batteries. © The Author 2016. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Visualization of Nanoplasmonic Coupling to Molecular Orbital in Light Emission Induced by Tunneling Electrons.

PubMed

Yu, Arthur; Li, Shaowei; Wang, Hui; Chen, Siyu; Wu, Ruqian; Ho, W

2018-05-09

The coupling between localized plasmon and molecular orbital in the light emission from a metallic nanocavity has been directly detected and imaged with sub-0.1 nm resolution. The light emission intensity was enhanced when the energy difference between the tunneling electrons and the lowest unoccupied molecular orbital (LUMO) of an azulene molecule matches the energy of a plasmon mode of the nanocavity defined by the Ag-tip and Ag (110) substrate of a scanning tunneling microscope (STM). The spatially resolved image of the light emission intensity matches the spatial distribution of the LUMO obtained by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. Our results highlight the near-field coupling of a molecular orbital to the radiative decay of a plasmonic excitation in a confined nanoscale junction.

A high-power spatial filter for Thomson scattering stray light reduction

NASA Astrophysics Data System (ADS)

Levesque, J. P.; Litzner, K. D.; Mauel, M. E.; Maurer, D. A.; Navratil, G. A.; Pedersen, T. S.

2011-03-01

The Thomson scattering diagnostic on the High Beta Tokamak-Extended Pulse (HBT-EP) is routinely used to measure electron temperature and density during plasma discharges. Avalanche photodiodes in a five-channel interference filter polychromator measure scattered light from a 6 ns, 800 mJ, 1064 nm Nd:YAG laser pulse. A low cost, high-power spatial filter was designed, tested, and added to the laser beamline in order to reduce stray laser light to levels which are acceptable for accurate Rayleigh calibration. A detailed analysis of the spatial filter design and performance is given. The spatial filter can be easily implemented in an existing Thomson scattering system without the need to disturb the vacuum chamber or significantly change the beamline. Although apertures in the spatial filter suffer substantial damage from the focused beam, with proper design they can last long enough to permit absolute calibration.

Density-transition scale at quasiperpendicular collisionless shocks.

PubMed

Bale, S D; Mozer, F S; Horbury, T S

2003-12-31

Measurements of a spacecraft floating potential, on the four Cluster spacecraft, are used as a proxy for electron plasma density to study, for the first time, the macroscopic density transition scale at 98 crossings of the quasiperpendicular terrestrial bow shock. A timing analysis gives shock speeds and normals; the shock speed is used to convert the temporal measurement to a spatial one. A hyperbolic tangent function is fitted to each density transition, which captures the main shock transition, but not overshoot or undershoot nor foot features. We find that, at a low Mach number M, the density transition is consistent with both ion inertial scales c/omega(pi) and convected gyroradii v(sh,n)/Omega(ci,2), while at M>/=4-5 only the convected gyroradius is the preferred scale for the shock density transition and takes the value L approximately 0.4v(sh,n)/Omega(ci,2).

Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements

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

Bohm, P., E-mail: bohm@ipp.cas.cz; Bilkova, P.; Melich, R.

2014-11-15

The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.

Injection of a coaxial-gun-produced magnetized plasma into a background helicon plasma

NASA Astrophysics Data System (ADS)

Zhang, Yue; Lynn, Alan; Gilmore, Mark; Hsu, Scott

2014-10-01

A compact coaxial plasma gun is employed for experimental investigation of plasma bubble relaxation into a lower density background plasma. Experiments are being conducted in the linear device HelCat at UNM. The gun is powered by a 120-uF ignitron-switched capacitor bank, which is operated in a range of 5 to 10 kV and 100 kA. Multiple diagnostics are employed to investigate the plasma relaxation process. Magnetized argon plasma bubbles with velocities 1.2Cs, densities 1020 m-3 and electron temperature 13eV have been achieved. The background helicon plasma has density 1013 m-3, magnetic field from 200 to 500 Gauss and electron temperature 1eV. Several distinct operational regimes with qualitatively different dynamics are identified by fast CCD camera images. Additionally a B-dot probe array has been employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify plasma bubble configurations. Experimental data and analysis will be presented.

The plasma filling factor of coronal bright points. II. Combined EIS and TRACE results

NASA Astrophysics Data System (ADS)

Dere, K. P.

2009-04-01

Aims: In a previous paper, the volumetric plasma filling factor of coronal bright points was determined from spectra obtained with the Extreme ultraviolet Imaging Spectrometer (EIS). The analysis of these data showed that the median plasma filling factor was 0.015. One interpretation of this result was that the small filling factor was consistent with a single coronal loop with a width of 1-2´´, somewhat below the apparent width. In this paper, higher spatial resolution observations with the Transition Region and Corona Explorer (TRACE) are used to test this interpretation. Methods: Rastered spectra of regions of the quiet Sun were recorded by the EIS during operations with the Hinode satellite. Many of these regions were simultaneously observed with TRACE. Calibrated intensities of Fe xii lines were obtained and images of the quiet corona were constructed from the EIS measurements. Emission measures were determined from the EIS spectra and geometrical widths of coronal bright points were obtained from the TRACE images. Electron densities were determined from density-sensitive line ratios measured with EIS. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma filling factor. Results: The median electron density of coronal bright points is 3 × 109 cm-3 at a temperature of 1.6 × 106 K. The volumetric plasma filling factor of coronal bright points was found to vary from 3 × 10-3 to 0.3 with a median value of 0.04. Conclusions: The current set of EIS and TRACE coronal bright-point observations indicate the median value of their plasma filling factor is 0.04. This can be interpreted as evidence of a considerable subresolution structure in coronal bright points or as the result of a single completely filled plasma loop with widths on the order of 0.2-1.5´´ that has not been spatially resolved in these measurements.

Monitoring long-range electron transfer pathways in proteins by stimulated attosecond broadband X-ray Raman spectroscopy

DOE PAGES

Zhang, Yu; Biggs, Jason D.; Govind, Niranjan; ...

2014-10-09

In this study, long-range electron transfer (ET) plays a key role in many biological energy conversion and synthesis processes. We show that nonlinear spectroscopy with attosecond X-ray pulses provides a real time movie of the evolving oxidation states and electron densities around atoms, and can probe these processes with high spatial and temporal resolution. This is demonstrated in a simulation study of the stimulated X-ray Raman (SXRS) signals in Re-modified azurin, which had long served as a benchmark for long-range ET in proteins. Nonlinear SXRS signals are sensitive to the local electronic structure and should offer a novel window formore » long-range ET.« less

Exchange and correlation effects on plasmon dispersions and Coulomb drag in low-density electron bilayers

NASA Astrophysics Data System (ADS)

Badalyan, S. M.; Kim, C. S.; Vignale, G.; Senatore, G.

2007-03-01

We investigate the effect of exchange and correlation (XC) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra- and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg [Solid State Commun. 123, 515 (2002)].

Magnetic field influences on the lateral dose response functions of photon-beam detectors: MC study of wall-less water-filled detectors with various densities.

PubMed

Looe, Hui Khee; Delfs, Björn; Poppinga, Daniela; Harder, Dietrich; Poppe, Björn

2017-06-21

The distortion of detector reading profiles across photon beams in the presence of magnetic fields is a developing subject of clinical photon-beam dosimetry. The underlying modification by the Lorentz force of a detector's lateral dose response function-the convolution kernel transforming the true cross-beam dose profile in water into the detector reading profile-is here studied for the first time. The three basic convolution kernels, the photon fluence response function, the dose deposition kernel, and the lateral dose response function, of wall-less cylindrical detectors filled with water of low, normal and enhanced density are shown by Monte Carlo simulation to be distorted in the prevailing direction of the Lorentz force. The asymmetric shape changes of these convolution kernels in a water medium and in magnetic fields of up to 1.5 T are confined to the lower millimetre range, and they depend on the photon beam quality, the magnetic flux density and the detector's density. The impact of this distortion on detector reading profiles is demonstrated using a narrow photon beam profile. For clinical applications it appears as favourable that the magnetic flux density dependent distortion of the lateral dose response function, as far as secondary electron transport is concerned, vanishes in the case of water-equivalent detectors of normal water density. By means of secondary electron history backtracing, the spatial distribution of the photon interactions giving rise either directly to secondary electrons or to scattered photons further downstream producing secondary electrons which contribute to the detector's signal, and their lateral shift due to the Lorentz force is elucidated. Electron history backtracing also serves to illustrate the correct treatment of the influences of the Lorentz force in the EGSnrc Monte Carlo code applied in this study.

Multispacecraft observations of the electron current sheet, neighboring magnetic islands, and electron acceleration during magnetotail reconnection

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

Chen Lijen; Bessho, Naoki; Bhattacharjee, Amitava

Open questions concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic reconnection are addressed based on data from the four-spacecraft mission Cluster and particle-in-cell simulations. Using time series of electron distribution functions measured by the four spacecraft, distinct electron regions around a reconnection layer are mapped out to set the framework for studying diffusion regions. A spatially extended electron current sheet (ecs), a series of magnetic islands, and bursts of energetic electrons within islands are identified during magnetotail reconnection with no appreciable guide field. The ecs is collocated with a layer of electron-scale electric fields normalmore » to the ecs and pointing toward the ecs center plane. Both the observed electron and ion densities vary by more than a factor of 2 within one ion skin depth north and south of the ecs, and from the ecs into magnetic islands. Within each of the identified islands, there is a burst of suprathermal electrons whose fluxes peak at density compression sites [L.-J. Chen et al., Nat. Phys. 4, 19 (2008)] and whose energy spectra exhibit power laws with indices ranging from 6 to 7.3. These results indicate that the in-plane electric field normal to the ecs can be of the electron scale at certain phases of reconnection, electrons and ions are highly compressible within the ion diffusion region, and for reconnection involving magnetic islands, primary electron acceleration occurs within the islands.« less

Specular reflectivity and hot-electron generation in high-contrast relativistic laser-plasma interactions

NASA Astrophysics Data System (ADS)

Kemp, Gregory Elijah

Ultra-intense laser (> 1018 W/cm2) interactions with matter are capable of producing relativistic electrons which have a variety of applications in state-of-the-art scientific and medical research conducted at universities and national laboratories across the world. Control of various aspects of these hot-electron distributions is highly desired to optimize a particular outcome. Hot-electron generation in low-contrast interactions, where significant amounts of under-dense pre-plasma are present, can be plagued by highly non-linear relativistic laser-plasma instabilities and quasi-static magnetic field generation, often resulting in less than desirable and predictable electron source characteristics. High-contrast interactions offer more controlled interactions but often at the cost of overall lower coupling and increased sensitivity to initial target conditions. An experiment studying the differences in hot-electron generation between high and low-contrast pulse interactions with solid density targets was performed on the Titan laser platform at the Jupiter Laser Facility at Lawrence Livermore National Laboratory in Livermore, CA. To date, these hot-electrons generated in the laboratory are not directly observable at the source of the interaction. Instead, indirect studies are performed using state-of-the-art simulations, constrained by the various experimental measurements. These measurements, more-often-than-not, rely on secondary processes generated by the transport of these electrons through the solid density materials which can susceptible to a variety instabilities and target material/geometry effects. Although often neglected in these types of studies, the specularly reflected light can provide invaluable insight as it is directly influenced by the interaction. In this thesis, I address the use of (personally obtained) experimental specular reflectivity measurements to indirectly study hot-electron generation in the context of high-contrast, relativistic laser-plasma interactions. Spatial, temporal and spectral properties of the incident and specular pulses, both near and far away from the interaction region where experimental measurements are obtained, are used to benchmark simulations designed to infer dominant hot-electron acceleration mechanisms and their corresponding energy/angular distributions. To handle this highly coupled interaction, I employed particle-in-cell modeling using a wide variety of algorithms (verified to be numerically stable and consistent with analytic expressions) and physical models (validated by experimental results) to reasonably model the interaction's sweeping range of plasma densities, temporal and spatial scales, electromagnetic wave propagation and its interaction with solid density matter. Due to the fluctuations in the experimental conditions and limited computational resources, only a limited number of full-scale simulations were performed under typical experimental conditions to infer the relevant physical phenomena in the interactions. I show the usefulness of the often overlooked specular reflectivity measurements in constraining both high and low-contrast simulations, as well as limitations of their experimental interpretations. Using these experimental measurements to reasonably constrain the simulation results, I discuss the sensitivity of relativistic electron generation in ultra-intense laser plasma interactions to initial target conditions and the dynamic evolution of the interaction region.

Formation of Surface and Quantum-Well States in Ultra Thin Pt Films on the Au(111) Surface

PubMed Central

Silkin, Igor V.; Koroteev, Yury M.; Echenique, Pedro M.; Chulkov, Evgueni V.

2017-01-01

The electronic structure of the Pt/Au(111) heterostructures with a number of Pt monolayers n ranging from one to three is studied in the density-functional-theory framework. The calculations demonstrate that the deposition of the Pt atomic thin films on gold substrate results in strong modifications of the electronic structure at the surface. In particular, the Au(111) s-p-type Shockley surface state becomes completely unoccupied at deposition of any number of Pt monolayers. The Pt adlayer generates numerous quantum-well states in various energy gaps of Au(111) with strong spatial confinement at the surface. As a result, strong enhancement in the local density of state at the surface Pt atomic layer in comparison with clean Pt surface is obtained. The excess in the density of states has maximal magnitude in the case of one monolayer Pt adlayer and gradually reduces with increasing number of Pt atomic layers. The spin–orbit coupling produces strong modification of the energy dispersion of the electronic states generated by the Pt adlayer and gives rise to certain quantum states with a characteristic Dirac-cone shape. PMID:29232833

Measurements of dynamo electric field and momentum transport induced by fluctuations on HIST

NASA Astrophysics Data System (ADS)

Hirono, H.; Hanao, T.; Hyobu, T.; Ito, K.; Matsumoto, K.; Nakayama, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2012-10-01

Coaxial Helicity injection (CHI) is an efficient current-drive method used in spheromak and spherical torus (ST) experiments. It is an important issue to investigate dynamo effect to explore CHI current drive mechanisms. To establish the dynamo model with two-fluid Hall effects, we verify the parallel mean-field Ohm's law balance. The spatial profiles of the MHD/Hall dynamo electric fields are measured by using Mach probe and Hall probe involving 3-axis magnetic pick-up coils. The MHD/Hall fluctuation-induced electromotive forces are large enough to sustain the mean toroidal current against the resistive decay. We have measured the electron temperature and the density with great accuracy by using a new electrostatic probe with voltage sweeping. The result shows that the electron temperature is high in the core region and low in the central open flux column (OFC), and the electron density is highest in the OFC region. The Hall dynamo becomes more dominant in a lower density region compared to the MHD dynamo. In addition, the fluctuation-induced Maxwell and Reynolds stresses are calculated to examine the fast radial transport of momentum from the OFC to the core region during the dynamo drive.

Analysis of rocket beacon transmissions for computerized reconstruction of ionospheric densities

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Huba, J. D.; Chaturvedi, P. K.; Fulford, J. A.; Forsyth, P. A.; Anderson, D. N.; Zalesak, S. T.

1993-01-01

Three methods are described to obtain ionospheric electron densities from transionospheric, rocket-beacon TEC data. First, when the line-of-sight from a ground receiver to the rocket beacon is tangent to the flight trajectory, the electron concentration can be obtained by differentiating the TEC with respect to the distance to the rocket. A similar method may be used to obtain the electron-density profile if the layer is horizontally stratified. Second, TEC data obtained during chemical release experiments may be interpreted with the aid of physical models of the disturbed ionosphere to yield spatial maps of the modified regions. Third, computerized tomography (CT) can be used to analyze TEC data obtained along a chain of ground-based receivers aligned along the plane of the rocket trajectory. CT analysis of TEC data is used to reconstruct a 2D image of a simulated equatorial plume. TEC data is computed for a linear chain of nine receivers with adjacent spacings of either 100 or 200 km. The simulation data are analyzed to provide an F region reconstruction on a grid with 15 x 15 km pixels. Ionospheric rocket tomography may also be applied to rocket-assisted measurements of amplitude and phase scintillations and airglow intensities.

Mechanism of VHF H2 plasma production at high pressures

NASA Astrophysics Data System (ADS)

Chen, Kuan-Chen; Chiu, Kuo-Feng; Chen, Chia-Fu; Lien, Cheng-Yang; Tsai, Yu-Jer; Lien, Ting-Kuei; Ogiwara, Kohei; Uchino, Kiichiro; Kawai, Yoshinobu

2016-06-01

A VHF H2 plasma was produced by a narrow-gap discharge at high pressures, and the plasma parameters were examined with the Langmuir probe. A bi-Maxwellian electron distribution was observed near the discharge electrode at a discharge gap of 10 mm, while a Maxwellian distribution was seen near the center. When the discharge gap was 15 mm, electrons had a Maxwellian distribution independent of the position. It was found that there must be a threshold in the discharge gap for stochastic heating to occur. The plasma potential near the discharge electrode was higher than that near the center of the interelectrode gap, suggesting the existence of negative ions. The simulation using the plasma hybrid code was carried out. The spatial profiles of the density and temperature of electrons were similar to the experimental results. The plasma potential had a hill-like profile that was quite different from the measured one. The negative ion density was negligible.

Challenges in quantitative crystallographic characterization of 3D thin films by ACOM-TEM.

PubMed

Kobler, A; Kübel, C

2017-02-01

Automated crystal orientation mapping for transmission electron microscopy (ACOM-TEM) has become an easy to use method for the investigation of crystalline materials and complements other TEM methods by adding local crystallographic information over large areas. It fills the gap between high resolution electron microscopy and electron back scatter diffraction in terms of spatial resolution. Recent investigations showed that spot diffraction ACOM-TEM is a quantitative method with respect to sample parameters like grain size, twin density, orientation density and others. It can even be used in combination with in-situ tensile or thermal testing. However, there are limitations of the current method. In this paper we discuss some of the challenges and discuss solutions, e.g. we present an ambiguity filter that reduces the number of pixels with a '180° ambiguity problem'. For that an ACOM-TEM tilt series of nanocrystalline Pd thin films with overlapping crystallites was acquired and analyzed. Copyright © 2017. Published by Elsevier B.V.

A global view of F-region electron density and temperature at solar maximum

NASA Technical Reports Server (NTRS)

Brace, L. H.; Theis, R. F.; Hoegy, W. R.

1982-01-01

It is pointed out that the thermal structure of the ionosphere represents a quasi-static balance between a variety of heat sources and sinks which vary spatially and temporally on a wide range of time scales. The present investigation has the objective to present selected early results from the Dynamics Explorer-2 (DE-2) Langmuir probe instrument and to make an initial evaluation of how the thermal structure of the ionosphere at solar maximum differs from that observed at solar minimum. Bowen et al. (1964) and Brace and Reddy (1965) devised early empirical models of the F region electron temperature (Te), based on satellite Langmuir probe measurements at low levels of solar activity. The global structure of Te and the electron density (Ne) obtained in the current investigation is not very different from that reported by Brace and Reddy. The primary difference at solar maximum is that Ne is everywhere much higher, but Te differs only in detail.

Assessment of Ionospheric Anomaly Prior to the Large Earthquake: 2D and 3D Analysis in Space and Time for the 2011 Tohoku Earthquake (Mw9.0)

NASA Astrophysics Data System (ADS)

Hattori, Katsumi; Hirooka, Shinji; Han, Peng

2016-04-01

The ionospheric anomalies possibly associated with large earthquakes have been reported by many researchers. In this paper, Total Electron Content (TEC) and tomography analyses have been applied to investigate the spatial and temporal distributions of ionospheric electron density prior to the 2011 Off the Pacific Coast of Tohoku earthquake (Mw9.0). Results show significant TEC enhancements and an interesting three dimensional structure prior to the main shock. As for temporal TEC changes, the TEC value increases 3－4 days before the earthquake remarkably, when the geomagnetic condition was relatively quiet. In addition, the abnormal TEC enhancement area in space was stalled above Japan during the period. Tomographic results show that three dimensional distribution of electron density decreases around 250 km altitude above the epicenter (peak is located just the east-region of the epicenter) and increases the mostly entire region between 300 and 400 km.

New Thomson scattering diagnostic on RFX-mod.

PubMed

Alfier, A; Pasqualotto, R

2007-01-01

This article describes the completely renovated Thomson scattering (TS) diagnostic employed in the modified Reversed Field eXperiment (RFX-mod) since it restarted operation in 2005. The system measures plasma electron temperature and density profiles along an equatorial diameter, measuring in 84 positions with 7 mm spatial resolution. The custom built Nd:YLF laser produces a burst of 10 pulses at 50 Hz with energy of 3 J, providing ten profile measurements in a plasma discharge of about 300 ms duration. An optical delay system accommodates three scattering volumes in each of the 28 interference filter spectrometers. Avalanche photodiodes detect the Thomson scattering signals and allow them to be recorded by means of waveform digitizers. Electron temperature is obtained using an alternative relative calibration method, based on the use of a supercontinuum light source. Rotational Raman scattering in nitrogen has supplied the absolute calibration for the electron density measurements. During RFX-mod experimental campaigns in 2005, the TS diagnostic has demonstrated its performance, routinely providing reliable high resolution profiles.

Global phase diagram of the spinless Falicov-Kimball model in d = 3 : renormalization-group theory

NASA Astrophysics Data System (ADS)

Sariyer, Ozan S.; Hinczewski, Michael; Berker, A. Nihat

2011-03-01

The global phase diagram of the spinless Falicov-Kimball model in d = 3 spatial dimensions is obtained by renormalization-group theory. This global phase diagram exhibits five distinct phases. Four of these phases are charge-ordered (CO) phases, in which the system forms two sublattices with different electron densities. The phase boundaries are second order, except for an intermediate interaction regime, where a first-order phase boundary between two CO phases occurs. The first-order phase boundary is delimited by special bicritical points. The cross-sections of the global phase diagram with respect to the chemical potentials of the localized and mobile electrons, at all representative interaction and hopping strengths, are calculated and exhibit three distinct topologies. The phase diagrams with respect to electron densities are also calculated. This research was supported by the Alexander von Humboldt Foundation, the Scientific and Technological Research Council of Turkey (TÜBITAK), and the Academy of Sciences of Turkey.

Flux-driven algebraic damping of m = 1 diocotron mode

NASA Astrophysics Data System (ADS)

Chim, Chi Yung; O'Neil, Thomas

2015-11-01

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 diocotron modes. Transport due to small field asymmetries produce a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius rres, where f = mfE × B (rres) . The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This poster explains with analytic theory and simulations the new algebraic damping due to both mobility and diffusive fluxes. As electrons are swept around the ``cat's eye'' orbits of resonant wave-particle interaction, they form a dipole (m = 1) density distribution, and the electric field from this distribution produces an E × B drift of the core back to the axis, i.e. damps the m = 1 mode. Supported by National Science Foundation Grant PHY-1414570.

Characterizing the performance of an affordable, multichannel conductivity probe for density measurements in stratified flows

NASA Astrophysics Data System (ADS)

Subramanian, Balaji; Carminati, Marco; Luzzatto-Fegiz, Paolo

2017-11-01

In stratified flows, conductivity (combined with temperature) is often used to measure density. The conductivity probes typically used can resolve very fine spatial scales, but on the downside they are fragile, expensive, sensitive to environmental noise and have only single channel capability. Recently a low-cost, robust, arduino-based probe called Conduino was developed, which can be valuable in a wide range of applications where resolving extremely small spatial scales is not needed. This probe uses micro-USB connectors as actual conductivity sensors with a custom designed electronic board for simultaneous acquisition from multiple probes, with conductivity resolution comparable to commercially available PME conductivity probe. A detailed assessment of performance of this Conduino probe is described here. To establish time response and sensitivity as a function of electrode geometry, we build a variety of shapes for different kinds of applications, with tip spacing ranging from 0.5-2.5 mm, and with electrode length ranging from 2.3-6 mm. We set up a two-layer density profile and traverse it rapidly, yielding a time response comparable to PME. The Conduino's multi-channel capability is used to operate probe arrays, which helps to construct density fields in stratified flows.

Nucleon localization and fragment formation in nuclear fission

DOE PAGES

Zhang, C. L.; Schuetrumpf, B.; Nazarewicz, W.

2016-12-27

An electron localization measure was originally introduced to characterize chemical bond structures in molecules. Recently, a nucleon localization based on Hartree-Fock densities has been introduced to investigate α-cluster structures in light nuclei. Compared to the local nucleonic densities, the nucleon localization function has been shown to be an excellent indicator of shell effects and cluster correlations. In this work, using the spatial nucleon localization measure, we investigated the emergence of fragments in fissioning heavy nuclei using the self-consistent energy density functional method with a quantified energy density functional optimized for fission studies. We studied the particle densities and spatial nucleonmore » localization distributions along the fission pathways of 264Fm, 232Th, and 240Pu. We demonstrated that the fission fragments were formed fairly early in the evolution, well before scission. To illustrate the usefulness of the localization measure, we showed how the hyperdeformed state of 232Th could be understood in terms of a quasimolecular state made of 132Sn and 100Zr fragments. Compared to nucleonic distributions, the nucleon localization function more effectively quantifies nucleonic clustering: its characteristic oscillating pattern, traced back to shell effects, is a clear fingerprint of cluster/fragment configurations. This is of particular interest for studies of fragment formation and fragment identification in fissioning nuclei.« less

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

Zhang, C. L.; Schuetrumpf, B.; Nazarewicz, W.

An electron localization measure was originally introduced to characterize chemical bond structures in molecules. Recently, a nucleon localization based on Hartree-Fock densities has been introduced to investigate α-cluster structures in light nuclei. Compared to the local nucleonic densities, the nucleon localization function has been shown to be an excellent indicator of shell effects and cluster correlations. In this work, using the spatial nucleon localization measure, we investigated the emergence of fragments in fissioning heavy nuclei using the self-consistent energy density functional method with a quantified energy density functional optimized for fission studies. We studied the particle densities and spatial nucleonmore » localization distributions along the fission pathways of 264Fm, 232Th, and 240Pu. We demonstrated that the fission fragments were formed fairly early in the evolution, well before scission. To illustrate the usefulness of the localization measure, we showed how the hyperdeformed state of 232Th could be understood in terms of a quasimolecular state made of 132Sn and 100Zr fragments. Compared to nucleonic distributions, the nucleon localization function more effectively quantifies nucleonic clustering: its characteristic oscillating pattern, traced back to shell effects, is a clear fingerprint of cluster/fragment configurations. This is of particular interest for studies of fragment formation and fragment identification in fissioning nuclei.« less

Optical Diagnostics on HIT-SI3

NASA Astrophysics Data System (ADS)

Everson, Christopher; Jarboe, Thomas; Morgan, Kyle

2016-10-01

Interferometry and Thomson Scattering are implemented on the HIT-SI3 (Helicity Injected Torus - Steady Inductive 3) device to provide time resolved measurements of electron density and spatially resolved measurements of electron temperature, respectively. HIT-SI3 is a modification of the original HIT-SI apparatus that uses three injectors instead of two. The scientific aim of HIT-SI3 is to develop a deeper understanding of how injector behavior and interactions influence current drive and spheromak stability. The interferometer system makes use of an intermediate frequency between two parallel 184.3 μm Far-Infrared (FIR) laser cavities which are optically pumped by a CO2 laser. The phase shift in this beat frequency due to the plasma index of refraction is used to calculate the line-integrated electron density. To measure the electron temperature, Thomson Scattered light from a 20 J (1 GW pulse) Ruby laser off of free electrons in the HIT-SI3 plasma is measured simultaneously at four locations across the spheromak (nominally 23 cm minor radius). Polychromators bin the collected light into 3 spectral bands to detect the relative level of scattering. Work supported by the D.O.E.

Implications of electron heating and non-uniformities in a VHF-CCP for sterilization of medical instruments

NASA Astrophysics Data System (ADS)

Stapelmann, Katharina; Fiebrandt, Marcel; Styrnoll, Tim; Baldus, Sabrina; Bibinov, Nikita; Awakowicz, Peter

2015-06-01

A capacitively coupled plasma driven at a frequency of 81.36 MHz from the VHF-band is investigated by means of optical emission spectroscopy (OES) and multipole resonance probe (MRP). The discharge is operated with hydrogen, yielding an electropositive discharge, as well as oxygen, yielding an electronegative discharge, and mixtures of both. Pressure is varied from p=5 Pa to p=25 Pa. Homogeneity of the discharge is investigated by CCD camera recordings as well as spatially resolved multipole resonance probe measurements. The results indicate the presence of electromagnetic edge effects as well as standing wave effects. Furthermore, a largely homogeneous discharge can be achieved with hydrogen as process gas at a pressure of p=5 -10 Pa. With increasing pressure as well as with increasing oxygen content, the discharge appears less homogeneously. The transition from an electropositive to an electronegative discharge leads to a change in electron heating mechanisms, with pronounced local maxima of electron density at the sheath edges. A comparison of OES and MRP results reveal a significant difference in electron density, which can be explained by a non-Maxwellian distribution function of electrons.

Synchrotron radiation from a runaway electron distribution in tokamaks

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

Stahl, A.; Fülöp, T.; Landreman, M.

2013-09-15

The synchrotron radiation emitted by runaway electrons in a fusion plasma provides information regarding the particle momenta and pitch-angles of the runaway electron population through the strong dependence of the synchrotron spectrum on these parameters. Information about the runaway density and its spatial distribution, as well as the time evolution of the above quantities, can also be deduced. In this paper, we present the synchrotron radiation spectra for typical avalanching runaway electron distributions. Spectra obtained for a distribution of electrons are compared with the emission of mono-energetic electrons with a prescribed pitch-angle. We also examine the effects of magnetic fieldmore » curvature and analyse the sensitivity of the resulting spectrum to perturbations to the runaway distribution. The implications for the deduced runaway electron parameters are discussed. We compare our calculations to experimental data from DIII-D and estimate the maximum observed runaway energy.« less

Temporal-Spatial Pattern of Pre-earthquake Signatures in Atmosphere and Ionosphere Associated with Major Earthquakes in Greece.

NASA Astrophysics Data System (ADS)

Calderon, I. S.; Ouzounov, D.; Anagnostopoulos, G. C.; Pulinets, S. A.; Davidenko, D.; Karastathis, V. K.; Kafatos, M.

2015-12-01

We are conducting validation studies on atmosphere/ionosphere phenomena preceding major earthquakes in Greece in the last decade and in particular the largest (M6.9) earthquakes that occurred on May 24, 2014 in the Aegean Sea and on February 14, 2008 in South West Peloponisos (Methoni). Our approach is based on monitoring simultaneously a series of different physical parameters from space: Outgoing long-wavelength radiation (OLR) on the top of the atmosphere, electron and electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC), and ULF radiation and radiation belt electron precipitation (RBEP) accompanied by VLF wave activity into the topside ionosphere. In particular, we analyzed prospectively and retrospectively the temporal and spatial variations of various parameters characterizing the state of the atmosphere and ionosphere several days before the two M6.9 earthquakes. Concerning the Methoni EQ, DEMETER data confirm an almost standard profile before large EQs, with TEC, ULF, VLF and RBEP activity preceding some (four) days the EQ occurrence and silence the day of EQ; furthermore, during the period before the EQ, a progressive concentration of ULF emission centers around the future epicenter was confirmed. Concerning the recent Greek EQ of May 24, 2014, thermal anomaly was discovered 30 days and TEC anomaly 38 hours in advance accordingly. The spatial characteristics of pre-earthquake anomalous behavior were associated with the epicentral region. Our analysis of simultaneous space measurements before the great EQs suggests that they follow a general temporal-spatial pattern, which has been seen in other large EQs worldwide.

Application of time–frequency wavelet analysis in the reflectometry of thin films

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

Astaf’ev, S. B., E-mail: bard@crys.ras.ru; Shchedrin, B. M.; Yanusova, L. G.

2017-03-15

The application of time–frequency wavelet analysis for solving the reflectometry inverse problem is considered. It is shown that a simultaneous transform of specular intensity curve, depending on the grazing angle and spatial frequency, allows one to determine not only the thickness but also the alteration order of individual regions (layers) with characteristic behavior of electron density. This information makes it possible to reconstruct the electron density profile in the film cross section as a whole (i.e., to solve the inverse reflectometry problem). The application of the time–frequency transform is illustrated by examples of reconstructing (based on X-ray reflectivity data) themore » layer alternation order in models of two-layer films with inverted arrangement of layers and a four-layer film on a solid substrate.« less

Emergence of kinetic behavior in streaming ultracold neutral plasmas

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

McQuillen, P.; Castro, J.; Bradshaw, S. J.

2015-04-15

We create streaming ultracold neutral plasmas by tailoring the photoionizing laser beam that creates the plasma. By varying the electron temperature, we control the relative velocity of the streaming populations, and, in conjunction with variation of the plasma density, this controls the ion collisionality of the colliding streams. Laser-induced fluorescence is used to map the spatially resolved density and velocity distribution function for the ions. We identify the lack of local thermal equilibrium and distinct populations of interpenetrating, counter-streaming ions as signatures of kinetic behavior. Experimental data are compared with results from a one-dimensional, two-fluid numerical simulation.

Conformable actively multiplexed high-density surface electrode array for brain interfacing

DOEpatents

Rogers, John; Kim, Dae-Hyeong; Litt, Brian; Viventi, Jonathan

2015-01-13

Provided are methods and devices for interfacing with brain tissue, specifically for monitoring and/or actuation of spatio-temporal electrical waveforms. The device is conformable having a high electrode density and high spatial and temporal resolution. A conformable substrate supports a conformable electronic circuit and a barrier layer. Electrodes are positioned to provide electrical contact with a brain tissue. A controller monitors or actuates the electrodes, thereby interfacing with the brain tissue. In an aspect, methods are provided to monitor or actuate spatio-temporal electrical waveform over large brain surface areas by any of the devices disclosed herein.

Quark matter droplets in neutron stars

NASA Technical Reports Server (NTRS)

Heiselberg, H.; Pethick, C. J.; Staubo, E. F.

1993-01-01

We show that, for physically reasonable bulk and surface properties, the lowest energy state of dense matter consists of quark matter coexisting with nuclear matter in the presence of an essentially uniform background of electrons. We estimate the size and nature of spatial structure in this phase, and show that at the lowest densities the quark matter forms droplets embedded in nuclear matter, whereas at higher densities it can exhibit a variety of different topologies. A finite fraction of the interior of neutron stars could consist of matter in this new phase, which would provide new mechanisms for glitches and cooling.

Effects of Digitization and JPEG Compression on Land Cover Classification Using Astronaut-Acquired Orbital Photographs

NASA Technical Reports Server (NTRS)

Robinson, Julie A.; Webb, Edward L.; Evangelista, Arlene

2000-01-01

Studies that utilize astronaut-acquired orbital photographs for visual or digital classification require high-quality data to ensure accuracy. The majority of images available must be digitized from film and electronically transferred to scientific users. This study examined the effect of scanning spatial resolution (1200, 2400 pixels per inch [21.2 and 10.6 microns/pixel]), scanning density range option (Auto, Full) and compression ratio (non-lossy [TIFF], and lossy JPEG 10:1, 46:1, 83:1) on digital classification results of an orbital photograph from the NASA - Johnson Space Center archive. Qualitative results suggested that 1200 ppi was acceptable for visual interpretive uses for major land cover types. Moreover, Auto scanning density range was superior to Full density range. Quantitative assessment of the processing steps indicated that, while 2400 ppi scanning spatial resolution resulted in more classified polygons as well as a substantially greater proportion of polygons < 0.2 ha, overall agreement between 1200 ppi and 2400 ppi was quite high. JPEG compression up to approximately 46:1 also did not appear to have a major impact on quantitative classification characteristics. We conclude that both 1200 and 2400 ppi scanning resolutions are acceptable options for this level of land cover classification, as well as a compression ratio at or below approximately 46:1. Auto range density should always be used during scanning because it acquires more of the information from the film. The particular combination of scanning spatial resolution and compression level will require a case-by-case decision and will depend upon memory capabilities, analytical objectives and the spatial properties of the objects in the image.

Theory of waves incoherently scattered

NASA Technical Reports Server (NTRS)

Bauer, P.

1974-01-01

Electromagnetic waves impinging upon a plasma at frequencies larger than the plasma frequency, suffer weak scattering. The scattering arises from the existence of electron density fluctuations. The received signal corresponds to a particular spatial Fourier component of the fluctuations, the wave vector of which is a function of the wavelength of the radiowave. Wavelengths short with respect to the Debye length of the medium relate to fluctuations due to non-interacting Maxwellian electrons, while larger wavelengths relate to fluctuations due to collective Coulomb interactions. In the latter case, the scattered signal exhibits a spectral distribution which is characteristic of the main properties of the electron and ion gases and, therefore, provides a powerful diagnosis of the state of the ionosphere.

On interaction of P-waves with one-dimensional photonic crystal consisting of weak conducting matter and transparent dielectric layers

NASA Astrophysics Data System (ADS)

Yushkanov, A. A.; Zverev, N. V.

2018-03-01

An influence of quantum and spatial dispersion properties of the non-degenerate electron plasma on the interaction of electromagnetic P-waves with one-dimensional photonic crystal consisting of conductor with low carrier electron density and transparent dielectric matter, is studied numerically. It is shown that at the frequencies of order of the plasma frequency and at small widths of the conducting and dielectric layers of the photonic crystal, optical coefficients in the quantum non-degenerate plasma approach differ from the coefficients in the classical electron gas approach. And also, at these frequencies one observes a temperature dependence of the optical coefficients.

Determination of Spatio-Temporal Characteristics of D-region Electron Density during Annular Solar Eclipse from VLF Network Observations

NASA Astrophysics Data System (ADS)

Basak, T.; Hobara, Y.

2015-12-01

A major part of the path of the annular solar eclipse of May 20, 2012 (magnitude 0.9439) was over southern Japan. The D-region ionospheric changes associated with that eclipse, led to several degree of observable perturbations of sub-ionospheric very low frequency (VLF) radio signal. The University of Electro-Communications (UEC) operates VLF observation network over Japan. The solar eclipse associated signal changes were recorded in several receiving stations (Rx) simultaneously for the VLF signals coming from NWC/19.8kHz, JJI/22.2kHz, JJY/40.0kHz, NLK/24.8kHz and other VLF transmitters (Tx). These temporal dependences of VLF signal perturbation have been analyzed and the spatio-temporal characteristics of respective sub-ionospheric perturbations has already been studied by earlier workers using 2D-Finite Difference Time Domain method of simulation. In this work, we determine the spatial scale, depth and temporal dependence of lower ionospheric perturbation in consistence with umbral and penumbral motion. We considered the 2-parameter D-region ionospheric model with exponential electron density profile. To model the solar obscuration effect over it, we assumed a generalized space-time dependent 2-dimensional elliptical Gaussian distribution for ionospheric parameters, such as, effective reflection height (h') and sharpness factor (β). The depth (△hmax, △βmax), center of shadow (lato(t), lono(t)) and spatial scale (σlat,lon) of that Gaussian distribution are used as model parameters. In the vicinity of the eclipse zone, we compute the VLF signal perturbations using Long Wave Propagation Capability (LWPC) code for several signal propagation paths. The propagation path characteristics, such as, ground and water conductivity and geomagnetic effect on ionosphere are considered from standard LWPC prescriptions. The model parameters are tuned to set an optimum agreement between our computation and observed positive and negative type of VLF perturbations. Thus, appropriate set of parameters lead us to the possible determination of spatial scale, depth and temporal dependence of eclipse associated D-region electron density perturbation solely from the VLF-network observations coupled with theoretical modeling.

A unifying approach to lattice dynamical and electronic properties of solids

NASA Astrophysics Data System (ADS)

Falter, C.

1988-06-01

A unified analysis of lattice dynamical and electronic properties of solids with special emphasis on the interaction between electrons and phonons is presented. The article is roughly divided into two parts reflecting different points of view. The density response of the electrons provides the link between these parts. In the first part, the microscopic theory in terms of the density response in crystals is discussed. Relations are pointed out between the density response approach and the density functional theory. The latter is used for a representation of the exchange-correlation interaction and the microscopic force constants. Relevant methods, as recently proposed by various authors for the calculation of the density response in inhomogeneous solids are discussed. Particular attention is paid to the development of a renormalized response description. Applications of this method to lattice dynamical and electronic properties are presented. In the second part an alternative physical concept, the quasi-ion approach, is outlined. This concept is shown to provide a microscopic basis for electronic charge localization in crystals and proves the importance of the correlation between crystal symmetry and many-body effects. Is is derived that within linear response theory an appropriate decomposition of the valence charge density leads uniquely to a spatially localized density contribution at the individual ion which follows its motion rigidly. The composite consisting of this partial density and the ion core is taken to be an individual entity, denoted as quasi-ion, from which the crystal is built up. In a certain sense this is a generalization of Ziman's concept of neutral pseudo-atoms being approximately valid in simple metals. New insight into the bonding mechanism and charge relaxation processes is shown to follow from this concept. In particular, we discuss the covalent, ionic and metallic bonding mechanisms, using the localized picture provided by the partial densities, on the same basis. The quasi-ion approach is also applied to the calculation of phonon-induced charge density redistributions and to the construction of a simplified formulation of microscopic lattice dynamics. Investigations of the phonon dispersion for different bonding types are given within a rigid quasi-ion model and extensions of this model are outlined. Among other things, these calculations indicate that bonding dynamics of (covalent) molecules and crystals can be described by relative rotations of the quasi-ions under the condition of rotational invariance of the system. Finally, possible applications of the quasi-ion concept to an approximate formulation of anharmonic lattice dynamics and the interaction between electrons and phonons are discussed. A numerical investigation of this interaction is presented and compared with the results from the rigid-ion model. As a consequence of the quasi-ion concept a consistent calculation of the phonon dispersion, the electronic band structure and the electron-phonon interaction becomes possible.

Numerical simulations used for a validity check on the laser induced photo-detachment diagnostic method in electronegative plasmas

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

Oudini, N.; Taccogna, F.; Bendib, A.

2014-06-15

Laser photo-detachment is used as a method to measure or determine the negative ion density and temperature in electronegative plasmas. In essence, the method consists of producing an electropositive channel (negative ion free region) via pulsed laser photo-detachment within an electronegative plasma bulk. Electrostatic probes placed in this channel measure the change in the electron density. A second pulse might be used to track the negative ion recovery. From this, the negative ion density and temperature can be determined. We study the formation and relaxation of the electropositive channel via a two-dimensional Particle-In-Cell/Mote Carlo collision model. The simulation is mainlymore » carried out in a Hydrogen plasma with an electronegativity of α = 1, with a parametric study for α up to 20. The temporal and spatial evolution of the plasma potential and the electron densities shows the formation of a double layer (DL) confining the photo-detached electrons within the electropositive channel. This DL evolves into two fronts that move in the opposite directions inside and outside of the laser spot region. As a consequence, within the laser spot region, the background and photo-detached electron energy distribution function relaxes/thermalizes via collisionless effects such as Fermi acceleration and Landau damping. Moreover, the simulations show that collisional effects and the DL electric field strength might play a non-negligible role in the negative ion recovery within the laser spot region, leading to a two-temperature negative ion distribution. The latter result might have important effects in the determination of the negative ion density and temperature from laser photo detachment diagnostic.« less

Numerical simulations used for a validity check on the laser induced photo-detachment diagnostic method in electronegative plasmas

NASA Astrophysics Data System (ADS)

Oudini, N.; Taccogna, F.; Bendib, A.; Aanesland, A.

2014-06-01

Laser photo-detachment is used as a method to measure or determine the negative ion density and temperature in electronegative plasmas. In essence, the method consists of producing an electropositive channel (negative ion free region) via pulsed laser photo-detachment within an electronegative plasma bulk. Electrostatic probes placed in this channel measure the change in the electron density. A second pulse might be used to track the negative ion recovery. From this, the negative ion density and temperature can be determined. We study the formation and relaxation of the electropositive channel via a two-dimensional Particle-In-Cell/Mote Carlo collision model. The simulation is mainly carried out in a Hydrogen plasma with an electronegativity of α = 1, with a parametric study for α up to 20. The temporal and spatial evolution of the plasma potential and the electron densities shows the formation of a double layer (DL) confining the photo-detached electrons within the electropositive channel. This DL evolves into two fronts that move in the opposite directions inside and outside of the laser spot region. As a consequence, within the laser spot region, the background and photo-detached electron energy distribution function relaxes/thermalizes via collisionless effects such as Fermi acceleration and Landau damping. Moreover, the simulations show that collisional effects and the DL electric field strength might play a non-negligible role in the negative ion recovery within the laser spot region, leading to a two-temperature negative ion distribution. The latter result might have important effects in the determination of the negative ion density and temperature from laser photo detachment diagnostic.

Opposite Latitudinal Dependence of the Premidnight and Postmidnight Oscillations in the Electron Density of Midlatitude F Layer

NASA Astrophysics Data System (ADS)

Chen, Gang; Wang, Jin; Zhang, Shaodong; Deng, Zhongxin; Zhong, Dingkun; Wu, Chen; Jin, Han; Li, Yaxian

2018-01-01

The dense observation points of the oblique-incidence ionosonde network in North China make it possible to discover the ionospheric regional variations with relatively high spatial resolution. The ionosonde network and the Beijing digisonde are used to investigate the ionospheric nighttime oscillations in January and February 2011. The electron density enhancements occurring before and after midnight present the obvious opposite latitudinal dependence in the time-latitude maps, which are composed by the differential critical frequency of F2 layer. The premidnight enhancements (PRMEs) appeared earlier in the north and then moved to south. The postmidnight enhancements (POMEs) did the opposite. The data analysis shows that the PRME was a part of the large-scale traveling ionospheric disturbance (LSTID), which may be produced by gravity waves. The southward propagation of the LSTIDs is considered to form the positive latitudinal dependence of the wave peaks and troughs. The postmidnight F layer oscillation was composed by a single enhancement and a single decline following it. The westward electric field-induced E × B drift, which pushed the F layer to lower altitudes with higher recombination loss, was most likely to compress the plasma and produce the POMEs. Along with the continuously dropping of the layer, the recombination loss exceeded the density increase due to the compression effect and then the electron density decline appeared.

Ultrafast large-amplitude relocation of electronic charge in ionic crystals

PubMed Central

Zamponi, Flavio; Rothhardt, Philip; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas

2012-01-01

The interplay of vibrational motion and electronic charge relocation in an ionic hydrogen-bonded crystal is mapped by X-ray powder diffraction with a 100 fs time resolution. Photoexcitation of the prototype material KH2PO4 induces coherent low-frequency motions of the PO4 tetrahedra in the electronically excited state of the crystal while the average atomic positions remain unchanged. Time-dependent maps of electron density derived from the diffraction data demonstrate an oscillatory relocation of electronic charge with a spatial amplitude two orders of magnitude larger than the underlying vibrational lattice motions. Coherent longitudinal optical and tranverse optical phonon motions that dephase on a time scale of several picoseconds, drive the charge relocation, similar to a soft (transverse optical) mode driven phase transition between the ferro- and paraelectric phase of KH2PO4. PMID:22431621

Structural “ δ Doping” to Control Local Magnetization in Isovalent Oxide Heterostructures

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

Moon, E. J.; He, Q.; Ghosh, S.

Modulation and δ-doping strategies, in which atomically thin layers of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here in this paper, we demonstrate a purely structural “δ-doping” strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected MnO 6 octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations.more » Finally, the combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to “doping” in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures.« less

Structural “ δ Doping” to Control Local Magnetization in Isovalent Oxide Heterostructures

DOE PAGES

Moon, E. J.; He, Q.; Ghosh, S.; ...

2017-11-08

Modulation and δ-doping strategies, in which atomically thin layers of charged dopants are precisely deposited within a heterostructure, have played enabling roles in the discovery of new physical behavior in electronic materials. Here in this paper, we demonstrate a purely structural “δ-doping” strategy in complex oxide heterostructures, in which atomically thin manganite layers are inserted into an isovalent manganite host, thereby modifying the local rotations of corner-connected MnO 6 octahedra. Combining scanning transmission electron microscopy, polarized neutron reflectometry, and density functional theory, we reveal how local magnetic exchange interactions are enhanced within the spatially confined regions of suppressed octahedral rotations.more » Finally, the combined experimental and theoretical results illustrate the potential to utilize noncharge-based approaches to “doping” in order to enhance or suppress functional properties within spatially confined regions of oxide heterostructures.« less

Control of target-normal-sheath-accelerated protons from a guiding cone

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

Zou, D. B.; Institut für Theoretische Physik I, Heinrich-Heine-Universität Düsseldorf, Düsseldorf 40225; Zhuo, H. B., E-mail: hongbin.zhuo@gmail.com

2015-06-15

It is demonstrated through particle-in-cell simulations that target-normal-sheath-accelerated protons can be well controlled by using a guiding cone. Compared to a conventional planar target, both the collimation and number density of proton beams are substantially improved, giving a high-quality proton beam which maintained for a longer distance without degradation. The effect is attributed to the radial electric field resulting from the charge due to the hot target electrons propagating along the cone surface. This electric field can effectively suppress the spatial spread of the protons after the expansion of the hot electrons.

Thermionic emission from monolayer graphene, sheath formation and its feasibility towards thermionic converters

NASA Astrophysics Data System (ADS)

Misra, Shikha; Upadhyay Kahaly, M.; Mishra, S. K.

2017-02-01

A formalism describing the thermionic emission from a single layer graphene sheet operating at a finite temperature and the consequent formation of the thermionic sheath in its proximity has been established. The formulation takes account of two dimensional densities of state configuration, Fermi-Dirac (f-d) statistics of the electron energy distribution, Fowler's treatment of electron emission, and Poisson's equation. The thermionic current estimates based on the present analysis is found to be in reasonably good agreement with experimental observations (Zhu et al., Nano Res. 07, 1 (2014)). The analysis has further been simplified for the case where f-d statistics of an electron energy distribution converges to Maxwellian distribution. By using this formulation, the steady state sheath features, viz., spatial dependence of the surface potential and electron density structure in the thermionic sheath are derived and illustrated graphically for graphene parameters; the electron density in the sheath is seen to diminish within ˜10 s of Debye lengths. By utilizing the graphene based cathode in configuring a thermionic converter (TC), an appropriate operating regime in achieving the efficient energy conversion has been identified. A TC configured with the graphene based cathode (operating at ˜1200 K/work function 4.74 V) along with the metallic anode (operating at ˜400 K/ work function 2.0 V) is predicted to display ˜56% of the input thermal flux into the electrical energy, which infers approximately ˜84% of the Carnot efficiency.

Application of Time-Dependent Density Functional and Natural Bond Orbital Theories to the UV-vis Absorption Spectra of Some Phenolic Compounds.

PubMed

Marković, Svetlana; Tošović, Jelena

2015-09-03

The UV-vis properties of 22 natural phenolic compounds, comprising anthraquinones, neoflavonoids, and flavonoids were systematically examined. The time-dependent density functional theory (TDDFT) approach in combination with the B3LYP, B3LYP-D2, B3P86, and M06-2X functionals was used to simulate the UV-vis spectra of the investigated compounds. It was shown that all methods exhibit very good (B3LYP slightly better) performance in reproducing the examined UV-vis spectra. However, the shapes of the Kohn-Sham molecular orbitals (MOs) involved in electronic transitions were misleading in constructing the MO correlation diagrams. To provide better understanding of redistribution of electron density upon excitation, the natural bond orbital (NBO) analysis was applied. Bearing in mind the spatial and energetic separations, as well as the character of the π bonding, lone pair, and π* antibonding natural localized molecular orbitals (NLMOs), the "NLMO clusters" were constructed. NLMO cluster should be understood as a part of a molecule characterized with distinguished electron density. It was shown that all absorption bands including all electronic transitions need to be inspected to fully understand the UV-vis spectrum of a certain compound, and, thus, to learn more about its UV-vis light absorption. Our investigation showed that the TDDFT and NBO theories are complementary, as the results from the two approaches can be combined to interpret the UV-vis spectra. Agreement between the predictions of the TDDFT approach and those based on the NLMO clusters is excellent in the case of major electronic transitions and long wavelengths. It should be emphasized that the approach for investigation of UV-vis light absorption based on the NLMO clusters is applied for the first time.

Millimeter-wave imaging diagnostics systems on the EAST tokamak (invited)

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

Zhu, Y. L.; Xie, J. L., E-mail: jlxie@ustc.edu.cn; Yu, C. X.

2016-11-15

Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This “4th generation” MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven bymore » fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy “general optics structure” has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.« less

Millimeter-wave imaging diagnostics systems on the EAST tokamak (invited)

NASA Astrophysics Data System (ADS)

Zhu, Y. L.; Xie, J. L.; Yu, C. X.; Zhao, Z. L.; Gao, B. X.; Chen, D. X.; Liu, W. D.; Liao, W.; Qu, C. M.; Luo, C.; Hu, X.; Spear, A. G.; Luhmann, N. C.; Domier, C. W.; Chen, M.; Ren, X.; Tobias, B. J.

2016-11-01

Millimeter-wave imaging diagnostics, with large poloidal span and wide radial range, have been developed on the EAST tokamak for visualization of 2D electron temperature and density fluctuations. A 384 channel (24 poloidal × 16 radial) Electron Cyclotron Emission Imaging (ECEI) system in F-band (90-140 GHz) was installed on the EAST tokamak in 2012 to provide 2D electron temperature fluctuation images with high spatial and temporal resolution. A co-located Microwave Imaging Reflectometry (MIR) will be installed for imaging of density fluctuations by December 2016. This "4th generation" MIR system has eight independent frequency illumination beams in W-band (75-110 GHz) driven by fast tuning synthesizers and active multipliers. Both of these advanced millimeter-wave imaging diagnostic systems have applied the latest techniques. A novel design philosophy "general optics structure" has been employed for the design of the ECEI and MIR receiver optics with large aperture. The extended radial and poloidal coverage of ECEI on EAST is made possible by innovations in the design of front-end optics. The front-end optical structures of the two imaging diagnostics, ECEI and MIR, have been integrated into a compact system, including the ECEI receiver and MIR transmitter and receiver. Two imaging systems share the same mid-plane port for simultaneous, co-located 2D fluctuation measurements of electron density and temperature. An intelligent remote-control is utilized in the MIR electronics systems to maintain focusing at the desired radial region even with density variations by remotely tuning the probe frequencies in about 200 μs. A similar intelligent technique has also been applied on the ECEI IF system, with remote configuration of the attenuations for each channel.

Helium like impurity in CdTe/ Cd1-xMnxTe semimagnetic semiconductors under magnetic field: Dimensionality effect on electron - Electron interaction

NASA Astrophysics Data System (ADS)

Kalpana, Panneer Selvam; Jayakumar, Kalyanasundaram

2017-11-01

We study the effect of magnetic field on the Coulomb interaction between the two electrons confined inside a CdTe/Cd1-xMnxTe Quantum Well (QW), Quantum Well Wire (QWW) and Quantum Dot (QD) for the composition of Mn2+ ion, x = 0.3. The two particle Schrodinger equation has been solved using variational technique in the effective mass approximation. The results show that the applied magnetic field tremendously alters the Coulomb interaction of the electrons and their binding to the donor impurity by shrinking the spatial extension of the two particle wavefunction and leads to tunnelling through the barrier. The qualitative phenomenon involved in such variation of electron - electron interaction with the magnetic field has also been explained through the 3D - plot of the probability density function.

Spatially Resolved Far-Infrared Spectroscopic Analysis of Planetary Nebulae

NASA Astrophysics Data System (ADS)

Rattray, Rebecca; Ueta, Toshiya

2015-01-01

Planetary Nebulae (PNs) are late-life intermediate-mass (1-8 solar mass) stars that have shed their outer layers. A wide variety of morphologies and physical conditions is seen in PNs, but a complete understanding of what causes these various conditions is still needed. Spatially resolved far-infrared spectroscopic analysis has been performed on 11 targets using both PACS and SPIRE instruments on the Herschel Space Observatory as part of the Herschel Planetary Nebula Survey (HerPlaNS). Far-IR lines probe the ionized parts of the nebulae and suffer less extinction than optical lines, so observations in the far-IR are critical to our complete understanding of PNs. Because PNs are extended objects, the spectral mapping capabilities of both PACS and SPIRE allow us to better understand the spatial variations of the objects by tracking line strengths as a function of location within the nebula. The far-IR lines detected in this study can be used as tracers of electron density and electron temperature which are critical parameters in radiative transfer modeling of PNs. Information on atomic, ionic, and molecular lines identified in these 11 targets will be presented.

Modulation of spatial spin polarization at organic spinterface by side groups

NASA Astrophysics Data System (ADS)

Qiu, Shuai; Zhang, Zhao; Miao, Yuan-yuan; Zhang, Guang-ping; Ren, Jun-feng; Wang, Chuan-kui; Hu, Gui-chao

2018-01-01

Spin polarization at benzene/Ni organic/ferromagnetic interface is investigated by applying different substituting side groups. Based on first-principle calculations, it is demonstrated that the spin polarization of the states may be tuned in magnitude and sign by the side groups, which depends on the type of side groups as well as their position in the aromatic ring. Especially, a spatial spin polarization modulation is realized at the surface with the utilization of electron donating group sbnd NH2 or electron accepting group sbnd NO2. The analysis of projected density of states onto the pz orbital of carbon atoms indicates that the side group reduces the structural symmetry of the molecule and changes the pz orbital of carbon atom at different position, which further modifies the pz-d orbital hybridization as well as the spin transfer between the molecule and the ferromagnet. This work indicates a feasible way to modulate the spatial spin polarization at organic spinterface by side groups, which deserves to be measured by spin-polarized scanning tunneling microscopy.

Langmuir Probe Measurements in an Inductively Coupled GEC Reference Cell Plasma

NASA Technical Reports Server (NTRS)

Ji, J. S.; Kim, J. S.; Cappelli, M. A.; Sharma, S. P.; Arnold, J. O. (Technical Monitor)

1998-01-01

Measurements of electron number density, electron temperature, and electron energy distribution function (EEDF) using a compensated Langmuir probe have been performed on an inductively (transformer ) coupled Gaseous Electronics Conference (GEC) reference cell plasma. The plasma source is operated with CH4, CF4, or their mixtures with argon. The effect of independently driving the electrode supporting the wafer on the probe data is studied. In particular, we find that the plasma structure depends on the phase in addition to the magnitude of the power coupled to the electrode relative to that of the transformer coil. The Langmuir probe is translated in a plane parallel to the electrode to investigate the spatial structure of the plasma. The probe data is also compared with fluid model predictions.

Spatial distribution of the RF power absorbed in a helicon plasma source

NASA Astrophysics Data System (ADS)

Aleksenko, O. V.; Miroshnichenko, V. I.; Mordik, S. N.

2014-08-01

The spatial distributions of the RF power absorbed by plasma electrons in an ion source operating in the helicon mode (ω ci < ω < ω ce < ω pe ) are studied numerically by using a simplified model of an RF plasma source in an external uniform magnetic field. The parameters of the source used in numerical simulations are determined by the necessity of the simultaneous excitation of two types of waves, helicons and Trivelpiece-Gould modes, for which the corresponding transparency diagrams are used. The numerical simulations are carried out for two values of the working gas (helium) pressure and two values of the discharge chamber length under the assumption that symmetric modes are excited. The parameters of the source correspond to those of the injector of the nuclear scanning microprobe operating at the Institute of Applied Physics, National Academy of Sciences of Ukraine. It is assumed that the mechanism of RF power absorption is based on the acceleration of plasma electrons in the field of a Trivelpiece-Gould mode, which is interrupted by pair collisions of plasma electrons with neutral atoms and ions of the working gas. The simulation results show that the total absorbed RF power at a fixed plasma density depends in a resonant manner on the magnetic field. The resonance is found to become smoother with increasing working gas pressure. The distributions of the absorbed RF power in the discharge chamber are presented. The achievable density of the extracted current is estimated using the Bohm criterion.

Modelling of plasma-wall interaction and impurity transport in fusion devices and prompt deposition of tungsten as application

NASA Astrophysics Data System (ADS)

Kirschner, A.; Tskhakaya, D.; Brezinsek, S.; Borodin, D.; Romazanov, J.; Ding, R.; Eksaeva, A.; Linsmeier, Ch

2018-01-01

Main processes of plasma-wall interaction and impurity transport in fusion devices and their impact on the availability of the devices are presented and modelling tools, in particular the three-dimensional Monte-Carlo code ERO, are introduced. The capability of ERO is demonstrated on the example of tungsten erosion and deposition modelling. The dependence of tungsten deposition on plasma temperature and density is studied by simulations with a simplified geometry assuming (almost) constant plasma parameters. The amount of deposition increases with increasing electron temperature and density. Up to 100% of eroded tungsten can be promptly deposited near to the location of erosion at very high densities (˜1 × 1014 cm-3 expected e.g. in the divertor of ITER). The effect of the sheath characteristics on tungsten prompt deposition is investigated by using particle-in-cell (PIC) simulations to spatially resolve the plasma parameters inside the sheath. Applying PIC data instead of non-resolved sheath leads in general to smaller tungsten deposition, which is mainly due to a density and temperature decrease towards the surface within the sheath. Two-dimensional tungsten erosion/deposition simulations, assuming symmetry in toroidal direction but poloidally spatially varying plasma parameter profiles, have been carried out for the JET divertor. The simulations reveal, similar to experimental findings, that tungsten gross erosion is dominated in H-mode plasmas by the intra-ELM phases. However, due to deposition, the net tungsten erosion can be similar within intra- and inter-ELM phases if the inter-ELM electron temperature is high enough. Also, the simulated deposition fraction of about 84% in between ELMs is in line with spectroscopic observations from which a lower limit of 50% has been estimated.

Imaging the square of the correlated two-electron wave function of a hydrogen molecule

DOE PAGES

Waitz, M.; Bello, R. Y.; Metz, D.; ...

2017-12-22

The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H 2 two-electron wave function in whichmore » electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Finally, our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.« less

Imaging the square of the correlated two-electron wave function of a hydrogen molecule.

PubMed

Waitz, M; Bello, R Y; Metz, D; Lower, J; Trinter, F; Schober, C; Keiling, M; Lenz, U; Pitzer, M; Mertens, K; Martins, M; Viefhaus, J; Klumpp, S; Weber, T; Schmidt, L Ph H; Williams, J B; Schöffler, M S; Serov, V V; Kheifets, A S; Argenti, L; Palacios, A; Martín, F; Jahnke, T; Dörner, R

2017-12-22

The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H 2 two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.

Imaging the square of the correlated two-electron wave function of a hydrogen molecule

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

Waitz, M.; Bello, R. Y.; Metz, D.

The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H 2 two-electron wave function in whichmore » electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Finally, our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.« less

Effects of emission layer doping on the spatial distribution of charge and host recombination rate density in organic light emitting devices: A numerical study

NASA Astrophysics Data System (ADS)

Li, Yanli; Zhou, Maoqing; Zheng, Tingcai; Yao, Bo; Peng, Yingquan

2013-12-01

Based on drift-diffusion theory, a numerical model of the doping of a single energy level trap in the emission layer of an organic light emitting device (OLED) was developed, and the effects of doping of this single energy level trap on the distribution of the charge density, the recombination rate density, and the electric field in single- and double-layer OLEDs were studied numerically. The results show that by doping the n-type (p-type) emission layer with single energy electron (hole) traps, the distribution of the recombination rate density can be tuned and shifted, which is useful for improvement of the device performance by reduced electrode quenching or for realization of desirable special functions, e.g., emission spectrum tuning in multiple dye-doped white OLEDs.

Improved density profile measurements in the C-2U advanced beam-driven Field-Reversed Configuration (FRC) plasmas

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

Beall, M., E-mail: mbeall@trialphaenergy.com; Deng, B. H.; Gota, H.

2016-11-15

In the prior C-2 experiment, electron density was measured using a two-color 6-chord CO{sub 2}/HeNe interferometer. Analysis shows that high-frequency common mode phase noise can be reduced by a factor of 3 by constructing a reference chord. In the system upgrade from C-2 to C-2U a 4-chord far-infrared laser interferometer was developed, which demonstrated superior sensitivity (1 × 10{sup 16} m{sup −2} at >1 MHz bandwidth) and solved the under spatial sampling issue of the C-2 interferometer system. Improved density-profile measurement results are presented in this paper, including evidence of fast-ion modified density profile and stabilization of the n =more » 1 plasma wobble mode.« less

Spatial correlation in matter-wave interference as a measure of decoherence, dephasing, and entropy

NASA Astrophysics Data System (ADS)

Chen, Zilin; Beierle, Peter; Batelaan, Herman

2018-04-01

The loss of contrast in double-slit electron diffraction due to dephasing and decoherence processes is studied. It is shown that the spatial intensity correlation function of diffraction patterns can be used to distinguish between dephasing and decoherence. This establishes a measure of time reversibility that does not require the determination of coherence terms of the density matrix, while von Neumann entropy, another measure of time reversibility, does require coherence terms. This technique is exciting in view of the need to understand and control the detrimental experimental effect of contrast loss and for fundamental studies on the transition from the classical to the quantum regime.

X-ray spatial frequency heterodyne imaging of protein-based nanobubble contrast agents

PubMed Central

Rand, Danielle; Uchida, Masaki; Douglas, Trevor; Rose-Petruck, Christoph

2014-01-01

Spatial Frequency Heterodyne Imaging (SFHI) is a novel x-ray scatter imaging technique that utilizes nanoparticle contrast agents. The enhanced sensitivity of this new technique relative to traditional absorption-based x-ray radiography makes it promising for applications in biomedical and materials imaging. Although previous studies on SFHI have utilized only metal nanoparticle contrast agents, we show that nanomaterials with a much lower electron density are also suitable. We prepared protein-based “nanobubble” contrast agents that are comprised of protein cage architectures filled with gas. Results show that these nanobubbles provide contrast in SFHI comparable to that of gold nanoparticles of similar size. PMID:25321797

Dynamic Characteristics of Positive Pulsed Dielectric Barrier Discharge for Ozone Generation in Air

NASA Astrophysics Data System (ADS)

Wei, Linsheng; Peng, Bangfa; Li, Ming; Zhang, Yafang; Hu, Zhaoji

2016-02-01

A comprehensive dynamic model consisting of 66 reactions and 24 species is developed to investigate the dynamic characteristics of ozone generation by positive pulsed dielectric barrier discharge (DBD) using parallel-plate reactor in air. The electron energy conservation equation is coupled to the electron continuity equation, the heavy species continuity equation, and Poisson's equation for a better description. The reliability of the model is experimentally confirmed. The model can be used to predict the temporal and spatial evolution of species, as well as streamer propagation. The simulation results show that electron density increases nearly exponentially in the direction to the anode at the electron avalanche. Streamer propagation velocity is about 5.26 × 104 m/s from anode to cathode in the simulated condition. The primary positive ion, negative ion, and excited species are O2+, O3- and O2(1Δg) in pulsed DBD in air, respectively. N2O has the largest density among nitrogen oxides. e and N2+ densities in the streamer head increase gradually to maximum values with the development of the streamer. Meanwhile, the O2+, O, O3, N2(A3Σ) and N2O densities reach maximum values in the vicinity of the anode. supported by National Natural Science Foundation of China (Nos. 51366012 and 11105067), Jiangxi Province Young Scientists (Jinggang Star) Cultivation Plan of China (No. 20133BCB23008), Natural Science Foundation of Jiangxi, China (No. 20151BAB206047) and Jiangxi Province Higher School Science and Technology Landing Plan of China (No. KJLD-14015)

Ion beam enhancement in magnetically insulated ion diodes for high-intensity pulsed ion beam generation in non-relativistic mode

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

Zhu, X. P.; Surface Engineering Laboratory, School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024; Zhang, Z. C.

High-intensity pulsed ion beam (HIPIB) with ion current density above Child-Langmuir limit is achieved by extracting ion beam from anode plasma of ion diodes with suppressing electron flow under magnetic field insulation. It was theoretically estimated that with increasing the magnetic field, a maximal value of ion current density may reach nearly 3 times that of Child-Langmuir limit in a non-relativistic mode and close to 6 times in a highly relativistic mode. In this study, the behavior of ion beam enhancement by magnetic insulation is systematically investigated in three types of magnetically insulated ion diodes (MIDs) with passive anode, takingmore » into account the anode plasma generation process on the anode surface. A maximal enhancement factor higher than 6 over the Child-Langmuir limit can be obtained in the non-relativistic mode with accelerating voltage of 200–300 kV. The MIDs differ in two anode plasma formation mechanisms, i.e., surface flashover of a dielectric coating on the anode and explosive emission of electrons from the anode, as well as in two insulation modes of external-magnetic field and self-magnetic field with either non-closed or closed drift of electrons in the anode-cathode (A-K) gap, respectively. Combined with ion current density measurement, energy density characterization is employed to resolve the spatial distribution of energy density before focusing for exploring the ion beam generation process. Consistent results are obtained on three types of MIDs concerning control of neutralizing electron flows for the space charge of ions where the high ion beam enhancement is determined by effective electron neutralization in the A-K gap, while the HIPIB composition of different ion species downstream from the diode may be considerably affected by the ion beam neutralization during propagation.« less

Electron-hole liquid in semiconductors and low-dimensional structures

NASA Astrophysics Data System (ADS)

Sibeldin, N. N.

2017-11-01

The condensation of excitons into an electron-hole liquid (EHL) and the main EHL properties in bulk semiconductors and low-dimensional structures are considered. The EHL properties in bulk materials are discussed primarily in qualitative terms based on the experimental results obtained for germanium and silicon. Some of the experiments in which the main EHL thermodynamic parameters (density and binding energy) have been obtained are described and the basic factors that determine these parameters are considered. Topics covered include the effect of external perturbations (uniaxial strain and magnetic field) on EHL stability; phase diagrams for a nonequilibrium exciton-gas-EHL system; information on the size and concentration of electron-hole drops (EHDs) under various experimental conditions; the kinetics of exciton condensation and of recombination in the exciton-gas-EHD system; dynamic EHD properties and the motion of EHDs under the action of external forces; the properties of giant EHDs that form in potential wells produced by applying an inhomogeneous strain to the crystal; and effects associated with the drag of EHDs by nonequilibrium phonons (phonon wind), including the dynamics and formation of an anisotropic spatial structure of the EHD cloud. In discussing EHLs in low-dimensional structures, a number of studies are reviewed on the observation and experimental investigation of phenomena such as spatially indirect (dipolar) electron-hole and exciton (dielectric) liquids in GaAs/AlGaAs structures with double quantum wells (QWs), EHDs containing only a few electron-hole pairs (dropletons), EHLs in type-I silicon QWs, and spatially direct and dipolar EHLs in type-II silicon-germanium heterostructures.

Electron-ion hybrid instability experiment upgrades to the Auburn Linear Experiment for Instability Studies.

PubMed

DuBois, A M; Arnold, I; Thomas, E; Tejero, E; Amatucci, W E

2013-04-01

The Auburn Linear EXperiment for Instability Studies (ALEXIS) is a laboratory plasma physics experiment used to study spatially inhomogeneous flows in a magnetized cylindrical plasma column that are driven by crossed electric (E) and magnetic (B) fields. ALEXIS was recently upgraded to include a small, secondary plasma source for a new dual source, interpenetrating plasma experiment. Using two plasma sources allows for highly localized electric fields to be made at the boundary of the two plasmas, inducing strong E × B velocity shear in the plasma, which can give rise to a regime of instabilities that have not previously been studied in ALEXIS. The dual plasma configuration makes it possible to have independent control over the velocity shear and the density gradient. This paper discusses the recent addition of the secondary plasma source to ALEXIS, as well as the plasma diagnostics used to measure electric fields and electron densities.

Propagation of atmospheric-pressure ionization waves along the tapered tube

NASA Astrophysics Data System (ADS)

Xia, Yang; Wang, Wenchun; Liu, Dongping; Yan, Wen; Bi, Zhenhua; Ji, Longfei; Niu, Jinhai; Zhao, Yao

2018-02-01

Gas discharge in a small radius dielectric tube may result in atmospheric pressure plasma jets with high energy and density of electrons. In this study, the atmospheric pressure ionization waves (IWs) were generated inside a tapered tube. The propagation behaviors of IWs inside the tube were studied by using a spatially and temporally resolved optical detection system. Our measurements show that both the intensity and velocity of the IWs decrease dramatically when they propagate to the tapered region. After the taper, the velocity, intensity, and electron density of the IWs are improved with the tube inner diameter decreasing from 4.0 to 0.5 mm. Our analysis indicates that the local gas conductivity and surface charges may play a role in the propagation of the IWs under such a geometrical constraint, and the difference in the dynamics of the IWs after the taper can be related to the restriction in the size of IWs.

Open-orbit theory of photoionization microscopy on nonhydrogenic atoms

NASA Astrophysics Data System (ADS)

Liu, F. L.; Zhao, L. B.

2017-04-01

Semiclassical open-orbit theory (OOT), previously developed to study photoionization of hydrogenic atoms in a uniform electric field [L. B. Zhao and J. B. Delos, Phys. Rev. A 81, 053417 (2010), 10.1103/PhysRevA.81.053417], has been generalized to describe the propagation of outgoing electron waves to macroscopic distances from a nonhydrogenic atomic source. The generalized OOT has been applied to calculate spatial distributions of electron probability densities and current densities, produced due to photoionization for lithium in a uniform electric field. The obtained results are compared with those from the fully quantum-mechanical coupled-channel theory (CCT). The excellent agreement between the CCT and OOT confirms the reliability of the generalized OOT. Comparison is also made with theoretical calculations from the wave-packet propagation technique and the recent photoionization microscopy experiment. The existing difference between theory and experiment is discussed.

Electron diamagnetic effect in a magnetic nozzle on a helicon plasma thruster performance

NASA Astrophysics Data System (ADS)

Takahashi, Kazunori; Lafleur, Trevor; Charles, Christine; Alexander, Peter; Boswell, Rod

2012-10-01

The axial force, which is called thrust sometimes, imparted from a magnetically expanding helicon plasma thruster is directly measured and the results are compared with a two-dimensional fluid theory. The force component solely transmitted to the expanding field is directly measured and identified as an axial force produced by the azimuthal current due to an electron diamagnetic drift and the radial component of the applied magnetic field. In this type of configuration, plasma diffusion in magnetic field affects a spatial profile of the plasma density and the resultant axial force onto the magnetic field. It is observed that the force component onto the magnetic field increases with an increase in the magnetic field strength, simultaneously with an increase in the plasma density downstream of the source exit, which could be due to suppression of the cross field diffusion in the magnetic nozzle.

Organic semiconductor density of states controls the energy level alignment at electrode interfaces

PubMed Central

Oehzelt, Martin; Koch, Norbert; Heimel, Georg

2014-01-01

Minimizing charge carrier injection barriers and extraction losses at interfaces between organic semiconductors and metallic electrodes is critical for optimizing the performance of organic (opto-) electronic devices. Here, we implement a detailed electrostatic model, capable of reproducing the alignment between the electrode Fermi energy and the transport states in the organic semiconductor both qualitatively and quantitatively. Covering the full phenomenological range of interfacial energy level alignment regimes within a single, consistent framework and continuously connecting the limiting cases described by previously proposed models allows us to resolve conflicting views in the literature. Our results highlight the density of states in the organic semiconductor as a key factor. Its shape and, in particular, the energy distribution of electronic states tailing into the fundamental gap is found to determine both the minimum value of practically achievable injection barriers as well as their spatial profile, ranging from abrupt interface dipoles to extended band-bending regions. PMID:24938867

Models of SOL transport and their relation to scaling of the divertor heat flux width in DIII-D

DOE PAGES

Makowski, M. A.; Lasnier, C. J.; Leonard, A. W.; ...

2014-10-06

Strong support for the critical pressure gradient model for the heat flux width has been obtained, in that the measured separatrix pressure gradient lies below and scales similarly to the pressure gradient limit obtained from the ideal, infinite-n stability codes, BALOO and 2DX, in all cases that have been examined. Predictions of a heuristic drift model for the heat flux width are also in qualitative agreement with the measurements. We obtained these results by using an improved high rep-rate and higher edge spatial resolution Thomson scattering system on DIII-D to measure the upstream electron temperature and density profiles. In ordermore » to compare theory and experiment, profiles of density, temperature, and pressure for both electrons and ions are needed as well values of these quantitities at the separatrix. We also developed a simple method to identify a proxy for the separatrix.« less

Amplitude fluctuations driven by the density of electron pairs within nanosize granular structures inside strongly disordered superconductors: evidence for a shell-like effect.

PubMed

Ghosh, Sanjib; Mandal, Sudhansu S

2013-11-15

Motivated by the recent observation of the shell effect in a nanoscale pure superconductor by Bose et al. [Nat. Mater. 9, 550 (2010)], we explore the possible shell-like effect in a strongly disordered superconductor as it is known to produce nanosize superconducting puddles (SPs). We find a remarkable change in the texture of the pairing amplitudes that is responsible for forming the SP, upon monotonic tuning of the average electron density, , and keeping the disorder landscape unaltered. Both the spatially averaged pairing amplitude and the quasiparticle excitation gap oscillate with . This oscillation is due to a rapid change in the low-lying quasiparticle energy spectra and thereby a change in the shapes and positions of the SPs. We establish a correlation between the formation of SPs and the shell-like effect. The experimental consequences of our theory are also discussed.

Influence of the Level of Protonation on the Geometry and the Electronic Structure of Emeraldine Oligomers

NASA Astrophysics Data System (ADS)

Petrova, Jasmina; Romanova, Julia; Madjarova, Galia; Ivanova, Anela; Tadjer, Alia; Gospodinova, Natalia

A number of studies prove the existence of magnetically active states in polyaniline and claim polaronic nature of conductivity, but the molecular structure of polarons and bipolarons with account of the solvent effect has not been exhausted. Alongside with conductivity, the optical and magnetic properties of the polymer related to its practical application could be rationalized by the elucidation of this problem. The purpose of this chapter is the assessment of the degree of protonation on the spatial and electronic structure of hydrated polyaniline oligomers. Neutral and protonated emeraldine octamers are modeled to this end. UHF, UBLYP, and UB3LYP with 6-31G* basis set were employed for optimization of the geometry in aqueous medium (PCM). Various structural parameters: bond lengths, valence, and torsion angles, were analyzed and compared. The distribution of Mulliken and NBO charge density and Mulliken atomic spin density was discussed.

Propagation of an ultrawideband electromagnetic signal in ionospheric plasma

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

Soldatov, A. V., E-mail: av-soldatov@vniief.ru; Terekhin, V. A.

2016-10-15

The propagation of an ultrawideband electromagnetic signal in the ionosphere—a plasma medium with spatially nonuniform characteristics—is studied analytically in the high-frequency approximation. The effect of the plasma dielectric properties and angular divergence on the shape and frequency spectrum of the propagating signal is investigated. It is shown that the spectral energy density of the signal is preserved if collisions of ionospheric plasma electrons are neglected.

Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH3NH3PbI3

DOE PAGES

Wang, Yun; Huang, Jingsong; Sumpter, Bobby G.; ...

2014-12-19

Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of the surface energies for the most stable configurations identified for various surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms,more » which are directly correlated with the numbers of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as the first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to achieve further breakthroughs in solar conversion efficiencies.« less

Measurements of Electron Density Profiles of Plasmas Produced by Nike KrF Laser for Laser Plasma Instability (LPI) Research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Obenschain, S. P.; Schmitt, A. J.; Kehne, D. M.; Karasik, M.; Chan, L.-Y.; Serlin, V.; Phillips, L.

2013-10-01

Knowing spatial profiles of electron density (ne) in the underdense coronal region (n

Characterization of twin boundaries in an Fe–17.5Mn–0.56C twinning induced plasticity steel

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

Patterson, Erin E., E-mail: erin.diedrich@yahoo.com; Field, David P., E-mail: dfield@wsu.edu; Zhang, Yudong, E-mail: yudong.zhang@univ-metz.fr

2013-11-15

A twinning-induced plasticity steel of composition Fe–17.5 wt.% Mn–0.56 wt.% C–1.39 wt.% Al–0.24 wt.% Si was analyzed for the purpose of characterizing the relationship between tensile strain and deformation twinning. Tensile samples achieved a maximum of 0.46 true strain at failure, and a maximum ultimate tensile strength of 1599 MPa. Electron backscatter diffraction (EBSD) analysis showed that the grain orientation rotated heavily to < 111 > parallel to the tensile axis above 0.3 true strain. Sigma 3 misorientations, as identified by EBSD orientation measurements, and using the image quality maps were used to quantify the number of twins present inmore » the scanned areas of the samples. The image quality method yielded a distinct positive correlation between the twin area density and deformation, but the orientation measurements were unreliable in quantifying twin density in these structures. Quantitative analysis of the twin fraction is limited from orientation information because of the poor spatial resolution of EBSD in relation to the twin thickness. The EBSD orientation maps created for a thin foil sample showed some improvement in the resolution of the twins, but not enough to be significant. Measurements of the twins in the transmission electron microscopy micrographs yielded an average thickness of 23 nm, which is near the resolution capabilities of EBSD on this material for the instrumentation used. Electron channeling contrast imaging performed on one bulk tensile specimen of 0.34 true strain, using a method of controlled diffraction, yielded several images of twinning, dislocation structures and strain fields. A twin thickness of 66 nm was measured by the same method used for the transmission electron microscopy measurement. It is apparent that the results obtain by electron channeling contrast imaging were better than those by EBSD but did not capture all information on the twin boundaries such as was observed by transmission electron microscopy. - Highlights: • Performed tensile tests to assess mechanical performance of TWIP alloy • Analyzed tensile specimens using EBSD, TEM, and ECCI • EBSD showed that most twinning occurred at or near the < 111 >//TA orientation. • EBSD, TEM and ECCI were used to measure average twin density. • Compared spatial resolution of EBSD, ECCI and TEM for the instrumentation used.« less

The Spatial Expansion of a Discharge in the Generation and the Channel Structure (in German)

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

Schlumbohm, H.

1962-02-01

The spatial expansion of a discharge was investigated under homogeneous field conditions, using an anode with a small central area separated from the remainder and wide band double beam oscillographic techniques. The discharge currents were initiated by electrons released along traces of single alpha particles in the gas between the electrodes. The k particles enter the gap volume through a small hole in the middle of the separated center of the anode. The measurements have shown that a secondary photon emission from the cathode causes a spreading over the total gap volume within the first few electron generations (N 2,more » air, and CO 2 at lower pressures). If a streamer mechanism occurs (O 2 and CO 2 at higher pressures), the discharge remains localized to the trace of the alpha particle, in which the avalanches yielded by the primary electrons have produced a high density of positive ions. New details of steamer mechanism are revealed by analyzing the rapid increase of the current during streamer formation.« less

Under-the-barrier dynamics in laser-induced relativistic tunneling.

PubMed

Klaiber, Michael; Yakaboylu, Enderalp; Bauke, Heiko; Hatsagortsyan, Karen Z; Keitel, Christoph H

2013-04-12

The tunneling dynamics in relativistic strong-field ionization is investigated with the aim to develop an intuitive picture for the relativistic tunneling regime. We demonstrate that the tunneling picture applies also in the relativistic regime by introducing position dependent energy levels. The quantum dynamics in the classically forbidden region features two time scales, the typical time that characterizes the probability density's decay of the ionizing electron under the barrier (Keldysh time) and the time interval which the electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time). In the relativistic regime, an electron momentum shift as well as a spatial shift along the laser propagation direction arise during the under-the-barrier motion which are caused by the laser magnetic field induced Lorentz force. The momentum shift is proportional to the Keldysh time, while the wave-packet's spatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature of the momentum shift is shown to be present in the ionization spectrum at the detector and, therefore, observable experimentally. In contrast, the signature of the Eisenbud-Wigner-Smith time delay disappears at far distances for pure quasistatic tunneling dynamics.

Spatially resolved mapping of electrical conductivity across individual domain (grain) boundaries in graphene.

PubMed

Clark, Kendal W; Zhang, X-G; Vlassiouk, Ivan V; He, Guowei; Feenstra, Randall M; Li, An-Ping

2013-09-24

All large-scale graphene films contain extended topological defects dividing graphene into domains or grains. Here, we spatially map electronic transport near specific domain and grain boundaries in both epitaxial graphene grown on SiC and CVD graphene on Cu subsequently transferred to a SiO2 substrate, with one-to-one correspondence to boundary structures. Boundaries coinciding with the substrate step on SiC exhibit a significant potential barrier for electron transport of epitaxial graphene due to the reduced charge transfer from the substrate near the step edge. Moreover, monolayer-bilayer boundaries exhibit a high resistance that can change depending on the height of substrate step coinciding at the boundary. In CVD graphene, the resistance of a grain boundary changes with the width of the disordered transition region between adjacent grains. A quantitative modeling of boundary resistance reveals the increased electron Fermi wave vector within the boundary region, possibly due to boundary induced charge density variation. Understanding how resistance change with domain (grain) boundary structure in graphene is a crucial first step for controlled engineering of defects in large-scale graphene films.

Spin-orbit driven magnetic insulating state with J eff=1/2 character in a 4d oxide

DOE PAGES

Calder, S.; Li, Ling; Okamoto, Satoshi; ...

2015-11-30

The unusual magnetic and electronic ground states of 5d iridates has been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogousmore » J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy and find a magnetic insulating ground state with J eff =1/2 character.The unusual magnetic and electronic ground states of 5d iridates have been shown to be driven by intrinsically enhanced spin-orbit coupling (SOC). The influence of appreciable but reduced SOC in creating the manifested magnetic insulating states in 4d oxides is less clear, with one hurdle being the existence of such compounds. Here, we present experimental and theoretical results on Sr 4RhO 6 that reveal SOC dominated behavior. Neutron measurements show the octahedra are both spatially separated and locally ideal, making the electronic ground state susceptible to alterations by SOC. Magnetic ordering is observed with a similar structure to an analogous J eff=1/2 Mott iridate. We consider the underlying role of SOC in this rhodate with density functional theory and x-ray absorption spectroscopy, and find a magnetic insulating ground state with J eff=12 character.« less

Non-flipping 13C spins near an NV center in diamond: hyperfine and spatial characteristics by density functional theory simulation of the C510[NV]H252 cluster

NASA Astrophysics Data System (ADS)

Nizovtsev, A. P.; Kilin, S. Ya; Pushkarchuk, A. L.; Pushkarchuk, V. A.; Kuten, S. A.; Zhikol, O. A.; Schmitt, S.; Unden, T.; Jelezko, F.

2018-02-01

Single NV centers in diamond coupled by hyperfine interaction (hfi) to neighboring 13C nuclear spins are now widely used in emerging quantum technologies as elements of quantum memory adjusted to a nitrogen-vacancy (NV) center electron spin qubit. For nuclear spins with low flip-flop rate, single shot readout was demonstrated under ambient conditions. Here we report on a systematic search for such stable NV-13C systems using density functional theory to simulate the hfi and spatial characteristics of all possible NV-13C complexes in the H-terminated cluster C510[NV]-H252 hosting the NV center. Along with the expected stable ‘NV-axial-13C’ systems wherein the 13C nuclear spin is located on the NV axis, we found for the first time new families of positions for the 13C nuclear spin exhibiting negligible hfi-induced flipping rates due to near-symmetric local spin density distribution. Spatially, these positions are located in the diamond bilayer passing through the vacancy of the NV center and being perpendicular to the NV axis. Analysis of available publications showed that, apparently, some of the predicted non-axial near-stable NV-13C systems have already been observed experimentally. A special experiment performed on one of these systems confirmed the prediction made.

Evolution of the properties of helium nanobubbles during in situ annealing probed by spectrum imaging in the transmission electron microscope

NASA Astrophysics Data System (ADS)

Alix, K.; David, M.-L.; Dérès, J.; Hébert, C.; Pizzagalli, L.

2018-03-01

The evolution of nanometric helium bubbles in silicon has been investigated using spatially resolved electron energy-loss spectroscopy during in situ annealing in the transmission electron microscope. This approach allows the simultaneous determination of both the morphology and the helium density in the bubbles at each step of the annealing. Structural modification and helium emission from bubbles of various diameters in the range 7.5 to 20 nm and various aspect ratios of 1.1 to 1.9 have been studied. We clearly show that helium emission takes place at temperatures where bubble migration had hardly started. At higher temperatures, the migration (and coalescence) of voids is clearly revealed. For helium density lower than 150 He nm-3 , the Cerofolini's model taking into account the thermodynamical properties of an ultradense fluid reproduces well the helium emission from the bubbles, leading to an activation energy of 1.8 eV. When bubbles exhibit a higher initial helium density, the Cerofolini's model fails to reproduce the helium emission kinetics. We ascribe this to the fact that helium may be in the solid phase and we propose a tentative model to take into account the properties of the solid.

Development of a large-area planar surface-wave plasma source with a cavity launcher driven by a 915 MHz UHF wave

NASA Astrophysics Data System (ADS)

Chang, Xijiang; Kunii, Kazuki; Liang, Rongqing; Nagatsu, Masaaki

2013-04-01

A large-area planar surface-wave plasma (SWP) source driven by a 915 MHz ultrahigh frequency (UHF) wave was developed. To avoid using large, thick dielectric plates as vacuum windows, we propose a cavity launcher consisting of a cylindrical cavity with several small quartz discs at the bottom. Three types of launchers with quartz discs located at different positions were tested to compare their plasma production efficiencies and spatial distributions of electron density. With the optimum launcher, large-area plasma discharges with a radial uniformity within ±10% were obtained in a radius of about 25-30 cm in Ar gas at 8 Pa for incident power in the range 0.5-2.5 kW. The maximum electron density and temperature were approximately (0.95-1.1) × 1011 cm-3 and 1.9-2.0 eV, respectively, as measured by a Langmuir probe located 24 cm below the bottom of the cavity launcher. Using an Ar/NH3 SWP with the optimum launcher, we demonstrated large-area amino-group surface modification of polyurethane sheets. Experimental results indicated that a uniform amino-group modification was achieved over a radius of approximately 40 cm, which is slightly larger than the radial uniformity of the electron density distribution.

Identical spin rotation effect and electron spin waves in quantum gas of atomic hydrogen

NASA Astrophysics Data System (ADS)

Lehtonen, L.; Vainio, O.; Ahokas, J.; Järvinen, J.; Novotny, S.; Sheludyakov, S.; Suominen, K.-A.; Vasiliev, S.; Khmelenko, V. V.; Lee, D. M.

2018-05-01

We present an experimental study of electron spin waves in atomic hydrogen gas compressed to high densities of ∼5 × 1018 cm‑3 at temperatures ranging from 0.26 to 0.6 K in the strong magnetic field of 4.6 T. Hydrogen gas is in a quantum regime when the thermal de-Broglie wavelength is much larger than the s-wave scattering length. In this regime the identical particle effects play a major role in atomic collisions and lead to the identical spin rotation effect (ISR). We observed a variety of spin wave modes caused by this effect with strong dependence on the magnetic potential caused by variations of the polarizing magnetic field. We demonstrate confinement of the ISR modes in the magnetic potential and manipulate their properties by changing the spatial profile of the magnetic field. We have found that at a high enough density of H gas the magnons accumulate in their ground state in the magnetic trap and exhibit long coherence, which has a profound effect on the electron spin resonance spectra. Such macroscopic accumulation of the ground state occurs at a certain critical density of hydrogen gas, where the chemical potential of the magnons becomes equal to the energy of their ground state in the trapping potential.

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

Pratapa, Phanisri P.; Suryanarayana, Phanish; Pask, John E.

We present the Clenshaw–Curtis Spectral Quadrature (SQ) method for real-space O(N) Density Functional Theory (DFT) calculations. In this approach, all quantities of interest are expressed as bilinear forms or sums over bilinear forms, which are then approximated by spatially localized Clenshaw–Curtis quadrature rules. This technique is identically applicable to both insulating and metallic systems, and in conjunction with local reformulation of the electrostatics, enables the O(N) evaluation of the electronic density, energy, and atomic forces. The SQ approach also permits infinite-cell calculations without recourse to Brillouin zone integration or large supercells. We employ a finite difference representation in order tomore » exploit the locality of electronic interactions in real space, enable systematic convergence, and facilitate large-scale parallel implementation. In particular, we derive expressions for the electronic density, total energy, and atomic forces that can be evaluated in O(N) operations. We demonstrate the systematic convergence of energies and forces with respect to quadrature order as well as truncation radius to the exact diagonalization result. In addition, we show convergence with respect to mesh size to established O(N 3) planewave results. In conclusion, we establish the efficiency of the proposed approach for high temperature calculations and discuss its particular suitability for large-scale parallel computation.« less

Instantaneous polarization statistic property of EM waves incident on time-varying reentry plasma

NASA Astrophysics Data System (ADS)

Bai, Bowen; Liu, Yanming; Li, Xiaoping; Yao, Bo; Shi, Lei

2018-06-01

An analytical method is proposed in this paper to study the effect of time-varying reentry plasma sheath on the instantaneous polarization statistic property of electromagnetic (EM) waves. Based on the disturbance property of the hypersonic fluid, the spatial-temporal model of the time-varying reentry plasma sheath is established. An analytical technique referred to as transmission line analogy is developed to calculate the instantaneous transmission coefficient of EM wave propagation in time-varying plasma. Then, the instantaneous polarization statistic theory of EM wave propagation in the time-varying plasma sheath is developed. Taking the S-band telemetry right hand circularly polarized wave as an example, effects of incident angle and plasma parameters, including the electron density and the collision frequency on the EM wave's polarization statistic property are studied systematically. Statistical results indicate that the lower the collision frequency and the larger the electron density and incident angle is, the worse the deterioration of the polarization property is. Meanwhile, in conditions of critical parameters of certain electron density, collision frequency, and incident angle, the transmitted waves have both the right and left hand polarization mode, and the polarization mode will reverse. The calculation results could provide useful information for adaptive polarization receiving of the spacecraft's reentry communication.

Improved Estimation of Electron Temperature from Rocket-borne Impedance Probes

NASA Astrophysics Data System (ADS)

Rowland, D. E.; Wolfinger, K.; Stamm, J. D.

2017-12-01

The impedance probe technique is a well known method for determining high accuracy measurements of electron number density in the Earth's ionosphere. We present analysis of impedance probe data from several sounding rockets at low, mid-, and auroral latitudes, including high cadence estimates of the electron temperature, derived from analytical fits to the antenna impedance curves. These estimates compare favorably with independent estimates from Langmuir Probes, but at much higher temporal and spatial resolution, providing a capability to resolve small-scale temperature fluctuations. We also present some considerations for the design of impedance probes, including assessment of the effects of resonance damping due to rocket motion, effects of wake and spin modulation, and aspect angle to the magnetic field.

Implementation of a multichannel soft x-ray diagnostic for electron temperature measurements in TJ-II high-density plasmas

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

Baiao, D.; Varandas, C.; Medina, F.

2012-10-15

Based on the multi-foil technique, a multichannel soft x-ray diagnostic for electron temperature measurements has been recently implemented in the TJ-II stellarator. The diagnostic system is composed by four photodiodes arrays with beryllium filters of different thickness. An in-vacuum amplifier board is coupled to each array, aiming at preventing induced noise currents. The Thomson scattering and the vacuum ultraviolet survey diagnostics are used for assessing plasma profiles and composition, being the analysis carried out with the radiation code IONEQ. The electron temperature is determined through the different signal-pair ratios with temporal and spatial resolution. The design and preliminary results frommore » the diagnostic are presented.« less

Plasmon dispersion and Coulomb drag in low-density electron bi-layers

NASA Astrophysics Data System (ADS)

Badalyan, S. M.; Kim, C. S.; Vignale, G.; Senatore, G.

2007-03-01

We investigate the effect of exchange and correlation (xc) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a new approach, which employs dynamic xc kernels in the calculation of the bi-layer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. We observe that both optical and acoustical plasmon modes are strongly affected by xc corrections and shift in opposite directions with decreasing density. This is in stark contrast with the tendency observed within the random phase approximation (RPA). We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the RPA is found to disappear when the xc corrections are included. Our numerical results are in good agreement with the results of recent experiments by M. Kellogg et al., Solid State Commun. 123, 515 (2002).

Structure of the first order reduced density matrix in three electron systems: A generalized Pauli constraints assisted study.

PubMed

Theophilou, Iris; Lathiotakis, Nektarios N; Helbig, Nicole

2018-03-21

We investigate the structure of the one-body reduced density matrix of three electron systems, i.e., doublet and quadruplet spin configurations, corresponding to the smallest interacting system with an open-shell ground state. To this end, we use configuration interaction (CI) expansions of the exact wave function in Slater determinants built from natural orbitals in a finite dimensional Hilbert space. With the exception of maximally polarized systems, the natural orbitals of spin eigenstates are generally spin dependent, i.e., the spatial parts of the up and down natural orbitals form two different sets. A measure to quantify this spin dependence is introduced and it is shown that it varies by several orders of magnitude depending on the system. We also study the ordering issue of the spin-dependent occupation numbers which has practical implications in reduced density matrix functional theory minimization schemes, when generalized Pauli constraints (GPCs) are imposed and in the form of the CI expansion in terms of the natural orbitals. Finally, we discuss the aforementioned CI expansion when there are GPCs that are almost "pinned."

Semi-analytical modelling of positive corona discharge in air

NASA Astrophysics Data System (ADS)

Pontiga, Francisco; Yanallah, Khelifa; Chen, Junhong

2013-09-01

Semianalytical approximate solutions of the spatial distribution of electric field and electron and ion densities have been obtained by solving Poisson's equations and the continuity equations for the charged species along the Laplacian field lines. The need to iterate for the correct value of space charge on the corona electrode has been eliminated by using the corona current distribution over the grounded plane derived by Deutsch, which predicts a cos m θ law similar to Warburg's law. Based on the results of the approximated model, a parametric study of the influence of gas pressure, the corona wire radius, and the inter-electrode wire-plate separation has been carried out. Also, the approximate solutions of the electron number density has been combined with a simplified plasma chemistry model in order to compute the ozone density generated by the corona discharge in the presence of a gas flow. This work was supported by the Consejeria de Innovacion, Ciencia y Empresa (Junta de Andalucia) and by the Ministerio de Ciencia e Innovacion, Spain, within the European Regional Development Fund contracts FQM-4983 and FIS2011-25161.

X-ray Spectroscopic Characterization of Plasma for a Charged-Particle Energy-Loss Experiment

NASA Astrophysics Data System (ADS)

Hoffman, Nm; Lee, Cl; Wilson, Dc; Barnes, Cris W.; Petrasso, Rd; Li, C.; Hicks, D.

2000-10-01

We are pursuing an approach to a charged-particle energy-loss experiment in which charged fusion products from an imploded ICF capsule travel through a well characterized, spatially separate plasma. For this purpose, a fully ionized, uniform, nearly steady-state carbon-hydrogen plasma will be created by laser irradiation of a plastic foil. The temperature and density structure of this plasma must be determined accurately in order to relate observed energy losses to predictions of theory. Various methods for diagnosing the plasma are possible, including Thomson scattering. Alternatively, if a small admixture of higher-Z material such as chlorine is included in the plastic, x-ray spectroscopic techniques will allow the plasma's temperature and density to be determined. Electron temperature is inferred from the ratios of line strengths of various chlorine ion stages, while electron density is determined from the spectra of lithium-like satellite lines near the He beta line of helium-like chlorine. We present results from detailed-configuration accounting (DCA) models of line emission from C+H+Cl plasmas, and estimate the accuracy with which such plasmas can be characterized.

GNSS-ISR data fusion: General framework with application to the high-latitude ionosphere

NASA Astrophysics Data System (ADS)

Semeter, Joshua; Hirsch, Michael; Lind, Frank; Coster, Anthea; Erickson, Philip; Pankratius, Victor

2016-03-01

A mathematical framework is presented for the fusion of electron density measured by incoherent scatter radar (ISR) and total electron content (TEC) measured using global navigation satellite systems (GNSS). Both measurements are treated as projections of an unknown density field (for GNSS-TEC the projection is tomographic; for ISR the projection is a weighted average over a local spatial region) and discrete inverse theory is applied to obtain a higher fidelity representation of the field than could be obtained from either modality individually. The specific implementation explored herein uses the interpolated ISR density field as initial guess to the combined inverse problem, which is subsequently solved using maximum entropy regularization. Simulations involving a dense meridional network of GNSS receivers near the Poker Flat ISR demonstrate the potential of this approach to resolve sub-beam structure in ISR measurements. Several future directions are outlined, including (1) data fusion using lower level (lag product) ISR data, (2) consideration of the different temporal sampling rates, (3) application of physics-based regularization, (4) consideration of nonoptimal observing geometries, and (5) use of an ISR simulation framework for optimal experiment design.

Observation of parametric instabilities in the quarter critical density region driven by the Nike KrF laser

NASA Astrophysics Data System (ADS)

Weaver, J. L.; Oh, J.; Phillips, L.; Afeyan, B.; Seely, J.; Kehne, D.; Brown, C. M.; Obenschain, S. P.; Serlin, V.; Schmitt, A. J.; Feldman, U.; Lehmberg, R. H.; Mclean, E.; Manka, C.

2013-02-01

The krypton-fluoride (KrF) laser is an attractive choice for inertial confinement fusion due to its combination of short wavelength (λ =248 nm), large bandwidth (up to 3 THz), and superior beam smoothing by induced spatial incoherence. These qualities improve the overall hydrodynamics of directly driven pellet implosions and should allow use of increased laser intensity due to higher thresholds for laser plasma instabilities when compared to frequency tripled Nd:glass lasers (λ =351 nm). Here, we report the first observations of the two-plasmon decay instability using a KrF laser. The experiments utilized the Nike laser facility to irradiate solid plastic planar targets over a range of pulse lengths (0.35 ns≤τ≤1.25 ns) and intensities (up to 2×1015 W/cm2). Variation of the laser pulse created different combinations of electron temperature and electron density scale length. The observed onset of instability growth was consistent with the expected scaling that KrF lasers have a higher intensity threshold for instabilities in the quarter critical density region.

I. Excitonic Phase Diagram in Silicon: Evidence for Two Condensed Phases. I. Motion of Photoexcited Carriers in GALLIUM-ARSENIDE/ALUMINUM(X)GALLIUM(1-X)ARSENIDE Multiple Quantum Wells-Anomalous Confinement at High Densities.

NASA Astrophysics Data System (ADS)

Smith, Leigh Morris

This thesis describes work on the thermodynamics and transport properties of photoexcited carriers in bulk and two-dimensional semiconductors. Two major topics are addressed. I. Photoluminescence experiments of excitons in unstressed silicon are presented which indicate the existence of a new non-degenerate condensed phase of plasma. This new liquid has a density one-tenth that of the ground state electron-hole liquid and is observed both above and below the liquid-gas critical point (~24.5K). A new phase diagram of excitons in silicon is presented which includes these two condensed plasmas. Consistent with the Gibbs phase rule, a triple point at 18.5 K is inferred from the luminescence data as the only temperature where the exciton gas, condensed plasma (CP) and electron-hole liquid (EHL) coexist. The low density condensed plasma persists up to a second critical point at 45 +/- 5K, above which the photoexcited carriers are observed to continuously decay into a partially ionized excitonic gas. II. We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 μm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n = 2 times 10^{11}cm ^{-2} is found to depend upon excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities. This remarkable behavior may be understood with consideration of the interactions of non-equilibrium phonons with the photoexcited carriers. We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot, while the rapidly moving component is driven by the flux of non-equilibrium phonons away from the excitation region.

Validation of COSMIC radio occultation electron density profiles by incoherent scatter radar data

NASA Astrophysics Data System (ADS)

Cherniak, Iurii; Zakharenkova, Irina

The COSMIC/FORMOSAT-3 is a joint US/Taiwan radio occultation mission consisting of six identical micro-satellites. Each microsatellite has a GPS Occultation Experiment payload to operate the ionospheric RO measurements. FS3/COSMIC data can make a positive impact on global ionosphere study providing essential information about height electron density distribu-tion. For correct using of the RO electron density profiles for geophysical analysis, modeling and other applications it is necessary to make validation of these data with electron density distributions obtained by another measurement techniques such as proven ground based facili-ties -ionosondes and IS radars. In fact as the ionosondes provide no direct information on the profile above the maximum electron density and the topside ionosonde profile is obtained by fitting a model to the peak electron density value, the COSMIC RO measurements can make an important contribution to the investigation of the topside part of the ionosphere. IS radars provide information about the whole electron density profile, so we can estimate the agreement of topside parts between two independent measurements. To validate the reliability of COS-MIC data we have used the ionospheric electron density profiles derived from IS radar located near Kharkiv, Ukraine (geographic coordinates: 49.6N, 36.3E, geomagnetic coordinates: 45.7N, 117.8E). The Kharkiv radar is a sole incoherent scatter facility on the middle latitudes of Eu-ropean region. The radar operates with 100-m zenith parabolic antenna at 158 MHz with peak transmitted power 2.0 MW. The Kharkiv IS radar is able to determine the heights-temporal distribution of ionosphere parameters in height range of 70-1500 km. At the ionosphere in-vestigation by incoherent scatter method there are directly measured the power spectrum (or autocorrelation function) of scattered signal. With using of rather complex procedure of the received signal processing it is possible to estimate the majority of the ionospheric parameters -density and kinetic temperature of electron and main ions, the plasma drift velocity and others. The comparison of RO reveals that usually COSMIC RO profiles are in a rather good agreement with ISR profiles both in the F2 layer peak electron density (NmF2) and the form of profiles. The coincidence of profiles is better in the cases when projection of the ray path of tangent points is closer to the ISR location. It is necessary to note that retrieved electron density profiles should not be interpreted as actual vertical profiles. The geographical location of the ray path tangent points at the top and at the bottom of a profile may differ by several hundred kilometers. So the spatial smearing of data takes place and RO technique represents an image of vertical and horizontal ionospheric structure. That is why the comparison with ground-based data has rather relative character. We derived quantitative parameters to char-acterize the differences of the compared profiles: the peak height difference, the relative peak density difference. Most of the compared profiles agree within error limits, depending on the accuracy of the occultation-and the radar-derived profiles. In general COSMIC RO profiles are in a good agreement with incoherent radar profiles both in the F2 layer peak electron density (NmF2) and the form of the profiles. The coincidence of COSMIC and incoherent radar pro-files is better in the cases when projection of the ray path tangent points is closer to the radar location. COSMIC measurements can be efficiently used to study the topside part of the iono-spheric electron density. To validate the reliability of the COSMIC ionospheric observations it must be done the big work on the analysis and statistical generalization of the huge data array (today the total number of ionospheric occultation is more than 2.300.000), but this technique is a very promising one to retrieve accurate profiles of the ionospheric electron density with ground-based measurements on a global scale. We acknowledge the Taiwan's National Space Organization (NSPO) and the University Corporation for Atmospheric Research (UCAR) for providing the COSMIC Data.

On the emergence of molecular structure from atomic shape in the 1/r2 harmonium model.

PubMed

Müller-Herold, Ulrich

2006-01-07

The formal similarity of the three-body Hamiltonians for helium and the hydrogen molecule ion is used to demonstrate the unfolding of a rotating dumbbell-like proton distribution from a (1s)2-type electron distribution by smooth variation of the particles' masses in the 1/r2 harmonium model. The 1/r2 harmonium is an exactly solvable modification of the harmonium model (also known as Hooke's law atom) where the attraction between different particles is harmonic and the repulsion between the two equal particles is given by a 1/r2 potential. The dumbbell-like molecular structure appears as an expression of increasing spatial correlation due to increasing mass. It gradually appears in the one-density distribution of the two equal particles if their mass exceeds a critical value depending on the mass of the third particle. For large mass of the equal particles, their one-density distribution approaches an asymptotic form derived from the Born-Oppenheimer treatment of H2+ in the 1/r2 harmonium model. Below the critical value, the one density is a spherical, Gaussian-type atomic density distribution with a maximum at the center of mass. The topological transition at the critical value separates molecular structure and atomic shape as two qualitatively different manifestations of spatial structure.

Local Electronic Structure Changes in Polycrystalline CdTe with CdCl 2 Treatment and Air Exposure

DOE PAGES

Berg, Morgann; Kephart, Jason M.; Munshi, Amit; ...

2018-03-12

Postdeposition CdCl 2 treatment of polycrystalline CdTe is known to increase the photovoltaic device efficiency. However, the precise chemical, structural, and electronic changes that underpin this improvement are still debated. In this work, spectroscopic photoemission electron microscopy was used to spatially map the vacuum level and ionization energy of CdTe films, enabling the identification of electronic structure variations between grains and grain boundaries (GBs). In vacuo preparation and inert transfer of oxide-free CdTe surfaces isolated the separate effects of CdCl 2 treatment and ambient oxygen exposure. Qualitatively, grain boundaries displayed lower work function and downward band bending relative to grainmore » interiors, but only after air exposure of CdCl 2-treated CdTe. Analysis of numerous space charge regions at grain boundaries showed an average depletion width of 290 nm and an average band bending magnitude of 70 meV, corresponding to a GB trap density of 10 11 cm –2 and a net carrier density of 10 15 cm –3. Finally, these results suggest that both CdCl 2 treatment and oxygen exposure may be independently tuned to enhance the CdTe photovoltaic performance by engineering the interface and bulk electronic structure.« less

Local Electronic Structure Changes in Polycrystalline CdTe with CdCl 2 Treatment and Air Exposure

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

Berg, Morgann; Kephart, Jason M.; Munshi, Amit

Postdeposition CdCl 2 treatment of polycrystalline CdTe is known to increase the photovoltaic device efficiency. However, the precise chemical, structural, and electronic changes that underpin this improvement are still debated. In this work, spectroscopic photoemission electron microscopy was used to spatially map the vacuum level and ionization energy of CdTe films, enabling the identification of electronic structure variations between grains and grain boundaries (GBs). In vacuo preparation and inert transfer of oxide-free CdTe surfaces isolated the separate effects of CdCl 2 treatment and ambient oxygen exposure. Qualitatively, grain boundaries displayed lower work function and downward band bending relative to grainmore » interiors, but only after air exposure of CdCl 2-treated CdTe. Analysis of numerous space charge regions at grain boundaries showed an average depletion width of 290 nm and an average band bending magnitude of 70 meV, corresponding to a GB trap density of 10 11 cm –2 and a net carrier density of 10 15 cm –3. Finally, these results suggest that both CdCl 2 treatment and oxygen exposure may be independently tuned to enhance the CdTe photovoltaic performance by engineering the interface and bulk electronic structure.« less

Magnetic Interactions at the Nanoscale in Trilayer Titanates

NASA Astrophysics Data System (ADS)

Cao, Yanwei; Yang, Zhenzhong; Kareev, M.; Liu, Xiaoran; Meyers, D.; Middey, S.; Choudhury, D.; Shafer, P.; Guo, Jiandong; Freeland, J. W.; Arenholz, E.; Gu, Lin; Chakhalian, J.

2016-02-01

We report on the phase diagram of competing magnetic interactions at the nanoscale in engineered ultrathin trilayer heterostructures of LaTiO3 /SrTiO3/YTiO3 , in which the interfacial inversion symmetry is explicitly broken. Combined atomic layer resolved scanning transmission electron microscopy with electron energy loss spectroscopy and electrical transport have confirmed the formation of a spatially separated two-dimensional electron liquid and high density two-dimensional localized magnetic moments at the LaTiO3 /SrTiO3 and SrTiO3 /YTiO3 interfaces, respectively. Resonant soft x-ray linear dichroism spectroscopy has demonstrated the presence of orbital polarization of the conductive LaTiO3 /SrTiO3 and localized SrTiO3 /YTiO3 electrons. Our results provide a route with prospects for exploring new magnetic interfaces, designing a tunable two-dimensional d -electron Kondo lattice, and potential spin Hall applications.

Enhanced dense attosecond electron bunch generation by irradiating an intense laser on a cone target

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

Hu, Li-Xiang; Yu, Tong-Pu, E-mail: tongpu@nudt.edu.cn; Shao, Fu-Qiu

By using two-dimensional particle-in-cell simulations, we demonstrate enhanced spatially periodic attosecond electron bunches generation with an average density of about 10n{sub c} and cut-off energy up to 380 MeV. These bunches are acquired from the interaction of an ultra-short ultra-intense laser pulse with a cone target. The laser oscillating field pulls out the cone surface electrons periodically and accelerates them forward via laser pondermotive force. The inner cone wall can effectively guide these bunches and lead to their stable propagation in the cone, resulting in overdense energetic attosecond electron generation. We also consider the influence of laser and cone target parametersmore » on the bunch properties. It indicates that the attosecond electron bunch acceleration and propagation could be significantly enhanced without evident divergency by attaching a plasma capillary to the original cone tip.« less

Fully Hydrated Yeast Cells Imaged with Electron Microscopy

PubMed Central

Peckys, Diana B.; Mazur, Peter; Gould, Kathleen L.; de Jonge, Niels

2011-01-01

We demonstrate electron microscopy of fully hydrated eukaryotic cells with nanometer resolution. Living Schizosaccaromyces pombe cells were loaded in a microfluidic chamber and imaged in liquid with scanning transmission electron microscopy (STEM). The native intracellular (ultra)structures of wild-type cells and three different mutants were studied without prior labeling, fixation, or staining. The STEM images revealed various intracellular components that were identified on the basis of their shape, size, location, and mass density. The maximal achieved spatial resolution in this initial study was 32 ± 8 nm, an order of magnitude better than achievable with light microscopy on pristine cells. Light-microscopy images of the same samples were correlated with the corresponding electron-microscopy images. Achieving synergy between the capabilities of light and electron microscopy, we anticipate that liquid STEM will be broadly applied to explore the ultrastructure of live cells. PMID:21575587

Fully hydrated yeast cells imaged with electron microscopy.

PubMed

Peckys, Diana B; Mazur, Peter; Gould, Kathleen L; de Jonge, Niels

2011-05-18

We demonstrate electron microscopy of fully hydrated eukaryotic cells with nanometer resolution. Living Schizosaccharomyces pombe cells were loaded in a microfluidic chamber and imaged in liquid with scanning transmission electron microscopy (STEM). The native intracellular (ultra)structures of wild-type cells and three different mutants were studied without prior labeling, fixation, or staining. The STEM images revealed various intracellular components that were identified on the basis of their shape, size, location, and mass density. The maximal achieved spatial resolution in this initial study was 32 ± 8 nm, an order of magnitude better than achievable with light microscopy on pristine cells. Light-microscopy images of the same samples were correlated with the corresponding electron-microscopy images. Achieving synergy between the capabilities of light and electron microscopy, we anticipate that liquid STEM will be broadly applied to explore the ultrastructure of live cells. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Modeling nitrogen plasmas produced by intense electron beams

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

Angus, J. R.; Swanekamp, S. B.; Schumer, J. W.

2016-05-15

A new gas–chemistry model is presented to treat the breakdown of a nitrogen gas with pressures on the order of 1 Torr from intense electron beams with current densities on the order of 10 kA/cm{sup 2} and pulse durations on the order of 100 ns. For these parameter regimes, the gas transitions from a weakly ionized molecular state to a strongly ionized atomic state on the time scale of the beam pulse. The model is coupled to a 0D–circuit model using the rigid–beam approximation that can be driven by specifying the time and spatial profiles of the beam pulse. Simulation results are inmore » good agreement with experimental measurements of the line–integrated electron density from experiments done using the Gamble II generator at the Naval Research Laboratory. It is found that the species are mostly in the ground and metastable states during the atomic phase, but that ionization proceeds predominantly through thermal ionization of optically allowed states with excitation energies close to the ionization limit.« less

Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energy-loss spectroscopy in high-resolution transmission electron microscopy and ab initio time-dependent density-functional theory

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

Guedj, C.; CEA, LETI, MINATEC Campus, F-38054 Grenoble; Hung, L.

2014-12-01

The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectricmore » permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.« less

Tempo-spatially resolved dynamics of elec- trons and holes in bilayer MoS2 -WS2

NASA Astrophysics Data System (ADS)

Galicia-Hernandez, J. M.; Turkowski, V.; Hernandez-Cocoletzi, G.; Rahman, T. S.

We have performed a Density-Matrix Time-Dependent Density-Functional Theory analysis of the response of bilayer MoS2-WS2 to external laser-pulse perturbations. Time-resolved study of the dynamics of electrons and holes, including formation and dissociation of strongly-bound intra- and inter-layer excitonic states, shows that the experimentally observed ultrafast inter-layer MoS2 to WS2 migration of holes may be attributed to unusually large delocalization of the hole state which extends far into the inter-layer region. We also argue that the velocity of the hole transfer may be further enhanced by its interaction with transfer phonon modes. We analyze other possible consequences of the hole delocalization in the system, including reduction of the effects of the electron-electron and hole-hole repulsion in the trions and biexcitons as compared to that in the monolayers Work supported in part by DOE Grant No. DOE-DE-FG02-07ER46354 and by CONACYT Scholarship No. 23210 (J.M.G.H.).

Order in dense hydrogen at low temperatures

PubMed Central

Edwards, B.; Ashcroft, N. W.

2004-01-01

By increase in density, impelled by pressure, the electronic energy bands in dense hydrogen attain significant widths. Nevertheless, arguments can be advanced suggesting that a physically consistent description of the general consequences of this electronic structure can still be constructed from interacting but state-dependent multipoles. These reflect, in fact self-consistently, a disorder-induced localization of electron states partially manifesting the effects of proton dynamics; they retain very considerable spatial inhomogeneity (as they certainly do in the molecular limit). This description, which is valid provided that an overall energy gap has not closed, leads at a mean-field level to the expected quadrupolar coupling, but also for certain structures to the eventual emergence of dipolar terms and their coupling when a state of broken charge symmetry is developed. A simple Hamiltonian incorporating these basic features then leads to a high-density, low-temperature phase diagram that appears to be in substantial agreement with experiment. In particular, it accounts for the fact that whereas the phase I–II phase boundary has a significant isotope dependence, the phase II–III boundary has very little. PMID:15028839

Flux-driven algebraic damping of m=2 diocotron mode

NASA Astrophysics Data System (ADS)

Chim, C. Y.; O'Neil, T. M.

2016-10-01

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 2 diocotron modes. Due to small field asymmetries a low density halo of electrons is transported radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius rres, where f = mfE × B (rres) . The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from the exponential spatial Landau damping in a linear wave-particle resonance. This poster uses analytic theory and simulations to explain the new flux-driven algebraic damping of the mode. As electrons are swept around the nonlinear ``cat's eye'' orbits of the resonant wave-particle interaction, they form a quadrupole (m = 2) density distribution, which sets up an electric field that acts back on the plasma core. The field causes an E × B drift motion that symmetrizes the core, i.e. damps the m = 2 mode. Supported by NSF Grant PHY-1414570, and DOE Grants DE-SC0002451.

Flux-driven algebraic damping of m = 1 diocotron mode

NASA Astrophysics Data System (ADS)

Chim, Chi Yung; O'Neil, Thomas M.

2016-07-01

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius r = Rw at the wall of the trap. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This paper explains with analytic theory the new algebraic damping due to particle transport by both mobility and diffusion. As electrons are swept around the "cat's eye" orbits of the resonant wave-particle interaction, they form a dipole (m = 1) density distribution. From this distribution, the electric field component perpendicular to the core displacement produces E × B-drift of the core back to the axis, that is, damps the m = 1 mode. The parallel component produces drift in the azimuthal direction, that is, causes a shift in the mode frequency.

Operation of large RF sources for H-: Lessons learned at ELISE

NASA Astrophysics Data System (ADS)

Fantz, U.; Wünderlich, D.; Heinemann, B.; Kraus, W.; Riedl, R.

2017-08-01

The goal of the ELISE test facility is to demonstrate that large RF-driven negative ion sources (1 × 1 m2 source area with 360 kW installed RF power) can achieve the parameters required for the ITER beam sources in terms of current densities and beam homogeneity at a filling pressure of 0.3 Pa for pulse lengths of up to one hour. With the experience in operation of the test facility, the beam source inspection and maintenance as well as with the results of the achieved source performance so far, conclusions are drawn for commissioning and operation of the ITER beam sources. Addressed are critical technical RF issues, extrapolations to the required RF power, Cs consumption and Cs ovens, the need of adjusting the magnetic filter field strength as well as the temporal dynamic and spatial asymmetry of the co-extracted electron current. It is proposed to relax the low pressure limit to 0.4 Pa and to replace the fixed electron-to-ion ratio by a power density limit for the extraction grid. This would be highly beneficial for controlling the co-extracted electrons.

A first principles investigation of electron transfer between Fe(II) and U(VI) on insulating Al- vs. semiconducting Fe-oxide surfaces via the proximity effect

NASA Astrophysics Data System (ADS)

Taylor, S. D.; Marcano, M. C.; Becker, U.

2017-01-01

This study investigates how the intrinsic chemical and electronic properties of mineral surfaces and their associated electron transfer (ET) pathways influence the reduction of U(VI) by surface-associated Fe(II). Density functional theory (DFT), including the Hubbard U correction to the exchange-correlation functional, was used to investigate sorption/redox reactions and ET mechanisms between Fe(II) and U(VI) coadsorbed on isostructural, periodic (0 0 1) surfaces of the insulator corundum (α-Al2O3) vs. the semiconductor hematite (α-Fe2O3). Furthermore, the coadsorbed Fe(II) and U(VI) ions are spatially separated from one another on the surfaces (⩾5.9 Å) to observe whether electronic-coupling through the semiconducting hematite surface facilitates ET between the adsorbates, a phenomenon known as the proximity effect. The calculations show that the different chemical and electronic properties between the isostructural corundum and hematite (0 0 1) surfaces lead to considerably different ET mechanisms between Fe(II) and U(VI). ET on the insulating corundum (0 0 1) surface is limited by the adsorbates' structural configuration. When Fe(II) and U(VI) are spatially separated and do not directly interact with one another (e.g. via an inner-sphere complex), U(VI) reduction by Fe(II) cannot occur as there is no physical pathway enabling ET between the adsorbates. In contrast to the insulating corundum (0 0 1) surface, the hematite (0 0 1) surface can potentially participate in ET reactions due to the high number of electron acceptor sites from the Fe d-states near the Fermi level at the hematite surface. The adsorption of Fe(II) also introduces d-states near the Fermi level as well as shifts unoccupied d-states of the Fe cations at the hematite surface to lower energies, making the surface more conductive. In turn, electronic coupling through the surface can link the spatially separated adsorbates to one another and provide distinct ET pathways for an electron from Fe(II) to travel through the hematite surface and reach U(VI). The progression and extent of ET occurring on the semiconducting hematite (0 0 1) surface via the proximity effect depends on the electronic properties of the surface. ET between the spatially separated U(VI) and Fe(II) occurs most readily when orbitals between the Fe and U adsorbates overlap with those of neighboring O and Fe ions at the hematite surface, as shown by calculations without the Hubbard U correction. Analyses of the spins densities confirm that the U and Fe adsorbates were reduced and oxidized, respectively, (acquiring 0.33 μB and 0.11-0.20 μB, respectively), while Fe cations at the hematite surface were reduced (losing ⩽0.6 μB). If electrons are highly localized, the amount of orbital mixing and electronic coupling through the hematite surface decreases and in turn leads to a lower degree of spin transfer, as predicted by calculations with the Hubbard U correction. Thus, the proximity effect is a potential mechanism on semiconducting surfaces facilitating surface-mediated redox reactions, although its significance varies depending on the electronic properties and subsequent charge-carrying ability of the surface. These results provide insight into ET pathways and mechanisms on insulating Al- and semiconducting Fe oxide surfaces influencing the reduction U(VI) by Fe(II) that may subsequently limit uranium's transport in the subsurface.

Midlatitude D region variations measured from broadband radio atmospherics

NASA Astrophysics Data System (ADS)

Han, Feng

The high power, broadband very low frequency (VLF, 3--30 kHz) and extremely low frequency (ELF, 3--3000 Hz) electromagnetic waves generated by lightning discharges and propagating in the Earth-ionosphere waveguide can be used to measure the average electron density profile of the lower ionosphere (D region) across the wave propagation path due to several reflections by the upper boundary (lower ionosphere) of the waveguide. This capability makes it possible to frequently and even continuously monitor the D region electron density profile variations over geographically large regions, which are measurements that are essentially impossible by other means. These guided waves, usually called atmospherics (or sferics for short), are recorded by our sensors located near Duke University. The purpose of this work is to develop and implement algorithms to derive the variations of D region electron density profile which is modeled by two parameters (one is height and another is sharpness), by comparing the recorded sferic spectra to a series of model simulated sferic spectra from using a finite difference time domain (FDTD) code. In order to understand the time scales, magnitudes and sources for the midlatitude nighttime D region variations, we analyzed the sferic data of July and August 2005, and extracted both the height and sharpness of the D region electron density profile. The heights show large temporal variations of several kilometers on some nights and the relatively stable behavior on others. Statistical calculations indicate that the hourly average heights during the two months range between 82.0 km and 87.2 km with a mean value of 84.9 km and a standard deviation of 1.1 km. We also observed spatial variations of height as large as 2.0 km over 5 degrees latitudes on some nights, and no spatial variation on others. In addition, the measured height variations exhibited close correlations with local lightning occurrence rate on some nights but no correlation with local lightning or displaced lightning on others. The nighttime profile sharpness during 2.5 hours in two different nights was calculated, and the results were compared to the equivalent sharpness derived from International Reference Ionosphere (IRI) models. Both the absolute values and variation trends in IRI models are different from those in broadband measurements. Based on sferic data similar to those for nighttime, we also measured the day-time D region electron density profile variations in July and August 2005 near Duke University. As expected, the solar radiation is the dominant but not the only determinant source for the daytime D region profile height temporal variations. The observed quiet time heights showed close correlations with solar zenith angle changes but unexpected spatial variations not linked to the solar zenith angle were also observed on some days, with 15% of days exhibiting regional differences larger than 0.5 km. During the solar flare, the induced height change was approximately proportional to the logarithm of the X-ray fluxes. During the rising and decaying phases of the solar flare, the height changes correlated more consistently with the short (wavelength 0.5--4 A), rather than the long (wavelength 1--8 A) X-ray flux changes. The daytime profile sharpness during morning, noontime and afternoon periods in three different days and for the solar zenith angle range 20 to 75 degrees was calculated. These broadband measured results were compared to narrowband VLF measurements, IRI models and Faraday rotation base IRI models (called FIRI). The estimated sharpness from all these sources was more consistent when the solar zenith angle was small than when it was large. By applying the nighttime and daytime measurement techniques, we also derived the D region variations during sunrise and sunset periods. The measurements showed that both the electron density profile height and sharpness decrease during the sunrise period while increase during the sunset period.

Thermal ion heating in the vicinity of the plasmapause: A Dynamics Explorer guest investigation

NASA Technical Reports Server (NTRS)

Comfort, R. H.

1986-01-01

The ion thermal structure of the plasmasphere was investigated in a series of experiments. It appears that energy may be generally available to ion and electrons in the vinicity of the plasmapause from Coulomb interactions between ambient thermal plasma and low energy ring current and suprathermal ions, particularly O+. The amount of energy transferred depends on the densities and energies of each of the components. The spatial distribution of heating in turn depends critically on the spatial distribution of the different populations, especially on the density gradients. The spatial distribution of the thermal plasma is found to vary significantly on a diurnal time scale and is complicated by the plasmasphere erosion and refilling processes associated with magnetic activity and its aftermath. Thermal ion composition also appears to be influenced by the heating taking place, often increasing the heavy ion population in the vicinity of the plasmapause. The observations of equatorial heating near the plasmapause in the presence of equatorial noise also raise the likelihood of a wave source of energy. It is not unreasonable to expect that both particle and wave heat sources are significant, although not necessarily at the same times and places.

Transport modeling of convection dominated helicon discharges in Proto-MPEX with the B2.5-Eirene code

NASA Astrophysics Data System (ADS)

Owen, L. W.; Rapp, J.; Canik, J.; Lore, J. D.

2017-11-01

Data-constrained interpretative analyses of plasma transport in convection dominated helicon discharges in the Proto-MPEX linear device, and predictive calculations with additional Electron Cyclotron Heating/Electron Bernstein Wave (ECH/EBW) heating, are reported. The B2.5-Eirene code, in which the multi-fluid plasma code B2.5 is coupled to the kinetic Monte Carlo neutrals code Eirene, is used to fit double Langmuir probe measurements and fast camera data in front of a stainless-steel target. The absorbed helicon and ECH power (11 kW) and spatially constant anomalous transport coefficients that are deduced from fitting of the probe and optical data are additionally used for predictive simulations of complete axial distributions of the densities, temperatures, plasma flow velocities, particle and energy fluxes, and possible effects of alternate fueling and pumping scenarios. The somewhat hollow electron density and temperature radial profiles from the probe data suggest that Trivelpiece-Gould wave absorption is the dominant helicon electron heating source in the discharges analyzed here. There is no external ion heating, but the corresponding calculated ion temperature radial profile is not hollow. Rather it reflects ion heating by the electron-ion equilibration terms in the energy balance equations and ion radial transport resulting from the hollow density profile. With the absorbed power and the transport model deduced from fitting the sheath limited discharge data, calculated conduction limited higher recycling conditions were produced by reducing the pumping and increasing the gas fueling rate, resulting in an approximate doubling of the target ion flux and reduction of the target heat flux.

Towards crack-free ablation cutting of thin glass sheets with picosecond pulsed lasers

NASA Astrophysics Data System (ADS)

Sun, Mingying; Eppelt, Urs; Hartmann, Claudia; Schulz, Wolfgang; Zhu, Jianqiang; Lin, Zunqi

2017-08-01

We investigated the morphology and mechanism of laser-induced damage in the ablation cutting of thin glass sheets with picosecond laser. Two kinds of damage morphologies observed on the cross-section of the cut channel, are caused by high-density free-electrons and the temperature accumulation, respectively. Notches and micro-cracks can be observed on the top surface of the sample near the cut edge. The surface micro-cracks were related to high energy free-electrons and also the heat-affected zone. Heat-affected-zone and visible-cracks free conditions of glass cutting were achieved by controlling the repetition rate and spatial overlap of laser pulses.

Integral electrical characteristics and local plasma parameters of a RF ion thruster

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

Masherov, P. E.; Riaby, V. A., E-mail: riaby2001@yahoo.com; Godyak, V. A.

2016-02-15

Comprehensive diagnostics has been carried out for a RF ion thruster based on inductively coupled plasma (ICP) source with an external flat antenna coil enhanced by ferrite core. The ICP was confined within a cylindrical chamber with low aspect ratio to minimize plasma loss to the chamber wall. Integral diagnostics of the ICP electrical parameters (RF power balance and coil current) allowed for evaluation of the antenna coils, matching networks, and eddy current loss and the true RF power deposited to plasma. Spatially resolved electron energy distribution functions, plasma density, electron temperatures, and plasma potentials were measured with movable Langmuirmore » probes.« less

Efficient and accurate modeling of electron photoemission in nanostructures with TDDFT

NASA Astrophysics Data System (ADS)

Wopperer, Philipp; De Giovannini, Umberto; Rubio, Angel

2017-03-01

We derive and extend the time-dependent surface-flux method introduced in [L. Tao, A. Scrinzi, New J. Phys. 14, 013021 (2012)] within a time-dependent density-functional theory (TDDFT) formalism and use it to calculate photoelectron spectra and angular distributions of atoms and molecules when excited by laser pulses. We present other, existing computational TDDFT methods that are suitable for the calculation of electron emission in compact spatial regions, and compare their results. We illustrate the performance of the new method by simulating strong-field ionization of C60 fullerene and discuss final state effects in the orbital reconstruction of planar organic molecules.

Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets

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

Merritt, Elizabeth C., E-mail: emerritt@lanl.gov; Adams, Colin S.; University of New Mexico, Albuquerque, New Mexico 87131

We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼10{sup 14} cm{sup −3}, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].

A generalized electron energy probability function for inductively coupled plasmas under conditions of nonlocal electron kinetics

NASA Astrophysics Data System (ADS)

Mouchtouris, S.; Kokkoris, G.

2018-01-01

A generalized equation for the electron energy probability function (EEPF) of inductively coupled Ar plasmas is proposed under conditions of nonlocal electron kinetics and diffusive cooling. The proposed equation describes the local EEPF in a discharge and the independent variable is the kinetic energy of electrons. The EEPF consists of a bulk and a depleted tail part and incorporates the effect of the plasma potential, Vp, and pressure. Due to diffusive cooling, the break point of the EEPF is eVp. The pressure alters the shape of the bulk and the slope of the tail part. The parameters of the proposed EEPF are extracted by fitting to measure EEPFs (at one point in the reactor) at different pressures. By coupling the proposed EEPF with a hybrid plasma model, measurements in the gaseous electronics conference reference reactor concerning (a) the electron density and temperature and the plasma potential, either spatially resolved or at different pressure (10-50 mTorr) and power, and (b) the ion current density of the electrode, are well reproduced. The effect of the choice of the EEPF on the results is investigated by a comparison to an EEPF coming from the Boltzmann equation (local electron kinetics approach) and to a Maxwellian EEPF. The accuracy of the results and the fact that the proposed EEPF is predefined renders its use a reliable alternative with a low computational cost compared to stochastic electron kinetic models at low pressure conditions, which can be extended to other gases and/or different electron heating mechanisms.

Electron Excitation of High Dipole Moment Molecules

NASA Astrophysics Data System (ADS)

Goldsmith, Paul; Kauffmann, Jens

2018-01-01

Emission from high-dipole moment molecules such as HCN allows determination of the density in molecular clouds, and is often considered to trace the “dense” gas available for star formation. We assess the importance of electron excitation in various environments. The ratio of the rate coefficients for electrons and H2 molecules, ~10^5 for HCN, yields the requirements for electron excitation to be of practical importance if n(H2) < 10^{5.5} /cm3 and X(e-) > 10^{-5}, where the numerical factors reflect critical values n_c(H2) and X^*(e-). This indicates that in regions where a large fraction of carbon is ionized, X(e-) will be large enough to make electron excitation significant. The situation is in general similar for other “high density tracers”, including HCO+, CN, and CS. But there are significant differences in the critical electron fractional abundance, X^*(e-), defined by the value required for equal effect from collisions with H2 and e-. Electron excitation is, for example, unimportant for CO and C+. Electron excitation may be responsible for the surprisingly large spatial extent of the emission from dense gas tracers in some molecular clouds (Pety et al. 2017, Kauffmann, Goldsmith et al. 2017, A&A, submitted). The enhanced estimates for HCN abundances and HCN/CO and HCN/HCO+ ratios observed in the nuclear regions of luminous galaxies may be in part a result of electron excitation of high dipole moment tracers. The importance of electron excitation will depend on detailed models of the chemistry, which may well be non-steady state and non--static.

Vlasov Simulations of Ionospheric Heating Near Upper Hybrid Resonance

NASA Astrophysics Data System (ADS)

Najmi, A. C.; Eliasson, B. E.; Shao, X.; Milikh, G. M.; Papadopoulos, K.

2014-12-01

It is well-known that high-frequency (HF) heating of the ionosphere can excite field- aligned density striations (FAS) in the ionospheric plasma. Furthermore, in the neighborhood of various resonances, the pump wave can undergo parametric instabilities to produce a variety of electrostatic and electromagnetic waves. We have used a Vlasov simulation with 1-spatial dimension, 2-velocity dimensions, and 2-components of fields, to study the effects of ionospheric heating when the pump frequency is in the vicinity of the upper hybrid resonance, employing parameters currently available at ionospheric heaters such as HAARP. We have found that by seeding theplasma with a FAS of width ~20% of the simulation domain, ~10% depletion, and by applying a spatially uniform HF dipole pump electric field, the pump wave gives rise to a broad spectrum of density fluctuations as well as to upper hybrid and lower hybrid oscillating electric fields. We also observe collisionless bulk-heating of the electrons that varies non-linearly with the amplitude of the pump field.

Experimental Observation of Thin-shell Instability in a Collisionless Plasma

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

Ahmed, H.; Doria, D.; Sarri, G.

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balancemore » between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.« less

Experimental Observation of Thin-shell Instability in a Collisionless Plasma

NASA Astrophysics Data System (ADS)

Ahmed, H.; Doria, D.; Dieckmann, M. E.; Sarri, G.; Romagnani, L.; Bret, A.; Cerchez, M.; Giesecke, A. L.; Ianni, E.; Kar, S.; Notley, M.; Prasad, R.; Quinn, K.; Willi, O.; Borghesi, M.

2017-01-01

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.

Theoretical studies on the possible sensitizers of DSSC: Nanocomposites of graphene quantum dot hybrid phthalocyanine/tetrabenzoporphyrin/tetrabenzotriazaporphyrins/cis-tetrabenzodiazaporphyrins/tetrabenzomonoazaporphyrins and their Cu-metallated macrocycles

NASA Astrophysics Data System (ADS)

Gao, Feng; Yang, Chuan-Lu; Wang, Mei-Shan; Ma, Xiao-Guang; Liu, Wen-Wang

2018-04-01

The feasibility of nanocomposites of cir-coronene graphene quantum dot (GQD) with phthalocyanine, tetrabenzoporphyrin, tetrabenzotriazaporphyrins, cis-tetrabenzodiazaporphyrins, tetrabenzomonoazaporphyrins and their Cu-metallated macrocycles as a sensitizer of dye-sensitized solar cells (DSSC) are investigated. Based on the first principles density functional theory (DFT), the geometrical structures of the separate GQD and 10 macrocycles, and their hybridized nanocomposites are fully optimized. The energy stabilities of the obtained structures are confirmed by harmonic frequency analysis. The optical absorptions of the optimized structures are calculated with time-dependent DFT. The feasibility of the nanocomposites as the sensitizer of DSSC is examined by the charge spatial separation, the electron transfer, the molecular orbital energy levels of the nanocomposites and the electrolyte, and the conduction band minimum of TiO2 electrode. The results demonstrate that all the nanocomposites have enhanced absorptions in the visible light range, and their molecular orbital energies satisfy the requirement of sensitizers. However, only two of the ten considered nanocomposites demonstrate significantly charge spatial separation. The GQD-Cu-TBP is identified as the most favorable candidate sensitizer of DSSC by the most enhanced in optical absorption, obvious charge spatial separation, suitable LUMO energy levels and driving force for electron transfer, and low recombination rate of electron and hole.

Energetic Electrons in Dipolarization Events: Spatial Properties and Anisotropy

NASA Technical Reports Server (NTRS)

Birn, J.; Runov, A.; Hesse, M.

2014-01-01

Using the electromagnetic fields of an MHD simulation of magnetotail reconnection, flow bursts, and dipolarization, we further investigate the acceleration of electrons to suprathermal energies. Particular emphasis is on spatial properties and anisotropies as functions of energy and time. The simulation results are compared with Time History of Events and Macroscale Interactions during Substorms observations. The test particle approach successfully reproduces several observed injection features and puts them into a context of spatial maps of the injection region(s): a dominance of perpendicular anisotropies farther down the tail and closer to the equatorial plane, an increasing importance of parallel anisotropy closer to Earth and at higher latitudes, a drop in energy fluxes at energies below approximately 10 keV, coinciding with the plasma density drop, together with increases at higher energy, a triple peak structure of flux increases near 0 deg, 90 deg, and 180 deg, and a tendency of flux increases to extend to higher energy closer to Earth and at lower latitudes. We identified the plasma sheet boundary layers and adjacent lobes as a main source region for both increased and decreased energetic electron fluxes, related to the different effects of adiabatic acceleration at high and low energies. The simulated anisotropies tend to exceed the observed ones, particularly for perpendicular fluxes at high energies. The most plausible reason is that the MHD simulation lacks the effects of anisotropy-driven microinstabilities and waves, which would reduce anisotropies.

Systematic spatial and stoichiometric screening towards understanding the surface of ultrasmall oxygenated silicon nanocrystal

NASA Astrophysics Data System (ADS)

Niaz, Shanawer; Zdetsis, Aristides D.; Koukaras, Emmanuel N.; Gülseren, Oǧuz; Sadiq, Imran

2016-11-01

In most of the realistic ab initio and model calculations which have appeared on the emission of light from silicon nanocrystals, the role of surface oxygen has been usually ignored, underestimated or completely ruled out. We investigate theoretically, by density functional theory (DFT/B3LYP) possible modes of oxygen bonding in hydrogen terminated silicon quantum dots using as a representative case of the Si29 nanocrystal. We have considered Bridge-bonded oxygen (BBO), Doubly-bonded oxygen (DBO), hydroxyl (OH) and Mix of these oxidizing agents. Due to stoichiometry, all comparisons performed are unbiased with respect to composition whereas spatial distribution of oxygen species pointed out drastic change in electronic and cohesive characteristics of nanocrytals. From an overall perspective of this study, it is shown that bridge bonded oxygenated Si nanocrystals accompanied by Mix have higher binding energies and large electronic gap compared to nanocrystals with doubly bonded oxygen atoms. In addition, it is observed that the presence of OH along with BBO, DBO and mixed configurations further lowers electronic gaps and binding energies but trends in same fashion. It is also demonstrated that within same composition, oxidizing constituent, along with their spatial distribution substantially alters binding energy, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (up to 1.48 eV) and localization of frontier orbitals.

An affordable and accurate conductivity probe for density measurements in stratified flows

NASA Astrophysics Data System (ADS)

Carminati, Marco; Luzzatto-Fegiz, Paolo

2015-11-01

In stratified flow experiments, conductivity (combined with temperature) is often used to measure density. The probes typically used can provide very fine spatial scales, but can be fragile, expensive to replace, and sensitive to environmental noise. A complementary instrument, comprising a low-cost conductivity probe, would prove valuable in a wide range of applications where resolving extremely small spatial scales is not needed. We propose using micro-USB cables as the actual conductivity sensors. By removing the metallic shield from a micro-B connector, 5 gold-plated microelectrodes are exposed and available for 4-wire measurements. These have a cell constant ~550m-1, an intrinsic thermal noise of at most 30pA/Hz1/2, as well as sub-millisecond time response, making them highly suitable for many stratified flow measurements. In addition, we present the design of a custom electronic board (Arduino-based and Matlab-controlled) for simultaneous acquisition from 4 sensors, with resolution (in conductivity, and resulting density) exceeding the performance of typical existing probes. We illustrate the use of our conductivity-measuring system through stratified flow experiments, and describe plans to release simple instructions to construct our complete system for around 200.

Noise-induced effects on multicellular biopacemaker spontaneous activity: Differences between weak and strong pacemaker cells

NASA Astrophysics Data System (ADS)

Aghighi, Alireza; Comtois, Philippe

2017-09-01

Self-organization of spontaneous activity of a network of active elements is important to the general theory of reaction-diffusion systems as well as for pacemaking activity to initiate beating of the heart. Monolayer cultures of neonatal rat ventricular myocytes, consisting of resting and pacemaker cells, exhibit spontaneous activation of their electrical activity. Similarly, one proposed approach to the development of biopacemakers as an alternative to electronic pacemakers for cardiac therapy is based on heterogeneous cardiac cells with resting and spontaneously beating phenotypes. However, the combined effect of pacemaker characteristics, density, and spatial distribution of the pacemaker cells on spontaneous activity is unknown. Using a simple stochastic pattern formation algorithm, we previously showed a clear nonlinear dependency of spontaneous activity (occurrence and amplitude of spontaneous period) on the spatial patterns of pacemaker cells. In this study, we show that this behavior is dependent on the pacemaker cell characteristics, with weaker pacemaker cells requiring higher density and larger clusters to sustain multicellular activity. These multicellular structures also demonstrated an increased sensitivity to voltage noise that favored spontaneous activity at lower density while increasing temporal variation in the period of activity. This information will help researchers overcome the current limitations of biopacemakers.

Ambipolar ion acceleration in an expanding magnetic nozzle

NASA Astrophysics Data System (ADS)

Longmier, Benjamin W.; Bering, Edgar A., III; Carter, Mark D.; Cassady, Leonard D.; Chancery, William J.; Díaz, Franklin R. Chang; Glover, Tim W.; Hershkowitz, Noah; Ilin, Andrew V.; McCaskill, Greg E.; Olsen, Chris S.; Squire, Jared P.

2011-02-01

The helicon plasma stage in the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) VX-200i device was used to characterize an axial plasma potential profile within an expanding magnetic nozzle region of the laboratory based device. The ion acceleration mechanism is identified as an ambipolar electric field produced by an electron pressure gradient, resulting in a local axial ion speed of Mach 4 downstream of the magnetic nozzle. A 20 eV argon ion kinetic energy was measured in the helicon source, which had a peak magnetic field strength of 0.17 T. The helicon plasma source was operated with 25 mg s-1 argon propellant and 30 kW of RF power. The maximum measured values of plasma density and electron temperature within the exhaust plume were 1 × 1020 m-3 and 9 eV, respectively. The measured plasma density is nearly an order of magnitude larger than previously reported steady-state helicon plasma sources. The exhaust plume also exhibits a 95% to 100% ionization fraction. The size scale and spatial location of the plasma potential structure in the expanding magnetic nozzle region appear to follow the size scale and spatial location of the expanding magnetic field. The thickness of the potential structure was found to be 104 to 105 λDe depending on the local electron temperature in the magnetic nozzle, many orders of magnitude larger than typical laboratory double layer structures. The background plasma density and neutral argon pressure were 1015 m-3 and 2 × 10-5 Torr, respectively, in a 150 m3 vacuum chamber during operation of the helicon plasma source. The agreement between the measured plasma potential and plasma potential that was calculated from an ambipolar ion acceleration analysis over the bulk of the axial distance where the potential drop was located is a strong confirmation of the ambipolar acceleration process.

Counting Cats: Spatially Explicit Population Estimates of Cheetah (Acinonyx jubatus) Using Unstructured Sampling Data

PubMed Central

Broekhuis, Femke; Gopalaswamy, Arjun M.

2016-01-01

Many ecological theories and species conservation programmes rely on accurate estimates of population density. Accurate density estimation, especially for species facing rapid declines, requires the application of rigorous field and analytical methods. However, obtaining accurate density estimates of carnivores can be challenging as carnivores naturally exist at relatively low densities and are often elusive and wide-ranging. In this study, we employ an unstructured spatial sampling field design along with a Bayesian sex-specific spatially explicit capture-recapture (SECR) analysis, to provide the first rigorous population density estimates of cheetahs (Acinonyx jubatus) in the Maasai Mara, Kenya. We estimate adult cheetah density to be between 1.28 ± 0.315 and 1.34 ± 0.337 individuals/100km2 across four candidate models specified in our analysis. Our spatially explicit approach revealed ‘hotspots’ of cheetah density, highlighting that cheetah are distributed heterogeneously across the landscape. The SECR models incorporated a movement range parameter which indicated that male cheetah moved four times as much as females, possibly because female movement was restricted by their reproductive status and/or the spatial distribution of prey. We show that SECR can be used for spatially unstructured data to successfully characterise the spatial distribution of a low density species and also estimate population density when sample size is small. Our sampling and modelling framework will help determine spatial and temporal variation in cheetah densities, providing a foundation for their conservation and management. Based on our results we encourage other researchers to adopt a similar approach in estimating densities of individually recognisable species. PMID:27135614

Counting Cats: Spatially Explicit Population Estimates of Cheetah (Acinonyx jubatus) Using Unstructured Sampling Data.

PubMed

Broekhuis, Femke; Gopalaswamy, Arjun M

2016-01-01

Many ecological theories and species conservation programmes rely on accurate estimates of population density. Accurate density estimation, especially for species facing rapid declines, requires the application of rigorous field and analytical methods. However, obtaining accurate density estimates of carnivores can be challenging as carnivores naturally exist at relatively low densities and are often elusive and wide-ranging. In this study, we employ an unstructured spatial sampling field design along with a Bayesian sex-specific spatially explicit capture-recapture (SECR) analysis, to provide the first rigorous population density estimates of cheetahs (Acinonyx jubatus) in the Maasai Mara, Kenya. We estimate adult cheetah density to be between 1.28 ± 0.315 and 1.34 ± 0.337 individuals/100km2 across four candidate models specified in our analysis. Our spatially explicit approach revealed 'hotspots' of cheetah density, highlighting that cheetah are distributed heterogeneously across the landscape. The SECR models incorporated a movement range parameter which indicated that male cheetah moved four times as much as females, possibly because female movement was restricted by their reproductive status and/or the spatial distribution of prey. We show that SECR can be used for spatially unstructured data to successfully characterise the spatial distribution of a low density species and also estimate population density when sample size is small. Our sampling and modelling framework will help determine spatial and temporal variation in cheetah densities, providing a foundation for their conservation and management. Based on our results we encourage other researchers to adopt a similar approach in estimating densities of individually recognisable species.

Charge density wave order in 1D mirror twin boundaries of single-layer MoSe 2

DOE PAGES

Barja, Sara; Wickenburg, Sebastian; Liu, Zhen-Fei; ...

2016-04-18

Here, We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe 2. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe 2 and MoS 2. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent densitymore » of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.« less

Seismo-ionospheric anomalies in ionospheric TEC and plasma density before the 17 July 2006 M7.7 south of Java earthquake

NASA Astrophysics Data System (ADS)

Tao, Dan; Cao, Jinbin; Battiston, Roberto; Li, Liuyuan; Ma, Yuduan; Liu, Wenlong; Zhima, Zeren; Wang, Lanwei; Wray Dunlop, Malcolm

2017-04-01

In this paper, we report significant evidence for preseismic ionospheric anomalies in total electron content (TEC) of the global ionosphere map (GIM) and plasma density appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. After distinguishing other anomalies related to the geomagnetic activities, we found a temporal precursor around the epicenter on day 2 before the earthquake (15 July 2006), which agrees well with the spatial variations in latitude-longitude-time (LLT) maps. Meanwhile, the sequences of latitude-time-TEC (LTT) plots reveal that the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator in the daytime from day 2 before the earthquake. This anomalous asymmetric structure disappears after the earthquake. To further confirm these anomalies, we studied the plasma data from DEMETER satellite in the earthquake preparation zone (2046.4 km in radius) during the period from day 45 before to day 10 after the earthquake, and also found that the densities of both electron and total ion in the daytime significantly increase on day 2 before the earthquake. Very interestingly, O+ density increases significantly and H+ density decreases, while He+ remains relatively stable. These results indicate that there exists a distinct preseismic signal (preseismic ionospheric anomaly) over the epicenter.

Electron and ion dynamics study of iron in warm dense matter regime by time-resolved XAS measurements and from first-principles

NASA Astrophysics Data System (ADS)

Ogitsu, T.; Fernandez-Paãella, A.; Correa, A.; Engelhorn, K.; Barbrel, B.; Prendergast, D. G.; Pemmaraju, D.; Beckwith, M.; Kraus, D.; Hamel, S.; Cho, B. I.; Jin, L.; Wong, J.; Heinman, P.; Collins, G. W.; Falcone, R.; Ping, Y.

2016-10-01

We present a study of the electron-phonon coupling of warm dense iron upon femtosecond laser excitation by time-resolved x-ray absorption near edge spectroscopy (XANES). The dynamics of iron in electron-ion non-equilibrium conditions was studied using ab-initio density-functional-theory (DFT) simulations combined with the Two Temperature Model (TTM) where spatial inhomogeneity of electron (and ion) temperature(s) due to short ballistic electron transport length in iron was explicitly taken into consideration. Detailed comparison between our simulation results and experiments indicates that the ion temperature dependence on specific heat and on electron-phonon coupling also plays a relevant role in modeling the relaxation dynamics of electrons and ions. These results are the first experimental evidence of the suppression of the electron-phonon coupling factor of a transition metal at electron temperatures ranging 5000- 10000 K. This work was performed under DOE contract DE-AC52-07NA27344 with support from OFES Early Career program and LLNL LDRD program.

Femtosecond Electron Wave Packet Propagation and Diffraction: Towards Making the ``Molecular Movie"

NASA Astrophysics Data System (ADS)

Miller, R. J. Dwayne

2003-03-01

Time-resolved electron diffraction harbors great promise for achieving atomic resolution of the fastest chemical processes. The generation of sufficiently short electron pulses to achieve this real time view of a chemical reaction has been limited by problems in maintaining short electron pulses with realistic electron densities to the sample. The propagation dynamics of femtosecond electron packets in the drift region of a photoelectron gun are investigated with an N-body numerical simulation and mean-field model. This analyis shows that the redistribution of electrons inside the packet, arising from space-charge and dispersion contributions, changes the pulse envelope and leads to the development of a spatially linear axial velocity distribution. These results have been used in the design of femtosecond photoelectron guns with higher time resolution and novel electron-optical methods of pulse characterization that are approaching 100 fs timescales. Time-resolved diffraction studies with electron pulses of approximately 500 femtoseconds have focused on solid-liquid phase transitions under far from equilibrium conditions. This work gives a microscopic description of the melting process and illustrates the promise of atomically resolving transition state processes.

Detection and Analysis of X Ray Emission from the Princeton-Field-Reversed Configuration (PFRC-2)

NASA Astrophysics Data System (ADS)

Bosh, Alexandra; Swanson, Charles; Jandovitz, Peter; Cohen, Samuel

2016-10-01

The PFRC is an odd-parity rotating-magnetic-field-driven field-reversed-configuration magnetic confinement experiment. Studying X rays produced via electron Bremsstrahlung with neutral particles is crucial to the further understanding of the energy and particle confinement of the PFRC. The data on the x rays are collected using a detector system comprised of two, spatially scannable Amptek XR-100 CR detectors and a Amptek XR-100 SDD detector that view the plasma column at two axial locations, one in the divertor and one near the axial midplane. These provide X-ray energy and arrival-time information. (Data analysis requires measurement of each detector's efficiency, a parameter that is modified by window transmission. Detector calibrations were performed with a custom-made X-ray tube that impinged 1-microamp 1-5 kV electron beams onto a carbon target.) From the analyzed data, the average electron energy, effective temperature, and electron density can be extracted. Spatial scans then allow the FRC's internal energy to be measured. We present recent measurements of the Bremsstrahlung spectrum from 0.8 to 6 keV and the inferred electron temperature in the PFRC device as functions of heating power, magnetic field and fill gas pressure. This work was supported, in part, by DOE Contract Number DE-AC02-09CH11466.

Electron beam induced current in the high injection regime.

PubMed

Haney, Paul M; Yoon, Heayoung P; Koirala, Prakash; Collins, Robert W; Zhitenev, Nikolai B

2015-07-24

Electron beam induced current (EBIC) is a powerful technique which measures the charge collection efficiency of photovoltaics with sub-micron spatial resolution. The exciting electron beam results in a high generation rate density of electron-hole pairs, which may drive the system into nonlinear regimes. An analytic model is presented which describes the EBIC response when the total electron-hole pair generation rate exceeds the rate at which carriers are extracted by the photovoltaic cell, and charge accumulation and screening occur. The model provides a simple estimate of the onset of the high injection regime in terms of the material resistivity and thickness, and provides a straightforward way to predict the EBIC lineshape in the high injection regime. The model is verified by comparing its predictions to numerical simulations in one- and two-dimensions. Features of the experimental data, such as the magnitude and position of maximum collection efficiency versus electron beam current, are consistent with the three-dimensional model.

Deleterious effects of nonthermal electrons in shock ignition concept.

PubMed

Nicolaï, Ph; Feugeas, J-L; Touati, M; Ribeyre, X; Gus'kov, S; Tikhonchuk, V

2014-03-01

Shock ignition concept is a promising approach to inertial confinement fusion that may allow obtaining high fusion energy gains with the existing laser technology. However, the spike driving laser intensities in the range of 1-10 PW/cm2 produces the energetic electrons that may have a significant effect on the target performance. The hybrid numerical simulations including a radiation hydrodynamic code coupled to a rapid Fokker-Planck module are used to asses the role of hot electrons in the shock generation and the target preheat in the time scale of 100 ps and spatial scale of 100 μm. It is shown that depending on the electron energy distribution and the target density profile the hot electrons can either increase the shock amplitude or preheat the imploding shell. In particular, the exponential electron energy spectrum corresponding to the temperature of 30 keV in the present HiPER target design preheats the deuterium-tritium shell and jeopardizes its compression. Ways of improving the target performance are suggested.

Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1

NASA Astrophysics Data System (ADS)

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W.

2012-06-01

The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-β (local β ˜ 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-β confinement.

Statistical density modification using local pattern matching

DOEpatents

Terwilliger, Thomas C.

2007-01-23

A computer implemented method modifies an experimental electron density map. A set of selected known experimental and model electron density maps is provided and standard templates of electron density are created from the selected experimental and model electron density maps by clustering and averaging values of electron density in a spherical region about each point in a grid that defines each selected known experimental and model electron density maps. Histograms are also created from the selected experimental and model electron density maps that relate the value of electron density at the center of each of the spherical regions to a correlation coefficient of a density surrounding each corresponding grid point in each one of the standard templates. The standard templates and the histograms are applied to grid points on the experimental electron density map to form new estimates of electron density at each grid point in the experimental electron density map.

Spatial correlations of Diceroprocta apache and its host plants: Evidence for a negative impact from Tamarix invasion

USGS Publications Warehouse

Ellingson, A.R.; Andersen, D.C.

2002-01-01

1. The hypothesis that the habitat-scale spatial distribution of the, Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1-m2 quadrats placed within the flood-plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m. 2. Apache cicadas were spatially aggregated in high-density clusters averaging 3m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non-spatial correlation analysis. No non-spatial association between cicada density and saltcedar canopy cover was detected. 3. Tests for spatial cross-correlation using the bivariate IYZ indicated the presence of a broad-scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill-over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture. 4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad-scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies.

Spatial correlations of Diceroprocta apache and its host plants: Evidence for a negative impact from Tamarix invasion

USGS Publications Warehouse

Ellingson, A.R.; Andersen, D.C.

2002-01-01

1. The hypothesis that the habitat-scale spatial distribution of the Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1-m2 quadrats placed within the flood-plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m.2. Apache cicadas were spatially aggregated in high-density clusters averaging 3 m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non-spatial correlation analysis. No non-spatial association between cicada density and saltcedar canopy cover was detected.3. Tests for spatial cross-correlation using the bivariate IYZ indicated the presence of a broad-scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill-over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture.4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad-scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies.

A molecular heterojunction of zinc phthalocyanine and peanut-shaped fullerene polymer: A density functional study

NASA Astrophysics Data System (ADS)

Tanikawa, Kousei; Ohno, Kaoru; Noda, Yusuke; Ono, Shota; Kuwahara, Riichi; Takashima, Akito; Nakaya, Masato; Onoe, Jun

2017-10-01

We have performed first-principles density functional calculations of a molecular heterojunction of a zinc phthalocyanine (ZnPc) molecule and a peanut-shaped fullerene polymer (PSFP) made from several coalesced cross-linked C60 molecules. The PSFP has many isomers and all have both spatially localized (near ZnPc) and metallic conducting levels. Here we consider four typical isomers. From the resulting electronic structure, we discuss the applicability of these isomers to organic photovoltaics (OPV), electrodes, and light harvesting materials. If one of the isomers called T3, which has the largest energy gap, is used together with ZnPc for OPV, this system shows more than 20% energy conversion efficiency.

Temperature Dependent Surface Structures and Electronic Properties of Organic-Inorganic Hybrid Perovskite Single Crystals

NASA Astrophysics Data System (ADS)

Jao, M.-H.; Teague, M. L.; Huang, J.-S.; Tseng, W.-S.; Yeh, N.-C.

Organic-inorganic hybrid perovskites, arising from research of low-cost high performance photovoltaics, have become promising materials not only for solar cells but also for various optoelectronic and spintronic applications. An interesting aspect of the hybrid perovskites is that their material properties, such as the band gap, can be easily tuned by varying the composition, temperature, and the crystalline phases. Additionally, the surface structure is critically important for their optoelectronic applications. It is speculated that different crystalline facets could show different trap densities, thus resulting in microscopically inhomogeneous performance. Here we report direct studies of the surface structures and electronic properties of hybrid perovskite CH3NH3PbI3 single crystals by scanning tunneling microscopy and spectroscopy (STM/STS). We found long-range spatially homogeneous tunneling conductance spectra with a well-defined energy gap of (1.55 +/- 0.1) eV at 300 K in the tetragonal phase, suggesting high quality of the single crystals. The energy gap increased to (1.81 +/- 0.1) eV in the orthorhombic phase, below the tetragonal-to-orthorhombic phase transition temperature at 150 K. Detailed studies of the temperature evolution in the spatially resolved surface structures and local density of states will be discussed to elucidate how these properties may influence the optoelectronic performance of the hybrid perovskites. We thank the support from NTU in Taiwan and from NSF in the US.

Isotope analysis in the transmission electron microscope.

PubMed

Susi, Toma; Hofer, Christoph; Argentero, Giacomo; Leuthner, Gregor T; Pennycook, Timothy J; Mangler, Clemens; Meyer, Jannik C; Kotakoski, Jani

2016-10-10

The Ångström-sized probe of the scanning transmission electron microscope can visualize and collect spectra from single atoms. This can unambiguously resolve the chemical structure of materials, but not their isotopic composition. Here we differentiate between two isotopes of the same element by quantifying how likely the energetic imaging electrons are to eject atoms. First, we measure the displacement probability in graphene grown from either 12 C or 13 C and describe the process using a quantum mechanical model of lattice vibrations coupled with density functional theory simulations. We then test our spatial resolution in a mixed sample by ejecting individual atoms from nanoscale areas spanning an interface region that is far from atomically sharp, mapping the isotope concentration with a precision better than 20%. Although we use a scanning instrument, our method may be applicable to any atomic resolution transmission electron microscope and to other low-dimensional materials.

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

PubMed Central

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-01-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field. PMID:26459874

Imaging of current density distributions with a Nb weak-link scanning nano-SQUID microscope

NASA Astrophysics Data System (ADS)

Shibata, Yusuke; Nomura, Shintaro; Kashiwaya, Hiromi; Kashiwaya, Satoshi; Ishiguro, Ryosuke; Takayanagi, Hideaki

2015-10-01

Superconducting quantum interference devices (SQUIDs) are accepted as one of the highest magnetic field sensitive probes. There are increasing demands to image local magnetic fields to explore spin properties and current density distributions in a two-dimensional layer of semiconductors or superconductors. Nano-SQUIDs have recently attracting much interest for high spatial resolution measurements in nanometer-scale samples. Whereas weak-link Dayem Josephson junction nano-SQUIDs are suitable to miniaturization, hysteresis in current-voltage (I-V) characteristics that is often observed in Dayem Josephson junction is not desirable for a scanning microscope. Here we report on our development of a weak-link nano-SQUIDs scanning microscope with small hysteresis in I-V curve and on reconstructions of two-dimensional current density vector in two-dimensional electron gas from measured magnetic field.

Spatially resolved spectroscopy analysis of the XMM-Newton large program on SN1006

NASA Astrophysics Data System (ADS)

Li, Jiang-Tao; Decourchelle, Anne; Miceli, Marco; Vink, Jacco; Bocchino, Fabrizio

2016-04-01

We perform analysis of the XMM-Newton large program on SN1006 based on our newly developed methods of spatially resolved spectroscopy analysis. We extract spectra from low and high resolution meshes. The former (3596 meshes) is used to roughly decompose the thermal and non-thermal components and characterize the spatial distributions of different parameters, such as temperature, abundances of different elements, ionization age, and electron density of the thermal component, as well as photon index and cutoff frequency of the non-thermal component. On the other hand, the low resolution meshes (583 meshes) focus on the interior region dominated by the thermal emission and have enough counts to well characterize the Si lines. We fit the spectra from the low resolution meshes with different models, in order to decompose the multiple plasma components at different thermal and ionization states and compare their spatial distributions. In this poster, we will present the initial results of this project.

Long-Range Repulsion Between Spatially Confined van der Waals Dimers

NASA Astrophysics Data System (ADS)

Sadhukhan, Mainak; Tkatchenko, Alexandre

2017-05-01

It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here, we demonstrate that the long-range interaction between spatially confined vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality; however, the long-range repulsion is expected to be a general phenomenon for spatially confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces.

Spatially resolved NMR spectra for the Swiss cheese model in heavy fermion PuCoGa5 superconductor

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Zhu, Jian-Xin; Balatsky, A. V.; Graf, M. J.

2011-03-01

Spatially resolved NMR experiments, which probe the local electronic excitations, play a vital role for studying the pairing symmetry of unconventional superconductors. Here we calculate the spatial modulation of the NMR spin-lattice relaxation rate (1/T1) for the Swiss cheese model as a function of impurity concentration in PuCoGa5 superconductor. The local suppression of the superconducting order parameter due to impurities is related to the number of holes in the Swiss cheese model. Our results indicate that Friedel-like oscillations,as seen in the local-density of states near an impurity, are also present in the behavior of 1/T1 as one moves away from the impurity site. We demonstrate that the gap nodes, which are filled by disorder, can be probed by NMR through the local information encoded in the spectra. The advantage of spatially resolved NMR compared to STM measurements is that the former probe is not sensitive to surface states. Work is supported by US DOE.

Polarization simulations of stellar wind bow-shock nebulae - I. The case of electron scattering

NASA Astrophysics Data System (ADS)

Shrestha, Manisha; Neilson, Hilding R.; Hoffman, Jennifer L.; Ignace, Richard

2018-06-01

Bow shocks and related density enhancements produced by the winds of massive stars moving through the interstellar medium provide important information regarding the motions of the stars, the properties of their stellar winds, and the characteristics of the local medium. Since bow-shock nebulae are aspherical structures, light scattering within them produces a net polarization signal even if the region is spatially unresolved. Scattering opacity arising from free electrons and dust leads to a distribution of polarized intensity across the bow-shock structure. That polarization encodes information about the shape, composition, opacity, density, and ionization state of the material within the structure. In this paper, we use the Monte Carlo radiative transfer code SLIP to investigate the polarization created when photons scatter in a bow-shock-shaped region of enhanced density surrounding a stellar source. We present results for electron scattering, and investigate the polarization behaviour as a function of optical depth, temperature, and source of photons for two different cases: pure scattering and scattering with absorption. In both regimes, we consider resolved and unresolved cases. We discuss the implications of these results as well as their possible use along with observational data to constrain the properties of observed bow-shock systems. In different situations and under certain assumptions, our simulations can constrain viewing angle, optical depth and temperature of the scattering region, and the relative luminosities of the star and shock.

Kinetic Temperature and Electron Density Measurement in an Inductively Coupled Plasma Torch using Degenerate Four-Wave Mixing

NASA Technical Reports Server (NTRS)

Schafer, Julia; Lyons, Wendy; Tong, WIlliam G.; Danehy, Paul M.

2008-01-01

Laser wave mixing is presented as an effective technique for spatially resolved kinetic temperature measurements in an atmospheric-pressure radio-frequency inductively-coupled plasma. Measurements are performed in a 1 kW, 27 MHz RF plasma using a continuous-wave, tunable 811.5-nm diode laser to excite the 4s(sup 3)P2 approaches 4p(sup 3)D3 argon transition. Kinetic temperature measurements are made at five radial steps from the center of the torch and at four different torch heights. The kinetic temperature is determined by measuring simultaneously the line shape of the sub-Doppler backward phase-conjugate degenerate four-wave mixing and the Doppler-broadened forward-scattering degenerate four-wave mixing. The temperature measurements result in a range of 3,500 to 14,000 K+/-150 K. Electron densities measured range from 6.1 (+/-0.3) x 10(exp 15)/cu cm to 10.1 (+/-0.3) x 10(exp 15)/cu cm. The experimental spectra are analyzed using a perturbative treatment of the backward phase-conjugate and forward-geometry wave-mixing theory. Stark width is determined from the collisional broadening measured in the phase-conjugate geometry. Electron density measurements are made based on the Stark width. The kinetic temperature of the plasma was found to be more than halved by adding deionized water through the nebulizer.

Density of Electronic States in the Conduction Band of Ultrathin Films of Naphthalenedicarboxylic Anhydride and Naphthalenetetracarboxylic Dianhydride on the Surface of Oxidized Silicon

NASA Astrophysics Data System (ADS)

Komolov, A. S.; Lazneva, E. F.; Gerasimova, N. B.; Panina, Yu. A.; Baramygin, A. V.; Zashikhin, G. D.; Pshenichnyuk, S. A.

2018-04-01

The results of examination of the electronic structure of the conduction band of naphthalenedicarboxylic anhydride (NDCA) films in the process of their deposition on the surface of oxidized silicon are presented. These results were obtained using total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The energy position of the primary maxima of the density of unoccupied states (DOUS) of an NDCA film was determined based on the experimental TCS data and calculated data and compared with the position of the DOUS maxima of a naphthalenetetracarboxylic dianhydride (NTCDA) film. The theoretical analysis involved calculating the energies and the spatial distribution of orbitals of the molecules under study at the B3LYP/6-31G(d) DFT (density functional theory) level and correcting the obtained energies in accordance with the procedure that was proven effective in earlier studies of the conduction band of films of small conjugated organic molecules. It was found that the DOUS maxima of the NTCDA film in the studied energy interval from 5 to 20 eV above the Fermi level are shifted toward lower electron energies by 1-2 eV relative to the corresponding DOUS maxima of the NDCA film Subdivision of the Ufa Federal Research Centre of the.

The effect of external magnetic field on the bremsstrahlung nonlinear absorption mechanism in the interaction of high intensity short laser pulse with collisional underdense plasma

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

Sedaghat, M.; Ettehadi-Abari, M.; Shokri, B., E-mail: b-shokri@sbu.ac.ir

2015-03-15

Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range Iλ{sup 2}≃10{sup 14}−10{sup 16}Wcm{sup −2}μm{sup 2}. The collisional effect is found to be significant when the incident laser intensity is less than 10{sup 16}Wcm{sup −2}μm{sup 2}. In the current work, the propagation of a high frequency electromagnetic wave, for underdense collisional plasma in the presence of an external magnetic field is investigated. It is shown that, by considering the effect of the ponderomotive force in collisional magnetized plasmas, the increase of laser pulse intensity leads to steepening of themore » electron density profile and the electron bunches of plasma makes narrower. Moreover, it is found that the wavelength of electric and magnetic fields oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison with the unmagnetized collisional plasma. Furthermore, the spatial damping rate of laser energy and the nonlinear bremsstrahlung absorption coefficient are obtained in the collisional regime of magnetized plasma. The other remarkable result is that by increasing the external magnetic field in this case, the absorption coefficient increases strongly.« less

Information hidden in the velocity distribution of ions and the exact kinetic Bohm criterion

NASA Astrophysics Data System (ADS)

Tsankov, Tsanko V.; Czarnetzki, Uwe

2017-05-01

Non-equilibrium distribution functions of electrons and ions play an important role in plasma physics. A prominent example is the kinetic Bohm criterion. Since its first introduction it has been controversial for theoretical reasons and due to the lack of experimental data, in particular on the ion distribution function. Here we resolve the theoretical as well as the experimental difficulties by an exact solution of the kinetic Boltzmann equation including charge exchange collisions and ionization. This also allows for the first time non-invasive measurement of spatially resolved ion velocity distributions, absolute values of the ion and electron densities, temperatures, and mean energies as well as the electric field and the plasma potential in the entire plasma. The non-invasive access to the spatially resolved distribution functions of electrons and ions is applied to the problem of the kinetic Bohm criterion. Theoretically a so far missing term in the criterion is derived and shown to be of key importance. With the new term the validity of the kinetic criterion at high collisionality and its agreement with the fluid picture are restored. All findings are supported by experimental data, theory and a numerical model with excellent agreement throughout.

Giant rectification in graphene nanoflake molecular devices with asymmetric graphene nanoribbon electrodes

NASA Astrophysics Data System (ADS)

Ji, Xiao-Li; Xie, Zhen; Zuo, Xi; Zhang, Guang-Ping; Li, Zong-Liang; Wang, Chuan-Kui

2016-09-01

By applying density functional theory based nonequilibrium Green's function method, we theoretically investigate the electron transport properties of a zigzag-edged trigonal graphene nanoflake (ZTGNF) sandwiched between two asymmetric zigzag graphene nanoribbon (zGNR) and armchair graphene nanoribbon (aGNR) electrodes with carbon atomic chains (CACs) as the anchoring groups. Significant rectifying effects have been observed for these molecular devices in low bias voltage regions. Interestingly, the rectifying performance of molecular devices can be optimized by changing the width of the aGNR electrode and the number of anchoring CACs. Especially, the molecular device displays giant rectification ratios up to the order of 104 when two CACs are used as the anchoring group between the ZTGNF and the right aGNR electrode. Further analysis indicates that the asymmetric shift of the perturbed molecular energy levels and the spatial parity of the electron wavefunctions in the electrodes around the Fermi level play key roles in determining the rectification performance. And the spatial distributions of tunneling electron wavefunctions under negative bias voltages can be modified to be very localized by changing the number of anchoring CACs, which is found to be the origin of the giant rectification ratios.

Method for local temperature measurement in a nanoreactor for in situ high-resolution electron microscopy.

PubMed

Vendelbo, S B; Kooyman, P J; Creemer, J F; Morana, B; Mele, L; Dona, P; Nelissen, B J; Helveg, S

2013-10-01

In situ high-resolution transmission electron microscopy (TEM) of solids under reactive gas conditions can be facilitated by microelectromechanical system devices called nanoreactors. These nanoreactors are windowed cells containing nanoliter volumes of gas at ambient pressures and elevated temperatures. However, due to the high spatial confinement of the reaction environment, traditional methods for measuring process parameters, such as the local temperature, are difficult to apply. To address this issue, we devise an electron energy loss spectroscopy (EELS) method that probes the local temperature of the reaction volume under inspection by the electron beam. The local gas density, as measured using quantitative EELS, is combined with the inherent relation between gas density and temperature, as described by the ideal gas law, to obtain the local temperature. Using this method we determined the temperature gradient in a nanoreactor in situ, while the average, global temperature was monitored by a traditional measurement of the electrical resistivity of the heater. The local gas temperatures had a maximum of 56 °C deviation from the global heater values under the applied conditions. The local temperatures, obtained with the proposed method, are in good agreement with predictions from an analytical model. Copyright © 2013 Elsevier B.V. All rights reserved.

Computation of the influence of scanning probe microscope (SPM) on quantum dot eigenstates and 2DEG potential

NASA Astrophysics Data System (ADS)

Stopa, Michael

2005-03-01

We calculate the electronic structure of GaAs-AlGaAs two-dimensional electron gas (2DEG) devices, such as quantum dots and quantum point contacts (QPCs) in the presence of a tip of a scanning probe microscope at some distance above the surface. The calculation employs standard density functional theory with exchange and correlation treated in the local density approximation. The position and voltage on the tip are varied and the conditions for depletion of the 2DEG are shown to compare favorably to experiment [1]. We show that the size of the depletion region created (by a negative tip voltage) is unexpectedly small due to focusing of the potential lines by the higher dielectric. We study the interaction of the tip with an isolated quantum dot that contains one or two electrons. The raster pattern of the difference between single particle energies reveals that the tip distorts the shape of the confining potential and suggests that excited state properties, if they can be measured experimentally, can contribute to the resolution of spatial information. [1] M.A. Topinka, R.M. Westervelt, E.J. Heller, ``http://meso.deas.harvard.edu/papers/Topinka, PT 56 12 (2003)'' (Imaging Electron Flow), Physics Today 56, 12 (2003).

Electronic and Spatial Structures of Water-Soluble Dinitrosyl Iron Complexes with Thiol-Containing Ligands Underlying Their Ability to Act as Nitric Oxide and Nitrosonium Ion Donors

PubMed Central

Vanin, Anatoly F.; Burbaev, Dosymzhan Sh.

2011-01-01

The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe+(NO+)2] core ({Fe(NO)2}7 according to the Enemark-Feltham classification). Similarly, the {(RS−)2Fe+(NO+)2}+ structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d7 electron configuration of the iron atom and predominant localization of the unpaired electron on MO(dz2) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC. PMID:22505886

Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors.

PubMed

Vanin, Anatoly F; Burbaev, Dosymzhan Sh

2011-01-01

The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

Dynamics and density distributions in a capillary-discharge waveguide with an embedded supersonic jet

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

Matlis, N. H., E-mail: nmatlis@gmail.com; Gonsalves, A. J.; Steinke, S.

We present an analysis of the gas dynamics and density distributions within a capillary-discharge waveguide with an embedded supersonic jet. This device provides a target for a laser plasma accelerator which uses longitudinal structuring of the gas-density profile to enable control of electron trapping and acceleration. The functionality of the device depends sensitively on the details of the density profile, which are determined by the interaction between the pulsed gas in the jet and the continuously-flowing gas in the capillary. These dynamics are captured by spatially resolving recombination light from several emission lines of the plasma as a function ofmore » the delay between the jet and the discharge. We provide a phenomenological description of the gas dynamics as well as a quantitative evaluation of the density evolution. In particular, we show that the pressure difference between the jet and the capillary defines three regimes of operation with qualitatively different longitudinal density profiles and show that jet timing provides a sensitive method for tuning between these regimes.« less

Simulated performance of the optical Thomson scattering diagnostic designed for the National Ignition Facility.

PubMed

Ross, J S; Datte, P; Divol, L; Galbraith, J; Froula, D H; Glenzer, S H; Hatch, B; Katz, J; Kilkenny, J; Landen, O; Manuel, A M; Molander, W; Montgomery, D S; Moody, J D; Swadling, G; Weaver, J

2016-11-01

An optical Thomson scattering diagnostic has been designed for the National Ignition Facility to characterize under-dense plasmas. We report on the design of the system and the expected performance for different target configurations. The diagnostic is designed to spatially and temporally resolve the Thomson scattered light from laser driven targets. The diagnostic will collect scattered light from a 50 × 50 × 200 μm volume. The optical design allows operation with different probe laser wavelengths. A deep-UV probe beam (λ 0 = 210 nm) will be used to Thomson scatter from electron plasma densities of ∼5 × 10 20 cm -3 while a 3ω probe will be used for plasma densities of ∼1 × 10 19 cm -3 . The diagnostic package contains two spectrometers: the first to resolve Thomson scattering from ion acoustic wave fluctuations and the second to resolve scattering from electron plasma wave fluctuations. Expected signal levels relative to background will be presented for typical target configurations (hohlraums and a planar foil).

A hybrid electron cyclotron resonance metal ion source with integrated sputter magnetron for the production of an intense Al{sup +} ion beam

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

Weichsel, T., E-mail: tim.weichsel@fep.fraunhofer.de; Hartung, U.; Kopte, T.

2015-09-15

A metal ion source prototype has been developed: a combination of magnetron sputter technology with 2.45 GHz electron cyclotron resonance (ECR) ion source technology—a so called magnetron ECR ion source (MECRIS). An integrated ring-shaped sputter magnetron with an Al target is acting as a powerful metal atom supply in order to produce an intense current of singly charged metal ions. Preliminary experiments show that an Al{sup +} ion current with a density of 167 μA/cm{sup 2} is extracted from the source at an acceleration voltage of 27 kV. Spatially resolved double Langmuir probe measurements and optical emission spectroscopy were usedmore » to study the plasma states of the ion source: sputter magnetron, ECR, and MECRIS plasma. Electron density and temperature as well as Al atom density were determined as a function of microwave and sputter magnetron power. The effect of ECR heating is strongly pronounced in the center of the source. There the electron density is increased by one order of magnitude from 6 × 10{sup 9} cm{sup −3} to 6 × 10{sup 10} cm{sup −3} and the electron temperature is enhanced from about 5 eV to 12 eV, when the ECR plasma is ignited to the magnetron plasma. Operating the magnetron at constant power, it was observed that its discharge current is raised from 1.8 A to 4.8 A, when the ECR discharge was superimposed with a microwave power of 2 kW. At the same time, the discharge voltage decreased from about 560 V to 210 V, clearly indicating a higher plasma density of the MECRIS mode. The optical emission spectrum of the MECRIS plasma is dominated by lines of excited Al atoms and shows a significant contribution of lines arising from singly ionized Al. Plasma emission photography with a CCD camera was used to prove probe measurements and to identify separated plasma emission zones originating from the ECR and magnetron discharge.« less

Improvement of GPS radio occultation retrieval error of E region electron density: COSMIC measurement and IRI model simulation

NASA Astrophysics Data System (ADS)

Wu, Kang-Hung; Su, Ching-Lun; Chu, Yen-Hsyang

2015-03-01

In this article, we use the International Reference Ionosphere (IRI) model to simulate temporal and spatial distributions of global E region electron densities retrieved by the FORMOSAT-3/COSMIC satellites by means of GPS radio occultation (RO) technique. Despite regional discrepancies in the magnitudes of the E region electron density, the IRI model simulations can, on the whole, describe the COSMIC measurements in quality and quantity. On the basis of global ionosonde network and the IRI model, the retrieval errors of the global COSMIC-measured E region peak electron density (NmE) from July 2006 to July 2011 are examined and simulated. The COSMIC measurement and the IRI model simulation both reveal that the magnitudes of the percentage error (PE) and root mean-square-error (RMSE) of the relative RO retrieval errors of the NmE values are dependent on local time (LT) and geomagnetic latitude, with minimum in the early morning and at high latitudes and maximum in the afternoon and at middle latitudes. In addition, the seasonal variation of PE and RMSE values seems to be latitude dependent. After removing the IRI model-simulated GPS RO retrieval errors from the original COSMIC measurements, the average values of the annual and monthly mean percentage errors of the RO retrieval errors of the COSMIC-measured E region electron density are, respectively, substantially reduced by a factor of about 2.95 and 3.35, and the corresponding root-mean-square errors show averaged decreases of 15.6% and 15.4%, respectively. It is found that, with this process, the largest reduction in the PE and RMSE of the COSMIC-measured NmE occurs at the equatorial anomaly latitudes 10°N-30°N in the afternoon from 14 to 18 LT, with a factor of 25 and 2, respectively. Statistics show that the residual errors that remained in the corrected COSMIC-measured NmE vary in a range of -20% to 38%, which are comparable to or larger than the percentage errors of the IRI-predicted NmE fluctuating in a range of -6.5% to 20%.

A Hydrodynamic Theory for Spatially Inhomogeneous Semiconductor Lasers: Microscopic Approach

NASA Technical Reports Server (NTRS)

Li, Jianzhong; Ning, C. Z.; Biegel, Bryan A. (Technical Monitor)

2001-01-01

Starting from the microscopic semiconductor Bloch equations (SBEs) including the Boltzmann transport terms in the distribution function equations for electrons and holes, we derived a closed set of diffusion equations for carrier densities and temperatures with self-consistent coupling to Maxwell's equation and to an effective optical polarization equation. The coherent many-body effects are included within the screened Hartree-Fock approximation, while scatterings are treated within the second Born approximation including both the in- and out-scatterings. Microscopic expressions for electron-hole (e-h) and carrier-LO (c-LO) phonon scatterings are directly used to derive the momentum and energy relaxation rates. These rates expressed as functions of temperatures and densities lead to microscopic expressions for self- and mutual-diffusion coefficients in the coupled density-temperature diffusion equations. Approximations for reducing the general two-component description of the electron-hole plasma (EHP) to a single-component one are discussed. In particular, we show that a special single-component reduction is possible when e-h scattering dominates over c-LO phonon scattering. The ambipolar diffusion approximation is also discussed and we show that the ambipolar diffusion coefficients are independent of e-h scattering, even though the diffusion coefficients of individual components depend sensitively on the e-h scattering rates. Our discussions lead to new perspectives into the roles played in the single-component reduction by the electron-hole correlation in momentum space induced by scatterings and the electron-hole correlation in real space via internal static electrical field. Finally, the theory is completed by coupling the diffusion equations to the lattice temperature equation and to the effective optical polarization which in turn couples to the laser field.

Low-pressure hydrogen discharge maintenance in a large-size plasma source with localized high radio-frequency power deposition

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

Todorov, D.; Shivarova, A., E-mail: ashiva@phys.uni-sofia.bg; Paunska, Ts.

2015-03-15

The development of the two-dimensional fluid-plasma model of a low-pressure hydrogen discharge, presented in the study, is regarding description of the plasma maintenance in a discharge vessel with the configuration of the SPIDER source. The SPIDER source, planned for the neutral-beam-injection plasma-heating system of ITER, is with localized high RF power deposition to its eight drivers (cylindrical-coil inductive discharges) and a large-area second chamber, common for all the drivers. The continuity equations for the charged particles (electrons and the three types of positive ions) and for the neutral species (atoms and molecules), their momentum equations, the energy balance equations formore » electrons, atoms and molecules and the Poisson equations are involved in the discharge description. In addition to the local processes in the plasma volume, the surface processes of particle reflection and conversion on the walls as well as for a heat exchange with the walls are included in the model. The analysis of the results stresses on the role of the fluxes (particle and energy fluxes) in the formation of the discharge structure. The conclusion is that the discharge behavior is completely obeyed to non-locality. The latter is displayed by: (i) maximum values of plasma parameters (charged particle densities and temperatures of the neutral species) outside the region of the RF power deposition, (ii) shifted maxima of the electron density and temperature, of the plasma potential and of the electron production, (iii) an electron flux, with a vortex structure, strongly exceeding the total ion flux which gives evidence of a discharge regime of non-ambipolarity and (iv) a spatial distribution of the densities of the neutral species resulting from their fluxes.« less

Using Moran's I and GIS to study the spatial pattern of forest litter carbon density in a subtropical region of southeastern China

NASA Astrophysics Data System (ADS)

Fu, W. J.; Jiang, P. K.; Zhou, G. M.; Zhao, K. L.

2014-04-01

Spatial pattern information of carbon density in forest ecosystem including forest litter carbon (FLC) plays an important role in evaluating carbon sequestration potentials. The spatial variation of FLC density in the typical subtropical forests in southeastern China was investigated using Moran's I, geostatistics and a geographical information system (GIS). A total of 839 forest litter samples were collected based on a 12 km (south-north) × 6 km (east-west) grid system in Zhejiang province. Forest litter carbon density values were very variable, ranging from 10.2 kg ha-1 to 8841.3 kg ha-1, with an average of 1786.7 kg ha-1. The aboveground biomass had the strongest positive correlation with FLC density, followed by forest age and elevation. Global Moran's I revealed that FLC density had significant positive spatial autocorrelation. Clear spatial patterns were observed using local Moran's I. A spherical model was chosen to fit the experimental semivariogram. The moderate "nugget-to-sill" (0.536) value revealed that both natural and anthropogenic factors played a key role in spatial heterogeneity of FLC density. High FLC density values were mainly distributed in northwestern and western part of Zhejiang province, which were related to adopting long-term policy of forest conservation in these areas, while Hang-Jia-Hu (HJH) Plain, Jin-Qu (JQ) Basin and coastal areas had low FLC density due to low forest coverage and intensive management of economic forests. These spatial patterns were in line with the spatial-cluster map described by local Moran's I. Therefore, Moran's I, combined with geostatistics and GIS, could be used to study spatial patterns of environmental variables related to forest ecosystem.

Extracting the redox orbitals in Li battery materials with high-resolution x-ray compton scattering spectroscopy.

PubMed

Suzuki, K; Barbiellini, B; Orikasa, Y; Go, N; Sakurai, H; Kaprzyk, S; Itou, M; Yamamoto, K; Uchimoto, Y; Wang, Yung Jui; Hafiz, H; Bansil, A; Sakurai, Y

2015-02-27

We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel Li_{x}Mn_{2}O_{4}, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16±0.05 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery.

Model interpretation of type III radio burst characteristics. I - Spatial aspects

NASA Technical Reports Server (NTRS)

Reiner, M. J.; Stone, R. G.

1988-01-01

The ways that the finite size of the source region and directivity of the emitted radiation modify the observed characteristics of type III radio bursts as they propagate through the interplanetary medium are investigated. A simple model that simulates the radio source region is developed to provide insight into the spatial behavior of the parameters that characterize radio bursts. The model is used to demonstrate that observed radio azimuths are systematically displaced from the geometric centroid of the exciter electron beam in such a way as to cause trajectories of the radio bursts to track back to the observer at low frequencies, rather than to follow expected Archimedean spiral-like paths. The source region model is used to investigate the spatial behavior of the peak intensities of radio bursts, and it is found that the model can qualitatively account for both the frequency dependence and the east-west asymmetry of the observed peak flux densities.

A spatially resolved pyrometer for measuring the blackbody temperature of a warm dense plasma

DOE PAGES

Coleman, Joshua Eugene

2016-12-30

A pyrometer has been developed to spatially resolve the blackbody temperature of a radiatively cooling warm dense plasma. The pyrometer is composed of a lens coupled fiber array, Czerny-Turner visible spectrometer, and an intensified gated CCD for the detector. The radiatively cooling warm dense plasma is generated by a ~100-ns-long intense relativistic electron bunch with an energy of 19.1 MeV and a current of 0.2 kA interacting with 100-μm-thick low-Z foils. The continuum spectrum is measured over 250 nm with a low groove density grating. These plasmas emit visible light or blackbody radiation on relatively long time scales (~0.1 tomore » 100 μs). Finally, we presented the diagnostic layout, calibration, and proof-of-principle measurement of a radiatively cooling aluminum plasma, which includes a spatially resolved temperature gradient and the ability to temporally resolve it also.« less

The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level

NASA Astrophysics Data System (ADS)

Cvikl, B.

2010-01-01

The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a single layer organic semiconductor structure characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminum/tris(8-hydroxyquinoline aluminum/calcium structure [W. Brütting et al., Synth. Met. 122, 99 (2001)] for which jexp∝Va3.4, within the interval of bias 0.4 V≤Va≤7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lower limit, i.e., their minimum values, is found to be in each case, to a good approximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the apparent electron mobility the spatial distribution of the organic bulk electric field as well as the total charge density turn out to be bias independent. The first case investigated is based on the boundary condition of zero electric field at the electron injection interface. It is shown that for minimum valued apparent mobilities, the strong but finite accumulation of electrons close to the anode is obtained, which characterize the inverted space charge limited current (SCLC) effect. The second example refers to the internal electric field allowing for self-adjustment of its boundary values. The total electron charge density is than found typically to be of U shape, which may, depending on the parameters, peak at both or at either Alq3 boundary. It is this example in which the proper SCLC effect is consequently predicted. In each of the above two cases, the calculations predict the minimum values of the electron apparent mobility, which substantially exceed the corresponding published measurements. For this reason the effect of the drift term alone is additionally investigated. On the basis of the published empirical electron mobilities and the diffusion term revoked, it is shown that the steady state electron current density within the Al/Alq3 (97 nm)/Ca single layer organic structure may well be pictured within the drift-only interpretation of the charge carriers within the Alq3 organic characterized by the single (shallow) trap energy level. In order to arrive at this result, it is necessary that the nonzero electric field, calculated to exist at the electron injecting Alq3/Ca boundary, is to be appropriately accounted for in the computation.

Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence.

PubMed

Thakur, S C; Brandt, C; Light, A; Cui, L; Gosselin, J J; Tynan, G R

2014-11-01

We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.

Gauge-origin dependence in electronic g-tensor calculations

NASA Astrophysics Data System (ADS)

Glasbrenner, Michael; Vogler, Sigurd; Ochsenfeld, Christian

2018-06-01

We present a benchmark study on the gauge-origin dependence of the electronic g-tensor using data from unrestricted density functional theory calculations with the spin-orbit mean field ansatz. Our data suggest in accordance with previous studies that g-tensor calculations employing a common gauge-origin are sufficiently accurate for small molecules; however, for extended molecules, the introduced errors can become relevant and significantly exceed the basis set error. Using calculations with the spin-orbit mean field ansatz and gauge-including atomic orbitals as a reference, we furthermore show that the accuracy and reliability of common gauge-origin approaches in larger molecules depends strongly on the locality of the spin density distribution. We propose a new pragmatic ansatz for choosing the gauge-origin which takes the spin density distribution into account and gives reasonably accurate values for molecules with a single localized spin center. For more general cases like molecules with several spatially distant spin centers, common gauge-origin approaches are shown to be insufficient for consistently achieving high accuracy. Therefore the computation of g-tensors using distributed gauge-origin methods like gauge-including atomic orbitals is considered as the ideal approach and is recommended for larger molecular systems.

Spatial variation and density-dependent dispersal in competitive coexistence.

PubMed Central

Amarasekare, Priyanga

2004-01-01

It is well known that dispersal from localities favourable to a species' growth and reproduction (sources) can prevent competitive exclusion in unfavourable localities (sinks). What is perhaps less well known is that too much emigration can undermine the viability of sources and cause regional competitive exclusion. Here, I investigate two biological mechanisms that reduce the cost of dispersal to source communities. The first involves increasing the spatial variation in the strength of competition such that sources can withstand high rates of emigration; the second involves reducing emigration from sources via density-dependent dispersal. I compare how different forms of spatial variation and modes of dispersal influence source viability, and hence source-sink coexistence, under dominance and pre-emptive competition. A key finding is that, while spatial variation substantially reduces dispersal costs under both types of competition, density-dependent dispersal does so only under dominance competition. For instance, when spatial variation in the strength of competition is high, coexistence is possible (regardless of the type of competition) even when sources experience high emigration rates; when spatial variation is low, coexistence is restricted even under low emigration rates. Under dominance competition, density-dependent dispersal has a strong effect on coexistence. For instance, when the emigration rate increases with density at an accelerating rate (Type III density-dependent dispersal), coexistence is possible even when spatial variation is quite low; when the emigration rate increases with density at a decelerating rate (Type II density-dependent dispersal), coexistence is restricted even when spatial variation is quite high. Under pre-emptive competition, density-dependent dispersal has only a marginal effect on coexistence. Thus, the diversity-reducing effects of high dispersal rates persist under pre-emptive competition even when dispersal is density dependent, but can be significantly mitigated under dominance competition if density-dependent dispersal is Type III rather than Type II. These results lead to testable predictions about source-sink coexistence under different regimes of competition, spatial variation and dispersal. They identify situations in which density-independent dispersal provides a reasonable approximation to species' dispersal patterns, and those under which consideration of density-dependent dispersal is crucial to predicting long-term coexistence. PMID:15306322

Electrical characterization of the flowing afterglow of N{sub 2} and N{sub 2}/O{sub 2} microwave plasmas at reduced pressure

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

Afonso Ferreira, J.; Stafford, L., E-mail: luc.stafford@umontreal.ca; Leonelli, R.

2014-04-28

A cylindrical Langmuir probe was used to analyze the spatial distribution of the number density of positive ions and electrons as well as the electron energy distribution function (EEDF) in the flowing afterglow of a 6 Torr N{sub 2} and N{sub 2}/O{sub 2} plasma sustained by a propagating electromagnetic surface wave in the microwave regime. In pure N{sub 2} discharges, ion densities were in the mid 10{sup 14} m{sup −3} in the pink afterglow and in the mid 10{sup 12} m{sup −3} early in the late afterglow. In both pink and late afterglows, the ion population was much higher than the electron population,more » indicating non-macroscopically neutral media. The EEDF was close to a Maxwellian with an electron temperature of 0.5 ± 0.1 eV, except in the pink afterglow where the temperature rose to 1.1 ± 0.2 eV. This latter behavior is ascribed to N{sub 2} vibration-vibration pumping in the pink afterglow that increases the concentration of high N{sub 2} vibrational states and thus rises the electron temperature by vibration-electron collisions. After addition of small amounts of O{sub 2} in the nominally pure N{sub 2} discharge, the charged particles densities and average electron energy first strongly increased and then decreased with increasing O{sub 2} concentration. Based on these data and the evolution of the N{sub 2}{sup +}(B) band emission intensities, it is concluded that a significant change in the positive ion composition of the flowing afterglow occurs, going from N{sub 2}{sup +} in nominally pure N{sub 2} discharges to NO{sup +} after addition of trace amounts of O{sub 2} in N{sub 2}.« less

Effect of the resonant magnetic perturbation on the plasma parameters in COMPASS tokamak’s divertor region

NASA Astrophysics Data System (ADS)

Dimitrova, M.; Cahyna, P.; Peterka, M.; Hasan, E.; Popov, Tsv K.; Ivanova, P.; Vasileva, E.; Panek, R.; Cavalier, J.; Seidl, J.; Markovic, T.; Havlicek, J.; Dejarnac, R.; Weinzettl, V.; Hacek, P.; Tomes, M.; the COMPASS Team; the EUROfusion MST1 Team

2018-02-01

The resonant magnetic perturbation (RMP) has proven to be a useful way to suppress edge-localized modes that under certain conditions can damage the device by the large power fluxes carried from the bulk plasma to the wall. The effect of RMP on the L-mode plasma parameters in the divertor region of the COMPASS tokamak was studied using the array of 39 Langmuir probes embedded into the divertor target. The current-voltage (IV) probe characteristics were processed by the first-derivative probe technique to obtain the plasma potential and the electron energy distribution function (EEDF) which was approximated by a bi-Maxwellian EEDF with a low-energy (4-6 eV) fraction and a high-energy (11-35 eV) one, the both factions having similar electron density. Clear splitting was observed during the RMP pulse in the low-field-side scrape-off-layer profiles of the floating potential U fl and the ion saturation current density J sat; these two quantities were obtained both by direct continuous measurement and by evaluation of the IV characteristics of probes with swept bias. The negative peaks of U fl induced by RMP spatially overlaps with the local minima of J sat (and n e) rather than with its local maxima which is partly caused by the spatial variation of the plasma potential and partly by the changed shape of the EEDF. The effective temperature of the whole EEDF is not correlated with the negative peaks of U fl, and the profile of the parallel power flux density shows secondary maxima due to RMP which mimic those of J sat.

Seismo-Ionospheric Coupling as Intensified EIA Observed by Satellite Electron Density and GPS-TEC Data

NASA Astrophysics Data System (ADS)

Ryu, K.; Jangsoo, C.; Kim, S. G.; Jeong, K. S.; Parrot, M.; Pulinets, S. A.; Oyama, K. I.

2014-12-01

Examples of intensified EIA features temporally and spatially related to large earthquakes observed by satellites and GPS-TEC are introduced. The precursory, concurrent, and ex-post enhancements of EIA represented by the equatorial electron density, which are thought to be related to the M8.7 Northern Sumatra earthquake of March 2005, the M8.0 Pisco earthquake of August 2007, and the M7.9 Wenchuan Earthquake of 12 May 2008, are shown with space weather condition. Based on the case studies, statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions satellite (DEMETER) over a period of 2005-2010 was executed in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the EIA intensity indices were performed for each region with excluding the possible effects from the geomagnetic and solar activity. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 7.0 in the low latitude region can accompany observable seismo-ionospheric coupling phenomena in the form of EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling to explain the observation and the possibility of earthquake prediction using the EIA intensity variation are discussed.

Calibrated simulations of Z opacity experiments that reproduce the experimentally measured plasma conditions

DOE PAGES

Nagayama, T.; Bailey, J. E.; Loisel, G.; ...

2016-02-05

Recently, frequency-resolved iron opacity measurements at electron temperatures of 170–200 eV and electron densities of (0.7 – 4.0) × 10 22 cm –3 revealed a 30–400% disagreement with the calculated opacities [J. E. Bailey et al., Nature (London) 517, 56 (2015)]. The discrepancies have a high impact on astrophysics, atomic physics, and high-energy density physics, and it is important to verify our understanding of the experimental platform with simulations. Reliable simulations are challenging because the temporal and spatial evolution of the source radiation and of the sample plasma are both complex and incompletely diagnosed. In this article, we describe simulationsmore » that reproduce the measured temperature and density in recent iron opacity experiments performed at the Sandia National Laboratories Z facility. The time-dependent spectral irradiance at the sample is estimated using the measured time- and space-dependent source radiation distribution, in situ source-to-sample distance measurements, and a three-dimensional (3D) view-factor code. The inferred spectral irradiance is used to drive 1D sample radiation hydrodynamics simulations. The images recorded by slit-imaged space-resolved spectrometers are modeled by solving radiation transport of the source radiation through the sample. We find that the same drive radiation time history successfully reproduces the measured plasma conditions for eight different opacity experiments. These results provide a quantitative physical explanation for the observed dependence of both temperature and density on the sample configuration. Simulated spectral images for the experiments without the FeMg sample show quantitative agreement with the measured spectral images. The agreement in spectral profile, spatial profile, and brightness provides further confidence in our understanding of the backlight-radiation time history and image formation. Furthermore, these simulations bridge the static-uniform picture of the data interpretation and the dynamic-gradient reality of the experiments, and they will allow us to quantitatively assess the impact of effects neglected in the data interpretation.« less

The density compression ratio of shock fronts associated with coronal mass ejections

NASA Astrophysics Data System (ADS)

Kwon, Ryun-Young; Vourlidas, Angelos

2018-02-01

We present a new method to extract the three-dimensional electron density profile and density compression ratio of shock fronts associated with coronal mass ejections (CMEs) observed in white light coronagraph images. We demonstrate the method with two examples of fast halo CMEs (˜2000 km s-1) observed on 2011 March 7 and 2014 February 25. Our method uses the ellipsoid model to derive the three-dimensional geometry and kinematics of the fronts. The density profiles of the sheaths are modeled with double-Gaussian functions with four free parameters, and the electrons are distributed within thin shells behind the front. The modeled densities are integrated along the lines of sight to be compared with the observed brightness in COR2-A, and a χ2 approach is used to obtain the optimal parameters for the Gaussian profiles. The upstream densities are obtained from both the inversion of the brightness in a pre-event image and an empirical model. Then the density ratio and Alfvénic Mach number are derived. We find that the density compression peaks around the CME nose, and decreases at larger position angles. The behavior is consistent with a driven shock at the nose and a freely propagating shock wave at the CME flanks. Interestingly, we find that the supercritical region extends over a large area of the shock and lasts longer (several tens of minutes) than past reports. It follows that CME shocks are capable of accelerating energetic particles in the corona over extended spatial and temporal scales and are likely responsible for the wide longitudinal distribution of these particles in the inner heliosphere. Our results also demonstrate the power of multi-viewpoint coronagraphic observations and forward modeling in remotely deriving key shock properties in an otherwise inaccessible regime.

Nanosecond pulsed humid Ar plasma jet in air: shielding, discharge characteristics and atomic hydrogen production

NASA Astrophysics Data System (ADS)

Yatom, Shurik; Luo, Yuchen; Xiong, Qing; Bruggeman, Peter J.

2017-10-01

Gas phase non-equilibrium plasmas jets containing water vapor are of growing interest for many applications. In this manuscript, we report a detailed study of an atmospheric pressure nanosecond pulsed Ar  +  0.26% H2O plasma jet. The plasma jet operates in an atmospheric pressure air surrounding but is shielded with a coaxial argon flow to limit the air diffusion into the jet effluent core. The jet impinges on a metal plate electrode and produces a stable plasma filament (transient spark) between the needle electrode in the jet and the metal plate. The stable plasma filament is characterized by spatially and time resolved electrical and optical diagnostics. This includes Rayleigh scattering, Stark broadening of the hydrogen Balmer lines and two-photon absorption laser induced fluorescence (TaLIF) to obtain the gas temperature, the electron density and the atomic hydrogen density respectively. Electron densities and atomic hydrogen densities up to 5 × 1022 m-3 and 2 × 1022 m-3 have been measured. This shows that atomic hydrogen is one of the main species in high density Ar-H2O plasmas. The gas temperature does not exceed 550 K in the core of the plasma. To enable in situ calibration of the H TaLIF at atmospheric pressure a previously published O density calibration scheme is extended to include a correction for the line profiles by including overlap integrals as required by H TaLIF. The line width of H TaLIF, due to collision broadening has the same trend as the neutral density obtained by Rayleigh scattering. This suggests the possibility to use this technique to in situ probe neutral gas densities.

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids

PubMed Central

Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

2014-01-01

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism. PMID:25202942

Spatially inhomogeneous electron state deep in the extreme quantum limit of strontium titanate

DOE PAGES

Bhattacharya, Anand; Skinner, Brian; Khalsa, Guru; ...

2016-09-29

When an electronic system is subjected to a sufficiently strong magnetic field that the cyclotron energy is much larger than the Fermi energy, the system enters the extreme quantum limit (EQL) and becomes susceptible to a number of instabilities. Bringing a three-dimensional electronic system deeply into the EQL can be difficult however, since it requires a small Fermi energy, large magnetic field, and low disorder. Here we present an experimental study of the EQL in lightly-doped single crystals of strontium titanate. Our experiments probe deeply into the regime where theory has long predicted an interaction-driven charge density wave or Wignermore » crystal state. A number of interesting features arise in the transport in this regime, including a striking re-entrant nonlinearity in the current-voltage characteristics. As a result, we discuss these features in the context of possible correlated electron states, and present an alternative picture based on magnetic-field induced puddling of electrons.« less

Magnetic Interactions at the Nanoscale in Trilayer Titanates

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

Cao, Yanwei; Yang, Zhenzhong; Kareev, M.

2016-02-17

We report on the phase diagram of competing magnetic interactions at the nanoscale in engineered ultrathin trilayer heterostructures of LaTiO3/SrTiO3/YTiO3, in which the interfacial inversion symmetry is explicitly broken. Combined atomic layer resolved scanning transmission electron microscopy with electron energy loss spectroscopy and electrical transport have confirmed the formation of a spatially separated two-dimensional electron liquid and high density two-dimensional localized magnetic moments at the LaTiO3/SrTiO3 and SrTiO3/YTiO3 interfaces, respectively. Resonant soft x-ray linear dichroism spectroscopy has demonstrated the presence of orbital polarization of the conductive LaTiO3/SrTiO3 and localized SrTiO3/YTiO3 electrons. Our results provide a route with prospects for exploringmore » new magnetic interfaces, designing a tunable two-dimensional d-electron Kondo lattice, and potential spin Hall applications.« less

Enhancement of gaps in thin graphitic films for heterostructure formation

NASA Astrophysics Data System (ADS)

Hague, J. P.

2014-04-01

There are a large number of atomically thin graphitic films with a structure similar to that of graphene. These films have a spread of band gaps relating to their ionicity and, also, to the substrate on which they are grown. Such films could have a range of applications in digital electronics, where graphene is difficult to use. I use the dynamical cluster approximation to show how electron-phonon coupling between film and substrate can enhance these gaps in a way that depends on the range and strength of the coupling. It is found that one of the driving factors in this effect is a charge density wave instability for electrons on a honeycomb lattice that can open a gap in monolayer graphene. The enhancement at intermediate coupling is sufficiently large that spatially varying substrates and superstrates could be used to create heterostructures in thin graphitic films with position-dependent electron-phonon coupling and gaps, leading to advanced electronic components.

Modeling of plasma distortions by laser-induced ablation spectroscopy (LIAS) and implications for the interpretation of LIAS measurements

NASA Astrophysics Data System (ADS)

Tokar, M. Z.; Gierse, N.; Philipps, V.; Samm, U.

2015-09-01

For the interpretation of the line radiation observed from laser induced ablation spectroscopy (LIAS) such parameters as the density and temperature of electrons within very compact clouds of atoms and singly charged ions of ablated material have to be known. Compared to the local plasma conditions prior to the laser pulse, these can be strongly changed during LIAS since new electrons are generated by the ionisation of particles ejected from the irradiated target. Because of their transience and spatial inhomogeneity it is technically difficult to measure disturbances induced in the plasma by LIAS. To overcome this uncertainty a numerical model has been elaborated, providing a self-consistent description for the spreading of ablated particles and accompanying modifications in the plasma. The results of calculations for LIAS performed on carbon-containing targets in Ohmic and additionally heated discharges in the tokamak TEXTOR are presented. Due to the increase in the electron density the ‘ionisation per photon’ ratio, S/XB factor, is significantly enhanced compared to unperturbed plasma conditions. The impact of the amount of material ablated and of the plasma conditions before LIAS on the level of the S/XB-enhancement is investigated.

Three-dimensional ionospheric tomography reconstruction using the model function approach in Tikhonov regularization

NASA Astrophysics Data System (ADS)

Wang, Sicheng; Huang, Sixun; Xiang, Jie; Fang, Hanxian; Feng, Jian; Wang, Yu

2016-12-01

Ionospheric tomography is based on the observed slant total electron content (sTEC) along different satellite-receiver rays to reconstruct the three-dimensional electron density distributions. Due to incomplete measurements provided by the satellite-receiver geometry, it is a typical ill-posed problem, and how to overcome the ill-posedness is still a crucial content of research. In this paper, Tikhonov regularization method is used and the model function approach is applied to determine the optimal regularization parameter. This algorithm not only balances the weights between sTEC observations and background electron density field but also converges globally and rapidly. The background error covariance is given by multiplying background model variance and location-dependent spatial correlation, and the correlation model is developed by using sample statistics from an ensemble of the International Reference Ionosphere 2012 (IRI2012) model outputs. The Global Navigation Satellite System (GNSS) observations in China are used to present the reconstruction results, and measurements from two ionosondes are used to make independent validations. Both the test cases using artificial sTEC observations and actual GNSS sTEC measurements show that the regularization method can effectively improve the background model outputs.

A Novel Damping Mechanism for Diocotron Modes

NASA Astrophysics Data System (ADS)

Chim, Chi Yung; O'Neil, Thomas M.

2014-10-01

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 and m = 2 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius, where f = mfE × B (r) . The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This poster explains with analytic theory and simulations the new algebraic damping due to both mobility and diffusive fluxes. The damping is due to transfer of canonical angular momentum from the mode to halo particles, as they are swept around the ``cat's eye'' orbits of resonant wave-particle interaction. Another picture is that the electrons in the resonant layer form a dipole (m = 1) or quadrupole (m = 2) density distribution, and the electric field for this distribution produces E × B drifts that symmetrizes the core and damps the mode. Supported by NSF/DOE Partnership Grants PHY-0903877 and DE-SC0002451.

Process diagnostics and monitoring using the multipole resonance probe in an inhomogeneous plasma for ion-assisted deposition of optical coatings

NASA Astrophysics Data System (ADS)

Styrnoll, T.; Harhausen, J.; Lapke, M.; Storch, R.; Brinkmann, R. P.; Foest, R.; Ohl, A.; Awakowicz, P.

2013-08-01

The application of a multipole resonance probe (MRP) for diagnostic and monitoring purposes in a plasma ion-assisted deposition (PIAD) process is reported. Recently, the MRP was proposed as an economical and industry compatible plasma diagnostic device (Lapke et al 2011 Plasma Sources Sci. Technol. 20 042001). The major advantages of the MRP are its robustness against dielectric coating and its high sensitivity to measure the electron density. The PIAD process investigated is driven by the advanced plasma source (APS), which generates an ion beam in the deposition chamber for the production of high performance optical coatings. With a background neutral pressure of p0 ˜ 20 mPa the plasma expands from the source region into the recipient, leading to an inhomogeneous spatial distribution. Electron density and electron temperature vary over the distance from substrate (ne ˜ 109 cm-3 and Te,eff ˜ 2 eV) to the APS (ne ≳ 1012 cm-3 and Te,eff ˜ 20 eV) (Harhausen et al 2012 Plasma Sources Sci. Technol. 21 035012). This huge variation of the plasma parameters represents a big challenge for plasma diagnostics to operate precisely for all plasma conditions. The results obtained by the MRP are compared to those from a Langmuir probe chosen as reference diagnostics. It is demonstrated that the MRP is suited for the characterization of the PIAD plasma as well as for electron density monitoring. The latter aspect offers the possibility to develop new control schemes for complex industrial plasma environments.

A global picture of ionospheric slab thickness derived from GIM TEC and COSMIC radio occultation observations

NASA Astrophysics Data System (ADS)

Huang, He; Liu, Libo; Chen, Yiding; Le, Huijun; Wan, Weixing

2016-01-01

The ionospheric equivalent slab thickness (EST), defined as the ratio of total electron content (TEC) to F2 layer peak electron density (NmF2), describes the thickness of the ionospheric profile. In this study, we retrieve EST from TEC data obtained from Global Ionospheric Map (GIM) and NmF2 retrieved from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data. The diurnal, seasonal, and solar activity variations of global EST are analyzed as the excellent spatial coverage of GIM and COSMIC data. During solstices, daytime EST in the summer hemisphere is larger than that in the winter hemisphere, except in some high-latitude regions, and the reverse is true for the nighttime EST. The peaks of EST often appear at 0400 local time. The presunrise enhancement in EST appears in all seasons, while the postsunset enhancement in EST is not readily observed in equinox. Both enhancements are attributed to the more remarkable electron density decay of NmF2 compared to that of TEC. The dependence of EST on solar activity is related to the inconsistent solar activity dependences of electron density at different altitudes. Furthermore, it is interesting that EST is enhanced from 0° to 120°E in longitude and 30° to 75°S in latitude during nighttime, just to the east of Weddell Sea Anomaly, during equinox and the Southern Hemisphere summer. This phenomenon is supposed to be related to the effects of geomagnetic declination-related plasma vertical drifts.

Stark width and shift for electron number density diagnostics of low temperature plasma: Application to silicon Laser Induced Breakdown Spectroscopy

NASA Astrophysics Data System (ADS)

Ivković, M.; Konjević, N.

2017-05-01

In this work we summarize, analyze and critically evaluate experimental procedures and results of LIBS electron number density plasma characterization using as examples Stark broadened Si I and Si II line profiles. Selected publications are covering the time period from very beginning of silicon LIBS studies until the end of the year 2015. To perform the analysis of experimental LIBS data, the testing of available semiclassical theoretical Stark broadening parameters for Si I and Si II lines was accomplished first. This is followed by the description of experimental setups, results and details of experimental procedure relevant for the line shape analysis of spectral lines used for plasma characterization. Although most of results and conclusions of this analysis are related to the application of silicon lines for LIBS characterization they are of general importance and may be applied to other elements and different low-temperature plasma sources. The analysis of experimental procedures used for LIBS diagnostics from emission profiles of non-hydrogenic spectral lines is carried out in the following order: the influence of laser ablation and crater formation, spatial and temporal plasma observation, line self-absorption and experimental profile deconvolution, the contribution of ion broadening in comparison with electron impacts contributions to the line width in case of neutral atom line and some other aspects of line shape analysis are considered. The application of Stark shift for LIBS diagnostics is demonstrated and discussed. Finally, the recommendations for an improvement of experimental procedures for LIBS electron number density plasma characterization are offered.

Inductive Electron Heating Revisited

NASA Astrophysics Data System (ADS)

Tuszewski, M.

1996-11-01

Inductively Coupled Plasmas (ICPs) have been studied for over a century. Recently, ICPs have been rediscovered by the multi-billion dollar semiconductor industry as an important class of high-density, low-pressure plasma sources suitable for the manufacture of next-generation integrated circuits. Present low-pressure ICP development is among the most active areas of plasma research. However, this development remains largely empirical, a prohibitively expensive approach for upcoming 300-mm diameter wafers. Hence, there is an urgent need for basic ICP plasma physics research, including experimental characterization and predictive numerical modeling. Inductive radio frequency (rf) power absorption is fundamental to the ICP electron heating and the resulting plasma transport but remains poorly understood. For example, recent experimental measurements and supporting fluid calculationsfootnote M. Tuszewski, Phys. Rev. Lett. 77 in press (1996) on a commercial deposition tool prototype show that the induced rf magnetic fields in the source can cause an order of magnitude reduction in plasma conductivity and in electron heating power density. In some cases, the rf fields penetrate through the entire volume of the ICP discharges while existing models that neglect the induced rf magnetic fields predict rf absorption in a thin skin layer near the plasma surface. The rf magnetic fields also cause more subtle changes in the plasma density and in the electron temperature spatial distributions. These data will be presented and the role of basic research in the applied world of semiconductor manufacturing will be discussed. ^*This research was conducted under the auspices of the U.S. DOE, supported by funds provided by the University of California for discretionary research by Los Alamos National Laboratory.

Mechanisms of transport and electron transfer at conductive polymer/liquid interfaces

NASA Astrophysics Data System (ADS)

Ratcliff, Erin

Organic semiconductors (OSCs) have incredible prospects for next-generation, flexible electronic devices including bioelectronics, thermoelectrics, opto-electronics, and energy storage and conversion devices. Yet many fundamental challenges still exist. First, solution processing prohibits definitive control over microstructure, which is fundamental for controlling electrical, ionic, and thermal transport properties. Second, OSCs generally suffer from poor electrical conductivities due to a combination of low carriers and low mobility. Third, polymeric semiconductors have potential-dependent, dynamically evolving electronic and chemical states, leading to complex interfacial charge transfer properties in contact with liquids. This talk will focus on the use of alternative synthetic strategies of oxidative chemical vapor deposition and electrochemical deposition to control physical, electronic, and chemical structure. We couple our synthetic efforts with energy-, time-, and spatially resolved spectroelectrochemical and microscopy techniques to understand the critical interfacial chemistry-microstructure-property relationships: first at the macroscale, and then moving towards the nanoscale. In particular, approaches to better understand electron transfer events at polymer/liquid interfaces as a function of: 1.) chemical composition; 2.) electronic density of states (DOS); and 3.) crystallinity and microstructure will be discussed.

Coherent infrared radiation from the ALS generated via femtosecond laser modulation of the electron beam

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

Byrd, J.M.; Hao, Z.; Martin, M.C.

2004-07-01

Interaction of an electron beam with a femtosecond laser pulse co-propagating through a wiggler at the ALS produces large modulation of the electron energies within a short {approx}100 fs slice of the electron bunch. Propagating around the storage ring, this bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories. The length of the perturbation evolves with a distance from the wiggler but is much shorter than the electron bunch length. This perturbation causes the electron bunch to emit short pulses of temporally and spatially coherent infrared light which are automatically synchronized to the modulating laser. Themore » intensity and spectra of the infrared light were measured in two storage ring locations for a nominal ALS lattice and for an experimental lattice with the higher momentum compaction factor. The onset of instability stimulated by laser e-beam interaction had been discovered. The infrared signal is now routinely used as a sensitive monitor for a fine tuning of the laser beam alignment during data accumulation in the experiments with femtosecond x-ray pulses.« less

Correlated electron-nuclear dissociation dynamics: classical versus quantum motion

NASA Astrophysics Data System (ADS)

Schaupp, Thomas; Albert, Julian; Engel, Volker

2017-01-01

We investigate the coupled electron-nuclear dynamics in a model system which undergoes dissociation. In choosing different initial conditions, the cases of adiabatic and non-adiabatic dissociation are realized. We treat the coupled electronic and nuclear motion in the complete configuration space so that classically, no surface hopping procedures have to be incorporated in the case that more than a single adiabatic electronic state is populated during the fragmentation. Due to the anharmonic interaction potential, it is expected that classical mechanics substantially deviate from quantum mechanics. However, we provide examples where the densities and fragmentation yields obtained from the two treatments are in astonishingly strong agreement in the case that one starts in the electronic ground state initially. As expected, larger deviations are found if one starts in electronically excited states where trajectories are sampled from the more spatially extended electronic wave function. In that case, higher initial energies are accessed, and the motion proceeds in regions with increasing degree of anharmonicity. Contribution to the Topical Issue "Dynamics of Molecular Systems (MOLEC 2016)", edited by Alberto Garcia-Vela, Luis Banares and Maria Luisa Senent.

Improvement in hardness of soda-lime-silica glass

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

Chakraborty, Riya; De, Moumita; Roy, Sudakshina

2012-06-05

Hardness is a key design parameter for structural application of brittle solids like glass. Here we report for the first time the significant improvement of about 10% in Vicker's hardness of a soda-lime-silica glass with loading rate in the range of 0.1-10 N.s{sup -1}. Corroborative dark field optical and scanning electron microscopy provided clue to this improvement through evidence of variations in spatial density of shear deformation band formation as a function of loading rate.

Non-modal analysis of the diocotron instability: Cylindrical geometry

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

Mikhailenko, V. V.; Lee, Hae June; Mikhailenko, V. S.

2013-04-15

The temporal evolution of the linear diocotron instability of the cylindrical annular plasma column is investigated by employing the extension of the shearing modes methodology to the cylindrical geometry. It was obtained that the spatial time-dependent distortion of the electron density initial perturbations by shear flows leads to the non-modal evolution of the potential, which was referred to as the manifestation of the continuous spectrum. The evolution process leads toward the convergence to the phase-locking configuration of the mutually growing normal modes.

Mapping atomic contact between pentacene and a Au surface using scanning tunneling spectroscopy.

PubMed

Song, Young Jae; Lee, Kyuho; Kim, Seong Heon; Choi, Byoung-Young; Yu, Jaejun; Kuk, Young

2010-03-10

We mapped spatially varying intramolecular electronic structures on a pentacene-gold interface using scanning tunneling spectroscopy. Along with ab initio calculations based on density functional theory, we found that the directional nature of the d orbitals of Au atoms plays an important role in the interaction at the pentacene-gold contact. The gold-induced interface states are broadened and shifted by various pentacene-gold distances determined by the various registries of a pentacene molecule on a gold substrate.