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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

3

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

4

The role of external electric fields in enhancing ion mobility, drift velocity, and drift-diffusion rates in aqueous electrolyte solutions.  

PubMed

Molecular simulations have been carried out using the method of molecular dynamics to investigate the role of external electric fields on the ion mobility, drift velocity, and drift-diffusion rate of ions in aqueous electrolyte solutions. These properties are critical for a range of processes including electrodialysis, electro-deionization, electrophoresis, and electroosmosis. Our results show that external electric fields relax the hydrated ion structure at significantly larger time scales (between 300 and 800 ps), than most other relaxation processes in solutions (generally of the order of 1 ps). Previous studies that did not account for the much longer relaxation times did not observe this behavior for ions even with very high electric fields. External electric fields must also overcome several (at least two or more) activation energy barriers to significantly change the structure of hydrated ions. As a result, the dynamic behavior changes almost in bands as a function of electric field strengths, rather than linearly. Finally, the effect of the field is much less dramatic on water than the ions. Thus electric fields will be of more significance in processes that involve the transport of ions (such as electro-deionization) than the transport of water (electroosmosis). PMID:21428629

Murad, Sohail

2011-03-21

5

Comparison of SuperDARN irregularity drift measurements and F-region ion velocities from the resolute bay ISR  

NASA Astrophysics Data System (ADS)

A number of studies have addressed the principal assumption used by the SuperDARN network of HF radars that the scatter from F region field-aligned irregularities has a Doppler shift given by the cosine component of the EXB plasma drift. However, the slopes of the best-fit line to the measured points have consistently been low, perhaps implying contamination from irregularities with smaller amplitude drifts. This work is motivated by testing the same assumption on a more optimal experimental setting: using the north face of the Resolute Bay incoherent scatter radar (RISR-N), which provides high resolution magnitude and direction measurements of EXB drift in a region where the ionospheric flow is mostly uniform relative to auroral latitudes, thereby reducing echo mixing due to spatio-temporal structuring. We compared the EXB drift measured by RISR-N to the line-of-sight Doppler velocities measured PolarDARN which is composed of Rankin Inlet and Inuvik HF radars, both having a field of view over Resolute Bay. An aggregate scatter plot of all the echoes observed during a 5-day period in early May 2011 contains two distinct groups of echoes. The first group is hypothesized to be from the E region because the echoes appear above a threshold EXB drift and at small flow angles, which are characteristics of primary Farley-Buneman waves. The Doppler velocity of the second group of echoes increase linearly with the EXB drift and is identified here as F region echoes. A special joint fit showed a slope of 0.85 for the F region echoes. During the observation period, the F region electron density has large variations between 1 and 10×1011, in particular due to the polar cap patches. Considering a representative F region electron density of 5×1011 m-3, which has a refraction index of 0.86 at 12.5 MHz (for PolarDARN frequencies) and the fact that the measured velocity is the product of the actual velocity and the refractive index, the expected slope is 0.86, in agreement with our measurement. The fit for E region Doppler velocities shows a saturation speed at 170 m/s, while the data were spread between 100 and 300 m/s. Although the saturation speed is somewhat lower than the ion acoustic speed, it is acceptable considering earlier work attributing similarly low velocities to large aspect angles at the scattering altitudes.

Bahcivan, Hasan; Nicolls, Michael J.; Perry, Gareth

2013-12-01

6

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

7

Comparison of drift velocities of nighttime equatorial plasma depletions with the ambient plasma drifts and the thermospheric neutral winds  

NASA Astrophysics Data System (ADS)

This study is for the first time to analyze satellite observations and compare the plasma depletion drifts with the ambient plasma drifts and the neutral winds in the post-sunset equatorial ionosphere. The local time and latitude variations of the drift velocities of O+ plasma depletions at 350--400 km altitude are derived from the observations of the Far Ultraviolet Imager (FUV) operated on the IMAGE satellite during March 10-June 7, 2002. The variations are compared with the simultaneous measurements of the ion drift velocities and the neutral winds by the ROCSAT-1 and the CHAMP satellites for a similar time period. The analysis shows that the zonal drift velocity of plasma depletions is smaller than both the ambient ion zonal drift velocity and the neutral zonal wind at 18-20 hour magnetic local time and after 21 hour the variations of these velocities are similar. The analysis also shows that the difference of the plasma depletion drift with the background is small at low latitudes. This is the first-ever satellite comparison of the plasma depletion drift with the ambient plasma drift as well as the neutral wind for a global scale, explaining many previous observations at single locations. Furthermore, the zonal drift velocity of the depletion is found in this study to have a large latitudinal gradient specifically at 12°-18° magnetic latitude, which again does not match the ambient ion drift and the neutral wind. This latitudinal difference has been reported by previous studies, but these studies use models and they only compare the depletion drifts with the modeled neutral winds. This study compares the satellite observations, and compares with both the neutral winds and the plasma drifts. The study provides a measure of the difference that has never been provided before by any study using global observations. It has been suggested that vertical polarization electric fields inside the plasma depletions are responsible for the eastward drift of the depletion structures. The difference in the latitudinal gradients seen here in this study could also be explained by the polarization electric fields. For the C-shaped depletion, the polarization electric fields drive a westward drift of plasma particles inside the depletion and this drift velocity changes with increasing latitude. Consequently, the depletion drifts eastward and the depletion drift has a larger latitudinal gradient than the ambient plasma drift.

Liu, G.; England, S.; Frey, H. U.; Immel, T. J.; Lin, C. S.; Pacheco, E.; Haeusler, K.; Doornbos, E.

2013-12-01

8

Comparison of drift velocities of nighttime equatorial plasma depletions with ambient plasma drifts and thermospheric neutral winds  

NASA Astrophysics Data System (ADS)

This is the first study to compare plasma depletion drifts with the ambient plasma drifts and neutral winds in the post sunset equatorial ionosphere using global-scale satellite observations. The local time and latitude variations of the drift velocities of O+ plasma depletions at 350-400 km altitude are derived from the observations of the far ultraviolet imager operated on the IMAGE satellite during 10 March to 7 June 2002. These depletion drift velocities are compared with the simultaneously measured ion drift velocities and neutral winds by the ROCSAT-1 and the CHAMP satellites for a similar time period. The analysis shows that the zonal drift velocity of plasma depletions is smaller than both the ambient ion zonal drift velocity and the neutral zonal wind at 18:00-20:00 magnetic local time, and after 21:00, the variations of these velocities are similar. The difference of the plasma depletion drift with the background is found to be smaller at lower latitudes. Furthermore, the zonal drift velocity of the depletion is found to have a large latitudinal gradient specifically at 12°-18° magnetic latitude, which again does not match the ambient ion drift and the neutral wind. This latitudinal difference has been reported by previous studies, but those studies use models and they only compare the depletion drifts with the modeled neutral winds. This study provides a measure of the difference that has never been studied before by any study using global observations. It has been suggested that polarization electric fields inside the plasma depletion structure drive the plasma to drift westward and thus the depletion structure moves to the east. The latitudinal gradient of the depletion drift velocity seen here in this study could also be explained by the polarization electric fields. For the C-shaped (reversed C) depletion, the polarization electric fields inside the depletion drive a westward drift of plasma and this drift velocity changes with increasing latitude. Consequently, the depletion drift has a latitudinal gradient becoming significant at higher latitudes.

Liu, Guiping; England, Scott L.; Frey, Harald U.; Immel, Thomas J.; Lin, Chin S.; Pacheco, Edgardo E.; Häusler, Kathrin; Doornbos, Eelco

2013-11-01

9

Drift velocity and pressure monitoring of the CMS muon drift chambers  

E-print Network

The drift velocity in drift tubes of the CMS muon chambers is a key parameter for the muon track reconstruction and trigger. It needs to be monitored precisely in order to detect any deviation from its nominal value. A change in absolute pressure, a variation of the gas admixture or a contamination of the chamber gas by air affect the drift velocity. Furthermore, the temperature and magnetic field influence its value. First data, taken with a dedicated Velocity Drift Chamber (VDC) built by RWTH Aachen IIIA are presented. Another important parameter to be monitored is the pressure inside the muon drift tube chambers. The differential pressure must not exceed a certain value and the absolute pressure has to be kept slightly above ambient pressure to prevent air from entering into the muon drift tube chambers in case of a leak. Latest drift velocity monitoring results are discussed.

Sonnenschein, Lars

2011-01-01

10

Drift velocity and pressure monitoring of the CMS muon drift chambers  

E-print Network

The drift velocity in drift tubes of the CMS muon chambers is a key parameter for the muon track reconstruction and trigger. It needs to be monitored precisely in order to detect any deviation from its nominal value. A change in absolute pressure, a variation of the gas admixture or a contamination of the chamber gas by air affect the drift velocity. Furthermore, the temperature and magnetic field influence its value. First data, taken with a dedicated Velocity Drift Chamber (VDC) built by RWTH Aachen IIIA are presented. Another important parameter to be monitored is the pressure inside the muon drift tube chambers. The differential pressure must not exceed a certain value and the absolute pressure has to be kept slightly above ambient pressure to prevent air from entering into the muon drift tube chambers in case of a leak. Latest drift velocity monitoring results are discussed.

Lars Sonnenschein

2011-07-02

11

Ion stochastic trapping and drift turbulence evolution.  

PubMed

Test modes on turbulent magnetized plasmas are studied taking into account the stochastic ion trapping or eddying that characterizes the E×B drift in the background turbulence. It is shown that ion trapping provides an important physical mechanism for the complex nonlinear processes in drift turbulence evolution: generation of large-scale correlations and of zonal flow modes. PMID:23767641

Vlad, Madalina

2013-05-01

12

Electrostatic drift shocks and drift wave instability in inhomogeneous rotating electron-positron-ion plasmas  

SciTech Connect

The electrostatic drift wave shocks are studied in inhomogeneous rotating e-p-i plasma of the pulsar atmosphere. In this regard, the dissipation due to ion-neutral collisions is considered, which facilitate the formation of shock structures. It is noticed that these structures can move with the velocity of the drift wave which is not possible without considering the rotational effects. Several limiting cases are also discussed. In addition, the drift wave instability is obtained when electrons and positrons could not cancel out the space charge effects along the magnetic field lines in the presence of electron-ion and positron-ion collisions. Further, it is found that this instability is sensitive to rotational frequency of the object. The importance of the results with relevance to astrophysical plasmas is also pointed out.

Haque, Q. [Theoretical Plasma Physics Division, PINSTECH P. O. Nilore, Islamabad (Pakistan) and National Centre for Physics, Islamabad (Pakistan)

2012-09-15

13

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

14

Drift compression of an intense neutralized ion beam  

SciTech Connect

Longitudinal compression of a tailored-velocity, intense neutralized ion beam 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.

2004-10-25

15

Separation of motile bacteria using drift velocity in a microchannel.  

PubMed

Separation of certain bacteria from liquids is important in the food, water quality management, bioengineering, and pharmaceutical industries. In this study, we developed a microfluidic device for the hydrodynamic separation of motile bacteria (Escherichia coli) using drift velocity. We first investigated drift tendencies of bacteria and found that cells tended to move in a spanwise direction with similar velocities regardless of the flow rate. When the drift distance was small compared to the wetted perimeter of the cross section, the cells were not separated efficiently. We then investigated the drift phenomenon in more detail using a numerical simulation. Interestingly, the drift phenomenon was observed even without a wall boundary, indicating that drift was caused mainly by the interaction of moving cells with the background shear flow. Finally, we developed a microfluidic device to separate motile bacteria from tracer particles or less motile cells. By decreasing the channel height, the device could successfully separate motile bacteria from other particles or cells with a separation efficiency of about 40%. Connecting microchannels in a series was also found to be effective, which achieved the separation efficiency of about 60%. The knowledge obtained in this study will facilitate the development of other microfluidics devices for use with bacteria. PMID:24448484

Ishikawa, Takuji; Shioiri, Tatsuya; Numayama-Tsuruta, Keiko; Ueno, Hironori; Imai, Yohsuke; Yamaguchi, Takami

2014-03-01

16

Height dependence of spread F bubble drift velocities  

NASA Technical Reports Server (NTRS)

Vertical bubble velocities in equatorial spread F have been investigated analytically by Ott (1978), Osakow and Chaturvedi (1978), all of whom found a proportionality of the vertical velocity to bubble depletion density. The paper presents radar data from two equatorial sites which support theoretical predictions that vertical drift velocities of spread F bubbles increase with height on the bottomside of the F layer. This increase is shown to result from the proportionality of bubble drift velocity to density depletion amplitude, which itself increases with height. The measured rate of increase is found to be dU/dh equals about 2 m/s km. It is concluded that this is consistent with numerical simulation results within a factor of 2.

Hudson, M. K.; Balsley, B. B.

1979-01-01

17

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

18

Longitudinal structure of the vertical E × B drift and ion density seen from ROCSAT-1  

Microsoft Academic Search

We investigate the longitudinal distribution of the vertical E × B drift velocity and ion density in the low-latitude ionosphere using the first Republic of China Satellite (ROCSAT-1) data acquired during 1999–2004. The ROCSAT-1 observations during daytime demonstrate the presence of the longitudinally periodic patterns of the vertical E × B drift and plasma density on the topside F region

Hyosub Kil; S.-J. Oh; M. C. Kelley; L. J. Paxton; S. L. England; E. Talaat; K.-W. Min; S.-Y. Su

2007-01-01

19

Longitudinal structure of the vertical E × B drift and ion density seen from ROCSAT-1  

Microsoft Academic Search

We investigate the longitudinal distribution of the vertical E × B drift velocity and ion density in the low-latitude ionosphere using the first Republic of China Satellite (ROCSAT-1) data acquired during 1999-2004. The ROCSAT-1 observations during daytime demonstrate the presence of the longitudinally periodic patterns of the vertical E × B drift and plasma density on the topside F region

Hyosub Kil; S.-J. Oh; M. C. Kelley; L. J. Paxton; S. L. England; E. Talaat; K.-W. Min; S.-Y. Su

2007-01-01

20

Second-order ion drift-kinetic equation  

NASA Astrophysics Data System (ADS)

A novel form of ion drift-kinetic equation is presented, well suited to close the fluid description of slow macroscopic dynamics in low-collisionality, magnetically confined plasmas. It features second-order accuracy in the gyroradius expansion, with diamagnetic-scale ordering of frequencies and flow velocities. This second-order drift-kinetic equation is derived in the moving reference frame of the ion macroscopic flow, which facilitates the precise consistency with the complementary fluid system, as well as the rigorous treatment of the electric field. Examples of intended applications are the precursor of the ``sawtooth'' internal disruption and the ``neoclassical tearing mode'' in fusion-relevant tokamak temperature regimes. With these applications to slow excursions from well confined equilibria in mind, the distribution function is assumed to be close to a Maxwellian. The Maxwellian part carries the density, mean flow and temperature in Chapman-Enskog-like fashion. The resulting drift-kinetic equation for the non-Maxwellian perturbation is shown to be automatically consistent with the required condition that the density, random parallel velocity and random kinetic energy moments of such non-Maxwellian part be equal to zero.

Ramos, J. J.

2010-11-01

21

Test particle study of ion transport in drift type turbulence  

SciTech Connect

Ion transport regimes in drift type turbulence are determined in the frame of a realistic model for the turbulence spectrum based on numerical simulations. The model includes the drift of the potential with the effective diamagnetic velocity, turbulence anisotropy, and dominant waves. The effects of the zonal flow modes are also analyzed. A semi-analytical method that is able to describe trajectory stochastic trapping or eddying is used for obtaining the transport coefficients as function of the parameters of the turbulence. Analytical approximations of the transport coefficients are derived from the results. They show the transition from Bohm to gyro-Bohm scaling as plasma size increases in very good agreement with the numerical simulations.

Vlad, M.; Spineanu, F. [National Institute of Laser, Plasma and Radiation Physics, Association EURATOM-MEdC, Atomistilor 409, 077125 Magurele, Bucharest (Romania)] [National Institute of Laser, Plasma and Radiation Physics, Association EURATOM-MEdC, Atomistilor 409, 077125 Magurele, Bucharest (Romania)

2013-12-15

22

Filament velocity scaling laws for warm ions  

SciTech Connect

The dynamics of filaments or blobs in the scrape-off layer of magnetic fusion devices are studied by magnitude estimates of a comprehensive drift-interchange-Alfvén fluid model. The standard blob models are reproduced in the cold ion case. Even though usually neglected, in the scrape-off layer, the ion temperature can exceed the electron temperature by an order of magnitude. The ion pressure affects the dynamics of filaments amongst others by adding up to the interchange drive and the polarisation current. It is shown how both effects modify the scaling laws for filament velocity in dependence of its size. Simplifications for experimentally relevant limit regimes are given. These are the sheath dissipation, collisional, and electromagnetic regime.

Manz, P. [Physik-Department E28, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany) [Physik-Department E28, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany); Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching (Germany); Carralero, D.; Birkenmeier, G.; Müller, H. W.; Scott, B. D. [Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching (Germany)] [Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching (Germany); Müller, S. H. [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego 92093 (United States)] [Center for Momentum Transport and Flow Organization, University of California at San Diego, San Diego 92093 (United States); Fuchert, G. [Insitut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart, 70569 Stuttgart (Germany)] [Insitut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Universität Stuttgart, 70569 Stuttgart (Germany); Stroth, U. [Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching (Germany) [Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Boltzmannstr. 2, 85748 Garching (Germany); Physik-Department E28, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany)

2013-10-15

23

Analysis of non-linear ion drift in spectrometers of ion mobility increment with cylindrical drift chamber.  

PubMed

A model for the drift of ions under a non-uniform, high-frequency electric field in the drift chamber of a spectrometer of ion mobility increment is developed. For the general dependence of the ion mobility on the electric field strength and the general time-dependence of the separating voltage, we suggest a procedure for calculating of the ion peak form. The shape of the peak for the ion focusing and defocusing conditions has been obtained. PMID:16819106

Elistratov, A A; Shibkov, S V; Nikolaev, E N

2006-01-01

24

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

25

Explaining the subpulse drift velocity of pulsar magnetosphere within the space-charge limited flow model  

NASA Astrophysics Data System (ADS)

We try to explain the subpulse drift phenomena adopting the space-charge limited flow model and comparing the plasma drift velocity in the inner region of pulsar magnetospheres with the observed velocity of drifting subpulses. We apply the approach described in a recent paper of van Leeuwen & Timokhin, where it was shown that the standard estimation of the subpulse drift velocity through the total value of the scalar potential drop in the inner gap gives inaccurate results, while the exact expression relating the drift velocity to the gradient of the scalar potential should be used instead. After considering a selected sample of sources taken from the catalogue of Weltevrede et al. with coherently drifting subpulses and reasonably known observing geometry, we show that their subpulse drift velocities would correspond to the drift of the plasma located very close or above the pair formation front. Moreover, a detailed analysis of PSR B0826-34 and PSR B0818-41 reveals that the variation of the subpulse separation with the pulse longitude can be successfully explained by the dependence of the plasma drift velocity on the angular coordinates.

Morozova, Viktoriya S.; Ahmedov, Bobomurat J.; Zanotti, Olindo

2014-10-01

26

In situ measurements of plasma drift velocity and enhanced NO/+/ in the auroral electrojet by the Bennett spectrometer on AE-C. [Atmosphere Explorer-C satellite  

NASA Technical Reports Server (NTRS)

Simultaneous measurements of ion composition and plasma drift velocity by the Bennett mass spectrometer on the Atmosphere Explorer-C satellite reveal a direct correlation between enhancements in NO(+) concentration and ion drift velocity in the southern auroral oval. Low altitude (137 to 250 km) data obtained between 1700 and 2400 hr magnetic local time on October 22, 1974, reveal a region of westward plasma flow at velocities up to 1.3 km/s between 62 and 68 deg invariant latitude, with corresponding NO(+) enhancements of up to a factor of 20. A narrow region of reverse flow at about 0.9 km/s was also measured. These drift observations are consistent with convective flow patterns derived from electric field measurements, and their correlation with NO(+) appears to support the suggestion that NO(+) enhancements would be expected in regions of drift owing to the dependence on ion energy of the reaction O(+) + N2 yields NO(+) + N.

Brinton, H. C.

1975-01-01

27

In situ measurements of plasma drift velocity and enhanced NO(+) in the auroral electroject by the Bennett spectrometer on AE-C  

NASA Technical Reports Server (NTRS)

Simultaneous measurements of ion composition and plasma drift velocity by the Bennett mass spectrometer on the Atmosphere Explorer-C satellite reveal a direct correlation between enhancements in NO(+) concentration and ion drift velocity in the southern auroral oval. Low altitude (137 to 250 km) nighttime data reveal a region of westward plasma flow at velocities up to 1.3 km/s between 62 deg and 68 deg invariant latitude, with corresponding NO(+) enhancements of up to a factor of 25. A narrow region of reverse flow at approximately 0.9 km/s was also measured. These drift observations are consistent with convective flow patterns derived from electric field measurements, and their correlation with NO(+) appears to support the suggestion that NO(+) enhancements would be expected in regions of drift owing to the dependence on ion energy of the reaction O(+) + N2 yields NO(+) + N.

Brinton, H. C.

1974-01-01

28

Drift theory of a dense gas interacting with walls in the presence of velocity selective excitation  

NASA Astrophysics Data System (ADS)

The drift of a dense gas in a cuvette, which is larger than the mean free path, is considered. Drift arises from the difference in the velocity of excited and unexcited particles in the gas. The drift velocity of the gas is calculated, together with the decrease in the concentration of the resonance component. It is shown that the mean free path of the gas becomes much smaller than the vessel when the dense transition is made from a rarefied gas to a dense gas. The feasibility of an experiment to observe the drift phenomenon is assessed.

Vaksman, M. A.; Gainer, A. V.

1985-07-01

29

The longitudinal variability of equatorial electrojet and vertical drift velocity in the African and American sectors  

NASA Astrophysics Data System (ADS)

While the formation of equatorial electrojet (EEJ) and its temporal variation is believed to be fairly well understood, the longitudinal variability at all local times is still unknown. This paper presents a case and statistical study of the longitudinal variability of dayside EEJ for all local times using ground-based observations. We found EEJ is stronger in the west American sector and decreases from west to east longitudinal sectors. We also confirm the presence of significant longitudinal difference in the dusk sector pre-reversal drift, using the ion velocity meter (IVM) instrument onboard the C/NOFS satellite, with stronger pre-reversal drift in the west American sector compared to the African sector. Previous satellite observations have shown that the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This study's results raises the question if the vertical drift, which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector - why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?

Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Biouele, C. M.; Damtie, B.; Mebrahtu, A.; Rabiu, B.; Valladares, C. F.; Stoneback, R.

2014-03-01

30

Loop voltage, inductance, and impurity ion velocity in toroidal discharges  

NASA Astrophysics Data System (ADS)

Strong co-current drift and substantial heating of impurity ions were reported in some early (˜1960) toroidal devices with low magnetic field B and high loop voltage, VL (Sceptre and ZETA in Britain and Al'fa in Russia). High frequency spikes in VL suggest rapid changes in the discharge inductance; VL should be treated as the sum of resistive [IR] and inductive [d(LI)/dt] terms. Experimental data can be used to estimate the resistive and inductive contributions. High-energy electrons and (impurity and hydrogenic) ions were observed, but the average energies were a few tens of eV. Calculations using a 1-D momentum equation with a toroidal electric field as driver and slowing in Coulomb collisions and inelastic processes yield impurity ion (average) drift velocities and apparent temperature (drift driven by voltage spikes) that are consistent with spectroscopic observations on Al'fa. These early experiments contrast with modern tokamaks, which are comparatively quiescent and usually have relatively higher toroidal B and lower VL. On the other hand, ZETA was a precursor of the reversed field pinch (RFP), some of whose characteristics seem related to their high VL. Toroidal drift ("rotation") velocities for tokamaks and RFPs can be calculated in the same way.

McNeill, D. H.

2009-03-01

31

Drift Velocity and Mobility of a Graphene Nanoribbon in a High Magnitude Electric Field  

NASA Astrophysics Data System (ADS)

We study the high-field transport behavior of a graphene nanoribbon in the degenerate and nondegenerate regimes by incorporating a previous low field mobility calculation modified for a high electric field in both regimes. The drift velocity model presented predicts that the transport behaviour is different in each regime when subject to an electric field. Our theoretical results are comparable with experimental data. The Fermi velocity (for the degenerate regime) and thermal velocity (for the nondegenerate regime) coupled with optical phonon emission have a large influence on the drift velocity leading to a velocity saturation preceded by a monotonic increase with increasing electric field.

Amin, N. A.; Ahmadi, M. T.; Johari, Z.; Webb, J. F.; Mousavi, S. M.; Ismail, R.

2011-06-01

32

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

33

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

34

The temporal evolution of the ionospheric signatures of subauroral ion drifts  

NASA Technical Reports Server (NTRS)

The effects of an imposed westward plasma drift on O(+) and molecular ion behavior in the nightside ionosphere are investigated using a model of the ionosphere and plasmasphere. A closed subauroral tube of the plasma is considered, and the velocity input persists for 30 min. The rapid increase in the F-region ion temperature resulting from ion-neutral frictional heating causes an immediate surge in the O(+) field-aligned velocity, upwards in the topside ionosphere and downwards below the F2-peak, but after about 10 min into the event the surge in the topside disappears. After the event there is a return flow of O(+) from the plasmasphere. The relative abundance of O(+) decreases during the event due to the increased rate of conversion of O(+) into NO(+) and O2(+); the decrease is more marked for greater values of the imposed westward ion drift. The implications of these results for satellite observations of subauroral ion drifts events and on EISCAT incoherent scatter radar observations of ion heating events is discussed.

Moffett, R. J.; Heelis, R. A.; Sellek, R.; Bailey, G. J.

1992-01-01

35

In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors  

NASA Astrophysics Data System (ADS)

Three-dimensional track reconstruction is a key issue for directional Dark Matter detection and it requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence needed as it is a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures: CF4 and CF4+CHF3. The latter has been chosen for the MIMAC detector as we expect that adding CHF3 to pure CF4 will lower the electron drift velocity. This is a key point for directional Dark Matter as the track sampling along the drift field will be improved while keeping almost the same Fluorine content of the gas mixture. We show that the drift velocity at 50 mbar is reduced by a factor of about 5 when adding 30% of CHF3.

Billard, J.; Mayet, F.; Bosson, G.; Bourrion, O.; Guillaudin, O.; Lamblin, J.; Richer, J. P.; Riffard, Q.; Santos, D.; Iguaz, F. J.; Lebreton, L.; Maire, D.

2014-01-01

36

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

37

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

38

Electrostatic drift-wave instability in a nonuniform quantum magnetoplasma with parallel velocity shear flows  

SciTech Connect

The propagation of high and low frequency (in comparison with the cyclotron frequency) electrostatic drift-waves is investigated in a nonuniform, dense magnetoplasma (composed of electrons and ions), in the presence of parallel shear flow, by employing the quantum magnetohydrodynamic (QMHD) model. Using QMHD model, a new set of equations is presented in order to investigate linear properties of electrostatic drift-waves with sheared plasma flows for dense plasmas. In this regard, dispersion relations for coupled electron-thermal and drift-ion acoustic modes are derived and several interesting limiting cases are discussed. For instance, it is found that sheared ion flow parallel to the external magnetic field can drive the quantum drift-ion acoustic wave unstable, etc. The present investigation may have relevance in dense astrophysical environments where quantum effects are significant.

Tariq, Sabeen; Mirza, Arshad M. [Department of Physics, Theoretical Plasma Physics Group, Quaid-i-Azam University, Islamabad 45320 (Pakistan); Masood, W. [Theoretical Plasma Physics Division, PINSTECH, P.O. Box. Nilore, Islamabad 44000, Pakistan and National Center for Physics (NCP), Islamabad 45320 (Pakistan)

2010-10-15

39

Numerical simulation of drift waves and trapped ion modes  

SciTech Connect

Two-dimensional numerical simulations are used to study the interaction of trapped electron drift waves (DW) and trapped ion modes (TIM). Wave-number ([ital k]) space is divided into long and short wave regions at a poloidal wave number corresponding to the ion bounce frequency. Two field models are used to describe trapped electron drift wave dynamics at short waves and trapped ion mode dynamics for long waves. The standard case has curvature effects and collisionality. The nonlinearity that couples the two regions includes a trapped ion banana width effect analogous to finite Larmor radius (FLR) polarization drift. The principal result of this study is that the TIM do not contribute to the diffusion significantly, regardless of the model for the nonlinear coupling to the DW. This conclusion is supported by a more general four field model that includes pressure dynamics and which allows ion temperature gradient (ITG) driven drift modes. When the collisionality is varied, the diffusion deviates from the [gamma]/[ital k][sup 2][sub [ital x

Kingsbury, O.T.; Waltz, R.E. (General Atomics, P.O. Box 85608, San Diego, California 92186-9784 (United States))

1994-07-01

40

Drift compression and final focus of intense heavy ion beams  

SciTech Connect

The longitudinal and transverse dynamics of a heavy ion fusion beam during the drift compression and final focus phase is studied. A lattice design with four time-dependent magnets is described that focuses the entire beam pulse onto a single focal point with the same spot size.

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

2003-05-01

41

Ion composition and drift observations in the nighttime equatorial ionosphere  

NASA Technical Reports Server (NTRS)

The first in situ measurements of ion composition in the nighttime equatorial E and F region ionospheres (90-300 km) are presented and discussed. These profiles were obtained by two rocket-borne ion mass spectrometers launched from Thumba, India on March 9-10, 1970 at solar zenith angles of 112 deg and 165 deg. Ionosonde data established that the composition was measured at times bounding a period of F region downward drift. During this period the ions O(+) and N(+) were enhanced by one to three orders of magnitude between 220 and 300 km. Below the drift region (200 km), O(+) ceased to be the major ionic constituent, but the concentrations of O(+) and N(+) remained larger than predicted from known radiation sources and loss processes. Here also, both the O2(+) and NO(+) profiles retained nearly the same shape and magnitude throughout the night in agreement with theories assuming scattered UV radiation to be the maintaining source. Light metallic ions including Mg(+), Na(+) and possibly Si(+) were observed to altitude approaching 300 km, while the heavier ions Ca(+) and K(+) were seen in reduced quantity to 200 km. All metal ion profiles exhibited changes which can be ascribed to vertical drifting.

Goldberg, R. A.; Aikin, A. C.; Murthy, B. V. K.

1974-01-01

42

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

43

Calculated nighttime eastward plasma drift velocities at low latitudes and their solar cycle dependence  

NASA Technical Reports Server (NTRS)

After calculating ambient electron densities as a function of altitude, latitude and local time, a simplified expression is used to calculate F-region eastward plasma drifts given a zonal neutral wind model. The derived eastward plasma drift on a magnetic flux tube is examined as a function of the flux tube apex height. If the neutral wind is assumed to be independent of latitude the plasma drift maximizes along the flux tube which intercepts the F-region peak concentration at the Appleton anomaly. Above this altitude the velocity decreases to reflect a decrease in the flux tube integrated F-region Pedersen conductivity. For a latitude dependent wind the plasma drift tends to maximize along the flux tube which intercepts the F-peak at the dip equator. Above this altitude the drift decreases to reflect the latitude distribution of the wind.

Anderson, D. N.; Heelis, R. A.; Mcclure, J. P.

1987-01-01

44

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

SciTech Connect

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{sub {infinity}}c{sub s} exp[-1-(M{sub parallel}{infinity}-M{sub perpendicular}cot {theta})], where {theta} is the angle (in the plane of field and drift velocity) of the object-surface to the magnetic-field and M{sub parallel{infinity}} is the external parallel flow. The perpendicular drift, M{sub perpendicular}, appearing here consists of the external E and 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. [Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2008-12-15

45

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

46

Asymptotic velocity of one dimensional diffusions with periodic drift  

E-print Network

We consider the asymptotic behaviour of the solution of one dimensional stochastic differential equations and Langevin equations in periodic backgrounds with zero average. We prove that in several such models, there is generically a non vanishing asymptotic velocity, despite of the fact that the average of the background is zero.

P. Collet S. Martinez

2007-05-10

47

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 Kadomstev–Petviashvilli (KP) equation in an inhomogeneous

W. Masood

2009-01-01

48

Direct measurements of plasma drift velocities at high magnetic latitudes.  

NASA Technical Reports Server (NTRS)

Description of an incoherent scatter radar experiment performed at the 23-cm radar facility in Chatanika, Alaska. The experiment has provided a direct method for measuring the ionospheric plasma transport velocity vector over long periods with relatively good time resolution. Since the F-region transport at this site is closely associated with magnetospheric convection, particularly at night, the radar can provide important information about the behavior of the magnetosphere.

Doupnik, J. R.; Banks, P. M.; Baron, M. J.; Rino, C. L.; Petriceks, J.

1972-01-01

49

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

50

Electron drift velocity and Townsend coefficient in DME-based gas mixtures  

NASA Astrophysics Data System (ADS)

Drift velocity and Townsend coefficients in pure DME, Ar-DME (50/50) and (80/20) and Ne-DME (50/50) and (80/20) mixtures have been measured for high and very high electric fields. The use of a modified pulsed Townsend technique allowed the study of electron transport close to the steady breakdown field of the gas.

Oettinger, Eva; Hildebrandt, Malte; Schmidt, Bernhard

51

2-D Drift Velocities from the IMAGE EUV Plasmaspheric Imager  

NASA Technical Reports Server (NTRS)

The IMAGE Mission extreme ultraviolet imager (EW) observes He(+) plasmaspheric ions throughout the inner magnetosphere. Limited by ionizing radiation and viewing close to the Sun, images of the He(+) distribution are available every 10 minutes for many hours as the spacecraft passes through apogee in its highly elliptical orbit. As a consistent constituent at about 15%, He(+) is an excellent surrogate for monitoring all of the processes that control the dynamics of plasmaspheric plasma. In particular, the motion of He' transverse to the ambient magnetic field is a direct indication of convective electric fields. The analysis of boundary motions has already achieved new insights into the electrodynamic coupling processes taking place between energetic magnetospheric plasmas and the ionosphere. Yet to be fulfilled, however, is the original promise that global E W images of the plasmasphere might yield two-dimensional pictures of mesoscale to macro-scale electric fields in the inner magnetosphere. This work details the technique and initial application of an IMAGE EUV analysis that appears capable of following thermal plasma motion on a global basis.

Gallagher, D. L.

2006-01-01

52

2-D Drift Velocities from the IMAGE EUV Plasmaspheric Imager  

NASA Technical Reports Server (NTRS)

The IMAGE Mission extreme ultraviolet imager (EUY) observes He+ plasmaspheric ions throughout the inner magnetosphere. Limited by ionizing radiation and viewing close to the Sun, images of the He+ distribution are available every 10 minutes for many hours as the spacecraft passes through apogee in its highly elliptical orbit. As a consistent constituent at about 15%, He+ is an excellent surrogate for monitoring all of the processes that control the dynamics of plasmaspheric plasma. In particular, the motion ofHe+ transverse to the ambient magnetic field is a direct indication of convective electric fields. The analysis of boundary motions has already achieved new insights into the electrodynamic coupling processes taking place between energetic magnetospheric plasmas and the ionosphere. Yet to be fulfilled, however, is the original promise that global EUY images of the plasmasphere might yield two-dimensional pictures of meso-scale to macro-scale electric fields in the inner magnetosphere. This work details the technique and initial application of an IMAGE EUY analysis that appears capable of following thermal plasma motion on a global basis.

Gallagher, D.; Adrian, M.

2007-01-01

53

Space charge effect in spectrometers of ion mobility increment with planar drift chamber.  

PubMed

The effect of space charge on the ion beam in a spectrometer of ion mobility increment with the planar drift chamber has been investigated. A model for the drift of ions under a non-uniform high-frequency electric field(1-3) has been developed recently. We have amplified this model by taking space charge effect into account. The ion peak shape taking into consideration the space charge effect is obtained. The output current saturation effect limiting the rise of the ion peak with increasing ion density at the input of the drift chamber of a spectrometer is observed. We show that the saturation effect is caused by the following phenomenon. The maximum possible output ion density exists, depending on the ion type (constant ion mobility, k(0)) and the time of the motion of ions through the drift chamber. At the same time, the ion density does not depend on the parameters of the drift chamber. PMID:17881778

Elistratov, A A; Sherbakov, L A

2007-01-01

54

The wind-induced drift velocity of the freshwater layer on the sea's surface  

NASA Astrophysics Data System (ADS)

The effect of an unsteady river plume on the wind drift was studied. Initially, the plume occurs as a horizontal homogeneous near-surface layer with a low density and different thicknesses being washed around by the wind in the course of time due to the vertical mixing with the underlying waters. This process is described using the one-dimensional Princeton Ocean Model (POM) with the integrated turbulence submodel. A series of numerical experiments yielded the empirical dependence of the normalized surface drift velocity modulus on the nondimensional parameters: the Ekman numbers and the relations between the buoyancy and Coriolis forces.

Zhurbas, N. V.

2013-03-01

55

Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas  

NASA Astrophysics Data System (ADS)

Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of ?) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg-de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.

Adnan, Muhammad; Mahmood, S.; Qamar, Anisa

2014-09-01

56

Intersaccadic drift velocity is sensitive to short-term hypobaric hypoxia.  

PubMed

Hypoxia, defined as decreased availability of oxygen in the body's tissues, can lead to dyspnea, rapid pulse, syncope, visual dysfunction, mental disturbances such as delirium or euphoria, and even death. It is considered to be one of the most serious hazards during flight. Thus, early and objective detection of the physiological effects of hypoxia is critical to prevent catastrophes in civil and military aviation. The few studies that have addressed the effects of hypoxia on objective oculomotor metrics have had inconsistent results, however. Thus, the question of whether hypoxia modulates eye movement behavior remains open. Here we examined the effects of short-term hypobaric hypoxia on the velocity of saccadic eye movements and intersaccadic drift of Spanish Air Force pilots and flight engineers, compared with a control group that did not experience hypoxia. Saccadic velocity decreased with time-on-duty in both groups, in correlation with subjective fatigue. Intersaccadic drift velocity increased in the hypoxia group only, suggesting that acute hypoxia diminishes eye stability, independently of fatigue. Our results suggest that intersaccadic drift velocity could serve as a biomarker of acute hypoxia. These findings may also contribute to our understanding of the relationship between hypoxia episodes and central nervous system impairments. PMID:24877213

Di Stasi, Leandro L; Cabestrero, Raúl; McCamy, Michael B; Ríos, Francisco; Catena, Andrés; Quirós, Pilar; Lopez, Jose A; Saez, Carolina; Macknik, Stephen L; Martinez-Conde, Susana

2014-04-01

57

Ion distribution profiles in the drift region of an ion mobility spectrometer  

NASA Astrophysics Data System (ADS)

The radial distribution of ions at atmospheric pressure in the drift region of two ion mobility spectrometers of dissimilar dimensions was determined using a concentric ring detector, a detector with annulus design, and metallic and non-metallic blocking rings. The radial density profile of ions at the detector plate exhibited a maximum off-center beyond which ion density declined rapidly. The intensity at the center was roughly 40% less than the maximum, which to some extent reflects the ion density profile in the source. A hole in the detector plate center with diameter of 3 mm or less did not measurably affect ion intensities measured at the detector, while incremental enlargement of the hole caused a considerable decline in intensity. Finally, the radial broadening of the ions throughout their transit in the drift region suggested that diffusion alone could not account for the observed results.

Karpas, Z.; Eiceman, G. A.; Ewing, R. G.; Algom, A.; Avida, R.; Friedman, M.; Matmor, A.; Shahal, O.

1993-08-01

58

Ion source with closed drift anode layer plasma acceleration  

NASA Astrophysics Data System (ADS)

Several versions of ion sources with closed drift anode layer plasma acceleration (ALPA sources) were built and tested. Robust, "all iron" design and water cooling permeate an unlimited operation with oxygen and with other high reactive gases. Long time operation of discharges in oxygen, nitrogen, argon, water vapor, propane, acetone, ethyl alcohol vapors, and in different gas cocktails has been tested. Beam parameters, generated in discharges with a voltage of Vd=0.3 to 3 kV will be presented. A simple design, only one simple power supply, and the operation without special electron source are advantages of discussed ALPA sources very suitable for many applications.

Dudnikov, V.; Westner, A.

2002-02-01

59

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 Jupiter’s 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 President’s 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

60

Drift Tube Studies of Ion-Neutral Reactions and Their Relevance to Interstellar Chemistry  

NASA Astrophysics Data System (ADS)

The principle of operation of drift tubes and their application to the determination of ion-neutral reaction rate coefficients, k, as a function of the ion/reactant molecule (Er) and the ion/buffer gas (Eb) centre-of-mass energies are discussed. It is shown that drift tube data of k versus Er, for atomic ion/neutral reactions can be used with confidence in modelling the ion chemistry of shocked interstellar gas. However, it is stressed that drift tube data relating to molecular ion reactions must be used with caution since internal excitation of the ions can occur in collisions with the buffer gas.

Smith, D.; Adams, N. G.

61

Equatorial F-region vertical ion drifts during quiet solar maximum  

NASA Astrophysics Data System (ADS)

Median values of ionosonde h' F data acquired at Ibadan (Geographic:7.4°N, 3.9°E, Magnetic: dip 6°S, and magnetic declination, 3°W), Nigeria, West Africa, have been used to determine vertical ion drift (electric field) characteristics in the postsunset ionosphere in the African region during a time of high solar activity (average F10.7 -208). The database spans from January and December 1958 during the era of International Geophysical Year (IGY) for geomagnetic quiet conditions. Bimonthly averaged diurnal variations patterns are very similar, but differ significantly in magnitude and in the evening reversal times. Also, monthly variations of F-region vertical ion drift reversal times inferred from the time of h' F maximum indicates early reversal during equinoxes and December solstice months except for the month of April. Late reversal is observed during the June solstice months. The equatorial evening prereversal enhancement in vertical ion drift ( V zp) occurs largely near 1900 LT with typical values ˜20-45 m/s. Comparison of Ibadan ionosonde V zp with the values of prereversal peak velocity reported for Jicamarca (South America), Kodaikanal (India), and Scherliess and Fejer global model show considerable disparity. The changes of postsunset peak in virtual height of F-layer ( h' F P) with prereversal velocity peak V zp are anti-correlated. Investigation of solar effects on monthly values of V zp and h' F P revealed that these parameters are independent of monthly averaged solar flux intensity during quiet-time sunspot maximum conditions.

Oyekola, O. S.

2009-06-01

62

Drift velocity of the ionospheric irregularities measured by closely-spaced GNSS receivers in Tromsoe, Norway  

NASA Astrophysics Data System (ADS)

A radio signal passing through small-scale irregularities in the ionospheric electron density fluctuates in amplitude and phase because the irregularities act as diffraction gratings. This phenomenon is known as scintillation. The GNSS (Global Navigation Satellite System) scintillation is caused by irregularities with a scale-size of several hundred meters. In this study, we use three GNSS receivers at the EISCAT radar site in Tromsoe, Norway, where optical and radio measurements are carried out. On January, 2012, we have installed a GNSS receiver at EISCAT radar site in Tromsoe, Norway. The receiver measures phase and signal-to-noise ratio of the radio wave from the GNSS satellites at dual frequency (L1 and L2) at 50 Hz, so that total electron content (TEC) and phase and amplitude scintillations of the ionosphere can be obtained. On September, 2012, we have installed two more receivers at Tromsoe. The distances between the three GNSS receivers are 172m, 242m and 218m, respectively. Drift velocities of irregularities can be measured using cross-correlation analysis for the time series of the GNSS signal intensity and phase obtained from the three receivers. Weak scintillation with an S4 index of 0.15 was observed at 1545 - 1605 UT on November 20, 2012. Period of the signal intensity variation was approximately 0.5 seconds. Since the scale-size of the irregularity causing the GPS scintillation, which corresponds to the Fresnel scale, is approximately 200 m, drift velocity of the irregularity causing the scintillation is estimated 400 m/s. On the other hand, the drift velocity was also estimated to be 350-400 m/s west-northwestward using cross-correlation analysis with the time series of the GPS signal intensity obtained from the three receivers. This velocity is similar to that estimated from the period of the signal intensity variation. The direction of aurora movement observed simultaneously using a digital camera at Tromsoe is also similar to that of the velocity estimated from the closely-spaced GNSS receivers. In this presentation, we discuss relationship of the irregularity drift velocity with aurora structure and movement based on these observations.

Ito, Y.; Otsuka, Y.; Shiokawa, K.; Hosokawa, K.; Ogawa, Y.

2013-12-01

63

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

PubMed

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 of electrodes and insulators and (2) a truly linear drift tube. One version of the alternating electrode/insulator drift tube and two versions of linear drift tubes were then fabricated. The stacked alternating electrodes/insulators were connected through a resistor network to generate the electrostatic gradient in the drift tube. The two linear drift tube designs consisted of two types of resistive drift tubes with one tube consisting of a resistive coating within an insulating tube and the other tube composed of resistive ferrites. The electrostatic fields within each type of drift tube were then evaluated by a noncontact method using a Kelvin-Zisman type electrostatic voltmeter and probe (results for alternative measurement methods provided in supplementary material). The experimental results were then compared with the electrostatic fields predicted by SIMION. Both the modeling and experimental measurements reveal that the electrostatic fields within a stacked ion mobility spectrometer drift tube are only pseudo-linear, while the electrostatic fields within a resistive drift tube approach perfect linearity. PMID:17411220

Scott, Jill R; Tremblay, Paul L

2007-03-01

64

A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor  

SciTech Connect

It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.

Pozela, J. K. [Semiconductor Physics Institute (Lithuania)], E-mail: pozela@spi.pfi.lt; Mokerov, V. G. [Russian Academy of Sciences, Institute of the Microwave Semiconductor Electronics (Russian Federation)

2006-03-15

65

Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity  

NASA Astrophysics Data System (ADS)

The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400-850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009-2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130-150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

Coley, W. R.; Stoneback, R. A.; Heelis, R. A.; Hairston, M. R.

2014-02-01

66

Low-latitude zonal and vertical ion drifts seen by DE 2  

Microsoft Academic Search

Horizontal and vertical ion drift data from the DE 2 spacecraft have been used to determine average zonal and vertical plasma flow (electric field) characteristics in the \\/plus minus\\/26\\/degree\\/ dip latitude region during a time of high solar activity. The data base consists of over 800 equatorial passes. Horizontal ion drift data were projected along magnetic field lines to the

W. R. Coley; R. A. Heelis

1989-01-01

67

Early-time velocity autocorrelation for charged particles diffusion and drift in static magnetic turbulence  

E-print Network

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 time-scale over which the particles "decorrelate" from the solution to the unperturbed equation of motion. Decorrelation time-scales are evaluated for parallel and perpendicular motions, including the drift of the particles from the local magnetic field line. The regimes of ...

Fraschetti, Federico

2012-01-01

68

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

69

Graphene, a material for high temperature devices - intrinsic carrier density, carrier drift velocity, and lattice energy  

NASA Astrophysics Data System (ADS)

Heat has always been a killing matter for traditional semiconductor machines. The underlining physical reason is that the intrinsic carrier density of a device made from a traditional semiconductor material increases very fast with a rising temperature. Once reaching a temperature, the density surpasses the chemical doping or gating effect, any p-n junction or transistor made from the semiconductor will fail to function. Here, we measure the intrinsic Fermi level (|EF| = 2.93 kBT) or intrinsic carrier density (nin = 3.87 × 106 cm-2K-2.T2), carrier drift velocity, and G mode phonon energy of graphene devices and their temperature dependencies up to 2400 K. Our results show intrinsic carrier density of graphene is an order of magnitude less sensitive to temperature than those of Si or Ge, and reveal the great potentials of graphene as a material for high temperature devices. We also observe a linear decline of saturation drift velocity with increasing temperature, and identify the temperature coefficients of the intrinsic G mode phonon energy. Above knowledge is vital in understanding the physical phenomena of graphene under high power or high temperature.

Yin, Yan; Cheng, Zengguang; Wang, Li; Jin, Kuijuan; Wang, Wenzhong

2014-07-01

70

Characteristics of ion velocity structure at high latitudes during steady southward interplanetary magnetic field conditions  

NASA Astrophysics Data System (ADS)

Variability or structure in the ion velocity at high latitudes in the F region is an important consideration when calculating an accurate Joule heating rate. Velocity structure in time and space may contribute significantly to heating of the F region and its inclusion could help improve our understanding of the energy budget of the atmosphere. In this paper we neglect temporal changes over periods less than 16 s and discuss the characteristic spatial structure in the ion drift in the F region ionosphere and how it relates to the bulk ion flow, the gradient on the bulk ion flow, and the ion temperature in the polar cap and auroral zone. This investigation uses data from the Dynamics Explorer 2 satellite and is limited to times of stable southward interplanetary magnetic field. Under these conditions time averaged enhancements in the Joule heating rate from the presence of spatial structure in the auroral zones have minimum values ranging from 4% to 13% depending on season.

Johnson, E. S.; Heelis, R. A.

2005-12-01

71

High Resolution Ion Mobility Spectrometry with Increased Ion Transmission: Exploring the Analytical Utility of Periodic-Focusing DC Ion Guide Drift Cells  

E-print Network

frequency of the ion with the neutral drift gas. Consequently, ions of different size will have different collision frequencies with the gas and be separated in the drift cell. A significant challenge for IMS, however, is to separate ions with very similar...

Blase, Ryan Christopher

2012-02-14

72

Designing Neutralized Drift Compression for Focusing of Intense Ion Beam Pulses in a Background Plasma  

SciTech Connect

Neutralized drift compression offers an effective method for particle beam focusing and current amplification. In neutralized drift compression, a linear radial and longitudinal velocity drift is applied to a beam pulse, so that the beam pulse compresses as it drifts in the drift-compression section. The beam intensity can increase more than a factor of 100 in both the radial and longitudinal directions, resulting in more than 10,000 times increase in the beam number density during this process. The self-electric and self-magnetic fields can prevent tight ballistic focusing and have to be neutralized by supplying neutralizing electrons. This paper presents a survey of the present theoretical understanding of the drift compression process and plasma neutralization of intense particle beams. The optimal configuration of focusing and neutralizing elements is discussed in this paper.

Kaganovich, I.D.; Davidson, R.C.; Dorf, M.; Startsev, E.A.; Barnard, J.J.; Friedman, A.; Lee, E.P.; Lidia, S.M.; Logan, B.G.; Roy, P.K.; Seidl, P.A.; Welch, D.R.; Sefkow, A.B.

2009-04-28

73

A quantum-dot heterostructure transistor with enhanced maximum drift velocity of electrons  

SciTech Connect

A new type of heterotransistor based on an AlGaAs/GaAs/InAs/GaAs/InAs structure with a layer of InAs quantum dots embedded directly into the GaAs channel is fabricated. High values of the maximum saturation current (up to 35 A/cm) and transconductance (up to 1300 mS/mm) are attained. The specific features of the current-voltage characteristics of the new device are explained in the context of a model that takes into account the ionization of quantum dots in high electric fields and tenfold enhancement of the electron drift velocity in a structure with an InAs quantum-dot layer in the vicinity of an AlGaAs/GaAs heterojunction.

Mokerov, V. [Russian Academy of Sciences, Institute of Microwave Semiconductor Electronics (Russian Federation); Pozela, J., E-mail: pozela@spi.pfi.lt; Pozela, K.; Juciene, V. [Semiconductor Physics Institute (Lithuania)

2006-03-15

74

Vertical Drift Velocities and East-West Electric Fields at the Magnetic Equator  

Microsoft Academic Search

Incoherent scatter observations of vertical drifts taken at Jicamarca (2 ø dip) are presented. Vertical drifts are found to be nearly constant as a function of height. These vertical drifts can also be taken as a direct measurement of the east-west electric fields at the magnetic equator. Their daily and seasonal behavior is presented. The effect of geomagnetic activity is

Ronald F. Woodman

1970-01-01

75

Stationary Plasma Thruster Ion Velocity Distribution  

NASA Technical Reports Server (NTRS)

A nonintrusive velocity diagnostic based on laser induced fluorescence of the 5d4F(5/2)-6p4D(5/2) singly ionized xenon transition was used to interrogate the exhaust of a 1.5 kW Stationary Plasma Thruster (SPT). A detailed map of plume velocity vectors was obtained using a simplified, cost-effective, nonintrusive, semiconductor laser based scheme. Circumferential velocities on the order of 250 m/s were measured which implied induced momentum torques of approximately 5 x 10(exp -2) N-cm. Axial and radial velocities were evaluated one mm downstream of the cathode at several locations across the width of the annular acceleration channel. Radial velocities varied linearly with radial distance. A maximum radial velocity of 7500 m/s was measured 8 mm from the center of the channel. Axial velocities as large as 16,500 m/s were measured.

Manzella, David H.

1994-01-01

76

Simultaneous observations of field-aligned currents and plasma drift velocities by Atmosphere Explorer C  

NASA Technical Reports Server (NTRS)

The three-axis flux gate magnetometer on board the Atmosphere Explorer C (AE-C) has provided an additional magnetic field data set to the already broad spectrum of AE-C measurement. The results of an investigation into the feasibility of using the magnetometer for scientific purposes are described. It is shown that within the limitations inherent in the device and in the data reduction technique used, meaningful results can be obtained when the spacecraft is in the spinning mode. From a comparison between the field-aligned current signatures and the simultaneously observed ion convection velocity, it proved possible to locate regions of ionospheric conductivity gradients.

Bythrow, P. F.; Heelis, R. A.; Hanson, W. B.; Power, R. A.

1980-01-01

77

Ion mixing in the plasma sheet boundary layer by drift instabilities  

NASA Technical Reports Server (NTRS)

The linear stability properties of collisionless drift instabilities are analyzed in a Harris equilibrium model of the plasma sheet boundary layer (PSBL). The strearmng ions with drift-type instabilities driven in the PSBL are considered. The fluid approximation leads to growth but predicts that the mode width approaches the gyroradius of the energetic ions. Thus an integral equation theory for the modes is developed taking into account that in the PSBL the curvature drift is weak compared with the grad-B drift. The exact wave particle resonance is kept in the nonlocal response functions. Plasma density, temperature, and magnetic gradient drift motions are taken into account. The drift modes produce an anomalous cross-field momentum transport mixing the PSBL ions on the time scale of tens of seconds. A nonlinear simulation is performed which shows the coalescence of the small scale, fast growing modes into large-scale vortices. The relation between these collective modes and plasma sheet transport phenomena is discussed including the comparison with the competing plasma mixing from single-particle stochasticity.

Horton, W.; Dong, J. Q.; Su, X. N.; Tajima, T.

1993-01-01

78

Drift compression and final focus systems for heavy ion inertial fusion  

SciTech Connect

Longitudinal compression of space-charge dominated beams can be achieved by imposing a head-to-tail velocity tilt on the beam. This tilt has to be carefully tailored, such that it is removed by the longitudinal space-charge repulsion by the time the beam reaches the end of the drift compression section. The transverse focusing lattice should be designed such that all parts of the beam stay approximately matched, while the beam smoothly expands transversely to the larger beam radius needed in the final focus system following drift compression. In this thesis, several drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression. The occurrence of mismatches due to a rapidly increasing current was analyzed. In addition, the sensitivity of drift compression to errors in the initial velocity tilt and current profile was studied. These calculations were done using a new computer code that accurately calculates the longitudinal electric field in the space-charge dominated regime.

de Hoon, M.J.L.

2001-05-01

79

Space charge effect in spectrometers of ion mobility increment with cylindrical drift chamber.  

PubMed

We have amplified the model for the drift of ions under a non-uniform high-frequency electric field by taking space charge effect into account. By this means, we have investigated the effect of space charge on the dynamics of a single type of ions in a spectrometer of ion mobility increment with a cylindrical drift chamber. The counteraction of the space charge effect and the focusing effect is investigated. The output ion current saturation caused by the effect of the space charge is observed. The shape of the ion peak taking into consideration the space charge effect has been obtained. We show that the effect of the space charge is sufficient for the relative ion density greater than 10 ppt by order of magnitude (for a cylindrical geometry spectrometer with typical parameters). PMID:17942976

Elistratov, A A; Sherbakov, L A

2007-01-01

80

Neoclassical polarization drift of collisionless single ions in a sheared radial electric field in a tokamak magnetic geometry  

Microsoft Academic Search

Neoclassical polarization drift is known to play critical role in the dynamical behavior of a sheared radial electric field Er in a toroidal confinement device. However, basic studies on the effect of radial electric shear on neoclassical polarization drift have not yet appeared in the literature. In the present report, the neoclassical polarization drift speed VNP of collisionless single ions

Hoyul Baek; Seunghoe Ku; C. S. Chang

2006-01-01

81

Development of Ion Drift-Chemical Ionization Mass Spectrometry  

E-print Network

as their oxidation products can be quantified simultaneously by PTR-MS. Some desirable features offered by PTR are chemically ionized into positive or negative product ions with a well- controlled ion-molecule reaction time to yield a product ion, which is analyzed by a quadrupole mass analyzer for species identification

82

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

83

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

84

Drift wave instability analysis in pair-ion-electron plasmas using kinetic approach  

SciTech Connect

Drift wave is studied in pair-ion plasmas in the presence of electrons using the Vlasov-Poisson set of equations. The growth rate of this universal instability depends on the concentration of electrons. The real frequency and the growth rate are reduced as the number density of electrons decreases. If the laboratory produced pair-ion plasmas contain relatively small amount of electrons then very low frequency almost stable drift waves can be produced which will indicate that the plasma is not a pure pair-ion plasma. The present investigation can be useful for future experiments on pair-ion plasmas and low density low temperature industrial plasmas which contain negative ions.

Ali, S.; Saleem, H. [National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan)

2010-09-15

85

The functional response of drift-feeding Arctic grayling: the effects of prey density, water velocity, and location efficiency  

Microsoft Academic Search

An important aspect of a predator-prey system is the functional response of the predator to changing prey densities. We studied the feeding rate response of drift-feeding Arctic grayling ( Thymallus arcticus) on a small inverte- brate prey, Daphnia middendorffiana, at densities ranging from 0.01 L-1 to 1.8 L-1 and current velocities of 25, 32, and 40 cm·s-1. We videotaped the

W. John O'Brien; Michael Barfield; Karen Sigler

2001-01-01

86

Electromagnetic instabilities attributed to a cross-field ion drift  

NASA Technical Reports Server (NTRS)

Instabilities due to a cross-field ion flow are reexamined by including the electromagnetic response of the ions, which has been ignored in existing discussions. It is found that this effect can lead to significant enhancement of the growth rate. Among the new results, a purely growing, electromagnetic unstable mode with a wave vector k parallel to the ambient magnetic field is found. The plasma configuration under consideration is similar to that used in the discussion of the well-known modified-two-stream instability. This instability has a growth rate faster than the ion cyclotron frequency, and is not susceptible to high-plasma-beta stabilization.

Chang, C. L.; Wong, H. K.; Wu, C. S.

1990-01-01

87

Ion velocities in a micro-cathode arc thruster  

SciTech Connect

Ion velocities in the plasma jet generated by the micro-cathode arc thruster are studied by means of time-of-flight method using enhanced ion detection system (EIDS). The EIDS triggers perturbations (spikes) on arc current waveform, and the larger current in the spike generates denser plasma bunches propagating along with the mainstream plasma. The EIDS utilizes double electrostatic probes rather than single probes. The average Ti ion velocity is measured to be around 2 Multiplication-Sign 10{sup 4} m/s without a magnetic field. It was found that the application of a magnetic field does not change ion velocities in the interelectrode region while leads to ion acceleration in the free expanding plasma plume by a factor of about 2. Ion velocities of about 3.5 Multiplication-Sign 10{sup 4} m/s were detected for the magnetic field of about 300 mT at distance of about 100-200 mm from the cathode. It is proposed that plasma is accelerated due to Lorentz force. The average thrust is calculated using the ion velocity measurements and the cathode mass consumption rate, and its increase with the magnetic field is demonstrated.

Zhuang Taisen; Shashurin, Alexey; Keidar, Michael [The George Washington University, Washington, DC 22202 (United States); Beilis, Isak [Tel Aviv University, Tel Aviv (Israel)

2012-06-15

88

Effect of the entrained air and initial droplet velocity on the release height parameter of a Gaussian spray drift model.  

PubMed

The increased concern about environmental effect of off-target deposits of pesticides use has resulted in the development of numerous spray drift models. Statistical models based on experimental field studies are used to estimate off-target deposits for different sprayers in various environmental conditions. Random-walk and computational fluid dynamics (CFD) models have been used to predict the effect of operational parameters and were extensively validated in wind tunnel. A third group, Gaussian dispersion models have been used for several years for the environmental assessment of the pesticide spray drift, mainly for aerial application. When these models were used for the evaluation of boom sprayer spray drift, their predictions were found unreliable in the short range, were the initial release conditions of the droplets have a significant effect on the spray deposits. For longer ranges, the results were found consistent with the field measurements as the characteristics of the source have a reduced influence on the small droplets drift. Three major parameters must be taken into account in order to define realistic initial conditions of the droplets in a spray drift model: the spray pattern of the nozzle, the boom movements and the effect of entrained air and droplet velocities. To take theses parameters into account in a Gaussian model, the nozzle droplet size distribution measured with a PIV setup to divide the nozzle output into several size classes. The spray deposits of each diameter class was computed for each successive position of the nozzle combining the nozzle spray distribution with drift computed with a Gaussian tilting plume model. The summation of these footprints resulted in the global drift of the nozzle. For increasing droplet size, the release height used in the Gaussian model was decreased from nozzle height to ground level using an experimental law to take into account the effect of entrained air and droplet initial velocity. The experimental law was adjusted on 2 m/s wind tunnel measurements and robustness was evaluated for 1 and 4 m/s. PMID:17390793

Stainier, C; Destain, M F; Schiffers, B; Lebeau, F

2006-01-01

89

Development of an ion drift chamber for Laser Induced Fluorescence studies  

E-print Network

. . Current distributions in nitrogen. 30 30 13 Current distributions in argon 31 INIRODUCIION The use of Laser Induced Fluorescence (LIF) has been suggested for ion detection in a new type of particle detector. & Such a detector would be a large, gas.... The proposed detector is intended for dark matter detection. This work describes the development of an ion drift chamber to study LIF of selected ions by producing a beam of ions in their parent gas that may be illuminated by a laser. The chamber...

Cain, Benjamin J

2012-06-07

90

Spectral anomalies of the light-induced drift effect caused by the velocity dependence of the collision broadening and shift of the absorption line  

SciTech Connect

We have theoretically investigated the spectral features of the light-induced drift (LID) effect, arising due to the dependence of the collision broadening {gamma} and shift {Delta} of the absorption line on the velocity of resonance particles, {nu}. It is shown that under certain conditions, account of this dependence can radically change the spectral shape of the LID signal, up to the appearance of additional zeros in the dependence of the drift velocity on the radiation frequency. (nonlinear optical phenomena)

Parkhomenko, A I; Shalagin, Anatolii M [Institute of Automation and Electrometry, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2013-02-28

91

Comparison of azimuthal ion velocity profiles using Mach probes, time delay estimation, and laser induced fluorescence in a linear plasma device.  

PubMed

We compare measurements of radially sheared azimuthal plasma flow based on time delay estimation (TDE) between two spatially separated Langmuir probes, Mach probes and laser induced fluorescence (LIF). TDE measurements cannot distinguish between ion fluid velocities and phase velocities. TDE and Mach probes are perturbative, so we compare the results against LIF, a non-perturbative, spatially resolved diagnostic technique that provides direct measurements of the ion velocity distribution functions. The bulk ion flow is determined from the Doppler shift of the Argon absorption line at 668.6139 nm. We compare results from all the three diagnostics, at various magnetic fields, which acts as a control knob for development of drift wave turbulence. We find that while Mach probes and LIF give similar profiles, TDE measurements typically overestimate the velocities and are also sensitive to the drift wave modes being investigated. PMID:23126882

Thakur, S Chakraborty; McCarren, D; Lee, T; Fedorczak, N; Manz, P; Scime, E E; Tynan, G R; Xu, M; Yu, J

2012-10-01

92

Ion profiling in an ambient drift tube-ion mobility spectrometer using a high pixel density linear array detector IonCCD.  

PubMed

A linear pixel-based detector array, the IonCCD, is characterized for use under ambient conditions with thermal (<1 eV) positive ions derived from purified air and a 10 mCi (63)Ni foil. The IonCCD combined with a drift tube-ion mobility spectrometer permitted the direct detection of gas phase ions at atmospheric pressure and confirmed a limit of detection of 3000 ions/pixel/frame established previously in both the keV (1-2 keV) and the hyper-thermal (10-40 eV) regimes. Results demonstrate the "broad-band" application of the IonCCD over 10(5) orders in ion energy and over 10(10) in operating pressure. The Faraday detector of a drift tube for an ion mobility spectrometer was replaced with the IonCCD providing images of ion profiles over the cross-section of the drift tube. Patterns in the ion profiles were developed in the drift tube cross-section by control of electric fields between wires of Bradbury Nielson and Tyndall Powell shutter designs at distances of 1-8 cm from the detector. Results showed that ion beams formed in wire sets, retained their shape with limited mixing by diffusion and Coulombic repulsion. Beam broadening determined as 95 ?m/cm for hydrated protons in air with moisture of ~10 ppmv. These findings suggest a value of the IonCCD in further studies of ion motion and diffusion of thermalized ions, enhancing computational results from simulation programs, and in the design or operation of ion mobility spectrometers. PMID:23802132

Davila, Stephen J; Hadjar, Omar; Eiceman, Gary A

2013-07-16

93

A mass-selective variable-temperature drift tube ion mobility-mass spectrometer for temperature dependent ion mobility studies.  

PubMed

A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400 K) drift tube is presented. The instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility spectrometer consists of a 30.2 cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80 K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer. This report describes the technological considerations for operating the instrument at variable temperature, and preliminary results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of Ti(+) formed by EI of TiCl(4) and hydration reactions of Ti(+) with residual water are presented. PMID:21953095

May, Jody C; Russell, David H

2011-07-01

94

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 2.45 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. PMID:21231054

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

2010-10-22

95

Acceleration and stochastic heating of ions drifting through an auroral arc  

SciTech Connect

The authors find that ions E [times] B drifting through an auroral arc can undergo transverse acceleration and stochastic heating. This result is very analogous to recent work regarding similar phenomena in the magnetotail. An analytic expression for the maximum arc width for which chaotic behavior is present is derived and numerically verified. The authors find, for example, that a 1.5-km-thick arc at [Lambda] = 65[degrees] requires a minimum potential drop of 3 kV for transverse ion acceleration and heating to occur. Thicker arcs require higher potential drops for stochasticity to occur. This mechanism could be a source for conic ions.

Rothwell, P.L. (Phillips Lab., Hanscom AFB, MA (United States)); Silevitch, M.B. (Northeastern Univ., Boston, MA (United States)); Block, L.P.; Faelthammar, C.G. (Royal Inst. of Technology, Stockholm (Sweden))

1992-12-01

96

Photons from Heavy-Ion Collisions at Fermi Velocity  

E-print Network

'I ~ (+l Ii & & .~ I + I I 'f Il I I PHYSICAL REVIEW C VOLUME 35, NUMBER 5 MAY 1987 Photons from heavy-ion collisions at Fermi velocity Che Ming Ko Center for Theoretical Physics, Physics Department and Cyclotron Institute, Texas Ad... December 1986) The production of photons from heavy-ion collisions at intermediate energies is studied in the model based on the Boltzmann-Uehling-Uhlenbeck equation. Taking into account photon produc- tion from nucleon-nucleon collisions...

Ko, Che Ming; Alchelin, J.

1987-01-01

97

Distributed drift chamber design for rare particle detection in relativistic heavy ion collisions  

SciTech Connect

This report describes a multi-plane drift chamber that was designed and constructed to function as a topological detector for the BNL AGSE896 rare particle experiment. The chamber was optimized for good spatial resolution, two track separation, and a high uniform efficiency while operating in a 1.6 Tesla magnetic field and subjected to long term exposure from a 11.6 GeV/nucleon beam of 10**6 Au ions per second.

Bellwied, R.; Bennett, M.J.; Bernardo, V.; Caines, H.; Christie, W.; Costa, S.; Crawford, H.J.; Cronqvist, M.; Debbe, R.; Dinnwiddie, R.; Engelage, J.; Flores, I.; Fuzesy, R.; Greiner, L.; Hallman, T.; Hoffmann, G.; Huang, H.Z.; Jensen, P.; Judd, E.G.; Kainz, K.; Kaplan, M.; Kelly, S.; Lindstrom, P.J; Llope, W.J.; LoCurto, G.; Longacre, R.; Milosevich, Z.; Mitchell, J.T.; Mitchell, J.W.; Mogavero, E.; Mutchler, G.; Paganis, S.; Platner, E.; Potenza, R.; Rotondo, F.; Russ, D.; Sakrejda, I.; Saulys, A.; Schambach, J.; Sheen, J.; Smirnoff, N.; Stokeley, C.; Tang, J.; Trattner, A.L.; Trentalange, S.; Visser, G.; Whitfield, J.P.; Witharm, F.; Witharm, R.; Wright, M.

2001-10-02

98

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

99

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

100

Climatology and Modelling of GPS L-band Scintillation and Irregularity Drift Velocities  

NASA Astrophysics Data System (ADS)

This work presents a regional picture at South-American sector of global positioning system (GPS) L-band scintillations. The differences in the occurrence statistics at observational sites located close to the magnetic equator and within the regions of the northern and southern crests of the Equatorial Ionization Anomaly (EIA) will be analyzed. Ground-based GPS data acquired during 15 years, from 1997 to 2012, are used in the study. In addition, by using the scintillation-based spaced antenna technique, the drift dynamics of the scintillation-producing Fresnel-scale irregularities are estimated at three different stations located in the Brazilian sector. The dependence of both scintillation occurrence and irregularity drifts, with the solar activity level, and their seasonal and daily variations are investigated in detail. In this work only geomagnetically quiet days with the sum of daily Kp less than 24 were used in the analysis statistics. Moreover, we used in this study the Yacoub alpha-mu model to describe the distribution of the GPS L1 signal amplitudes during scintillation fading events. We show that the obtained results with the alpha-mu distribution performed better than the widely used Nakagami-m model in the statistical characterization of amplitude scintillation. This work is important to evaluate the spatial-temporal distribution and variability of the ionospheric scintillation at the tropical ionosphere, which is a relevant theme in the space weather studies.

Muella, Marcio; De Paula, Eurico; Moraes, Alison; Rezende, Luiz Felipe C.

101

Kinetic effects on the Kelvin-Helmholtz instability in ion-to-magnetohydrodynamic scale transverse velocity shear layers: Particle simulations  

PubMed Central

Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated Kelvin–Helmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B??<0 case than in B??>0 case, where ? is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B??<0 (B??>0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B??<0 (B??>0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth. PMID:20838425

Nakamura, T. K. M.; Hasegawa, H.; Shinohara, I.

2010-01-01

102

International Reference Ionosphere: Past, present, and future. I - Electron density. II - Plasma temperatures, ion composition and ion drift  

NASA Technical Reports Server (NTRS)

The most important investigations leading to the International Reference Ionosphere 1990 (IRI-90) are overviewed, and the latest version of the model is described. The shortcomings and limitations of the IRI-90 are pointed out, together with the ways of overcoming them. The list of studies that the IRI group has yet to carry out includes the investigations of magnetic storm effects as the highest priority. This paper discusses determinations of and the available data on the electron density, plasma temperatures, ion composition, and ion drift in the ionosphere, together with future improvements needed on these parameters.

Bilitza, D.; Rawer, D.; Bossy, L.; Guliaeva, T.

1993-01-01

103

Development of An Ion-Drift Time-of-Flight Chemical Ionization Mass Spectrometry Technique for Measurements of Aerosol Precursor Gases  

NASA Astrophysics Data System (ADS)

We have developed a new technique, i.e., ion-drift time-of-flight chemical ionization mass spectrometry (ID-ToF-CIMS) for measurements of aerosol precursor gases, including ammonia, amines, organic acids and oxygenated VOCs at pptv level with a response time less than 1 s. The ID-ToF-CIMS was modified from an Aerodyne high resolution ToF-CIMS with a custom-designed ion-drift tube, which can control the ion flight velocity and hence the ion-molecular reaction time. In addition, the tunable electric field generated by the drift tube can break up water clusters to select the major reagent ions. The advantages of the ID-ToF-CIMS over the traditional quadrupole-based ID-CIMS were the high mass-resolving power of the ToF mass analyzer and the capability of simultaneous measurement of the full mass range (typically up to 300 m/z) of product ions. Using hydronium ion based reagent ions, we demonstrated that the ID-ToF-CIMS can unambiguously measure ammonia (NH3) at 18.03 m/z, methyl amine (CH3NH2) at 32.05 m/z, formic acid (HCOOH) at 47.01 m/z and acetone (CH3COCH3) at 59.05 m/z. Calibrations were performed with both compressed commercial standard gases and permeation tubes and the results showed that the instrument detection limit can reach pptv level for 1 s average time or less. The ID-ToF-CIMS was also field tested in a mobile laboratory on the campus of Nanjing University of Information Science & Technology (NUIST). The preliminary results will be discussed.

Zheng, J.; Ma, Y.; Chen, M.

2012-12-01

104

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.-Y.; Kwan, J.W.; Lee, E.P.; Leitner, M.A.; Logan, B.G.; Vay, J.-L.; Waldron, W.L.; Davidson, R.C.; Dorf, M.; Gilson, E.P.; Kaganovich, I.D.

2009-12-19

105

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

106

The effects of hyper-velocity dust-particle impacts on the LOFT Silicon Drift Detectors  

NASA Astrophysics Data System (ADS)

Solid-state detectors that operate in orbit are required to withstand harsh space environment conditions. Among the various phenomena able to damage the sensors, X-ray detectors are subjected to impacts of orbital debris and micrometeoroids whenever, to be sensitive to low energy photons, they need to be ``directly'' exposed to the sky. The LOFT mission, proposed for the M3 class opportunity of the ESA Cosmic Vision, has a very-large sensitive area (greater than 10 m2) made of Silicon Drift Detectors (SDD). Moreover, the satellite includes an X-ray Wide-Field Monitor based on the same SDD detectors. Here we present the results of a test campaign at the Cosmic Dust Accelerator Facility at MPIK in Heidelberg aimed at the space qualification of the detectors with respect to this phenomenon.

Zampa, G.; Del Monte, E.; Perinati, E.; Rashevskaya, I.; Rachevski, A.; Zampa, N.; Bugiel, S.; Kendziorra, E.; Tenzer, C.; Feroci, M.; Santangelo, A.; Vacchi, A.

2014-07-01

107

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

SciTech Connect

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 [Applied Low Temperature Plasma Laboratory, Shenzhen Key Laboratory of Sensors Technology, School of Physics, Shenzhen University, Shenzhen 518060 (China)] [Applied Low Temperature Plasma Laboratory, Shenzhen Key Laboratory of Sensors Technology, School of Physics, Shenzhen University, Shenzhen 518060 (China)

2013-07-15

108

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.

109

On Drift Effects in Velocity and Displacement of Greek Uncorrected Digital Strong Motion Data  

Microsoft Academic Search

Fifty years after the first installation of analog accelerographs, digital instruments recording the strong-motion came in operation. Their advantages comparing to the analog ones are obvious and they have been described in detail in several works. Nevertheless it has been pointed out that velocity and displacement values derived from several accelerograms, recorded in various strong earthquakes worldwide (e.g. 1999 Chi-Chi,

A. Skarlatoudis; B. Margaris

2005-01-01

110

The Digital Ion Drift-Meter on CHAMP; Status, Calibration, and Data  

NASA Astrophysics Data System (ADS)

The Digital Ion Drift Meter (DIDM), developed by Amptek, Bedford, MA USA, for AFRL, was launched on July 15, 2000 aboard the Challenging Minisatellite Payload (CHAMP) -- developed by the GeoForschungsZentrum, Potsdam, Germany -- into a 421 x 475 km polar orbit. All components and functions of DIDM are performing nominally except for two notable problems. The first was the immediate loss of one of the two nearly redundant sensors. The malfunctioning sensor passes all diagnostic tests and the problem has been attributed to a blockage of the aperture screen. The other problem has been an uneven gain evolution of the micro-channel-plate used for the ion detection. Although the sensor is still functional, the gain evolution has forced us to develop an in-space calibration procedure. This procedure is now complete and we now have reasonable DIDM results for selected periods of the mission, and will soon be extending the new procedure to the entire mission. The data includes ion density and temperature, in-track and cross-track ion drift, and electron temperature. It is important to note that the surviving sensor had the lower geometric factor of the two sensors. This low geometric factor was selected to guarantee that one sensor would not experience dead-time effects during periods of extreme high plasma density. As a result, the DIDM data will always suffer from statistical limitation regardless of calibration, and we can now characterize the performance as about 100 m/s at a density 10000 /cc. This presentation will explain in detail the instrument design, the laboratory and in-space calibration procedures, and the data processing scheme and formats.

Cooke, D. L.; Roth, C. J.

2002-05-01

111

Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica  

E-print Network

Measurements of the small,intermediate, and large ion concentrations and the airearth current density along with simultaneous measurements of the concentration and size-distribution of aerosol particles in the size ranges 4.4 to 163 nm and 0.5 to 20 micrometer diameters are reported for a drifting snow period after the occurrence of a blizzard at a coastal station, Maitri, Antarctica. Ion concentrations of all categories and the airearth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 meter per sec. The rate of decrease is the highest for large ions, lowest for small ions and in between the two for intermediate ions. Total aerosol number concentration decreases in the 4.4 to 163 nm size range but increases in 0.5 to 20 micrmetr size range with wind speed. Size distribution of the nanometer particles show a dominant maximum at 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, lar...

Kamra, A K; Pant, Vimlesh; 10.1016/j.atmosres.2008.02.018

2009-01-01

112

Analysis of Microturbulence within the Foot of Supercritical Quasiperpendicular Shocks for Different reflected ion vs electron Drifts  

NASA Astrophysics Data System (ADS)

Supercritical shocks are characterized by a fraction of the incoming ions which is reflected at the steep front and stream across the magnetic field in the foot. These ions accumulate and are responsible for the shock front self-reformation. The drift of the reflected ion beam versus the electrons can easily destabilize waves in the electron cyclotron frequency range. By means of linear analysis, we show that several Bernstein harmonics can be unstable, their number being proportional to the drift, yet limited by the ion beam's temperature. Separate electromagnetic PIC simulations restricted to the ion and electron populations of the foot region are performed for various drifts in order to investigate with high spatial resolution and high particle statistics the nonlinear characteristics of these waves. For drifts less than (T_e/m)^{1/2}, the waves saturate at weak intensity levels. For larger drifts, yet still below the ion acoustic threshold, they reach significant levels and exhibit an interesting nonlinear evolution. First, high cyclotron harmonics develop in good agreement with linear dispersion properties and over timescales much shorter than the period of the shock front self-reformation. Second, as the high k-modes saturate by trapping ions of the reflected beam, the spectral power shifts toward lower k-modes to eventually accumulate on the first harmonic in a process that appears like an inverse cascade. Third, one surprising result in the late phase is the development of a magnetic component to a spectrum that had so far been mostly electrostatic. The late phase also exhibits a significant energy transfer from the ion beam to the electrons which experience a marked increase in temperature.

Muschietti, L.; Lembege, B.

2011-12-01

113

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

114

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

115

Kinetic water-bag model of global collisional drift waves and ion temperature gradient instabilities in cylindrical geometry  

SciTech Connect

Collisional drift waves and ion temperature gradient (ITG) instabilities are studied using a linear water-bag kinetic model [P. Morel et al., Phys. Plasmas 14, 112109 (2007)]. An efficient spectral method, already validated in the case of drift waves instabilities [E. Gravier et al., Eur. Phys. J. D 67, 7 (2013)], allows a fast solving of the global linear problem in cylindrical geometry. The comparison between the linear ITG instability properties thus computed and the ones given by the COLUMBIA experiment [R. G. Greaves et al., Plasma Phys. Controlled Fusion 34, 1253 (1992)] shows a qualitative agreement. Moreover, the transition between collisional drift waves and ITG instabilities is studied theoretically as a function of the ion temperature profile.

Gravier, E. [Institut Jean Lamour, UMR 7198 CNRS-Universite de Lorraine, Bd des Aiguillettes, 54 506 Vandoeuvre-les-Nancy Cedex (France); Plaut, E. [LEMTA, UMR 7563 CNRS-Universite de Lorraine, 2, av. de la Foret de Haye, 54 518 Vandoeuvre-les-Nancy Cedex (France)

2013-04-15

116

Mobility-resolved ion selection in uniform drift field ion mobility spectrometry/mass spectrometry: dynamic switching in structures for lossless ion manipulations.  

PubMed

A Structures for Lossless Ion Manipulations (SLIM) module that allows ion mobility separations and the switching of ions between alternative drift paths is described. The SLIM switch component has a "Tee" configuration and allows the efficient switching of ions between a linear path and a 90-degree bend. By controlling switching times, ions can be efficiently directed to an alternative channel as a function of their mobilities. In the initial evaluation the switch is used in a static mode and shown compatible with high performance ion mobility separations at 4 Torr. In the dynamic mode, we show that mobility-selected ions can be switched into the alternative channel, and that various ion species can be independently selected based on their mobilities for time-of-flight mass spectrometer (TOF MS) IMS detection and mass analysis. This development also provides the basis of, for example, the selection of specific mobilities for storage and accumulation, and the key component of modules for the assembly of SLIM devices enabling much more complex sequences of ion manipulations. PMID:25222548

Webb, Ian K; Garimella, Sandilya V B; Tolmachev, Aleksey V; Chen, Tsung-Chi; Zhang, Xinyu; Cox, Jonathan T; Norheim, Randolph V; Prost, Spencer A; LaMarche, Brian; Anderson, Gordon A; Ibrahim, Yehia M; Smith, Richard D

2014-10-01

117

Maximum drift velocity of electrons in selectively doped InAlAs/InGaAs/InAlAs heterostructures with InAs inserts  

SciTech Connect

The dependence of the electron mobility and drift velocity on the growth conditions, thickness, and doping of an InAs insert placed at the center of the quantum well in a selectively doped InAlAs/InGaAs/InAlAs heterostructure has been investigated. Record enhancement of the maximum drift velocity to (2-4) Multiplication-Sign 10{sup 7} cm/s in an electric field of 5 Multiplication-Sign 10{sup 3} V/cm has been obtained in a 17-nm-wide quantum well with an undoped 4-nm-thick InAs insert. In the structures with additional doping of the InAs insert, which facilitates an increase in the density of electrons in the quantum well to 4.0 Multiplication-Sign 10{sup 12} cm{sup -2}, the maximum drift velocity is as high as 2 Multiplication-Sign 10{sup 7} cm/s in an electric field of 7 Multiplication-Sign 10{sup 3} V/cm.

Silenas, A.; Pozela, Yu., E-mail: pozela@pfi.lt; Pozela, K.; Juciene, V. [Center for Physical Sciences and Technology, Semiconductor Physics Institute (Lithuania); Vasil'evskii, I. S.; Galiev, G. B.; Pushkarev, S. S.; Klimov, E. A. [Russian Academy of Sciences, Institute of Microwave Semiconductor Electronics (Russian Federation)

2013-03-15

118

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

119

Influence of the interplanetary magnetic field orientation on polar cap ion trajectories - Energy gain and drift effects  

NASA Technical Reports Server (NTRS)

The influence of the interplanetary magnetic field (IMF) orientation on the transport of low-energy ions injected from the ionosphere is investigated using three-dimensional particle codes. It is shown that, unlike the auroral zone outflow, the ions originating from the polar cap region exhibit drastically different drift paths during southward and northward IMF. During southward IMF orientation, a 'two-cell' convection pattern prevails in the ionosphere, and three-dimensional simulations of ion trajectories indicate a preferential trapping of the light ions H(+) in the central plasma sheet, due to the wide azimuthal dispersion of the heavy ions, O(+). In contrast, for northward IMF orientation, the 'four-cell' potential distribution predicted in the ionosphere imposes a temporary ion drift toward higher L shells in the central polar cap. In this case, while the light ions can escape into the magnetotail, the heavy ions can remain trapped, featuring more intense acceleration (from a few electron volts up to the keV range) followed by precipitation at high invariant latitudes, as a consequence of their further travel into the tail.

Delcourt, D. C.; Horwitz, J. L.; Swinney, K. R.

1988-01-01

120

Drift Tube Measurements of Mobilities and Longitudinal Diffusion Coefficients of Ions in Gases.  

NASA Astrophysics Data System (ADS)

The zero-field mobilities of Br('-) and NH(,4)('+) in O(,2) were determined as a function of gas temperature in a high pressure drift tube mass spectrometer. The mobilities and longitudinal diffusion coefficients of the ion-gas combinations Br('-) in Ne and Kr, Li('+) in Xe, and Tl('+) in Kr and Xe were determined as a function of E/N, where E is the electric field strength and N is the gas number density in a low pressure drift tube mass spectrometer. The measured longitudinal diffusion coefficients were used for a test and comparison of the generalized Einstein relations of Viehland-Mason and Waldman-Mason theories. The measured mobilities of Br('-) in Kr and Tl('+) in Kr were used in an iterative-inversion scheme from which the ion-neutral interaction potentials were determined. The zero-field reduced mobility of Br('-) in O(,2) ranged from 2.6 cm('2)/(V-sec) at 297(DEGREES)K to 3.0 cm('2)/(V-sec) at 600(DEGREES)K. The zero-field reduced mobility of NH(,4)('+) in O(,2) ranged from 3.4 cm('2)/(V -sec) at 418(DEGREES)K to 3.7 cm('2)/(V-sec) at 561(DEGREES)K. The zero-field values of the reduced mobilities measured as a function of E/N in units of cm('2)/(V-sec) are as follows: Br('-) in Kr (1.47 (+OR-) .03), Br('-) in Ne (6.94 (+OR -) .14), Li('+) in Xe (2.68 (+OR-) .05), Tl('+) in Kr (1.15 (+OR-) .03), and Tl('+) in Xe (.78 (+OR-) .02). The ion -gas combinations of Br('-) in Kr, Li('+) in Xe, and Tl('+) in Kr displayed the typical mobility peaks. The peak values in cm('2)/(V-sec) are for Br('-) in Kr, Li('+) in Xe, and Tl('+) in Kr respectively: (1.81 (+OR-) 0.4) at 130 Td, 4.47 (+OR-) .09 at 135 Td, and 1.42 (+OR-) .04 at 285 Td. The measured longitudinal diffusion coefficients were compared to the Einstein values in the low-field limit. Comparisons between the experimental values and the generalized Einstein relations (GER) of Viehland-Mason and Waldman-Mason were made at all E/N values. All comparisons were favorable within the error ranges. In general, the Waldman-Mason GER values were closer to the experimental data than the Viehland-Mason values. Interaction potentials for Br('-) in Kr and Tl('+) in Kr were determined. Initial potentials for the iterative -inversion scheme were of the 4-6-n type, the coefficients for the r('-4) term being the polarizability of Kr gas. The Tl('+) in Kr case represents the first time an ion-neutral interaction potential has been determined from a measured mobility in which the structure of the ion was not that of a rare gas.

Chelf, Roger Dale

121

Solar cycle, seasonal, and diurnal variations of subauroral ion drifts: Statistical results  

NASA Astrophysics Data System (ADS)

solar cycle, seasonal, and diurnal variations of the subauroral ion drifts (SAIDs) are investigated for the first time to use such a large database of 18,226 SAID events observed by the DMSP satellites during 1987-2012. Statistical results show that SAIDs occur mostly at 60.1° invariant latitude and 2230 magnetic local time with a typical half width of 0.57°, move equatorward during high solar activities with large widths, and have two occurrence peaks in spring and fall equinoxes and two valleys in summer and winter solstices. The seasonal variation of SAID latitude has two valleys in spring and fall, and SAID width has a valley distribution with a minimum in summer. SAIDs exhibit a clear day-to-night difference in latitude. The diurnal variation of SAID width has a morning valley and an afternoon peak. The generation mechanism of SAID associated with the electron precipitation and the downward field-aligned current is also supported in this study.

He, Fei; Zhang, Xiao-Xin; Chen, Bo

2014-06-01

122

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

PubMed

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. PMID:21033923

Gupta, D; Bolte, N; Gota, H; Hayashi, R; Kiyashko, V; Marsili, P; Morehouse, M; Primavera, S; Roche, T; Wessel, F

2010-10-01

123

Application of time-sliced ion velocity imaging to crossed molecular beam experiments  

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) ion velocity imaging method was developed to measure the product velocity distributions in crossed molecular beam experiments. While maintaining conventional two-dimension velocity mapping, the third velocity component was mapped linearly to the ion time of flight. A weak extraction field was used to spread the ion turnaround time to several hundred nanoseconds, which permits good resolution for selection of the longitudinal velocity. A fast gated (?5 ns) intensified charge coupled device camera was used to record time-sliced ion images. Calibration of the apparatus was done by measuring O+ images from the multiphoton dissociation/ionization of O2. The resolution in velocity achieved was about 1% (?v/v) in slicing through the center of a Newton sphere. The overall performance was examined by observing product ion images from the F+CD4?DF+CD3 reaction. To detect CD3+ with kinetic energy release of about 1 eV, 50 ns time slicing provides sufficient velocity resolution, such that resolution of the image is mainly limited by the spread in velocity of the two molecular beams. These ion optics can focus on a large volume of ion cloud, which is crucial in crossed molecular beam experiments. Direct 3D imaging also simplifies data analysis. This direct 3D ion imaging method provides a powerful tool with which to study systems with no cylindrical symmetry.

Lin, Jim J.; Zhou, Jingang; Shiu, Weicheng; Liu, Kopin

2003-04-01

124

Drift waves in the corona: heating and acceleration of ions at frequencies far below the gyrofrequency  

Microsoft Academic Search

In the solar corona, several mechanisms of the drift wave instability can make the mode grow to amplitudes at which particle acceleration and stochastic heating by the drift wave take place. The stochastic heating, well known from laboratory plasma physics where it has been confirmed in numerous experiments, has been completely ignored in past studies of coronal heating. However, in

J. Vranjes; S. Poedts

2010-01-01

125

Low energy electron and nuclear recoil thresholds in the DRIFT-II negative ion TPC for dark matter searches  

Microsoft Academic Search

Understanding the ability to measure and discriminate particle events at the lowest possible energy is an essential requirement in developing new experiments to search for weakly interacting massive particle (WIMP) dark matter. In this paper we detail an assessment of the potential sensitivity below 10 keV in the 1 m3 DRIFT-II directionally sensitive, low pressure, negative ion time projection chamber

S. Burgos; E. Daw; J. Forbes; C. Ghag; M. Gold; C. Hagemann; V. A. Kudryavtsev; T. B. Lawson; D. Loomba; P. Majewski; D. Muna; A. St. J. Murphy; S. M. Paling; A. Petkov; S. J. S. Plank; M. Robinson; N. Sanghi; D. P. Snowden-Ifft; N. J. C. Spooner; J. Turk; E. Tziaferi

2009-01-01

126

The effects of nonthermal electron distributions on ion-temperature-gradient driven drift-wave instabilities in electron-ion plasma  

SciTech Connect

The effects of nonthermal electron distributions on electrostatic ion-temperature-gradient (ITG) driven drift-wave instabilities in the presence of equilibrium density, temperature, and magnetic field gradients are investigated here. By using Braginskii's transport equations for ions and Cairns as well as Kappa distribution for electrons, the coupled mode equations are derived. The modified ITG driven modes are derived, and it is found both analytically as well as numerically that the nonthermal distribution of electrons significantly modify the real frequencies as well as the growth rate of the ITG driven drift wave instability. The growth rate of ion-temperature-gradient driven instability is found to be maximum for Cairns, intermediate for Kappa, and minimum for the Maxwellian distributed electron case. The results of present investigation might be helpful to understand several wave phenomena in space and laboratory plasmas in the presence of nonthermal electrons.

Batool, Nazia [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan); National Center of Physics (NCP), Quaid-i-Azam University campus, Islamabad (Pakistan); Masood, W. [National Center of Physics (NCP), Quaid-i-Azam University campus, Islamabad (Pakistan); Theoretical Plasma Physics Division, PINSTECH P. O. Nilore, Islamabad (Pakistan); Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

2012-08-15

127

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

128

An Effective Approach for Coupling Direct Analysis in Real Time with Atmospheric Pressure Drift Tube Ion Mobility Spectrometry  

NASA Astrophysics Data System (ADS)

Drift tube ion mobility spectrometry (DTIMS) has evolved as a robust analytical platform routinely used for screening small molecules across a broad suite of chemistries ranging from food and pharmaceuticals to explosives and environmental toxins. Most modern atmospheric pressure IM detectors employ corona discharge, photoionization, radioactive, or electrospray ion sources for efficient ion production. Coupling standalone DTIMS with ambient plasma-based techniques, however, has proven to be an exceptional challenge. Device sensitivity with near-ground ambient plasma sources is hindered by poor ion transmission at the source-instrument interface, where ion repulsion is caused by the strong electric field barrier of the high potential ion mobility spectrometry (IMS) inlet. To overcome this shortfall, we introduce a new ion source design incorporating a repeller point electrode used to shape the electric field profile and enable ion transmission from a direct analysis in real time (DART) plasma ion source. Parameter space characterization studies of the DART DTIMS setup were performed to ascertain the optimal configuration for the source assembly favoring ion transport. Preliminary system capabilities for the direct screening of solid pharmaceuticals are briefly demonstrated.

Keelor, Joel D.; Dwivedi, Prabha; Fernández, Facundo M.

2014-09-01

129

An effective approach for coupling direct analysis in real time with atmospheric pressure drift tube ion mobility spectrometry.  

PubMed

Drift tube ion mobility spectrometry (DTIMS) has evolved as a robust analytical platform routinely used for screening small molecules across a broad suite of chemistries ranging from food and pharmaceuticals to explosives and environmental toxins. Most modern atmospheric pressure IM detectors employ corona discharge, photoionization, radioactive, or electrospray ion sources for efficient ion production. Coupling standalone DTIMS with ambient plasma-based techniques, however, has proven to be an exceptional challenge. Device sensitivity with near-ground ambient plasma sources is hindered by poor ion transmission at the source-instrument interface, where ion repulsion is caused by the strong electric field barrier of the high potential ion mobility spectrometry (IMS) inlet. To overcome this shortfall, we introduce a new ion source design incorporating a repeller point electrode used to shape the electric field profile and enable ion transmission from a direct analysis in real time (DART) plasma ion source. Parameter space characterization studies of the DART DTIMS setup were performed to ascertain the optimal configuration for the source assembly favoring ion transport. Preliminary system capabilities for the direct screening of solid pharmaceuticals are briefly demonstrated. PMID:24903510

Keelor, Joel D; Dwivedi, Prabha; Fernández, Facundo M

2014-09-01

130

Ion velocity distributions in the vicinity of the current sheet in Earth`s distant magnetotail  

SciTech Connect

Observations of the three-dimensional velocity distributions of positive ions and electrons have been recently gained for the first time in Earth`s distant magnetotail with the Galileo and Geotail spacecraft. For this brief discussion of these exciting results the focus is on the overall character of the ion velocity distributions during substorm activity. The ion velocity distributions within and near the magnetotail current sheet are not accurately described as convecting, isotropic Maxwellians. The observed velocity distributions are characterized by at least two robust types. The first type is similar to the `lima bean`-shaped velocity distributions that are expected from the nonadiabatic acceleration of ions which execute Speiser-type trajectories in the current sheet. The second distribution is associated with the presence of cold ion beams that presumably also arise from the acceleration of plasma mantle ions in the electric and weak magnetic fields in the current sheet. The ion velocity distributions in a magnetic field structure that is similar to that for plasmoids are also examined. Again the velocity distributions are not Maxwellian but are indicative of nonadiabatic acceleration. An example of the pressure tensor within the plasmoid-like event is also presented because it is anticipated that the off-diagonal elements are important in a description of magnetotail dynamics. Thus the concept of magnetotail dynamics must advance from the present assumption of co-moving electron and ion Maxwellian distributions into reformulations in terms of global kinematical models and nonadiabatic particle motion.

Frank, L.A.; Paterson, W.R.; Ackerson, K.L.; Kokubun, S.; Kivelson, M.G.; Yamamoto, T.; Fairfield, D.H.

1994-04-01

131

Ion velocity distributions in the vicinity of the current sheet in Earth's distant magnetotail  

NASA Technical Reports Server (NTRS)

Observations of the three-dimensional velocity distributions of positive ions and electrons have been recently gained for the first time in Earth's distant magnetotail with the Galileo and Geotail spacecraft. For this brief discussion of these exciting results the focus is on the overall character of the ion velocity distributions during substorm activity. The ion velocity distributions within and near the magnetotail current sheet are not accurately described as convecting, isotropic Maxwellians. The observed velocity distributions are characterized by at least two robust types. The first type is similar to the 'lima bean'-shaped velocity distributions that are expected from the nonadiabatic acceleration of ions which execute Speiser-type trajectories in the current sheet. The second distribution is associated with the presence of cold ion beams that presumably also arise from the acceleration of plasma mantle ions in the electric and weak magnetic fields in the current sheet. The ion velocity distributions in a magnetic field structure that is similar to that for plasmoids are also examined. Again the velocity distributions are not Maxwellian but are indicative of nonadiabatic acceleration. An example of the pressure tensor within the plasmoid-like event is also presented because it is anticipated that the off-diagonal elements are important in a description of magnetotail dynamics. Thus our concept of magnetotail dynamics must advance from the present assumption of co-moving electron and ion Maxwellian distributions into reformulations in terms of global kinematical models and nonadiabatic particle motion.

Frank, L. A.; Paterson, W. R.; Ackerson, K. L.; Kokubun, S.; Kivelson, M. G.; Yamamoto, T.; Fairfield, D. H.

1994-01-01

132

Swift heavy ion-induced silicon dioxide nanostructuration: experimental observation of velocity effect  

NASA Astrophysics Data System (ADS)

Thanks to atomic force microscope observation of swift heavy ion-induced structural modifications of SiO2-Si layer, we show that for a given linear energy transfer value the radial atomic modification along the ion track depends on the ion velocity regime.

Touboul, A. D.; Privat, A.; Arinero, R.; Wrobel, F.; Lorfèvre, E.; Saigné, F.

2012-10-01

133

Performance evaluation of a miniature ion mobility spectrometer drift cell for application in hand-held explosives detection ion mobility spectrometers  

Microsoft Academic Search

The implementation of hand-held ion mobility spectrometers (IMS) requires the development and evaluation of miniature drift\\u000a cells providing high sensitivity while maintaining reasonable resolution. This manuscript describes the construction of a\\u000a miniature IMS designed for such an application and its characterization by evaluation of the detection limits and resolution\\u000a of the system with seven explosive compounds including trinitrotoluene (TNT), cyclotrimethylenetrinitramine

J. S. Babis; R. P. Sperline; A. K. Knight; D. A. Jones; C. A. Gresham; M. B. Denton

2009-01-01

134

Measurements of velocity shear and ion viscosity profile in a magnetohydrodynamic plasma jet  

NASA Astrophysics Data System (ADS)

Time-dependent, two-dimensional profiles of the axial flow velocity, density, electron temperature, and magnetic field components are measured at two axial locations in a screw pinch plasma column of the reconnection scaling experiment. The results show that the ion momentum flux for a given column radius is dissipated by the ion-ion Coulomb scattering viscosity due to a significant radial shear of the axial velocity. By comparing the terms of the magnetohydrodynamic momentum balance equation, radial profile of ion viscosity is determined. Chord-integrated ion temperature measurements performed at several radial locations using Doppler broadening spectroscopy show ion temperature of about 1 eV. Measured ion viscosity agrees within a factor of 2 with the classical Braginskii expectations.

Dorf, L. A.; Intrator, T.; Sun, X.; Hendryx, J.; Wurden, G. A.; Furno, I.; Lapenta, G.

2010-10-01

135

Physics-Based Model Driven by Plasma Drifts Obtained From the C\\/NOFS Satellite  

Microsoft Academic Search

An important parameter in determining low-latitude ionospheric plasma density is the plasma drift. Two instruments on-board the Communication\\/Navigation Outage System (C\\/NOFS) satellite were designed to directly or indirectly measure the plasma drifts: the Ion Velocity Drift Meter (IVM) and the Vector Electric Field Instrument (VEFI). By using the electric field measurements obtained from VEFI, the physics-based model (PBMOD) developed at

Y. Su; J. M. Retterer; R. Stoneback; O. de La Beaujardiere; P. A. Roddy; R. A. Heelis; R. F. Pfaff

2010-01-01

136

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

137

Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes  

NASA Technical Reports Server (NTRS)

Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.

Basu, Sunanda; Mackenzie, E.; Basu, S.; Coley, W. R.; Sharber, J. R.; Hoegy, W. R.

1990-01-01

138

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

139

Phase velocities of irregularities in the equatorial electrojet.  

NASA Technical Reports Server (NTRS)

Spectral decomposition of the power spectrum of radar echoes at 50 MHz from the equatorial electrojet reveals information as to the phase velocities of several classes of electron density irregularities and permits inferences as to the electron drift velocity and the electron and ion temperatures in the electrojet. In particular, it is shown that the phase velocity of two-stream irregularities is comparable to the ion-acoustic speed and independent of the horizontal phase velocity of coexistent non-two-stream irregularities. The latter can exceed the ion-acoustic speed and is probably a measure of the electron drift velocity. Thus a probable inference is that the electron drift velocity can itself be supersonic, contrary to some existing theoretical opinions.

Cohen, R.

1973-01-01

140

Ion velocities in direct current arc plasma generated from compound cathodes  

NASA Astrophysics Data System (ADS)

Arc plasma from Ti-C, Ti-Al, and Ti-Si cathodes was characterized with respect to charge-state-resolved ion energy. The evaluated peak velocities of different ion species in plasma generated from a compound cathode were found to be equal and independent on ion mass. Therefore, measured difference in kinetic energies can be inferred from the difference in ion mass, with no dependence on ion charge state. The latter is consistent with previous work. These findings can be explained by plasma quasineutrality, ion acceleration by pressure gradients, and electron-ion coupling. Increasing the C concentration in Ti-C cathodes resulted in increasing average and peak ion energies for all ion species. This effect can be explained by the "cohesive energy rule," where material and phases of higher cohesive energy generally result in increasing energies (velocities). This is also consistent with the here obtained peak velocities around 1.37, 1.42, and 1.55 (104 m/s) for ions from Ti0.84Al0.16, Ti0.90Si0.10, and Ti0.90C0.10 cathodes, respectively.

Zhirkov, I.; Eriksson, A. O.; Rosen, J.

2013-12-01

141

Ion collection by a conducting sphere in a magnetized or drifting collisional plasma  

E-print Network

Ion collection by dust grains and probes in plasmas with a neutral background is of interest in the study of both space and terrestrial plasmas, where charge-exchange collisions can play an important role in ion collection. ...

Haakonsen, Christian Bernt, 1985-

2011-01-01

142

Ion temperature gradient driven impurity modes  

Microsoft Academic Search

The presence of two (or more) species of ions in an inhomogeneous magnetically confined plasma can present opportunities for a new class of drift-type modes to become unstable. When the thermal velocity of a minority ion species (the impurity) is much smaller than that of the primary species, waves with parallel phase velocities intermediate between the two thermal velocities can

S. Migliuolo

1992-01-01

143

Effect of drift-acoustic waves on magnetic island stability in slab geometry  

SciTech Connect

A mathematical formalism is developed for calculating the ion polarization term in the Rutherford island width evolution equation in the presence of drift-acoustic waves. The calculation is fully nonlinear, includes both ion and electron diamagnetic effects, as well as ion compressibility, but is performed in slab geometry. Magnetic islands propagating in a certain range of phase velocities are found to emit drift-acoustic waves. Wave emission gives rise to rapid oscillations in the ion polarization term as the island phase velocity varies, and also generates a net electromagnetic force acting on the island region. Increasing ion compressibility is found to extend the range of phase velocities over which drift-acoustic wave emission occurs in the electron diamagnetic direction.

Fitzpatrick, R.; Waelbroeck, F.L. [Department of Physics, Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2005-12-15

144

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

145

Necessary conditions for peak resolution in an ion mobility increment spectrometer with a flat drift chamber  

NASA Astrophysics Data System (ADS)

New analytical characteristics are proposed to describe the performance of an ion mobility increment spectrometer (IMIS). The dispersion describes the ability of such a spectrometer to separate ions with close values of the variable component of mobility. The necessary resolution limit with respect to this component characterizes the ability to separately detect different ion species. In accordance with the principle of ion separation in this instrument, it is suggested to redefine the resolving power of IMIS as the inverse of the necessary resolution limit with respect to the variable component of mobility.

Shibkov, S. V.; Elistratov, A. A.; Shcherbakov, L. A.

2008-08-01

146

Effect of ion ?B drift direction on density fluctuation poloidal flow and flow shear  

Microsoft Academic Search

The divertor magnetic geometry has a significant effect on the poloidal velocity and resulting velocity shear of turbulent density fluctuations in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with beam emission spectroscopy on DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)]. Plasmas with similar parameters, except that in one case the

C. Fenzi; G. R. McKee; R. J. Fonck; K. H. Burrell; T. N. Carlstrom; R. J. Groebner

2005-01-01

147

Regulation of Ion Drifts and Anisotropies by Parametrically Unstable Finite-amplitude Alfvén-cyclotron Waves in the Fast Solar Wind  

NASA Astrophysics Data System (ADS)

We study the preferential heating and differential acceleration of minor ions by dissipation of ion-acoustic waves (IAWs) generated by parametric instabilities of a finite-amplitude monochromatic Alfvén-cyclotron pump wave. We consider the associated kinetic effects of Landau damping and nonlinear pitch-angle scattering of protons and ? particles in the tenuous plasma of coronal holes and the fast solar wind. Various data collected by Wind spacecraft show signatures for a local transverse heating of the minor ions, presumably by Alfvén-cyclotron wave dissipation, and an unexpected parallel heating by a so far unknown mechanism. Here, we present the results from a set of 1.5 dimensional hybrid simulations in search for a plausible explanation for the observed field-aligned kinetic features in the fast solar wind minor ions. We investigate the origin and regulation of ion relative drifts and temperature anisotropies in low plasma ?, fast solar wind conditions. Depending on their initial drifts, both ion species can heat up not only transversely through cyclotron resonance and non-resonant wave-particle interactions, but also strongly in the parallel direction by Landau damping of the daughter IAWs. We discuss the dependence of the relative ion drifts and temperature anisotropies on the plasma ? of the individual species and we describe the effect of the pump wave amplitude on the ion heating and acceleration.

Maneva, Y. G.; Araneda, J. A.; Marsch, E.

2014-03-01

148

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

149

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

150

Thermal Plasma Imager (TPI): An Imaging Thermal Ion Mass and 3-D Velocity Analyzer  

NASA Astrophysics Data System (ADS)

The Thermal Plasma Imager (TPI) is an imaging thermal ion mass and 3-dimensional (3-D) velocity analyzer. It is designed to measure the instantaneous mass composition and detailed, mass-resolved, 3-dimensional, velocity distributions of thermal-energy (0.5-50 eV/q) ions on a 3-axis stabilized spacecraft. It consists of a pair of semi-toroidal deflection and fast-switching time-of-flight (TOF) electrodes, a hemispherical electrostatic analyzer (HEA), and a micro-channel plate (MCP) detector. It uses the TOF electrodes to clock the flight times of individual incident ions, and the HEA to focus ions of a given energy-per-charge and incident angle (elevation and azimuth) onto a single point on the MCP. The TOF/HEA combination produces an instantaneous and mass-resolved "image" of a 2-D cone of the 3-D velocity distribution for each ion species, and combines a sequence of concentric 2-D conical samples into a 3-D distribution covering 360° in azimuth and 120° in elevation. It is currently under development for the Enhanced Polar Outflow Probe (e-POP) and Planet-C Venus missions. It is an improved, "3-dimensional" version of the SS520-2 Thermal Suprathermal Analyzer (TSA), which samples ions in its entrance aperture plane and uses the spacecraft spin to achieve 3-D ion sampling. In this paper, we present its detailed design characteristics and prototype instrument performance, and compare these with the ion velocity measurement performances from its 2-D TSA predecessor on SS520-2.

Yau, A. W.; Amerl, P. V.; King, E. P.; Miyake, W.; Abe, T.

2003-04-01

151

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

152

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

153

Measurement of Plasma Ion Temperature and Flow Velocity from Chord-Averaged Emission Line Profile  

NASA Astrophysics Data System (ADS)

The distinction between Doppler broadening and Doppler shift has been analysed, the differences between Gaussian fitting and the distribution of chord-integral line shape have also been discussed. Local ion temperature and flow velocity have been derived from the chord-averaged emission line profile by a chosen-point Gaussian fitting technique.

Wei, Xu

2011-06-01

154

Energy loss and straggling of ions with any velocity in dense plasmas at any temperature  

SciTech Connect

The exact random-phase-approximation dielectric function is used to compute the energy loss and straggling of nonrelativistic charged particles in very dense electron fluids (r/sub s/< or =1) at any degeneracy and for any velocity ratio V/V/sub F/. Relevance to ion-driven inertial fusion is stressed.

Maynard, G.; Deutsch, C.

1982-07-01

155

Assessment of turbulent beam ion redistribution in tokamaks through velocity space-dependent gyrokinetic analyses  

NASA Astrophysics Data System (ADS)

We present the interface between a gyrokinetic code and a guiding centre code dedicated to the study of fast ion turbulent transport. A set of velocity space-dependent (kinetic) transport quantities, representing the link between the two codes, is presented. The code suite is applied to DEMO and TCV plasmas. While negligible alpha particle transport is observed for both tokamaks, important beam ion redistribution is obtained for simulations of DEMO. Results for the TCV tokamak demonstrate that the influence of turbulent fields on fast ion transport strongly depends on the plasma scenario.

Albergante, M.; Fasoli, A.; Graves, J. P.; Brunner, S.; Cooper, W. A.

2012-09-01

156

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

PubMed

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 ?=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??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 ?T(i)/T(i)?1%. PMID:21033907

Uzun-Kaymak, I U; Fonck, R J; McKee, G R; Schoenbeck, N; Smith, D; Winz, G; Yan, Z

2010-10-01

157

Electron impact ionization and attachment, drift velocities and longitudinal diffusion in CF3I and CF3I N2 mixtures  

NASA Astrophysics Data System (ADS)

This paper reports the measurement of the electron drift velocity ve, the longitudinal diffusion coefficient NDL and the density-normalized effective ionization coefficient (? - ?)/N in pure CF3I and in the CF3I-N2 mixtures, where ? and ? are the electron impact ionization and attachment coefficients, respectively, and N is the gas density. The E/N range covered was 100-850 Td (1 Td = 10-17 V cm2). The present results were derived from a pulsed Townsend experiment. For pure CF3I, the values of ve and (? - ?)/N were found to increase linearly with E/N. Moreover, the E/N value at which ionization equals attachment, commonly referred to as the limiting field strength, was found to be E/Nlim = 437 Td, which is greater than that of SF6 (360 Td), a widely used insulating gas. For the CF3I-N2 mixture with 70% CF3I, this E/Nlim value was found to be essentially the same as that for pure SF6.

de Urquijo, J.; Juárez, A. M.; Basurto, E.; Hernández-Ávila, J. L.

2007-04-01

158

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 V·cm2), 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

159

Analogous saturation mechanisms of the ion and electron temperature gradient drift wave turbulence.  

PubMed

New experimental results and theoretical arguments indicate that a novel saturation mechanism of the electron temperature gradient modes is related to its coupling to a damped ion acoustic mode. The experimental bicoherence data show multimode coupling between two high frequency radial harmonics of electron temperature gradient in the vicinity of (?2??MHz) and one low frequency ion acoustic (?45??kHz) mode. A unique feedback diagnostic also verifies this coupling. It is pointed out that a near identical mechanism is responsible for ITG mode saturation [V. Sokolov, and A.?K. Sen, Phys. Rev. Lett. 92, 165002 (2004)], indicating its plausible generic nature. PMID:25215988

Sokolov, V; Sen, A K

2014-08-29

160

Analogous Saturation Mechanisms of the Ion and Electron Temperature Gradient Drift Wave Turbulence  

NASA Astrophysics Data System (ADS)

New experimental results and theoretical arguments indicate that a novel saturation mechanism of the electron temperature gradient modes is related to its coupling to a damped ion acoustic mode. The experimental bicoherence data show multimode coupling between two high frequency radial harmonics of electron temperature gradient in the vicinity of (˜2 MHz) and one low frequency ion acoustic (˜45 kHz) mode. A unique feedback diagnostic also verifies this coupling. It is pointed out that a near identical mechanism is responsible for ITG mode saturation [V. Sokolov, and A. K. Sen, Phys. Rev. Lett. 92, 165002 (2004)], indicating its plausible generic nature.

Sokolov, V.; Sen, A. K.

2014-08-01

161

Instabilities of magnetohydrodynamic waves driven by the velocity anisotropy of the energetic ions  

NASA Astrophysics Data System (ADS)

The destabilization of fast magnetoacoustic waves (FMWs) and Alfvén waves (AWs) in plasmas with energetic ions having strongly anisotropic velocity distribution is considered. It is shown that when the ratio of the energetic ion velocity to the Alfvén velocity is large enough, the growth rate of the low-frequency FMW instability has sharp maxima at certain angles of the wave propagation. On the other hand, low-frequency FMWs are always stable, whereas the AWs and high-frequency FMWs can be unstable when the waves propagate along the magnetic field. The developed theory is applied to a plasma of the flashing loops of the Solar Corona. It is found that the presence of a very small amount of the energetic ions can lead to instabilities with the growth rate, which considerably exceeds the inverse characteristic collisional times. It is concluded that the frequency spectrum of the destabilized waves can be rather wide, which may lead to the heating of the bulk plasma ions on the sub-harmonics of the ion gyrofrequency due to the mechanism suggested by Chen et al.

Kolesnychenko, Oleh Ya.; Yukhimuk, Adam K.

2004-04-01

162

Measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry during the 2009 SHARP field campaign  

NASA Astrophysics Data System (ADS)

We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift-chemical ionization mass spectrometry (ID-CIMS). HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. During the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) Field Campaign, HONO measurements were continuously conducted from 1 May to 1 June at a site located on the campus of the University of Houston. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise. The nighttime HONO peaks show close correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry likely contributes to HONO formation. A higher nighttime HONO peak concentration typically precedes a higher and earlier ozone peak concentration of the following day, by about 20 ppb higher and four hours earlier than those with a lower preceding HONO peak concentration. Because of its high detection sensitivity and fast-responding time, the ID-CIMS method described in this work may greatly facilitate HONO detection under typical tropospheric conditions.

Levy, Misti; Zhang, Renyi; Zheng, Jun; Zhang, Annie L.; Xu, Wen; Gomez-Hernandez, Mario; Wang, Yuan; Olaguer, Eduardo

2014-09-01

163

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

164

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

Microsoft Academic Search

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,

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

2004-01-01

165

Ion velocity distribution at the termination shock: 1-D PIC simulation  

NASA Astrophysics Data System (ADS)

The Voyager 2 (V2) plasma observations of the proton temperature downstream of the quasi-perpendicular heliospheric termination shock (TS) showed that upstream thermal solar wind ions played little role in the shock dissipation mechanism and their downstream temperature is an order of magnitude smaller than predicted by MHD Rankine-Hugoniot conditions. While pickup ions (PUI) are generally expected to play an important role in energy dissipation at the shock, the details remain unclear. Here, one-dimensional (1-D) Particle-in-cell (PIC) code is used to examine kinetic properties and downstream velocity distribution functions of pickup ions (the hot supra-thermal component) and solar wind protons (SWs, the cold component) at the perpendicular heliospheric termination shock. The code treats the pickup ions self-consistently as a third component. Present results show that: (1) both of the incident SWs and PUIs can be separated into two parts: reflected (R) ions and directly transmitted (DT) ions, the energy gain of the R ions at the shock front is much larger than that of the DT ions; (2) the fraction of reflected SWs and their downstream temperature decrease with the relative percentage PUI%; (3) no matter how large the PUI% is, the downstream ion velocity distribution function always can be separated into three parts: 1. a high energy tail (i.e. the wings) dominated by the reflected PUIs, 2. a low energy core mainly contributed by the directly transmitted SWs, and 3. a middle energy part which is a complicated superposition of reflected SWs and directly transmitted PUIs. The significance of the presence of pickup ions on shock front micro-structure and nonstationarity is also discussed.

Lu, Quanming; Yang, Zhongwei; Lembège, Bertrand

2012-11-01

166

Collision-induced dissociation of mobility-separated ions using an orifice-skimmer cone at the back of a drift tube.  

PubMed

An ion mobility-mass spectrometry technique that incorporates a differentially pumped orifice-skimmer cone (OSC) region at the exit of the drift tube has been developed. The OSC region is similar in design to those used in electrospray ionization sources and offers improvements in ion transmission (by factors of approximately 5-10 compared with previous designs) and the ability to induce fragmentation of mobility-separated ions. The separation of ions prior to dissociation at the skimmer cone allows the origin of fragment ions to be examined. Here, we describe the experimental design and demonstrate the approach by examining fragment ions that are common to multiple charge states and different gas-phase ion conformations of electrosprayed angiotensin II and [Sar1, Val5, Ala8] angiotensin II peptides. PMID:11510817

Lee, Y J; Hoaglund-Hyzer, C S; Taraszka, J A; Zientara, G A; Counterman, A E; Clemmer, D E

2001-08-01

167

Conformational ordering of biomolecules in the gas phase: nitrogen collision cross sections measured on a prototype high resolution drift tube ion mobility-mass spectrometer.  

PubMed

Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (±0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid "omni-omic" characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field. PMID:24446877

May, Jody C; Goodwin, Cody R; Lareau, Nichole M; Leaptrot, Katrina L; Morris, Caleb B; Kurulugama, Ruwan T; Mordehai, Alex; Klein, Christian; Barry, William; Darland, Ed; Overney, Gregor; Imatani, Kenneth; Stafford, George C; Fjeldsted, John C; McLean, John A

2014-02-18

168

Conformational Ordering of Biomolecules in the Gas Phase: Nitrogen Collision Cross Sections Measured on a Prototype High Resolution Drift Tube Ion Mobility-Mass Spectrometer  

PubMed Central

Ion mobility-mass spectrometry measurements which describe the gas-phase scaling of molecular size and mass are of both fundamental and pragmatic utility. Fundamentally, such measurements expand our understanding of intrinsic intramolecular folding forces in the absence of solvent. Practically, reproducible transport properties, such as gas-phase collision cross-section (CCS), are analytically useful metrics for identification and characterization purposes. Here, we report 594 CCS values obtained in nitrogen drift gas on an electrostatic drift tube ion mobility-mass spectrometry (IM-MS) instrument. The instrument platform is a newly developed prototype incorporating a uniform-field drift tube bracketed by electrodynamic ion funnels and coupled to a high resolution quadrupole time-of-flight mass spectrometer. The CCS values reported here are of high experimental precision (±0.5% or better) and represent four chemically distinct classes of molecules (quaternary ammonium salts, lipids, peptides, and carbohydrates), which enables structural comparisons to be made between molecules of different chemical compositions for the rapid “omni-omic” characterization of complex biological samples. Comparisons made between helium and nitrogen-derived CCS measurements demonstrate that nitrogen CCS values are systematically larger than helium values; however, general separation trends between chemical classes are retained regardless of the drift gas. These results underscore that, for the highest CCS accuracy, care must be exercised when utilizing helium-derived CCS values to calibrate measurements obtained in nitrogen, as is the common practice in the field. PMID:24446877

2014-01-01

169

Stokes Drift for Random Gravity Waves  

Microsoft Academic Search

Introduction. The modified form of the Stokes drift velocity [Stokes, 1847] for a random sea is briefly considered. For a statistically stationary and horizontally homogeneous wave field, the total wave drift is the sum of the drifts of the individual wave components. The expression for the Stokes drift, given here in terms of the full two-dimensionM energy spectrum for arbitrary

Kern E. Kenyon

1969-01-01

170

Nonlinear drift-diffusion model of gating in K and nACh ion channels  

NASA Astrophysics Data System (ADS)

The configuration of a sensor regulates the transition between the closed and open states of both voltage and ligand gated channels. The closed state dwell-time distribution f(t) derived from a Fokker Planck equation with a nonlinear diffusion coefficient is in good agreement with experimental data and can account for the power law approximation to f(t) for a delayed rectifier K channel and a nicotinic acetylcholine (nACh) ion channel. The solution of a master equation which approximates the Fokker Planck equation provides a better description of the small time behaviour of the dwell-time distribution and can account for the empirical rate-amplitude correlation for these ion channels.

Vaccaro, S. R.

2007-09-01

171

Interpretation of nonlinear wave structures in the F-region of the ionosphere, registered by DE2 satellite as ion-cyclotron gradient-drift solitons with chirp  

NASA Astrophysics Data System (ADS)

On the basis of satellite DE2 data in the middle latitude ionosphere authors show that wave fluctuations exhibit properties of nonlinear ion-cyclotron gradient-drift structures, theoretically considered by the authors earlier [1,2]. The main property of the structures is excitation on transversal gradient of single ion concentration. For geomagnetically calm days distributions of the fluctuations along satellite trajectory are analyzed. The total ion concentration monotonically grows or decreases and has no sharp gradients along trajectory but concentrations of O+, N+ or H+ ions has sharp gradients. The fluctuations power follow O+, N+ tranversal gradient in middle and low latitudes and H+, He+ gradient in subauroral latitudes. The variations of electric field do not influence the fluctuation power. The theoretical structure is composed of the ion concentration asymmetric hump or hole and wave packet (ion-cyclotron envelope soliton - oscilliton) on the trailing sharp edge of it. The spike form of experimental signal confirms this hypothesis. The authors give some examples (when instrument resolution is appropriate) where wave packets are situated on the sharp edge of density hump or hole. Analysis confirms the justification of the interpretation of these signals as ion-cyclotron gradient-drift solitons with chirp-oscillitons. [1]Kovaleva I.Kh.//Phys plasmas, 19, 102905, doi: 10.1063/1.4763561,2012 [2]Kovaleva I.Kh.//Plasma Phys Reports 39, 3, pp226-235, 2013

Kovaleva, Irina

172

Low energy electron and nuclear recoil thresholds in the DRIFT-II negative ion TPC for dark matter searches  

NASA Astrophysics Data System (ADS)

Understanding the ability to measure and discriminate particle events at the lowest possible energy is an essential requirement in developing new experiments to search for weakly interacting massive particle (WIMP) dark matter. In this paper we detail an assessment of the potential sensitivity below 10 keV in the 1 m3 DRIFT-II directionally sensitive, low pressure, negative ion time projection chamber (NITPC), based on event-by-event track reconstruction and calorimetry in the multiwire proportional chamber (MWPC) readout. By application of a digital smoothing polynomial it is shown that the detector is sensitive to sulfur and carbon recoils down to 2.9 and 1.9 keV respectively, and 1.2 keV for electron induced events. The energy sensitivity is demonstrated through the 5.9 keV gamma spectrum of 55Fe, where the energy resolution is sufficient to identify the escape peak. The effect of a lower energy sensitivity on the WIMP exclusion limit is demonstrated. In addition to recoil direction reconstruction for WIMP searches this sensitivity suggests new prospects for applications also in KK axion searches.

Burgos, S.; Daw, E.; Forbes, J.; Ghag, C.; Gold, M.; Hagemann, C.; Kudryavtsev, V. A.; Lawson, T. B.; Loomba, D.; Majewski, P.; Muna, D.; Murphy, A. St. J.; Paling, S. M.; Petkov, A.; Plank, S. J. S.; Robinson, M.; Sanghi, N.; Snowden-Ifft, D. P.; Spooner, N. J. C.; Turk, J.; Tziaferi, E.

2009-04-01

173

Effects of nonresonant hot ions with large orbits on Alfvén cascades and on magnetohydrodynamic instabilities in tokamaks  

Microsoft Academic Search

The effects of nonresonating hot ions on the spectrum of magnetohydrodynamic (MHD) waves and instabilities in tokamaks are studied in the limit when the width of the hot ion drift orbits is much larger than the radial scale length of the MHD perturbations. Due to the large magnetic drift velocities the hot ions cannot contribute to the MHD perturbations directly,

S. E. Sharapov; A. B. Mikhailovskii; G. T. A. Huysmans

2004-01-01

174

Effects of nonresonant hot ions with large orbits on Alfve´n cascades and on magnetohydrodynamic instabilities in tokamaks  

Microsoft Academic Search

The effects of nonresonating hot ions on the spectrum of magnetohydrodynamic (MHD) waves and instabilities in tokamaks are studied in the limit when the width of the hot ion drift orbits is much larger than the radial scale length of the MHD perturbations. Due to the large magnetic drift velocities the hot ions cannot contribute to the MHD perturbations directly,

S. E. Sharapov; A. B. Mikhailovskii; G. T. A. Huysmans

2004-01-01

175

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

NASA Astrophysics Data System (ADS)

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 RFP geometry by modifying the gyrokinetic code GYROfootnotetextJ. Candy and R.E. Waltz, J. Comp. Phys. 186, 545 (2003). in a low beta, collisionless limit with and without non-adiabatic electrons. A simple toroidal equilibrium has been devised that is specified by just two parameters: the pinch parameter and the radial position. The level of transport is shown to be sensitive to temperature and density gradients and the threshold is found. To determine the nature of the instability, we study parametric scaling and also compare results with the well-known CYCLONE base case for tokamak simulations. We also estimate mixing level transport for MST parameters using linear simulations to determine if the instability is relevant to the small-scale turbulence observed in MST.

Tangri, Varun; Terry, Paul; Waltz, R. E.

2009-11-01

176

Velocity filter mechanism for ion bowl disributions (Bimodal conics). [in high altitude auroral regions  

NASA Technical Reports Server (NTRS)

The 'bowl-shaped' ion distributions in the high altitude auroral region observed by Klumpar et al. (1984) were originally interpreted as being due to a two-stage acceleration involving transverse ion heating and upward-aligned electric field acceleration. In this paper, it is shown that qualitatively similar bowl-shaped distributions can also be formed by transverse heating in a region of finite horizontal extent, followed by essentially adiabatic convective flow to the observation location. The latter stage contributes a velocity-filtering effect which produces some characteristics of the distributions observed. It is suggested it may be possible to use ion species observations to distinguish the mechanism proposed by Klumpar et al. from the alternative mechanism outlined in the present study.

Horwitz, J. L.

1986-01-01

177

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

178

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

179

Drift model of the cathode region of a glow discharge  

NASA Astrophysics Data System (ADS)

A one-dimensional drift model of the cathode region of a glow discharge with allowance for both electron-impact ionization and charged particle loss is proposed. An exact solution to the model equations is obtained for the case of similar power-law dependences of the ion and electron drift velocities on the electric field strength. It is shown that, even in the drift approximation, a relatively wide transition layer in which the ion-to-electron current ratio approaches a constant value typical of the positive column of a glow discharge should occur between the thin space-charge sheath and the quasineutral plasma, the voltage drop across the space-charge sheath being comparable to that across the transition layer. The calculated parameters of the normal and anomalous glow discharges are in good agreement with available experimental data.

Kozhevnikov, V. Yu.; Kozyrev, A. V.; Korolev, Yu. D.

2006-11-01

180

Ion heating and saturation in the presence of transverse velocity-shear-driven waves  

NASA Astrophysics Data System (ADS)

The nature of ion heating and saturation in the presence of waves driven by transverse-velocity shear is investigated in a Q-machine(N. Rynn and N. D'Angelo, Rev. Sci. Instrum. 31), 1326 (1960). using laser-induced-fluorescence (LIF)(D.N. Hill, S. Fornaca and M.G. Wickham, Rev. Sci. Instrum. 54), 301 (1983). techniques. Correlations in space and time between the waves and heating are presented. Ion heating for shear-driven waves is compared to that for current-driven waves, with the expectation that shear-driven waves are better suited for ion heating than the current-driven waves, since the shear-driven growth rate decreases substantially less than the current-driven growth rate as the ion-to-electron temperature ratio increases.(V. Gavrishchaka, M.E. Koepke and G. Ganguli, Phys. Plasmas 3), 3091 (1996). Relevance to ion heating in space plasmas will be addressed.(Norqvist et al.), J. Geophys. Res. 101, 13179 (1996); Ganguli et al., Geophys. Res. Lett. 12, 643 (1985). Work sponsored by ONR and NSF.

Zintl, M. W.; Koepke, M. E.; Carroll, J. J., III; Selcher, C. A.

1996-11-01

181

Phase-Resolved Measurements of Ion Velocity in a Radio-Frequency Sheath Brett Jacobs,1,* Walter Gekelman,1  

E-print Network

Phase-Resolved Measurements of Ion Velocity in a Radio-Frequency Sheath Brett Jacobs,1,* Walter by Stern and Johnson [4]. The first experi- ments used low power cw lasers and signal averaging to study

California at Los Angles, University of

182

MEASUREMENTS OF ANISOTROPIC ION TEMPERATURES, NON-THERMAL VELOCITIES, AND DOPPLER SHIFTS IN A CORONAL HOLE  

SciTech Connect

We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities, as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as an independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low-latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived ion temperatures T {sub i,} and T {sub i, Parallel-To} and non-thermal velocities v {sub nt,} and v {sub nt, Parallel-To }. T {sub i,} was cooler than off-limb polar coronal hole measurements, suggesting increasing collisional cooling with decreasing height. T {sub i, Parallel-To} is consistent with a uniform temperature of (1.8 {+-} 0.2) Multiplication-Sign 10{sup 6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R {sub Sun }. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for v {sub nt,} agree with Alfven wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our v {sub nt, Parallel-To} results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time-varying intensity fluctuations. Doppler shift measurements yield outflows of Almost-Equal-To 5 km s{sup -1} for ions formed over a broad temperature range. This differs from other studies that found a strong Doppler shift dependence on formation temperature.

Hahn, M.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States)] [Columbia Astrophysics Laboratory, Columbia University, MC 5247, 550 West 120th Street, New York, NY 10027 (United States)

2013-02-15

183

Design and test of a superconducting structure for high-velocity ions  

SciTech Connect

Following the successful development of a niobium coaxial half-wave structure we have designed, built and tested a new half-wave geometry: the spoke resonator. This geometry is better suited for high frequency resonators and for the acceleration of high velocity ions. The prototype cavity is a 2-gap structure resonating at 855 MHz, and optimized for particle velocity of 0.30 c. It is easier to manufacture than the coaxial half-wave resonator and the geometry can be straightforwardly extended to multigap designs. Rf-tests have been performed on this cavity both prior to and after high temperature annealing. An accelerating gradient of 7.2 MV/m (cw) and 7.8 MV/m (pulsed) was observed at 4.2 K. After annealing, a low power Q{sub 0} of 1.2 {times}10{sup 8} was observed with small Q degradation due to field emission at high accelerating fields.

Delayen, J.R.; Kennedy, W.L.; Roche, C.T.

1992-01-01

184

Design and test of a superconducting structure for high-velocity ions  

SciTech Connect

Following the successful development of a niobium coaxial half-wave structure we have designed, built and tested a new half-wave geometry: the spoke resonator. This geometry is better suited for high frequency resonators and for the acceleration of high velocity ions. The prototype cavity is a 2-gap structure resonating at 855 MHz, and optimized for particle velocity of 0.30 c. It is easier to manufacture than the coaxial half-wave resonator and the geometry can be straightforwardly extended to multigap designs. Rf-tests have been performed on this cavity both prior to and after high temperature annealing. An accelerating gradient of 7.2 MV/m (cw) and 7.8 MV/m (pulsed) was observed at 4.2 K. After annealing, a low power Q{sub 0} of 1.2 {times}10{sup 8} was observed with small Q degradation due to field emission at high accelerating fields.

Delayen, J.R.; Kennedy, W.L.; Roche, C.T.

1992-10-01

185

Drift waves in the corona: heating and acceleration of ions at frequencies far below the gyro frequency  

Microsoft Academic Search

In the solar corona, several mechanisms of the drift wave instability can\\u000amake the mode growing up to amplitudes at which particle acceleration and\\u000astochastic heating by the drift wave take place. The stochastic heating, well\\u000aknown from laboratory plasma physics where it has been confirmed in numerous\\u000aexperiments, has been completely ignored in past studies of coronal heating.\\u000aHowever,

J. Vranjes; S. Poedts

2010-01-01

186

On velocity-space sensitivity of fast-ion D-alpha spectroscopy  

NASA Astrophysics Data System (ADS)

The velocity-space observation regions and sensitivities in fast-ion D? (FIDA) spectroscopy measurements are often described by so-called weight functions. Here we derive expressions for FIDA weight functions accounting for the Doppler shift, Stark splitting, and the charge-exchange reaction and electron transition probabilities. Our approach yields an efficient way to calculate correctly scaled FIDA weight functions and implies simple analytic expressions for their boundaries that separate the triangular observable regions in (v?, v?)-space from the unobservable regions. These boundaries are determined by the Doppler shift and Stark splitting and could until now only be found by numeric simulation.

Salewski, M.; Geiger, B.; Moseev, D.; Heidbrink, W. W.; Jacobsen, A. S.; Korsholm, S. B.; Leipold, F.; Madsen, J.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

2014-10-01

187

Ion Bernstein waves in a plasma with a kappa velocity distribution  

SciTech Connect

Using a Vlasov-Poisson model, a numerical investigation of the dispersion relation for ion Bernstein waves in a kappa-distributed plasma has been carried out. The dispersion relation is found to depend significantly on the spectral index of the ions, ?{sub i}, the parameter whose smallness is a measure of the departure from thermal equilibrium of the distribution function. Over all cyclotron harmonics, the typical Bernstein wave curves are shifted to higher wavenumbers (k) if ?{sub i} is reduced. For waves whose frequency lies above the lower hybrid frequency, ?{sub LH}, an increasing excess of superthermal particles (decreasing ?{sub i}) reduces the frequency, ?{sub peak}, of the characteristic peak at which the group velocity vanishes, while the associated k{sub peak} is increased. As the ratio of ion plasma to cyclotron frequency (?{sub pi}/?{sub ci}) is increased, the fall-off of ? at large k is smaller for lower ?{sub i} and curves are shifted towards larger wavenumbers. In the lower hybrid frequency band and harmonic bands above it, the frequency in a low-?{sub i} plasma spans only a part of the intraharmonic space, unlike the Maxwellian case, thus exhibiting considerably less coupling between adjacent bands for low ?{sub i}. It is suggested that the presence of the ensuing stopbands may be a useful diagnostic for the velocity distribution characteristics. The model is applied to the Earth's plasma sheet boundary layer in which waves propagating perpendicularly to the ambient magnetic field at frequencies between harmonics of the ion cyclotron frequency are frequently observed.

Nsengiyumva, F.; Mace, R. L.; Hellberg, M. A. [School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa)] [School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4000 (South Africa)

2013-10-15

188

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

SciTech Connect

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 [Department of Physics, West Virginia University, Morgantown West Virginia 26508 (United States); Space Plasma and Plasma Processing group, Plasma Research Laboratory, Research School of Physical Sciences and Engineering, The Australian National University, Canberra ACT 0200 (Australia)

2005-09-15

189

Ion-cyclotron waves in the presence of transverse-velocity shear  

NASA Astrophysics Data System (ADS)

Maximum velocity and radial dimension associated with a thin layer of sheared E×B flow are measured and adjusted within a range relevant to the velocity-shear instability of Ganguli et al.(Ganguli et al.), Phys. Fluids 31, 823 (1988). These two parameters influence the properties of ion-cyclotron turbulence excited in the shear layer.(Gavrishchaka et al.), Phys. Plasmas 3, 3091 (1996). Comparisons are made between experiment and theory, especially excitation thresholds, frequency, wavelength, and mode amplitude. An adjustable-diameter iris diaphragm and a fixed-diameter disk are used in the double-ended operation of the WVU Q-machine to generate the desired radial profiles of electric field and magnetic field-aligned current. Efforts to document the transition between predominately dissipative (Koepke et al.), Phys. Plasmas 2, 2523 (1995). and predominately reactive (Amatucci et al.), Phys. Rev. Lett. (accepted 1996). responses of the instability mechanism will be presented. These waves have been invoked to explain ion heating in space.(Moore et al.), J. Geophys. Res. 101, 5279 (1996). Work supported by ONR and NSF.

Carroll, J. J., III; Koepke, M. E.; Zintl, M. W.; Selcher, C. A.

1996-11-01

190

ION TEMPERATURE AND NON-THERMAL VELOCITY IN A SOLAR ACTIVE REGION: USING EMISSION LINES OF DIFFERENT ATOMIC SPECIES  

SciTech Connect

We have studied the characteristics of the ion thermal temperature and non-thermal velocity in an active region observed by the EUV Imaging Spectrometer onboard Hinode. We used two emission lines of different atomic species (Fe XVI 262.98 A and S XIII 256.69 A) to distinguish the ion thermal velocity from the observed full width at half-maximum. We assumed that the sources of the two emission lines are the same thermal temperature. We also assumed that they have the same non-thermal velocity. With these assumptions, we could obtain the ion thermal temperature, after noting that M{sub sulfur} approx 0.6M{sub iron}. We have carried out the ion thermal temperature analysis in the active region where the photon counts are sufficient (>4500). What we found is as follows: (1) the common ion thermal temperatures obtained by Fe XVI and S XIII are approx2.5 MK, (2) the typical non-thermal velocities are approx13 km s{sup -1}, (3) the highest non-thermal velocities (>20 km s{sup -1}) are preferentially observed between the bright points in Fe XVI, while (4) the hottest material (>3 MK) is observed relatively inside the bright points compared with the highest non-thermal velocity region.

Imada, S.; Hara, H.; Watanabe, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka-shi, Tokyo 181-8588 (Japan)

2009-11-10

191

Ion heating in the presheath  

SciTech Connect

A one-dimensional model of a small plasma ion source (10 cm long) is studied. A hybrid simulation where ions are treated as particles and electrons as a fluid obeying the Boltzmann relation is used to investigate ion heating in the plasma presheath. At low pressure (below a few mTorr), the ion velocity distribution is Maxwellian in the bulk and becomes a drifting Maxwellian distribution while transiting the presheath. The distribution remains essentially isotropic as the ions are accelerated through the presheath to satisfy the Bohm criterion. At intermediate pressures (around 10 mTorr), ion-neutral collisions scatter a significant part of the ion kinetic energy from the parallel direction to the perpendicular direction, leading to a net heating of the ions. In addition, the ion velocity distribution becomes distinctly anisotropic. At higher pressure (above a few tens of mTorr), ion heating is still observed, but yields isotropic ion velocity distributions.

Meige, Albert; Sutherland, Orson; Smith, Helen B.; Boswell, Rod W. [Space Plasma Power and Propulsion Group, Research School of Physical Sciences and Engineering, Australian National University, ACT 0200 (Australia)

2007-03-15

192

Global equatorial ionospheric vertical plasma drifts measured by the AE-E satellite  

NASA Technical Reports Server (NTRS)

Ion drift meter observations from the Atmosphere Explorer E (AE-E) satellite during the period of January 1977 to December 1979 are used to study the dependence of equatorial (dip latitudes less than or equal to 7.5 deg) F region vertical plasma drifts (east-west electric fields) on solar activity, season, and longitude. The satellite-observed ion drifts show large day-to-day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The diuurnal, seasonal, and solar cycle dependence of the logitudinally averaged drifts are consistent with results from the Jicamarca radar except near the June solstice when the AE-E nighttime downward velocities are significantly smaller than those observed by the radar. Pronounced presunrise downward drift enhancements are often observed over a large longituudinal range but not in the Peruvian equatorial region. The satellite data indicate that longitudinal variations are largest near the June solstice, particularly near dawn and dusk but are virtually absent during equinox. The longitudinal dependence of the AE-E vertical drifts is consistent with results from ionosonde data. These measurements were also used to develop a description of equatorial F region vertical drifts in four longitudinal sectors.

Fejer, B. G.; De Paula, E. R.; Heelis, R. A.; Hanson, W. B.

1995-01-01

193

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

194

Generalized drift-flux correlation  

SciTech Connect

A one-dimensional drift-flux model with five conservation equations is frequently employed in major computer codes, such as TRAC-PD2, and in simulator codes. In this method, the relative velocity between liquid and vapor phases, or slip ratio, is given by correlations, rather than by direct solution of the phasic momentum equations, as in the case of the two-fluid model used in TRAC-PF1. The correlations for churn-turbulent bubbly flow and slug flow regimes were given in terms of drift velocities by Zuber and Findlay. For the annular flow regime, the drift velocity correlations were developed by Ishii et al., using interphasic force balances. Another approach is to define the drift velocity so that flooding and liquid hold-up conditions are properly simulated, as reported here. The generalized correlation is used to reanalyze the MB-2 test data for two-phase flow in a large-diameter pipe. The results are applied to the generalized drift flux velocity, whose relationship to the other correlations is discussed. Finally, the generalized drift flux correlation is implemented in TRAC-PD2. Flow reversal from countercurrent to cocurrent flow is computed in small-diameter U-shaped tubes and is compared with the flooding curve.

Takeuchi, K.; Young, M.Y.; Hochreiter, L.E. (Westinghouse Electric Corp., Pittsburgh, PA (United States))

1991-01-01

195

Characterization of Oscillations in Closed Drift Thrusters Edgar Y. Choueiri  

E-print Network

(especially compared to electrostatic ion propulsion). Nominal operating conditions wiCharacterization of Oscillations in Closed Drift Thrusters Edgar Y. Choueiri Electric Propulsion propagating "transit-time" os- cillations, high frequency azimuthal drift waves, ion- ization instability

Choueiri, Edgar

196

Drift-tearing magnetic islands in tokamak plasmas  

SciTech Connect

A systematic fluid theory of nonlinear magnetic island dynamics in conventional low-{beta}, 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 Alfven 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. [Institute for Fusion Studies, Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

2008-01-15

197

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

198

Interpretation of neutral particle analyzer measurements on plasmas having azimuthal drift  

NASA Technical Reports Server (NTRS)

The theoretical model accounts for drift and cyclotron components of ion motion in a partially ionized plasma. Density and velocity distributions are systematically prescribed. The flux into the neutral particle analyzer (NPA) from this plasma is determined by summing over all charge exchange neutrals in phase space which are directed into apertures. Calculation of the process is continued through the NPA using appropriate cross section data to obtain analyzer output distributions. Theoretical results were compared with NPA measurements on four plasma heating devices having radial electric, E, and axial magnetic, B, fields. Drift velocity, in the azimuthal direction is identified with E/B. Selection of randomized cyclotron velocity distributions about mean azimuthal drift yield energy distributions which compare well with experiment.

Englert, G. W.; Reinmann, J. J.; Lauver, M. R.

1975-01-01

199

Ion velocity measurements on NSTX using the SWIFT diagnostic (Shifted Wavelength/lnterference Filter Technique)  

NASA Astrophysics Data System (ADS)

Using a split-image interference filter technique, the measurement of ion flows is being extended from individual analog channels (as implemented on Columbia's HBT-EP tokamak) to a 2-D view on NSTX. A beam-splitter duplicates the image, each of which is then filtered with separate interference filters whose passbands have opposite linear slopes. A high frame-rate Photron Ltd. U1tima SE CMOS digital camera views He II line emission at 468.6 nm at the edge of the center stack. A white-plate calibration of two 64 x 64 pixel regions of the detector in necessary to measure relative gain and linearity of the corresponding pixes. A spectral high-resolution wavelength calibration is done for each pixel-pair, probably requiring the use of a tunable, narrow-band, bright light source such as a dye-laser. But once completed, the ion velocity can be calculated very simply from the ratio of the intensities from the two images. From data taken when viewing through a He II interference filter, the light level in helium discharges in NSTX is adequate to make observations at 1,150 frames per second. A preliminary optical system was bench-tested and the lens used can image a 20 x 20 cm region of the plasma with 0.3 mm spatial resolution.

Paul, Stephen; Kaita, Robert; Roquemore, A. Lane; Nishino, Nobuhiro

2006-10-01

200

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

201

Ion Beam Heating in the Auroral Zone  

NASA Technical Reports Server (NTRS)

Recent satellite observations at high altitudes (greater than 5000 km) in the auroral zone have shown the existence of hybrid or bimodal ion beam distributions that are evidence of both parallel and perpendicular ion acceleration. Acceleration parallel to the magnetic field is most likely due to quasi-static electric fields (double layers) which can create outflowing ion beams; since ions of different mass will have different drift speeds due to this acceleration, a plasma configuration unstable to the ion-ion two-stream acoustic mode develops. When the net drift velocity (U) between the two ion species is greater than the sound speed (C(sub 0)), the ion-ion instability has maximum growth at oblique wave propagation. To study the nonlinear effects of the ion-ion instability in terms of plasma heating, a numerical simulation parametric study has been performed. It was found that the parallel acceleration that forms the ion beams occurs on a time scale faster than ion- ion wave growth at low drifts; thus ion-ion wave growth is expected to occur primarily for higher drift speeds (U greater than C(sub 0)) which results in strong oblique heating of the ions (both hydrogen and oxygen) forming elevated ion conics (sometimes called 'bowl' distributions). Also, strong parallel electron heating in the direction of the ion beams can occur, and electrons near the top of the acceleration region may attain a net upward drift along with the elevated ion conics. Variation of the oxygen density greatly affects the ion heating due to the ion-ion instability; as the oxygen density decreases, oxygen heating increases, in agreement with observations (Collin et al., 1987). Ion-ion electrostatic wave properties and the plasma heating that results over a wide range of auroral zone parameters are included.

Schriver, David; Ashour-Abdalla, Maha; Collin, Henry; Lallande, Nicole

1990-01-01

202

Analysis of Operation Gas Contamination Sources in the PHENIX Drift Chamber Using Electron Drift  

E-print Network

of operation gas. Original methodic was developed to indirectly estimate the absolute value of admixtures flow distinguishing the different sources of gas contamination according to their influence on drift velocity in Ar/C2Analysis of Operation Gas Contamination Sources in the PHENIX Drift Chamber Using Electron Drift

Titov, Anatoly

203

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

SciTech Connect

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 [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)] [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Zhang, Yiting; Kushner, Mark J. [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)

2013-08-15

204

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

205

Genetic Drift  

NSDL National Science Digital Library

In this biology simulation, students use a mathematical simulation of genetic drift to answer questions about the factors that influence this evolutionary process. Students run a series of simulations varying allele frequency and population size and then analyze their data and propose a model to explain their results.

Cooper, Scott

206

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

207

Effects of large zonal plasma drifts on the subauroral ionosphere  

NASA Technical Reports Server (NTRS)

A model of the earth's ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift of maximum velocity 2 km/s. A closed subauroral tube of plasma is considered and the velocity spike persists for 10 min. Ion-neutral frictional heating causes rapid elevation of the F-region O(+) temperature. The F-layer O(+) concentration is decreased due to increased O(+) loss rate and rapid ion flows both upward and downward from the F-region. The upward flux of O(+) through the topside ionosphere can each 5 x 10 exp 9/sq cm/s; when the velocity spike ceases there is a return flow of O(+) that tends to replenish the F-layer. Most of the features revealed by the model for the F-region and topside ionosphere are in accord with observations of subauroral ion drifts. Downward flows that are predicted to be persistently present around the 300 km altitude level appear to agree with observations only occasionally; suggestions are made to resolve this discrepancy.

Sellek, R.; Bailey, G. J.; Moffett, R. J.; Heelis, R. A.; Anderson, P. C.

1991-01-01

208

Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging  

NASA Astrophysics Data System (ADS)

Dissociative photoionization of methyl bromide (CH3Br) in an excitation energy range of 10.45-16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X2E of CH3Br+ is stable, and both A2A1 and B2E ionic excited states are fully dissociative to produce the unique fragment ion of CH3+. From TPEPICO 3D time-sliced velocity images of CH3+ dissociated from specific state-selected CH3Br+ ion, kinetic energy release distribution (KERD) and angular distribution of CH3+ fragment ion are directly obtained. Both spin-orbit states of Br(2P) atom can be clearly observed in fast dissociation of CH3Br+(A2A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br+(B2E) ion. With the aid of the re-calculated potential energy curves of CH3Br+ including spin-orbit coupling, dissociation mechanisms of CH3Br+ ion in A2A1 and B2E states along C-Br rupture are revealed. For CH3Br+(A2A1) ion, the CH3+ + Br(2P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br(2P3/2) formation is through vibronic coupling to the high vibrational level of X2E state followed by rapid dissociation. C-Br bond breaking of CH3Br+(B2E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

Tang, Xiaofeng; Zhou, Xiaoguo; Sun, Zhongfa; Liu, Shilin; Liu, Fuyi; Sheng, Liusi; Yan, Bing

2014-01-01

209

High-velocity, multistage, nozzled, ion driven wind generator and method of operation of the same adaptable to mesoscale realization  

NASA Technical Reports Server (NTRS)

Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, a methodology for increasing their flow velocities includes exploitation of the divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. The design becomes particularly advantageous when implemented in mesoscale domains.

Dunn-Rankin, Derek (Inventor); Rickard, Matthew J. A. (Inventor)

2011-01-01

210

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

Microsoft Academic Search

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,

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

2005-01-01

211

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

National Technical Information Service (NTIS)

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 ...

H. Qin, R. C. Davidson, J. J. Barnard, E. P. Lee

2005-01-01

212

Effects of ion drift on time-over-threshold charge estimates using first-order integrators in thermal neutron MWPC  

E-print Network

Time-over-threshold measurements of the output of a first order integration amplifier can be used as a cheap way to estimate the charge deposited on a wire in an MWPC. Even if the time scale of the first order system is seemingly much larger than the signal development time, we noticed experimentally a significant deviation from the relationship of time-over-threshold and the charge, as would be naively expected from the exponential response of the amplifier. We strongly suspect the current induced by the residual ion movement to be at least partially responsible for this observation. It is of course well-known that the ion movement is responsible for the bulk of the signal generation in a wire chamber, this is not the point ; however, the surprise is rather that this movement has influences on time scales which are so long that the finite ion movement could be thought negligible. In this paper we will treat theoretically the influence of ion movement and of AC coupling on the expected time-over-threshold rel...

Van Esch, P; Durand, Thomas; Esch, Patrick Van

2006-01-01

213

Continental Drift  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on Alfred Wegener's theory of Continental Drift and the evidence used to support it. Using fossil types and maps, students view similarities between continents that led Wegener to conclude that they had once been together as a supercontinent, Pangea. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

214

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

215

Search for auroral belt E-parallel fields with high-velocity barium ion injections  

NASA Technical Reports Server (NTRS)

In April 1984, four high-velocity shaped-charge Ba(+) injections were conducted from two sounding rockets at 770-975 km over northern Alaska under conditions of active auroral and magnetic disturbance. Spatial ionization (brightness) profiles of high-velocity Ba(+) clouds from photometric scans following each release were found to be consistent with the 28-sec theoretical time constant for Ba photoionization determined by Carlsten (1975). These observations therefore revealed no evidence of anomalous fast ionization predicted by the Alfven critical velocity hypothesis.

Heppner, J. P.; Ledley, B. G.; Miller, M. L.; Marionni, P. A.; Pongratz, M. B.

1989-01-01

216

Long wavelength gradient drift instability in Hall plasma devices. II. Applications  

SciTech Connect

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/?(m){sub i}. 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. [Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon SK S7N 5E2 (Canada)] [Department of Physics and Engineering Physics, University of Saskatchewan, 116 Science Place, Saskatoon SK S7N 5E2 (Canada); Kaganovich, Igor D.; Raitses, Yevgeny [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2013-05-15

217

Nonlinear Interactions in Drift Wave Spectrum  

NASA Astrophysics Data System (ADS)

Wave-wave interaction measurements for drift wave spectrum are performed in a linearly magnetized device by using Laser Induced Fluorescence(LIF). These experiments are performed by using inductively coupled plasma source producing the ArII plasma immersed in 1KG magnetic field along the axis of the cylindrical vessel. For every parallel ion particle velocity component of the distribution function, LIF is carried by pumping ArII metastables with a CW tunable dye laser. The collection of the signal by using two movable periscopes directed to PMTs allows us to determine the amplitude fluctuations along spatial variations. After the digitization of LIF data, cross and auto spectral components can be calculated. By using the power spectrum and the bispectrum measurements, we can model the interaction, and estimate the nonlinear transfer functions and the interaction coefficients.

Uzun, Ilker; Skiff, Frederick

2004-11-01

218

Snow saltation threshold measurements in a drifting-snow wind tunnel  

Microsoft Academic Search

Wind tunnel measurements of snowdrift in a turbulent, logarithmic velocity boundary layer have been made in Davos, Switzerland, using natural snow. Regression analysis gives the drift threshold friction velocity (u*t), assuming an exponential drift profile and a simple drift to friction velocity relationship. Measurements over 15 snow covers show that u*t is influenced more by snow density and particle size

Andrew Clifton; Jean-Daniel Rüedi; Michael Lehning

2006-01-01

219

Ion velocity distributions in the presence of cylindrically symmetric electric field perturbations: the collision-free case  

NASA Astrophysics Data System (ADS)

Because of the strong ambient magnetic field, particularly at ionospheric altitudes, the auroral regions are flush with cylindrical structures covering an impressive range of scales which include lower hybrid cavities on decameter scales, auroral rays on km scales and vortices on tens to hundreds of km scales. In addition, a plethora of in-situ magnetic field and electric field observations and groundbased radar observations strongly suggests that very large parallel current densities are triggered in the upper ionosphere. These observations and just simple geometric considerations have motivated us to study the ion velocity distributions that would accompany strong perpendicular electric fields in a cylindrically symmetric geometry. The applications of the work have to do with the transport coefficients in such regions as well as with local instrumental observations of distribution functions with particle detectors. We have evolved a kinetic theoretical framework in which we have obtained analytical solutions for a number of important limits. We have also developed a semi-numerical method by which to obtain the ion velocity distribution under more general conditions for which analytical solutions are not possible. Our presentation will focus strongly on collision-free results, which stem from the following assumptions: (1) a perpendicular electric field is introduced initially on a time scale that is fast compared to the local ion gyrofrequency (but slow compared to electron plasma and gyrofrequencies); (2) the ion collision frequency is much smaller than the ion gyrofrequency, so that we can calculate meaningful collisionfree solutions. We will present analytical solutions for the distribution functions and their velocity moments inside regions for which the electric field can be assumed to increase linearly with distance from the axis of the cylindrical region, this for a number of initial cylindrically symmetric density distributions. We will also present our semi-numerical results for the distributions and their velocity moments for more realistic electric field configurations, as pertains, in particular, to the edge of the cylindrical regions. We will show that, even for Maxwellian initial conditions, the pulsating distributions can take a multitude of shapes that depend on the electric field strength, the initial density configuration, time, position, and, of course, on the particular way by which the electric field changes as a function of distance from the cylindrical axis. Owing to time limitations we shall present only one collisional case, with our main point in this case to illustrate the connection between collisional situations lower down in the ionosphere and collision-free solutions higher up. Indeed, to first order, we will show that there is a strong connection between collisional solutions and the collision-free solution averaged over one cycle of oscillation.

Ma, John Zhen Guo; Ma, John Zhen Guo; St-Maurice, Jean-Pierre

220

Surface drift effect on wind energy transfer to waves  

Microsoft Academic Search

The effect of surface drift velocity on the energy transfer from the wind to ocean waves and the growth rate of the dominant surface wave was studied analytically. The model analyzed considered first the airflow above the surface wave to be turbulent, the thin drift shear layer to be viscous, and the flow beneath the drift flow to be potential.

Donghuo Zhou; Cesar Mendoza

1993-01-01

221

Particle drift in a resonance tube-a numerical study  

Microsoft Academic Search

The paper considers longitudinal drift of small particles in a resonance tube, caused by periodic shock waves, and its effect on particle agglomeration. It is found that depending on particle size, drift is caused by shock waves and\\/or gas acceleration and compression. It is also shown that the drift velocity and direction can be controlled by the frequency of the

A. Alexeev; C. Gutfinger

2003-01-01

222

Effect of ion-temperature gradients on the formation of drift-Alfven vortices in electron-positron-ion magnetoplasma with equilibrium flows  

SciTech Connect

A set of coupled nonlinear equations which governs the dynamics of low-frequency electromagnetic waves in a nonuniform electron-positron-ion magnetoplasma with non-zero ion-temperature-gradients is derived and solved analytically under various approximations. In the linear limit, a local dispersion relation has been derived and analyzed in several interesting limiting cases. On the other hand, a quasi-stationary solution of the mode coupling equations in the absence of collisions can be represented in the form of dipolar and vortex-chain solutions. The results of the present investigation should be useful to understand the wave phenomena in laboratory and astrophysical plasmas.

Azeem, M.; Mirza, Arshad M. [Theoretical Plasma Physics Group, Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

2005-05-15

223

Hypersonic drift-tearing magnetic islands in tokamak plasmas  

SciTech Connect

A two-fluid theory of long wavelength, hypersonic, drift-tearing magnetic islands in low-collisionality, low-{beta} plasmas possessing relatively weak magnetic shear is developed. The model assumes both slab geometry and cold ions, and neglects electron temperature and equilibrium current gradient effects. The problem is solved in three asymptotically matched regions. The 'inner region' contains the island. However, the island emits electrostatic drift-acoustic waves that propagate into the surrounding 'intermediate region', where they are absorbed by the plasma. Since the waves carry momentum, the inner region exerts a net force on the intermediate region, and vice versa, giving rise to strong velocity shear in the region immediately surrounding the island. The intermediate region is matched to the surrounding 'outer region', in which ideal magnetohydrodynamic holds. Isolated hypersonic islands propagate with a velocity that lies between those of the unperturbed local ion and electron fluids, but is much closer to the latter. The ion polarization current is stabilizing, and increases with increasing island width. Finally, the hypersonic branch of isolated island solutions ceases to exist above a certain critical island width. Hypersonic islands whose widths exceed the critical width are hypothesized to bifurcate to the so-called 'sonic' solution branch.

Fitzpatrick, R.; Waelbroeck, F. L. [Institute for Fusion Studies, Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States)

2007-12-15

224

Analysis of digisonde drift measurements quality  

NASA Astrophysics Data System (ADS)

Ionosondes underwent significant improvements since their invention in 1924 (Breit and Tuve, 1926). At the beginning, ionospheric sounders measured only vertical profile of electron concentration. Contemporary modern digital ionosondes usually provide ionospheric drift measurement as a part of the routine monitoring in addition to the classical vertical ionospheric sounding (ionogram measurement). Ionospheric plasma motion monitoring has a large potential to improve our understanding of an ionospheric dynamics. However the measurement quality is highly variable. In this paper we deal with conditions and assumptions necessary for the correct drift velocity estimation, particularly differences in measurements for E and F regions. Correct and accurate drift velocity estimation requires recording of a sufficient number of reflection points during the measurement. We discuss how to obtain good quality drift data and how to estimate data quality. Large number of recorded drift measurements are eliminated from further use for drift velocity estimation due to low number of detected reflection points. Our analysis done for a large dataset strongly supports the idea that even low number of recorded reflection points may indicate an expressive horizontal stratification of the ionosphere. For our study we used drift data collected in 2006 from a mid-latitude station Pruhonice. Data were collected during a period of low geomagnetic and solar activity. We show statistical properties of drift velocity components for both E and F regions. We illustrate the influence of geomagnetic activity on drift velocities on maximal daily value of F region horizontal component (geomagnetic activity is represented by Kp). We also show statistics for poor-quality data associated with horizontal stratification of ionosphere.

Kouba, Daniel; Koucká Knížová, Petra

2012-12-01

225

Ion Velocity Phase Space Studies of the VASIMR Engine Exhaust Plasma  

NASA Astrophysics Data System (ADS)

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is a high power engine capable of Isp/thrust modulation at constant power. The plasma is produced by helicon discharge. The bulk of the energy is added by ion cyclotron resonance heating (ICRH.) Axial momentum is obtained by adiabatic expansion of the plasma in a magnetic nozzle. Thrust/specific impulse ratio control in the VASIMR is primarily achieved by the partitioning of the RF power to the helicon and ICRH systems, with the proper adjustment of the propellant flow. Ion dynamics in the exhaust were studied using probes, gridded energy analyzers (RPAÂ's), microwave interferometry and optical techniques. This paper will focus on the RPA data. We will examine the ion dynamics in a deuterium exhaust plasma using ˜9 kW of RF power to the helicon ionization stage and varying power levels to the ICRH acceleration stage. Ion heating of ˜70 eV/ion/kW of applied ICRH has been demonstrated. Results also confirm conversion of transverse ion motion to axial motion.

Bering, III; Chang-Diaz, F. R.; Squire, J.; Jacobson, V.; Tarditi, A.; Bengtson, R. D.; Glover, T. W.; Brukardt, M.; McCaskill, G. E.

2004-11-01

226

Predicted Z/sub 2/ structure and gas-solid difference in low-velocity stopping power of light ions  

SciTech Connect

Atomic stopping cross sections for low-velocity light ions have been evaluated for the atomic numbers 1< or =Z/sub 2/< or =36 on the basis of the kinetic theory of electronic stopping. Valence electrons make the main contribution. A pronounced Z/sub 2/ structure in stopping cross sections is found, with minima for noble gases where our estimates agree well with experimental results and with the Lindhard-Scharff formula. Pronounced maxima are predicted for alkalis, where large gas-solid differences are to be expected.

Oddershede, J.; Sabin, J.R.; Sigmund, P.

1983-10-10

227

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

228

Ion acceleration from laser-driven electrostatic shocksa)  

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

229

Ion acceleration from laser-driven electrostatic shocks  

SciTech Connect

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. [GoLP—Instituto de Plasmas e Fusão Nuclear—Laboratório Associado, Instituto Superior Técnico, 1049-001 Lisbon (Portugal)] [GoLP—Instituto de Plasmas e Fusão Nuclear—Laboratório Associado, Instituto Superior Técnico, 1049-001 Lisbon (Portugal); Haberberger, D.; Tochitsky, S.; Mori, W. B.; Joshi, C. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)] [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)

2013-05-15

230

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

231

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

232

Background and Pickup Ion Velocity Distribution Dynamics in Titan's Plasma Environment: 3D Hybrid Simulation and Comparison with CAPS T9 Observations  

NASA Technical Reports Server (NTRS)

In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. In our model the background, pickup, and ionospheric ions are considered as a particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. We also take into account the collisions between the ions and neutrals. The current simulation shows that mass loading by pickup ions H(+); H2(+), CH4(+) and N2(+) is stronger than in the previous simulations when O+ ions are introduced into the background plasma. In our hybrid simulations we use Chamberlain profiles for the atmospheric components. We also include a simple ionosphere model with average mass M = 28 amu ions that were generated inside the ionosphere. The moon is considered as a weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS T9 observations. Our simulation shows an asymmetry of the ion density distribution and the magnetic field, including the formation of the Alfve n wing-like structures. The simulation also shows that the ring-like velocity distribution for pickup ions relaxes to a Maxwellian core and a shell-like halo.

Lipatov, A. S.; Sittler, E. C., Jr.; Hartle, R. E.; Cooper, J. F.; Simpson, D. G.

2011-01-01

233

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  

SciTech Connect

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. [Fusion Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)] [Fusion Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2013-09-15

234

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

235

Multi-point, high-speed passive ion velocity distribution diagnostic on the Pegasus Toroidal Experimenta)  

NASA Astrophysics Data System (ADS)

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 Å/mm in 4th order and a bandpass of 0.14 Å (˜13 km/s) at 3131 Å in 4th order with 100 ?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 Te low (˜100 eV) and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (Ti ? 1.2 keV, Te ? 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.

2012-10-01

236

Dynamics of positive probes in underdense, strongly magnetized, E×B drifting plasma: Particle-in-cell simulations  

SciTech Connect

Electron trapping, electron heating, space-charge wings, wake eddies, and current collection by a positive probe in E×B 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 (?{sub pe}drift 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. [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)] [Air Force Research Laboratory, Kirtland Air Force Base, New Mexico 87117 (United States)

2013-09-15

237

Dynamics of positive probes in underdense, strongly magnetized, E ×B 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 E ×B 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

238

Electron capture from oriented hydrogen molecular ions by protons at high velocity  

SciTech Connect

Electron capture from oriented hydrogen molecules by protons was studied recently within a second-order Born approximation, the amplitude being evaluated using a propagator linearized in the intermediate momenta. Prominent interference minima, arising from virtual electronic scattering off the two target nuclei, were found in the differential cross section at fixed incident energy as the scattering angle varied and at fixed scattering angle as the incident energy was varied. To test whether the locations and shapes (depths and widths) of the minima depend significantly on the amplitude evaluation, an exact calculation of the second-order Born amplitude is being carried out. However, collisions of protons on hydrogen molecular ions are being treated since target-electron correlation contributions, which would require an effective electron-target-core potential greatly complicating the exact calculation, do not enter. Cross sections for molecular orientations both parallel and perpendicular to the incident direction will be presented for incident energies of a few MeV.

Alston, S. [Pennsylvania State Univ., Lehman, PA (United States)

1996-05-01

239

Properties of Drift and ALFVÉN Waves in Collisional Plasmas  

NASA Astrophysics Data System (ADS)

The stability is discussed of the drift-Alfvén wave which is driven by the equilibrium density gradient, in both unbounded and bounded, collisional plasmas, including the effects of both hot ions and a finite ion Larmor radius. The density gradient in combination with the electron collisions with heavier plasma species is the essential source of the instability of the electrostatic drift mode which is coupled to the dispersive Alfvén mode. In the analysis of modes in an unbounded plasma the exchange of identity between the electrostatic and electromagnetic modes is demonstrated. Due to this, the frequency of the electromagnetic part of the mode becomes very different compared to the case without the density gradient. In the case of a bounded plasma the dispersion properties of modes involve a discrete poloidal mode number, and eigen-functions in terms of Bessel functions with discrete zeros at the boundary. The results are applied to the solar plasma. A physical background is presented and an analytical description is given for the electrostatic drift mode in partially ionized magnetized plasmas with inelastic collisions. In such plasmas the creation of plasma particles is balanced by a certain number of phenomena in which ions and electrons are lost. Dispersion equation is derived for the drift mode, with the appropriate instability conditions, indicating that inelastic collisions can make the mode unstable. The physics of Alfvén waves in weakly ionized plasmas like the solar photosphere is discussed. The magnetization and the collision frequencies of the plasma constituents are quantitatively examined. It is shown that the ions and electrons in the photosphere are both un-magnetized, their collision frequency with neutrals is much larger than the gyro-frequency. This implies that eventual Alfvén-type electromagnetic perturbations must involve the neutrals as well. It follows that in the presence of perturbations the whole fluid (plasma + neutrals) moves, the Alfvén velocity includes the total (plasma + neutrals) density and is thus considerably smaller compared to the collision-less case, the perturbed velocity of a unit volume, which now includes both plasma and neutrals, becomes much smaller compared to the ideal (collision-less) case, and finally the corresponding wave energy flux for the given parameters becomes much smaller compared to the ideal case.

Vranjes, J.; Poedts, S.; Pandey, B. P.

2008-03-01

240

Ionization Fractions of Slow Ions in a Plasma with Kappa Distributions for the Electron Velocity  

NASA Astrophysics Data System (ADS)

The interpretation of a wide variety of astrophysical observations requires an understanding of how ionization fractions depend on plasma parameters. Observations have indicated that electron velocity distributions in space plasmas generally have enhanced high-energy tails. Instead of a Maxwellian distribution, they are better described by a kappa distribution, characterized by the kinetic temperature, T, and a parameter, ?, that quantifies the deviation from a Maxwellian. We calculate and tabulate the equilibrium ionization fractions of N, O, Ne, Mg, S, Si, Ar, Ca, Fe, and Ni, based on a balance of ionization and recombination processes, for 104K<=T<=108K (or up to 109 K for Fe and Ni) and for various Maxwellian and kappa distributions. For a Maxwellian distribution of electrons, the mean charge as a function of temperature is characterized by plateaux corresponding to closed-shell charge states, with transitions over narrow ranges of logT. However, for kappa distributions, which are more realistic models of the observed electron distributions in coronal or space plasmas, those transitions are substantially broader. We find that a lower ? value (more suprathermal electrons) frequently leads to a higher mean charge, especially for low temperatures, but can also lead to a lower mean charge in certain temperature ranges; these effects are associated with the sharp energy thresholds and resonances of ionization and dielectronic recombination cross sections, respectively. The results provide information for various applications in which observed ionization fractions are used as diagnostics of astrophysical plasmas.

Wannawichian, S.; Ruffolo, D.; Kartavykh, Yu. Yu.

2003-06-01

241

DRIFT BOTTLE RELEASES DRIFT BOTTLE RELEASES  

E-print Network

, consisting of a solution of sulphuric acid and farrous sijlphatej from an industrial plant in New Jersey and recovery points of November 1, 1948 m · · · · 16 · « - > ? 1 a 1 #12;INTRODUCTION Waste by-products J phases, but the present paper concerns only the possible drift of the waste=productSo Drift bottles

242

Observation of a quasimolecular ionization window in low-to-intermediate impact velocity collisions of He+ ions with H2 and He  

NASA Astrophysics Data System (ADS)

The ionization of H2, leading to H+2 recoil ions in nondissociative states, and the ionization of He by incident He+ ions were investigated in the 0.25-1.23-a.u. impact velocity range employing electron and target recoil-ion momentum-imaging techniques. Similarities as well as differences were observed in the electron velocity distributions from H2 and He targets. In both cases the data strongly suggest of the promotion of molecular orbitals formed between target and projectile within a rather well-defined projectile velocity window. In particular, the data support the promotion of the 2p? molecular orbital populated via rotational coupling. Outside this molecular promotion window, in particular at lower velocities, mechanisms of a different kind appear to dominate the ionization process, and electron momentum distributions are very dissimilar for He and H2. Reduced projectile scattering cross sections, derived from measured target recoil-ion transverse momentum distributions, support these conclusions and point to the coexistence, at certain impact velocities, of different ionization mechanisms.

Abdallah, M. A.; Wolff, W.; Wolf, H. E.; Coelho, L. F. S.; Cocke, C. L.; Stöckli, M.

2000-07-01

243

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

244

Effect of the ion distribution over longitudinal velocities on the efficiency and separating parameters of the ICR method of isotope separation  

Microsoft Academic Search

In the context of the ICR method of isotope separation, resonance RF heating of the ions in an electric field propagating\\u000a along a constant magnetic field while simultaneously rotating in the direction perpendicular to it is calculated in a linear\\u000a approximation. The analysis is carried out for two types of the initial ion distribution function over longitudinal velocities:\\u000a a function

E. P. Potanin

2005-01-01

245

Physics-Based Model Driven by Plasma Drifts Obtained From the C/NOFS Satellite  

NASA Astrophysics Data System (ADS)

An important parameter in determining low-latitude ionospheric plasma density is the plasma drift. Two instruments on-board the Communication/Navigation Outage System (C/NOFS) satellite were designed to directly or indirectly measure the plasma drifts: the Ion Velocity Drift Meter (IVM) and the Vector Electric Field Instrument (VEFI). By using the electric field measurements obtained from VEFI, the physics-based model (PBMOD) developed at the Air Force Research Laboratory has been shown to qualitatively reproduce post-midnight density trenches observed in June 2008. In this presentation, we will demonstrate simulation results obtained from PBMOD driven by averaged IVM [Stoneback and Heelis, 2010] and VEFI data [Pfaff et al., 2010]. A wave-4 structure has been identified in averaged IVM data. Based on our preliminary study, the ion density output from IVM-driven PBMOD also presents a similar wave-four structure in geographical longitudes (GLON). In addition, the lowest density region occurs near 300 degree GLON for all seasons, where the magnetic equator declination is largest. Model results will be compared with those driven by the Scherliess-Fejer drift model, as well as in-situ density measurements obtained from the Planar Langmuir Probe (PLP). Stoneback, R. and R. Heelis (2010), Equatorial ion densities and meridional ion drifts in 2009, C/NOFS Science Workshop at Breckenridge, Colorado. Pfaff, R. , H. Freudenreich, J. Klenzing, D. Rowland, and K. Bromund (2010), DC electric fields as observed on the C/NOFS satellite during solar minimum conditions, C/NOFS Science Workshop at Breckenridge, Colorado.

Su, Y.; Retterer, J. M.; Stoneback, R.; de La Beaujardiere, O.; Roddy, P. A.; Heelis, R. A.; Pfaff, R. F.

2010-12-01

246

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

247

Dynamics of pickup ion velocity distribution function in Titan's plasma environment (TA encounter): 3D hybrid kinetic modeling and comparison with CAPS observations  

NASA Astrophysics Data System (ADS)

Wave-particle interactions play a very important role in the plasma dynamics near Titan: mass loading, excitation of the low-frequency waves and the formation of the particle velocity distribution function, e.g. ring/shell-like distributions, etc. The kinetic approach is important for estimation of the collision processes e.g. a charge exchange. The particle velocity distribution function also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution function dynamics from 3D hybrid modeling. The modeling is based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the TA flyby. In our model the background ions, all pickup ions, and ionospheric ions are considered as particles, whereas the electrons are described as a fluid. Inhomogeneous photoionization, electron-impact ionization and charge exchange are included in our model. The temperatures of the background electrons and pickup electrons were also included into the generalized Ohm's law. We also take into account the collisions between the ions and neutrals. We use Chamberlain profiles for the exosphere's components and include a simple ionosphere model with M=28 ions that were generated inside the ionosphere. The moon is considered as a weakly conducting body. Our modeling shows that interaction between background plasma and pickup ions H+, H2+, CH4+ and N2+ has a more complicated structure than was observed in the T9 flyby and modeling due to the large gyroradius of the background O+ ions [1,2,3,4]. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS TA observations. We also compare our kinetic modeling with other hybrid and MHD modeling of Titan's environment. References [1] Sittler, E.C., et al., Energy Deposition Processes in Titan's Upper Atmosphere and Its Induced Magnetosphere. In: Titan from Cassini-Huygens, Brown, R.H., Lebreton J.P., Waite, J.H., Eds., Springer, (Dordrecht, Heidelberg, London, New York, pp. 393-455, 2009). [2] Sittler, E.C., et al., Saturn's Magnetospheric Interaction with Titan as Defined by Cassini Encounters T9 and T18: New Results, Planet. Space Sci., doi.10.1016/j.pss.2009.09.017. [3] Coates, A.J., Interaction of Titan's ionosphere with Saturn's magnetosphere. Phil. Trans. R. Soc. A (2009) 367, 773-788, doi: 10.1098/rsta.2008.0248. [4] Lipatov, A.S., et al., Background and pickup ion velocity distribution dynamics in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS T9 observations. Adv. Space Res. 48, 1114-1125, 2011.

Simpson, D. G.; Lipatov, A. S.; Sittler, E. C.; Hartle, R. E.; Cooper, J. F.

2013-12-01

248

Drift Velocity Calibration of the G.P.Gilfoyle a , S.Levy a , H.Lan a , Y.Opoku a , M.Mestayer b , and F.Roudot b  

E-print Network

will collect the data to reconstruct the trajectories of the scattered, charged particles. To reach the desired and analySIS code (RECSIS) will be described with results of performance tests. 2 Extraction of the Drift Time In a typical CLAS event a charged particle produced at the target passes through thirty

Gilfoyle, Jerry

249

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

250

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

251

Approximate Stokes Drift Profiles in Deep Water  

E-print Network

A deep-water approximation to the Stokes drift velocity profile is explored as an alternative to the monochromatic profile. The alternative profile investigated relies on the same two quantities required for the monochromatic profile, viz the Stokes transport and the surface Stokes drift velocity. Comparisons with parametric spectra and profiles under wave spectra from the ERA-Interim reanalysis and buoy observations reveal much better agreement than the monochromatic profile even for complex sea states. That the profile gives a closer match and a more correct shear has implications for ocean circulation models since the Coriolis-Stokes force depends on the magnitude and direction of the Stokes drift profile and Langmuir turbulence parameterizations depend sensitively on the shear of the profile. The alternative profile comes at no added numerical cost compared to the monochromatic profile.

Breivik, Øyvind; Bidlot, Jean-Raymond

2014-01-01

252

Adiabatic particle motion in a nearly drift-free magnetic field: Application to the geomagnetic tail  

NASA Technical Reports Server (NTRS)

The guiding center motion of particles in a nearly drift free magnetic field is analyzed in order to investigate the dependence of mean drift velocity on equatorial pitch angle, the variation of local drift velocity along the trajectory, and other properties. The mean drift for adiabatic particles is expressed by means of elliptic integrals. Approximations to the twice-averaged Hamiltonian W near z = O are derived, permitting simple representation of drift paths if an electric potential also exists. In addition, the use of W or of expressions for the longitudinal invariant allows the derivation of the twice averaged Liouville equation and of the corresponding Vlasov equation. Bounce times are calculated (using the drift-free approximation), as are instantaneous guiding center drift velocities, which are then used to provide a numerical check on the formulas for the mean drift.

Stern, D. P.

1977-01-01

253

Magnetic drift instability in a collisionless plasma  

Microsoft Academic Search

In this paper the stability of plasma in a toroidal system is investigated, for drift type oscillations which have phase velocities in the range vTc » ?\\/k|| » vTi. Making the assumption that the shear is not too small, our main attention is turned to finding out whether or not curvature of the lines of force causes any new instabilities

O P Pogutse

1968-01-01

254

Dike/Drift Interactions  

SciTech Connect

This report presents and documents the model components and analyses that represent potential processes associated with propagation of a magma-filled crack (dike) migrating upward toward the surface, intersection of the dike with repository drifts, flow of magma in the drifts, and post-magma emplacement effects on repository performance. The processes that describe upward migration of a dike and magma flow down the drift are referred to as the dike intrusion submodel. The post-magma emplacement processes are referred to as the post-intrusion submodel. Collectively, these submodels are referred to as a conceptual model for dike/drift interaction. The model components and analyses of the dike/drift interaction conceptual model provide the technical basis for assessing the potential impacts of an igneous intrusion on repository performance, including those features, events, and processes (FEPs) related to dike/drift interaction (Section 6.1).

E. Gaffiney

2004-11-23

255

Free Drifting Buoys  

NASA Technical Reports Server (NTRS)

Information was exchanged between people directly involved with the development, use, and/or potential use of free drifting buoys. Tracking systems and techniques, where methods and accuracy of optical, radio, radar, satellite, and sonic tracking of free-drifting buoys were discussed. Deployment and retrieval covering methods currently used or planned in the deployment and retrieval of free-drifting buoys from boats, ships, helicopters, fixed platforms, and fixed-wing aircraft were reported. Simulation, sensors, and data emphasizing the status of water circulation modeling, and sensors useful on free-drifting buoys, and data display and analysis were described.

1974-01-01

256

Gradient drift eigenmodes in the equatorial electrojet  

NASA Technical Reports Server (NTRS)

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential perturbations is solved numerically by a relaxation technique. Under some approximations, the fourth-order system can be shown to reduce to a second-order differential equation for the perturbed potential or density. The latter is solved using a shooting technique and provides initial guesses for numerical solutions to the full problem. It is shown that the linear growth rate peaks for kilometer-scale waves, contrary to the findings of recent initial-value studies. This occurs because the equilibrium velocity shear is much more effective as a damping mechanism for short-wavelength modes than it is for the longer, kilometer-scale modes. These results provide a natural qualitative explanation for the observed dominance of kilometer-scale structures in the daytime electrojet spectrum.

Wang, X.-H.; Bhattacharjee, A.

1994-01-01

257

Ion heating mechanism in a modified Penning discharge  

NASA Technical Reports Server (NTRS)

Ions with Maxwellian energy distributions and kinetic temperatures ranging from 20 eV to 7 keV have been observed in a modified Penning discharge operating in the steady state. Investigation of the plasma revealed two distinct spoke-like concentrations of charge rotating with different velocities in the sheath between the plasma and the anode ring. The faster spoke consists of electrons rotating with the E/B drift velocity, where E is the electric field and B is the magnetic field strength. The slow spoke consists of ions, the thermal velocity of which is observed to be proportional to the spoke velocity. The experimental data are consistent with a model whereby the ion drift velocity in this spoke, corresponding to kilovolt ion energies, is Maxwellianized by strong electrostatic turbulence in the sheath. Theoretical expressions are derived for the frequency of the electron and ion spoke rotation, for the ion kinetic temperature, and for the ion heating efficiency as functions of the discharge parameters. These expressions are shown to be consistent with extensive experimental data.

Roth, J. R.

1972-01-01

258

Ion Temperature Anisotropy Effects on Threshold Conditions of Shear-Modified Current Driven Electrostatic Ion-Acoustic Instability in the Auroral F Region  

NASA Astrophysics Data System (ADS)

Temperature anisotropies occur in space plasmas when there is, for instance, a strong magnetic or electric field. In this study, a shear-modified current driven electrostatic ion-acoustic instability dispersion relation is generalized to include ion temperature anisotropy and collisions with neutrals in order to make it most relevant to F region radar observations at high latitudes. The corresponding incoherent scatter radar spectrum is calculated for a stable plasma near destabilization. A new fluid-like expression for the critical drift required for instability which depends explicitly on ion anisotropy is derived. Fluid-like results in terms of electron parallel drift and ion velocity shear for different aspect angles and anisotropy factors are compared with solutions of the kinetic dispersion relation. For ion to electron temperature ratios typical of F-region and for small aspect angles, results show that ion temperature anisotropy may significantly lower the drift threshold minima required for instability to smaller positive shears. In some cases, a perpendicular to parallel ion temperature ratio of 2 may lower the ion shear requirement by 50%. Also, ion temperature anisotropy may significantly lower the drift threshold required for instability, especially at intermediate and large aspect angles. Therefore, ion temperature anisotropy should be adequately accounted for in future studies of ion-acoustic waves and instabilities in the auroral F-region.

Perron, P.; Noel, J. A.; Kabin, K.; St-Maurice, J.

2012-12-01

259

Characterization of Gas Mixtures for Ultra-Light Drift Chambers  

NASA Astrophysics Data System (ADS)

Low pressure helium/hydrocarbons mixtures are a key ingredient for next generation ultra-light drift chambers. Besides the obvious advantage of limiting the contribution to the momentum measurement due to multiple scattering, the operation at low pressure allows for a broad range of the drift chamber working parameters like drift velocity, diffusion, specific ionization and gas gain. Low pressure operation is of particular advantage for experiments where the tracking detector operates in vacuum. We present our campaign to characterize electron drift, primary ionization yield, gas gain, stability and the relative spatial resolution in helium based mixtures at absolute pressures down to 100 mbar.

Cascella, M.; Grancagnolo, F.; Mazzotta, P.; Miccoli, A.; Panareo, M.; Spedicato, M.; Tassielli, G.

2014-03-01

260

Basic plasma physics, plasma theory and modeling (BP): Study on modes in a plasma having electrons, positrons and cold drifting ions  

Microsoft Academic Search

In contrast to the usual plasma consisting of electrons and positive ions, it has been observed that nonlinear waves in plasmas having an additional component of positron behave differently. Electron-positron-ion plasma appears in the early universe, in the active galactic nuclei, pulsar magnetosphere, and also in the solar atmosphere. An Electron-positron-ion plasma was studied theoretically and it was shown that

Ravish Sharma; Khushvant Singh; A. K. Singh; Krishan Pal Singh

2010-01-01

261

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

262

On the initial velocity of ions generated by matrix-assisted laser desorption ionization and its effect on the calibration of delayed extraction time-of-flight mass spectra  

Microsoft Academic Search

A novel method was developed to measure the initial velocity of ions generated by matrix-assisted laser desorption ionization\\u000a (MALDI). It is shown both experimentally and theoretically that with a delayed extraction (DE) technique, the flight time\\u000a of an ion changes linearly with extraction delay. The initial velocity of the ion, a consequence of the desorption process,\\u000a can be determined from

Peter Juhasz; Marvin L. Vestal; Stephen A. Martin

1997-01-01

263

Influence of the magnetic field on the velocity of the ion component of the particle beam generated during a nanosecond vacuum dielectric flashover  

NASA Astrophysics Data System (ADS)

Results of experimental investigations into the influence of the direction of magnetic field of 0.06 T on the velocity of ion component of particle flux generated during anode surface flashover of dielectrics in vacuum with voltage pulses of 230 kV are presented. It is demonstrated that the magnetic field applied in the plane of the sample surface decelerates the ion particle beam generated by the discharge. If the [ E × B] vector is collinear with the external normal to the sample surface, the beam is decelerated less than in the case of the opposite orientation of the magnetic field.

Gilev, A. S.; Morozov, P. A.; Emlin, R. V.; Punanov, I. F.; Cholakh, S. O.

2012-11-01

264

Ion beams from laser-generated plasmas  

NASA Technical Reports Server (NTRS)

The paper describes the space-charge-limited beams produced by the plasma blowoffs generated by 20-MW bursts of 1.06-micron radiation from an active Q-switched Nd:YAG laser. Laser power densities near 10 to the 11th/sq cm on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and electrostatically focused; the spatially defined ion beams are then magnetically analyzed to determine the charge state content in the beams formed from carbon, aluminum, copper, and lead targets. This technique preserves time-of-flight (TOF) information in the plasma drift region, which permits plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.

Hughes, R. H.; Anderson, R. J.; Gray, L. G.; Rosenfeld, J. P.; Manka, C. K.; Carruth, M. R.

1980-01-01

265

Particle drift in the Earth's plasma sheet  

NASA Technical Reports Server (NTRS)

We generalize the derivation of the average gradient/curvature-drift for a flux tube filled with an isotropic distribution of particles at specified kinetic energy. The present treatment is restricted to a two-dimensional magnetic field with zero electric field, but it includes all chaotic and Speiser orbits, which do not correspond to the simple picture of gradient/curvature drift. We assume that particles are evenly distributed throughout the regions of phase space allowed by their energy and canonical momentum. This assumption is closely related but not exactly equivalent to the assumption of isotropic pitch-angle distribution. Our derivation assumes that the maximum Larmor radius is small compared to the scale length for equatorial variations in the flux tube volume, but it does not involve any restrictions on the curvature of the field line. The resulting expression for the drift rate is valid for situations where the particle drift velocity is comparable to the thermal speed in some regions. The apparent implication of this generalized treatment is that the existence of very complex non-adiabatic particle trajectories in the plasma sheet may not invalidate previous estimates of the average rate of particle drift out the sides of the tail, estimates that were made under the assumption of simple guiding-center drifts.

Wolf, R. A.; Pontius, D. H., Jr.

1993-01-01

266

Semiconductor drift chambers  

SciTech Connect

Semiconductor drift chambers for position and energy measurements have been invented, built and tested. A short 'Ccount is here given on the principles of the drift chamber and on the experimental results. Detailed reports have been written on the quoted bibliography and new reports will be published shortly.

Lutz, G.; Goulding, F.; Luke, P.N.; Madden, N.W.; Waltor, J.; Wylie, A.

1985-04-01

267

Gyrokinetic theory of electrostatic lower-hybrid drift instabilities in a current sheet with guide field  

NASA Astrophysics Data System (ADS)

A kinetic electrostatic eigenvalue equation for the lower-hybrid drift instability (LHDI) in a thin Harris current sheet with a guide field is derived based on the gyrokinetic electron and fully kinetic ion(GeFi) description. Three-dimensional nonlocal analyses are carried out to investigate the influence of a guide field on the stabilization of the LHDI by finite parallel wavenumber, k?. Detailed stability properties are first analyzed locally, and then as a nonlocal eigenvalue problem. Our results indicate that at large equilibrium drift velocities, the LHDI is further destabilized by finite k? in the short-wavelength domain. This is demonstrated in a local stability analysis and confirmed by the peak in the eigenfunction amplitude. We find the most unstable modes localized at the current sheet edges, and our results agree well with simulations employing the GeFi code developed by Lin et al. [Plasma Phys. Controlled Fusion 47, 657 (2005); Plasma Phys. Controlled Fusion 53, 054013 (2011)].

Tummel, K.; Chen, L.; Wang, Z.; Wang, X. Y.; Lin, Y.

2014-05-01

268

Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas  

SciTech Connect

A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1 MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and v? on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and uclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

Hill, K W; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E; Scott, S

2008-01-29

269

Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas  

SciTech Connect

A new imaging high resolution x-ray crystal spectrometer (XCS) has been developed to measure continuous profiles of ion temperature and rotation velocity in fusion plasmas. Following proof-of-principle tests on the Alcator C-Mod tokamak and the NSTX spherical tokamak, and successful testing of a new silicon, pixilated detector with 1MHz count rate capability per pixel, an imaging XCS is being designed to measure full profiles of Ti and v? on C-Mod. The imaging XCS design has also been adopted for ITER. Ion-temperature uncertainty and minimum measurable rotation velocity are calculated for the C-Mod spectrometer. The affects of x-ray and nuclear-radiation background on the measurement uncertainties are calculated to predict performance on ITER.

Hill, K W; Broennimann, Ch; Eikenberry, E F; Ince-Cushman, A; Lee, S G; Rice, J E; Scott, S

2008-02-27

270

Development of A Cryogenic Drift Cell Spectrometer and Methods for Improving the Analytical Figures of Merit for Ion Mobility-Mass Spectrometry Analysis  

E-print Network

A cryogenic (325-80 K) ion mobility-mass spectrometer was designed and constructed in order to improve the analytical figures-of-merit for the chemical analysis of small mass analytes using ion mobility-mass spectrometry. The instrument incorporates...

May, Jody C.

2010-10-12

271

Comment on ``Nonplanar dust-ion acoustic Gardner solitons in a dusty plasma with q-nonextensive electron velocity distribution'' [Phys. Plasmas 19, 033703 (2012)  

NASA Astrophysics Data System (ADS)

The basic characteristics of cylindrical and spherical dust-ion acoustic Gardner solitary waves in a dusty plasma with q-nonextensive electron velocity distribution have been represented by Ghosh et al. [Phys. Plasmas 19, 033703 (2012)]. In this manuscript, they use the double layer stationary solution of the standard Gardner equation but they explain the whole article in terms of Gardner solitons which is completely incorrect.

Mannan, A.; Tanjia, F.; Yasmin, S.

2013-04-01

272

Comment on 'Nonplanar dust-ion acoustic Gardner solitons in a dusty plasma with q-nonextensive electron velocity distribution' [Phys. Plasmas 19, 033703 (2012)  

SciTech Connect

The basic characteristics of cylindrical and spherical dust-ion acoustic Gardner solitary waves in a dusty plasma with q-nonextensive electron velocity distribution have been represented by Ghosh et al.[Phys. Plasmas 19, 033703 (2012)]. In this manuscript, they use the double layer stationary solution of the standard Gardner equation but they explain the whole article in terms of Gardner solitons which is completely incorrect.

Mannan, A. [Dipartimento di Matematica e Fisica, Seconda Universita degli Studi di Napoli, Caserta (Italy); Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II' and INFN Napoli (Italy); Yasmin, S. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

2013-04-15

273

Abstraction of Drift Seepage  

SciTech Connect

This model report documents the abstraction of drift seepage, conducted to provide seepage-relevant parameters and their probability distributions for use in Total System Performance Assessment for License Application (TSPA-LA). Drift seepage refers to the flow of liquid water into waste emplacement drifts. Water that seeps into drifts may contact waste packages and potentially mobilize radionuclides, and may result in advective transport of radionuclides through breached waste packages [''Risk Information to Support Prioritization of Performance Assessment Models'' (BSC 2003 [DIRS 168796], Section 3.3.2)]. The unsaturated rock layers overlying and hosting the repository form a natural barrier that reduces the amount of water entering emplacement drifts by natural subsurface processes. For example, drift seepage is limited by the capillary barrier forming at the drift crown, which decreases or even eliminates water flow from the unsaturated fractured rock into the drift. During the first few hundred years after waste emplacement, when above-boiling rock temperatures will develop as a result of heat generated by the decay of the radioactive waste, vaporization of percolation water is an additional factor limiting seepage. Estimating the effectiveness of these natural barrier capabilities and predicting the amount of seepage into drifts is an important aspect of assessing the performance of the repository. The TSPA-LA therefore includes a seepage component that calculates the amount of seepage into drifts [''Total System Performance Assessment (TSPA) Model/Analysis for the License Application'' (BSC 2004 [DIRS 168504], Section 6.3.3.1)]. The TSPA-LA calculation is performed with a probabilistic approach that accounts for the spatial and temporal variability and inherent uncertainty of seepage-relevant properties and processes. Results are used for subsequent TSPA-LA components that may handle, for example, waste package corrosion or radionuclide transport.

J.T. Birkholzer

2004-11-01

274

Progress on 3D global simulation of drift wave turbulence  

SciTech Connect

A global 3D (m,n,r) code for simulating drift wave turbulence in a tokamak has been developed. Progress is reported on the application of the code to toroidal ion temperature gradient mode turbulence to determine its q dependence and to electron drift mode turbulence to examine the standard assumption of locality.

Waltz, R.E.

1987-02-01

275

Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces  

SciTech Connect

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.; Chen, H. Y.; Thornton, K.; Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Sofferman, D. L. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, Adelphi University, Garden City, New York 11530-0701 (United States); Beskin, I. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

2013-08-12

276

Gradient drift eigenmodes in the equatorial electrojet  

Microsoft Academic Search

The problem of kilometer-scale irregularities in the daytime equatorial electrojet is revisited by means of an eigenmode analysis of the gradient drift instability. Realistic physical parameters are used, including the modeled altitude variations of ion and electron collision frequencies and mobilities. The full fourth-order system of two coupled differential equations (each of second order) for the denisty and electrostatic potential

X.-H. Wang; A. Bhattacharjee

1994-01-01

277

Gradient and curvature drifts in magnetic fields with arbitrary spatial variation. [charged particle distribution in plasmas  

NASA Technical Reports Server (NTRS)

It is shown that, for a magnetic field of arbitrary spatial variation, a nearly isotropic distribution of charged particles drifts with a velocity given by the usual first-order orbit theory drifts averaged over pitch angle. It is assumed that the near-isotropy brought about by scattering, but conclusions concerning drift are insensitive to the details of the scattering process. It is found that this drift velocity is correct even for arbitrarily large ratios of particle gyroradius to magnetic spatial scale, although this velocity must, like all drift effects, be viewed on a scale larger than a gyroradius. Hence for many astrophysical applications, such as cosmic rays, where anisotropies are small, the usual drift velocities provide a valid approximation to convective motions even if the magnetic field scales are very small.

Isenberg, P. A.; Jokipii, J. R.

1979-01-01

278

Thermal force drift wave  

NASA Astrophysics Data System (ADS)

A drift instability of a collisional magnetized plasma, unstable due to the Braginskii thermal force but not requiring any direct dissipation such as resistivity or electron inertia, is examined. Unlike conventional drift-modes, the maximum growth rate of the thermal force drift wave (TFDW) is of order the drift frequency, making for a strongly turbulent nonlinear state. A 3D, magnetized two-fluid code is developed to allow the study of both ideal MHD modes as well as lower frequency drift modes. The governing equations are essentially the ideal MHD equations with the inclusion of Hall and thermal force terms in Ohm's law. This set of equations is reduced in a finite ?, long parallel wavelength, and small but significant Larmor radius ordering and tested for shear Alfven waves, parallel sound waves, and drift modes. The code is employed to recover the TFDW instability, to verify the code against the mode's analytic linear characteristics, and to study the nonlinear behavior of the TFDW. The TFDW growth is strongly suppressed by parallel thermal conduction and thus this mode is more likely to be observed in low temperature plasmas.

Hung, C. P.; Hassam, A. B.

2012-02-01

279

Nonmodal energetics of electromagnetic drift waves Suzana J. Camargoa),b)  

E-print Network

and temperature gradients.3 Drift waves produce anomalous particle and energy diffusion along these spatial plasma instabilities related to ion temperature gradient modes change into drift- type mode near gradients. There is also experimental evidence of waves with drift-wave characteristics in the central

Camargo, Suzana J.

280

Equatorial distributions of the plasma sheet ions, their electric and magnetic drifts, and magnetic fields under different interplanetary magnetic field Bz conditions  

Microsoft Academic Search

To understand the nightside plasma sheet structure under different interplanetary magnetic field (IMF) Bz conditions, we have investigated statistically the equatorial distributions of ions and magnetic fields from Geotail when the IMF has been continuously northward or southward for shorter or longer than 1 hour. A dawn-dusk density (temperature) asymmetry with higher density (temperature) on the dawn (dusk) side is

Chih-Ping Wang; Larry R. Lyons; James M. Weygand; Tsugunobu Nagai; Richard W. McEntire

2006-01-01

281

Ion-streaming induced order transition in three-dimensional dust clusters  

NASA Astrophysics Data System (ADS)

Dust dynamics simulations utilizing a dynamical screening approach are performed to study the effect of ion-streaming on the self-organized structures in a three-dimensional spherically confined complex (dusty) plasma. Varying the Mach number M, the ratio of ion drift velocity to the sound velocity, the simulations reproduce the experimentally observed cluster configurations in the two limiting cases: at M = 0 strongly correlated crystalline structures consisting of nested spherical shells (Yukawa balls) and, for M ? 1, flow-aligned dust chains, respectively. In addition, our simulations reveal a discontinuous transition between these two limits. It is found that already a moderate ion drift velocity (M ? 0.1 for the plasma conditions considered here) destabilizes the highly ordered Yukawa balls and initiates an abrupt melting transition. The critical value of M is found to be independent of the cluster size.

Ludwig, Patrick; Kählert, Hanno; Bonitz, Michael

2012-04-01

282

Drift Scale THM Model  

SciTech Connect

This model report documents the drift scale coupled thermal-hydrological-mechanical (THM) processes model development and presents simulations of the THM behavior in fractured rock close to emplacement drifts. The modeling and analyses are used to evaluate the impact of THM processes on permeability and flow in the near-field of the emplacement drifts. The results from this report are used to assess the importance of THM processes on seepage and support in the model reports ''Seepage Model for PA Including Drift Collapse'' and ''Abstraction of Drift Seepage'', and to support arguments for exclusion of features, events, and processes (FEPs) in the analysis reports ''Features, Events, and Processes in Unsaturated Zone Flow and Transport and Features, Events, and Processes: Disruptive Events''. The total system performance assessment (TSPA) calculations do not use any output from this report. Specifically, the coupled THM process model is applied to simulate the impact of THM processes on hydrologic properties (permeability and capillary strength) and flow in the near-field rock around a heat-releasing emplacement drift. The heat generated by the decay of radioactive waste results in elevated rock temperatures for thousands of years after waste emplacement. Depending on the thermal load, these temperatures are high enough to cause boiling conditions in the rock, resulting in water redistribution and altered flow paths. These temperatures will also cause thermal expansion of the rock, with the potential of opening or closing fractures and thus changing fracture permeability in the near-field. Understanding the THM coupled processes is important for the performance of the repository because the thermally induced permeability changes potentially effect the magnitude and spatial distribution of percolation flux in the vicinity of the drift, and hence the seepage of water into the drift. This is important because a sufficient amount of water must be available within a drift to transport any exposed radionuclides out of the drift to the groundwater below, and eventually to people within the accessible environment. Absent sufficient water, radionuclides cannot be transported and there would be no significant health effect on people, even if radioactive waste containers were damaged or corroded to such an extent that radionuclides were exposed to water.

J. Rutqvist

2004-10-07

283

Numerical simulation of drifting snow sublimation in the saltation layer  

NASA Astrophysics Data System (ADS)

Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525 m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625 m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation.

Dai, Xiaoqing; Huang, Ning

2014-10-01

284

Numerical simulation of drifting snow sublimation in the saltation layer.  

PubMed

Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525?m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625?m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation. PMID:25312383

Dai, Xiaoqing; Huang, Ning

2014-01-01

285

Numerical simulation of drifting snow sublimation in the saltation layer  

PubMed Central

Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525?m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625?m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation. PMID:25312383

Dai, Xiaoqing; Huang, Ning

2014-01-01

286

Stability of Electrostatic Electron Cyclotron Waves in a Multi-Ion Plasma  

NASA Astrophysics Data System (ADS)

We have studied the stability of the electrostatic electron cyclotron wave in a plasma composed of hydrogen, oxygen and electrons. To conform to satellite observations in the low latitude boundary layer we model both the ionic components as drifting perpendicular to the magnetic field. Expressions for the frequency and the growth rate of the wave have been derived. We find that the plasma can support electron cyclotron waves with a frequency slightly greater than the electron cyclotron frequency ? ce ; these waves can be driven unstable when the drift velocities of both the ions are greater than the phase velocity of the wave. We thus introduce another source of instability for these waves namely multiple ion beams drifting perpendicular to the magnetic field.

Abraham, Noble P.; George, Samuel; Sreekala, G.; Sebastian, Sijo; Venugopal, Chandu; Renuka, G.

2014-05-01

287

Drift Degradation Analysis  

SciTech Connect

Degradation of underground openings as a function of time is a natural and expected occurrence for any subsurface excavation. Over time, changes occur to both the stress condition and the strength of the rock mass due to several interacting factors. Once the factors contributing to degradation are characterized, the effects of drift degradation can typically be mitigated through appropriate design and maintenance of the ground support system. However, for the emplacement drifts of the geologic repository at Yucca Mountain, it is necessary to characterize drift degradation over a 10,000-year period, which is well beyond the functional period of the ground support system. This document provides an analysis of the amount of drift degradation anticipated in repository emplacement drifts for discrete events and time increments extending throughout the 10,000-year regulatory period for postclosure performance. This revision of the drift degradation analysis was developed to support the license application and fulfill specific agreement items between the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE). The earlier versions of ''Drift Degradation Analysis'' (BSC 2001 [DIRS 156304]) relied primarily on the DRKBA numerical code, which provides for a probabilistic key-block assessment based on realistic fracture patterns determined from field mapping in the Exploratory Studies Facility (ESF) at Yucca Mountain. A key block is defined as a critical block in the surrounding rock mass of an excavation, which is removable and oriented in an unsafe manner such that it is likely to move into an opening unless support is provided. However, the use of the DRKBA code to determine potential rockfall data at the repository horizon during the postclosure period has several limitations: (1) The DRKBA code cannot explicitly apply dynamic loads due to seismic ground motion. (2) The DRKBA code cannot explicitly apply loads due to thermal stress. (3) The DRKBA code, which determines structurally controlled key-block failure, is not applicable for stress-controlled failure in the lithophysal units. To address these limitations, additional numerical codes have been included that can explicitly apply seismic and thermal loads, providing significant improvements to the analysis of drift degradation and extending the validity of drift degradation models.

D. Kicker

2004-09-16

288

A Spatially Resolving X-ray Crystal Spectrometer for Measurement of Ion-temperature and Rotation-velocity Profiles on the AlcatorC-Mod Tokamak  

SciTech Connect

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (?/d? > 6000) of He-like and H-like Ar K? lines with good spatial (~1 cm) and temporal (~10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (v?) from the line Doppler widths and shifts. The data analysis techniqu

Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Reinke, M.; Rice, J. E.; Beiersdorfer, P.; Gu, M. F.; Lee, S. G.; Broennimann, C. H.; Eikenberry, E. F.

2009-03-24

289

Study of plasma meniscus and beam halo in negative ion sources using three dimension in real space and three dimension in velocity space particle in cell model.  

PubMed

Our previous study by two dimension in real space and three dimension in velocity space-particle in cell model shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources. The negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. The purpose of this study is to verify this mechanism with the full 3D model. It is shown that the above mechanism is essentially unchanged even in the 3D model, while the fraction of the beam halo is significantly reduced to 6%. This value reasonably agrees with the experimental result. PMID:24593471

Nishioka, S; Miyamoto, K; Okuda, S; Goto, I; Hatayama, A; Fukano, A

2014-02-01

290

DC Electric Fields, Associated Plasma Drifts, and Irregularities Observed on the C/NOFS Satellite  

NASA Technical Reports Server (NTRS)

Results are presented from the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. The VEFI instrument includes a vector DC electric field detector, a fixed-bias Langmuir probe operating in the ion saturation regime, a flux gate magnetometer, an optical lightning detector, and associated electronics including a burst memory. Compared to data obtained during more active solar conditions, the ambient DC electric fields and their associated E x B drifts are variable and somewhat weak, typically < 1 mV/m. Although average drift directions show similarities to those previously reported, eastward/outward during day and westward/downward at night, this pattern varies significantly with longitude and is not always present. Daytime vertical drifts near the magnetic equator are largest after sunrise, with smaller average velocities after noon. Little or no pre-reversal enhancement in the vertical drift near sunset is observed, attributable to the solar minimum conditions creating a much reduced neutral dynamo at the satellite altitude. The nighttime ionosphere is characterized by larger amplitude, structured electric fields, even where the plasma density appears nearly quiescent. Data from successive orbits reveal that the vertical drifts and plasma density are both clearly organized with longitude. The spread-F density depletions and corresponding electric fields that have been detected thus far have displayed a preponderance to appear between midnight and dawn. Associated with the narrow plasma depletions that are detected are broad spectra of electric field and plasma density irregularities for which a full vector set of measurements is available for detailed study. The VEFI data represents a new set of measurements that are germane to numerous fundamental aspects of the electrodynamics and irregularities inherent to the Earth s low latitude ionosphere.

Pfaff, R.; Freudenreich, H.; Klenzing, J.

2011-01-01

291

Particle drift in a resonance tube--a numerical study.  

PubMed

The paper considers longitudinal drift of small particles in a resonance tube, caused by periodic shock waves, and its effect on particle agglomeration. It is found that depending on particle size, drift is caused by shock waves and/or gas acceleration and compression. It is also shown that the drift velocity and direction can be controlled by the frequency of the piston that causes gas oscillations in the resonance tube. The obtained numerical solutions indicate that particle drift in a resonance tube enhances aerosol agglomeration. An agglomeration kernel is derived for this case, accounting for particle drift, leading to an estimate of agglomeration time. The time predicted by present model is of the same order of magnitude as that obtained from experiments in the literature. PMID:14514188

Alexeev, A; Gutfinger, C

2003-09-01

292

Mapping climatological seasonal variations of surface currents in the tropical Atlantic using ship drifts  

Microsoft Academic Search

The seasonal variability of current velocities in the tropical Atlantic was studied by grouping ship drift velocity observations into 2°×5° boxes and calculating monthly mean velocity values. These values were used to calculate and map the annual mean velocity, the seasonal variation about the mean, the annual and semiannual harmonics, and the first two empirical orthogonal functions (EOFs).The seasonal variation

Philip L. Richardson; David Walsh

1986-01-01

293

Slow drift mirror kinetic instability at a finite electron temperature in a nonmaxwellian space plasma  

NASA Astrophysics Data System (ADS)

A slow drift mirror (SDM) instability has been analyzed in the scope of kinetic approximation, with accounting for the electron pressure for different particle distribution functions. The dependence of the SDM instability increment growth rate on the parameters of the anisotropic ? distribution with the loss cone, which is used to model real space plasma particle distributions, has been studied. An analysis indicated that the appearance of the loss cone in the ion distribution function results in a decrease in the SDM mode frequency, and an enhancement of the suprathermal tail (a decrease in ?) increases the SDM mode frequency as compared to the Maxwellian distribution. In other words, particle redistribution from the region of low velocities into that of high velocities results in an increase in the SDM mode frequency.

Feygin, F. Z.; Khabazin, Yu. G.

2014-11-01

294

Evidence for Transient Electric Field Gradients in H-like Ions Traversing Gd Targets at High Velocities  

SciTech Connect

Transient electric field gradients have been observed in measurements of particle-{gamma}-angular correlations of Coulomb excited nuclei in H-like ions during traversal through thick metallic layers. The V{sub ZZ} values deduced for {sup 20}Ne( 2{sup +}) , {sup 32}S( 2{sup +}) , {sup 40}Ar( 2{sup +}) , {sup 52}Cr( 2{sup +}) , {sup 54}Fe( 2{sup +}) , and {sup 62}Ni( 2{sup +}) are found to be of the order of 10{sup 21} V/cm{sup 2} with consistently positive sign. They arise from distortions of the 1s electron orbit of the H-like ions by the wake field gradient induced in the solid by the charge of the moving ion. The observed interaction frequencies reflect the sign of the quadrupole moment of the excited 2{sup +} states. {copyright} {ital 1997} {ital The American Physical Society}

Grabowy, U.; Speidel, K.; Busch, H.; Gohla, A. [Institut fuer Strahlen- und Kernphysik, Universitaet Bonn, Nussallee 14-16, D-53115 Bonn (Germany)] [Institut fuer Strahlen- und Kernphysik, Universitaet Bonn, Nussallee 14-16, D-53115 Bonn (Germany); Cub, J.; Wollersheim, H. [Gesellschaft fuer Schwerionenforschung, Postfach 110552, D-64220 Darmstadt (Germany)] [Gesellschaft fuer Schwerionenforschung, Postfach 110552, D-64220 Darmstadt (Germany); Jakob, G. [Physik-Dept.Technische Universitaet Muenchen, James-Franck-Str., D-85748 Garching (Germany)] [Physik-Dept.Technische Universitaet Muenchen, James-Franck-Str., D-85748 Garching (Germany); Gerber, J. [Institut de Recherches Subatomique, F-67037 Strasbourg (France)] [Institut de Recherches Subatomique, F-67037 Strasbourg (France); Loewe, M. [Sektion Physik Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)] [Sektion Physik Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)

1997-12-01

295

Laser initiated reactions in N{sub 2}O clusters studied by time-sliced ion velocity imaging technique  

SciTech Connect

Laser initiated reactions in N{sub 2}O clusters were studied by a time-sliced velocity imaging technique. The N{sub 2}O clusters, (N{sub 2}O){sub n}, generated by supersonic expansion were irradiated by an ultraviolet laser around 204 nm to convert reactant pairs, O({sup 1}D{sub 2})-(N{sub 2}O){sub n?1}. The NO molecules formed from these reactant pairs were ionized by the same laser pulse and their velocity distribution was determined by the time-sliced velocity imaging technique. At low nozzle pressure, lower than 1.5 atm, the speed distribution in the frame moving with the clusters consists of two components. These components were ascribed to the products appeared in the backward and forward directions in the center-of-mass frame, respectively. The former consists of the vibrational ground state and the latter consists of highly vibrational excited states. At higher nozzle pressure, a single broad speed distribution became dominant for the product NO. The pressure and laser power dependences suggested that this component is attributed to the product formed in the clusters larger than dimer, (N{sub 2}O){sub n} (n ? 3)

Honma, Kenji [Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297 (Japan)] [Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297 (Japan)

2013-07-28

296

Interstory drift ratio of building structures subjected to near-fault ground motions based on generalized drift spectral analysis  

Microsoft Academic Search

This paper focuses on the interstory drift ratio (IDR) demands of building structures subjected to near-fault ground motions having different impulsive characteristics based on generalized interstory drift spectral analysis. The near-fault ground motions considered include the idealized simple pulses and three groups of near-fault ground motions with forward directivity pulses, fling-step pulses and without velocity pulse. Meanwhile, the building systems

Dixiong Yang; Jianwei Pan; Gang Li

2010-01-01

297

Measuring the Effect of Ion-Induced Drift-Gas Polarization on the Electrical Mobilities of Multiply-Charged Ionic Liquid Nanodrops in Air  

NASA Astrophysics Data System (ADS)

The electrical mobilities of multiply-charged nanodrops of the ionic liquid 1-ethyl, 3-methylimidazolium dicyanamide (EMI-N[CN]2) were accurately measured in air at 20 °C for mass-selected clusters of composition [EMI-N[CN]2] n [EMI+] z , with 2 ? n ? 369 and 1 ? z ? 10. We confirm prior reports that the mobility Z of a globular ion of mass m is given approximately by the modified Stokes-Millikan law for spheres, Z = Z SM, mod ( d m + d g , z, m), where d m = (6 m/ ??)1/3 is the nanodrop mass-diameter based on the density ? of the liquid (corrected for the capillary compression and electrostatic deformation of the nanodrop), and d g is an effective air molecule diameter. There is however a measurable (up to 7 %) and systematic z-dependent departure of Z from Z SM,mod . As theoretically expected at small ? * , this effect is accurately described by a simple correction factor of the form Z/ Z SM, mod = ?(1 - ?? *), where kT? * is the potential energy due to the ion-induced dipole ( polarization) attraction between a perfectly-conducting charged nanodrop and a polarized neutral gas-molecule at a distance ( d m + d g )/2 from its center. An excellent fit of this model to hundreds of data points is found for d g ? 0.26 nm, ? ? 0.36, and ? ? 0.954. Accounting for the effect of polarization decreases d g considerably with respect to values inferred from earlier nanodrop measurements that ignored this effect. In addition, and in spite of ambiguities in the mobility calibration scale, the measured constant ? smaller than unity increases Millikan's drag enhancement factor from the accepted value ? m ? 1.36 to the new value ? ? ? m / ? ? 1.42 ± 0.03.

Fernández-García, Juan; Fernández de la Mora, Juan

2013-12-01

298

Edge Ion Velocity and Temperature Measurements in NSTX T.M. Biewer, R.E. Bell, D. W. Johnson  

E-print Network

Princeton Plasma Physics Lab, Princeton, NJ 08543 T.M. Biewer, October 29th, 2003 45th Annual American electric field, Er, from both Helium (majority) and Carbon (impurity) measurements. When High Harmonic Fast power is applied. This suggests that ion confinement is degraded in the edge during the time that the RF

Biewer, Theodore

299

Effects of particle drifts on the solar modulation of galactic cosmic rays  

NASA Technical Reports Server (NTRS)

Gradient and curvature drifts in an Archimedean-spiral magnetic field are shown to produce a significant effect on the modulation of galactic cosmic rays by the solar wind. The net modulation, heliocentric radial gradient, and average energy change of particles which reach the inner solar system are significantly reduced. The effects of drifts are due to the fact that cosmic rays for which the drift velocity is comparable to the wind velocity or larger, have more rapid access to the inner solar system than in the absence of drifts.

Jokipii, J. R.; Levy, E. H.

1977-01-01

300

High resolution drift chambers  

SciTech Connect

High precision drift chambers capable of achieving less than or equal to 50 ..mu..m resolutions are discussed. In particular, we compare so called cool and hot gases, various charge collection geometries, several timing techniques and we also discuss some systematic problems. We also present what we would consider an ''ultimate'' design of the vertex chamber. 50 refs., 36 figs., 6 tabs.

Va'vra, J.

1985-07-01

301

The KLOE drift chamber  

Microsoft Academic Search

The stringent requirements of the KLOE experiment on dimensions, efficiency, resolution and transparency of its drift chamber led to building a tracking device which can be considered innovative from many points of view.Details of the design and construction of this detector, together with preliminary results from the test of its full scale prototype, constructed and operated under a test beam

A. Andryakov; A. Antonelli; R. Baldini-Ferroli; G. Bencivenni; L. Bucci; A. Calcaterra; P. L Campana; S Dell'Agnello; R De Sangro; P De Simone; G. Felici; C. Forti; G. Finocchiaro; V. Kulikov; S. Moccia; A. Nedosekin; V. Patera; M. Piccolo; A. Denig; M. Imhof; W. Kluge; U Von Hagel; S. Weseler; G. Cataldi; P. Creti; V. Elia; V. Golovatyuk; E. Gorini; F. Grancagnolo; M. Panareo; M. Primavera; S. Spagnolo; C. Bacci; F. Ceradini; E De Lucia; F La Cava; C. Luisi; G. Margutti; D. Picca; L. Pontecorvo; R. Messi; L. Paoluzi; E. Pasqualucci; P. Valente

1996-01-01

302

Antarctica and Continental Drift.  

National Technical Information Service (NTIS)

Continental drift reconstructions by computerized matching of the 1,000 fm isobaths are presented for Africa/Antarctica, Australia/Antarctica and India/Antarctica. Sufficiently good congruency is obtained for the first two to suggest that they are probabl...

R. S. Dietz, J. C. Holden, W. P. Sproll

1972-01-01

303

Drift wave turbulence in the presence of a dust density gradient.  

PubMed

We present turbulent properties of electrostatic drift waves in a nonuniform collisional plasma composed of magnetized electrons and ions in the presence of immobile dust particles. For this purpose, we derive a pair of nonlinear quasi-two-dimensional equations exhibiting the coupling between the generalized ion vorticity and the density fluctuations associated with collisional drift waves. The effect of a dust density gradient on the initial drift instability and fully developed turbulence is examined numerically. PMID:22181281

Kendl, A; Shukla, P K

2011-10-01

304

Dual mode ion mobility spectrometer and method for ion mobility spectrometry  

DOEpatents

Ion mobility spectrometer apparatus may include an ion interface that is operable to hold positive and negative ions and to simultaneously release positive and negative ions through respective positive and negative ion ports. A first drift chamber is operatively associated with the positive ion port of the ion interface and encloses an electric field therein. A first ion detector operatively associated with the first drift chamber detects positive ions from the first drift chamber. A second drift chamber is operatively associated with the negative ion port of the ion interface and encloses an electric field therein. A second ion detector operatively associated with the second drift chamber detects negative ions from said second drift chamber.

Scott, Jill R [Idaho Falls, ID; Dahl, David A [Idaho Falls, ID; Miller, Carla J [Idaho Falls, ID; Tremblay, Paul L [Idaho Falls, ID; McJunkin, Timothy R [Idaho Falls, ID

2007-08-21

305

Drift wave instability in the Io plasma torus  

NASA Technical Reports Server (NTRS)

A linear normal mode analysis of the drift wave instability in the Io plasma torus was carried out on the basis of the Richmond (1973) and Huang et al. (1990) analyses of drift waves in the vicinity of the earth's plasmapause. Results indicate that the outer torus boundary is linearly unstable to the growth of electrostatic drift waves. It is shown that the linear growth rate is proportional to the ion drift frequency and to the ratio of the flux tube charge content to the Jovian ionospheric Pedersen conductance. It is also shown that various theoretical models of global radial transport in Jupiter's atmosphere (including corotating convection, interchange diffusion, and transient flux tube convection) can be understood as plausible nonlinear evolutions of electrostatic drift waves.

Huang, T. S.; Hill, T. W.

1991-01-01

306

Drift compression and final focus options for heavy ionfusion  

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. The authors 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 1D 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.

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

2005-01-18

307

Dike Propagation Near Drifts  

SciTech Connect

The purpose of this Analysis and Model Report (AMR) supporting the Site Recommendation/License Application (SR/LA) for the Yucca Mountain Project is the development of elementary analyses of the interactions of a hypothetical dike with a repository drift (i.e., tunnel) and with the drift contents at the potential Yucca Mountain repository. This effort is intended to support the analysis of disruptive events for Total System Performance Assessment (TSPA). This AMR supports the Process Model Report (PMR) on disruptive events (CRWMS M&O 2000a). This purpose is documented in the development plan (DP) ''Coordinate Modeling of Dike Propagation Near Drifts Consequences for TSPA-SR/LA'' (CRWMS M&O 2000b). Evaluation of that Development Plan and the work to be conducted to prepare Interim Change Notice (ICN) 1 of this report, which now includes the design option of ''Open'' drifts, indicated that no revision to that DP was needed. These analyses are intended to provide reasonable bounds for a number of expected effects: (1) Temperature changes to the waste package from exposure to magma; (2) The gas flow available to degrade waste containers during the intrusion; (3) Movement of the waste package as it is displaced by the gas, pyroclasts and magma from the intruding dike (the number of packages damaged); (4) Movement of the backfill (Backfill is treated here as a design option); (5) The nature of the mechanics of the dike/drift interaction. These analyses serve two objectives: to provide preliminary analyses needed to support evaluation of the consequences of an intrusive event and to provide a basis for addressing some of the concerns of the Nuclear Regulatory Commission (NRC) expressed in the Igneous Activity Issue Resolution Status Report.

NA

2002-03-04

308

Microsaccade and drift dynamics reflect mental fatigue.  

PubMed

Our eyes are always in motion. Even during periods of relative fixation we produce so-called 'fixational eye movements', which include microsaccades, drift and tremor. Mental fatigue can modulate saccade dynamics, but its effects on microsaccades and drift are unknown. Here we asked human subjects to perform a prolonged and demanding visual search task (a simplified air traffic control task), with two difficulty levels, under both free-viewing and fixation conditions. Saccadic and microsaccadic velocity decreased with time-on-task whereas drift velocity increased, suggesting that ocular instability increases with mental fatigue. Task difficulty did not influence eye movements despite affecting reaction times, performance errors and subjective complexity ratings. We propose that variations in eye movement dynamics with time-on-task are consistent with the activation of the brain's sleep centers in correlation with mental fatigue. Covariation of saccadic and microsaccadic parameters moreover supports the hypothesis of a common generator for microsaccades and saccades. We conclude that changes in fixational and saccadic dynamics can indicate mental fatigue due to time-on-task, irrespective of task complexity. These findings suggest that fixational eye movement dynamics have the potential to signal the nervous system's activation state. PMID:23675850

Di Stasi, Leandro L; McCamy, Michael B; Catena, Andrés; Macknik, Stephen L; Cañas, José J; Martinez-Conde, Susana

2013-08-01

309

Density drift instabilities and weak collisions. [in space plasmas  

NASA Technical Reports Server (NTRS)

A model is developed which describes the effects of weak collisions on the linear kinetic theory of electrostatic density drift instabilities. A dispersion equation valid at all frequencies and wave numbers is derived using the assumptions of a weak, uniform density gradient; a uniform magnetic field; and the BGK collision operator with a modification of the local approximation. The properties of the universal and collisional density drift instabilities at maximum growth rates are examined in detail. The thresholds of the instabilities are examined for an ionospheric model which includes ion-neutral, electron-neutral, and electron-ion collisions, and are compared with the threshold of the lower hybrid density drift instability. It is concluded that the k to the -5th short wavelength density power spectra observed above 280 km in the PLUMEX experiment are due to the effects of the universal density drift instability.

Gary, S. P.; Bernhardt, P. A.; Cole, T. E.

1983-01-01

310

Kinetics of copper drift in low-? polymer interlevel dielectrics  

Microsoft Academic Search

This paper addresses the drift of copper ions (Cu+) in various low-permittivity (low-?) polymer dielectrics to identify copper barrier requirements for reliable interconnect integration in future ULSI. Stressing at temperatures of 150-275°C and electric fields up to 1.5 MV\\/cm was conducted on copper-insulator-silicon capacitors to investigate the penetration of Cu+ into the polymers. The drift properties of Cu+ in six

Alvin L. S. Loke; Jeffrey T. Wetzel; Paul H. Townsend; Tsuneaki Tanabe; Raymond N. Vrtis; Melvin P. Zussman; Devendra Kumar; Changsup Ryu; S. Simon Wong

1999-01-01

311

Coupled-cavity drift-tube linac  

DOEpatents

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the {pi}-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is {beta}{lambda}, where {lambda} is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range. 5 figs.

Billen, J.H.

1996-11-26

312

Molecular Communication Using Brownian Motion with Drift  

E-print Network

Inspired by biological communication systems, molecular communication has been proposed as a viable scheme to communicate between nano-sized devices separated by a very short distance. Here, molecules are released by the transmitter into the medium, which are then sensed by the receiver. This paper develops a preliminary version of such a communication system focusing on the release of either one or two molecules into a fluid medium with drift. We analyze the mutual information between transmitter and the receiver when information is encoded in the time of release of the molecule. Simplifying assumptions are required in order to calculate the mutual information, and theoretical results are provided to show that these calculations are upper bounds on the true mutual information. Furthermore, optimized degree distributions are provided, which suggest transmission strategies for a variety of drift velocities.

Kadloor, Sachin; Eckford, Andrew W

2010-01-01

313

Coupled-cavity drift-tube linac  

DOEpatents

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the .pi.-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is .beta..lambda., where .lambda. is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a .pi./2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range.

Billen, James H. (Los Alamos, NM)

1996-01-01

314

Molecular communication using Brownian motion with drift.  

PubMed

Inspired by biological communication systems, molecular communication has been proposed as a viable scheme to communicate between nano-sized devices separated by a very short distance. Here, molecules are released by the transmitter into the medium, which are then sensed by the receiver. This paper develops a preliminary version of such a communication system focusing on the release of either one or two molecules into a fluid medium with drift. We analyze the mutual information between transmitter and the receiver when information is encoded in the time of release of the molecule. Simplifying assumptions are required in order to calculate the mutual information, and theoretical results are provided to show that these calculations are upper bounds on the true mutual information. Furthermore, optimized degree distributions are provided, which suggest transmission strategies for a variety of drift velocities. PMID:22434820

Kadloor, Sachin; Adve, Raviraj S; Eckford, Andrew W

2012-06-01

315

A spatially resolving x-ray crystal spectrometer for measurement of ion-temperature and rotation-velocity profiles on the Alcator C-Mod tokamak  

SciTech Connect

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra ({lambda}/d{lambda}>6000) of He-like and H-like Ar K{alpha} lines with good spatial ({approx}1 cm) and temporal ({approx}10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (T{sub i}), and toroidal plasma rotation velocity (v{sub {phi}}) from the line Doppler widths and shifts. The data analysis techniques, T{sub i} and v{sub {phi}} profiles, analysis of fusion-neutron background, and predictions of performance on other tokamaks, including ITER, will be presented.

Hill, K. W.; Bitter, M. L.; Scott, S. D. [PPPL, Princeton University, P.O. Box 451, Princeton, New Jersey 08543 (United States); Ince-Cushman, A.; Reinke, M.; Rice, J. E. [PSFC, MIT, Cambridge, Massachusetts 02139 (United States); Beiersdorfer, P.; Gu, M.-F. [LLNL, Livermore, California 94550 (United States); Lee, S. G. [National Fusion Research Institute, Taejeon 305-333 (Korea, Republic of); Broennimann, Ch.; Eikenberry, E. F. [DECTRIS Ltd., CH-5232 Villigen-PSI (Switzerland)

2008-10-15

316

A drift-magnetohydrodynamical fluid model of helical magnetic island equilibria in the pedestals of H-mode tokamak plasmas  

SciTech Connect

A drift-magnetohydrodynamical (MHD) fluid model is developed for an isolated, steady-state, helical magnetic island chain, embedded in the pedestal of a large aspect ratio, low-beta, circular cross section, H-mode tokamak plasma, to which an externally generated, multiharmonic, static magnetic perturbation whose amplitude is sufficiently large to fully relax the pedestal toroidal ion flow is applied. The model is based on a set of single helicity, reduced, drift-MHD fluid equations which take into account neoclassical poloidal and toroidal flow damping, the perturbed bootstrap current, diamagnetic flows, anomalous cross-field diffusion, average magnetic-field line curvature, and coupling to drift-acoustic waves. These equations are solved analytically in a number of different ordering regimes by means of a systematic expansion in small quantities. For the case of a freely rotating island chain, the main aims of the calculation are to determine the chain's phase velocity, and the sign and magnitude of the ion polarization term appearing in its Rutherford radial width evolution equation. For the case of a locked island chain, the main aims of the calculation are to determine the sign and magnitude of the polarization term.

Fitzpatrick, R.; Waelbroeck, F. L. [Department of Physics, Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2010-06-15

317

Swarm studies on elementary processes and ion-molecule reactions in low-temperature plasmas  

NASA Astrophysics Data System (ADS)

This paper deals with the presentation and discussion of some recent measurements on the interaction of electron and ion swarms in gases, with particular emphasis on flourinated gases. The processes to be discussed are related to electron impact ionization and attachment, including Penning ionization and electron detachment. Electron transport is discussed in mixtures of SF6 and fluorocarbon gases, where interesting regions of negative differential conductivity have been observed in C2F4, and apparent pressure dependences of the drift velocity in C4F8. Ion transport is discussed in terms of recent measurements on positive and negative ions in SF6 and Ar. Finally, the subject of ion-molecule reactions is illustrated with the dissociation and charge transfer processes of daughter ions in nitrogen. Throughout the paper, the advantages and limitations of both the pulsed Townsend technique and the drift tube-mass spectrometer are highlighted.

de Urquijo, J.

2002-08-01

318

Fermilab drift tube Linac revisited  

SciTech Connect

Using the PARMILA code running under PC-WINDOWS, the present performance of the Fermilab Drift Tube Linac has been analyzed in the light of new demands on the Linac/Booster complex (the Proton Source). The Fermilab Drift Tube Linac (DTL) was designed in the sixties as a proton linac with a final energy of 200 MeV and a peak current of 100mA. In the seventies, in order to enable multi-turn charge exchange injection into the Booster, the ion source was replaced by an H- source with a peak beam current of 25mA. Since then the peak beam current was steadily increased up to 55mA. In the early nineties, part of the drift tube structure was replaced with a side-coupled cavity structure in order to increase the final energy to 400 MeV. The original and still primary purpose of the linac is to serve as the injector for the Booster. As an added benefit, the Neutron Therapy Facility (NTF) was built in the middle seventies. It uses 66MeV protons from the Linac to produce neutrons for medical purposes. The Linac/Booster complex was designed to run at a fundamental cycling rate of 15Hz, but beam is accelerated on every cycle only when NTF is running. Until recently the demand from the High Energy Physics program resulted in an average linac beam repetition rate of order 1 Hz. With the MiniBoone experiment and the NuMI program, the demands on the Proton Source have changed, with emphasis on higher beam repetition rates up to 7.5Hz. Historically the beam losses in the linac were small, localized at one spot, so activation was not an important issue. With higher beam rate, this has the potential to become the dominant issue. Until today all tuning in the linac and Proton Source was governed by two goals: to maximize the peak beam current out of the linac and to minimize the beam losses in the linac. If maximal peak current from the linac is no longer a primary goal, then the linac quadrupoles can be adjusted differently to achieve different goals.

Milorad Popovic

2004-05-12

319

Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears  

SciTech Connect

Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and the much smaller profile shear residual stress component.

Waltz, R. E.; Staebler, G. M. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)

2011-04-15

320

Gyrokinetic simulation of momentum transport with residual stress from diamagnetic level velocity shears  

NASA Astrophysics Data System (ADS)

Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E ×B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E ×B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E ×B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and the much smaller profile shear residual stress component.

Waltz, R. E.; Staebler, G. M.; Solomon, W. M.

2011-04-01

321

Motion of step pairs during drift-induced step bunching on a Si(0 0 1) vicinal face  

NASA Astrophysics Data System (ADS)

By Monte Carlo simulation of a lattice model with the periodic boundary condition, we study the motion of step pairs during step bunching on a Si(0 0 1) vicinal face heated by direct electric current. When the anisotropy of the surface diffusion is taken into account, step bunching occurs with the drift of adatoms. When the system width along the steps is so large that bunches fluctuate widely, the bunches with step-up drift recombine with neighboring bunches more frequently and grow faster than those with step-down drift. When the system width along the steps is so small that bunches are straight, the recombination is suppressed irrespective of the drift direction. The bunches with step-up drift grow slower than those with step-down drift. With increasing the drift velocity, separation of the step pair from the bunch occurs. The separated step pairs recede with step-down drift and advances with step-up drift.

Sato, Masahide; Uwaha, Makio; Takahashi, Tetsu

2007-05-01

322

Macroinvertebrate drift in a Rocky Mountain stream  

Microsoft Academic Search

An extensive series of drift collections from a Rocky Mountain stream was used to investigate quantitative patterns in the taxonomic composition of drift throughout spring, summer and fall for 1975–1978. Drift was estimated by drift rate, the number of organisms drifting past a point per 24 h; and by drift density, the numbers of organisms collected per 100 m3 of

J. David Allan

1987-01-01

323

Ion temperature troughs in the equatorial topside ionosphere  

NASA Technical Reports Server (NTRS)

It is noted that the retarding potential analyzer aboard OGO 6 sometimes records pronounced minima of ion temperature when the satellite crosses the magnetic equator and that the variation of ion temperature along the satellite path takes the form of a trough about 20 to 30 deg wide in latitude and up to 1200 K in depth. Observations of night-time, daytime, and dawn-dusk ion-temperature troughs are discussed along with ion concentration and composition in the troughs, ion drift velocities, and comparisons with Jacchia's (1971) thermospheric model. An explanation of trough morphology is given in terms of thermospheric winds which produce a transequatorial plasma flow along geomagnetic field lines. The effect of such a plasma flow on 630-nm nightglow is considered, and it is shown how ion composition affects the extent of ion-temperature troughs. Some questions for further study are suggested.

Rishbeth, H.; Van Zandt, T. E.; Hanson, W. B.

1977-01-01

324

High-resolution photofragment spectroscopy of the O2+ b4Sigmag- (v' = 3, 4, 5) <-- a4Piu (v' = 3, 4, 5) First Negative system using coaxial dye-laser and velocity-tuned ion beams  

Microsoft Academic Search

A new photofragment spectrometer employing coaxial tunable single-mode laser and velocity-tuned fast-ion beams has been used to measure transition energies in the O2+ b4Sigmag- <-- a4Piu First Negative system to an accuracy and precision that are an order of magnitude better than was previously possible in Doppler-limited emission spectroscopy. The technique consists of velocity-tuning a beam of metastable O2+ a4Piu

P. C. Cosby; J.-B. Ozenne; J. T. Moseley; D. L. Albritton

1980-01-01

325

Describing Velocity  

NSDL National Science Digital Library

Learn to connect position-time and velocity-time graphs. Explore velocity using an animated car icon connected to either a position-time or a velocity-time graph, or both. Then investigate other motion graphs. Describing Velocity is the fourth of five SmartGraphs activities designed for a typical physical science unit of study on the motion of objects.

Consortium, The C.

2012-02-07

326

Effects of non-Maxwellian electron velocity distribution functions and nonspherical geometry on minor ions in the solar wind  

NASA Technical Reports Server (NTRS)

A previous model has shown that in order to account for the charge state distribution in the low-speed solar wind, a high coronal temperature is necessary and that this temperature peak goes together with a peak of nx/np in the corona. In the present paper, one of the assumptions made previously, i.e., that coronal electrons are Maxwellian, is relaxed, and a much cooler model is presented, which could account for the same oxygen charge states in the solar wind due to the inclusion of non-Maxwellian electrons. Also, due to a different choice of the coronal magnetic field geometry, this model would show no enhancement of the coronal nx/np. Results of the two models are then compared, and observational tests to distinguish between the two scenarios are proposed: comparison of directly measured coronal Te to charge state measurements in the solar wind, determination of the coronal nx/np measurement of ion speeds in the acceleration region of the solar wind, and measurement of the frozen-in silicon charge state distribution.

Burgi, A.

1987-01-01

327

Quaternary contourite drifts of the Western Spitsbergen margin  

NASA Astrophysics Data System (ADS)

The study of contourite drifts is an increasingly used tool for understanding the climate history of the oceans. In this paper we analyse two contourite drifts along the continental margin west of Spitsbergen, just south of the Fram Strait where significant water mass exchanges impact the Arctic climate. We detail the internal geometry and the morphologic characteristics of the two drifts on the base of multichannel seismic reflection data, sub-bottom profiles and bathymetry. These mounded features, that we propose to name Isfjorden and Bellsund drifts, are located on the continental slope between 1200 and 1800 m depth, whereas the upper slope is characterized by reduced- or non-deposition. The more distinct Isfjorden Drift is about 25 km wide and 45 km long, and over 200 ms TWT thick. We revise the 13 years-long time series of velocity, temperature, and salinity obtained from a mooring array across the Fram Strait. Two distinct current cores are visible in the long-term average. The shallower current core has an average northward velocity of about 20 cm/s, while the deeper bottom current core at about 1450 m depth has an average northward velocity of about 9 cm/s. We consider Norwegian Sea Deep Water episodically ventilated by relatively dense and turbid shelf water from the Barents Sea responsible for the accumulation of the contourites. The onset of the drift growth west of Spitsbergen is inferred to be about 1.3 Ma and related to the Early Pleistocene glacial expansion recorded in the area. The lack of mounded contouritic deposits on the continental slope of the Storfjorden is related to consecutive erosion by glacigenic debris flows. The Isfjorden and Bellsund drifts are inferred to contain the record of the regional palaeoceanography and glacial history and may constitute an excellent target of future scientific drilling.

Rebesco, Michele; Wåhlin, Anna; Laberg, Jan Sverre; Schauer, Ursula; Beszczynska-Möller, Agnieszka; Lucchi, Renata Giulia; Noormets, Riko; Accettella, Daniela; Zarayskaya, Yulia; Diviacco, Paolo

2013-09-01

328

Carrier drift-mobilities and solar cell models for amorphous and nanocrystalline silicon  

E-print Network

of 10-3 to 1 cm2 /Vs at room-temperature. These low drift mobilities establish corresponding hole mobility limits to the power generation and useful thicknesses of the solar cells. The properties of as The mobility of a charge carrier describes its drift-velocity v in the presence of an electric field F: v = F

Schiff, Eric A.

329

Electromagnetic nonlinear gyrokinetics with polarization drift  

NASA Astrophysics Data System (ADS)

A set of new nonlinear electromagnetic gyrokinetic Vlasov equation with polarization drift and gyrokinetic Maxwell equations is systematically derived by using the Lie-transform perturbation method in toroidal geometry. For the first time, we recover the drift-kinetic expression for parallel acceleration [R. M. Kulsrud, in Basic Plasma Physics, edited by A. A. Galeev and R. N. Sudan (North-Holland, Amsterdam, 1983)] from the nonlinear gyrokinetic equations, thereby bridging a gap between the two formulations. This formalism should be useful in addressing nonlinear ion Compton scattering of intermediate-mode-number toroidal Alfvén eigenmodes for which the polarization current nonlinearity [T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266 (1995)] and the usual finite Larmor radius effects should compete.

Duthoit, F.-X.; Hahm, T. S.; Wang, Lu

2014-08-01

330

Fundamentals of traveling wave ion mobility spectrometry.  

PubMed

Traveling wave ion mobility spectrometry (TW IMS) is a new IMS method implemented in the Synapt IMS/mass spectrometry system (Waters). Despite its wide adoption, the foundations of TW IMS were only qualitatively understood and factors governing the ion transit time (the separation parameter) and resolution remained murky. Here we develop the theory of TW IMS using derivations and ion dynamics simulations. The key parameter is the ratio (c) of ion drift velocity at the steepest wave slope to wave speed. At low c, the ion transit velocity is proportional to the squares of mobility (K) and electric field intensity (E), as opposed to linear scaling in drift tube (DT) IMS and differential mobility analyzers. At higher c, the scaling deviates from quadratic in a way controlled by the waveform profile, becoming more gradual with the ideal triangular profile but first steeper and then more gradual for realistic profiles with variable E. At highest c, the transit velocity asymptotically approaches the wave speed. Unlike with DT IMS, the resolving power of TW IMS depends on mobility, scaling as K(1/2) in the low-c limit and less at higher c. A nonlinear dependence of the transit time on mobility means that the true resolving power of TW IMS differs from that indicated by the spectrum. A near-optimum resolution is achievable over an approximately 300-400% range of mobilities. The major predicted trends are in agreement with TW IMS measurements for peptide ions as a function of mobility, wave amplitude, and gas pressure. The issues of proper TW IMS calibration and ion distortion by field heating are also discussed. The new quantitative understanding of TW IMS separations allows rational optimization of instrument design and operation and improved spectral calibration. PMID:18986171

Shvartsburg, Alexandre A; Smith, Richard D

2008-12-15

331

The DRIFT Dark Matter Experiments  

Microsoft Academic Search

The current status of the DRIFT (Directional Recoil Identification From Tracks) experiment at Boulby Mine is presented, including the latest limits on the WIMP spin-dependent cross-section from 1.5 kg days of running with a mixture of CS2 and CF4. Planned upgrades to DRIFT IId are detailed, along with ongoing work towards DRIFT III, which aims to be the world's first

E. Daw; A. Dorofeev; J. R. Fox; J.-L. Gauvreau; C. Ghag; L. J. Harmon; J. L. Harton; M. Gold; E. R. Lee; D. Loomba; E. H. Miller; A. St. J. Murphy; S. M. Paling; J. M. Landers; N. Phan; M. Pipe; K. Pushkin; M. Robinson; S. W. Sadler; D. P. Snowden-Ifft; N. J. C. Spooner; D. Walker; D. Warner

2011-01-01

332

Obliquely propagating ion acoustic waves in the auroral E region: Further evidence of irregularity production by field-aligned electron streaming  

SciTech Connect

Common volume observations of E region high-latitude irregularities at decameter wavelengths have been obtained with the JHU/APL HF radar located at Goose Bay, Labrador, and the SHERPA HF radar located at Schefferville, Quebec. In this paper, the authors analyze an event with characteristics similar to those of a distinctive type of event described by Villain et al. (1987). The experimental configuration, which combines the azimuthal-scanning capability of the Goose Bay radar with the frequency-scanning operation of the Schefferville radar, has provided unambiguous evidence of the existence of two irregularity layers at different altitudes within the E region. The layers, which exhibit different characteristics, can be related to the action of the gradient drift and ion acoustic instability mechanisms. It is shown that the ion acoustic modes have phase velocities in the range of 400 to 550 m/s and are produced in regions of subcritical perpendicular electron Hall drift. They infer that the observed irregularities are produced through a combination of perpendicular and field-aligned relative electron-ion drifts. Features previously observed but no t satisfactorily explained by perpendicular drift excitation alone can be understood in terms of field-aligned drift excitation. They conclude that the role of electron-ion field-aligned drift may be much more important than previously realized.

Villain, J.P. (Centre National de la Recherche Scientifique, Orleans (France)); Hanuise, C. (Univ. de Toulon, La Garde (France)); Greenwald, R.A.; Baker, K.B.; Ruohoniemi, J.M. (Johns Hopkins Univ., Laurel, MD (USA))

1990-06-01

333

A Parametric Study of Extended-MHD Drift Tearing  

E-print Network

The linear drift-tearing mode is analyzed for different regimes of the plasma-$\\beta$, ion-skin-depth parameter space with an unreduced, extended-MHD model. New dispersion relations are found at moderate plasma $\\beta$ and previous drift-tearing results are classified as applicable at small plasma $\\beta$. The drift stabilization of the mode in the regimes varies from non-existent/weak to complete. As the diamagnetic-drift frequency is proportional to the plasma $\\beta$, verification exercises with unreduced, extended-MHD models in the small plasma-$\\beta$ regimes are impractical. The new dispersion relations in the moderate plasma-$\\beta$ regimes are used to verify the extended-MHD implementation of the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. Given the small boundary-layer skin depth, discussion of the validity of the first-order finite-Larmour-radius model is presented.

King, Jacob R

2014-01-01

334

Lower hybrid drift waves: space observations.  

PubMed

Lower hybrid drift waves (LHDWs) are commonly observed at plasma boundaries in space and laboratory, often having the strongest measured electric fields within these regions. We use data from two of the Cluster satellites (C3 and C4) located in Earth's magnetotail and separated by a distance of the order of the electron gyroscale. These conditions allow us, for the first time, to make cross-spacecraft correlations of the LHDWs and to determine the phase velocity and wavelength of the LHDWs. Our results are in good agreement with the theoretical prediction. We show that the electrostatic potential of LHDWs is linearly related to fluctuations in the magnetic field magnitude, which allows us to determine the velocity vector through the relation ??Edt·v = ?(?B)(?). The electrostatic potential fluctuations correspond to ?10% of the electron temperature, which suggests that the waves can strongly affect the electron dynamics. PMID:23006181

Norgren, Cecilia; Vaivads, Andris; Khotyaintsev, Yuri V; André, Mats

2012-08-01

335

Impact on electron velocity of hollow electron beam in HIRFL-CSR e-cooler system  

NASA Astrophysics Data System (ADS)

Cooling efficiency in electron cooling systems is closely related to the velocity of electron. The velocity of electron has offset due to the space charge of the intense electron beam in the drift tube of the cooling section and thus increases the temperature of electrons. In order to minimize this effect, a new type of electron gun is adopted to produce a hollow electron beam in HIRFL-CSR e-cooler project. The hot ion beam is cooled by Coulomb interaction with intense and cold hollow electron beams. Using typical parameters of the CSRm e-cooler, theoretical calculations comparing the impact of the space charge field on electron velocity for solid and hollow electron beam are carried out.

Xia, G. X.; Xia, J. W.; Yang, J. C.; Liu, W.; Wu, J. X.; Yin, X. J.; Zhao, H. W.; Wei, B. W.

2003-08-01

336

Effect of ion and ion-beam mass ratio on the formation of ion-acoustic solitons in magnetized plasma in the presence of electron inertia  

SciTech Connect

The propagation of ion-acoustic solitary waves in magnetized plasma with cold ions and ion-beams together with electron inertia has been investigated theoretically through the Korteweg-de Vries equation. Subject to the drift velocity of the ion beam, the existence of compressive solitons is found to become extinct as {alpha} (=cold ion mass/ion-beam mass) tends to 0.01 when {gamma}=0.985 ({gamma} is the beam velocity/phase velocity). Interestingly, a transitional direction of propagation of solitary waves has been unearthed for change over, from compressive solitons to rarefactive solitons based on {alpha} and {sigma}{sub {upsilon}}(=cosine of the angle {theta} made by the wave propagation direction {xi} with the direction of the magnetic field) for fixed Q(=electron mass/ion mass). Further, the direction of propagation of ion-acoustic waves is found to be the deterministic factor to admit compressive or rarefactive solitons subject to beam outsource.

Kalita, B. C. [Department of Mathematics, Gauhati University, Guwahati 781 014, Assam (India); Barman, S. N. [Department of Mathematics, Arya Vidyapeeth College, Guwahati 781 016, Assam (India)

2009-05-15

337

Effects of grids in drift tubes  

SciTech Connect

In 2011, we upgraded a 201 MHz buncher in the proton injector for the alternating gradient synchrotron (AGS) - relativistic heavy ion collider (RHIC) complex. In the buncher we installed four grids made of tungsten to improve the transit time factor. The grid installed drift tubes have 32 mm of inner diameter and the each grid consists of four quadrants. The quadrants were cut out precisely from 1mm thick tungsten plates by a computerized numerically controlled (CNC) wire cutting electrical discharge machining (EDM). The 3D electric field of the grid was simulated.

Okamura M.; Yamauchi, H.

2012-05-20

338

Drift effects on geodesic acoustic modes  

NASA Astrophysics Data System (ADS)

We present a fluid model for geodesic acoustic modes including diamagnetic effects due to inhomogeneous plasma density and temperature. Effects of ion parallel viscosity (pressure anisotropy), which allows to recover exactly the adiabatic index obtained in kinetic theory are considered. We show that diamagnetic effects lead to the positive up-shift of the GAM frequency and appearance of the second (lower frequency) branch related to the drift frequency. The latter is a result of modification of the degenerate (zero frequency) zonal flow branch which acquires a finite frequency or becomes unstable in regions of high temperature gradients.

Sgalla, R. J. F.; Smolyakov, A. I.; Elfimov, A. G.; Bashir, M. F.

2013-01-01

339

Effect of solenoidal magnetic field on drifting laser plasma  

SciTech Connect

An ion source for accelerators requires to provide a stable waveform with a certain pulse length appropriate to the application. The pulse length of laser ion source is easy to control because it is expected to be proportional to plasma drifting distance. However, current density decay is proportional to the cube of the drifting distance, so large current loss will occur under unconfined drift. We investigated the stability and current decay of a Nd:YAG laser generated copper plasma confined by a solenoidal field using a Faraday cup to measure the current waveform. It was found that the plasma was unstable at certain magnetic field strengths, so a baffle was introduced to limit the plasma diameter at injection and improve the stability. Magnetic field, solenoid length, and plasma diameter were varied in order to find the conditions that minimize current decay and maximize stability.

Takahashi, Kazumasa; Sekine, Megumi [Tokyo Institute of Technology, Yokohama 226-8502 (Japan); Okamura, Masahiro [Brookhaven National Laboratory, Upton, NY 11973 (United States) and RIKEN, Wako-shi, Saitama 351-0198 (United States); Cushing, Eric [Pennsylvania State University, University Park, PA 16802 (United States); Jandovitz, Peter [Cornell University, Ithaca, NY 14853 (United States)

2013-04-19

340

Bouchaud walks with variable drift  

E-print Network

In this paper we study a sequence of Bouchaud trap models on $\\mathbb{Z}$ with drift. We analyze the possible scaling limits for a sequence of walks, where we make the drift decay to 0 as we rescale the walks. Depending on the speed of the decay of the drift we obtain three different scaling limits. If the drift decays slowly as we rescale the walks we obtain the inverse of an \\alpha$-stable subordinator as scaling limit. If the drift decays quickly as we rescale the walks, we obtain the F.I.N. diffusion as scaling limit. There is a critical speed of decay separating these two main regimes, where a new process appears as scaling limit. This critical speed is related to the index $\\alpha$ of the inhomogeneity of the environment.

Parra, Manuel Cabezas

2010-01-01

341

Drift-Tearing Magnetic Islands in Tokamak Plasmas R. Fitzpatrick and F.L. Waelbroeck  

E-print Network

Drift-Tearing Magnetic Islands in Tokamak Plasmas R. Fitzpatrick and F.L. Waelbroeck Institute theory of nonlinear magnetic island dynamics in conventional low-, large aspect-ratio, circular cross gyroviscosity, fast parallel electron heat transport, the ion sound wave, the drift-wave, and av- erage magnetic

Fitzpatrick, Richard

342

Drift-pump coil design for a tandem mirror reactor  

SciTech Connect

This paper describes both the theory and mechanical design behind a new concept for trapped ion removal from tandem mirror end plugs. The design has been developed for the Mirror Advanced Reactor Study (MARS). The new drift-pump coils replace charge-exchange pump beams. Pump beams consume large amounts of power and seriously reduce reactor performance. Drift-pump coils consume only a few megawatts of power and introduce no added burden to the reactor vacuum pumps. In addition, they are easy to replace. The coils are similar in shape to a paper clip and are located at two positions in each end plug. The coils between the transition coil and the first anchor yin-yang serve to remove ions trapped in the magnetic well just outboard of the high field choke coil. The coils located between the anchor coil set and the plug coil set remove sloshing ions and trapped cold ions from the plug region.

Logan, B.G.; Neef, W.S.

1983-12-01

343

Velocity determination from velocity spectra  

E-print Network

VELOCITY DETERMINATION FRON VELOCITY SPECTRA A Thesis by SUNG JIN YANG Submutted to the Graduate C:lleEe of Texas ASM University in partial fulfill sent of requirement for the degree of EASTER GF SCIENCE December 1973 Naj or Subject...: Ccophysics VELOCITY DETEPddINATION FROM VELOCITY SPECTRA A Thesis by SUNG JIN YANG Approved as to style and content by: ( Chai~ of C a0nitte ) (Read oi: Doper ent-IL irber) ( Meraber ) (i~ &r) Decen'bex' 1973 487460 ABSTRACT Velocity Determinati...

Yang, Sung Jin

2012-06-07

344

First-principles study of the threshold effect in the electronic stopping power of LiF and SiO2 for low-velocity protons and helium ions  

NASA Astrophysics Data System (ADS)

Nonadiabatic dynamics simulations are performed to investigate the electronic stopping power of LiF and SiO2-cristobalite-high crystalline thin films when protons and helium ions are hyperchanneling in the <001> axis. In this theoretical framework, ab initio time-dependent density-functional theory calculations for electrons are combined with molecular dynamics simulations for ions in real time and real space. The energy transfer process between the ions and the electronic subsystem of LiF and SiO2 nanostructures is studied. The velocity-proportional stopping power of LiF and SiO2 for protons and helium ions is predicted in the low-energy range. The measured velocity thresholds of protons in LiF and SiO2, and helium ions in LiF are reproduced. The convergence of the threshold effect with respect to the separation of grid points is confirmed. The underlying physics of the threshold effect is clarified by analyzing the conduction band electron distribution. In addition, the electron transfer processes between the projectile ions and solid atoms in hyperchanneling condition are studied, and its effects on the energy loss is investigated.

Mao, Fei; Zhang, Chao; Dai, Jinxia; Zhang, Feng-Shou

2014-02-01

345

Fast Correction Optics to Reduce Chromatic Aberrations in Longitudinally Compressed Ion Beams  

SciTech Connect

Longitudinally compressed ion beam pulses are currently employed in ion-beam based warm dense matter studies [1]. Compression arises from an imposed time-dependent longitudinal velocity ramp followed by drift in a neutralized channel. Chromatic aberrations in the final focusing system arising from this chirp increase the attainable beam spot and reduce the effective fluence on target. We report recent work on fast correction optics that remove the time-dependent beam envelope divergence and minimizes the beam spot on target. We present models of the optical element design and predicted ion beam fluence.

Lidia, S.M.; Lee, E.P.; Ogata, D.; Seidl, P.A.; Waldron, W.L.; Lund, S.M.

2009-04-30

346

Theory of semicollisional drift-interchange modes in cylindrical plasmas  

SciTech Connect

Resistive interchange instabilities in cylindrical plasmas are studied, including the effects of electron diamagnetic drift, perpendicular resistivity, and plasma compression. The analyses are pertinent to the semicollisional regime where the effective ion gyro-radius is larger than the resistive layer width. Both analytical and numerical results show that the modes can be completely stabilized by the perpendicular plasma transport. Ion sound effects, meanwhile, are found to be negligible in the semicollisional regime.

Hahm, T.S.; Chen, L.

1985-01-01

347

Ion Mobility Sensor In Environmental Analytical Chemistry—Concept And First Results  

Microsoft Academic Search

Ion mobility spectrometry is a technique for generating ions at atmospheric pressure via ion-molecule reactions, and for analysing them in an ion drift tube.The time required for the ions to traverse the length of the drift tube is mainly a function of the mass and the charge of the ions. Besides, ion shape and polarizability also affect the drift time.Ion

J. I. Baumbach; D. Berger; J. W. Leonhardt; D. Klockow

1993-01-01

348

ON PLASMA ROTATION AND DRIFTING SUBPULSES IN PULSARS: USING ALIGNED PULSAR B0826-34 AS A VOLTMETER  

SciTech Connect

We derive the exact drift velocity of plasma in the pulsar polar cap, in contrast to the order-of-magnitude expressions presented by Ruderman and Sutherland and generally used throughout the literature. We emphasize that the drift velocity depends not on the absolute value, as is generally used, but on the variation of the accelerating potential across the polar cap. If we assume that drifting subpulses in pulsars are indeed due to this plasma drift, several observed subpulse-drift phenomena that are incompatible with the Ruderman and Sutherland family of models can now be explained: we show that variations of drift rate, outright drift reversals, and the connection between drift rates and mode changes have natural explanations within the frame of the 'standard' pulsar model, when derived exactly. We apply this model for drifting subpulses to the case of PSR B0826-34, an aligned pulsar with two separate subpulse-drift regions emitted at two different colatitudes. Careful measurement of the changing and reversing drift rate in each band independently sets limits on the variation of the accelerating potential drop. The derived variation is small, {approx}10{sup -3} times the vacuum potential drop voltage. We discuss the implications of this result for pulsar modeling.

Van Leeuwen, J. [Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo (Netherlands); Timokhin, A. N., E-mail: leeuwen@astron.nl, E-mail: andrey.timokhin@nasa.gov [Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2012-06-20

349

3-dimensional Oil Drift Simulations  

NASA Astrophysics Data System (ADS)

Simulation of oil drift has been an ongoing activity at the Norwegian Meteorological Institute since the 1970's. The Marine Forecasting Centre provides a 24-hour service for the Norwegian Pollution Control Authority and the oil companies operating in the Norwegian sector. The response time is 30 minutes. From 2002 the service is extended to simulation of oil drift from oil spills in deep water, using the DeepBlow model developed by SINTEF Applied Chemistry. The oil drift model can be applied both for instantaneous and continuous releases. The changes in the mass of oil and emulsion as a result of evaporation and emulsion are computed. For oil spill at deep water, hydrate formation and gas dissolution are taken into account. The properties of the oil depend on the oil type, and in the present version 64 different types of oil can be simulated. For accurate oil drift simulations it is important to have the best possible data on the atmospheric and oceanic conditions. The oil drift simulations at the Norwegian Meteorological Institute are always based on the most updated data from numerical models of the atmosphere and the ocean. The drift of the surface oil is computed from the vectorial sum of the surface current from the ocean model and the wave induced Stokes drift computed from wave energy spectra from the wave prediction model. In the new model the current distribution with depth is taken into account when calculating the drift of the dispersed oil droplets. Salinity and temperature profiles from the ocean model are needed in the DeepBlow model. The result of the oil drift simulations can be plotted on sea charts used for navigation, either as trajectory plots or particle plots showing the situation at a given time. The results can also be sent as data files to be included in the user's own GIS system.

Wettre, C.; Reistad, M.; Hjøllo, B.Å.

350

Drifting subpulses and inner acceleration regions in radio pulsars  

E-print Network

The classical vacuum gap model of Ruderman & Sutherland, in which spark-associated subbeams of subpulse emission circulate around the magnetic axis due to the EB drift, provides a natural and plausible physical mechanism of the subpulse drift phenomenon. Recent progress in the analysis of drifting subpulses in pulsars has provided a strong support to this model by revealing a number of subbeams circulating around the magnetic axis in a manner compatible with theoretical predictions. However, a more detailed analysis revealed that the circulation speed in a pure vacuum gap is too high when compared with observations. Moreover, some pulsars demonstrate significant time variations of the drift rate, including a change of the apparent drift direction, which is obviously inconsistent with the EB drift scenario in a pure vacuum gap. We resolved these discrepancies by considering a partial flow of iron ions from the positively charged polar cap, coexisting with the production of outflowing electron-positron plasmas. By fitting the observationally deduced drift-rates to the theoretical values, we managed to estimate polar cap surface temperatures in a number of pulsars. The estimated surface temperatures correspond to a small charge depletion of the order of a few percent of the corotational charge density. We also argue that if the thermionic electron outflow from the surface of a negatively charged polar cap is slightly below the Goldreich-Julian density, then the resulting small charge depletion will have similar consequences as in the case of the ions outflow. We thus believe that the sparking discharge of a partially shielded acceleration potential drop occurs in all pulsars, with both positively (``pulsars'') and negatively (``anti-pulsars'') charged polar caps.

Janusz Gil; George I. Melikidze; Ulrich Geppert

2003-05-23

351

Drift-Kinetic Simulations of Neoclassical Transport  

SciTech Connect

We present results from numerical studies of neoclassical transport for multi-species plasmas. The code, NEO, provides a first-principles based calculation of the neoclassical transport coefficients directly from solution of the distribution function by solving a hierarchy of equations derived by expanding the fundamental drift-kinetic equation in powers of {rho}{sub *i}, the ratio of the ion gyroradius to system size. It extends previous studies by including the self-consistent coupling of electrons and multiple ion species and strong toroidal rotation effects. Systematic calculations of the second-order particle and energy fluxes and first-order plasma flows and bootstrap current and comparisons with existing theories are given for multi-species plasmas. The ambipolar relation {sigma}{sub a}z{sub a}{gamma}{sub a} = 0, which can only be maintained with complete cross-species collisional coupling, is confirmed. The effects of plasma shaping are also explored.

Belli, E. A.; Candy, J. [General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 (United States)

2008-11-01

352

Quantum diffusion with drift and the Einstein relation. I  

NASA Astrophysics Data System (ADS)

We study the dynamics of a quantum particle hopping on a simple cubic lattice and driven by a constant external force. It is coupled to an array of identical, independent thermal reservoirs consisting of free, massless Bose fields, one at each site of the lattice. When the particle visits a site x of the lattice it can emit or absorb field quanta of the reservoir at x. Under the assumption that the coupling between the particle and the reservoirs and the driving force are sufficiently small, we establish the following results: The ergodic average over time of the state of the particle approaches a non-equilibrium steady state describing a non-zero mean drift of the particle. Its motion around the mean drift is diffusive, and the diffusion constant and the drift velocity are related to one another by the Einstein relation.

De Roeck, Wojciech; Fröhlich, Jürg; Schnelli, Kevin

2014-07-01

353

SPIV measurements around the DELFT 372 catamaran in steady drift  

NASA Astrophysics Data System (ADS)

The present work concerns the experimental measurements of the velocity field around a catamaran advancing in static drift. The main aim of the paper was to investigate the dynamics of the vortices generated by catamaran hulls with particular emphasis on the mechanisms of generation, detachment, downstream evolution and destabilization. In this context, a Stereo-PIV campaign has been performed to map the velocity fields on some cross-planes along and downstream of the catamaran. Froude numbers equal to 0.4 and 0.5 at drift angles as large as 6° and 9° have been selected as testing conditions. In all the tests, the model has been fixed at the dynamical values of trim and sinkage, measured in a preliminary static drift experiments. Major geometrical and kinematical characteristics of the keel vortices have been documented in the paper through the analysis of the mean and fluctuating components of the velocity and vorticity field. Vortex interaction with the wave pattern has been investigated as well through the use of a conditional average technique of the velocity snapshots with the free surface elevation. As a secondary, but important, outcome, a valuable experimental dataset for CFD benchmarking in severe off-design conditions has been collected.

Falchi, M.; Felli, M.; Grizzi, S.; Aloisio, G.; Broglia, R.; Stern, F.

2014-11-01

354

High Performance Ion Mobility Spectrometry Using Hourglass Electrodynamic Funnel And Internal Ion Funnel  

DOEpatents

A method and apparatus enabling increased sensitivity in ion mobility spectrometry/mass spectrometry instruments which substantially reduces or eliminates the loss of ions in ion mobility spectrometer drift tubes utilizing a device for transmitting ions from an ion source which allows the transmission of ions without significant delay to an hourglass electrodynamic ion funnel at the entrance to the drift tube and/or an internal ion funnel at the exit of the drift tube. An hourglass electrodynamic funnel is formed of at least an entry element, a center element, and an exit element, wherein the aperture of the center element is smaller than the aperture of the entry element and the aperture of the exit elements. Ions generated in a relatively high pressure region by an ion source at the exterior of the hourglass electrodynamic funnel are transmitted to a relatively low pressure region at the entrance of the hourglass funnel through a conductance limiting orifice. Alternating and direct electrical potentials are applied to the elements of the hourglass electrodynamic funnel thereby drawing ions into and through the hourglass electrodynamic funnel thereby introducing relatively large quantities of ions into the drift tube while maintaining the gas pressure and composition at the interior of the drift tube as distinct from those at the entrance of the electrodynamic funnel and allowing a positive gas pressure to be maintained within the drift tube, if desired. An internal ion funnel is provided within the drift tube and is positioned at the exit of said drift tube. The advantage of the internal ion funnel is that ions that are dispersed away from the exit aperture within the drift tube, such as those that are typically lost in conventional drift tubes to any subsequent analysis or measurement, are instead directed through the exit of the drift tube, vastly increasing the amount of ions exiting the drift tube.

Smith, Richard D. (Richland, WA); Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA)

2005-11-22

355

The production of ion conics by oblique double layers. [of auroral arcs  

NASA Technical Reports Server (NTRS)

Magnetized test ions are subjected to acceleration through a numerically simulated oblique double layer in order to determine whether they emerge with velocity vectors aligned with or oblique to the ambient magnetic field. A criterion for oblique alignment, depending on the double-layer parameters and on the external magnetization, is obtained. When it is applied to observed and theoretical auroral double layers, this criterion predicts that accelerated heavy ions will be substantially less magnetic field aligned than will accelerated hydrogen ions, thus suggesting auroral double layers as a source of high-energy ion conics. Test particle simulations are also used to investigate the perpendicular heating of ions at low altitudes by the electric fields associated with moving auroral arcs. The rapid motion of small-scale structures in the arcs is suggested as a source of low-energy conical ion distributions, and the slow drifts of the entire arc forms are inferred to heat ionospheric ions.

Borovsky, J. E.

1984-01-01

356

Hall thruster plasma fluctuations identified as the E×B electron drift instability: Modeling and fitting on experimental data  

SciTech Connect

Microturbulence has been implicated in anomalous transport at the exit of the Hall thruster, and recent simulations have shown the presence of an azimuthal wave which is believed to contribute to the electron axial mobility. In this paper, the 3D dispersion relation of this E×B electron drift instability is numerically solved. The mode is found to resemble an ion acoustic mode for low values of the magnetic field, as long as a non-vanishing component of the wave vector along the magnetic field is considered, and as long as the drift velocity is small compared to the electron thermal velocity. In these conditions, an analytical model of the dispersion relation for the instability is obtained and is shown to adequately describe the mode obtained numerically. This model is then fitted on the experimental dispersion relation obtained from the plasma of a Hall thruster by the collective light scattering diagnostic. The observed frequency-wave vector dependences are found to be similar to the dispersion relation of linear theory, and the fit provides a non-invasive measurement of the electron temperature and density.

Cavalier, J.; Lemoine, N.; Bonhomme, G. [IJL, Université de Lorraine, CNRS (UMR 7198), BP 70239, 54506 Vandoeuvre-lès-Nancy (France)] [IJL, Université de Lorraine, CNRS (UMR 7198), BP 70239, 54506 Vandoeuvre-lès-Nancy (France); Tsikata, S. [ICARE, CNRS (UPR 3021), 1C av. de la Recherche Scientifique, 45071 Orléans (France)] [ICARE, CNRS (UPR 3021), 1C av. de la Recherche Scientifique, 45071 Orléans (France); Honoré, C.; Grésillon, D. [LPP, CNRS (UMR 7648), École Polytechnique, 91128 Palaiseau (France)] [LPP, CNRS (UMR 7648), École Polytechnique, 91128 Palaiseau (France)

2013-08-15

357

Hall thruster plasma fluctuations identified as the E ×B electron drift instability: Modeling and fitting on experimental data  

NASA Astrophysics Data System (ADS)

Microturbulence has been implicated in anomalous transport at the exit of the Hall thruster, and recent simulations have shown the presence of an azimuthal wave which is believed to contribute to the electron axial mobility. In this paper, the 3D dispersion relation of this E ×B electron drift instability is numerically solved. The mode is found to resemble an ion acoustic mode for low values of the magnetic field, as long as a non-vanishing component of the wave vector along the magnetic field is considered, and as long as the drift velocity is small compared to the electron thermal velocity. In these conditions, an analytical model of the dispersion relation for the instability is obtained and is shown to adequately describe the mode obtained numerically. This model is then fitted on the experimental dispersion relation obtained from the plasma of a Hall thruster by the collective light scattering diagnostic. The observed frequency-wave vector dependences are found to be similar to the dispersion relation of linear theory, and the fit provides a non-invasive measurement of the electron temperature and density.

Cavalier, J.; Lemoine, N.; Bonhomme, G.; Tsikata, S.; Honoré, C.; Grésillon, D.

2013-08-01

358

THE 15 LAYER SILICON DRIFT DETECTOR TRACKER IN EXPERIMENT 896.  

SciTech Connect

Large linear silicon drift detectors have been developed and are in production for use in several experiments. Recently 15 detectors were used as a tracking device in BNL-AGS heavy ion experiment (E896). The detectors were successfully operated in a 6.2 T magnetic field. The behavior of the detectors, such as drift uniformity, resolution, and charge collection efficiency are presented. The effect of the environment on the detector performance is discussed. Some results from the experimental run are presented. The detectors performed well in an experimental environment. This is the first tracking application of these detectors.

PANDY,S.U.

1998-11-08

359

Plasmon dispersion and electron heating in a drifting two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

We present Raman-scattering and photoluminescence measurements on a laterally drifting two-dimensional electron gas (2DEG) formed at a GaAs-Al0.3Ga0.7As heterojunction. The backscattering geometry employed allows both the direction, parallel, antiparallel, or perpendicular to the drift direction, and magnitude of the in-plane scattering wave vector to be varied. For a fixed wave vector the drift current produces a Doppler shift and broadening of the intrasubband plasmon Raman peak. For small drift velocities the energy shift is linear, and in opposite directions for the Stokes and anti-Stokes spectra, but becomes nonlinear for large drift velocities, and in the same direction in both cases. This change in behavior is ascribed to increasing carrier density with drift. Single-particle relaxation times were determined from the broadening of the plasmon Raman peaks. The ratio of the intensities of the Stokes and anti-Stokes plasmon peaks provides an estimate of the 2DEG temperature under drift conditions; this increased considerably with drift current, as confirmed by the high-energy tail of the band-gap photoluminescence from the 2DEG.

Bhatti, A. S.; Richards, D.; Hughes, H. P.; Ritchie, D. A.; Frost, J. E. F.; Jones, G. A. C.

1995-01-01

360

Comparison between African equatorial station ground-based inferred vertical E × B drift, Jicamarca direct measured drift, and IRI model  

NASA Astrophysics Data System (ADS)

The Incoherent Scatter Radar measurement over Jicamarca, together with the IRI model-2007 measurements were compared with ground-based digisonde inferred E × B drift over Ilorin in the African region during year of solar minima (F10.7 = 81). Seasonally, Ilorin pre-reversal enhancement (PRE) had peak drift velocities of 7.2, 3.7 and 7.9 m/s for March equinox, September equinox and December solstice respectively, while Jicamarca drifts indicated 13.0, 10.5 and 5.2 m/s; as well as the IRI model with 14.3, 8.4 and 0.7 m/s in similar order. PRE value was insignificant during June solstice. The PRE magnitude of the IRI-model during the equinoxes is twice the value obtained at Ilorin. The daytime E × B drift peaked over Ilorin 1-2 h earlier than both the modeled and Jicamarca observations. This could be due to the difference in sunset time at the conjugate points corresponding to the altitude of the observation. During the evening time PRE, the respective correlation coefficients (R) for Vz-F10.7 relation over Jicamarca, Ilorin and the modeled observations are -0.5559, 0.4796 and -0.4979. Similarly, the Vz-Ap relation exhibit excellent anti-correlation coefficient (R = -0.8637) for the IRI-model, -0.4827 over Jicamarca and 0.3479 for Ilorin. Annual mean drift velocities over Jicamarca, Ilorin and IRI model measurements respectively are 10, 5.6 and 10 m/s for the peak PRE observation; 15, 16 and 21 m/s for the daytime pre-sunrise peak values; and -21, -9 and -16 m/s for the nighttime downward reversals. The root-mean square (RMS) deviation between IRI-model and the Ilorin drift between 2000 and 0500 h is 4.37, 2.03, 3.71 and 2.42 m/s for March equinox, June solstice, September equinox and December solstice respectively. For Jicamarca-Ilorin drift relation, RMS deviation is 5.48, 2.30, 3.47 and 1.27 m/s in the same order respectively. Annual hmF2 inferred drift over Ilorin during daytime is higher by a factor of ?2 and 3 at Jicamarca and IRI model measurements respectively; and by a factor of ?5 for both during the night-time period. The limitations in using hmF2 to infer drifts are discussed.

Adeniyi, J. O.; Adebesin, B. O.; Adimula, I. A.; Oladipo, O. A.; Olawepo, A. O.; Ikubanni, S. O.; Reinisch, B. W.

2014-10-01

361

Effect of drift waves on plasma blob dynamics.  

PubMed

Most of the work to date on plasma blobs found in the edge region of magnetic confinement devices is limited to 2D theory and simulations which ignore the variation of blob parameters along the magnetic field line. However, if the 2D convective rate of blobs is on the order of the growth rate of unstable drift waves, then drift wave turbulence can drastically alter the dynamics of blobs from that predicted by 2D theory. The density gradients in the drift plane that characterize the blob are mostly depleted during the nonlinear stage of drift waves resulting in a much more diffuse blob with a greatly reduced radial velocity. Sheath connected plasma blobs driven by effective gravity forces are considered in this Letter and it is found that the effects of resistive drift waves occur at earlier stages in the 2D motion for smaller blobs and in systems with a smaller effective gravity force. These conclusions are supported numerically by a direct comparison of 2D and 3D seeded blob simulations. PMID:23003271

Angus, Justin R; Umansky, Maxim V; Krasheninnikov, Sergei I

2012-05-25

362

Effects of finite plasma beta on the lower-hybrid-drift instability  

NASA Technical Reports Server (NTRS)

The local dispersion relation for the lower-hybrid-drift (LHD) instability is derived and analyzed, taking into account the finite-beta effects associated with transverse electromagnetic perturbations as well as with resonant and nonresonant electron-orbit modifications due to magnetic-field gradients. The influence of finite-beta effects on the LHD instability is calculated in a fully self-consistent manner for arbitrary values of electron-ion temperature ratio, local beta, cross-field ExB velocity/ion thermal speed ratio, and other plasma parameters. Stability properties are investigated analytically for the case of cold electrons, and the local dispersion relation is solved numerically in the parameter regime of most interest for high-density plasma pinches. The results show that for all parameter regimes studied, the net effect of finite plasma beta is to reduce the maximum growth rate of the LHD instability, although the details can vary, depending on the plasma parameters. Except in the limit where the electron/ion temperature ratio tends to zero, it is found that there is a critical value of plasma beta above which the LHD instability is completely stabilized.

Davidson, R. C.; Gladd, N. T.; Wu, C. S.; Huba, J. D.

1977-01-01

363

Snow particle speeds in drifting snow  

NASA Astrophysics Data System (ADS)

of snow particle speeds is necessary for deepening our understanding of the internal structures of drifting snow. In this study, we utilized a snow particle counter (SPC) developed to observe snow particle size distributions and snow mass flux. Using high-frequency signals from the SPC transducer, we obtained the sizes of individual particles and their durations in the sampling area. Measurements were first conducted in the field, with more precise measurements being obtained in a boundary layer established in a cold wind tunnel. The obtained results were compared with the results of a numerical analysis. Data on snow particle speeds, vertical velocity profiles, and their dependence on wind speed obtained in the field and in the wind tunnel experiments were in good agreement: both snow particle speed and wind speed increased with height, and the former was always 1 to 2 m s-1 less than the latter below a height of 1 m. Thus, we succeeded in obtaining snow particle speeds in drifting snow, as well as revealing the dependence of particle speed on both grain size and wind speed. The results were verified by similar trends observed using random flight simulations. However, the difference between the particle speed and the wind speed in the simulations was much greater than that observed under real conditions. Snow transport by wind is an aeolian process. Thus, the findings presented here should be also applicable to other geophysical processes relating to the aeolian transport of particles, such as blown sand and soil.

Nishimura, Kouichi; Yokoyama, Chika; Ito, Yoichi; Nemoto, Masaki; Naaim-Bouvet, Florence; Bellot, Hervé; Fujita, Koji

2014-08-01

364

Velocity diagrams  

NASA Technical Reports Server (NTRS)

The selection and design of velocity diagrams for axial flow turbines are considered. Application is treated in two parts which includes: (1) mean-section diagrams, and (2) radial variation of diagrams. In the first part, the velocity diagrams occurring at the mean section are assumed to represent the average conditions encountered by the turbine. The different types of diagrams, their relation to stage efficiency, and their selection when staging is required are discussed. In the second part, it is shown that in certain cases the mean-section diagrams may or may not represent the average flow conditions for the entire blade span. In the case of relatively low hub- to tip-radius ratios, substantial variations in the velocity diagrams are encountered. The radial variations in flow conditions and their effect on the velocity diagrams are considered.

Whitney, W. J.; Stewart, W. L.

1972-01-01

365

Apparatus and method for laser velocity interferometry  

DOEpatents

An apparatus and method for laser velocity interferometry employing a fixed interferometer cavity and delay element. The invention permits rapid construction of interferometers that may be operated by those non-skilled in the art, that have high image quality with no drift or loss of contrast, and that have long-term stability even without shock isolation of the cavity.

Stanton, Philip L. (Bernalillo County, NM); Sweatt, William C. (Albuquerque, NM); Crump, Jr., O. B. (Albuquerque, NM); Bonzon, Lloyd L. (Albuquerque, NM)

1993-09-14

366

Relative Velocity  

NSDL National Science Digital Library

This applet simulates a boat crossing a river. The user can set the speed at which the river flows, and the magnitude and direction of the boat's velocity. The applet then displays the path taken by the boat. It also calculates the velocity of the boat with respect to the river and the shore, as well as the time it takes for the boat to cross the river.

Duffy, Andrew

2008-07-31

367

Drift coefficients of motor proteins moving along sidesteps  

NASA Astrophysics Data System (ADS)

In the paper, we investigate two motor proteins moving along the sidesteps: a motor protein moving along a two-dimensional sidestep and another protein moving along a three-dimensional sidestep. The drift coefficients (or stationary average velocities) of these two motor proteins are calculated. We believe that our investigation of the motor proteins moving along the sidesteps in the present paper can benefit the investigation of the transport of the motor proteins to some extent.

Li, Jing-Hui

2014-10-01

368

Atlas of Dutch drift sands  

NASA Astrophysics Data System (ADS)

The Netherlands is well known for its aeolian landscapes. Frequent storms during the High Middle Ages (1000-1300 AD) reactivated Pleistocene coversands and river dunes and are responsible for the formation of the Holocene drift sands at a scale which is unique for Europe. A hypothesized relationship with farmer practices for making plaggensoils has recently been refuted, because drift sand formation began centuries earlier. The coastal dune belt with their parabolic dunes dates from the same period as the drift sand. An estimate of the extent of drift sands can be made from soil maps: drift sands are too young to show much profile development (Regosols). With this method Koster estimated the maximum extent of Holocene drift sands in the Netherlands to be about 800 km2 (Koster 2005). Laser altimetry allows a more precise estimate of the total surface affected by wind from the characteristic relief patterns produced by the Holocene wind, which is different from the smooth surface of cover sand deposits. Laser altimetry has been used before to investigate the mechanism of drift sand formation (Jungerius & Riksen 2010). Most of the surface affected by wind is not active anymore, but the tell-tale rough surface survived ages of different landuse. The total affected surface amounts to 825 km2. It is noteworthy that both methods give comparable results. We recorded a total number of 367 of affected areas of varying shapes, ranging in size from 1.6 ha to a large complex of drif sands of 7,119.5 ha. As is to be expected from their mode of origin, most occurrences are associated with cover sands, and with river dunes along the river Meuse and smaller rivers in other parts of the country. Particularly the final phases of cover sand and river dunes that show more relief as parabolic dunes were affected. There are also small aeolian deposits at the lee side blown from fallow agricultural fields but they are (sub)recent. Most of the relief is irregular, but the larger occurrences associated with push moraines show that drift sand occurs in elongated cells that are parallel to the prevailing SW wind. Their internal structure reflects the characteristic sequence of geomorphological processes: deflation dominant in the south-west, transport and accumulation towards the north east. Literature • Jungerius, P.D., Riksen, M.J.P.M., 2010. Contribution of laser altimetry images to the geomorphology of the Late Holocene inland drift sands of the European Sand Belt. Baltica 23, 1: 59-70. • Koster EA. 2005. Aeolian environments. In The physical Geography of Western Europe, Koster EA (ed). Oxford Regional Environments, Oxford University Press;139-160.

Riksen, Michel; Jungerius, Pieter

2013-04-01

369

Towards a complete parametrization of the ordinary-mode electromagnetic instability in counterstreaming plasmas. II. Ion effects  

SciTech Connect

The linear marginal instability analysis of the ordinary perpendicular mode instability of drifting bi-Maxwellian plasma particle distributions with and without temperature anisotropy is extended by including the modifications of heavier ion species. For general values of the temperature anisotropy, the streaming velocity, and the parallel plasma beta, accurate marginal stability conditions are derived, which enable a better understanding of the interplay of counterstreaming and temperature anisotropy.

Ibscher, D.; Schlickeiser, R. [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2013-04-15

370

In-Drift Microbial Communities  

SciTech Connect

As directed by written work direction (CRWMS M and O 1999f), Performance Assessment (PA) developed a model for microbial communities in the engineered barrier system (EBS) as documented here. The purpose of this model is to assist Performance Assessment and its Engineered Barrier Performance Section in modeling the geochemical environment within a potential repository drift for TSPA-SR/LA, thus allowing PA to provide a more detailed and complete near-field geochemical model and to answer the key technical issues (KTI) raised in the NRC Issue Resolution Status Report (IRSR) for the Evolution of the Near Field Environment (NFE) Revision 2 (NRC 1999). This model and its predecessor (the in-drift microbial communities model as documented in Chapter 4 of the TSPA-VA Technical Basis Document, CRWMS M and O 1998a) was developed to respond to the applicable KTIs. Additionally, because of the previous development of the in-drift microbial communities model as documented in Chapter 4 of the TSPA-VA Technical Basis Document (CRWMS M and O 1998a), the M and O was effectively able to resolve a previous KTI concern regarding the effects of microbial processes on seepage and flow (NRC 1998). This document supercedes the in-drift microbial communities model as documented in Chapter 4 of the TSPA-VA Technical Basis Document (CRWMS M and O 1998a). This document provides the conceptual framework of the revised in-drift microbial communities model to be used in subsequent performance assessment (PA) analyses.

D. Jolley

2000-11-09

371

A theory of non-local linear drift wave transport  

SciTech Connect

Transport events in turbulent tokamak plasmas often exhibit non-local or non-diffusive action at a distance features that so far have eluded a conclusive theoretical description. In this paper a theory of non-local transport is investigated through a Fokker-Planck equation with fractional velocity derivatives. A dispersion relation for density gradient driven linear drift modes is derived including the effects of the fractional velocity derivative in the Fokker-Planck equation. It is found that a small deviation (a few percent) from the Maxwellian distribution function alters the dispersion relation such that the growth rates are substantially increased and thereby may cause enhanced levels of transport.

Moradi, S.; Anderson, J. [Department of Applied Physics, Nuclear Engineering, Chalmers University of Technology and Euratom-VR Association, Goeteborg (Sweden); Weyssow, B. [EFDA-CSU, D-85748 Garching, Muenchen (Germany)

2011-06-15

372

A theory of non-local linear drift wave transport  

E-print Network

Transport events in turbulent tokamak plasmas often exhibit non-local or non-diffusive action at a distance features that so far have eluded a conclusive theoretical description. In this paper a theory of non-local transport is investigated through a Fokker-Planck equation with fractional velocity derivatives. A dispersion relation for density gradient driven linear drift modes is derived including the effects of the fractional velocity derivative in the Fokker-Planck equation. It is found that a small deviation (a few percent) from the Maxwellian distribution function alters the dispersion relation such that the growth rates are substantially increased and thereby may cause enhanced levels of transport.

S. Moradi; J. Anderson; B. Weyssow

2011-03-15

373

Extended-MHD modeling of diamagnetic-drift tearing instabilities  

NASA Astrophysics Data System (ADS)

We use analytics and computations with the NIMROD code to examine tearing stability in large-guide-field slab cases with a nonzero equilibrium pressure gradient. A well known result from drift-reduced MHD is the diamagnetic drift associated with the pressure gradient has a stabilizing influence were the dispersion relation becomes (?+i?*e)^3?(?+i?*i)=?rMHD^5 [1]. Here ?*i and ?*e are the ion- and electron-diamagnetic frequencies and ?rMHD is the tearing growth rate with a resistive-MHD model. Preliminary computational results with an unreduced extended-MHD model do not produce the expected drift-reduced result. For moderate values of ?*i (?*i<=3?rMHD), the computations follow the dispersion relation that would result if the ?pe term were not included in the drift-reduced parallel Ohm's law: (?+i?*e)^4(?+i?*i)=?rMHD^5. Analytics, guided by computational diagnostics, are used to examine the significant terms in the flux evolution equation and investigate the discrepancy with the drift-reduced result.[4pt] [1] For example Coppi, PoF 7, 1501 (1964); Biskamp, NF 18, 1059 (1978).

King, Jacob; Kruger, Scott

2012-03-01

374

High-Performance Ion Mobility Spectrometry Using Hourglass Electrodynamic Funnel And Internal Ion Funnel  

DOEpatents

A method and apparatus enabling increased sensitivity in ion mobility spectrometry/mass spectrometry instruments which substantially reduces or eliminates the loss of ions in ion mobility spectrometer drift tubes utilizing an hourglass electrodynamic ion funnel at the entrance to the drift tube and/or an internal ion funnel at the exit of the drift tube. An hourglass electrodynamic funnel is formed of at least an entry element, a center element, and an exit element, wherein the aperture of the center element is smaller than the aperture of the entry element and the aperture of the exit elements. Ions generated in a relatively high pressure region by an ion source at the exterior of the hourglass electrodynamic funnel are transmitted to a relatively low pressure region at the entrance of the hourglass funnel through a conductance limiting orifice. Alternating and direct electrical potentials are applied to the elements of the hourglass electrodynamic funnel thereby drawing ions into and through the hourglass electrodynamic funnel thereby introducing relatively large quantities of ions into the drift tube while maintaining the gas pressure and composition at the interior of the drift tube as distinct from those at the entrance of the electrodynamic funnel and allowing a positive gas pressure to be maintained within the drift tube, if desired. An internal ion funnel is provided within the drift tube and is positioned at the exit of said drift tube. The advantage of the internal ion funnel is that ions that are dispersed away from the exit aperture within the drift tube, such as those that are typically lost in conventional drift tubes to any subsequent analysis or measurement, are instead directed through the exit of the drift tube, vastly increasing the amount of ions exiting the drift tube.

Smith, Richard D. (Richland, WA); Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA)

2004-11-16

375

Non-gyrotropic proton and alpha-particle velocity distributions in the solar wind: TAUS observations and stability analysis  

NASA Technical Reports Server (NTRS)

Ion velocity distribution functions have been measured with high time resolution by the TAUS plasma instrument on the PHOBOS mission to Mars in 1989. The unambiguous separation of protons and alpha-particles by TAUS enabled us to study the nonthermal features of their distributions separately and to analyze the stability of the distributions against excitation of waves in the cyclotron-frequency domain. Typical nonthermal features include temperature anisotropies, with T(sub perpendicular) larger than T(sub parallel), and ion beam populations drifting along the local magnetic field direction. Also, distinctly non-gyrotropic alpha-particle velocity distributions were sometimes found. Non-gyrotropy strongly changes the wave dispersion and gives rise to new growing modes, related to the coupling of the standard wave modes existing in gyrotropic plasma. It is found that for the measured non-gyrotropic ion distributions the right-hand polarized wave can also be excited by a temperature anistropy instead of the usual beam drift.

Astudillo, H. F.; Marsch, E.; Livi, S.; Rosenbauer, H.

1995-01-01

376

STATUS OF THE NEUTRALIZED DRIFT COMPRESSION EXPERIMENT (NDCX-II)  

SciTech Connect

The Neutralized Drift Compression Experiment (NDCX-II) is an 11 M$ induction accelerator project currently in construction at Lawrence Berkeley National Laboratory for warm dense matter (WDM) experiments investigating the interaction of ion beams with matter at elevated temperature and pressure. The machine consists of a lithium injector, induction accelerator cells, diagnostic cells, a neutralized drift compression line, a final focus solenoid, and a target chamber. The induction cells and some of the pulsed power systems have been reused from the decommissioned Advanced Test Accelerator at Lawrence Livermore National Laboratory after refurbishment and modification. The machine relies on a sequence of acceleration waveforms to longitudinally compress the initial ion pulse from 600 ns to less than 1 ns in {approx} 12 m. Radial confinement of the beam is achieved with 2.5 T pulsed solenoids. In the initial hardware configuration, 50 nC of Li{sup +} will be accelerated to 1.25 MeV and allowed to drift-compress to a peak current of {approx}40 A. The project started in the summer of 2009. Construction of the accelerator will be completed in the fall of 2011 and will provide a worldwide unique opportunity for ion-driven warm dense matter experiments as well as research related to novel beam manipulations for heavy ion fusion drivers.

Waldron, W.L.; Kwan, J.W.

2011-04-21

377

The ion experiment onboard the Interball-Aurora satellite; initial results on velocity-dispersed structures in the cleft and inside the auroral oval  

Microsoft Academic Search

The Toulouse ION experiment flown on the Russian Interball-Aurora mission performs simultaneous ion and electron measurements. Two mass spectrometers looking in opposing directions perpendicular to the satellite spin axis, which points toward the sun, measure ions in the mass and energy ranges 1–32 amu and ~0-14 000 eV. Two electron spectrometers also looking in opposing directions perform measurements in the

J. A. Sauvaud; H. Barthe; C. Aoustin; J. J. Thocaven; J. Rouzaud; E. Penou; D. Popescu; R. A. Kovrazhkin; K. G. Afanasiev

1998-01-01

378

Effects of particle drift on cosmic-ray transport. I. General properties, application to solar modulation  

Microsoft Academic Search

Although gradient and curvature drifts are explicitly contained in the general equations of cosmic-ray transport, they have been almost universally neglected in applications of these equations. We evaluate the drifts explicitly for the Parker spiral magnetic field and show that, for particles with rigidities greater than approx.0.3 GV in the solar wind, they are larger than the solar-wind velocity over

J. R. Jokipii; E. H. Levy; W. B. Hubbard

1977-01-01

379

Application of a drift-flux model to flashing in straight pipes  

Microsoft Academic Search

A computer program, SOLA-DF, was written to solve the unsteady, two-dimensional equations of motion for a two-phase mixture. The equations solved are based on the drift-flux approximation and include a phase transition model and a general drift velocity calculation. The SOLA-DF code is used for a study of the blowdown of straight pipes initially filled with water at high temperature

C. W. Hirt

1976-01-01

380

Further development of low noise MEVVA ion source  

SciTech Connect

Based on the idea of a space-charge-limited mode of operation, the influence of a pair of electrostatic meshes on the beam parameters of the LBNL MEVVA-5 ion source was investigated. The meshes were placed in the expansion zone of the vacuum arc plasma. Apart from reducing the level of beam current fluctuations, this mode of operation provides significant control over the ion charge state distribution of the extracted beam. These effects can be understood taking not only space charge but also the high-directed ion drift velocities into account that are the same for different ion charge states of a material. The results of simulations of the processes involved are in good agreement with the experimental results.

Oks, Efim; Yushkov, George; Litovko, Irina; Anders, Andre; Brown, Ian

2001-08-28

381

The Great Continental Drift Mystery  

NSDL National Science Digital Library

This unit introduces students to the development of the theory of continental drift. They will examine the early work of Alfred Wegener and Alexander DuToit, investigate lines of evidence that resulted in the development of the theory, and learn about the final lines of evidence that resulted in the theory's acceptance. There is a set of activities in which the students construct a map of Pangea using Wegener's clues, familiarize themselves with some important geographic locations, and investigate how fossil distribution can be used to enhance the study of continental drift. Study questions and a bibliography are included.

382

Propagation of cylindrical lower hybrid drift solitary wave in an inhomogeneous plasma  

NASA Astrophysics Data System (ADS)

The nonlinear cylindrical lower hybrid drift solitary wave in an inhomogeneous, magnetized plasma with the combined effects of electron density inhomogeneity and electron temperature inhomogeneity is investigated in a two-fluid model. The amplitude and width of the solitary wave are found to decrease as the electronic density inhomogeneity increases. When the electron temperature inhomogeneity grows, the amplitude of the soliton decays and the width never changes. It is noted that the decrease of diamagnetic drift velocity will strengthen the cylindrical lower hybrid drift solitary wave height and width.

Liu, Hai-Feng; Wang, Shi-Qing; Li, Ke-Hua; Wang, Zhan-He; Zhang, Wei-Bing; Wang, Zhi-Long; Qiang-Xiang, Kai-Huang, Yao-Liu, Sili-Li, Fa-Zhan Yang, Lan-Chang

2013-04-01

383

Propagation of cylindrical lower hybrid drift solitary wave in an inhomogeneous plasma  

SciTech Connect

The nonlinear cylindrical lower hybrid drift solitary wave in an inhomogeneous, magnetized plasma with the combined effects of electron density inhomogeneity and electron temperature inhomogeneity is investigated in a two-fluid model. The amplitude and width of the solitary wave are found to decrease as the electronic density inhomogeneity increases. When the electron temperature inhomogeneity grows, the amplitude of the soliton decays and the width never changes. It is noted that the decrease of diamagnetic drift velocity will strengthen the cylindrical lower hybrid drift solitary wave height and width.

Liu Haifeng; Wang Shiqing; Fazhan Yang [Southwestern Institute of Physics, Chengdu 610041 (China); Engineering and Technical College of Chengdu University of Technology, Leshan 614000 (China); Li Kehua; Wang Zhanhe; Zhang Weibing; Wang Zhilong; Qiangxiang; Kaihuang; Yaoliu; Silili; Lanchang [Engineering and Technical College of Chengdu University of Technology, Leshan 614000 (China)

2013-04-15

384

Structure of parallel-velocity-shear driven mode in toroidal plasmas  

SciTech Connect

It is shown that the Fourier-ballooning representation is appropriate for the study of short wavelength drift-like perturbation in toroidal plasmas with a parallel velocity shear (PVS). The radial structure of the mode driven by a PVS is investigated in a torus. The Reynolds stress created by PVS turbulence and proposed as one of the sources for a sheared poloidal plasma rotation is analyzed. It is demonstrated that a finite ion temperature may strongly enhance the Reynolds stress creation ability from PVS driven turbulence. The correlation of this observation with the requirement that ion heating power be higher than a threshold value for the formation of an internal transport barrier is discussed.

Dong, J.Q.; Xu, W.B.; Zhang, Y.Z. [Southwestern Inst. of Physics, Chengdu (China); Horton, W. [Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies

1998-09-15

385

Terminal Velocity  

NSDL National Science Digital Library

This lab is an inquiry activity in that students have not been exposed to the idea of terminal velocity, though they are using skills that they already have to analyze the balloon's motion. The lab is both a review of graphing and translating distance ver

Horton, Michael

2009-05-30

386

Relative drifts and temperature anisotropies of protons and $\\alpha$ particles in the expanding solar wind -- 2.5D hybrid simulations  

E-print Network

We perform 2.5D hybrid simulations to investigate the origin and evolution of relative drift speeds between protons and $\\alpha$ particles in the collisionless turbulent low-$\\beta$ solar wind plasma. We study the generation of differential streaming by wave-particle interactions and absorption of turbulent wave spectra. Next we focus on the role of the relative drifts for the turbulent heating and acceleration of ions in the collisionless fast solar wind streams. The energy source is given by an initial broad-band spectrum of parallel propagating Alfv\\'en-cyclotron waves, which co-exists with the plasma and is self-consistently coupled to the perpendicular ion bulk velocities. We include the effect of a gradual solar wind expansion, which cools and decelerates the minor ions. This paper for the first time considers the combined effect of self-consistently initialized dispersive turbulent Alfv\\'enic spectra with differentially streaming protons and $\\alpha$ particles in the expanding solar wind outflows withi...

Maneva, Y G; Viñas, A

2014-01-01

387

Universal Velocity-Field Characteristics for a Nanowire Arbitrary Degeneracy  

SciTech Connect

The effects of electric field on the carrier motion and drift velocity in nanowire (NW) are presented in this paper. When the electric field is applied in NW, the electron is expected to move in anti-parallel direction to the electric field. This is so-called randomness motion is transformed into streamlined motion in extremely high electric field. The normalized Fermi energy and relative electron population as a function of electric field are examined for various degeneracies. It was found that the electric field has lesser influence on the relative electron population with the increased degeneracy. The drift velocity in NW is shown to increase with electric field until it reaches the saturation velocity. Two approximations have been made to simplify the theoretical equation. It is also shown in this paper that when the quantum emission is taken into account, the drift and saturation velocity degrades.

Chek, Desmond C. Y.; Hashim, Abdul Manaf [Faculty of Electrical Eng., Universiti Teknologi Malaysia, 81310 Skudai, Johor (Malaysia); Tan, Michael Loong Peng [Faculty of Electrical Eng., Universiti Teknologi Malaysia, 81310 Skudai, Johor (Malaysia); Electrical Engineering Division, Engineering Department, University of Cambridge, 9 J.J. Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Arora, Vijay K. [Faculty of Electrical Eng., Universiti Teknologi Malaysia, 81310 Skudai, Johor (Malaysia); Division of Engineering and Physics, Wilkes University, Wilkes-Barre, PA 18766 (United States)

2011-05-25

388

Universal Velocity-Field Characteristics for a Nanowire Arbitrary Degeneracy  

NASA Astrophysics Data System (ADS)

The effects of electric field on the carrier motion and drift velocity in nanowire (NW) are presented in this paper. When the electric field is applied in NW, the electron is expected to move in anti-parallel direction to the electric field. This is so-called randomness motion is transformed into streamlined motion in extremely high electric field. The normalized Fermi energy and relative electron population as a function of electric field are examined for various degeneracies. It was found that the electric field has lesser influence on the relative electron population with the increased degeneracy. The drift velocity in NW is shown to increase with electric field until it reaches the saturation velocity. Two approximations have been made to simplify the theoretical equation. It is also shown in this paper that when the quantum emission is taken into account, the drift and saturation velocity degrades.

Chek, Desmond C. Y.; Tan, Michael Loong Peng; Hashim, Abdul Manaf; Arora, Vijay K.

2011-05-01

389

Forecast of iceberg ensemble drift  

SciTech Connect

The objectives of the study are to gain a better understanding of the characteristics of iceberg motion and the factors controlling iceberg drift, and to develop an iceberg ensemble drift forecast system to be operated by the Canadian Atmospheric Environment Service. An extensive review of field and theoretical studies on iceberg behaviour, and the factors controlling iceberg motion has been carried out. Long term and short term behaviour of icebergs are critically examined. A quantitative assessment of the effects of the factors controlling iceberg motion is presented. The study indicated that wind and currents are the primary driving forces. Coriolis Force and ocean surface slope also have significant effects. As for waves, only the higher waves have a significant effect. Iceberg drift is also affected by iceberg size characteristics. Based on the findings of the study a comprehensive computerized forecast system to predict the drift of iceberg ensembles off Canada's east coast has been designed. The expected accuracy of the forecast system is discussed and recommendations are made for future improvements to the system.

El-Tahan, M.S.; El-Tahan, H.W.; Venkatesh, S.

1983-05-01

390

Magnetohydrodynamic Slow Mode with Drifting He++: Implications for Coronal Seismology and the Solar Wind  

NASA Astrophysics Data System (ADS)

The MHD slow mode wave has application to coronal seismology, MHD turbulence, and the solar wind where it can be produced by parametric instabilities. We consider analytically how a drifting ion species (e.g. He++) affects the linear slow mode wave in a mainly electron-proton plasma, with potential consequences for the aforementioned applications. Our main conclusions are as follows. 1. For wavevectors highly oblique to the magnetic field, we find solutions that are characterized by very small perturbations of total pressure. Thus, our results may help to distinguish the MHD slow mode from kinetic Alfvén waves and non-propagating pressure-balanced structures, which can also have very small total pressure perturbations. 2. For small ion concentrations, there are solutions that are similar to the usual slow mode in an electron-proton plasma, and solutions that are dominated by the drifting ions, but for small drifts the wave modes cannot be simply characterized. 3. Even with zero ion drift, the standard dispersion relation for the highly oblique slow mode cannot be used with the Alfvén speed computed using the summed proton and ion densities, and with the sound speed computed from the summed pressures and densities of all species. 4. The ions can drive a non-resonant instability under certain circumstances. For low plasma beta, the threshold drift can be less than that required to destabilize electromagnetic modes, but damping from the Landau resonance can eliminate this instability altogether, unless Te /Tp Gt 1.

Hollweg, Joseph V.; Verscharen, Daniel; Chandran, Benjamin D. G.

2014-06-01

391

Helium, hydrogen, and oxygen velocities observed on ISEE-3  

NASA Technical Reports Server (NTRS)

The velocities of hydrogen, helium, and oxygen ions over a full range of solar wind conditions were recorded by the ion composition instrument and Los Alamos National Laboratory plasma instrument aboard the International Sun Earth Explorer. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s(-1) the helium velocity exceeded the hydrogen velocity by 5 km s(-1) the average difference was 14 km s(-1), however no evidence was found for a nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Generally helium hydrogen velocity differences are bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. The electrostatic potential change across a shock produces differences between the velocities of ions having different charges.

Ogilvie, K. W.; Coplan, M. A.; Zwicki, R. D.

1982-01-01

392

Commissioning Results of the Upgraded Neutralized Drift Compression Experiment  

SciTech Connect

Recent changes to the NDCX beamline offer the promise of higher charge compressed bunches (>15nC), with correspondingly large intensities (>500kW/cm2), delivered to the target plane for ion-beam driven warm dense matter experiments. We report on commissioning results of the upgraded NDCX beamline that includes a new induction bunching module with approximately twice the volt-seconds and greater tuning flexibility, combined with a longer neutralized drift compression channel.

Lidia, S.M.; Roy, P.K.; Seidl, P.A.; Waldron, W.L.; Gilson, E.P.

2009-04-30

393

Excitation of zonal flow by drift waves in toroidal plasmas Department of Physics and Astronomy, University of California, Irvine, California 92697  

E-print Network

the nonlin- ear evolution of electrostatic drift-wave instabilities such as the ion temperature gradient ITG-dimensional global gyrokinetic simulations of the ion-temperature-gradient mode. Nonlinear equations for mode

Chen, Liu

394

Understanding ion transport in conjugated polymers  

NASA Astrophysics Data System (ADS)

Electron transport and ion transport are two critical processes taking place during electrochemical oxidation/reduction of conjugated polymers. Because they accompany and depend on each other, research on the individual processes is difficult. We present a device that allows us to measure ion transport directly and independently from electron transport in conjugated polymers. The device geometry makes the ion path much longer than the electron path, ensuring that ion transport is the rate-limiting step. Ion transport is also visualized directly through the color change of the film (electrochromism) as the electrochemical reaction proceeds, allowing one to precisely and quantitatively track the ion velocity. During reduction at sufficiently negative potentials, a phase front between the oxidized and reduced states was observed to travel into the film, the speed of which was proportional to the applied voltage, demonstrating that migration (rather than diffusion) is the key driving force. At less negative reducing potentials, the film gradually and more uniformly changed color, indicating that diffusion plays a large role. A simple first-cut model with drift and diffusion terms is presented. The simulated ion concentration profile matched the experimentally measured intensity profile strikingly well.

Wang, Xuezheng; Smela, Elisabeth; Shapiro, Benjamin

2004-07-01

395

Performance of drift tubes under high radiation  

E-print Network

In this thesis, the aging and the rejuvenation of an ATLAS proportional drift tube are described. Firstly, the Diethorn model of gain is tested using pressure and sense-wire voltage measurements. The drift tube was then ...

Shi, Yue, S.B. Massachusetts Institute of Technology

2005-01-01

396

Drift correction for scanning-electron microscopy  

E-print Network

Scanning electron micrographs at high magnification (100,000x and up) are distorted by motion of the sample during image acquisition, a phenomenon called drift. We propose a method for correcting drift distortion in images ...

Snella, Michael T

2010-01-01

397

Rotating field mass and velocity analyzer  

NASA Technical Reports Server (NTRS)

A rotating field mass and velocity analyzer having a cell with four walls, time dependent RF potentials that are applied to each wall, and a detector. The time dependent RF potentials create an RF field in the cell which effectively rotates within the cell. An ion beam is accelerated into the cell and the rotating RF field disperses the incident ion beam according to the mass-to-charge (m/e) ratio and velocity distribution present in the ion beam. The ions of the beam either collide with the ion detector or deflect away from the ion detector, depending on the m/e, RF amplitude, and RF frequency. The detector counts the incident ions to determine the m/e and velocity distribution in the ion beam.

Smith, Steven Joel (Inventor); Chutjian, Ara (Inventor)

1998-01-01

398

Preferential heating of light ions during an ionospheric AR(+) injection experiment  

NASA Technical Reports Server (NTRS)

The ARCS 4 sounding rocket was launched northward into high altitude from Poker Flat Research Range on February 23, 1990. The vehicle crossed geomagnetic field lines containing discrete auroral activity. An instrumented subpayload released 100 ev and 200 ev Ar(+) ion beams sequentially, in a direction largely perpendicular to both the local geomagnetic field and the subpayload spin axis. The instrumented main payload was separated along field lines from the beam emitting subpayload by a distance which increased at a steady rate of approx. 2.4 m/s. Three-dimensional mass spectrometric ion observations of ambient H(+) and O(+) ions, obtained onboard the main payload, are presented. Main payload electric field observations in the frequency range 0-16 kHz, are also presented. These observations are presented to demonstrate the operation of transverse ion acceleration, that was differential with respect to ion mass, primarily during 100-ev beam operations. The preferential transverse acceleration of ambient H(+) ions, as compared with ambient O(+) ions during the second, third, fourth, and fifth 100-ev beam operations, is attributed to a resonance at the injected the beam drift velocity among the thermal H(+) ions and plasma waves generated by the injected beam and propagating at the beam drift speed. This work provides experimental support of processes predicted by previously published theory and simulations.

Pollock, C. J.; Moore, T. E.; Arnoldy, R. L.; Kintner, P. M.; Cahill, L. J., Jr.

1994-01-01

399

Stokes drift for inertial particles transported by water waves  

E-print Network

We study the effect of surface gravity waves on the motion of inertial particles in an incompressible fluid. Using the multiple-scale technique, we perform an analytical calculation which allows us to predict the dynamics of such particles; results are shown for both the infinite- and finite-depth regimes. Numerical simulations based on the velocity field resulting from the second-order Stokes theory for the surface elevation have been performed, and an excellent agreement with the analytical predictions is observed. Such an agreement seems to hold even beyond the formal applicability of the theory. We find that the presence of inertia leads to a non-negligible correction to the well-known horizontal Stokes drift; moreover, we find that the vertical velocity is also affected by a drift. The latter result may have some relevant consequences on the rate of sedimentation of particles of finite size. We underline that such a drift would also be observed in the (hypothetical) absence of the gravitational force.

G. Boffetta; M. Martins Afonso; A. Mazzino; M. Onorato; F. Santamaria

2012-10-08

400

The collisional drift mode in a partially ionized plasma. [in the F region  

NASA Technical Reports Server (NTRS)

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Hudson, M. K.; Kennel, C. F.

1974-01-01

401

Quasicoherent Nonlinear Interactions in Ion Density Fluctuations  

NASA Astrophysics Data System (ADS)

Using Laser Induced Fluorescence(LIF) diagnostics, we present the phase-space resolved measurement of ion density fluctuations in a linearly magnetized device. These experiments are conducted in singly ionized ArII plasma, which is created by an inductively coupled plasma source, immersed in 1KG magnetic field along the axis of a cylindrical chamber. Cross and auto spectral estimates are calculated after the digitization of LIF signals collected from two independent periscopes having axially aligned mobility. The cross-power spectrum has a distinctive, broad peak near the drift wave frequency(&*circ;) that can be dissected into two components; the one having a long wavelength consistent with drift wave theory, and the other, which we call the `kinetic component,' with a shorter correlation length and ion particle velocity dependence. Bispectrum and bicoherence calculations, on the other hand, suggest a quasicoherent nonlinear interaction between the kinetic and the fluid components. As the neutral pressure and thus the ion-neutral collision frequency increase, we observe a certain threshold where the kinetic component vanishes from the cross-power spectrum. Meanwhile, in bicoherence calculations, the nonlinear coupling of &*circ; to its sub-harmonics is taken over by another nonlinear interaction that is between &*circ; and its second harmonic. We propose an explanation for these changes in the spectra and bispectra.

Uzun, Ilker

2005-10-01

402

Ion convection and the formation of the mid-latitude F region ionization trough  

NASA Technical Reports Server (NTRS)

Total ion concentration and ion drift velocity data from Atmospheric Explorer C are used to examine the convective flow of plasma in the vicinity of the midlatitude F region ionization trough. It is found that the low-latitude portion of the premidnight trough is a region of slow eastward plasma drift while the poleward portion is characterized by generally westward flow. The reversal from eastward to westward flow is described. It is proposed that the plasma flux tubes within the premidnight trough have corotated eastward into the evening local time sector from dusk before stagnating and flowing westward at higher latitudes in the nighttime sector. The role of F region recombination in trough formation is considered.

Spiro, R. W.; Heelis, R. A.; Hanson, W. B.

1978-01-01

403

Anisotropic ion heating and parallel O(+) acceleration in regions of rapid E x B convection  

NASA Technical Reports Server (NTRS)

A numerical solution to the 20-moment set of transport equations has been found in order to study subauroral ionospheric outflows during periods of enhanced perpendicular ion drifts. The numerical model solves the time-dependent O(+) density, momentum, and both the parallel and perpendicular energy and heat flow equations in the 200-6000 km altitude range. Assuming perpendicular drifts of 3 km/s relative to the neutral atmosphere, we have found that anisotropic heating of O(+) (a result of ion-neutral collisions) leads to a temperature anisotropy, with perpendicular temperatures exceeding 8000 K and parallel temperatures greater than 5000 K (near 200 km altitude). Above approximately 2000 km, transport processes dominate the effects of collisions and wavelike oscillations in O(+) velocity, temperature and heat flux were noted.

Korosmezey, A.; Rasmussen, C. E.; Gombosi, T. I.; Khazanov, G. V.

1992-01-01

404

Experimental study of particle formation by ion-ion recombination  

NASA Astrophysics Data System (ADS)

Particle formation by ion-ion recombination has been studied using an ion-ion recombination drift tube (IIR-DT). IIR-DT uses two DC corona ionizers to produce positive and negative ions at the ends of the drift tube. The ions of different polarity move in opposite directions along the electric field in the drift tube. We observed significant particle formation using ions generated in purified air containing H2O, SO2, and NH3. Particle formation was suppressed when no drift field was applied. We also observed few particles when we used a single discharge (positive or negative only). These results clearly show that particle formation observed in the IIR-DT was caused by nucleation by ion-ion recombination. Positive and negative ion species produced by corona ionizers were investigated using an atmospheric pressure ionization mass spectrometer. The ions involved in the particle formation were suggested to include H3O+(H2O)n and NH4+(H2O)n for positive ions and sulfur-based ions such as SO5-, SO5-NO2, and HSO4- for negative ions.

Nagato, Kenkichi; Nakauchi, Masataka

2014-10-01

405

Experimental study of particle formation by ion-ion recombination.  

PubMed

Particle formation by ion-ion recombination has been studied using an ion-ion recombination drift tube (IIR-DT). IIR-DT uses two DC corona ionizers to produce positive and negative ions at the ends of the drift tube. The ions of different polarity move in opposite directions along the electric field in the drift tube. We observed significant particle formation using ions generated in purified air containing H2O, SO2, and NH3. Particle formation was suppressed when no drift field was applied. We also observed few particles when we used a single discharge (positive or negative only). These results clearly show that particle formation observed in the IIR-DT was caused by nucleation by ion-ion recombination. Positive and negative ion species produced by corona ionizers were investigated using an atmospheric pressure ionization mass spectrometer. The ions involved in the particle formation were suggested to include H3O(+)(H2O)n and NH4 (+)(H2O)n for positive ions and sulfur-based ions such as SO5 (-), SO5 (-)NO2, and HSO4 (-) for negative ions. PMID:25362301

Nagato, Kenkichi; Nakauchi, Masataka

2014-10-28

406

How ions really flow to objects in magnetized plasmas  

NASA Astrophysics Data System (ADS)

A new exact, 3-D, analytic solution has been obtained of the drift equations for the plasma perturbation around an ion-collecting object of essentially arbitrary shape in a flowing strongly-magnetized plasma [1]. It provides a direct rigorous theory of magnetized Langmuir probes, especially Mach probes, and of other diverse plasma-object interactions. The cross-field flow is a combination of external drifts and self-consistent perturbation by the object. This convective calculation is valid for objects smaller than the characteristic size of turbulent plasma flow structures: the usual situation. The Mach probe calibration obtained agrees with prior diffusive theory, but now accounts for cross-field diamagnetic drifts, which are not ignorable. Their contribution is non-intuitive, in that the electron diamagnetic velocity is dominant. Consequently, transverse Mach probes measure a combination of ExB and diamagnetic drifts. The analytic fluid solution compares very favorably with numerical kinetic-parallel-distribution calculations [2]. And 3-D PIC calculations for a spherical object, accounting for finite gyro-radius, also verify its regime of applicability.[4pt] [1] I.H. Hutchinson, Phys Plasmas, 15, 123503 (2008)[0pt] [2] L. Patacchini and I.H. Hutchinson submitted to Phys Rev E.

Hutchinson, Ian H.

2009-11-01

407

Improved sliced velocity map imaging apparatus optimized for H photofragments  

NASA Astrophysics Data System (ADS)

Time-sliced velocity map imaging (SVMI), a high-resolution method for measuring kinetic energy distributions of products in scattering and photodissociation reactions, is challenging to implement for atomic hydrogen products. We describe an ion optics design aimed at achieving SVMI of H fragments in a broad range of kinetic energies (KE), from a fraction of an electronvolt to a few electronvolts. In order to enable consistently thin slicing for any imaged KE range, an additional electrostatic lens is introduced in the drift region for radial magnification control without affecting temporal stretching of the ion cloud. Time slices of ~5 ns out of a cloud stretched to >=50 ns are used. An accelerator region with variable dimensions (using multiple electrodes) is employed for better optimization of radial and temporal space focusing characteristics at each magnification level. The implemented system was successfully tested by recording images of H fragments from the photodissociation of HBr, H2S, and the CH2OH radical, with kinetic energies ranging from <0.4 eV to >3 eV. It demonstrated KE resolution <~1%-2%, similar to that obtained in traditional velocity map imaging followed by reconstruction, and to KE resolution achieved previously in SVMI of heavier products. We expect it to perform just as well up to at least 6 eV of kinetic energy. The tests showed that numerical simulations of the electric fields and ion trajectories in the system, used for optimization of the design and operating parameters, provide an accurate and reliable description of all aspects of system performance. This offers the advantage of selecting the best operating conditions in each measurement without the need for additional calibration experiments.

Ryazanov, Mikhail; Reisler, Hanna

2013-04-01

408

Multi-water-bag models of ion temperature gradient instability in cylindrical geometry  

SciTech Connect

Ion temperature gradient instabilities play a major role in the understanding of anomalous transport in core fusion plasmas. In the considered cylindrical geometry, ion dynamics is described using a drift-kinetic multi-water-bag model for the parallel velocity dependency of the ion distribution function. In a first stage, global linear stability analysis is performed. From the obtained normal modes, parametric dependencies of the main spectral characteristics of the instability are then examined. Comparison of the multi-water-bag results with a reference continuous Maxwellian case allows us to evaluate the effects of discrete parallel velocity sampling induced by the Multi-Water-Bag model. Differences between the global model and local models considered in previous works are discussed. Using results from linear, quasilinear, and nonlinear numerical simulations, an analysis of the first stage saturation dynamics of the instability is proposed, where the divergence between the three models is examined.

Coulette, David [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)] [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France); Besse, Nicolas [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux and Institut Elie Cartan UMR CNRS 7502 INRIA Calvi Team, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)] [Institut Jean Lamour UMR CNRS 7198 Département Physique de la Matière et des Matériaux and Institut Elie Cartan UMR CNRS 7502 INRIA Calvi Team, Université de Lorraine, Faculté des Sciences et Technologie, Campus Victor Grignard BP 70239, 54506 Vandoeuvre-lès-Nancy Cedex (France)

2013-05-15

409

Drift wave instabilities in a high beta multispecies plasma. [in Jupiter and Saturn atmosphere  

NASA Technical Reports Server (NTRS)

The dispersion relation for drift-Alfven waves in two-component (cold and hot), high beta inhomogeneous multispecies plasma containing protons, oxygen, and sulfur ions is solved numerically. The magnetic field is assumed to have a gradient in simple slab geometry configuration. The plasma ion composition consists of H, O, S, SO2, and Na ions. The effect of heavy ions and multiple charge states on the growth rates has been numerically estimated for assumed ion compositions. The numerical calculations of growth rates also have been performed by using ion composition and plasma parameters based on Voyager spacecraft in the magnetospheres of Jupiter and Saturn.

Patel, V. L.; Ng, P. H.; Ludlow, G. R.

1984-01-01

410

Kinetic effects on a tokamak pedestal ion flow, ion heat transport and bootstrap current  

NASA Astrophysics Data System (ADS)

We consider the effects of a finite radial electric field on ion orbits in a subsonic pedestal. Using a procedure that makes a clear distinction between a transit average and a flux surface average we are able to solve the kinetic equation to retain the modifications due to finite {{\\vec{{\\bit E}}}}\\times {{\\vec{{\\bit B}}}} drift orbit departures from flux surfaces. Our approach properly determines the velocity space localized, as well as the nonlocal, portion of the ion distribution function in the banana and plateau regimes in the small aspect ratio limit. The rapid variation of the poloidal ion flow coefficient and the electrostatic potential in the total energy modify previous banana regime evaluations of the ion flow, the bootstrap current, and the radial ion heat flux in a subsonic pedestal. In the plateau regime, the rapid variation of the poloidal flow coefficient alters earlier results for the ion flow and bootstrap current, while leaving the ion heat flux unchanged since the rapid poloidal variation of the total energy was properly retained.

Catto, Peter J.; Parra, Felix I.; Kagan, Grigory; Parker, Jeffrey B.; Pusztai, Istvan; Landreman, Matt

2013-04-01

411

Effects of particle drift on cosmic ray transport. II - Analytical solution to the modulation problem with no latitudinal diffusion  

NASA Technical Reports Server (NTRS)

An analytical solution to a model of the modulation of galactic cosmic rays in the presence of particle drifts is presented and discussed. The solution assumes an energy-independent radial diffusion coefficient proportional to distance and no latitudinal diffusion, and includes energy-independent particle drift velocities similar to those expected in a Parker spiral magnetic field with an equatorial current sheet. The solutions clearly demonstrate the large effects of drifts on the modulated cosmic-ray intensity. For values of the radial diffusion coefficient and particle drift velocity which are plausible for 1-GV-rigidity protons, the logarithmic radial gradient in the inner solar system is reduced by more than a factor of 5 over the value calculated in the absence of drifts. It is found that even for much smaller values of particle drift velocity and radial diffusion coefficient, such as might be expected for protons with energies of the order of 10 MeV, the effects of the drifts can be substantial.

Isenberg, P. A.; Jokipii, J. R.

1978-01-01

412

T.M. Biewer, April 4th, 2003 US/EU Transport Task Force Meeting, Madison, WI Edge Impurity Ion Velocity and  

E-print Network

, April 4th, 2003 US/EU Transport Task Force Meeting, Madison, WI Abstract A new spectroscopic diagnosticT.M. Biewer, April 4th, 2003 US/EU Transport Task Force Meeting, Madison, WI Edge Impurity Ion Plasma Physics Laboratory April 4th, 2003 Transport Task Force Meeting Madison, Wisconsin #12;T.M. Biewer

Biewer, Theodore

413

Diagnostics for ion beam driven high energy density physics experiments.  

PubMed

Intense beams of heavy ions are capable of heating volumetric samples of matter to high energy density. Experiments are performed on the resulting warm dense matter (WDM) at the NDCX-I ion beam accelerator. The 0.3 MeV, 30 mA K(+) beam from NDCX-I heats foil targets by combined longitudinal and transverse neutralized drift compression of the ion beam. Both the compressed and uncompressed parts of the NDCX-I beam heat targets. The exotic state of matter (WDM) in these experiments requires specialized diagnostic techniques. We have developed a target chamber and fielded target diagnostics including a fast multichannel optical pyrometer, optical streak camera, laser Doppler-shift interferometer (Velocity Interferometer System for Any Reflector), beam transmission diagnostics, and high-speed gated cameras. We also present plans and opportunities for diagnostic development and a new target chamber for NDCX-II. PMID:21033977

Bieniosek, F M; Henestroza, E; Lidia, S; Ni, P A

2010-10-01