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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

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

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

4

Parallel-velocity-shear-modified drift wave in negative ion plasmas  

NASA Astrophysics Data System (ADS)

A systematic investigation of the effects of a parallel velocity shear and negative ions on the collisionless drift wave instability has for the first time been realized by simultaneously using a segmented tungsten hot plate of a Q-machine and sulfur hexafluoride (SF6) gas in a magnetized potassium plasma. The parallel velocity shear of the positive ion flow tends to decrease the fluctuation level of the drift wave. The introduction of negative ions first increases the fluctuation level and then starts to decrease it at the negative ion exchange fraction of around 10%, while keeping the above-mentioned shear effect qualitatively. In addition, a simple dispersion relation based on the local model has been calculated to show that it can predict wave characteristics similar to the experimental results. Our findings provide a potential for gaining a more profound insight into the physics of space/circumterrestrial plasmas.

Ichiki, R.; Kaneko, T.; Hayashi, K.; Tamura, S.; Hatakeyama, R.

2009-03-01

5

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

NASA Astrophysics Data System (ADS)

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

Guo, Jun; Li, Bo

2013-09-01

6

Comparison of DMSP F13 Cross-Track Ion Drift Velocities With AMIE Results  

NASA Astrophysics Data System (ADS)

The Assimilative Mapping Of Ionospheric Electrodynamics (AMIE) model [Richmond et al., J. Geophys. Res., 93, 5741, 1988] has been used in a wide range of studies pertaining to the magnetosphere, ionosphere and thermosphere. In these studies historical data from several different data sources (electric fields from radars and satellites, electric currents from satellites, magnetic perturbations from satellites and magnetometers) have been assimilated. In its real-time mode (rt-AMIE), only data from an array of ground-based magnetometers are assimilated in and convection patterns are produced in one-minute increments. However, the reliability of these real-time patterns for applications involving ionosphere-thermosphere specifications and forecasts has never been systematically tested. To address this issue, a comparison of one year of DMSP F13 cross-track ion drift velocities with AMIE convection patterns based on data from 80 ground-based magnetometers has been conducted. First, for each high-latitude DMSP velocity observation, the corresponding AMIE value was calculated. Then, the measured and calculated cross-track ion drift velocities along the high-latitude pass were compared and criteria were established to determine whether or not the AMIE patterns fit the measurements adequately. The comparisons were done for one year (1998) of satellite crossings of the northern polar region (4300 consecutive satellite crossings). The results indicate that the AMIE patterns adequately represented the DMSP observations about 32% of the time, which is a significant improvement over statistical convection patterns (6% of the time) [Bekerat et al., J. Geophys. Res., 108, 1413, 2003]. This is particularly impressive in view of the fact that only a limited number of ground-based magnetometers are included in the AMIE patterns used in this study.

Bekerat, H. A.; Schunk, R. W.; Scherliess, L.; Ridley, A.

2004-12-01

7

Comparison of satellite ion drift velocities with AMIE deduced convection patterns  

NASA Astrophysics Data System (ADS)

The Assimilative Mapping of Ionospheric Electrodynamics (AMIE) model has been used in a wide range of studies pertaining to the magnetosphere, ionosphere and thermosphere. In these studies historical data from several different data sources (electric fields from radars and satellites, electric currents from satellites, magnetic perturbations from satellites and ground-based magnetometers) have been assimilated. In its real-time mode (rt-AMIE), only data from an array of ground-based magnetometers are assimilated and convection patterns are produced in 1-min increments. However, the reliability of these real-time patterns for applications involving ionosphere thermosphere specifications and forecasts has never been systematically tested. To address this issue, a comparison of a 1-year dataset of DMSP F13 cross-track ion drift velocities with AMIE convection patterns, based on data from 80 ground-based magnetometers, has been conducted. First, for each high-latitude DMSP velocity observation, the corresponding AMIE value was calculated. Then, the measured and calculated cross-track ion drift velocities along the high-latitude pass were compared and criteria were established to determine whether or not the AMIE patterns adequately fit the measurements. The comparisons were done for a full year (1998) of satellite crossings of the northern polar region (4300 consecutive satellite crossings). The comparisons indicate that the AMIE patterns adequately represented the DMSP observations about 32% of the time, which is a significant improvement over statistical convection patterns (6% of the time). This is particularly impressive in view of the fact that only a limited number of ground-based magnetometers were included in the AMIE patterns used in this study.

Bekerat, Hamed A.; Schunk, Robert W.; Scherliess, Ludger; Ridley, Aaron

2005-11-01

8

Subauroral ion drift (SAID) velocity behavior as inferred from Dynamics Explorer-B and Intercosmos "Bulgaria-1300" data  

NASA Astrophysics Data System (ADS)

Rapid westward subauroral ion motion in the nighttime auroral oval during geomagnetically disturbed conditions had been first reported by ion drift measurements carried out on ``Cosmos--184'' satellite. The observed narrow band ion drift velocity jets at evening magnetic local times on the equatorward boundary of the auroral oval often exceed few km/s drift speed. In the present paper we use ion drift velocity data from Dynamics Explorer-2 (DE-2) and Intercosmos "BULGARIA-1300" (ICB-1300) satellites. DE-2 was launched on August 3 1981 with an inclination of 90, perigee of 300km and apogee 1000km. On board plasma diagnostics instrumentation had been addressed to study upper atmosphere dynamics as a manifestation of the ionosphere-magnetosphere interaction processes in the Earth's ionosphere. ICB-1300 was launched on August 7 1981 on a near circular orbit with an orbital inclination of 82, initial apogee 906km and perigee 825km under the same scientific objectives with a similar scientific instrumentation. Both satellites were in active operation almost of two years period. Here, DE-2 Ion Drift Meter (IDM) and Retarding Potential Analyzer (RPA) data together with ICB-1300 Electric Field Experiment (IESP-1) and Spherical Ion Trap (P-6) data are used. In the present work we examine subauroral ion drift (SAID) velocity behavior as inferred by ion drift data from both DE-2 and ICB-1300 satellites in respect to the geomagnetic activity at different magnetic local times (MLT). Relative changes in invariant latitude position of SAID jets vs. AE index show a larger equatorward shift of almost 9.8° ILAT in a 2100-2200 MLT sector (AE=1000). Corresponding statistics for dusk MLT sector show a 3.4° ILAT equatorward shift of the SAID position and a 6.4 o for earlier morning MLT hours respectively.

Bankov, L.; Vassileva, A.

9

Equatorial vertical E × B drift velocities inferred from ionosonde measurements over Ouagadougou and the IRI-2007 vertical ion drift model  

NASA Astrophysics Data System (ADS)

F-region vertical plasma drift velocities were deduced from the hourly hmF2 values acquired from ionogram data over a near dip equatorial station Ouagadougou (12.4°N, 358.5°E, dip angle 5.9°N) in Africa. Our results are compared against the global empirical model of Scherliess and Fejer (1999) incorporated in the IRI model (IRI-2007) for 1600 to 0800 LT from 1 year of data during sunspot maximum year of 1989 (yearly average solar flux intensity, F10.7 = 192) corresponding to the peak phase of solar cycle 22, under magnetically quiet conditions. The drifts are entirely downward between 2000 and 0500 LT bin for both techniques and the root mean square error (RMSE) between the modeled and the ionosonde vertical plasma drifts during these periods is 3.80, 4.37, and 4.74 m/s for June solstice, December solstice and equinox, respectively. Ouagadougou average vertical drifts show evening prereversal enhancement (PRE) velocity peaks ( VZP) of about 16, 14, and 17 m/s in June solstice, December solstice, and equinox, respectively, at 1900-2000 LT; whereas global empirical model average drifts indicate VZP of approximately 33 m/s (June solstice), 29 m/s (December solstice), and 50 m/s (equinox) at 1800 LT. We find very weak and positive correlation (+0.10376) between modeled VZP versus F10.7, while ionosonde VZP against F10.7 gives worst and opposite correlation (-0.05799). The results also show that modeled VZP- Ap indicates good and positive correlation (+0.64289), but ionosonde VZP- Ap exhibits poor and negative correlation (-0.22477).

Oyekola, O. S.; Kolawole, L. B.

2010-09-01

10

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

Microsoft Academic Search

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

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

1985-01-01

11

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

PubMed

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

Murad, Sohail

2012-02-21

12

Measurements of the ion drift velocities in the presheaths of plasmas with multiple ion species  

NASA Astrophysics Data System (ADS)

We have used a variety of diode lasers to perform laser-induced fluorescence (LIF) measurements that were the first to test the Bohm Criterion for multiple ion species plasmas. These measurements led to the discovery that a collective effect, ion-ion instability enhanced friction, is important for sheath formation in multiple ion species plasmas. New LIF schemes were pioneered in order to complete these experiments with diode lasers. With respect to a new LIF scheme for KrII, accessible to diode lasers, challenges remain fielding an ion flow diagnostic in low temperature plasmas.

Severn, G.; Yip, C.-S.; Hershkowitz, N.

2013-11-01

13

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

14

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

15

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 Resolute Bay incoherent scatter radar, 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 measured EXB drift to PolarDARN which is composed of Rankin Inlet and Inuvik 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 points corresponding to E and F regions. The E region echoes were identified by their sudden appearance at a threshold EXB drift magnitude and at small flow angles, which are characteristics of primary Farley-Buneman waves. A special joint fit to all the data points has a slope of 0.85 for the F region echoes. Considering an F region electron density of 5x10^11 m-3 , which has a refraction index of 0.86 at 12.5 MHz (for Polar-DARN 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 excellent agreement with our measurement (0.85). The fit for E region Doppler velocities show a saturation speed at 170 m/s, while the data were spread between 100-300 m/s. Although the saturation speed is somewhat lower than 300 m/s (the ion acoustic speed), it is acceptable considering earlier work attributing similarly low velocities to large aspect angles at the scattering altitudes.

Chen, S.; Bahcivan, H.; Nicolls, M. J.; Perry, G. W.

2012-12-01

16

A case study of subauroral ion drift velocity jets by means of dynamics explorer-2 and intercosmos Bulgaria-1300 satellites data  

NASA Astrophysics Data System (ADS)

Satellites INTERCOSMOS ``Bulgaria-1300'' (ICB-1300) and Dynamics Explorer-2 (DE-2) were launched close together early in August 1981. The satellite data base from both DE-2 and ICB-1300 covers almost a two years period. Data from both satellites were used to examine the longitudinal behavior of a few selected simultaneous subauroral ion drift (SAID) events in the late evening and earlier morning hours of magnetic local time (MLT). SAID velocity jets occur as a narrow region at the equatorward edge of the auroral oval in the westward direction in the evening hours, simultaneously in both hemispheres. It is shown, that the polward component of the DC electric field measured from ICB-1300 corresponds well to the ion drift velocity jets observed in the Ion Drift Meter (IDM) on DE-2 with some longitudinal extent of more than three hours MLT in the evening sector. In a specific case (orbit 705 of ICB-1300), we observe downward current associated with a SAID event of about 1.8 muA/m^2, corresponding to the previously reported current measurements on DE-2 (orbit 796) of about 2.1 muA/m^2. The simultaneous SAID observation taken in the earlier morning hours of the ion drift velocity distribution, shows an existence of velocity jets up to 0130 MLT.

Bankov, L. G.; Stanev, G. A.; Vassileva, A. K.; Kirova, V. A.; Danov, D. L.; Hanson, W. B.; Heelis, R. A.; Anderson, P. C.

17

Remote-sensing observations of F-region ion drift velocities using Dynamics Explorer-2 Doppler measurements of the O+(2P) 732.0 nm emission  

NASA Technical Reports Server (NTRS)

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

Carr, S. S.; Killeen, T. L.; Coley, W. R.

1992-01-01

18

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

19

First comparison of STARE and EISCAT electron drift velocity measurements  

SciTech Connect

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

Nielsen, E.; Schlegel, K.

1983-07-01

20

Ion Drift-Chemical Ionization Mass Spectrometry.  

National Technical Information Service (NTIS)

A method and apparatus for conducting mass spectrometry. The mass spectrometry may be accomplished by ion drift-chemical ionization mass spectrometry. One embodiment includes a chemical ionization mass spectrometer comprising an ion drift zone having an i...

R. Zhang

2005-01-01

21

Dimethylether: a low velocity, low diffusion drift chamber gas  

SciTech Connect

There are two main motivations to look for a low electron mobility gas: the first is that a low drift velocity relaxes the need to measure drift times with nanosecond (or even subnanosecond) precision; the second is that (in an ideal drift geometry), the capability of resolving two closely spaced tracks depends upon the ratio of electron mobility to ion mobility ..mu../sub e//..mu../sub i/. Since ..mu../sub i/ is rather constant, the way to separate two tracks is to slow down the electrons. Many other properties are required besides low mobility and low drifting electron temperature: the gas should have a large (> 10/sup 3/) stable gain; it must be chemically stable and not oxic; it should not attack materials commonly used to fabricate drift chambers, etc. With these requirements in mind, we have tried a few promising (on paper) gases, either pure or in admixture with Argon. One of the gases examined, dimethylether ((CH/sub 3/)/sub 2/)), has shown interesting characteristics.

Villa, F.

1983-01-01

22

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

SciTech Connect

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

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

1995-12-01

23

Direct measurements of ion drift velocity in the upper ionosphere during a magnetic storm. Part 1: Experiment description and some results of measurements during magnetically quiet time  

Microsoft Academic Search

In October-November 1967, asymmetry of the free-stream flow of ambient ionospheric plasma around a satellite caused mainly by the plasma drift or convection under action of the dc electric field was measured onboard the Cosmos-184 Satellite. Geometry and reduction techniques for these measurements from a satellite oriented along the velocity vector were considered. The deviations of the satellite orientation relative

Y. I. Galperin; V. N. Ponomarev; A. G. Zosimova

1973-01-01

24

Ion Temperature Gradient Driven Drift Cyclotron Instabilities.  

National Technical Information Service (NTIS)

The role of ion temperature gradient driven drift cyclotron instabilities in both mirror machines and tokamaks is examined. Destabilizing temperature gradient modifications to the drift cyclotron loss cone mode are found to exist even when the loss cone i...

P. J. Catto R. E. Aamodt

1977-01-01

25

Nonlinear drift waves in electron-positron-ion plasmas.  

PubMed

It is suggested that low-frequency drift waves can play an important role in the dynamics of electron-positron plasmas comprising some concentration of ions. In the electromagnetic case the drift wave couples with the shear Alfvén wave in an electron-positron-ion plasma. The drift wave frequency can be very low in such plasmas depending on the concentration and density scale lengths of the plasma components. In the nonlinear regime these waves can give rise to dipolar vortices in both electrostatic and electromagnetic limits. The velocity of the nonlinear structure turns out to be different compared to the case of an electron-ion plasma. PMID:12786328

Saleem, H; Haque, Q; Vranjes, J

2003-05-01

26

Dimethylether: A Low Velocity, Low Diffusion Drift Chamber Gas.  

National Technical Information Service (NTIS)

There are two main motivations to look for a low electron mobility gas: the first is that a low drift velocity relaxes the need to measure drift times with nanosecond (or even subnanosecond) precision; the second is that (in an ideal drift geometry), the ...

F. Villa

1983-01-01

27

Construction update and drift velocity calibration for the CLAS drift chamber system  

Microsoft Academic Search

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

M. D. Mestayer; F. J. Barbosa; P. Bonneau; E. Burtin; S. Christo; G. Doolittle; S. A. Dytman; Gerard Gilfoyle; C. E. Hyde-Wright; A. Klein; M. V. Kossov; S. E. Kuhn; R. Magahiz; R. A. Miskimen; L. Y. Murphy; J. E. O'Meara; T. D. Pyron; L. Qin; B. A. Raue; R. A. Schumacher; W. Tuzel; L. B. Weinstein; A. Yegneswaran

1995-01-01

28

Coherent radar doppler measurements and their relationship to the ionospheric electron drift velocity  

SciTech Connect

We have examined the relationship between the radial mean Doppler velocities observed with coherent radars, such as in the STARE (Scandinavian Twin Auroral Radar Experiment) system, and the electron drift velocities observed with an incoherent scatter facility. The two sets of measurements were made simultaneously and can with high accuracy be related to a common magnetic flux tube. We find that the Doppler velocities of electron density irregularities produced by the two-stream instability in the E region are limited to a value near the ion acoustic velocity. Moreover, we find that this value is a strong function of the electron drift velocity, in agreement with theoretical predictions. An algorithm has been determined which enables us to use the STARE data to derive estimates of the electron drift velocity which are in excellent agreement with values deduced from EISCAT (European Incoherent Scatter Facility) data.

Nielsen, E.; Schlegel, K.

1985-04-01

29

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

30

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

31

Distribution Parameter and Drift Velocity of Drift-Flux Model in Bubbly Flow  

SciTech Connect

In view of the practical importance of the drift-flux model for two-phase flow analysis in general and in the analysis of nuclear-reactor transients and accidents in particular, the distribution parameter and the drift velocity have been studied for bubbly-flow regime. The constitutive equation that specifies the distribution parameter in the bubbly flow has been derived by taking into account the effect of the bubble size on the phase distribution, since the bubble size would govern the distribution of the void fraction. A comparison of the newly developed model with various fully-developed bubbly-flow data over a wide range of flow parameters shows a satisfactory agreement. The constitutive equation for the drift velocity developed by Ishii has been reevaluated by the drift velocity obtained from local flow parameters such as void fraction, gas velocity and liquid velocity measured under steady fully-developed bubbly flow conditions. It has been confirmed that the newly developed model of the distribution parameter and the drift velocity correlation developed by Ishii can also be applicable to developing bubbly flows. (authors)

Takashi Hibiki [Kyoto University, Kumatori, Sennan, Osaka 590-0494 (Japan); Mamoru Ishii [Purdue University, West Lafayette, IN 47907 (United States)

2002-07-01

32

Distribution parameter and drift velocity of drift-flux model in bubbly flow  

Microsoft Academic Search

In view of the practical importance of the drift-flux model for two-phase flow analysis in general and in the analysis of nuclear-reactor transients and accidents in particular, the distribution parameter and the drift velocity have been studied for bubbly flow regime. The constitutive equation that specifies the distribution parameter in the bubbly flow has been derived by taking into account

Takashi Hibiki; Mamoru Ishii

2002-01-01

33

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

Microsoft Academic Search

Measurements of the electron drift velocity as a function of the electric field have been made in a small drift chamber with uniform electric field for Ar\\/CHâ, Ar\\/i-CâHââ, Ar\\/COâ, and SQS gas mixtures. The value of the electric field ranges from about 0.3 to 2.5 kV\\/cm. The results of the measurements are discussed.

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

1985-01-01

34

Cap Bubble Drift Velocity in a Confined Test Section  

SciTech Connect

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

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

2002-10-09

35

Experimental Study of the Drift Velocity in Progressive Waves.  

National Technical Information Service (NTIS)

The second order drift component of the velocity field under progressive water waves is the subject of this experimental work. It is an Eulerian representation of the mass transport phenomenon in water waves. In the present study the primary attention was...

L. Zhan W. Dursthoff T. Bruce C. A. Greated

1992-01-01

36

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

37

Drift-Alfvén vortices at the ion Larmor radius scale  

NASA Astrophysics Data System (ADS)

The theory of nonlinear drift-Alfvén 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-Alfvén 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.; Pokhotelov, O. A.

2008-02-01

38

Ion drift simulation of sudden appearance of sub-keV structured ions in the inner magnetosphere  

NASA Astrophysics Data System (ADS)

Energy-latitude dispersed structured sub-keV ions in the inner magnetosphere often show significant development or intensification (by more than factor of 3) within 1-2 h near noon or afternoon where the azimuthal ion drift velocity at the sub-keV range is expected to be near zero. To examine whether such sudden appearances in the dayside can be explained by the drift motion of ions that are formed during substorm-related injections, we numerically simulated two such examples, one at noon and the other in the afternoon, based on the ion drift model. For both cases, the ion drift model with finite duration of proton source in the nightside can explain the observed large inbound-outbound differences in the sub-keV proton population without any new sources. Ion drift motion can thus cause rapid changes of complicated ion populations, at remote places from the source a long time after the substorm activities.

Yamauchi, M.; Ebihara, Y.; Nilsson, H.; Dandouras, I.

2014-02-01

39

Direct measurement of light-induced drift velocities in Rb-Ar mixtures  

Microsoft Academic Search

We report on the first direct measurement of light-induced drift velocities of rubidium in an argon buffer gas. The effect of hyperfine pumping on the drift velocity has been eliminated by using two-frequency excitation. The results for the drift velocity are in good agreement with calculations based on a rate equation model.

F. Wittgrefe; A. D. Streater; M. D. Hoogerland; E. R. Eliel; J. P. Woerdman

1989-01-01

40

Time of Flight (TOF) mode of operation in ionospheric ion drift measurements  

NASA Astrophysics Data System (ADS)

During the past 30 years, ion drift measurements were a very powerful way to study the Earth's ionosphere dynamics in the context of the Sun-Earth relation processes. Here, we propose a combined use of Time-Of-Flight reflectron as a part of the modified Ion Drift Meter (IDM) sensor to obtain valuable mass-spectra and ram ion speed in parallel to the IDM transverse ion drift velocity measurements. This in fact could reduce the measuring technique to a single-sensor IDM/TOF mass-spectrometer.

Bankov, L. G.; Vassileva, A. K.

41

A first comparison of STARE and EISCAT electron drift velocity measurements  

Microsoft Academic Search

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

E. Nielsen; K. Schlegel

1983-01-01

42

Drift and ion sound instabilities of the magnetic field aligned shear flow with inhomogeneous ion temperature  

NASA Astrophysics Data System (ADS)

The effects of the ion temperature gradient across the magnetic field on the development of the drift and ion-sound shear flow modified and shear flow driven instabilities of the magnetic field aligned shear flow are studied analytically and numerically on the ground of a kinetic approach. The cases of cold and hot ions with respect to electrons are considered. Dominant excitation mechanisms (ion-kinetic, electron-kinetic, and hydrodynamic) of each instability is determined in different domains of the wave number space, velocity shearing rate and temperature ratio of the ions and electrons. Applications of the developed theory to fusion and space plasmas are given.

Mykhaylenko, Volodymyr; Lee, Hae June; Mykhaylenko, Volodymyr S.; Koepke, Mark

2012-10-01

43

Magnetometer-inferred, Equatorial, Daytime Vertical ExB Drift Velocities Observed in the African Longitude Sector  

NASA Astrophysics Data System (ADS)

A recent paper has investigated the sharp longitude gradients in the dayside ExB drift velocities associated with the 4-cell, non-migrating structures thought to be connected with the eastward propagating, diurnal, non-migrating (DE3) tides. Observations of vertical ExB drift velocities obtained from the Ion Velocity Meter (IVM) on the Communication/Navigation Outage Forecast System (C/NOFS) satellite were obtained in the Western Pacific, Eastern Pacific, Peruvian and Atlantic sectors for a few days during the months of October, March and December, 2009. Respective ExB drift velocity gradients at the cell boundaries for these 4 longitude sectors were a.) -1.3m/sec/degree, b.) 3m/sec/degree, c.) -4m/sec/degree and d.) 1m/sec/degree and were observed on a day-to-day basis. In this talk, we estimate the longitude gradients in the dayside, vertical ExB drift velocities from magnetometer H-component observations in the African sector. We briefly describe the technique for obtaining realistic ExB drift velocities associated with the difference in the H-component values between a magnetometer on the magnetic equator and one off the magnetic equator at 6 to 9 degrees dip latitude (delta H). We present magnetometer-inferred, dayside ExB drift velocities obtained from the AMBER (African Meridian B-field Education and Research) magnetometer chain in the East Africa (Ethiopian) longitude sector and the West African (Nigerian) longitude sector. We compare the longitude gradients in ExB drift velocities in the African sector with the C/NOFS- observed longitude gradients mentioned above. We also discuss the advantages of using ground-based magnetometer observations to infer ExB drift velocities compared with the C/NOFS satellite observations.

Anderson, D. N.; Yizengaw, E.

2011-12-01

44

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

45

Filament velocity scaling laws for warm ions  

NASA Astrophysics Data System (ADS)

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.; Carralero, D.; Birkenmeier, G.; Müller, H. W.; Müller, S. H.; Fuchert, G.; Scott, B. D.; Stroth, U.

2013-10-01

46

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

47

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

SciTech Connect

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

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

1990-11-01

48

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

SciTech Connect

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

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

2012-07-01

49

Identifying equatorial ionospheric irregularities using in situ ion drifts  

NASA Astrophysics Data System (ADS)

Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (?N/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.

Stoneback, R. A.; Heelis, R. A.

2014-04-01

50

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

51

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

52

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

53

Hot-electron drift velocity in III V semiconductors under the condition of impact ionization  

NASA Astrophysics Data System (ADS)

A calculation has been carried out for the drift velocity of electrons in the highfield region under the condition of impact ionization in III V semiconductor compounds. The energy-balance equation of the one-electron model has been solved considering alloy scattering and carrier-carrier interaction, in addition to optical phonon and ionization scattering. Fairly good agreement is obtained for GaAs with the available experimental and Monte-Carlo results. Graphs for the high-field drift velocity has also been plotted for Ga1- x InxAs ( x = 0.53) at different ratios of ionization mean-free path and optical phonon mean-free path. The plot of high-field drift velocity versus ionization rate reveals that the high-field drift velocity strongly depends on the ionization rate of carriers, and vice versa.

Singh, S. R.; Pal, B. B.

1987-05-01

54

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

SciTech Connect

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

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

2009-04-15

55

DRIFT VELOCITY OF CHARGED PARTICLES IN THE MAGNETIC DIPOLE FIELD  

Microsoft Academic Search

A charged particle which moves spirally around a line of force of a ; magnetic dipole field is also at the same time deflected perpendicularly to the ; field. The usual relationship expressing this drift should include a third terms ; dependent on the central force. This term is derived and the relationship is ; corrected. (J.S.R.);

Siebert

1960-01-01

56

A transient two-phase velocity difference model for drift calculation in CANDU thermohydraulic codes  

SciTech Connect

A realistic velocity difference scheme has been developed for calculating the drift parameters in both horizontally and vertically oriented sections of the primary heat transport systems of CANDU reactors. This model predicts the unequal velocity effects, spatially and temporally. It can be used to describe the slip in transient and multipurpose thermohydraulic codes. The transient velocity difference equation of this model is an arrangement of the two-fluid model equations. This equation describes the time-dependent relation between the phase velocities. This is a function of the pressure gradient, phase inertias, volume fraction, flow regime, inerfacial forces, and additional constitutive relations. In addition, the model includes a package of momentum exchange constitutive laws to calculate the interphase momentum exchange parameters and virtual mass coefficients. The parameters necessary for the integration of this model into CANDU thermohydraulic codes (SOPHT, FIREBIRD) are expressed in terms of the dynamic difference velocity. These parameters are the drift mass flow rate, drift velocity, distribution parameter, flow quality, effective density, and flow enthalpy. Numerical results revealed that the velocity difference model fairly predicted the drift flux parameters when compared with those calculated by existing slipdrift correlations in the SOPHT and FIREBIRD codes, other drift flux models, and with certain experimental data reported in the literature.

Sami, S.M.

1986-12-01

57

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

58

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

59

Modelling of drift wave turbulence with a finite ion temperature gradient  

SciTech Connect

With the use of consistent orderings in {var epsilon} = {rho}{sub s}/a and {delta} = k{sub {perpendicular}}{rho}{sub s} model equations are derived for the drift instabilities from the electrostatic two-fluid equations. The electrical resistivity {eta} included in the system allows the dynamics of both the collisional drift wave instability ({eta} {ne} 0) and the collisionless ion temperature gradient driven instability ({eta} = 0). The model equations used extensively in earlier nonlinear studies are obtained as appropriate limits of the model equations derived in the present work. The effects of sheared velocity flows in the equilibrium plasma and electron temperature fluctuations are also discussed. 14 refs.

Hamaguchi, S.; Horton, W.

1990-10-01

60

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

61

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

SciTech Connect

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

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

2007-06-28

62

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

SciTech Connect

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

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

2007-08-15

63

Average equatorial zonal and vertical ion drifts determined from San Marco D electric field measurements  

NASA Astrophysics Data System (ADS)

San Marco D electric field measurements have been averaged in terms of their equivalent ion drift to produce an average pattern of equatorial zonal and vertical ion drifts. Variations with season, solar activity, Kp, lunar phase and longitude have been analyzed. Similarities and some differences from previous Jicamarca, DE 2 and AE-E results are seen. Confirmation is given of the dominance of the F region dynamo in the 1900-2100 local time region. The daytime zonal ion drift is larger for high F 10.7 values than that for low values. There is little variation between high and low values of Kp. Superrotation is evident in this data set and is larger at equinox compared to solstice. At the June solstice there are significant differences between the average ion drifts in the longitude sector where the geomagnetic equator is north of the geographic equator (Indian sector) and the sector where the geomagnetic equator is south of the geographic equator (Peruvian sector). The daytime upward velocity is larger in the Indian sector than in the Peruvian sector, and it reverses later in the evening in the Indian sector. Daytime westward zonal velocities are larger and the nighttime eastward velocities are smaller in the Indian sector. A presunrise enhancement is seen in the downward velocity in the Indian sector but not in the Peruvian sector. Significant variations are also seen with the phase of the moon. In light of current theory, the lunar variations suggest a complex interaction of E and F region dynamo sources with conductivity, changing in phase and character with latitude.

Maynard, Nelson C.; Aggson, Thomas L.; Herrero, Federico A.; Liebrecht, M. Carmen; Saba, Jack L.

1995-09-01

64

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

Microsoft Academic Search

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

I. C. Kizilyalli; M. Artaki

1989-01-01

65

Negative effective mass mechanism of negative differential drift velocity and terahertz generation  

Microsoft Academic Search

The negative-differential-drift-velocity instability, which forms the basis of Gunn high-frequency generators, can originate from Ridley-Watkins-Hilsum or negative effective mass (NEM) mechanisms. The first mechanism is dissipative by nature. The second is mainly drift-related. Therefore, the second mechanism promises to be more effective. We show the existence of stationary oscillatory regimes in the ballistic NEM p+ p p+-diodes, which have a

Zinovi S. Gribnikov; Rustam R. Bashirov; Vladimir V. Mitin

2001-01-01

66

Drift-Alfvén vortices at the ion Larmor radius scale: Cluster observations versus theory  

NASA Astrophysics Data System (ADS)

Recently Cluster satellites have discovered short-scale drift-kinetic Alfven vortices in Cusp region of the Earth magnetosphere (Sundkvist et al., 2005). This discovery raised the question what are the critical parameters that determine the characteristics of vortex type structures observed. To adress these questions it was necessary to develop the theoretical model to describe nonlinear structures of such a type with the spatial scales comparable to the ion Larmor radius. New theoretical model was developed by Onishchenko et al., (2008). It was shown that the set of equations describing the nonlinear dynamics of drift-Alfvén waves in a quasistationary regime e 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 were shown to 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 were analyzed. It was 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 presumably 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 shown. Sundkvist,D., V. Krasnoselskikh, P. Shukla, A. Vaivads, M. Andre, S. Buchert, H. Reme, In situ multi-satellite detection of coherent vortices as a manifestation of Alfvenic turbulence, Nature, v. 436, doi:10.1038/nature03931, August 2005; Onishchenko, O.G., V. Krasnoselskikh, O. Pokhotelov, Drift-Alfvén vortices at e the ion Larmor radius scale, Physics of Plasmas, 15, 2008.

Krasnoselskikh, Vladimir; Pokhotelov, Oleg; Onishchenko, Oleg. G.; Sundkvist, David

67

Cross-tail ion drift in a realistic model magnetotail  

NASA Technical Reports Server (NTRS)

By integrating the exact equations of motion, particle orbits have been followed in a good model magnetospheric field consisting of a planetary dipole, forward magnetosphere, and magnetotail current system. Proton energies from 2 eV to 20 keV were used for the full range of equatorial pitch angles and phase. Despite considerable pitch angle scattering in the equatorial plane crossings, it is found, first, that the bounce-averaged cross-tail drift velocity is approximately independent of pitch angle. Second, it is found that, averaged over initial gyrophase, the drift velocity (due to field curvature and gradient) is proportional to proton energy and is given to good approximation by adiabatic approximations, even up to 20 keV, despite the extreme lack of meeting the adiabatic criteria.

Propp, K.; Beard, D. B.

1984-01-01

68

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

69

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

70

Drift compression of an intense neutralized ion beam  

SciTech Connect

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

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

2005-09-08

71

Drift Compression of an Intense Neutralized Ion Beam  

SciTech Connect

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

Roy, P.K.; Yu, S.S.; Henestroza, E.; Anders, A.; Bieniosek, F.M.; Coleman, J.; Eylon, S.; Greenway, W.G.; Leitner, M.; Logan, B.G.; Waldron, W.L. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720 (United States); Welch, D. R.; Thoma, C. [ATK Mission Research, Albuquerque, New Mexico 87110-3946 (United States); Sefkow, A.B.; Gilson, E.P.; Efthimion, P.C.; Davidson, R.C. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451 (United States)

2005-12-02

72

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

National Technical Information Service (NTIS)

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

J. Weiland

1991-01-01

73

Non-Maxwellian ion velocity distributions observed using EISCAT  

SciTech Connect

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

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

1987-02-01

74

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

75

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

76

Drift Mode Growth Rate and Associated Ion Thermal Transport in Reversed Magnetic Shear Tokamak Plasma  

NASA Astrophysics Data System (ADS)

Drift mode linear growth rate and quasi-linear ion thermal transport in the reversed magnetic shear plasma are investigated by using the two-fluid theory, previously developed by Weiland and the Chalmers group [J. Nucl. Fusion, 29 (1989) 1810; ibid. 30 (1990) 983]. The theory is here extended to include both the radial electrical field shear (dEr/dr) and the electron fluid velocity (Ve) in the sheared coordinate system. Here, Ve describes the coupling between the safety factor q and the Er×B velocity VE. Their influences on the growth rate and associated ion thermal transport are obtained numerically. In addition, the ion heat pinch in the reversed shear plasma is observed. Qualitatively, the present conclusions are in good agreement with the experimental results.

Wang, Ai-Ke; Qiu, Xiao-Ming

2001-05-01

77

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

78

Gyrokinetic particle simulation of ion temperature gradient drift instabilities  

SciTech Connect

Ion temperature gradient drift instabilities have been investigated using gyrokinetic particle simulation techniques for the purpose of identifying the mechanisms responsible for their nonlinear saturation as well as the associated anomalous transport. For simplicity, the simulation has been carried out in a shear-free slab geometry, where the background pressure gradient is held fixed in time to represent quasistatic profiles typical of tokamak discharges. It is found that the nonlinearly generated zero-frequency responses for the ion parallel momentum and pressure are the dominant mechanisms giving rise to saturation. This is supported by the excellent agreement between the simulation results and those obtained from mode coupling calculations.

Lee, W.W.; Tang, W.M.

1987-04-01

79

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

80

Ion-acoustic instabilities driven by an ion velocity ring  

NASA Technical Reports Server (NTRS)

A ring distribution of ions in velocity space can generate electrostatic waves which propagate predominantly along an ambient magnetic field at frequencies comparable with the ion plasma frequency. A dispersion equation which accounts for these waves is presented, and solved analytically and numerically. It was found that ion-acoustic-like waves are excited in a plasma even if the electron temperature is comparable with the in temperature under the assumption of an anisotropic ion distribution.

Akimoto, K.; Papadopoulos, K.; Winske, D.

1985-01-01

81

Optimum drift velocity for single molecule fluorescence bursts in micro/nano-fluidic channels  

NASA Astrophysics Data System (ADS)

Photonic burst histograms can be used to identify single protein molecules in micro/nano-fluidic channels provided the width of the histogram is narrow. Photonic shot noise and residence time fluctuations, caused by longitudinal diffusion, are the major sources of the histogram width. This paper is a sequel to an earlier one of ours [L. L. Kish et al., Appl. Phys. Lett. 99, 143121 (2011)] and demonstrates that, for a given diffusion coefficient, an increase of the drift velocity enhances the relative shot noise and decreases the relative residence time fluctuations. This leads to an optimum drift velocity that minimizes the histogram width and maximizes the ability to identify single molecules, which is an important result for applications.

Kish, Lazar L.; Kameoka, Jun; Granqvist, Claes G.; Kish, Laszlo B.

2012-07-01

82

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

Microsoft Academic Search

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

J. L. Pack; A. V. Phelps

1961-01-01

83

Self-alignment of ions drifting in plasma  

NASA Astrophysics Data System (ADS)

The hypothesis that drift of ions in a plasma causes their spontaneous alignment with a quadrupole orientation of their angular momentum was confirmed in an experiment with ionization of argon in a 100 to 400 V hollow-cathode discharge tube 5 cm long and 3 cm in diameter. Distinct difference signals corresponding to the fine structure were recorded within the narrow low-pressure range of 0.1 to 0.5 torr at discharge currents of 10 to 60 mA. A comparison of difference signals from atomic argon and from weakly ionized argon proves the drift hypothesis of self-alignment most directly. The experimental data confirm also other predictions, namely that self-alignment of ions is closely associated with collisional mixing of half-levels in the fine structure of ions and that the self-alignment signal originates from a deviation of the ratio (N sub 1)/(N sub 2) of respective half-level populations from the ratio (g sub 1)/(g sub 2) of their statistical weights.

Kazantsev, S. A.; Petrashen, A. G.; Polezhayeva, N. T.; Rebane, V. N.; Rebane, T. K.

1987-06-01

84

East-west ion drifts at mid-latitudes observed by Dynamics Explorer 2  

SciTech Connect

Zonal ion drifts measured from the polar orbiting DE 2 spacecraft are examined to determine the effects of dynamo electric fields and penetration of high latitude electric fields at middle latitudes. Construction of a local time distribution from satellite data results in a mixture of local time and season as well as a range of magnetic activity encompassing Kp [le] 2 and Kp [ge] 3. Thus some combination of magnetospheric effects, expected to dominate during disturbed times, are seen during both quiet and disturbed times and solar tidal influences are most easily observed during quiet times. During quiet times, at invariant latitudes near 25[degrees], the solar diurnal tide dominates the local time distribution of the ion drift. At latitudes above 50[degrees] a diurnal component of comparable magnitude is also present, but its magnetospheric origin produces a shift in phase of almost 180[degrees] from the lower latitude diurnal tide. In the intervening region, between 20[degrees] and 50[degrees] invariant latitude, semidurnal and terdiurnal components in the local time distribution of the drift velocity are also seen. These components are generally larger than those seen by ground based radars during quiet times and may be attributable in part to a difference in solar activity and in part to a combination of the solar tides and magnetospheric penetration fields.

Heelis, R.A.; Coley, W.R. (Univ. of Texas, Richardson (United States))

1992-12-01

85

Drift wave vortices in multicomponent plasmas  

Microsoft Academic Search

The effect of negative ions in the dynamics of the drift vortex in inhomogeneous plasma is analytically studied. It is found that when the drift velocity is not constant, vortex solutions exist only in the short wavelength region. It is observed that the gradient of drift velocity is responsible for the formation of monopole vortices.

G. Gogoi; K. S. Goswami

2002-01-01

86

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

87

The influence of anisotropic electron drift velocity on the signal shapes of closed-end HPGe detectors  

Microsoft Academic Search

This study is concerned with the anisotropy of the electron drift velocity in germanium crystals at high electric fields and low temperature, and its influence on the charge collection process in n-type, high-purity germanium (HPGe) detectors of closed-end, coaxial geometry. The electron trajectories inside HPGe detectors are simulated using a phenomenological model to calculate the dependence of the drift velocity

L. Mihailescu; W. Gast; R. M Lieder; H. Brands; H. Jäger

2000-01-01

88

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

89

Metal impurities in ion and electron drift directions, for different TEXTOR discharges  

NASA Astrophysics Data System (ADS)

A probe system for time-resolved impurity flux measurements has been used with transmitting slit apertures open in two or four directions, for the collection of impurities in ion and electron drift directions, and perpendicularly (from top and from bottom). Adjustments of limiters caused changes in the connection lengths. We found higher fluxes of impurities on the ion drift side regardless of whether the connection length was larger or smaller than on the electron drift side. A flatter radial decay of impurity fluxes was found on the electron drift side. The impurity fluxes became nearly equal on both the ion and electron drift sides 8 cm into the scrape-off layer. From top and from bottom, the collected impurity fluxes were at least 100 times smaller than the fluxes measured on the ion drift side. Experiments performed in hydrogen, deuterium and helium gave similar results, but total impurity production was different.

Emmoth, B.; Nagata, S.; Bergsåker, H.; Sätherblom, H. E.; Wienhold, P.; Winter, J.; Waelbroeck, F.

1987-02-01

90

Ion temperature and velocity in a 300 mm diameter capacitively coupled plasma reactor driven at 13, 60 and 162 MHz  

Microsoft Academic Search

Spatially resolved temperature, radial drift velocity and relative density of an argon ion metastable state were measured in a capacitively coupled, parallel-plate reactor. The argon plasma was generated using single-frequency excitation of 13, 60, 162 MHz and dual frequency excitation of 13 and 60 MHz. For the conditions investigated, the ion temperatures were between 400 and 750 K. At the

G A Hebner; A M Paterson

2010-01-01

91

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

SciTech Connect

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 magnetic equator,using a dipole model to yield their apex height dependence. The 'average data' local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time (SLT) with a maximum westward velocity of 80 m/s in the early afternoon. There is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m/s. A secondary nighttime maximum exists a 0430 SLT preceeding the reversal to westward flow. This profile is in good agreement with Jicamarca radar measurements made under similar solar maximum conditions. Harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes. The diurnal term is dominant, but higher order terms through th quatradiurnal are significant. Vertical ion data taken at low (/plus minus/5/degree/) dip latitudes, while possessing greater scatter, generally agree wtih Jicamarca values. /copyright/ American Geophysical Union 1989

Coley, W. R.; Heelis, R. A.

1989-06-01

92

Influence of anisotropic F region ion velocity distributions on ionospheric ion outflows into the magnetosphere  

SciTech Connect

The contribution to the field-aligned ionospheric ion momentum equation, due to coupling between pressure anisotropy and the inhomogeneous geomagnetic field, is investigated. We term this contribution the ''hydrodynamic mirror force'' and investigate its dependence on the ion drift and the resulting deformations of the ion velocity distribution function from an isotropic form. It is shown that this extra upforce increases rapidly with ion drift relative to the neutral gas but is not highly dependent on the ion-neutral collision model employed. An example of a burst of flow observed by EISCAT, thought to be the ionospheric signature of a flux transfer event at the magnetopause, is studied in detail and it is shown that the nonthermal plasma which results is subject to a hydrodynamic mirror force which is roughly 10% of the gravitational downforce. In addition, predictions by the coupled University College London: Sheffield University model of the ionosphere and thermosphere show that the hydrodynamic mirror force in the auroral oval is up to 3% of the gravitational force for Kp of about 3, rising to 10% following a sudden increase in cross-cap potential. The spatial distribution of the upforce shows peaks in the cusp region and in the post-midnight auroral oval, similar to that of observed low-energy heavy ion flows from the ionosphere into the magnetosphere. We suggest the hydrodynamic mirror force may modulate these outflows by controlling the supply of heavy ions to regions of ion acceleration and that future simulations of the effects of Joule heating on ion outflows should make allowance for it. copyright American Geophysical Union 1989

Suvanto, K.; Lockwood, M.; Fuller-Rowell, T.J.

1989-02-01

93

Velocity scaling of ion neutralization in low energy ion scattering.  

PubMed

The ion fraction P+ is measured for He+ ions scattered by 129 degrees from a Cu surface. Both the primary energy and the angles of incidence and of exit are varied. From our results we conclude the following: along the incoming and outgoing trajectories, neutralization is due to Auger processes and depends on the normal velocity component v( perpendicular ) only. At higher energies, additional charge exchange is due to collision induced neutralization and reionization, both depending on the total ion energy only. Also in this regime P+ depends on v( perpendicular ), but via a two-valued function of the scattering geometry at fixed energy. PMID:12484817

Draxler, M; Gruber, R; Brongersma, H H; Bauer, P

2002-12-23

94

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

PubMed Central

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

2014-01-01

95

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

PubMed

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 × 10(6)?cm(-2)K(-2)·T(2)), 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. PMID:25044003

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

2014-01-01

96

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

SciTech Connect

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

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

2008-07-15

97

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

NASA Astrophysics Data System (ADS)

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 2F7/2-->6p 2D5/20 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+ ions. A realistic picture of the ion trajectory in the E×B drift plane is obtained when adding a velocity component directed toward the external cathode.

Bourgeois, G.; Mazouffre, S.; Sadeghi, N.

2010-11-01

98

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

Microsoft Academic Search

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

V. K Arora

2000-01-01

99

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

SciTech Connect

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

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

2006-07-08

100

Effective drift velocity and initiation times of interplanetary type-III radio bursts  

NASA Astrophysics Data System (ADS)

We derive an ``effective drift velocity'' (EDV) from dynamic WIND/WAVES spectrograms of interplanetary type-III fast-drift radio bursts associated with 171 near-relativistic electron events observed at 1 AU during the past 6 year (1997-2003). The EDV should be regarded as a phenomenological parameter that characterizes the burst drift rate. It is a weighted spatial average of the exciter-front velocities within the extended burst. A frequency-time contour at a constant observed intensity is a sample of emission from an irregular volume within which the extended exciter region encounters plasma frequency corresponding to the observing frequency. Therefore the contour of the spectrogram that defines the ``leading edge'' of the emission is produced by the earliest exciter electrons to reach regions with that particular plasma frequency in sufficient numbers to produce type-III emission measurable at the WIND spacecraft. The weighting involves not only the spatial distribution of the exciter electrons, but also the intrinsic brightness and radiation pattern of the type-III emission (as well as refraction effects). Nonetheless, even with all these caveats, the EDV derived from the ``leading edge'' will be formed by the fastest exciter velocities sampled from the entire burst pattern. The ``leading edge'' is established by a best fit of multiple time-frequency points obtained from different frequency cuts. The onset point for each given frequency is determined when the intensity curve rises above background. The same analysis technique also yields an estimate of the time at which the interplanetary type-III radio burst was initiated in the low corona. In this sense, the EDV and initiation times derived from the ``leading edge'' of the type-III bursts is a useful phenomenological parameter for the characterization of burst propagation. It is certainly a more robust a parameter than the ill-defined ``transit time'', when a contour of the emission pattern reaches the local plasma frequency. We examine the EDVs and initiation times with respect to the delayed injection of near-relativistic electrons, measured at ACE, to determine whether the EDVs are correlated with the observed delays.

Haggerty, D. K.; Roelof, E. C.

101

Effective drift velocity and initiation times of interplanetary type-III radio bursts  

NASA Astrophysics Data System (ADS)

We derive an "effective drift velocity" (EDV) from dynamic WIND/WAVES spectrograms of interplanetary type-III fast-drift radio bursts associated with 171 (1997-2003) near-relativistic electron events observed at 1 AU. The EDV should be regarded as a phenomenological parameter that characterizes the burst drift. It is a weighted spatial average of the exciter front velocities within the extended burst. A frequency-time contour at a constant observed intensity is a sample of emission from an irregular volume where the extended exciter region encounters the density corresponding to the frequency. Therefore the contour of the spectrogram that defines the "leading edge" of the emission is produced by the earliest exciter electrons to reach regions with that particular plasma frequency in sufficient numbers to produce type-III emission at the WIND spacecraft. The weighting involves not only the spatial distribution of the exciter electrons, but also the intrinsic brightness and radiation pattern of the type-III emission (as well as possible refraction effects). Nonetheless, even with all these caveats, the EDV derived from the "leading edge" will be among the fastest exciter velocities sampled from the entire burst pattern. The "leading edge" is established by a best fit of multiple time-frequency points obtained from different frequency cuts. The onset point for each given frequency is determined when the intensity curve rises above background. The same analysis technique also yields an estimate of the time at which the interplanetary type-III radio burst was initiated in the low corona. In this sense, the EDV and initiation times derived from the "leading edge" as well as the "peak" and "trailing edge" of the type-III burst are useful phenomenological parameters for the characterization of burst propagation. It is certainly a more robust a parameter than the ill-defined "transit time", when a contour of the emission pattern reaches the local plasma frequency. We examine the EDVs and initiation times with respect to the delayed injection of near-relativistic electrons and plasma density, measured at ACE, to determine whether the EDVs are correlated with the observed delays. No statistically significant correlations have been found.

Haggerty, D. K.; Roelof, E. C.

2004-05-01

102

Two Types of Ion Velocity Distributions on Reconnected Field Lines  

NASA Astrophysics Data System (ADS)

O. Vasiberg, L. Avanov and G. Koinash High-latitude reconnection events observed at Interball-Tail give facilitate identification of transmitted ion velocity distributions due to high deHoffmann-Teller frame velocity. Within reconnected flux tube magnetosheath and magnetospheric transmitted ions acquire high velocity due to sling-shot effect, and are easily separated from original ions. Occasionally within reconnected events the ion velocity distribution of magnetosheath component is significantly wider. In this case magnetospheric ion component can be hardly separated within ion velocity distribution. We argue that within reconnected magnetic flux tubes or segments of them with easily separated ion components reconnection processes ceased, and they are convecting from upstream reconnection site. The flux tubes with wide ion velocity distribution are still active, and reconnection is still is in the progress.

Avanov, L. A.; Vaisberg, O. L.; Koinash, G.

2009-12-01

103

Application of the Dopplionogram to Doppler-sorted interferometry measurements of ionospheric drift velocity  

NASA Astrophysics Data System (ADS)

The Dopplionogram was developed as a method of displaying Doppler shifts along the frequency axis of ionograms recorded using B-mode soundings of the Dynasonde, an early type of HF digital ionosonde. The basic idea of recording Doppler shifts in an ionogram format is applied and extended to the Doppler velocity mode of the Digisonde Portable Sounder-4 (DPS-4), a related and more recent type of digital ionosonde. In order to describe our mode of operation a Dopplionogram is redefined to mean a set of stepped-frequency soundings that yields a set of ionospheric Doppler shifts particular to the chosen transmission frequencies. Extension of the technique to include Doppler-sorted interferometry (DSI) analysis of the Doppler spectra facilitates a detailed analysis of ionospheric velocity variations in time and group height. This revitalized approach to DSI should prove useful for the study of ionospheric dynamics for which knowledge of the height profile of electric currents, drift velocity, and neutral winds is required. The technique is demonstrated using measurements of polar cap plasma winds obtained with a DPS-4 located at Casey, Antarctica (66.3°S, 110.5°E).

Parkinson, M. L.; Breed, A. M.; Dyson, P. L.; Morris, R. J.

1999-07-01

104

Effects of applied rotating magnetic perturbations on ion drift orbits in the Compact Auburn Torsatron  

Microsoft Academic Search

Ion drift surfaces in the presence of applied rotating magnetic perturbations in the Compact Auburn Torsatron (CAT) [Fusion Technol. 18, 281 (1990)] have been studied. A compact, monoenergetic ion gun was used to launch a continuous beam of 6Li+ ions in the vacuum magnetic fields of the CAT. The ions are detected on a paddle probe that is swept though

D. C. Pritchard; R. F. Gandy; J. D. Hanson; S. F. Knowlton; H. Lin; G. E. Sasser; E. Thomas Jr.; J. Cooney

1997-01-01

105

Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere  

NASA Astrophysics Data System (ADS)

We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4-6 RS (1 RS = 60,268 km) from the center of Saturn. The ion densities ni vary from an average of ˜35 cm-3 around noon up to ˜70 cm-3 around midnight. The ion velocities vi,? vary from ˜28-32 km/s at the lowest dayside values to ˜36-40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1-2 mV/m for 10-50 nm sized grains.

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

2014-06-01

106

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

107

Non-Maxwellian ion velocity distributions observed using EISCAT  

Microsoft Academic Search

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

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

1987-01-01

108

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

PubMed Central

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

May, Jody C.; McLean, John A.

2013-01-01

109

Artificial neural networks for the prediction of peptide drift time in ion mobility mass spectrometry  

PubMed Central

Background There is an increasing usage of ion mobility-mass spectrometry (IMMS) in proteomics. IMMS combines the features of ion mobility spectrometry (IMS) and mass spectrometry (MS). It separates and detects peptide ions on a millisecond time-scale. IMS separates peptide ions based on drift time that is determined by the collision cross-section of each peptide ion in a given experiment condition. A peptide ion's collision cross-section is related to the ion size and shape resulted from the peptide amino acid sequence and their modifications. This inherent relation between the drift time of peptide ion and peptide sequence indicates that the drift time of peptide ions can be used to infer peptide sequence and therefore, for peptide identification. Results This paper describes an artificial neural networks (ANNs) regression model for the prediction of peptide ion drift time in IMMS. Each peptide in this work was represented using three descriptors (i.e., molecular weight, sequence length and a two-dimensional sequence index). An ANN predictor consisting of four input nodes, three hidden nodes and one output node was constructed for peptide ion drift time prediction. For the model training and testing, a 10-fold cross-validation strategy was employed for three datasets each containing different charge states. Dataset one contains 212 singly-charged peptide ions, dataset two has 306 doubly-charged peptide ions, and dataset three has 77 triply-charged peptide ions. Our proposed method achieved 94.4%, 93.6% and 74.2% prediction accuracy for singly-, doubly- and triply-charged peptide ions, respectively. Conclusions An ANN-based method has been developed for predicting the drift time of peptide ions in IMMS. The results achieved here demonstrate the effectiveness and efficiency of the prediction model. This work can enhance the confidence of protein identification by combining with current database search approaches for protein identification.

2010-01-01

110

Regional, scale size, and interplanetary magnetic field variability of magnetic field and ion drift structures in the high-latitude ionosphere  

Microsoft Academic Search

Using data from the Dynamics Explorer 2 satellite's ion drift meter and magnetometer, we have examined fluctuations in the high-latitude velocity and magnetic field structure to better understand the coupling between the magnetosphere and ionosphere. Our study examines perturbations in the frequency range from 0.25 to 8 Hz, equivalent to static scale sizes between about 30 and 1 km. Seasonal

John P. Keady; R. A. Heelis

1999-01-01

111

Regional, scale size, and interplanetary magnetic field variability of magnetic field and ion drift structures in the high-latitude ionosphere  

Microsoft Academic Search

Using data from the Dynamics Explorer 2 sateilite's ion drift meter and magnetometer, we have examined fluctuations in the high-latitude velocity and mag- netic field structure to better understand the coupling between the magnetosphere and ionosphere. Our study examines perturbations in the frequency range from 0.25 to 8 Hz, equivalent to static scale sizes between about 30 and I kin.

John P. Kedynd; R. A. Heelis

1999-01-01

112

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

National Technical Information Service (NTIS)

The use of lithium-ion (Li(sup +)) drifting to study the properties of point defects in p-type Floating-Zone (FZ) silicon crystals is reported. The Li(sup +) drift technique is used to detect the presence of vacancy-related defects (D defects) in certain ...

J. T. Walton Y. K. Wong W. Zulehner

1997-01-01

113

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

SciTech Connect

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

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

2007-10-01

114

Effects of parallel ion dynamics on drift-Alfven vortices in plasmas  

Microsoft Academic Search

The formation and propagation of drift-Alfven vortices in magnetized plasmas is investigated analytically, with a focus on the effects of nonlinear ion dynamics parallel to the external magnetic field. The governing equations are derived, and it is shown that the sound term restricts the propagation speed of the drift-Alfven vortices and modifies the decay lengths of the outer and inner

P. K. Shukla

1988-01-01

115

Evolution of tropospheric ions observed by an ion mobility spectrometer with a drift tube  

NASA Astrophysics Data System (ADS)

The evolution of tropospheric ions has been studied by investigating the change in the mobility spectrum of ions generated in laboratory air as a function of aging time. An ion mobility spectrometer with a drift tube was constructed to get high-resolution measurements of mobility spectra of ions aged for about 0.03-5 s. Mobility spectra and their changes with ion age obtained in the present study showed the following features of tropospheric ion evolution near the ground: The positive ion mobility spectrum changes significantly with aging time, in which the peak mobility value shifts from 1.8 to about 1.0 cm2 V-1 s-1. Six peaks are usually distinguished in the mobility range between 2.0 and 1.0 cm2 V-1 s-1 in the positive spectrum, and a tendency of positive ions to evolve to have lower mobilities with increasing ion age is observed. Four additional peaks are sometimes resolved at around 0.9 cm2 V-1 s-1, indicating formation of heavy positive ions (probably over 400 amu). The negative ion mobility spectrum obtained is characterized by two prominent peaks at 1.9 and 1.7 cm2 V-1 s-1. The relative intensity of the two peaks varies with ion age, and the ions with a mobility of 1.9 cm2 V-1 s-1 dominate after about 1 s. Further conversions of the negative ions to those with lower mobilities can be expected from a comparison with the natural ion spectra obtained so far by the Gerdien type aspiration condenser.

Nagato, Kenkichi; Ogawa, Toshio

1998-06-01

116

A pulsed drift cavity to capture 30 keV ion bunches at ground potential  

Microsoft Academic Search

To capture radioactive ion beams of tens of keV in an ion trap, the use of a pulsed drift cavity allows one to avoid placing the complete setup on a high voltage (HV) platform. By pulsing down the voltage on a long electrode while the ion bunch is inside it, the electric potential zero level can be shifted down over

S. Coeck; B. Delauré; M. Herbane; M. Beck; V. V. Golovko; S. Kopecky; V. Yu. Kozlov; I. S. Kraev; A. Lindroth; T. Phalet; D. Beck; P. Delahaye; A. Herlert; F. Wenander; N. Severijns

2007-01-01

117

Determination of the void fraction and drift velocity in a two-phase flow with a boiling solar collector  

Microsoft Academic Search

This paper presents an approach to determine the void fraction and the drift velocity in a two-phase flow with a boiling solar collector using easily obtained experimental data. The solar collector operates in a thermal siphon circuit, where the working fluid absorbs solar radiation mostly while boiling. The vapor bubbles release their latent heat in a condenser, while heating up

M. E. Vieira; P. O. O. Duarte; H. L. B. Buarque

2000-01-01

118

Monte Carlo simulation of electron drift velocity in low-temperature-grown gallium arsenide in a Schottky-barrier model  

NASA Astrophysics Data System (ADS)

We present a method of simulating the electron transport in low-temperature-grown GaAs by the Monte Carlo method. Low-temperature-grown GaAs contains microscopic inclusions of As and these inhomogeneities render impossible the standard Monte Carlo mobility simulations. Our method overcomes this difficulty and allows the quantitative prediction of electron transport on the basis of principal microscopic material parameters, including the impurity and the precipitate concentrations and the precipitate size. The adopted approach involves simulations of a single electron trajectory in real space, while the influence of As precipitates on the GaAs matrix is treated in the framework of a Schottky-barrier model. The validity of this approach is verified by evaluation of the drift velocity in homogeneous GaAs where excellent agreement with other workers' results is reached. The drift velocity as a function of electric field in low-temperature-grown GaAs is calculated for a range of As precipitate concentrations. Effect of compensation ratio on drift velocity characteristics is also investigated. It is found that the drift velocity is reduced and the electric field at which the onset of the negative differential mobility occurs increases as the precipitate concentration increases. Both these effects are related to the reduced electron mean free path in the presence of precipitates. Additionally, comparatively high low-field electron mobilities in this material are theoretically explained.

Arifin, P.; Goldys, E.; Tansley, T. L.

1995-08-01

119

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

120

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

121

Modeling Drift Compression in an Integrated Beam Experiment for Heavy-Ion-Fusion  

NASA Astrophysics Data System (ADS)

The Integrated Beam Experiment (IBX) is an induction accelerator being designed to further develop the science base for heavy-ion fusion. The experiment is being developed jointly by Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, and Princeton Plasma Physics Laboratory. One conceptual approach would first accelerate a 0.5-1 A beam of singly charged potassium ions to 5 MeV, impose a head-to-tail velocity tilt to compress the beam longitudinally, and finally focus the beam radiallly using a series of quadrupole lenses. The lengthwise compression is a critical step because the radial size must be controlled as the current increases, and the beam emittance must be kept minimal. The work reported here first uses the moment-based model HERMES to design the drift-compression beam line and to assess the sensitivity of the final beam profile to beam and lattice errors. The particle-in-cell code WARP is then used to validate the physics design, study the phase-space evolution, and quantify the emittance growth.

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

2003-10-01

122

Effects of ion diamagnetic drift on the m?n = 1 high-order harmonic modes in rotating tokamak plasmas  

NASA Astrophysics Data System (ADS)

The effects of ion diamagnetic drift on the m/n=1 high-order harmonic modes in rotating tokamak plasmas are numerically investigated by using a cylindrical reduced magnetohydrodynamic model. It is found that the ion diamagnetic drift has a stabilizing effect on the high-order tearing modes in the small ion diamagnetic drift regime and can excite the m/n=1 high-order Kelvin–Helmholtz (KH) instability in the large ion diamagnetic drift regime. The effects of ion diamagnetic drift flow on the tearing modes are different from those of the poloidal E\\times B shear flow. Moreover, the combined effect of the two flows on tearing modes and KH modes depends on their relative direction. The eigenmode structures of the tearing modes and KH modes under the influence of ion diamagnetic drift flow are also presented. Finally, the numerical results are verified reasonably by the scalings on resistivity.

Fan, Dong-Mei; Wang, Zheng-Xiong; Wei, Lai

2014-06-01

123

BEAM DYNAMICS LAYOUT OF H-TYPE DRIFT TUBE LINACS FOR INTENSE LIGHT ION BEAMS  

Microsoft Academic Search

H-type cavities have been successfully developed dur- ing the last 30 years for a large variety of applications in the field of ion acceleration. Radio Frequency Quadrupole (RFQ) and Drift Tube Linac (DTL) versions were de- signed in the H11(0)- and in the H21(0)-mode. The Inter- digital H-type (IH) drift tube structure is efficient for an energy range from 0.1

A. Sauer; H. Deitinghoff; H. Klein; H. Lieb; H. Podlech; U. Ratzinger; R. Tiede

2002-01-01

124

Optically Induced Measurement of Electron and Hole Drift Velocities in a Germanium <100> CDMS Detector at 50 mK  

NASA Astrophysics Data System (ADS)

We report on precise drift velocity measurements of electrons and holes in 50 mK, ultrapure (?1010 net shallow impurities per cm3) germanium <100> CDMS dark matter detectors as a function of electric field up to 4 V/cm. A laser diode connected to an optical fiber extending from room-temperature to the detector creates electron-hole pairs on one surface of the crystal. High-speed electronics measure the drift current as the generated carriers travel to the opposite face of the crystal. CDMS detectors measure the ionization and phonon response of particle interactions within the crystal. Stable charge collection is necessary for successful background discrimination when looking for a possible dark matter signal. While biased, however, ionization performance degrades over time due to the build-up of space charge. Free electrons and holes created by particle interactions are subject to drift-diffusion dynamics occurring simultaneously with the trapping of carriers to localized surface and bulk states. The combination of these processes determine the evolution of space charge within the crystal, making it important that we understand carrier transport under our unique operating condition of low-temperature and low-field. We find good agreement between our measured drift velocities and our theoretical predictions, indicating carrier scattering is dominated by spontaneous phonon emission. In addition, we present preliminary measurements of effective longitudinal carrier trapping lengths for both n-type and p-type crystals at 50 mK.

Phipps, A.; Sundqvist, K. M.; Lam, A.; Sadoulet, B.

2012-06-01

125

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

126

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

127

Zonal drift velocities of the ionospheric plasma bubbles over brazilian region using oi630nm airglow digital images  

NASA Astrophysics Data System (ADS)

The zonal drift velocities of the ionospheric plasma bubbles over the Brazilian region are analyzed in this study that is based on OI630nm airglow digital images. These digital images were obtained by an all-sky imager system between October 1998 and August 2000, at Cachoeira Paulista (22.5°S, 45°W), a low latitude region. In this period, 138 nights of OI 630 nm airglow experiments were carried out of which 30 nights detected the ionospheric plasma bubbles. These 30 nights correspond to magnetically quiet days (?K_P<24+) and were grouped according approximately to their season. KEY WORDS: Imager System, Ionospheric Plasma Bubbles, Zonal drift velocities, OI630nm.

Arruda, D. C. S.; Sobral, J. H. A.; Abdu, M. A.; Castilho, V. M.; Takahashi, H.

128

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

Microsoft Academic Search

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

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

1984-01-01

129

Parametric Excitation of Drift Waves with the Pump Near the Ion Cyclotron Frequency in a Two-Ion-Species Plasma.  

National Technical Information Service (NTIS)

Parametric excitation of drift waves in a multi-ion species plasma is observed in a range of pump frequencies, omega /sub pi// omega /sub i/ much greater than omega /sub o// omega /sub i/ approximately equal to 1.3 to 1.6 and the ion concentration ratio, ...

M. Ono M. Porkolab R. P. H. Chang

1978-01-01

130

Electron drift velocities in gas mixtures of He, N/sub 2/, and CO/sub 2/  

SciTech Connect

An electron swarm experiment has been used to obtain electron drift velocities in the He:CO/sub 2/:N/sub 2/ mixtures 0:1:1, 3:1:2, and 3:1:1. The E/N range of 3 to 57 Td was studied with total gas pressure varied from 50 to 200 Torr. These particular mixtures have not been previously studied experimentally. Good agreement is observed between theoretical calculations and experimental data.

Cornell, M.C.; Littlewood, I.M.; Brooks, H.L.; Nygaard, K.J.

1983-04-01

131

A Study of Ion Velocities Observed by TIDE and How It Relates to Magnetospheric Circulation  

NASA Technical Reports Server (NTRS)

The high-latitude ion velocities measured by the Thermal Ion Dynamics Experiment (TIDE) instrument on the Polar spacecraft will be examined in relation to magnetospheric circulation. TIDE derives ion velocities from moments of measured distribution functions. Hydrogen and oxygen ions are E X B drifting in the polar cap and cleft regions with a speed of about 5-20 km/s at apogee (approximately 9 Re) and a speed of 1-2 km/s at perigee (approximately 1.8 Re). At perigee 0+ is typically seen flowing down in the polar cap and outflowing from the cleft. At the transition from downflowing to upflowing there is also seen a reversal in the ion convection. The convection at perigee is consistent with standard ionospheric convection models for given Interplanetary Magnetic Field (IMF) conditions. Convection at high altitude (approximately 8.9 Re) polar regions has not been studied very much since there have not been many satellites in this region. Unlike previous missions to this region TIDE in conjunction the Plasma Source Instrument (PSI) can measure ions with as low an energy as several electron Volts. The outflowing ions observed by TIDE at apogee are believed to be important to the overall circulation of the magnetosphere. The convection of these outflowing ions at apogee will be related to the IMF. This study tries to answer the question of how the IMF response of the convection influences the overall circulation of the magnetosphere.

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.

1998-01-01

132

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

SciTech Connect

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

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

2009-10-05

133

Using Langmuir Probes to Measure Ion Velocities in Pyrotechnic Plasmas.  

National Technical Information Service (NTIS)

The very fluctuations that often complicate measurements of plasma parameters can be used to measure ion velocities in pyrotechnic plasmas. When burned in a vacuum, many pyrotechnic devices will form exhaust plumes that are hot enough to contain small qua...

D. L. Cohen

1989-01-01

134

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

135

Ion velocity distributions in electron cyclotron resonance plasmas  

NASA Astrophysics Data System (ADS)

For applications in ultra-large scale integration, low pressure, high density plasmas are being developed for etching and deposition of thin films. To control critical parameters such as the flux and energy distribution of ions impacting surfaces, it is necessary to understand how these parameters are influence by physical and electromagnetic design. In this work, we report measurements of ion velocity distributions in Ar/He and Cl2/He electron cyclotron resonance plasmas. Using Doppler-shifted laser-induced fluorescence spectroscopy, we measure metastable Ar and Cl ion velocity distributions parallel and perpendicular to the magnetic field as a function of magnetic field amplitude, pressure, and microwave power. We also examine the effects of wafer platen on the distribution functions by repeating the measurements after removing the platen. We find nearly isotropic ion velocity distributions when the source is operated as a magnetic mirror and the He partial pressure is low; higher He pressure tend to cool the parallel velocity distribution. Downstream, we consistently observe bimodal ion velocity distributions: the fast component, created in the source, follows magnetic flux lines into the reactor; the slow component, created mostly where the plasma expands from the source into the reaction chamber, is more isotropic. The relative amplitudes of these two components, the average ion energy, and the ion energy distribution are easily controlled by changing pressure and magnetic field.

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

1992-01-01

136

Ion drift in the earth's inner plasmasphere during magnetospheric disturbances and proton temperature dynamics  

NASA Astrophysics Data System (ADS)

Based on the thermal plasma measurements in the Earth’s inner plasmasphere on the INTER-BALL-2 and MAGION-5 satellites it has been indicated that the plasmaspheric ion temperature as a rule decreases during the main phase of magnetic storms; in this case the plasma density increases or remains at the level typical of undisturbed conditions. The physical mechanism by which the ion drift during a magnetic storm results in a temperature decrease is described. It is shown that the third adiabatic invariant also remains in processes with a characteristic time shorter than the period of charged particle drift around the Earth for cold equatorial plasma. The constructed model of the drift shell displacement from the Earth caused by a decrease in the magnetic field in the inner magnetosphere during the development of a magnetic storm satisfactorily describes the decrease in the proton temperature near the equatorial plane.

Verigin, M. I.; Kotova, G. A.; Bezrukikh, V. V.; Bogdanov, V. V.; Kaisin, A. V.

2011-02-01

137

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

138

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

139

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

SciTech Connect

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

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

1990-12-01

140

Electron-temperature-gradient drift wave instabilities in magnetized electron--ion plasmas  

SciTech Connect

A general local dispersion relation is derived for the circulating electron-temperature-gradient-driven drift waves in an inhomogeneous magnetized electron--ion plasma. By taking specific limits, two new instabilities are shown to exist. The resulting quasilinear electron energy and particle fluxes are also obtained.

Murtaza, G.; Nadeem, M. (Quaid-i-Azam University, Islamabad, Pakistan (PK)); Shukla, P.K. (Institut fuer Theoretische Physik IV, Ruhr-Universitat, Bochum, D-4630 Bochum 1, Germany (DE))

1991-06-01

141

Two-conductor strips with drift tubes excited by an electron beam in an ion accelerator  

SciTech Connect

Excitation by a heavy-current electron beam in an ion accelerator is studed for a two-conductor strip with drift tubes whose supports on one bar are displaced at half the distance between the supports of another bar. The relations obtained on the basis of harmonic analysis and the equations from TWT theory indicate the potential of constructing such a system.

Gavrilov, N.M.; Gromov, E.V.; Nesterovich, A.V.; Nikitin, I.B.; Shal'nov, A.V.

1986-12-01

142

Low Velocity Ion Stopping in Dense and Multicomponent Plasmas  

NASA Astrophysics Data System (ADS)

We focus attention on low velocity ion slowing down (LIVSD) in dense and multicomponent plasmas of ICF and astrophysical interest. The target is treated in a dielectric formalism with classical electrons neutralizing binary ionic mixtures (BIM) of any relative proportion.We consider first charge symmetric BIM such as deuterium-tritium, proton-heliumlike iron ions in the solar interior or proton-helium ions considered in planetology as well as other mixtures of relevance to the heavy ion production of warm dense matter at Bragg peak conditions. We single out ion projectile velocities (so-called critical) at which target electron LIVSD matches the sum of target ion ones. Proton stopping in the white dwarf crust (carbon-helium BIM) is also considered.

Tashev, Bekbolat; Deutsch, Claude; Fromy, Patrice

2009-11-01

143

Low velocity ion stopping in binary ionic mixtures  

SciTech Connect

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

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

2008-10-15

144

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

Microsoft Academic Search

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

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

1996-01-01

145

Using Langmuir probes to measure ion velocities in pyrotechnic plasmas  

NASA Astrophysics Data System (ADS)

When burned in vacuum, the exhaust plumes generated by many pyrotechnic devices will contain small quantities of singly-ionized atoms. The fluctuating intensity of the burning pyrotechnic yields commensurately large fluctuations in the plasma which render dependable determinations of the plasma parameter values very difficult. The Langmuir electrical probe is presently used in this environment to supply reliable estimates of the average ion velocity in the pyrotechnic exhaust plume. By measuring the time it takes for ion concentrations created by the variation in a given pyrotechnic's rate of combustion to traverse a known distance after escape from the reaction chamber, the ion velocity within the plume can be estimated.

Cohen, Douglas L.

146

Nonuniform charging effects on ion drag force in drifting dusty plasmas  

SciTech Connect

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

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

2006-03-01

147

Low Velocity Ion Stopping in Dense and Multicomponent Plasmas  

NASA Astrophysics Data System (ADS)

We focus attention on low velocity ion slowing down (LIVSD) in dense and multicomponent plasmas of ICF and astrophysical interest as well. The target is treated in a dielectric formalism with classical electrons neutralizing binary ionic mixtures (BIM) of any relative proportion. We consider first and mostly charge symmetric BIM such as deuterium-tritium of current fusion interest, proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology as well as other mixtures of relevance to the heavy ion production of warm dense matter at Bragg peak conditions. We single out ion projectile velocities (so-called critical) for which target electron LIVSD matches the sum of target ions one. Proton stopping in the white dwarf crust (carbon-helium BIM)is also considered.

Tashev, Bekbolat; Deutsch, Claude; Fromy, Patrice

2008-11-01

148

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

NASA Technical Reports Server (NTRS)

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

Walton, J. T.; Wong, Y. K.; Zulehner, W.

1997-01-01

149

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

150

Pic Modeling of a Closed Drift Ion Source for Material Surface Processing  

NASA Astrophysics Data System (ADS)

The closed drift ion source is a technology that uses a DC discharge in a gas cell (Ar, O2) to produce a uniform, linear 300-1500 eV ion beam for in-line surface treatment and cleaning of materials. Maximum ion beam currents are on the order of 1 A / meter of source length. A permanent dipole magnet forms a magnetic circuit with the ferromagnetic cathode enclosure, producing a focusing field in the ion extraction gap that confines electrons. The focusing field shape is controlled by the beveling of the gap. We have developed 2- and 3- dimensional PIC models of the closed drift ion source using the OOPIC Pro and Vorpal codes. We will present numerical results on the ion beam properties, including the ion energy spectrum on the target, and compare them to measurements. We will also investigate possible design modifications such as to the magnetic field shape and discharge electrode geometry that might lead to increased ion current.

Schoessow, Paul; Cary, John; Shaw, Denis; Stoltz, Peter

2005-10-01

151

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

NASA Astrophysics Data System (ADS)

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 TiCl4 and hydration reactions of Ti+ with residual water are presented.

May, Jody C.; Russell, David H.

2011-07-01

152

Poloidal velocity of impurity ions in neoclassical theory  

SciTech Connect

A formula for the poloidal velocity of impurity ions in a two-species plasma is derived from neoclassical theory in the banana regime, with corrections from the boundary layer separating the trapped and transiting ions. The formula is applicable to plasmas with toroidal rotations that can approach the thermal speeds of the ions. Using the formula to determine the poloidal velocity of C{sup +6} ions in a recently reported experiment [W. M. Solomon et al., Phys. Plasmas 13, 056116 (2006)] leads to agreement in the direction of the central region when it is otherwise from theories without strong toroidal rotations. Comparisons among these theories are made, demonstrating the degree of uncertainty of theoretical predictions.

Wong, S. K.; Chan, V. S. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Solomon, W. M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2008-08-15

153

Comparing daytime, equatorial E×B drift velocities and TOPEX/TEC observations associated with the 4-cell, non-migrating tidal structure  

NASA Astrophysics Data System (ADS)

We investigate the seasonal and longitude dependence of the daytime, vertical E×B drift velocities, on a day-to-day basis, using a recently-developed technique for inferring realistic E×B drifts from ground-based magnetometer observations. We have chosen only quiet days, Ap<10, from January 2001 through December 2002, so that the main contribution to the variability is due to the variability in the tidal forcing from below. In order to study the longitude dependence in daytime E×B drift velocities, we use appropriately-placed magnetometers in the Peruvian, Philippine, Indonesian and Indian longitude sectors. Since we are particularly interested in quantifying the E×B drift velocities associated with the 4-cell, non-migrating tidal structure, we compare the seasonal and longitude E×B drift structure with TOPEX satellite observations of Total Electron Content (TEC). We outline a plan to establish the magnitude of the longitude gradients that exist in the daytime, vertical E×B drift velocities at the boundaries of the observed 4-cell patterns and to theoretically identify the physical mechanisms that account for these sharp gradients. The paper demonstrates that sharp gradients in E×B drift velocities exist at one of the 4-cell boundaries and outlines how the C/NOFS IVM and VEFI sensor observations could be used to establish the E×B drift longitude gradients at the boundaries of each of the 4 cells. In addition, the paper identifies one of the theoretical, atmosphere/ionosphere models that could be employed to identify the physical mechanisms that might explain these observations.

Anderson, D.; Araujo-Pradere, E.; Scherliess, L.

2009-07-01

154

Semiconductor Lithium-Ion Drift Diodes as High-Resolution Gamma-Ray Pair Spectrometers  

Microsoft Academic Search

Germanium and silicon p-i-n diodes with active volumes up to 2 cm3 have been fabricated using the lithium-ion drift technique. p-type germanium doped with either gallium or zinc (5-10 ohm-cm) and boron-doped silicon (1100 ohm-cm) were the base materials. Diodes were operated at 77°K in conjunction with a low noise amplifier system (270 RMS electron-holes). They have been used as

A. J. Tavendale

1964-01-01

155

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

156

Novel design for drift tubes in ion mobility spectrometry for optimised resolution of peak clusters  

Microsoft Academic Search

In the past decade, Ion Mobility Spectrometry has established a very strong foot hold in medical and biological applications\\u000a due to its numerous advantages including sensitivity, ruggedness and reproducibility. During the analysis of complex samples\\u000a such as human breath, it is very probable that two or more analytes form peak clusters due to similar drift times and pre-separation\\u000a times, thus

Chandrasekhara Bharadwaj Hariharan; Luzia Seifert; Jörg Ingo Baumbach; Wolfgang Vautz

2011-01-01

157

Closed electron drift in a self-magnetically insulated ion diode  

SciTech Connect

The paper investigates a spiral geometry self-magnetically insulated ion diode with an explosive-emission cathode made from graphite. The experiments have been carried out using the TEMP-4M accelerator, with the accelerator configured to operate in double-pulse mode: the first negative pulse (300–500 ns, 100–150 kV) and the second positive pulse (150 ns, 250–300 kV). The ion beam energy density was 0.4–0.8 J/cm{sup 2} and the beam was composed of carbon ions (80%–85%) and protons. In order to increase the efficiency of ion current generation, we have developed a new diode with a spiral-shaped grounded electrode. Using this geometry, it seems possible to realize closed electron drift in a diode with self-magnetic insulation. In the spiral diode, the efficiency of accelerated ions is increased from 5%–9% (conventional self-insulated diodes) up to 30%–40%. The realization of closed electron drift in the diode increases the efficiency of C{sup +} ion generation up to 40–50 times the Childe-Langmuir limit, which is more than 4 times higher than with other known constructions of self-magnetically insulated diodes.

Pushkarev, A. I.; Isakova, Y. I. [Tomsk Polytechnic University, 2a Lenin Ave., Tomsk 634050 (Russian Federation)] [Tomsk Polytechnic University, 2a Lenin Ave., Tomsk 634050 (Russian Federation)

2013-05-15

158

Scavenging of atmospheric ions and aerosols by drifting snow in Antarctica  

NASA Astrophysics Data System (ADS)

Measurements of the small-, intermediate-, and large-ion concentrations and the air-earth current density along with simultaneous measurements of the concentration and size distribution of aerosol particles in the size ranges 4.4-163 nm and 0.5-20 ?m diameter 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 air-earth current simultaneously decrease by approximately an order of magnitude as the wind speed increases from 5 to 10 ms - 1 . 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 4.4-163 nm size range but increases in the 0.5-20 ?m size range with wind speed. The size distribution of the nanometer particles shows a dominant maximum at ~ 30 nm diameter throughout the period of observations and the height of the maximum decreases with wind speed. However, larger particles show a maximum at ~ 0.7 ?m diameter but the height of the maximum increases with increasing wind speed. The results are explained in terms of scavenging of atmospheric ions and aerosols by the drifting snow particles.

Kamra, A. K.; Siingh, Devendraa; Pant, Vimlesh

2009-02-01

159

Simulations of High Velocity Clouds: High-Velocity High-Stage Ions  

NASA Astrophysics Data System (ADS)

We present the results of hydrodynamic simulations of high velocity clouds (HVCs) carried out using FLASH. The simulations self-consistently trace the non-equilibrium ionization evolution of carbon, nitrogen, and oxygen in a realistic HVC geometry, in which a cool dense spherical cloud moves through hot, tenuous halo gas. In our simulations, H I is ablated from the clouds through shear instabilities and undergoes turbulent mixing with the hot ambient gas. High-stage ions (C IV, N V, and O VI) are abundant in these turbulent mixing layers. We investigate a suite of models with a range of model parameters (cloud size, cloud velocity, cloud density). The simulations run for 60-240 Myr, depending on the model parameters. We find that the cloud's initial velocity does not affect the rates of H I ablation or ionization or high-stage ion production over a wide range of velocities, from subsonic through transonic to supersonic. However, we find that the cloud's initial size does affect the rate at which cloud material is ablated and/or ionized: a smaller cloud loses its H I mass relative to its initial mass more rapidly than a larger cloud. We also find that large HVCs are able to survive as far as the Galactic disk in the form of neutral hydrogen and thus fuel star formation. Our models compare well with Complex C observations in terms of the observed high-stage ion column densities, the trend between N(O VI)/N(H I) and N(H I), the ion-to-H I ratios, and the ion-to-ion ratios.

Kwak, Kyujin; Henley, D. B.; Shelton, R. L.

2011-05-01

160

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

161

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

Microsoft Academic Search

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

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

2003-01-01

162

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

PubMed

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

2010-04-01

163

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.

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

2010-01-01

164

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations: initial results  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this allows the drift velocities of each depletion to be determined as a function of magnetic latitude as well as local time. Previous ground-based airglow observations from a small number of locations have indicated that the drift velocities of depletions may vary rapidly with magnetic latitude. Here we shall present the first results from TOAD of this shear in drift velocities from our global sample of depletion drift velocities.

England, S. L.; Immel, T. J.; Park, S. H.; Frey, H. U.; Mende, S. B.

2007-12-01

165

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this automation allows the drift velocities of each bubble to be determined as a function of magnetic latitude, which will give us the capability of retrieving geophysically important parameters such as the electric field, which are believed to vary rapidly with magnetic latitude.

Park, S. H.; England, S. L.; Immel, T. J.; Frey, H. U.; Mende, S. B.

2007-11-01

166

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

167

Coulomb explosion at low and high ion velocities  

NASA Astrophysics Data System (ADS)

The ion-induced electric field is calculated for estimating the effect of the Coulomb explosion (CE) mechanism. The increase of the kinetic energy of lattice ions in the electric field of the track core is ?? ? (q(0))4, where q(r) is the induced initial charge density. Estimates are made for the irradiation of SiO2 by 2 MeV/nucleon Kr beam: the mean energy of lattice ions reaches 8.1 eV within 4 fs in the track core. The Lorentzian and Gaussian charge density distributions lead to similar results. The type of solids affects ?? through the charge neutralization time. As a result of the decrease of q(0), ?? is reduced by about an order of magnitude in the range 2-8 MeV/nucleon. The projectile velocity may affect the formation of ion-induced tracks by the CE mechanism.

Szenes, G.

2013-03-01

168

Low Velocity Ion Stopping in Binary Ionic Mixtures  

NASA Astrophysics Data System (ADS)

We investigate the basic features underlying the low ion velocity (Vp) slowing down (LIVSD) in multicomponent and dense target plasmas built of quasi-classical electron fluids neutralizing binary ionic mixtures (BIM)such as deuterium-tritium of current fusion interest,proton-heliumlike iron in the solar interior or proton-helium ions considered in planetology, as well as other mixtures of fiducial concern in the heavy ion beam production of warm dense matter (WDM) at Bragg peak conditions [1]. The target plasma is taken in a multicomponent dielectric Fried-Conte formulation. We also focus attention on so-called critical Vp values featuring same LIVSD on target ions and electrons,respectively. BIM including negative hydrogen are also given attention [2].[4pt] [1] B. Tashev, F. Baimbetov, C. Deutsch and P. Fromy, PoP 15, 102701 (2008)[0pt] [2] B. Tashev, P. Fromy and C. Deutsch, PRSTAB 13, 10130 (2010)

Deutsch, Claude; Ceban, Victor; Fromy, Patrice; Tashev, Bekbolat

2011-11-01

169

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

NASA Astrophysics Data System (ADS)

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

Stano, M.; Pinhão, N.; Loffhagen, D.; Ku?era, M.; Donkó, Z.; Matej?ík, Š.

2011-12-01

170

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

171

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

172

A Monte Carlo simulation of the effect of ion self-collisions on the ion velocity distribution function in the high-latitude F-region  

NASA Technical Reports Server (NTRS)

Non-Maxwellian ion velocity distribution functions have been theoretically predicted and confirmed by observations, to occur at high latitudes. These distributions deviate from Maxwellian due to the combined effect of the E x B drift and ion-neutral collisions. At high altitude and/or for solar maximum conditions, the ion-to-neutral density ratio increases and, hence, the role of ion self-collisions becomes appreciable. A Monte Carlo simulation was used to investigate the behavior of O(+) ions that are E x B-drifting through a background of neutral O, with the effect of O(+) (Coulomb) self-collisions included. Wide ranges of the ion-to-neutral density ratio n(sub i)/n(sub n) and the electrostatic field E were considered in order to investigate the change of ion behavior with solar cycle and with altitude. For low altitudes and/or solar minimum (n(sub i)/n(sub n) less than or equal to 10(exp -5)), the effect of self-collisions is negligible. For higher values of n(sub i)/n(sub n), the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O(+) distribution are reduced. The Monte Carlo results were compared to those that used simplified collision models in order to assess their validity. In general, the simple collision models tend to be more accurate for low E and for high n(sub i)/n(sub n).

Barghouthi, I. A.; Barakat, A. R.; Schunk, R. W.

1994-01-01

173

Drift compression and final focus systems for heavy ion inertial fusion  

NASA Astrophysics Data System (ADS)

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. 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. In final focus, the beam is usually expanded transversely before it is focused onto a small spot. This may cause third-order aberrations to significantly affect the beam quality. Previously, it has been suggested that octupoles be used to correct these aberrations. However, it is shown that for modest convergence angles of the beam, a considerable improvement can be achieved by rematching the quadrupoles in the final focus system, if these aberrations are taken into account in the rematching process. For larger convergence angles, third-order aberrations cause a significant halo formation. Detailed particle-in-cell simulations were performed to better understand the experimental results from the Scaled Final Focus Experiment at LBNL, which is a replica of a driver-scale final focus system. The simulations showed that expanding beams may suffer a substantial emittance increase due to their nonlinear space-charge field. Phase-space comparisons between the experiment and simulations showed reasonable agreement. Of particular interest was the beam rotation that has been measured in the experiment. Simulations showed that this may have been caused by a minor rotation of one or more of the quadrupoles in the experiment.

de Hoon, Michiel Jan Laurens

174

Li{sup +} alumino-silicate ion source development for the neutralized drift compression experiment  

SciTech Connect

We report results on lithium alumino-silicate ion source development in preparation for warm dense matter heating experiments on the new neutralized drift compression experiment II. The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of {approx_equal}1275 deg. C, a space-charge limited Li{sup +} beam current density of J {approx_equal}1 mA/cm{sup 2} was obtained. The lifetime of the ion source was {approx_equal}50 h while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 {mu}s.

Roy, Prabir K.; Greenway, Wayne G.; Kwan, Joe W.; Seidl, Peter A.; Waldron, William L.; Wu, James K. [Lawrence Berkeley National Laboratory (LBNL), One Cyclotron Road, Berkeley, California 94720 (United States)

2011-01-15

175

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

SciTech Connect

Satellite in-situ measurements made by the Dynamics Explorer 2 satellite were utilized to describe the nature of plasma structuring at high latitudes caused by the gradient-drift instability process. The non-midnight and dawn-dusk orbits of the DE 2 satellite were used to study the simultaneous density and electric field spectra of convecting large scale (approximately hundreds of kilometers) plasma density enhancements in the polar cap (known as patches) in directions parallel and perpendicular to their antisunward convection. Distinct differences were noted in the behavior of the ac and dc electric field structure and short scale (<125 m) density irregularities in these two mutually orthogonal directions perpendicular to the geomagnetic field. However, since these two orthogonal directions were not sampled simultaneously, the observed differences cannot be unequivocally related to the direction of convection. Structured plasma density enhancements in the auroral oval (known as blobs) were found to have considerable power spectral density at these short scales in the presence of significant Pedersen and Hall conductances in the 10 to 20-mho range. While density irregularity amplitudes (DeltaN/N){sub RMS} were found to be as large as 15-20% using 8-s samples of the DE 2 data, the corresponding dc electric field fluctuation DeltaE was found to be less than a few millivolts for both patches and blobs. This (DeltaN/N){sub RMS} vis-a-vis DeltaE behavior for the gradient drift process provided a fairly dramatic contrast with velocity shear driven processes where the DeltaE magnitudes were found to be at least an order of magnitude larger for the same levels of density irregularities.

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

1990-06-01

176

Day/night asymmetry of ion density and velocity in Saturn's inner magnetosphere - Cassini RPWS/LP observations  

NASA Astrophysics Data System (ADS)

We present Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) data that show a day/night asymmetry in the ion density and velocity in the inner plasma disk of Saturn. We use data from 131 Cassini orbits, recorded between the years 2005 to 2010, to map the structure and dynamics of the inner plasma disk of Saturn, from magnetic L shell 2.5 to 10. The derived ion densities shows a clear minimum on the day side close to LT noon, of around 35 cm-3, and higher values on the night side close to midnight, of around 80 cm-3. The estimated ion velocities also shows a minimum on the day side with velocities of around 28-32 km/s around noon and a maximum on the night side with 36-40 km/s close to midnight. The asymmetry is largest in the region 4 and 6 RS from the planet. The detected day/night asymmetry could be explained by a noon to midnight electric field of the strength 0.1-1 mV/m previously suggested by Andriopoulou et al., 2012. Such an electric field would give the ions an extra ExB drift component adding to the ion drift in the region around midnight and slowing the ions down in the region around noon. This would alter the particle orbits and cause the density to be lower on the dayside and higher on the night side for the same radial distance. Our results can be interpreted as an additional evidence for the existence of the previously suggested electric field.

Holmberg, M.; Wahlund, J.; Morooka, M.

2013-12-01

177

A gated atmospheric pressure drift tube ion mobility spectrometer-time-of-flight mass spectrometer.  

PubMed

Identifying the compounds of an unknown gas mixture by using an ion mobility spectrometer (IMS) is a difficult task, because several ion species can be generated in the ionization process. One method to analyze the occurring peaks in an IMS spectrum is coupling an IMS to a mass spectrometer (MS). In our setup we coupled a (3)H drift tube IMS to a Bruker micrOTOF II. Therefore, the detector plate of the IMS is pierced and a transfer capillary is inserted. The ions are transferred via gas flow and electric fields into the MS. The transmission of the ions through the transfer capillary can be shuttered very precisely by increasing the electric potential of the detector generating a repulsive electric field. Thus, it is possible to transfer single ion clouds of generated IMS spectra into the mass spectrometer where a corresponding mass spectrum is generated. In this work we analyze the positive and negative IMS spectra of single analytes as well as gas mixtures and characterize the occurring ion species. PMID:25015244

Heptner, Andre; Reinecke, Tobias; Langejuergen, Jens; Zimmermann, Stefan

2014-08-22

178

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

179

Detailed measurements of anisotropic mirror plasma ion energy distributions during drift cyclotron loss-cone instability  

SciTech Connect

Using improved computer filtering and a reconstruction analysis we have been able to extract additional details on a mirror plasma's midplane ion energy distribution from the current--voltage (I--V) curve of a voltage-swept electrostatic end loss analyzer (ELA). For the University of Maryland's MIX-1 plasma (Phys. Fluids 23, 3439 (1976)), the diagnostic technique has provided us with important information on the ''loss-cone region'' of an anisotropic ion distribution during drift cyclotron loss-cone (DCLC) instability experiments. Observations include convincing verification of ion distribution modification during DCLC evolution and an enhancement of the loss-region boundary over that predicted by simplified trapping theory. The reconstruction analysis involves matching the differentiated I--V curves (i.e., dI/dV vs V) to theoretically predicted curves based on model midplane ion distribution functions. The theoretical curves are obtained from the model midplane distributions by a mapping transformation based on conservation of magnetic moment and total energy of each ion along lines of magnetic flux.

Booske, J.H.; McCarrick, M.J.; Ellis, R.F.; Paquette, J.A.

1988-02-01

180

Very Low velocity Ion Slowing Down in Binary Ionic Mixtures  

NASA Astrophysics Data System (ADS)

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

Fromy, Patrice; Tashev, Bekbolat; Deutsch, Claude

2010-11-01

181

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

PubMed

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

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

2012-10-16

182

Lower-hybrid drift instability saturation mechanisms in one-dimensional simulations  

SciTech Connect

The linear properties and saturation mechanisms of the lower-hybrid drift instability have been investigated using a one-dimensional particle-hybrid simulation. For low drift velocities (V sub d much less than V sub ti), ion trapping and current relaxation (V sub d approaches limit of 0) are competing processes for stabilization. If the relative electron-ion drift velocity is kept constant in time, ion trapping causes the end of instability growth; if this drift is allowed to decrease consistent with momentum balance, then saturation is due to current relaxation.

Chen, Y.J.; Birdsall, C.K.

1980-09-19

183

Lower-hybrid drift instability saturation mechanisms in one-dimensional simulations  

SciTech Connect

The linear properties and saturation mechanisms of the lower-hybrid drift instability have been investigated using a one-dimensional particle-hybrid simulation. For low drift velocities (v/sub d/<ion trapping and current relaxation (v/sub d/..-->..0) are competing processes for stabilization. If the relative electron--ion drift velocity is kept constant in time, ion trapping causes the end of instability growth; if this drift is allowed to decrease consistent with momentum balance, then saturation is due to current relaxation.

Chen, Y.; Birdsall, C.K.

1983-01-01

184

Measurement of two-point two-velocity correlation functions in the ion phase-space  

NASA Astrophysics Data System (ADS)

Using two single frequency tunable lasers we generalize the technique used previously to measure two-point correlation functions to allow two different selected velocities as well. A steady-state singly-ionized Argon plasma with density 10^9 cm-3, electron temperature of 2 eV, and ion temperature of 0.1 eV in a uniformly magnetized plasma cylinder is produced using a CW radio-frequency source. The plasma column is 10 cm in diameter and the main chamber is 200 cm in length. The measurements concern the low-frequency electrostatic fluctuations that occur naturally near the electron drift frequency driven by the radial electron temperature gradient. Two independent LIF systems, with detection systems on movable carriages, are scanned using computer-controlled stepper motors. One system involves a Argon-ion pumped single-frequency dye laser at 611nm with detection at 461 nm. The second system uses a single-frequency tunable diode laser at 668nm with detection at 443nm. By looking at cross-correlation between the two detection systems it is a measurement of is realized. We will describe the tests and validations used to rule out instrumental effects on the measurement and compare the results to previous measurements of made using a single laser beam.

Skiff, Fred

2008-11-01

185

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

NASA Astrophysics Data System (ADS)

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

Biloiu, Ioana A.; Scime, Earl E.

2010-11-01

186

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

NASA Astrophysics Data System (ADS)

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.; Plaut, E.

2013-04-01

187

Theoretical relationship between maximum value of the post-sunset drift velocity and peak-to-valley ratio of anomaly TEC  

Microsoft Academic Search

Theoretical study of electron density distribution in the nighttime equatorial ionosphere shows that linear relationships with statistically significant correlation coefficients exist between the maximum value of the post-sunset plasma drift velocity and the peak-to-valley ratio of anomaly TEC. The study is based on the low-latitude density model of Air Force Research Laboratory (AFRL) and the obtained relationships are valid for

B. Basu; J. M. Retterer; O. de La Beaujardière; C. E. Valladares; E. Kudeki

2004-01-01

188

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

SciTech Connect

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

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

2011-09-20

189

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

190

Periodic modulation of ion velocities within the magnetodisk of Saturn  

NASA Astrophysics Data System (ADS)

The results of recent numerical simulations [Jia and Kivelson, 2012] show that in the magnetodisk of Saturn fluctuating magnetic field perturbations are accompanied by other oscillatory phenomena. They investigated the magnetotail response for a dual periodicity driver in the case when the solar wind flow was perpendicular to the rotation axis. As demonstrated in Fig. 7 of their paper the components of the flow velocity extracted at different radial distances plotted versus time exhibit periodic modulation. Andrews et al. [2012] and Provan et al. [2012] investigated magnetic field modulations in Saturn's magnetosphere. They have shown that in the high latitude regions single period modulations can be observed, but near the current sheet dual periodicities are characteristic. In this study we investigate periodicities in the azimuthal flow velocities using the numerical ion moments derived from the measurements of Cassini Plasma Spectrometer. Ramer et al. [2012] investigated these periodicities in the inner magnetosphere near the equatorial plane. We extend our study to include higher latitude passes in the outer magnetosphere to the orbit of Titan and beyond. To have a close match with the model assumptions of Jia and Kivelson, we investigated the behaviour of the ion velocities in the time range DOY 092-285, 2009, around Saturnian equinox, along different passes all containing a Titan flyby, and crossing the magnetodisk at different angles. We have found that the azimuthal velocities show oscillatory behavior. The amplitude of the oscillation is comparable with the corrotation speed. We have also compared the structure of the velocity variations to the variations of ion densities along the different passes, and compared those to the model as well. The results of the current study is reported in this presentation. References Andrews, D. J., S. W. H. Cowley, M. K. Dougherty, L. Lamy, G. Provan, and D. J. Southwood (2012), Planetary period oscillations in Saturn's magnetosphere: Evolution of magnetic oscillation properties from southern summer to postequinox, J. Geophys. Res., 117, A04224, doi:10.1029/2011JA017444. Jia and Kivelson (2012),Driving Saturn's magnetospheric periodicities from the upper atmosphere/ionosphere: Magnetotail response to dual sources, J. Geophys. Res., 117, A11219, doi:10.1029/2012JA018183. Ramer, K. M., M. G. Kivelson1, K. K. Khurana, N. Sergis, R. J. Walke1, X. Jia (2012), Forces and Phases: An Investigation of Azimuthal Plasma and Field Periodicities in Saturn's Inner Magnetosphere, AGU Fall Meeting 2012, SM51B-2303 Provan, G., D. J. Andrews, C. S. Arridge, A. J. Coates, S. W. H. Cowley, G. Cox, M. K. Dougherty, and C. M. Jackman (2012), Dual periodicities in planetary-period magnetic field oscillations in Saturn's tail, J. Geophys. Res., 117, A01209, doi:10.1029/2011JA017104.

Nemeth, Zoltan; Szego, Karoly; Foldy, Lajos; Kivelson, Margaret; Jia, Xianzhe; Ramer, Katherine; Cowley, Stanley W. H.; Provan, Gabrielle

2013-04-01

191

Lower-hybrid instabilities driven by an ion velocity ring  

NASA Technical Reports Server (NTRS)

The lower-hybrid instabilities in high-beta (ratio of plasma to magnetic pressure) plasmas driven by ring-ion distributions in velocity space are investigated. A dispersion equation including electromagnetic effects is derived. In the low-beta limit, analytic expressions are obtained which illuminate the physical nature of the instabilities. The complete dispersion equation is solved numerically as a function of ring speed and plasma beta for several types of ring distribution. Electromagnetic effects are important for relatively energetic rings even in the low-beta regime, suppressing growth rates and shifting the angle of propagation to more oblique angles. Stabilization by thermal effects is also discussed. Application of these results to the earth's bow shock, AMPTE, comets and solar flares is suggested.

Akimoto, K.; Papadopoulos, K.; Winske, D.

1985-01-01

192

Relative ion expansion velocity in laser-produced plasmas  

NASA Technical Reports Server (NTRS)

The spectra of highly ionized titanium, Ti XIII through Ti XXI, and C VI Lyman lines were excited in laser-produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24-beam Omega laser system produced short, 0.6 ns, and high-intensity, 4 x 10 to the 14th W/sq cm, laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p-3s Ti XIII resonance lines had an average shift of + 0.023 A relative to the C VI and Ti XX spectral lines. No shift was found between the C VI, Ti XIX, and Ti XX lines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6 + or - 0.2) x 10 to the 7th cm/s in the expansion velocities of Ti XIX and Ti XX ions compared to Ti XIII ions.

Goldsmith, S.; Moreno, J. C.; Griem, H. R.; Cohen, Leonard; Richardson, M. C.

1988-01-01

193

Investigation of beam stability in a high intensity drift tube linac for heavy ion inertial fusion  

NASA Astrophysics Data System (ADS)

With the new concept of indirectly driven targets for heavy ion inertial fusion, the driver scenarios had to be reconsidered. A European study group (HIDIF collaboration) investigated the feasibility of a driver facility based on a linac and storage ring approach (Hofmann and Plass (Eds.), GSI-98-06 GEP, Darmstadt, 1998). In a preinjector consisting of an array of ion sources, rf-linacs and funnel devices a 400 mA Bi + beam is formed, which is further accelerated in a main linac from about 2 GeV to its final energy of 10 GeV and then injected into the rings for storage and pulse compression. The most important requirements for the beam dynamics layout of this high intensity heavy ion linac are transmission rates of nearly 100% and very low emittance growth to avoid particle losses along the linac and at ring injection which may cause radioactivation of the structures. A particle dynamics design of an Alvarez type drift tube linac (DTL) has been successfully carried out with respect to high stability of the beam against errors and mismatch, which was checked by multiparticle simulations. Statistical errors of rf field amplitude and phase and quadrupole gradients were taken into account as well as current fluctuations, initial mismatch modes and changes of particle input distributions and combinations of different errors. Results of Monte Carlo simulations with up to 20,000 particles show a smooth behaviour of the beam and small halo development only. In addition the "telescoping" option, where three different ion species are accelerated, and the necessary modifications for the linac, have been investigated.

Deitinghoff, H.; Parisi, G.; Sauer, A.; Bongardt, K.; Pabst, M.

2001-05-01

194

Added discussion of ``Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves''  

NASA Astrophysics Data System (ADS)

A recent paper [S. J. Sanders, P. M. Bellan, and R. A. Stern, Phys. Plasmas 5, 716, (1998)] identified neutral particle recycling as one important aspect of severe heating and cooling cycles observed in large-amplitude drift waves. An apparent inconsistency in the ionization mean free path of these neutrals, left as an open question in the original paper, is resolved in this comment.

Sanders, S. J.; Boivin, R. F.; Bellan, P. M.; Stern, R. A.

1999-10-01

195

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

SciTech Connect

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

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

2011-04-20

196

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

NASA Astrophysics Data System (ADS)

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

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

197

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

SciTech Connect

Neoclassical polarization drift is known to play critical role in the dynamical behavior of a sheared radial electric field E{sub r} 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 V{sub NP} of collisionless single ions is studied using a guiding-center code in a time-varying, spatially sheared E{sub r} in a realistic tokamak geometry. It is found numerically that the V{sub NP} for single ions is not only a function of the time derivative {partial_derivative}E{sub r}/{partial_derivative}t, but also a strong function of the radial shear {delta}r{partial_derivative}E{sub r}/{partial_derivative}r if the shear length is on the same order as the ion banana width {delta}r. Comparison with an analytic investigation reveals that this effect is simply due to the finite banana modification to the orbital average E{sub r}. An approximate analytic formula has been presented for collisionless single banana ions in a conventional tokamak magnetic geometry. The trapped-passing boundary layer physics is not treated.

Baek, Hoyul; Ku, Seunghoe; Chang, C. S. [Department of Physics, Korea Advanced Institute of Science and Technology, Yusong-Ku, Daejon, 305-701 (Korea, Republic of); Department of Physics, Korea Advanced Institute of Science and Technology, Yusong-Ku, Daejon, 305-701 (Korea, Republic of) and Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, New York 10012 (United States)

2006-01-15

198

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

199

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

SciTech Connect

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

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

2010-10-15

200

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

National Technical Information Service (NTIS)

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

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

1990-01-01

201

Velocity dependence of Z1-oscillations in stopping power of solids for channeled heavy ions  

NASA Astrophysics Data System (ADS)

The model used by Briggs and Pathak to calculate the electronic energy loss of low velocity channeled heavy ions has been explored further to study the velocity dependence of Z1-oscillations in electronic stopping power. For increasing ion velocities where validity of neglecting the target electron velocities increases, it is found that the magnitude of Z1-oscillations decreases and already by about 2 a.u. velocity, the first maxima at Z1=6 and the first minima at Z1=10 are washed out completely.

Pathak, Anand P.

1980-03-01

202

Systematic study of channeling stopping-power oscillations for low-velocity heavy ions  

NASA Astrophysics Data System (ADS)

The model used by Briggs and Pathak to calculate the electronic energy loss of low-velocity channeled heavy ions has been explored further to study the velocity dependence of Z1 oscillations in electronic stopping power. For increasing ion velocities, where the validity of neglecting the target-electron velocities increases, it is found that the magnitude of Z1 oscillations decreases and by about 2-a.u. velocity the first maxima at Z1=6 and the first minima at Z1=10 are washed out completely.

Pathak, Anand P.

1980-07-01

203

Systematic study of channeling stopping-power oscillations for low-velocity heavy ions  

SciTech Connect

The model used by Briggs and Pathak to calculate the electronic energy loss of low-velocity channeled heavy ions has been explored further to study the velocity dependence of Z/sub 1/ oscillations in electronic stopping power. For increasing ion velocities, where the validity of neglecting the target-electron velocities increases, it is found that the magnitude of Z/sub 1/ oscillations decreases and by about 2-a.u. velocity the first maxima at Z/sub 1/=6 and the first minima at Z/sub 1/=10 are washed out completely.

Pathak, A.P.

1980-07-01

204

Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: I. general description  

NASA Astrophysics Data System (ADS)

Neutralized drift compression offers an effective means for particle beam pulse compression and current amplification. In neutralized drift compression, a linear longitudinal velocity tilt (head-to-tail gradient) is applied to the non-relativistic beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam current can increase by more than a factor of 100 in the longitudinal direction. We have performed an analytical study of how errors in the velocity tilt acquired by the beam in the induction bunching module limit the maximum longitudinal compression. It is found that the compression ratio is determined by the relative errors in the velocity tilt. That is, one-percent errors may limit the compression to a factor of one hundred. However, a part of the beam pulse where the errors are small may compress to much higher values, which are determined by the initial thermal spread of the beam pulse. It is also shown that sharp jumps in the compressed current density profile can be produced due to overlaying of different parts of the pulse near the focal plane. Examples of slowly varying and rapidly varying errors compared to the beam pulse duration are studied. For beam velocity errors given by a cubic function, the compression ratio can be described analytically. In this limit, a significant portion of the beam pulse is located in the broad wings of the pulse and is poorly compressed. The central part of the compressed pulse is determined by the thermal spread. The scaling law for maximum compression ratio is derived. In addition to a smooth variation in the velocity tilt, fast-changing errors during the pulse may appear in the induction bunching module if the voltage pulse is formed by several pulsed elements. Different parts of the pulse compress nearly simultaneously at the target and the compressed profile may have many peaks. The maximum compression is a function of both thermal spread and the velocity errors. The effects of the finite gap width of the bunching module on compression are analyzed analytically.

Kaganovich, Igor D.; Massidda, Scott; Startsev, Edward A.; Davidson, Ronald C.; Vay, Jean-Luc; Friedman, Alex

2012-06-01

205

Dynamics of intact immunoglobulin?g explored by drift-tube ion-mobility mass spectrometry and molecular modeling.  

PubMed

Collision cross-sections (CCS) of immunoglobulins G1 and G4 have been determined using linear drift-tube ion-mobility mass spectrometry. Intact antibodies and Fc-hinge fragments present with a larger range of CCS than proteins of comparable size. This is rationalized with MD simulations, which indicate significant in?vacuo dynamics between linked folded domains. The IgG4 subclass presents over a wider CCS range than the IgG1 subclass. PMID:24916519

Pacholarz, Kamila J; Porrini, Massimiliano; Garlish, Rachel A; Burnley, Rebecca J; Taylor, Richard J; Henry, Alistair J; Barran, Perdita E

2014-07-21

206

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

207

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

PubMed Central

A novel compensation method for Zirconium dioxide gated Ion Sensitive Field Effect Transistors (ISFETs) to improve pH-dependent drift was demonstrated. Through the sequential measurements for both the n-channel and p-channel ISFETs, 75–100% pH-dependent drift could be successfully suppressed for the first seven hours. As a result, a nearly constant drift rate versus pH value was obtained, which increases the accuracy of pH measurements. Meanwhile, the drawback of the hyperbolic-like change with time of the common drift behavior for ISFETs was improved. A state-of-the-art integrated scheme adopting this method was also illustrated.

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

2010-01-01

208

Ion Velocity Distribution of a Weakly Ionized Gas in a Uniform Electric Field of Arbitrary Strength  

Microsoft Academic Search

The velocity-distribution function of ions in a neutral gas is studied. A uniform electric field of arbitrary strength is assumed and only binary-ion-neutral-particle collisions are considered. Under these conditions part of the Boltzmann-equation collision operator is replaced by a kinetic model which enables the ion velocity distribution to be found in compact analytical form if the mean free time between

John H. Whealton; Shien-Biau Woo

1972-01-01

209

Ion Velocity Measurements Within the Acceleration Channel of a Low-Power Hall Thruster  

Microsoft Academic Search

This paper presents axial ion velocity measurements within the acceleration channel of the 200-W Busek Company Inc. BHT-200 laboratory Hall thruster derived from laser-induced fluorescence measurements of the 5d[4]7\\/2 - 6p[3]5\\/2 xenon-ion excited-state transition. Acceleration-channel-centerline ion velocities were measured for one nominal and six related cases. These six cases were chosen to be representative of small variations of the applied

William A. Hargus; Michael R. Nakles

2008-01-01

210

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.

2014-06-01

211

Cerenkov Detector for Heavy-Ion Velocity Measurements.  

National Technical Information Service (NTIS)

We have developed a highly sensitive velocity measuring detector using total-internal-reflection Cerenkov counters of a type mentioned by Jelly in 1958. If the velocity of the particle is above the threshold for total-internal-reflection these counters ha...

D. L. Olson M. Baumgartner J. P. Dufour J. G. Girard D. E. Greiner

1984-01-01

212

Slow drift mirror modes in finite electron-temperature plasma: Hydrodynamic and kinetic drift mirror instabilities  

Microsoft Academic Search

We develop a fully kinetic linear theory of the drift mirror (DM) instability accounting for arbitrary particle velocity distribution functions including nonzero electron temperature effects and plasma pressure anisotropy. In the quasi-hydrodynamic limiting case the theory reproduces the results obtained for the ion mirror instability. However, for the very low frequency electron DM modes which can develop in a nonuniform

Oleg A. Pokhotelov; Ingmar Sandberg; Roald Z. Sagdeev; Rudolf A. Treumann; Oleg G. Onishchenko; Michael A. Balikhin; Vladimir P. Pavlenko

2003-01-01

213

Thermal iron ions in high speed solar wind streams. II - Temperatures and bulk velocities  

NASA Technical Reports Server (NTRS)

Mitchel and Roelof (1980) reported the detection of iron in high speed solar wind flows using the small, but finite sensitivity of solid state detectors to Fe ions in the low energy (50-200 keV protons) L1 channel of the NOAA/JHU energetic particle experiment (EPE). In the current investigation, the EPE response is modeled to a convected Maxwellian to obtain the thermal velocity, flow angle, and bulk velocity of the iron distribution. It is assumed that the iron bulk flow velocity can be represented as a vector sum of the hydrogen bulk velocity and an interplanetary magnetic field (IMF) aligned velocity increment. It is found that the velocity increment is smaller than the local Alfven speed in magnitude, and that the iron thermal velocity is comparable with or greater than the proton thermal velocity, with the 'thermal' velocity defined as the square root of 2kT/m.

Mitchell, D. G.; Roelof, E. C.; Feldman, W. C.; Bame, S. J.; Williams, D. J.

1981-01-01

214

Numerical simulations of type II gradient drift irregularities in the equatorial electrojet  

Microsoft Academic Search

Two-dimensional numerical studies of the development of type II irregularities in the equatorial electrojet have been carried out using a method similar to that of McDonald et al., (1974) except that ion inertia has been neglected. This simplification is shown to be a valid approximation whenever the electron drift velocity is small in comparison with the ion acoustic velocity and

R. L. Ferch; R. N. Sudan

1977-01-01

215

Non-Lorentzian ion cyclotron resonance line shapes arising from velocity-dependent ion-neutral collision frequencies  

NASA Technical Reports Server (NTRS)

An asymptotic solution of the Boltzmann equation is developed for ICR absorption, without restrictions on the ion-neutral collision frequency or mass ratio. Velocity dependence of the collision frequency causes deviations from Lorentzian line shape.

Whealton, J. H.; Mason, E. A.

1973-01-01

216

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

PubMed

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

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

2011-03-15

217

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

218

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

Microsoft Academic Search

The collective Thomson scattering (CTS) diagnostic proposed for ITER is designed to measure projected 1D fast-ion velocity distribution functions at several spatial locations simultaneously. The frequency shift of scattered radiation and the scattering geometry place fast ions that caused the collective scattering in well-defined regions in velocity space, here dubbed interrogation regions. Since the CTS instrument measures entire spectra of

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

2011-01-01

219

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

SciTech Connect

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. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2010-10-15

220

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

Microsoft Academic Search

A visible spectroscopic imaging system has been developed on TdeV, providing profile measurements of the ion temperature and plasma poloidal and toroidal rotation velocity. A matrix inversion technique was used to deduce local profiles from the BV and CIII brightness and line-integrated temperature and velocity. Top poloidal and toroidal emissivities present strong asymmetries due to the divertor plates and the

I. Condrea; E. Haddad; B. C. Gregory

1999-01-01

221

Photometric Track Width - Velocity Relations for Heavy Ions in Ilford G5 Nuclear Emulsions.  

National Technical Information Service (NTIS)

The relation between the photometrically determined track width, W, and the velocity, beta, of some heavy ions with charge numbers Z = 14, 16, 24 and 26 has been established in Ilford G5 nuclear research emulsions. It was found that in the velocity interv...

L. Larsson R. Andersson O. Mathiesen

1972-01-01

222

Ion cyclotron diffusion of velocity distributions in the extended solar corona  

Microsoft Academic Search

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

Steven R. Cranmer

2001-01-01

223

On the velocity distributions of dust-related inner-source pickup ions  

NASA Astrophysics Data System (ADS)

We simulate velocity distributions for inner-source pickup ions in two scenarios for their origin. One scenario creates inner-source pickup ions by charge exchange and energy loss in very small (typically submicron-sized) dust grains (Wimmer-Schweingruber and Bochsler 2003), while the other liberates solar wind ions previously implanted in larger (typically 1 ?m) dust grains (Geiss et al. 1995; and Gloeckler and Geiss 1998). The two scenarios differ by the initial velocity with which the pickup ions are created; the fine-dust model produces a wide initial velocity distribution, while the coarse-dust model releases them essentially at rest. We investigate the differences in the distributions once these ions have been transported out to an observer at 1 AU or beyond.

Bochsler, P.; Möbius, E.; Wimmer-Schweingruber, R. F.

2006-03-01

224

Solar energetic particle drifts in the Parker spiral  

NASA Astrophysics Data System (ADS)

Drifts in the Parker spiral interplanetary magnetic field are known to be an important component in the propagation of galactic cosmic rays, while they are thought to be negligible for solar energetic particles (SEPs). As a result, they have so far been ignored in SEP propagation modeling and data analysis. We examine drift velocities in the Parker spiral within single particle first-order adiabatic theory, in a local coordinate system with an axis parallel to the magnetic field. We show that, in the presence of scattering in interplanetary space, protons at the high end of the SEP energy range experience significant gradient and curvature drift. In the scatter-free case, drift due to magnetic field curvature is present. The magnitude of drift velocity increases by more than an order of magnitude at high heliographic latitudes compared to near the ecliptic; it has a strong dependence on radial distance r from the Sun, reaching a maximum at r˜1 AU at low heliolatitudes and r˜10 AU at high heliolatitudes. Due to the mass over charge dependence of drift velocities, the effect of drift for partially ionized SEP heavy ions is stronger than for protons. Drift is therefore likely to be a considerable source of cross-field transport for high-energy SEPs.

Dalla, S.; Marsh, M. S.; Kelly, J.; Laitinen, T.

2013-10-01

225

Simulation of the Ion-Beam-Driven Drift Instability in a Magnetic Trap II.  

National Technical Information Service (NTIS)

Recent Experiments on the TMX-U device at LLNL have indicated the possibility of a low frequency drift wave being driven unstable by the injection of neutral beams in the thermal barrier region. Nonlocal linear theory is performed for this instability usi...

V. A. Thomas W. M. Nevins Y. J. Chen

1984-01-01

226

Simulation of the Ion-Beam-Driven Drift Instability in a Magnetic Trap I.  

National Technical Information Service (NTIS)

Recent experiments on the TMX-U device at LLNL have indicated the possibility of a drift wave being driven unstable by the injection of neutral beams in the thermal barrier region. A review of linear theory is presented in the local approximation. In addi...

V. A. Thomas W. M. Nevins Y. J. Chen

1984-01-01

227

Ion velocities in direct current arc plasma generated from compound cathodes  

SciTech Connect

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 (10{sup 4} m/s) for ions from Ti{sub 0.84}Al{sub 0.16}, Ti{sub 0.90}Si{sub 0.10}, and Ti{sub 0.90}C{sub 0.10} cathodes, respectively.

Zhirkov, I.; Rosen, J. [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)] [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Eriksson, A. O. [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden) [Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Oerlikon Balzers Coating AG, Iramali 18, 9496 Balzers (Liechtenstein)

2013-12-07

228

Temporal evolution of confined fast-ion velocity distributions measured by collective Thomson scattering in TEXTOR.  

PubMed

Fast ions created in the fusion processes will provide up to 70% of the heating in ITER. To optimize heating and current drive in magnetically confined plasmas insight into fast-ion dynamics is important. First measurements of such dynamics by collective Thomson scattering (CTS) were recently reported [Bindslev, Phys. Rev. Lett. 97, 205005 2006]. Here we extend the discussion of these results which were obtained at the TEXTOR tokamak. The fast ions are generated by neutral-beam injection and ion-cyclotron resonance heating. The CTS system uses 100-150kW of 110-GHz gyrotron probing radiation which scatters off the collective plasma fluctuations driven by the fast-ion motion. The technique measures the projected one-dimensional velocity distribution of confined fast ions in the scattering volume where the probe and receiver beams cross. By shifting the scattering volume a number of scattering locations and different resolved velocity components can be measured. The temporal resolution is 4ms while the spatial resolution is approximately 10cm depending on the scattering geometry. Fast-ion velocity distributions in a variety of scenarios are measured, including the evolution of the velocity distribution after turnoff of the ion heating. These results are in close agreement with numerical simulations. PMID:18351944

Nielsen, S K; Bindslev, H; Porte, L; Hoekzema, J A; Korsholm, S B; Leipold, F; Meo, F; Michelsen, P K; Michelsen, S; Oosterbeek, J W; Tsakadze, E L; Van Wassenhove, G; Westerhof, E; Woskov, P

2008-01-01

229

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

231

Flute mode waves near the lower hybrid frequency excited by ion rings in velocity space  

NASA Technical Reports Server (NTRS)

Discrete emissions at the lower hybrid frequency are often seen on the S3-3 satellite. Simultaneous observation of perpendicularly heated ions suggests that these ions may provide the free energy necessary to drive the instability. Studies of the dispersion relation for flute modes excited by warm ion rings in velocity space show that waves are excited with real frequencies near the lower hybrid frequency and with growth rates ranging from about 0.01 to 1 times the ion cyclotron frequency. Numerical results are therefore consistent with the possibility that the observed ions are the free energy source for the observed waves.

Cattell, C.; Hudson, M.

1982-01-01

232

Low Ion Velocity Slowing Down in a Demixing Binary Ionic Mixture  

NASA Astrophysics Data System (ADS)

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

Deutsch, Claude; Leger, Daniel; Tashev, Bekbolat

2010-11-01

233

Low Ion Velocity Slowing Down in a Demixing Binary Ionic Mixture  

NASA Astrophysics Data System (ADS)

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

Deutsch, Claude; Leger, Daniel; Tashev, Bekbolat

2011-11-01

234

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift  

NASA Astrophysics Data System (ADS)

With the 100-m telescope at Effelsberg, 19 ammonia (NH3) maser lines have been detected toward the prominent massive star forming region W51-IRS2. Eleven of these inversion lines, the (J, K) = (6, 2), (5, 3), (7, 4), (8, 5), (7, 6), (7, 7), (9, 7), (10, 7), (9, 9), (10, 9), and (12, 12) transitions, are classified as masers for the first time in outer space. All detected masers are related to highly excited inversion doublets. The (5, 4) maser originates from an inversion doublet ~340 K above the ground state, while the (12, 12) transition, at ~1450 K, is the most highly excited NH3 maser line so far known. Strong variability is seen not only in ortho- but also in para-NH3 transitions. Bright narrow emission features are observed, for the first time, in (mostly) ortho-ammonia transitions, at VLSR ~ 45 km s-1, well separated from the quasi-thermal emission near 60 km s-1. These features were absent ~25 years ago and show a velocity drift of about +0.2 km s-1 yr-1. The component is likely related to the SiO maser source in W51-IRS2 and a possible scenario explaining the velocity drift is outlined. The 57 km s-1 component of the (9, 6) maser line is found to be strongly linearly polarised. Maser emission in the (J, K) to (J + 1, K) inversion doublets is strictly forbidden by selection rules for electric dipole transitions in the ground vibrational state. However, such pairs (and even triplets with (J + 2, K)) are common toward W51-IRS2. Similarities in line widths and velocities indicate that such groups of maser lines arise from the same regions, which can be explained by pumping through vibrational excitation. The large number of NH3 maser lines in W51-IRS2 is most likely related to the exceptionally high kinetic temperature and NH3 column density of this young massive star forming region.

Henkel, C.; Wilson, T. L.; Asiri, H.; Mauersberger, R.

2013-01-01

235

Observation of coherent nonlinear interactions in the ion velocity distribution function  

NASA Astrophysics Data System (ADS)

Using laser induced fluorescence (LIF) and higher order spectral analysis, we present the first measurements of phase space resolved coherent nonlinear interactions among the components of low frequency density fluctuations, (?<=?ci), in a linearly magnetized device. The bicoherence calculations employing the two point correlation technique suggest that there are two different coherent nonlinear wave-wave interactions in the measured spectrum. The first one, having a short correlation length and existing for slow moving ions, for which |?i?|<=|?ith|, is an interaction between fluctuations below the electron drift frequency, ?*. The second one is the strongest for fast moving ions, for which |?i?|>=|?ith|, and is a mode coupling between the azimuthal drift wave modes, m=1 and m=2. Combining these bispectral results with earlier linear analysis based on the power spectra of the fluctuations, we suggest that the nonlinear coupling observed between the spectral components below ?* for the case of slow moving ions is associated with the anomalous kinetic component. For slow moving ions, as we increase the neutral collision frequencies, the nonlinear interaction observed for spectral components below ?* decreases and the harmonic mode coupling for ?* takes over.

Uzun-Kaymak, Ilker Ü.; Skiff, Frederick

2006-11-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

237

Swift heavy ions in magnetic insulators: A damage-cross-section velocity effect  

SciTech Connect

The damage in ferrimagnetic yttrium iron garnet, Y[sub 3]Fe[sub 5]O[sub 12] or YIG, induced by energetic heavy-ion bombardment in the electronic stopping-power regime has been studied in the low-velocity range (for a beam energy [ital E][le]3.6 MeV/amu). Epitaxial thin films of YIG on [111]-Gd[sub 3]Ga[sub 5]O[sub 12] substrates were thus irradiated at room temperature with 15-MeV [sup 19]F, 50-MeV [sup 32]S, 650-MeV [sup 181]Ta, 750-MeV [sup 208]Pb, and 666-MeV [sup 238]U. The damage-cross-section [ital A] is extracted from channeling-Rutherford-backscattering spectroscopy and compared to previous works. All the experimental results show that at one given value of [ital dE]/[ital dx], the damage cross section is higher for low-velocity ions than for high-velocity ions over a large range of [ital dE]/[ital dx]. At constant [ital dE]/[ital dx], the larger the difference between the ion velocities is, the larger the difference between the damage cross sections. Such a deviation might be explained by the effect of the energy deposition being more localized for the low-velocity ions than for the high-velocity ions. This work clearly indicates that the electronic stopping power is not the only key parameter in the creation of ion tracks, and that the damage cross section depends on the lateral distribution of the energy deposition.

Meftah, A. (Centre Interdisciplinaire de Recherches avec les Ions Lourds, BP 5133, F-14040 Caen CEDEX (France)); Brisard, F.; Costantini, J.M. (Commissariat a l'Energie Atomique, Service PTN, BP 12, F-91680 Bruyeres le Chatel (France)); Hage-Ali, M.; Stoquert, J.P. (Centre de Recherches Nucleaires, Groupe Phase, F-67037 Strasbourg CEDEX (France)); Studer, F. (Crismat enInstitut des Sciences de la Matiere et du Rayonnement, Universite de Caen, 14032 Caen CEDEX (France)); Toulemonde, M. (Centre Interdisciplinaire de Recherches avec les Ions Lourds, BP 5133, F-14040 Caen CEDEX (France))

1993-07-01

238

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

SciTech Connect

The ion velocity distribution function (IVDF) above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time through the sheath to the RF period is {tau}{sub ion}/{tau}{sub RF} = 0.3). The position of the presheath/sheath edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath region. The characteristic bimodal structure of the time-averaged ion distributions found in previous experiments is observed to arise from the time-dependent ion dynamics, in accord with existing theory. The large temporal variation of the IVDF has implications for the plasma chemistry and etching quality.

Jacobs, B.; Gekelman, W.; Pribyl, P. [University of California, Los Angeles, California 90095 (United States); Barnes, M. [MS Barnes Engineering, San Ramon, California 94583 (United States)

2011-05-15

239

Electron-ion hybrid instabilities driven by velocity shear in a magnetized plasma  

NASA Technical Reports Server (NTRS)

The stability of a magnetized plasma is investigated in which a sheared electron flow channel is present. The flow's peak velocity and shear scale length are denoted by V and L, respectively. If the velocity channel is perpendicular to the confining magnetic field and L is less than the ion Larmor radius, an electrostatic instability develops whose frequency is on the order of the lower hybrid frequency. It is concluded that velocity shear is the only source of free energy. Further, it is shown that density gradients do not stabilize this mode. It follows that the mode presented in this work can not be identified with the well-known modified two-stream instability. If the velocity channel is parallel to the confining magnetic field and the plasma is weakly magnetized, an instability driven by velocity shear is shown to exist.

Romero, H.; Ganguli, G.; Lee, Y. C.; Palmadesso, P. J.

1992-01-01

240

Ion velocity and plasma potential measurements of a cylindrical cusped field thruster  

NASA Astrophysics Data System (ADS)

Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition centered at ?=834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.

MacDonald, N. A.; Young, C. V.; Cappelli, M. A.; Hargus, W. A.

2012-05-01

241

Ion velocity and plasma potential measurements of a cylindrical cusped field thruster  

SciTech Connect

Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]{sub 7/2}-6p[3]{sub 5/2} xenon ion excited state transition centered at {lambda}=834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.

MacDonald, N. A.; Young, C. V.; Cappelli, M. A. [Stanford Plasma Physics Laboratory, Stanford University, Stanford, California 94305 (United States); Hargus, W. A. Jr. [Spacecraft Propulsion Branch, Air Force Research Laboratory, Edwards AFB, California 93524 (United States)

2012-05-01

242

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

243

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

244

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

Microsoft Academic Search

We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D? (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble

M. Salewski; B. Geiger; S. K. Nielsen; H. Bindslev; M. García-Muñoz; W. W. Heidbrink; S. B. Korsholm; F. Leipold; F. Meo; P. K. Michelsen; D. Moseev; M. Stejner; G. Tardini

2012-01-01

245

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

246

Electromagnetic ion cyclotron wave generation by planetary pickup ions: One-dimensional hybrid simulations at sub-Alfvénic pickup velocities  

NASA Astrophysics Data System (ADS)

Enhanced electromagnetic plasma waves generated by unstable pickup ion distributions have been detected by spacecraft in several planetary environments including those of Venus, Earth, Mars, comets, Jupiter and Saturn. These waves are important because they can be used as a diagnostic of the local plasma and the ion pickup conditions. Interpretation of these waves relies on understanding the source of free energy and how that free energy is reduced through instability growth. In this manuscript, we focus on the regime where the pickup velocity is sub-Alfvénic and systematically illustrate some basic differences in instability behavior by carrying out one-dimensional hybrid simulations of pickup ion-generated waves for varying pickup angle, ?. Although several pickup ion-driven instabilities are possible in this regime, the dominant electromagnetic instability that is observed is the ion cyclotron ring instability, which generates waves in the spacecraft frame with frequencies near the pickup ion cyclotron frequency. To better understand the instability behavior as well as what wave properties a spacecraft would potentially observe, we carry out the simulations in the bulk plasma frame and in the planetary rest frame (i.e. spacecraft frame). The simulations presented here are not meant to reproduce any particular planetary environment but are intended to illustrate the general behavior in the sub-Alfvénic pickup velocity regime. We also review the previous observations and dispersion analyses of pickup ion-driven waves in the relevant planetary environments, and discuss them in terms of our simulation results.

Cowee, M. M.; Gary, S. P.

2012-06-01

247

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

248

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

249

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

SciTech Connect

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

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

2008-08-15

250

The heavy ions of the solar wind: pseudo-heating by velocity filtration and acceleration  

Microsoft Academic Search

Due to their different mass and charge states, heavy solar coronal and solar wind ions provide invaluable information on the physical mechanisms responsible for the heating of the corona and for the solar wind acceleration. In the present work, it is shown that key characteristics observed in the corona are predicted by the velocity filtration effect. This mechanism originally proposed

V. Pierrard; H. Lamy; J. Lemaire

2003-01-01

251

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

National Technical Information Service (NTIS)

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

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

1984-01-01

252

Investigation of beam stability in a high intensity drift tube linac for heavy ion inertial fusion  

Microsoft Academic Search

With the new concept of indirectly driven targets for heavy ion inertial fusion, the driver scenarios had to be reconsidered. A European study group (HIDIF collaboration) investigated the feasibility of a driver facility based on a linac and storage ring approach (Hofmann and Plass (Eds.), GSI-98-06 GEP, Darmstadt, 1998). In a preinjector consisting of an array of ion sources, rf-linacs

H. Deitinghoff; G. Parisi; A. Sauer; K. Bongardt; M. Pabst

2001-01-01

253

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

254

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

255

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

256

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

SciTech Connect

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; Lembege, Bertrand [CAS Key Laboratory of Basic Plasma Physics, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136 (China); LATMOS-UVSQ-IPSL-CNRS, Guyancourt 78280 (France)

2012-11-20

257

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.

2014-01-01

258

and Two-Electron Processes in the Collisions of Multiply Charged Ions with Helium from Low to High Velocities  

Microsoft Academic Search

Ionization and electron capture in collisions of multiply charged ions with He from low to high velocities are investigated using novel coincident recoil momentum spectroscopy. The cross-over between dominance of capture and ionization is observed for highly charged ions. Strong onset of target direct ionization (SI) is observed at collision velocities around 1.5 a.u. This effective \\

Wuchun Wu

1994-01-01

259

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

SciTech Connect

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

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

2012-06-01

260

Positive/negative ion velocity mapping apparatus for electron-molecule reactions  

SciTech Connect

In molecular dissociative ionization by electron collisions and dissociative electron attachment to molecule, the respective positively and negatively charged fragments are the important products. A compact ion velocity mapping apparatus is developed for the angular distribution measurements of the positive or negative fragments produced in the electron-molecule reactions. This apparatus consists of a pulsed electron gun, a set of ion velocity mapping optic lenses, a two-dimensional position detector including two pieces of micro-channel plates, and a phosphor screen, and a charge-coupled-device camera for data acquisition. The positive and negative ion detections can be simply realized by changing the voltage polarity of ion optics and detector. Velocity sliced images can be directly recorded using a narrow voltage pulse applied on the rear micro-channel plate. The efficient performance of this system is evaluated by measuring the angular distribution of O{sup -} from the electron attachments to NO at 7.3 and 8.3 eV and O{sup +} from the electron collision with CO at 40.0 eV.

Wu Bin; Xia Lei; Li Hongkai; Zeng Xianjin; Tian Shanxi [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-01-15

261

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

PubMed

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM-MS) using drift-gases with varying masses and polarizabilities. Despite the reduced length of the cell (18?cm), a pair of constitutional isomers, N-butylaniline and para-butylaniline, with theoretical collision cross-section values in helium (?He ) differing by as little as 1.2?Å(2) (1.5%) but possessing contrasting charge distribution, showed baseline peak-to-peak resolution (Rp-p ) for their protonated molecules, using carbon dioxide (CO2), nitrous oxide (N2O) and ethene (C2H4 ) as the TWIM drift-gas. Near baseline Rp-p was also obtained in CO2 for a group of protonated haloanilines (para-chloroaniline, para-bromoaniline and para-iodoaniline) which display contrasting masses and theoretical ?He , which differ by as much as 15.7?Å(2) (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans-oleic acid and cis-oleic acid possessing nearly identical theoretical ?He and ?N2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift-times were observed for the 1,3-dialkylimidazolium ions when comparing He, N2 and N2O. Using density functional theory as a means of examining the ions electronic structure, and He and N2-based trajectory method algorithm, we discuss the effect of the long-range charge induced dipole attractive and short-range Van der Waals forces involved in the TWIM separation in drift-gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift-gases could improve separation and the overall success of TWIM-MS analysis. PMID:24078238

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

2013-09-01

262

Laboratory Course on Drift Chambers  

SciTech Connect

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

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

2006-09-25

263

Differential cross sections for ionization of methane, ammonia, and water vapor by high velocity ions  

SciTech Connect

Cross sections, differential in the energy of secondary electrons, for ionization of methane, ammonia, and water vapor by high energy protons are presented. The results are based on a model that uses photoabsorption and ion impact ionization data to evaluate the coefficients in Bethe's asymptotic cross section for inelastic scattering of high velocity ions. Model cross sections are compared with previously published data and new data on ionization of methane and water vapor by 3.0 and 4.2 MeV protons. The simple, analytic model should be very useful in transport calculations where differential ionization cross sections over a broad range of primary and secondary energies are needed.

Wilson, W.E.; Miller, J.H.; Toburen, L.H.; Manson, S.T.

1984-06-01

264

Theoretical investigations on plasma processes in the Kaufman thruster. [electron and ion velocity distribution  

NASA Technical Reports Server (NTRS)

An analysis of the sputtering of metal surfaces and grids by ions of medium energies is given and it is shown that an exact, nonlinear, hyperbolic wave equation for the temperature field describes the transient transport of heat in metals. Quantum statistical and perturbation theoretical analysis of surface sputtering by low energy ions are used to develop the same expression for the sputtering rate. A transport model is formulated for the deposition of sputtered atoms on system components. Theoretical efforts in determining the potential distribution and the particle velocity distributions in low pressure discharges are briefly discussed.

Wilhelm, H. E.

1974-01-01

265

Gyrophase drifts and the orbital evolution of dust at Jupiter's Gossamer Ring  

NASA Technical Reports Server (NTRS)

The 'gyrophase drift' phenomenon in Jupiter's fine-dust 'gossamer ring' is presently shown to exceed the plasma-drag drift, and may be able to move small, charged grains either toward or away from synchronous radius. The grain gyrophase drifts toward the higher temperature in the presence of a radial gradient in plasma temperature; gyrophase drift will also occur in conjunction with a radial gradient in the relative concentrations of different plasma ion species, or even due to plasma-grain velocity variation associated with the grain's cycloidal motion through the plasma. The Poynting-Robertson drift is noted to be diminutive by comparison with either the plasma-drag or gyrophase drifts.

Northrop, T. G.; Mendis, D. A.; Schaffer, Les

1989-01-01

266

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

SciTech Connect

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

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

2005-09-09

267

Apparent velocity threshold in the electronic stopping of slow hydrogen ions in LiF.  

PubMed

The electronic energy loss of hydrogen ions (protons and deuterons) in thin supported films of LiF has been studied in backscattering geometry for specific energies from 700 eV/u to 700 keV/u, using Rutherford backscattering spectroscopy and time-of-flight low-energy ion scattering spectroscopy. For specific energies below 8 keV/u, our data confirm velocity proportionality for the stopping cross section epsilon (like in a metal) down to 3.8 keV/u, as observed previously for protons and antiprotons despite the large band gap (14 eV) of LiF. Below 3.8 keV/u, the present results indicate an apparent velocity threshold at about 0.1 a.u. for the onset of electronic stopping. PMID:16197001

Draxler, M; Chenakin, S P; Markin, S N; Bauer, P

2005-09-01

268

Kinetic Alfvén wave and ion velocity distribution functions in the solar wind  

NASA Astrophysics Data System (ADS)

Using 1D test particle simulations, the effect of a kinetic Alfvén wave on the velocity distribution function of protons in the collisionless solar wind is investigated. We first use linear Vlasov theory to obtain the property of a kinetic Alfvén wave numerically (the wave propagates in the direction almost perpendicular to the background magnetic field). We then numerically simulate how the wave will shape the proton velocity distribution function. It is found that Landau resonance may be able to generate two components in the initially Maxwellian proton velocity distribution function: a tenuous beam component along the direction of the background magnetic field and a core component. The streaming speed of the beam relative to the core proton component is about 1.2 -- 1.3 Alfvén speed. However, no perpendicular ion heating is observed from the simulation. Reference: Li, X., Lu, Q.M., Chen, Y., Li, B., Xia, L.D., ApJ, 719, L190, 2010.

Li, X.; Lu, Q.; Chen, Y.; Li, B.; Xia, L.

2010-12-01

269

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

NASA Astrophysics Data System (ADS)

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

Fromy, Patrice; Tashev, Bekbolat; Deutsch, Claude

2010-10-01

270

First operation of bulk micromegas in low pressure negative ion drift gas mixtures for dark matter searches  

NASA Astrophysics Data System (ADS)

A bulk micromegas micropattern charge readout device has, for the first time, been operated at room temperature in low pressure carbon disulphide vapour. This is a key step opening prospects for use of micromegas readout for large volume negative ion time projection chambers (TPCs) without magnets, such as proposed for directional dark matter detectors and other rare event applications. The dependence of the gain on the amplification field, pressure and drift field has been evaluated. For the available gap size of 75 ?m a maximum gain of 1300 ± 120 was achieved in 40 torr vapour with an energy resolution of 22% for 5.9 keV 55Fe X-rays. From a fit to the data, the Townsend coefficient gas parameters A and B have been derived. Operation has also been successfully achieved in xenon:carbon disulphide blends over a range of partial and total pressures. A gain of 890 ± 130 at an energy resolution of 35% has been recorded for a 1:1 blend at a total pressure of 80 torr. Possible improvements are discussed in the context of operation in directional dark matter TPCs as a replacement for multi-wire proportional counters.

Lightfoot, P. K.; Spooner, N. J. C.; Lawson, T. B.; Aune, S.; Giomataris, I.

2007-07-01

271

Measurements of Nitrous Acid (HONO) Using Ion Drift - Chemical Ionization Mass Spectrometry during the 2009 SHARP Field Campaign  

NASA Astrophysics Data System (ADS)

During the 2009 SHARP Field Campaign in Houston, TX, measurements of HONO were continuously conducted from May 1 to June 1 at a site located on the campus of the University of Houston. We have developed a novel approach for ambient measurements of nitrous acid (HONO) using ion drift - chemical ionization mass spectrometry (ID-CIMS). In our innovative method, HONO is ionized using the sulfur hexafluoride anion, representing the first application of this reagent ion under humid tropospheric conditions. In this presentation, we will discuss the temporal trends and sources of HONO, as well as, as the involvement of HONO in the formation of key atmospheric constituents, such as ozone. Diurnally, HONO concentration accumulates in the late afternoon, reaches a nighttime maximum, and declines rapidly after sunrise; the averaged daytime and nighttime concentrations are 0.15 × 0.05 and 0.26 × 0.04, respectively. The nighttime measured HONO peaks show strong correlations with the NO2 concentration, particle surface area, and soot mass concentration, indicating that the aerosol-phase chemistry represents a significant contributor to the HONO yield. A higher nighttime HONO peak concentration consistently 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 do. Using a kinetic approach, we estimate an uptake coefficient in the range of 6 x 10-4 to 2 x 10-3 for the heterogeneous conversion of NO2 to HONO on aerosol surfaces, which is necessary to account for the measured nighttime HONO peaks. Our results underscore the importance of aerosol heterogeneous chemistry in HONO production and the contributions of this non-photolytic HONO source to the radical budget and the photochemical ozone production in this region. Furthermore, 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, M. E.; Zhang, R.

2013-12-01

272

Investigation of localized 2D convection mapping based on artificially generated Swarm ion drift data  

NASA Astrophysics Data System (ADS)

Ionospheric plasma flow is an indicator of the interconnection between the solar wind, interplanetary magnetic field (IMF), and Earth’s magnetosphere. Ionospheric convection has been mapped in the past using either a widespread data set for instantaneous convection mapping over a short time period or data from an instrument measuring convection in a spatially confined region over a long time period for the purpose of building a statistically averaged convection pattern. This study explores convection mapping using a spherical cap harmonic analysis (SCHA) technique within a localized spherical cap based on data that will be available from the Swarm three-satellite constellation. Convection is mapped in the vicinity of hypothetical Swarm satellite tracks where it is adequately constrained by data. By using statistical models to emulate Swarm measurements, we demonstrate that such mapping can be successful based on data from the Swarm A and Swarm B satellites. Convection is divided into well constrained and poorly constrained subsets to determine parameters characterizing goodness-of-fit based on known quantities. Using the subset of well constrained maps, it is determined that convection is best mapped for a spherical cap having an angular radius of ?c=10°. The difference between the maximum mapped convection and the maximum velocity measured along the satellite track (?v) is introduced to evaluate goodness-of-fit. For the examples presented in this paper, we show that a threshold value of ?v=281 m/s successfully differentiates between well and poorly constrained maps 77.6% of the time. It is shown that convection can be represented over a larger region through the use of multiple spherical caps.

Fiori, R. A. D.; Boteler, D. H.; Koustov, A. V.; Knudsen, D.; Burchill, J. K.

2014-07-01

273

Ion Bernstein waves in a plasma with a kappa velocity distribution  

NASA Astrophysics Data System (ADS)

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, ?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 ?i is reduced. For waves whose frequency lies above the lower hybrid frequency, ?LH, an increasing excess of superthermal particles (decreasing ?i) reduces the frequency, ?peak, of the characteristic peak at which the group velocity vanishes, while the associated kpeak is increased. As the ratio of ion plasma to cyclotron frequency (?pi/?ci) is increased, the fall-off of ? at large k is smaller for lower ?i and curves are shifted towards larger wavenumbers. In the lower hybrid frequency band and harmonic bands above it, the frequency in a low-?i plasma spans only a part of the intraharmonic space, unlike the Maxwellian case, thus exhibiting considerably less coupling between adjacent bands for low ?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.

2013-10-01

274

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

SciTech Connect

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

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

2006-08-15

275

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

276

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

277

Giotto-IMS observations of ion flow velocities and temperatures outside the contact surface of Comet Halley. [Ion Mass Spectrometer (IMS)  

NASA Technical Reports Server (NTRS)

Fluid parameters for He(++) ions obtained from the Giotto ion mass spectrometer are presented. Proton densities and velocities and thermal speeds of protons, alpha particles, and heavy ions in the hour before closest approach are discussed. A region of enhanced He(++) ion densities, and velocity, and decreased temperature is observed from 20:26 to 21:45. Sharp decreases in the proton density are observed at 23:30 and at 23:41. There is a relative flow velocity between alpha particles and oxygen ions of 30 km/sec during a period from 22:55 to 23:30; the difference in flow velocity is less than the experimental uncertainities. The flow properties of protons observed during this period are also discussed.

Goldstein, B. E.; Neugebauer, M.; Balsiger, H.; Drake, J.; Fuselier, S. A.; Goldstein, R.; Ip, WING-H.; Rettenmund, U.; Rosenbauer, H.; Schwenn, R.

1986-01-01

278

Ion densities and velocities in the inner plasma torus of Saturn  

NASA Astrophysics Data System (ADS)

We present plasma data from the Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP), mapping the ion density and velocity of Saturn's inner plasma torus. Data from 129 orbits, recorded during the period from the 1st of February 2005 to the 27th of June 2010, are used to map the extension of the inner plasma torus. The dominant part of the plasma torus is shown to be located in between 2.5 and 8 Saturn radii (1 RS=60,268 km) from the planet, with a north-southward extension of ±2RS. The plasma disk ion density shows a broad maximum in between the orbits of Enceladus and Tethys. Ion density values vary between 20 and 125 cm-3 at the location of the density maximum, indicating considerable dynamics of the plasma disk. The equatorial density structure, |z|<0.5RS, shows a slower decrease away from the planet than towards. The outward decrease, from 5 RS, is well described by the relation neq=2.2×104(1/R)3.63. The plume of the moon Enceladus is clearly visible as an ion density maximum of 105 cm-3, only present at the south side of the ring plane. A less prominent density peak, of 115 cm-3, is also detected at the orbit of Tethys, at ˜4.9RS. No density peaks are recorded at the orbits of the moons Mimas, Dione, and Rhea. The presented ion velocity v shows a clear general trend in the region between 3 and 7 RS, described by v=1.5R2-8.7R+39. The average v starts to deviate from corotation at around 3 RS, reaching ˜68% of corotation close to 5 RS.

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

2012-12-01

279

Velocity distribution of mass-selected nano-size cluster ions  

NASA Astrophysics Data System (ADS)

The paper reports on an experimental investigation of the ion velocity distribution function (IVDF) for mass-selected copper cluster ions with a diameter in the range 5-10 nm. The cluster ion beam is produced by a dc magnetron-based gas aggregation source. The measurements are carried out by means of a quadrupole mass filter combined with a basic retarding field analyser. The most probable cluster velocities are in the range 80-180 m s-1 decreasing with cluster size and increasing with buffer gas (Ar) flow. Experimental results are compared with the theoretical model of Smirnov et al. Noted discrepancies are explained by the interaction of clusters with buffer gas atoms outside the aggregation chamber during the passage from the orifice towards the detector. This interaction is not included in the theoretical model. Both positively and negatively charged clusters are investigated. The density ratio of positively to negatively charged clusters in the beam is evaluated from the measured IVDFs and compared with the theoretical model.

Ganeva, Marina; Pipa, Andrei V.; Smirnov, Boris M.; Kashtanov, Pavel V.; Hippler, Rainer

2013-08-01

280

Initial results on charge and velocity discrimination for heavy ions using silicon-Timepix detectors  

NASA Astrophysics Data System (ADS)

The Timepix ASIC is a version of the hybrid pixel detector technology developed by the Medipix2 Collaboration [1]. Within the 256 by 256 pixel matrix, the electronics for each of the 55?m individual pixels are contained in the footprint of that pixel. The Timepix has a charge-sensitive pre-amp and an associated discriminator attached to a logic unit capable of being employed in one of several different modes. For the present work, the Time-Over-Threshold mode was used to allow measurement of deposited energy in the silicon sensor layer. The general properties of a Timepix-based device with a silicon sensor have been described in [2,3], and [4]. Ionization along heavy ion particle tracks in the silicon sensor results in the production of free charge carriers in the detector. The charge carrier motion under the influence of an applied bias voltage leads to charge collection at the Timepix-sensor interface in one or more pixels. Signatures within the pixel cluster patterns are currently being examined, and initial results indicate that such signatures, when coupled with stopping power information, provide enough discrimination capability to begin to resolve heavy ion charge and velocity. Here we present the salient characteristics that have been identified for heavy ion charge and velocity discrimination using Timepix Silicon detectors and discuss the application of this method for particle track characterization.

Stoffle, N.; Pinsky, L.; Hoang, S.; Idarraga, J.; Kroupa, M.; Jakubek, J.; Turecek, D.; Pospíšil, S.

2012-12-01

281

Time-sliced ion-velocity imaging study of the reaction Y + O2 ? YO + O.  

PubMed

The oxidation reaction dynamics of the gas-phase yttrium atoms by oxygen molecules was studied under crossed-beam conditions. The product YO was detected using a time-of-flight mass spectrometer combined with laser single-photon ionization. An acceleration lens system designed for the ion-velocity mapping conditions, a two-dimensional (2-D) detector, and a time-slicing technique were used to obtain the velocity and angular distributions of the products. Two ionization wavelengths were used for the internal (vibrational and/or electronic) energy selective detection of YO. The single photon of the shorter wavelength (202.0 nm) can ionize all states of YO(X?(2)?, A'?(2)?, and A?(2)?), while electronically excited YO(A' and A) are dominantly ionized at a longer wavelength (285.0 nm). Time-sliced images were converted to the velocity and angular distributions in the center-of-mass frame. The general features of the velocity distributions of YO, determined at two wavelengths, were well represented by those expected from the statistical energy disposal model. The forward-backward symmetry was also observed for two images. These results suggest that the reaction proceeds via long-lived intermediates, and that this mechanism is consistent with previous chemiluminescence/LIF studies. PMID:21423981

Honma, Kenji; Matsumoto, Yoshiteru

2011-05-14

282

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

283

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

284

One and two electron processes in collisions of highly charged ions with He at velocities around 1 a.u  

Microsoft Academic Search

We have studied one and two electron processes in collisions of Ar16+ and O8+ ions with He atoms at velocities between 0.23 and 1.67 a.u. These processes were identified by measuring the final charges of the projectile and recoil ions in coincidence. Single electron capture (SC) is the dominant process at all our velocities. Transfer ionization (TI), where the He

J. P. Giese; W. Wu; I. Ben-Itzhak; C. L. Cocke; R. Ali; P. Richard; M. Stoeckli; H. Schoene

1993-01-01

285

Analysis of an ion atom collision at intermediate velocities by means of quantum trajectories  

NASA Astrophysics Data System (ADS)

We present the results of a quantum calculation designed to discuss the dynamics of an ion-atom collision at intermediate velocities. The description is based on a quantum fluid picture. The time-dependent Schrödinger equation is integrated numerically for a model proton-hydrogen collision and quantum trajectories are computed. By these means, we obtain a pictural view of the scattering process. Analysis of the resulting trajectories yields insights into the dynamics of the physical phenomena involved, with special emphasis on ionization.

Ponce, Lino

2007-02-01

286

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

287

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

NASA Astrophysics Data System (ADS)

A visible spectroscopic imaging system has been developed on Tokamak de Varennes (TdeV) that provides profile measurements of the ion temperature and plasma rotation velocity. Multiple poloidal and tangential chords were coupled to the entrance slit of a spectrometer equipped with a back-illuminated charge coupled device camera at its exit slit. The camera records spatially and spectrally resolved emission profiles with real time digitization and up to 70 ms/frame as temporal resolution. Line-integrated radiation from different ionization stages in the visible range (B V, C III, He II, and N IV) were chosen as representative of the plasma in their regions of maximum emission. Three types of plasma discharges are compared: ohmic and electron cyclotron resonance heated L and H modes. Preliminary results show that with an L-H transition, there is a 20%-30% increase of the ion temperature at midradius, without a pedestal and an increase of the toroidal velocity shear at r/a~0.8.

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

1999-01-01

288

Atomic physics effects on tokamak edge drift-tearing modes  

SciTech Connect

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

Hahm, T.S.

1993-03-01

289

Atomic physics effects on tokamak edge drift-tearing modes  

SciTech Connect

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

Hahm, T.S.

1993-03-01

290

Fully kinetic theory of drift-mirror modes in space plasmas. Electron drift-mirror instability  

NASA Astrophysics Data System (ADS)

The fully kinetic linear theory of drift-mirror (DM) instability accounting for arbitrary particle velocity distribution functions is developed. This approach includes nonzero electron temperature effects and plasma pressure anisotropy such that it contains the previous results, obtained in quasi-hydrodynamic approach, as limiting cases. In addition to the previous analysis, two novel instabilities, the hydrodynamic and kinetic electron drift-mirror (EDM) instabilities, have been revealed in the fully kinetic regime. The first one appears in the narrow range of the ion temperature anisotropies in the presence of nonzero electron temperature effects and plasma inhomogeneity below the ion mirror instability threshold. The second instability occurs in kinetic regime when the condition for the ion DM instability is satisfied. The frequency of the kinetic EDM mode is much lower than that of the ion DM mode but when the electron temperature is of the order of the parallel ion temperature the instability growth rate may become comparable or even higher than of the ion DM instability. The free energy necessary for these new instabilities is taken from two sources. On one hand, similar to the usual mirror instability, it is stored in the ion pressure anisotropy. On the other hand, the additional source of free energy arises from the electron pressure gradient which builds up in a plasma with nonzero electron temperature.

Pokhotelov, O. A.; Treumann, R. A.; Sagdeev, R. Z.; Onishchenko, O. G.; Balikhin, M. A.; Pavlenko, V. P.; Sandberg, I.

2002-10-01

291

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

NASA Astrophysics Data System (ADS)

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

Whalen, James A.

2004-07-01

292

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

Microsoft Academic Search

We have built a velocity map imaging (VMI) spectrometer optimized for angle-resolved photoionization experiments with synchrotron radiation (SR) in the VUV and soft X-ray range. The spectrometer is equipped 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

D. Rolles; Z. D. Peši?; M. Perri; R. C. Bilodeau; G. D. Ackerman; B. S. Rude; A. L. D. Kilcoyne; J. D. Bozek; N. Berrah

2007-01-01

293

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 [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. 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 the 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 e-foldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (lower-hybrid-drift instability, modified two-stream instability, etc.) studied previously, we believe the instability we found 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 Yansong; Kulsrud, Russell; Ji, Hantao [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08549 (United States)

2008-12-15

294

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

295

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

296

Predicting the lifetime of copper/barrier/dielectric systems: Insights for designing better barriers for reducing copper ion drift/diffusion into the dielectric  

NASA Astrophysics Data System (ADS)

Our previous drift/diffusion model describing the effect of the transport and accumulation of copper ions on the time to failure of dielectrics was extended here to include metallic barriers and the effect of an elastic drift term. The results of the model were compared with experimental data on the time to failure of SiO2 dielectrics that included Ru(P) and TaN barriers. Excellent agreement was found, and the success of the Ru(P) compared to the TaN barrier was attributed to the former's lower copper ion solubility and diffusivity. There is a change in the value of the field acceleration parameter (?) with barriers that leads to an increase in the projected lifetime. We link this change in ? to a number of factors including the transport of oxidizing species through the barrier responsible for copper ion formation, and the injection and motion of electrons and holes, which are altered in the presence of a barrier between the metal and dielectric.

Achanta, Ravi S.; Gill, William N.; Plawsky, Joel L.

2009-10-01

297

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

298

Ion acoustic mode in permeating plasmas  

NASA Astrophysics Data System (ADS)

In the presence of an electron drift relative to ions, the ion acoustic wave is subject to the kinetic instability which takes place if the directed electron speed exceeds the ion acoustic speed. The instability threshold is very different in the case of one quasi-neutral electron-ion plasma propagating through another quasi-neutral (target) plasma. The threshold velocity of the propagating plasma may be well below the ion acoustic speed of the static plasma.

Vranjes, J.; Poedts, S.

2014-05-01

299

Hybrid simulation of ion cyclotron resonance in the solar wind: Evolution of velocity distribution functions  

Microsoft Academic Search

Resonant interaction between ions (oxygen ions O+5 and protons) and ion cyclotron waves is investigated using a one dimensional hybrid code. Ion cyclotron waves are self-consistently generated by an ion cyclotron anisotropy instability. We focus on the detailed acceleration process of ions. The energization of oxygen ions due to waves is found to have two stages. During the first stage,

Xing Li; Shadia R. Habbal

2005-01-01

300

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

301

Bifurcations of dust ion acoustic travelling waves in a magnetized dusty plasma with a q-nonextensive electron velocity distribution  

SciTech Connect

Nonlinear ion acoustic waves in the magnetized dusty plasma in the presence of superthermal electron have been studied. We have used the reductive perturbation method to derive a Kadomtsev-Petviashili equation for dust ion acoustic waves in a magnetized dusty plasma with q-nonextensive velocity distributed electrons. By applying the bifurcation theory of planar dynamical systems to this equation, the existence of solitary wave solutions and periodic travelling wave solutions is proved. Two exact solutions of the above waves are obtained.

Kumar Samanta, Utpal [Department of Mathematics, Bankura Christian College, Bankura, West Bengal (India); Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiniketan (India); Saha, Asit [Department of Mathematics, Sikkim Manipal Institute of Technology, Majitar, Rangpo, East-Sikkim (India); Chatterjee, Prasanta [Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiniketan (India)

2013-02-15

302

Measurements of mean initial velocities of analyte and matrix ions in infrared matrix-assisted laser desorption ionization mass spectrometry  

Microsoft Academic Search

The mean initial velocities of analyte ions ranging in molecular weight from 1000 Da to 150 kDa and desorbed with a pulsed\\u000a Er:YAG laser from various solid-state and liquid IR MALDI matrices were measured along with those of the matrix ions. Experiments\\u000a with UV MALDI were performed for comparison in addition for a 2,5-dihydroxybenzoic acid preparation. Two different measurement\\u000a principles

Stefan Berkenkamp; Christoph Menzel; Franz Hillenkamp; Klaus Dreisewerd

2002-01-01

303

Study of the drift energies to localise the ring current: a comparison between the terrestrial and the kronian magnetosphere.  

NASA Astrophysics Data System (ADS)

In the Earth magnetosphere, a ring current can be observed in the dipolar region, between 2 and 9 RE. In the inner magnetosphere, the low energy particles (ions and electrons) corotate. Due to the gradient and the curvature of the field lines, the dipolar magnetic field influences the movement of the particles. Gradient and curvature are responsible of the existence of drift velocities perpendicular to the magnetic field lines. Above limit energy, the total drift velocity will be higher than the corotation velocity. Due to the orientation of the terrestrial magnetic field, the ions drift velocity is directed in an opposite direction than the corotation direction, and the electron drift velocity is directed in the same direction than the corotation direction. This explain the existence of the ring current. The same phenomenon can exist in the kronian magnetosphere. To localise this ring current it is necessary to determine the limit energy in the different part of the magnetosphere. In this paper, we will map the limit energy in the kronian magnetosphere and study the contribution of the different drift movements to this energy. Looking at the similarities and the differences between the Earth and the kronian magnetosphere, we'll present a comparative study. This work will give important information to study the kronian ring current. It also will be a start of a ring current model for the kronian magnetosphere.

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

2008-12-01

304

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

NASA Astrophysics Data System (ADS)

The dynamics of ions traversing sheaths in low temperature plasmas are important to the formation of the ion energy distribution incident onto surfaces during microelectronics fabrication. Ion dynamics have been measured using laser-induced fluorescence (LIF) in the sheath above a 30 cm diameter, 2.2 MHz-biased silicon wafer in a commercial inductively coupled plasma processing reactor. The velocity distribution of argon ions was measured at thousands of positions above and radially along the surface of the wafer by utilizing a planar laser sheet from a pulsed, tunable dye laser. Velocities were measured both parallel and perpendicular to the wafer over an energy range of 0.4-600 eV. The resulting fluorescence was recorded using a fast CCD camera, which provided resolution of 0.4 mm in space and 30 ns in time. Data were taken at eight different phases during the 2.2 MHz cycle. The ion velocity distributions (IVDs) in the sheath were found to be spatially non-uniform near the edge of the wafer and phase-dependent as a function of height. Several cm above the wafer the IVD is Maxwellian and independent of phase. Experimental results were compared with simulations. The experimental time-averaged ion energy distribution function as a function of height compare favorably with results from the computer model.

Moore, Nathaniel B.; Gekelman, Walter; Pribyl, Patrick; Zhang, Yiting; Kushner, Mark J.

2013-08-01

305

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

306

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

307

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

308

Dynamics of pickup ion velocity distribution in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS's observations  

NASA Astrophysics Data System (ADS)

The 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 also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. The simulations are based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the T9 flyby through the induced magnetic tail of Titan [1]. In our model the background ions, all pickup ions, 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. The temperature of the background electrons and pickup electrons was also included into the generalized Ohm's law. 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. We consider two models for the upstream composition: (a) only magnetospheric H+ and H2+, (b) only H+ and H2+ pickup ions. In our hybrid simulations we use Chamberlain profiles for the exosphere's components. We also include a simple ionosphere model with M=28 ions that were generated inside the ionosphere. The moon is considered as weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS's T9 (events 1 and 2) observations. We also compare our realistic 3D kinetic simulation with a 1D kinetic simulation that was performed with a fine spatial resolution [2]. References [1] 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. [2] Cowee, M.M., Tokar, R.L., Gary S.P., Wei, H.Y., Russell, C.T., and Sittler, E.C., 2009. 1D Hybrid Simulations of Ion Cyclotron Wave Generation by Pickup Ions at Titan, Fall AGU 2009 Meeting, 14-18 Dec., 2009, San Francisco, CA.

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

2010-12-01

309

Background and pickup ion velocity distribution dynamics in Titan's plasma environment: 3D hybrid simulation and comparison with CAPS's observations  

NASA Astrophysics Data System (ADS)

The wave-particle interactions play 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 distri-bution also plays a key role for understanding the observed particle fluxes. In this report we discuss the ion velocity distribution dynamics from the 3D hybrid simulation. The simulations are based on recent analysis of the Cassini Plasma Spectrometer (CAPS) ion measurements during the T9 and T18 flybys through the induced magnetic tail of Titan [1]. In our model the background ions, all pickup ions, 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. The temperature of the background electrons and pickup electrons was also included into the generalized Ohm's law. 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. + We consider two models for the upstream composition: (a) only magnetospheric H + and H2 , + + (b) only H and H2 pickup ions. In our hybrid simulations we use Chamberlain profiles for the exosphere's components. We also include a simple ionosphere model with M = 28 ions that were generated inside the ionosphere. The moon is considered as weakly conducting body. Special attention will be paid to comparing the simulated pickup ion velocity distribution with CAPS's T9 and T18 observations. We also compare our realistic 3D kinetic simulation with 1D kinetic simulation that was performed with a fine spatial resolution [2]. References 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. [2] Cowee, M.M., Tokar, R.L., Gary S.P., Wei, H.Y., Russell, C.T., and Sittler, E.C., 2009. 1D Hybrid Simulations of Ion Cyclotron Wave Generation by Pickup Ions at Titan, Fall AGU 2009 Meeting, 14-18 Dec., 2009, San Francisco, CA.

Lipatov, Alexander; Sittler, Edward; Hartle, Richard; Simpson, David

310

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

311

Broadband Velocity Modulation Spectroscopy of Molecular Ions for Use in the Jila Electron Edm Experiment  

NASA Astrophysics Data System (ADS)

The JILA electron electric dipole moment (eEDM) experiment will use a low-lying, metastable ^3?_1 state in trapped molecular ions of HfF^+ or ThF^+. Prior to this work, the low-lying states of these molecules had been investigated by PFI-ZEKE spectroscopy. However, there were no detailed studies of the electronic structure. The recently developed technique of frequency comb velocity modulation spectroscopy (VMS) provides broad-bandwidth, high-resolution, ion-sensitive spectroscopy, allowing the acquisition of 150 cm^{-1} of continuous spectra in 30 minutes over 1500 simultaneous channels. By supplementing this technique with cw-laser VMS, we have investigated the electronic structure of HfF^+ in the frequency range of 9950 to 14600 cm^{-1}, accurately fitting and assigning 16 rovibronic transitions involving 8 different electronic states including the X^1?^+ and a^3?_1 states. In addition, an observed ^3?_{0+} state with coupling to both the X and a states has been used in the actual eEDM experiment to coherently transfer population from the rovibronic ground state of HfF^+ to the eEDM science state. Furthermore, we report on current efforts of applying frequency comb VMS at 700 - 900 nm to the study of ThF^+, which has a lower energy ^3?_1 state and a greater effective electric field, and will provide increased sensitivity for a measurement of the eEDM. A. E. Leanhardt et. al., Journal of Molecular Spectroscopy 270, 1-25 (2011). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, Journal of Chemical Physics 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, Physical Review Letters 107, 093002 (2011). K.C. Cossel et. al., Chemical Physics Letters 546, 1-11 (2012).

Gresh, Daniel N.; Cossel, Kevin C.; Cornell, Eric A.; Ye, Jun

2013-06-01

312

A velocity map ion imaging study of difluorobenzene-water complexes: Binding energies and recoil distributions  

NASA Astrophysics Data System (ADS)

The binding energies of the p-, m-, and o-difluorobenzene-H2O complexes have been measured by velocity map ion imaging to be 922+/-10, 945+/-10, and 891+/-4 cm-1, respectively. The lack of variation provides circumstantial evidence for water binding to the three isomers via the same interaction, viz. an in-plane O-H...F hydrogen bond to one of the fluorine atoms on the ring, with a second, weaker interaction of the water O atom with an ortho hydrogen, as determined previously for the p-difluorobenzene-H2O complex [Kang et al., J. Phys. Chem. A 109, 767 (2005)]. The ground state binding energies for the difluorobenzene-H2O complexes are ~5%-11% larger than that for benzene-H2O, where binding occurs to the ? electrons out-of-plane. However, in the S1 state the binding energies of the o- and p-difluorobenzene-H2O complexes are smaller than the benzene-H2O value, raising an interesting question about whether the geometry at the global energy minimum remains in-plane in the excited electronic states of these two complexes. Recoil energy distributions for dissociation of p-difluorobenzene-H2O have been measured from the 31, 52, and 3151 levels of the excited electronic state. These levels are 490, 880, and 1304 cm-1, respectively, above the dissociation threshold. Within the experimental uncertainty, the recoil energy distributions are the same for dissociation from these three states, with average recoil energies of ~100 cm-1. These recoil energies are 60% larger than was observed for the dissociation of p-difluorobenzene-Ar, which is a substantially smaller increase than the 400% seen in a comparable study of dissociation within the triplet state for pyrazine-Ar, -H2O complexes. The majority of the available energy is partitioned into vibration and rotation of the fragments.

Bellm, Susan M.; Moulds, Rebecca J.; van Leeuwen, Matthew P.; Lawrance, Warren D.

2008-03-01

313

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

314

Ion-wind effects on Poiseuille and Blasius flow  

NASA Technical Reports Server (NTRS)

In order to study the effects of ion wind on the plane Poiseuille flow in a channel and Blasius flow on a flat plate, the equations of electrogasdynamics are solved numerically under the assumptions that the flow is incompressible, that the electric field is steady, and that the fluid velocity is negligible compared to ion drift velocity. The results show that ion wind strongly affects the skin-friction distribution for these flows.

Van Rosendale, J. R.; Malik, M. R.; Hussaini, M. Y.

1988-01-01

315

The effect of vertical drift on the equatorial F-region stability  

NASA Technical Reports Server (NTRS)

Time-dependent ionospheric model calculations for day-time and night-time solutions are presented. The behavior of the growth rate and ion-electron recombination rate for the Rayleigh-Taylor instability on the F-region bottomside is examined as a function of the vertical eastward electric field-magnetic field strength drift velocity. It is observed that on the bottomside F-layer the growth rate exceeds the ion-electron recombination rate even without vertical drift; however, an eastward electric field-magnetic field strength drift can produce an increase in the growth rate by an order of magnitude. The calculated data are compared with previous research and good correlation is detected. The formation of bubbles from a seeding mechanism is investigated.

Hanson, W. B.; Cragin, B. L.; Dennis, A.

1986-01-01

316

Sound velocity of glassy Pd{sub 80}Si{sub 20} after heavy-ion irradiation at low temperatures.  

SciTech Connect

Specimens of glassy Pd{sub 80}Si{sub 20} were irradiated at temperatures below 100K with 3.5 MeV krypton ions. After irradiation, changes in the sound velocity were measured at 80 K without warm-up by Brillouin scattering. The sound velocity decreased with increasing ion fluence and exponentially approached a saturation value of -4.7%. The change in the shear elastic modulus per unit concentration n of defects was estimated to be d(ln C)/dn = -9.4 to -4.7. The results of the present study are compared with changes in the elastic properties predicted recently by an interstitialcy model for glassy metals, and with the elastic properties of glassy metals after thermal treatment.

Schumacher, G.; Birtcher, R. C.; Renusch, D. P.; Grimsditch, M.; Rehn, L. E.; Materials Science Division

2002-01-01

317

Excitation of ion-acoustic-like waves by subcritical currents in a plasma having equal electron and ion temperatures.  

PubMed

The effect of a magnetic-field-aligned plasma flow with a transverse velocity gradient on the excitation of current-driven ion-acoustic-like waves in a plasma having equal electron and ion temperatures (T(e) = T(i)) was investigated experimentally. In agreement with theoretical predictions, the presence of sheared plasma flow substantially reduces the critical electron drift velocity needed to produce the ion-acoustic instability. PMID:11384478

Agrimson, E; D'Angelo, N; Merlino, R L

2001-06-01

318

Effect of Cross-Field Drifts and Core Rotation on Flows in the Main Scrape-Off Layer of DIII-D L-mode Plasmas  

SciTech Connect

The flow velocities of deuterons and low charge-state carbon ions have been measured simultaneously for the first time at the crown of the main SOL for low-density plasmas in DIII-D. The dependences of the flow fields on the direction of the cross-field drifts (E x B and B x {del}B) and core plasma rotation were investigated. The measurements indicate that the carbon ion flow direction and magnitude along the magnetic field lines are not necessarily determined by the deuteron flow field, but other physics must also play a role. The deuteron velocities at the plasma crown are high (20-30 km/s) in configurations with the ion B x {del}B drift toward the divertor X-point, while nearly zero in configurations with the opposite B x {del}B drift direction. The flow velocities of doubly charged carbon ions are independent of the ion B x {del}B drift direction, and the measurements suggest a stagnation point in the flow field at the crown of the plasma. Both deuteron and carbon ion flow velocities in the SOL were found to be independent of the direction of core plasma rotation. Simulations with the UEDGE code have been carried out to better understand the underlying physics processes. Including the cross-field drifts in the simulations produced divertor solutions that are in significantly closer agreement with the measurements. They do not, however, reproduce the measured flow fields at the crown for the configuration with the ion B x {del}B drift toward the divertor X-point.

Groth, M; Boedo, J A; Brooks, N H; Isler, R C; Leonard, A W; Porter, G D; Watkins, J G; West, W P; Bray, B D; Fenstermacher, M E; Groebner, R J; Moyer, R A; Rudakov, D L; Yu, J H; Zeng, L

2008-10-13

319

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.

320

Electron Capture and Drift in Polyatomic Gases.  

National Technical Information Service (NTIS)

Electron drift velocities and lateral diffusion coefficients for a number of polyatomic gases were employed to determine mobilities, mean fractional energy losses per collision, stopping rates, derivatives of stopping rates with respect to the mean electr...

K. S. Gant

1976-01-01

321

Kinetics of copper drift in PECVD dielectrics  

Microsoft Academic Search

We quantified the drift of Cu ions into various PECVD dielectrics by measuring shifts in capacitance-voltage behavior after subjecting Cu-gate MOS capacitors to bias-temperature stress. At a field of 1.0 MV\\/cm and temperature of 100°C, Cu ions drift readily into PECVD oxide with a projected accumulation of 2.7×1013 ions\\/cm 2 after 10 years. However, in PECVD oxynitride, the projected accumulation

Alvin L. S. Loke; Changsup Ryu; C. Patrick Yue; James S. H. Cho; S. Simon Wong

1996-01-01

322

Mobilities of Mass-Identified H3+ and H+ Ions in Hydrogen.  

National Technical Information Service (NTIS)

The drift velocities of mass identified H3(+) and H(+) ions in hydrogen gas at room temperature were measured. The H3(+) ions were found to be in thermal equilibrium with the gas at E/po less than about 10 V/cm-Torr; the H(+) ions, at E/po less than about...

D. L. Albritton T. E. Miller D. W. Martin E. W. McDaniel

1967-01-01

323

The Mobilities of Mass-Identified H3(+) And H(+) Ions in Hydrogen.  

National Technical Information Service (NTIS)

The drift velocities of mass-identified H3(+) and H(+) ions in hydrogen gas at room temperature were measured. The H3(+) ions were found to be in thermal equilibrium with the gas at E/p sub o less than about 10 V/cm Torr and H(+) ions at E/p sub o less th...

D. L. Albritton T. M. Miller D. W. Martin E. W. McDaniel

1968-01-01

324

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

325

Development of pitch angle anisotropy and velocity diffusion of pickup ion shell distribution by solar wind turbulence  

NASA Technical Reports Server (NTRS)

The evolution of pitch angle anisotropy in initially isotropic spherical shell distribution of pickup ions subjected to a continuous influence of weak or moderate intrinsic solar wind turbulence is investigated using a physical model which assumes that the wave of the solar wind turbulence is propagating mainly in the direction parallel to the ambient magnetic field. It is shown that, because of the pitch angle dependence of the velocity diffusion process, a significant pitch angle anisotropy of pickup ion shell distribution develops in the early stage of the diffusion process. Although it is smeared out later on, the result can be of significant importance, especially if the pickup ion density is large, because the pitch angle anisotropy can excite collective instabilities and increase the wave level, thus accelerating the diffusion process.

Yoon, Peter H.; Ziebell, L. F.

1990-01-01

326

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

327

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

NASA Astrophysics Data System (ADS)

Hall plasma devices with electron E × B drift are subject to a class of long wavelength instabilities driven by the electron current, gradients of plasma density, temperature, and magnetic field. In the first companion paper [Frias et al., Phys. Plasmas 19, 072112 (2012)], the theory of these modes was revisited. In this paper, we apply analytical theory to show that modern Hall thrusters exhibit azimuthal and axial oscillations in the frequency spectrum from tens KHz to few MHz, often observed in experiments. The azimuthal phase velocity of these modes is typically one order of magnitude lower than the E × B drift velocity. The growth rate of these modes scales inversely with the square root of the ion mass, ~1/mi. It is shown that several different thruster configurations share the same common feature: the gradient drift instabilities are localized in two separate regions, near the anode and in the plume region, and absent in the acceleration region. Our analytical results show complex interaction of plasma and magnetic field gradients and the E × B drift flow as the sources of the instability. The special role of plasma density gradient is revealed and it is shown that the previous theory is not applicable in the region where the ion flux density is not uniform. This is particularly important for near anode region due to ionization and in the plume region due to diverging ion flux.

Frias, Winston; Smolyakov, Andrei I.; Kaganovich, Igor D.; Raitses, Yevgeny

2013-05-01

328

Development of Frequency Comb Velocity-Modulation Spectroscopy, Spectroscopy of Hafnium Fluoride Ion (+) and the JILA eEDM Experiment  

NASA Astrophysics Data System (ADS)

Broad bandwidth, precision spectroscopy of the molecular ions of interest to the JILA electron electric dipole moment experiment, HfF+ and ThF+, is necessary due to the limited amount of spectroscopic information available and the large theoretical uncertainties in the energy level structure (thousands of wavenumbers). This thesis covers the development of a novel spectroscopic technique, frequency comb velocity-modulation spectroscopy, that provides high resolution, broad spectral bandwidth, ion discrimination and high sensitivity simultaneously. Frequency comb velocity-modulation spectroscopy as well as single-frequency velocity-modulation spectroscopy have been used to identify five rotational bands of HfF+. This work discusses the first spectroscopic information for HfF+ which came from our measurement of the 1pi1 -- 1Sigma+ (0,0) band recorded with single-frequency velocitymodulation spectroscopy with a sensitivity of 3x10-7 Hz-1/2. The development of frequency comb velocity-modulation spectroscopy allowed us to cover a thousand wavenumbers of spectral bandwidth and to identify an additional four HfF + bands. The achieved sensitivity for frequency-comb velocity-modulation spectroscopy was 4x10-8 Hz-1/2 (spectral element) -1/2 with 1500 simultaneous detection channels spanning 150 cm -1 of bandwidth. For a 30 minute acquisition time using 30 interleaved images to densely sample the whole spectrum, this corresponded to a 3x10 -7 single-pass fractional absorption sensitivity for each of the 45,000 measurement channels. The spectroscopic information from all five HfF + rotational bands is presented and molecular constants for the 1Sigma+, 3pi1, and 1pi1 states were extracted.

Sinclair, Laura C.

329

Upper bound estimates of anomalous ion production in space-based critical ionization velocity experiments  

SciTech Connect

The authors model sounding rocket gas release experiments in the ionosphere, to study the apparant lack of observation of critical ionization velocity phenomena in space plasmas. Laboratory evidence has been seen for the occurance of critical ionization velocity effects. Their simulations indicate that in space plasmas it is necessary to have some type of a seed ionization process to initiate the process, and mechanisms such as charge exchange are too slow to accomplish this.

Biasca, R.; Hastings, D.; Cooke, D. [Hanscom Air Force Base, MA (United States)

1993-10-01

330

F Region East-West Drifts at Jicamarca  

Microsoft Academic Search

F region east-west drifts have observations with other related data (such as the been measured at Jicamarca for almost 10 years, Indian results) and with available theory. using incoherent scatter. The drifts are west- ward during the day and eastward at night. The Measurement Techniques daytime drift velocities are about 50 m\\/s and change very little with season or solar

B. G. Fejer; D. T. Farley; C. A. Gonzales; R. F. Woodman; C. Calderon

1981-01-01

331

Temporal evolution of confined fast-ion velocity distributions measured by collective Thomson scattering in TEXTOR  

Microsoft Academic Search

Fast ions created in the fusion processes will provide up to 70% of the heating in ITER. To optimize heating and current drive in magnetically confined plasmas insight into fast-ion dynamics is important. First measurements of such dynamics by collective Thomson scattering (CTS) were recently reported [Bindslev , Phys. Rev. Lett. 97, 205005 2006]. Here we extend the discussion of

S. K. Nielsen; H. Bindslev; L. Porte; J. A. Hoekzema; S. B. Korsholm; F. Leipold; F. Meo; P. K. Michelsen; S. Michelsen; J. W. Oosterbeek; E. L. Tsakadze; G. van Wassenhove; E. Westerhof; P. Woskov

2008-01-01

332

Suppressing drift chamber diffusion without magnetic field  

NASA Astrophysics Data System (ADS)

The spatial resolution in drift chamber detectors for ionizing radiation is limited by diffusion of the primary electrons. A strong magnetic field along the drift direction is often applied (Fancher et al., Nucl. Instr. and Meth. A 161 (1979) 383) because it suppresses the transverse diffusion, improving the resolution but at considerable increase in cost and complexity. Here we show that transverse track diffusion can be strongly suppressed without any magnetic field. This is achieved by using a gas additive which reversibly captures primary ionization electrons, forming negative ions. The ions drift with thermal energies even at very high drift fields and low pressures ( E/P=28.5 V/ cm torr), and the diffusion decreases with increasing drift field. Upon arrival at the avalanche region of the chamber the negative ions are efficiently stripped and ordinary avalanche gain is obtained. Using this technique, r.m.s. transverse diffusion less than 200 ?m has been achieved over a 15 cm drift path at 40 torr with zero magnetic field. The method can provide high spatial resolution in detectors with long drift distances and zero magnetic field. Negative ion drift chambers would be particularly useful at low pressures and in situations such as space-based or underground experiments where detector size scaleability is important and cost, space, or power constraints preclude the use of a magnetic field.

Martoff, C. J.; Snowden-Ifft, D. P.; Ohnuki, T.; Spooner, N.; Lehner, M.

2000-02-01

333

A comparison of ion velocity measurements from retarding field energy analyzer (RFEA) and laser induced fluorescence (LIF) in expanding helicon plasma  

NASA Astrophysics Data System (ADS)

We present a comparison of ion velocity measurements from RFEA and LIF where we specially focus on the ability to diagnose flow and ion beams due to current free double layers in expanding helicon plasma. An RFEA in a plasma will be surrounded by a sheath so the velocities measured by the RFEA will be the velocities of the ions after they have been accelerated by the sheath and any potential drops inside the probe. Different methods exist to relate the velocities measured by the RFEA to the velocities in the plasma. Most of them include some simple assumptions about the acceleration in the sheath. We will compare measurements from two different RFEAs, one with a grounded front grid and one with a floating front grid, with LIF measurements to assess the validity of these simple models.

Gulbrandsen, Njål; Fredriksen, Åshild; Carr, Jerry, Jr.; Scime, Earl; McCarren, Dustin W.; Vandervort, Robert; Galante, Matthew E.; Magee, Richard M.; Lusk, Greg; Sears, Stephanie H.; Miloch, Wojciech J.

2012-10-01

334

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

335

Spherical and Cylindrical Ion Acoustic Shock Structures in Plasmas with q-Nonextensive Electron Velocity Distribution  

NASA Astrophysics Data System (ADS)

The propagation of ion acoustic shock waves in cylindrical and spherical geometries has been investigated. The plasma system consists of cold ions, nonextensive electrons and thermal positrons. Spherical and cylindrical Korteweg-de Vries-Burger equations have been derived by reductive perturbation method and their shock behavior is studied by employing finite difference method. It is found that shock waves can be produced in this medium. The important effects of the q-nonextensive electron on the properties of ion acoustic waves are discussed. Furthermore, it is observed that the positron concentration, ratio of electron to positron temperature, geometry parameter and the plasma kinematic viscosity significantly modifies the shock structure.

Eslami, Parvin; Pakzad, Hamid Reza; Mottaghizadeh, Marzieh

2012-12-01

336

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

337

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

338

A comparison of velocity measurements from the CUTLASS Finland radar and the EISCAT UHF system  

NASA Astrophysics Data System (ADS)

The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift velocity and F-region ion velocity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of velocity signatures including that characteristic of the convection reversal and a rapidly fluctuating velocity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the velocity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.

Davies, J. A.; Lester, M.; Milan, S. E.; Yeoman, T. K.

1999-07-01

339

Zero Electron Kinetic Energy/Velocity Map Imaging (ZEKE/VMI) Spectroscopy of Negative Ions.  

National Technical Information Service (NTIS)

Construction of the slow photoelectron, velocity-map imaging (SEVI) instrument was completed and the first results were obtained, demonstrating the power of the technique in measuring high-resolution (approx. 0.5 meV) photodetachment spectra of negative i...

D. M. Neumark

2004-01-01

340

Scattering of electromagnetic waves by drift modes  

NASA Astrophysics Data System (ADS)

It is shown that high-frequency electromagnetic waves can parametrically excite the convection and ion drift waves in a slightly inhomogeneous magnetized plasma. The growth rates of the nonlinear decay instabilities are obtained analytically.

Shukla, P. K.; Yu, M. Y.; El-Nadi, Adel

1984-12-01

341

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

NASA Astrophysics Data System (ADS)

We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, Te ~ 4 eV and n ~ 5 × 1011 cm-3). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 × 109 cm-3 to 1 × 1013 cm-3 and target species temperatures less than 20 eV.

Chakraborty Thakur, Saikat; McCarren, Dustin; Carr, Jerry; Scime, Earl E.

2012-02-01

342

Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma.  

PubMed

We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, T(e) ? 4 eV and n ? 5 × 10(11) cm(-3)). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 × 10(9) cm(-3) to 1 × 10(13) cm(-3) and target species temperatures less than 20 eV. PMID:22380092

Chakraborty Thakur, Saikat; McCarren, Dustin; Carr, Jerry; Scime, Earl E

2012-02-01

343

The Steady Drift of an Incompressible  

Microsoft Academic Search

The steady drift of pack ice in an idealized arctic basin has been calculated by assuming that the ice is incompressible and inviscid. The momentum and continuity equations tbr the ice are solved tbr the velocity and the ice pressure. The divergence of velocity is assumed to be 0.33 X 10 -5 s -. The boundary conditions require that no

D. A. ROTHROCK

1975-01-01

344

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

345

Drifting of honeybees  

Microsoft Academic Search

Summary: Drifting of honeybees depends on the arrangement, the colouring of the hives and on various environmental factors. Bees are able to distinguish between related and non-related individuals, so one aim of this study was to determine whether drifting also depends on relatedness. In addition we wanted to examine whether there are differences in survival of drifted bees and non-drifted

K. J. Pfeiffer; K. Crailsheim

1998-01-01

346

Diffusion behavior of chloride ions in concrete  

Microsoft Academic Search

In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations

Tiewei Zhang; Odd E. Gjørv

1996-01-01

347

Electrostatic drift vortices in quantum magnetoplasmas  

SciTech Connect

A nonlinear equation similar to the Hasegawa-Mima equation for drift waves in dense quantum plasmas has been obtained. Therefore, electrostatic drift vortices can appear in nonuniform dense magnetoplasmas. These nonlinear structures can be of dipolar form as well as street-type vortices. It is noticed that these structures are formed on very short spatial scales. Further, it is discussed that quantum drift waves can couple with quantum ion acoustic waves, like classical plasmas, if the ion parallel dynamics is also considered.

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

2008-09-15

348

Hybrid simulations of the termination shock: Suprathermal ion velocity distributions in the heliosheath  

Microsoft Academic Search

The Los Alamos hybrid simulation code is used to examine kinetic properties of pickup ions at the heliospheric termination shock and in the downstream heliosheath. All simulations are one-dimensional in spatial variations, represent the electrons as a zero-mass fluid, and address only perpendicular shocks. Interpretation of measurements from the IBEX and Voyager spacecraft depend sensitively on the properties of the

Pin Wu; Kaijun Liu; Dan Winske; S. Peter Gary; Nathan A. Schwadron; Herbert O. Funsten

2010-01-01

349

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

350

Detailed Measurements of Ion Anisotropies by the Cassini INCA Experiment and Calculated Convection Velocities in Saturn's Magnetosphere  

NASA Astrophysics Data System (ADS)

The Ion and Neutral Camera (INCA), part of a cluster of instruments on the Cassini spacecraft, measures intensities of hydrogen and oxygen ions and neutral atoms in the Saturnian magnetosphere. We use the measured intensity spectrum and anisotropy of hot hydrogen and oxygen ions to calculate the plasma bulk velocity. We find that, throughout a wide region of this magnetosphere, the bulk plasma is capable of nearly rigid co-rotation within Titan's orbit, beyond which the bulk flow falls increasingly further behind the rigid rate. The anisotropies are sometimes characterized well by convecting isotropic populations, but at other times are not. In some cases time aliasing due to a dynamic or inhomogeneous ion population convecting past the spacecraft prevents such a calculation. However, we have performed calculations in a wide region of the magnetosphere, where some ion populations are nearly isotropic in their convection frame. We find that, in the dawn and dusk regions, convection approaching rigid co-rotation speeds can be maintained out to the vicinity of the Titan orbit. We have examined equatorial orbits as well as data at low to moderate latitudes in the dusk side. Thus far, we find no evidence for a dusk side depression similar to that found within Jupiter's magnetosphere. We have performed calculations at low to moderate latitudes within orbits highly inclined to Saturn's equatorial plane on the night side and find evidence of convection at substantial fractions of the rigid co-rotation as determined by the given L-shell equatorial distance, consistent with the pattern found within equatorial orbits. We find evidence of similar behavior in the day side region.

Kane, M.; Mitchell, D. G.; Carbary, J. F.; Krimigis, S. M.

2008-12-01

351

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

352

Ionization of highly charged iodine ions in collisions near the Bohr velocity  

NASA Astrophysics Data System (ADS)

The L-shell X-rays of iodine induced by 3MeV Iq+(q=20,22,25,26) ions impacting on Fe target were measured. The results indicated that, in addition to the ionization of L-shell, the projectile M- and N-shell were multiply ionized. The ratios of the sub-shell X-ray relative intensity were also investigated.

Xianming, Zhou; Yongtao, Zhao; Rui, Cheng; Jieru, Ren; Yu, Lei; Yuanbo, Sun; Yuyu, Wang; Shidong, Liu; Ge, Xu; Guoqing, Xiao

2014-04-01

353

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

354

Measurements of HNO3 and N2O5 using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign  

NASA Astrophysics Data System (ADS)

An ion drift-chemical ionization mass spectrometer (ID-CIMS) was deployed in Mexico City between 7 and 31 March to measure gas-phase nitric acid (HNO3) and dinitrogen pentoxide (N2O5 during the Mexico City Metropolitan Area (MCMA)-2006 field campaign. The observation site was located at the Instituto Mexicano del Petróleo in the northern part of Mexico City urban area with major emissions of pollutants from residential, vehicular and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and early morning. The concentration of HNO3 increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and then declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good agreement between the two HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with submicron-sized aerosol nitrate, suggesting that the gas-particle partitioning process was a major factor in determining the gaseous HNO3 concentration. Losses by irreversible reactions with mineral dust and via dry deposition also could be important at this site. Most of the times during the MCMA 2006 field campaign, N2O5 was found to be below the detection limit (about 30 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio at the surface (>100 ppb) during the night. An exception occurred on 26 March 2006, when about 40 ppt N2O5 was observed during the late afternoon and early evening hours under cloudy conditions before the build-up of NO at the surface site. The results revealed that during the MCMA-2006 field campaign HNO3 was primarily produced from the reaction of OH with NO2 and regulated by gas/particle transfer and dry deposition. The production of HNO3 from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

Zheng, J.; Zhang, R.; Fortner, E. C.; Volkamer, R. M.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gaeggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

2008-11-01

355

Measurements of HNO3 and N2O5 using Ion drift - Chemical Ionization Mass Spectrometry during the MCMA - 2006 Campaign  

NASA Astrophysics Data System (ADS)

An ion drift - chemical ionization mass spectrometry (ID-CIMS) was deployed in Mexico City between 5 and 31 March to measure HNO3 and N2O5 during the 2006 Mexico City Metropolitan Area (MCMA) field campaign. The observation site, T0, was located at the Instituto Mexicano del Petróleo at the center of the Mexico City Basin with major emissions of pollutants from both domestic and industrial sources. Diurnally, HNO3 was less than 200 parts per trillion (ppt) during the night and in the early morning, increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good correlation in the HNO3 measurements (R2=0.75). The HNO3 mixing ratio was found to anti-correlate with aerosol nitrate, suggesting that the gaseous HNO3 concentration was controlled by the gas-particle partitioning process. During most times of the MCMA 2006 field campaign, N2O5 was found to be under the detection limit (about 20 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio (>100 ppb) during the night. With one exception on 26 March 2006, about 40 ppt N2O5 was observed during the late afternoon and early evening hours under a cloudy condition, before NO built up at the surface site. The results revealed that during the 2006 MCMA field campaign HNO3 was primarily produced by the reaction of OH with NO2 and regulated by gas/particle partitioning, and HNO3 production from N2O5 hydrolysis during the nighttime was small because of high NO and low O3 concentrations near the surface.

Zheng, J.; Zhang, R.; Fortner, E. C.; Molina, L.; Aiken, A. C.; Jimenez, J. L.; Gäggeler, K.; Dommen, J.; Dusanter, S.; Stevens, P. S.; Tie, X.

2008-03-01

356

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

357

Local Drift Parameter, j/n/sub e/ and Resistivity Anomaly Measurements in CTX Spheromaks.  

National Technical Information Service (NTIS)

The ratio of the electron drift velocity to the electron thermal velocity, also known as the drift parameter (streaming parameter), and j/n/sub e/(approx.V/sub d/) have been measured locally at the magnetic axis in CTX spheromaks at Los Alamos. The drift ...

H. W. Hoida C. W. Barnes I. Henins T. R. Jarboe C. J. Buchenauer

1985-01-01

358

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

359

Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-Resonance Waves in Tokamaks  

SciTech Connect

The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q=1 surface resides within a narrow region centered about the shifted fundamental cyclotron resonance.

Graves, J. P.; Coda, S. [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association EURATOM-Confederation Suisse, 1015 Lausanne (Switzerland); Chapman, I. [UKAEA/Euratom Fusion Association, Culham Science Centre, Abingdon (United Kingdom); Eriksson, L.-G. [Association EURATOM-CEA, CEA/DSM/IRFM, CEA-Cadarache, F-13108 St. Paul lez Durance (France); Johnson, T. [Euratom-VR Association, EES, KTH, Stockholm (Sweden)

2009-02-13

360

Intermediate-velocity atomic collisions. IV. Ar K-shell ionization and capture by C5+ and C6+ ions  

NASA Astrophysics Data System (ADS)

Ar K x rays produced by 22- and 42-MeV C5+ and C6+ ions were measured in coincidence with the various emergent charge states resulting from the collision process. Single-electron K-shell capture and ionization cross sections are obtained through an analysis based on the independent-particle model (IPM). The comparison among various theoretical models and the present experiment shows that the present theoretical description of the electron capture is more precarious than that of ionization in the intermediate-velocity regime studied. The IPM analysis also allows one to obtain estimates of the probability of C5+ electron loss for small-impact-parameter collisions.

Montenegro, E. C.; Xu, Xiang-Yuan; Meyerhof, W. E.; Anholt, R.

1988-10-01

361

A NOVEL X-RAY IMAGING CRYSTAL SPECTROMETER FOR DOPPLER MEASUREMENTS OF ION TEMPERATURE AND PLASMA ROTATION VELOCITY PROFILES  

SciTech Connect

A new type of X-ray imaging crystal spectrometer has been implemented on Alcator CMod for Doppler measurements of ion temperature and plasma rotation velocity profiles. The instrument consists of two spherically bent (102)-quartz crystals with radii of curvature of 1444 and 1385 mm and four 'PILATUS II' detector modules. It records spectra of He-like argon from the entire, 72 cm high, elongated plasma cross-section and spectra of H-like argon from a 20 cm high, central region of the plasma, with a spatial resolution of 1.3 cm and a time resolution of less than 20 ms. The new spectrometer concept is also of interest for the diagnosis of burning plasmas on future machines. This paper presents recent experimental results from Aclator C-Mod and discusses challenges in X-ray spectroscopy for the diagnosis of fusion plasmas on future machines.

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

2008-06-06

362

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

363

Parallel ion velocity shear driven electromagnetic fluctuations and associated particle transport in partially ionized plasmas  

NASA Astrophysics Data System (ADS)

A nonuniform partially ionized magnetized plasma is shown to be unstable against electromagnetic perturbations. The source of free energy for the instability is sheared magnetic-field-aligned ion flow, which is coupled to the electromagnetic waves via charged particle-neutral collisions. Analytical expressions for the growth rate and threshold are obtained. Numerical studies for the ionospheric parameters suggest that electromagnetic waves grow faster than their electrostatic counterparts. Furthermore, linearly excited electromagnetic waves in partially ionized collisional plasmas are shown to cause nonthermal cross-field transport of plasma particles. The results can have relevance to the current filamentation and the plasma diffusion in the ionosphere of the Earth, as well as in low-temperature laboratory plasmas.

Shukla, P. K.; Mirza, Arshad M.; Faria, R. T.

1998-05-01

364

Comparison of measured and simulated fast ion velocity distributions in the TEXTOR tokamak  

NASA Astrophysics Data System (ADS)

Here we demonstrate a comprehensive comparison of collective Thomson scattering (CTS) measurements with steady-state Monte Carlo simulations performed with the ASCOT and VENUS codes. The measurements were taken at a location on the magnetic axis as well as at an off-axis location, using two projection directions at each location. The simulations agree with the measurements on-axis, but for the off-axis geometries discrepancies are observed for both projection directions. For the near perpendicular projection direction with respect to the magnetic field, the discrepancies between measurement and simulations can be explained by uncertainty in plasma parameters. However, the discrepancies between measurement and simulations for the more parallel projection direction cannot be explained solely by uncertainties in plasma parameters. Here anomalous fast ion transport is a possible explanation for the discrepancy.

Moseev, D.; Meo, F.; Korsholm, S. B.; Koskela, T.; Albergante, M.; Asunta, O.; Bindslev, H.; Bürger, A.; Furtula, V.; Kantor, M. Yu; Leipold, F.; Michelsen, P. K.; Nielsen, S. K.; Salewski, M.; Schmitz, O.; Stejner, M.; Westerhof, E.; TEXTOR Team

2011-10-01

365

Diffusion behavior of chloride ions in concrete  

SciTech Connect

In the present paper, an analysis of the diffusion behavior of chloride ions in concrete is presented. In concentrated electrolytic aqueous solutions such as seawater or that typically used in laboratory experiments, the effect of ionic interaction may significantly reduce the chemical potential and thus the driving force of the diffusing species. Because of different drift velocities of the cations and chloride ions in the solution, the lagging motion of the cations will also retard the drift velocity of the chlorides. In addition, both the electrical double layer forming on the solid surface and the chemical binding may significantly interfere with the transport of the chloride ions. As a result, the diffusion behavior of the chloride ions in concrete is a more complex and complicated transport process than what can be described by Fick`s law of diffusion.

Zhang, T.; Gjoerv, O.E. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials] [Norwegian Univ. of Science and Technology, Trondheim (Norway). Div. of Building Materials

1996-06-01

366

Profile Measurement of Ion Temperature and Toroidal Rotation Velocity with Charge Exchange Recombination Spectroscopy Diagnostics in the HL-2A Tokamak  

NASA Astrophysics Data System (ADS)

This paper deals with the profile measurement of impurity ion temperature and toroidal rotation velocity that can be achieved by using the charge exchange recombination spectrum (CXRS) diagnostics tool built on the HL-2A tokamak. By using CXRS, an accurate impurity ion temperature and toroidal plasma rotation velocity profile can be achieved under the condition of neutral beam injection (NBI) heating. Considering the edge effect of the line of CVI 529.06 nm (n = 8~7), which contains three lines (active exciting spectral line (ACX), passivity exciting spectral line (PCX) and electron exciting spectral line (ICE)), and using three Gaussian fitted curves, we obtain the following experimental results: the core ion temperature of HL-2A device is nearly thousands of eV, and the plasma rotation velocity reaches about 104 m · s-1. At the end of paper, some explanations are presented for the relationship between the curves and the inner physical mechanism.

Wu, Jing; Yao, Lieming; Zhu, Jianhua; Han, Xiaoyu; Li, Wenzhu

2012-11-01

367

Large amplitude double-layers in a dusty plasma with a q-nonextensive electron velocity distribution and two-temperature isothermal ions  

NASA Astrophysics Data System (ADS)

Arbitrary amplitude dust-acoustic (DA) double-layers in a plasma with nonextensive electrons, two-temperature thermal ions, and warm drifting dust grains are addressed. It is shown that DA double-layer structures, the onset of which depends sensitively on the plasma parameters, can exist. In particular, it may be noted that the electron nonextensivity may affect drastically the existence of these localized structures. In view of recent observation, our results should assist in the interpretation of the nonlinear double-layers observed in the downward current region of the aurora.

Roy, Kaushik; Saha, Taraknath; Chatterjee, Prasanta; Tribeche, Mouloud

2012-04-01

368

Critical Ionization Velocity (CIV) experiment XANI onboard the INTERCOSMOS 24 - ``ACTIVE'' satellite  

NASA Astrophysics Data System (ADS)

Satellite INTERCOSMOS-24 ``ACTIVE'' was launched on September 30 1989, with an initial apogee 2500 km, perigee 530 km and an orbital inclination of 82.2°. Under ``ACTIVE'' project, a wide number of plasma diagnostics instruments were especially designed to study the ionospheric response to high power VLF transmitter emissions, by means of satellite-subsatellite system during this mission. As a separate part of this project, a Critical Ionization Velocity (CIV) experiment called XANI (Xenon ANomalous Ionization) had been carried out to study neutral gas/plasma interaction processes in the ionosphere using neutral Xe gas injection. Seven Xe gas release experiments had been realized at daytime high latitude ionosphere. In this paper an Ion Drift Meter (IDM) and Retarding Potential Analyzer (RPA) data concerning transverse ion drift velocity vector measurements and total ion density variations during gas release experiment are shown. Two examples of the RPA data, taken after the beginning of Xe injection, show some prompt ionization at the ionization front about 30% in comparison with the background ion concentration. Horizontal ion drift of few hundred meters per second, transversal to the satellite velocity vector, had been observed at the ionization front.

Bankov, L.; Gousheva, M.; Lefterov, A.; Binev, G.; Vassileva, A.; Potanin, Yu.; Dubinin, E.

1993-10-01

369

NO+ formation pathways in dissociation of N2O+ ions at the C2Sigma+ state revealed from threshold photoelectron-photoion coincidence velocity imaging  

Microsoft Academic Search

Using the novel threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging technique, the dissociative photoionization of N2O molecule via the C2Sigma+ ionic state has been investigated. Four fragment ions, NO+, N2+, O+, and N+, are observed, respectively, and the NO+ and N+ ions are always dominant in the whole excitation energy range of the C2Sigma+ ionic state. Subsequently, the TPEPICO three-dimensional time-sliced

Xiaofeng Tang; Mingli Niu; Xiaoguo Zhou; Shilin Liu; Fuyi Liu; Xiaobin Shan; Liusi Sheng

2011-01-01

370

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

371

Toward a physics design for NDCX-II, an ion accelerator for warm dense matter and HIF target physics studies  

Microsoft Academic Search

The Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL), a collaborationof LBNL, LLNL, and PPPL, has achieved 60-fold pulse compression of ion beams on the Neutralized Drift Compression eXperiment (NDCX) at LBNL. In NDCX, a ramped voltage pulse from an induction cell imparts a velocity\\

A. Friedman; J. J. Barnard; R. J. Briggs; R. C. Davidson; M. Dorf; D. P. Grote; E. Henestroza; E. P. Lee; M. A. Leitner; B. G. Logan; A. B. Sefkow; W. M. Sharp; W. L. Waldron; D. R. Welch; S. S. Yu

2008-01-01

372

Reduction effect of neutral density on the excitation of turbulent drift waves in a linear magnetized plasma with flow  

SciTech Connect

The importance of reducing the neutral density to reach strong drift wave turbulence is clarified from the results of the extended magnetohydrodynamics and Monte Carlo simulations in a linear magnetized plasma. An upper bound of the neutral density relating to the ion-neutral collision frequency for the excitation of drift wave instability is shown, and the necessary flow velocity to excite this instability is also estimated from the neutral distributions. Measurements of the Mach number and the electron density distributions using Mach probe in the large mirror device (LMD) of Kyushu University [S. Shinohara et al., Plasma Phys. Control. Fusion 37, 1015 (1995)] are reported as well. The obtained results show a controllability of the neutral density and provide the basis for neutral density reduction and a possibility to excite strong drift wave turbulence in the LMD.

Saitou, Y.; Yonesu, A.; Shinohara, S.; Ignatenko, M. V.; Kasuya, N.; Kawaguchi, M.; Terasaka, K.; Nishijima, T.; Nagashima, Y.; Kawai, Y.; Yagi, M.; Itoh, S.-I.; Azumi, M.; Itoh, K. [Faculty of Engineering, Utsunomiya University, Utsunomiya, Tochigi 321-8585 (Japan); Faculty of Engineering, Ryukyu University, Nishihara, Okinawa 903-0213 (Japan); Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Japan Atomic Energy Agency, Naka, Ibaraki 319-1184 (Japan); National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

2007-07-15

373

The Cosmic Background Radiation and the New Aether Drift  

Microsoft Academic Search

The discussion of the cosmic background radiation covers the origin of this radiation, is used as an information source for the universe, temperature constancy, the effects of gravity wave generation, the ether drift, possible experiments to detect this drift, and the velocity of milky way motion. (JFP)

Richard A. Muller

1978-01-01

374

Magnetic island evolution in hot ion plasmas  

SciTech Connect

Effects of finite ion temperature on magnetic island evolution are studied by means of numerical simulations of a reduced set of two-fluid equations which include ion as well as electron diamagnetism in slab geometry. The polarization current is found to be almost an order of magnitude larger in hot than in cold ion plasmas, due to the strong shear of ion velocity around the separatrix of the magnetic islands. As a function of the island width, the propagation speed decreases from the electron drift velocity (for islands thinner than the Larmor radius) to values close to the guiding-center velocity (for islands of order 10 times the Larmor radius). In the latter regime, the polarization current is destabilizing (i.e., it drives magnetic island growth). This is in contrast to cold ion plasmas, where the polarization current is generally found to have a healing effect on freely propagating magnetic island.

Ishizawa, A.; Nakajima, N. [National Institute for Fusion Science, Toki 509-5292 (Japan); Waelbroeck, F. L.; Fitzpatrick, R.; Horton, W. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2012-07-15

375

Time-slice velocity-map ion imaging studies of the photodissociation of NO in the vacuum ultraviolet region  

NASA Astrophysics Data System (ADS)

The time-slice velocity-map ion imaging and the resonant four-wave mixing techniques are combined to study the photodissociation of NO in the vacuum ultraviolet (VUV) region around 13.5 eV above the ionization potential. The neutral atoms, i.e., N(2Do), O(3P2), O(3P1), O(3P0), and O(1D2), are probed by exciting an autoionization line of O(1D2) or N(2Do), or an intermediate Rydberg state of O(3P0,1,2). Old and new autoionization lines of O(1D2) and N(2Do) in this region have been measured and newer frequencies are given for them. The photodissociation channels producing N(2Do) + O(3P), N(2Do) + O(1D2), N(2Do) + O(1S0), and N(2Po) + O(3P) have all been identified. This is the first time that a single VUV photon has been used to study the photodissociation of NO in this energy region. Our measurements of the angular distributions show that the recoil anisotropy parameters (?) for all the dissociation channels except for the N(2Do) + O(1S0) channel are minus at each of the wavelengths used in the present study. Thus direct excitation of NO by a single VUV photon in this energy region leads to excitation of states with ? or ? symmetry (?? = +/-1), explaining the observed perpendicular transition.

Gao, Hong; Pan, Yang; Yang, Lei; Zhou, Jingang; Ng, C. Y.; Jackson, William M.

2012-04-01

376

Gyrobunching and wave-particle resonance in the lower hybrid drift instability  

NASA Astrophysics Data System (ADS)

We report a first principles study of the coupled evolution of energetic ions, background majority ions, electrons and electromagnetic fields in magnetized plasma during the linear phase of the lower hybrid drift instability. A particle-in-cell code, with one spatial and three velocity space co-ordinates, is used to analyse the evolving distribution of a drifting ring-beam population of energetic protons in physical space and gyrophase angle. This analysis is carried out for bulk plasma parameters that approximate to core conditions in large tokamaks, with an energetic ion distribution that is motivated by observations of ion cyclotron emission and may be relevant to alpha channelling. Resonant energy transfer occurs at the two gyrophase angles at which the instantaneous speed of an energetic proton on its cyclotron orbit precisely matches the phase velocity of the lower hybrid wave along the simulation domain. Electron space-charge oscillations determine the wavelength of the propagating lower hybrid wave, and thereby govern the spatial distribution of gyrobunching of the energetic protons that drive the instability.

Cook, J. W. S.; Dendy, R. O.; Chapman, S. C.

2011-07-01

377

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

378

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

379

Second-sound velocities in hexagonal crystals  

NASA Astrophysics Data System (ADS)

The velocities of "drifting" and "driftless" second sound at very low temperatures are calculated for 12 dielectrics having hexagonal crystal structure. The variation of the two second-sound velocities with density is studied for hcp 4He. It is shown that the discrepancy pointed out by Maris between the experimental and theoretical values of the drifting second-sound velocities in hcp 4He can be reduced if another set of elastic constants is used in the calculations.

Singh, David; Varshni, Y. P.

1982-06-01

380

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

381

Gradient drift eigenmodes in the equatorial electrojet  

SciTech Connect

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 density 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 shooter 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. 27 refs., 9 figs.

Wang, X.H.; Bhattacharjee, A. [Univ. of Iowa, Iowa City, IA (United States)

1994-07-01

382

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

383

Low-Frequency Electrostatic Waves in Plasmas with Negative Ions.  

NASA Astrophysics Data System (ADS)

Three types of low-frequency, electrostatic waves (or instabilities) in a plasma containing negative ions are studied experimentally and/or theoretically. For grid-launched ion-acoustic waves, the phase velocity of the ion-acoustic "fast" mode increases with increasing epsilon, the negative ion concentration. Wave-damping decreases with increasing epsilon. For the current-driven ion-acoustic instability, as the negative ion concentration is increased, the frequency of ion-acoustic waves increases, and the critical electron drift needed for their excitation decreases. These results are in agreement with predictions from Vlasov theory. It was found that dusty plasmas behave in a manner similar to negative ion plasmas, as far as ion-acoustic waves are concerned. Electrostatic ion-cyclotron (EIC) waves are internally excited by drawing an electron current along the magnetic field to an 11 mm diameter exciting disk. Both SF _sp{6}{-} and K ^+ EIC waves can be simultaneously excited over a large range of negative ion concentrations. The frequency of both modes increases and the electron drift velocities, along the magnetic field, needed to excite either mode decrease with increasing epsilon , the negative ion concentration. A dispersion relation for the electrostatic Kelvin -Helmholtz instability in a plasma with negative ions is derived when a velocity shear exists in the positive ion flow along the magnetic field. It is found that the negative ions have, generally, a destabilizing effect, as seen for ion acoustic and EIC waves. The influence of the negative ion to positive ion mass ratio, m_- /m_+ , on the instability is also examined. The m _- /m_+ gg 1 case is that of a dusty plasma with negatively charged dust grains. It is found that the negative charge has a strong damping effect for velocity shear instabilities.

Song, Bin

384

FREQUENCY DRIFT AND TIME PROFILE OF 200 Mc\\/s BURSTS OF TYPE III AND THE ELECTRON TEMPERATURE OF THE CORONA  

Microsoft Academic Search

Frequency drift velocity determinations on type III solar bursts were ; made from high-resolution swept-frequency observations at the Oslo Solar ; Observatory. No bursts were observed with frequency drift velocities less than --; 20 Mc\\/sec². The total number of bursts included in the analysis was 68. ; Wild found that frequency drift velocity was approximately proportional to the ; frequency

O. Elgaroey; H. Roedberg

1963-01-01

385

Anomalous drift of spiral waves in heterogeneous excitable media.  

PubMed

We study the drift of spiral waves in a simple model of heterogeneous excitable medium, having gradients in the distribution of ion-channel expression or cellular coupling. We report the anomalous drift of spiral waves toward regions having shorter period or stronger coupling, in reaction-diffusion models of excitable media. Such anomalous drift can promote the onset of complex spatiotemporal patterns, e.g., those responsible for life-threatening arrhythmias in the heart. PMID:21230501

Sridhar, S; Sinha, Sitabhra; Panfilov, Alexander V

2010-11-01

386

Drift hole structure and dynamics with turbulence driven flows  

SciTech Connect

The role of turbulence driven flows in describing drift hole structure and dynamics is discussed. Turbulence driven flows enter the plasma medium response and alter drift hole structures by changing the screening length of the drift hole potential. Specifically, turbulence driven flows shift the drift hole potential radially, and absorb drift hole energy via the hole-flow resonance. It is shown that the absorption shifts the phase of a momentum flux, and so enables the irreversible coupling of drift holes to turbulence driven flows. We show that drift holes and turbulence driven flows are dynamically coupled, and self-regulate each other, so that a stationary state can be achieved with non-zero turbulence driven flows. As an application, a bound on the fluctuation amplitude in the coupled system is derived. The bound is obtained by requiring that the resultant zonal flow velocity should be smaller than the critical flow velocity for the drift hole potential to be self-bound (i.e., the velocity that the screening length be positive). The result predicts Double-Vertical-Line {phi}(tilde sign) Double-Vertical-Line {sub max}{sup 2}{approx}({nu}{sub d}/{omega}{sub ci})(k{sub Parallel-To }/k{sub y}), where zonal flow damping appears as a control parameter. The implications of this result for the problem of edge-core coupling (i.e., explaining turbulence and transport in 'No Man's Land') are discussed.

Kosuga, Y.; Diamond, P. H. [Center for Astrophysics and Space Sciences and Center for Momentum Transport and Flow Organization, University of California at San Diego, La Jolla, California 92093 (United States); WCI Center for Fusion Theory, National Fusion Research Institute, Gwahangno 113, Yusung-gu, Daejeon 305-333 (Korea, Republic of)

2012-07-15

387

Collisional effects on nonlinear ion drag force for small grains  

NASA Astrophysics Data System (ADS)

The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

Hutchinson, I. H.; Haakonsen, C. B.

2013-08-01

388

Collisional effects on nonlinear ion drag force for small grains  

SciTech Connect

The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

Hutchinson, I. H.; Haakonsen, C. B. [Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2013-08-15

389

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

390

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

391

Solitons in Negative Ion Plasmas  

NASA Astrophysics Data System (ADS)

Properties of ion acoustic solitons are studied in a plasma consisting of positive ions, electrons and negative ions--a negative ion plasma. In one dimension these solitons are perturbations described by either the Korteweg-deVries (KdV) or modified Korteweg-deVries equation. In two dimensions, they are planar solitons described by the Kadomtsev-Petviashvili equation or cylindrical and spherical solitons described by a geometric KdV equation. Solitons in a negative ion plasma can be easily launched from metal surfaces or from grids using small excitation voltages. These methods of excitation are demonstrated in this thesis. The soliton phenomena investigated include overtaking collisions in one dimension, oblique collisions in two dimensions that result in a soliton resonance and the reflection of KdV solitons by the sheath of a conductor. Many properties of positive ion-electron plasmas change when the electrons are replaced with much heavier negative ions. The changes discussed include modifications to the Langmuir curve, to the dispersion characteristics and phase velocity of ion acoustic perturbations and to the Bohm drift velocity. Negative ions also alter sheath dimensions in a plasma. Changes of the Debye, Langmuir and ion-matrix sheaths are examined. A pseudopotential method presented also shows that positive excitation produces shocks and solitary waves in negative ion plasmas for only a limited range of negative ion concentrations.

Cooney, Jamie

392

Solitons in negative ion plasmas  

NASA Astrophysics Data System (ADS)

Properties of ion acoustic solitons are studied in a plasma consisting of positive ions, electrons and negative ions -- a negative ion plasma. In one dimension these solitons are perturbations described by either the Korteweg-deVries (KdV) or modified Korteweg-deVries equation. In two dimensions, they are planar solitons described by the Kadomtsev-Petviashvili equation or cylindrical and spherical solitons described by a geometric KdV equation. Solitons in a negative ion plasma can be easily launched from metal surfaces or from grids using small excitation voltages. These methods of excitation are demonstrated in this thesis. The soliton phenomena investigated include overtaking collisions in one dimension, oblique collisions in two dimensions that result in a soliton resonance and the reflection of KdV solitons by the sheath of a conductor. Many properties of positive ion-electron plasmas change when the electrons are replaced with much heavier negative ions. The changes discussed include modifications to the Langmuir curve, to the dispersion characteristics and phase velocity of ion acoustic perturbations and to the Bohm drift velocity. Negative ions also alter sheath dimensions in a plasma. Changes of the Debye, Langmuir and ion-matrix sheaths are examined. A pseudopotential method presented also shows that positive excitation produces shocks and solitary waves in negative ion plasmas for only a limited range of negative ion concentrations.

Cooney, Jamie

393

Collisional drift fluids and drift waves.  

National Technical Information Service (NTIS)

The usual theoretical description of drift-wave turbulence (considered to be one possible cause of anomalous transport in a plasma), e.g. the Hasegawa-Wakatani theory, makes use of various approximations, the effect of which is extremely difficult to asse...

D. Pfirsch D. Correa-Restrepo

1995-01-01

394

Generalized Drift-Diffusion Model In Semiconductors  

SciTech Connect

A new drift-diffusion model is proposed based on the computation of the stationary nonlocal current density. The semi classical Boltzmann equation is solved keeping all the anisotropies of the distribution function with the use of the continued fractions. The conductivity is calculated in the linear approximation and for arbitrary collision frequency with respect to Kv{sub t} where K{sup -1} is the characteristic length scale of the system and V{sub t} is the thermal velocity. The nonlocal conductivity can be used to close the generalized drift-diffusion equations valid for arbitrary collisionality.

Mesbah, S.; Bendib-Kalache, K.; Bendib, A. [Laboratoire d'Electronique Quantique, Faculte de Physique, USTHB, El Allia, BP 32, Bab Ezzouar 16111, Algiers (Algeria)

2008-09-23

395

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

396

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

397

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

398

Effect of non-uniform electric fields on drift instabilities  

Microsoft Academic Search

A general equation describing drift instabilities in a low beta plasma, in the presence of non-uniform electric fields perpendicular to the magnetic field, is derived using a guiding centre fluid picture for the ions and the drift kinetic equation with Krook-like collision term for the electrons. Both the collisionless and the collisional regime, and therefore also the transition between them,

M. Dobrowolny

1970-01-01

399

Radar and satellite global equatorial F region vertical drift model  

Microsoft Academic Search

We present the first global empirical model for the quiet time F region equatorial vertical drifts based on combined incoherent scatter radar observations at Jicamarca and Ion Drift Meter observations on board the Atmospheric Explorer E satellite. This analytical model, based on products of cubic-B splines and with nearly conservative electric fields, describes the diurnal and seasonal variations of the

L. Scherliess

1999-01-01

400

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

401

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

402

Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization  

NASA Technical Reports Server (NTRS)

SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

Adrian, Mark L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

403

Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization  

NASA Astrophysics Data System (ADS)

SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale ( ~100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

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

2001-12-01

404

Variable-energy drift-tube linacs  

Microsoft Academic Search

Practical applications of ion linacs are more viable now than ever before because of the recent development of the radio-frequency quadrupole accelerating structure, as well as other technological advances developed under the Pion Generator for Medical Irradiations program. A practical technique for varying the energy of drift-tube linacs and thus further broadening the possibilities for linac applications is described. This

D. A. Swenson; T. J. Jr. Boyd; J. M. Potter; J. E. Stovall

1981-01-01

405

Variable-energy drift-tube linacs  

Microsoft Academic Search

Practical applications of ion linacs are more viable now than ever before because of the recent development of the radio-frequency quadrupole accelerating structure, as well as other technological advances developed under the Pion Generator for Medical Irradiations program. This report describes a practical technique for varying the energy of drift-tube linacs and thus further broadening the possibilities for linac applications.

D. A. Swenson; T. J. Boyd; J. M. Potter; J. E. Stovall

1981-01-01

406

Observation of Drift Motion of a Collisional Plasma in Cross Fields.  

National Technical Information Service (NTIS)

The drift velocity of particles undergoing approaching E x approaching B rotation in a collisional plasma is investigated by test wave technique and Langmuir probe. The velocity determined by probe is corrected by including effect of cylindrical geometry ...

A. Hussain

1975-01-01

407

Stimulated microwave emission from E×B drifting electrons in slow-wave cavities: A quantum approach  

Microsoft Academic Search

Stimulated microwave emission from E×B drifting electrons in slow-wave cavities occurs when the Doppler-shifted radiation frequency is either near zero or the electron cyclotron frequency. The former case, characterized by the synchronous drift velocity u, omega-ku~=0, corresponds to the ``pure drift'' instability, while the latter, satisfying omega-ku~=+\\/-Omega, is termed the ``drift-cyclotron'' mode. In both cases the drift kinetic energy and

Spilios Riyopoulos

1995-01-01

408

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

409

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

NASA Astrophysics Data System (ADS)

We have examined the origins of ion irradiation-induced nanoparticle (NP) motion. Focused-ion-beam irradiation of GaAs surfaces induces random walks of Ga NPs, which are biased in the direction opposite to that of ion beam scanning. Although the instantaneous NP velocities are constant, the NP drift velocities are dependent on the off-normal irradiation angle, likely due to a difference in surface non-stoichiometry induced by the irradiation angle dependence of the sputtering yield. It is hypothesized that the random walks are initiated by ion irradiation-induced thermal fluctuations, with biasing driven by anisotropic mass transport.

Kang, M.; Wu, J. H.; Sofferman, D. L.; Beskin, I.; Chen, H. Y.; Thornton, K.; Goldman, R. S.

2013-08-01

410

Ion composition aspects of magnetotail plasma flows  

NASA Astrophysics Data System (ADS)

Recent archiving of energetic (<18 keV /e) ion composition data from the ISEE 1 satellite has created a 4.5-year World Wide Web based set well suited for statistical investigations of magnetospheric plasmas inside of 23 RE, especially with regard to signatures of solar (He++) or terrestrial (O+) origins. This is an application that investigates tail ion flows in the 10-23 RE radial range, specifically the (spacecraft spin plane) GSE x and y flows of H+, He++, and O+ ions in the 0.1-16 keV/e energy range. The plasma sheet is divided into (1) ``high,'' (2) ``intermediate,'' and (3) ``low'' latitude regions based on magnetic field GSE elevation angle ? and ion beta (sum of H+, He++, He+, and O+ ions), such that regions 1 and 2 both have |?|<=9°, i.e., |Bz|<<(Bx2+By2)1/2, with region 1 being at ?<0.1 and region 2 being at ?>0.1, and region 3 has |Bz|>(Bx2+By2)1/2 and ?>0.1. A fourth region has remaining plasma sheet samples (30%). In region 1 the most common drift is within +/-30° of the tailward magnetic field direction for all ions, including, somewhat surprisingly, the He++ ions (about half the time). Tailward drift speeds (<100 km s-1) are substantially smaller than thermal speeds (~500 km s-1) for both He++ and H+ ions. Only the O+ ions have a net field-aligned (and tailward) distribution (<2??2>-1~6). On average, the He++/H+ number density and mean energy ratios are ~4% and ~4, respectively, indicating a mostly solar origin of both species. The second most common drift of He++ and H+ ions (~20%) is aligned near the earthward field direction and has the largest speeds (>100 km s-1). It also has velocity dispersion, however, and seems to be associated with the leading edge of intermittent bursts of ions expanding earthward from the downtail plasma sheet. Superimposed on these drifts is E×B drift of varying speed and direction, which has a net average of the order of 10 km s-1 toward local midnight, away from the tail flanks. Comparing times (2-hour intervals) of northward and southward interplanetary magnetic field, drift speeds are some 50% larger in the southward case, and thermal speeds are 10-20% larger. In region 2, drifts are more random in direction and somewhat slower, whereas thermal speeds are 30-50% larger than in region 1. Only the O+ ions maintain dominantly tailward (field-aligned) drift. The average E×B drift is reversed, away from local midnight, but still of the order of 10 km s-1. In region 3, average E×B drift is sunward and away from midnight. Sunward drift occurs ~2.5 times more often than tailward drift with northward interplanetary magnetic field and almost 8