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1

Ion acoustic solitons in a plasma with finite temperature drifting ions: Limit on ion drift velocity  

Microsoft Academic Search

Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity [ital u][sub 0] for which the

H. K. Malik; Sanjay Singh; R. P. Dahiya

1994-01-01

2

Negative hydrogen ion densities and drift velocities in a multicusp ion source  

Microsoft Academic Search

We have determined densities of negative hydrogen ions in a discharge by a laser detachment technique. We measured the electron density, the electron temperature, and the positive ion density using a Langmuir probe. We also performed extraction measurements. Combination of H⁻ density measurements and extraction measurements yields information about the H⁻ drift velocity. It was found that the velocity scaled

P. J. Eenshuistra; M. Gochitashvilli; R. Becker; A. W. Kleyn; H. J. Hopman

1990-01-01

3

Ion drift velocity measurements on the nose cone during the first Araks experiment  

Microsoft Academic Search

During the first flight of the Araks experiments, ion composition, temperature, and drift velocity measurements have been obtained by retarding potential ion analyzers. No polarization quasi-static electric field associated with the electron beam was detected; the simultaneous analysis of the double probe dc electric field data and the ion analyzer data concerning the dc electric field of natural origin has

M. Pirre; J.-J. Berthelier

1980-01-01

4

Negative ion drift velocity and longitudinal diffusion in mixtures of carbon disulfide and methane  

NASA Astrophysics Data System (ADS)

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

Dion, M. P.; Son, S.; Hunter, S. D.; de Nolfo, G. A.

2011-08-01

5

The electron drift velocity, ion acoustic speed and irregularity drifts in high-latitude E-region  

NASA Astrophysics Data System (ADS)

The purpose of this study is to examine the STARE irregularity drift velocity dependence on the EISCAT line-of-sight (los or l-o-s) electron drift velocity magnitude, VEBlos, and the flow angle ΘN,F (superscript N and/or F refer to the STARE Norway and Finland radar). In the noon-evening sector the flow angle dependence of Doppler velocities, VirrN,F, inside and outside the Farley-Buneman (FB) instability cone (|VEBlos|>Cs and |VEBlos|ion acoustic speed), is found to be similar and much weaker than suggested earlier. In a band of flow angles 45<ΘN,F<85 it can be reasonably described by |VirrN,F|?AN,FCscosnΘN,F, where AN,F?1.2 1.3 are monotonically increasing functions of VEB and the index n is ~0.2 or even smaller. This study (a) does not support the conclusion by Nielsen and Schlegel (1985), Nielsen et al. (2002, their #[18]) that at flow angles larger than ~60 (or |VirrN,F|?300 m/s) the STARE Doppler velocities are equal to the component of the electron drift velocity. We found (b) that if the data points are averages over 100 m/s intervals (bins) of l-o-s electron velocities and 10 deg intervals (bins) of flow angles, then the largest STARE Doppler velocities always reside inside the bin with the largest flow angle. In the flow angle bin 80 the STARE Doppler velocity is larger than its driver term, i.e. the EISCAT l-o-s electron drift velocity component, |VirrN,F|>|VEBlos|. Both features (a and b) as well as the weak flow angle velocity dependence indicate that the l-o-s electron drift velocity cannot be the sole factor which controls the motion of the backscatter ~1-m irregularities at large flow angles. Importantly, the backscatter was collected at aspect angle ~1 and flow angle Θ>60, where linear fluid and kinetic theories invariably predict negative growth rates. At least qualitatively, all the facts can be reasonably explained by nonlinear wave-wave coupling found and described by Kudeki and Farley (1989), Lu et al. (2008) for the equatorial electrojet and studied in numerical simulation by Otani and Oppenheim (1998, 2006).

Uspensky, M. V.; Pellinen, R. J.; Janhunen, P.

2008-10-01

6

Effects of Errors of Velocity Modulation on Maximum Longitudinal Drift Compression of an Intense Neutralized Ion Beam  

NASA Astrophysics Data System (ADS)

Neutralized drift compression offers an effective means for particle beam focusing and current amplification with applications to heavy ion fusion. An ion beam pulse is passed through an inductive bunching module that produces a longitudinal velocity modulation. Due to applied velocity tilt the beam pulse compresses during neutralized drift. The ion beam pulse can be compressed by a factor of more than 100; however errors in the velocity modulation affect this compression in complicated ways. We have preformed an analytical and numerical study of how the longitudinal compression of the ion beam is affected by the initial errors in velocity. Higher errors generally proportionally decrease compression. However, some parts of a beam pulse with large errors in the velocity tilt compress to high values while other parts do not compress at all. Without any errors an ideal compression is limited only by the initial thermal velocity of the ion beam. Compression with an experiential velocity tilt is compared to an ideal limit.

Massidda, S.; Kaganovich, I.; Startsev, E.; Davidson, R.

2010-11-01

7

The electron-ion streaming instabilities driven by drift velocities of the order of electron thermal velocity in a nonmagnetized plasma  

NASA Astrophysics Data System (ADS)

We examine the electron-ion streaming instabilities driven by drift velocities of the order of the electron thermal velocity in a nonmagnetized plasma by using one-dimensional electrostatic particle-in-cell code which adopts an ion-to-electron mass ratio of 1600. An initial state is set up where the ion bulk speed is zero while the electrons drift relative to ions, and where electrons are much hotter. We examine in detail four runs where the drift velocity is systematically varied from lower than to larger than the electron thermal velocity. In all runs the Langmuir waves with Doppler-shifted frequencies dominate early on when streaming instabilities are too weak to discern. And then intense ion-acoustic waves or Buneman instabilities appear, which tend to be accompanied by localized electron and ion beams. Ion-acoustic modes and Buneman modes co-exist in the system when the initial drift velocity is just over the electron thermal speed. Beam modes are excited when localized beams with large enough velocities appear. In the developed stage of instabilities, the direction in which density depressions propagate is always opposite to that of the localized ion beams. When the initial drift velocity is close to the electron thermal speed, categorizing the relevant instabilities is not easy, and one needs to examine in detail the wave dispersion diagrams at various stages of the evolution of the system.

Guo, Jun; Li, Bo

2013-09-01

8

Calculation of poloidal velocity in the tokamak plasma with allowance for density inhomogeneity and diamagnetic drift of ions  

SciTech Connect

A one-dimensional evolution equation for the angle-averaged poloidal momentum of the tokamak plasma is derived in the framework of reduced magnetohydrodynamics with allowance for density inhomogeneity and diamagnetic drift of ions. In addition to fluctuations of the E Multiplication-Sign B drift velocity, the resulting turbulent Reynolds stress tensor includes fluctuations of the ion density and ion pressure, as well as turbulent radial fluxes of particles and heat. It is demonstrated numerically by using a particular example that the poloidal velocity calculated using the refined one-dimensional evolution equation differs substantially from that provided by the simplified model. When passing to the new model, both the turbulent Reynolds force and the Stringer-Winsor force increase, which leads to an increase in the amplitude of the ion poloidal velocity. This, in turn, leads to a decrease in turbulent fluxes of particles and heat due to the effect of shear decorrelation.

Shurygin, R. V. [National Research Centre Kurchatov Institute, Institute of Tokamak Physics (Russian Federation)

2012-02-15

9

A SAFARI-EISCAT comparison between the velocity of F region small-scale irregularities and the ion drift  

Microsoft Academic Search

Simultaneous measurements carried out using the Scandinavian And French Auroral Radar Investigation (SAFARI) coherent radars and the EISCAT incoherent scatter detectors were compared in order to study the relationship between the velocity of small-scale irregularities in the F-region and ion drift. The radars were located at Lycksele, Sweden and Oulu, Finland and operated at a pulse repetition frequency in the

J. P. Villain; C. Hanuise; G. Caudal

1985-01-01

10

Note: the role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions [J. Chem. Phys. 134, 114504 (2011)].  

PubMed

The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual nonlinear behavior observed when the solution concentration matches seawater is also observed when the concentration is reduced to half of that value. These results are of significance in designing processes for desalinating seawater using electro-deionization in which the concentration would decrease during salt removal, and for purification of brackish waters which also have lower salt content. PMID:22360264

Murad, Sohail

2012-02-21

11

Velocity-shear-driven drift waves with simultaneous azimuthal modes in a barium-ion Q-machine plasma  

SciTech Connect

Low-frequency instabilities modified by a field-aligned flow velocity shear are investigated, where the shear is controlled using a concentrically three-segmented ion emitter in a modified double-ended Q-machine [T. Kaneko et al., Rev. Sci. Instrum. 73, 4218 (2002)]. When the barium-ion flow velocity shear is produced by applying different bias voltages to two of the three segments of the ion source, drift waves having azimuthal mode number m=1, 2, and 3 are observed to be excited simultaneously. It is found that the excitation-threshold value of the shear strength depends on the azimuthal mode number, as expected from a model based on kinetic theory, suggesting that the observations are explained by the competition between inverse electron Landau damping and shear-modified ion Landau damping.

Kaneko, T.; Reynolds, E.W.; Hatakeyama, R.; Koepke, M.E. [Department of Electronic Engineering, Tohoku University, Sendai 980-8579 (Japan); Physics Department, West Virginia University, Morgantown, West Virginia 26505-6315 (United States); Department of Electronic Engineering, Tohoku University, Sendai 980-8579 (Japan); Physics Department, West Virginia University, Morgantown, West Virginia 26505-6315 (United States)

2005-10-01

12

Modeling the daytime, equatorial ionospheric ion densities associated with the observed, four-cell longitude patterns in E B drift velocities  

NASA Astrophysics Data System (ADS)

Previous studies have quantified the longitude gradients in E Bdrift associated with the four-cell tidal structures and have confirmed that these sharp gradients exist on a day-to-day basis. For this paper, we incorporate the Ion Velocity Meter (IVM) sensor on the Communications/Navigation Outage Forecasting System satellite to obtain the daytime, verticalE B drift velocities at the magnetic equator as a function of longitude, local time, and season and to theoretically calculate the F region ion densities as a function of altitude, latitude, longitude, and local time using the Global Ionosphere Plasmasphere model. We compare calculated ion densities assuming no longitude gradients in E Bdrift velocities with calculated ion densities incorporating the IVM-observedE Bdrift at the boundaries of the four-cell tidal structures in the Peruvian and the Atlantic longitude sectors. Incorporating the IVM-observedE B drift velocities, the ion density crests rapidly converge to the magnetic equator between 285 and 300E geographic longitude, are absent between 300 and 305, and move away from the magnetic equator between 305 and 340. In essence, the steeper the longitude gradient in E B drifts, the steeper the longitude gradient in the equatorial anomaly crest location.

Araujo-Pradere, Eduardo A.; Fang, Tzu-Wei; Anderson, David N.; Fedrizzi, Mariangel; Stoneback, Russell

2012-04-01

13

Laser induced fluorescence measurements of ion velocity and temperature of drift turbulence driven sheared plasma flow in a linear helicon plasma device  

SciTech Connect

Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband ({approx}1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasma fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared.

Chakraborty Thakur, S.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego, California 92093 (United States); Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States); McCarren, D.; Scime, E. E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Lee, T. [Center for Energy Research, University of California at San Diego, San Diego, California 92093 (United States)

2012-08-15

14

Effects of ion drift on small-amplitude ion-acoustic solitons  

Microsoft Academic Search

Some properties of small-amplitude ion-acoustic solitons in a plasma consisting of nondrifting electrons and drifting ions are investigated. Electron inertia effects are shown to be considerably more important than relativistic effects. It is also shown that ion-acoustic soliton solutions exist only if the ion drift velocity is less than the electron thermal velocity.

H. H. Kuehl; C. Y. Zhang

1991-01-01

15

First comparison of STARE and EISCAT electron drift velocity measurements  

SciTech Connect

The Scandinavian twin auroral radar experiment (STARE) has a demonstratedcapability of providing estimates of the ionospheric electron drift velocities,which are useful for a wide range of geophysical studies. The accuracy of suchestimates has for the first time been tested by comparison with simultaneousvelocity measurements made with the European incoherent scatter facility(EISCAT). The magnitudes of the estimated drift velocities are in agreementwith the EISCAT measurements for small velocities (<700 ms/sup -1/), but we find the estimates to be increasingly too low as the velocities become larger. The directions of the estimated vectors are in agreement with the EISCAT measurements for all drift magnitudes. The measured phase velocities are even lower than those predicted by the kinetic theory of the two stream instability. Agreement can only be obtained for relatively large neutral densities. The data are not inconsistent with an assumption that the possible phase velocities in the plasma are limited upward by the ion-acoustic velocity (which is an increasing function of the ionospheric electric field). Power spectral observations and an improved modelling with the kinetic theory suggest that a backscatter region, extended in altitude and allowing several values of k/sub parallel/ to influence observations, leads to an improved theoretical fit to the measurements.

Nielsen, E.; Schlegel, K.

1983-07-01

16

Monitoring of electron drift velocity in drift chambers with alpha-decay recoils  

Microsoft Academic Search

Electron drift velocity is measured by detecting alpha-decay recoils in a drift chamber in coincidence with alpha-particles registered with a Si detector. The precision of the measurements is demonstrated to be better than 0.1%.

A. A. Vorobyov; V. S. Guselnikov; A. Yu. Maiorov; O. E. Prokofiev; V. M. Zaitsev

1991-01-01

17

Construction Update and Drift Velocity Calibration for the CLAS Drift Chamber System  

SciTech Connect

We briefly describe the drift chamber system for the CLAS detector at CEBAF, concentrating on the method which will be used to calibrate the drift velocity function. We identify key features of the function which should apply to any small-cell drift chamber geometry in which the cathode and anode surfaces are wires. Using these ideas, we describe a simple method to compensate for variations in the drift velocity function due to environmental changes.

Andreas Klein; Amrit Yegneswaran; Brian Raue; Charles Hyde-Wright; Etienne Burtin; Fernando Barbosa; Gretchen Doolittle; Gerard Gilfoyle; J.E. O'Meara; Liming Qin; Lawrence Weinstein; Luc Murphy; Mac Mestayer; Mikhail Kossov; Peter Bonneau; Richard Magahiz; Rory Miskimen; Reinhard Schumacher; Steven Christo; Steven Dytman; Sebastian Kuhn; T.D. Pyron; Walter Tuzel

1995-12-01

18

Empirical equations for drift velocities in silicon  

NASA Astrophysics Data System (ADS)

Hardening against the electromagnetic pulse and high power microwave radiation is discussed. Vital to semiconductor modeling of burnout are the transport properties of semiconductors at high fields and high temperatures. At present, there is no single expression valid for this hot electron regime. The results of this study will be used in the thermal modification of the DIODE2D program, now underway. A recent report of the National Reseach Council, Evaluation of Methodologies for Estimating Vulnerability to Electromagnetic Pulse Effects, recommended that there should be a better understanding of the mechanisms of component failure. The theoretical work included in this report provides physical insight into the damage mechanisms and should lead to nondestructive means of characterizing specific devices. Empirical equations for the drift velocities of electron and holes in silicon are given as a function of electric field, temperature, and doping density. A single equation, which is valid above room temperature, results from the inverse dependence of the saturation velocity upon the square root of the temperature.

Ward, A. L.

1985-10-01

19

Planar Drift Tube for Ion Mobility Spectrometry  

Microsoft Academic Search

The drift tube in ion mobility spectrometry is the component of central importance, where sample vapors are ionized and where ions are separated on the basis of gaseous mobility in a comparatively weak electric field. Construction of drift tubes is labor intensive and costly when built with precision machined components and an alternative design, fabricated using photolithography methods with planar

Gary A. Eiceman; Hartwig Schmidt; Jaime E. Rodriguez; Corey R. White; Evgeny V. Krylov; John A. Stone

2007-01-01

20

Multistatic Incoherent Scatter Measurements of Ionospheric Drift Velocity  

Microsoft Academic Search

THE observed behaviour of the ionospheric F-region has proved difficult to understand, and one of the principal difficulties has been that, until recently, there was little reliable information about the true plasma drift velocities. Apparent horizontal drift speeds have been measured for many years by means of the ``fading'' method1: interpretation of data from these experiments is complex2, and it

G. N. Taylor

1973-01-01

21

Drift velocity in non-isothermal inhomogeneous systems.  

PubMed

Drift velocity and driving force are not directly proportional in the case of inhomogeneous suspensions, where a space dependent mobility induces an additional contribution to the drift velocity. Similarly, particle flux and drift velocity are related not only by the gradient of density but also by an additional contribution given by the gradient of the self-diffusion coefficient. We provide quantitative support to this scenario in a non-equilibrium system by means of computer simulations with a temperature gradient. Moreover, our simulation results demonstrate that the temperature gradient-induced mass transport coefficient, namely thermal diffusion coefficient, is not directly proportional to the drift velocity so that the well-accepted relation of proportionality is just an approximation. PMID:22667572

Yang, Mingcheng; Ripoll, Marisol

2012-05-28

22

Remote-sensing observations of F-region ion drift velocities using Dynamics Explorer-2 Doppler measurements of the O[sup +]([sup 2]P) [lambda]732. 0 nm emission  

SciTech Connect

Limb-scan observations of Doppler line profiles from the O[sup +]([sup 2]P) [lambda]732.0 nm emission at F-region altitudes, made with the Fabry-Perot interferometer (FPI) on the Dynamics Explorer-2 (DE-2) spacecraft, have been analyzed to provide measurements of the meridional component of the ion convection velocity along the instrument line-of-sight. The initial DE-2 results presented here demonstrate the first spaceborne use of the remote-sensing Doppler technique for measurements of ionospheric convection. The FPI meridional ion drift measurements have been compared with nearly simultaneous in-situ ion drift measurements from the Retarding Potential Analyzer (RPA) on DE 2. Once allowance is made for the temporal lag between the in-situ and remote measurements, the results from the two techniques are in good agreement. The results of a simulation study demonstrate that the spaceborne interferometric technique has future utility for 2-D imaging of the quasi-instantaneous ion convection pattern.

Carr, S.S.; Killeen, T.L. (Univ. of Michigan, Ann Arbor (United States)); Coley, W.R. (Univ. of Texas, Richardson (United States))

1992-07-24

23

Simulation of Drift-Compression for Heavy-Ion-Fusion  

SciTech Connect

Lengthwise compression of space-charge-dominated beams is needed to obtain the high input power required for heavy-ion fusion. The ''drift-compression'' scenario studied here first applies a head-to-tail velocity variation with the beam tail moving faster than the head. As the beam drifts, the longitudinal space-charge field slows compression, leaving the beam nearly monoenergetic as it enters the final-focus magnets. This paper presents initial work to model this compression scenario. Fluid and particle simulations are compared, and several strategies for setting up the compression schedule are discussed.

Sharp, W M; Barnard, J J; Grote, D P; Celata, C M; Yu, S S

2005-03-16

24

The ion velocity distribution in a toroidal plasma  

Microsoft Academic Search

The ?B drift in the toroidal magnetic field leads to relatively large radial displacements as the parallel velocity of an ion passes through zero. If collisional scattering into this velocity band is unable to balance the enhanced radial diffusion, a minimum will develop in the velocity distribution. This happens when ???\\/rn > (r?i\\/v?), where ? = r\\/R is the inverse

T. E. Stringer

1974-01-01

25

Drift chamber with uniform electric field and measurements of the electron drift velocity  

SciTech Connect

Measurements of the electron drift velocity as a function of the electric field have been made in a small drift chamber with uniform electric field for Ar/CH/sub 4/, Ar/i-C/sub 4/H/sub 10/, Ar/CO/sub 2/, and SQS gas mixtures. The value of the electric field ranges from about 0.3 to 2.5 kV/cm. The results of the measurements are discussed.

MA Chi-mao; MAO Ze-pu; ZHOU Jie; YAN Jie

1985-07-01

26

Cap Bubble Drift Velocity in a Confined Test Section  

SciTech Connect

In the two-group interfacial area transport equation, bubbles are categorized into two groups, i.e., spherical/distorted bubbles as group 1 and cap/slug/churn-turbulent bubbles as group 2. The bubble rise velocities for both groups of bubbles may be estimated by the drift flux model by applying different distribution parameters and drift velocities for both groups. However, the drift velocity for group 2 bubbles is not always applicable (when the wall effect becomes important) as in the current test loop of interest where the flow channel is confined by two parallel flat walls, with a dimension of 200-mm in width and 10-mm in gap. The previous experiments indicated that no stable slug flow existed in this test section, which was designed to permit visualization of the flow patterns and bubble characteristics without the distortion associated with curved surfaces. In fact, distorted cap bubbly and churn-turbulent flow was observed. Therefore, it is essential to developed a correlation for cap bubble drift velocity in this confined flow channel. Since the rise velocity of a cap bubble depends on its size, a high-speed movie camera is used to capture images of cap bubbles to obtain the bubble size information. Meanwhile, the rise velocity of cap and elongated bubbles (called cap bubbles hereafter) is investigated by examining the captured images frame by frame. As a result, the conventional correlation of drift velocity for slug bubbles is modified and acceptable agreements between the measurements and correlation estimation are achieved.

Xiaodong Sun; Seungjin Kim; Mamoru Ishii; Frank W. Lincoln; Stephen G. Beus

2002-10-09

27

Mean drift velocity in the Stokes interfacial edge wave  

NASA Astrophysics Data System (ADS)

The Stokes interfacial edge wave in a viscous rotating two-layer system is studied theoretically. The mean wave-induced Lagrangian drift velocity is obtained from the vertically integrated Eulerian equations of momentum and mass, correct to second order in wave steepness. The analysis is valid for shallow-water waves in the case when the upper layer is much thicker than the lower layer. In the lower layer the effect of viscosity is confined to a frictional boundary layer at the bottom. The waves are trapped by the bottom slope and can propagate in either direction along the bottom contours (in the y direction). Assuming that the waves attenuate in space as they propagate, this yields a Stokes drift velocity and a mean energy density E that decay exponentially in y. In this problem -?E/?y is the relevant radiation stress forcing in the wave propagation direction. It is explained why this differs from the radiation-stress forcing of -??E/?y for plane waves in an unbounded nonrotating shallow ocean. The bottom stress acting on the mean Eulerian wave-induced flow is modeled by a turbulent friction coefficient. The results show that the maximum mean Eulerian drift current is considerably larger than the maximum Stokes drift velocity. Since the Eulerian current becomes negative at larger seaward distances, the total mean Lagrangian drift current is confined to a rather narrow wedge in the lower layer.

Weber, Jan Erik H.; StYlen, Eivind

2011-04-01

28

Drift-Alfven vortices at the ion Larmor radius scale  

SciTech Connect

The theory of nonlinear drift-Alfven waves with the spatial scales comparable to the ion Larmor radius is developed. It is shown that the set of equations describing the nonlinear dynamics of drift-Alfven waves in a quasistationary regime admits a solution in the form of a solitary dipole vortex. The vortex structures propagating perpendicular to the ambient magnetic field faster than the diamagnetic ion drift velocity possess spatial scales larger than the ion Larmor radius, and vice versa. The variation of the vortex impedance and spatial scale as the function of the vortex velocity is analyzed. It is shown that incorporation of the finite electron temperature effects results in the appearance of a minimum in the dependence of the vortex impedance on the vortex velocity. This leads to the existence of the vortex structures with the smallest impedance. These structures are probably the most favorable energetically and can easily be excited in space plasmas. The relevance of theoretical results obtained to the Cluster observations in the magnetospheric cusp and magnetosheath is stressed.

Onishchenko, O. G.; Krasnoselskikh, V. V. [LPCE/CNRS, 3A, Avenue de la Recherche Scientifique, 45071 Orleans Cedex 2 (France); Pokhotelov, O. A. [Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield S13JD (United Kingdom)

2008-02-15

29

Linear and nonlinear coupled drift and ion acoustic waves in collisional pair ion-electron magnetoplasma  

SciTech Connect

Linear and nonlinear coupled electrostatic drift and ion acoustic waves are studied in inhomogeneous, collisional pair ion-electron plasma. The Korteweg-de Vries-Burgers (KdVB) equation for a medium where both dispersion and dissipation are present is derived. An attempt is made to obtain exact solution of KdVB equation by using modified tanh-coth method for arbitrary velocity of nonlinear drift wave. Another exact solution for KdVB is obtained, which gives a structure of shock wave. Korteweg-de Vries (KdV) and Burgers equations are derived in limiting cases with solitary and monotonic shock solutions, respectively. Effects of species density, magnetic field, obliqueness, and the acoustic to drift velocity ratio on the solitary and shock solutions are investigated. The results discussed are useful in understanding of low frequency electrostatic waves at laboratory pair ion plasmas.

Mushtaq, A. [Theoretical Plasma Physics Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad 45660 (Pakistan); School of Physics, University of Sydney, New South Wales 2006 (Australia); Saeed, R.; Haque, Q. [Theoretical Plasma Physics Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad 45660 (Pakistan)

2011-04-15

30

A first comparison of STARE and EISCAT electron drift velocity measurements  

Microsoft Academic Search

The accuracy of Scandinavian Twin Auroral Radar Experiment (STARE) estimates of ionospheric electron drift velocities has been tested by comparison with simultaneous velocity measurements of the European Incoherent Scatter facility (EISCAT). While STARE estimated drift velocity magnitudes are in agreement with EISCAT figures for velocities smaller than 700 m\\/sec, the estimates become too low with increasing velocity. Agreement is obtained

E. Nielsen; K. Schlegel

1983-01-01

31

Coupled nonlinear drift and ion acoustic waves in dense dissipative electron-positron-ion magnetoplasmas  

SciTech Connect

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous electron-positron-ion (e-p-i) quantum magnetoplasma with neutrals in the background using the well known quantum hydrodynamic model. In this regard, Korteweg-de Vries-Burgers (KdVB) and Kadomtsev-Petviashvili-Burgers (KPB) equations are obtained. Furthermore, the solutions of KdVB and KPB equations are presented by using the tangent hyperbolic (tanh) method. The variation in the shock profile with the quantum Bohm potential, collision frequency, and the ratio of drift to shock velocity in the comoving frame, v{sub *}/u, is also investigated. It is found that increasing the positron concentration and collision frequency decreases the strength of the shock. It is also shown that when the localized structure propagates with velocity greater than the diamagnetic drift velocity (i.e., u>v{sub *}), the shock strength decreases. However, the shock strength is observed to increase when the localized structure propagates with velocity less than that of drift velocity (i.e., u

Masood, W.; Siddiq, M. [TPPD, PINSTECH, P.O. Nilore, 44000 Islamabad (Pakistan); Karim, S.; Shah, H. A. [Department of Physics, GC University, 54000 Lahore (Pakistan)

2009-11-15

32

Modeling Drift-Compression for Heavy-Ion Fusion  

NASA Astrophysics Data System (ADS)

Beams for heavy-ion fusion (HIF) must be compressed lengthwise by a factor of more than ten between an induction accelerator and the final-focus magnets. The compression scenario favored by the US HIF program is to impose a head-to-tail velocity increase or "tilt", so the beam tail approaches the head in a "drift-compression" section. The beam current and velocity must be accurately tailored before drift-compression so that the longitudinal space-charge field removes the velocity tilt just as the beam traverses the final-focus lattice. The principle physics questions posed by this section are how much the total emittance grows, whether a beam halo develops, and how these processes scale with beam and lattice parameters. A second broad area of research is optimizing the initial pulse-shaping schedule to minimize the bandwidth and volt-seconds requirements of the pulsed power. This paper presents recent theoretical work to model the final longitudinal compression of HIF beams. Pulse-shaping fields are calculated using a fluid/envelope dynamics model and then used in the three-dimensional electrostatic particle-in-cell (PIC) code WARP3d to study beam transport during pulse-shaping and drift-compression. Possible low-energy, near-term experiments are discussed, and for these, we examine how emittance growth and sensitivity to errors scale with the beam and lattice parameters.

Sharp, W. M.; Barnard, J. J.; Friedman, A.; Grote, D. P.; Celata, C. M.; Yu, S. S.

2004-11-01

33

Kinetic effects on the toroidal ion pressure gradient drift mode  

Microsoft Academic Search

The question of the threshold of the ion pressure gradient drift mode in toroidal geometry is examined from the drift-kinetic equation retaining the grad-B and curvature drift resonances of the ions with the mode. Analytic criteria for the onset of the instability are derived which exhibit the parametric dependence on toroidicity, pressure gradient and perpendicular wavenumber.

P. Terry; W. Anderson; W. Horton

1982-01-01

34

STARE and EISCAT measurements: Evidence for the limitation of STARE Doppler velocity observations by the ion acoustic velocity  

SciTech Connect

Measurements of the phase velocity of ionospheric plasma waves using the STARE radar system are compared with the electron drift velocity and the ion acoustic velocity calculated from data measured by EISCAT. This comparison shows that for those flow angles that are smaller than the largest flow angle ({theta}{sub S}) for which the component of the electron drift velocity along the radar line of sight equals the ion acoustic velocity, the phase velocity observed by STARE tends to be limited by, or lower than, the ion acoustic velocity. Using observations with flow angles larger than {theta}{sub s}, one can infer the electron drift from STARE measurements by the well-known cosine relation.

Kofman, W.; Nielsen, E. (Centre National de la Recherche Scientifique, St. Martin D'Heres (France))

1990-11-01

35

A Longitudinal Variation of Electron Drift Velocity in the Equatorial Electrojet  

Microsoft Academic Search

Measurements of electron drift velocity in the equatorial electrojet near the Peruvian coast indicate that the velocities to the west of the observatory are normally greater than those to the east. This is true during the day when the electrons are drifting westward, as well as at night when the drift is reversed. Possible explanations include the effect of the

Ben B. Balsley

1970-01-01

36

Role of ionization and electron drift velocity profile to Rayleigh instability in a Hall thruster plasma  

SciTech Connect

Role of ionization to Rayleigh instability is clarified in a Hall thruster plasma under the variety of profiles of electron drift velocity, namely, step-like profile (SLP) and two different super-Gaussian profiles (SGP1 and SGP2). For this, a relevant Rayleigh equation is derived and solved numerically using fourth-order Runge-Kutta method. Interestingly, an upper cutoff frequency of oscillations {omega}{sub max} is realized for the occurrence of the instability that shows dependence on the ionization rate {alpha}, electron drift velocity u{sub 0}, electron cyclotron frequency {Omega}, azimuthal wave number k{sub y}, plasma density n{sub 0}, density gradient {partial_derivative}n{sub 0}/{partial_derivative}x, ion (electron) thermal speed V{sub thI}(V{sub thE}), and ion (electron) plasma frequency {omega}{sub pi}({omega}{sub pe}). The frequency {omega}{sub max} follows the trend {omega}{sub max} (for SGP2) >{omega}{sub max} (for SLP) >{omega}{sub max} (for SGP1) and shows a similar behaviour with ionization for all types of the velocity profiles. The instability is found to grow faster for the higher {alpha} and the ion temperature but it acquires lower rate under the effect of the higher electron temperature; the perturbed potential also varies in accordance with the growth rate. The electron temperature influences the growth rate and cutoff frequency less significantly in comparison with the ion temperature.

Singh, Sukhmander; Malik, Hitendra K. [Plasma Waves and Particle Acceleration Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110 016 (India)

2012-07-01

37

Role of ionization and electron drift velocity profile to Rayleigh instability in a Hall thruster plasma  

NASA Astrophysics Data System (ADS)

Role of ionization to Rayleigh instability is clarified in a Hall thruster plasma under the variety of profiles of electron drift velocity, namely, step-like profile (SLP) and two different super-Gaussian profiles (SGP1 and SGP2). For this, a relevant Rayleigh equation is derived and solved numerically using fourth-order Runge-Kutta method. Interestingly, an upper cutoff frequency of oscillations ?max is realized for the occurrence of the instability that shows dependence on the ionization rate ?, electron drift velocity u0, electron cyclotron frequency ?, azimuthal wave number ky, plasma density n0, density gradient ?n0/?x, ion (electron) thermal speed VthI(VthE), and ion (electron) plasma frequency ?pi(?pe). The frequency ?max follows the trend ?max (for SGP2) >?max (for SLP) >?max (for SGP1) and shows a similar behaviour with ionization for all types of the velocity profiles. The instability is found to grow faster for the higher ? and the ion temperature but it acquires lower rate under the effect of the higher electron temperature; the perturbed potential also varies in accordance with the growth rate. The electron temperature influences the growth rate and cutoff frequency less significantly in comparison with the ion temperature.

Singh, Sukhmander; Malik, Hitendra K.

2012-07-01

38

CHARACTERISTICS OF ION DRIFTED PIN JUNCTION PARTICLE DETECTORS  

Microsoft Academic Search

Ion drift techniques are used to produce p-i-n junction particle ; detectors by drifting lithium in p-type silicon. Depletion widths greater than ; 4mm are obtained. Agreement is found between calculated and measured drift rates. ; In these junctions the predominant contribution to the d-c reverse current is ; caused by thermally generated carriers in the depletion region. At elevated

J. W. Mayer; N. A. Baily; H. J. Dunlap

1961-01-01

39

Oblique ion collection in the drift approximation: How magnetized Mach probes really work  

NASA Astrophysics Data System (ADS)

The anisotropic fluid equations governing a frictionless obliquely flowing plasma around an essentially arbitrarily shaped three-dimensional ion-absorbing object in a strong magnetic field are solved analytically in the quasineutral drift approximation, neglecting parallel temperature gradients. The effects of transverse displacements traversing the magnetic presheath are also quantified. It is shown that the parallel collection flux density dependence upon the external Mach number is n?cs exp[-1-(M??-M? cot ?)], where ? is the angle (in the plane of field and drift velocity) of the object-surface to the magnetic-field and M?? is the external parallel flow. The perpendicular drift, M?, appearing here consists of the external E?B drift plus a weighted sum of the ion and electron diamagnetic drifts that depends upon the total angle of the surface to the magnetic field. It is that somewhat counterintuitive combination that an oblique (transverse) Mach probe experiment measures.

Hutchinson, I. H.

2008-12-01

40

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma  

NASA Astrophysics Data System (ADS)

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum Kadomstev-Petviashvilli (KP) equation in an inhomogeneous quantum plasma is derived using the drift approximation. The solution of quantum KP equation using the tangent hyperbolic (tanh) method is also presented. The variation of the soliton with the quantum Bohm potential, the ratio of drift to soliton velocity in the co-moving frame, vu, and the increasing magnetic field are also investigated. It is found that the increasing number density decreases the amplitude of the soliton. It is also shown that the fast drift soliton (i.e., v>u) decreases whereas the slow drift soliton (i.e., vdrift ion acoustic soliton. The stability of the quantum KP equation is also investigated. The relevance of the present investigation in dense astrophysical environments is also pointed out.

Masood, W.

2009-04-01

41

Nonlinear ion turbulent heating in electron drift wave turbulence  

NASA Astrophysics Data System (ADS)

The total turbulent heat transfer is composed of quasilinear electron cooling, quasilinear ion heating, nonlinear ion heating and zonal flow frictional heating. In a previous paper [1], we discussed quasilinear turbulent heating and zonal flow frictional heating. Here we apply weak turbulence theory to calculate the nonlinear ion turbulent heating via the beat mode resonance in electron drift wave turbulence [2]. The nonlinear diffusion in velocity space, affected by E x B motion and by the parallel velocity scattering, is further analyzed. This calculation proposes and analyzes a new collisionless turbulent energy transfer channel through nonlinear Landau damping. This process enters the electron-ion energy coupling. We estimate it by using the saturation balance. The results show that the collisionless turbulent energy transfer through the nonlinear Landau damping and the zonal flow frictional damping can both be important in a low collisionality, electron heated plasma, such as ITER. [4pt] [1] L. Zhao and P. H. Diamond, submitted to Phys. Plasma, 2012.[0pt] [2] W.M. Manheimer and T.H. Dupree, Phys. Fluid, 11, 2709 (1968).

Zhao, Lei; Diamond, Patrick H.

2012-10-01

42

Ion Collection by a Sphere in a Drifting Collisional Plasma  

SciTech Connect

SCEPTIC3D now includes charge-exchange collisions, and is used to examine ion collection by a floating conducting sphere (small compared to the electron debye length) in the presence of a background neutral drift. The enhancement of ion collection at moderate collisionalities seen for the stationary case is weakened as the drift speed increases from the ion thermal speed to the ion sound speed, above which no enhancement is seen.

Haakonsen, Christian Bernt; Hutchinson, Ian H. [Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2011-11-29

43

The Evolution of Instabilities Driven by a Drift Between Ions and Electrons in Nonmagnetized Plasma  

NASA Astrophysics Data System (ADS)

The electron-ion beam instability is studied by one-dimensional electrostatic particle-in-cell simulation. When the relative drift velocity between the electron and ion is sufficiently less than the electron thermal speed, the dominant mode is the Langmuir wave; the ion-acoustic instability is very weak; the Buneman instability is not excited. When the relative drift speed is equal to the electron thermal speed, the Langmuir wave, the ion-acoustic and the Buneman instability nearly exist simultaneously. The three instabilities now appear to have almost equal intensities. When the relative drift speed exceeds the electron thermal speed, the ion-acoustic instability turns into the Buneman instability which appears to have much higher intensity than the Langmuir wave.

Guo, Jun

2013-04-01

44

High-precision measurement of the electron drift velocity in Ne CO2  

NASA Astrophysics Data System (ADS)

The baseline gas mixture which will be used in the ALICE TPC is 90% Ne and 10% CO2. The change of the drift velocity due to changes of the CO2 concentration as well as N2 addition has been studied in high-precision measurements at drift fields between 100 and 900 V/cm. Also a precise absolute measurement of the drift velocity has been made. All measurements are compared with calculations.

Wiechula, J.; Braun-Munzinger, P.; Daues, H.; Frankenfeld, U.; Garabatos, C.; Hehner, J.; Renfordt, R.; Schmidt, H. R.; Stelzer, H.; Vrani?, D.

2005-08-01

45

Auroral bright spot sequence near 1,400 MLT: Coordinated optical and ion drift observations  

Microsoft Academic Search

Optical observations of a dayside auroral brightening sequence, by means of all-sky TV cameras and meridian scanning photometers, have been combined with EISCAT ion drift observations within the same invariant latitude - MLT sector. The characteristic intermittent optical events, covering 300 km in east-west extent, move eastward (antisunward) along the poleward boundary of the persistent background aurora at velocities of

P. E. Sandholt; B. Lybekk; M. Lockwood; A. D. Farmer

1990-01-01

46

Calibration of the CMS drift tube chambers and measurement of the drift velocity with cosmic rays  

Microsoft Academic Search

This paper describes the calibration procedure for the drift tubes of the CMS barrel muon system and reports the main results obtained with data collected during a high statistics cosmic ray data-taking period. The main goal of the calibration is to determine, for each drift cell, the minimum time delay for signals relative to the trigger, accounting for the drift

S. Chatrchyan; V. Khachatryan; A. M. Sirunyan; W. Adam; B. Arnold; H. Bergauer; T. Bergauer; M. Dragicevic; M. Eichberger; J. Ero; M. Friedl; R. Fruhwirth; V. M. Ghete; J. Hammer; S. Hansel; M. Hoch; N. Hormann; J. Hrubec; M. Jeitler; G. Kasieczka; K. Kastner; M. Krammer; D. Liko; I. M. de Abril; I. Mikulec; F. Mittermayr; B. Neuherz; M. Oberegger; M. Padrta; M. Pernicka; H. Rohringer; S. Schmid; R. Schofbeck; T. Schreiner; R. Stark; H. Steininger; J. Strauss; A. Taurok; F. Teischinger; T. Themel; D. Uhl; P. Wagner; W. Waltenberger; G. Walzel; E. Widl; C. E. Wulz; V. Chekhovsky; O. Dvornikov; I. Emeliantchik; A. Litomin; V. Makarenko; I. Marfin; V. Mossolov; N. Shumeiko; A. Solin; R. Stefanovitch; J. S. Gonzalez; A. Tikhonov; A. Fedorov; A. Karneyeu; M. Korzhik; V. Panov; R. Zuyeuski; P. Kuchinsky; W. Beaumont; L. Benucci; M. Cardaci; E. A. De Wolf; E. Delmeire; D. Druzhkin; M. Hashemi; X. Janssen; T. Maes; L. Mucibello; S. Ochesanu; R. Rougny; M. Selvaggi; H. Van Haevermaet; P. Van Mechelen; N. Van Remortel; V. Adler; S. Beauceron; S. Blyweert; J. DHondt; S. De Weirdt; O. Devroede; J. Heyninck; A. Kalogeropoulos; J. Maes; M. Maes; M. U. Mozer; S. Tavernier; W. Van Doninck; P. Van Mulders; I. Villella; O. Bouhali; E. C. Chabert; O. Charaf; B. Clerbaux; G. De Lentdecker; V. Dero; S. Elgammal; A. P. R. Gay; G. H. Hammad; P. E. Marage; S. Rugovac; C. V. Velde; P. Vanlaer; J. Wickens; M. Grunewald; B. Klein; A. Marinov; D. Ryckbosch; F. Thyssen; M. Tytgat; L. Vanelderen; P. Verwilligen; S. Basegmez; G. Bruno; J. Caudron; C. Delaere; P. Demin; D. Favart; A. Giammanco; G. Gregoire; V. Lemaitre; O. Militaru; S. Ovyn; K. Piotrzkowski; L. Quertenmont; N. Schul; N. Beliy; E. Daubie; G. A. Alves; M. E. Pol; M. H. G. Souza; W. Carvalho; D. D. J. Damiao; C. D. O. Martins; S. F. De Souza; L. Mundim; V. Oguri; A. Santoro; S. M. S. Do Amaral; A. Sznajder; Trfp Tomei; M. A. F. Dias; E. M. Gregores; S. F. Novaes; K. Abadjiev; T. Anguelov; J. Damgov; N. Darmenov; L. Dimitrov; V. Genchev; P. Iaydjiev; S. Piperov; S. Stoykova; G. Sultanov; R. Trayanov; I. Vankov; A. Dimitrov; M. Dyulendarova; V. Kozhuharov; L. Litov; E. Marinova; M. Mateev; B. Pavlov; P. Petkov; Z. Toteva; G. M. Chen; H. S. Chen; W. Guan; C. H. Jiang; D. Liang; B. Liu; X. Meng; J. Tao; J. Wang; Z. Wang; Z. Xue; Z. Zhang; Y. Ban; J. Cai; Y. Ge; S. Guo; Z. Hu; Y. Mao; S. J. Qian; H. Teng; B. Zhu; C. Avila; M. B. Ruiz; C. A. C. Montoya; A. Gomez; B. G. Moreno; A. A. O. Rios; A. F. O. Oliveros; D. R. Romero; J. C. Sanabria; N. Godinovic; K. Lelas; R. Plestina; D. Polic; I. Puljak; Z. Antunovic; M. Dzelalija; V. Brigljevic; S. Duric; K. Kadija; S. Morovic; R. Fereos; M. Galanti; J. Mousa; A. Papadakis; F. Ptochos; P. A. Razis; D. Tsiakkouri; Z. Zinonos; A. Hektor; M. Kadastik; K. Kannike; M. Muntel; M. Raidal; L. Rebane; E. Anttila; S. Czellar; J. Harkonen; A. Heikkinen; V. Karimaki; R. Kinnunen; J. Klem; M. J. Kortelainen; T. Lampen; K. Lassila-Perini; S. Lehti; T. Linden; P. Luukka; T. Maenpaa; J. Nysten; E. Tuominen; J. Tuominiemi; D. Ungaro; L. Wendland; K. Banzuzi; A. Korpela; T. Tuuva; P. Nedelec; D. Sillou; M. Besancon; R. Chipaux; M. Dejardin; D. Denegri; J. Descamps; B. Fabbro; J. L. Faure; F. Ferri; S. Ganjour; F. X. Gentit; A. Givernaud; P. Gras; G. H. de Monchenault; P. Jarry; M. C. Lemaire; E. Locci; J. Malcles; M. Marionneau; L. Millischer; J. Rander; A. Rosowsky; D. Rousseau; M. Titov; P. Verrecchia; S. Baffioni; L. Bianchini; M. Bluj; P. Busson; C. Charlot; L. Dobrzynski; R. G. de Cassagnac; M. Haguenauer; P. Mine; P. Paganini; Y. Sirois; C. Thiebaux; A. Zabi; J. L. Agram; A. Besson; D. Bloch; D. Bodin; J. M. Brom; E. Conte; F. Drouhin; J. C. Fontaine; D. Gele; U. Goerlach; L. Gross; P. Juillot; A. C. Le Bihan; Y. Patois; J. Speck; P. Van Hove; C. Baty; M. Bedjidian; J. Blaha; G. Boudoul; H. Brun; N. Chanon; R. Chierici; D. Contardo; P. Depasse; T. Dupasquier; H. El Mamouni; F. Fassi; J. Fay; S. Gascon; B. Ille; T. Kurca; T. Le Grand; M. Lethuillier; N. Lumb; L. Mirabito; S. Perries; M. V. Donckt; P. Verdier; N. Djaoshvili; N. Roinishvili; V. Roinishvili; N. Amaglobeli; R. Adolphi; G. Anagnostou; R. Brauer; W. Braunschweig; M. Edelhoff; H. Esser; L. Feld; W. Karpinski; A. Khomich; K. Klein; N. Mohr; A. Ostaptchouk; D. Pandoulas; G. Pierschel; F. Raupach; S. Schael; A. S. von Dratzig; G. Schwering; D. Sprenger; M. Thomas; M. Weber; B. Wittmer; M. Wlochal; O. Actis; G. Altenhofer; W. Bender; P. Biallass; M. Erdmann; G. Fetchenhauer; J. Frangenheim; T. Hebbeker; G. Hilgers; A. Hinzmann; K. Hoepfner; C. Hof; M. Kirsch; T. Klimkovich; P. Kreuzer; D. Lanskey; M. Merschmeyer; A. Meyer; B. Philipps; H. Pieta; H. Reithler; S. A. Schmitz; L. Sonnenschein; M. Sowa; J. Steggemann; H. Szczesny; D. Teyssier; C. Zeidler; M. Bontenackels; M. Davids; M. Duda; G. Flugge; H. Geenen; M. Giffels; W. H. Ahmad; T. Hermanns; D. Heydhausen; S. Kalinin

2010-01-01

47

Fluid simulation of ion pressure gradient driven drift modes  

Microsoft Academic Search

The nonlinear evolution of the ion pressure gradient driven drift wave instability is investigated through three-dimensional fluid simulations. The anomalous thermal transport produced in the saturated state is reported as a function of the system parameters.

W. Horton; R. D. Estes; D. Biskamp

1980-01-01

48

Comparison of surface velocities determined from altimeter and drifting buoy data  

Microsoft Academic Search

Surface velocities determined from trajectory of a drifting buoy from March through November 1987 are compared with surface geostrophic velocities determined from sea surface dynamic topography (SSDT) obtained from altimetry data with the aid of long-term hydrographic observation data. In general, these velocities show similar temporal variations in both zonal and meridional components, except in a period when obvious error

Kaoru Ichikawa; Shiro Imawaki; Haruo Ishii

1995-01-01

49

Drift ion acoustic shock waves in an inhomogeneous two-dimensional quantum magnetoplasma  

SciTech Connect

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous quantum plasma with neutrals in the background employing the quantum hydrodynamics (QHD) model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived for the first time. It is shown that the ion acoustic wave couples with the drift wave if the parallel motion of ions is taken into account. Discrepancies in the earlier works on drift solitons and shocks in inhomogeneous plasmas are also pointed out and a correct theoretical framework is presented to study the one-dimensional as well as the two-dimensional propagation of shock waves in an inhomogeneous quantum plasma. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation of the shock profile with the quantum Bohm potential, collision frequency, and ratio of drift to shock velocity in the comoving frame, v{sub *}/u, are also investigated. It is found that increasing the number density and collision frequency enhances the strength of the shock. It is also shown that the fast drift shock (i.e., v{sub *}/u>0) increases, whereas the slow drift shock (i.e., v{sub *}/u<0) decreases the strength of the shock. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Masood, W.; Siddiq, M. [TPPD, PINSTECH, P. O. Nilore, Islamabad 54000 (Pakistan); Karim, S.; Shah, H. A. [Department of Physics, GC University, Lahore 54000 (Pakistan)

2009-04-15

50

Drift ion acoustic shock waves in an inhomogeneous two-dimensional quantum magnetoplasma  

NASA Astrophysics Data System (ADS)

Linear and nonlinear propagation characteristics of drift ion acoustic waves are investigated in an inhomogeneous quantum plasma with neutrals in the background employing the quantum hydrodynamics (QHD) model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived for the first time. It is shown that the ion acoustic wave couples with the drift wave if the parallel motion of ions is taken into account. Discrepancies in the earlier works on drift solitons and shocks in inhomogeneous plasmas are also pointed out and a correct theoretical framework is presented to study the one-dimensional as well as the two-dimensional propagation of shock waves in an inhomogeneous quantum plasma. Furthermore, the solution of KPB equation is presented using the tangent hyperbolic (tanh) method. The variation of the shock profile with the quantum Bohm potential, collision frequency, and ratio of drift to shock velocity in the comoving frame, v*/u, are also investigated. It is found that increasing the number density and collision frequency enhances the strength of the shock. It is also shown that the fast drift shock (i.e., v*/u>0) increases, whereas the slow drift shock (i.e., v*/u<0) decreases the strength of the shock. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Masood, W.; Karim, S.; Shah, H. A.; Siddiq, M.

2009-04-01

51

Computation of the drift velocity of spiral waves using response functions  

NASA Astrophysics Data System (ADS)

Rotating spiral waves are a form of self-organization observed in spatially extended systems of physical, chemical, and biological nature. In the presence of a small perturbation, the spiral waves center of rotation and fiducial phase may change over time, i.e., the spiral wave drifts. In linear approximation, the velocity of the drift is proportional to the convolution of the perturbation with the spirals response functions, which are the eigenfunctions of the adjoint linearized operator corresponding to the critical eigenvalues ?=0,i? . Here, we demonstrate that the response functions give quantitatively accurate prediction of the drift velocities due to a variety of perturbations: a time dependent, periodic perturbation (inducing resonant drift); a rotational symmetry-breaking perturbation (inducing electrophoretic drift); and a translational symmetry-breaking perturbation (inhomogeneity induced drift) including drift due to a gradient, stepwise, and localized inhomogeneity. We predict the drift velocities using the response functions in FitzHugh-Nagumo and Barkley models, and compare them with the velocities obtained in direct numerical simulations. In all cases good quantitative agreement is demonstrated.

Biktasheva, I. V.; Barkley, D.; Biktashev, V. N.; Foulkes, A. J.

2010-06-01

52

Electron viscosity effects on electron drift velocity in silicon MOS inversion layers  

Microsoft Academic Search

Electron drift mobility in MOS inversion layers was analyzed by applying the classical kinetic theory of gases for the viscosity in electron gases and the collision with the oxide interface. Drift velocity profiles for electrons, perpendicular to the MOS interface, were calculated by solving the transport equations for electrons with shear stresses due to electron viscosity. Considering the momentum balance

Y. Ohno

1991-01-01

53

A Comparison of ship drift, drifting buoy, and current meter mooring velocities in the Pacific South Equatorial Current  

NASA Astrophysics Data System (ADS)

In this note we compare mean seasonal cycles of zonal and meridional velocity in the Pacific South Equatorial Current based on current meter mooring data, drifting buoy data, and ship drift data. Monthly averages of ship drift and drifting buoy data were computed over 2 latitude by 10 longitude rectangles centered at the positions of multiyear current meter moorings near 0, 110W, and 0, 140W. All three representations of the flow field show the basic character of the annual mean and its variations, provided that the sampling characteristics associated with each measurement technique are taken into account. In particular we find that more than 15 days of drifter data (regardless of year) are required on a 2 latitude by 10 longitude basis to produce monthly mean estimates that agree with moored estimates to within about 5-10 cm s-1 rms. We also infer that windage affects climatological monthly mean ship drift velocities, although uncertainties in the data limit a precise determination of the windage magnitude. An upper bound appears to be about 3% of the surface wind speed, though the actual effect of windage may be considerably smaller.

McPhaden, M. J.; Hansen, D. V.; Richardson, P. L.

1991-01-01

54

Drift Compression and Final Focus Options for Heavy Ion Fusion  

SciTech Connect

A drift compression and final focus lattice for heavy ion beams should focus the entire beam pulse onto the same focal spot on the target. We show that this requirement implies that the drift compression design needs to satisfy a self-similar symmetry condition. For un-neutralized beams, the Lie symmetry group analysis is applied to the warm-fluid model to systematically derive the self-similar drift compression solutions. For neutralized beams, the 1-D Vlasov equation is solved explicitly, and families of self-similar drift compression solutions are constructed. To compensate for the deviation from the self-similar symmetry condition due to the transverse emittance, four time-dependent magnets are introduced in the upstream of the drift compression such that the entire beam pulse can be focused onto the same focal spot.

Hong Qin; Ronald C. Davidson; John J. Barnard; Edward P. Lee

2005-02-14

55

Toroidal drift modes driven by ion pressure gradients  

NASA Astrophysics Data System (ADS)

Ion pressure gradient-driven drift modes are analyzed for their parametric dependence on the shear, the toroidal aspect ratio, and the pressure gradient using the ballooning toroidal mode theory. An approximate formula for the anomalous ion thermal conductivity is derived for the turbulent regime.

Horton, W., Jr.; Choi, D.-I.; Tang, W. M.

1981-06-01

56

Toroidal drift modes driven by ion pressure gradients  

Microsoft Academic Search

Ion pressure gradient-driven drift modes are analyzed for their parametric dependence on the shear, the toroidal aspect ratio, and the pressure gradient using the ballooning toroidal mode theory. An approximate formula for the anomalous ion thermal conductivity is derived for the turbulent regime.

Wendell Horton; Duk-In Choi; W. M. Tang

1981-01-01

57

Lower-hybrid drift instability in a thin current sheet with {kappa} velocity distribution  

SciTech Connect

The lower-hybrid drift instability (LHDI) in a thin current sheet in the intermediate-wavelength (k{sub y}{radical}({rho}{sub i}{rho}{sub e}){approx}1, where k{sub y}, {rho}{sub e}, and {rho}{sub i} are the wave vector and the electron and ion gyroradii, respectively) regime for particles with {kappa} velocity distribution is studied. The latter is more suitable for describing nonthermal distributions with an enhanced high-energy tail and includes the Maxwellian as a limiting case. It is shown that linear electromagnetic LHDI can be excited near the center of the current sheet. The growth rate decreases, but the electromagnetic component of the LHD mode increases with increase in hot particles.

Huang Feng; Chen Yinhua; Shi Guifen; Hu Zuquan; Peng Haiou; Zheng Jugao [Key Laboratory of Basic Physics, USTC, Chinese Academy of Sciences, 230026 Hefei (China) and Department of Modern Physics, University of Science and Technology of China, 230026 Hefei (China); Yu, M. Y. [Department of Physics, Institute for Fusion Theory and Simulation, Zhejiang University, 310027 Hangzhou (China)

2009-04-15

58

Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data  

Microsoft Academic Search

Sea-surface geostrophic velocities for the Kuroshio region calculated from TOPEX\\/POSEIDON altimetry data together within situ oceanographic data are compared with surface velocities derived from drifting buoy trajectories. The geostrophic velocities\\u000a agree well with the observed velocities, suggesting that the Kuroshio surface layer is essentially in geostrophic balance,\\u000a within measurement error. The comparison is improved a little when the centrifugal acceleration

Hiroshi Uchida; Shiro Imawaki; Jian-Hwa Hu

1998-01-01

59

Drift and ion acoustic wave driven vortices with superthermal electrons  

SciTech Connect

Linear and nonlinear analysis of coupled drift and acoustic mode is presented in an inhomogeneous electron-ion plasma with {kappa}-distributed electrons. A linear dispersion relation is found which shows that the phase speed of both the drift wave and the ion acoustic wave decreases in the presence of superthermal electrons. Several limiting cases are also discussed. In the nonlinear regime, stationary solutions in the form of dipolar and monopolar vortices are obtained. It is shown that the condition for the boundedness of the solution implies that the speed of drift wave driven vortices reduces with increase in superthermality effect. Ignoring density inhomogeniety, it is investigated that the lower and upper limits on the speed of the ion acoustic driven vortices spread with the inclusion of high energy electrons. The importance of results with reference to space plasmas is also pointed out.

Ali Shan, S. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan); Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad (Pakistan); Haque, Q. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan); National Centre For Physics (NCP), Shahdra Valley Road, QAU Campus, 44000 Islamabad (Pakistan)

2012-08-15

60

An empirical model of the drift velocity of equatorial plasma depletions  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager on the IMAGE spacecraft (IMAGE-FUV) has been used to observe O+plasma depletions in the post-sunset equatorial ionosphere. Small-scale density irregularities associated with such depletions are believed to adversely affect trans-ionospheric radio signals such as GPS. Prediction of the motion of these plasma depletions is a necessary component of the ability to forecast the occurrence of such radio signal interference. An automated method has recently been developed to identify and track the position and zonal drift velocity of these depletions. Here we use this method to create a large database of the zonal drift velocities of these depletions. We present an empirical model based on these observations that describes the observed drift velocities as a function of both local time and magnetic latitude, which is essential to represent their behavior. A comparison of the observed drift velocities with zonal winds from both an empirical model (Horizontal Wind Model; HWM07) and a first-principles model (the TIEGCM) reveals that the plasma depletions' drift velocities have a latitudinal gradient that cannot be explained solely by the F-region dynamo in the post-sunset period, at least by these climatological models. This suggests that these plasma depletions may not simply drift with the background F-region plasma. It has previously been suggested that vertical polarization electric fields associated with the plasma depletions are responsible for their zonal drifts exceeding the background flow, which may explain the previously-observed discrepancy in the drift velocities and the discrepancy in their gradients reported here.

England, S. L.; Immel, T. J.

2012-12-01

61

Ion Mobility Spectrometry Mass Spectrometry Performance Using Electrodynamic Ion Funnels and Elevated Drift Gas Pressures  

SciTech Connect

The ability of ion mobility spectrometry coupled with mass spectrometry (IMS-MS) to characterize biological mixtures has been illustrated over the past eight years. However, the challenges posed by the extreme complexity of many biological samples have demonstrated the need for higher resolution IMS-MS measurements. We have developed a higher resolution ESI-IMS-TOF MS by utilizing high pressure electrodynamic ion funnels at both ends of the IMS drift cell and operating the drift cell at an elevated pressure compared to a previous design. The ESI-IMS-TOF MS instrument consists of an ESI source, an hourglass ion funnel used for ion accumulation/injection into an 88 cm drift cell followed by a 10 cm ion funnel and a commercial orthogonal time-of-flight mass spectrometer providing high mass measurement accuracy. It was found that the rear (exit) ion funnel could be effectively operated as an extension of the drift cell when the DC fields were matched, allowing the instrument to have an effective drift region of 98 cm. Two differentially pumped quadrupole regions were used to couple the IMS and TOF MS to focus and minimize the ion transient time between the stages. The resolution of the instrument was evaluated at pressures ranging from 4 to12 Torr and ion mobility drift voltages of 16 V/cm (4 Torr) to 43 V/cm (12 Torr). An increase in resolution from 55 to 80 was observed from 4 to 12 Torr nitrogen drift gas with no loss in sensitivity. Given the increased usage of ion funnels prior to ion mobility separations, additional attention was directed towards the influence of drift gas on the observed ion populations trapped and transmitted using an electrodynamic ion funnel. The choice of drift gas was shown to influence the degree of ion heating and relative trapping efficiency within the ion funnel.

Baker, Erin Shammel; Clowers, Brian H.; Li, Fumin; Tang, Keqi; Tolmachev, Aleksey V.; Prior, David C.; Belov, Mikhail E.; Smith, Richard D.

2007-06-28

62

Shear-flow-driven ion cyclotron and ion sound-drift instabilities of cylindrical inhomogeneous plasma  

SciTech Connect

The effects of the shear flow along the magnetic field on the development of the ion cyclotron, ion sound, and drift instabilities in the radially inhomogeneous cylindrical plasma are studied on the ground of a kinetic approach. It is shown that flow shear not only modifies the frequencies and growth rates of known current driven electrostatic ion cyclotron, ion sound, and drift instabilities, but is the source of the development of specific shear-flow-driven ion cyclotron, ion sound, and drift instabilities. These instabilities are excited at the levels of current along the ambient magnetic field which is below the critical value for the development of the modified by flow shear current driven ion cyclotron, ion sound, and drift instabilities.

Mikhailenko, V. S.; Chibisov, D. V. [Kharkov National University, 61108, Kharkov (Ukraine)

2007-08-15

63

Edge magnetoplasmons in graphene: determination of carrier drift velocity in Quantum Hall regime  

NASA Astrophysics Data System (ADS)

Edge Magneto-Plasmons (EMP) are gapless quasi 1D elementary excitations which are split off from the bulk magneto-plasmon modes by the sample boundary, and are a tool of choice to investigate the structure of the edge of a 2D electron gas. We give a first experimental demonstration of their presence in graphene in the quantum Hall regime and use our results to evaluate the carrier drift velocity along the edge [1]. The group velocity of these modes is a sum of the Hall conductivity contribution and the carrier drift velocity at the edge. In graphene, due to its particular dynamics and an abrupt edge, the drift velocity is expected to be of the order of the Fermi velocity, thus becoming experimentally accessible. We show EMP to exist by timing the travel of narrow wave-packets on picosecond time scales around exfoliated samples. They show chiral propagation with low attenuation at a velocity which is quantized on Hall plateaus. We extract the carrier drift contribution and find it to be slightly less than the Fermi velocity, as expected for an abrupt edge. We also extract the spatial spread of edge accumulated charge and find it to be narrower than for soft edge systems.[4pt] [1] I. Petkovic, F.I.B. Williams, K. Bennaceur, F. Portier, P. Roche and D.C. Glattli, Phys. Rev. Lett.(2012).

Petkovic, Ivana; Williams, F. I. B.; Bennaceur, Keyan; Portier, Fabien; Roche, Patrice; Glattli, D. C.

2013-03-01

64

Simulation of a GaAs MESFET including velocity overshoot: an extended drift-diffusion formalism  

Microsoft Academic Search

Numerical simulations are described for GaAs MESFETs. They are based on an extended drift-diffusion equation formalism which allows for the inclusion of the velocity overshoot effect. The overshoot correction term which augments the drift-diffusion current equation is proportional to the gradient of the local electric field. The proportionality constant has been calculated by Monte Carlo methods as a function of

I. C. Kizilyalli; M. Artaki

1989-01-01

65

Numerical simulation of ion dynamics in closed-drift systems  

Microsoft Academic Search

Aspects of the simulation of ion dynamics in closed-drift plasma-optic systems are discussed. The beam is considered as a rarefied plasma structure consisting of several components, i.e., heavy relatively slow particles (ions and neutral atoms) and light rapid particles (electrons). The plasma as a whole is not in thermodynamic equilibrium; each group of particles has its own temperature and must

B. I. Volkov; A. I. Morozov; A. G. Sveshnikov; S. A. Iakunin

1981-01-01

66

Determination of the Sharp, Longitudinal Gradients in Equatorial ExB Drift Velocities Associated with the 4-cell, Non-migrating Structures  

NASA Astrophysics Data System (ADS)

Previous studies have established the existence of a 4-cell, longitude pattern in equatorial F region ionospheric parameters such as TEC and electron densities and in daytime, equatorial ExB drift velocities. A recent paper, for the first time, quantified the longitude gradients in ExB drift associated with the 4-cell tidal structures and confirmed that these sharp gradients exist on a day-to-day basis. Using the Ion Velocity Meter (IVM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite to obtain daytime, vertical ExB drift velocities, it was found, for example, that for October 5, 6 and 7, 2009 in the Atlantic sector, the ExB drift velocity gradient was about 1m/sec/degree. For March 23, 24 and 25, 2009 in the Peruvian sector, it was about -4m/sec/degree. This talk summarizes past observations of the sharp longitude gradients in vertical ExB drift velocities and the effect of these sharp gradients on theoretically-calculated ion density distributions as a function of latitude and longitude. We also present initial, ground-based magnetometer-inferred vertical ExB drift velocities from the LISN (Low-latitude Ionospheric Sensor Network) chain of magnetometers at 295 E. geographic longitude and 310 E. geographic longitude that provide the day-to-day and seasonal variability in ExB drifts at the boundary between the Peruvian longitude sector and the Atlantic longitude sector. The advantages of these continuous, daytime observations are discussed.

Anderson, D. N.

2011-12-01

67

Effect of primary electron drift on the negative ion efficiency of a volume hybrid multicusp H[sup [minus  

SciTech Connect

A new, large, hybrid volume negative ion source is described. Observations of curvature and [ital grad] [ital B] primary electron drift in the multicusp magnetic field are reported. The direction of the electron drift changes from one filament to the neighboring one, because of the change in the direction of the magnetic field. For a given discharge current the extracted negative ion current and the plasma density at the center of the extraction region are affected by the direction of the primary electron drift of the active filaments. It was shown, however, that the negative ion current is controlled by the plasma density at the center of the extraction region. A trajectory calculation, effected in the guiding center approximation, allows to estimate the average drift velocity.

Courteille, C.; Bruneteau, J.; Valckx, F.P.G.; Sledziewski, Z.; Bacal, M. (Laboratoire de Physique des Milieux Ionises, Laboratoire du CNRS, Ecole Polytechnique, 91128 Palaiseau Cedex (France))

1992-10-05

68

Drift velocity and gain in argon- and xenon-based mixtures  

NASA Astrophysics Data System (ADS)

We present measurements of drift velocities and gains in gas mixtures based on Ar and Xe, with CO2, CH4, and N2 as quenchers, and compare them with calculations. In particular, we show the dependence of Ar- and Xe-CO2 drift velocities and gains on the amount of nitrogen contamination in the gas, which in real experiments may build up through leaks. A quantification of the Penning mechanism which contributes to the Townsend coefficients of a given gas mixture is proposed.

Andronic, A.; Biagi, S.; Braun-Munzinger, P.; Garabatos, C.; Tsiledakis, G.

2004-05-01

69

Effect of burst ions on the excitation of ion-acoustic solitons in a drifting plasma  

Microsoft Academic Search

The characteristics of fast burst ions and ion-acoustic solitons in a drifting plasma, as well as their interaction, are investigated experimentally. It is shown that the soliton evolves from the normal fast ion-beam mode excited locally in the presheath region of an excitation grid. The burst ions are created by applying a positive ramp voltage to the grid. Adjusting the

De-Long Xiao; J. X. Ma; Yi-Ren Li; Yang-Fang Li; M. Y. Yu

2007-01-01

70

Drift ion acoustic solitons in an inhomogeneous 2-D quantum magnetoplasma  

Microsoft Academic Search

Linear and nonlinear propagation characteristics of quantum drift ion acoustic waves are investigated in an inhomogeneous two-dimensional plasma employing the quantum hydrodynamic (QHD) model. In this regard, the dispersion relation of the drift ion acoustic waves is derived and limiting cases are discussed. In order to study the drift ion acoustic solitons, nonlinear quantum KadomstevPetviashvilli (KP) equation in an inhomogeneous

W. Masood

2009-01-01

71

Comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities  

NASA Astrophysics Data System (ADS)

A one-year dataset spanning March 2011 to March 2012 of coincident observations of nighttime thermospheric zonal neutral winds, equatorial plasma bubble (EPB) velocities, and zonal plasma drifts is used to examine the relationship between the thermosphere and the ionosphere near the geomagnetic equator over Peru. Thermospheric neutral winds are determined by using a bistatic Fabry-Perot interferometer (FPI) experiment located at Merihill and Nazca in Peru. The ambient plasma drift velocities were obtained using the incoherent scatter radar at the Jicamarca Radio Observatory in Peru. The EPB zonal velocities were estimated utilizing images of the OI 630.0 nm emission recorded by a narrow-field optical imaging system at the Cerro Tololo Inter-American Observatory in Chile. The joint analysis of these datasets illustrates that the nighttime and night-to-night variations in the zonal neutral winds, EPB velocities, and plasma drifts are well correlated. This consistent result of the local time variations of the neutral winds with that of EPB and plasma drifts illustrates that the F-region dynamo is, in general, fully activated. However, at times, the magnitude of the EPB velocities and the plasma drifts are different from the neutral winds. It is plausible that such a difference is due either to the effect of polarization electric fields developed inside the EPB or due to the latitudinal gradient of the neutral winds and EPB velocity measurements since the EPB velocities are estimated at a higher latitude, corresponding to an apex altitude of ~400 km, than the wind estimates, which derive from an apex altitude of ~250 km.

Chapagain, Narayan P.; Fisher, Daniel J.; Meriwether, John W.; Chau, Jorge L.; Makela, Jonathan J.

2013-04-01

72

Drift compression of an intense neutralized ion beam  

SciTech Connect

Longitudinal compression of a velocity-tailored, intense neutralized K{sup +} beam at 300 keV, 25 mA has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. This measurement has been confirmed independently with two different diagnostic systems.

Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J.; Eylon, S.; Greenway, W. G.; Leitner, M.; Logan, B.G.; Waldron, W.L.; Welch, D.R.; Thoma, C.; Sefkow, A.B.; Gilson, E.P.; Efthimion, P.C.; Davidson, R.C.

2005-09-08

73

Instability of a magnetic drift wave in the vicinity of the dust-ion hybrid resonance  

SciTech Connect

Low-frequency electromagnetic waves propagating perpendicular to the gradients of the density and magnetic field in an inhomogeneous dusty plasma whose mass density is determined primarily by the dust component are analyzed. It is shown that, in analyzing the dispersion properties of inhomogeneous plasma, it is important to take into account the dynamic properties of ions in the vicinity of the dust-ion hybrid resonance. The conditions for the onset of instability of a magnetic drift wave are investigated for different relations between parameters of the inhomogeneity and the value of the Alfven velocity. The differences from the previous results, as well as possible astrophysical applications, are discussed.

Prudskikh, V. V. [South Federal University, Institute of Physics (Russian Federation)

2012-06-15

74

Atmospheric pressure-ion drift chemical ionization mass spectrometry for detection of trace gas species.  

PubMed

This paper describes atmospheric pressure-ion drift chemical ionization mass spectrometry (AP-ID-CIMS) for monitoring of ambient trace species. Operation of the drift tube at atmospheric pressure allows a significantly longer ion-molecule reaction time and eliminates dilution of the ambient samples, while a well-defined electric field inside the drift tube provides the benefits to confine the flight path and velocity of reagent/product ions, to break down ion clusters, and to control the ion-molecule reaction time. The AP-ID-CIMS exhibits advantages over the conventional low pressure ID-CIMS and flow tube AP-CIMS, improving the detection sensitivity by 3 orders of magnitude and a factor of 3, respectively. We demonstrate that the AP-ID-CIMS allows quantification of sulfuric acid concentrations and is capable of detecting gaseous sulfuric acid with a detection limit of less than 10(5) molecules cm(-3), on the basis of 3sigma of the baseline noise and an integration time of 12 s. A field evaluation of the AP-ID-CIMS is presented for ambient H(2)SO(4) measurements. PMID:20695435

Zheng, Jun; Khalizov, Alexei; Wang, Lin; Zhang, Renyi

2010-09-01

75

The Effects of Relative Drift Velocities Between Proton and He2+ on the Magnetic Spectral Signatures in the Plasma Depletion Layer  

NASA Astrophysics Data System (ADS)

Magnetic spectrum of the electromagnetic ion cyclotron waves in the terrestrial plasma depletion layer (PDL) are sometimes observed to have a BIF (bifurcated) signature, where a diminution around 0.5?p with ?p the proton gyrofrequency, occurs between two activity peaks in the spectrum. By one-dimensional hybrid simulations, the effect of relative drift velocities between protons and He2+ on the magnetic spectral signatures in the PDL is studied. The results show that the relative drift velocity enhances the development of proton cyclotron waves and declines the development of helium cyclotron waves. The proton cyclotron waves are firstly excited, and followed by the excitation of helium cyclotron waves due to the increase in the relative drift velocity. Moreover, the boundary between two activity peaks gets obscure.

Guo, Jun

2011-10-01

76

Non-Maxwellian ion velocity distributions observed using EISCAT  

SciTech Connect

Recent observations from the EISCAT incoherent scatter radar have revealed bursts of poleward ion flow in the dayside auroral ionosphere which are consistent with the ionospheric signature of flux transfer events at the magnetopause. These bursts frequently contain ion drifts which exceed the neutral thermal speed and, because the neutral thermospheric wind is incapable of responding sufficiently rapidly, toroidal, non-Maxwellian ion velocity distributions are expected. The EISCAT observations are made with high time resolution (15 seconds) and at a large angle to the geomagnetic field (73.5/sup 0/), allowing the non-Maxwellian nature of the distribution to be observed remotely for the first time. The observed features are also strongly suggestive of a toroidal distribution: characterstic spectral shape, increased scattered power (both cosistent with reduced Landau damping and enhanced electric field fluctuations) and excessively high line-of-sight ion temperatures deduced if a Maxwellian distribution is assumed. These remote sensing observations allow the evolution of the distributions to be observed. They are found to be non-Maxwellian whenever the ion drift exceeds the neutral thermal speed, indicating that such distributions can exist over the time scale of the flow burst events (several minutes). Copyright American Geophysical Union 1987

Lockwood, M.; Bromage, B.J.I.; Horne, R.B.; St-Maurice, J.H.; Willis, D.M.; Cowley, S.W.H.

1987-02-01

77

Linear ion source with closed drift and extended acceleration region.  

PubMed

Ion source with closed drift, which is caused by E x B field, and extended acceleration region is discussed. Though conventional circular-type closed drift ion source has advantages of high efficiency of gas ionization and low ion beam energy, there is a limitation in enlarging the beam size. Linear ion source with horse-track shape with 270 mm ceramic channel width is newly designed and tested. Inert gas (Ar) and reactive gas (O(2)) are discharged. Discharge is ignited with voltage of 90 V. Discharge current is proportional to discharge voltage and increases up to 16.3 A in argon and 15.6 A in oxygen at discharge voltage of 320 V. Extracted ion beam current is also proportional to discharge voltage and is saturated after 280 V for both gases. It is measured up to 0.78 mA/cm(2) in argon beam and 0.73 mA/cm(2) in oxygen beam at a distance of 100 mm from the ion source. Argon ion beam shows better space uniformity than oxygen across the beam extraction region. PMID:18315178

Park, Dong-Hee; Kim, Ji-Hwan; Ermakov, Yury; Choi, Won-Kook

2008-02-01

78

Linear ion source with closed drift and extended acceleration region  

SciTech Connect

Ion source with closed drift, which is caused by ExB field, and extended acceleration region is discussed. Though conventional circular-type closed drift ion source has advantages of high efficiency of gas ionization and low ion beam energy, there is a limitation in enlarging the beam size. Linear ion source with horse-track shape with 270 mm ceramic channel width is newly designed and tested. Inert gas (Ar) and reactive gas (O{sub 2}) are discharged. Discharge is ignited with voltage of 90 V. Discharge current is proportional to discharge voltage and increases up to 16.3 A in argon and 15.6 A in oxygen at discharge voltage of 320 V. Extracted ion beam current is also proportional to discharge voltage and is saturated after 280 V for both gases. It is measured up to 0.78 mA/cm{sup 2} in argon beam and 0.73 mA/cm{sup 2} in oxygen beam at a distance of 100 mm from the ion source. Argon ion beam shows better space uniformity than oxygen across the beam extraction region.

Park, Dong-Hee; Kim, Ji-Hwan; Ermakov, Yury; Choi, Won-Kook [Materials Science and Technology Research Division, Korea Institute of Science and Technology, Cheongryang, P.O. Box 131, Seoul 130-650 (Korea, Republic of); Materials Science and Technology Research Division, Korea Institute of Science and Technology, Cheongryang, P.O. Box 131, Seoul 130-650, Republic of Korea and Department of Materials Science and Engineering, Korea University, Anam-Dong 5-1, Sungbuk-Ku, Seoul 136-701 (Korea, Republic of); Institute of Nuclear Physics of the Lomonosov, Moscow State University, Moscow 119992 (Russian Federation); Materials Science and Technology Research Division, Korea Institute of Science and Technology, Cheongryang, P.O. Box 131, Seoul 130-650 (Korea, Republic of)

2008-02-15

79

Nonlinear effects in velocity space and drift wave transport in tokamaks.  

National Technical Information Service (NTIS)

It is pointed out that the use of kinetic models for drift wave transport in general makes it necessary to treat consistently the transport in both real space and velocity space. For a broad class of collisionless or marginally collisionless plasmas, nonl...

J. Weiland

1991-01-01

80

Drift velocity of C(60)(+) in gases follows rarefied gas dynamics.  

PubMed

The drift velocities of C(60)(+) in He, Ne, Ar, and Kr were found to be estimated with high accuracy using the drag coefficient of a solid body in free molecule flow. That is, massive C(60)(+) behaves in gases as if it were a large classical body. PMID:11415148

Nanbu, K; Wakayama, G

2001-05-29

81

Remote-sensing of F-Region ion drifts and ion temperatures at Sondre Stromfjord, Greenland using Doppler measurements of the O[sup +]([sup 2]P) state  

SciTech Connect

Ground-based observations of Doppler line profiles from the F-Region O[sup +]([sup 2]P) state, made with the Fabry-Perot interferometer (FPI) at Sondre Stromfjord, Greenland have been analyzed to provide measurements of the ion convection velocity and ion temperature. The FPI line-of-sight (LOS) ion drift and temperature measurements have been compared with simultaneous incoherent scatter radar (ISR) measurements: the results from the two techniques are in good agreement.

Carr, S.S.; Niciejewski, R.J.; Killeen, T.L.

1993-10-08

82

NUCLEAR PHYSICS: Measurement of Electron-Drift Velocity in Ar+CH4 Mixtures Using Double-Grid Method  

NASA Astrophysics Data System (ADS)

Based on analyzing the induced signals from the double-grids of an ionization chamber, the electron-drift time between the two grids is determined and the electron-drift velocity is derived. A waveform digitizer is employed to record pulses from the two grids of the ionization chamber. The electron-drift velocity is measured as a function of the reduced electric field E/p for eight different ratios of Ar+CH4 mixtures. By analyzing the experimental data of this study, self-consistency of experimental data is achieved, and formulae for calculating electron-drift velocity in any ratio of Ar+CH4 mixtures are obtained.

Zhang, Jia-Guo; Zhang, Guo-Hui; Chen, Jin-Xiang

2009-11-01

83

Toroidal Momentum Pinch Velocity due to the Coriolis Drift Effect on Small Scale Instabilities in a Toroidal Plasma  

Microsoft Academic Search

In this Letter, the influence of the ``Coriolis drift'' on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is

A. G. Peeters; C. Angioni; D. Strintzi

2007-01-01

84

Long range collision effects for drifting velocity distributions  

NASA Astrophysics Data System (ADS)

The interparticle force acting during a binary encounter is usually modeled by a potential of the inverse power law form. The influence of one particle on the other decays with distance and here the effects felt around the so called cutoff distance are considered. Attention is given to the Fokker-Planck model in generalized and restricted forms to describe the collisional consequences of this sort of interaction. Particular emphasis is placed on the peculiar details of the Coulomb collision theory overlooked in earlier works on this matter as: (a) the form of the collision term, (b) the definition of the Coulomb logarithm and (c) the value of the effective cross section. Only the long range effects are focused. To combine close and long ranges into a unique collision term the cross section corresponding to each range must be added. The classical use of the same expression for the cross section in both ranges is shown to be inappropriate. The proposed approach is valid regardless the form of the distribution function, on the magnitude of the flow velocity, besides being applicable to other types of interparticle forces as Maxwell molecule interactions. The material is relevant for solar plasma, interplanetary transport and planetary magnetosphere studies.

Zamlutti, C. J.

1998-12-01

85

Noncontact measurement of electrostatic fields: Verification of modeled potentials within ion mobility spectrometer drift tube designs  

Microsoft Academic Search

The heart of an ion mobility spectrometer is the drift region where ion separation occurs. While the electrostatic potentials within a drift tube design can be modeled, no method for independently validating the electrostatic field has previously been reported. Two basic drift tube designs were modeled using SIMION 7.0 to reveal the expected electrostatic fields: (1) A traditional alternating set

Jill R. Scott; Paul L. Tremblay

2007-01-01

86

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide-angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry-Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night-to-night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Chapagain, Narayan P.; Makela, Jonathan J.; Meriwether, John W.; Fisher, Daniel J.; Buriti, Ricardo A.; Medeiros, Amauri F.

2012-06-01

87

Measuring drift velocity and electric field in mirror machine by fast photography  

NASA Astrophysics Data System (ADS)

The flute instability in mirror machines is driven by spatial charge accumulation and the resulting E B plasma drift. On the other hand, E B drift due to external electrodes or coils can be used as a stabilizing feedback mechanism. Fast photography is used to visualize Hydrogen plasma in a small mirror machine and infer the plasma drift and the internal electric field distribution. Using incompressible flow and monotonic decay assumptions we obtain components of the velocity field from the temporal evolution of the plasma cross section. The electric field perpendicular to the density gradient is then deduced from E=-V B. With this technique we analyzed the electric field of flute perturbations and the field induced by electrodes immersed in the plasma.

Be'ery, I.; Seemann, O.; Fruchtman, A.; Fisher, A.; Nemirovsky, J.

2013-02-01

88

Drift Velocities of Slow Electrons in Helium, Neon, Argon, Hydrogen, and Nitrogen  

Microsoft Academic Search

The drift velocities of electrons in helium, neon, argon, hydrogen, and nitrogen have been measured for Ep values between 10-4 and 10 volt\\/cm-mm Hg at temperatures between 77K and 373K. The data were obtained from measurements of electron transit time in an improved version of the double-shutter tube developed by Bradbury and Nielsen. By applying sufficiently small voltage pulses to

J. L. Pack; A. V. Phelps

1961-01-01

89

Change In The Drift Velocity Of A Jupiter Anticyclone In The Ssstc  

NASA Astrophysics Data System (ADS)

Richard W. Schmude, Jr., Gordon College, 419 College Dr., Barnesville, GA 30204 A white oval (anticyclone) in Jupiters South South South Temperate Current (SSSTC) was tracked between 10 July 2011 and 19 January 2012. Tracking was accomplished with the software package WinJUPOS. The northern, southern eastern and western extremities of the anticyclone were measured on 83 different visible light images. All images were on the ALPO Japan Latest website. The longitude, latitude, north-to-south and east-to-west dimensions were measured over the time period. The main findings were that the drift velocity of the anticyclone changed abruptly on about 1 October. The average drift velocity before this date was 5.6 m s-1 and the average rate after this date was -2.1 m s-1. At about the same time as the drift velocity changed the latitude of the center of the anticyclone changed from 50.93 S (0.10) to 49.79 S (0.09) and the north-to-south dimension changed from 2.12 (0.06) to 2.47 (0.06). Uncertainties are in parentheses. It is suggested that the change in latitude led to the change in drift velocity. An interaction with a folded filamentary region nearby may have led to the change in latitude. Acknowledgements: This work was supported by a grant from the Presidents Faculty Development Initiative at Gordon College. The writer is also grateful to the 37 individuals who submitted their images for analysis.

Schmude, Richard W.

2012-10-01

90

Enhanced magnetization drift velocity and current polarization in (CoFe)1-xGex alloys  

NASA Astrophysics Data System (ADS)

We present measurements of current spin polarization and magnetization drift velocity in (CoFe)1-xGex alloys (x <=0 <=0.3), using a spin wave Doppler technique where spin wave transmission is measured between fixed-wavevector antennas coupled to current-carrying wires [1,2]. In a current density J, the transmission resonance frequency is shifted by ?f = kv/2?, where v=Jg?BP/(2eMs) is a magnetization drift velocity. Measurement of ?f allows calculation of v and current spin polarization P. With increasing Ge concentration, v increases dramatically from (3.1 0.2) m/s for CoFe to (8.2 0.6) m/s for (CoFe)0.7Ge0.3 (J= 10^11 A/m^2). We attribute this increase in drift velocity primarily to decreased magnetization. The current polarization increases from 0.84 0.04 for CoFe and reaches a maximum of 0.95 0.05 at approximately 25% Ge.[4pt] [1] V. Vlaminck and M. Bailleul, Science, 322, 410 (2008)[0pt] [2] M. Zhu, C. L. Dennis and R. D. McMichael, Phys. Rev. B. 81, 140407R (2010).

McMichael, Robert; Zhu, Meng; Soe, Brian; Carey, Matt; Maat, Stefan; Childress, Jeff

2011-03-01

91

Resolute Bay CADI ionosonde drifts, PolarDARN HF velocities, and cross polar cap potential  

NASA Astrophysics Data System (ADS)

In this study, velocities measured by the Rankin Inlet and Inuvik PolarDARN HF radars over Resolute Bay (RB) are compared with measurements from the RB CADI ionosonde to investigate the consistency of the measurements. Two types of comparisons are performed: 1-D, where each PolarDARN radar line-of-sight velocity is plotted against CADI velocity projected onto appropriate radar beam, and 2-D, where the PolarDARN merged velocity is compared with the full CADI vector. In both cases, velocities were found to statistically agree. For the 1-D comparison, the velocities were comparable in 85% of cases. For the 2-D comparison, a minor tendency for larger PolarDARN merge velocities (60 m/s) was noticed. The second task performed is a comparison of the SuperDARN cross polar cap potential (CPCP) and the CADI-based CPCP and their dependence on the CADI velocity. Linear dependences were found allowing for inter-conversion between these parameters. For large plasma drifts, the SuperDARN CPCPs were found to be much smaller than the CADI-based CPCPs hinting that the separation between the foci of a large-scale convection pattern is often underestimated in the SuperDARN convection mapping.

Mori, D.; Koustov, A. V.; Jayachandran, P. T.; Nishitani, N.

2012-01-01

92

Parametric excitation of a drift wave and associated ion heating by a modulated ion beam  

NASA Astrophysics Data System (ADS)

An ion beam modulated near the lower-hybrid frequency is injected into a low-beta plasma immersed in a longitudinal magnetic field. Parametric excitation of a drift wave and a lower-hybrid wave is observed. From the measurement of the threshold electric field, an RF field parallel to the magnetic field is found to play an important role in the excitation of the instability. Substantial increase of the ion and electron temperatures has been observed with the growth of the instability. Such a rapid heating may be principally due to the drift wave instability driven parametrically.

Yatsuzuka, M.; Satoh, K.; Nobuhara, S.; Yatsui, K.; Yokoyama, M.

1983-05-01

93

Ion mobility mass spectrometry of peptide ions: effects of drift gas and calibration strategies.  

PubMed

One difficulty in using ion mobility (IM) mass spectrometry (MS) to improve the specificity of peptide ion assignments is that IM separations are performed using a range of pressures, gas compositions, temperatures, and modes of separation, which makes it challenging to rapidly extract accurate shape parameters. We report collision cross section values (?) in both He and N(2) gases for 113 peptide ions determined directly from drift times measured in a low-pressure, ambient temperature drift cell with radio-frequency (rf) ion confinement. These peptide ions have masses ranging from 231 to 2969 Da, ?(He) of 89-616 (2), and ?(N(2)) of 151-801 (2); thus, they are ideal for calibrating results from proteomics experiments. These results were used to quantify the errors associated with traveling-wave ? measurements of peptide ions and the errors concomitant with using drift times measured in N(2) gas to estimate ?(He). More broadly, these results enable the rapid and accurate determination of calibrated ? for peptide ions, which could be used as an additional parameter to increase the specificity of assignments in proteomics experiments. PMID:22845859

Bush, Matthew F; Campuzano, Iain D G; Robinson, Carol V

2012-08-10

94

Experimental test of Baalrud's model for ion velocity at the sheath edge for a two ion species plasma  

NASA Astrophysics Data System (ADS)

Recent experiments have shown that ions in plasmas containing two ion species reach a common velocity at the sheath-presheath boundary [1]. A new theory [2] suggests that collisional friction between the two ion species enhanced by two stream instability affects the drift velocity of each ion species near the sheath edge and finds that the difference in ion velocities at the sheath-presheath boundary is given by ?12? (v^2th1+ ?v^2th2), where ?= n1M1/(n2M2). We report the first experimental test of this model. We measure ion velocity distribution functions (ivdfs) near sheath edge in Argon/Xenon and Argon/Helium plasmas as a function of the concentration ratios. We show that for sufficiently great relative Xenon concentration, ions do not reach a common speed at the sheath edge. The relative concentration of the two ion species, which determines ?, is inferred from Ion Acoustic Wave phase velocity measurements, the ivdfs are determined by Laser Induced Florescence. [1] Lee, D; Hershkowitz, N; Severn, GD. Appl. Phys. Lett. 91, 041505 (2007) [2] S.D. Baalrud, J.D. Callen, and C.C. Hegna, GEC 2009

Hershkowitz, Noah; Yip, Chi-Shung; Severn, Greg

2009-11-01

95

Measurements of Ion Drifts and Thermospheric Neutral Winds at the Jicamarca Radio Observatory  

Microsoft Academic Search

Measurements of ion drifts and thermospheric neutral winds obtained simultaneously with zonal and vertical ion drift measurements of F-region plasma have been made at the Jicamarca Radio Observatory at different times during the year since August, 2009. This period is coincident with an anomalous period of extremely low solar activity. For campaigns taking place in September, 2009, March, 2010, and

J. W. Meriwether; L. Navarro; J. L. Chau; B. G. Fejer

2010-01-01

96

A study of vacuum arc ion velocities using a linear set of probes  

SciTech Connect

The most likely velocity of ions moving away from vacuum arc cathode spots was measured using a set of probes along the path of plasma expansion. The goal was to determine how much, if any, change of the ion drift velocity occurs in the expanded plasma. The arc discharge current was perturbed to create plasma density markers whose travel is picked up by the set of probes. It was found that the perturbation with current oscillations did not result in consistent data because ion current maxima and minima are not only determined by the plasma production but by the transients of the arc pulse and by the asymmetry of the ion velocity distribution function. Perturbation with a short current spike was more conclusive. The ion velocity was measured to be slightly reduced with increasing distance from the cathode, which can be explained by collisions of ions with the background of neutrals. The ion velocity was increased when the arc current was increased, which correlated with enhanced arc voltage and power dissipation. The ion velocity could be enhanced when the plasma was produced in a non-uniform magnetic field.

Hohenbild, Stefan; Grubel, Christoph; Yushkov, Georgy Yu.; Oks, Efim M.; Anders, Andre

2008-07-15

97

Using Fiber Optics to Measure Carrier Drift Velocity of Germanium at 40mK  

NASA Astrophysics Data System (ADS)

The Cryogenic Dark Matter Search (CDMS) uses ultrapure germanium detectors at milliKelvin temperatures to attempt to directly detect weakly interacting massive particles (WIMPs), a candidate for dark matter. When some particle interacts with the crystal structure, ionization and phonon signals are produced. Each particle interaction gives off a unique ratio of ionization signal to phonon signal. In this way, background noise can be separated from events that may involve WIMPs. Current germanium detectors are about the size of a hockey puck. If detectors can be made larger, there would be a greater probability of having a WIMP interaction. To make larger detectors, we need to better understand carrier transport processes in the germanium detectors. So, we measured the carrier drift velocity at 40milliKelvin, the temperature at which detectors operate. The carrier drift velocity gives us insight into how much impurity is present in the germanium detectors. We made this measurement using a fiber optics line. The fiber optics line allowed us to carry light from a 780nm laser diode at room temperature, into our dilution refrigerator and onto a germanium detector at 40milliKelvin. A laser diode allowed us to create electron-hole pairs on the surface of a germanium detector in a much more precise way than a radiation source.

Lam, Albert

2010-11-01

98

Neutralized Drift Compression Experiments (NDCX) with a HighIntensity Ion Beam  

SciTech Connect

To create high energy density matter and fusion conditions, high-power drivers, such as lasers, ion beams, and x-ray drivers, are employed to heat targets with pulses short compared to hydro-motion. Both high energy density physics and ion-driven inertial fusion require the simultaneous transverse and longitudinal compression of an ion beam to achieve high intensities. We have previously studied the effects of plasma neutralization for transverse beam compression. The scaled experiment, the Neutralized Transport Experiment (NTX), demonstrated that an initially un-neutralized beam can be compressed transversely to {approx}1 mm radius when charge neutralization by background plasma electrons is provided. Here we report longitudinal compression of a velocity-tailored, intense, neutralized 25 mA K+ beam at 300 keV. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity tilt that longitudinally compresses the neutralized beam, enhances the beam peak current by a factor of 50 and produces a pulse duration of about 3 ns. The Physics of longitudinal compression, experimental procedure, and the results of the compression experiments are presented.

Roy, P.K.; Yu, S.S.; Waldron, W.L.; Anders, A.; Baca, D.; Barnard, J.J.; Bieniosek, F.M.; Coleman, J.; Davidson, R.C.; Efthimion,P.C.; Eylon, S.; Friedman, A.; Gilson, E.P.; Greenway, W.G.; Henestroza,E.; Kaganovich, I.; Leitner, M.; Logan, B.G.; Sefkow, A.B.; Seidl, P.A.; Sharp, W.M.; Thoma, C.; Welch, D.R.

2006-07-08

99

Toroidal ion-pressure-gradient-driven drift instabilities and transport revisited  

Microsoft Academic Search

A unified theory of ion-pressure-gradient-driven drift wave instabilities and transport is presented, which ties the long-wavelength trapped-ion mode to the moderate-wavelength hydrodynamic mode in toroidal geometry. An analytic dispersion relation that retains ion drift resonances, and keeps the leading-order contribution from finite Larmor radius effects and parallel compressibility, is derived. Results indicate that the slab and toroidal branches of these

H. Biglari; P. H. Diamond; M. N. Rosenbluth

1989-01-01

100

Quantum engineering of nanoelectronic devices: the role of quantum emission in limiting drift velocity and diffusion coefficient  

Microsoft Academic Search

Quantum emission is possible when an electron, after traversing an inelastic scattering length, emits a quantum of energy. Diffusive and drift electron transport in a semiconductor subjected to an applied electric field is evaluated using a steady-state asymmetric distribution function that takes into account quantum-emission-induced modification of the mean free path. The drift velocity of an electron is shown to

V. K Arora

2000-01-01

101

Impurity effect on the toroidal ion temperature gradient driven drift mode in a multispecies plasma  

Microsoft Academic Search

The effect of an impurity ion species on the toroidal-ion temperature-gradient driven drift mode is analysed using the fluid model. It is found that the impurity exerts a stabilizing influence when the main species and the impurity ion density profiles are either flat or inwardly peaked and the ion thermal conductivity is neglected; however, when the latter is included, this

G. Murtaza; M. Nadeem; P. K. Shukla

1993-01-01

102

High frequency drift waves with wavelengths below the ion gyroradius in equatorial spread F. Interim report  

Microsoft Academic Search

Evidence is given for intense VHF and UHF radar backscatter during equatorial Spread F resulting from irregularities of 1 meter and 36 cm, respectively. The linear theory for high frequency drift waves, generated by the drift-cyclotron and lower-hybrid-drift instabilities, is presented. This linear theory is set forth as a possible explanation for the occurrence of these irregularities below the ion

J. D. Huba; P. K. Chaturvedi; S. L. Ossakow; D. M. Towle

1978-01-01

103

The Influence of Drift Gas Composition on the Separation Mechanism in Traveling Wave Ion Mobility Spectrometry: Insight from Electrodynamic Simulations  

PubMed Central

The influence of three different drift gases (helium, nitrogen, and argon) on the separation mechanism in traveling wave ion mobility spectrometry is explored through ion trajectory simulations which include considerations for ion diffusion based on kinetic theory and the electrodynamic traveling wave potential. The model developed for this work is an accurate depiction of a second-generation commercial traveling wave instrument. Three ion systems (cocaine, MDMA, and amphetamine) whose reduced mobility values have previously been measured in different drift gases are represented in the simulation model. The simulation results presented here provide a fundamental understanding of the separation mechanism in traveling wave, which is characterized by three regions of ion motion: (1) ions surfing on a single wave, (2) ions exhibiting intermittent roll-over onto subsequent waves, and (3) ions experiencing a steady state roll-over which repeats every few wave cycles. These regions of ion motion are accessed through changes in the gas pressure, wave amplitude, and wave velocity. Resolving power values extracted from simulated arrival times suggest that momentum transfer in helium gas is generally insufficient to access regions (2) and (3) where ion mobility separations occur. Ion mobility separations by traveling wave are predicted to be effectual for both nitrogen and argon, with slightly lower resolving power values observed for argon as a result of band-broadening due to collisional scattering. For the simulation conditions studied here, the resolving power in traveling wave plateaus between regions (2) and (3), with further increases in wave velocity contributing only minor improvements in separations.

May, Jody C.; McLean, John A.

2013-01-01

104

A Multiscale Analysis of the Relationship Between Current Velocity and Invertebrate Drift: Do Faster Currents Transport More Food?  

NASA Astrophysics Data System (ADS)

Salmonids may select feeding stations to maximize their net energy intake (NEI). Variation in NEI is based on the assumption that there is a positive linear relationship between food availability and current velocity. Three to four drift samples were collected from each of three riffles nested in three reach types nested in three Rocky Mountain streams for 4 to 6 weeks. We calculated regressions between current velocity at the net, Reynolds number for a riffle, and slope for a reach against the biomass of invertebrates collected for 10 hours during the day and again at night at each scale. We expected positive correlations between drift and current velocity within the same riffle because the effects of other factors on drift should be similar within the same riffle (e.g. benthic densities). Ninety percent of the regression slopes for nets within riffles were not different from zero. However, the number of positive slopes increased as scale increased when we compared hydraulically rough to smooth riffles and steep to low-gradient reaches. Rougher riffles and steeper reaches tended to produce more drift than smooth riffles and low-gradient reaches. Drift density was not correlated with current velocity within riffles, but became more predictable at intermediate scales.

Rader, R. B.

2005-05-01

105

Toroidal Momentum Pinch Velocity due to the Coriolis Drift Effect on Small Scale Instabilities in a Toroidal Plasma  

SciTech Connect

In this Letter, the influence of the ''Coriolis drift'' on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiment000.

Peeters, A. G.; Angioni, C. [Max Planck Institut fuer Plasmaphysik, EURATOM Association, Boltzmannstrasse 2 85748 Garching (Germany); Strintzi, D. [National Technical University of Athens, Euratom Association, GR-15773 Athens (Greece)

2007-06-29

106

Toroidal momentum pinch velocity due to the coriolis drift effect on small scale instabilities in a toroidal plasma.  

PubMed

In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments. PMID:17678096

Peeters, A G; Angioni, C; Strintzi, D

2007-06-28

107

Visualization of Trajectories of Electron Beams Emitted by an IonSource with Closed Electron Drift  

SciTech Connect

Trajectories of electron beams emitted by an ion source with an anode layer and Hall electron closed drift orbits were visualized using light emission from a working gas excited by electrons. Gas discharge of magnetron type, arising in the beam drift region under the influence of an electric field of a target bias potential, was visualized.

Institue of Physics, National Academy of Sciences of Ukraine; Brown, Ian G.; Bordenjuk, Ian V.; Panchenko, Oleg A.; Sologub, Sergei V.; Brown, Ian G.

2007-10-01

108

Non-Maxwellian ion velocity distributions observed using EISCAT  

Microsoft Academic Search

Recent observations from the EISCAT incoherent scatter radar have revealed bursts of poleward ion flow in the dayside auroral ionosphere which are consistent with the ionospheric signature of flux transfer events at the magnetopause. These bursts frequently contain ion drifts which exceed the neutral thermal speed and, because the neutral thermospheric wind is incapable of responding sufficiently rapidly, toroidal, non-Maxwellian

M. Lockwood; B. J. I. Bromage; R. B. Horne; J. H. St-Maurice; D. M. Willis; S. W. H. Cowley

1987-01-01

109

Ion velocity distribution function measurements in a helium helicon plasma  

Microsoft Academic Search

Summary form only given. The scarcity of strong absorption lines in accessible tuning ranges along with plasma saturation due to low ion population densities makes laser absorption spectroscopy of helium ions in plasma notoriously difficult. Helicon plasmas, with their characteristically high ion densities are a good candidate for helium ion spectroscopy experiments. Initial measurements of Doppler broadened ion velocity distribution

E. Scime; R. Murphy; I. Biloiu; C. Compton

2006-01-01

110

Auroral bright spot sequence near 14 MLT. Coordinated optical and ion drift observations.  

National Technical Information Service (NTIS)

Optical observations of a dayside auroral brightening sequence, by means of all-sky TV cameras and meridian scanning photometers, have been combined with EISCAT ion drift observations within the same invariant latitude - MLT sector. The reported events, c...

P. E. Sandholt B. Lybekk M. Lockwood A. D. Farmer

1990-01-01

111

Ion upflow enhanced by drifting F-region plasma structure along the nightside polar cap boundary  

NASA Astrophysics Data System (ADS)

Conjugate observations by the incoherent scatter radar at Sondrestrom, Greenland, and the Wideband Imaging Camera (WIC) on the IMAGE satellite have been used to establish a causal relationship between drifting F-region plasma structure in the polar ionosphere and upward ion number flux near the poleward edge of the auroral oval. A longitudinally extended patch of enhanced F-region density was observed as it advected equatorward across the open-closed field line boundary and into a region of discrete auroral rays and strong ion upflow (Vi > 800 m/s at 900 km altitude). Upward velocities within the upflow region remained constant during the patch transit, such that the upflowing number flux was directly controlled by F-region density (both increased by a factor of 2 within the patch). Because polar cap patches and ion upflows are both longitudinally extended, quasi-stable features of the nightside polar cap boundary, the observed interaction can produce a global-scale increase in plasma density at higher altitudes where suprathermal outflows are initiated.

Semeter, J.; Heinselman, C. J.; Thayer, J. P.; Doe, R. A.; Frey, H. U.

2003-11-01

112

Early-time Velocity Autocorrelation for Charged Particles Diffusion and Drift in Static Magnetic Turbulence  

NASA Astrophysics Data System (ADS)

Using test-particle simulations, we investigate the temporal dependence of the two-point velocity correlation function for charged particles scattering in a time-independent spatially fluctuating magnetic field derived from a three-dimensional isotropic turbulence power spectrum. Such a correlation function allowed us to compute the spatial coefficients of diffusion both parallel and perpendicular to the average magnetic field. Our simulations confirm the dependence of the perpendicular diffusion coefficient on turbulence energy density and particle energy predicted previously by a model for early-time charged particle transport. Using the computed diffusion coefficients, we exploit the particle velocity autocorrelation to investigate the timescale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation timescales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of strong and weak magnetic turbulence are compared for various values of the ratio of the particle gyroradius to the correlation length of the magnetic turbulence. Our simulation parameters can be applied to energetic particles in the interplanetary space, cosmic rays at the supernova shocks, and cosmic-rays transport in the intergalactic medium.

Fraschetti, F.; Giacalone, J.

2012-08-01

113

Drift tubes for a focusing channel of ion linear accelerator  

Microsoft Academic Search

An open-to-vacuum drift tube with nonorganic (i.e. rare-earth) magnetic quadrupole lens elements has been developed. This design almost completely eliminates local deteriorations of vacuum quality leading to multipactor RF discharges. Drift tubes of this type have been manufactured and installed in the 56-MeV proton linac. The resonator would provide an output energy of 10 MeV. Descriptions are given of the

I. M. Kapchinskij; V. S. Skachkov; A. M. Kozodaev; V. V. Kurakin; R. P. Kuybida; N. V. Lazarev; E. A. Levashova; A. P. Preobragenskij; A. V. Selin; R. M. Vengrov; V. L. Zuev

1989-01-01

114

A Multiscale Analysis of the Relationship Between Current Velocity and Invertebrate Drift: Do Faster Currents Transport More Food?  

Microsoft Academic Search

Salmonids may select feeding stations to maximize their net energy intake (NEI). Variation in NEI is based on the assumption that there is a positive linear relationship between food availability and current velocity. Three to four drift samples were collected from each of three riffles nested in three reach types nested in three Rocky Mountain streams for 4 to 6

R. B. Rader

2005-01-01

115

Alkalinity, Discharge, Average Velocity, and Invertebrate Drift Concentration in Subarctic Alaskan Streams  

Microsoft Academic Search

This study measured the associations of alkalinity, current and invertebrate drift among 13 streams in subarctic Alaska. A significant positive correlation was found between alkalinity and drift concentration expressed as numbers per unit volume. Significant inverse relations were found between stream discharge and drift concentration expressed as either numbers or weight. This dilution was to be expected since stream wetted

Jacqueline Doyle LaPerriere

1983-01-01

116

Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions  

NASA Astrophysics Data System (ADS)

From most in-situ plasma observations made in the outer heliosphere it became evident that above the injection border of pick-up ions (?1 keV), an extended suprathermal ion tail is found which in most cases can be fitted by a power law with velocity power indices of (-6) ? ?v ? (-4). As has been shown by theory such energetic ion tails cannot be explained by Fermi-2 type velocity diffusion, since in the outer heliosphere both Alfvenic and magnetoacoustic turbulences become too weak. Here we come to a new solution of this unsolved problem by studying the action of solar wind bulk velocity fluctuations on ions co-moving with the wind. As we show the passage of such fluctuations results in energization of each individual ion and systematic evolution of the ion distribution function towards suprathermal tails. From the basic knowledge that we can obtain on this process we can calculate the velocity divergence of the ion phasespace flow and thus can derive a velocity diffusion operator. As we can show here this operator leads to a velocity diffusion coefficient proportional to the square of the ion velocity and, when employed in the phasespace transport equation, together with terms for convective changes, cooling processes and pick-up ion injection, interestingly enough, permits to find solutions for suprathermal power law tails with power indices of ?v ? -5 as very often observed.

Fahr, H.-J.; Chashei, I. V.; Siewert, M.

2012-01-01

117

Velocity distribution of ion beams from the RIKEN IGISOL  

Microsoft Academic Search

A direct measurement of the velocity distribution of ion beams from an ion-guide isotope separator on-line (IGISOL) was carried out at RIKEN with a technique of laser spectroscopy. The skimmer-potential and gas-cell pressure dependence of the velocity distribution were also measured. The velocity distribution was found to be about two times narrower than that estimated from the mass resolving power

M. Koizumi; A. Yoshida; K. Morita; M. Takami; T. T. Inamura; M. Azuma; H. Katsuragawa; M. Nakaoka; I. Nakamura; T. Ishizuka; T. Murayama; A. Iivonen; K. Valli; K. Shimomura; S. Matsuki; I. Sugai

1992-01-01

118

Parametric excitation of the drift wave by a modulated ion beam  

NASA Astrophysics Data System (ADS)

Parametric excitation of the drift wave is observed by an ion beam modulated near the lower-hybrid frequency. An rf field parallel to the magnetic field is found to play an important role in the excitation of the instability. Substantial increase of the ion and electron temperatures is observed.

Yatsuzuka, Mitsuyasu; Satoh, Kikoh; Nobuhara, Sadao; Yatsui, Kiyoshi; Yokoyama, Masahiro

1983-05-01

119

Renormalized turbulence theory of ion pressure gradient driven drift modes  

Microsoft Academic Search

From the nonlinear gyrokinetic equation we formulate the renormalized turbulence equation for the eta\\/sub i\\/-mode drift wave instability. The study shows that the dominant nonlinear damping mechanism is from the E x B convection of the pressure fluctuation and that the kinetic modifications to the fluid E x B mode coupling, studied earlier, shift the spectrum toward the shorter wavelengths.

B. G. Hong; D. I. Choi; W. Jr. Horton

1985-01-01

120

High velocity ion microprobes and their source requirements (invited)  

SciTech Connect

For many years, beams of high velocity ions have been widely used for relatively nondestructive investigation of surfaces or thin films. Many properties may be investigated, associated with the large number of interactions, most of the information obtained being complementary to that from high velocity electron beams or low velocity ion beams. Recently there has been increasing interest in the application of microbeams of these high velocity ions and two streams of activity have emerged{emdash}one using traditional techniques and requiring beams of hundreds of picoamps to give spatial resolutions of the order of 1 {mu}m, the other using many new techniques and requiring currents from femtoamps down to single ions to give resolutions of an order of magnitude better. In both cases, the resolution is limited by the low brightness of ion sources commonly used in high energy ion accelerators. These energies commonly are of the order of 3 MeV for very light ions, but there are several developing fields in which much higher energies and heavier ions are of interest. This paper looks at the wide range of information obtainable with these high velocity ion microprobes, the limitations placed on them by their ion optics, the great improvements which would flow in all cases from the development of better ion sources, the best candidates for such sources, and some recent progress. {copyright} {ital 1996 American Institute of Physics.}

Legge, G.J.; Moloney, G.R.; Colman, R.A.; Allan, G.L. [School of Physics, Micro Analytical Research Centre (MARC), The University of Melbourne, Parkville, Vic. 3052 (Australia)

1996-03-01

121

EISCAT measurements of ion temperatures which indicate nonisotropic ion-velocity distributions  

Microsoft Academic Search

Substantial increases of the ion temperature can be observed at high latitudes as a consequence of strong convection electric fields. EISCAT measurements of three independent components of the ion velocity vector and temperature in the same scattering volume at about 300 km are reported. During periods of strong variations in ion velocity (consequently of the E-field), the ion temperatures derived

S. Perraut; A. Brekke; M. Baron; D. Hubert

1984-01-01

122

Variation of Surface - Acoustic - Wave Velocity Produced by Ion Implantation  

Microsoft Academic Search

The elastic and piezoelectric properties of substrates used in SAW devices have been changed by ion implantation. A crystalline structure is perturbed by implanted ions and an amorphous region can be obtained. The velocities of the Rayleigh waves on the implanted and unimplanted surfaces are different. The thickness of the perturbed layer depends on the kind of ion and substrate,

P. Hartemann; M. Morizot

1974-01-01

123

Renormalized turbulence theory of ion pressure gradient driven drift modes  

Microsoft Academic Search

From the nonlinear gyrokinetic equation we formulate the renormalized turbulence equation for the &eegr;i -mode drift wave instability. The study shows that the dominant nonlinear damping mechanism is from the EB convection of the pressure fluctuation and that the kinetic modifications to the fluid EB mode coupling, studied earlier, shift the spectrum toward the shorter wavelengths. Balancing the linear growth

Bong-Guen Hong; Duk-In Choi; W. Horton Jr.

1986-01-01

124

Toroidal drift-wave fluctuations driven by ion pressure gradients  

Microsoft Academic Search

Dynamic equations for the electrostatic potential and pressure fluctuations in the ballooning drift modes are shown to lead to a turbulent state described by the mixing length theory for saturation. The nonlinear states are compared with previously given formulae for the root-mean-square amplitudes of the fluctuations and the k, omega structure of the fluctuations. The parametric dependence of the root-mean-square

D. Brock; W. Horton

1982-01-01

125

First simultaneous measurements of thermospheric winds and zonal ion drifts from the Jicamarca Radio Observatory  

NASA Astrophysics Data System (ADS)

The first simultaneous observations of thermospheric winds and zonal ion drifts have been ob-tained at the Jicamarca Radio Observatory using a new Fabry-Perot interferometer observatory installed on a mountain ridge overlooking the valley where the JRO radar is located. The re-sults show that the neutral winds and ion drifts generally have the same speed and temporal variation characteristics. These results illustrate the simultaneous detection of the midnight temperature maximum as well. The paper will also describe efforts to obtain common volume measurements of thermospheric winds and temperatures utilizing the FPI Arequipa observatory which is located 4 degrees south of the geomagnetic equator.

Meriwether, John; Baker, Brooke; Twork, Greg; Chau, Jorge; Veliz, Oskar; Woodman, Ronald; Hedden, Russell; Hysell, David

126

CRADA Final Report CRADA No. LB05-001820"Ion Beam Drift Compression Technology for NDCX"  

SciTech Connect

Summary of the specific research and project accomplishments: Through this collaboration, LBNL and FPSI determined the specific energy manipulations that apply to the Neutralized Drift Compression Experiment (NDCX) ion beam and developed the preliminary design of a Fast Induction Energy Corrector (FIEC). This effort was successfully completed, firmly establishing the technical feasibility of the proposed approach for regulating the longitudinal energy distribution of the NDCX ion beam. This is a critical step in achieving the NDCX goal of axial compression of the beam by a factor of 100 during neutralized drift.

First point Scientific, Inc.; E.O. Lawrence Berkeley National Laboratory; Waldron, William L.

2009-10-05

127

Spectator-velocity pions from heavy ions  

SciTech Connect

The discussion centers on pions in the velocity regions of target and projectile, where strong spectral features appear. The topics covered include stopped-pion studies, and convoy pions in the projectile frame. (GHT)

Rasmussen, J.; Ridout, J.; Murphy, D.; Radi, H.M.A.

1982-11-01

128

Hybrid drift-kinetic electron/full kinetic ion PIC simulation of RF plasma discharge in magnetic mirror machine  

NASA Astrophysics Data System (ADS)

We present numerical simulations of a radio-frequency- (RF-) induced plasma discharge in magnetic mirror machines, with relevance to Electron Cyclotron Ion Source (ECRIS) devices. The simulations are done in 2D cylindrically symmetric geometry. The code SIMPL is a PIC code, which uses drift-kinetic electron and full kinetic ion description. The RF wave heating is implemented as a ``kick'' model, i.e., electrons get an increment in their perpendicular velocity when they cross the magnetic resonance surface. Atomic physics is for Argon and includes the following basic reactions: single ionization by electron impact, excitation, elastic scattering, and charge exchange. We will discuss the steady-state spatial structure of the discharge.

Evstatiev, Evstati

2012-10-01

129

Kolmogorov spectra of long wavelength ion-drift waves in dusty plasmas  

NASA Astrophysics Data System (ADS)

Weakly turbulent Kolmogorov spectra of ion-drift waves in dusty plasmas with an arbitrary ratio between the ion-drift and the Shukla-Varma frequencies are investigated. It is shown that in the long wavelength limit, when the contribution to the wave dispersion associated with the inhomogeneity of the dust component is larger than that related to the plasma inhomogeneity, the wave dispersion and the matrix interaction element coincide with those for the Rossby or the electron-drift waves described by the Charney or Hasegawa-Mima equations with an accuracy of unessential numerical coefficients. It is found that the weakly turbulent spectra related to the conservation of the wave energy are local and thus the energy flux is directed towards smaller spatial scales.

Onishchenko, O. G.; Pokhotelov, O. A.; Sagdeev, R. Z.; Pavlenko, V. P.; Stenflo, L.; Shukla, P. K.; Zolotukhin, V. V.

2002-05-01

130

Measurement of Effective Drift Velocities of Electrons and Holes in Shallow Multiple Quantum Well P-I Modulators  

NASA Astrophysics Data System (ADS)

P-i-n diodes containing multiple quantum wells (MQWs) in the i-region are the building blocks for photonic devices. When we apply electric field across these devices and illuminate it with light, photo-carriers are created in the i-region. These carriers escape from the wells and drift toward the electrodes; thus photo-voltage is created. The rise- and decay-times of photo-voltages are related to the transport of carriers. In this dissertation, we present theoretical and experimental studies on carrier transport mechanisms of three shallow MQW GaAs/Al _{x}Ga_{1-x}As p-i-n diodes (x = 0.02, 0.04, 0.08) at various bias voltages. We start with the description of the sample structures and their package. We then present the characteristics of these samples including their transmission spectra and responsivity. We will demonstrate that the over-all high quality of these samples, including a strong exciton resonant absorption, ~100% internal quantum efficiencies and completely depleted i-region at bias between +0.75 V to -5 V bias. In our theoretical studies, we first discuss the possible carrier sweep-out mechanisms and estimate the response times associated with these mechanisms. Based on our theoretical model, we conclude that only the drift times of carriers and enhanced diffusion times are important for shallow MQW p-i-n diodes: at high bias, the fast drift times of electrons and holes control the rise-times; at low bias, the slow drift times of holes and the enhanced diffusion times control the decay-times. We have performed picosecond time-resolved pump/probe electro-absorption measurements on these samples. We then obtained the drift times, effective drift velocities and effective mobilities of electrons and holes for these devices. We find that the carrier effective drift velocities (especially for holes) seemed insensitive to the Al concentration in the barriers (in the range of x = 2% to 8%), even though the x = 2% sample does show an overall faster response time. We think the slight difference of the rise- and decay-times of these devices may also be affected by random differences between the samples.

Yang, Ching-Mei

1995-01-01

131

Auroral bright spot sequence near 1,400 MLT: Coordinated optical and ion drift observations  

SciTech Connect

Optical observations of a dayside auroral brightening sequence, by means of all-sky TV cameras and meridian scanning photometers, have been combined with EISCAT ion drift observations within the same invariant latitude - MLT sector. The characteristic intermittent optical events, covering {approximately}300 km in east-west extent, move eastward (antisunward) along the poleward boundary of the persistent background aurora at velocities of {approximately}1.5 in s {sup {minus}1} and are associated with ion flows which swing from eastward to westward, with a subsequent return to eastward, during the interval of a few minutes when there is enhanced auroral emission within the radar field of view. The breakup of discrete auroral forms occurs at the reversal (negative potential) that forms between eastward plasma flow, maximizing near the persistent arc poleward boundary, and strong transient westward flow to the south. These observations are discussed in relation to recent models of boundary layer plasma dynamics and the associated magnetosphere-ionosphere coupling. The ionospheric events may correspond to large-scale wavelike motions of the low-latitude boundary layer (LLBL)/plasma sheet (PS) boundary. On the basis of this interpretation the observed spot size, speed and repetition period ({approximately}10 min) give a wavelength (the distance between spots) of {approximately}900 km in the present case. The events can also be explained as ionospheric signatures of newly opened flux tubes associated with reconnection bursts at the magnetopause near 1,400 MLT. The authors also discuss these data in relation to random, patchy reconnection.

Sandholt, P.E.; Lybekk, B. (Univ. of Oslo (Norway)); Lockwood, M.; Farmer, A.D. (Rutherford Appleton Lab., Chilton (England))

1990-12-01

132

Generation of zonal flows by electrostatic drift waves in electron-positron-ion plasmas  

NASA Astrophysics Data System (ADS)

Generation of large-scale zonal flows by comparatively small-scale electrostatic drift waves in electron-positron-ion plasmas is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves having arbitrary wavelengths (as compared with the ion Larmor radius of plasma ions at the plasma electron temperature). Temperature inhomogeneity of electrons and positrons is taken into account assuming ions to be cold. To describe the generation of zonal flow generalized Hasegawa-Mima equation containing both vector and two scalar (of different nature) nonlinearities is used. A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. Enriched possibilities of zonal flow generation with different growth rates are revealed. The present theory can be used for interpretations of drift wave observations in laboratory and astrophysical plasmas.

Kaladze, T. D.; Shad, M.; Tsamalashvili, L. V.

2010-02-01

133

Ion velocity distributions in electron cyclotron resonance plasmas  

Microsoft Academic Search

For applications in ultra-large scale integration, low pressure, high density plasmas are being developed for etching and deposition of thin films. To control critical parameters such as the flux and energy distribution of ions impacting surfaces, it is necessary to understand how these parameters are influence by physical and electromagnetic design. In this work, we report measurements of ion velocity

Richard A. Gottscho; Toshiki Nakano; Nader Sadeghi; Dennis J. Trevor; R. W. Boswell

1992-01-01

134

Effects of Applied Rotating Magnetic Perturbations on Ion Drift Orbits in the Compact Auburn Torsatron  

Microsoft Academic Search

A technique of modification of the drift orbits of ions by the application of swept-frequency, rotating magnetic perturbations has been successfully applied on the Compact Auburn Torsatron(B=0.1T). In this experiment, test particle lithium ions in the energy range 10-20 eV were produced by a collimated, movable source. Driven magnetic perturbations of variable rotation frequency are imposed with ac currents in

D. Pritchard; R. Gandy; S. Knowlton; E. Thomas Jr.

1996-01-01

135

Nonuniform charging effects on ion drag force in drifting dusty plasmas  

SciTech Connect

The nonuniform polarization charging effects on the ion drag force are investigated in drifting dusty plasmas. The ion drag force due to the ion-dust grain interaction is obtained as a function of the dust charge, ion charge, plasma temperature, Mach number, Debye length, and collision energy. The result shows that the nonuniform charging effects enhance the momentum transfer cross section as well as the ion drag force. It is found that the momentum transfer cross section and the ion drag force including nonuniform polarization charging effects increase with increasing the Mach number and also the ion drag force increases with increasing the temperature. In addition, it is found that the ion drag force is slightly decreasing with an increase of the Debye length.

Chang, Dong-Man; Chang, Won-Seok; Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2006-03-01

136

Fully toroidal ion temperature gradient driven drift modes  

Microsoft Academic Search

A simple quadratic dispersion relation is derived for electrostatic ion temperature gradient driven modes without expansion in the inverse aspect ratio. It is also shown that these modes experience the local curvature only on the outside of the magnetic surface.

A. Jarmn; P. Andersson; J. Weiland

1987-01-01

137

Low velocity ion stopping in binary ionic mixtures  

SciTech Connect

Attention is focused on the low ion velocity stopping mechanisms in multicomponent and dense target plasmas built of quasiclassical electron fluids neutralizing binary ionic mixtures, such as, deuterium-tritium of current fusion interest, proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam production of warm dense matter at Bragg peak conditions. The target plasma is taken in a multicomponent dielectric formulation a la Fried-Conte. The occurrence of projectile ion velocities (so-called critical) for which target electron slowing down equals that of given target ion components is also considered. The corresponding multiquadrature computations, albeit rather heavy, can be monitored analytical through a very compact code operating a PC cluster. Slowing down results are systematically scanned with respect to target temperature and electron density, as well as ion composition.

Tashev, Bekbolat; Baimbetov, Fazylkhan [Department of Physics, Kazakh National University, Tole Bi 96, Almaty 480012 (Kazakhstan); Deutsch, Claude [LPGP (UMR-CNRS 8578), Universite Paris XI, 91405 Orsay (France); Fromy, Patrice [Direction de l'Informatique, Universite Paris XI, 91405 Orsay (France)

2008-10-15

138

Digital ionosonde measurements of the height variation of drift velocity in the southern polar cap ionosphere: Initial results  

NASA Astrophysics Data System (ADS)

During the late austral summer of 1995-1996 we operated an HF digital ionosonde located at Casey, Antarctica (66.3S, 110.5E, -80.8 corrected geomagnetic (CGM) latitude), in an experimental drift mode with the aim of resolving the height variation of drift velocity in the polar cap ionosphere. We devised control programs for a Digisonde Portable Sounder 4 to collect data at separate frequency-range gates corresponding to the E and F regions to investigate the differences in their motions. During a 4-day campaign commencing March 11, 1996, the mode values of the drift perpendicular to the magnetic field (V?) were 85ms-1 in the E region and 485ms-1 in the F region (using 10ms-1 bins and echoes from all heights in each region). Vertical profiles of drift velocity were obtained by sorting echoes into 10-km group-height bins. For measurements obtained within +/-3 hours of magnetic noon the average profile showed that in the lower E region V? increased approximately exponentially with true height. The corresponding velocity scale height was <9.0km at 105 km, where the gradient was >46.7ms-1km-1. The mean value of V? leveled off to about 700ms-1 above 120 km, where it remained up to the F region peak height. The vertical gradient was caused by the increase in collision frequencies at the lower heights. The F region field-aligned component of drift (V?) showed a strong diurnal variation, with mean values of -30ms-1 near noon and +60ms-1 during the night at a height of 180 km. The average over the whole day reveals a net upward drift of 30ms-1. This behavior is attributed to the interaction between the meridional components of the generally antisunward neutral wind (UN) and perpendicular drift (V?S) moving plasma down the field lines during the day and up the field lines during the night, with UN and V?S having net equatorward values when averaged over all day. While the E region drift direction tended to be aligned with the basic antisunward convection which dominates the F region above Casey, it also tended to show greater temporal variability in direction, suggesting a smaller-scale size and lifetime for the E region structures giving rise to the echoes. There were events lasting over 2 hours during which the drifts in the two regions were clearly resolved into different azimuths (by nearly 180 for two events). These transient directional shears show the time variability in the phase transition between an F region collisionless, magnetized plasma driven by the EB/B2 convection to an E region collisional, unmagnetized plasma driven by E and irregular neutral winds.

Parkinson, M. L.; Monselesan, D. P.; Smith, P. R.; Dyson, P. L.; Morris, R. J.

1997-10-01

139

Measurements of Ion Drifts and Thermospheric Neutral Winds at the Jicamarca Radio Observatory  

NASA Astrophysics Data System (ADS)

Measurements of ion drifts and thermospheric neutral winds obtained simultaneously with zonal and vertical ion drift measurements of F-region plasma have been made at the Jicamarca Radio Observatory at different times during the year since August, 2009. This period is coincident with an anomalous period of extremely low solar activity. For campaigns taking place in September, 2009, March, 2010, and September, 2010, the Jicamarca 50 MHz radar operated to measure both vertical ion drifts and horizontal neutral winds from 200 to 800 km. The Jicamarca Fabry-Perot interferometer (FPI) was installed in August, 2009, and measurements have been ongoing since first light on 15 August, 2010. The FPI instrument is located in an observatory installed on a hill overlooking the Jicamarca valley and located above the cloud inversion layer, which improved the chances of observing during local summer. This instrument after an upgrade in August 2010 is able to make zonal and meridional thermospheric wind and temperature measurements with an accuracy of 5 to 10 ms-1 and 15 to 30 K. Also obtained during the measurement campaigns with the JRO radar facility were simultaneous measurements of thermospheric winds from the FPI observatory located in Arequipa, Peru, which is located 4 degrees latitude to the south of Jicamarca. The results obtained generally showed good agreement between the observed neutral winds and ion drifts. The vertical variation of the ion drifts is significant from the early evening twilight period to midnight suggesting that the transition from the E-region dynamo to the F-region dynamo takes place rather slowly as compared with more active solar flux periods.

Meriwether, J. W.; Navarro, L.; Chau, J. L.; Fejer, B. G.

2010-12-01

140

Low velocity ion stopping in binary ionic mixtures  

Microsoft Academic Search

Attention is focused on the low ion velocity stopping mechanisms in multicomponent and dense target plasmas built of quasiclassical electron fluids neutralizing binary ionic mixtures, such as, deuterium-tritium of current fusion interest, proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam production of warm

Bekbolat Tashev; Fazylkhan Baimbetov; Claude Deutsch; Patrice Fromy

2008-01-01

141

Low-velocity ion slowing down in binary ionic mixtures  

Microsoft Academic Search

We focus our attention on the low ion velocity stopping mechanisms in a multicomponent and dense target plasmas built of quasi-classical electron fluids neutralizing binary ionic mixtures such as deuteriumtritium of current fusion interest, proton-helium like iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam

Bekbolat Tashev; Fazylkhan Baimbetov; Claude Deutsch; Patrice Fromy

2009-01-01

142

Low velocity ion stopping in multicomponent plasmas for WDM production  

NASA Astrophysics Data System (ADS)

In order to comply with several converging international endeavors (Berkeley, Darmstadt, Princeton...) aiming at heating thin solid foils into warm dense matter(solid density and eV temperature range)through the impact of intense and low velocity ion beams we focus our attention on multispecies target.Collisional and dielectric approaches are contrasted in the Bragg peak region of current operational interest.We evidence a critical ion projectile velocity Vp such as target electron stopping turns comparable to target ion stopping.Various simplifying approximations qualifying target ion stopping are thus thoroughly compared. The given critical velocity being somewhat reminiscent of an equivalent one in MFE associated with tokamak anomalous heating,we extend our investigation to the heating of magnetized targets as well.

Tashev, Bekbolat; Deutsch, Claude

2007-11-01

143

Studies of ions in a drift field: laser diagnostics of excited states and measurements of thermochemical properties at equilibrium  

SciTech Connect

A major technique for investigating the thermochemical properties of ions and their related clusters is the high pressure drift/mass spectrometer detection technique. A crucial question in this regard is the extent to which ions drifting in an electric field are thermalized. This paper is divided into two parts, one describing some laser techniques which are enabling an investigation of the possible presence of excited ions in a drift field, and secondly, a reporting of some recent findings and trends in the stability of ion clusters of single and mixed constituents.

Castleman, A.W. Jr.; Keesee, R.G.

1983-01-01

144

A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies  

Microsoft Academic Search

A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80400K) drift tube is presented. The\\u000a instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the\\u000a IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam\\u000a modulation for the ion mobility experiment is accomplished by an

Jody C. May; David H. Russell

2011-01-01

145

Drift wave driven zonal flows in electron-positron-ion plasmas  

NASA Astrophysics Data System (ADS)

The generation of large-scale zonal flows by small-scale electrostatic drift waves in electron-positron-ion (EPI) plasma is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves. To describe this process, the Hasegawa-Mima equation generalized for the case of EPI plasma is used. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. Dependence of the growth rate on the spectrum purity of the wave packet is also investigated. The relevant instability conditions are determined.

Kaladze, T. D.; Pokhotelov, O. A.; Shad, M.

2010-08-01

146

Prediction of peptide drift time in ion mobility mass spectrometry from sequence-based features  

PubMed Central

Background Ion mobility-mass spectrometry (IMMS), an analytical technique which combines the features of ion mobility spectrometry (IMS) and mass spectrometry (MS), can rapidly separates ions on a millisecond time-scale. IMMS becomes a powerful tool to analyzing complex mixtures, especially for the analysis of peptides in proteomics. The high-throughput nature of this technique provides a challenge for the identification of peptides in complex biological samples. As an important parameter, peptide drift time can be used for enhancing downstream data analysis in IMMS-based proteomics. Results In this paper, a model is presented based on least square support vectors regression (LS-SVR) method to predict peptide ion drift time in IMMS from the sequence-based features of peptide. Four descriptors were extracted from peptide sequence to represent peptide ions by a 34-component vector. The parameters of LS-SVR were selected by a grid searching strategy, and a 10-fold cross-validation approach was employed for the model training and testing. Our proposed method was tested on three datasets with different charge states. The high prediction performance achieve demonstrate the effectiveness and efficiency of the prediction model. Conclusions Our proposed LS-SVR model can predict peptide drift time from sequence information in relative high prediction accuracy by a test on a dataset of 595 peptides. This work can enhance the confidence of protein identification by combining with current protein searching techniques.

2013-01-01

147

A Statistical Model of the Electric Field and Field-aligned Ion Drift over Millstone Hill  

NASA Astrophysics Data System (ADS)

All Millstone Hill incoherent scatter radar data collected since 1978 are available through the Madrigal Database at MIT Haystack Observatory. A set of empirical models for basic and derived incoherent scatter parameters, including electron density Ne, electron and ion temperatures Te and Ti, electric field and parallel ion drift is being developed from this extensive dataset. Such models of the average behavior of key ionosphere-thermosphere (IT) parameters, based on long term accumulated data, are important for space weather studies not only in terms of quantitative descriptions of the IT system but also in terms of clarifying several outstanding scientific problems. This paper presents statistical models of the local electric field and geomagnetic-field-aligned ion drift in the ionospheric F-layer. All local (radar elevation > 45 degrees) ion line-of sight measurements are sorted into bins. The binning parameters are local time (0000-2400 LT), and day of year (season). Each data point has a corresponding solar flux index F10.7 and geomagnetic activity index Ap. A least-squares fit to all the data in each bin is computed to determine the electric field as a function of Ap and the field-aligned drift as a function of F107 and Ap. Unlike previous Millstone Hill local electric field models, the components of the drift are determined in a statistical sense rather than by first computing the parallel and perpendicular drift components from triplets of line-of-sight measurements. We will present the data distribution in each bin and discuss the main features of the results.

Holt, J. M.; Zhang, S.

2001-12-01

148

Resolving Structural Isomers of Monosaccharide Methyl Glycosides Using Drift Tube and Traveling Wave Ion Mobility Mass Spectrometry  

PubMed Central

Monosaccharide structural isomers including sixteen methyl-D-glycopyranosides and four methyl-N-acetylhexosamines were subjected to ion mobility measurements by electrospray ion mobility mass spectrometry. Two ion mobility-MS systems were employed: atmospheric pressure drift tube ion mobility time-of-flight mass spectrometry and a Synapt G2 HDMS system which incorporates a low pressure traveling wave ion mobility separator. All the compounds were investigated as [M+Na]+ ions in the positive mode. A majority of the monosaccharide structural isomers exhibited different mobility drift times in either system, depending on differences in their anomeric and stereochemical configurations. In general, drift time patterns (relative drift times of isomers) matched between the two instruments. Higher resolving power was observed using the atmospheric pressure drift tube. Collision cross section values of monosaccharide structural isomers were directly calculated from the atmospheric pressure ion mobility experiments and a collision cross section calibration curve was made for the traveling wave ion mobility instrument. Overall, it was demonstrated that ion mobility-mass spectrometry using either drift tube or traveling wave ion mobility is a valuable technique for resolving subtle variations in stereochemistry among the sodium adducts of monosaccharide methyl glycosides.

Li, Hongli; Giles, Kevin; Bendiak, Brad; Kaplan, Kimberly; Siems, William F.; Hill, Herbert H.

2013-01-01

149

Models and numerical simulation of velocity distribution of pickup ions  

NASA Astrophysics Data System (ADS)

Large manned spacecraft release and carry up a huge amounts of water in its orbital motion. Some of the neutral water molecules undergo charge exchange with the ambient ionospheric plasma and become what are called pick-up ions at Low Earth Orbit (LEO) altitudes. The purpose of this dissertation is to model those ions and predicts their effect on a space vehicle mounted ion probe so that a comparison between the model and measured data can be made. The velocity distribution of the pickup ions ( H2O+ ), which are created by charge exchange between released neutral water molecules from a space shuttle orbiter and the ambient ionospheric plasma at LEO altitudes, is systematically studied. The factors which affect the velocity distribution of the pickup ions are discussed. A partial differential equation of the pickup ion's distribution function in the frame fixed on the earth is derived based on the analysis of the pickup ion's source, loss, and collisions with other particles. The trajectories of the pickup ions in the frame moving with the space orbiter are analyzed. The influence of collisions between the pickup ions and other particles on the number of the ions collected by a payload ion probe is discussed and the probability of the collision in the path of the pickup ions from their creation place to an instrument mounted on the orbiter is studied. Three integral models are developed to calculated the velocity distribution of the pickup ions in the frame moving with the orbiter. The first one is for the pickup ions created in very cold neutral water gas, the second one is for the pickup ions created in warm neutral water gas and the third one is for the pickup ions created in very hot neutral water gas. The algorithms are discussed to numerically calculate the velocity distribution of the pickup ions in the frame fixed on the orbiter with the three models. To compare the models with the data from the Spherical Retarding Potential Analyzer (SRPA) mounted on the orbital space shuttle, a model and an algorithm are developed to calculate the velocity magnitude distribution of the pickup ions in the frame moving with the orbiter. The method to numerically simulate a payload SRPA output is studied and a method to estimate the ratio of the pickup ions in the total ions collected by the payload SRPA is obtained. The comparison between the simulation result and actual measurement data from the SRPA on mission TSS-1R and earlier missions on which the SRPA was flown shows that the models and algorithms obtained in the dissertation are correct for the situation of a large space platform at LEO altitudes and useful in analyzing the data of the ion probes mounted on similar spacecraft. With the models obtained in the dissertation, the influence of some factors to the velocity magnitude distribution of the ions collected by the payload SRPA and the to the telemetered output signal of the payload SRPA are analyzed. These factors include the angle between the magnetic induction vector of the geomagnetic field and the orbital velocity vector of the orbiter, the density of the released water source of the orbiter, some selected attitude angles of the orbiter and the payload position of the payload SRPA.

Zhang, Yinghui

1998-10-01

150

Lithium-ion drifting: Application to the study of point defects in floating-zone silicon  

SciTech Connect

The use of lithium-ion (Li{sup +}) drifting to study the properties of point defects in p-type Floating-Zone (FZ) silicon crystals is reported. The Li{sup +} drift technique is used to detect the presence of vacancy-related defects (D defects) in certain p-type FZ silicon crystals. SUPREM-IV modeling suggests that the silicon point defect diffusivities are considerably higher than those commonly accepted, but are in reasonable agreement with values recently proposed. These results demonstrate the utility of Li{sup +} drifting in the study of silicon point defect properties in p-type FZ crystals. Finally, a straightforward measurement of the Li{sup +} compensation depth is shown to yield estimates of the vacancy-related defect concentration in p-type FZ crystals.

Walton, J.T.; Wong, Y.K. [Lawrence Berkeley National Lab., CA (United States); Zulehner, W. [Wacker-Siltronic GmbH, Burghausen (Germany)] [and others

1997-04-01

151

Fundamental mode of ultra-low frequency electrostatic dust-cyclotron surface waves in a magnetized complex plasma with drifting ions  

NASA Astrophysics Data System (ADS)

The electrostatic dust-cyclotron (EDC) waves in a magnetized dusty plasma was reported that they could be excited by gravity in a collisional plasma [1]. Rosenberg suggested that EDC waves could be excited by ions drifting along the magnetic field in a collisional plasma containing dust grains with large thermal speeds [2]. The existing investigations, however, focus on EDC volume waves in which the boundary effects are not considered. In this work, we attempt to obtain some physical results concerning the fundamental mode of EDC surface wave and the stability of wave by utilizing a kinetic method. The EDC surface wave is assumed to propagate along an external magnetic field at the interface between the plasma and the vacuum. The plasma is comprised of drifting ions flowing along an external magnetic field. To derive the growth rate of surface waves, we employ the specular reflection boundary conditions. The EDC surface wave is found to be unstable when the ion drift velocity is larger than the phase velocity of the wave. In addition, the wave becomes to be more unstable if dust particles carry more negative charges.[4pt] [1] N. D'Angelo, Phys. Lett. A 323, 445 (2004).[0pt] [2] M. Rosenberg, Phys. Scr. 82, 035505 (2010).

Lee, Seungjun; Lee, Myoung-Jae

2012-10-01

152

Observation of Anomalous Ion Heating by Broadband Drift-Wave Turbulence  

SciTech Connect

Using laser induced fluorescence and passive spectroscopy on a magnetically confined low-temperature plasma, anomalous ion heating is observed which exceeds collisional heating from the electrons by a factor of up to five. Direct wave heating due to the 2.45 GHz microwave as well as stochastic heating by large-amplitude fluctuations could be ruled out as explanations. Good quantitative agreement is found when comparing the missing power in the ion species with heating power due to the dissipation of drift-wave turbulence. This turbulent energy transfer into the ion channel could have important consequences for the interpretation of transport in fusion plasmas.

Enge, S.; Birkenmeier, G.; Manz, P.; Ramisch, M.; Stroth, U. [Institut fuer Plasmaforschung, Universitaet Stuttgart, 70569 Stuttgart (Germany)

2010-10-22

153

Observation of anomalous ion heating by broadband drift-wave turbulence.  

PubMed

Using laser induced fluorescence and passive spectroscopy on a magnetically confined low-temperature plasma, anomalous ion heating is observed which exceeds collisional heating from the electrons by a factor of up to five. Direct wave heating due to the 2.45GHz microwave as well as stochastic heating by large-amplitude fluctuations could be ruled out as explanations. Good quantitative agreement is found when comparing the missing power in the ion species with heating power due to the dissipation of drift-wave turbulence. This turbulent energy transfer into the ion channel could have important consequences for the interpretation of transport in fusion plasmas. PMID:21231054

Enge, S; Birkenmeier, G; Manz, P; Ramisch, M; Stroth, U

2010-10-21

154

High-velocity tails on the velocity distribution of solar wind ions  

SciTech Connect

Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity [open quotes]tails[close quotes] on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1% of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V[sub B] + 10V[sub th] or beyond, where V[sub B] is the bulk velocity and V[sub th] the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved. 21 refs., 6 figs., 2 tabs.

Ogilvie, K.W. (Goddard Space Flight Center, Greenbelt, MD (United States)); Geiss, J. (Univ. of Bern (Swaziland)); Gloeckler, G. (Univ. of Maryland, College Park (United States)); Berdichevsky, D. (Highes-STX, Lanham, MD (United States)); Wilken, B. (Max-Plank-Institut fuer Aeronomie Katlenburg-Lindau (Germany))

1993-03-01

155

Arbitrary amplitude dust-acoustic double-layers in a warm dusty plasma with suprathermal electrons, two-temperature thermal ions, and drifting dust grains  

NASA Astrophysics Data System (ADS)

Arbitrary amplitude dust-acoustic double-layers (DA-DLs) in a plasma with suprathermal electrons, two-temperature thermal ions, and warm drifting dust grains are investigated. Our results reveal that the spatial patterns of the DA-DLs are affected by the degree of the electron suprathermality. The electron thermalization involves a decrease of the cold ion component density, for the existence of localized DA-DLs. An increase of the dust drift velocity requires a decrease of ? (the electron spectral index), for the onset of dust-acoustic double-layers. An increase of the Mach number M leads to an increase of the DL amplitude as well as the corresponding electron spectral index for which the DL occurs.

Tribeche, Mouloud; Younsi, Smain; Zerguini, Taha Houssine

2012-06-01

156

Electron drift velocities in mixtures of helium and xenon and experimental verification of corrections to Blanc's law  

SciTech Connect

Measurements of electron drift velocities were performed in pure Xe and He and in a number of mixtures ranging up to 70% of Xe. The data were obtained by using a pulsed Townsend technique over the density-normalized electric field strength E/N between 1 and 100 Td. Even for pure gases there are no data in the entire range covered here, and these data represent an extension of accurate drift velocities to higher E/N. A selection of well-established cross sections for low energies, which was extended to higher energies, led to a reasonably good agreement of the calculated transport coefficients with the available data. At the same time we have applied the standard (common E/N) Blanc's law and two forms of common mean energy (CME, due to Chiflykian) procedures. Blanc's law fails for most mixtures at low and moderate E/N, while the CME procedure is capable of following the experimental data for the mixtures much more closely, and even predicting the negative differential conductivity region when such effect does not exist for pure gases. Thus the present paper also represents an experimental test of procedures to correct the standard Blanc's law. Finally, we have used the data for two mixtures to obtain results for the third mixture and in all cases this procedure gave excellent results even though only the standard Blanc's law was used in the process.

Sasic, O.; Jovanovic, J.; Petrovic, Z. Lj.; Urquijo, J. de; Castrejon-Pita, J.R.; Hernandez-Avila, J.L.; Basurto, E. [Institute of Physics, P.O.B. 68, 11080 Zemun-Belgrade (Serbia and Montenegro); Centro de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, P.O. Box 48-3, 62251, Cuernavaca Mor. (Mexico); Departamento de Energia, Universidad Autonoma Metropolitana, Av. San Pablo 180, 02200 Mexico, D.F. (Mexico); Departamento de Ciencias Basicas, Universidad Autonoma Metropolitana, Av. San Pablo 180, 02200 Mexico, D.F. (Mexico)

2005-04-01

157

Equatorial plasma bubble zonal velocity using 630.0 nm airglow observations and plasma drift modeling over Ascension Island  

NASA Astrophysics Data System (ADS)

We present OI (630.0 nm) airglow image data from Ascension Island (geographic: 7.9S, 14.4W dip latitude: 16S) in the southern Atlantic Ocean taken with the Utah State University all-sky CCD camera during 20 March to 7 April 1997 in order to study plasma bubbles occurring in the low-latitude nighttime ionosphere. The initial plasma bubble onset occurs in the early evening hours at 19:15-20:00 LST and is followed by eastward propagation with an average speed of 90-120 m/s prior to local midnight, rapidly decreasing around the midnight and postmidnight periods. The Ascension results are compared with similar observations from Christmas Island in order to examine the longitudinal variations of EPB development and propagation. The observed EPB velocities from Ascension Island are also compared with the results of a plasma drift model. In a case study during the night of 4-5 April, the velocity reveals unusual latitudinal shear, up to 0.12 m/s/km, with a reversal to westward flow at low latitudes while eastward flow is maintained at higher latitudes. Consequently, the bubble rotates counterclockwise and tilts eastward, significantly away from alignment with the geomagnetic field lines. The westward reversal of the drift motion near the geomagnetic equator is most likely the result of a reversal in the F region dynamo or from a large increase in the altitude of the shear node in the F region plasma drift at the geomagnetic equator.

Chapagain, Narayan P.; Taylor, Michael J.; Makela, Jonathan J.; Duly, Timothy M.

2012-06-01

158

Plasma Physics of Sub-Auroral Ion Drifts: A turbulent Plasmaspheric Boundary Layer  

NASA Astrophysics Data System (ADS)

We present a new scenario of the subauroral ion drifts (SAID) phenomenon based on recent magnetically conjugate Cluster-DMSP-Polar satellite observations and natural analogy with plasmoids penetrating a magnetic barrier. The SAID features are explained in terms of a turbulent boundary layer formed over the plasmapause due to a short circuit of substorm-injected plasma jets (plasmoids). Nonlinear wave-particle interactions provide fast magnetic diffusion at the plasmoid leading edge and define the circuit resistivity. As in a number of laboratory and active space experiments, nonlinear plasma processes, including but not limited to gradient-drift and current-driven instabilities, define the SAID features near the outer/poleward boundary. Near the inner/equatorward boundary and next to the channel dominate anisotropic ion-driven processes. The observed level of lower hybrid/fast magnetosonic waves is in good quantitative agreement with theoretical predictions.

Mishin, Evgeny

2011-11-01

159

Closed electron drift in a self-magnetically insulated ion diode  

NASA Astrophysics Data System (ADS)

The paper investigates a spiral geometry self-magnetically insulated ion diode with an explosive-emission cathode made from graphite. The experiments have been carried out using the TEMP-4M accelerator, with the accelerator configured to operate in double-pulse mode: the first negative pulse (300-500 ns, 100-150 kV) and the second positive pulse (150 ns, 250-300 kV). The ion beam energy density was 0.4-0.8 J/cm2 and the beam was composed of carbon ions (80%-85%) and protons. In order to increase the efficiency of ion current generation, we have developed a new diode with a spiral-shaped grounded electrode. Using this geometry, it seems possible to realize closed electron drift in a diode with self-magnetic insulation. In the spiral diode, the efficiency of accelerated ions is increased from 5%-9% (conventional self-insulated diodes) up to 30%-40%. The realization of closed electron drift in the diode increases the efficiency of C+ ion generation up to 40-50 times the Childe-Langmuir limit, which is more than 4 times higher than with other known constructions of self-magnetically insulated diodes.

Pushkarev, A. I.; Isakova, Y. I.

2013-05-01

160

Drift-Tube Studies of Exoergic Ion-Molecule Collisions and Photon-Induced Charge Transfer.  

NASA Astrophysics Data System (ADS)

Rate coefficients and product-ion yields were determined for ion-molecule collisions at near-thermal energies involving the molecule dimethyl-methylphosphonate (DMMP) and several atmospheric ions. A similar study was done with He^{++} ions and several atmospheric gases. A third experiment was an attempt to observe the laser-stimulated charge transfer in collisions of Ne^+ with He. All measurements were carried out using a selected-ion drift tube mass spectrometer. The results of the study with DMMP showed that most reactions appear to proceed by dissociative charge transfer, although some evidence for ion-molecule reaction was found in the case of O_sp{2} {+}. Also, the only loss mechanism for ground state NO^+ ions is three -body association, and hydronium ions transfer a proton to DMMP. Rate coefficients obtained in the study with He^{++} ions were found to be quite close to the predictions of ion-molecule capture theories. Singly and doubly charged product ions were observed in several cases, indicating that both single and double charge transfer, and possibly transfer ionization, occur. The experiment on laser-stimulated charge transfer produced measurements of upper limits to the cross section that are considerably lower than some theoretical predictions.

Tosh, Ronald E.

1992-01-01

161

Drift compression and final focus for intense heavy ion beams with nonperiodic, time-dependent lattice  

NASA Astrophysics Data System (ADS)

In the currently envisioned configurations for heavy ion fusion, it is necessary to longitudinally compress the beam bunches by a large factor after the acceleration phase. Because the space-charge force increases as the beam is compressed, the beam size in the transverse direction will increase in a periodic quadrupole lattice. If an active control of the beam size is desired, a larger focusing force is needed to confine the beam in the transverse direction, and a nonperiodic quadrupole lattice along the beam path is necessary. In this paper, we describe the design of such a focusing lattice using the transverse envelope equations. A drift compression and final focus lattice should focus the entire beam pulse onto the same focal spot on the target. This is difficult with a fixed lattice, because different slices of the beam may have different perveance and emittance. Four time-dependent magnets are introduced in the upstream of drift compression to focus the entire pulse onto the same focal spot. Drift compression and final focusing schemes are developed for a typical heavy ion fusion driver and for the integrated beam experiment being designed by the Heavy Ion Fusion Virtual National Laboratory.

Qin, Hong; Davidson, Ronald C.; Barnard, John J.; Lee, Edward P.

2004-10-01

162

Simulating Ion Permeation Through the ompF Porin Ion Channel Using Three-Dimensional Drift-Diffusion Theory  

Microsoft Academic Search

Ionic channels, natural nanotubes found in biological cells, are interesting to the electronics community because they display a range of device-like functions. The purpose of this paper is to illustrate how the solution methodology, developed for 3-D drift-diffusion models of semiconductor devices, can be applied to ion permeation in ionic channels. For this study we select the ompF porin channel,

T. A. VAN DER STRAATEN; J. M. TANG; U. RAVAIOLI; R. S. EISENBERG

2003-01-01

163

Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields  

SciTech Connect

The drift and diffusion of a cloud of ions in a fluid are distorted by an inhomogeneous electric field. If the electric field carries the center of the distribution in a straight line and the field configuration is suitably symmetric, the distortion can be calculated analytically. We examine the specific examples of fields with cylindrical and spherical symmetry in detail assuming the ion distributions to be of a generally Gaussian form. The effects of differing diffusion coefficients in the transverse and longitudinal directions are included.

Cahn, Robert; Cahn, Robert N.; Jackson, John David

2008-05-30

164

Ion Temperature and Rotational Velocity Measurement in SSPX  

NASA Astrophysics Data System (ADS)

Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. Anomalous ion heating and acceleration has been observed in spheromaks, although the precise mechanism that gives rise to this phenomenon is still unclear. In order to elucidate this, an ion Doppler spectrometer (IDS) has been designed and constructed to measure the ion temperatures and rotational velocities of impurity ions in SSPX plasmas. The IDS consists of a telescope, spectrometer with a grating density of 2400 lines/inch, and a 16 channel PMT. The output from the PMT is digitized and fit to a Gaussian curve, from which the ion temperature and Doppler-shift of the line is obtained. A dispersion of 0.02 nm/mm is calculated at the spectrometer output, allowing ion temperatures to 800 eV to be measured. This work follows on from initial investigations made last year, in which ion temperatures of 600eV and rotational velocities of 2km/s were observed in SSPX (Nagata et al Bull. Am. Phys. Soc. Seattle, 1999) This work was performed under the auspices of US DOE by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Auerbach, D. W.; Hill, D. N.; McLean, H. S.; Sspx Team

2000-10-01

165

Behavior of zonal ion drifts in low and middle latitude ionosphere  

NASA Astrophysics Data System (ADS)

The Earth's environment consists of a neutral and an ionized atmosphere. The neutral atmosphere can be divided by its temperature profile into the troposphere (0-12 km), the stratosphere (12-45 km), the mesosphere (45-85 km), the thermosphere (85-1000 km) and exosphere (>1000 km). The Earth's ionized atmosphere is typically divided by density and composition into the ionosphere (70-1000 km), the plasmasphere (1000 km to 4 Re for MLAT less than 60), and the magnetosphere extending to nearly 8 Re on the dayside and to approximately 1000 Re on the nightside. The Earth's ionosphere does not get direct energy from the solar wind because it is shielded by its magnetic field. The region of geospace is dominated by Earth's magnetic field is called the magnetosphere and outermost edge of the magnetosphere, called the magnetopause is maintained by the charged particles from the solar wind flowing along the boundary. The largest energy transfer from the solar wind to the magnetosphere is driven by an electric field directed dawn to dusk. This limited study shows that during large magnetic storms, ion drifts driven by the magnetosphere penetrate to latitudes as low as the dip equator on the dusk side and extend a few degrees equatorward of the auroral zone on the dawn side. A description of the evolution of the auroral precipitation and the zonal ion drifts at high latitudes during times of extreme storm activity is produced by applying some quantitative definitions that allow us to identify the expansion and penetration of the high-latitude zonal ion drifts to middle and low latitudes in the ionosphere. Times are identified when ion drifts driven from the magnetosphere exist at latitudes inside the plasmasphere and when regions below the auroral zone may be influenced by a disturbance dynamo. The resolved boundaries in the ion drifts and the electron precipitation allow us to distinguish penetration events from sub-auroral polarization fields. This limited study also shows that during large magnetic storms in the northern hemisphere dusk sector at 1800 MLT the equatorward extent of the region-2 current signature extends to as low as 39 MLAT. We have also figured out that at low and middle latitudes small variations in the magnetic perturbations that are removed as a baseline may represent reproducible storm-time signatures.

Mohapatra, Sasmita

166

Signatures of turbulent heating in heavy-ion velocity distribution functions  

NASA Astrophysics Data System (ADS)

The kinetic properties of the solar wind are a result of complex interactions in the solar corona and interplanetary space. Sofar, observations of velocity distribution functions (VDFs) of solar wind heavy ions have been solely 1D. They are known to exhibit non-thermal features , but because they are 1D projections of the 3D velocity phase space it is difficult to interpret them properly. Based on 3D observations of H+ and He2+ from Helios, we have set up a model for heavy-ion VDFs. In it, the magnetic field vector plays a crucial role by defining the symmetry axis of the VDFs. A thermal anisotropy T?/T??1 and a beam drifting along the magnetic field vector at a relative speed of approximately the Alfvn speed are included. The modeled VDFs are analyzed using a virtual detector and then compared with ACE/SWICS data. Our observations give striking evidence for turbulent heating and the existence of heavy-ion beams. The projection of these beams can explain observed differential streaming. We present in-situ measurements at 1 AU and implications for wave-paricle interactions between the Sun and Earth.

Berger, L.; Wimmer-Schweingruber, R. F.; Koeten, M.; Rodde, R.; Gloeckler, G.; Lepri, S.; Raines, J.

2008-12-01

167

Beam dynamics of the Neutralized Drift Compression Experiment-II (NDCX-II), a novel pulse-compressing ion accelerator  

SciTech Connect

Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at {approx}1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of {approx}50-100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at LBNL. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam's longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutralized compression onto the target. This paper describes the discrete-particle simulation models (1-D, 2-D, and 3-D) employed and the space-charge-dominated beam dynamics being realized.

Friedman, A; Barnard, J J; Cohen, R H; Grote, D P; Lund, S M; Sharp, W M; Faltens, A; Henestroza, E; Jung, J; Kwan, J W; Lee, E P; Leitner, M A; Logan, B G; Vay, J; Waldron, W L; Davidson, R C; Dorf, M; Gilson, E P; Kaganovich, I

2009-11-19

168

Diagnosis of ion velocity distribution from pin to plate geometry in atmospheric argon dielectric barrier discharge  

NASA Astrophysics Data System (ADS)

A new method, fast Fourier transform, is presented to calculate ion velocity distribution by analyzing electromagnetic radiation signal from plasma. This method is based on a dipole model that does not require the assumption of thermodynamic equilibrium. To understand the discharge evolution, the ion velocity distribution is calculated in different oscillation cycles. Results show that the ion velocity distribution deviates from Maxwell distribution over time. The ion velocity and relative ion number fluctuate regularly with time.

Qi, Bing; Pan, Lizhu; Huang, Jianjun; Liu, Ying

2013-07-01

169

Measurements of drift velocity of artificial small-scale field-aligned irregularities using multi-position HF radars  

NASA Astrophysics Data System (ADS)

In report the results of multi-position radar measurements of Doppler frequency shift DFS scattered signals by artificial small-scale field-aligned irregularities FAI are presented In measurements two pairs of bistatic configurations HF radars have been used Kaliningrad 54 7 r N 20 6 r E -- SURA 56 1 r N 46 1 r E - IZMIRAN 55 3 r N 37 2 r E path 1 and RVI 55 8 r N 38 3 r E - SURA - Rostov-Don 47 2 r N 39 6 r E path 2 Such geometry of paths has allowed to determine the value and direction of drift velocity of FAI in a plane orthogonal to magnetic field Observations were carried out in March 2005 in the evening hours from 16 00 to 19 00 UT On the first path the probing transmitter operated at frequency 9300 kHz in a pulse mode tau 100 mu s F rep 25 Hz on the second path as the probing transmitter was used the RVI station of precise times which operated at frequency 14996 kHz in continuous carrier mode The heating facility SURA operated in a mode 5 min -- radiation and 5 min - pause on pump wave frequency f p close to critical frequency of F-layer f p le f o F2 According to results of spectral measurements in an operating time of heating facility on both paths scattered signals from artificial small-scale field-aligned irregularities were observed On the basis of DFS measurements of the scattered signal SS we have calculated value V and direction azimuth A of the irregularities drift velocity It is obtained that during moderate disturbance period magnetic

Uryadov, V. P.; Frolov, V. L.; Vertogradov, G. G.; Vertogradov, V. G.; Kim, V. Yu.; Panchenko, V. A.; Polimatidi, V. P.; Ivanov, V. P.

170

An updated climatology of thermospheric neutral winds and F region ion drifts above Millstone Hill  

NASA Astrophysics Data System (ADS)

Incoherent scatter radar data from 63 experiments during the period 1984-1997 have been used to update earlier published climatologies of ion drifts and neutral thermospheric winds at Millstone Hill. Data are binned according to season, solar activity, geomagnetic activity, and local solar time. The derived ion drift patterns are similar to those previously published, but we now find that the main effect of the increased magnetic activity is an enhancement of the usual nighttime west-ward ion drift. A tidal decomposition of the winds from geomagnetically quiet conditions is carried out for each season/solar activity level to extract diurnal means, diurnal amplitudes and phases, and semidiurnal components. These winds are compared with previous results at Millstone Hill and the HWM-93 model. Using our expanded wind database, statistically significant semidiurnal components are now found in both summer and winter, at both solar maximum and solar minimum. Our bin-averaged results confirm earlier published findings that at all seasons the diurnal mean winds are more strongly equatorward and the diurnal amplitudes are stronger at solar cycle minimum than at solar cycle maximum. Diurnal amplitudes derived in the present work are larger than those found previously because we now use a smaller value for the O+,O collision frequency. Differences in the diurnal mean and diurnal amplitude between recent solar minimum data (1993-1997) and data from the previous solar minimum (1984-1986) are attributed to a difference in the EUV flux as inferred from Millstone Hill electron density data which one would not expect from the F10.7 index. This affects the ion drag and apparently also the relative importance of the EUV and high latitude heat sources.

Buonsanto, M. J.; Witasse, O. G.

1999-11-01

171

Effect of small admixtures of N2, H2 or O2 on the electron drift velocity in argon: experimental measurements and calculations  

NASA Astrophysics Data System (ADS)

The electron drift velocity in argon with admixtures of up to 2% of nitrogen, hydrogen or oxygen is measured in a pulsed Townsend system for reduced electric fields ranging from 0.1 Td to 2.5 Td. The results are compared with those obtained by Monte Carlo simulations and from the solution of the electron Boltzmann equation using two different solution techniques: a multiterm method based on Legendre polynomial expansion of the angular dependence of the velocity distribution function and the S n method applied to a density gradient expansion representation of the distribution function. An almost perfect agreement between the results of the three numerical methods and, in general, very good agreement between the experimental and the calculated results is obtained. Measurements in Ar-O2 mixtures were limited by electron attachment to oxygen molecules, which contributes to the measured drift velocity. As a result of this attachment contribution, the bulk drift velocity becomes larger than the flux drift velocity if attachment is more probable for electrons with energy below the mean value and smaller in the opposite case. Attachment also contributes to the negative differential conductivity observed in Ar-O2 mixtures.

Stano, M.; Pinho, N.; Loffhagen, D.; Ku?era, M.; Donk, Z.; Matej?k, .

2011-12-01

172

Vertical ionization drift velocities and range type spread F in the evening equatorial ionosphere  

SciTech Connect

Range type spread F indices in the post sunset hours, determined from ionograms, are compared with F layer vertical velocities, also deduced from ionograms, for a period of one year, over the magnetic equatorial station Fortaleza (geographic coordinates: 4/sup 0/S, 38/sup 0/W; dip latitude: 1.8/sup 0/S), Brazil. Besides good correlation between the two parameters, the results suggest the presence of a certain threshold value for the vertical ionization velocity and a corresponding threshold height for the base of the evening F layer, as one of the necessary conditions for the occurrence of spread F irregularities valid for southern solstice (summer) and equinoctial months. The nature of the possible variabilities in the amplitude of the initial perturbation in the ionization (seeding mechanism), which is another prerequisite for the generation of irregularities, is discussed briefly.

Abdu, M.A.; de Medeiros, R.T.; Bittencourt, J.A.; Batista, I.S.

1983-01-01

173

Li+ alumino-silicate ion source development for the Neutralized Drift Compression Experiment (NDCX)  

SciTech Connect

We report results on lithium alumino-silicate ion source development in preparation for warmdense-matter heating experiments on the new Neutralized Drift Compression Experiment (NDCXII). The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of ~;;1275 oC, a space-charge-limited Li+ beam current density of J ~;;1 mA/cm2 was obtained. The lifetime of the ion source was ~;;50 hours while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 mu s.

Roy, Prabir K.; Greenway, Wayne G.; Kwan, Joe W.; Seidl, Peter A.; Waldron, William L.; Wu, James K.

2010-10-01

174

Properties of ion temperature gradient drift instabilities in H-mode plasmas  

SciTech Connect

Experimental results from tokamaks such as DIII-D and JET have indicated that the electron density profile in H-mode (''high- confinement'') discharges can be nearly flat over most of the plasma, and, in some cases, even inverted (outwardly peaked). These conditions have very interesting implications for pictures of anomalous thermal transport based on the presence of ion temperature gradient drift instabilities. The present paper includes a new derivation of the ion temperature gradient threshold for weak density gradient /eta//sub i/ modes when ion transit resonances are taken into account; and the first derivation of threshold conditions for the onset of /eta//sub i/-modes when /eta//sub i/ is negative along with the properties of these negative /eta//sub i/ instabilities when the thresholds are exceeded. Possible consequences for confinement in H-mode plasmas are discussed. 32 refs., 8 figs.

Hahm, T.S.; Tang, W.M.

1988-11-01

175

Comparison of Nighttime Zonal Neutral Winds and Plasma Bubble Drift Velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present the first simultaneous measurements of equatorial thermospheric neutral wind measurements and plasma bubble (EPB) zonal speeds over northeastern Brazil during September-December 2009 and 2010. The wind data are obtained from a bi-static Fabry-Perot interferometer experiment measuring the Doppler shift of the 630.0-nm spectral emission. The FPIs are located at Cajazeiras (6.86S, 38.56W) and Cariri (7.38S, 36.53W). The EPB zonal speed, which is assumed to be equal to the drift of the background plasma, is measured using images of the 630.0-nm emission obtained from a wide-angle imaging system collocated with the FPI at Cajazeiras. In general, the simultaneous measurement of the zonal neutral wind and the EPB zonal speed show excellent agreement. However, the EPB zonal speed is slower than that of the wind motion in the early evening hours on several occasions, suggesting the F-region dynamo is not fully activated.

Chapagain, N. P.; Makela, J. J.; Meriwether, J. W.; Buriti, R. A.; Medeiros, A.

2011-12-01

176

Effects of electrode geometry on the ion beam extraction of closed drift type anode layer linear ion source  

SciTech Connect

Closed drift type anode layer linear ion source was investigated with focusing on the electrode geometry effects on ion beam emission and anode layer formation. In the electrode geometry, the discharge gap between anode and cathode plays an important role to control anode layer formation as well as electron generation. When the discharge gap is increased from 2 to 3 mm, the ion current density was enhanced from 0.9 to 1.35 mA/cm{sup 2}. Computational simulation by using an object oriented particle in cell showed that the discharge volume was extended due to enhanced electron generation and the electric field at the anode layer was enhanced from 1.32 to 1.52 MV/cm.

Lee, Seunghun; Kim, Jong-Kuk; Kim, Do-Geun [Korea Institute of Materials Science, Changwon, 642-831 (Korea, Republic of)

2012-02-15

177

Effects of electrode geometry on the ion beam extraction of closed drift type anode layer linear ion source.  

PubMed

Closed drift type anode layer linear ion source was investigated with focusing on the electrode geometry effects on ion beam emission and anode layer formation. In the electrode geometry, the discharge gap between anode and cathode plays an important role to control anode layer formation as well as electron generation. When the discharge gap is increased from 2 to 3 mm, the ion current density was enhanced from 0.9 to 1.35 mA?cm(2). Computational simulation by using an object oriented particle in cell showed that the discharge volume was extended due to enhanced electron generation and the electric field at the anode layer was enhanced from 1.32 to 1.52 MV?cm. PMID:22380308

Lee, Seunghun; Kim, Jong-Kuk; Kim, Do-Geun

2012-02-01

178

Tandem flowing afterglow-SIFT-Drift: developments and applications to gas phase ion chemistry  

SciTech Connect

This thesis describes the detailed design of the Tandem Flowing Afterglow-SIFT-Drift and applications of this technique and other flow tube techniques to gas phase ion chemistry. The versatile ion source and high sensitivity and resolution of the instrument allows generation and study of a variety of ions including highly reactive ions (CH/sub 2//sup -/), solvated ions (HO/sup -/(H/sub 2/O)), ions which must be synthesized by a series of ion molecule reactions (C/sub 3/H/sub 3/N/sub 2//sup -/) as well as isotopically labelled ions (/sup 37/Cl, /sup 34/S, /sup 13/C, /sup 18/O) from unenriched precursors. The acidities of a series of ..beta..-branched and polycyclic hydrocarbons are probed using the kinetic acidity method developed by DePuy, et al. (1984). A preliminary investigation of a more sensitive extension of this method is also presented. The chemistry of diazomethyl anion is described. Addition with loss of nitrogen is a common reaction. The acidity of diazomethane is bracketted as 373 +/- 4 kcal/mol and the electron affinity of diazomethyl radical is estimated to be approx. 48 kcal/mol. The product ion of the O/sub 2//sup +/ + CH/sub 4/ room temperature reaction is identified as methylene hydroperoxide. A comprehensive study of the chemistry of this cation is discussed. A qualitative and semi-quantitative model for the reaction mechanism for O/sub 2//sup +/ + CH/sub 4/ at room temperature is prepared.

Van Doren, J.M.

1987-01-01

179

Giotto-IMS (Ion Mass Spectrometer) Observations of Ion Flow Velocities and Temperatures Outside the Contact Surface of Comet Halley.  

National Technical Information Service (NTIS)

Fluid parameters for He(++) ions obtained from the Giotto ion mass spectrometer are presented. Proton densities and velocities and thermal speeds of protons, alpha particles, and heavy ions in the hour before closest approach are discussed. A region of en...

B. E. Goldstein H. Balsiger J. Drake M. Neugebauer S. A. Fuselier

1986-01-01

180

Drift and clustering of daughter negative ions of H2O in parent gas  

NASA Astrophysics Data System (ADS)

The mobility of daughter negative ions of H2O in parent gas has been measured with a pulsed Townsend technique over the density-reduced field strength, E/N, range 9-100 Td and a pressure range 2-16 Torr. It has been found that the mobility of the anions is dependent on the gas pressure. Using a transport theory considering the influence of the permanent dipole field of H2O, we have found that the pressure-dependent mobilities can be associated with a series of cluster ions of the type OH-(H2O)n (n = 1-3), with the mass of the cluster species increasing with the total gas pressure. Also, the mobility of H- and OH- could be estimated. Using a Townsend avalanche simulator we have been able to explain the measured ionic currents in terms of an ion-molecule reaction scheme with a single set of swarm and reaction coefficients for each value of the density-reduced field strength, E/N, at several pressures. Regarding the positive ions, the only drifting ion is H3O+, the mobility of which could be estimated. The rate constants relative to the formation of the OH-(H2O)n (n = 1-3) species were also derived from this study.

de Urquijo, J.; Bekstein, A.; Ruiz-Vargas, G.; Gordillo-Vzquez, F. J.

2013-01-01

181

Dust drift shock waves with non-Maxwellian ion population in nonuniform collisional dusty plasmas in planetary environments  

NASA Astrophysics Data System (ADS)

Linear and nonlinear propagation of dust drift waves are investigated in the presence of Cairns and Kappa distributed ion population and Boltzmannian electrons. It is found the frequency of the dust drift wave is greatest for the Cairns, intermediate for Kappa and the least for the Maxwellian distributed ions. Using the drift approximation, a nonlinear equation is derived for the dust drift shock waves which reduces to a Korteweg-de Vries-Burgers (KdVB)-like equation in the comoving frame of reference. The solution of the KdVB-like equation is obtained using the tanh method. It is found that the non-Maxwellian ion population, dust neutral collision frequency as well as the inverse dust density scale length inhomogeneity alter the propagation characteristics of the nonlinear dust drift shock waves. Interestingly, it is found that the non-Maxwellian ion population modifies the scale lengths over which the nonlinear structures are formed. The work presented here may be useful to understand the low frequency electrostatic shock waves in inhomogeneous dusty plasmas such as those found in planetary environments.

Masood, W.; Rizvi, H.; Hasnain, Haseeb; Batool, N.

2013-05-01

182

Very Low velocity Ion Slowing Down in Binary Ionic Mixtures  

NASA Astrophysics Data System (ADS)

Binary ionic mixtures (BIM) in dense and hot plasmas of specific concern for inertial confinement fusion (ICF) and white dwarf crust are considered as targets for incoming light ions with a velocity smaller than thermal electron one in target.The given BIM formalism worked out within a dielectric approach [1] is specifically investigated in terms of charge-and mass-asymmetry in the target BIM components.Results are scanned w.r.t density, temperature and relative BIM composition as well.A certain attention is paid to the so-called critical regime when target electron stopping equals the target ion contribution. [4pt] [1] B.Tashev et al, Phys.Plasmas 15,102701(2008) and NIMA 606,218(2009)

Fromy, Patrice; Tashev, Bekbolat; Deutsch, Claude

2010-11-01

183

Effects of drift gas on collision cross sections of a protein standard in linear drift tube and traveling wave ion mobility mass spectrometry.  

PubMed

There has been a significant increase in the use of ion mobility mass spectrometry (IM-MS) to investigate conformations of proteins and protein complexes following electrospray ionization. Investigations which employ traveling wave ion mobility mass spectrometry (TW IM-MS) instrumentation rely on the use of calibrants to convert the arrival times of ions to collision cross sections (CCS) providing "hard numbers" of use to structural biology. It is common to use nitrogen as the buffer gas in TW IM-MS instruments and to calibrate by extrapolating from CCS measured in helium via drift tube (DT) IM-MS. In this work, both DT and TW IM-MS instruments are used to investigate the effects of different drift gases (helium, neon, nitrogen, and argon) on the transport of multiply charged ions of the protein myoglobin, frequently used as a standard in TW IM-MS studies. Irrespective of the drift gas used, recorded mass spectra are found to be highly similar. In contrast, the recorded arrival time distributions and the derived CCS differ greatly. At low charge states (7 ? z ? 11) where the protein is compact, the CCS scale with the polarizability of the gas; this is also the case for higher charge states (12 ? z ? 22) where the protein is more unfolded for the heavy gases (neon, argon, and nitrogen) but not the case for helium. This is here interpreted as a different conformational landscape being sampled by the lighter gas and potentially attributable to increased field heating by helium. Under nanoelectrospray ionization (nESI) conditions, where myoglobin is sprayed from an aqueous solution buffered to pH 6.8 with 20 mM ammonium acetate, in the DT IM-MS instrument, each buffer gas can yield a different arrival time distribution (ATD) for any given charge state. PMID:22974196

Jurneczko, Ewa; Kalapothakis, Jason; Campuzano, Iain D G; Morris, Michael; Barran, Perdita E

2012-09-26

184

Unexpected transverse velocity component of Xe{sup +} ions near the exit plane of a Hall thruster  

SciTech Connect

The velocity component of singly charged xenon ions in a plane perpendicular to the thrust axis of the 1 kW-class PPS100-ML Hall effect thruster is deduced from laser induced fluorescence measurements on the 5d {sup 2}F{sub 7/2}{yields}6p {sup 2}D{sub 5/2}{sup 0} electronic transition at 834.72 nm. Measurements are carried out at several locations in the near field of the channel exhaust. Thruster operating parameters, such as magnetic field strength, discharge voltage, and xenon mass flow rate, are varied over a wide range. The initial aim of this work was to measure the azimuthal velocity of the ions due to their weak magnetic deflection. Surprisingly, experimental results cannot be explained by the one and only Lorentz force acting on Xe{sup +} ions. A realistic picture of the ion trajectory in the ExB drift plane is obtained when adding a velocity component directed toward the external cathode.

Bourgeois, G.; Mazouffre, S. [ICARE, CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orleans (France); Sadeghi, N. [LSP, Joseph Fourier University and CNRS, 140 Ave. de la Physique, 38402 St. Martin d'Heres (France)

2010-11-15

185

Observations of the velocity distribution of solar wind ions  

SciTech Connect

Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of /sup 3/He/sup + +/, /sup 4/He/sup + +/, /sup 16/O/sup 6 +/, and /sup 16/O/sup 7 +/ in the solar wind. It is found that these temperatures generally obey the relation that T/sub i//m/sub i/=const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. Whether this relation applies to ions with masses greater than 16 requires more analysis to determine. The temperature of oxygen sometimes rises above 10/sup 6/ /sup 0/K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non-Maxwellian, with a pronounced high velocity tail. As this is one condition for heating by wave dissipation, this mechanism must still be considered as a heating mechanism.

Ogilvie, K.W.; Bochsler, P.; Geiss, J.; Coplan, M.A.

1980-11-01

186

A study of the performance of an ion shutter for drift tubes in atmospheric pressure ion mobility spectrometry: Computer models and experimental findings  

SciTech Connect

Ion mobility spectra are initiated when ions, derived from a sample, are pulsed or injected through ion shutters into a drift region. The effect on signal intensity from electric fields arising from the shutter grids (E{sub s}) and a superimposed electric field of the drift tube (E{sub d}) was determined experimentally and simulated computationally for ion motion at ambient pressure. The combination of these two fields influenced shutter performance in three ways: (1) intensity of an ion peak was suppressed by increased current in the baseline due to continuous leakage of ions into the drift region from insufficient E{sub s} to block ion motion when needed, at a given value of E{sub d}; (2) the ion shutter provided maximum peak intensity with some optimal ratio of E{sub s}/E{sub d} when ions were fully blocked except using the injection time; (c) the signal intensity was reduced when the blocking voltage of the ion shutter exceeded this optimal E{sub s}/E{sub d} ratio from ion depletion at the shutter grids. The optimal ratio from the computer models was equal to 1.50, whereas a value of 2.50 was obtained from the experimental findings. This difference was attributed to nonideal geometry with the grids of the shutter and the conducting elements in the drift tube establishing both E{sub s} and E{sub d}. As both the experimental and modeling results demonstrated, a mobility dependence of ion yield from the ionization source was found to cause a mobility dependent ion signal at the collector electrode.

Tadjimukhamedov, Fatkhulla K.; Eiceman, Gary A. [Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003 (United States); Puton, Jaroslaw [Department of Environmental Sciences, Laboratory of Applied Environmental Chemistry, University of Kuopio, Mikkeli FIN-50100 (Finland); Stone, John A. [Department of Chemistry, Queens University, Kingston, Ontario K7L 3N6 (Canada)

2009-10-15

187

Generation of convective cells by ion-drift waves in dusty plasmas  

NASA Astrophysics Data System (ADS)

The parametric excitation of large-scale convective cells in non-uniform dusty plasmas with non-zero ion temperature is considered. A set of two coupled nonlinear equations (for the variation of the electrostatic potential and the ion pressure) governing the nonlinear dynamics of ion-drift waves in dusty plasmas (IDWDPs) is obtained. The equations are then simplified by using a standard multiscale expansion technique. A nonlinear dispersion relation, which describes the nonlinear electrostatic and thermal convective cells, is obtained. The analysis of our dispersion relation shows that only the electrostatic mode yields a non-zero growth rate. The thermal convective cell is found to be stable. A simple expression for the maximum instability growth rate and the optimal dimension of the convective mode is deduced. The fastest growing wave appears to be a zero-frequency mode, elongated perpendicularly to the plasma inhomogeneity. The electrostatic convective cell growth rate is compared with that for the traditional parametric IDWDP decay.

Pokhotelov, O. A.; Onishchenko, O. G.; Sagdeev, R. Z.; Stenflo, L.; Shukla, P. K.; Beloff, N.

188

Ion flux energy distributions in a hydrogen-filled drift tube at high E/N  

NASA Astrophysics Data System (ADS)

Ion flux energy distributions are calculated for H^+, H2^+, and H3^+ ions in H2 for low-current, uniform-electric-field drift tubes at 1 kTd < E/N < 10 kTd and 5x10^20 <=N d <=3x10^21 m^2, where E is the electric field, N is the gas density, and d is the electrode separation. We use updated cross sections in a multi-beam model of the spatial and energy dependent particle fluxes. Calculated distributions at the cathode are compared with experiments by Rao et al. and detailed theory by Bretagne et al. Hypothetical large increases in the total momentum transfer cross sections for H^+ and H3^+ at 100 to 1000 eV yield approximate fits to the relative experimental distributions at high energies at moderate E/N. However, these fitted distributions are much too small at low ion energies. Similar discrepancies occur for analytic solutions of the Boltzmann equations using simplified reaction cross sections and the almost free-fall conditions for H^+ at 10 kTd.

Phelps, Arthur

2008-10-01

189

Ion Dissociation in the Drift Tube of a Time-of-Flight Mass Spectrometer: Spurious Fragments Arising from Charge-Transfer and Dissociation Reactions of Retarded Ions  

Microsoft Academic Search

Spurious fragment peaks that simulate fragment-ion dissociation products formed in the drift-tube reaction region have been observed in a time-of-flight mass spectrometer adapted for kinetic studies of ion dissociation processes. These peaks arise from processes occurring after the reactant ion has passed through the reaction region and entered the potential barrier that is normally used to separate reactants and products

W. W. Hunt Jr.; K. E. McGee

1964-01-01

190

Stabilizing effect of ion pressure gradient on magnetic curvature-driven drift modes located at rational surface of tokamak plasma  

Microsoft Academic Search

In the fluid model, we derive a dispersion relation for the toroidal drift modes of tokamak plasmas, including the ion pressure gradient and the magnetic field gradient and curvature. It is shown that the magnetic field gradient and curvature (MFGC) can cause instabilities at the rational surface, which are of toroidicity-induced (TI) modes. On the other hand, it is discovered

Ai-Ke Wang

2005-01-01

191

Electron drift velocity control in GaAs-in-Al2O3 quantum wire transistor structure due to the electron scattering rate alteration  

Microsoft Academic Search

Electron transport in the transistor structure based on thin undoped GaAs-in-Al2O3 quantum wire is simulated by ensemble Monte-Carlo method taking into account electron scattering by the phonons and surface roughness. The influence of surface roughness height on electron drift velocity at 77 and 300 K is investigated for the values of longitudinal electric field strength of 0.1 and 1.0 kV\\/cm.

Andrei Borzdov; Dmitry Pozdnyakov; Vladimir Borzdov

2008-01-01

192

SIMULATIONS OF HIGH-VELOCITY CLOUDS. I. HYDRODYNAMICS AND HIGH-VELOCITY HIGH IONS  

SciTech Connect

We present hydrodynamic simulations of high-velocity clouds (HVCs) traveling through the hot, tenuous medium in the Galactic halo. A suite of models was created using the FLASH hydrodynamics code, sampling various cloud sizes, densities, and velocities. In all cases, the cloud-halo interaction ablates material from the clouds. The ablated material falls behind the clouds where it mixes with the ambient medium to produce intermediate-temperature gas, some of which radiatively cools to less than 10,000 K. Using a non-equilibrium ionization algorithm, we track the ionization levels of carbon, nitrogen, and oxygen in the gas throughout the simulation period. We present observation-related predictions, including the expected H I and high ion (C IV, N V, and O VI) column densities on sightlines through the clouds as functions of evolutionary time and off-center distance. The predicted column densities overlap those observed for Complex C. The observations are best matched by clouds that have interacted with the Galactic environment for tens to hundreds of megayears. Given the large distances across which the clouds would travel during such time, our results are consistent with Complex C having an extragalactic origin. The destruction of HVCs is also of interest; the smallest cloud (initial mass {approx} 120 M{sub sun}) lost most of its mass during the simulation period (60 Myr), while the largest cloud (initial mass {approx} 4 x 10{sup 5} M{sub sun}) remained largely intact, although deformed, during its simulation period (240 Myr).

Kwak, Kyujin; Henley, David B.; Shelton, Robin L., E-mail: kkwak@physast.uga.edu, E-mail: dbh@physast.uga.edu, E-mail: rls@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2011-09-20

193

On the fitting of displaced Maxwellians to laser-produced plasma ion velocity distributions  

Microsoft Academic Search

The empirical fitting of displaced Maxwellians to ion velocity distributions measured at some distance from the target in laser-produced plasma studies is shown to lack a theoretical basis. A similar ion velocity spectrum to a displaced Maxwellian is obtained if a simple self-similar plasma expansion is assumed. The discussion is illustrated by experimental ion velocity distributions measured at 0.8 m

G. J. Tallents

1981-01-01

194

Parametric Excitation of Geodesic Acoustic Modes by Electron Drift Waves and Ion Temperature Gradient Modes in Tokamak Plasmas  

SciTech Connect

Geodesic Acoustic Modes (GAMs) have been predicted and subsequently observed in many toroidal plasma devices. Bicoherence studies on various devices have suggested three-wave mode coupling processes between GAMs and high frequency turbulence. Thus the parametric coupling of GAMS to drift waves and/or ion temperature gradient(ITG{r_brace} modes is a potential candidate for excitation of these modes. In this paper we discuss the resonant three-wave coupling mechanism for the excitation of GAMs by ITG and finite beta drift waves in homogeneous and inhomogeneous plasmas and compare theoretical predictions with observed characteristics of the GAMs.

Guzdar, P. N.; Kleva, R. G. [IREAP, University of Maryland, College Park, MD 20742 (United States); Chakrabarti, N. [SINP, Kolkata (India); Kaw, P. K.; Singh, R. [IPR, Gandhinagar, 308423 (India); Naulin, V.; Rasmussen, J. J. [EURATOM, Roskilde (Denmark)

2008-11-01

195

Parametric Excitation of Geodesic Acoustic Modes by Electron Drift Waves and Ion Temperature Gradient Modes in Tokamak Plasmas  

NASA Astrophysics Data System (ADS)

Geodesic Acoustic Modes (GAMs) have been predicted and subsequently observed in many toroidal plasma devices. Bicoherence studies on various devices have suggested three-wave mode coupling processes between GAMs and high frequency turbulence. Thus the parametric coupling of GAMS to drift waves and/or ion temperature gradient(ITG} modes is a potential candidate for excitation of these modes. In this paper we discuss the resonant three-wave coupling mechanism for the excitation of GAMs by ITG and finite beta drift waves in homogeneous and inhomogeneous plasmas and compare theoretical predictions with observed characteristics of the GAMs.

Guzdar, P. N.; Chakrabarti, N.; Kleva, R. G.; Kaw, P. K.; Singh, R.; Naulin, V.; Rasmussen, J. J.

2008-11-01

196

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the eff ects of polarizable drift gases and ionic charge distribution.  

PubMed

Coupling ion mobility (IM) with MS offers a potential solution for resolving structural isomers. Ion mobility separates ions according to size and shape because they interact differently with the neutral drift-gas molecules. However, the majority of routine IM-MS measurements rely on drift-gases with low polarizability such as He and N2. In the Special Feature Lalli et al. investigate polarizable molecules as drift-gas to determine if the dipolar ion-neutral interactions enhance ion mobility separations of shape-similar analytes. Their results suggest that the polarizability of the drift-gas and the distribution of charge on the ion influence the degree of IM separation. PMID:24078248

Lalli, Priscila M; Corilo, Yuri E; Fasciotti, Mara; Riccio, Maria Francesca; de S, Gilberto Fernandes; Daroda, Romeu J; Souza, Gustavo H M F; McCullagh, Michael; Bartberger, Michael D; Eberlin, Marcos N; Campuzano, Iain

2013-09-01

197

Drift and mirror modes in magnetized plasmas  

Microsoft Academic Search

Low frequency plasma instabilities driven by plasma inhomogeneity and velocity anisotropies are major candidates for the explanation of various phenomena observed in fusion and space plasmas. For low-beta fusion plasma, the influence of plasma rotation and finite ion temperature on the structure and the type of toroidal drift eigenmodes in tokamaks is investigated rigorously, including the effects induced by the

Ingmar Sandberg

2002-01-01

198

Ion acceleration in Ar-Xe and Ar-He plasmas. II. Ion velocity distribution functions  

SciTech Connect

Ion velocity distribution functions (ivdfs) are investigated by laser induced fluorescence in Ar-Xe and Ar-He expanding helicon plasmas as a function of gas composition. In the case of Ar-Xe plasma, it was found that in the helicon source, both the Ar{sup +} and Xe{sup +} vdfs are unimodal. Their parallel speeds are subsonic and unaffected by changes in gas composition. At the end of the source, the argon ivdf shows a bimodal structure indicative of an electric double layer upstream of the measurement location. The fast argon ion component parallel velocity increases with Xe fraction from 6.7 to 8 km/s as the Xe fraction increases from 0% to 4%. In the expansion region, the bimodal character of Ar ivdf is maintained with a supersonic fast component reaching parallel speeds of 10.5 km/s. For all the studied plasma conditions and different spatial locations, the Xe{sup +} vdf exhibits a unimodal structure with a maximum parallel flow velocity of 2.2 km/s at the end of the source. For Ar-He plasma, the Ar ivdf is bimodal with the fast ion component parallel velocity increasing from 5.2 to 7.8 km/s as the He fraction increases from 0% to 30%. For the same He fraction range, the slow argon ion population distribution changes from a single Gaussian to a wide distribution extending all the way from the speed of the fast population to 0 m/s.

Biloiu, Ioana A.; Scime, Earl E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

2010-11-15

199

Stabilizing effect of ion pressure gradient on magnetic curvature-driven drift modes located at rational surface of tokamak plasma  

NASA Astrophysics Data System (ADS)

In the fluid model, we derive a dispersion relation for the toroidal drift modes of tokamak plasmas, including the ion pressure gradient and the magnetic field gradient and curvature. It is shown that the magnetic field gradient and curvature (MFGC) can cause instabilities at the rational surface, which are of toroidicity-induced (TI) modes. On the other hand, it is discovered that the ion pressure gradient can stabilize the present MFGC instabilities. The critical threshold of ion pressure gradient, which makes the growth rate reduced to zero, is obtained both analytically and numerically.

Wang, Ai-Ke

2005-08-01

200

Dependence of the equatorial anomaly and of equatorial spread F on the maximum prereversal E B drift velocity measured at solar maximum  

NASA Astrophysics Data System (ADS)

The relation of equatorial bubbles to the equatorial anomaly is important because scintillation that is most disruptive to transionospheric RF propagation occurs when it passes through the intersection of the two. However, measurement of the relation between the two and of the electric field from which both arise is difficult because of large separations in space and time. This first attempt to perform these measurements employs a latitudinal array of ionospheric sounders spanning 0 to 40 dip latitude (DLAT) in the Western American sector. Measured on each day of a solar maximum year are the following: (1) the maximum electron density of the postsunset equatorial anomaly, Ne, at 16 and at 20.3 DLAT at 2100 LT, the time when the anomaly crest is at its maximum latitude; (2) equatorial spread F (ESF), detected by the occurrence of macroscopic bubbles and of bottomside spread F (BSSF), the latter recorded at levels of none, weak and strong; (3) Kp averaged over the 6 hours before sunset. Ne and ESF are considered functions of the maximum prereversal F layer drift E B drift velocity measured by the Jicamarca incoherent scatter radar also during solar maximum and at the same longitude. Parameters are averaged over two levels of Kp for the three seasons, the E months (March, April, September, and October), D months (November-February), and J months (May-August) to yield the following results: (1) Ne measured at 16, at 20.3 DLAT or at the anomaly crest are linearly dependent on maximum E B drift velocity. (2) Occurrence of each level of ESF increases with Ne approximately linearly during the E and J months but not during the D months. (3) ESF occurrence is dependent on and increases approximately linearly with maximum E B drift velocity during the E and J months. During the D months this dependence is absent. Except for the D months, these results indicate that scintillation increases with maximum prereversal E B drift velocity: at L-band at the bubble-anomaly intersection because bubble occurrence increases, Ne increases, and the latitudinal extent of the anomaly increases; and at VHF/UHF near the equator because the occurrence of strong BSSF increases.

Whalen, J. A.

2003-05-01

201

Li+ alumino-silicate ion source development for the Neutralized Drift Compression Experiment (NDCX-II)  

SciTech Connect

To heat targets to electron-volt temperatures for the study of warm dense matter with intense ion beams, low mass ions, such as lithium, have an energy loss peak (dE/dx) at a suitable kinetic energy. The Heavy Ion Fusion Sciences (HIFS) program at Lawrence Berkeley National Laboratory will carry out warm dense matter experiments using Li{sup +} ion beam with energy 1.2-4 MeV in order to achieve uniform heating up to 0.1-1 eV. The accelerator physics design of Neutralized Drift Compression Experiment (NDCX-II) has a pulse length at the ion source of about 0.5 {micro}s. Thus for producing 50 nC of beam charge, the required beam current is about 100 mA. Focusability requires a normalized (edge) emittance {approx}2 {pi}-mm-mrad. Here, lithium aluminosilicate ion sources, of {beta}-eucryptite, are being studied within the scope of NDCX-II construction. Several small (0.64 cm diameter) lithium aluminosilicate ion sources, on 70%-80% porous tungsten substrate, were operated in a pulsed mode. The distance between the source surface and the mid-plane of the extraction electrode (1 cm diameter aperture) was 1.48 cm. The source surface temperature was at 1220 C to 1300 C. A 5-6 {micro}s long beam pulsed was recorded by a Faraday cup (+300 V on the collector plate and -300 V on the suppressor ring). Figure 1 shows measured beam current density (J) vs. V{sup 3/2}. A space-charge limited beam density of {approx}1 mA/cm{sup 2} was measured at 1275 C temperature, after allowing a conditioning time of about {approx} 12 hours. Maximum emission limited beam current density of {ge} 1.8mA/cm{sup 2} was recorded at 1300 C with 10-kV extractions. Figure 2 shows the lifetime of two typical sources with space-charge limited beam current emission at a lower extraction voltage (1.75 kV) and at temperature of 1265 {+-} 7 C. These data demonstrate a constant, space-charge limited beam current for 20-50 hours. The lifetime of a source is determined by the loss of lithium from the alumino-silicate material either as ions or as neutral atoms. Our measurements suggest that for the low duty factor ({approx}10{sup -8}) required for NDCX-II, the lifetime of an emitter depends mostly on the duration that the emitter spends at elevated temperature, that is, at {ge} 1250 C. At this temperature, lithium loss is due mostly to neutral loss (not charged ion extraction). Extension of the lifetime of the source may be possible by lowering the temperature between beam pulses, when the idling time is sufficiently long between shots. The NDCX-II design seeks to operate the ion source at the maximum current density without running into heat management and lifetime problems. In preparation to fabricate a large (10.9 cm in diameter) source for the NDCXII experiment, recently a 7.6 cm diameter source has been fabricated. The method of fabrication of this larger source is similar to that of fabrication of a 6.3mm diameter source, except a longer furnace heating time was used due to mass differences. NDCX-II construction is in progress. Progress of lithium source study for NDCX-II is available in literature.

LBNL; Roy, P.K.; Greenway, W.; Kwan, J.W.; Seidl, P.A.; Waldron, W.

2011-04-20

202

Measurement of High Frequency Perturbations to the Ion Velocity Distribution in the HELIX Helicon Plasma Source  

Microsoft Academic Search

Using lasers to measure plasma parameters has become more common in recent years. Lasers can provide information about plasma parameters without perturbing the plasma. The most common technique for ion parameter measurements is Laser Induced Fluorescence (LIF). LIF typically measures the ion velocity distribution and provides information about the ion temperatures and ion flows in the plasma. More recently, Skiff

J. L. Kline; R. F. Boivin; C. Franck; T. Klinger; E. E. Scime

2001-01-01

203

Fast-Ion Velocity Distributions in JET Measured by Collective Thomson Scattering  

Microsoft Academic Search

Results on fast ion diagnosis by collective Thomson scattering at JET are presented. 400 kW, 2 mm radiation was scattered in plasmas with energetic proton minority populations heated by 4-8 MW ion cyclotron resonance heating. There is clear evidence of scattering from plasma fluctuations driven by the fast ion population. In a few cases ion velocity distributions with energies in

H. Bindslev; J. A. Hoekzema; J. Egedal; J. A. Fessey; T. P. Hughes; J. S. Machuzak

1999-01-01

204

Laser-Induced Fluorescence Measurements of Ion Temperatures and Drifts Associated with Shear Alfvn Waves in Argon  

NASA Astrophysics Data System (ADS)

Laser-induced fluorescence (LIF) has been used in conjunction with Langmuir probe techniques to make preliminary measurements of the ion temperatures and ion drifts associated with shear Alfvn waves in an argon plasma at the Large Plasma Device at UCLA. The waves are lauched with a helical antenna into a relatively-uniform 40 cm diameter cylindrical plasma column with n_e=1.110^12 cm-3, T_e=5 eV, T_i=1.1 eV, and B_0=1500 G. A narrow-bandwidth tunable dye laser with output around 611.492 nm is used to excite 3d ^2G_9/2 metastable ions to 4p ^2F_7/2, which then spontaneously decay to 4s ^2D_5/2 by emitting light at 460.957 nm. At the center of the wave pattern where the wave fields and currents are most intense (B_wave/B0 ~ 10-3), a local density perturbation and electron heating are observed, along with ion drifts perpendicular to the background magnetic field. From these measured drifts the perpendicular (to B_0) component of the wave electric field is computed. Then, using the wave dispersion relation, the parallel component of the wave electric field is estimated. Both LIF and Langmuir probe data are presented.

Palmer, Nathan E.; Gekelman, Walter

1999-11-01

205

Equatorial vertical plasma drift velocities and electron densities inferred from ground-based ionosonde measurements during low solar activity  

NASA Astrophysics Data System (ADS)

Average values of ionosonde hmF2 data acquired from an African equatorial station have been used to determine vertical plasma drift (Vz) measurements during period of low solar activity. Pre-noon peak was around 1000 h LT for all seasons. The peak daytime F2 drift is higher during the equinoctial months with an average of 18.1 m/s than the solsticial months (14.7 m/s). At nighttime, Vz is characterized first by upward enhancement around 1900 h LT with a range of 0.3-8.0 m/s, then by a downward reversal. The highest enhancement was recorded in December solstice and start earliest during the March equinox. The peak reversal values are 13.3, 10.7, 9.0 and 4.2 m/s for December Solstice, September Equinox, March Equinox and June Solstice respectively. The observed simultaneous post-sunset rise in hmF2 and in vertical EB drift together with a sharp drop in NmF2 at all season infer that electrons moving away from the equator are at a region of low recombination loss rate. The abrupt faster drift of the plasma away from the equator as indicated by the pre-reversal enhancement (PRE) in upward plasma drift is responsible for the sharp drop in NmF2 immediately after sunset. Some past results were also confirmed in this work.

Adebesin, B. O.; Adeniyi, J. O.; Adimula, I. A.; Reinisch, B. W.

2013-05-01

206

Characteristics of nocturnal ionospheric zonal plasma drift velocities determined from OI 630.0 nm and 777.4 nm all sky imaging observations  

NASA Astrophysics Data System (ADS)

In the Brazilian sector, mostly during the period from October to March, the equatorial and low latitude Fregions present quasi north-south magnetic field- aligned large-scale ionospheric irregularities, which are one of the most remarkable features of these regions of the upper atmosphere. These ionospheric irregularities may be observed by different observational techniques (e.g., radar, digisonde, GPS and optical instruments) and its time evolution and propagation can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. Simultaneous observations of the OI 630.0 nm and 777.4 nm nightglow emissions using all-sky imaging systems at So Jos dos Campos (23.21o S, 45.86o W; dip latitude 17.6o S), Brazil, have been used to determine the nighttime variations of zonal plasma bubble drift velocities. The OI 630.0 nm and 777.4 nm emissions come from altitudes of about 250 km and 350 km, respectively. The optical signatures of the OI 777.4 nm emission are more closely related to the actual ionospheric plasma bubble structures, owing to the fact that it is a prompt emission and depends only on the electron density profiles, with no F-region height dependence. On the other hand, the OI 630.0 nm emission comes from the bottomside of the F layer with a strong F region height dependence and shows- blurred images due to its 110-s lifetime. The all-sky imaging systems used in the present studies have CCDs, with high quantum efficiency which provide excellent capabilities for quantitative measurements of faint and low contract emissions. Both the emissions (OI 630.0 nm and 777.4 nm) show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale F-region plasma bubbles. Thus, it is possible to infer the nocturnal ionospheric zonal plasma drift velocities by just following the space-time displacements of the intensity-depleted bands seen in the images. The nocturnal zonal plasma drift velocities obtained from the two emissions are presented and discussed in this communication. Also, a comparison of the observed zonal plasma drift velocities with the zonal neutral wind velocities obtained from the horizontal wind model (HWM- 90) are presented.

Abalde, J.; Pimenta, A.; Fagundes, P.; Sahai, Y.; Bittencourt, J.

207

Ultrafast ion temperature and toroidal velocity fluctuation spectroscopy diagnostic design  

SciTech Connect

High sensitivity measurements of localized, long-wavelength ion temperature, and toroidal velocity fluctuations (T-tilde{sub i}/T{sub i},v-tilde{sub ||})/v{sub ||}) are required to address critical issues pertaining to turbulent transport. This diagnostic design exploits emission from charge exchange recombination between neutral beam atoms and the intrinsic carbon impurity. The n=8-7 transition of C VI at {lambda}{sub 0}=529.05 nm will be measured. The key difference between this diagnostic design and conventional charge exchange spectrometers is the use of high-efficiency prism-coupled transmission gratings, avalanche photodiode detectors, and high-throughput collection optics. The spectrometer achieves a spectral resolution of 0.25 nm, and observes 528.0-530.0 nm with eight discrete spectral channels, with an entrance throughput of 1.6 mm{sup 2} sr, two orders of magnitude larger than conventional charge exchange system. The diagnostic will achieve a turbulence-relevant time resolution of 1 {mu}s. System modeling demonstrates a sensitivity of T-tilde{sub i}/T{sub i}{<=}1%.

McKee, G. R.; Schlossberg, D. J.; Shafer, M. W. [University of Wisconsin-Madison, 1500 Engineering Dr., Madison, Wisconsin 53706 (United States)

2008-10-15

208

Spectroscopic measurement of ion temperature and ion velocity distributions in the flux-coil generated FRC  

SciTech Connect

One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.

Gupta, D.; Gota, H.; Hayashi, R.; Kiyashko, V.; Morehouse, M.; Primavera, S. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Bolte, N. [Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States); Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Marsili, P. [Department of Physics, University of Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); Roche, T. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Wessel, F. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Tri Alpha Energy, Inc., Rancho Santa Margarita, California 92688 (United States)

2010-10-15

209

Techniques for obtaining velocity distributions of atoms or ions from Doppler-broadened spectral line profiles  

Microsoft Academic Search

Analysis of the doppler-broadened profiles of spectral lines radiated by atoms or ions in plasmas yields information about their velocity distributions. Researchers have analysed profiles of lines radiated by atoms in isotropic velocity distributions in several ways, one being the inversion of the integral equation which relates the velocity distribution to the line profile. This inversion formula was derived for

1986-01-01

210

Inverse velocity trends in secondary ion mass spectrometry; a new method for quantification?  

NASA Astrophysics Data System (ADS)

Secondary ions from the elements of As, Cu, Ni, P, and Zn, from two standard reference materials analysed with a Cameca IMS 3f SIMS instrument were found to exhibit strong exponential-like dependences on escape velocity, particularly over the higher emission energy range. These dependences were noted under O-, O2+, and Cs+ primary ion beam conditions. After accounting for their known concentrations, the inverse velocity curves (secondary ion intensities corrected for instrument transmission and sputter yield effects plotted against the inverse of the velocity) were found to merge as infinite velocity was approached. These observations agree with quantum mechanical arguments used to describe secondary ion formation, and, in addition, suggests a new method for undertaking quantitative analysis by secondary ion mass spectrometry (SIMS). Quantification would be carried out by referencing infinite velocity values for each element of interest to that obtained from an element for which the concentration is already known.

van der Heide, P. A. W.

1994-04-01

211

High Frequency Drift Waves with Wavelengths Below the Ion Gyroradius in Equatorial Spread F.  

National Technical Information Service (NTIS)

Evidence is given for intense VHF and UHF radar backscatter during equatorial Spread F resulting from irregularities of 1 meter and 36 cm, respectively. The linear theory for high frequency drift waves, generated by the drift-cyclotron and lower-hybrid-dr...

D. M. Towle J. D. Huba P. K. Chaturvedi S. L. Ossakow

1978-01-01

212

A Novel pH-dependent Drift Improvement Method for Zirconium Dioxide Gated pH-Ion Sensitive Field Effect Transistors  

PubMed Central

A novel compensation method for Zirconium dioxide gated Ion Sensitive Field Effect Transistors (ISFETs) to improve pH-dependent drift was demonstrated. Through the sequential measurements for both the n-channel and p-channel ISFETs, 75100% pH-dependent drift could be successfully suppressed for the first seven hours. As a result, a nearly constant drift rate versus pH value was obtained, which increases the accuracy of pH measurements. Meanwhile, the drawback of the hyperbolic-like change with time of the common drift behavior for ISFETs was improved. A state-of-the-art integrated scheme adopting this method was also illustrated.

Chang, Kow-Ming; Chang, Chih-Tien; Chao, Kuo-Yi; Lin, Chia-Hung

2010-01-01

213

Drift Compression and Final Focus for Intense Heavy Ion Beams with Non-periodic, Time-dependent Lattice  

SciTech Connect

In the currently envisioned configurations for heavy ion fusion, it is necessary to longitudinally compress the beam bunches by a large factor after the acceleration phase. Because the space-charge force increases as the beam is compressed, the beam size in the transverse direction will increase in a periodic quadrupole lattice. If an active control of the beam size is desired, a larger focusing force is needed to confine the beam in the transverse direction, and a non-periodic quadrupole lattice along the beam path is necessary. In this paper, we describe the design of such a focusing lattice using the transverse envelope equations. A drift compression and final focus lattice should focus the entire beam pulse onto the same focal spot on the target. This is difficult with a fixed lattice, because different slices of the beam may have different perveance and emittance. Four time-dependent magnets are introduced in the upstream of drift compression to focus the entire pulse onto the sam e focal spot. Drift compression and final focusing schemes are developed for a typical heavy ion fusion driver and for the Integrated Beam Experiment (IBX) being designed by the Heavy Ion Fusion Virtual National Laboratory.

Hong Qin; Ronald C. Davidson; John J. Barnard; Edward P. Lee

2005-02-14

214

Plasma Structuring by the Gradient Drift Instability at High Latitudes and Comparison with Velocity Shear Driven Processes.  

National Technical Information Service (NTIS)

Satellite in-situ measurements made by the Dynamics Explorer 2 satellite were utilized to describe the nature of plasma structuring at high latitudes caused by the gradient-drift instability process. The non-midnight and dawn-dusk orbits of the DE 2 satel...

S. Basu S. Basu E. MacKenzie W. R. Coley

1990-01-01

215

Helium cluster ions RgHe{\\/x +} (Rg=Ne, Ar and Kr, x≦14) formed in a drift tube cooled by liquid helium  

Microsoft Academic Search

Rare gas ions Ne+, Ar+ and Kr+ are injected into a drift tube which is filled with helium gas and cooled by liquid helium. Helium cluster ions RgHe{\\/x +} (Rg=Ne, Ar and Kr, x≦14) are observed as products. Information regarding the stability of RgHe{\\/x +} is obtained from drift field dependence of the size distribution of the clusters, and magic

T. M. Kojima; N. Kobayashi; Y. Kaneko

1992-01-01

216

Cerenkov detector for heavy-ion velocity measurements  

Microsoft Academic Search

We have developed a highly sensitive velocity measuring detector using total-internal-reflection Cerenkov counters of a type mentioned by Jelly in 1958. If the velocity of the particle is above the threshold for total-internal-reflection these counters have a charge resolution of sigma = 0.18e for a 3mm thick glass radiator. For the velocity measurement we use a fused silica radiator so

D. L. Olson; M. Baumgartner; J. P. Dufour; J. G. Girard; D. E. Greiner; P. J. Lindstrom; T. J. M. Symons; H. J. Crawford

1984-01-01

217

Ion velocity distributions in the sheath and presheath of a biased object in plasma  

NASA Astrophysics Data System (ADS)

Ion velocity distributions in the vicinity of a spherical object with a negative potential with respect to collisionless, source-free plasma are studied with three-dimensional numerical simulations. The ion dynamics around the object leads to distorted radial velocity distributions in the presheath and the sheath edge region. Far in the sheath, an increase in the thermal velocity in the radial direction is observed. Different potentials of the object, ion temperatures, and ion masses are considered, as well as the role of spatial and temporal resolutions in laboratory measurements of ion velocity distributions. The simulations are carried out with the DiP3D, a three-dimensional particle-in-cell numerical code.

Miloch, W. J.; Gulbrandsen, N.; Mishra, L. N.; Fredriksen, A.?.

2011-08-01

218

Ion velocity distributions in the sheath and presheath of a biased object in plasma  

SciTech Connect

Ion velocity distributions in the vicinity of a spherical object with a negative potential with respect to collisionless, source-free plasma are studied with three-dimensional numerical simulations. The ion dynamics around the object leads to distorted radial velocity distributions in the presheath and the sheath edge region. Far in the sheath, an increase in the thermal velocity in the radial direction is observed. Different potentials of the object, ion temperatures, and ion masses are considered, as well as the role of spatial and temporal resolutions in laboratory measurements of ion velocity distributions. The simulations are carried out with the DiP3D, a three-dimensional particle-in-cell numerical code.

Miloch, W. J.; Gulbrandsen, N.; Mishra, L. N.; Fredriksen, A. [Department of Physics and Technology, University of Tromsoe, 9037 Tromsoe (Norway)

2011-08-15

219

A Measurement of Electron and Hole Drift Velocities in a Germanium <100> CDMS Detector, at a Temperature of 31 milliKelvin  

NASA Astrophysics Data System (ADS)

The Cryogenic Dark Matter Search (CDMS) uses ultrapure germanium detectors at a temperature of approximately 40 mK. These detectors are maintained in a state where shallow impurities are well neutralized. Free electrons and holes, generated by particle events, are ``hot'' and remain out of equilibrium in the bulk. In this system, carrier drift and diffusion occur simultaneously with the generation of free carriers, and with recombination to localized bulk and surface states. These processes jointly affect the space charge distribution in the bulk and at the surfaces of our detectors. The impact of space charge on the electric field likely accounts for much of the phenomenology found in our detectors. Any ability to predict the evolution of the space charge distribution requires a fundamental understanding of carrier transport processes under our operating conditions. To this end, we have measured carrier drift velocities as a function of electric field in an high-purity CDMS detector of germanium <100> at a temperature of 31 mK. We adapted CDMS electronics to perform a high-bandwidth measurement of charge propagation times for near-surface events in our detector under test. We find that measured velocities coincide reasonably well with predictions made in our previous theory treatment. This indicates that carrier mobility is limited solely by phonon emission.

Sundqvist, K. M.; Phipps, A. T. J.; Bailey, C. N.; Brink, P. L.; Cabrera, B.; Daal, M.; Lam, A. C. Y.; Mirabolfathi, N.; Novak, L.; Pyle, M.; Sadoulet, B.; Serfass, B.; Seitz, D.; Tomada, A.; Yen, J. J.

2009-12-01

220

Direct analysis in real time coupled to multiplexed drift tube ion mobility spectrometry for detecting toxic chemicals.  

PubMed

Current and future chemical threats to homeland security motivate the need for new chemical detection systems to provide border, transportation, and workplace security. We present the first successful coupling of a commercial direct analysis in real time (DART) ion source to a resistive glass monolithic drift tube ion mobility spectrometer (DTIMS) as the basis for a low maintenance, versatile, and robust chemical monitoring system. in situ ionization within the electric field gradient of the instrument enhances sensitivity and provides a safe sampling strategy. The instrument uses nitrogen as both the DART discharge and DTIMS drift gases, allowing for a high electric field to be used for ion separation while keeping cost-of-use low. With the use of a traditional signal averaging acquisition mode, the 95% probability of detection (POD) for analytes sampled from melting point capillary tubes was 11.81% v/v for DMMP, 1.13% v/v for 2-CEES, and 10.61 mM for methamidophos. Sensitivity was improved via a prototype transmission-mode geometry interface, resulting in an almost 2 orders of magnitude decrease in the POD level for DMMP (0.28% v/v). As an alternative to transmission mode operation, digital multiplexing of the DTIMS ion injection step was also implemented, finding a 3-fold improvement in signal-to-noise ratios for 200 ?s gate injections and a 4.5-fold for 400 ?s gate injections. PMID:21319810

Harris, Glenn A; Kwasnik, Mark; Fernndez, Facundo M

2011-02-14

221

Daytime, low latitude, vertical ExB drift velocities, inferred from ground-based magnetometer observations in the Peruvian, Philippine and Indian longitude sectors under quiet and disturbed conditions  

NASA Astrophysics Data System (ADS)

Recent studies have demonstrated that ground-based magnetometer observations can be used to infer realistic, daytime vertical ExB drift velocities in the Peruvian longitude sector. It has also been demonstrated that under certain conditions the time variability of the Interplanetary Electric Field (IEF) - minutes to hours - is reflected in the daytime, prompt penetration of high latitude electric fields to low latitudes. In this paper, we incorporate magnetometer-inferred ExB drift techniques to extend this study to include the Philippine and Indian sector ExB drift velocities and to investigate the relationships between IEF conditions and daytime, low latitude electric field observations under both geomagnetically quiet and disturbed conditions. This paper addresses two basic questions: 1.) How well do the quiet-time, ?H-inferred ExB drift velocities compare with the Fejer-Scherliess, quiet-time, climatological model (Scherliess and Fejer, 1999) in the Peruvian, Philippine and Indian sectors and 2.) What are the relationships between the Interplanetary Electric Fields (IEF) and low latitude electric fields during disturbed periods? We address the above questions by analyzing magnetometer-inferred ExB drift velocities between January 2001 and December 2004 when there exists more than 450 quiet days and more than 235 geomagnetically disturbed days, defined by daily Ap values greater than 20. It is demonstrated that the neural network approach that provides realistic ExB drift velocities based on magnetometer observations in the Peruvian sector can be applied at all longitudes where appropriately placed magnetometers exist. It is found that 1.) The average quiet, daytime upward ExB drift velocity vs Local Time is comparable to the Fejer-Scherliess climatological model and 2.) During disturbed conditions, it is observed that promptly penetrating electric fields occur, simultaneously, in the Philippine, Indian and Peruvian sectors.

Anderson, D.; Anghel, A.; Chau, J.; Yumoto, K.; Bhattacharyya, A.; Alex, S.

222

Effect of Ion Escape Velocity and Conversion Surface Material on H- Production  

NASA Astrophysics Data System (ADS)

According to generally accepted models surface production of negative ions depends on ion escape velocity and work function of the surface. We have conducted an experimental study addressing the role of the ion escape velocity on H- production. A converter-type ion source at Los Alamos Neutron Science Center was employed for the experiment. The ion escape velocity was affected by varying the bias voltage of the converter electrode. It was observed that due to enhanced stripping of H- no direct gain of extracted beam current can be achieved by increasing the converter voltage. The conversion efficiency of H- was observed to vary with converter voltage and follow the existing theories in qualitative manner. We present calculations predicting relative H- yields from different cesiated surfaces with comparison to experimental observations from different types of H- ion sources. Utilizing materials exhibiting negative electron affinity and exposed to UV-light is considered for Cesium-free H-/D- production.

Tarvainen, O.; Kalvas, T.; Komppula, J.; Koivisto, H.; Geros, E.; Stelzer, J.; Rouleau, G.; Johnson, K. F.; Carmichael, J.

2011-09-01

223

Observations of ion and electron velocity distributions associated with slow-mode shocks in Earth's distant magnetotail  

Microsoft Academic Search

Three-dimensional observations of ion and electron velocity distributions with the Geotail spacecraft for three crossings of slow-mode shocks encountered in Earth's distant magnetotail are presented. Important findings from the observations are (1) the ion velocity distributions in the shock layer and the downstream region of the shocks are highly anisotropic because of the presence of multiple ion components in velocity

J. Seon; L. A. Frank; W. R. Paterson; J. D. Scudder; F. V. Coroniti; S. Kokubun; T. Yamamoto

1996-01-01

224

Cerenkov detector for heavy-ion velocity measurements  

SciTech Connect

We have developed a highly sensitive velocity measuring detector using total-internal-reflection Cerenkov counters of a type mentioned by Jelly in 1958. If the velocity of the particle is above the threshold for total-internal-reflection these counters have a charge resolution of sigma = 0.18e for a 3mm thick glass radiator. For the velocity measurement we use a fused silica radiator so that the velocity of the particles are near the threshold for total-internal reflection. For momentum-analyzed projectile fragments of 1.6 GeV/nucleon /sup 40/Ar, we have measured a mass resolution of sigma = 0.1u for isotope identification.

Olson, D.L.; Baumgartner, M.; Dufour, J.P.; Girard, J.G.; Greiner, D.E.; Lindstrom, P.J.; Symons, T.J.M.; Crawford, H.J.

1984-08-01

225

Phase-Resolved Measurements of Ion Velocity in a Radio-Frequency Sheath  

SciTech Connect

The time-dependent argon-ion velocity distribution function above and within the plasma sheath of an rf-biased substrate has been measured using laser-induced fluorescence in a commercial plasma processing tool. Discharge parameters were such that the 2.2 MHz rf-bias period was on the order of the ion transit time through the sheath ({tau}{sub ion}/{tau}{sub rf}=0.3). This work embodies the first time-resolved measurement of ion velocity distribution functions within an rf-biased sheath over a large area (30 cm diameter) silicon wafer substrate.

Jacobs, Brett; Gekelman, Walter; Pribyl, Pat [Department of Physics and Astronomy, University of California--Los Angeles, Los Angeles, California 90024 (United States); Barnes, Michael [MS Barnes Engineering, San Ramon, California 94583 (United States)

2010-08-13

226

Models and numerical simulation of velocity distribution of pickup ions  

Microsoft Academic Search

Large manned spacecraft release and carry up a huge amounts of water in its orbital motion. Some of the neutral water molecules undergo charge exchange with the ambient ionospheric plasma and become what are called pick-up ions at Low Earth Orbit (LEO) altitudes. The purpose of this dissertation is to model those ions and predicts their effect on a space

Yinghui Zhang

1998-01-01

227

Combination of fast-ion diagnostics in velocity-space tomographies  

NASA Astrophysics Data System (ADS)

Fast-ion D? (FIDA) and collective Thomson scattering (CTS) diagnostics provide indirect measurements of fast-ion velocity distribution functions in magnetically confined plasmas. Here we present the first prescription for velocity-space tomographic inversion of CTS and FIDA measurements that can use CTS and FIDA measurements together and that takes uncertainties in such measurements into account. Our prescription is general and could be applied to other diagnostics. We demonstrate tomographic reconstructions of an ASDEX Upgrade beam ion velocity distribution function. First, we compute synthetic measurements from two CTS views and two FIDA views using a TRANSP/NUBEAM simulation, and then we compute joint tomographic inversions in velocity-space from these. The overall shape of the 2D velocity distribution function and the location of the maxima at full and half beam injection energy are well reproduced in velocity-space tomographic inversions, if the noise level in the measurements is below 10%. Our results suggest that 2D fast-ion velocity distribution functions can be directly inferred from fast-ion measurements and their uncertainties, even if the measurements are taken with different diagnostic methods.

Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; Garca-Muoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.; Tardini, G.; the ASDEX Upgrade Team

2013-06-01

228

Ion cyclotron diffusion of velocity distributions in the extended solar corona  

Microsoft Academic Search

en waves. This process naturally produces departures from Maxwellian and bi-Maxwellian velocity distributions. Here it is argued that these departures must be taken into account in order to understand the resonant velocity-space diffusion, the wave damping, and the formation of ultraviolet emission lines. Time-dependent ion velocity distributions are computed for a fixed spectrum of waves in a homogeneous plasma, and

Steven R. Cranmer

2001-01-01

229

Instability of the Parallel-Propagating Alfvn/Ion-Cyclotron Wave Driven by Drifting Alpha Particles in High-Beta Solar Wind Streams  

NASA Astrophysics Data System (ADS)

Alpha particles are known to drift with respect to the protons along the background magnetic field in the fast solar wind. Their typical drift speed is observed to be limited to a value of order the local proton Alfvn speed vA as long as collisional deceleration can be neglected. Since vA decreases with increasing distance from the Sun, a continuous deceleration takes place converting the drift energy to other forms of energy such as thermal energy or wave energy. We derive an instability of the parallel-propagating Alfvn/ion-cyclotron mode driven by drifting alpha particles in a high-beta plasma (? ? 2). To the best of our knowledge, this alpha-particle-driven drift instability has not been described previously, although it is similar in several respects to the well-studied cosmic-ray streaming instability. Using quasilinear theory, we derive an approximate analytic expression for the instability threshold. We compare this expression with numerical solutions of the full hot-plasma dispersion relation and find good agreement. The described instability is a result of the competition between driving by resonant alpha particles and damping by resonant protons. Other drift instabilities are known to set "speed limits" to the relative drift of ion species in the solar wind depending on the required plasma parameters. We present a comparison with measured drift speeds and show that the instability threshold of the parallel Alfvnic drift instability indeed limits the alpha particle drift in high-beta fast-solar-wind streams.

Verscharen, Daniel; Bourouaine, Sofiane; Chandran, Benjamin D. G.

2013-04-01

230

Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere  

NASA Astrophysics Data System (ADS)

The JOULE-II sounding rocket salvo was launched from Poker Flat Rocket Range into weak pulsating aurora following a moderate substorm at 0345 LT on 19 January 2007. We present in situ measurements of ion flow velocity and electric and magnetic fields combined with neutral wind observations derived from ground observations of in situ chemical tracers. Measured ion drifts in the 150-198 km and 92-105 km altitude ranges are consistent with ${\\vec{E} ${\\vec{B} motion to within 16 m s-1 rms and with neutral wind velocity to within 20 m s-1, respectively. From these measurements we have calculated the ratio $\\kappa$ of the ion cyclotron and ion collision frequencies, finding $\\kappa$ = 1 at an altitude of 118 0.3 km. Using direct measurements of ion current, we calculate the Joule heating rate and Pedersen and Hall conductivity profiles for this moderately active event and find height-integrated values of 390 W km-2 and 0.59 and 2.22 S, respectively. We also find that these values would have errors of up to tens of percent without coincident neutral wind measurements, and presumably more so during more active conditions. Ion flow vectors were measured at a rate of 125 s-1 however, no significant fluctuations were observed at spatial/temporal scales below 350 m and 0.5 s. Observational limits were 5.5 m and 0.016 s.

Sangalli, L.; Knudsen, D. J.; Larsen, M. F.; Zhan, T.; Pfaff, R. F.; Rowland, D.

2009-04-01

231

SIMULATIONS OF HIGH-VELOCITY CLOUDS. II. ABLATION FROM HIGH-VELOCITY CLOUDS AS A SOURCE OF LOW-VELOCITY HIGH IONS  

SciTech Connect

In order to determine if the material ablated from high-velocity clouds (HVCs) is a significant source of low-velocity high ions (C IV, N V, and O VI) such as those found in the Galactic halo, we simulate the hydrodynamics of the gas and the time-dependent ionization evolution of its carbon, nitrogen, and oxygen ions. Our suite of simulations examines the ablation of warm material from clouds of various sizes, densities, and velocities as they pass through the hot Galactic halo. The ablated material mixes with the environmental gas, producing an intermediate-temperature mixture that is rich in high ions and that slows to the speed of the surrounding gas. We find that the slow mixed material is a significant source of the low-velocity O VI that is observed in the halo, as it can account for at least {approx}1/3 of the observed O VI column density. Hence, any complete model of the high ions in the halo should include the contribution to the O VI from ablated HVC material. However, such material is unlikely to be a major source of the observed C IV, presumably because the observed C IV is affected by photoionization, which our models do not include. We discuss a composite model that includes contributions from HVCs, supernova remnants, a cooling Galactic fountain, and photoionization by an external radiation field. By design, this model matches the observed O VI column density. This model can also account for most or all of the observed C IV, but only half of the observed N V.

Henley, David B.; Kwak, Kyujin; Shelton, Robin L., E-mail: dbh@physast.uga.edu, E-mail: rls@physast.uga.edu, E-mail: kkwak@kasi.re.kr [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2012-07-01

232

Collective particle kinetics in the lower hybrid drift instability  

NASA Astrophysics Data System (ADS)

We study the coupled evolution of energetic minority ions, background majority ions, electrons, and electromagnetic fields in magnetised plasma undergoing the lower hybrid drift instability. The evolving distribution of a drifting ring-beam population of energetic ions is simulated using a particle-in-cell code, fully kinetic for all species, with one spatial and three velocity space co-ordinates. Bulk plasma parameters approximate tokamak core conditions, in a scenario motivated by observations of ion cyclotron emission and relevant to alpha channelling (Cook et al, PRL 105, 25503 (2010)). Resonant energy transfer occurs at the two gyrophase angles where the speed of an energetic ion on its cyclotron orbit matches the phase velocity of the lower hybrid wave along the simulation domain. Electron space-charge oscillations determine the wavelength of the propagating wave. This governs the bunching of energetic ions, in physical space and gyrophase angle (Cook et al, PPCF 53, 074019 (2011)), as they drive the instability.

Dendy, Richard; Cook, James; Chapman, Sandra

2011-11-01

233

A velocity map imaging spectrometer for electron?ion and ion?ion coincidence experiments with synchrotron radiation  

SciTech Connect

We have built a velocity imaging (VMI) spectrometer optimized for angle-resolved photoionization experiments with synchrotron radiation (SR) in the VUV and soft X-tay range. The spectrometer is equiped with four electrostatic lenses that focus the charged photoionization products onto a position-sensitive multi-hit delay-line anode. The use of two additional electrostatic lens elements as compared to the standard design of Eppink and Parker [T.J.B. Eppink and D.H. Parker, Rev. Sci. Instrum. 68 (1997) 3477]provides better focusing of an extended interaction region, which is crucial for most SR applications. Furthermore, the apparatus is equipped with a second micro-channel plate detector opposite to the VMI spectrometer, enabling electron-ion coincidence experiments and thereby mass-resolved ion spectroscopy independent of the time structure of the synchrotron radiation. First results for the photofragmentation of CO2 molecules are presented.

Advanced Light Source; Kilcoyne, Arthur L; Rolles, D.; Pesic, Z.D.; Perri, M.; Bilodeau, R.C.; Ackerman, G.D.; Rude, B.S.; Kilcoyne, A.L.D.; Bozek, J.D.; Berrah, N.

2007-04-27

234

Acoustic-surface-wave velocity decrease produced by ion implantation in lithium niobate  

Microsoft Academic Search

Ion implantation was found to reduce the velocity of an acoustic surface wave propagating in lithium niobate. This frequency-dependent decrease may be mainly attributed to a reduction of the effective electromechanical coupling coefficient as reported in this letter. The impedance of 138-MHz interdigital transducers deposited on implanted niobate substrates has been determined versus ion dose.

P. Hartemann; J. K. Howard

1975-01-01

235

Low-velocity ion slowing-down in strongly asymmetric and binary ionic mixtures  

NASA Astrophysics Data System (ADS)

Attention is focused on the low-ion-velocity stopping mechanisms in multicomponent and dense target plasmas built of quasi-classical electron fluids neutralizing binary ionic mixtures. The target plasma is taken in a multicomponent dielectric formulation la Fried-Conte. The occurrence of projectile ion velocities (so-called critical) for which target electron slowing-down equals that of given target ion components is also considered. We emphasize the strongly asymmetric BIM targets such as the proton-boron 11 of thermonuclear concern and the strongly mass-asymmetric proton-U238+.

Fromy, P.; Tashev, B.; Deutsch, C.

2010-10-01

236

Kr II and Xe II axial velocity distribution functions in a cross-field ion source  

SciTech Connect

Laser induced fluorescence measurements were carried out in a cross-field ion source to examine the behaviour of the axial ion velocity distribution functions (VDFs) in the expanding plasma. In the present paper, we focus on the axial VDFs of Kr II and Xe II ions. We examine the contourplots in a 1D-phase space (x,v{sub x}) representation in front of the exhaust channel and along the centerline of the ion source. The main ion beam, whose momentum corresponds to the ions that are accelerated through the whole potential drop, is observed. A secondary structure reveals the ions coming from the opposite side of the channel. We show that the formation of the neutralized ion flow is governed by the annular geometry. The assumption of a collisionless shock or a double layer due to supersonic beam interaction is not necessary. A non-negligible fraction of slow ions originates in local ionization or charge-exchange collision events between ions of the expanding plasma and atoms of the background residual gas. Slow ions that are produced near the centerline in the vicinity of the exit plane are accelerated toward the source body with a negative velocity leading to a high sputtering of front face. On the contrary, the ions that are produced in the vicinity of the channel exit plane are partially accelerated by the extended electric field.

Lejeune, A.; Bourgeois, G.; Mazouffre, S. [ICARE, CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orlans Cedex 2 (France)

2012-07-15

237

Noninversive partial velocity amplification of radiation by ions due to their rotation in a magnetic field  

Microsoft Academic Search

It is shown that upon the application of an external magnetic field, a gas of ionized particles may experience noninversive\\u000a partial velocity amplification of radiation by ions due to their Larmor rotation. In this case, virtually all ions may be\\u000a in the ground state. It may happen that approximately half the number of ions in the medium amplify the incident

A. I. Parkhomenko

2002-01-01

238

Low Ion Velocity Slowing Down in a Demixing Binary Ionic Mixture  

NASA Astrophysics Data System (ADS)

we pay attention to ion projectile slowing down at low velocity Vp < Vthe, target thermal electron velocity, in a strongly coupled and demixing H-He ionic mixture. It is investigated in terms of quasi- static and critical charge-charge structure factors [1]. Non- polarizable as well as polarizable and partialy degenerate electron backgrounds are given attention. The low velocity ion slowing down can turn negative in the presence of long wavelength and low frequency hydromodes, signaling a first order critrical demixtion. Such a process is shown to document a superelastic energy transfer from target plasma ions to the incoming and slow ion projectile [2].[4pt] [1] D. Leger and C. Deutsch, Phys.Rev. A37, 4916, 4930 (1988)[0pt] [2] C. Deutsch, D. Leger and B. Tashev, Laser Part.Beams 29, 121 (2011)

Deutsch, Claude; Leger, Daniel; Tashev, Bekbolat

2011-11-01

239

Low Ion Velocity Slowing Down in a Demixing Binary Ionic Mixture  

NASA Astrophysics Data System (ADS)

We consider ion projectile slowing down at low velocity Vp < Vthe, target electron velocity, in a strongly coupled and demixing hydrogen-helium ionic mixture of mostly astrophysical concern. It is investigated in terms of quasi-static and critical charge-charge structure factor [1]. Non-polarizable as well as polarizable and partially degenerate electron backgrounds are successively given attention. The focussed low ion velocity slowing down [2] turns negative in the presence of long wavelength and low frequency hydrodynamic modes,thus signaling a first order critical demixtion. Such a process actually documents an energy transfer from target ion plasma to the incoming ion projectile, i.e a superelastic process. [4pt] [1] D.Leger and C.Deutsch, PRA 37, 4916, 4930 (1988)[0pt] [2] B.Tashev et al, PoP 15, 102701(2008)

Deutsch, Claude; Leger, Daniel; Tashev, Bekbolat

2010-11-01

240

Kinetic effects in drift wave fluctuations  

NASA Astrophysics Data System (ADS)

We present ion velocity resolved measurements of drift wave fluctuations in a linearly magnetized device using Laser Induced Fluorescence (LIF). These experiments are performed in ArII plasma immersed in a 1kG magnetic field. A density of the order of 10^9cm-3 is obtained under a regulated neutral background pressure ranging from 0.2 to 0.8 mTorr. Typical electron and ion temperatures are respectively 4eV and 0.1eV. LIF is performed using two spatially separated detection systems and the complex two-point correlation function < f(v_i||,z_1,?)f(v_i||,z_2,?)> is determined as a function of ion parallel velocity v_i|| , frequency ?, and ? d = z_2-z_1. Using a two-phasor decomposition of the complex correlation function, we observe correlations which propagate near the ion thermal speed, but with phase velocities which depend on ion particle velocity. These kinetic effects are associated with a broadening of the drift wave spectrum.

Diallo, Ahmed; Skiff, Fred

2004-11-01

241

Computer simulations of H{sup +} and H{sup +} transport parameters in hydrogen drift tubes  

Microsoft Academic Search

The coupled transport of H{sup +} and H{sup +} ions in molecular hydrogen is theoretically studied by using drift-tube-like computer simulations. The drift velocity and the longitudinal and the transverse diffusion coefficients of these ions are calculated for the reduced electric field E\\/n (where n is the gas density) ranging from 10 to 600 Td (1 Td=10⁻¹⁷ Vcm²). A large

T. Simko; V. Martisovits; J. Bretagne; G. Gousset

1997-01-01

242

Cold ion-polar-molecule reactions studied with a combined Stark-velocity-filter-ion-trap apparatus  

NASA Astrophysics Data System (ADS)

We have developed a combined Stark-velocity-filter-ion-trap apparatus for the purpose of reaction-rate measurements between cold trapped ions and slow polar molecules under ultrahigh vacuum conditions. The prerequisite steps such as the characterization of velocity-selected polar molecules (PM), namely ND3, H2CO, and CH3CN, were performed using time-of-flight (TOF) measurements. We confirmed the generation of slow ND3, H2CO, and CH3CN molecules having thermal energies of a few Kelvin. Additionally, the number densities of the slow velocity-filtered polar molecules were determined to be in the range of n=104 to 106 cm-3 by calibrating the TOF signals. In a first experiment, the Stark velocity filter was connected to a cryogenic linear Paul trap and reaction-rate measurements between laser-cooled Ca+ Coulomb crystals and velocity-selected polar molecules were carried out. The observed reaction rates are of the order of 10-5 s-1, which are much slower than typical reaction rates of molecular ion-polar-molecule reactions at low temperatures. The present results confirm that reaction-rate measurements between velocity-selected polar molecules and sympathetically cooled molecular ions cooled by a laser-cooled Ca+ Coulomb crystal can be performed. Next we measured the reaction rates between sympathetically cooled nonfluorescent stored ion molecules namely N2H+ ions and velocity-selected CH3CN molecules at the average reaction energy of about 3 K. The measured reaction rate of 2.0(2)10-3 s-1 is much faster than those of the Ca++PM reactions. This is strong evidence that the velocity-selected polar molecules undergo reactive collisions. We also confirmed that the present reaction-rate constant of CH3CN+N2H+ ? CH3CNH++N2 is consistent with the estimated values from the room temperature results and the trajectory-scaling formula of Su In the future, the present velocity-filter combined cryogenic trap apparatus will enable us to perform systematic measurements of cold ion-polar-molecule reactions, which are important problems from a fundamental viewpoint and also contribute to astrochemistry.

Okada, Kunihiro; Suganuma, Takuya; Furukawa, Takahiro; Takayanagi, Toshinobu; Wada, Michiharu; Schuessler, Hans A.

2013-04-01

243

Nonlinear evolution of drift instabilities  

SciTech Connect

The nonlinear evolution of collisionless drift instabilities in a shear-free magnetic field has been studied by means of gyrokinetic particle simulation as well as numerical integration of model mode-coupling equations. The purpose of the investigation is to identify relevant nonlinear mechanisms responsible for the steady-state drift wave fluctuations. It is found that the saturation of the instability is mainly caused by the nonlinear E x B convection of the resonant electrons and their associated velocity space nonlinearity. The latter also induces energy exchange between the competing modes, which, in turn, gives rise to enhanced diffusion. The nonlinear E x B convection of the ions, which contributes to the nonlinear frequency shift, is also an important ingredient for the saturation.

Lee, W.W.; Krommes, J.A.; Oberman, C.R.; Smith, R.A.

1984-01-01

244

Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements  

NASA Astrophysics Data System (ADS)

We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D? (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble the original fast-ion velocity distribution functions but nevertheless show their coarsest features. For CTS or FIDA systems with many simultaneous views on the same measurement volume, the resemblance improves with the number of available views, even if the resolution in each view is varied inversely proportional to the number of views, so that the total number of measurements in all views is the same. With a realistic four-view system, tomographies of a beam ion velocity distribution function at ASDEX Upgrade reproduce the general shape of the function and the location of the maxima at full and half injection energy of the beam ions. By applying our method to real many-view CTS or FIDA measurements, one could determine tomographies of 2D fast-ion velocity distribution functions experimentally.

Salewski, M.; Geiger, B.; Nielsen, S. K.; Bindslev, H.; Garca-Muoz, M.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.; Tardini, G.; the ASDEX Upgrade Team

2012-10-01

245

Electrostatic shocks excited by velocity modulation of an ion beam in a plasma.  

PubMed

Nonlinear evolutions of electrostatic shocks excited by a velocity-modulated ion beam along a magnetized plasma column are investigated by computer simulation for a Q-machine experiment. In the case of a beam velocity modulation, the perturbations grow spatially with subsequent saturation due to an ion bunching of the beam. With an increase in modulation ratio an electrostatic shock is formed, accompanied with a steepening of the propagating front. In the case of a beam density-modulation, however, the initial density jump decays simply. The velocity modulation method is quite effective for an excitation of electrostatic shocks in the Q-machine plasma with finite Landau damping. The simulation results using velocity modulation are consistent with the experimental results. PMID:14995381

Gohda, Takuma; Ishiguro, Seiji; Iizuka, Satoru; Sato, Noriyoshi

2004-01-27

246

Retarding potential analyzer measurement of the effect of ion-neutral collisions on the ion velocity distribution in the auroral ionosphere  

Microsoft Academic Search

The action of strong dc electric fields at high latitudes combined with a predominance of ion-neutral collisions has for some time been expected to create appreciable departures of the ion velocity distribution from the equilibrium Maxwellian configuration. We present new evidence gathered with the retarding potential analyzer on the AE-C satellite that shows that the ion velocity distribution departs significantly

J.-P. St.-Maurice; W.B. Hanson; J.C.G. Walker

1976-01-01

247

Observation of Direct Ionization of He by Highly Charged Ions at Low Velocity  

Microsoft Academic Search

We have observed direct target ionization of He at low velocity (0.2 to 1.7 a.u.) by highly charged ions of C6+, N7+, O8+, Ar16+, and Xe30+. The measured single ionization cross sections increase rapidly with increasing velocity. The cross sections, divided by the charge of the incident projectile, are found to lie on a universal curve when plotted versus the

W. Wu; C. L. Cocke; J. P. Giese; F. Melchert; M. L. A. Raphaelian; M. Stoeckli

1995-01-01

248

Hot-electron drift velocity in AlGaN/AlN/AlGaN/GaN camelback channel  

NASA Astrophysics Data System (ADS)

Nanosecond pulses were employed to study hot-electron transport in a nominally undoped Al0.33Ga0.67N/AlN/{Al0.1Ga0.9N/GaN} heterostructure where the mobile electrons are spread in a composite {Al0.1Ga0.9/GaN} dual channel exhibiting a camelback electron density profile at high electric fields. The highest velocity of 1.6 107 cm s-1 was obtained at electric field of 160 kV cm-1 in the channel with the electron density of 0.8 1013?cm-2 owing to its proximity to the LO-phonon-plasmon resonance.

Ardaravi?ius, L.; Kiprijanovi?, O.; Liberis, J.; Matulionis, A.; Li, X.; Zhang, F.; Wu, M.; Avrutin, V.; zgr, .; Morko, H.

2012-12-01

249

Threshold conditions for transitions to I-mode and H-mode with unfavourable ion grad B drift direction  

NASA Astrophysics Data System (ADS)

Transitions from the L-mode regime to the I-mode regime, with an energy transport barrier, and to the H-mode regime with both an energy and particle transport barrier are studied on the Alcator C-Mod tokamak. Steady I-mode plasmas have been produced over a wide range of plasma field (3-6 T), current (0.8-1.35 MA), density and shaping in the unfavourable ion B ?B configuration. The power threshold for the L-I transition is higher than scalings for the L-H transition with favourable drift, and increases with plasma current as well as density. Threshold conditions for the I-H transition are more variable. In some conditions I-mode is maintained up to the maximum available ICRF power of 5 MW, nearly a factor of two above the L-I threshold, giving a robust operating window. Edge Te at the L-I transition is in the range 250-450 eV, over a range of current and density, about a factor of two higher than with favourable drift, while at the I-H transition it can be much higher (up to 1.1 keV) but is again widely variable. Heat pulses due to sawteeth may play a role in transitions. Controlled I-L back transitions indicate little power hysteresis.

Hubbard, A. E.; Whyte, D. G.; Churchill, R. M.; Dominguez, A.; Hughes, J. W.; Ma, Y.; Marmar, E. S.; Lin, Y.; Reinke, M. L.; White, A. E.

2012-11-01

250

EISCAT measurements of ion velocities during Coordinated Auroral Experiment using Scatter And Rockets (CAESAR) campaign  

NASA Astrophysics Data System (ADS)

The EISCAT radar measured ion velocities underneath a rocket trajectory scanning over seven locations along an auroral arc. From the ion velocities electric fields were derived and compared with in-situ measurements on board the rocket. South of the arc region there is good agreement between both measurements. Inside the arc region, however, there are large discrepancies. It is concluded that localized field aligned currents play an important part, together with the fact that the rocket trajectory deviated from the EISCAT points of observation.

Kohl, H.; Rinnert, K.

1987-08-01

251

Negative ion productions in high velocity collision between small carbon clusters and Helium atom target  

NASA Astrophysics Data System (ADS)

We measured absolute double capture cross section of Cn+ ions (n=1,5) colliding, at 2.3 and 2.6 a.u velocities, with an Helium target atom and the branching ratios of fragmentation of the so formed electronically excited anions Cn-*. We also measured absolute cross section for the electronic attachment on neutral Cn clusters colliding at same velocities with He atom. This is to our knowledge the first measurement of neutral-neutral charge exchange in high velocity collision.

M, Chabot; K, Broff; T, Pino; G, Fraud; N, Dothi; Padellec A, Le; G, Martinet; S, Bouneau; Y, Carpentier

2012-11-01

252

Inelastic energy loss of medium energy H and He ions in Au and Pt: Deviations from velocity proportionality  

NASA Astrophysics Data System (ADS)

Electronic energy loss of light ions in nm films of Au and Pt has been studied at keV ion energies. For H the electronic stopping power S is found to exhibit the expected velocity proportionality at low ion velocities, which confirms the anticipated excitation mechanisms responsible for the energy transfer between ions and the electrons in the solid. In contrast, for He, S shows a clear deviation from velocity proportionality for both materials at ion velocities below 0.8 atomic units, i.e., 64 keV. This result indicates a change in the interaction mechanisms active at the investigated ion velocities, which cannot exclusively be interpreted from the density of states of the target. Instead, the more complex electronic structure of the He ion enables an additional energy loss channel due to charge exchange by atomic level promotion. Associated energy losses together with a changed equilibrium charge state permit an explanation of the observed phenomenon.

Primetzhofer, D.

2012-09-01

253

Ion Velocity Distribution Function Investigated Inside an Unstable Magnetized Plasma Exhibiting a Rotating Nonlinear Structure  

SciTech Connect

The frequent situation where a strongly nonlinear rotating structure develops in a linear magnetized plasma column is investigated experimentally with emphasis on the ion velocity distribution function (IVDF). Most often, a mode m=2 appears exhibiting a large density and potential perturbation with angular frequency slightly above the ion cyclotron frequency. For the first time the spatiotemporal evolution of the IVDF is studied using time-resolved laser induced fluorescence to explore the ion's interaction with the nonlinear wave propagating inside the column and at the origin of plasma transport outside the limiter. The ion fluid exhibits an alternance from azimuthal to radial velocity due to the electric field inside the rotating structure. A fluid model also allows us to locally reconstruct the self-consistent electric field evolution which contradicts all existing theories.

Rebont, C.; Claire, N.; Pierre, Th.; Doveil, F. [PIIM, UMR6633 CNRS/Universite de Provence, case 321, centre universitaire de Saint-Jerome, 13397 Marseille (France)

2011-06-03

254

Temporally resolved ion velocity distribution measurements in a radio-frequency plasma sheath  

Microsoft Academic Search

The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average

B. Jacobs; W. Gekelman; P. Pribyl; M. Barnes

2011-01-01

255

Temporally-resolved ion velocity distribution measurements in a radio-frequency plasma sheath  

Microsoft Academic Search

The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence (LIF) diagnostic in an industrial plasma etch tool. Temporally-resolved measurements taken at 8 different phases of the 2.2 MHz bias waveform show the ion dynamics to vary dramatically throughout the RF cycle (the ratio of the average

Brett Jacobs

2010-01-01

256

Fast ion velocity distributions measured by Collective Thomson Scattering in TEXTOR  

Microsoft Academic Search

We will present the first measurements of confined fast ion velocity distributions in TEXTOR, inferred from Collective Thomson Scattering (CTS). The fast ions result from NBI and ICRH. The data were obtained with the TEXTOR mm--wave CTS diagnostic [1]. Probing radiation is provided by a gyrotron (350 kW, 200 ms, 110 GHz). At B_phi = 2.6 T the ECE is

H. Bindslev; L. Porte; J. S. Machuzak; P. Woskov; J. A. Hoekzema

2000-01-01

257

A comparative study of in-situ and remote intermediate layer measurements against wind model predictions of vertical ion drift  

NASA Astrophysics Data System (ADS)

Measurements from a sequence of rockets launched from Wallops Island (37.95N, 75.47W) on a single night in 1968 still provide the only in-situ data on the midlatitude intermediate layer phenomenon. TMA vapor trail observations made during this sequence of rocket flights were the first to experimentally examine the wind shear theory for the formation and slow downward motion of the layers. Using these rocket data from solar maximum, as well as several intermediate layer data sets from the Arecibo Observatory (18.35N, 66.75W) at solar minimum, we compare the location and motion of the layer observations to the predictions of two widely used thermospheric wind models: the HWM-93 thermospheric wind model and the TIEGCM. HWM-93 is an empirical model derived largely from measurements that had limited capabilities for determining night-time winds at lower thermospheric altitudes, and TIEGCM is a self consistent first principles model. Like an earlier study by [Szuszczewicz et al., 1995], we find that some of our intermediate layer data agree quite well with the location of a convergent null in the meridional wind predicted by TIEGCM, but the correlation between layer altitude and the null in the vertical ion drift is in general poor. This finding contradicts theoretical expectations based on the two fluid plasma equations. We also demonstrate that uncertainties in the ion neutral collision frequency do not improve the agreement between the model vertical drifts and the observed layer behavior. Furthermore, we find some evidence that the HWM-93 model may overemphasize diurnal tidal effects in the winter, post-midnight period. The discrepancies found in this study demonstrate that our present understanding of midlatitude lower thermospheric wind systems is inadequate for predicting intermediate layer dynamics in the post-sunset period.

Earle, G. D.; Bishop, R. L.; Zhou, Q. H.; Wallace, S. P.

1998-09-01

258

Asymmetry in electron and ion charge collection in a drifting plasma bunch  

SciTech Connect

We report on the different behavior of electron and ion currents recorded by a Faraday cup in a plasma bunch generated via laser ablation. An excimer laser was employed to irradiate a Ge target. The current signals were recorded equipping the Faraday cup collector by a set of diaphragms. We found that the electron time-of-flight spectra were fairly similar to the ion ones, but the collected charge yield for electrons was up to 200 times larger than the corresponding ion yield. We ascribed such a discrepancy to the different cup collection efficiency for ions and electrons forming the plasma which was heavily influenced by the plume geometry, the energy of the particles, as well as the diaphragm size. Our findings would suggest that the overall electron charge 'tended' to be collected, unlike the ion charge which scaled upon the collection solid angle.

Belloni, F.; Lorusso, A.; Nassisi, V. [Laboratory of Applied Electronics, Department of Physics, University of Lecce and INFN-sect. of Lecce, C.P. 193, via Arnesano, 73100 Lecce, Italy and European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, D-76125 Karlsruhe (Germany); Laboratory of Applied Electronics, Department of Physics, University of Lecce and INFN-sect. of Lecce, C.P. 193, via Arnesano, 73100 Lecce (Italy)

2007-05-01

259

Effect of ion excape velocity and conversion surface material on H- production  

SciTech Connect

According to generally accepted models surface production of negative ions depends on ion escape velocity and work function of the surface. We have conducted an experimental study addressing the role of the ion escape velocity on H{sup -} production. A converter-type ion source at Los Alamos Neutron Science Center was employed for the experiment. The ion escape velocity was changed by varying the bias voltage of the converter electrode. It was observed that due to enhanced stripping of H{sup -} no direct gain of extracted beam current can be achieved by increasing the converter voltage. At the same time the conversion efficiency of H{sup -} was observed to vary with converter voltage and follow the existing theories in qualitative manner. We discuss the role of surface material on H{sup -} formation probability and present calculations predicting relative H{sup -} yields from different cesiated surfaces. These calculations are compared with experimental observations from different types of H{sup -} ion sources. The effects caused by varying cesium coverage are also discussed. Finally, we present a novel idea of utilizing materials exhibiting so-called negative electron affinity in H{sup -}/D{sup -} production under UV-light exposure.

Johnson, Kenneth F [Los Alamos National Laboratory; Tarvainen, Olli A [Los Alamos National Laboratory; Geros, E. [Los Alamos National Laboratory; Stelzer, J. [Los Alamos National Laboratory; Rouleau, G. [Los Alamos National Laboratory; Kalvas, T. [UNIV OF JYVASKYLA; Komppula, J. [UNIV OF JYASKYLA; Carmichael, J. [ORNL

2010-10-05

260

Effect of Ion Escape Velocity and Conversion Surface Material on H{sup -} Production  

SciTech Connect

According to generally accepted models surface production of negative ions depends on ion escape velocity and work function of the surface. We have conducted an experimental study addressing the role of the ion escape velocity on H{sup -} production. A converter-type ion source at Los Alamos Neutron Science Center was employed for the experiment. The ion escape velocity was affected by varying the bias voltage of the converter electrode. It was observed that due to enhanced stripping of H{sup -} no direct gain of extracted beam current can be achieved by increasing the converter voltage. The conversion efficiency of H{sup -} was observed to vary with converter voltage and follow the existing theories in qualitative manner. We present calculations predicting relative H{sup -} yields from different cesiated surfaces with comparison to experimental observations from different types of H{sup -} ion sources. Utilizing materials exhibiting negative electron affinity and exposed to UV-light is considered for Cesium-free H{sup -}/D{sup -} production.

Tarvainen, O. [University of Jyvaeskylae, Department of Physics, P.O. Box 35 (YFL) 40500 Jyvaeskylae (Finland); Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico, 87545 (United States); Kalvas, T.; Komppula, J.; Koivisto, H. [University of Jyvaeskylae, Department of Physics, P.O. Box 35 (YFL) 40500 Jyvaeskylae (Finland); Geros, E.; Stelzer, J.; Rouleau, G.; Johnson, K. F. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico, 87545 (United States); Carmichael, J. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee, 37831 (United States)

2011-09-26

261

On velocity space interrogation regions of fast-ion collective Thomson scattering at ITER  

NASA Astrophysics Data System (ADS)

The collective Thomson scattering (CTS) diagnostic proposed for ITER is designed to measure projected 1D fast-ion velocity distribution functions at several spatial locations simultaneously. The frequency shift of scattered radiation and the scattering geometry place fast ions that caused the collective scattering in well-defined regions in velocity space, here dubbed interrogation regions. Since the CTS instrument measures entire spectra of scattered radiation, many different interrogation regions are probed simultaneously. We here give analytic expressions for weight functions describing the interrogation regions, and we show typical interrogation regions of the proposed ITER CTS system. The backscattering system with receivers on the low-field side is sensitive to fast ions with pitch |p| = |vpar/v| < 0.5-0.9 depending on the ion energy and the frequency shift of the scattered radiation. A forward scattering system with receivers on the high-field side would be sensitive to co- and counter-passing fast ions in narrow interrogation regions with pitch |p| > 0.6-0.8. Additionally, we use weight functions to reconstruct 2D fast-ion distribution functions, given two projected 1D velocity distribution functions from simulated simultaneous measurements with the back- and forward scattering systems.

Salewski, M.; Nielsen, S. K.; Bindslev, H.; Furtula, V.; Gorelenkov, N. N.; Korsholm, S. B.; Leipold, F.; Meo, F.; Michelsen, P. K.; Moseev, D.; Stejner, M.

2011-08-01

262

Electron drift time in silicon drift detectors: A technique for high precision measurement of electron drift mobility  

Microsoft Academic Search

This paper presents a precise absolute measurement of the drift velocity and mobility of electrons in high resistivity silicon at room temperature. The electron velocity is obtained from the differential measurement of the drift time of an electron cloud in a silicon drift detector. The main features of the transport scheme of this class of detectors are: the high uniformity

A. Castoldi; P. Rehak

1995-01-01

263

Effect of spatial and velocity distributions on the generation of ion cyclotron emission from fusion products  

SciTech Connect

Cyclotron motion of fusion products (FPs) or other superthermal ions has been shown theoretically to generate ion cyclotron emission (ICE) which is strongly dependent upon the ratio of ion velocity to the background Alfven velocity (C. Chu and J. L. Sperling, J. Plasma Phys. {bold 40}, 40 (1988)). This initial work described ICE assuming a uniform plasma embedded in a constant magnetic field; in addition, a delta function velocity distribution was used for the superthermal ions. These assumptions lead to ICE spectra which exist as a series of delta functions at harmonics of the fundamental cyclotron frequency of the superthermal species. It is shown here that source distributions with finite spatial extent such as a higher order parabolic model (({ital S}({ital R})={ital S}{sub 0}{l brace}1{minus}(({ital R}{minus}{ital R}{sub 0}) /{ital a}){sup 2}{r brace}{sup {ital N}},{ital N}=6--10)), in conjunction with the magnetic field profile (({ital B}({ital R})={ital B}{sub 0}{ital R0} /{ital R})), lead to a significant broadening of the ICE spectra; this is the case even for a delta function velocity distribution. The spectra are further modified when realistic superthermal distributions are employed in the model. In the latter case, a Green's function approach is employed to calculate the spectra. Results of the ICE calculations are presented for FP protons.

Dooling, J.C.; Sperling, J.L.; Moses, K.G. (Fusion Physics and Technology, Inc., Torrance, CA (USA))

1990-10-01

264

Ion temperature and plasma rotation velocity measurements using visible spectroscopy on TdeV  

Microsoft Academic Search

A visible spectroscopic imaging system has been developed on Tokamak de Varennes (TdeV) that provides profile measurements of the ion temperature and plasma rotation velocity. Multiple poloidal and tangential chords were coupled to the entrance slit of a spectrometer equipped with a back-illuminated charge coupled device camera at its exit slit. The camera records spatially and spectrally resolved emission profiles

I. Condrea; E. Haddad; B. C. Gregory; D. Lafrance; J. L. Lachambre; G. Pacher; F. Meo; H. H. Mai

1999-01-01

265

Ion Velocity Distributions from Spherical 1054 nm and 351 nm Laser Plasmas.  

National Technical Information Service (NTIS)

We report the observation of ion velocity distributions from spherically illuminated targets, and compare the results to the predictions of analytical ablation models and the 1-D hydrodynamic code LILAC. Low-Z spherical targets were irradiated at 351 nm a...

B. Boswell T. Boehly J. Delettrez L. M. Goldman M. C. Richardson

1984-01-01

266

Very low velocity ion slowing down in binary ionic mixtures: Charge and mass-asymmetry effects  

Microsoft Academic Search

A binary ionic mixture (BIM) in dense and hot plasmas of specific concern for inertial confinement fusion and white dwarf crust is considered as a target for incoming light ions with a velocity smaller than the thermal electron one. The given target stopping power, mostly BIM monitored, is specifically studied in terms of charge and mass asymmetry in its ionic

Patrice Fromy; Bekbolat Tashev; Claude Deutsch

2010-01-01

267

Probing High-Velocity Transient-Field Strength Using Heavy-ions Traversing Fe and Gd  

SciTech Connect

The transient field strength for {sup 76}Ge ions, passing through iron and gadolinium layers at velocities approxZv{sub 0}, has been measured. Although a sizeable value has been obtained for Gd, a vanishing strength has been observed in Fe.

Fiori, E.; Georgiev, G.; Cabaret, S.; Lozeva, R. [CSNSM, CNRS/IN2P3, Universite Paris-Sud 11, UMR8609, F-91405 ORSAY-Campus (France); Stuchbery, A. E. [Department of Nuclear Physics, Australian National University, Canberra (Australia); Jungclaus, A.; Modamio, V.; Walker, J. [Instituto de Estructura de la Materia, CSIC, Madrid (Spain); Balabanski, D. L. [INRNE-BAS, Sofia (Bulgaria); Blazhev, A. [IKP, Cologne (Germany); Clement, E.; Grevy, S.; Stodel, C.; Thomas, J. C. [GANIL, Caen (France); Danchev, M. [University of Sofia (Bulgaria); Daugas, J. M. [CEA, DAM, DIF, 91297 Arpajon cedex (France); Hass, M.; Kumar, V. [The Weizmann Institute, Rehovot (Israel); Leske, J.; Pietralla, N. [TU Darmstadt, Darmstadt (Germany)

2009-08-26

268

The effective ionization coefficients and electron drift velocities in gas mixtures of CF3I with N2 and CO2 obtained from Boltzmann equation analysis  

NASA Astrophysics Data System (ADS)

The electron swarm parameters including the density-normalized effective ionization coefficients (?-?)/N and the electron drift velocities Ve are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend (SST) experiment. The overall density-reduced electric field strength is from 100 Td to 1000 Td (1 Td = 10-17 Vcm2), while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%. From the variation of (?-?)/N with the CF3I mixture ratio k, the limiting field strength (E/N)lim for each CF3I concentration is derived. It is found that for the mixtures with 70% CF3I, the values of (E/N)lim are essentially the same as that for pure SF6. Additionally, the global warming potential (GWP) and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.

Deng, Yun-Kun; Xiao, Deng-Ming

2013-03-01

269

Nonlinear electrostatic drift waves in dense electron-positron-ion plasmas  

SciTech Connect

The Korteweg-de Vries-Burgers (KdVB)-type equation is obtained using the quantum hydrodynamic model in an inhomogeneous electron-positron-ion quantum magnetoplasma with neutral particles in the background. The KdV-type solitary waves, Burgers-type monotonic, and oscillatory shock like solutions are discussed in different limits. The quantum parameter is also dependent on the positron concentration in dense multicomponent plasmas. It is found that both solitary hump and dip are formed and their amplitude and width are dependent on percentage presence of positrons in electron-ion plasmas. The height of the monotonic shock is decreased with the increase of positron concentration and it is independent of the quantum parameter in electron-positron-ion magnetized quantum plasmas. However, the amplitude of the oscillatory shock is dependent on positron concentration and quantum parameter in electron-positron-ion plasmas.

Haque, Q.; Mahmood, S.; Mushtaq, A. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore Islamabad (Pakistan)

2008-08-15

270

Ultrafast spectroscopy diagnostic to measure localized ion temperature and toroidal velocity fluctuations  

SciTech Connect

A dual-channel high-efficiency, high-throughput custom spectroscopic system has been designed and implemented at DIII-D to measure localized ion thermal fluctuations associated with drift wave turbulence. A large-area prism-coupled transmission grating and high-throughput collection optics are employed to observe C VI emission centered near {lambda}=529 nm. The diagnostic achieves 0.25 nm resolution over a 2.0 nm spectral band via eight discrete spectral channels. A turbulence-relevant time resolution of 1 {mu}s is achieved using cooled high-speed avalanche photodiodes and ultralow-noise preamplifiers. The system sensitivity is designed to provide measurements of normalized ion temperature fluctuations on the order of {delta}T{sub i}/T{sub i}{<=}1%.

Uzun-Kaymak, I. U.; Fonck, R. J.; McKee, G. R.; Schoenbeck, N.; Smith, D.; Winz, G.; Yan, Z. [Engineering Physics, University of Wisconsin-Madison, Wisconsin 53706 (United States)

2010-10-15

271

Ion Transport in Real and Velocity Space and Confinement in the GAMMA 10 Tandem Mirror  

NASA Astrophysics Data System (ADS)

Loss regions in the plasma particles' velocity space are decreased by the electrostatic potentials created on both sides of the plasma, which results in the improvement of the axial confinement in the tandem mirror. We found experimentally that the ion loss region was in contact mainly with both a plug potential bounce region and the outer mirror throat bounce region in which ions were bounced near the outer mirror throat of the plug/barrier cell. These bounce ions play an important role in tandem mirror confinement. The outer mirror throat bounce region is caused by the relatively high potential in the neighborhood of the outer mirror throat. The core plasma's radial potential profile was controlled by changing the potential of coaxially separated end plates, and it was found that control of the radial potential profile was useful for retardation of the radial loss of the bounce ions. We observed a hump structure on the energy distribution function of the end-loss ions, and found that the enhancement of the end-loss ions was caused by ion flow from the trapped region to the loss region due to Alfvn Ion Cyclotron (AIC) fluctuations. Although the ion diffusion due to the fluctuations enhances the axial ion loss, the axial loss can be reduced by creation of a higher confining potential.

Ishii, Kameo; Itakura, Akiyosi; Ichimura, Makoto; Katanuma, Isao; Kawamori, Eiichirou; Kohagura, Junko; Saito, Teruo; Takemura, Yuichiro; Tatematsu, Yoshinori; Cho, Teruji; Nakashima, Yousuke; Higaki, Hiroyuki; Hirata, Mafumi; Hojo, Hitoshi; Yatsu, Kiyoshi; Yoshikawa, Masayuki

272

Molecular Ion and Non-Zero Birth Velocity Effects in IEC Modeling  

NASA Astrophysics Data System (ADS)

An inertial-electrostatic confinement (IEC) chamber contains nearly transparent, concentric wire grids with a high voltage difference between them. At typical 0.3 Pa (2 mtorr) pressures, atomic and molecular processes can be important. Source region ions pass through the anode grid as a mixture of D^+, D2^+, and D3^+ ions, accelerate radially, and interact with the background gas to produce a cold ions (D^+ and D2^+) through interactions with the background D2 gas. These cold ions accelerate and produce additional cold ions through interactions with the background gas. A 1-D model for the effect of various molecular and atomic processes between deuterium ions (D^+, D2^+, and D3^+) and the background gas on the performance of spherical, gridded IEC devices has been developed. This formalism includes the bouncing motion of ions in the potential well and sums over all generations of cold ions. This leads to a set of coupled Volterra integral equations, which are solved numerically to yield the energy spectrum of the ion and fast neutral flux plus the neutron production. Recent improvements in the model, including non-zero ion birth velocities, will be discussed. Parametric surveys and comparison with experimental data for the Wisconsin IEC devices will be presented.

Emmert, Gilbert; Santarius, John

2008-11-01

273

Non-solar UV produced ions observed optically from the 'Crit I' critical velocity ionization experiment  

NASA Astrophysics Data System (ADS)

A critical velocity ionization experiment was carried out with a heavily instrumented rocket launched from Wallops Island on May 13, 1986. Two neutral barium beams were created by explosive shaped charges released from the rocket and detonated at 48 deg to B at altitudes near 400 km and below the solar UV cutoff. Critical velocity ionization was expected to form a detectable ion jet along the release field line, but, instead, an ion cloud of fairly uniform intensity was observed stretching from the release field line across to where the neutral barium jet reached sunlight. The process creating these ions must have been present from the time of the release; the efficiency is estimated to be equivalent to an ionization time constant of 1800 sec. This ionization is most likely from collisions between the neutral barium jet and the ambient atmospheric oxygen, and, if so, the cross section for collisional ionization is 9 x 10 to the -18th sq cm.

Stenbaek-Nielsen, H. C.; Wescott, E. M.; Rees, D.; Valenzuela, A.; Brenning, N.

1990-06-01

274

The role of Nonlinear Ion Temperature Gradient Driven Drift Modes in a Reversed Field Pinch Plasma  

Microsoft Academic Search

The Ion Temperature gradient (ITG) mode has been rarely investigated in Reversed Field pinch (RFP) plasmas, although its role tokamak turbulence has been studied extensively. In this work, we investigate if it is plausible that ITG may play a role in particle and heat confinement in such devices. The linear stability and nonlinear saturation of ITG is investigated in the

Varun Tangri; Paul Terry; R. E. Waltz

2009-01-01

275

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the effects of polarizable drift gases and ionic charge distribution.  

PubMed

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM-MS) using drift-gases with varying masses and polarizabilities. Despite the reduced length of the cell (18?cm), a pair of constitutional isomers, N-butylaniline and para-butylaniline, with theoretical collision cross-section values in helium (?He ) differing by as little as 1.2?(2) (1.5%) but possessing contrasting charge distribution, showed baseline peak-to-peak resolution (Rp-p ) for their protonated molecules, using carbon dioxide (CO2 ), nitrous oxide (N2 O) and ethene (C2 H4 ) as the TWIM drift-gas. Near baseline Rp-p was also obtained in CO2 for a group of protonated haloanilines (para-chloroaniline, para-bromoaniline and para-iodoaniline) which display contrasting masses and theoretical ?He , which differ by as much as 15.7?(2) (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans-oleic acid and cis-oleic acid possessing nearly identical theoretical ?He and ?N2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift-times were observed for the 1,3-dialkylimidazolium ions when comparing He, N2 and N2 O. Using density functional theory as a means of examining the ions electronic structure, and He and N2 -based trajectory method algorithm, we discuss the effect of the long-range charge induced dipole attractive and short-range Van der Waals forces involved in the TWIM separation in drift-gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift-gases could improve separation and the overall success of TWIM-MS analysis. Copyright 2013 John Wiley & Sons, Ltd. PMID:24078238

Lalli, Priscila M; Corilo, Yuri E; Fasciotti, Mara; Riccio, Maria Francesca; de Sa, Gilberto F; Daroda, Romeu J; Souza, Gustavo H M F; McCullagh, Michael; Bartberger, Michael D; Eberlin, Marcos N; Campuzano, Iain D G

2013-09-01

276

Laboratory Course on Drift Chambers  

SciTech Connect

Drift chambers play an important role in particle physics experiments as tracking detectors. We started this laboratory course with a brief review of the theoretical background and then moved on to the the experimental setup which consisted of a single-sided, single-cell drift chamber. We also used a plastic scintillator paddle, standard P-10 gas mixture (90% Ar, 10% CH4) and a collimated 90Sr source. During the laboratory session the students performend measurements of the following quantities: a) drift velocities and their variations as function of the drift field; b) gas gains and c) diffusion of electrons as they drifted in the gas.

Garcia-Ferreira, Ix-B.; Garcia-Herrera, J.; Villasenor, L. [Institute of Physics and Mathematics, University of Michoacan, Bdg. C3-Ciudad Universitaria, Morelia, Michoacan, 58040 (Mexico)

2006-09-25

277

Spatio-temporal characteristics of ion velocity in a Hall thruster discharge  

NASA Astrophysics Data System (ADS)

The time evolution of the axial velocity of a metastable Xe+ ion was examined in the crossed-field discharge of a PPS100-ML Hall thruster fired at 250 V by means of laser-induced fluorescence spectroscopy at 834.72 nm. A pulse-counting detection technique was employed to achieve a time resolution of 0.1 s. A periodic break of 10 s duration of the anode current is used to stabilize the discharge and allow the investigation of both forced and natural plasma oscillations. Measurements were carried out along the channel axis throughout the region of large magnetic field strength. The mean ion flow velocity was found to oscillate at the discharge breathing mode frequency of about 21 kHz. By contrast, the ion velocity dispersion appears not to depend on time, which suggests a strong correlation between ionization and acceleration processes. The spatio-temporal behavior of the electric field was computed from experimental data using a Lagrangian description of the ion fluid motion. As expected, the field amplitude varies significantly at 21 kHz. More surprisingly, an electric field front seems to propagate periodically from the exterior toward the interior of the discharge chamber with a speed close to the thermal speed of the Xe atom.

Mazouffre, S.; Bourgeois, G.

2010-12-01

278

Computed versus measured ion velocity distribution functions in a Hall effect thruster  

SciTech Connect

We compare time-averaged and time-varying measured and computed ion velocity distribution functions in a Hall effect thruster for typical operating conditions. The ion properties are measured by means of laser induced fluorescence spectroscopy. Simulations of the plasma properties are performed with a two-dimensional hybrid model. In the electron fluid description of the hybrid model, the anomalous transport responsible for the electron diffusion across the magnetic field barrier is deduced from the experimental profile of the time-averaged electric field. The use of a steady state anomalous mobility profile allows the hybrid model to capture some properties like the time-averaged ion mean velocity. Yet, the model fails at reproducing the time evolution of the ion velocity. This fact reveals a complex underlying physics that necessitates to account for the electron dynamics over a short time-scale. This study also shows the necessity for electron temperature measurements. Moreover, the strength of the self-magnetic field due to the rotating Hall current is found negligible.

Garrigues, L. [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d'Energie), 118 route de Narbonne, F-31062 Toulouse cedex 9 (France); CNRS, LAPLACE, F-31062 Toulouse (France); Mazouffre, S.; Bourgeois, G. [ICARE (Institut de Combustion, Aerothermique, Reactivite et Environnement), 1 C avenue de la recherche scientifique, 45071 Orleans (France)

2012-06-01

279

Energy-conserving finite-{beta} electromagnetic drift-fluid equations  

SciTech Connect

Nonlinear energy-conserving drift-fluid equations that are suitable to describe self-consistent finite-{beta} low-frequency electromagnetic (drift-Alfven) turbulent fluctuations in a nonuniform, anisotropic, magnetized plasma are derived from a variational principle. The variational principle is based on a drift-fluid Lagrangian that contains linear and nonlinear ExB velocities derived directly from the corresponding single-particle finite-{beta} gyrocenter Hamiltonian (in the zero-Larmor-radius limit). Covariant electromagnetic effects introduce a magnetic generalization to the standard ion polarization density as well as introduce a new ion magnetization current, which appear in finite-{beta} gyrokinetic theory [T. S. Hahm, W. W. Lee, and A. J. Brizard, Phys. Fluids 31, 1940 (1988)] but are both missing from existing gyrofluid and drift-fluid Poisson-Ampere equations. An exact energy conservation law is also derived directly from the drift-fluid Lagrangian by application of the Noether method.

Brizard, A.J. [Department of Chemistry and Physics, Saint Michael's College, Colchester, Vermont 05439 (United States)

2005-09-15

280

Apparent Velocity Threshold in the Electronic Stopping of Slow Hydrogen Ions in LiF  

SciTech Connect

The electronic energy loss of hydrogen ions (protons and deuterons) in thin supported films of LiF has been studied in backscattering geometry for specific energies from 700 eV/u to 700 keV/u, using Rutherford backscattering spectroscopy and time-of-flight low-energy ion scattering spectroscopy. For specific energies below 8 keV/u, our data confirm velocity proportionality for the stopping cross section {epsilon} (like in a metal) down to 3.8 keV/u, as observed previously for protons and antiprotons despite the large band gap (14 eV) of LiF. Below 3.8 keV/u, the present results indicate an apparent velocity threshold at about 0.1 a.u. for the onset of electronic stopping.

Draxler, M.; Chenakin, S.P.; Markin, S.N.; Bauer, P. [Institut fuer Experimentalphysik, Johannes-Kepler Universitaet, Altenbergerstr. 69, A-4040 Linz (Austria)

2005-09-09

281

Retarding potential analyzer measurement of the effect of ion-neutral collisions on the ion velocity distribution in the auroral ionosphere  

Microsoft Academic Search

The presented data, obtained with a retarding potential analyzer mounted on the AE-C satellite, show that the ion velocity distribution at high latitudes and below the F2 peak departs significantly from the Maxwellian configuration at ion temperatures greater than 1500 K. The current status of the theory of non-Maxwellian ion velocity distributions in the auroral ionosphere is reviewed, and the

J.-P. Saint Maurice; W. B. Hanson; J. C. G. Walker

1976-01-01

282

The initial-ion velocity as a marker for different desorption-ionization mechanisms in MALDI  

Microsoft Academic Search

While the high, mass-independent and matrix-determined initial velocity of matrix-assisted laser desorption ionization (MALDI) ions has been proposed to be a meaningful characteristic feature of the MALDI process and indicative for the generation of a jet of clusters, considerably lower values as obtained for some low-mass non-protein analytes and certain preparation protocols pointed to a possible second and different process

Michael Karas; Ute Bahr; Isabelle Fournier; Matthias Glckmann; Anja Pfenninger

2003-01-01

283

Very low velocity ion slowing down in binary ionic mixtures: Charge- and mass-asymmetry effects  

NASA Astrophysics Data System (ADS)

A binary ionic mixture (BIM) in dense and hot plasmas of specific concern for inertial confinement fusion and white dwarf crust is considered as a target for incoming light ions with a velocity smaller than the thermal electron one. The given target stopping power, mostly BIM monitored, is specifically studied in terms of charge and mass asymmetry in its ionic component. The classical plasma target is worked out within a dielectric framework, and scanned with respect to density, temperature, and BIM composition.

Fromy, Patrice; Tashev, Bekbolat; Deutsch, Claude

2010-10-01

284

Properties of energetic-particle continuum modes destabilized by energetic ions with beam-like velocity distributions  

SciTech Connect

Properties of energetic-particle continuum modes (EPMs) destabilized by energetic ions in tokamak plasmas were investigated using a hybrid simulation code for magnetohydrodynamics and energetic particles. The energetic ions are assumed to have beam-like velocity distributions for the purpose of clarifying the dependence on energetic ion velocity. It was found that for beam velocities lower than the Alfven velocity, the unstable modes are EPMs while the toroidal Alfven eigenmodes are unstable for the beam velocities well above the Alfven velocity. The EPMs destabilized by the copassing energetic ions and those destabilized by the counterpassing energetic ions differ in primary poloidal harmonics and spatial locations. The frequencies of the EPMs are located close to the shear Alfven continuous spectrum when they are compared at the spatial peak locations of the primary poloidal harmonic or compared at the spatial tails if the primary poloidal harmonic is m=1. The frequencies of the EPMs were carefully compared with the energetic-ion orbital frequencies. It was found that the frequencies of the EPMs are in good agreement with the energetic-ion orbital frequencies with a correction for the toroidal circulation frequency. This demonstrates that the energetic-ion orbital frequency determines the EPM frequency.

Todo, Y. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

2006-08-15

285

Parallel and perpendicular velocity sheared flows driven tripolar vortices in an inhomogeneous electron-ion quantum magnetoplasma  

SciTech Connect

Nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves are derived by taking into account sheared ion flows parallel and perpendicular to the ambient magnetic field in a quantum magnetoplasma comprised of electrons and ions. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on very short scales in dense quantum plasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, W. [TPPD, PINSTECH, P.O. Nilore, Islamabad (Pakistan) and National Centre for Physics (NCP), Shahdara Valley Road, 44000 Islamabad (Pakistan)

2011-12-15

286

Continuous wave cavity ring down spectroscopy measurements of ion velocity distribution functions in argon helicon plasma  

NASA Astrophysics Data System (ADS)

The West Virginia University helicon source group routinely employs laser induced fluorescence (LIF) to measure velocity distribution functions (VDFs) of argon ions, argon neutrals, helium neutrals and xenon ions. We are developing a continuous wave cavity ring down spectroscopy (CW-CRDS) diagnostic with a narrow linewidth, tunable diode laser as an alternative technique to measure VDFs in species where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopy technique, CRDS can also provide a direct measurement of the absolute metastable state density. Here we present Ar II ion VDFs obtained through measurements of the Doppler broadened absorption spectrum of Ar II at 668.614 nm (in vacuum), a standard initial state for conventional Ar II LIF.

Chakraborty Thakur, Saikat; Carr, Jerry, Jr.; McCarren, Dustin; Galante, Matthew; Hansen, Alex; Scime, Earl

2010-11-01

287

Observation of Low Frequency Ion Mode Turbulence in Tokamak Plasma  

Microsoft Academic Search

Features of a low frequency ion mode were observed together with the electron drift wave type fluctuations by a Langmuir probe array in the bulk plasma inside the velocity shear layer in the KT-5C tokamak. The measured ion mode wavenumber, scaling of the ion mode with chord-averaged density, and the estimated etai value suggest that the observed ion mode may

Gui-ding Wang; Wan-dong Liu; Chang-xuan Yu; Yi-zhi Wen; Chao Wang; Ge-sheng Pan; Ge Zhuang; Kan Zhai; Yu-hong Xu; Cheng Wang; Shu-de Wan

1998-01-01

288

Atomic collision experiments utilizing low-velocity, highly-charged ion beams  

SciTech Connect

Intense beams of highly-stripped ions are now routinely produced at low velocities using the Brookhaven dual MP-tandens in a unique four-stage accel/decel mode. This mode of operation combines three stages of acceleration, stripping at high energy, and one stage of deceleration to near-zero velocity. To date, experiments have used 10-100 nA beams of bare and few-electron heavy ions at energies as low as 0.2 MeV/amu, and upgrades of the facility should push the lower limit below 0.1 MeV/amu. Recent experiments, such as measurements of charge transfer and x-ray production for S/sup 6-16+/ on He and Ar at 6 to 20 MeV and P(b) measurements for MO x-rays produced in Cl/sup 16 +/ + Ar collisions at 20, 10, and 5 MeV have demonstrated the usefulness of highly-stripped, low-velocity projectiles. These experiments and a few possibilities for future experiments are discussed.

Johnson, B.M.; Jones, K.W.; Meron, M.

1982-01-01

289

Velocity dependence of free-ion production in K( np )-SF sub 6 collisions: Internal-to-translational energy transfer  

SciTech Connect

The velocity dependence of the rate constant for free-ion production via the Rydberg electron-transfer reaction K({ital np})+SF{sub 6}{r arrow}K{sup +}+SF{sub 6}{sup {minus}*} has been investigated at intermediate {ital n}. The data provide evidence of a postattachment interaction between the product ions in which internal energy from the SF{sub 6}{sup {minus}*} ion is converted into translational energy. A similar conclusion is reached from measurements of the velocity and angular distributions of the product K{sup +} ions.

Popple, R.A.; Durham, M.A.; Marawar, R.W.; Lindsay, B.G.; Smith, K.A.; Dunning, F.B. (Department of Space Physics and Astronomy and the Rice Quantum Institute, Rice University, Houston, Texas 77251 (United States))

1992-01-01

290

Study of the drift energies in the kronian magnetosphere: a comparison between model results and experimental data  

NASA Astrophysics Data System (ADS)

In the inner magnetosphere, the low energy particles (ions and electrons) corotate. Due to the gradient and the curvature of the field lines, the magnetic field influences the motion of the particles. Gradient and curvature are responsible of the existence of drift velocities perpendicular to the magnetic field lines. Above a critical energy, the total drift velocity will be higher than the corotation velocity. The electrons and the ions then rotate in opposite directions. We have developed a model which calculates the drift and corotation velocities, and apply it to determine the minimum energy. In this paper, we use data from the Cassini CAPS and MIMI instruments to compare the observed particle energy spectra with model result in order to explain the behaviour of the particles.

Grimald, S.; Arridge, C. S.; Rochel, A.; Dandouras, I.

2009-04-01

291

Drift and Hysteresis Effects on AlN/SiO2 Gate pH Ion-Sensitive Field-Effect Transistor  

NASA Astrophysics Data System (ADS)

The nonideal and unstable factors of AlN-based ion-sensitive field-effect transistor (ISFET) devices including the drift and hysteresis effects have been investigated in this study. The drift and hysteresis of AlN-based pH-ISFET devices have been measured using a constant current constant voltage (CCCV) readout circuit. The drift rates were obtained by long-time monitoring for 12 h in pH = 1, 3, 5, 7, 9, and 11 buffer solutions, which indicated that the drift rate increased with the pH value. The hysteresis effect was investigated by exposing the AlN gate ISFET in pH = 7-3-7-11-7 loop cycles with loop times of 960 s, 1920 s and 3840 s, and the magnitudes of hysteresis of 1.0, 1.5 and 4.5 mV were obtained, respectively. The temperature coefficient of hysteresis was found to be approximately 0.234 mV/C. In addition, it was also found that the hysteresis width with pH started from acid side is smaller than that started from basic side, which results in an asymmetric hysteresis effect.

Chiang, Jung-Lung; Chou, Jung-Chuan; Chen, Ying-Chung; Liau, Guo Shiang; Cheng, Chien-Chuan

2003-08-01

292

Advanced Ion Temperature and Velocity Fluctuation Diagnostic Design and Preliminary Measurements  

NASA Astrophysics Data System (ADS)

A high-efficiency, high-throughput custom spectroscopic system is being designed and implemented at DIII-D to measure localized, long-wavelength ion thermal fluctuations associated with drift wave turbulence. A high-transmission grism (prism-coupled transmission grating) and high-throughput collection optics are employed to observe Doppler-shifted emission from the n=,8-7 transition of C VI centered near ?=,529 nm. The diagnostic achieves 0.25 nm resolution for 2.0 nm spectral band using eight discrete spectral channels. A turbulence-relevant time resolution of 1 ?s will be achieved using high-speed photodiodes and low-noise preamplifiers. The system sensitivity should allow for measurements of normalized ion temperature fluctuations on the order of TI/TI<=1%. These measurements will be combined with 2D BES measurements to determine the local multi-field turbulence dynamics. The predicted signal-to-noise for turbulence measurements, signal analysis techniques, and preliminary data will be presented.

Uzunkaymak, I. U.; Fonck, R. J.; McKee, G. R.; Schlossberg, D. J.; Shafer, M. W.; Winz, G.; Yan, Z.

2009-11-01

293

Modeling and prediction of peptide drift times in ion mobility spectrometry using sequence-based and structure-based approaches.  

PubMed

The mobile behavior of 1481 peptides in ion mobility spectrometry (IMS), which are generated by protease digestion of the Drosophila melanogaster proteome, is modeled and predicted based on two different types of characterization methods, i.e. sequence-based approach and structure-based approach. In this procedure, the sequence-based approach considers both the amino acid composition of a peptide and the local environment profile of each amino acid in the peptide; the structure-based approach is performed with the CODESSA protocol, which regards a peptide as a common organic compound and generates more than 200 statistically significant variables to characterize the whole structure profile of a peptide molecule. Subsequently, the nonlinear support vector machine (SVM) and Gaussian process (GP) as well as linear partial least squares (PLS) regression is employed to correlate the structural parameters of the characterizations with the IMS drift times of these peptides. The obtained quantitative structure-spectrum relationship (QSSR) models are evaluated rigorously and investigated systematically via both one-deep and two-deep cross-validations as well as the rigorous Monte Carlo cross-validation (MCCV). We also give a comprehensive comparison on the resulting statistics arising from the different combinations of variable types with modeling methods and find that the sequence-based approach can give the QSSR models with better fitting ability and predictive power but worse interpretability than the structure-based approach. In addition, though the QSSR modeling using sequence-based approach is not needed for the preparation of the minimization structures of peptides before the modeling, it would be considerably efficient as compared to that using structure-based approach. PMID:21439562

Zhang, Yiming; Jin, Quan; Wang, Shuting; Ren, Ren

2011-03-24

294

Ion densities and velocities in the inner plasma torus of Saturn  

NASA Astrophysics Data System (ADS)

We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn's inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1 RS=60,268 km) from the planet, with a north-southward extension of 2RS. The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125 cm-3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, |z|<0.5RS, shows a slower decrease away from the planet than towards. The outward decrease, from 5 RS, is well described by the relation neq=2.2104(1/R)3.63. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane. A less prominent density peak, of 115 cm-3, is also detected at the orbit of Tethys, at 4.9RS. No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity v shows a clear general trend in the region between 3 and 7 RS, described by v=1.5R2-8.7R+39. The average v starts to deviate from corotation at around 3 RS, reaching 68% of corotation close to 5 RS.

Holmberg, M. K. G.; Wahlund, J.-E.; Morooka, M. W.; Persoon, A. M.

2012-12-01

295

Collective Thomson scattering for ion temperature and velocity measurements on Magnum-PSI: a feasibility study  

NASA Astrophysics Data System (ADS)

In this paper, collective Thomson scattering (CTS) is proposed for measuring the ion temperature and axial/rotational velocity of a plasma jet in the linear plasma generator Magnum-PSI, where ITER-relevant plasma conditions will be simulated. CTS is feasible at Magnum-PSI, because high electron densities (ne) can be obtained at low electron temperatures, which means that small Debye lengths are achievable. Calculations show that CTS is possible at the fundamental wavelength (1064 nm) of a Nd : YAG laser. At this wavelength, a scattering angle of 17-35 is sufficiently small to achieve a scattering parameter 1 < ? < 3. The estimated observational error in the ion temperature Ti is expected to be below 10% at ne = 5.0 1020 m-3 and Ti = 2.5 eV, for a scattering volume with a length of 2.4 mm using an accumulated scattering energy of 12 J (10 pulses of 1.2 J at 10 Hz). The accuracy in the determination of axial velocity is expected to be about 15%. Setting the required accuracy for ion temperature measurements at 15%, single pulse CTS is expected to be feasible for ne > 1.5 1021 m-3. The design considerations of the CTS diagnostic are described in this paper.

van der Meiden, H. J.

2010-04-01

296

Atomic collision studies at moderate projectile velocities using highly charged, decelerated heavy ions from the GSI-UNILAC  

Microsoft Academic Search

Beams of highly ionized, very heavy atoms at moderate velocities have been produced at the UNILAC using the acceleration-stripping-deceleration method. The available ion species range from Kr33+ to U66+ in the energy region between 2 and 5 MeV\\/u. A survey on first experiments at GSI using these moderate velocity, few electron, heavy ion beams is given. The effectiveness of the

P. M. Mokler; D. H. H. Hoffmann; W. A. Schnfeldt; D. Maor; W. E. Meyerhof; Z. Stachura

1984-01-01

297

Laser-induced-fluorescence observation of ion velocity distribution functions in a plasma sheath  

SciTech Connect

Experimental results obtained by laser-induced-fluorescence on metastable ion velocity distribution functions (MIVDF) in electrostatic presheaths and sheaths in argon plasmas produced by the thermoionic effect in a multipolar dc discharge are presented. The shape of the measured MIVDF are in qualitative agreement, for the presheath, with Emmert's model and exhibit: (1) a Maxwellian profile at the center of the device where the potential is zero; (2) a distribution function's shape made of three distinct parts at the entrance of the presheath. Inside the sheath the recorded MIVDF recovers a Maxwellian profile with a width unexpectedly related to the background neutral pressure. The velocity and potential profiles that can be deduced from the measured MIVDF show a strong influence of the primary electrons emitted by the filaments.

Claire, N.; Bachet, G.; Stroth, U.; Doveil, F. [Equipe Turbulence Plasma, LPIIM, CNRS-Universite de Provence, Marseille (France); Universitaet Stuttgart Institut fuer Plasmaforschung, Pfaffenwaldring, 31 D-70569 Stuttgart (Germany); Equipe Turbulence Plasma, LPIIM, CNRS-Universite de Provence, Marseille (France)

2006-06-15

298

The Velocities of Ion Transport Into and Through the Xylem of Roots  

PubMed Central

Excised corn roots, Zea mays, had radioactively labeled solution applied at two points along their length, for 1 minute, and were then kept in dilute, unlabeled nutrient solution. During this chase period, exudate was collected at 1-minute intervals, and its content of radioions was determined. Two pulses of label appeared in succession, originating at the points of application near the cut end of the root and farther from the cut end, respectively. Calculation yields the velocity at which the ions moved radially across the root into the xylem (vr) and the velocity at which they moved longitudinally within the xylem (vl). For Rb+ labeled with 86Rb, vr was 1.8 and vl, 35 cm/hr. For Br? labeled with 82Br, vr was 1.4 and vl, 103 cm/hr.

Epstein, Emanuel; Norlyn, J. D.

1973-01-01

299

Charge-state correlated cross sections for the production of low-velocity highly charged Ne ions by heavy-ion bombardment. [1 MeV\\/amu  

Microsoft Academic Search

We report measured cross sections for the collisional production of highly charged low-velocity Ne recoil ions resulting from the bombardment of a thin Ne gas target by highly charged 1-MeV\\/amu C, N, O, and F projectiles. The measurements were made using time-of-flight techniques which allowed the simultaneous identification of the final charge state of both the low-velocity recoil ion and

Tom Gray; C. L. Cocke; E. Justiniano

1980-01-01

300

Charge-state correlated cross sections for the production of low-velocity highly charged Ne ions by heavy-ion bombardment  

Microsoft Academic Search

We report measured cross sections for the collisional production of highly charged low-velocity Ne recoil ions resulting from the bombardment of a thin Ne gas target by highly charged 1-MeV\\/amu C, N, O, and F projectiles. The measurements were made using time-of-flight techniques which allowed the simultaneous identification of the final charge state of both the low-velocity recoil ion and

Tom J. Gray; C. L. Cocke; E. Justiniano

1980-01-01

301

Multielectron Processes in Heavy Ion{endash}Atom Collisions at Intermediate Velocity  

SciTech Connect

Using high resolution x-ray spectroscopy, we have measured projectile electron single and multiple cross sections when a two-electron Ar{sup 16+} ion collides with neutral target atoms. For a fixed impact velocity (v{sub p}=23 a.u. ) , but using various targets from He to Xe, a range from the perturbative regime to the strong interaction regime has been investigated. Double excitation cross sections are found to be well reproduced by an independent electron model. First measurements of capture-ionization cross sections are also reported and show the importance of this often-neglected process. {copyright} {ital 1997} {ital The American Physical Society}

Vernhet, D.; Rozet, J.P.; Wohrer, K.; Chetioui, A. [GPS (CNRS UMR 75-88), Universites Paris 7 et 6, 2 Place Jussieu, 75251 Paris Cedex 05 (France); Adoui, L.; Cassimi, A.; Grandin, J.P.; Ramillon, J.M. [CIRIL (UMR N11 CEA/CNRS), Rue Claude Bloch, B.P.5133, 14070 Caen Cedex 5 (France); Cornille, M. [DARC, Observatoire de Paris Meudon, Place Jansen, 92195 Meudon Cedex (France); Stephan, C. [NIM, IPN, Universite Paris 11, B.P.N1, 91405 Orsay Cedex (France)

1997-11-01

302

Time scales for formation and spreading of velocity shells of pickup ions in the solar wind  

SciTech Connect

The pickup of newborn ions in the solar wind by means of low-frequency, electromagnetic waves, either due to the intrinsic turbulence of the solar wind or induced turbulence due to instabilities excited by the newborn ions, is discussed. The pickup process is envisioned to occur in three stages, formation of a ring-beam distribution, rapid pitch angle scattering of this initial distribution into a thin shell, and slower velocity diffusion that spreads out the shell. The process of shell formation and evolution are studied by means of numerical simulations, first for the situation of relatively low levels of turbulence such as would occur naturally in the solar wind and then for higher levels of turbulence characteristic of those encountered near cometary bow shocks. The results of the numerical experiments are compared with theory.

Gaffey J.D. Jr.; Winske, D.; Wu, C.S.

1988-06-01

303

Atomic physics effects on tokamak edge drift-tearing modes  

SciTech Connect

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold [Delta][sup Th], produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Hahm, T.S.

1993-03-01

304

Atomic physics effects on tokamak edge drift-tearing modes  

SciTech Connect

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold {Delta}{sup Th}, produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Hahm, T.S.

1993-03-01

305

Kinetic theory of the electromagnetic drift modes driven by pressure gradients  

Microsoft Academic Search

Kinetic equations for the electromagnetic drift modes are derived and analyzed for the stability of tokamaks in the local approximation. In the dissipationless, hydrodynamic limit, the fifth-order polynomial dispersion relation previously studied is recovered. The kinetic velocity space integrals in the ion dynamics are shown to modify the five principal modes of oscillation and their polarizations. It is shown that

W. Horton; J. E. Sedlak; Duk-In Choi; B. G. Hong

1985-01-01

306

The ion velocity distribution function in a current-free double layer  

NASA Astrophysics Data System (ADS)

A portable, low-power, diode laser-based laser-induced fluorescence (LIF) diagnostic incorporating a heated iodine cell for absolute wavelength reference was installed on the Chi-Kung helicon source [K. K. Chi, T. E. Sheridan, and R. W. Boswell, Plasma Sources Sci. Technol. 8, 421 (1999)] to measure the ion velocity distribution function of argon ions as they transited a current-free double layer (DL) created where the solenoidal magnetic field diverges at the junction of the plasma source and the diffusion chamber. Based on LIF measurements of the transiting ion beam energy, the strength of the potential drop across the DL increases with decreasing neutral pressure and increasing magnetic field strength in the source. The location of the double layer also moves further downstream of the helicon source with increasing pressure. LIF measurements of the ion beam energy were found to be in good agreement with measurements obtained with a retarding field energy analyzer and also with numerical predictions.

Keesee, Amy M.; Scime, Earl E.; Charles, Christine; Meige, Albert; Boswell, Rod

2005-09-01

307

Distribution function of precipitating ion beams with velocity dispersion observed near the poleward edge of the nightside auroral oval  

SciTech Connect

Using low energy ion data obtained by Akebono satellite, the authors have calculated distribution functions of velocity-dispersed ion beams observed at the poleward edge of the auroral electron precipitation region. The calculated distribution functions can well be fitted by one-dimensional shifted-Maxwellians, whose bulk energy and temperature are several keV and several hundreds of eV, respectively. The bulk energy and temperature show a positive correlation, which may indicate that when the ions are accelerated to higher energy, they are heated to higher temperature simultaneously. A relation has been found between the invariant latitude width of the observed ion beams divided by the square root of the temperature and their bulk velocity, which indicates that the source region of the ion beam is compact. These ion beams are obtained with high occurrence probability, suggesting that they are supplied from a steady X-type neutral line in the earth's magnetotail. 12 refs., 4 figs.

Saito, Y.; Mukai, T.; Machida, S.; Hirahara, M.; Kaya, N.

1992-11-03

308

Velocity distribution function of ion swarm in a weakly ionised gas in a constant mean free time encounter region  

Microsoft Academic Search

The theoretical analysis of the velocity distribution function of ions in weakly ionised gases is developed under the condition of induced dipole interaction between ion and molecule by using the BGK approximation in the Boltzmann equation. The derived functions is valid for arbitrary reduced field strength E\\/N and ion-neutral mass ratio m\\/M. The results are compared with the previous works

T. Makabe; K. Misawa; T. Mori

1981-01-01

309

Quantification of ions with identical mass-to-charge (m/z) ratios by velocity-map imaging mass spectrometry.  

PubMed

By integrating a velocity-map imaging lens and position sensitive detector into an electron-impact time-of-flight mass spectrometer, it becomes possible to record ion kinetic energy release (KER) distributions for each fragment ion alongside the time-of-flight mass spectrum. The KER distributions allow ions of identical mass-to-charge ratio to be distinguished and quantified. PMID:23860732

Bull, James N; Lee, Jason W L; Vallance, Claire

2013-07-16

310

Linear dependence of the postsunset equatorial anomaly electron density on solar flux and its relation to the maximum prereversal E B drift velocity through its dependence on solar flux  

NASA Astrophysics Data System (ADS)

The postsunset equatorial ionization anomaly, with maximum F layer electron density, Nemax, occurring near 2100 LT, has been found during solar maximum to be a linear function of the maximum prereversal E B drift velocity (E B drift). In order to examine this relation at all levels of solar flux, Nemax is measured during 13 years of an entire solar cycle by eight ionospheric sounders located in the anomaly in both north and south dip latitudes and in eastern Asia, the Pacific, and South America. At each location the monthly median Nemax increases linearly with the monthly average solar flux, Sa, over the range from 70 to 285 sfu. The linear function varies markedly with location and by month at each location. The relation to E B drift, which is also a linear function of Sa, is determined using measurements of Nemax versus Sa measured at Bogota in the anomaly plotted as a function of E B versus Sa measured at Jicamarca at the dip equator. The result is that Nemax is a linear function of E B, which is in agreement with that found previously during solar maximum. Accordingly, the Nemax versus E B relation is independent of Sa. The fact that Nemax is linear in Sa at each site implies Nemax is linear in E B at each but with a functional dependence that varies with latitude and longitude.

Whalen, James A.

2004-07-01

311

Effect of ion temperature on ion-acoustic solitary waves in a plasma with a q-nonextensive electron velocity distribution  

SciTech Connect

The effect of ion temperature on the existence of arbitrary amplitude ion-acoustic solitary waves is studied in a two component plasma in presence of a q-nonextensive velocity distributed electrons by using Sagdeev's pseudo potential technique. The range of relevent parameters for which solitons may exist is discussed. It is observed that both q, the nonextensive parameter and the ion temperature {sigma}, play significant roles in the formation and existence of solitons.

Roy, Kaushik; Saha, Taraknath; Chatterjee, Prasanta [Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiniketan-731235 (India)

2012-10-15

312

Drift wave vortices in nonuniform plasmas with sheared magnetic fields  

SciTech Connect

Nonlinear coherent structures governed by the coupled drift wave-ion acoustic mode equations in nonuniform plasmas with sheared magnetic fields are studied analytically and numerically. A solitary vortex equation that includes the effects of density and temperature gradients, and magnetic shear is derived and analyzed. The analytic and numerical studies show that for a plasma in a sheared magnetic field, even without the temperature and drift velocity gradients, solitary vortex solutions are possible; however, these solutions are not exponentially localized due to the presence of a nonstructurally stable perturbative tail that connects to the core of the vortex. The new coherent vortex structures are dipole-like in their symmetry, but are not the modons of Larichev and Reznik. In the presence of a small temperature or drift velocity gradient, the new shear-induced dipole can not survive and will separate into monopoles, like the case of the modon in a sheared drift velocity as studied in Su et al. The solitary solutions are found from the nonlinear eigenvalue problem for the effective potential in a quasi-one-dimensional approximation. The numerical simulations are performed in 2-D with the coupled vorticity and parallel mass flow equations.

Su, X.N.; Horton, W.; Morrison, P.J.

1991-11-01

313

Drift-tearing magnetic islands in tokamak plasmas  

NASA Astrophysics Data System (ADS)

A systematic fluid theory of nonlinear magnetic island dynamics in conventional low-?, large aspect-ratio, circular cross-section tokamak plasmas is developed using an extended magnetohydrodynamics model that incorporates diamagnetic flows, ion gyroviscosity, fast parallel electron heat transport, the ion sound wave, the drift wave, and average magnetic field-line curvature. The model excludes the compressible Alfvn wave, geodesic field-line curvature, neoclassical effects, and ion Landau damping. A collisional closure is used for plasma dynamics parallel to the magnetic field. Two distinct branches of island solutions are found, namely the ``sonic'' and ``hypersonic'' branches. Both branches are investigated analytically, using suitable ordering schemes, and in each case the problem is reduced to a relatively simple set of nonlinear differential equations that can be solved numerically via iteration. The solution determines the island phase velocity, relative to the plasma, and the effect of local currents on the island stability. Sonic islands are relatively wide, flatten both the temperature and density profiles, and tend to propagate close to the local ion fluid velocity. Hypersonic islands, on the other hand, are relatively narrow, only flatten the temperature profile, radiate drift-acoustic waves, and tend to propagate close to the local electron fluid velocity. The hypersonic solution branch ceases to exist above a critical island width. Under normal circumstances, both types of island are stabilized by local ion polarization currents.

Fitzpatrick, R.; Waelbroeck, F. L.

2008-01-01

314

Analytical Solutions for the Nonlinear Longitudinal Drift Compression (Expansion) of Intense Charged Particle Beams  

SciTech Connect

To achieve high focal spot intensities in heavy ion fusion, the ion beam must be compressed longitudinally by factors of ten to one hundred before it is focused onto the target. The longitudinal compression is achieved by imposing an initial velocity profile tilt on the drifting beam. In this paper, the problem of longitudinal drift compression of intense charged particle beams is solved analytically for the two important cases corresponding to a cold beam, and a pressure-dominated beam, using a one-dimensional warm-fluid model describing the longitudinal beam dynamics.

Edward A. Startsev; Ronald C. Davidson

2004-04-09

315

Kinetic waves near the drift frequency  

NASA Astrophysics Data System (ADS)

We consider the possibility of dynamically significant kinetic waves, of the type observed previously in the ion acoustic and ion-cyclotron frequency range, in a weakly- collisional, nearly-maxwellian plasma. The calculation is motivated by recent experimental results of drift-wave fluctuations which are clearly outside of a fluid description. Experiments and theory have shown that in non-maxwellian weakly collisional plasma there can exist multiple modes, in addition to the fluid modes. These are effectively other Landau poles; remnants of the Case-Van Kampen continuum. Normally, kinetic modes represent rapidly phase-mixed perturbations (and thus strongly damped modes), but in non-maxwellian plasma these modes may be weakly damped. Experimentally, these kinetic modes can account for a large fraction of the plasma fluctuation. Even a relatively small component of kinetic waves could change the phase between density and ExB velocity and have a significant impact on particle transport. A technique for finding the dispersion relation using a Hilbert transform on measured ion distribution functions, that has been used at ion cyclotron frequencies, is generalized to treat fluctuations at drift wave frequencies.

Skiff, Fred

2003-10-01

316

Effect of anisotropic velocity distribution on the linear polarization of coronal lines. Does the ion cyclotron exist in the inner corona?  

Microsoft Academic Search

The effect of an anisotropic velocity field distribution of scattering ions on the polarization parameters of a spectral line emitted by resonance scattering is considered. The anisotropy of the velocity field distribution can be interpreted in terms of the ion-cyclotron effect that is believed to influence some heavy ions in the solar corona. We present a theoretical study of the

N.-E. Raouafi; S. K. Solanki

2003-01-01

317

Numerical analysis of plasma transport in tandem volume magnetic multicusp ion sources  

Microsoft Academic Search

A one-dimensional fluid model of plasma transport in tandem volume magnetic multicusp ion sources is explored. The model, a positive ion source code, calculates plasma density, drift velocity, electron temperature, and ion temperature in an ion source. The usefulness of the model is limited in the following ways: (1) the plasma density trend runs opposite to experimental results, and electron

Todd R. Vitko

1992-01-01

318

Electron motion in fast magnetically insulated ion probes  

Microsoft Academic Search

Simulations have been performed to determine the time-dependent response of an intense ion beam incident on a transverse magnetic field. The geometry is appropriate for the simulation of a magnetically insulated ion probe. For a case with parameters such that the beam electrons should be stripped from the ions, the electrons nevertheless drift with the beam at a reduced velocity.

T. R. Lockner; J. W. Poukey

1983-01-01

319

Improved charge exchange spectroscopy on the Joint European Torus for ion temperature and rotation velocity profiles  

SciTech Connect

The Joint European Torus (JET) edge charge exchange recombination spectroscopy diagnostic has recently been enhanced to extend its spatial coverage and improve its time resolution. Two identical periscopes have been installed on opposite ports so that they have perfectly symmetrical views of the edge plasma. This matched viewing geometry allows both the poloidal and toroidal components of the impurity ion rotation velocity to be accurately resolved. These measurements play a crucial role in the understanding of the physics of edge phenomena such as edge transport barrier formation and enhanced light microscopes. The diagnostic also has a more central view of the plasma with a third periscope that faces up towards the top of the vessel. This is a new configuration for the diagnostic and allows the poloidal rotation velocity profile to be measured further in towards the plasma core than previously possible. The new upward facing, core plasma viewing arrangement provides the advantage that the spatial evolution of the internal transport barrier can be tracked from its formation. An additional spectrometer-detector system doubles the total number of charge exchange recombination spectroscopy lines of sight that are analyzed and improves time resolution from 50 to 10 ms.

Andrew, Yasmin; Hawkes, N. C.; Crombe, K. [Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Department of Applied Physics, Ghent University, Rozier 44, B-9000, Ghent (Belgium)

2006-10-15

320

Accel-Decel method of producing high-Q low velocity ions  

SciTech Connect

The double EN tandem Van de Graaff accelerators at the University of Pittsburgh's Nuclear Physics Laboratory have been used in part since 1978, operating in the 3-stage mode, as a source of highly stripped but low velocity ions for experiments of interest to atomic physics. Much of the work has involved investigating the technical details of this new accel-decel technique and gaining practical experience in operating the accelerators in the accel-decel mode. Decelerations to a final energy factor of approx. = 50 less than the stripping energy have been achieved for fully stripped oxygen ions and some charge exchange measurements on He published, demonstrating the potential of the accel-decel technique for supplying atomic physics with data from a previously unattainable energy and charge state regime. Practical problems encountered and the technical developments leading to these first prototype experiments will be reviewed. Subsequent developmental work, the present status of the project, and future technical plans at Pittsburgh are summarized. Finally, the future possibilities of the accel-decel technique generally are discussed.

Saylor, T.K.; Bayfield, J.E.; Gardner, L.D.; Gulkok, Y.Z.; Sharma, S.D.

1981-04-01

321

Shields to Reduce Spray Drift  

Microsoft Academic Search

The effects of several spray-boom shield designs and low-drift nozzles on spray drift are presented. Results are based on experiments conducted in a wind tunnel. Performances of all experimental shields were evaluated under two spray pressures (015 and 03MPa), and two air velocities (275 and 480m\\/s) in the wind tunnel. The distance to the centre of mass of the

HE Ozkan; A Miralles; C Sinfort; H Zhu

1997-01-01

322

Generation of lower hybrid and whistler waves by an ion velocity ring distribution  

NASA Astrophysics Data System (ADS)

Using fully kinetic simulations in two and three spatial dimensions, we consider the generation and nonlinear evolution of lower hybrid waves produced by a cold ion ring velocity distribution in a low beta plasma. We show that the initial development of the instability is very similar in two and three dimensions and not significantly modified by electromagnetic effects, consistent with linear theory. At saturation, the level of electric field fluctuations is a small fraction of the background thermal energy; the electric field and corresponding density fluctuations consist of long, field-aligned striations. Energy extracted from the ring goes primarily into heating the background ions and the electrons at comparable rates. The initial growth and saturation of the magnetic components of the lower hybrid waves are related to the electric field components, consistent with linear theory. As the growing electric field fluctuations saturate, parallel propagating whistler waves develop by the interaction of two lower hybrid waves. At later times, these whistlers are replaced by longer wavelength, parallel propagating whistlers that grow through the decay of the lower hybrid fluctuations. Wave matching conditions demonstrate these conversion processes of lower hybrid waves to whistler waves. The conversion efficiency (=ratio of the whistler wave energy to the energy in the saturated lower hybrid waves) is computed and found to be significant (~15%) for the parameters of the three-dimensional simulation (and even larger in the two-dimensional simulation), although when normalized in terms of the initial kinetic energy in the ring ions the overall efficiency is very small (<10-4). The results are compared with relevant linear and nonlinear theory.

Winske, D.; Daughton, W.

2012-07-01

323

Ionic liquid lubrication: influence of ion structure, surface potential and sliding velocity.  

PubMed

Colloid probe atomic force microscopy (AFM) has been employed to investigate the nanotribology of the ionic liquid (IL)-Au(111) interface. Data is presented for four ILs, 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM] FAP), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP) and 1-butyl-3-methylimidazolium iodide ([BMIM] I), at different Au(111) surface potentials. Lateral forces vary as a function of applied surface potential and ion structure because the composition of the confined ion layer changes from cation-enriched (at negative potentials) to mixed (at 0 V), and to anion-enriched (at positive potentials). ILs with FAP(-) anions all exhibit similar nanotribology: low friction at negative potentials and higher friction at positive potentials. [BMIM] I displays the opposite behaviour, as an I(-) anion-enriched layer is more lubricating than either the [BMIM](+) or FAP(-) layers. The effect of cation charged group (charge-delocalised versus charged-localised) was investigated by comparing [BMIM] FAP with 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py(1,4)] FAP). [BMIM] FAP is less lubricating at negative potentials, but more lubricating at positive potentials. This indicated that even at positive potentials the cation concentration in the boundary layer is sufficiently high to influence lubricity. The influence of sliding velocity on lateral force was investigated for the [EMIM] FAP-Au(111) system. At neutral potentials the behaviour is consistent with a discontinuous sliding process. When a positive or negative potential bias is applied, this effect is less pronounced as the colloid probe slides along a better defined ion plane. PMID:23836254

Li, Hua; Rutland, Mark W; Atkin, Rob

2013-09-21

324

Generation of lower hybrid and whistler waves by an ion velocity ring distribution  

SciTech Connect

Using fully kinetic simulations in two and three spatial dimensions, we consider the generation and nonlinear evolution of lower hybrid waves produced by a cold ion ring velocity distribution in a low beta plasma. We show that the initial development of the instability is very similar in two and three dimensions and not significantly modified by electromagnetic effects, consistent with linear theory. At saturation, the level of electric field fluctuations is a small fraction of the background thermal energy; the electric field and corresponding density fluctuations consist of long, field-aligned striations. Energy extracted from the ring goes primarily into heating the background ions and the electrons at comparable rates. The initial growth and saturation of the magnetic components of the lower hybrid waves are related to the electric field components, consistent with linear theory. As the growing electric field fluctuations saturate, parallel propagating whistler waves develop by the interaction of two lower hybrid waves. At later times, these whistlers are replaced by longer wavelength, parallel propagating whistlers that grow through the decay of the lower hybrid fluctuations. Wave matching conditions demonstrate these conversion processes of lower hybrid waves to whistler waves. The conversion efficiency (=ratio of the whistler wave energy to the energy in the saturated lower hybrid waves) is computed and found to be significant ({approx}15%) for the parameters of the three-dimensional simulation (and even larger in the two-dimensional simulation), although when normalized in terms of the initial kinetic energy in the ring ions the overall efficiency is very small (<10{sup -4}). The results are compared with relevant linear and nonlinear theory.

Winske, D.; Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-07-15

325

On the ballooning instability of the coupled Alfvn and drift compressional modes  

NASA Astrophysics Data System (ADS)

The paper examines the ballooning instability in gyrokinetic approximation taking into account the effects of finite-?, magnetic field line curvature, and diamagnetic drift. We used a simple model with a constant curvature of magnetic field lines which enabled us to obtain analytical results. The possible plasma oscillatory modes comprise the poloidal Alfvn and drift compressional modes, coupled due to the magnetic field line curvature and plasma inhomogeneity. The frequencies of these modes depend on the westward current value. As this value grows, the frequencies of these two branches approach to each other, and the branches are merged at some critical value of the current. Then an instability develops which is called the drift ballooning coupling instability. There are three major differences of the drift ballooning coupling instability from the ordinary MHD ballooning instability: (1) the drift ballooning coupling instability is not aperiodic, there is a real part of the oscillation frequency of the order of the drift frequency, (2) only the mode with the same direction of the azimuthal phase speed as the velocity of the ion diamagnetic drift can be unstable, (3) the instability threshold depends on the diamagnetic drift frequency.

Klimushkin, D. Yu.; Mager, P. N.; Pilipenko, V. A.

2012-09-01

326

Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations  

NASA Astrophysics Data System (ADS)

In this paper we estimate zonal plasma drift in the equatorial ionospheric F region without counting on ion drift meters. From June 2001 to June 2004 zonal plasma drift velocity is estimated from electron, neutral, and magnetic field observations of Challenging Mini-satellite Payload (CHAMP) in the 09:00-20:00 LT sector. The estimated velocities are validated against ion drift measurements by the Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics Instrument (ROCSAT-1/IPEI) during the same period. The correlation between the CHAMP (altitude ~ 400 km) estimates and ROCSAT-1 (altitude ~ 600 km) observations is reasonably high (R ? 0.8). The slope of the linear regression is close to unity. However, the maximum westward drift and the westward-to-eastward reversal occur earlier for CHAMP estimates than for ROCSAT-1 measurements. In the equatorial F region both zonal wind and plasma drift have the same direction. Both generate vertical currents but with opposite signs. The wind effect (F region wind dynamo) is generally larger in magnitude than the plasma drift effect (Pedersen current generated by vertical E field), thus determining the direction of the F region vertical current.

Park, J.; Lhr, H.

2013-06-01

327

2-dimensional ion velocity distributions measured by laser-induced fluorescence above a radio-frequency biased silicon wafer  

NASA Astrophysics Data System (ADS)

The dynamics of ions traversing sheaths in low temperature plasmas are important to the formation of the ion energy distribution incident onto surfaces during microelectronics fabrication. Ion dynamics have been measured using laser-induced fluorescence (LIF) in the sheath above a 30 cm diameter, 2.2 MHz-biased silicon wafer in a commercial inductively coupled plasma processing reactor. The velocity distribution of argon ions was measured at thousands of positions above and radially along the surface of the wafer by utilizing a planar laser sheet from a pulsed, tunable dye laser. Velocities were measured both parallel and perpendicular to the wafer over an energy range of 0.4-600 eV. The resulting fluorescence was recorded using a fast CCD camera, which provided resolution of 0.4 mm in space and 30 ns in time. Data were taken at eight different phases during the 2.2 MHz cycle. The ion velocity distributions (IVDs) in the sheath were found to be spatially non-uniform near the edge of the wafer and phase-dependent as a function of height. Several cm above the wafer the IVD is Maxwellian and independent of phase. Experimental results were compared with simulations. The experimental time-averaged ion energy distribution function as a function of height compare favorably with results from the computer model.

Moore, Nathaniel B.; Gekelman, Walter; Pribyl, Patrick; Zhang, Yiting; Kushner, Mark J.

2013-08-01

328

Experimental Test of Instability-Enhanced Collisional Friction for Determining Ion Loss in Two Ion Species Plasmas  

SciTech Connect

Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities nearly reach a common velocity at the sheath edge. A new theory suggests that collisional friction between the two ion species enhanced by two stream instability reduces the drift velocity of each ion species relative to each other near the sheath edge and finds that the difference in velocities at the sheath edge depends on the relative concentrations of the species. It is small when the concentrations are comparable and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, ion drift velocities were measured with laser-induced fluorescence in argon-xenon plasmas. We show that the predictions are in excellent agreement with the first experimental tests of the new model.

Yip, Chi-Shung; Hershkowitz, Noah; Severn, Greg [Department of Engineering Physics, University of Wisconsin, Madison, Madison, Wisconsin 53706 (United States); Department of Physics, University of San Diego, San Diego, California 92110 (United States)

2010-06-04

329

An Analytic Study of the Perpendicularly Propagating Electromagnetic Drift Instabilities in the Magnetic Reconnection Experiment  

SciTech Connect

A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients and modest collisions as in the Magnetic Reconnection Experiment (MRX) [10]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough efoldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (LHDI, MTSI et.) studied previously, we believe the instability we find is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross current layer direction.

Wang, Y., Kulsrud, R., Ji, H

2008-12-03

330

Formation of an anisotropic electron velocity distribution function and production of multicharged ions in the micropinch discharge plasma  

SciTech Connect

Analysis of the results of polarimetric measurements of X-ray line radiation of multicharged ions in a Z-pinch discharge indicates that the formation of an anisotropic electron velocity distribution in the neck of the current channel and the generation of highly charged ions are separated in time. The generation of a fast electron beam in the longitudinal ohmic electric field in the stage of plasma compression in the neck results in the polarization of X-ray bremsstrahlung continuum. In the stage of expansion of the hot dense micropinch plasma, the radial electric field prevails, due to which X-ray line radiation of multicharged ions becomes linearly polarized.

Dolgov, A. N.; Zemchenkova, N. V.; Klyachin, N. A.; Prokhorovich, D. E. [National Research Nuclear University, Moscow Engineering Physics Institute (Russian Federation)

2011-01-15

331

Determination of laser intensity and hot-electron temperature from fastest ion velocity measurement on laser-produced plasma  

SciTech Connect

Measurements of the velocity of the fastest ion emitted by a CO/sub 2/-laser-produced plasma were made, and it was found that the relationship between velocity and laser flux was given by V/sub i/ = 5.7 x 10/sup 6/ phi/sup 1/6//sub l/ for single-beam illumination. Comparison with computer simulation, ion velocity spectrum, and x-ray data indicate that the hot-electron temperature is given by T/sub h/ = 7.5 x 10/sup -18/ V/sup 2//sub i/. Measurements of emission from multiple-beam experiments and from experiments at 1.06 ..mu..m wavelength are also described. Some simple models are used for discussion and correlation of the data.

Tan, T.H.; McCall, G.H.; Williams, A.H.

1984-01-01

332

The Relation between Relaxation Time, Mean Free Path, Collision Time and Drift Velocity--Pitfalls and a Proposal for an Approach Illustrating the Essentials  

ERIC Educational Resources Information Center

|The collision model is frequently introduced to describe electronic conductivity in solids. Depending on the chosen approach, the introduction of the collision time can lead to erroneous results for the average velocity of the electrons, which enters the expression for the electrical conductivity. In other textbooks, correct results are obtained

Jakoby, Bernhard

2009-01-01

333

Broadband Velocity Modulation Spectroscopy of Molecular Ions for Use in the Jila Electron Edm Experiment  

NASA Astrophysics Data System (ADS)

The JILA electron electric dipole moment (eEDM) experiment will use a low-lying, metastable ^3?_1 state in trapped molecular ions of HfF^+ or ThF^+. Prior to this work, the low-lying states of these molecules had been investigated by PFI-ZEKE spectroscopy. However, there were no detailed studies of the electronic structure. The recently developed technique of frequency comb velocity modulation spectroscopy (VMS) provides broad-bandwidth, high-resolution, ion-sensitive spectroscopy, allowing the acquisition of 150 cm^{-1} of continuous spectra in 30 minutes over 1500 simultaneous channels. By supplementing this technique with cw-laser VMS, we have investigated the electronic structure of HfF^+ in the frequency range of 9950 to 14600 cm^{-1}, accurately fitting and assigning 16 rovibronic transitions involving 8 different electronic states including the X^1?^+ and a^3?_1 states. In addition, an observed ^3?_{0+} state with coupling to both the X and a states has been used in the actual eEDM experiment to coherently transfer population from the rovibronic ground state of HfF^+ to the eEDM science state. Furthermore, we report on current efforts of applying frequency comb VMS at 700 - 900 nm to the study of ThF^+, which has a lower energy ^3?_1 state and a greater effective electric field, and will provide increased sensitivity for a measurement of the eEDM. A. E. Leanhardt et. al., Journal of Molecular Spectroscopy 270, 1-25 (2011). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, Journal of Chemical Physics 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, Physical Review Letters 107, 093002 (2011). K.C. Cossel et. al., Chemical Physics Letters 546, 1-11 (2012).

Gresh, Daniel N.; Cossel, Kevin C.; Cornell, Eric A.; Ye, Jun

2013-06-01

334

Drift motions of small-scale irregularities in the high-latitude F region: An experimental comparison with plasma drift motions  

SciTech Connect

On the evening of January 6, 1986, coordinated observations were carried out with the Johns Hopkins University Applied Physics Laboratory HF coherent scatter radar at Goose Bay, Labrador, and the SRI International incoherent scatter radar at Sondre Stromfjord, Greenland. The common field of view comprised a section of high-latitude F region ionosphere centered on the great circle plane between the radar sites. Over a 40-min period, the HF radar observed strong backscatter from small-scale (13.9 m) field-aligned irregularities. The bulk line-of-sight drift velocity of the irregularities is deduced from the backscatter data. The returns collected simultaneously with the incoherent scatter radar are processed for estimates of the mean line-of-sight ion velocity. Approximately 100 distinct comparisons are possible between the two sets of velocity estimates. Reversals exceeding 1,000 m/s are present in both. In this paper, the authors demonstrate a correspondence between the measured irregularity and ion drifts that is consistent with the supposition that the motion of the irregularities is dominated by convective drift of the ambient plasma. This indicates that the small-scale irregularities detected by HF radars in the high-latitude F region can serve as tracers of ionospheric convective drift.

Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B.; Villain, J.P. (Johns Hopkins Univ., Laurel, MD (United States)); McCready, M.A. (SRI International, Menlo Park, CA (United States))

1987-05-01

335

Mechanisms of double excitation in ion-atom collisions at high velocities  

SciTech Connect

Double-excitation cross sections of helium atoms by bare heavy-ion projectiles at high energies are calculated within the one-center atomic-orbital expansion method including the electron-electron interaction between correlated helium wave functions. The resulting excitation cross sections to 2{ital s}{sup 2} {sup 1}{ital S}{sup {ital e}}, 2{ital p}{sup 2} {sup 1}{ital D}{sup {ital e}}, 2{ital s}2{ital p} {sup 1}{ital P}{sup {ital o}}, and 2{ital p}{sup 2} {sup 1}{ital S}{sup {ital e}} states are analyzed. We conclude that double excitations at high energies by low-{ital Z}{sub {ital p}} projectiles are dominated by a first-order process in which the two-electron transition proceeds through one electron-projectile interaction in conjunction with shakeup or rearrangement due to electron-electron interactions. For high-{ital Z}{sub {ital p}} projectiles at a given velocity, on the other hand, the excitation is dominated by a second-order process in which the transition proceeds through two successive electron-projectile interactions.

Fritsch, W. (Bereich Physik, Hahn-Meitner-Institut Berlin, D-1000 Berlin 39, West Germany (DE)); Lin, C.D. (Department of Physics, Kansas State University, Manhattan, Kansas 66506 (USA))

1990-05-01

336

Ion-wind effects on Poiseuille and Blasius flow  

SciTech Connect

In order to study the effects of ion wind on the plane Poiseuille flow in a channel and Blasius flow on a flat plate, the equations of electrogasdynamics are solved numerically under the assumptions that the flow is incompressible, that the electric field is steady, and that the fluid velocity is negligible compared to ion drift velocity. The results show that ion wind strongly affects the skin-friction distribution for these flows. 19 references.

Van Rosendale, J.R.; Malik, M.R.; Hussaini, M.Y.

1988-08-01

337

Ionospheric drift measurements: Skymap points selection  

NASA Astrophysics Data System (ADS)

In this paper we concentrate on the plasma drift measurement performed by Digisonde Portable Sounder DPS 4 developed by the UMLCAR, Lowell. Special attention is paid to the quality control of data acquired prior to drift velocity calculations. Risks of carefree use of raw Doppler spectra for the plasma motion analysis have been recognized in the Digisonde community. In this paper we propose improvements of Digisonde drift data processing for velocity evaluation and provide a detailed step-by step description: (1) robust height range selection, (2) setting limits on the Doppler frequency shift, and (3) setting limits on the echo arrival angle. Raw data that passed our quality control were then used to derive three velocity components of the bulk plasma drift in the ionosphere. In the paper we discuss, in detail, application of the method on the DPS measurements. However, this technique can be efficiently applied on any other digital ionosondes drift data processing.

Kouba, D.; BoKa, J.; Galkin, I. A.; SantolK, O.; Auli, P.

2008-02-01

338

Notched velocity profiles and the radial electric field in high ion temperature plasmas in the Tokamak Fusion Test Reactor  

SciTech Connect

A large {open_quotes}notch,{close_quotes} or non-monotonic feature, appears in measured toroidal velocity profiles of the carbon impurity in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion {bold 26}, 11 (1984)], centered near the radius of strongest ion temperature gradient. This is explained as a consequence of radial momentum transport dominated by anomalous diffusion together with parallel heat friction on the impurity ions arising from the hydrogenic neoclassical parallel heat flow. The toroidal velocity profile of the hydrogenic species is predicted to be monotonic, from measurements of the impurity toroidal velocity, consistent with the anomalous radial diffusion of toroidal momentum. This supports a neoclassical calculation of the radial electric field for near-balanced beam injection. In supershot plasmas [Phys. Rev. Lett. {bold 58}, 1004 (1987)], a well structure in the radial electric field profile is found in the enhanced confinement region. An associated shear layer separates the core, where the local confinement trends are favorable, from the degraded outer region. This provides a mechanism for the nonlinear coupling of the ion temperature gradient, ion thermal confinement, and the radial electric field, which may help explain the favorable core confinement trends of very high temperature supershot plasmas. {copyright} {ital 1998 American Institute of Physics.}

Ernst, D.R. [Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139 (United States); Bell, M.G.; Bell, R.E.; Bush, C.E.; Chang, Z.; Fredrickson, E.; Grisham, L.R.; Hill, K.W.; Jassby, D.L.; Mansfield, D.K.; McCune, D.C.; Park, H.K.; Ramsey, A.T.; Scott, S.D.; Strachan, J.D.; Synakowski, E.J.; Taylor, G.; Thompson, M.; Wieland, R.M. [Princeton Plasma Physics Laboratory, Princeton University, P.O. Box 451, Princeton, New Jersey 08543 (United States)

1998-03-01

339

Invertebrate drift A review  

Microsoft Academic Search

This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 1015 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.

John E. Brittain; Tor Jan Eikeland

1988-01-01

340

Influence of H{sup -} velocity on H{sup -} extraction probability from a negative ion source  

SciTech Connect

We investigate influence of H{sup -} initial transport direction and kinetic energy on H{sup -} extraction probability with three-dimensional Monte Carlo calculation. As a result, lower energy H{sup -} ions are strongly trapped by the electrical potential structure, so that initial condition of H{sup -} transport direction is cancelled by alignment of the electric field; thus, it has lower influence for H{sup -} extraction probability. Besides, the potential hill induced by the beam extraction voltage more effectively enhances H{sup -} extraction probability for the lower energy H{sup -} ions. The correlation between the magnitude of the local plasma potential near the extraction region and the mean velocity of H{sup -} ions in the region should determine the H{sup -} extraction probability from the ion source.

Matsumoto, Y. [Tokushima Bunri University, Nishihama, Yamashiro-cho, Tokushima 770-8514 (Japan); Nishiura, M. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Shinto, K. [Japan Atomic Energy Agency, Rokkasho, Aomori 039-3212 (Japan); Yamaoka, H. [Harima Institute, RIKEN, Hyogo 679-5148 (Japan); Sasao, M. [Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan); Wada, M. [Graduate School of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321 (Japan)

2010-02-15

341

Ion mobilities in Xe\\/Ne and other rare-gas mixtures  

Microsoft Academic Search

The ion mobility or drift velocity data important for modeling glow discharges in rare gas mixtures are not generally available, nor are the ion-neutral scattering cross sections needed to calculate these data. In this paper we propose a set of cross sections for Xe+ and Ne+ collisions with Xe and Ne atoms. Ion mobilities at 300 K calculated using this

D. Piscitelli; A. V. Phelps; J. de Urquijo; E. Basurto; L. C. Pitchford

2003-01-01

342

Evidence for the incoming-velocity effect on negative fluorine ions scattering from a highly-oriented-pyrolytic-graphite surface  

NASA Astrophysics Data System (ADS)

Negative-ion fractions depending on incident energies and angles have been measured for keV-energy fluorine negative ions scattering on a graphite surface at a scattering angle of 38. For specular scattering, the fraction increases monotonously with increasing incident energy. A specific feature is the nonmonotonic angular dependence of the fraction with the variation of incident angles. It strongly indicates the interaction-time-dependent electron transfer process. The incident-velocity effect has been taken into account to analyze the experimental results, in which an exponential scaling is found.

Chen, Lin; Ding, Bin; Li, Yuan; Qiu, Shunli; Xiong, Feifei; Zhou, Hu; Guo, Yanling; Chen, Ximeng

2013-10-01

343

Tomographic Approach Using an Electrostatic Analyzer for the Measurement of the Three-Dimensional Ion Velocity Distribution of Plasma  

NASA Astrophysics Data System (ADS)

The measurement of the ion velocity distribution in full three-dimensional velocity space is studied with a planar retarding-grid rotating analyzer immersed in plasma. In spite of the plane geometry of the analyzer, the current-voltage measurement in different directions can provide useful information for the three-dimensional measurement with the aid of numerical techniques of computerized tomography. The practical usefulness of this method as a diagnostic tool is shown experimentally for a weakly ionized collisionless argon plasma into which a low-energy ion beam is injected uniformly. Discussions are made with emphasis on the optimization of measurement by compromising the contradiction between the spatial resolution and the statistical accuracy.

Iwama, Naofumi; Lehner, Thierry; Noziri, Hisayoshi; Okado, Masataka

1988-09-01

344

Deconvolution of ion velocity distributions from laser-induced fluorescence spectra of xenon electrostatic thruster plumes  

Microsoft Academic Search

This thesis presents a method for extracting singly-ionized xenon (Xe II) velocity distribution estimates from single-point laser-induced fluorescence (LIF) spectra at 605.1 nm. Unlike currently-popular curve-fitting methods for extracting bulk velocity and temperature data from LIF spectra, this method makes no assumptions about the velocity distribution, and thus remains valid for non-equilibrium and counterstreaming plasmas. The well-established hyperfine structure and

Timothy B. Smith

2003-01-01

345

Empirically Determined Anisotropic Velocity Distributions and Outflows of O5+ Ions in a Coronal Streamer at Solar Minimum  

NASA Astrophysics Data System (ADS)

Empirical constraints on the O5+ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 Rsolar are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 1996 October 12 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) satellite and three-dimensional electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle and Spectrometric Coronagraph (LASCO) also on SOHO. Four conclusions result from this work: (1) our analysis shows O5+ velocity distribution anisotropy in the streamer legs and stalk and gives strong evidence that the microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction; (2) there is preferential heating of the O5+ ions over the protons in the streamer stalk and legs; (3) there is no evidence for preferential O5+ heating in the core; and (4) the outflow velocity of the O5+ ions is determined at heights above 4.6 Rsolar. All results have a confidence level of at least 70%.

Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.

2003-11-01

346

Kinetics of copper drift in PECVD dielectrics  

Microsoft Academic Search

We quantified the drift of Cu ions into various PECVD dielectrics by measuring shifts in capacitance-voltage behavior after subjecting Cu-gate MOS capacitors to bias-temperature stress. At a field of 1.0 MV\\/cm and temperature of 100C, Cu ions drift readily into PECVD oxide with a projected accumulation of 2.71013 ions\\/cm 2 after 10 years. However, in PECVD oxynitride, the projected accumulation

Alvin L. S. Loke; Changsup Ryu; C. Patrick Yue; James S. H. Cho; S. Simon Wong

1996-01-01

347

Long wavelength gradient drift instability in Hall plasma devices. II. Applications  

NASA Astrophysics Data System (ADS)

Hall plasma devices with electron E B drift are subject to a class of long wavelength instabilities driven by the electron current, gradients of plasma density, temperature, and magnetic field. In the first companion paper [Frias et al., Phys. Plasmas 19, 072112 (2012)], the theory of these modes was revisited. In this paper, we apply analytical theory to show that modern Hall thrusters exhibit azimuthal and axial oscillations in the frequency spectrum from tens KHz to few MHz, often observed in experiments. The azimuthal phase velocity of these modes is typically one order of magnitude lower than the E B drift velocity. The growth rate of these modes scales inversely with the square root of the ion mass, ~1/mi. It is shown that several different thruster configurations share the same common feature: the gradient drift instabilities are localized in two separate regions, near the anode and in the plume region, and absent in the acceleration region. Our analytical results show complex interaction of plasma and magnetic field gradients and the E B drift flow as the sources of the instability. The special role of plasma density gradient is revealed and it is shown that the previous theory is not applicable in the region where the ion flux density is not uniform. This is particularly important for near anode region due to ionization and in the plume region due to diverging ion flux.

Frias, Winston; Smolyakov, Andrei I.; Kaganovich, Igor D.; Raitses, Yevgeny

2013-05-01

348

Fast-Ion Velocity Distributions in JET Measured by Collective Thomson Scattering  

Microsoft Academic Search

Introduction. In magnetically confined fusion plas- mas, populations of energetic ions are generated by fusion reactions and auxiliary heating. Representing a signifi- cant source of free energy (13 of plasma energy), the fast ions affect the bulk plasma dynamics, possibly driving modes which can increase transport and lead to prompt fast ion losses (1,2). Both the interaction of the energetic

H. Bindslev; J. A. Hoekzema; J. Egedal; J. A. Fessey; T. P. Hughes; J. S. Machuzak

1999-01-01

349

A Comparison of Invertebrate Drift in Three Michigan Streams.  

National Technical Information Service (NTIS)

The purpose was to measure the rate of drift in three contrasting streams and determine what relationship exists between drift rate and degree of enrichment. Additionally an attempt was made to determine how drift is related to current velocity. The three...

L. D. Eyman

1969-01-01

350

Vertical Distrubution in the Water Column of Drifting Stream Macroinvertebrates  

Microsoft Academic Search

We examined the macroinvertebrate composition and drift density in a Mediterranean lotic system, the Erro River (northwestern Italy). Drift density and composition were sampled for one year at three levels of the water column; temperature and flow velocity were also measured. We found that drift density was generally highest near the bottom. We also noticed that various taxa tended to

Stefano Fenoglio; Tiziano Bo; Giuseppe Gallina; Marco Cucco

2004-01-01

351

Number-conserving linear-response study of low-velocity ion stopping in a collisional magnetized classical plasma  

SciTech Connect

The results of a theoretical investigation of the low-velocity stopping power of ions in a magnetized collisional and classical plasma are reported. The stopping power for an ion is calculated through the linear-response (LR) theory. The collisions, which lead to a damping of the excitations in the plasma, are taken into account through a number-conserving relaxation time approximation in the LR function. In order to highlight the effects of collisions and magnetic field, we present a comparison of our analytical and numerical results obtained for nonzero damping or magnetic field with those for vanishing damping or magnetic field. It is shown that the collisions remove the anomalous friction obtained previously [Nersisyan et al., Phys. Rev. E 61, 7022 (2000)] for the collisionless magnetized plasmas at low ion velocities. One of the major objectives of this paper is to compare and to contrast our theoretical results with those obtained through a diffusion coefficient formulation based on the Dufty-Berkovsky relation evaluated for a magnetized one-component plasma modeled with target ions and electrons.

Nersisyan, Hrachya B. [Institute of Radiophysics and Electronics, 0203 Ashtarak (Armenia); Centre of Strong Fields Physics, Yerevan State University, Alex Manoogian Street 1, 0025 Yerevan (Armenia); Deutsch, Claude [LPGP - UMR-CNRS 8578, Universite Paris XI, F-91405 Orsay (France); Das, Amal K. [Department of Physics, Dalhousie University, Halifax, Nova Scotia B3H 3J5 (Canada)

2011-03-15

352

Space-time velocity behaviour of self-organized ion structures induced by electrostatic perturbations observed by laser induced fluorescence  

NASA Astrophysics Data System (ADS)

A multipolar discharge plasma device is used in a double plasma configuration to generate various types of non linear ion acoustic shock waves which propagate in the low density collisionless argon discharge plasma. A great effort has been devoted to ensure the stationarity of the plasma parameters (neutral presure, discharge current, discharge voltage). A time resolved laser induced fluorescence diagnostic is applied to investigate the reaction of the plasma to a step density perturbation. It clearly exhibits the propagation of self-organized coherent ion structures looking like solitons and cavitons. The phase space propagation of the perturbation is shown. Because the ion distribution function is determined in space time and velocity, the Vlasov equation can be checked at any given spatial position.

Bachet, G.; Dindelegan, M.; Doveil, F.; Skiff, F.; Stern, R. A.

1997-11-01

353

Exact Solution for the Generalized Bohm Criterion in a Two-Ion-Species Plasma  

SciTech Connect

For a weakly collisional two-ion species plasma, it is shown that the minimum phase velocity of ion acoustic waves (IAWs) at the sheath-presheath boundary is equal to twice the phase velocity in the bulk plasma. This condition provides a theoretical basis for the experimental results that each ion species leaves the plasma with a drift velocity equal to the IAW phase velocity in the bulk plasma [D. Lee et al., Appl. Phys. Lett. 91, 041505 (2007)]. It is shown that this result is a consequence of the generalized Bohm criterion and fluid expressions for the IAW phase velocities.

Lee, Dongsoo; Hershkowitz, Noah [Department of Engineering Physics, University of Wisconsin at Madison, Madison, Wisconsin 53706 (United States); Oksuz, Lutfi [Department of Engineering Physics, University of Wisconsin at Madison, Madison, Wisconsin 53706 (United States); Department of Physics, Suleyman Demirel Universitesi, Isparta 32260 (Turkey)

2007-10-12

354

Generation of zonal flows by ion-temperature-gradient and related modes in the presence of neoclassical viscosity  

Microsoft Academic Search

Generation of zonal flows by primary waves that are more complex than those considered in the standard drift-wave model is studied. The effects of parallel ion velocity and ion perturbed temperature and the part of the nonlinear mode interaction proportional to the ion pressure are taken into account. This generalization of the standard model allows the analysis of generation of

A. B. Mikhailovskii; A. I. Smolyakov; E. A. Kovalishen; M. S. Shirokov; V. S. Tsypin

2006-01-01

355

Velocity distribution and yield measurements of Fe ejected from FeS2 during ion bombardment  

Microsoft Academic Search

Secondary neutrals sputtered by 3-keV Ar+ from FeS2 and Fe were studied by use of laser postionization mass spectrometry and laser-induced fluorescence spectroscopy. The velocity distribution and yield of Fe from the FeS2 sample were measured. The velocity distribution of Fe sputtered from the sulfide is very similar to that of sputtered Fe from the pure metal with both distributions

S. Nikzad; W. F. Calaway; C. E. Young; M. J. Pellin; D. M. Gruen; T. A. Tombrello; R. M. Housley

1992-01-01

356

Mass filter and focusing ion detector for use with time-of-flight velocity distribution measurements  

Microsoft Academic Search

A novel mass filter and focusing ion detector for time-of-flight studies of dissociative ionization fragments is described. The filterdector combination is particularly suited for measuring the kinetic energy released in the molecular dissociation process. The mass filter utilizes a computer-controlled, time-dependent retarding potential synchronized with, and located a distance L from, a pulsed electron-bombardment ion source. Ions arriving at the

M. D. Burrows; S. R. Ryan; W. E. Lamb; L. C. McIntyre

1979-01-01

357

A comparison of ion velocity measurements from retarding field energy analyzer (RFEA) and laser induced fluorescence (LIF) in expanding helicon plasma  

NASA Astrophysics Data System (ADS)

We present a comparison of ion velocity measurements from RFEA and LIF where we specially focus on the ability to diagnose flow and ion beams due to current free double layers in expanding helicon plasma. An RFEA in a plasma will be surrounded by a sheath so the velocities measured by the RFEA will be the velocities of the ions after they have been accelerated by the sheath and any potential drops inside the probe. Different methods exist to relate the velocities measured by the RFEA to the velocities in the plasma. Most of them include some simple assumptions about the acceleration in the sheath. We will compare measurements from two different RFEAs, one with a grounded front grid and one with a floating front grid, with LIF measurements to assess the validity of these simple models.

Gulbrandsen, Njl; Fredriksen, shild; Carr, Jerry, Jr.; Scime, Earl; McCarren, Dustin W.; Vandervort, Robert; Galante, Matthew E.; Magee, Richard M.; Lusk, Greg; Sears, Stephanie H.; Miloch, Wojciech J.

2012-10-01

358

Production of highly charged low-velocity recoil ions by heavy-ion bombardment of rare-gas targets  

Microsoft Academic Search

The author has measured charge-state (q) spectra of recoil ions generated in single collisions of 25-45-MeV chlorine ions with targets of helium, neon, and argon. A high-efficiency time-of-flight spectrometer was used to identify the charge-to-mass ratio of the slowly moving recoils. Recoil q up to + 8 (neon) and + 11 (argon) were observed. Cross sections for recoil production were

C. L. Cocke

1979-01-01

359

Single-fluid stability of stationary plasma equilibria with velocity shear and magnetic shear  

SciTech Connect

By using incompressible single-fluid equations with a generalized Ohm's law neglecting the electron inertia, a linear eigenmode equation for a magnetic field perturbation is derived for stationary equilibria in a slab geometry with velocity and magnetic shears. The general eigenmode equation contains a fourth-order derivative of the perturbation in the highest order and contains Alfven and whistler mode components for a homogeneous plasma. The ratio of the characteristic ion inertia length to the characteristic inhomogeneity scale length is chosen as a small parameter for expansion. Neglecting whistler mode in the lowest order, the eigenmode equation becomes a second-order differential equation similar to the ideal magnetohydrodynamic eigenmode equation except for the fact that the unperturbed perpendicular velocity contains both electric and ion diamagnetic drifts. A sufficient condition for stability against the Kelvin-Helmholtz instability driven by shear in the ion diamagnetic drift velocity is derived and then applied to tokamaks.

Miura, Akira [Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033 (Japan)

2009-10-15

360

Temporal evolution of confined fast-ion velocity distributions measured by collective Thomson scattering in TEXTOR  

Microsoft Academic Search

Fast ions created in the fusion processes will provide up to 70% of the heating in ITER. To optimize heating and current drive in magnetically confined plasmas insight into fast-ion dynamics is important. First measurements of such dynamics by collective Thomson scattering (CTS) were recently reported [Bindslev , Phys. Rev. Lett. 97, 205005 2006]. Here we extend the discussion of

S. K. Nielsen; H. Bindslev; L. Porte; J. A. Hoekzema; S. B. Korsholm; F. Leipold; F. Meo; P. K. Michelsen; S. Michelsen; J. W. Oosterbeek; E. L. Tsakadze; G. van Wassenhove; E. Westerhof; P. Woskov

2008-01-01

361

Temporal evolution of drift Alfvn waves and instabilities in an inhomogeneous plasma with homogeneous shear flow.  

PubMed

The temporal evolution of drift Alfvn waves in an inhomogeneous plasma of low and finite pressure with homogeneous shear flow is studied as an initial value problem without the use of spectral expansion in time. The cases of plasma with cold and hot ions, weak and strong flow shear are considered separately. It is shown that the conventional modal structure of the stable and unstable drift and Alfvn waves holds only for a limited time in the initial stage of its evolution. For larger times, nonmodal effects due to the velocity shear define the development of drift Alfvn waves and drift Alfvn instabilities. For the regimes of low flow shear, which corresponds to the period of the low-to-high transition, the long time evolution of these instabilities as well as their saturation are determined by the nonlinear effects such as the nonlinear decorrelation effect. In contrast, the plasma with strong flow shear, which corresponds to the regime of the developed transport barriers, is stable against the development hydrodynamic drift Alfvn and resistive drift Alfvn instabilities. The frequency increase caused by the shear flow brings the Alfvn wave phase speed close to the electron thermal speed where strong electron Landau damping occurs. At this stage, a kinetic approach for the description of these waves becomes necessary. PMID:12513414

Mikhailenko, Vladimir S; Mikhailenko, Vladimir V; Heyn, Martin F; Mahajan, Swadesh M

2002-12-16

362

Influence of the Proton Pressure Tensor on the Turbulent Velocity Spectrum at Ion Kinetic Scales  

NASA Astrophysics Data System (ADS)

Numerical hybrid simulations with particle protons and fluid electrons are presented for turbulent fluctuations with spatial variations in a plane perpendicular to the background magnetic field. The steepened portion of the proton bulk velocity spectrum is found at smaller wavenumbers for larger background proton temperature. The velocity spectrum is determined, in part, by the proton pressure tensor. The proton pressure tensor is shown to possess non-gyrotropic and finite off-diagonal components in the places where the turbulent fluctuations have developed strong gradients. Proton demagnetization at these places is a factor in the departure from a Maxwellian velocity distribution function. How demagnetization could connect with both reversible and effectively irreversible aspects of the pressure tensor is considered. The effectively irreversible aspect corresponds to the net heating of the protons and to the dissipation of the turbulent energy cascade.

Vasquez, B. J.; Markovskii, S.

2011-12-01

363

Ion acceleration from laser-driven electrostatic shocks  

NASA Astrophysics Data System (ADS)

Multi-dimensional particle-in-cell simulations are used to study the generation of electrostatic shocks in plasma and the reflection of background ions to produce high-quality and high-energy ion beams. Electrostatic shocks are driven by the interaction of two plasmas with different density and/or relative drift velocity. The energy and number of ions reflected by the shock increase with increasing density ratio and relative drift velocity between the two interacting plasmas. It is shown that the interaction of intense lasers with tailored near-critical density plasmas allows for the efficient heating of the plasma electrons and steepening of the plasma profile at the critical density interface, leading to the generation of high-velocity shock structures and high-energy ion beams. Our results indicate that high-quality 200 MeV shock-accelerated ion beams required for medical applications may be obtained with current laser systems.

Fiuza, F.; Stockem, A.; Boella, E.; Fonseca, R. A.; Silva, L. O.; Haberberger, D.; Tochitsky, S.; Mori, W. B.; Joshi, C.

2013-05-01

364

Stopping power for low-velocity heavy ions: (0-1.0)-MeV/nucleon Mg ions in 17 (Z=22-79) elemental solids  

NASA Astrophysics Data System (ADS)

The stopping power for 24,26Mg ions in 17 (Z=22-79) elemental solids has been studied in the energy region 0-1.0 MeV/nucleon by application of the Doppler-shift attenuation method. At velocities 2v0velocity), the scaling factors 1.10 (Ti), 0.90 (V), 0.93 (Fe), 0.97 (Co), 0.99 (Ni), 1.03 (Cu), 1.05 (Ge), 1.05 (Nb), 1.15 (Mo), 1.05 (Pd), 1.08 (Ag), 1.09 (Hf), 1.07 (Ta), 1.05 (W), 1.05 (Re), 1.05 (Pt), and 0.96 (Au) to the commonly used empirical electronic stopping power by Ziegler, Biersack, and Littmark were determined to an accuracy of +/-5%. At velocities v<2v0, much higher electronic stopping power and different velocity dependence than predicted by the empirical model were obtained. The electronic stopping power was determined to an accuracy of +/-5%. The reduction of the nuclear stopping power due to the polycrystalline structure of the slowing-down materials was taken into account in the deduction of the electronic stopping power.

Arstila, K.; Keinonen, J.; Tikkanen, P.

1990-04-01

365

Stopping power for low-velocity heavy ions: (0--1. 0)-MeV/nucleon Mg ions in 17 ( Z =22--79) elemental solids  

SciTech Connect

The stopping power for {sup 24,26}Mg ions in 17 ({ital Z}=22--79) elemental solids has been studied in the energy region 0--1.0 MeV/nucleon by application of the Doppler-shift attenuation method. At velocities 2{ital v}{sub 0}{lt}{ital v}{lt}5{ital v}{sub 0} ({ital v}{sub 0} the Bohr velocity), the scaling factors 1.10 (Ti), 0.90 (V), 0.93 (Fe), 0.97 (Co), 0.99 (Ni), 1.03 (Cu), 1.05 (Ge), 1.05 (Nb), 1.15 (Mo), 1.05 (Pd), 1.08 (Ag), 1.09 (Hf), 1.07 (Ta), 1.05 (W), 1.05 (Re), 1.05 (Pt), and 0.96 (Au) to the commonly used empirical electronic stopping power by Ziegler, Biersack, and Littmark were determined to an accuracy of {plus minus}5%. At velocities {ital v}{lt}2{ital v}{sub 0}, much higher electronic stopping power and different velocity dependence than predicted by the empirical model were obtained. The electronic stopping power was determined to an accuracy of {plus minus}5%. The reduction of the nuclear stopping power due to the polycrystalline structure of the slowing-down materials was taken into account in the deduction of the electronic stopping power.

Arstila, K.; Keinonen, J.; Tikkanen, P. (Accelerator Laboratory, University of Helsinki, Haemeentie 100, SF-00550 Helsinki, Finland (FI))

1990-04-01

366

Ion acoustic double layers in the presence of positrons beam and q-nonextensive velocity distributed electrons  

NASA Astrophysics Data System (ADS)

Linear and nonlinear studies are presented for an electron-ion plasma system which is being energized with an external beam of positrons. The electrons are assumed to follow the q-nonextensive velocity distribution. The growth rates of instability due to positron beam are analyzed numerically. The compressive and rarefactive double layers are studied in the system and it is found that by varying the entropic index parameter q, positron beam speed v po and concentration of positrons p, the dynamics of nonlinear profile is changing quite effectively. The relevance of the work regarding to astrophysical space plasma is pointed out.

Ali Shan, S.; Mushtaq, A.; Akhtar, N.

2013-08-01

367

Shear driven electromagnetic drift-waves in a nonuniform dense magnetoplasma  

SciTech Connect

Linear characteristic properties of high- and low-frequency (in comparison with the cyclotron frequency) electromagnetic drift-waves are studied in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel (magnetic field-aligned) velocity shear, by using quantum magnetohydrodynamic model. By applying the drift-approximation (viz., |{partial_derivative} {sub t}|<<{omega}{sub ci}<<{omega}{sub ce}) to the quantum momentum equations, together with the continuity equations and the Poisson equation, we derive the governing equations for electromagnetic drift-waves with the shear flow. These linear equations are then Fourier transformed to obtain the dispersion relation in both high-frequency and low-frequency regimes. The dispersion relations are then discussed under various limiting cases.

Tariq, Sabeen; Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, Waqas [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad 44000 (Pakistan); National Center for Physics (NCP), Islamabad 44000 (Pakistan)

2011-08-15

368

A DRIFT ORDERED SHORT MEAN-FREE DESCRIPTION FOR PARTIALLY IONIZED MAGNETIZED PLASMA  

SciTech Connect

Effects of neutral particles, most prominently the associated heat flux and viscosity, can be very important or even dominant at the edge of a tokamak and so must be self-consistently accounted for in a description of magnetized tokamak edge plasma. To the best of our knowledge, this has only been done so far for short mean-free path plasma under MHD-like Braginskii's orderings i.e. assuming that species velocities are on the order of the ion thermal speed. Since plasma flows in modern tokamaks are usually slow compared with the ion thermal speed (at least in the absence of strong external momentum sources) it is more appropriate to use drift orderings in which the plasma flow velocity is instead comparable with the diamagnetic heat flow divided by pressure. Employing drift orderings and evaluating species distribution functions through second order in the small gyroradius and mean-free path expansion parameters allows accounting for the important effects of heat fluxes on species momentum transport (viscosities), which are missing from the large flow ordered treatments. In this work we consider short mean-free path plasma consisting of electrons and single species of singly-charged ions and neutrals. We neglect neutral-neutral and elastic electron-neutral collisions and approximate the neutral-ion charge-exchange cross-section with a constant. We employ drift orderings to evaluate ion, neutral, and electron heat fluxes, viscosity tensors, and momentum and energy exchange terms and formulate a self-consistent system of electron, ion, and neutral fluid equations, thereby generalizing the drift-ordered treatment of fully ionized plasma.

SIMAKOV, ANDERI N. [Los Alamos National Laboratory

2007-02-08

369

Experimental studies of transverse metastable ion velocity distribution functions in the presheath of a weakly collisional argon plasma  

SciTech Connect

Laser-induced fluorescence measurements of the transverse metastable ion velocity distribution function near a negatively biased plate in a low temperature (T{sub e}<1 eV), low pressure (p{sub 0}<1 mTorr) dc multi-dipole argon discharge plasma have been made with a diode laser. The metastable argon ions in the 3s{sup 2}3p{sup 4}({sup 3}P)3d{sup 4}F{sub 7/2} state are found to be characterized by a Maxwellian temperature transverse to the direction normal to the plate. For a neutral pressure of 0.3 mTorr, the transverse temperature increases along the presheath from 0.026 eV in the bulk plasma to 0.058 eV at the presheath sheath boundary.

Lee, Dongsoo; Hershkowitz, Noah [Department of Engineering Physics, University of Wisconsin at Madison, Madison, Wisconsin 53706 (United States); Severn, Greg [Department of Physics, University of San Diego, San Diego, California 92110 (United States)

2008-08-15

370

Study of Incomplete Fusion for Light Heavy-Ion Systems Using Velocity Distributions.  

National Technical Information Service (NTIS)

Experimental results on incomplete fusion for light systems are discussed by studying the velocity distribution of fusion-like residues in the energy range of 6 to 20 MeV/nucleon. Original experimental work and results from other groups including the Hahn...

Y. Chan C. Albiston M. Bantel A. Budzanowski D. DiGregorio

1986-01-01

371

An investigation of some effects of drifts and magnetic field direction in the scrape-off layer and divertor of tokamak plasmas  

SciTech Connect

Various effects of particle drifts in the scrape-off layer (SOL) and divertor of tokamaks have been calculated. The predictions are consistent with several experimentally observed phenomena, e.g., the double reversal of parallel ion velocity in the SOL and the enhanced core penetration of argon injected into the divertor when the grad-B ion drift is into, rather than away from, the divertor. Other interesting phenomena, such as the structure of the parallel current flowing in the SOL and the reversal of the sign of the electrostatic potential in the SOL when the toroidal field direction is reversed, are also predicted.

Stacey, W. M. [Fusion Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2009-04-15

372

Mass filter and focusing ion detector for use with time-of-flight velocity distribution measurements  

Microsoft Academic Search

The paper describes a high-pass mass filter and an electrostatically focused ion detector for time-of-flight (TOF) studies of dissociative ionization fragments. The mass filter uses a time-dependent voltage barrier in the flight path to reject ions with mass less than a given value. It has been operated in a mode which separates individual ionic species, providing unity mass resolution at

M. D. Burrows; S. R. Ryan; W. E. Lamb Jr.; L. C. McIntyre Jr.

1979-01-01

373

Analysis of the projectile track charging by H + secondary ion velocity distribution measurements  

Microsoft Academic Search

Secondary ions, emitted from LiF, Al (covered with layers of Al2O3) and Au bombarded by a MeV argon (25 keV\\/u) beam, are analyzed by a XY-TOF detection system. This new method allows, for each emitted ion, the simultaneous measurement of its time-of flight (TOF) and its impact coordinates (XY) on the detector surface, after acceleration by a homogenous electric field.

T. Jalowy; L. S. Farenzena; M. Hattass; E. F. da Silveira; H. Schmidt-Bcking; K. O. Groeneveld

2004-01-01

374

Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind  

SciTech Connect

The present study is dedicated to the analysis of dynamical processes relevant to the interaction of newborn ions with turbulence in the solar wind, when the level of turbulence is moderately low so that quasi-linear theory is applicable. It is assumed that the low-frequency turbulence is at saturation level and not affected by the newborn ions. In order to follow the time evolution of the ion distribution, the quasi-linear diffusion equation is derived and numerically solved, starting from a ring-beam initial distribution. A simplified treatment of the resonance broadening effect is included in the diffusion equation, and its role in the pickup process is discussed. Two different configurations of wave polarization and direction of propagation are considered, using model turbulence spectra. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as well as the conditions leading to significant acceleration of the ions.

Ziebell, L.F.; Yoon, P.H. (Univ. of Maryland, College Park (USA))

1990-12-01

375

Interferometric determination of broadband ELF wave phase velocity within a region of transverse auroral ion acceleration  

NASA Astrophysics Data System (ADS)

Broadband electric field fluctuations with typical amplitudes of 10-20 mV/m peak-to-peak and frequencies from 0 Hz to 3 kHz (BB-ELF) were observed coincident with a region of ?200 eV transverse H+ acceleration (TAI) near the poleward edge of the pre-midnight aurora. The coherence and phase velocity of the electric fields were measured using a interferometric antenna array over the frequency range of ? 100 Hz to 3 kHz. These electric field fluctuations were found to have the following characteristics: 1) incoherence perpendicular to the geomagnetic field, 2) coherence parallel to the the geomagnetic field, 3) parallel phase velocity (?/k?) of 30-35 km/s upwards, 4) 0 < |k?/k?| < 0.22. We show that these properties are compatible with the emission being electrostatic H+ cyclotron (EHC) waves. We also discuss possible generation mechanisms for the waves, and their relationship to the TAI.

Bonnell, J.; Kintner, P.; Wahlund, J.-E.; Lynch, K.; Arnoldy, R.

376

Interactions between waves and mean drift in an ice pack  

NASA Astrophysics Data System (ADS)

In a drifting ice pack, the mean drag depends upon the amplitude of oscillations present, and it reaches a maximum when the amplitude of oscillations along the direction of mean drift equals the drift velocity. The damping of waves entering a pack increases with increasing drift velocity, so waves entering a drifting pack will vary in amplitude because of dissipation. The dispersion of surface gravity waves in an ice pack under compression shows that the group velocity of the waves decreases with increasing mean compressive stress, so there can also be dispersive mechanisms causing wave amplitude variations within the ice pack. The observations in the Norwegian Remote Sensing Experiment, namely that the drag in a drifting pack varied with distance from the pack edge, are in general concord with these results.

Mollo-Christensen, Erik

1983-03-01

377

Dynamics of positive probes in underdense, strongly magnetized, EB drifting plasma: Particle-in-cell simulations  

NASA Astrophysics Data System (ADS)

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in EB drifting plasma were studied in three-dimensional electromagnetic particle-in-cell simulations. In these simulations, electrons and ions were magnetized with respect to the probe and the plasma was underdense (?pedrift velocity (Mach 4.5 with respect to the ion acoustic speed) between the plasma and probe was created with background electric and magnetic fields. Four distinct regions developed in the presences of the positive probe: a quasi-trapped electron region, an electron-depletion wing, an ion-rich wing, and a wake region. We report on the observations of strong electron heating mechanisms, space-charge wings, ion cyclotron charge-density eddies in the wake, electron acceleration due to a magnetic presheath, and the current-voltage relationship.

Heinrich, Jonathon R.; Cooke, David L.

2013-09-01

378

High-latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction  

NASA Astrophysics Data System (ADS)

A series of new high-latitude ionospheric convection models have been constructed using Defense Meteorological Satellite Program (DMSP) thermal ion drift measurements. The models are obtained by sorting cross polar cap electrostatic potentials into magnetic latitude/magnetic local time bins. A regression analysis of the potentials in each bin is then implemented for establishing the relationships to the interplanetary magnetic field (IMF) for three seasons: summer, winter, and equinox. A linear modeling formula for the ionospheric electrodynamics (LIMIE) yields a convection response to the average solar wind (i.e., the ``quasi-viscous'' interaction) and to changes in the IMF By, Bz <= 0, and Bz > 0 components. The modeled convection is a superposition of the first two parameters with either the IMF Bz <= 0 or the Bz > 0 component. A global model is created by fitting the regression analysis results to a spherical harmonic function. The resulting DMSP-based ionospheric convection model (DICM) is fully parameterized by the IMF strength and direction. With this model, ionospheric convection patterns can be generated for any IMF configuration during quiet to moderate geomagnetic conditions. We compare the DICM model with other available high-latitude convection patterns organized by the IMF. The new elements in DICM are its quasi-viscous and separate IMF-dependent terms for both the northern and southern polar regions, which are not explicitly found in other ionospheric convection studies. The DICM's seasonal dependence and interhemispheric symmetry/asymmetry features show that the summer cross-polar potentials are 10-15% smaller than the winter potentials. The latter is in agreement with the seasonal dependence of field-aligned currents and with the voltage-current relationship required for the proper magnetosphere-ionosphere coupling.

Papitashvili, Vladimir O.; Rich, Frederick J.

2002-08-01

379

Effects of projectile track charging on the H ? secondary ion velocity distribution  

Microsoft Academic Search

The bombardment of insulating targets by MeV projectiles produces a positive track delivering secondary electrons to the solid. These electrons are eventually captured by adsorbed hydrogen-containing molecules, inducing fragmentation and initiating the H? secondary ion emission. The dynamics of this process is very sensitive to the track electric field and depends on the emission site and on the H? initial

P. Iza; L. S. Farenzena; E. F. da Silveira

2007-01-01

380

Effects of projectile track charging on the H- secondary ion velocity distribution  

Microsoft Academic Search

The bombardment of insulating targets by MeV projectiles produces a positive track delivering secondary electrons to the solid. These electrons are eventually captured by adsorbed hydrogen-containing molecules, inducing fragmentation and initiating the H- secondary ion emission. The dynamics of this process is very sensitive to the track electric field and depends on the emission site and on the H- initial

P. Iza; L. S. Farenzena; E. F. da Silveira

2007-01-01

381

Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging  

SciTech Connect

For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H{sup +} ions emerging from the photodissociation of HCl following the two photon excitation to the V {sup 1}{Sigma}{sup +} state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers {Delta}v/v=0.022 compared to 0.086 at v{approx_equal}17 000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.

Kauczok, S.; Goedecke, N.; Veckenstedt, M.; Maul, C.; Gericke, K.-H. [Institut fuer Physikalische und Theoretische Chemie, TU Braunschweig, 38106 Braunschweig (Germany); Chichinin, A. I. [Institut fuer Physikalische und Theoretische Chemie, TU Braunschweig, 38106 Braunschweig (Germany); Institute of Chemical Kinetics and Combustion, 630090 Novosibirsk (Russian Federation)

2009-08-15

382

Effect of ion orbit loss on the structure in the H-mode tokamak edge pedestal profiles of rotation velocity, radial electric field, density, and temperature  

NASA Astrophysics Data System (ADS)

An investigation of the effect of ion orbit loss of thermal ions and the compensating return ion current directly on the radial ion flux flowing in the plasma, and thereby indirectly on the toroidal and poloidal rotation velocity profiles, the radial electric field, density, and temperature profiles, and the interpretation of diffusive and non-diffusive transport coefficients in the plasma edge, is described. Illustrative calculations for a high-confinement H-mode DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] plasma are presented and compared with experimental results. Taking into account, ion orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure of the radial profiles of these quantities in the edge plasma, indicating the necessity of taking ion orbit loss effects into account in interpreting or predicting these quantities.

Stacey, Weston M.

2013-09-01

383

Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experiment  

SciTech Connect

A passive ion temperature polychromator has been deployed on Pegasus to study power balance and non-thermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 Czerny-Turner polychromator whose output is recorded by an intensified high-speed camera. The use of high orders allows for a dispersion of 0.02 A/mm in 4th order and a bandpass of 0.14 A ({approx}13 km/s) at 3131 A in 4th order with 100 {mu}m entrance slit. The instrument temperature of the spectrometer is 15 eV. Light from the output of an image intensifier in the spectrometer focal plane is coupled to a high-speed CMOS camera. The system can accommodate up to 20 spatial points recorded at 0.5 ms time resolution. During helicity injection, stochastic magnetic fields keep T{sub e} low ({approx}100 eV) and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (T{sub i} Almost-Equal-To 1.2 keV, T{sub e} Almost-Equal-To 0.1 keV) using spectral lines from carbon III, nitrogen III, and boron IV.

Burke, M. G.; Fonck, R. J.; Bongard, M. W.; Schlossberg, D. J.; Winz, G. R. [Department of Engineering Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2012-10-15

384

Bulk properties and velocity distributions of water group ions at Comet Halley - Giotto measurements  

NASA Astrophysics Data System (ADS)

In the region upstream of Comet Halley, pickup heavy ions of cometary origin were directly observed by the implanted ion spectrometer on Giotto. Diffusion of this population in pitch angle and in energy, during the approach to the comet and on the outbound leg is discussed. The two data sets are compared and qualitative ideas on scattering timescales are inferred. In addition the bulk parameters of these distributions have been computed and a comparison of the observed speed in the solar wind frame and the observed density with expectations is presented. Pitch angle scattering occurs more slowly than expected with filled shells appearing at 2,500,000 km, and significant energy diffusion does not occur until the bow shock region. Also the shell distributions downstream of the shock flow at the bispherical bulk speed (related to the Alfven speed) along the magnetic field with respect to the solar wind in accordance with conservation of energy between the pickup ions and the wave turbulence.

Coates, A. J.; Johnstone, A. D.; Wilken, B.; Jockers, K.; Glassmeier, K.-H.

1990-07-01

385

Influence of partial activation on force-velocity properties of frog skinned muscle fibers in millimolar magnesium ion.  

PubMed

Segments of briefly glycerinated muscle fibers from Rana pipiens were activated rapidly by a brief exposure to 2.5 mM free calcium followed by a solution containing calcium buffered with EGTA to produce the desired level of force. Steps to isotonic loads were made using a servomotor, usually 3-5 s after the onset of activation. The relative isotonic forces (P/P0) and velocities from contractions obtained under similar circumstances were grouped together and fitted with hyperbolic functions. Under the condition of 6 mM MgCl2 and 5 mM ATP, there was no significant difference in the relative force-velocity relations obtained at full activation compared with those obtained at partial activation when developed force was approximately 40% of its full value. Control experiments showed that a variety of factors did not alter either the relative force-velocity relations or the finding that partial activation did not change these properties. The factors investigated included the decline in force that occurs with each successive contraction of skinned fibers, the segment length (over a range of 1-3 mm), the sarcomere length (over a range of 1.9-2.2 microns), the magnesium ion concentration (26 microM and 1.4 mM were tested), the ATP concentration, the presence of free calcium, and the age of the preparation (up to 30 h). Attempts to repeat earlier experiments by others showing a dependence of shortening velocity on activation were unsuccessful because the low ionic strength used in those experiments caused the fibers to break after a few contractions. The main conclusion, that the shortening velocity is independent of the level of activation, is consistent with the hypothesis that the cross-bridges act independently and that activating calcium acts only as an all-or-none switch for individual cross-bridge attachment sites, and does not otherwise influence the kinetics of cross-bridge movement. PMID:3486252

Podolin, R A; Ford, L E

1986-04-01

386

Cross sections for resonant charge transfer between atoms and their positive ions: Collision velocity approx lt 1 a. u  

SciTech Connect

Calculated cross sections for resonant charge transfer between atoms and their positive ions are presented in tables and graphs for all nontransition elements in the range of low and intermediate collision velocities ({approx lt}1 a.u.). Experimental data obtained since the 1930s are compiled. The cross sections have been calculated by the impact-parameter and close-coupling methods. To solve the one-electron, time-dependent, spinless electronic wave function in a two-atom system, the wave function was expanded, time-dependent, spinless electronic wave function in a two-atom system, the wave function was expanded in terms of a set traveling atomic wave functions centered about either nucleus. As the eigenfunction of each atom, Hartree-Fock-Slater wave functions were used. The calculated results are in fairly good agreement with the compiled experimental results for the thoroughly studied elements and thus provide a useful interpolation/extrapolation of the experimental data.

Sakabe, Shuji; Izawa, Yasukazu (Osaka Univ. (Japan))

1991-11-01

387

Cusp-shape studies with He+ ions at 1.41- and 2.41-a.u. impact velocities  

NASA Astrophysics Data System (ADS)

The electron loss to the continuum (ELC) process was investigated in He+-(He,Ar) collisions at 1.41- and 2.41-a.u. impact velocities. The cusp-shaped energy distributions of electrons ejected into the forward direction were measured in coincidence with the scattered He2+ projectile ions. The shape of these cusps was studied by fitting the multipole series expansion [Meckbach, Nemirovsky, and Garibotti, Phys. Rev. A 24, 1793 (1981)] of the measured spectra using Bnj, the nth-order expansion coefficients of the jth-order Legendre polynomials, as fitting parameters. The observed skewness of the spectra (nonzero ?1=B01/B00 values) indicates the importance of the higher-order theories in the description of the distribution of ELC electrons. A dip at the top of the peak (``cusp inversion''), reflected by a positive ?2=B02/B00 value, was observed in the 1.41-a.u. He+-He collision.

Gulys, L.; Sarkadi, L.; Plinks, J.; Kvr, .; Vajnai, T.; Szab, Gy.; Vgh, J.; Bernyi, D.; Elston, S. B.

1992-04-01

388

A NOVEL X-RAY IMAGING CRYSTAL SPECTROMETER FOR DOPPLER MEASUREMENTS OF ION TEMPERATURE AND PLASMA ROTATION VELOCITY PROFILES  

SciTech Connect

A new type of X-ray imaging crystal spectrometer has been implemented on Alcator CMod for Doppler measurements of ion temperature and plasma rotation velocity profiles. The instrument consists of two spherically bent (102)-quartz crystals with radii of curvature of 1444 and 1385 mm and four 'PILATUS II' detector modules. It records spectra of He-like argon from the entire, 72 cm high, elongated plasma cross-section and spectra of H-like argon from a 20 cm high, central region of the plasma, with a spatial resolution of 1.3 cm and a time resolution of less than 20 ms. The new spectrometer concept is also of interest for the diagnosis of burning plasmas on future machines. This paper presents recent experimental results from Aclator C-Mod and discusses challenges in X-ray spectroscopy for the diagnosis of fusion plasmas on future machines.

Bitter, M; Hill, K W; Scott, S; Ince-Cushman, A; Reinke, M; Rice, J E; Beiersdorfer, P; Gu, M F; Lee, S G; Broennimann, C; Eikenberry, E F

2008-06-06

389

Profile Measurement of Ion Temperature and Toroidal Rotation Velocity with Charge Exchange Recombination Spectroscopy Diagnostics in the HL-2A Tokamak  

NASA Astrophysics Data System (ADS)

This paper deals with the profile measurement of impurity ion temperature and toroidal rotation velocity that can be achieved by using the charge exchange recombination spectrum (CXRS) diagnostics tool built on the HL-2A tokamak. By using CXRS, an accurate impurity ion temperature and toroidal plasma rotation velocity profile can be achieved under the condition of neutral beam injection (NBI) heating. Considering the edge effect of the line of CVI 529.06 nm (n = 8~7), which contains three lines (active exciting spectral line (ACX), passivity exciting spectral line (PCX) and electron exciting spectral line (ICE)), and using three Gaussian fitted curves, we obtain the following experimental results: the core ion temperature of HL-2A device is nearly thousands of eV, and the plasma rotation velocity reaches about 104 m s-1. At the end of paper, some explanations are presented for the relationship between the curves and the inner physical mechanism.

Wu, Jing; Yao, Lieming; Zhu, Jianhua; Han, Xiaoyu; Li, Wenzhu

2012-11-01

390

An investigation of the velocity spectrum of excited particles by fast ions from a solid as a means to study its electronic level structure  

Microsoft Academic Search

In this work is shown that by measurement of the velocity of excited particles ejected by a beam of fast ions from the surface of a solid, some characteristics of its electronic level structure may be determined. The velocity spectrum of Ti, Na and Li atoms ejected respectively from targets of titanium and NaCl- and LiF-crystals by a beam of

V. V. Gritsyna; T. S. Kijan; A. G. Koval; Ya. M. Fogel

1972-01-01

391

Drift compression experiments on MBE-4 and related emittance growth phenomena  

SciTech Connect

We have recently conducted a series of experiments on the MBE-4 heavy ion accelerator in which a velocity tilt was placed on the beam in the first accelerating section beyond the injector, followed by drift compression over the remaining 11 meters. Depending upon the magnitude of the velocity tilt and the accompanying mismatch in the focusing lattice, emittance growth was observed, manifested by butterfly'' shapes in x {minus} x{prime} phase space. We discuss various analytical limits on ion beam compression and relate them to these experiments and also to a driver for a heavy ion fusion reactor. We also present numerical simulations which investigate various aspects of compression and consequent emittance growth. 2 refs., 3 figs., 1 tab.

Eylon, S.; Faltens, A.; Fawley, W.; Garvey, T.; Hahn, K.; Henestroza, E.; Smith, L.

1991-04-01

392

Drift waves in stellarator geometry  

SciTech Connect

Drift waves are investigated in a real three-dimensional stellarator geometry. A linear system, based on the cold ion fluid model and a ballooning mode formalism, is solved numerically in the geometry of the stellarator H1-NF. The spectra of stable and unstable modes, as well as localization, are discussed. The dependence of the spectrum of the unstable modes on the wavevector, plasma density variation, and the location in the plasma is presented.

Persson, M.; Nadeem, M.; Lewandowski, J.L.V.; Gardner, H.J.

2000-02-07

393

Swarm Analysis by Using Transport Equations. III. Steady-State Swarm Behavior of Positive Ions in a Uniform Medium  

Microsoft Academic Search

Steady-state behavior of a uniform swarm of positive ions has been analyzed by using transport equations. First, general transport equations for positive ions are presented and then simplified by assuming spatial uniformity. Next, the equations are applied to the case in which the electrons are absent and swarm parameters such as the drift velocity and the random energy are numerically

Toshihiko Dote; Masatoshi Shimada

1981-01-01

394

Comparison of measured and simulated fast ion velocity distributions in the TEXTOR tokamak  

NASA Astrophysics Data System (ADS)

Here we demonstrate a comprehensive comparison of collective Thomson scattering (CTS) measurements with steady-state Monte Carlo simulations performed with the ASCOT and VENUS codes. The measurements were taken at a location on the magnetic axis as well as at an off-axis location, using two projection directions at each location. The simulations agree with the measurements on-axis, but for the off-axis geometries discrepancies are observed for both projection directions. For the near perpendicular projection direction with respect to the magnetic field, the discrepancies between measurement and simulations can be explained by uncertainty in plasma parameters. However, the discrepancies between measurement and simulations for the more parallel projection direction cannot be explained solely by uncertainties in plasma parameters. Here anomalous fast ion transport is a possible explanation for the discrepancy.

Moseev, D.; Meo, F.; Korsholm, S. B.; Koskela, T.; Albergante, M.; Asunta, O.; Bindslev, H.; Brger, A.; Furtula, V.; Kantor, M. Yu; Leipold, F.; Michelsen, P. K.; Nielsen, S. K.; Salewski, M.; Schmitz, O.; Stejner, M.; Westerhof, E.; TEXTOR Team

2011-10-01

395

Experimental test of instability enhanced collisional friction for determining ion loss in two ion species plasmas  

SciTech Connect

Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.

Hershkowitz, N.; Yip, C.-S. [Department of Engineering Physics, University of Wisconsin, Madison, Madison, Wisconsin 53706 (United States); Severn, G. D. [Department of Physics, University of San Diego, San Diego, California 92110 (United States)

2011-05-15

396

A refocusing modified velocity map imaging electron/ion spectrometer adapted to synchrotron radiation studies  

NASA Astrophysics Data System (ADS)

We present a modified velocity map imaging (VMI) spectrometer to be used in angle-resolved molecular photoionization studies in the gas phase with synchrotron radiation (SR) in the VUV/soft x-ray range. The main modifications as compared to the original design of Eppink and Parker [A. T. J. B. Eppink and D. H. Parker, Rev. Sci. Instrum. 68, 3477 (1997)] are an open repeller which allows the VMI spectrometer to be coupled to an independent dispersive electrostatic analyzer for combined operation in coincidence mode experiments, and the introduction of a coupled double Einzel lens in the flight tube in order to collect the full 4? solid angle for higher kinetic energy particles. The length and position of the lenses have been optimized by a genetic algorithm to obtain the maximum kinetic energy possible without compromising the energy resolution. Ray-tracing simulations and SR experiments show that the lenses can increase the kinetic energy bandwidth by a factor of up to 2.5. Furthermore, a remarkable improvement in the radial focusing of the particles' momenta can be achieved when the lens array is operated in optimum fashion. The accuracy in the determination of the angular parameters, already satisfactory in the original VMI design, is not compromised by the lens operation. Experimentally, we succeeded in collecting 4? electrons with 14 eV kinetic energy and 6% relative energy resolution with a detector of 36 mm effective diameter, despite the larger ionization volume given by the SR as compared to laser multiphoton experiments. We predict that, by changing to a detector diameter of 70 mm and reducing the focal length by a third, particles with energies up to 200 eV could be collected by applying 10 kV to the repeller electrode.

Garcia, Gustavo A.; Nahon, Laurent; Harding, Chris J.; Mikajlo, Elisabeth A.; Powis, Ivan

2005-05-01

397

Plasma drifts associated with a system of sun-aligned arcs in the polar cap  

SciTech Connect

A series of four sun-aligned arcs passed over Sondre Stromfjord, Greenland, on the night of the 17th and 18th of February, 1985. Observations of these arcs were made using the Sondrestrom incoherent scatter radar and an intensified all-sky imaging TV system that was operated at the radar site. The first of the four arcs crossed the Sondre Stromfjord meridian just before local midnight moving westward, and the other three arcs followed at approximately half-hour intervals. When we account for the earth's rotation, the arc drift in an inertial frame was eastward, or dusk to dawn. The half-hour interval between meridian crossings of the arcs implies that the mean spacing between the arcs was 180 km. A Defense Meteorological Satellite Program (DMSP) F6 satellite pass at 0110 UT revealed the presence of highly structured electron and ion precipitation throughout the polar cap. The DMSP visible imager detected a single, sun-aligned arc associated with the largest peak in precipitating electron flux. This arc was also observed at Thule, Greenland, with an intensified film camera. These observations suggest that at least one of the arcs that were observed at Sondre Stromfjord extended across a large part of the polar cap. The radar at Sondre Stromfjord measured electron density and ion drift velocities associated with the four arcs. The radar drift measurements were superimposed on the all-sky video images to determine the location of the measurements relative to the arcs. Plasma drifts outside the arcs were found to be both sunward and antisunward, while within the arcs the drifts were predominantly antisunward. The variability of the drifts in the direction parallel to the arcs indicates that the electric fields were highly structured even though the configuration and motion of the arcs were well behaved.

Mende, S.B.; Doolittle, J.H.; Robinson, R.M.; Vondrak, R.R.; Rich, F.J.

1988-01-01

398

Development of a very-low-velocity superconducting linac  

SciTech Connect

Four types of superconducting accelerator structures are being developed for use in a low velocity positive-ion injector linac for the ATLAS heavy-ion accelerator. Prototypes of the first two of these have been tested. The structures are all variants of a quarter-wave line terminated with a four-gap interdigital drift-tube array. The two structure types so far tested operate at 48.5 mHz and have an active length of 10 cm (for the particle velocity - .008c type) and 16.5 cm (for the velocity - .014c type). Effective accelerating fields of 10 MV/m have been achieved with the 10 cm structure, corresponding to an effective accelerating potential of 1 MV. The 16.5 cm structure has been operated at field levels of 6 MV/m, also giving an effective potential of 1 MV. Prototypes of the remaining two resonant geometries are under construction.

Shepard, K.W.

1987-01-01

399

Magnetic island evolution in hot ion plasmas  

SciTech Connect

Effects of finite ion temperature on magnetic island evolution are studied by means of numerical simulations of a reduced set of two-fluid equations which include ion as well as electron diamagnetism in slab geometry. The polarization current is found to be almost an order of magnitude larger in hot than in cold ion plasmas, due to the strong shear of ion velocity around the separatrix of the magnetic islands. As a function of the island width, the propagation speed decreases from the electron drift velocity (for islands thinner than the Larmor radius) to values close to the guiding-center velocity (for islands of order 10 times the Larmor radius). In the latter regime, the polarization current is destabilizing (i.e., it drives magnetic island growth). This is in contrast to cold ion plasmas, where the polarization current is generally found to have a healing effect on freely propagating magnetic island.

Ishizawa, A.; Nakajima, N. [National Institute for Fusion Science, Toki 509-5292 (Japan); Waelbroeck, F. L.; Fitzpatrick, R.; Horton, W. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2012-07-15

400

Parametric excitation of drift waves in a sheared slab geometry  

SciTech Connect

The threshold for parametric excitation of drift waves in a sheared slab geometry is calculated for a drift-wave pump which has a standing wave structure along the magnetic field, and the coupling is achieved by the Hasegawa--Mima vector product-type nonlinearity. The usual shear damping is counteracted by the parametric interaction which causes a reversal of the direction of the drift wave group velocity, and the nonlinear eigenvalue problem is solved analytically using Taylor's strong coupling approximation.

Davydova, T.A. (Institute for Nuclear Research, Ukrainian Academy of Sciences, Prospekt Nauki 47, 252 028 Kiev (Ukraine)); Jovanovic, D. (Institute of Physics, P.O. Box 57, Yu-11001 Belgrade (Yugoslavia)); Vranjes, J. (Institute of Physics, P.O. Box 57, Yu-11001 Belgrade (Yugoslavia)); Weiland, J. (Institute for Electromagnetic Field Theory, Chalmers University of Technology and EURATOM-NFR Association, S-412 96 Gothenburg (Sweden))

1994-04-01

401

The Westward Drift of the Earth's Magnetic Field  

Microsoft Academic Search

The westward drift of the non-dipole part of the earth's magnetic field and of its secular variation is investigated for the period 1907-45 and the uncertainty of the results discussed. It is found that a real drift exists having an angular velocity which is independent of latitude. For the non-dipole field the rate of drift is 0.18 0.015 o \\/year,

E. C. Bullard; Cynthia Freedman; H. Gellman; Jo Nixon

1950-01-01

402

Mechanisms of velocity constancy.  

PubMed

Human observers can compare the physical velocities of objects (cm/sec) moving at different distances quite well, although the objects' retinal velocities (deg/sec) may vary considerably. This perceptual ability is called velocity constancy. We conducted a number of experiments to investigate what mechanisms observers use to attain this constancy and if pure motion signals can also be matched according to their physical speeds. Subjects were asked to match the velocities of two moving stimuli presented at different viewing distances. The stimuli consisted of sparse random-dot kinematograms or drifting Julesz patterns. The subjects matched the true physical velocities of the stimuli provided that the two visual scenes contained identical size references. Knowledge of the actual viewing distances proved to be irrelevant for evaluating the physical velocities of the stimuli. We conclude that velocity constancy is based upon a relative scaling algorithm. PMID:8249327

Zohary, E; Sittig, A C

1993-12-01

403

Habitat effects on invertebrate drift in a small trout stream: implications for prey availability to drift-feeding fish  

Microsoft Academic Search

In this study, we focused on the drivers of micro- and mesohabitat variation of drift in a small trout stream with the goal\\u000a of understanding the factors that influence the abundance of prey for drift-feeding fish. We hypothesized that there would\\u000a be a positive relationship between velocity and drift abundance (biomass concentration, mg\\/m3) across multiple spatial scales, and compared seasonal

Elaine S. Leung; Jordan S. Rosenfeld; Joanna R. Bernhardt

2009-01-01

404

Prompt striations in ionospheric barium clouds due to a velocity space instability  

NASA Astrophysics Data System (ADS)

The linear theory of electrostatic instabilities of the drift loss-cone type has been developed for a velocity distribution appropriate to the shaped-charge barium injection experiment Buaro. The dispersion relation for the instability in a Vlasov plasma has been solved numerically. The results show a low-frequency instability that we interpret as the source of prompt striations observed in Buaro and cyclotron instabilities that appear to correspond to observed ion cyclotron fluctuations. These instabilities have much faster growth rates than drift instabilities of fluid theories and therefore provide a better description of the observations.

Simons, D. J.; Pongratz, M. B.; Gary, S. P.

1980-02-01

405

General ignition requirements in TMR's with drift pumping  

SciTech Connect

Drift pumping of collisionally trapped DT ions and thermal alpha ash in the transitions and thermal barriers of TMR plugs can be shown by simple models to dominate the central cell energy losses, requiring in fact more radial ion loss by drift pumping than axial ion loss through the potential plugs, and setting a minimum central cell length for ignition. Induced electron transport due to drift pumping is shown to be small, so grids are not needed on the direct converter to separate ion and electron currents.

Logan, B.G.

1983-01-01

406

Very wide bandwidth Faraday cup suitable for measuring gigahertz structure on ion beams with velocities down to (beta) (lt) 0.01.  

National Technical Information Service (NTIS)

A stripline Faraday Cup of exceptional bandwidth (DC to 6.1 gigahertz) has been developed. An electrostatic shield in the ground-plane geometry prevents electric-field coupling of incoming ions so that the time distribution of low-velocity ((beta) (approx...

J. M. Bogaty R. C. Pardo B. E. Clifft

1990-01-01

407

Modelling Sediment Transport and Drifts  

NASA Astrophysics Data System (ADS)

Understanding the processes and phases of sediment transport and drift formation is essential for a reconstruction of their evolution. Our approach to evaluate the contribution of different processes to drift growth, especially the alongslope vs. downslope transport component, is numerical modelling. For this work, we have selected the area of ODP Leg 178 on the western side of the Antarctic Penninsula, where a dense grid (~4000 km) of seismic profiles and numerous cores document the presence of 8 sediment mounds along the continental slope. These mounds are interpreted to be drifts, though a contrasting model proposes a turbidity-current-dominated origin. We concentrate on Drift 7, which was covered by ~1500 km of seismic reflection lines, four CTD sites and two ODP Leg 178 sites (1095 and 1096). Numerical modelling of the processes involved could favour one of the proposed models and answer the question regarding mound origin. The forward modelling process needs a 3-D framework of seismostratigraphic and sedimentological input parameters to define the input data and boundary conditions of the numerical model. These include (a) boundaries of seismostratigraphic units or event horizons (e.g. events of erosion or non-deposition), (b) seismostratigraphic unit thicknesses, (c) granulometric changes i.e. grain-size distributions within seismostratigraphic units (d) physical properties of sediments at event horizons and, (e) lithological changes. In general, we aim at the inversion of an observed sediment structure into the depositional process. I.e. from the observation we want to deduce information on the generating current. This information comprises of current (steady and tidal) velocity and direction, the epoch when the current was active and its duration. This will lead to a better understanding of the processes responsible for sediment transport and erosions by oceanic currents. The problems we want to solve can be summarised as follows: 1. Is an initial topography (large-scale or mesoscale topography or inhomogeneity in sediment distribution) necessary for the formation of a structure like a sediment drift? 2. What current velocities are needed to a) transport and b) deposit sediment? 3. Does the current velocity need to be maintained for the whole period or is the shaping of the sediment drift favoured by episodic changes in current velocity? 4. How long would an episode of current activity have to be in order to generate the morphology observed in a sediment drift? Preliminary work on the high-resolution seismic reflection data and granulometric work within the seismostratigraphic units has shown clear variability in the grain size that could be correlated, if only tentatively at this time, to know changes in the development of the Antarctic ice sheet in response to climatic change. Further analysis and correlation between the geological and geophysical data form work in progress.

Rendle, R. H.; Uenzelmann-Neben, G.; Beckmann, A.; Grobe, H.

2002-12-01

408

Computer simulations of H+ and H+3 transport parameters in hydrogen drift tubes  

NASA Astrophysics Data System (ADS)

The coupled transport of H+ and H+3 ions in molecular hydrogen is theoretically studied by using drift-tube-like computer simulations. The drift velocity and the longitudinal and the transverse diffusion coefficients of these ions are calculated for the reduced electric field E/n (where n is the gas density) ranging from 10 to 600 Td (1 Td=10-17 V cm2). A large influence of the rotational and vibrational H+-H2 excitations is noted even at low E/n for H+ ions. The presence of ion conversion reactions in collisions with background gas during the transport is shown to influence the transport parameters from about 150 Td. A comparison with experimentally determined transport parameters is performed with the aim of testing available scattering models: the collisional cross-section values are adjusted to get a good agreement with experimental ion mobilities. A relatively good agreement is obtained also for the longitudinal and the transverse diffusion coefficients, which indicates the consistency of the refined cross-section set. However, the transverse diffusion coefficient of H+3 ions exhibits larger deviation from experimental results at higher E/n; as a possible explanation the role of proton-transfer and vibrational-excitation channels in H+3-H2 collisions is discussed.

imko, T.; Martiovit, V.; Bretagne, J.; Gousset, G.

1997-11-01

409

Kink-tearing mode conversions with current interchange and small parallel ion velocity effects taken into account  

NASA Astrophysics Data System (ADS)

The conversions of kink type of modes, such as n=1 internal kink mode, RWMs, etc., to tearing modes are widely observed experimentally. In this presentation we explain these conversions using the theory of newly discovered current interchange tearing modes [CITMs, Zheng and Furukawa, Phys. Plasmas 17, 052508 (2010)], with the kinetic enhancement of parallel inertia by the so-called small parallel ion velocity effect [SPIV, Zheng and Tessarotto, Phys. Plasmas 3, 1209 (1996)] taken into account. Interchange-type (i.e., kink) modes exchange not only thermal and magnetic energies, but also current, between flux tubes, so that current sheet can be formed at mode rational surfaces and kink type of modes are converted to tearing type of modes. It is pointed out that, when the so-called SPIV inertia enhancement is taken into account, the current interchange effect becomes the dominant driving force for field line reconnection. The underlying physics will be explained intuitively. Both analytical and numerical results will be presented. Extension of AEGIS code to study the kink-tearing mode conversion processes will also be discussed.

Zheng, Linjin

2010-11-01

410

Collisional effects on nonlinear ion drag force for small grains  

NASA Astrophysics Data System (ADS)

The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

Hutchinson, I. H.; Haakonsen, C. B.

2013-08-01

411

Drift wave driven zonal flows in plasmas  

NASA Astrophysics Data System (ADS)

The generation of large-scale zonal flows by small-scale electrostatic drift waves in a plasma is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves. To describe this process a generalized Hasegawa-Mima equation containing both vector and scalar nonlinearities is used. The drift waves are supposed to have arbitrary wavelengths (as compared with the ion Larmor radius). A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. The generation of zonal flows turns out to be due to Reynolds stresses produced by finite amplitude drift waves. It is found that the wave vector of the fastest growing mode is perpendicular to that of the drift pump wave. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. A comparison with previous results is carried out. The present theory can be used for interpretations of drift wave observations in laboratory plasmas.

Kaladze, T. D.; Wu, D. J.; Pokhotelov, O. A.; Sagdeev, R. Z.; Stenflo, L.; Shukla, P. K.

2005-12-01

412

Drift wave driven zonal flows in plasmas  

SciTech Connect

The generation of large-scale zonal flows by small-scale electrostatic drift waves in a plasma is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves. To describe this process a generalized Hasegawa-Mima equation containing both vector and scalar nonlinearities is used. The drift waves are supposed to have arbitrary wavelengths (as compared with the ion Larmor radius). A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. The generation of zonal flows turns out to be due to Reynolds stresses produced by finite amplitude drift waves. It is found that the wave vector of the fastest growing mode is perpendicular to that of the drift pump wave. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. A comparison with previous results is carried out. The present theory can be used for interpretations of drift wave observations in laboratory plasmas.

Kaladze, T.D.; Wu, D.J.; Pokhotelov, O.A.; Sagdeev, R.Z.; Stenflo, L.; Shukla, P.K. [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008 (China) and Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University Str., 0143 Tbilisi (Georgia); Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210008 (China); Automatic Control and Systems Engineering, University of Sheffield, Sheffield (United Kingdom) and Institute of Physics of the Earth, 10 B. Gruzinskaya Str., 123995 Moscow (Russian Federation); Department of Physics, University of Maryland, College Park, Maryland 20740 (United States); Department of Physics, Umeaa University, SE-90 187 Umeaa (Sweden); Department of Physics, Umeaa University, SE-90 187 Umeaa (Sweden) and Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2005-12-15

413

Electrostatic drift-like waves in a bounded dusty plasma  

NASA Astrophysics Data System (ADS)

A number of different types of obliquely propagating dust-associated electrostatic drift-like waves, namely, the Shukla-Varma mode, the lower-hybrid mode, coupled electron-drift-dust-ion-acoustic waves, coupled ion-drift-dust-electron-acoustic waves, coupled dust-drift-dust-acoustic waves, and coupled dust-drift-dust-cyclotron waves, in a nonuniform bounded dusty magnetoplasma are theoretically investigated. The last two are studied by considering the dynamics of the negatively charged dust grains, whereas the other ones are studied by considering the presence of the static dust grains. The dispersion properties of these drift-like waves, which are found to be significantly modified by the combined effects of plasma density inhomogeneity, finite boundary of the dusty plasma, obliqueness of the propagating mode, and external magnetic field, are examined. The relevance of this investigation to low-temperature laboratory dusty magnetoplasmas is discussed.

Mamun, A. A.; Shukla, P. K.

2000-09-01

414

Kinetic instability of ion acoustic mode in permeating plasmas  

SciTech Connect

In plasmas with electron drift (current) relative to static ions, the ion acoustic wave is subject to the kinetic instability which takes place if the directed electron speed exceeds the ion acoustic speed. The instability threshold becomes different in the case of one quasineutral electron-ion plasma propagating through another static quasineutral (target) plasma. The threshold velocity of the propagating plasma may be well below the ion acoustic speed of the static plasma. Such a currentless instability may frequently be expected in space and astrophysical plasmas.

Vranjes, J.; Poedts, S. [Center for Plasma Astrophysics and Leuven Mathematical Modeling and Computational Science Center (LMCC), K. U. Leuven, Celestijnenlaan 200B, 3001 Leuven (Belgium); Ehsan, Zahida [Salam Chair in Department of Physics, GC University, Lahore 54000, Pakistan and Plasma Physics Group, Blackett Laboratory, Imperial College, London SW7 2AZ (United Kingdom)

2009-07-15

415

Ion acceleration in plasmas emerging from a helicon-heated magnetic-mirror device  

Microsoft Academic Search

Using laser-induced fluorescence, measurements have been made of metastable argon-ion, Ar+*(3d4F7\\/2), velocity distributions on the major axis of an axisymmetric magnetic-mirror device whose plasma is sustained by helicon wave absorption. Within the mirror, these ions have sub-eV temperature and, at most, a subthermal axial drift. In the region outside the mirror coils, conditions are found where these ions have a

S. A. Cohen; N. S. Siefert; S. Stange; R. F. Boivin; E. E. Scime; F. M. Levinton

2003-01-01

416

Electromagnetic drift modes driven by pressure gradients in tokamaks  

Microsoft Academic Search

A hybrid of hydrodynamics and kinetics is used to study the effect of finite plasma pressure on the pressure-gradient driven toroidal drift modes. The linear drift modes of the system are given by a fifth-order polynomial describing the coupling of the electron-drift, the ion-acoustic, and the shear Alfven oscillations. The characteristic frequencies, growth rates, and polarization of the electromagnetic modes

W. Horton; Duk-In Choi; Bong-Guen Hong

1983-01-01

417

Drift Degradation Analysis  

SciTech Connect

A statistical description of the probable block sizes formed by fractures around the emplacement drifts has been developed for each of the lithologic units of the repository host horizon. A range of drift orientations with the drift azimuth varied in 15{sup o} increments has been considered in the static analysis. For the quasi-static seismic analysis, and the time-dependent and thermal effects analysis, two drift orientations have been considered: a drift azimuth of 105{sup o} and the current emplacement drift azimuth of 75{sup o}. The change in drift profile resulting from progressive deterioration of the emplacement drifts has been assessed both with and without backfill. Drift profiles have been determined for four different time increments, including static (i.e., upon excavation), 200 years, 2,000 years, and 10,000 years. The effect of seismic events on rock fall has been analyzed. Block size distributions and drift profiles have been determined for three seismic levels, including a 1,000-year event, a 5,000-year event, and a 10,000-year event. Data developed in this modeling and analysis activity have been entered into the TDMS (DTN: MO0109RDDAAMRR.003). The following conclusions have resulted from this drift degradation analysis: (1) The available fracture data are suitable for supporting a detailed key block analysis of the repository host horizon rock mass. The available data from the north-south Main Drift and the east-west Cross Drift provide a sufficient representative fracture sample of the repository emplacement drift horizon. However, the Tptpln fracture data are only available from a relatively small section of the Cross Drift, resulting in a smaller fracture sample size compared to the other lithologic units. This results in a lower degree of confidence that the key block data based on the Tptpln data set is actually representative of the overall Tptpln key block population. (2) The seismic effect on the rock fall size distribution for all events analyzed is relatively minor. (3) The analysis of thermal and time-dependent effects on rock fall in this study is based on a reduction in the joint cohesion. Joint cohesion has been conservatively reduced from a laboratory test value of 0.86 MPa to a value of 0.01 MPa after 10,000 years. The results from this analysis indicate that time-dependent and thermal effects have a minor impact on rock fall. (4) Both the 75 percentile and the worst-case drift degradation profiles have been provided in this analysis for the current emplacement drift azimuth of approximately 75{sup o}. Most of the emplacement drift openings were not affected by rock fall. For the current emplacement drift alignment, the highest percentage of drift affected by rock fall was 8% in the Tptpmn unit. The Tptpmn unit produced the highest frequency of key blocks per kilometer compared to the other lithologic units (Tables 26 and 41). (5) This key block analysis has shown that the current drift alignment is relatively favorable in terms of reducing the potential maximum size rock block compared to most drift orientations.

Dwayne C. Kicker

2001-09-28

418

Frequency dependent ion kinetics in a 300 mm dual-frequency capacitively coupled plasma reactor  

NASA Astrophysics Data System (ADS)

Argon ion kinetics were measured in a dual frequency, capacitively coupled 300 mm chamber. Laser induced fluorescence measurements of the argon ion metastable lineshape yield information on the ion temperature, density and drift velocity. The spatially-resolved LIF technique is a nonperturbative probe to investigate energy deposition mechanisms, ion energy distribution functions, charge exchange reactions, neutral heating, and plasma potential gradients within the plasma. This talk will discuss ion characteristics for a single rf frequency drive (13, 60 and 160 MHz), combinations of rf drive frequencies, as well as scaling with pressure (10 -- 70 mTorr) , rf power, and radial position. We find that the ion density increased linearly with rf power, as did the electron density, indicating the ion metastable state is formed from direct impact ionization. The ion temperature was on the order of 500 K. Radially resolved ion drift velocity measurements show the radial drift velocity can be lower at 60 MHZ than 13 MHz. Additional details will be discussed. This work was supported by Applied Materials and Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Hebner, G. A.; Barnat, E. V.; Miller, P. A.; Paterson, A. M.; Holland, J. P.

2006-10-01

419

Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces  

NASA Astrophysics Data System (ADS)

We have examined the origins of ion irradiation-induced nanoparticle (NP) motion. Focused-ion-beam irradiation of GaAs surfaces induces random walks of Ga NPs, which are biased in the direction opposite to that of ion beam scanning. Although the instantaneous NP velocities are constant, the NP drift velocities are dependent on the off-normal irradiation angle, likely due to a difference in surface non-stoichiometry induced by the irradiation angle dependence of the sputtering yield. It is hypothesized that the random walks are initiated by ion irradiation-induced thermal fluctuations, with biasing driven by anisotropic mass transport.

Kang, M.; Wu, J. H.; Sofferman, D. L.; Beskin, I.; Chen, H. Y.; Thornton, K.; Goldman, R. S.

2013-08-01

420

Experimental verification of Boltzmann equilibrium for negative ions in weakly collisional electronegative plasmas  

SciTech Connect

Weakly collisional Ar-O{sub 2} electronegative plasmas are investigated in a dc multidipole chamber. An electronegative core and an electropositive halo are observed. The density ratio of negative ions to electrons ({alpha}) in the nondrifting bulk is found to be 0.43. The profile of {alpha} is found using both the phase velocity of ion acoustic waves and the drift velocity of positive ions determined by laser-induced fluorescence. The experiment shows that negative ions are in Boltzmann equilibrium with a temperature of 0.06{+-}0.02 eV. Double layers are not found separating the electronegative core and the electropositive halo.

Ghim, Young-chul [Department of Physics, University of Oxford, Oxford OX1 3NP (United Kingdom); Hershkowitz, Noah [Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2009-04-13