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1

Dynamics of energetic plasma sheet electrons  

NASA Astrophysics Data System (ADS)

The dynamics of energetic plasma sheet electrons plays an important role in many geomagnetic processes. The intent of this thesis is to extend the current understanding of the relationship between the solar wind and energetic plasma sheet electrons (~> 40 keV ), as well as the variability of these electrons within the plasma sheet. The statistical relationship between tens of keV plasma sheet electrons and the solar wind, as well as > 2 MeV geosynchronous electrons, is investigated, using plasma sheet measurements from Cluster (2001 - 2005) and Geotail (1998 - 2005), and concurrent solar wind measurements from ACE. Statistically, plasma sheet electron flux variations are compared to solar wind velocity, density, dynamic pressure, IMF B z , and solar wind energetic electrons, as well as > 2 MeV electrons at geosynchronous orbit. Several new results are revealed: (1) there is a strong positive correlation between energetic plasma sheet electrons and solar wind velocity; (2) this correlation is valid throughout the plasma sheet and extends to distances of X GSM =-30 R E ; (3) there is evidence of a weak negative correlation between energetic plasma sheet electrons and solar wind density; (4) energetic plasma sheet electrons are enhanced during times of southward interplanetary magnetic field (IMF); (5) there is no clear correlation between energetic plasma sheet electrons and solar wind electrons of comparable energies; and (6) there is a strong correlation between energetic electrons in the plasma sheet and > 2 MeV electrons at geosynchronous orbit measured 2 days later. In addition, the variability of energetic electron fluxes within the plasma sheet is explored. Interesting events were found using a combination of automated methods and visual inspection. Events are classified into 4 main types: (1) plasma sheet empty of energetic electrons; (2) decreasing plasma sheet energetic electron fluxes; (3) increasing plasma sheet energetic electron fluxes; and (4) sharp (rising and falling) variations in plasma sheet energetic electron fluxes during a single plasma sheet crossing. Case studies are presented for each type of event. The time it takes to fill/empty the plasma sheet of energetic electrons is quantified based on these events. Extreme events, most of which are associated with enhanced geomagnetic activity, showed that energetic electrons in the plasma sheet can vary up to several orders of magnitude. Interestingly, the energetic electron fluxes inside the plasma sheet can still undergo rapid variations when the solar wind is calm and geomagnetic activity is low.

Burin Des Roziers, Edward

2009-06-01

2

Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail study  

E-print Network

Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail February 2009. [1] The statistical relationship between tens of kiloelectron volts plasma sheet electrons and the solar wind, as well as >2 MeV geosynchronous electrons, is investigated using plasma sheet measurements

Li, Xinlin

3

On energetic electrons (>38 keV) in the central plasma sheet: Data analysis and modeling  

E-print Network

On energetic electrons (>38 keV) in the central plasma sheet: Data analysis and modeling Bingxian] The spatial distribution of >38 keV electron fluxes in the central plasma sheet (CPS) and the statistical relationship between the CPS electron fluxes and the upstream solar wind and interplanetary magnetic field (IMF

Li, Xinlin

4

Heliospheric plasma sheets  

Microsoft Academic Search

As a high-beta feature on scales of hours or less, the heliospheric plasma sheet (HPS) encasing the heliospheric current sheet shows a high degree of variability. A study of 52 sector boundaries identified in electron pitch angle spectrograms in Wind data from 1995 reveals that only half concur with both high-beta plasma and current sheets, as required for an HPS.

N. U. Crooker; C.-L. Huang; S. M. Lamassa; D. E. Larson; S. W. Kahler; H. E. Spence

2004-01-01

5

Graphene sheets embedded carbon film prepared by electron irradiation in electron cyclotron resonance plasma  

SciTech Connect

We used a low energy electron irradiation technique to prepare graphene sheets embedded carbon (GSEC) film based on electron cyclotron resonance plasma. The particular {pi} electronic structure of the GSEC film similar to bilayer graphene was verified by Raman spectra 2D band analyzing. The phase transition from amorphous carbon to GSEC was initiated when electron irradiation energy reached 40 eV, and the growth mechanism of GSEC was interpreted as inelastic scattering of low energy electrons. This finding indicates that the GSEC film obtained by low energy electron irradiation can be excepted for widely applications with outstanding electric properties.

Wang Chao; Diao Dongfeng; Fan Xue; Chen Cheng [Key Laboratory of Education Ministry for Modern Design and Rotor-Bearing System, School of Mechanical Engineering, Xi'an Jiaotong University, 710049 Xi'an (China)

2012-06-04

6

Counter-Streaming Electron Beams in the Plasma Sheet Associated with Auroral Activity  

E-print Network

shortly after large fluctuations in the magnetic field, are centered about 1 keV and are confined to pitch: Keogram (auroral power vs. latitude) Auroral power vs. MLT Plasma sheet magnetic field e- density e in the auroral region show a similar electron spectrum. The source of the field-aligned beams is unknown

Fillingim, Matthew

7

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources  

NASA Technical Reports Server (NTRS)

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the en- tire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8) eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Khazanov, G. V.; Liemohn, M. W.; Kozyra, J. U.; Moore, T. E.

1998-01-01

8

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources  

NASA Technical Reports Server (NTRS)

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the entire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function, and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8)eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Khazanov, G. V.; Liemohn, M. W.; Kozyra, J. U.; Moore, Thomas E.

1998-01-01

9

Counter-streaming electron beams in the plasma sheet associated with auroral activity  

NASA Astrophysics Data System (ADS)

Electron observations by the WIND plasma instruments in the near-Earth plasma sheet (at a radial distance of about 10 Earth radii) during a substorm expansion and recovery reveal the presence of counter-streaming electron beams. The beams, which appear shortly after large fluctuations in the magnetic field, are centered at about 1 keV and are confined to pitch angles less than about 10 degrees. These beams appear to be unstable and rapidly decay resulting in bi-directional field-aligned electron distributions. The resulting distributions contain two components: a thermal, relatively isotropic plasma sheet component, and a lower energy, more strongly field-aligned beam remnant. The bi-directional field-aligned distributions are observed for more than one hour. Simultaneous FAST plasma measurements near the magnetic footprint of WIND in the auroral region show a similar two component electron spectrum. The source of the field-aligned beams is unknown, but based on the narrowness of the beams in the plasma sheet, we contend that the source is at low altitude and that the source mechanism is related to the auroral acceleration processes.

Fillingim, M.; Parks, G.; Lin, R.; Wilber, M.; Carlson, C.; Chua, D.; Peticolas, L.

2002-12-01

10

Spectral characteristics of plasma sheet ion and electron populations during undisturbed geomagnetic conditions  

SciTech Connect

The authors analyze 127 one-hour average samples of central plasma sheet ions and electrons in order to determine spectral characteristics of thee magnetotail particle populations during periods of low geomagnetic activity (AE<100nT). Particle data from the low energy proton and electron differential energy analyzer (LEPEDEA) and medium energy particle instrument (MEPI) on ISEE 1 were combined to obtain differential energy spectra in the plasma sheet at geocentric radial distances R > 12 R{sub E}. They find that, for even the longest periods sampled, the nearly isotropic central plasma sheet total ion and electron populations were measured to be continuous particle distributions from the lowest energy of tens of eV/e to a few hundred keV. The kappa distribution most often reproduces the observed differential energy spectra. Spectra dominated by a single kappa functional form are observed during 83 (99) hours for ions (electrons). Spectra which are not dominated by a single kappa functional form can usually be closely approximated by superposed kappa functional forms. For both ions and electrons {kappa} is typically in the range 4-8, with a most probable value between 5 and 6, so that the spectral shape is distinctly non-Maxwellian. E{sub oi} and E{sub oe} are highly correlated, whereas {kappa}{sub i} and {kappa}{sub e} are not correlated; {kappa}{sub i} is roughly proportional to E{sub oi}{sup 1/2}, whereas {kappa}{sub e} is not correlated with E{sub oe}. They statistically investigate the importance of flux and energy contributions from extramagnetospheric sources by separately analyzing intervals when simultaneously measured interplanetary particle fluxes are either enhanced or at low levels.

Christon, S.P.; Williams, D.J.; Mitchell, D.G. (Johns Hopkins Univ., Laurel, MD (USA)); Frank, L.A.; Huang, C.Y. (Univ. of Iowa, Iowa City (USA))

1989-10-01

11

Energetic ion and electron beams at the plasma-sheet boundary in the distant tail  

NASA Technical Reports Server (NTRS)

Several energetic particle bursts observed by ISEE 3 in the distant tail are analyzed. The energetic particle data are supplemented by the electron plasma and magnetic field measurements. These bursts are characterized by large velocity-dispersion effects, with energetic electrons observed first, followed by ions with continuously lower velocities. Both ions and electrons stream in the tailward direction. Protons and alpha particles of the same energy per nucleon are observed at the same time. The dispersion effects are observed in reverse order when the spacecraft leaves from the boundary layer into the lobe. No obvious signature indicating the passage of a plasmoid has been observed in the particle or magnetic field data during or immediately following these bursts. It is concluded that these beams at the plasma-sheet boundary originate at a steady source, presumably close to a neutral line, and not at a time varying source. The velocity filter effect in a dawn-dusk electric field arranges particles with progressively lower velocity further inside the wedge-shaped region of reconnected field lines. The plasma electron distribution exhibits a tailward directed heat flux within this layer.

Scholer, M.; Klecker, B.; Hovestatd, D.; Gloeckler, G.; Ipavich, F. M.; Galvin, A. B.; Baker, D. N.; Tsurutani, B. T.

1987-01-01

12

The relationship between diffuse auroral and plasma sheet electron distributions near local midnight  

SciTech Connect

A study of the relationship between diffuse auroral and plasma sheet electron distributions in the energy range from 50 eV to 20 keV in the midnight region was conducted using data from the P78-1 and SCATHA satellites. From 1 1/2 years of data, 14 events were found where the polar-orbiting P78-1 satellite and the near-geosynchronous SCATHA satellite were approximately on the same magnetic field line simultaneously, with SCATHA in the plasma sheet and P78-1 in the diffuse auroral region. For all cases the spectra from the two satellites are in good quantitative agreement. For 13 of the 14 events the pitch angle distribution measured at P78-1 was isotropic for angles mapping into the loss cone at the SCATHA orbit. For one event the P78-1 electron flux decreased with pitch angle toward the field line direction. At SCATHA the distributions outside the loss cone were most commonly butterfly or pancake, although distributions peaked toward the field line were sometimes observed at energies below 1 keV. Electron distributions, as measured where there is isotropy within the loss cone but anisotropy outside the loss cone, are inconsistent with current theories for the scattering of cone for the distribution measured at SCATHA, the electron precipitation lifetimes were calculated for the 14 events. Because the distributions are anisotropic at pitch angles away from the loss cone, the calculated lifetimes significantly exceed the lifetimes in the limit when the flu is isotropic at all pitch angles. The computed precipitation lifetimes are found to be weakly dependent on magnetic activity. The average lifetimes exceed those for the case of isotropy at all pitch angles by a factor between 2 and 3 for {ital Kp}{le}2 and approximately 1.5 for {ital Kp}{gt}2. {copyright} American Geophysical Union 1989

Schumaker, T.L. (Physics Department, Boston College, Chestnut Hill, Massachusetts (US)); Gussenhoven, M.S. (Physics Department, Boston College, Chestnut Hill, Massachusetts (US)); Hardy, D.A. (Air Force Geophysics Laboratory, Hanscom Air Force Base, Massachusetts); Carovillano, R.L. (Physics Department, Boston College, Chestnut Hill, Massachusetts)

1989-08-01

13

Observations of correlated broadband electrostatic noise and electron-cyclotron emissions in the plasma sheet. Technical report  

SciTech Connect

Electric field wave observations in the central plasma sheet of the earth's magnetosphere show the correlated occurrence of broadband electrostatic noise and electrostatic electron cyclotron harmonic emissions. A model is proposed in which the broadband emissions are electron acoustic waves generated by an observed low energy electron beam, and the cyclotron emissions are generated by the hot electron loss cone instability. The high degree of correlation between the two emissions is provided in the model by the presence of the cold electron beam population, which allows both of the plasma instabilities to grow.

Roeder, J.L.; Angelopoulos, V.; Baumjohann, W.; Anderson, R.R.

1991-11-15

14

A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events  

E-print Network

-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS), JA statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) S. Lee,1 K

California at Berkeley, University of

15

Effect of an MLT dependent electron loss rate on the inner magnetosphere electrodynamics and plasma sheet penetration to the ring current region  

NASA Astrophysics Data System (ADS)

Transport of plasma sheet particles into the ring current region is strongly affected by the penetrating convection electric field, which is the result of the large-scale magnetosphere-ionosphere (M-I) electromagnetic coupling. One of the main factors controlling this coupling is the ionospheric conductance. As plasma sheet electrons drift earthward, they get scattered into the loss cone due to wave-particle interactions and precipitate to the ionosphere, producing auroral conductance. Realistic electron loss is thus important for modeling the (M-I) coupling and penetration of plasma sheet into the inner magnetosphere. To evaluate the significance of electron loss rate, we used the Rice Convection Model (RCM) coupled with a force-balanced magnetic field to simulate plasma sheet transport under different electron loss rates and under self-consistent electric and magnetic field. The plasma sheet ion and electron sources for the simulations are based on the Geotail observations. Two major rates are used: different portions of i) strong pitch-angle diffusion everywhere electron loss rate (strong rate) and ii) a more realistic loss rate with its MLT dependence determined by wave activity (MLT rate). We found that the dawn-dusk asymmetry in the precipitating electron energy flux under the MLT rate, with much higher energy flux at dawn than at dusk, agrees better with statistical DMSP observations. Electrons trapped inside L ~ 8 RE can remain there for many hours under the MLT rate, while those under the strong rate get lost within minutes. Compared with the strong rate, the remaining electrons under the MLT rate cause higher conductance at lower latitudes, allowing for less efficient electric field shielding to convection enhancement, thus further earthward penetration of the plasma sheet into the inner magnetosphere. Therefore, our simulation results indicate that the electron loss rate can significantly affect the electrodynamics of the ring current region. Development of a more realistic electron loss rate model for the inner magnetosphere is thus much needed and will become feasible with new observations from the upcoming RBSP mission.

Gkioulidou, M.; Wang, C.; Wing, S.; Lyons, L. R.; Wolf, R. A.; Hsu, T.

2012-12-01

16

Ring current dynamics and plasma sheet sources. [magnetic storms  

NASA Technical Reports Server (NTRS)

The source of the energized plasma that forms in geomagnetic storm ring currents, and ring current decay are discussed. The dominant loss processes for ring current ions are identified as charge exchange and resonant interactions with ion-cyclotron waves. Ring current ions are not dominated by protons. At L4 and energies below a few tens of keV, O+ is the most abundant ion, He+ is second, and protons are third. The plasma sheet contributes directly or indirectly to the ring current particle population. An important source of plasma sheet ions is earthward streaming ions on the outer boundary of the plasma sheet. Ion interactions with the current across the geomagnetic tail can account for the formation of this boundary layer. Electron interactions with the current sheet are possibly an important source of plasma sheet electrons.

Lyons, L. R.

1984-01-01

17

Sheet shaped plasma production using microwave-plasma interaction with ECR region  

Microsoft Academic Search

Summary form only given. To control the shape of high density plasma has been one of the issues for the application of plasma to industrial usages. Therefore, ECR plasma is a good candidate of a high density plasma. A sheet shaped high density plasma could be used to modify the surface of materials uniformly and as the basis for electron

M. Yoshida; K. Kajinishi

2002-01-01

18

Rapid loss of the plasma sheet energetic electrons associated with the growth of whistler mode waves inside the bursty bulk flows  

NASA Astrophysics Data System (ADS)

During the interval 07:45:36- 07:54:24 UT on 24 August 2005, Cluster satellites (C1 and C3) observed an obvious loss of energetic electrons (3.2- 95keV) associated with the growth of whistler mode waves inside some bursty bulk flows (BBFs) in the midtail plasma sheet (X _{GSM}= -17.25 R _{E}). However, the fluxes of the higher-energy electrons (>128keV) and energetic ions (10- 160 keV) were relatively stable in the BBF-impacted regions. The energy-dependent electron loss inside the BBFs is mainly due to the energy-selective pitch angle scatterings by whistler mode waves within the time scales from several seconds to several minutes, and the electron scatterings in different pitch angle distributions are different in the wave growth regions. The plasma sheet energetic electrons have mainly a quasi-perpendicular pitch angle distribution (30() electrons, the low-energy electrons (0.073- 2.1keV) have initially a field-aligned pitch angle distribution (0() electrons inside the BBFs is not obvious in the presence of their large background fluxes. These observations indicate that the resonant electrons in an anisotropic pitch angle distribution mainly undergo the rapid pitch angle scattering loss during the wave-particle resonances.

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

19

Rapid loss of the plasma sheet energetic electrons associated with the growth of whistler mode waves inside the bursty bulk flows  

NASA Astrophysics Data System (ADS)

the interval ~07:45:36-07:54:24 UT on 24 August 2005, Cluster satellites (C1 and C3) observed an obvious loss of energetic electrons (~3.2-95 keV) associated with the growth of whistler mode waves inside some bursty bulk flows (BBFs) in the midtail plasma sheet (XGSM ~ -17.25 RE). However, the fluxes of the higher-energy electrons (?128 keV) and energetic ions (10-160 keV) were relatively stable in the BBF-impacted regions. The energy-dependent electron loss inside the BBFs is mainly due to the energy-selective pitch angle scatterings by whistler mode waves within the time scales from several seconds to several minutes, and the electron scatterings in different pitch angle distributions are different in the wave growth regions. The plasma sheet energetic electrons have mainly a quasi-perpendicular pitch angle distribution (30electrons, the low-energy electrons (~0.073-2.1 keV) have initially a field-aligned pitch angle distribution (0???30 and 150???180) in the absence of whistler mode waves, and their loss in field-aligned directions is accompanied by their increase in quasi-perpendicular directions in the wave growth regions, but the loss of the low-energy electrons inside the BBFs is not obvious in the presence of their large background fluxes. These observations indicate that the resonant electrons in an anisotropic pitch angle distribution mainly undergo the rapid pitch angle scattering loss during the wave-particle resonances.

Li, L. Y.; Yu, J.; Cao, J. B.; Zhang, D.; Wei, X. H.; Rong, Z. J.; Yang, J. Y.; Fu, H. S.

2013-11-01

20

Kinetic ballooning/interchange instability in a bent plasma sheet  

NASA Astrophysics Data System (ADS)

We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) and GOES observations to investigate the plasma sheet evolution on 28 February 2008 between 6:50 and 7:50 UT, when there developed strong magnetic field oscillations with periods of 100 s. Using multispacecraft analysis of the plasma sheet observations and an empirical plasma sheet model, we determine both the large-scale evolution of the plasma sheet and the properties of the oscillations. We found that the oscillations exhibited signatures of kinetic ballooning/interchange instability fingers that developed in a bent current sheet. The interchange oscillations had a sausage structure, propagated duskward at a velocity of about 100 km/s, and were associated with fast radial electron flows. We suggest that the observed negative gradient of the ZGSM magnetic field component (?BZ/?X) was a free energy source for the kinetic ballooning/interchange instability. Tens of minutes later a fast elongation of ballooning/interchange fingers was detected between 6 and 16 RE downtail with the length-to-width ratio exceeding 20. The finger elongation ended with signatures of reconnection in an embedded current sheet near the bending point. These observations suggest a complex interplay between the midtail and near-Earth plasma sheet dynamics, involving localized fluctuations in both cross-tail and radial directions before current sheet reconnection.

Panov, E. V.; Nakamura, R.; Baumjohann, W.; Kubyshkina, M. G.; Artemyev, A. V.; Sergeev, V. A.; Petrukovich, A. A.; Angelopoulos, V.; Glassmeier, K.-H.; McFadden, J. P.; Larson, D.

2012-06-01

21

Kinetic Ballooning/Interchange Instability in a Bent Plasma Sheet  

NASA Astrophysics Data System (ADS)

We use THEMIS and GOES observations to investigate the plasma sheet evolution on 28 February 2008 between 6:50 and 7:50 UT, when there developed strong magnetic field oscillations with period of 100 s. Using multi-spacecraft analysis of the plasma sheet observations and an empirical plasma sheet model, we determine both the large-scale evolution of the plasma sheet and the properties of the oscillations. We found that the oscillations exhibited signatures of kinetic ballooning/interchange instability fingers that developed in a bent current sheet. The interchange oscillations had a sausage structure, propagated duskward at a velocity of about 100 km/s, and were associated with periodical radial electron flows. We suggest that the observed negative gradient of the ZGSM magnetic field component (dBZ/dX) was a free energy source for the kinetic ballooning/interchange instability. Tens of minutes later a fast elongation of ballooning/interchange fingers was detected between 6 and 16 RE downtail with the legnth-to-width ratio exceeding 20. The finger elongation ended with signatures of reconnection in an embedded current sheet near the bending point. These observations suggest a complex interplay between the midtail and near-Earth plasma sheet dynamics, involving localized fluctuations both in cross-tail and radial directions before current sheet reconnection.

Panov, E. V.; Nakamura, R.; Baumjohann, W.; Kubyshkina, M. G.; Artemyev, A. V.; Sergeev, V. A.; Petrukovich, A. A.; Angelopoulos, V.; Glassmeier, K.-H.; McFadden, J. P.; Larson, D.

2012-04-01

22

Sheet-shaped plasma production using microwave-plasma interaction with ECR region  

Microsoft Academic Search

New phenomena in producing sheet-shaped plasma under electron cyclotron resonance (ECR) condition have been found and investigated by experiment. Sheet-shaped Ar plasma with density of ?1018 m-3 was successfully obtained at ?10-3 torr by using 2.45-GHz microwave with ECR condition. The plasma was generated uniformly and stably in the cross section of 15.5 cm width2.0 cm thickness with the use

Mitsuhiro Yoshida; Kuniyuki Kajinishi

2003-01-01

23

Realistic Plasma Sheet Models: Kinetic Reconstructions Using Cluster  

NASA Astrophysics Data System (ADS)

The Harris model has served for many years as the de-facto standard kinetic model for the tail plasma sheet. However, the model only rarely agrees with detailed satellite observations beyond roughly fitting the current profile. We present a reconstruction technique which can be used to fit the generalized quasi-isotropic class of models (which includes the Harris model and many others) to Cluster data. The resulting time-stationary reconstructions are self-consistent, with kinetic ions and fluid-like electrons. We apply the reconstruction technique to 30 Cluster plasma sheet crossings when the scale size was comparable to the ion inertial length. The 30 reconstructions show 3 different typical cases. Most commonly, the current is carried by diamagnetic ion currents, with small embedded perturbations from electron currents. Less common are thin, bifurcated sheets driven by electron Hall currents. A few cases are supported by anisotropic electron currents. The reconstructions point out the essential properties of a realistic plasma sheet model, and give insight into the stable thin current sheets that provide the initial conditions for reconnection and/or current disruption

Cully, C. M.; Ergun, R. E.

2008-12-01

24

Systematic study of plasma flow during plasma sheet thinnings  

NASA Technical Reports Server (NTRS)

On the basis of a study of Imp 6 measurements of plasma flow, it is concluded that there is no clear indication of a predominance of tailward plasma flow beyond about X = -15 R sub E in the midnight sector of the plasma sheet during the expansive phase of a substorm. In fact, it is shown statistically that sunward plasma flow is more frequently observed in the midnight sector within about 30 R sub E from the earth than in any other direction during plasma sheet thinning at the substorm expansion. This result supports the conclusion that there is no definite evidence for the formation of a reconnection neutral line in the near-earth plasma sheet during most substorms.

Lui, A. T. Y.; Frank, L. A.; Ackerson, K. L.; Meng, C.-I.; Akasofu, S.-I.

1977-01-01

25

CURRENT SHEETS AND COLLISIONLESS DAMPING IN KINETIC PLASMA TURBULENCE  

SciTech Connect

We present the first study of the formation and dissipation of current sheets at electron scales in a wave-driven, weakly collisional, three-dimensional kinetic turbulence simulation. We investigate the relative importance of dissipation associated with collisionless damping via resonant wave-particle interactions versus dissipation in small-scale current sheets in weakly collisional plasma turbulence. Current sheets form self-consistently from the wave-driven turbulence, and their filling fraction is well correlated to the electron heating rate. However, the weakly collisional nature of the simulation necessarily implies that the current sheets are not significantly dissipated via Ohmic dissipation. Rather, collisionless damping via the Landau resonance with the electrons is sufficient to account for the measured heating as a function of scale in the simulation, without the need for significant Ohmic dissipation. This finding suggests the possibility that the dissipation of the current sheets is governed by resonant wave-particle interactions and that the locations of current sheets correspond spatially to regions of enhanced heating.

TenBarge, J. M.; Howes, G. G., E-mail: jason-tenbarge@uiowa.edu [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)

2013-07-10

26

Plasma sheet pressure evolution related to substorms  

NASA Astrophysics Data System (ADS)

We have investigated the inner equatorial plasma sheet plasma pressure evolution associated with substorm onsets using the five THEMIS spacecraft data during the 2008 tail season. The central plasma sheet thermal pressure is estimated from the thermal and magnetic pressure based on one dimensional pressure balance. The results show that for a majority of substorm cases, the plasma pressure enhances after onset earthward of 12 RE radial distance. On the other hand, the plasma pressure beyond 16 RE shows a remarkable decrease near onset. During the recovery phase, the pressure gradually returns to its original level. These results indicate that during the substorm expansion phase, the current wedge usually expands to the region tailward of 16 RE with the inner edge earthward of this radial distance. The pressure increase earthward of 12 RE could be associated with an increase of cross-tail current, though this is not necessarily so due to the nontail-like magnetic field geometry after dipolarization. For a minority of cases, the pressure fluctuates without net change or reduces at 11 RE. During these events, the ground magnetic perturbations and the estimated center of the westward electrojet extend further equatorward than for the pressure increase cases. There is also evidence that aurora breakup occurs further equatorward when there is a pressure reduction, indicating a more earthward penetration of the plasma sheet. During these cases, the current wedge represented by pressure reduction is clearly observed earthward to 11 RE. The relationship between the auroral break up arc, which is believed to map to 10 RE, and may be associated with a precursor pressure enhancement, and the inner plasma sheet pressure and current evolution near onset warrants more careful analysis.

Xing, X.; Lyons, L. R.; Angelopoulos, V.; Larson, D.; Carlson, C.; Runov, A.; Auster, U.

2010-01-01

27

Electronic properties of curved graphene sheets  

E-print Network

A model is proposed to study the electronic structure of slightly curved graphene sheets with an arbitrary number of pentagon-heptagon pairs and Stone-Wales defects based on a cosmological analogy. The disorder induced by curvature produces characteristic patterns in the local density of states that can be observed in scanning tunnel and transmission electron microscopy.

Alberto Cortijo; Maria A. H. Vozmediano

2006-03-27

28

Current Sheet Permeability in Electromagnetic Pulsed Plasma Thrusters  

E-print Network

Current Sheet Permeability in Electromagnetic Pulsed Plasma Thrusters J.W. Berkery and E.Y. Choueiri Electric Propulsion and Plasma Dynamics Laboratory (EPPDyL) Mechanical and Aerospace Engineering for the existence of permeability of current sheets in electromagnetic pulsed plasma thrusters. Permeability refers

Choueiri, Edgar

29

Plasma Sheet Source and Loss Processes  

NASA Technical Reports Server (NTRS)

Data from the TIMAS ion mass spectrometer on the Polar satellite, covering 15 ev/e to 33 keV/e in energy and essentially 4(pi) in view angles, are used to investigate the properties of earthward (sunward) field-aligned flows of ions, especially protons, in the plasma sheet-lobe transition region near local midnight. A total of 142 crossings of this region are analyzed at 12-sec time resolution, all in the northern hemisphere, at R(SM) approx. 4 - 7 R(sub E), and most (106) in the poleward (sunward) direction. Earthward proton flows are prominent in this transition region (greater than 50% of the time), typically appearing as sudden "blasts" with the most energetic protons (approx. 33 keV) arriving first with weak flux, followed by protons of decreasing energy and increasing flux until either: (1) a new "blast" appears, (2) the flux ends at a sharp boundary, or (3) the flux fades away within a few minutes as the mean energy drops to a few keV. Frequent step-like changes (less than 12 sec) of the flux suggest that perpendicular gradients on the scale of proton gyroradii are common. Peak flux is similar to central plasma sheet proton flux (10(exp 5) - 10(exp 6)/[cq cm sr sec keV/e] and usually occurs at E approx. 4 - 12 keV. Only the initial phase of each "blast" (approx. 1 min) displays pronounced field-alignment of the proton velocity distribution, consistent with the time-of-flight separation of a more or less isotropic source distribution with df/d(nu) less than 0. The dispersive signatures are often consistent with a source at R(SM) less than or equal to 30 R(sub E). No systematic latitudinal velocity dispersion is found, implying that the equatorial plasma source is itself convecting. In short, the proton "blasts" appear as sudden local expansions of central plasma sheet particles along reconfigured ("dipolarized") magnetic field lines.

Lennartsson, O. W.

2000-01-01

30

Casimir interaction between spherical and planar plasma sheets  

E-print Network

We consider the interaction between a spherical plasma sheet and a planar plasma sheet due to the vacuum fluctuations of electromagnetic fields. We use the mode summation approach to derive the Casimir interaction energy and study its asymptotic behaviors. In the small separation regime, we confirm the proximity force approximation and calculate the first correction beyond the proximity force approximation. This study has potential application to model Casimir interaction between objects made of materials that can be modeled by plasma sheets such as graphene sheets.

L. P. Teo

2014-03-03

31

Multi-spacecraft observations of the heliospheric plasma sheet  

NASA Astrophysics Data System (ADS)

The heliospheric plasma sheet (HPS) has been described both as quasi-stationary and transient in nature. In order to better quantify the temporal and spatial scales under which each description is appropriate we have compared observations of the HPS from the two STEREO observatories and Wind. Identification criteria of the HPS included a change in magnetic sector from "towards" to "away" (or vice versa, identified using electron pitch angle distributions), an increase in proton density, and minima in the proton specific entropy argument (T/n?-1) and alpha to proton number density ratio. Following the technique of Liu et al. (2010), we have classified each plasma sheet as leading, following, straddling, or absent from the heliospheric current sheet. We find the configuration of the HPS agrees between the three spacecraft when longitudinal separation between observation points is 10 degrees or less (temporal separation of less than 1 day). Preliminary results show that in some cases the HPS is quasi-stationary over longitudinal scales of at least 25 degrees.

Simunac, K. D. C.; Galvin, A. B.; Farrugia, C. J.; Liu, Y. C.-M.; Luhmann, J. G.

2013-06-01

32

Early results of microwave transmission experiments through an overly dense rectangular plasma sheet with microparticle injection  

NASA Astrophysics Data System (ADS)

These experiments utilize a linear hollow cathode to create a dense, rectangular plasma sheet to simulate the plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Injection of fine dielectric microparticles significantly reduces the electron density and therefore lowers the electron plasma frequency by binding a significant portion of the bulk free electrons to the relatively massive microparticles. Measurements show that microwave transmission through this previously overly dense, impenetrable plasma layer increases with the injection of alumina microparticles approximately 60 ?m in diameter. This method of electron depletion is a potential means of mitigating the radio communications blackout experienced by hypersonic vehicles.

Gillman, Eric D.; Amatucci, W. E.

2014-06-01

33

Azimuthal plasma pressure gradient in quiet time plasma sheet  

NASA Astrophysics Data System (ADS)

We have investigated the quiet-time azimuthal plasma pressure gradient in the plasma sheet at a radial distance of 10 RE to 12 RE using two THEMIS spacecraft that were in overlapping orbits during the 2008 THEMIS tail season. The equatorial plasma pressure is estimated by using the in-situ measurement of the plasma pressure and magnetic pressure based on pressure balance assumption. The results show a persistent duskward pressure gradient in the entire observed nightside region, which indicates upward field-aligned current from the ionosphere maps to this entire region. This current corresponds to the Region-2 current system in the post-midnight sector and the Region 1 current system in pre-midnight sector. The pressure gradients indicate that the upward field-aligned currents peak in the vicinity of midnight and decrease towards dusk and dawn, perhaps approaching zero near dusk. The downward Region-2 current system in the pre-midnight sector is expected to be located earthward of 11 RE.

Xing, X.; Lyons, L. R.; Angelopoulos, V.; Larson, D.; McFadden, J.; Carlson, C.; Runov, A.; Auster, U.

2009-07-01

34

Energy spectra of plasma sheet ions and electrons from about 50 eV/e to about 1 MeV during plamsa temperature transitions  

NASA Technical Reports Server (NTRS)

ISEE-1 charged-particle measurements obtained during eight plasma temperature transitions (PTTs) in 1978-1979 are compiled in tables and graphs and analyzed in detail, comparing the ion and electron differential energy spectra with the predictions of theoretical models. PTTs are defined as approximately 1-h periods of low bulk plasma velocity and steadily increasing or decreasing thermal energy. A Maxwellian distribution is found to be inadequate in describing the PTT energy spectra, but velocity-exponential and kappa distributions are both successful, the latter especially at higher energies. The power-law index kappa varies from PTT to PTT, but the high-energy spectral index and overall shape of the distribution remain constant during a PTT; both spatial and temporal effects are observed.

Christon, S. P.; Mitchell, D. G.; Williams, D. J.; Frank, L. A.; Huang, C. Y.; Eastman, T. E.

1988-01-01

35

Particle drift in the Earth's plasma sheet  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

36

Stratification in a neutral current sheet with counterstreaming plasma  

Microsoft Academic Search

A model is proposed for a neutral current sheet formed by a two-stream plasma flow in which the relative velocity of the streams is independent of the transverse coordinate. The linear initial-value problem of the dynamics of stratification modes is analyzed for sheets of arbitrary thickness in the collisionless kinetic approximation. These stratification modes are unstable in this model of

V. M. Gubchenko

1985-01-01

37

Cold ions in the hot plasma sheet of Earth's magnetotail.  

PubMed

Most visible matter in the Universe exists as plasma. How this plasma is heated, and especially how the initial non-equilibrium plasma distributions relax to thermal equilibrium (as predicted by Maxwell-Boltzman statistics), is a fundamental question in studies of astrophysical and laboratory plasmas. Astrophysical plasmas are often so tenuous that binary collisions can be ignored, and it is not clear how thermal equilibrium develops for these 'collisionless' plasmas. One example of a collisionless plasma is the Earth's plasma sheet, where thermalized hot plasma with ion temperatures of about 5 x 10(7) K has been observed. Here we report direct observations of a plasma distribution function during a solar eclipse, revealing cold ions in the Earth's plasma sheet in coexistence with thermalized hot ions. This cold component cannot be detected by plasma sensors on satellites that are positively charged in sunlight, but our observations in the Earth's shadow show that the density of the cold ions is comparable to that of hot ions. This high density is difficult to explain within existing theories, as it requires a mechanism that permits half of the source plasma to remain cold upon entry into the hot turbulent plasma sheet. PMID:12686993

Seki, Kanako; Hirahara, Masafumi; Hoshino, Masahiro; Terasawa, Toshio; Elphic, Richard C; Saito, Yoshifumi; Mukai, Toshifumi; Hayakawa, Hajime; Kojima, Hirotsugu; Matsumoto, Hiroshi

2003-04-10

38

Direct observation of warping in the plasma sheet of Saturn  

NASA Astrophysics Data System (ADS)

The ENA images from the Ion Neutral CAmera (INCA) on the Cassini spacecraft are projected onto the noon-midnight plane of Sun-Saturn orbital coordinates, and a composite ``image'' of Saturn's plasma sheet is constructed from dawn-side observations of 20-50 keV hydrogens obtained from days 352 to 361 in 2004. The maxima in the intensity contours define the center of the plasma sheet in the noon-midnight plane. This plasma sheet surface displays a distinct bending or ``warping'' above Saturn's equatorial plane at radial distances of beyond ~15 RS on the nightside. On the dayside, the plasma sheet lies close to the equator all the way to the magnetopause. The observed warping agrees with the ``bowl'' model derived from measurements of Saturn's magnetic field, but fits more closely a simple third-order polynomial.

Carbary, J. F.; Mitchell, D. G.; Paranicas, C.; Roelof, E. C.; Krimigis, S. M.

2008-12-01

39

Thinning and expansion of the substorm plasma sheet  

SciTech Connect

The authors present a large statistical study of satellite crossings of the plasma sheet, taken during 39 major magnetic storms. They find that for distances between 10 and 19 R{sub E} that they observe a thinning of the plasma sheet in the 30 to 45 minutes before the onset of the storm, followed by a steady increase in thickness which does not recover the previous thickness until the recovery phase of the storm begins.

Baumjohann, W.; Paschmann, G. [Max-Planck-Institute fuer Extraterrestrische Physic, Garching (Germany); Nagai, T. [Metorological Research Institute, Tsukuba (Japan)

1992-11-01

40

Auroral ionospheric signatures of the plasma sheet boundary layer in the evening sector  

NASA Technical Reports Server (NTRS)

We report on particles and fields observed during Defense Meteorological Satellite Program (DMSP) F9 and DE 2 crossings of the polar cap/auroral oval boundary in the evening magnetic local time (MLT) sector. Season-dependent, latitudinally narrow regions of rapid, eastward plasma flows were encountered by DMSP near the poleward boundary of auroral electron precipitation. Ten DE 2 orbits exhibiting electric field spikes that drive these plasma flows were chosen for detailed analysis. The boundary region is characterized by pairs of oppositely-directed, field-aligned current sheets. The more poleward of the two current sheets is directed into the ionosphere. Within this downward current sheet, precipitating electrons either had average energies of a few hundred eV or were below polar rain flux levels. Near the transition to upward currents, DE 2 generally detected intense fluxes of accelerated electrons and weak fluxes of ions, both with average energies between 5 and 12 keV. In two instances, precipitating ions with energies greater than 5 keV spanned both current sheets. Comparisons with satellite measurements at higher altitudes suggest that the particles and fields originated in the magnetotail inside the distant reconnection region and propagated to Earth through the plasma sheet boundary layer. Auroral electrons are accelerated by parallel electric fields produced by the different pitch angle distributions of protons and electrons in this layer interacting with the near-Earth magnetic mirror. Electric field spikes driving rapid plasma flows along the poleward boundaries of intense, keV electron precipitation represent ionospheric responses to the field-aligned currents and conductivity gradients. The generation of field-aligned currents in the boundary layer may be understood qualitatively as resulting from the different rates of earthward drift for electrons and protons in the magnetotail's current sheet.

Burke, W. J.; Machuzak, J. S.; Maynard, N. C.; Basinska, E. M.; Erickson, G. M.; Hoffman, R. A.; Slavin, J. A.; Hanson, W. B.

1994-01-01

41

Current Sheet in a non-Maxwellian collisionless plasma: Self-consistent theory, simulation, and comparison with spacecraft observations  

SciTech Connect

A self-consistent theory is constructed of anisotropic current equilibria maintained in a non-Maxwellian plasma consisting of cold electrons and two hot ion components of different temperatures. The ion plasma components are described in the quasi-adiabatic approximation, and the plasma electrons, in the MHD approximation. Approximate steady solutions to the set of Vlasov-Maxwell equations are obtained and investigated parametrically. It is shown that the solutions can describe various current sheet profiles: from thin current structures with a maximum current density in the neutral sheet to comparatively 'thick' current sheets with two to three maxima of the current density. It is also shown that the electron plasma component predominates at the current sheet center and can maintain a narrow central peak in the current density. The ion plasma component predominates at the edge of the current sheet, thereby determining the characteristic sheet thickness. The results of numerical simulations of a two-temperature plasma by the macroparticle method are compared with the experimental data from the Cluster spacecraft. Good agreement between the theoretical, numerical, and experimental results leads to the conclusion that the theory developed here provides a fairly adequate description of collisionless current sheets in space plasmas.

Malova, Kh. V. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation); Zelenyi, L. M. [Russian Academy of Sciences, Institute for Space Research (Russian Federation); Mingalev, O. V.; Mingalev, I. V. [Russian Academy of Sciences, Polar Geophysics Institute, Kola Scientific Center (Russian Federation); Popov, V. Yu. [Russian Academy of Sciences, Institute for Space Research (Russian Federation); Artemyev, A. V. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation); Petrukovich, A. A. [Russian Academy of Sciences, Institute for Space Research (Russian Federation)

2010-10-15

42

Current Sheet in a non-Maxwellian collisionless plasma: Self-consistent theory, simulation, and comparison with spacecraft observations  

NASA Astrophysics Data System (ADS)

A self-consistent theory is constructed of anisotropic current equilibria maintained in a non-Maxwellian plasma consisting of cold electrons and two hot ion components of different temperatures. The ion plasma components are described in the quasi-adiabatic approximation, and the plasma electrons, in the MHD approximation. Approximate steady solutions to the set of Vlasov-Maxwell equations are obtained and investigated parametrically. It is shown that the solutions can describe various current sheet profiles: from thin current structures with a maximum current density in the neutral sheet to comparatively thick current sheets with two to three maxima of the current density. It is also shown that the electron plasma component predominates at the current sheet center and can maintain a narrow central peak in the current density. The ion plasma component predominates at the edge of the current sheet, thereby determining the characteristic sheet thickness. The results of numerical simulations of a two-temperature plasma by the macroparticle method are compared with the experimental data from the Cluster spacecraft. Good agreement between the theoretical, numerical, and experimental results leads to the conclusion that the theory developed here provides a fairly adequate description of collisionless current sheets in space plasmas.

Malova, Kh. V.; Zelenyi, L. M.; Mingalev, O. V.; Mingalev, I. V.; Popov, V. Yu.; Artemyev, A. V.; Petrukovich, A. A.

2010-10-01

43

Ballooning instability at the plasma sheetlobe interface and its implications for polar arc formation  

Microsoft Academic Search

Huang et al. (1987, 1989) reported hot filaments of plasma sheet origin filling the magnetospheric lobes during northward interplanetary magnetic field (IMF). On the other hand, cold plasma transients of presumably lobe origin are often observed in the plasma sheet. These features can be interpreted in terms of plasma exchange at the plasma sheetlobe interface (PSLI) proceeding in a filamentary

I. V. Golovchanskaya; A. Kullen; Y. P. Maltsev; H. Biernat

2006-01-01

44

Ballooning instability at the plasma sheet-lobe interface and its implications for polar arc formation  

Microsoft Academic Search

Huang et al. (1987, 1989) reported hot filaments of plasma sheet origin filling the magnetospheric lobes during northward interplanetary magnetic field (IMF). On the other hand, cold plasma transients of presumably lobe origin are often observed in the plasma sheet. These features can be interpreted in terms of plasma exchange at the plasma sheet-lobe interface (PSLI) proceeding in a filamentary

I. V. Golovchanskaya; A. Kullen; Y. P. Maltsev; H. Biernat

2006-01-01

45

Wavelet analysis of magnetic turbulence in the Earth's plasma sheet  

E-print Network

Recent studies provide evidence for the multi-scale nature of magnetic turbulence in the plasma sheet. Wavelet methods represent modern time series analysis techniques suitable for the description of statistical characteristics of multi-scale turbulence. Cluster FGM (fluxgate magnetometer) magnetic field high-resolution (~67 Hz) measurements are studied during an interval in which the spacecraft are in the plasma sheet. As Cluster passes through different plasma regions, physical processes exhibit non-steady properties on magnetohydrodynamic (MHD) and small, possibly kinetic scales. As a consequence, the implementation of wavelet-based techniques becomes complicated due to the statistically transitory properties of magnetic fluctuations and finite size effects. Using a supervised multi-scale technique which allows existence test of moments, the robustness of higher-order statistics is investigated. On this basis the properties of magnetic turbulence are investigated for changing thickness of the plasma sheet.

Baumjohann, W; Runov, A; Volwerk, M; Zhang, T L; Balogh, A

2004-01-01

46

Microwave plasmas applied for the synthesis of free standing graphene sheets  

NASA Astrophysics Data System (ADS)

Self-standing graphene sheets were synthesized using microwave plasmas driven by surface waves at 2.45 GHz stimulating frequency and atmospheric pressure. The method is based on injecting ethanol molecules through a microwave argon plasma environment, where decomposition of ethanol molecules takes place. The evolution of the ethanol decomposition was studied in situ by plasma emission spectroscopy. Free gas-phase carbon atoms created in the plasma diffuse into colder zones, both in radial and axial directions, and aggregate into solid carbon nuclei. The main part of the solid carbon is gradually withdrawn from the hot region of the plasma in the outlet plasma stream where nanostructures assemble and grow. Externally forced heating in the assembly zone of the plasma reactor has been applied to engineer the structural qualities of the assembled nanostructures. The synthesized graphene sheets have been analysed by Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The presence of sp3 carbons is reduced by increasing the gas temperature in the assembly zone of the plasma reactor. As a general trend, the number of mono-layers decreases when the wall temperature increases from 60 to 100 C. The synthesized graphene sheets are stable and highly ordered.

Tatarova, E.; Dias, A.; Henriques, J.; Botelho do Rego, A. M.; Ferraria, A. M.; Abrashev, M. V.; Luhrs, C. C.; Phillips, J.; Dias, F. M.; Ferreira, C. M.

2014-09-01

47

Central Plasma Sheet Ion Properties as Inferred from Ionospheric Observations  

NASA Technical Reports Server (NTRS)

A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirely, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and F11 satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, widens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X less than approx. 10 to -12 R(sub E), depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

Wing, Simon; Newell, Patrick T.

1998-01-01

48

Interpretation of high-speed flows in the plasma sheet  

NASA Technical Reports Server (NTRS)

Pursuing an idea suggested by Pontius and Wolf (1990), we propose that the `bursty bulk flows' observed by Baumjohann et al. (1990) and Angelopoulos et al. (1992) are `bubbles' in the Earth's plasma sheet. Specifically, they are flux tubes that have lower values of pV(exp 5/3) than their neighbors, where p is the thermal pressure of the particles and V is the volume of a tube containing one unit of magnetic flux. Whether they are created by reconnection or some other mechanism, the bubbles are propelled earthward by a magnetic buoyancy force, which is related to the interchange instability. Most of the major observed characteristics of the bursty bulk flows can be interpreted naturally in terms of the bubble picture. We propose a new `stratified fluid' picture of the plasma sheet, based on the idea that bubbles constitute the crucial transport mechanism. Results from simple mathematical models of plasma sheet transport support the idea that bubbles can resolve the pressure balance inconsistency, particularly in cases where plasma sheet ions are lost by gradient/curvature drift out the sides of the tail or bubbles are generated by reconnection in the middle of plasma sheet.

Chen, C. X.; Wolf, R. A.

1993-01-01

49

Slow Mode Waves in the Heliospheric Plasma Sheet  

NASA Technical Reports Server (NTRS)

We report the results of a search for waves/turbulence in the Heliospheric Plasma Sheet (HPS) surrounding the Heliospheric Current Sheet (HCS). The HPS is treated as a distinctive heliospheric structure distinguished by relatively high Beta, slow speed plasma. The data used in the investigation are from a previously published study of the thicknesses of the HPS and HCS that were obtained in January to May 2004 when Ulysses was near aphelion at 5 AU. The advantage of using these data is that the HPS is thicker at large radial distances and the spacecraft spends longer intervals inside the plasma sheet. From the study of the magnetic field and solar wind velocity components, we conclude that, if Alfven waves are present, they are weak and are dominated by variations in the field magnitude, B, and solar wind density, NP, that are anti-correlated.

Smith, Edward. J.; Zhou, Xiaoyan

2007-01-01

50

Entropy Constraints On The Origin Of Plasma Sheet Populations And Mechanisms Of Plasma Entry  

NASA Astrophysics Data System (ADS)

Entropy provides important constraints on how the plasma sheet is populated. The local (intensive) and global (extensive) entropies each provide information about source populations and accessibility of those populations to regions of the plasma sheet. Changes in entropy are indicators of nonadiabatic processes that may be associated with plasma entry and/or transport within the plasma sheet. We present DMSP measurements of plasma density, pressure, temperature and entropy and discuss the origin of the hot and cold populations. We discuss changes in the entropy in the context of entry mechanisms such as poleward of the cusp reconnection, Kelvin-Helmholtz instability, kinetic Alfven wave turbulence, and ionospheric outflows. We also discuss possible sources of asymmetries in the cold, dense plasma sheet and the dependence on the Parker spiral orientation.

Johnson, J.; Wing, S.; Lin, Y.

2011-12-01

51

The inner edge of the plasma sheet and the diffuse aurora  

NASA Technical Reports Server (NTRS)

Three dimensional measurements from the ISEE-1 low energy electron spectrometer are used to map the location of the inner edge of the plasma sheet and study the anisotropies in the electron distribution function associated with this boundary. Lower energy plasma sheet electrons have inner edges closer to the Earth than higher energies with the separations at different energies being larger near dawn and after dusk than at midnight. Lowest energy inner edges are frequently located adjacent to the plasmapause in the dawn hemisphere but are often separated from it in the dusk hemisphere by a gap of at least several Re. The energy dispersion is minimal in the afternoon quadrant where the inner edge is near the magnetopause and frequently oscillating on a time scale of minutes. The location of the inner edge is probably determined primarily by the motion of electrons in the existing electric and magnetic fields rather than by strong diffusion as has sometimes been supposed.

Fairfield, D. H.; Vinas, A. F.

1983-01-01

52

Detection of localized, plasma-depleted flux tubes or bubbles in the midtail plasma sheet  

Microsoft Academic Search

Recent studies have shown that most Earthward transport in the midtail, high-beta plasma sheet takes place in the form of short-lived, high-speed plasma flow bursts. Bursty bulk flows are observed both when the plasma sheet ishin, such as during substorm expansion, and when it is thick, such as during substorm recovery. We present multi-instrument observations from the ISEE 1 and

V. A. Sergeev; V. Angelopoulos; J. T. Gosling; C. A. Cattell; C. T. Russell

1996-01-01

53

Plasma Sheet Velocity Measurement Techniques for the Pulsed Plasma Thruster SIMP-LEX  

NASA Technical Reports Server (NTRS)

The velocity of the first plasma sheet was determined between the electrodes of a pulsed plasma thruster using three measurement techniques: time of flight probe, high speed camera and magnetic field probe. Further, for time of flight probe and magnetic field probe, it was possible to determine the velocity distribution along the electrodes, as the plasma sheet is accelerated. The results from all three techniques are shown, and are compared for one thruster geometry.

Nawaz, Anuscheh; Lau, Matthew

2011-01-01

54

Magnetic configuration of the distant plasma sheet - ISEE 3 observations  

NASA Technical Reports Server (NTRS)

The influence of the IMF orientation and magnitude and substorm activity on the magnetic configuration of the central plasma sheet at 20-240 earth radii down the geomagnetic tail is investigated on the basis of ISEE-3 data. The results are presented graphically, and high-speed antisolar bulk flows threaded by southward magnetic fields are shown to be present in the distant plasma sheet after periods of substorm activity and southward IMF Bz. The effective dayside reconnection efficiency is estimated as 25 + or - 4 percent, in good agreement with theoretical models.

Slavin, J. A.; Smith, E. J.; Daly, P. W.; Sanderson, T. R.; Wenzel, K.-P.; Lepping, R. P.

1987-01-01

55

On the interaction of a charge with a thin plasma sheet  

E-print Network

The interaction of the electromagnetic field with a two dimensional plasma sheet intended to describe the pi-electrons of a carbon nano-tube or a $C_{60}$ molecule is investigated. By integrating out first the displacement field of the plasma or first the electromagnetic field different representations for quantities like the Casimir energy are derived which are shown to be consistent with one another. Starting from the covariant gauge for the electromagnetic field it is shown that the matching conditions to which the presence of the plasma sheet can be reduced are different from the commonly used ones. The difference in the treatments does not show up in the Casimir force between two parallel sheets, but it is present in the Casimir-Polder force between a charge or a neutral atom and a sheet. At once, since the plasma sheet is a regularization of the conductor boundary conditions, this sheds light on the difference in physics found earlier in the realization of conductor boundary conditions as 'thin' or 'thick' boundary conditions in Phys.Rev.D70(2004)085010.

M. Bordag

2007-04-29

56

On the interaction of a charge with a thin plasma sheet  

E-print Network

The interaction of the electromagnetic field with a two dimensional plasma sheet intended to describe the pi-electrons of a carbon nano-tube or a $C_{60}$ molecule is investigated. By integrating out first the displacement field of the plasma or first the electromagnetic field different representations for quantities like the Casimir energy are derived which are shown to be consistent with one another. Starting from the covariant gauge for the electromagnetic field it is shown that the matching conditions to which the presence of the plasma sheet can be reduced are different from the commonly used ones. The difference in the treatments does not show up in the Casimir force between two parallel sheets, but it is present in the Casimir-Polder force between a charge or a neutral atom and a sheet. At once, since the plasma sheet is a regularization of the conductor boundary conditions, this sheds light on the difference in physics found earlier in the realization of conductor boundary conditions as 'thin' or 'thi...

Bordag, M

2007-01-01

57

Electron channeling and EBIC studies of polycrystalline silicon sheets  

SciTech Connect

Electron channeling and EBIC studies have been performed on silicon sheets grown by the edge-supported pulling (ESP) and low-angle silicon sheet (LASS) processes. We have found that the dominant grain structure of the ESP sheets is long, narrow grains with surface normals oriented near (011); grains with this structure tend to have better electronic quality than random grains. We have also studied the twin-stabilized planar growth material of LASS sheets. This material, grown at 200 cm/sup 2//min, is essentially single-crystal.

Tsuo, Y.S.; Matson, R.J.

1984-05-01

58

The structure of the plasma sheet under northward IMF  

NASA Astrophysics Data System (ADS)

Studies on the properties of the plasma sheet have shown that it becomes cold and dense (T < 2 keV, n > 1 cm-3) during extended northward IMF periods and this change in the plasma status is most prominent close to the flanks. When these Cold and Dense Ions (CDIs) are transported earthward, it is reasonable to expect the compression to keep the density high whereas the temperature is elevated by adiabatic heating upon compression. This process should produce Hot-Dense Ions (HDIs) at the inner-edge of the plasma sheet. By defining HDIs with the criteria T > 2 keV, n > 1 cm-3, HDIs have been searched for using five years data of the Geotail spacecraft. HDIs are indeed found, and when focusing on those HDIs obtained under nominal solar wind dynamic pressures, we find them to appear only on the dawnside plasma sheet inner-edge and that during extended northward IMF intervals. That is, the result supports the idea that HDIs are the inner-magnetosphere extension of CDIs, and further imply that such a connection between the two populations takes place only on dawnside. In this paper, we describe the statistical study that reveals this structure of the plasma sheet. This picture suggesting significant dawn-dusk asymmetry in heating and transport in the magnetotail under northward IMF is also tested by case studies in which we inspect data from fortuitous orbits that transverse more than one key region under steady IMF/SW conditions. We also study data from multi-spacecraft monitoring the key regions simultaneously. Expected features are seen in these independent studies implying that the picture obtained by the statistic study indeed reflects the spatial structure of the plasma sheet under northward IMF.

Fujimoto, M.; Phan, T.; Bonnell, J.; McFadden, J.; Carlson, C.; Seki, K.; Kistler, L.; Reme, H.; Mukai, T.

2004-12-01

59

Kinetic theory of the electron bounce instability in two dimensional current sheets-Full electromagnetic treatment  

NASA Astrophysics Data System (ADS)

In the general context of understanding the possible destabilization of a current sheet with applications to magnetospheric substorms or solar flares, a kinetic model is proposed for studying the resonant interaction between electromagnetic fluctuations and trapped bouncing electrons in a 2D current sheet. Tur et al. [A. Tur et al., Phys. Plasmas 17, 102905 (2010)] and Fruit et al. [G. Fruit et al., Phys. Plasmas 20, 022113 (2013)] already used this model to investigate the possibilities of electrostatic instabilities. Here, the model is completed for full electromagnetic perturbations. Starting with a modified Harris sheet as equilibrium state, the linearized gyrokinetic Vlasov equation is solved for electromagnetic fluctuations with period of the order of the electron bounce period. The particle motion is restricted to its first Fourier component along the magnetic field and this allows the complete time integration of the non local perturbed distribution functions. The dispersion relation for electromagnetic modes is finally obtained through the quasineutrality condition and the Ampere's law for the current density. It is found that for mildly strechted current, undamped modes oscillate at typical electron bounce frequency with wavelength of the order of the plasma sheet half thickness. As the stretching of the plasma sheet becomes more intense, the frequency of these normal modes decreases and beyond a certain threshold in ? = Bz/Blobes, the mode becomes explosive with typical growth rate of a few tens of seconds. The free energy contained in the bouncing motion of the electrons may trigger an electromagnetic instability able to disrupt the cross-tail current in a few seconds. This new instability-electromagnetic electron-bounce instability-may explain fast and global scale destabilization of current sheets as required to describe substorm phenomena.

Tur, A.; Fruit, G.; Louarn, P.; Yanovsky, V.

2014-03-01

60

Evolution of Inner Plasma Sheet Pressure Associated with Substorm Onset  

NASA Astrophysics Data System (ADS)

We have investigated the evolution of plasma pressure associated with substorms onsets within the inner equatorial plasma sheet using the five THEMIS spacecraft data during the 2008 tail season. The central plasma sheet thermal pressure is estimated from the measured off-equatorial plane thermal pressure and magnetic pressure. Based on simple pressure balance, we expect the reduction of cross-tail current associated with current wedge formation to be associated with a reduction of the plasma sheet pressure that initiates at a radial distance of ~-10RE and expands tailward. However, our results show that associated with substorm, the plasma pressure undergoes a large enhancement after onset earthward of ~-11RE. Also, associated with the onset, a gradual precursor pressure increase is found several minutes before the large enhancement, and the precursor appears to be associated with the gradual enhancement of the substorm breakup arc that has been observed a few minutes prior to the dramatic brightening and breakup of that arc. One the other hand, the plasma pressure beyond ~-16RE shows a remarkable decrease after onset. During the recovery phase, the pressure gradually returns to its original level. These results indicate that during the substorm expansion phase, the current wedge connects to the region further tailward than ~-16RE. The pressure increase earthward of ~-11RE could be related to the substorm current system oppositely directed to the substorm current wedge, which has recently been observed equatorward of the substorm onset region in the ionosphere. The relationship between the auroral break up arc, which is believed to map to ~-10RE, and the pressure and current evolution in that region of the plasma sheet near the time of onset becomes an interesting question for future study.

Xing, X.; Lyons, L.; Angelopoulos, V.; Larson, D.; McFadden, J.; Carlson, C.; Runov, A.; Glassmeier, K.; Auster, U.

2008-12-01

61

Enhancement mechanism of H- production and suitable configurations for materials processing in a magnetized sheet plasma  

NASA Astrophysics Data System (ADS)

A magnetized sheet plasma ion source was developed for steady state high density plasma with strong density and high temperature gradients. This feature provides efficient formation of negative hydrogen (H-) ions over a wide beam extraction area through the electron volume process. A hexapole confinement at the cathode, addition of argon and magnesium seeding led to the increase of H- yield. The device configuration is suitable for plasma based materials processing namely, synthesis of TiN, SiH, SnO2, and the formation of advanced MAX phase materials Ti2AlC, Ti2CdC and NbAlC.

Ramos, Henry J.; Villamayor, Michelle Marie S.; Mella, Aubrey Faith M.; Salamania, Janella Mae R.; Villanueva, Matthew Bryan P.; Viloan, Rommel Paulo B.

2014-08-01

62

Numerical study of the current sheet and plasma sheet boundary layer in a magnetotail model  

NASA Astrophysics Data System (ADS)

The current sheet and plasma sheet boundary layer (PSBL) in a magnetotail model are discussed. A test particle code is used to study the response of ensembles of particles to a two-dimensional, time-dependent model of the geomagnetic tail, and test the proposition (Coroniti, 1985a, b; Buchner and Zelenyi, 1986; Chen and Palmadesso, 1986; Martin, 1986) that the stochasticity of the particle orbits in these fields is an important part of the physical mechanism for magnetospheric substorms. The realistic results obtained for the fluid moments of the particle distribution with this simple model, and their insensitivity to initial conditions, is consistent with this hypothesis.

Doxas, I.; Horton, W.; Sandusky, K.; Tajima, T.; Steinolfson, R.

1990-08-01

63

Current Sheet in a Coaxial Plasma Gun  

Microsoft Academic Search

Magnetic- and electric-probe measurements were made on the thin carrent ; layer which is accelerated in a coaxial (Marshall) plasma gun. It is found that ; this layer does not act as a snowplow, but rather has the character of a strong ; shock wave. (auth);

L. C. Burkhardt; R. H. Lovberg

1962-01-01

64

Phase-independent generation of relativistic electron sheets  

SciTech Connect

A uniform and stable relativistic electron sheet can be generated by the two-layer target scheme, where a linearly polarized drive laser is originally employed. The energy and density of the electron layer are found to be sensitive to carrier-envelope phases of few-cycle laser pulses. To circumvent this problem, the present letter proposes to use a circularly polarized laser. The produced electron layer becomes completely independent of the phase of the laser, avoiding the rigorous requirement for phase stabilization in an ultra-intense few-cycle laser system. The improved scheme makes coherent x-ray sources based on relativistic electron sheets more attainable.

Wu, H.-C.

2011-07-11

65

Equilibrium structure of the plasma sheet boundary layer-lobe interface  

NASA Technical Reports Server (NTRS)

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

66

Near-Earth plasma sheet azimuthal pressure gradient and associated auroral development soon before substorm onset  

NASA Astrophysics Data System (ADS)

The azimuthal plasma pressure gradient in the near-Earth plasma sheet makes crucial contributions to field-aligned current (FAC) formation. Numerical simulations and statistical observations have shown that a plasma pressure peak tends to build up in the premidnight region of the near-Earth plasma sheet during the substorm growth phase owing to enhanced magnetic drift. This leads to azimuthal pressure gradients in this region. The temporal variation of the azimuthal pressure gradient may provide an indication for the FAC variations associated with the substorm growth phase and may set up a plasma sheet precondition for the substorm onset being triggered near this region. We take advantage of two of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft separated azimuthally near the orbit apogee and investigate the azimuthal plasma pressure gradient before substorm onset in the R 10-12 RE region. Equatorial plasma pressure is estimated by removing the curvature force effect. Five events with the spacecraft footprints mapped very close to the aurora onset region were selected. These events show substantial duskward pressure gradient enhancement 1-5 min before onset. The onset arc, which results from enhanced energetic electron precipitation, was found to intensify simultaneously with the pressure gradient enhancement before onset breakup occurs. Since the energy and energy flux of precipitating electrons reflect the upward FAC strength, these results indicate that the duskward azimuthal pressure gradient enhancement is associated with enhanced upward FAC during the late growth phase and leads to the intensification of the onset auroral arc soon before it breaks up. It is possible that this pressure gradient enhancement may lead to ballooning mode instability and thus substorm onset along the intensifying arc.

Xing, X.; Lyons, L. R.; Nishimura, Y.; Angelopoulos, V.; Donovan, E.; Spanswick, E.; Liang, J.; Larson, D.; Carlson, C.; Auster, U.

2011-07-01

67

Theory of the plasma-wave photoresponse of a gated graphene sheet  

NASA Astrophysics Data System (ADS)

The photoresponse of graphene has recently received considerable attention. The main mechanisms yielding a finite dc response to an oscillating radiation field which have been investigated include responses of photovoltaic, photothermoelectric, and bolometric origin. In this article, we present a fully analytical theory of a photoresponse mechanism which is based on the excitation of plasma waves in a gated graphene sheet. By employing the theory of relativistic hydrodynamics, we demonstrate that plasma-wave photodetection is substantially influenced by the massless Dirac fermion character of carriers in graphene, and that the efficiency of photodetection can be improved with respect to that of ordinary parabolic-band electron fluids in semiconductor heterostructures.

Tomadin, Andrea; Polini, Marco

2013-11-01

68

Interchange motion as a transport mechanism for formation of cold-dense plasma sheet  

NASA Astrophysics Data System (ADS)

evaluate whether interchange motion can provide the transport for the formation of the cold-dense plasma sheet in the near-Earth region, we present an event of cold-dense plasma sheet observed by five THEMIS probes after the interplanetary magnetic field turned northward, as well as their comparisons with the simulation results from the Rice Convection Model (RCM) combined with a modified Dungey force-balanced magnetic field solver. The observations of cold-dense plasma at different locations show quite different characteristics: (1) closer to the flank, the appearance is more periodic and exhibits larger fluctuations in plasma moments and magnetic field; (2) further away from the flank, the cold plasma appears later; (3) in the mixture with the cold plasma, the decrease in high-energy particle fluxes becomes less significant further away from the flank; (4) there is energy-dispersion in the cold particles at some locations; and (5) near the magnetopause, the fluctuations have the characteristics of the Kelvin-Helmholtz (K-H) vortices and the colder-denser plasma is likely to have lower entropy. In the RCM simulations, lower entropy plasma consisting of colder-denser ions and electrons was periodically released locally at the outer boundary to represent the plasma created within a K-H vortex. This lower entropy perturbation is interchange unstable and the resulting interchange motion through the magnetosphere-ionosphere coupling pushes the colder-denser plasma radially inward. The simulated particle energy spectrums at different locations qualitatively reproduce the observations, strongly suggesting that the seemingly different characteristics of cold-dense plasma observed by different probes are all a result of the same interchange-related transport mechanism.

Wang, Chih-Ping; Gkioulidou, Matina; Lyons, Larry R.; Xing, Xiaoyan; Wolf, Richard A.

2014-10-01

69

Resonant Alfven wave heating of the plasma sheet boundary layer  

NASA Astrophysics Data System (ADS)

The exchange of energy between the plasma mantle and the plasma sheet boundary layer (PSBL) is examined with a one-dimensional magnetotail model. The energy exchange occurs via Poynting flux generated by the localized mode conversion of a surface wave to an Alfven wave. This Poynting flux propagates through the lobe and into the PSBL where it is absorbed by two processes. The first arises from a gradient in the plasma beta causing a smooth absorption of Poynting flux. The second process results from the localized mode conversion of the decaying surface wave to an Alfven wave, causing a localized absorption of energy. A numerical solution of the linearized ideal MHD equations is obtained by assuming an adiabatic equation of state.

Harrold, B. G.; Goertz, C. K.; Smith, R. A.; Hansen, P. J.

1990-09-01

70

Survey of the plasma electron environment of Jupiter: A view from Voyager  

NASA Technical Reports Server (NTRS)

The plasma environment within Jupiter's bow shock is considered in terms of the in situ, calibrated electron plasma measurements made between 10 eV and 5.95 keV by the Voyager plasma science experiment (PLS). Measurements were analyzed and corrected for spacecraft potential variations; the data were reduced to nearly model independent macroscopic parameters of the local electron density and temperature. It is tentatively concluded that the radial temperature profile within the plasma sheet is caused by the intermixing of two different electron populations that probably have different temporal histories and spatial paths to their local observation. The cool plasma source of the plasma sheet and spikes is probably the Io plasma torus and arrives in the plasma sheet as a result of flux tube interchange motions or other generalized transport which can be accomplished without diverting the plasma from the centrifugal equator. The hot suprathermal populations in the plasma sheet have most recently come from the sparse, hot mid-latitude "bath" of electrons which were directly observed juxtaposed to the plasma sheet.

Scudder, J. D.; Sittler, E. C., Jr.; Bridge, H. S.

1980-01-01

71

Role of Plasma Sheet Source Population in Ring Current Dynamics (Invited)  

NASA Astrophysics Data System (ADS)

Understanding the dynamics of ring current particles during disturbed conditions remains a long-standing challenge, moreover these particles represent a seed population for the hazardous radiation belts. The formation of the storm-time ring current depends on two main factors: 1) the plasma sheet as a reservoir supplying particles that are transported earthward, and 2) the electric field as a mechanism that energizes them. To investigate ring current development on a global scale, we use our four-dimensional (4-D) ring current-atmosphere interactions model (RAM-SCB) [Jordanova et al., 2010; Zaharia et al., 2010] which solves the kinetic equation for H+, O+, and He+ ions and electrons using a self-consistently calculated magnetic field in force balance with the anisotropic ring current plasma pressure. The model boundary was recently expanded from geosynchronous orbit to 9 RE, where the plasma boundary conditions are specified from the empirical plasma sheet model TM03 [Tsyganenko and Mukai, 2003] based on Geotail data. We simulate the transport, acceleration, and loss of energetic particles from the magnetotail to the inner magnetosphere during several geomagnetic storms that occurred since the launch of the Van Allen Probes in August 2012. We compare our results with simultaneous plasma and field observations from the Energetic particle, Composition, and Thermal plasma (ECT) [Spence et al., 2013] and the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) [Kletzing et al., 2013] investigations on the Van Allen Probes. We investigate the role of the plasma sheet source population in global ring current simulations considering various boundary conditions and electric field formulations. An improved understanding of the highly coupled inner magnetosphere system is provided.

Jordanova, V.; Yu, Y.; Reeves, G. D.; Kletzing, C.; Spence, H.; Sazykin, S. Y.

2013-12-01

72

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

E-print Network

ionosphere during sub- storms. Collisionless magnetic reconnection is thought to un- derlie this impulsiveMultispacecraft observations of the electron current sheet, neighboring magnetic islands concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic

Santolik, Ondrej

73

Ion kinetic properties in Mercury's pre-midnight plasma sheet  

NASA Astrophysics Data System (ADS)

data from the Fast Imaging Plasma Spectrometer sensor on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, we demonstrate that the average distributions for both solar wind and planetary ions in Mercury's pre-midnight plasma sheet are well-described by hot Maxwell-Boltzmann distributions. Temperatures and densities of the H+-dominated plasma sheet, in the ranges ~1-10 cm-3 and ~5-30 MK, respectively, maintain thermal pressures of ~1 nPa. The dominant planetary ion, Na+, has number densities about 10% that of H+. Solar wind ions retain near-solar-wind abundances with respect to H+ and exhibit mass-proportional ion temperatures, indicative of a reconnection-dominated heating in the magnetosphere. Conversely, planetary ion species are accelerated to similar average energies greater by a factor of ~1.5 than that of H+. This energization is suggestive of acceleration in an electric potential, consistent with the presence of a strong centrifugal acceleration process in Mercury's magnetosphere.

Gershman, Daniel J.; Slavin, James A.; Raines, Jim M.; Zurbuchen, Thomas H.; Anderson, Brian J.; Korth, Haje; Baker, Daniel N.; Solomon, Sean C.

2014-08-01

74

Study of plasma flow reversal in the near-Earth plasma sheet using numerical computations  

NASA Astrophysics Data System (ADS)

Tailward flow in the near-Earth plasma sheet associated with a rebound of the earthward bursty bulk flow (BBF) is investigated using three-dimensional magnetohydrodynamics simulations of magnetic reconnection in the magnetotail on the basis of the spontaneous fast reconnection model. In order to investigate the properties of this tailward flow, virtual satellites are located at different positions in the plasma sheet within the simulation region, so that we can directly observe the temporal variations of plasma quantities in accordance with the growth and preceding the flow reversal associated with the magnetic reconnection. The time profile of the plasma flow velocity in the course of the BBF depends on the satellite position. Furthermore, the time profile of the magnetic field strength in the course of the reverse flow depends on the satellite position in the dawn-dusk direction. As a result of the rebound of the earthward flow, the accumulation of the plasma density and the plasma pressure is observed at any position in the plasma sheet during the interval between the BBF and the reverse flow.

Kondoh, Koji; Shimizu, Tohru

2014-12-01

75

Topological Features of a Compressible Plasma Vortex Sheet: 6 Cases  

NSDL National Science Digital Library

The Voyager and Pioneer Spacecraft have detected large-scale quasi-periodic plasma fluctuations in the outer heliosphere beyond 20 AU. A plasma vortex sheet model can explain these fluctuations and the observed correlations between various physical variables. The large scale outer heliosphere is modeled by solving the 3-D compressible magnetohydrodynamic equations involving three interacting shear layers. Computations were done on a Cray computer at the NASA Center for Computational Sciences. Six cases are animated: Weak magnetic field and strong magnetic field, each at three values of tau, the vortex street characteristic time. Contours of density are shown as dark transparent tubes. Critical points of the velocity field are represented by Glyphs. Vortex cores are shown in orange and blue.

Starr, Cindy; Oneil, Pamela; Siregar, Edouard; Ghosh, Sanjoy

1993-12-17

76

Kinetic electron bounce instability in a 2D current sheet - Implication for substorm dynamics  

NASA Astrophysics Data System (ADS)

In the general context of understanding the possible destabilization of the magnetotail before a substorm, we propose a kinetic model for electromagnetic ballooning-type instabilities in resonant interaction with trapped bouncing electrons in a 2D current sheet. Tur et al. 2010 and Fruit et al. 2013 already used this model to investigate the possibilities of electrostatic instabilities. Here, we generalize the model for full electromagnetic perturbations. Starting with a modified Harris sheet as equilibrium state, the linearized gyrokinetic Vlasov equation is solved for electromagnetic fluctuations with period of the order of the electron bounce period. The particle motion is restricted to its first Fourier component along the magnetic field and this allows the complete time integration of the non local perturbed distribution functions. The dispersion relation for electromagnetic modes is finally obtained through the quasineutrality condition and the Ampere's law for the current density. It is found that for mildly stretched current sheet (Bz > 0.1 Blobes) undamped and stable modes oscillate at typical electron bounce frequency with wavelength (in y) of the order of the plasma sheet thickness. As the stretching of the plasma sheet becomes more intense, the frequency of these normal modes decreases and beyond a certain threshold in epsilon=Bz/Blobes < 0.05 typically, the mode becomes explosive (pure imaginary frequency) with typical growing rate of a few tens of seconds. The free energy contained in the electron bouncing motion could thus trigger and drive an electromagnetic instability able to disrupt the cross-tail current in a few seconds. The role of the temperature ratio Te/Ti is also evaluated.

Fruit, G.; Tur, A.; Louarn, P.

2013-12-01

77

Ibid-CaltechLibrarySystem Electronic Delivery Cover Sheet  

E-print Network

Ibid-CaltechLibrarySystem Electronic Delivery Cover Sheet WARNING CONCERNING COPYRIGHT RESTRICTIONS that control the transport and fate of these contaminants is an important aspect of protecting the ocean provide unprecedented capability for high-density sampling and measurement of a wide range of trace

Adkins, Jess F.

78

A Gridded Electron Gun for a Sheet Beam Klystron  

SciTech Connect

This paper describes the development of an electron gun for a sheet beam klystron. Initially intended for accelerator applications, the gun can operate at a higher perveance than one with a cylindrically symmetric beam. Results of 2D and 3D simulations are discussed.

Read, M.E.; Miram, G.; Ives, R.L.; /Calabazas Creek Res., Saratoga; Ivanov, V.; Krasnykh, A.; /SLAC

2008-04-25

79

The inner edge of the plasma sheet and the diffuse aurora  

NASA Technical Reports Server (NTRS)

Three dimensional measurements from the ISEE-1 low energy electron spectrometer are used to map the location of the inner edge of the plasma sheet and study the anisotropies in the electron distribution function associated with this boundary. Lower energy plasma sheet electrons have inner edges closer to the earth than higher energies with the separations at different energies being larger near dawn and after dusk than at midnight. Lowest energy inner edges are frequently located adjacent to the plasmapause in the dawn hemisphere but are often separated from it in the dusk hemisphere by a gap of at least several Re. The energy dispersion is minimal in the afternoon quadrant where the inner edge is near the magnetopause and frequently oscillating on a time scale of minutes. The location of the inner edge is probably determined primarily by the motion of electrons in the existing electric and magnetic fields rather than by strong diffusion as has sometimes been supposed. Previously announced in STAR as N83-32595

Fairfield, D. H.; Vinas, A. F.

1984-01-01

80

Plasma treatment of thin film coated with graphene flakes for the reduction of sheet resistance.  

PubMed

We investigated the effects of plasma treatment on the sheet resistance of thin films spray-coated with graphene flakes on polyethylene terephthalate (PET) substrates. Thin films coated with graphene flakes show high sheet resistance due to defects within graphene edges, domains, and residual oxygen content. Cl2 plasma treatment led to decreased sheet resistance when treatment time was increased, but when thin films were treated for too long the sheet resistance increased again. Optimum treatment time was related to film thickness. The reduction of sheet resistance may be explained by the donation of holes due to forming pi-type covalent bonds of Cl with carbon atoms on graphene surfaces, or by C--Cl bonding at the sites of graphene defects. However, due to radiation damage caused by plasma treatment, sheet resistance increased with increased treatment time. We found that the sheet resistance of PET film coated with graphene flakes could be decreased by 50% under optimum conditions. PMID:24266197

Kim, Sung Hee; Oh, Jong Sik; Kim, Kyong Nam; Seo, Jin Seok; Jeon, Min Hwan; Yang, Kyung Chae; Yeom, Geun Young

2013-12-01

81

Embedding a Hall MHD plasma sheet simulation inside the Lyon-Fedder-Mobarry global MHD model  

NASA Astrophysics Data System (ADS)

We have developed a 3D Hall magnetohydrodynamic (MHD) model with the goal of embedding this high-resolution module into the plasma sheet region of the Lyon-Fedder-Mobarry global MHD model. We intend to investigate the effect of the Hall term on the size and structure of fast flow channels observed in the plasma sheet. Owing to insufficient spatial spacecraft coverage of plasma sheet flow bursts, we appeal to global simulations possessing similar tail flow channels to assess the relative importance of the Hall term in plasma sheet transport. Current global ideal MHD models, however, contain features that are highly resolution dependent. The Hall term imposes a physical size scale on the equations in the plasma sheet, and we plan to quantify the effect of that term on the characteristics of fast flow channels.

Guild, T.; Spence, H.; Lyon, J.; Goodrich, C.; Merkin, V.; Kepko, L.

2005-12-01

82

Energetic particle beams in the plasma sheet boundary layer following substorm expansion: Simultaneous near-earth and distant tail observations  

SciTech Connect

We present simultaneous observations of energetic particles by ISEE 1 in the near-earth geomagnetic tail and by ISEE 3 in the distant geomagnetic tail following the onset of a major substorn as indicated by ground magnetograms and synchronous orbit particle data. At substorm onset, both spacecraft are in the tail lobes. About 8 min after onset, ISEE 1 enters the plasma sheet; at the plasma sheet boundary, earthward directed ion beams are observed. At the same time (within the 128-s time resolution) tailward directed ion and electron beams are observed at ISEE 3. These beams persist intermittently for 25 min. The observations are explained in terms of the substorm neutral line model, wherein the near-earth and distant plasma sheet are disconnected after reconnection has proceeded to the last closed field line within the plasma sheet. Electron plasma and magnetic field data on ISEE 3 show that during the whole time period, ISEE 3 stays in the distant lobe and does not enter the plasma sheet. The plasmoid, expected to be released after reconnection has proceeded to the lobe field, is sensed by ISEE 3 as traveling compression region. The velocity dispersion effects during the appearance and disappearance of the beams indicate that these beams are not due to temporal effects but due to crossing of layers with particles of different velocity emitted from a steady source. From the observation of gradient anisotropy effects in the high energy protons, the spacing of the layers of particles with different velocity can be derived. This allows determination of the maximum electric potential along the new neutral line. The corresponding electric field is considerably smaller than the energy of the highest energy particles observed.

Scholer, M.; Baker, D.N.; Gleockler, G.; Klecker, B.; Ipavich, F.M.; Terasawa, T.; Tsurutani, B.T.; Galvin, A.B.

1986-04-01

83

Observation of the plasma boundary layer at lunar distances - Direct injection of plasma into the plasma sheet  

NASA Technical Reports Server (NTRS)

The paper presents observational evidence from the Apollo suprathermal ion detector experiments that the injection of magnetosheath particles at the low-latitude magnetopause operates at lunar distances as well. An interface between the magnetosheath and the plasma sheet, termed the plasma sheet boundary layer (PSBL), is identified and believed to be the extension of the magnetospheric boundary layer (also called the plasma boundary layer) observed on the dayside. Using measurements of the PSBL's thickness, magnetic field, and plasma velocity the average electric potential drop across the PSBL is estimated at 4.2 kV and compared with the potential drop which is needed to insure that the magnetopause is an equipotential for a closed magnetosphere. It was concluded though that the magnetosphere is open since this drop is much larger than 4.2 kV.

Sanders, G. D.; Maher, L. J.; Freeman, J. W.

1980-01-01

84

Cluster observations of currents in the plasma sheet during reconnection  

NASA Astrophysics Data System (ADS)

We present Cluster PEACE observations of parallel electron currents near a reversal of accelerated ion flows which indicated that the spacecraft were in the vicinity of an active reconnection X-line (XL). Moments calculated from the PEACE electron spectrometer 3D 4s resolution data are analysed. We surveyed the electron current structure to reveal their dependence on distance from the neutral sheet (NS). The electron density and the magnetic field component parallel to the lobe magnetic field were selected as proxies of the distance to the NS. We found that earthward from the XL the electron parallel current switches direction: tailward closer to the NS and earthward nearer to the lobe. On the interface between the tailward and earthward currents we found a narrow layer of strong earthward current. At the same place the largest transverse magnetic disturbances were detected. The observed current structure is consistent with the collisionless reconnection model. However, tailward of the XL no such structure was evident in the data.

Alexeev, I. V.; Owen, C. J.; Fazakerley, A. N.; Runov, A.; Dewhurst, J. P.; Balogh, A.; Rme, H.; Klecker, B.; Kistler, L.

2005-02-01

85

A new approach to nanoporous graphene sheets via rapid microwave-induced plasma for energy applications.  

PubMed

We developed a novel approach to the fabrication of three-dimensional, nanoporous graphene sheets featuring a high specific surface area of 734.9 m(2) g(-1) and an ultrahigh pore volume of 4.1 cm(3) g(-1) through a rapid microwave-induced plasma treatment. The sheets were used as electrodes for supercapacitors and for the oxygen reduction reaction (ORR) for fuel cells. Argon-plasma grown sheets exhibited a 44% improvement of supercapacitive performance (203 F g(-1)) over the plasma grown sheets (141 F g(-1)). N-doped sheets with Co3O4 showed an outstanding ORR activity evidenced from the much smaller Tafel slope (42 mV/decade) than that of Pt/C (82 mV/decade), which is caused by the high electrical conductivity of the graphene sheets, the planar N species content and the nanoporous morphology. PMID:25410325

Odedairo, Taiwo; Ma, Jun; Gu, Yi; Zhou, Wei; Jin, Jian; Zhao, X S; Zhu, Zhonghua

2014-12-12

86

Modelling the LLBL as the source of plasma for the plasma sheet during very quiet conditions  

NASA Astrophysics Data System (ADS)

The plasma sheet characteristics during very quiet conditions at the northward IMF hardly can be modelled if the only source is the mantle. On the other hand, satellite observations show that the stagnant part of the LLBL is thick and dense during such conditions. In this study there are analyzed some sample trajectories of the particles injected at the magnetosphere flanks and traced in the Earth's magnetotail. Magnetic and electric fields are taken from Tsyganenko and the Rich-Maynard-Heppner models, respectively.

Zwolakowska, D.

87

Embedding a Hall MHD plasma sheet simulation inside the Lyon-Fedder-Mobarry global MHD model  

Microsoft Academic Search

We have developed a 3D Hall magnetohydrodynamic (MHD) model with the goal of embedding this high-resolution module into the plasma sheet region of the Lyon-Fedder-Mobarry global MHD model. We intend to investigate the effect of the Hall term on the size and structure of fast flow channels observed in the plasma sheet. Owing to insufficient spatial spacecraft coverage of plasma

T. Guild; H. Spence; J. Lyon; C. Goodrich; V. Merkin; L. Kepko

2005-01-01

88

Bursty bulk flows in the inner central plasma sheet  

NASA Technical Reports Server (NTRS)

High-speed flows in the inner central plasma sheet (first reported by Baumjohann et al. (1990) are studied, together with the concurrent behavior of the plasma and magnetic field, by using AMPTE/IRM data from about 9 to 19 R(E) in the earth magnetotail. The conclusions drawn from the detailed analysis of a representative event are reinforced by a superposed epoch analysis applied on two years of data. The high-speed flows organize themselves in 10-min time scale flow enhancements called here bursty-bulk flow (BBF) events. Both temporal and spatial effects are responsible for their bursty nature. The flow velocity exhibits peaks of very large amplitude with a characteristic time scale of the order of a minute, which are usually associated with magnetic field dipolarizations and ion temeperature increases. The BBFs represent intervals of enhanced earthward convection and energy transport per unit area in the y-z GSM direction of the order of 5 x 10 exp 19 ergs/R(E-squared).

Angelopoulos, V.; Baumjohann, W.; Kennel, C. F.; Coronti, F. V.; Kivelson, M. G.; Pellat, R.; Walker, R. J.; Luehr, H.; Paschmann, G.

1992-01-01

89

Injection into electron plasma traps  

SciTech Connect

Computational studies and experimental measurements of plasma injection into a Malmberg-Penning trap reveal that the number of trapped particles can be an order of magnitude higher than predicted by a simple estimates based on a ballistic trapping model. Enhanced trapping is associated with a rich nonlinear dynamics generated by the space-charge forces of the evolving trapped electron density. A particle-in-cell simulation is used to identify the physical mechanisms that lead to the increase in trapped electrons. The simulations initially show strong two-stream interactions between the electrons emitted from the cathode and those reflected off the end plug of the trap. This is followed by virtual cathode oscillations near the injection region. As electrons are trapped, the initially hollow longitudinal phase-space is filled, and the transverse radial density profile evolves so that the plasma potential matches that of the cathode. Simple theoretical arguments are given that describe the different dynamical regimes. Good agreement is found between simulation and theory.

Gorgadze, Vladimir; Pasquini, Thomas A.; Fajans, Joel; Wurtele, Jonathan S.

2003-12-02

90

Poleward leaping auroras, the substorm expansive and recovery phases and the recovery of the plasma sheet  

SciTech Connect

The auroral motions and geomagnetic changes the characterize the substorm`s expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.

Hones, E.W.

1992-05-01

91

Poleward leaping auroras, the substorm expansive and recovery phases and the recovery of the plasma sheet  

SciTech Connect

The auroral motions and geomagnetic changes the characterize the substorm's expansive phase, maximum epoch, and recovery phase are discussed in the context of their possible associations with the dropout and, especially, the recovery of the magnetotail plasma sheet. The evidence that there may be an inordinately sudden large poleward excursion or displacement (a poleward leap) of the electrojet and the auroras at the expansive phase-recovery phase transition is described. The close temporal association of these signatures with the recovery of the plasma sheet, observed on many occasions, suggests a causal relationship between substorm maximum epoch and recovery phase on the one hand and plasma sheet recovery on the other.

Hones, E.W.

1992-01-01

92

Multiple harmonic ULF waves in the plasma sheet boundary layer observed by Cluster  

NASA Astrophysics Data System (ADS)

The passage of the Cluster satellites in a polar orbit through Earth's magnetotail has provided numerous observations of harmonically related Pc 1-2 ULF wave events, with the fundamental near the local proton cyclotron frequency ?cp. Broughton et al. (2008) reported observations by Cluster of three such events in the plasma sheet boundary layer, and used the wave telescope technique to determine that their wave vectors k were nearly perpendicular to B. This paper reports the results of a search for such waves throughout the 2003 Cluster tail passage. During the 4 month period of July-October 2003, 35 multiple-harmonic wave events were observed, all in the plasma sheet boundary layer (PSBL). From the first observed event (22 July) to the last (28 October), 13 of Cluster's 42 tail passes had at least one event. The wave events were rather evenly distributed from XGSE = -7 RE out to the Cluster apogee distance of -18 RE, with one event observed at -4 RE. ZGSE for these events ranged from -10 to -3 RE and +3 to +7 RE (i.e., there were no events for ?Z? < 3 RE). The wave events, with durations from 1 to 50 min, were consistently associated with signatures of the PSBL: elevated fluxes of counterstreaming ions with energies ranging from 3 to 30 keV, and elevated fluxes of electrons with energies ranging from 0.25 to 5 keV. Analysis of plasma parameters suggests that although waves occurred only when the ion beta exceeded 0.1 (somewhat larger than typical for the PSBL), ion particle pressure may be of more physical importance in controlling wave occurrence. Electron distributions were more isotropic in pitch angles than the ion distributions, but some evidence of counterstreaming electrons was detected in 83% of the events. The ions also showed clear signatures of shell-like or ring-like distributions; i.e., with reduced fluxes below the energy of maximum flux. The suprathermal ion fluxes were asymmetric in all events studied, with more ions streaming earthward (for events both north and south of the central plasma sheet). Good agreement between the observed frequency of the fundamental harmonic and the local ?cp suggests that the waves were observed near the region of their origin and did not propagate along B, consistent with the wave telescope analysis.

Engebretson, M. J.; Kahlstorf, C. R. G.; Posch, J. L.; Keiling, A.; Walsh, A. P.; Denton, R. E.; Broughton, M. C.; Owen, C. J.; FornaOn, K.-H.; RMe, H.

2010-12-01

93

Tearing instabilities driven by nonideal effects in the tail plasma sheet  

SciTech Connect

Using an extended magnetohydrodynamic description, the excitation of tearing modes is analytically investigated in the tail plasma sheet region that includes the magnetic field components B{sub 0x}(x,z) and B{sub 0z}(x,z). Taking electron inertia and the Hall effect into account, a generalized technique is displayed for obtaining the tearing solutions near the singular layer, where the B{sub 0x}(x,z) field reverses sign at z=0. In two-dimensional tail geometry for scale lengths of order c/{omega}{sub pe}, it is shown that a localized tearing mode as well as a mode with broad spatial extent ({delta}{sup '}-driven mode) is excited near the field reversal region and these modes are mainly driven by electron inertia. For appropriate current sheet parameters, it is found that the localized mode becomes unstable in a couple of minutes while the mode with broad spatial width grows faster in 10 s. For three-dimensional perturbations wherein k{sub x},k{sub y}{ne}0, the combined effects of the Hall term and the electron inertia are shown to excite new localized tearing modes with considerably enhanced growth rates ({gamma}>{omega}{sub ci})

Sundaram, A. K

2008-05-15

94

Plasma Wave Wigglers for Free Electron Lasers  

Microsoft Academic Search

We explore the possibility of using relativistic plasma density waves as wigglers for producing free electron laser radiation. Two possi- ble wave and beam geometries are explored. In the first, the wiggler is a purely electric wiggler with frequency ma (plasma frequency) but (approximately) zero wavenumber k,. If an electron beam is injected parallel to a wide plasma wave wavefront,

C. Joshi; F. F. Chen; J. M. Dawson; T. Katsouleas; Y. T. Yan

1987-01-01

95

Electron Plasma Orbits from Competing Diocotron Drifts  

NASA Astrophysics Data System (ADS)

The perpendicular dynamics of a pure electron plasma column are investigated when the plasma spans two Penning-Malmberg traps with noncoinciding axes. The plasma executes noncircular orbits described by competing image-charge electric-field (diocotron) drifts from the two traps. A simple model is presented that predicts a set of nested orbits in agreement with observed plasma trajectories.

Hurst, N. C.; Danielson, J. R.; Baker, C. J.; Surko, C. M.

2014-07-01

96

Energetic particle beams in the plasma sheet boundary layer following substorm expansion - Simultaneous near-earth and distant tail observations  

NASA Technical Reports Server (NTRS)

Simultaneous observations of ions and electron beams in the near-earth and deep magnetotail following the onset of substorm are analyzed in terms of the substorm neutral line model. The observations were collected on March 20, 1983 with ISSE 1 and 3. Energy fluxes and intensity-time profiles of protons and electrons are studied. The data reveal that the reconnection at the near-earth neutral line produces ions and electrons for the plasma sheet boundary layer. The maximum electric potential along the neutral line is evaluated.

Scholer, M.; Baker, D. N.; Gloeckler, G.; Ipavich, F. M.; Galvin, A. B.; Klecker, B.; Terasawa, T.; Tsurutani, B. T.

1986-01-01

97

The thermal and plasma-physical evolution of laminar current sheets formed in the solar atmosphere by emerging flux  

NASA Technical Reports Server (NTRS)

A time-dependent analysis of emerging flux is carried out, and the time evolution of both the current sheet energetics and the plasma state is calculated. This evolution is determined in two different regimes. In the first case the width of the current sheet is assumed to be independent of the sheet thermodynamics and is fixed by the initial conditions. In the second, the width of the current sheet is a function of the resistivity and is allowed to decrease to its minimum given by the electron gyroradius. In both cases the resistivity is computed according to the marginal stability hypothesis. In each case the thermodynamic evolution is found to be quite rapid, with the temperature increasing from 10,000 to 1,000,000 K in a second or less. In contrast to previous studies, it is found that the resistivity is not significantly enhanced by the current-driven plasma wave turbulence. It is concluded that a laminar current sheet cannot be responsible for the activity associated with emerging flux.

Larosa, T. N.

1992-01-01

98

Effects of pressure gradients and convection on the inner plasma sheet stability  

Microsoft Academic Search

We present a computer model that solves the system of nonlinear MHD equations in dipolar coordinates and is designed specifically to simulate the near-Earth plas ma sheet region which has a near-dipolar field line topology. The objective of this work is a detailed study of the inner plasma sheet as a region of particular importance for auroral processes including the

V. Prosolin; I. Voronkov; E. Donovan

2006-01-01

99

Growth model for plasma-CVD growth of carbon nano-tubes on Ni-sheets  

Microsoft Academic Search

The plasma enhanced chemical vapor deposition (PECVD) of carbon nano-tubes (CNT) on nickel sheets is considered as efficient production method of great technologically interest. Different morphologies of CNT on Ni-sheets can be achieved by a variation of the process parameters, like partial pressure of the acetylene and ammoniac inlet gas mixture, the total gas pressure, and temperature. The results are

Wilfried Wunderlich

2007-01-01

100

Energy conversion regions as observed by Cluster in the plasma sheet  

Microsoft Academic Search

First in situ observations of the average load behavior of the plasma sheetCluster PS energy conversion observations are consistent with MHD simulationsECRs and BBFs are likely to be related, although details need to be explored

M. Hamrin; O. Marghitu; P. Norqvist; S. Buchert; M. Andr; B. Klecker; L. M. Kistler; I. Dandouras

2011-01-01

101

Electron-electron interactions in doped graphene sheets  

NASA Astrophysics Data System (ADS)

In this talk I will review some of the most important electronic properties of graphene. I will first discuss the appearance of plasmaron satellite bands in both angle-resolved photoemission [1] and STM spectra [2,3], emphasizing the important role of the sublattice pseudospin degree of freedom. I will then illustrate some unusual features, which appear only beyond the widely used Random Phase Approximation, characterizing plasmons and Drude weight of the electron gas in this material [4].[4pt] [1] A. Bostwick et al., Science 328, 999 (2010).[0pt] [2] V.W. Brar et al., Phys. Rev. Lett. 104, 036805 (2010).[0pt] [3] A. Principi, M. Polini, and A.H. MacDonald, to be submitted[0pt] [4] S.H. Abedinpour et al., Phys. Rev. B 84, 045429 (2011).

Polini, Marco

2012-02-01

102

A THEMIS multicase study of dipolarization fronts in the magnetotail plasma sheet  

NASA Astrophysics Data System (ADS)

We discuss results of a superposed epoch analysis of dipolarization fronts, rapid (?t < 30 s), high-amplitude (?Bz > 10 nT) increases in the northward magnetic field component, observed during six Time History of Events and Macroscale Interactions during Substorms (THEMIS) conjunction events. All six fronts propagated earthward; time delays at multiple probes were used to determine their propagation velocity. We define typical magnetic and electric field and plasma parameter variations during dipolarization front crossings and estimate their characteristic gradient scales. The study reveals (1) a rapid 50% decrease in plasma density and ion pressure, (2) a factor of 2-3 increase in high-energy (30-200 keV) electron flux and electron temperature, and (3) transient enhancements of 5 mV/m in duskward and earthward electric field components. Gradient scales of magnetic field, plasma density, and particle flux were found to be comparable to the ion thermal gyroradius. Current densities associated with the Bz increase are, on average, 20 nA/m2, 5-7 times larger than the current density in the cross-tail current sheet. Because j E > 0, the dipolarization fronts are kinetic-scale dissipative regions with Joule heating rates of 10% of the total bursty bulk flow energy.

Runov, A.; Angelopoulos, V.; Zhou, X.-Z.; Zhang, X.-J.; Li, S.; Plaschke, F.; Bonnell, J.

2011-05-01

103

On the propagation of low-frequency fluctuations in the plasma sheet: 1. Cluster observations and magnetohydrodynamic analysis  

Microsoft Academic Search

Low-frequency pressure and magnetic oscillations observed by Cluster in the plasma sheet are investigated with the aim of determining if they are magnetohydrodynamic (MHD) eigenmodes. We analyze the plasma sheet crossing occurring on 22 August 2001, as the magnetosphere was first quiet and then active, and compare the observations with theoretical results concerning the MHD propagation in a Harris sheet.

P. Louarn; G. Fruit; E. Budnik; J. A. Sauvaud; C. Jacquey; D. Le Quau; H. Rme; E. Lucek; A. Balogh

2004-01-01

104

The plasma-cathode electron gun  

Microsoft Academic Search

The development of a new type of plasma-cathode electron gun suitable for pulsed as well as CW operation withe-beam lasers is reported. This device employs a plasma generated within a low-voltage hollow-cathode discharge rather than a thermionic emitter as the source of electrons. Electrons extracted from the plasma pass through a triode-type control grid structure and are accelerated to high

J. Bayless; R. Knechtli; G. Mercer

1974-01-01

105

Geotail observations of spiky electric fields and low-frequency waves in the plasma sheet and plasma sheet boundary  

NASA Technical Reports Server (NTRS)

Electric field data from the Geotail spacecraft provide an opportunity to extend the observations of spiky fields made by International Sun Earth Explorer-1 (ISEE-1) to a region of the magnetosphere where quasistatic electric field measurements have not previously been msde, to examine their possible importance in the dynamics of the middle and distant tail, and to test some hypotheses about their formation. In this paper, examples of large fields in the plasma sheet and its boundary at radial distances up to approximately 90 R(sub E) are presented. It is shown that three different types of large electric fields can occur: (1) spiky fields; (2) 'DC' fields; and (3) waves at frequencies comparable to the lower hybrid frequency. There is usually a gradation between (1) and (3), and often large electric field spikes are embedded in regions of lower amplitude waves. The waves tend to occur in short (few to 10's of seconds) packets whose start and stop times are not always correlated with changes in the magnetic field and/or density (as indicated by the spacecraft potential). The peak frequency is often less than but comparable to the lower hybrid frequency in agreement with theories of lower hybrid drift waves in the magnetotail. The largest spikes are not always associated with the largest changes in the spacecraft potential and/or magnetic field. It is suggested that the spiky fields may represent the nonlinear development of the waves.

Cattell, C.; Mozer, F.; Tsuruda, K.; Hayakawa, H.; Nakamura, M.; Okada, T.; Kokubun, S.; Yamamoto, T.

1994-01-01

106

Electron and photon beams interacting with plasma.  

PubMed

A comparison is made between the interaction of electron bunches and intense laser pulses with plasma. The laser pulse is modelled with photon kinetic theory, i.e. a representation of the electromagnetic field in terms of classical quasi-particles with space and wave number coordinates, which enables a direct comparison with the phase space evolution of the electron bunch. Analytical results are presented of the plasma waves excited by a propagating electron bunch or laser pulse, the motion of electrons or photons in these plasma waves and collective effects, which result from the self-consistent coupling of the particle and plasma wave dynamics. PMID:16483954

Reitsma, Albert; Jaroszynski, Dino

2006-03-15

107

Thinning and functionalization of few-layer graphene sheets by CF4 plasma treatment  

PubMed Central

Abstract Structural changes of few-layer graphene sheets induced by CF4 plasma treatment are studied by optical microscopy and Raman spectroscopy, together with theoretical simulation. Experimental results suggest a thickness reduction of few-layer graphene sheets subjected to prolonged CF4 plasma treatment while plasma treatment with short time only leads to fluorine functionalization on the surface layer by formation of covalent bonds. Raman spectra reveal an increase in disorder by physical disruption of the graphene lattice as well as functionalization during the plasma treatment. The F/CF3 adsorption and the lattice distortion produced are proved by theoretical simulation using density functional theory, which also predicts p-type doping and Dirac cone splitting in CF4 plasma-treated graphene sheets that may have potential in future graphene-based micro/nanodevices. PACS 81.05.ue; 73.22.Pr; 52.40.Hf. PMID:22625875

2012-01-01

108

Study of simultaneous reduction and nitrogen doping of graphene oxide Langmuir-Blodgett monolayer sheets by ammonia plasma treatment  

NASA Astrophysics Data System (ADS)

Graphene oxide (GO) monolayer sheets, transferred onto Si by the Langmuir-Blodgett technique, were subjected to ammonia plasma treatment at room temperature with the objective of simultaneous reduction and doping. Scanning electron microscopy and atomic force microscopy studies show that plasma treatment at a relatively low power (10 W) for up to 15 min does not affect the morphological stability and monolayer character of GO sheets. X-ray photoelectron spectroscopy has been used to study de-oxygenation of GO monolayers and the incorporation of nitrogen in graphitic-N, pyrrolic-N and pyridinic-N forms due to the plasma treatment. The corresponding changes in the valence band electronic structure, density of states at the Fermi level and work function have been investigated by ultraviolet photoelectron spectroscopy. These studies, supported by Raman spectroscopy and electrical conductivity measurements, have shown that a short duration plasma treatment of up to 5 min results in an increase of sp2-C content along with a substantial incorporation of the graphitic-N form, leading to the formation of n-type reduced GO. Prolonged plasma treatment for longer durations results in a decrease of electrical conductivity, which is accompanied by a substantial decrease of sp2-C and an increase in defects and disorder, primarily attributed to the increase in pyridinic-N content.

Singh, Gulbagh; Sutar, D. S.; Divakar Botcha, V.; Narayanam, Pavan K.; Talwar, S. S.; Srinivasa, R. S.; Major, S. S.

2013-09-01

109

Substorm-related plasma sheet motions as determined from differential timing of plasma changes at the ISEE satellites  

NASA Technical Reports Server (NTRS)

From an ISEE survey of substorm dropouts and recoveries during the period February 5 to May 25, 1978, 66 timing events observed by the Los Alamos Scientific Laboratory/Max-Planck-Institut Fast Plasma Experiments were studied in detail. Near substorm onset, both the average timing velocity and the bulk flow velocity at the edge of the plasma sheet are inward, toward the center. Measured normal to the surface of the plasma sheet, the timing velocity is 23 + or - 18 km/s and the proton flow velocity is 20 + or - 8 km/s. During substorm recovery, the plasma sheet reappears moving outward with an average timing velocity of 133 + or - 31 km/s; however, the corresponding proton flow velocity is only 3 + or - 7 km/s in the same direction. It is suggested that the difference between the average timing velocity for the expansion of the plasma sheet and the plasma bulk flow perpendicular to the surface of the sheet during substorm recovery is most likely the result of surface waves moving past the position of the satellites.

Forbes, T. G.; Hones, E. W., Jr.; Bame, S. J.; Asbridge, J. R.; Paschmann, G.; Sckopke, N.; Russell, C. T.

1981-01-01

110

Effect of self-consistent magnetic field on plasma sheet penetration to the inner magnetosphere under enhanced convection: RCM simulations combined with force-balance magnetic field solver  

NASA Astrophysics Data System (ADS)

Transport of plasma sheet particles into the inner magnetosphere is strongly affected by the penetration of the convection electric field, which is the result of the large-scale magnetosphere-ionosphere electromagnetic coupling. This transport, on the other hand, results in plasma heating and magnetic field stretching, which become very significant in the inner plasma sheet (inside 20 RE). We have previously run simulations with the Rice Convection Model (RCM) to investigate how the earthward penetration of convection electric field, and therefore plasma sheet population, depends on plasma sheet boundary conditions. Outer boundary conditions at r ~20 RE are a function of MLT and interplanetary conditions based on 11 years of Geotail data. In the previous simulations, Tsyganenko 96 magnetic field model (T96) was used so force balance between plasma pressure and magnetic fields was not maintained. We have now integrated the RCM with a magnetic field solver (Liu et al., 2006) to obtain the required force balance in the equatorial plane. We have run the self-consistent simulations under enhanced convection with different boundary conditions in which we kept different parameters (flux tube particle content, plasma pressure, plasma beta, or magnetic fields) at the outer boundary to be MLT-dependent but time independent. Different boundary conditions result in qualitatively similar plasma sheet profiles. The results show that magnetic field has a dawn dusk asymmetry with field lines being more stretched in the pre-midnight sector, due to relatively higher plasma pressure there. The asymmetry in the magnetic fields in turn affects the radial distance and MLT of plasma sheet penetration into the inner magnetosphere. In comparison with results using the T96, plasma transport under self-consistent magnetic field results in proton and electron plasma sheet inner edges that are located in higher latitudes, weaker pressure gradients, and more efficient shielding of the near-Earth convection electric field (since auroral conductance is also confined to higher latitudes). We are currently evaluating the simulated plasma sheet properties by comparing them with statistical results obtained from Geotail and THEMIS observations.

Gkioulidou, M.; Wang, C.; Lyons, L. R.; Wolf, R. A.

2010-12-01

111

ATS-5 observations of plasma sheet particles before the expansion-phase onset, appendix C.. [plasma-particle interactions, magnetic storms and auroras  

NASA Technical Reports Server (NTRS)

Behavior of the plasma sheet around its earthward edge during substorms was studied by using high resolution (every 2.6 sec) measurements of proton and electron fluxes by ATS-5. In the injection region near midnight the flux increase at the expansion-phase onset is shown to lag behind the onset of the low-latitude positive bay by several minutes. Depending upon the case, before the above increase (1) the flux stays at a constant level, (2) it gradually increases for some tens of minutes, or (3) it briefly drops to a low level. Difference in the position of the satellite relative to the earthward edge and to the high-latitude boundary of the plasma sheet is suggested as a cause of the above difference in flux variations during the growth phase of substorms. Magnetograms and tables (data) are shown.

Fujii, K.; Nishida, A.; Sharp, R. D.; Shelley, E. G.

1975-01-01

112

[Emission spectroscopy diagnostics of plasma electron temperature].  

PubMed

Electron temperature is one of the important parameters of plasma. It is very difficult to measure the electron temperature exactly and instantly owing to its complexity during discharge. As a plasma diagnostics technique, emission spectroscopy is widely applied in the study and diagnosis of any kind of plasma, because of its simple instrument system, noninterference of measurement, high sensitivity and fast responsibility. In the present paper, some methods for plasma electron temperature diagnosis, such as two lines method, multiline slope method, isoelectronic line method, Saha-Boltzmann equation, absolute intensity method, were introduced. And the applications of these methods were reviewed to provide reference for choosing appropriate methods in practice. PMID:18619285

Wu, Rong; Li, Yan; Zhu, Shun-Guan; Feng, Hong-Yan; Zhang, Lin; Wang, Jun-De

2008-04-01

113

Review of Solar Wind Entry into and Transport Within the Plasma Sheet  

NASA Astrophysics Data System (ADS)

The plasma sheet is populated in part by the solar wind plasma. Four solar entry mechanisms are examined: (1) double cusp or double lobe reconnection, (2) Kelvin-Helmholtz Instability (KHI), (3) Kinetic Alfvn waves (KAW), and (4) Impulsive Penetration. These mechanisms can efficiently fill the plasma sheet with cold dense ions during northward interplanetary magnetic field (IMF). The solar wind ions appear to have been heated upon entry along the plasma sheet dawn flank. The cold-component (solar wind origin) ion density is higher on the dawn flank than the dusk flank. The asymmetric evolution of the KAW and magnetic reconnection in association with the KHI at the dawn and dusk flank magnetopause may partly produce the dawn-dusk temperature and density asymmetries. Solar wind that crosses the magnetopause lowers the specific entropy ( s= p/ ? ? ) of the plasma sheet along the flanks. Subsequent transport of the cold ions from the flanks to the midnight meridian increases s by a factor of 5. T i , T e , s i , and s e increase when the solar wind particles are transported across the magnetopause, but T i / T e is roughly conserved. Within the magnetotail, E B and curvature and gradient drifts play important roles in the plasma transport and can explain the large features seen in the plasma sheet. Turbulence can also play a significant role, particularly in the cold plasma transport from the flanks to the midnight meridian. Total entropy ( S= pV ? ) conservation provides important constraints on the plasma sheet transport, e.g., fast flows.

Wing, S.; Johnson, J. R.; Chaston, C. C.; Echim, M.; Escoubet, C. P.; Lavraud, B.; Lemon, C.; Nykyri, K.; Otto, A.; Raeder, J.; Wang, C.-P.

2014-11-01

114

Electron "bite-outs" in Dusty Plasmas  

NASA Astrophysics Data System (ADS)

The study of dusty plasmas is still an emerging new field that bridges a number of traditionally separate subjects, including for example, celestial mechanics, and plasma physics. Dust particles immersed in plasmas and UV radiation collect electrostatic charges and respond to electromagnetic forces in addition to all the other forces acting on uncharged grains. Simultaneously, dust can alter its plasma environment. Dust particles in plasmas are unusual charge carriers. They are many orders of magnitude heavier than any other plasma particles, and they can have many orders of magnitude larger (negative or positive) time-dependent charges. Dust particles can communicate non-electromagnetic effects (gravity, drag, radiation pressure) to the plasma that can represent new free energy sources. Their presence can influence the collective plasma behavior, for example, by altering the traditional plasma wave modes and by triggering new types of waves and instabilities. Dusty plasmas represent the most general form of space, laboratory, and industrial plasmas. Interplanetary space, comets, planetary rings, asteroids, the Moon, aerosols in the atmosphere, are all examples where electrons, ions, and dust particles coexist. This talk will focus on "electron bite-outs", the apparent reduction of the electron density due to dust charging in a plasma comprised of electrons, ions and dust particles We will compare the recent observations of the plasma conditions near Enceladus at Saturn to the decades old measurements in the Earth's mesosphere. We present model calculations of dust charging in a region where plasma is maintained by UV radiation, and present the time-dependent charge distribution of grains as function of dust density and size distribution. We will also make estimates for possible dusty plasma wave activities as function of the magnitude of the electron "bite-outs".

Horanyi, M.; Hsu, S.; Kempf, S.

2012-12-01

115

Hierarchical regrowth of flowerlike nanographene sheets on oxygen-plasma-treated carbon nanowalls  

NASA Astrophysics Data System (ADS)

Cauliflorous nanographene sheets were hierarchically regrown on the spearlike structures of carbon nanowalls (CNWs) produced by O2-plasma etching. The spears on the CNWs acted as a stem for the growth of flowerlike flaky nanographene sheets, where the root of the nanoflower was located at a defect or disordered site. The defects on the graphitic structures were induced by irradiation with oxygen-related radicals and ions in the O2-based plasmas and acted as sites for the nucleation of flowerlike nanographene. The porous carbon nanostructures regrown after O2-plasma treatment have a relatively higher surface area and are thus promising materials for electrochemical applications.

Shimoeda, Hironao; Kondo, Hiroki; Ishikawa, Kenji; Hiramatsu, Mineo; Sekine, Makoto; Hori, Masaru

2014-04-01

116

Three-dimensional analyses of electric currents and pressure anisotropies in the plasma sheet  

E-print Network

suggests that the net effect of chaotic ion motion near the neutral sheet is to create a weak source cone by an electric field with a parallel component near the neutral sheet. The parallel electric field is small but is required to maintain charge neutrality in the region containing guiding center electron and nonguiding

Kaufmann, Richard L.

117

Estimating local plasma sheet PV5\\/3 from single-spacecraft measurements  

Microsoft Academic Search

The theory of plasma transport in Earth's plasma sheet depends critically on the entropy parameter PV5\\/3, where P is particle pressure and V is the volume of a closed flux tube containing one unit of magnetic flux. Theory suggests that earthward moving flow bursts that inject plasma into the inner magnetosphere consist of flux tubes that have PV5\\/3 values that

R. A. Wolf; V. Kumar; F. R. Toffoletto; G. M. Erickson; A. M. Savoie; C. X. Chen; C. L. Lemon

2006-01-01

118

Interchange Modes in the Magnetotail and Their Role in Generating N-S Auroral Streamers and Plasma Sheet Disruption (Invited)  

NASA Astrophysics Data System (ADS)

The most common description of magnetotail dynamics including the generation of bursty bulk flows and plasma sheet disruption involves magnetic reconnection. This scenario, however, must deal with the problems of reconnection onset in the presence of a normal magnetic field and the inability to explain the east-west localization of the flow bursts and disruptions. An alternative mechanism involves the excitation of interchange modes that are driven by the need to return earthward magnetic flux that has been convected tailward during the growth phase of substorms. Fully kinetic 3D particle-in-cell simulations have demonstrated the existence of kinetic interchange modes with east-west wavelength of the order of the equatorial ion gyroradius and frequency about 60% of the midplane ion cyclotron frequency in regions of the midtail where the electron dynamics is adiabatic. In their nonlinear evolution the modes steepen into Rayleigh-Taylor type fingers and propagate earthward. As the structures steepen, the total magnetic flux contained within them remains constant, and the structures represent a dynamical realization of underpopulated flux tubes. The field-aligned currents associated with the head of the flows have the signature of a N-S auroral streamer. The interaction of such interchange heads with the near-Earth plasma sheet is observed in some cases to produce a violent localized disruption of the plasma sheet in which the particles are strongly energized and high speed flows are triggered both earthward and tailward. The implications of these results for substorm onset will be discussed.

Pritchett, P. L.; Coroniti, F. V.

2010-12-01

119

Structured plasma sheet thinning observed by Galileo and 1984-129  

SciTech Connect

On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that is crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984-129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near-Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near-Earth tail during the growth phase of substorms. This period is unique in that Galileo provided a rapid radial profile of the near-Earth plasma sheet while 1984-129 provided an azimuthal profile. With measurements from these two spacecraft the authors can distinguish between spatial structures and temporal changes. Their observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft`s magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours. 28 refs., 10 figs.

Reeves, G.D.; Belian, R.D.; Fritz, T.A. [Los Alamos National Lab., NM (United States)] [and others

1993-12-01

120

Structured plasma sheet thinning observed by Galileo and 1984-129  

NASA Technical Reports Server (NTRS)

On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that it crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984-129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near-Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near-profile of the near-Earth plasma sheet while 1984-129 provided an azimuthal profile. With measurements from these two spacecraft we can distinguish between spatial structures and temporal change. Our observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft's magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours.

Reeves, G. D.; Belian, R. D.; Fritz, T. A.; Kivelson, M. G.; Mcentire, R. W.; Roelof, E. C.; Wilken, B.; Williams, D. J.

1993-01-01

121

Cluster Observations of Currents In The Plasma Sheet During Substorm Expansions  

NASA Astrophysics Data System (ADS)

From 00 to 12 UT on August 15, 2001 the Cluster spacecraft passed through the plasma sheet at 0100 lt and distance 18 Re. During this passage three substorms with multiple onsets were observed in the magnetic field and plasma. The North American ground sector was well located to provide the context and timing of these substorms. We find that each substorm was initially associated with strong Earthward directed field-aligned current. The first substorm occurred when the Cluster array was at the boundary of the plasma sheet. The effects of the substorm appear at Cluster in associ- ation with an intensification of the expansion into the morning sector and are initiated by a wave of plasma sheet thickening followed by vertical oscillations of the plasma sheet boundary. The third substorm occurred with Cluster at the neutral sheet. It began with a transient pulse of southward Bz followed by a burst of tailward flow. Subse- quently a sequence of bursts of Earthward flow cause stepwise dipolarization of the local magnetic field. Our goal is to present a coherent three-dimensional representa- tion of the Cluster observations for each of these various substorms.

McPherron, R. L.; Kivelson, M. G.; Khurana, K.; Balogh, A.; Conners, M.; Creutzberg, F.; Moldwin, M.; Rostoker, G.; Russell, C. T.

122

Intrinsic electronic and transport properties of graphyne sheets and nanoribbons  

NASA Astrophysics Data System (ADS)

Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry.Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03167e

Wu, Wenzhi; Guo, Wanlin; Zeng, Xiao Cheng

2013-09-01

123

Plasma behavior during energetic electron streaming events further evidence for substorm-associated magnetic reconnection  

NASA Technical Reports Server (NTRS)

A recent study showed that streaming energetic (more than 200 keV) electrons in earth's magnetotail are statistically associated with southward magnetic fields and with enhancements of the AE index. It is shown here that the streaming electrons characteristically are preceded by an approximately 15-minute period of tailward plasma flow and followed by a dropout of the plasma sheet, thus demonstrating a clear statistical association between substorms and the classical signatures of magnetic reconnection and plasmoid formation. Additionally, a brief upward surge of mean electron energy preceded plasma dropout in several of the events studied, providing direct evidence of localized, reconnection-associated heating processes.

Bieber, J. W.; Stone, E. C.; Hones, E. W., Jr.; Baker, D. N.; Bame, S. J.

1982-01-01

124

Investigation of a staged plasma-focus apparatus. [pinch construction and current sheet dynamics investigation  

NASA Technical Reports Server (NTRS)

A new staged plasma-focus geometry combining two Mather-type plasma-focus guns was constructed, and the current-sheet dynamics were investigated. The production of simultaneous pairs of plasma foci was achieved. The intensities of X-ray and fusion-neutron emission were measured and found to agree with the scaling law for a plasma focus. Advantages of this new geometry include the possibility of using plasma-focus type pinches in multiple arrays at power levels beyond the validity regime of the current scaling law for a single gun.

Lee, J. H.; Mcfarland, D. R.; Harries, W. L.

1978-01-01

125

Model of electron collecting plasma contactors  

NASA Technical Reports Server (NTRS)

In laboratory experiments, plasma contactors are observed to collect ampere-level electron currents with low impedance. In order to extend the laboratory experience to the low-earth-orbit environment, a model of plasma contactors is being developed. Laboratory results are being used to support and validate the model development. The important physical processes observed in the laboratory are that the source plasma is separated from the background plasma by a double layer and that ionization of the expellant gas by the collected electrons creates the bulk of the ions that leave the source plasma. The model, which uses Poisson's equation with a physical charge density that includes the ion and electron components of both the source and the ambient plasmas, reproduces this phenomenon for typical experimental parameters. The calculations, in agreement with the laboratory results, show little convergence of the accelerated electrons. The angular momentum of the incoming electrons dramatically reduces the peak electron density. These electrons ionize enough gas to generate the source plasma. Calculations show that the increase in ionization rate with potential produces a steep rise in collected current with increasing potential as seen in the laboratory.

Davis, V. A.; Katz, I.; Mandell, M. J.; Parks, D. E.

1991-01-01

126

Intrinsic electronic and transport properties of graphyne sheets and nanoribbons.  

PubMed

Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry. PMID:23949158

Wu, Wenzhi; Guo, Wanlin; Zeng, Xiao Cheng

2013-10-01

127

Energetic (greater than 100 keV) O(+) ions in the plasma sheet  

NASA Technical Reports Server (NTRS)

The first measurements of very energetic (112 - 157 keV) O(+) ions in the earth's magnetosphere are presented. The observations were made with the UMd/MPE ULECA sensor on ISEE-1 on 5 March 1981 at geocentric distances approximately 20 R(E) in the earth's magnetotail. During this time period an Energetic Storm Particle event was observed by the nearly identical sensor on the ISEE-3 spacecraft, located approximately 250 R(E) upstream of the earth's magnetosphere. The ISEE-1 sensor observed a similar temporal profile except for several sharp intensity enhancements, corresponding to substorm recoveries during which the plasma sheet engulfed the spacecraft. During these plasma sheet encounters we observe O(+)/H(+) abundance ratios, at approximately 130 kev, as large as 0.35. In between plasma sheet encounters the O(+)/H(+) ratio at this energy is consistent with zero.

Ipavich, F. M.; Galvin, A. B.; Gloeckler, G.; Hovestadt, D.; Klecker, B.; Scholer, M.

1984-01-01

128

Energetic (>100 keV) 0/sup +/ ions in the plasma sheet  

SciTech Connect

We present the first measurements of very energetic (112-157 keV) 0/sup +/ ions in the earth's magnetosphere. The observations were made with the UMd/MPE ULECA sensor on ISEE-1 on 5 March 1981 at geocentric distances approx.20 R/sub E/ in the earth's magnetotail. During this time period an Energetic Storm Particle event was observed by our nearly identical sensor on the ISEE-3 space-craft, located approx.250 R/sub E/ upstream of the earth's magnetosphere. The ISEE-1 sensor observed a similar temporal profile except for several sharp intensity enhancements, corresponding to substorm recoveries during which the plasma sheet engulfed the spacecraft. During these plasma sheet encounters we observe 0/sup +//H/sup +/ abundance ratios, at approx.130 keV, as large as 0.35. In between plasma sheet encounters with 0/sup +//H/sup +/ ratio at this energy is consistent with zero.

Ipavich, F.M.; Galvin, A.B.; Gloeckler, G.; Hovestadt, D.; Klecker, B.; Scholer, M.

1984-05-01

129

Plasma wave mediated electron pairing effects  

E-print Network

Pairing of particles, in particular electrons, in high temperature plasma is generally not expected to occur. Here we investigate, based on earlier work, the possibility for electron pairing mediated in the presence of various kinds of plasma waves. We confirm the possibility for pairing in ion- and electron-acoustic waves, pointing out the importance of the former and the expected consequences. While electron-acoustic waves probably do not play any role, ion-acoustic waves may cause formation of heavy electron compounds. Lower hybrid waves also mediate pairing but under different conditions. Buneman modes which evolve from strong currents may cause pairing among trapped electrons constituting a heavy electron component that populates electron holes. All pairing processes are found to generate cold pair populations. They provide a mechanism of electron cooling which can be interpreted as kind of classical condensation, in some cases possibly accompanied by formation of current filaments, weak soft-X-ray emiss...

Treumann, R A

2014-01-01

130

The relationship between sawtooth events and O+ in the plasma sheet  

NASA Astrophysics Data System (ADS)

order to study the relationship between sawtooth events and the composition of the plasma sheet, we perform a superposed epoch analysis (SEA) of the O+ concentration inside the near-Earth plasma sheet during sawtooth events and substorms sorted by different geomagnetic storm phases, using Cluster/Composition Distribution Function data. The SEA shows that the O+ content increases during sawtooth growth phase, regardless of storm phase, and reaches 20% around the onset of dipolarization. For storm main phase events, the plasma sheet O+ concentration during sawtooth events is only slightly higher than that observed during substorm events. However, for storm recovery phase and nonstorm time events, there is significantly more O+ within the plasma sheet during sawtooth events than during substorm events. No difference is found in the comparison between the O+/H+ density ratio changes during the first tooth and the subsequent teeth in a series of a sawtooth interval. Hence, there is no evidence to support the hypothesis that due to the higher O+ inside the plasma sheet, subsequent teeth will lead to a closer near-Earth X line and then a wider magnetic local time response. Finally, despite the association between sawtooth events and high O+/H+ ratio, there are times when the O+/H+ density ratio is high in the plasma sheet but no sawtooth event is observed, and there are sawtooth events when the O+/H+ ratio is low. This indicates that enhanced O+ is neither a necessary nor a sufficient condition but is likely one of many factors that play a role in triggering sawtooth events.

Liao, J.; Cai, X.; Kistler, L. M.; Clauer, C. R.; Mouikis, C. G.; Klecker, B.; Dandouras, I.

2014-03-01

131

Dynamic Harris current sheet thickness from Cluster current density and plasma measurements  

NASA Technical Reports Server (NTRS)

We use the first accurate measurements of current densities in the plasma sheet to calculate the half-thickness and position of the current sheet as a function of time. Our technique assumes a Harris current sheet model, which is parameterized by lobe magnetic field B(o), current sheet half-thickness h, and current sheet position z(sub o). Cluster measurements of magnetic field, current density, and plasma pressure are used to infer the three parameters as a function of time. We find that most long timescale (6-12 hours) current sheet crossings observed by Cluster cannot be described by a static Harris current sheet with a single set of parameters B(sub o), h, and z(sub o). Noting the presence of high-frequency fluctuations that appear to be superimposed on lower frequency variations, we average over running 6-min intervals and use the smoothed data to infer the parameters h(t) and z(sub o)(t), constrained by the pressure balance lobe magnetic field B(sub o)(t). Whereas this approach has been used in previous studies, the spatial gnuhen& now provided by the Cluster magnetometers were unavailable or not well constrained in earlier studies. We place the calculated hdf&cknessa in a magnetospheric context by examining the change in thickness with substorm phase for three case study events and 21 events in a superposed epoch analysis. We find that the inferred half-thickness in many cases reflects the nominal changes experienced by the plasma sheet during substorms (i.e., thinning during growth phase, thickening following substorm onset). We conclude with an analysis of the relative contribution of (Delta)B(sub z)/(Delta)X to the cross-tail current density during substorms. We find that (Delta)B(sub z)/(Delta)X can contribute a significant portion of the cross-tail c m n t around substorm onset.

Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; McPherron, R. L.; Weygand, J. M.; Balogh, A.; Reme, H.; Kistler, L. M.

2005-01-01

132

Application of Nonlocalpp Electron Kinetics to Plasma  

E-print Network

Interest "Interest. · Report on Scientific Directions for Low Temperature Plasma sponsored by Department not captured in fluid models: · Explosive generation of cold electrons with power increase.Explosive generation and dc discharges for plasma processing and electric propulsion. 3 p p #12;Nonlocality is not just

Kaganovich, Igor

133

Plasma effects in a free electron laser  

Microsoft Academic Search

The introduction of a plasma and a strong guide magnetic field in a free electron laser (FEL) slows down the phase velocity of radiation, significantly reducing the requirements on beam energy for generating frequencies below the electron-cyclotron frequency (?1≲?c). Around plasma resonance (?1~?p), the FEL mode couples to two-stream instability (TSI), attaining a large growth rate, comparable to that of

VIPIN K. TRIPATHI; CHUAN SHENG LIU

1990-01-01

134

Development of plasma cathode electron guns  

NASA Astrophysics Data System (ADS)

The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable operation even in the presence of aggressive background gas media and at fore-vacuum gas pressure ranges such as achieved by mechanical pumps. Depending on the required beam parameters, different kinds of plasma discharge systems can be used in plasma cathode electron guns, such as vacuum arcs, constricted gaseous arcs, hollow cathode glows, and two kinds of discharges in crossed EB fields: Penning and magnetron. At the present time, plasma cathode electron guns provide beams with transverse dimension from fractional millimeter up to about one meter, beam current from microamperes to kiloamperes, beam current density up to about 100 A/cm2, pulse duration from nanoseconds to dc, and electron energy from several keV to hundreds of keV. Applications include electron beam melting and welding, surface treatment, plasma chemistry, radiation technologies, laser pumping, microwave generation, and more.

Oks, Efim M.; Schanin, Peter M.

1999-05-01

135

Diffusive transport of particles from the flank toward midnight resulting from fluctuating electric and magnetic fields in the plasma sheet  

Microsoft Academic Search

Cold plasma sheet particles can be an order of magnitude more abundant during northward interplanetary magnetic field (IMF) than during southward IMF. These cold particles are believed to come from the flanks. Flow fluctuations in the plasma sheet can result in diffusive transport that may be important in bringing these particles further toward midnight. To quantitatively evaluate the effectiveness of

C. Wang; L. R. Lyons

2009-01-01

136

Substorm-associated explosive magnetic field stretching near the earthward edge of the plasma sheet  

NASA Astrophysics Data System (ADS)

report a detailed analysis of explosive local magnetic field line stretching just before dipolarization observed by one of Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites during the pseudo-breakup followed by local substorm of 6 January 2008. At the end of the substorm growth phase, this satellite (THEMIS-C) was located at r ~ 6.3 RE near the convection boundary of 10 keV electrons. Penetration of the hot electron plasma sheet to the region of trapped energetic ions was a precondition for the substorm onset in the premidnight sector. Observed oscillations of fields and particles with period 50-60 s are consistent with the ballooning mode in the near-Earth magnetotail and with the near-Earth initiation current disruption model. Basing on the simple line-current model, the explosive stretching and following dipolarization observed by THEMIS-C satellite are interpreted as a manifestation of the magnetospheric generator of the 3-D meridional current system with the driving electric field in the meridional direction during nonlinear growth of ballooning instability when non-MHD processes are also turning on.

Kozelova, T. V.; Kozelov, B. V.

2013-06-01

137

Electron heating in capacitively coupled plasmas revisited  

NASA Astrophysics Data System (ADS)

We revisit the problem of electron heating in capacitively coupled plasmas (CCPs), and propose a method for quantifying the level of collisionless and collisional heating in plasma simulations. The proposed procedure, based on the electron mechanical energy conservation equation, is demonstrated with particle-in-cell simulations of a number of single and multi-frequency CCPs operated in regimes of research and industrial interest. In almost all cases tested, the total electron heating is comprised of collisional (ohmic) and pressure heating parts. This latter collisionless component is in qualitative agreement with the mechanism of electron heating predicted from the recent re-evaluation of theoretical models. Finally, in very electrically asymmetric plasmas produced in multi-frequency discharges, we observe an additional collisionless heating mechanism associated with electron inertia.

Lafleur, T.; Chabert, P.; Booth, J. P.

2014-06-01

138

Auroral Poleward Boundary Intensifications and Modes of Energy Transport in the Plasma Sheet  

NASA Astrophysics Data System (ADS)

Auroral poleward boundary intensifications (PBIs) have an auroral signature in ground meridional scanning photometer (MSP) data that appears as an increase in intensity at or near the magnetic separatrix. This increase is often seen to extend equatorward through the ionospheric mapping of the plasma sheet. PBIs are also associated with fast flows in the tail plasma sheet and are thus important to plasma sheet dynamics. We have recently used simultaneous auroral observations from the CANOPUS MSPs and either the Freja UV imager or the CANOPUS Gillam all-sky imager (ASI) to investigate the two-dimensional structure of auroral intensifications near the poleward boundary of the oval. We found that equatorward extending PBIs are either north-south aligned structures or east-west arcs that mostly propagate equatorward, but we have not been able to determine without doubt which type is the most prevalent. The different two-dimensional orientations for equatorward extending PBIs suggests that they may be the auroral footprint of two major modes of energy transfer in the plasma sheet: multiple, narrow, earthward fast-flow channels (associated with the north-south structures) and sequences of azimuthally broad and primarily earthward propagating phase fronts initiating near the separatrix (associated with the east-west arcs). We test this hypothesis by combining data from the CANOPUS MSPs, the all-sky imagers of the newly installed NORSTAR array in northern Canada which cover the poleward boundary of the auroral oval, auroral images from the IMAGE spacecraft, and magnetic field and plasma data from the Geotail spacecraft. We have identified a number of events from early 2001 when Geotail was in the midtail plasma sheet and seek to answer the following questions: a) Are PBI structures observed at one location associated with structures which simultaneously cover many hours of local time on the nightside, b) Are all north-south PBI structures associated with narrow channels of fast flows in the plasma sheet, and c) Are the east-west PBI structures also associated with fast flows or with some other dynamic structure in the plasma sheet? Finally, we use events with overlapping images from both the ground ASIs and the spacecraft imager to relate the two-dimensional structure seen with high spatial resolution on the ground to the much larger spatial scale structure observable from the spacecraft.

Zesta, E.; Lyons, L.; Donovan, E.; Frey, H. U.; Nagai, T.

2001-12-01

139

Oxygen plasma-treated thermoresponsive polymer surfaces for cell sheet engineering.  

PubMed

Although cell sheet tissue engineering is a potent and promising method for tissue engineering, an increase of mechanical strength of a cell sheet is needed for easy manipulation of it during transplantation or 3D tissue fabrication. Previously, we developed a cell sheet-polymer film complex that had enough mechanical strength that can be manipulated even by tweezers (Fujita et al., 2009. Biotechnol Bioeng 103(2): 370-377). We confirmed the polymer film involving a temperature sensitive polymer and extracellular matrix (ECM) proteins could be removed by lowering temperature after transplantation, and its potential use in regenerative medicine was demonstrated. However, the use of ECM proteins conflicted with high stability in long-term storage and low cost. In the present study, to overcome these drawbacks, we employed the oxygen plasma treatment instead of using the ECM proteins. A cast and dried film of thermoresponsive poly-N-isopropylacrylamide (PNIPAAm) was fabricated and treated with high-intensity oxygen plasma. The cells became possible to adhere to the oxygen plasma-treated PNIPAAm surface, whereas could not to the inherent surface of bulk PNIPAAm without treatment. Characterizations of the treated surface revealed the surface had high stability. The surface roughness, wettability, and composition were changed, depending on the plasma intensity. Interestingly, although bulk PNIPAAm layer had thermoresponsiveness and dissolved below lower critical solution temperature (LCST), it was found that the oxygen plasma-treated PNIPAAm surface lost its thermoresponsiveness and remained insoluble in water below LCST as a thin layer. Skeletal muscle C2C12 cells could be cultured on the oxygen plasma-treated PNIPAAm surface, a skeletal muscle cell sheet with the insoluble thin layer could be released in the medium, and thus the possibility of use of the cell sheet for transplantation was demonstrated. PMID:20091737

Shimizu, Kazunori; Fujita, Hideaki; Nagamori, Eiji

2010-06-01

140

Detailed observations of the plasma sheet during a substorm on April 24, 1979  

NASA Technical Reports Server (NTRS)

Plasma, magnetic field, and energetic particle data obtained by ISEE 1 and 2 satellites for the April 24, 1979 substorm are studied in relation to the neutral line model and the boundary layer model. The ISEE 1 and 2 instruments and experiments utilized to collect the data are discussed. The major reconfiguration of the tail plasma and magnetic field plasma region, and the plasma ion flows observed support the neutral line model for interpreting substorms. The plasma ion distribution function and plasma flow are examined. The region of lobe-plasma sheet interface referred to as the separatrix layer is identified. The differences in times of plasma sheet dropout and recovery, and absence or presence of flux anisotropies are investigated. Energetic particle measurements are analyzed to study the relationship between energetic ions and plasma ions, and the velocity distributions. The data support the application of the neutral line model to the evaluation of substorms; however, the data are inconsistent with the boundary layer dynamics model.

Hones, E. W., Jr.; Fritz, T. A.; Birn, J.; Cooney, J.; Bame, S. J.

1986-01-01

141

RICHTMYER-MESHKOV-TYPE INSTABILITY OF A CURRENT SHEET IN A RELATIVISTICALLY MAGNETIZED PLASMA  

SciTech Connect

The linear stability of a current sheet that is subject to an impulsive acceleration due to shock passage with the effect of a guide magnetic field is studied. We find that a current sheet embedded in relativistically magnetized plasma always shows a Richtmyer-Meshkov-type instability, while the stability depends on the density structure in the Newtonian limit. The growth of the instability is expected to generate turbulence around the current sheet, which can induce the so-called turbulent reconnection, the rate of which is essentially free from plasma resistivity. Thus, the instability can be applied as a triggering mechanism for rapid magnetic energy release in a variety of high-energy astrophysical phenomena such as pulsar wind nebulae, gamma-ray bursts, and active galactic nuclei, where the shock wave is thought to play a crucial role.

Inoue, Tsuyoshi, E-mail: inouety@phys.aoyama.ac.jp [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 252-5258 (Japan)

2012-11-20

142

Non-self-similar scaling of plasma sheet and solar wind probability distribution functions of magnetic field fluctuations  

Microsoft Academic Search

Solar wind magnetometer and plasma data and magnetometer data acquired by Cluster in the magnetospheric plasma sheet are employed to construct probability distribution functions (PDFs) of magnetic field fluctuations over various temporal and spatial scales. This technique, often used in analysis of laboratory plasmas, is used to look for intermittent plasma turbulence and non-self-similar properties in the fluctuations. We examine

J. M. Weygand; M. G. Kivelson; K. K. Khurana; H. K. Schwarzl; R. J. Walker; A. Balogh; L. M. Kistler; M. L. Goldstein

2006-01-01

143

Relativistic electron beam plasma heating experiment  

SciTech Connect

An intense (5 x 10/sup 5/ Amp/cm/sup 2/), relativistic (5 MeV), electron beam will be used to investigate the heating of small volumes (approx. 5 to 10 cm/sup 3/) of dense plasma (10/sup 17/ to 10/sup 18/ electrons/cm/sup 3/) to kilovolt temperatures via the electrostatic two-stream instability.

Montgomery, M.D.; Parker, J.V.

1980-04-01

144

Canted Current Sheet Mass Leakage and its Impact on Pulsed Plasma Thruster Performance  

E-print Network

and E.Y. Choueiri Electric Propulsion and Plasma Dynamics Laboratory (EPPDyL) Mechanical and Aerospace An analytical model of the leakage of the current sheet in a parallel plate pulsed electromagnetic accelerator. INTRODUCTION In a parallel plate pulsed electromagnetic accel- erator, two non-ideal behaviors have been

Choueiri, Edgar

145

Plasma sheet pressure evolution related to substorms L. R. Lyons,1  

E-print Network

Plasma sheet pressure evolution related to substorms X. Xing,1 L. R. Lyons,1 V. Angelopoulos,2 D and current evolution near onset warrants more careful analysis. Citation: Xing, X., L. R. Lyons, V., 1996; Lyons et al., 2003a, 2003b] but all the models place onset earthward of X $ ?30 RE. Thus most

Lyons, Larry

146

Tearing mode in a neutral current sheet in a plasma flow  

Microsoft Academic Search

The linear stage of the tearing mode is analyzed for a diffuse neutral current sheet in a plasma flow along the magnetic field. It follows from the dispersion characteristics derived that the flow tends to stabilize the tearing mode and gives rise to a drift phase velocity.

V. M. Gubchenko

1982-01-01

147

3d solar corona at heliospheric sheet and structures in current carrying plasma with flows  

Microsoft Academic Search

Magnetic island and magnetic rope elements are basic topological structures of space plasma for construction of its 3D state. As for islands in the solar corona they observed near Sun like coronal mass ejections (CME), blobs, transients, as for ropes they observed like streamer belt and rays located above and submerged into forming heliospheric current sheet. Corona here is hot

V. Gubchenko; V. Zaitsev; H. Biernat; M. Khodachenko; H. Rucker

2004-01-01

148

Tearing mode in a neutral current sheet in a plasma flow  

SciTech Connect

The linear stage of the tearing mode is analyzed for a diffuse neutral current sheet in a plasma flow along the magnetic field. It follows from the dispersion characteristics derived that the flow tends to stabilize the tearing mode and gives rise to a drift phase velocity.

Gubchenko, V.M.

1982-09-01

149

ON PLASMA KINETIC MODEL OF A 3D SOLAR CORONA AND SOLAR WIND AT HELIOSPHERIC SHEET  

Microsoft Academic Search

The dynamical solar corona in 3D consists of transient type magnetic island elements and radial type magnetic flux rope structures in a heliospheric sheet. During the formation and relaxation these elements produce inductive elec- tromagnetic fields where energetic particles are produced. We study the 3D corona formation in the kinetic approach and parameterize it like a hot current-carrying collisionless plasma

V. M. GUBCHENKO; M. L. KHODACHENKO; H. K. BIERNAT

150

Penetration of the Interplanetary Magnetic Field B(sub y) into Earth's Plasma Sheet  

NASA Technical Reports Server (NTRS)

There has been considerable recent interest in the relationship between the cross-tail magnetic field component B(sub y) and tail dynamics. The purpose of this paper is to give an overall description of the penetration of the interplanetary magnetic field (IMF) B(sub y) into the near-Earth plasma sheet. We show that plasma sheet B(sub y) may be generated by the differential shear motion of field lines and enhanced by flux tube compression. The latter mechanism leads to a B(sub y) analogue of the pressure-balance inconsistency as flux tubes move from the far tail toward the Earth. The growth of B(sub y), however, may be limited by the dawn-dusk asymmetry in the shear velocity as a result of plasma sheet tilting. B(sub y) penetration into the plasma sheet implies field-aligned currents flowing between hemispheres. These currents together with the IMF B(sub y) related mantle field-aligned currents effectively shield the lobe from the IMF B(sub y).

Hau, L.-N.; Erickson, G. M.

1995-01-01

151

Multifluid MHD simulation of Saturn's magnetosphere: Dynamics of mass- and momentum-loading, and seasonal variation of the plasma sheet  

NASA Astrophysics Data System (ADS)

Saturn's magnetosphere is driven externally, by the solar wind, and internally, by the planet's strong magnetic field, rapid rotation rate, and the addition of new plasma created from Saturn's neutral cloud. Externally, the alignment of the rotational and magnetic dipole axes, combined with Saturn's substantial inclination to its plane of orbit result in substantial curvature of the plasma sheet during solstice. Internally, new water group ions are produced in the inner regions of the magnetosphere from photoionization and electron-impact ionization of the water vapor and OH cloud sourced from Enceladus and other icy bodies in Saturn's planetary system. In addition to this, charge-exchange collisions between the relatively fast-moving water group ions and the slower neutrals results in a net loss of momentum from the plasma. In order to study these phenomena, we have made significant modifications to the Saturn multifluid model. This model has been previously used to investigate the external triggering of plasmoids and the interchange process using a fixed internal source rate. In order to improve the fidelity of the model, we have incorporated a physical source of mass- and momentum-loading by including an empirical representation of Saturn's neutral cloud and modifying the multifluid MHD equations to include mass- and momentum-loading terms. Collision cross-sections between ions, electrons, and neutrals are calculated as functions of closure velocity and energy at each grid point and time step, enabling us to simulate the spatially and temporally varying plasma-neutral interactions. In addition to this, by altering the angle of incidence of the solar wind relative to Saturn's rotational axis and applying a realistic latitudinally- and seasonally-varying ionospheric conductivity, we are also able to study seasonal effects on Saturn's magnetosphere. We use the updated multifluid simulation to investigate the dynamics of Saturn's magnetosphere, focusing specifically on the production of new plasma, the resulting radial outflow, and corotation lag profiles. The simulation has produced well-defined interchange fingers, regions of cold inner-magnetosphere plasma that lag corotation and move radially outwards, which are balanced by the inward flow of hot tenuous plasma from the outer magnetosphere. We quantify the rate of interchange finger production, and from these calculate the net outward rate of plasma flow. We then compare simulation output with observational data from the Cassini spacecraft to validate the new physics that we have incorporated. In addition to internal mass production and corotation, we also investigate external driver effects, in particular the seasonal variation of curvature of the plasma sheet.

Rajendar, A.; Paty, C. S.; Arridge, C. S.; Jackman, C. M.; Smith, H. T.

2013-12-01

152

Survey of low energy plasma electrons in Saturn's magnetosphere: Voyagers 1 and 2  

NASA Technical Reports Server (NTRS)

The low energy plasma electron environment within Saturn's magnetosphere was surveyed by the Plasma Science Experiment (PLS) during the Voyager encounters with Saturn. Over the full energy range of the PLS instrument (10 eV to 6 keV) the electron distribution functions are clearly non-Maxwellian in character; they are composed of a cold (thermal) component with Maxwellian shape and a hot (suprathermal) non-Maxwellian component. A large scale positive radial gradient in electron temperature is observed, increasing from less than 1 eV in the inner magnetosphere to as high as 800 eV in the outer magnetosphere. Three fundamentally different plasma regimes were identified from the measurements: (1) the hot outer magnetosphere, (2) the extended plasma sheet, and (3) the inner plasma torus.

Sittler, E. C., Jr.; Ogilvie, K. W.; Scudder, J. D.

1983-01-01

153

Nature of axial tail instability and bubble-blob formation in near-Earth plasma sheet  

NASA Astrophysics Data System (ADS)

revious global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn-dusk direction in the near-Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two-dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble-blob pairs in the pressure and entropy profiles in the near-Earth plasma sheet.

Zhu, P.; Raeder, J.; Hegna, C. C.; Sovinec, C. R.

2013-02-01

154

The structure of the plasma sheet-lobe boundary in the Earth's magnetotail  

NASA Technical Reports Server (NTRS)

The structure of the magnetotail plasma sheet-plasma lobe boundary was studied by observing the properties of tailward flowing O+ ion beams, detected by the ISEE 2 plasma experiment inside the boundary during three time periods. The computed value of the north-south electric field component as well as the O+ parameters are shown to change at the boundary. The results are related to other observations made in this region. The O+ parameters and the Ez component behavior are shown to be consistent with that expected from the topology of the electric field lines in the tail as mapped from the ionosphere.

Orsini, S.; Candidi, M.; Formisano, V.; Balsiger, H.; Ghielmetti, A.; Ogilvie, K. W.

1982-01-01

155

Control of the area irradiated by the sheet-type plasma jet in atmospheric pressure  

NASA Astrophysics Data System (ADS)

The sterilization effect has been investigated using the sheet-type plasma jet, which was generated between asymmetric electrodes with dielectric plates in gas flow released into the atmospheric air. In this paper, it is indicated there is a possibility that the plasma jet irradiation area can be controlled only by supplied gases without changing a generator structure. The irradiation area control was evaluated from both the sterilization area size and the oxidizing substances distribution. The oxidizing substance distribution was obtained using the chemical reagent prepared in our laboratory. The width of the sheet-type plasma jet was able to be controlled by N2 addition into He gas. As a result, the width of the sterilization area was able to be controlled within the range of 2 to 12 mm at a constant height without changing the generator structure. On the other hand, the evaluation from the oxidizing substances distribution indicated that the irradiation area cannot be controlled in one direction.

Kawasaki, T.; Kawano, K.; Mizoguchi, H.; Yano, Y.; Yamashita, K.; Sakai, M.; Uchida, G.; Koga, K.; Shiratani, M.

2014-06-01

156

Visualization of Current Sheet Canting in a Pulsed Plasma Accelerator  

E-print Network

.Y. Choueiri Electric Propulsion and Plasma Dynamics Laboratory (EPPDyL) Mechanical and Aerospace Engineering which entrains gas as it propagates along the acceleration channel, acting as an electromagnetic Propulsion Con- ference, Kitakyushu, JAPAN, October 17-21,1999. sweeping characteristics is essential

Choueiri, Edgar

157

Microwave reflections from a vacuum ultraviolet laser produced plasma sheet  

E-print Network

. The reflectivity can be described by the plasma dielectric constant6 p 1 p 2 i , 1 where p 2 (ne2 )/(m detection system with a response time of 10 ns is utilized to determine the amplitude and phase wave at a dielectric boundary is given by the Fresnel reflection coef- ficient, Ereflected Eincident p

Scharer, John E.

158

Reconnection and electron temperature anisotropy in electron scale plasma turbulence  

E-print Network

We study the turbulent decay of fluctuations using results from 2D, particle-in-cell (PIC) collisionless plasma simulations with realistic electron-proton mass ratio and a guide field out of the simulation plane. A fluctuation power spectrum with approximately power law form is created down to scales of order the electron gyroradius. Where there is an X-point magnetic field line geometry we find signatures of reconnection such as electron bulk inflows and outflows. The reconnection signatures persist even when the reconnection sites are only several electron gyroradii across. Although the reconnection sites do not dominate the electron temperature variation, they are generally associated with regions of strong parallel electron temperature anisotropy. By tracking simulation particles we find that electrons are accelerated along the guide field near reconnection sites, and that in the reconnection outflows there is a mixing of electrons from spatially separated locations. The topology of magnetic field lines c...

Haynes, Christopher T; Camporeale, Enrico

2013-01-01

159

Electron cyclotron emission imaging in tokamak plasmas  

SciTech Connect

We discuss the recent history and latest developments of the electron cyclotron emission imaging diagnostic technique, wherein electron temperature is measured in magnetically confined plasmas with two-dimensional spatial resolution. The key enabling technologies for this technique are the large-aperture optical systems and the linear detector arrays sensitive to millimeter-wavelength radiation. We present the status and recent progress on existing instruments as well as new systems under development for future experiments. We also discuss data analysis techniques relevant to plasma imaging diagnostics and present recent temperature fluctuation results from the tokamak experiment for technology oriented research (TEXTOR).

Munsat, Tobin; Domier, Calvin W.; Kong, Xiangyu; Liang, Tianran; Luhmann, Jr.; Neville C.; Tobias, Benjamin J.; Lee, Woochang; Park, Hyeon K.; Yun, Gunsu; Classen, Ivo. G. J.; Donne, Anthony J. H.

2010-07-01

160

ELF wave intensification in conjunction with fast earthward flow in the mid-tail plasma sheet ------- A THEMIS survey  

NASA Astrophysics Data System (ADS)

A number of recent studies have revealed a close association between the fast earthward flows and dipolarization fronts in the magnetotail and the plasma wave intensifications in the ELF/VLF range, including the lower-hybrid waves, whistler-mode and electron cyclotron waves. Those waves may play crucial roles in the acceleration and pitch-angle scattering of the plasma sheet electrons, and in turn produce a macroscopic effect accompanying the fast flows. In this study, we perform a statistical survey of the THEMIS B/C data over the 2008 and 2009 tail seasons, and select ~110 fast earthward flow intervals in which the probes were mostly located in the mid-tail central plasma sheet (CPS) region. We investigate the filterbank (FBK) dataset of the electric field instrument (EFI) and search coil magnetometer (SCM) during the collected fast flow intervals, and identify an unambiguous trend of increasing ELF wave intensities with the convective flow enhancement. Notwithstanding the relatively wide bandwidth of FBK data we may still distinguish the existence of the lower-hybrid waves, the whistler-mode waves, and the electrostatic waves at f>f_ce. On a further examining of the flow-associated whistler-mode waves we notice a mixture of the quasi-electrostatic and electromagnetic wave modes, implying a broad distribution of the wave normal angles. We tentatively suggest that the energetic electron beam originated from the reconnection site and/or the local dipolarizatoin front might be the main driving mechanism of the flow-associated ELF wave intensifications.

Liang, J.; Ni, B.; Cully, C. M.; Donovan, E. F.; Thorne, R. M.; Themis Team

2010-12-01

161

Kinetic Theory of Plasma Sheaths Surrounding Electron-Emitting Surfaces  

NASA Astrophysics Data System (ADS)

A one-dimensional kinetic theory of sheaths surrounding planar, electron-emitting surfaces is presented which accounts for plasma electrons lost to the surface and the temperature of the emitted electrons. It is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. The sheath potential goes to zero as the plasma electron temperature equals the emitted electron temperature, which can occur in the afterglow of an rf plasma and some low-temperature plasma sources. These results were validated by particle in cell simulations. The theory was tested by making measurements of the sheath surrounding a thermionically emitting cathode in the afterglow of an rf plasma. The measured sheath potential shrunk to zero as the plasma electron temperature cooled to the emitted electron temperature, as predicted by the theory.

Sheehan, J. P.; Hershkowitz, N.; Kaganovich, I. D.; Wang, H.; Raitses, Y.; Barnat, E. V.; Weatherford, B. R.; Sydorenko, D.

2013-08-01

162

Using PEACE Data from the four CLUSTER Spacecraft to Measure Compressibility, Vorticity, and the Taylor Microscale in the Magnetosheath and Plasma Sheet  

NASA Technical Reports Server (NTRS)

We present determinations of compressibility and vorticity in the magnetosheath and plasma sheet using moments from the four PEACE thermal electron instruments on CLUSTER. The methodology used assumes a linear variation of the moments throughout the volume defined by the four satellites, which allows spatially independent estimates of the divergence, curl, and gradient. Once the vorticity has been computed, it is possible to estimate directly the Taylor microscale. We have shown previously that the technique works well in the solar wind. Because the background flow speed in the magnetosheath and plasma sheet is usually less than the Alfven speed, the Taylor frozen-in-flow approximation cannot be used. Consequently, this four spacecraft approach is the only viable method for obtaining the wave number properties of the ambient fluctuations. Our results using electron velocity moments will be compared with previous work using magnetometer data from the FGM experiment on Cluster.

Goldstein, Melvyn L.; Parks, George; Gurgiolo, C.; Fazakerley, Andrew N.

2008-01-01

163

Electron density measurements for plasma adaptive optics  

NASA Astrophysics Data System (ADS)

Over the past 40 years, there has been growing interest in both laser communications and directed energy weapons that operate from moving aircraft. As a laser beam propagates from an aircraft in flight, it passes through boundary layers, turbulence, and shear layers in the near-region of the aircraft. These fluid instabilities cause strong density gradients which adversely affect the transmission of laser energy to a target. Adaptive optics provides corrective measures for this problem but current technology cannot respond quickly enough to be useful for high speed flight conditions. This research investigated the use of plasma as a medium for adaptive optics for aero-optics applications. When a laser beam passes through plasma, its phase is shifted proportionally to the electron density and gas heating within the plasma. As a result, plasma can be utilized as a dynamically controllable optical medium. Experiments were carried out using a cylindrical dielectric barrier discharge plasma chamber which generated a sub-atmospheric pressure, low-temperature plasma. An electrostatic model of this design was developed and revealed an important design constraint relating to the geometry of the chamber. Optical diagnostic techniques were used to characterize the plasma discharge. Single-wavelength interferometric experiments were performed and demonstrated up to 1.5 microns of optical path difference (OPD) in a 633 nm laser beam. Dual-wavelength interferometry was used to obtain time-resolved profiles of the plasma electron density and gas heating inside the plasma chamber. Furthermore, a new multi-wavelength infrared diagnostic technique was developed and proof-of-concept simulations were conducted to demonstrate the system's capabilities.

Neiswander, Brian W.

164

Electron acoustic solitons in a relativistic plasma with nonthermal electrons  

SciTech Connect

Electron acoustic solitary waves (EASWs) are studied using Sagdeev's pseudopotential technique for a plasma comprising relativistic ions, cold relativistic electrons, and nonthermal hot electrons. The parametric range considered here is valid for the auroral zone. It is found that the present plasma model supports EASWs having negative potential. It is seen that the relativistic effect significantly restricts the region of existence for solitary waves. The region of existence of solitary waves also depends crucially on {alpha}, the parameter that determines the population of the energetic nonthermal electrons. For example, for {alpha}>0.18 with the soliton velocity 1.05 and u{sub 0c}/c=0.001, solitary wave solutions will not exist. We also find that for small values of {alpha}, solitary waves would exist for V<1.

Sahu, Biswajit; Roychoudhury, Rajkumar [Department of Mathematics, Dinhata College, Coochbehar-736135 (India); Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata-700108 (India)

2006-07-15

165

Free electron laser with small period wiggler and sheet electron beam: A study of the feasibility of operation at 300 GHz with 1 MW CW output power  

SciTech Connect

The use of a small period wiggler (/ell//sub ..omega../ < 1 cm) together with a sheet electron beam has been proposed as a low cost source of power for electron cyclotron resonance heating (ECRH) in magnetic fusion plasmas. Other potential applications include space-based radar systems. We have experimentally demonstrated stable propagation of a sheet beam (18 A. 1 mm /times/ 20 mm) through a ten-period wiggler electromagnet with peak field of 1.2 kG. Calculation of microwave wall heating and pressurized water cooling have also been carried out, and indicate the feasibility of operating a near-millimeter, sheet beam FEL with an output power of 1 MW CW (corresponding to power density into the walls of 2 kW/cm/sup 2/). Based on these encouraging results, a proof-of-principle experiment is being assembled, and is aimed at demonstrating FEL operating at 120 GHz with 300 kW output power in 1 ..mu..s pulses: electron energy would be 410 keV. Preliminary design of a 300 GHz 1 MW FEL with an untapered wiggler is also presented. 10 refs., 5 figs., 3 tabs.

Booske, J.H.; Granatstein, V.L.; Antonsen, T.M. Jr.; Destler, W.W.; Finn, J.; Latham, P.E.; Levush, B.; Mayergoyz, I.D.; Radack, D.; Rodgers, J.

1988-01-01

166

Development of plasma cathode electron guns  

Microsoft Academic Search

The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of

Efim M. Oks; Peter M. Schanin

1999-01-01

167

Vertical sheets of dense plasma in the topside Martian ionosphere  

Microsoft Academic Search

The low-frequency radar, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), on board the Mars Express spacecraft is used to sound electron densities in the topside Martian ionosphere. The radar records the delay times to echoes of reflected radio waves as a function of frequency, yielding spectrograms with traces of radar echoes. At times, two traces are present in

E. Nielsen; X.-D. Wang; D. A. Gurnett; D. L. Kirchner; R. Huff; R. Orosei; A. Safaeinili; J. J. Plaut; G. Picardi

2007-01-01

168

Stall control at high angle of attack with plasma sheet actuators  

Microsoft Academic Search

We analyzed the modifications of the airflow around an NACA 0015 airfoil when the flow was perturbed with electrohydrodynamic\\u000a forces. The actuation was produced with a plasma sheet device (PSD) consisting in two bare electrodes flush mounted on the\\u000a surface of the wing profile operated to obtain a discharge contouring the body in the inter-electrode space. We analyze the\\u000a influence

Roberto Sosa; Guillermo Artana; Eric Moreau; Grard Touchard

2007-01-01

169

Multiple intensifications inside the auroral bulge and their association with plasma sheet activities  

NASA Astrophysics Data System (ADS)

In this coordinated ground and space study, we report multiprobe measurements from Time History of Events and Macroscale Interactions during Substorms (THEMIS), LANL-97A, Polar, and ground observatories for a substorm that occurred on 23 March 2007. The THEMIS fleet and LANL-97A were located in the premidnight, near-Earth plasma sheet in the radial range from 6.6 to 13 RE, placing the spacecraft into different plasma environments which were subject to different activities. Simultaneous global Polar Ultraviolet Imager images of the aurora revealed a fine structure in the auroral bulge in the form of several time-delayed regions of brightening. We demonstrate a correspondence between this fine structure and the spatially separated plasma sheet activities (substorm injections with energies >100 keV) by showing that both executed periodic (100-150 s) one-to-one correlated modulations. Additionally, the different auroral brightening regions were modulated approximately out of phase to one another, as were the separated plasma sheet activities. The periodic plasma sheet and optical modulations were also one-to-one correlated with large-amplitude (?H 150 nT) ground Pi2 pulsations. In contrast to the most energetic ions (>100 keV), the lower-energetic plasma sheet ions executed separate oscillations during the development of the substorm, including the preintensification phase, and showed the following properties. (1) The oscillation periods were different at different spacecraft locations and had a tendency to increase during the evolution of the substorm. During the preintensification phase, multiple (possibly harmonic) spectral components existed. (2) The oscillations were coupled to westward moving perturbations of an energized plasma boundary. The boundary perturbations were likely conjugate to azimuthally spaced auroral forms ("beads") observed by Polar-UVI during the preintensification phase and could play a role in the onset of the substorm intensification. (3) The oscillations of the lower-energetic ions were also one-to-one correlated with smaller-amplitude ground Pi2 pulsations (<15 nT). In conclusion, the combination of these observations allowed us to construct a 3-D picture of low-frequency, near-Earth plasma sheet phenomena associated with a substorm and their connection to aurora and the ground. It appeared that not only one substorm current wedge, but additional current structures existed which started at different times, pulsated out of phase, and mapped from different active regions into the ionosphere. The active space regions appeared to be coupled and transferring energy from one region to the other while pulsating. We propose that the wave-like structures in the plasma sheet, observed before and during the substorm/intensification phase, and their demonstrated properties support a wave phenomenon (such as a ballooning-type mode) for the onset and development of the substorm/intensification, rather than directly driven periodic bursty bulk flow activations.

Keiling, A.; Angelopoulos, V.; Larson, D.; McFadden, J.; Carlson, C.; Fillingim, M.; Parks, G.; Frey, S.; Glassmeier, K.-H.; Auster, H. U.; Magnes, W.; Liu, W.; Li, X.

2008-12-01

170

A statistical study of plasma sheet dynamics using ISEE 1 and 2 energetic particle flux data  

NASA Technical Reports Server (NTRS)

Plasma sheet dynamics during substorms are studied by analyzing 461 cases of transient dropout events of the 1.5 and 6-keV particle fluxes detected by ISEE 1 and 2 satellites. The instruments for detecting low- and high-energy particles are described. The spatial distribution of flux dropout events, and the events' relationship to magnetospheric activity level are examined. Substorm events without observed flux dropout events are investigated. The data reveal that the flux dropout distribution is isotropic, between 12-23 earth radii, and is present in the entire nightside plasma sheet; and the substorms without flux dropout are more frequent near earth and magnetospheric flanks. It is observed that tailward of 12 earth radii the flux dropout events and substorms without flux dropout are similar. The Chao et al. (1977) MHD rarefaction wave propagation model and the Hones (1973, 1980) near-tail, X-type magnetic neutral line formation model are discussed and compared to the experimental data. It is noted that neither model explains the plasma sheet dynamics observed.

Dandouras, J.; Reme, H.; Saint-Marc, A.; Sauvaud, J. A.; Parks, G. K.

1986-01-01

171

Travelling convection vortices in the ionosphere map to the central plasma sheet  

NASA Astrophysics Data System (ADS)

We investigate the magnetospheric domain responsible for the generation of ionospheric travelling convection vortices (TCV) by comparing the location of the TCV to the locations of the low-altitude particle-precipitation boundaries deduced from the DMSP satellite measurements. For three very well documented TCV events we are able to identify suitable satellite passes, in the sense that for each event we can identify two to three passes occurring close to the TCV observation in both time and space. In all three cases the comparisons place the TCV centres at or equatorward of the central plasma sheet/boundary plasma sheet precipitation boundary. Thus our results indicate that the field-aligned currents related to the TCV originate in the plasma sheet rather than at the magnetopause or in the low-latitude boundary layer, as previous studies suggest. Acknowledgements. We gratefully appreciate the on-line DMSP database facility at APL (Newell et al., 1991) from which this study has benefited greatly. We wish to thank E. Friis-Christensen for his encouragement and useful discussions. A. Y. would like to thank the Danish Meteorological Institute, where this work was done, for its hospitality during his stay there and the Nordic Baltic Scholarship Scheme for its financial support of this stay. Topical Editor K.-H. Glassmeier thanks M. J. Engebretson and H. Lhr for their help in evaluating this paper.--> Correspondence to: A. Yahnin-->

Yahnin, A.; Moretto, T.

1996-10-01

172

Artificial plasma density structures produced by energetic electron beams from rockets and spacecraft  

NASA Technical Reports Server (NTRS)

Recent rocket and Space Shuttle experiments have demonstrated the capability to launch electron beams of moderate power (100 W to 10 kW) into the earth's ionosphere and magnetosphere. This letter describes how such beams, when fired from rockets or satellites, can create significant ionization in the E- and F-regions of the ionosphere. Through proper selection of beam-related parameters, an interesting variety of plasma density structures, including plasma sheets and plasma filaments, can be created and studied over periods of 30 minutes to 1 hour, depending on the rate of plasma recombination and the density of the ambient plasma. Observations of these structures can give new information relating to the physics of plasma density structures in the ionosphere, and the effects these features have upon the scattering of radio waves. It is also possible that observations of the density structures will provide a new means for studying neutral winds and electrodynamic phenomena in the ionosphere.

Banks, P. M.; Gilchrist, B. E.

1985-01-01

173

THEMIS observations of penetration of the plasma sheet into the ring current region during a magnetic storm  

E-print Network

a magnetic storm Chih-Ping Wang,1 Larry R. Lyons,1 Vassilis Angelopoulos,2 Davin Larson,3 J. P. McFadden,3 magnetic storm clearly show that the inner edge of the ion plasma sheet near dusk moved from r $ 6 RE of the plasma sheet into the ring current region during a magnetic storm, Geophys. Res. Lett., 35, L17S14, doi

California at Berkeley, University of

174

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet  

NASA Technical Reports Server (NTRS)

A qualitative model of cross-tail current flow is considered. It is suggested that when magnetic reconnection begins, the current effectively flows across the plasma sheet both earthward and tailward of the disruption region near the neutral line. It is shown that an enhanced cross-tail current earthward of this region would thin the plasma sheet substantially due to the magnetic pinch effect. The results explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.; Mcpherron, R. L.

1990-01-01

175

Turbulent electron thermal transport in fusion plasmas  

NASA Astrophysics Data System (ADS)

Electron heat transport at the scale of electron gyroradius are investigated via numerical simulation of a fluid model and a role of E x B shear flow with intermediate E x B shearing rate is explored in Euler's equation. The anomalous transport, enhanced transport due to turbulent electromagnetic fields caused by plasma instabilities, has been a focus of the international fusion research communities. Among the instabilities, the drift-type instabilities from the pressure-gradient universal in magnetic fusion devices are considered responsible for the anomalous transport. In the current status of wide use of wave heating on electrons and subsequent high core electron temperature, the turbulent heat loss through electrons has one of the most important science element in preventing the large fusion tokamaks from reaching breakeven in the past decade. The Electron Temperature Gradient fluid model consists of electrostatic potential, toroidal magnetic flux function and electron temperature (or pressure) describing electron drift waves. The fluid model proves to be highly useful to electron heat flux analysis in fusion machines. We analyze the discharges in National Spherical Tokamak eXperiment(NSTX) and Tokamak Configuration Variable (TCV) and found that the electron thermal diffusivities can be explained in terms of the mixing length argument based on electron gyroradius, linear theory and our nonlinear fluid simulation. The nonlinear fluid model predicts reasonable heat flux observed in the experiments. Based on the analysis, we investigate the dependences of the dynamics on the ratio of electron and ion temperature Te/Ti and plasma beta betae . The nonlinear dynamics such as saturation mechanism of the ETG turbulence and the electromagnetic dynamics in terms of micro-tearing at the scale of electron gyroradius are discussed briefly. In most of plasma confinement devices, the equilibrium radial electric field exists and the turbulence-generated electric field is observed. The coherent structure, called as zonal flow, has been know to be effective to suppress the micro-turbulence. But at intermediate E x B shear, where the vortex eddy turn-over time is comparable to E x B shearing rate, the suppression is weak and the flow shear can leads to vortex amplification through interaction of nonlinear dynamics and shear flow.

Kim, Juhyung

176

Electron Scattering in Hot/Warm Plasmas  

SciTech Connect

Electrical and thermal conductivities are presented for aluminum, iron and copper plasmas at various temperatures, and for gold between 15000 and 30000 Kelvin. The calculations are based on the continuum wave functions computed in the potential of the temperature and density dependent self-consistent 'average atom' (AA) model of the plasma. The cross sections are calculated by using the phase shifts of the continuum electron wave functions and also in the Born approximation. We show the combined effect of the thermal and radiative transport on the effective Rosseland mean opacities at temperatures from 1 to 1000 eV. Comparisons with low temperature experimental data are also presented.

Rozsnyai, B F

2008-01-18

177

Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator  

NASA Technical Reports Server (NTRS)

Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration that accompanies the radial compression of the plasma in conical theta pinches.

Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

2011-01-01

178

Transition in Electron Physics of Magnetic Reconnection in Weakly Collisional Plasma  

NASA Astrophysics Data System (ADS)

Using self-consistent fully kinetic simulations with a Monte-Carlo treatment of the Coulomb collision operator, we explore the transition between collisional and kinetic regimes of magnetic reconnection in high-Lundquist-number current sheets. Recent research in collisionless reconnection has shown that electron kinetic physics plays a key role in the evolution. Large-scale electron current sheets may form, leading to secondary island formation and turbulent flux rope interactions in 3D. The new collisional simulations demonstrate how increasing collisionality modifies or eliminates these electron structures in the kinetic regimes. Additional basic questions that are addressed include how the reconnection rate and the release of magnetic energy into electrons and ions vary with collisionality. The numerical study provides insight into reconnection in dense regions of the solar corona, the solar wind, and upcoming laboratory experiments at MRX (Princeton) and MPDX (UW-Madison). The implications of these results for studies of turbulence dissipation in weakly collisional plasmas are discussed.

Le, A.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.; Egedal, J.; Forest, C.

2013-12-01

179

Electron Cyclotron Heating in RFP plasmas  

SciTech Connect

Reversed field pinches (RFP) plasmas are typically overdense ({omega}{sub pe}>{omega}{sub ce}) and thus not suitable for conventional electron cyclotron (EC) heating and current drive. In recent high plasma current discharges (I{sub p}>1.5 MA), however, the RFX-mod device was operated in underdense conditions ({omega}{sub pe}<{omega}{sub ce}) for the first time in an RFP. Thus, it is now possible to envisage heating the RFP plasma core by conventional EC at the 2nd harmonic, in the ordinary or extraordinary mode. We present a preliminary study of EC-heating feasibility in RFX-mod with the use of beam-tracing and full-wave codes. Although not competitive - as a heating system - with multi-MW Ohmic heating in an RFP, EC might be useful for perturbative transport studies, even at moderate power (hundreds of kW), and, more generally, for applications requiring localized power deposition.

Bilato, R.; Poli, E. [MPI fuer Plasmaphysik-Euratom Association Boltzmannstr. 2, D-85748 Garching (Germany); Volpe, F. [Department of Engineering Physics, University of Wisconsin, Madison, WI (United States); Koehn, A. [Institut fuer Plasmaforschung, Universitaet Stuttgart-Stuttgart (Germany); Cavazzana, R.; Paccagnella, R. [Consorzio RFX-Associazione EURATOM-ENEA sulla fusione-Padova (Italy); Farina, D. [IFP-CNR, EURATOM-ENEA-CNR Association-Milano (Italy)

2009-11-26

180

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

181

Analysis of an extended period of earthward plasma sheet flow at @220 R sub E : CDAW 8  

SciTech Connect

Statistical studies of the ISEE 3 deep magnetic tail data (r {approx gt} 120 R{sub E}) show that the bulk electron plasma flow is virtually always tailward during both quiet and geomagnetically active times. This aspect of the magnetotail data has been interpreted as suggesting that ISEE 3 is nearly always tailward of the distant neutral line when the spacecraft is at distances {approx gt} 120 R{sub E}. During an extended period ({approximately}0900 to {approximately}1230 UT) on January 29, 1983, however, ISEE 3 observed substantial earthward plasma flows while located in the distant plasma sheet at X{sub GSM} = {minus}217 R{sub E}. The authors have analyzed the distant neutral line location within the context of the distant tail, geostationary orbit, auroral zone, and solar wind data for this case based on an extension of the Coroniti and Kennel (1972) flaring tail theory. They conclude from known solar wind conditions that for a typical neutral line location at {approximately}135 R{sub E}, an {approximately}30% increase of the near-Earth lobe field strength would be required to cause the distant neutral line to move tailward beyond 220 R{sub E}. The available data suggest that this is quite plausible and that, therefore, the earthward flow episode is due to an exceptionally distant neutral line position. The question of why substorms did not terminate the growth phase earlier is also addressed.

Schindler, K. (Ruhr Univ., Bochum (Germany, F.R.)); Baker, D.N. (Los Alamos National Lab., NM (USA) NASA Goddard Space Flight Center, Greenbelt, MD (USA)); Birn, J.; Hones, E.W. Jr. (Los Alamos National Lab., NM (USA)); Slavin, J.A. (NASA Goddard Space Flight Center, Greenbelt, ND (USA) NASA Headquarters, Washington, DC (USA)); Galvin, A.B. (Univ. of Maryland, College Park (USA))

1989-11-01

182

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet  

NASA Technical Reports Server (NTRS)

A qualitative model of magnetic field reconfiguration as might result from neutral line formation in the central plasma sheet late in a substorm growth phase is considered. It is suggested that magnetic reconnection probably begins before the substorm expansion phase and that cross-tail current is enhanced across the plasma sheet both earthward and tailward of a limited region near the neutral line. Such an enhanced cross-tail current earthward of the original X line region may contribute to thinning the plasma sheet substantially, and this would in turn affect the drift currents in that location, thus enhancing the current even closer toward the earth. In this way a redistribution and progressive diversion of normal cross-tail current throughout much of the inner portion of the plasma sheet could occur. The resulting intensified current, localized at the inner edge of the plasma sheet, would lead to a very thin plasma confinement region. This would explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.; Mcpherron, R. L.

1990-01-01

183

Effect of self-consistent magnetic field on plasma sheet penetration to the inner magnetosphere under enhanced convection: RCM simulations combined with force-balance magnetic field solver  

Microsoft Academic Search

Transport of plasma sheet particles into the inner magnetosphere is strongly affected by the penetration of the convection electric field, which is the result of the large-scale magnetosphere-ionosphere electromagnetic coupling. This transport, on the other hand, results in plasma heating and magnetic field stretching, which become very significant in the inner plasma sheet (inside 20 RE). We have previously run

M. Gkioulidou; C. Wang; L. R. Lyons; R. A. Wolf

2010-01-01

184

A research of W-band folded waveguide traveling wave tube with elliptical sheet electron beam  

SciTech Connect

Folded waveguide (FWG) traveling wave tube (TWT), which shows advantages in high power capacity, moderate bandwidth, and low-cost fabrication, has become the focus of vacuum electronics recently. Sheet electron beam devices are better suited for producing radiation sources with large power in millimeter wave spectrum due to their characteristics of relatively low space charge fields and large transport current. A FWG TWT with elliptical sheet beam working in W-band is presented in this paper, with the analysis of its dispersion characteristics, coupling impedance, transmission properties, and interaction characteristics. A comparison is also made with the traditional FWG TWT. Simulation results lead to the conclusion that the FWG TWT with elliptical sheet beam investigated in this paper can make full use of relatively large electric fields and thus generate large output power with the same electric current density.

Guo Guo; Wei Yanyu; Yue Lingna; Gong Yubin; Zhao Guoqing; Huang Minzhi; Tang Tao; Wang Wenxiang [National Key Laboratory of Science and Technology on Vacuum Electronics, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2012-09-15

185

A THEMIS multicase study of dipolarization fronts in the magnetotail plasma sheet  

E-print Network

are kineticscale dissipative regions with Joule heating rates of 10% of the total bursty bulk flow energy. Citation their characteristic gradient scales. The study reveals (1) a rapid 50% decrease in plasma density and ion pressure, (2) a factor of 2­3 increase in highenergy (30­200 keV) electron flux and electron temperature, and (3

California at Berkeley, University of

186

Electron Capture in a Fully Ionized Plasma  

E-print Network

Properties of fully ionized water plasmas are discussed including plasma charge density oscillations and the screening of the Coulomb law especially in the dilute classical Debye regime. A kinetic model with two charged particle scattering events determines the transition rate per unit time for electron capture by a nucleus with the resulting nuclear transmutations. Two corrections to the recent Maiani et al. calculations are made: (i) The Debye screening length is only employed within its proper domain of validity. (ii) The WKB approximation employed by Maiani in the long De Broglie wave length limit is evidently invalid. We replace this incorrect approximation with mathematically rigorous Calogero inequalities in order to discuss the scattering wave functions. Having made these corrections, we find a verification for our previous results based on condensed matter electro-weak quantum field theory for nuclear transmutations in chemical batteries.

A. Widom; J. Swain; Y. N. Srivastava

2014-09-17

187

Electron Capture in a Fully Ionized Plasma  

E-print Network

Properties of fully ionized water plasmas are discussed including plasma charge density oscillations and the screening of the Coulomb law especially in the dilute classical Debye regime. A kinetic model with two charged particle scattering events determines the transition rate per unit time for electron capture by a nucleus with the resulting nuclear transmutations. Two corrections to the recent Maiani et al. calculations are made: (i) The Debye screening length is only employed within its proper domain of validity. (ii) The WKB approximation employed by Maiani in the long De Broglie wave length limit is evidently invalid. We replace this incorrect approximation with mathematically rigorous Calogero inequalities in order to discuss the scattering wave functions. Having made these corrections, we find a verification for our previous results based on condensed matter electro-weak quantum field theory for nuclear transmutations in chemical batteries.

Widom, A; Srivastava, Y N

2014-01-01

188

Energy Measurements of Trapped Electrons from a Plasma Wakefield Accelerator  

SciTech Connect

Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC indicate trapping of plasma electrons. More charge came out of than went into the plasma. Most of this extra charge had energies at or below the 10 MeV level. In addition, there were trapped electron streaks that extended from a few GeV to tens of GeV, and there were mono-energetic trapped electron bunches with tens of GeV in energy.

Kirby, Neal; /SLAC; Auerbach, David; Berry, Melissa; Blumenfeld, Ian; Clayton, Christopher E.; Decer, Franz-Josef; Hogan, Mark J.; Huang, Chengkun; Ischebeck, Rasmus; Iverson, Richard; Johnson, Devon; Joshi, Chadrashekhar; Katsouleas, Thomas; Lu, Wei; Marsh, Kenneth A.; Mori, Warren B.; Muggli, Patric; Oz, Erdem; Siemann, Robert H.; Walz,; Zhou, Miaomiao; /SLAC /UCLA /Southern California U.

2007-01-03

189

Angular anisotropy of electron energy distributions in inductively coupled plasmas  

E-print Network

Angular anisotropy of electron energy distributions in inductively coupled plasmas Alex V of Physics. DOI: 10.1063/1.1614428 I. INTRODUCTION Low- and intermediate-pressure inductively coupled plasmas coupled plasmas ICPs has the potential to produce highly anisotropic angle-dependent electron energy

Kushner, Mark

190

Scattering from electron density irregularities in a compressible anisotropic plasma  

Microsoft Academic Search

The cold-plasma model of the radio wave scattering from spatially random fluctuations of electron density in an anisotropic plasma is extended to the warm-plasma model, in which the effect of electron pressure is taken into account. Since the medium is compressible as well as anisotropic, there is the additional possibility of mode conversion from an incident electromagnetic wave to a

T. Okuzawa; T. H. Nguyen

1980-01-01

191

Attachment of alginate microcapsules onto plasma-treated PDMS sheet for retrieval after transplantation.  

PubMed

Although transplantation of microencapsulated islets has been proposed as a therapy for the treatment of diabetes mellitus, limited retrievability of the cells has impeded its medical usage. To achieve retrieval of microencapsulated islets, capsules were attached to polydimethylsiloxane (PDMS) with a biocompatible adhesive. Because the hydrophobic nature of the PDMS surface prevents attachment, surface modification is essential. Alginate microcapsules were attached to modified PDMS sheets, and the mechanical stability of the resulting constructs was determined. Acrylic acid (AA) and acrylamide (AM) mixtures were grafted on the surfaces of PDMS sheets using a two-step oxygen plasma treatment (TSPT). TSPT-PDMS was characterized according to water contact angle and zeta-potential measurements. The contact angle was altered by changing the ratio of AM to AA to generate hydrophilic surface. Evaluation of the surface charge at pH 2, 7, and 12 confirmed the presence of polar groups on the modified surface. Microcapsules were attached to TSPT-PDMS using Histoacryl and shown to be in a monolayered and half-exposed state. The shear stress resistance of alginate capsules attached to the PDMS sheet indicates the possibility of transplantation of encapsulated cells without scattering in vivo. This method is applicable to retrieve microencapsulated porcine islets when required. PMID:23668815

Shin, Soojeong; Shin, Jeong Eun; Yoo, Young Je

2013-01-01

192

Quantification of ridging in ferritic stainless steel sheets by electron backscattered diffraction R-value maps.  

PubMed

In ferritic stainless steel (FSS), undesirable surface defects of ridging appear during deep drawing. The formation of these defects is attributed to the inhomogeneous distribution of orientations of individual grains. In the present work, a new electron backscattered diffraction R(?)-value map was introduced, and the dependence of the tensile directions on the formation of ridging in an FSS sheet was discussed using this map. The results showed that large grain colonies in the R(?)-value maps lead to the formation of severe ridging in an FSS sheet. PMID:23920166

Lee, Kye-Man; Park, Jieon; Kim, Sangseok; Park, Sooho; Huh, Moo-Young

2013-08-01

193

Topological Features of a Compressible Plasma Vortex Sheet - a Model of the Outer Heliospheric Wind  

NSDL National Science Digital Library

The Voyager and Pioneer Spacecraft have detected large-scale quasi-periodic plasma fluctuations in the outer heliosphere beyond 20 AU. A plasma vortex sheet model can explain these fluctuations and the observed correlations between various physical variables. The large scale outer heliosphere is modeled by solving the 3-D compressible magnetohydrodynamic equations involving three interacting shear layers. Computations were done on a Cray computer at the NASA Center for Computational Sciences. Six cases are animated: Weak magnetic field and strong magnetic field, each at three values of tau, the vortex street characteristic time. Contours of density are shown as dark transparent tubes. Critical points of the velocity field are represented by Glyphs. Vortex cores are shown in orange and blue.

Starr, Cindy; Siregar, Edouard; Ghosh, Sanjoy

1993-12-17

194

Dispersive O+ conics observed in the plasma-sheet boundary layer with CRRES/LOMICS during a magnetic storm  

NASA Astrophysics Data System (ADS)

We present initial results from the Low-energy magnetospheric ion composition sensor (LOMICS) on the Combined release and radiation effects satellite (CRRES) together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion species (H+, He++, He+, O++, O+) simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the time resolution afforded by the spacecraft spin period of 30 s. During the geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT to 0816 UT) the LOMICS ion mass spectrometer observed an apparent O+ conic flowing away from the southern hemisphere with a bulk velocity that decreased exponentially with time from 300 km/s to 50 km/s, while its temperature also decreased exponentially from 700 to 5 eV. At the onset of the O+ conic, intense low-frequency electromagnetic wave activity and strong pitch-angle scattering were also observed. At the time of the observations the CRRES spacecraft was inbound at Lapprox7.5 near dusk, magnetic local time (MLT), and at a magnetic latitude of -23. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary layer (PSBL) when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particle interactions. We are unable to conclude whether the conic was causally associated with spatial structures of the PSBL or the central plasma sheet. Acknowledgements. This study is supported in part by the Ministry of Education, Science, Sports, and Culture in Japan, under a Grant-in-Aid for Scientific Research (Category B). Topical Editor D. Alcayd thanks M. Lockwood and N. J. Fox for their help in evaluating this paper.->

West, M.; Young, D. T.; Thomsen, M. F.; Barraclough, B. L.; Singer, H. J.; Anderson, R. R.

1996-06-01

195

High and low frequency instabilities driven by counter-streaming electron beams in space plasmas  

NASA Astrophysics Data System (ADS)

A four-component plasma composed of a drifting (parallel to ambient magnetic field) population of warm electrons, drifting (anti-parallel to ambient magnetic field) cool electrons, stationary hot electrons, and thermal ions is studied in an attempt to further our understanding of the excitation mechanisms of broadband electrostatic noise (BEN) in the Earth's magnetospheric regions such as the magnetosheath, plasmasphere, and plasma sheet boundary layer (PSBL). Using kinetic theory, beam-driven electrostatic instabilities such as the ion-acoustic, electron-acoustic instabilities are found to be supported in our multi-component model. The dependence of the instability growth rates and real frequencies on various plasma parameters such as beam speed, number density, temperature, and temperature anisotropy of the counter-streaming (relative to ambient magnetic field) cool electron beam are investigated. It is found that the number density of the anti-field aligned cool electron beam and drift speed play a central role in determining which instability is excited. Using plasma parameters which are closely correlated with the measurements made by the Cluster satellites in the PSBL region, we find that the electron-acoustic and ion-acoustic instabilities could account for the generation of BEN in this region.

Mbuli, L. N.; Maharaj, S. K.; Bharuthram, R.

2014-05-01

196

Electron-acoustic solitons in an electron-beam plasma system Matthieu Berthomiera)  

E-print Network

Electron-acoustic solitons in an electron-beam plasma system Matthieu Berthomiera) Swedish Physics, Uppsala, Sweden Received 18 November 1999; accepted 16 March 2000 Electron-acoustic solitons exist in a two electron temperature plasma with ``cold'' and ``hot'' electrons and take the form

California at Berkeley, University of

197

Forced magnetic reconnection in a plasma sheet with localized resistivity profile excited by lower hybrid drift type instability  

NASA Technical Reports Server (NTRS)

A forced magnetic reconnection process with a temporal evolution of resistivity is studied for a plasma sheet with a nonuniform resistivity profile based on the nonlocal mode structure of the lower hybrid drift type instability. The growth rate of the mode found is almost independent of the resistivity at the neutral sheet, but depends on the resistivity of the region of maximum density gradient away from the neutral sheet. This is studied by using both a nonlinear numerical MHD simulation and a linear theory. The mode may be relevant to the prevalent theoretical concept of MHD reconnection and the localized anomalous resistivity profile based on the lower hybrid drift instability.

Hoshino, M.

1991-01-01

198

Electron acceleration by surface plasma waves in double metal surface structure  

SciTech Connect

Two parallel metal sheets, separated by a vacuum region, support a surface plasma wave whose amplitude is maximum on the two parallel interfaces and minimum in the middle. This mode can be excited by a laser using a glass prism. An electron beam launched into the middle region experiences a longitudinal ponderomotive force due to the surface plasma wave and gets accelerated to velocities of the order of phase velocity of the surface wave. The scheme is viable to achieve beams of tens of keV energy. In the case of a surface plasma wave excited on a single metal-vacuum interface, the field gradient normal to the interface pushes the electrons away from the high field region, limiting the acceleration process. The acceleration energy thus achieved is in agreement with the experimental observations.

Liu, C. S.; Kumar, Gagan; Singh, D. B.; Tripathi, V. K. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Physics Department, Indian Institute of Technology, New Delhi 110016 (India); Laser Science and Technology Centre, Metcalfe House, Delhi 110054 (India); Physics Department, Indian Institute of Technology, New Delhi 110016 (India)

2007-12-01

199

Non-vacuum electron beam welding through a plasma window  

NASA Astrophysics Data System (ADS)

The plasma window is a novel apparatus that utilizes a stabilized plasma arc as interface between vacuum and atmosphere or pressurized targets without solid material. Additionally, the plasma has a lensing effect on charged particles. This feature enables beam focusing to very small spot sizes and overcoming beam dispersion due to scattering by atmospheric atoms and molecules. Recently, the plasma window was mated to a conventional electron beam welder. And, electron beam welding in atmosphere was accomplished with electron beams of unprecedented low power and energy. Weld quality for the non-vacuum plasma window electron beam welding approached the quality of in-vacuum electron beam welding. Indications exist that electron beam attenuation is lower than theoretically predicted. Results suggest that air boring was achieved with 6-15 mA, 90-150 keV electron beams compared to the previously used kA, MeV electron beams. It may explain the better than expected welding results.

Hershcovitch, Ady

2005-12-01

200

Nonnuclear nearly free electron conduction channels induced by doping charge in nanotube-molecular sheet composites.  

PubMed

Nearly free electron (NFE) states with density maxima in nonnuclear (NN) voids may have remarkable electron transport properties ranging from suppressed electron-phonon interaction to Wigner crystallization. Such NFE states, however, usually exist near the vacuum level, which makes them unsuitable for transport. Through first principles calculations on nanocomposites consisting of carbon nanotube (CNT) arrays sandwiched between boron nitride (BN) sheets, we describe a stratagem for stabilizing the NN-NFE states to below the Fermi level. By doping the CNTs with negative charge, we establish Coulomb barriers at CNTs walls that, together with the insulating BN sheets, define the transverse potentials of one-dimensional (1D) transport channels, which support the NN-NFE states. PMID:24401149

Zhao, Jin; Zheng, Qijing; Petek, Hrvoje; Yang, Jinlong

2014-09-01

201

Studies of Cryogenic Electron Plasmas in Magnetic Mirror Fields  

E-print Network

Studies of Cryogenic Electron Plasmas in Magnetic Mirror Fields by Ramesh Gopalan A.B. (University: Chair Date Date Date University of California at Berkeley 1998 #12;Studies of Cryogenic Electron Plasmas in Magnetic Mirror Fields Copyright 1998 by Ramesh Gopalan #12;1 Abstract Studies of Cryogenic Electron

Fajans, Joel

202

Electron and photon production from relativistic laser plasma interactions  

Microsoft Academic Search

The interaction of short and intense laser pulses with plasmas is a very efficient source of relativistic electrons with tunable properties. In low-density plasmas, we observed bunches of electrons up to 200 MeV, accelerated in the wakefield of the laser pulse. Less energetic electrons (tens of megaelectronvolt) have been obtained, albeit with a higher efficiency, during the interaction with a

E. Lefebvre; N. Cochet; S. Fritzler; V. Malka; M.-M. Alonard; J.-F. Chemin; S. Darbon; L. Disdier; J. Faure; A. Fedotoff; O. Landoas; G. Malka; V. Mot; P. Morel; M. Rabec LeGloahec; A. Rouyer; Ch. Rubbelynck; V. Tikhonchuk; R. Wrobel; P. Audebert; C. Rousseaux

2003-01-01

203

Dynamic focusing of an electron beam through a long plasma  

Microsoft Academic Search

The focusing effects of a 1.4m long, (0-2)1014 cm-3 plasma on a single 28.5GeV electron bunch are studied experimentally in the underdense or blowout regime, where the beam density is much greater than the plasma density. As the beam propagates through the plasma, the density of plasma electrons along the incoming bunch drops from the ambient density to zero leaving

C. O'Connell; F.-J. Decker; M. J. Hogan; R. Iverson; P. Raimondi; R. H. Siemann; D. Walz; B. Blue; C. E. Clayton; C. Joshi; K. A. Marsh; W. B. Mori; S. Wang; T. Katsouleas; S. Lee; P. Muggli

2002-01-01

204

DYNAMIC FOCUSING OF AN ELECTRON BEAM THROUGH A LONG PLASMA  

Microsoft Academic Search

The focusing effects of a 1.4 m long, (0-2) x 10¹⁴ cm⁻³ plasma on a single 28.5 GeV electron bunch are studied experimentally in the underdense or blowout regime, where the beam density is much greater than the plasma density. As the beam propagates through the plasma, the density of plasma electrons along the incoming bunch drops from the ambient

OConnell; Caolionn L

2002-01-01

205

The Relationship of Ion Beams and Fast Flows in the Plasma Sheet Boundary Layer  

NASA Technical Reports Server (NTRS)

We report new findings on the behavior of plasmas in the vicinity of the plasma sheet boundary layer (PSBL). A large geometrical factor detector on WIND (3D plasma experiment) has discovered a unidirectional ion beam streaming in the tailward direction missed by previous observations. This tailward beam is as intense as the earthward streaming beam and it is found just inside the outer edge of the PSBL where earthward streaming beams are observed. The region where this tailward beam is observed includes an isotropic plasma component which is absent in the outer edge where earthward streaming beams are found. When these different distributions are convolved to calculate the velocity moments, fast flows (greater than 400 km/s) result in the earthward direction and much slower flows (less than 200 km/s) in the tailward direction. These new findings are substantially different from previous observations. Thus, the interpretation of fast flows and earthward and counterstreaming ion beams in terms of a neutral line model must be reexamined.

Parks, G. K.; Reme, H.; Lin, R. P.; Sanderson, T.; Germany, G. A.; Spann, James F., Jr.; Brittnacher, M. J.; McCarthy, M.; Chen, L. J.; Larsen, D.; Phan, T. D.

1998-01-01

206

Effects of emitted electron temperature on the plasma sheath  

NASA Astrophysics Data System (ADS)

It has long been known that electron emission from a surface significantly affects the sheath surrounding that surface. Typical fluid theory of a planar sheath with emitted electrons assumes that the plasma electrons follow the Boltzmann relation and the emitted electrons are emitted with zero energy and predicts a potential drop of 1.03Te/e across the sheath in the floating condition. By considering the modified velocity distribution function caused by plasma electrons lost to the wall and the half-Maxwellian distribution of the emitted electrons, it is shown that ratio of plasma electron temperature to emitted electron temperature significantly affects the sheath potential when the plasma electron temperature is within an order of magnitude of the emitted electron temperature. When the plasma electron temperature equals the emitted electron temperature the emissive sheath potential goes to zero. One dimensional particle-in-cell simulations corroborate the predictions made by this theory. The effects of the addition of a monoenergetic electron beam to the Maxwellian plasma electrons were explored, showing that the emissive sheath potential is close to the beam energy only when the emitted electron flux is less than the beam flux.

Sheehan, J. P.; Kaganovich, I. D.; Wang, H.; Sydorenko, D.; Raitses, Y.; Hershkowitz, N.

2014-06-01

207

Simulation of laserplasma interactions and fast-electron transport in inhomogeneous plasma  

Microsoft Academic Search

A new framework is introduced for kinetic simulation of laserplasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther

B. I. Cohen; A. J. Kemp; L. Divol

2010-01-01

208

Auroral source region: Plasma properties of the high-latitude plasma sheet  

E-print Network

with average densities 0.1 cm?3 and average temperatures which are about half of those in the central plasma. Scudder Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA E. E. Dors Los Alamos National Laboratory, Los Alamos, New Mexico, USA C. Curto Department of Mathematics, Duke

Logan, David

209

Anisotropy of the Taylor scale and the correlation scale in plasma sheet magnetic field fluctuations as a function of auroral electrojet activity  

Microsoft Academic Search

Magnetic field data from the Cluster spacecraft in the magnetospheric plasma sheet are employed to determine the correlation scale and the magnetic Taylor microscale from simultaneous multiple-point measurements for multiple intervals over a range of mean magnetic field directions for three different levels of geomagnetic activity. We have determined that in the plasma sheet the correlation scale along the mean

James M. Weygand; W. H. Matthaeus; M. El-Alaoui; S. Dasso; M. G. Kivelson

2010-01-01

210

Preparation of Ti-Al alloy sheet by electron beam physical vapor deposition  

Microsoft Academic Search

Ti-Al thin sheet with dimension of 450 mm450 mm0.2 mm was prepared by electron beam physical vapor deposition(EB-PVD) technology. The surface and cross-section pattern of as-deposited sample were studied by SEM and AFM, and then the composition and phase were analysed by XRD and EPMA. Finally, the effect on deposit by re-evaporation of Al was explored by calculating the ratio

MA Li

211

Electron beam welding, laser beam welding and gas tungsten arc welding of titanium sheet  

Microsoft Academic Search

Microstructures, properties and technical parameters of welding specimen of 0.5 mm thick sheets of commercial purity titanium (C.P. Ti) have been studied via high vacuum electron beam welding (EBW-HV), CO2 laser beam welding (LBW) and gas tungsten arc welding (TIG), as well as optical microscope (OM) observation and microhardness measuring. The results indicate that the EBW is more suitable for

Qi Yunlian; Deng Ju; Hong Quan; Zeng Liying

2000-01-01

212

Transmission and consequences of solar wind fluctuations in the plasma sheet  

NASA Astrophysics Data System (ADS)

The purpose of this study is to quantify how solar wind conditions affect the energy and plasma transport in the geomagnetic tail and it's large-scale configuration. To uniquely identify the role of various effects, the magnetospheric data will be sorted according to different solar wind plasma and interplanetary magnetic field (IMF) parameters: Speed, dynamic pressure, Alfven mach number, IMF north-south component, and the power in the dynamic pressure and IMF Ultra Low Frequency (ULF) fluctuations. We will study and compare the magnetospheric magnetic field magnitude and configuration as well as the variations of the average flow speed pattern and the occurrence and properties of flow bursts in different solar wind conditions. Magnetospheric data from five THEMIS spacecrafts and solar wind data from NASA's omniweb will be used in this study. During the studied time period the five THEMIS spacecraft were periodically aligned in the night-side plasma sheet parallel to the Sun-Earth line covering distances from about 10 Re to 30 Re downtail. The studied time interval covers years from 2007 to 2009 and it corresponds to the extended and prolonged solar activity minimum between solar cycles 23 and 24, which will allow investigating magnetospheric processes and solar wind-magnetospheric coupling during the relatively quiet state of the magnetosphere. The motivation of this study is to improve our understanding on solar wind-magnetosphere coupling and thus ultimately improve space weather forecasting.

Myllys, Minna; Kilpua, Emilia; Pulkkinen, Tuija

2014-05-01

213

Emittance Measurements of Trapped Electrons from a Plasma Wakefield Accelerator  

SciTech Connect

Recent electron beam driven plasma wakefield accelerator experiments carried out at SLAC showed trapping of plasma electrons. These trapped electrons appeared on an energy spectrometer with smaller transverse size than the beam driving the wake. A connection is made between transverse size and emittance; due to the spectrometer's resolution, this connection allows for placing an upper limit on the trapped electron emittance. The upper limit for the lowest normalized emittance measured in the experiment is 1 mm {center_dot} mrad.

Kirby, N.; Berry, M.; Blumenfeld, I.; Decker, F.-J.; Hogan, M.J.; Ischebeck, R.; Iverson, R.; Siemann, R.; Walz, D.; /SLAC; Clayton, C.E.; Huang, C.; Joshi, C.; Lu, W.; Marsh, K.A.; Mori, W.B.; Zhou, M.; /UCLA; Katsouleas, T.C.; Muggli, P.; Oz, E.; /Southern California U.

2007-06-28

214

Wind survey of high-speed bulk flows and field-aligned beams in the near-Earth plasma sheet  

Microsoft Academic Search

We have surveyed all high-speed (>250 km\\/s) flows detected by Wind during its 17 perigee passes across the near-Earth (xGSE = -25 to 0 RE) plasma sheet in the period between 1995 and 1997. By classifying high-speed flow events based on their ion distribution characteristics rather than their plasma moments or the regions in which these flows were detected, we

Arjun Raj; Tai Phan; Robert P. Lin; V. Angelopoulos

2002-01-01

215

Wind survey of high-speed bulk flows and field-aligned beams in the near-Earth plasma sheet  

Microsoft Academic Search

We have surveyed all high-speed (>250 km\\/s) flows detected by Wind during its 17 perigee passes across the near-Earth (xGSE = ?25 to 0 RE) plasma sheet in the period between 1995 and 1997. By classifying high-speed flow events based on their ion distribution characteristics rather than their plasma moments or the regions in which these flows were detected, we

Arjun Raj; Tai Phan; Robert P. Lin; V. Angelopoulos

2002-01-01

216

Integration issues of a plasma contactor Power Electronics Unit  

Microsoft Academic Search

A hollow cathode-based plasma contactor is baselined on International Space Station Alpha (ISSA) for spacecraft charge control. The plasma contactor system consists of a hollow cathode assembly (HCA), a power electronics unit (PEU), and an expellant management unit (EMU). The plasma contactor has recently been required to operate in a cyclic mode to conserve xenon expellant and extend system life.

Luis R. Pinero; Kenneth W. York; Glen E. Bowers

1995-01-01

217

Vortices, Reconnection and Turbulence in High Electron-Beta Plasmas  

SciTech Connect

Plasmas in which the kinetic energy exceeds the magnetic energy by a significant factor are common in space and in the laboratory. Such plasmas can convect magnetic fields and create null points in whose vicinity first the ions become unmagnetized, then the electrons. This project focuses on the detailed study of the transition regime of these plasmas.

Stenzel, R. L.

2004-08-31

218

Whistler excitation by electron beams in laboratory plasmas  

Microsoft Academic Search

Laboratory plasma experiments have demonstrated their prime importance as essential and powerful tools for modeling and understanding many basic plasma physics phenomena as well as space and astrophysical processes. This review discusses laboratory experiments devoted to electron beam interaction with waves in magnetized plasmas, in physical conditions relevant to natural space phenomena or controlled experiments involving artificial beam injection. The

C. Krafft; M. Starodubtsev

2002-01-01

219

The 3 DLE instrument on ATS-5. [plasma electron counter  

NASA Technical Reports Server (NTRS)

The performance and operation of the DLE plasma electron counter on board the ATS 5 are described. Two methods of data presentation, microfilm line plots and spectrograms, are discussed along with plasma dynamics, plasma flow velocity, electrostatic charging, and wave-particle interactions.

Deforest, S. E.

1973-01-01

220

Simulation of sheet-shaped lithium beam probe performance for two-dimensional edge plasma measurement  

SciTech Connect

A sheet-shaped thermal lithium beam probe has been developed for two-dimensional density measurements in the edge region of the torus plasma. A numerical simulation was carried out to confirm the validity of the diagnostics for fast and transient phenomena such as edge localized modes or blobs, etc., where the velocity of blobs is faster than that of the probe beam. It was found in the simulation that the density of the blob itself is reconstructed to be low and unexpected ghosts appear in the reconstructed density profile near the blob, if the conventional reconstruction method is employed. These results invite our attention to the numerical errors in the density reconstruction process. On the other hand, the errors can be corrected by using the simulation results.

Tsuchiya, H.; Morisaki, T.; Komori, A.; Motojima, O. [Graduate University for Advanced Studies, Toki 509-5292 (Japan); National Institute for Fusion Science, Toki 509-5292 (Japan)

2006-10-15

221

Anisotropy of the Taylor scale and the correlation scale in plasma sheet and solar wind magnetic field fluctuations  

Microsoft Academic Search

Magnetic field data from nine spacecraft in the magnetospheric plasma sheet and the solar wind are employed to determine the correlation scale and the magnetic Taylor microscale from simultaneous multiple-point measurements for multiple intervals with a range of mean magnetic field directions. We have determined that in the solar wind the Taylor scale is independent of direction relative to the

James M. Weygand; W. H. Matthaeus; S. Dasso; M. G. Kivelson; L. M. Kistler; C. Mouikis

2009-01-01

222

Taylor scale and effective magnetic Reynolds number determination from plasma sheet and solar wind magnetic field fluctuations  

Microsoft Academic Search

Cluster data from many different intervals in the magnetospheric plasmas sheet and the solar wind are employed to determine the magnetic Taylor microscale from simultaneous multiple point measurements. For this study we define the Taylor scale as the square root of the ratio of the mean square magnetic field (or velocity) fluctuations to the mean square spatial derivatives of their

James M. Weygand; W. H. Matthaeus; S. Dasso; M. G. Kivelson; R. J. Walker

2007-01-01

223

Taylor scale and effective magnetic Reynolds number determination from plasma sheet and solar wind magnetic field fluctuations  

Microsoft Academic Search

(1) Cluster data from many different intervals in the magnetospheric plasmas sheet and the solar wind are employed to determine the magnetic Taylor microscale from simultaneous multiple point measurements. For this study we define the Taylor scale as the square root of the ratio of the mean square magnetic field (or velocity) fluctuations to the mean square spatial derivatives of

James M. Weygand; W. H. Matthaeus; S. Dasso; M. G. Kivelson; R. J. Walker

2007-01-01

224

On a plasma kinetic model of a 3D solar corona and solar wind at the heliospheric sheet  

Microsoft Academic Search

The dynamical solar corona in 3D consists of transient type magnetic island elements and radial type magnetic flux rope structures in a heliospheric sheet. During the formation and relaxation these elements produce inductive electromagnetic fields where energetic particles are produced. We study the 3D corona formation in the kinetic approach and parametrize it like a hot current-carrying collisionless plasma with

V. M. Gubchenko; M. L. Khodachenko; H. K. Biernat; V. V. Zaitsev; H. O. Rucker

2004-01-01

225

ISEE-1 and 2 observations of magnetic flux ropes in the magnetotail - FTE's in the plasma sheet?  

NASA Technical Reports Server (NTRS)

Magnetic field observations on ISEE-1 and 2 in and near the neutral sheet about 20 Re down the near-earth magnetotail reveal the occurrence of structures resembling magnetic flux ropes. Both electric field and fast plasma data show that these structures convect across the spacecraft at speeds of 200 - 600 km/s, and that they have scale sizes of roughly 3 5 Re. The rope axis orientation is across the tail, approximately in the -Y GSM direction. Their magnetic structure is strikingly similar to magnetic flux ropes observed in the Venus ionosphere, and to flux transfer events observed at the dayside magnetopause. The total field-aligned current within these ropes may approach a million amps. These structures may arise because of patchy reconnection within the plasma sheet, or may be tearing islands formed when the plasma sheet magnetic field has a cross-tail component. Plasma sheet flux ropes are not a common feature at ISEE orbital altitudes; this suggests that near-earth neutral line formation within ISEE apogee (22 Re) may be equally rare.

Elphic, R. C.; Russell, C. T.; Cattell, C. A.; Takahasi, K.; Bame, S. J.

1986-01-01

226

Simultaneous observations of ions of ionospheric origin over the ionosphere and in the plasma sheet at storm-time substorms  

NASA Astrophysics Data System (ADS)

We investigate variations of ion flux over the ionosphere and in the plasma sheet when storm-time substorms are initiated, using simultaneous observations of neutral atoms in the energy range of up to a few keV measured by the low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite and energetic (9-210 keV/e) ion flux measured by the Energetic Particles and Ion Composition/Suprathermal Ion Composition Spectrometer (EPIC/STICS) on board the Geotail satellite. We examined three storm intervals during which the IMAGE satellite was located near its apogee and the Geotail satellite was in the plasma sheet on the nightside. Low-energy neutral atoms traveling from the direction of the Earth can be created by outflowing ionospheric ions through charge exchange processes. The observed neutral atom flux enhancement at storm-time substorms indicates that substorms can cause an immediate increase of low-energy ion flux over the ionosphere by a factor of 3-10. In the plasma sheet, the flux ratio of O+/H+ is rapidly enhanced at storm-time substorms and then increased gradually or stayed at a constant level in a timescale of <60 minutes, suggesting a mass-dependent acceleration of ions at local dipolarization and a subsequent additional supply to the plasma sheet of O+ ions extracted from the ionosphere at the substorms.

Nose, M.; Taguchi, S.; Moore, T. E.; Collier, M. R.; Hosokawa, K.; Christon, S. P.; McEntire, R. W.

2006-12-01

227

Whistler Solitons in Plasma with Anisotropic Hot Electron Admixture  

NASA Technical Reports Server (NTRS)

The longitudinal and transverse modulation instability of whistler waves in plasma, with a small admixture of hot anisotropic electrons, is discussed. If the hot particles temperature anisotropy is positive, it is found that, in such plasma, longitudinal perturbations can lead to soliton formation for frequencies forbidden in cold plasma. The soliton is enriched by hot particles. The frequency region unstable to transverse modulation in cold plasma in the presence of hot electrons is divided by stable domains. For both cases the role of hot electrons is more significant for whistlers with smaller frequencies.

Khazanov, G. V.; Krivorutsky, E. N.; Gallagher, D. L.

1999-01-01

228

Energy transport by kinetic-scale electromagnetic waves in fast plasma sheet flows  

NASA Astrophysics Data System (ADS)

We report observations from the THEMIS spacecraft characterizing the nature and importance of low frequency electromagnetic fluctuations on kinetic scales embedded within fast flows in the Earth's plasma sheet. A consideration of wave property variations with frequency and flow speed suggest that for spacecraft frame frequencies satisfying |vf|/i ? sc ? 100|vf|/i (or 0.2 ? fsc ? 20 Hz) these fluctuations can generally be described as kinetic Alfvn waves. Here vf is the flow speed, i the ion gyroradius, and sc and fsc are the angular and cyclical frequencies respectively in the spacecraft frame. The statistics of energy transport via Poynting flux (S) in these fluctuations and ion energy flux () in the flow follow log normal distributions with mean values of = 101.1 0.7 and = 102.4 0.4 mW/m2 respectively where the values are mapped to a reference magnetic field at 100 km altitude. Here the indices following correspond to one standard deviation. We find that = 10-1.3 0.7 or that kinetic Alfvn waves on average transport 5% of the total energy transport in the flow but note that the values larger than 25% are within one standard deviation of the mean. Our observations show that these waves are continually radiated outward from the flow toward the auroral oval, low latitude boundary layer or lobes and that over several Earth-radii the integrated energy loss from the flow channel can be comparable to the total energy content of the flow itself. We find that this plasma sheet energy loss process is particularly effective within |XGSE| ? 15 RE.

Chaston, C. C.; Bonnell, J. W.; Clausen, L.; Angelopoulos, V.

2012-09-01

229

Electron energy distribution function control in gas discharge plasmas  

SciTech Connect

The formation of the electron energy distribution function (EEDF) and electron temperature in low temperature gas discharge plasmas is analyzed in frames of local and non-local electron kinetics. It is shown, that contrary to the local case, typical for plasma in uniform electric field, there is the possibility for EEDF modification, at the condition of non-local electron kinetics in strongly non-uniform electric fields. Such conditions naturally occur in some self-organized steady state dc and rf discharge plasmas, and they suggest the variety of artificial methods for EEDF modification. EEDF modification and electron temperature control in non-equilibrium conditions occurring naturally and those stimulated by different kinds of plasma disturbances are illustrated with numerous experiments. The necessary conditions for EEDF modification in gas discharge plasmas are formulated.

Godyak, V. A. [Electrical Engineering and Computer Science Department, University of Michigan, Ann Arbor, Michigan 48109, USA and RF Plasma Consulting, Brookline, Massachusetts (United States)] [Electrical Engineering and Computer Science Department, University of Michigan, Ann Arbor, Michigan 48109, USA and RF Plasma Consulting, Brookline, Massachusetts (United States)

2013-10-15

230

Plasma plume oscillations during welding of thin metal sheets with a CW CO2 laser  

NASA Astrophysics Data System (ADS)

An analysis is presented of the oscillations of keyhole pressure and plasma radiation emitted during welding with a continuous wave (CW) CO2 laser. Welding was done with a CW CO2 laser, Photon Sources VFA 2500, operating at the power of 1.75 kW. The welded materials were mild and stainless steel sheets, 0.8-2 mm thick. The shielding gas was argon or helium. Oscillations of plasma radiation were registered in monochromatic or broad band radiation with the use of a photomultiplier or photodiode and pressure variations with a microphone in the frequency range of 20-2104 Hz. It has been found that the optical signal from the plasma plume is closely connected with the acoustic signal and that the source of the acoustic signal is the pulsating movement of the plasma plume. Spectral analysis of the measured oscillations shows differences in power spectra depending on the welding conditions. Generally, two intrinsic frequency peaks in the range of 0.5-4 kHz are always present but the amplitude, frequency and width of the peaks depend on the material and welding conditions. The results show that the optical and acoustic signals emitted during the welding process can be useful for process monitoring. The behaviour of the observed oscillations is characteristic for deterministic chaos. Considerable regularization of the process was observed as an effect of modulation of the laser beam. The modulation factor (Pmax -Pmin )/Pmax was equal to 0.2 and the modulation frequency was 2 kHz. In this case, the intense peak corresponding to the modulation frequency was observed in the power spectrum together with smaller peaks corresponding to the harmonic frequencies.

Szymanski, Z.; Hoffman, J.; Kurzyna, J.

2001-01-01

231

Response of ions of ionospheric origin to storm time substorms: Coordinated observations over the ionosphere and in the plasma sheet  

NASA Astrophysics Data System (ADS)

We investigate variations of ion flux over the ionosphere and in the plasma sheet when storm time substorms are initiated, using simultaneous observations of neutral atoms in the energy range of up to a few keV measured by the low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite, outflowing ion flux of <1 keV measured by the ion electrostatic analyzer (IESA) on board the Fast Auroral SnapshoT (FAST) satellite, and energetic (9-210 keV/e) ion flux measured by the energetic particle and ion composition (EPIC) instrument on board the Geotail satellite. We examined three storm intervals during which the IMAGE or FAST satellite was in a suitable location to observe ionospheric ion outflow and the Geotail satellite was in the plasma sheet on the nightside. The neutral atom flux observed by IMAGE/LENA in the first interval and outflowing ion flux observed by FAST/IESA in the second and third intervals indicate that storm time substorms can cause increases of low-energy ion flux over the ionosphere by a factor of 3-50 with time delay of less than several minutes. In the plasma sheet, the flux ratio of O+/H+ is rapidly enhanced at the storm time substorms and then increased gradually or stayed at a constant level in a time scale of 1 h, suggesting a mass-dependent acceleration of ions at local dipolarization and a subsequent additional supply of O+ ions to the plasma sheet which have been extracted from the ionosphere at the substorms. These coordinated observations revealed that substorms have both an immediate effect and a delayed effect (i.e., two-step effect) on the ion composition in the plasma sheet.

Nos, M.; Taguchi, S.; Christon, S. P.; Collier, M. R.; Moore, T. E.; Carlson, C. W.; McFadden, J. P.

2009-05-01

232

Plasma response to electron energy filter in large volume plasma device  

SciTech Connect

An electron energy filter (EEF) is embedded in the Large Volume Plasma Device plasma for carrying out studies on excitation of plasma turbulence by a gradient in electron temperature (ETG) described in the paper of Mattoo et al. [S. K. Mattoo et al., Phys. Rev. Lett. 108, 255007 (2012)]. In this paper, we report results on the response of the plasma to the EEF. It is shown that inhomogeneity in the magnetic field of the EEF switches on several physical phenomena resulting in plasma regions with different characteristics, including a plasma region free from energetic electrons, suitable for the study of ETG turbulence. Specifically, we report that localized structures of plasma density, potential, electron temperature, and plasma turbulence are excited in the EEF plasma. It is shown that structures of electron temperature and potential are created due to energy dependence of the electron transport in the filter region. On the other hand, although structure of plasma density has origin in the particle transport but two distinct steps of the density structure emerge from dominance of collisionality in the source-EEF region and of the Bohm diffusion in the EEF-target region. It is argued and experimental evidence is provided for existence of drift like flute Rayleigh-Taylor in the EEF plasma.

Sanyasi, A. K.; Awasthi, L. M.; Mattoo, S. K.; Srivastava, P. K.; Singh, S. K.; Singh, R.; Kaw, P. K. [Institute for Plasma Research, Gandhinagar, 382 428 Gujarat (India)] [Institute for Plasma Research, Gandhinagar, 382 428 Gujarat (India)

2013-12-15

233

Electron transfer from sulfate-reducing becteria biofilm promoted by reduced graphene sheets  

NASA Astrophysics Data System (ADS)

Reduced graphene sheets (RGSs) mediate electron transfer between sulfate-reducing bacteria (SRB) and solid electrodes, and promote the development of microbial fuel cells (MFC). We have investigated RSG-promoted electron transfer between SRB and a glassy carbon (GC) electrode. The RGSs were produced at high yield by a chemical sequence involving graphite oxidation, ultrasonic exfoliation of nanosheets, and N2H4 reduction. Cyclic voltammetric testing showed that the characteristic anodic peaks (around 0.3 V) might arise from the combination of bacterial membrane surface cytochrome c3 and the metabolic products of SRB. After 6 d, another anodic wave gradually increased to a maximum current peak and a third anodic signal became visible at around 0 V. The enhancements of two characteristic anodic peaks suggest that RSGs mediate electron-transfer kinetics between bacteria and the solid electrode. Manipulation of these recently-discovered electron-transport mechanisms will lead to significant advances in MFC engineering.

Wan, Yi; Zhang, Dun; Wang, Yi; Wu, Jiajia

2012-01-01

234

Electronically swept millimetre-wave interferometer for spatially resolved measurement of plasma electron  

E-print Network

electron density John Howard and David Oliver Plasma Research Laboratory, Research School of Physical, located in the Plasma Research Laboratory at the Australian National University, is a flexible, medium

Howard, John

235

A novel biotinylated lipid raft reporter for electron microscopic imaging of plasma membrane microdomains[S  

PubMed Central

The submicroscopic spatial organization of cell surface receptors and plasma membrane signaling molecules is readily characterized by electron microscopy (EM) via immunogold labeling of plasma membrane sheets. Although various signaling molecules have been seen to segregate within plasma membrane microdomains, the biochemical identity of these microdomains and the factors affecting their formation are largely unknown. Lipid rafts are envisioned as submicron membrane subdomains of liquid ordered structure with differing lipid and protein constituents that define their specific varieties. To facilitate EM investigation of inner leaflet lipid rafts and the localization of membrane proteins therein, a unique genetically encoded reporter with the dually acylated raft-targeting motif of the Lck kinase was developed. This reporter, designated Lck-BAP-GFP, incorporates green fluorescent protein (GFP) and biotin acceptor peptide (BAP) modules, with the latter allowing its single-step labeling with streptavidin-gold. Lck-BAP-GFP was metabolically biotinylated in mammalian cells, distributed into low-density detergent-resistant membrane fractions, and was readily detected with avidin-based reagents. In EM images of plasma membrane sheets, the streptavidin-gold-labeled reporter was clustered in 2050 nm microdomains, presumably representative of inner leaflet lipid rafts. The utility of the reporter was demonstrated in an investigation of the potential lipid raft localization of the epidermal growth factor receptor. PMID:22822037

Krager, Kimberly J.; Sarkar, Mitul; Twait, Erik C.; Lill, Nancy L.; Koland, John G.

2012-01-01

236

Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks  

PubMed Central

Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large (?5 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution (?1 ?m) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing high-performance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature (?100C) annealing to increase the on/off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic inks to form sheets of electronic paper. PMID:11320233

Rogers, John A.; Bao, Zhenan; Baldwin, Kirk; Dodabalapur, Ananth; Crone, Brian; Raju, V. R.; Kuck, Valerie; Katz, Howard; Amundson, Karl; Ewing, Jay; Drzaic, Paul

2001-01-01

237

Density and temperature evolution of the plasma sheet during a simulated interval of northward interplanetary magnetic field  

NASA Astrophysics Data System (ADS)

We investigate the evolution of the hot component of plasma sheet ions during an extended interval of northward interplanetary magnetic field and assess whether transport can explain the observed cooling of the hot component ions reported by Wing et al. (2005). Our approach is to trace the guiding center particle drift of protons in a magnetic field from the Tsyganenko 2001 (T01) model and in an electric field from the Weimer 2000 model. We then map the phase space distributions to realistic source distributions based on Time History of Events and Macroscale Interactions during Substorms observations. Our simulation results show that magnetic drift is not a significant cooling mechanism for the hot component ions of the plasma sheet on the duskside of the magnetopause, but gradient drift does cool the hot component plasma on the dawnside of the magnetopause.

Mata, Wendy J.; Lemon, Colby; Wang, Chih-Ping; Lyons, Larry R.

2014-06-01

238

Electron Plasmas in a Magnetic Mirror  

E-print Network

with an axial gradient in the magnetic field. We find that this mode is surprisingly long-lived despite the plasma to isolate a small section and then dumping the plasma out onto a pinhole. By mapping the field of the charge from the low field region, even allowing for the natural expansion of the plasma as it streams out

Wurtele, Jonathan

239

Electron and ion thermal forces in complex (dusty) plasmas  

SciTech Connect

Expressions for the ion and electron thermal forces acting on a charged grain, suspended in a weakly ionized plasma subject to temperature gradients, are derived. The main emphasize is on the conditions pertinent to the investigations of complex (dusty) plasmas in gas discharges. Estimates show that for the electron temperature gradients {approx}O(eV/cm) typically encountered in laboratory gas discharges, the electron thermal force can become an important player among other forces acting on micron-size grains.

Khrapak, Sergey A. [Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching (Germany)

2013-01-15

240

Electron energy distribution function and plasma parameters across magnetic filters  

SciTech Connect

The electron energy distribution function (EEDF) is measured across a magnetic filter in inductively coupled plasmas. The measured EEDFs are found to be Maxwellian in the elastic energy range with the corresponding electron temperature monotonously decreasing along the positive gradient of the magnetic field. At the maximum of the magnetic field, the electron temperature reaches its minimum and remains nearly constant in the area of the negative gradient of the field, where the plasma density distribution exhibits a local minimum.

Aanesland, A.; Bredin, J.; Chabert, P. [Laboratoire de Physique des Plasmas, CNRS--Ecole Polytechnique, 91128 Palaiseau Cedex (France); Godyak, V. [RF Plasma Consulting, Brookline, Massachusetts 02446 (United States)

2012-01-23

241

Self-consistent theory of the multiscale and split current sheets in collisionless non-Maxwellian plasma  

NASA Astrophysics Data System (ADS)

In view of a large number of the observational and theoretical indications of the complicated non-Maxwellian plasma configurations in the magnetospheres of planets and stars, we develop an analytical approach to the description of the stationary planar neutral current sheets in a collisionless multicomponent plasma, relativistic or not. It is based on the method of the invariants of particle motion and admits a functional freedom in the choice of the particle distribution functions and spatial profiles of current density and corresponding magnetic field. Using a general theory (Phys. Rev. Lett. 104, 215002 (2010)) and a variety of novel examples, we show that splitting of the current sheets is typical for the non-Maxwellian distributions of particles and the multiscale current sheets might exist in plasma with essentially different anisotropies of the particle species. The examples of splitting include the self-consistent sheets with two or three separate components of current density with either parallel or antiparallel directions of the current which may be formed by one or several particle species. The examples of the multiscale sheets include two or three current components, embedded in one another and formed by one, two or three particle species. We describe general properties of the split and multiscale sheets for a wide class of the particle distribution functions with the polynomial and/or exponential dependences on a momentum directed along the current. We investigate in detail possible interrelation of the spatial scales and magnitudes of the magnetic field, anisotropy, and density of particles of different species. In particular, we apply these results to the description of the current structures in the Earths magnetotail using observational data from the Cluster spacecraft mission. We compare our analytical results with the known numerical analysis and qualitative estimates of multiscale properties and splitting effects in the magnetospheric current structures.

Kocharovsky, Vladimir; Martyanov, Vladimir; Kocharovsky, Vitaly

242

Resistive collimation of electron beams in relativistic and degenerate plasma  

NASA Astrophysics Data System (ADS)

The purpose of this research is the study of the effects of plasma state and fiber on collimating relativistic electron beam in fast ignition. In this paper, for collimating relativistic electrons produced at the laser plasma interaction, a thin fiber of aluminum, lithium or CH either in the classical, degenerate or relativistic plasma states is considered. The fast electron beam could be collimated down to radii of 10 ?m, in that case, the best results are achieved when there is a sharp transition in resistance. This ensures that the correct magnetic growth rate is used for hot electrons at different energy levels. Calculations show that the resistivity of the material surrounding the CH fiber in the degenerate plasma is smaller than that for classical and relativistic plasma.

Mahdavi, M.; Khodadadi Azadboni, F.

2014-09-01

243

Energy loss of fast nonthermal electrons in plasmas  

NASA Technical Reports Server (NTRS)

Simple analytical expressions for equilibration times of nonrelativistic monoenergetic electrons in plasmas are evaluated in the 'weak'-beam approximation when the density of the monoenergetic electrons is much smaller than the plasma density. The equilibration time is defined as the time needed by the beam of monenergetic electrons to lose most of its energy as a result of collisions with plasma particles having a Maxwellian energy distribution. The process of energy equilibration is treated as a statistical superposition of both elastic and inelastic collisions in the plasma. The possibility of collisionless equilibration is discussed. Comparison of the equilibration times with the Spitzer relaxation times indicates that the former times are more appropriate for an estimate of the energy loss of the 'weak' electron beams in highly ionized plasmas.

Kunc, Joseph A.

1989-01-01

244

The Role of Bubbles in the Transport of Particles From the Plasma Sheet to the Inner Magnetosphere (Invited)  

NASA Astrophysics Data System (ADS)

Essentially the whole closed-field-line region of the magnetosphere is stratified, with layers of highest PV5/3 on field lines that stretch far into the tail and lowest PV5/3 deep in the inner magnetosphere. (Here V is the volume of a flux tube containing a unit of magnetic flux.) The magnetosphere is like an atmosphere with heavy gases on the bottom and lighter ones on the top. The entropy parameter PV5/3 is strictly conserved in ideal MHD. Transport nevertheless occurs between layers, because a non-ideal process like a patch of reconnection can create a bubble of low PV5/3 that propagates rapidly earthward, forming a bursty bulk flow. During that rapid earthward motion, the earthward boundary of the bubble forms a dipolarization front, where the magnetic field switches from the background stretched configuration to a more dipolar shape inside the bubble. A thin layer of high-PV5/3 flux tubes gets pushed earthward ahead of the bubble (known feature of dipolarization fronts). The bubble slows after it reaches the region where the PV5/3 of the surrounding medium matches its own, and it is sometimes observed to oscillate about an equilibrium position. While bubbles have obvious effects in the plasma sheet, their effects on the inner magnetosphere are much less obvious. Gradient/curvature drift, which is strong in the inner magnetosphere, causes higher-energy ions in the bubble to drift west compared to the bubble center and lower-energy ions and electrons to drift east. Thus the bubble blends into its surroundings. This picture of transport by bubbles has become well established for the plasma sheet, but conventional ring current models do not consider it, envisaging injection as a result of an increase in global convection. The key question is: do bubbles have any observable signatures in the storm-time ring current? Results will be presented from RCM-E runs designed to answer this question.

Wolf, R.; Yang, J.; Toffoletto, F.; Sazykin, S. Y.

2013-12-01

245

Nonlinear evolution of three-dimensional instabilities of thin and thick electron scale current sheets: Plasmoid formation and current filamentation  

NASA Astrophysics Data System (ADS)

Nonlinear evolution of three dimensional electron shear flow instabilities of an electron current sheet (ECS) is studied using electron-magnetohydrodynamic simulations. The dependence of the evolution on current sheet thickness is examined. For thin current sheets (half thickness =de=c /?pe), tearing mode instability dominates. In its nonlinear evolution, it leads to the formation of oblique current channels. Magnetic field lines form 3-D magnetic spirals. Even in the absence of initial guide field, the out-of-reconnection-plane magnetic field generated by the tearing instability itself may play the role of guide field in the growth of secondary finite-guide-field instabilities. For thicker current sheets (half thickness 5 de), both tearing and non-tearing modes grow. Due to the non-tearing mode, current sheet becomes corrugated in the beginning of the evolution. In this case, tearing mode lets the magnetic field reconnect in the corrugated ECS. Later thick ECS develops filamentary structures and turbulence in which reconnection occurs. This evolution of thick ECS provides an example of reconnection in self-generated turbulence. The power spectra for both the thin and thick current sheets are anisotropic with respect to the electron flow direction. The cascade towards shorter scales occurs preferentially in the direction perpendicular to the electron flow.

Jain, Neeraj; Bchner, Jrg

2014-07-01

246

Modulational instability of an electron plasma wave in a dusty plasma  

SciTech Connect

The modulational instability of an electron plasma wave in a homogeneous, unmagnetized, hot, and collisionless dusty plasma has been investigated analytically. The Vlasov equation has been solved perturbatively to find the nonlinear response of the plasma particles with random static distribution of massive and charged dust grains having certain correlation. It is noticed that the growth rate of the modulational instability of the electron plasma wave through a new ultra-low-frequency dust mode is more efficient than that through the usual ion-acoustic mode in the dusty plasma. {copyright} {ital 1997 American Institute of Physics.}

Amin, M.R.; Ferdous, T.; Salimullah, M. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)] [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

1997-03-01

247

Electronic detection of collective modes of an ultracold plasma.  

PubMed

Using a new technique to directly detect current induced on a nearby electrode, we measure plasma oscillations in ultracold plasmas, which are influenced by the inhomogeneous and time-varying density and changing neutrality. Electronic detection avoids heating and evaporation dynamics associated with previous measurements and allows us to test the importance of the plasma neutrality. We apply dc and pulsed electric fields to control the electron loss rate and find that the charge imbalance of the plasma has a significant effect on the resonant frequency, in excellent agreement with recent predictions suggesting coupling to an edge mode. PMID:22401078

Twedt, K A; Rolston, S L

2012-02-10

248

Linear theory of the electron beam-wave-plasma interactions in a magnetized plasma waveguide  

SciTech Connect

The theoretical study on the electron beam-wave interactions in a plasma waveguide immersed in a finite magnetic field is given in the article, in which both the plasma and the electron beam are considered as special media. Making use of the constitutive transformation and the Lorentz transformation in the four-dimensional space, the permittivity tensor of the stationary magnetized plasma, the permittivity tensor, the permeability tensor, and the chiral tensor of the electron beam in the rest (laboratory) frame are acquired. Therefore, two coupled wave equations for the magnetized plasma and electron beam have been obtained and the dispersion relations are then achieved by solving these coupled equations together with the boundary conditions including the surface current density due to the ripple of the plasma/beam. As an example of the applications of this approach, the beam-wave interactions in a practical plasma Cherenkov maser have been studied and the numerical calculations have been carried out in detail. It has been found that the present approach is more accurate and can provide clearer mode information for the electron beam-wave interactions in a magnetized plasma waveguide. This approach can be exploited in a number of electron beam-wave interaction systems including some kinds of free electron devices, plasma filled Cherenkov radiated free electron lasers and masers.

Liu, Shenggang; Wei, Yanyu; Yuan, XueSong; Yan, Yang [Research Institute of High Energy Electronics, University of Electronic Science and Technology of China, 610054, Chengdu (China)

2007-03-01

249

A stochastic sea: The source of plasma sheet boundary layer ion structures observed by Cluster  

NASA Astrophysics Data System (ADS)

On 14 February 2001 the Cluster Ion Spectrometry (CIS) experiment onboard three of the Cluster spacecraft observed velocity-dispersed ion structures (VDIS) as the spacecraft passed from the tail lobes into the plasma sheet boundary layer. These are the first multiple spacecraft observations of the VDIS phenomenon. The Cluster 1 spacecraft (SC1) observed a dispersed ion signature with beamlets and a second structure like that expected to be produced by an echo, while Cluster 3 (SC3) observed much less pronounced structuring a few minutes later. During this same event and over an extended interval the ACE spacecraft observed an interplanetary magnetic field that was directed southward. We have inferred the sources and acceleration mechanisms of the ions in these VDIS observations by following millions of ion trajectories backward and forward in time through time-dependent electric and magnetic fields obtained from a global MHD simulation. ACE data were used as input for the MHD model. We found that almost all of the particles comprising the first (A1) and second (A2) beamlets observed by SC1 had been nonadiabatic earlier in their history, while particles in the A3 beamlet exhibited a combination of adiabatic and nonadiabatic behavior. Beamlet A4 particles were always adiabatic. Moreover, for all of the beamlets the current sheet crossing that took place prior to their detection occurred between x = -13 RE and x = -16 RE in the tail, well earthward of the permanent stochastic "sea" from which all of the beamlets originated. Our model does not favor the multiple source scenario suggested by A. Keiling et al. Instead, it indicates that the source regions of the structures are spatially correlated. We have carried out a similar analysis of the SC3 observations. In general, SC3 beamlets have higher ? values, partly because of the depolarization of the field lines during these observations. In time forward calculations only a small fraction of ions from SC1 A structures returned to the spacecraft location. "Echoes" were more pronounced on SC3. In addition, in our calculations, some particles from SC1 A structures interacted with the current sheet and returned to the SC3 location, at the time when SC3 observed the A structures. When Cluster observations were organized by latitude instead of time, we found that all three Cluster spacecraft seemed to observe the same primary structure that persisted throughout the interval of observation.

Ashour-Abdalla, M.; Bosqued, J. M.; El-Alaoui, M.; Peroomian, V.; Zelenyi, L. M.; Walker, R. J.; Wright, J.

2005-12-01

250

Gyrokinetic Electron and Fully Kinetic Ion Particle Simulation of Collisionless Plasma Dynamics  

SciTech Connect

Fully kinetic-particle simulations and hybrid simulations have been utilized for decades to investigate various fundamental plasma processes, such as magnetic reconnection, fast compressional waves, and wave-particle interaction. Nevertheless, due to disparate temporal and spatial scales between electrons and ions, existing fully kinetic-particle codes have to employ either unrealistically high electron-to-ion mass ratio, me/mi, or simulation domain limited to a few or a few ten's of the ion Larmor radii, or/and time much less than the global Alfven time scale in order to accommodate available computing resources. On the other hand, in the hybrid simulation, the ions are treated as fully kinetic particles but the electrons are treated as a massless fluid. The electron kinetic effects, e.g., wave-particle resonances and finite electron Larmor radius effects, are completely missing. Important physics, such as the electron transit time damping of fast compressional waves or the triggering mechanism of magnetic reconnection in collisionless plasmas is absent in the hybrid codes. Motivated by these considerations and noting that dynamics of interest to us has frequencies lower than the electron gyrofrequency, we planned to develop an innovative particle simulation model, gyrokinetic (GK) electrons and fully kinetic (FK) ions. In the GK-electron and FK-ion (GKe/FKi) particle simulation model, the rapid electron cyclotron motion is removed, while keeping finite electron Larmor radii, realistic me/mi ratio, wave-particle interactions, and off-diagonal components of electron pressure tensor. The computation power can thus be significantly improved over that of the full-particle codes. As planned in the project DE-FG02-05ER54826, we have finished the development of the new GK-electron and FK-ion scheme, finished its benchmark for a uniform plasma in 1-D, 2-D, and 3-D systems against linear waves obtained from analytical theories, and carried out a further convergence test and benchmark for a 2-D Harris current sheet against tearing mode and other instabilities in linear theories/models. More importantly, we have, for the first time, carried out simulation of linear instabilities in a 2-D Harris current sheet with a broad range of guide field BG and the realistic mi/me, and obtained important new results of current sheet instabilities in the presence of a finite BG. Indeed the code has accurately reproduced waves of interest here, such as kinetic Alfven waves, compressional Alfven/whistler wave, and lower-hybrid/modified two-stream waves. Moreover, this simulation scheme is capable of investigating collisionless kinetic physics relevant to magnetic reconnection in the fusion plasmas, in a global scale system for a long-time evolution and, thereby, produce significant new physics compared with both full-particle and hybrid codes. The results, with mi/me=1836 and moderate to large BG as in the real laboratory devices, have not been obtained in previous theory and simulations. The new simulation model will contribute significantly not only to the understanding of fundamental fusion (and space) plasma physics but also to DOE's SciDAC initiative by further pushing the frontiers of simulating realistic fusion plasmas.

Yu Lin; Xueyi Wang; Liu Chen; Zhihong Lin

2009-08-11

251

Electron Beam Biasing of Substrates during Plasma Etching [1  

Microsoft Academic Search

Electron beam biasing of substrates is being studied as an alternative to the usual method of using a capacitively coupled, rf-powered wafer chuck. The advantage of biasing with an electron beam is that the electrons which arrive at the wafer do so with an anisotropic velocity distribution similar to the plasma sheath-accelerated ions. This becomes important when etching large aspect

A. K. Quick; N. Hershkowitz

1997-01-01

252

Potential applications of an electron cyclotron resonance multicusp plasma source  

SciTech Connect

An electron cyclotron resonance (ECR) multicusp plasmatron has been developed by feeding a multicusp bucket arc chamber with a compact ECR plasma source. This novel source produced large (about 25-cm-diam), uniform (to within {plus minus}10%), dense (>10{sup 11}-cm{sup -3}) plasmas of argon, helium, hydrogen, and oxygen. It has been operated to produce an oxygen plasma for etching 12.7-cm (5-in.) positive photoresist-coated silicon wafers with uniformity within {plus minus}8%. Results and potential applications of this new ECR plasma source for plasma processing of thin films are discussed. 21 refs., 10 figs.

Tsai, C.C.; Berry, L.A.; Gorbatkin, S.M.; Haselton, H.H.; Roberto, J.B.; Stirling, W.L.

1989-01-01

253

Electron plasma oscillations associated with type 3 radio emissions and solar electrons  

NASA Technical Reports Server (NTRS)

An extensive study of the IMP-6 and IMP-8 plasma and radio wave data was performed to try to find electron plasma oscillations associated with type III radio noise bursts and low-energy solar electrons. It is shown that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU. For the one case in which electron plasma oscillations are definitely produced by the electrons ejected by the solar flare the electric field strength is relatively small. Electromagnetic radiation, believed to be similar to the type III radio emission, is observed coming from the region of the more intense electron plasma oscillations upstream. Quantitative calculations of the rate of conversion of the plasma oscillation energy to electromagnetic radiation are presented for plasma oscillations excited by both solar electrons and electrons from the bow shock. These calculations show that neither the type III radio emissions nor the radiation from upstream of the bow shock can be adequately explained by a current theory for the coupling of electron plasma oscillations to electromagnetic radiation.

Gurnett, D. A.; Frank, L. A.

1975-01-01

254

Association of an auroral surge with plasma sheet recovery and the retreat of the substorm neutral line  

SciTech Connect

One of the periods being studied in the PROMIS CDAW (CDAW-9) workshops is the interval 0000-1200 UT on May 3, 1986, designated Event 9C.'' A well-defined substorm, starting at 0919 UT, was imaged by both DE 1 over the southern hemisphere and Viking over the northern hemisphere. The images from Viking, at 80-second time resolution, showed a surge-like feature forming at about 0952 UT at the poleward edge of the late evening sector of the oval. The feature remained relatively stationary until about 1000 UT when it seemed to start advancing westward. ISEE 1 and 2 were closely conjugate to the surge as mapped from both the DMSP and Viking images. We conclude that the plasma sheet recovery was occasioned by the arrival at ISEE 1,2 of a westward traveling wave of plasma sheet thickening, the wave itself being formed by westward progression of the substorm neutral line's tailward retreat. The westward traveling surge was the auroral manifestation of this nonuniform retreat of the neutral line. We suggest that the upward field aligned current measured by DMSP F7 above the surge head was driven by plasma velocity shear in the plasma sheet at the duskward kink'' in the retreating neutral line. By analogy with this observation we propose that the westward traveling surges and the current wedge field aligned currents that characterize the expanding auroral bulge during substorm expansive phase are manifestations of (and are driven by) velocity shear in the plasma sheet near the ends of the extending substorm neutral line.

Hones, E.W. (Mission Research Corp., Los Alamos, NM (USA)); Elphinstone, R.; Murphree, J.S. (Calgary Univ., AB (Canada). Dept. of Physics); Galvin, A.B. (Maryland Univ., College Park, MD (USA). Dept. of Space Physics); Heinemann, N.C. (Boston Coll., Chestnut Hill, MA (USA). Dept. of Physics); Parks, G.K. (Washington Univ., Seattle, WA (USA)); Rich, F.J. (Air Force Geophysics Lab., Hanscom AFB, MA

1990-01-01

255

On the formation of pre-onset azimuthal pressure gradient in the near-Earth plasma sheet  

NASA Astrophysics Data System (ADS)

Xing et al. (2011) demonstrated by case study that the plasma sheet pressure gradient at 11 REnear the substorm onset meridian undergoes a substantial duskward enhancement shortly before substorm onset as identified from the auroral poleward expansion. It was suggested that the increased upward FAC driven by this pressure gradient enhancement lead to the thin onset arc intensification from which the poleward expansion initiates. In the present study, we employ the multiTHEMIS spacecraft in azimuthal conjunction -at -11 REand examine the ion flux and distributions during the period of pressure gradient enhancement, and identify two categories of events. For events with pressure gradient change ?2 min prior to onset, strong earthward ion flux enhancements covering the energy range from several keV to above 25 keV were observed by the spacecraft identifying the higher pressure increase, while at the same time the ion distributions show a substantial earthward shift in velocity space. These resemble the ion acceleration ahead of earthward moving dipolarization fronts. On the other hand, the spacecraft observing the lower pressure increase found weaker or no ion flux enhancements and had nearly isotropic distributions, indicating that longitudinally localized dipolarization fronts are responsible for the pressure gradient development. These pressure gradient enhancements were in the duskward (dawnward) direction for measurements to the east (west) of the onset region. For pressure gradient enhancement >2 min prior to onset, stronger plasma sheet thinning was observed by the spacecraft identifying the larger pressure increase and the ion distributions appear nearly isotropic, which suggests plasma redistribution in the undisturbed plasma sheet. These two categories suggest that both dipolarization fronts and growth phase plasma sheet localized thinning can drive azimuthal pressure gradient enhancement near the onset meridian and cause pre-onset thin auroral arc intensification, though the dipolarization front events appear to be substantially more common based on our 14 events.

Xing, X.; Lyons, L. R.; Zhou, X.-Z.; Angelopoulos, V.; Donovan, E.; Larson, D.; Carlson, C.; Auster, U.

2012-08-01

256

Analyses of Voyager 2 Plasma Observations in the Heliosheath: Near the Heliospheric Current Sheet and Streamer Belt  

NASA Astrophysics Data System (ADS)

The Voyager plasma experimenters reported that Voyager 2 (V2) in the heliosheath at 99 AU and 30 South measured a large plasma density increase in mid-2012, the culmination of a gradual density increase that commenced in early 2011. This mid-2012 plasma density increase of more than a factor of two was accompanied by an increase in plasma temperature of 50%. They reported that the magnitude of the plasma radial speed remained constant. The Voyager plasma experimenters attributed the changes in plasma density and temperature to increased solar wind pressure resulting in the outward motion of the termination shock. In contrast we attribute these heliosheath plasma characteristics primarily to the heliospheric current sheet (HCS) approaching and crossing the location of V2. Our explanation implies that V2 entered the region associated with the HCS and at times V2 was in the region associated with the solar streamer belt located even closer to the solar equator than the HCS. Near the Sun the HCS and these solar mid-latitude features are often associated with plasma that has higher density and lower speed than the plasma associated with the polar coronal holes. We also analyzed V2 energetic particle data which appeared to substantiate our suggestion that at this time V2 entered the mid-latitude HCS/solar streamer belt region.

Intriligator, D. S.; Webber, W. R.

2014-05-01

257

Plasma Chemistry and Plasma Processing, Vol. 22, No. 2, June 2002 ( 2002) Electron Density and Energy Distributions in  

E-print Network

Plasma Chemistry and Plasma Processing, Vol. 22, No. 2, June 2002 ( 2002) Electron Density in the corona plasma is required to quantify the chemical processes. In this paper, the electron density- ness of the plasma and the electron energy distribution are not affected. Smaller electrodes produce

Chen, Junhong

258

Relativistic electromagnetic waves in an electron-ion plasma  

NASA Technical Reports Server (NTRS)

High power laser beams can drive plasma particles to relativistic energies. An accurate description of strong waves requires the inclusion of ion dynamics in the analysis. The equations governing the propagation of relativistic electromagnetic waves in a cold electron-ion plasma can be reduced to two equations expressing conservation of energy-momentum of the system. The two conservation constants are functions of the plasma stream velocity, the wave velocity, the wave amplitude, and the electron-ion mass ratio. The dynamic parameter, expressing electron-ion momentum conversation in the laboratory frame, can be regarded as an adjustable quantity, a suitable choice of which will yield self-consistent solutions when other plasma parameters were specified. Circularly polarized electromagnetic waves and electrostatic plasma waves are used as illustrations.

Chian, Abraham C.-L.; Kennel, Charles F.

1987-01-01

259

Electron current extraction from a permanent magnet waveguide plasma cathode  

NASA Astrophysics Data System (ADS)

An electron cyclotron resonance plasma produced in a cylindrical waveguide with external permanent magnets was investigated as a possible plasma cathode electron source. The configuration is desirable in that it eliminates the need for a physical antenna inserted into the plasma, the erosion of which limits operating lifetime. Plasma bulk density was found to be overdense in the source. Extraction currents over 4 A were achieved with the device. Measurements of extracted electron currents were similar to calculated currents, which were estimated using Langmuir probe measurements at the plasma cathode orifice and along the length of the external plume. The influence of facility effects and trace ionization in the anode-cathode gap are also discussed.

Weatherford, B. R.; Foster, J. E.; Kamhawi, H.

2011-09-01

260

Electron current extraction from a permanent magnet waveguide plasma cathode.  

PubMed

An electron cyclotron resonance plasma produced in a cylindrical waveguide with external permanent magnets was investigated as a possible plasma cathode electron source. The configuration is desirable in that it eliminates the need for a physical antenna inserted into the plasma, the erosion of which limits operating lifetime. Plasma bulk density was found to be overdense in the source. Extraction currents over 4 A were achieved with the device. Measurements of extracted electron currents were similar to calculated currents, which were estimated using Langmuir probe measurements at the plasma cathode orifice and along the length of the external plume. The influence of facility effects and trace ionization in the anode-cathode gap are also discussed. PMID:21974587

Weatherford, B R; Foster, J E; Kamhawi, H

2011-09-01

261

Fundamental electron collision processes relevant to low-temperature plasmas  

SciTech Connect

This paper attempts to elucidate the mutually beneficial interaction between electron collision physics and the physics and chemistry that govern the properties of low temperature plasmas, in particular technologically relevant low-temperature processing plasmas. We hope to demonstrate how recent developments in collision physics contributed to an improved understanding of the fundamental collision processes in low-temperature plasmas, how they made possible more sophisticated modelling efforts of such plasmas and how they advanced the development of more sensitive plasma diagnostics techniques. At the same time, we hope to show how some of the many unanswered questions and challenges faced by the plasma processing community have stimulated new developments and novel approaches in atomic and electron collision physics. {copyright} {ital 1996 American Institute of Physics.}

Becker, K.H. [Physics Department, City College of C.U.N.Y., Convent Avenue and 138th Street, New York, New York 10031-9198 (United States)

1996-03-01

262

Electromagnetic solitary pulses in a magnetized electron-positron plasma  

SciTech Connect

A theory for large amplitude compressional electromagnetic solitary pulses in a magnetized electron-positron (e-p) plasma is presented. The pulses, which propagate perpendicular to the external magnetic field, are associated with the compression of the plasma density and the wave magnetic field. Here the solitary wave magnetic field pressure provides the restoring force, while the inertia comes from the equal mass electrons and positrons. The solitary pulses are formed due to a balance between the compressional wave dispersion arising from the curl of the inertial forces in Faraday's law and the nonlinearities associated with the divergence of the electron and positron fluxes, the nonlinear Lorentz forces, the advection of the e-p fluids, and the nonlinear plasma current densities. The compressional solitary pulses can exist in a well-defined speed range above the Alfven speed. They can be associated with localized electromagnetic field excitations in magnetized laboratory and space plasmas composed of electrons and positrons.

Shukla, P. K. [RUB International Chair, International Centre for Advanced Studies in Physical Sciences, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Eliasson, B. [Institut fuer Theoretische Physik, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Stenflo, L. [Department of Physics, Linkoeping University, SE-58183 Linkoeping (Sweden)

2011-03-15

263

Electromagnetic solitary pulses in a magnetized electron-positron plasma.  

PubMed

A theory for large amplitude compressional electromagnetic solitary pulses in a magnetized electron-positron (e-p) plasma is presented. The pulses, which propagate perpendicular to the external magnetic field, are associated with the compression of the plasma density and the wave magnetic field. Here the solitary wave magnetic field pressure provides the restoring force, while the inertia comes from the equal mass electrons and positrons. The solitary pulses are formed due to a balance between the compressional wave dispersion arising from the curl of the inertial forces in Faraday's law and the nonlinearities associated with the divergence of the electron and positron fluxes, the nonlinear Lorentz forces, the advection of the e-p fluids, and the nonlinear plasma current densities. The compressional solitary pulses can exist in a well-defined speed range above the Alfvn speed. They can be associated with localized electromagnetic field excitations in magnetized laboratory and space plasmas composed of electrons and positrons. PMID:22060541

Shukla, P K; Eliasson, B; Stenflo, L

2011-09-01

264

Influence of Nongyrotropy in the Electron Beam-plasma Interaction  

E-print Network

Influence of Nongyrotropy in the Electron Beam-plasma Interaction M. A. E. de Moraes£ , Y. Omura, with the associated free energy enhancing previously existing (gyrotropic) instabilities or, in otherwise stable media

265

Ponderomotive Acceleration of Hot Electrons in Tenuous Plasmas  

SciTech Connect

The oscillation-center Hamiltonian is derived for a relativistic electron injected with an arbitrary momentum in a linearly polarized laser pulse propagating in tenuous plasma, assuming that the pulse length is smaller than the plasma wavelength. For hot electrons generated at collisions with ions under intense laser drive, multiple regimes of ponderomotive acceleration are identified and the laser dispersion is shown to affect the process at plasma densities down to 1017 cm?3. Assuming a/?g << 1, which prevents net acceleration of the cold plasma, it is also shown that the normalized energy ? of hot electrons accelerated from the initial energy ?o < , ? does not exceed ? ~ a?g, where a is the normalized laser field, and ?g is the group velocity Lorentz factor. Yet ? ~ ? is attained within a wide range of initial conditions; hence a cutoff in the hot electron distribution is predicted.

V.I. Geyko and G.M. Fraiman, I.Y. Dodin and N.J. Fisch

2009-02-17

266

Measurement of electron density and temperature in plasmas  

NASA Technical Reports Server (NTRS)

Application of two laser wavelengths passing through plasma measures electron density and temperature. Function depends on determining absorption of light at two wavelengths. Nature of reaction is explained and schematic diagram of equipment is included.

Billman, K. W.; Rowley, P. D.; Presley, L. L.; Stallcop, J.

1972-01-01

267

The Role of Self-Organized Criticality in the Substorm Phenomenon and its Relation to Localized Reconnection in the Plasma Sheet  

NASA Technical Reports Server (NTRS)

Recent observations of the magnetotail plasma sheet have shown it to be a dynamic and turbulent region. Research has found strong turbulence in the plasma sheet at approximately 20 Earth's Radius tailward of Earth; the turbulence is observed at all activity levels. The existence of strong turbulence in the plasma sheet in the region associated with substorm onset might be thought difficult to reconcile with the coherence and repeatability of the substorm cycle. We review a variety of evidence that strongly suggests the magnetotail is driven, through magnetic flux transfer, into a state of "self-organized criticality" (SOC). It is an important property of physical systems that evolve into SOC that they self-organize into a unique, global dynamic state. This global state is inevitable, and repeatable. In this state, however, small-spatiotemporal-scale system fluctuations are unpredictable and can be only described statistically. This is the basis, we think, for the global coherence and repeatability of the substorm phenomenon in the turbulent plasma sheet. At, or near, substorm onset the plasma sheet can be described by a global SOC state containing significant small scale turbulence. In several recent studies, "sandpile" models were driven into SOC and then shown to reproduce various measures of substorm activity. We discuss the plasma physical foundation of these sandpile models. The evolution of simple continuum plasma sheet models into SOC-like states of many small reconnection events in the turbulent plasma sheet under the will be demonstrated. We view the substorm phenomenon as an avalanche assumption that the plasma sheet is in a SOC state.

Klimas, A. J.; Vassiliadis, D.; Valdivia, J. A.; Baker, D. N.; Hesse, M.

1999-01-01

268

Effect of Time Dependent Bending of Current Sheets in Response to Generation of Plasma Jets and Reverse Currents  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is a basis for many impulsive phenomena in space and laboratory plasmas accompanied by effective transformation of magnetic energy. Reconnection processes usually occur in relatively thin current sheets (CSs), which separate magnetic fields of different or opposite directions. We report on recent observations of time dependent bending of CSs, which results from plasma dynamics inside the sheet. The experiments are carried out with the CS-3D laboratory device (Institute of General Physics RAS, Moscow) [1]. The CS magnetic structure with an X line provides excitation of the Hall currents and plasma acceleration from the X line to both side edges [2]. In the presence of the guide field By the Hall currents give rise to bending of the sheet: the peripheral regions located away from the X line are deflected from CS middle plane (z=0) in the opposite directions z [3]. We have revealed generation of reverse currents jy near the CS edges, i.e. the currents flowing in the opposite direction to the main current in the sheet [4]. There are strong grounds to believe that reverse currents are generated by the outflow plasma jets [5], accelerated inside the sheet and penetrated into the regions with strong normal magnetic field component Bz [4]. An impressive effect of sudden change in the sign of the CS bend has been disclosed recently, when analyzing distributions of plasma density [6] and current away from the X line, in the presence of the guide field By. The CS configuration suddenly becomes opposite from that observed at the initial stage, and this effect correlates well with generation of reverse currents. Consequently this effect can be related to excitation of the reverse Hall currents owing to generation of reverse currents jy in the CS. Hence it may be concluded that CSs may exhibit time dependent vertical z-displacements, and the sheet geometry depends on excitation of the Hall currents, acceleration of plasma jets and generation of reverse currents. The work was supported in part by the Program (OFN-15) Plasma Processes in Space and Laboratory of the Division of Physical Sciences of the Russian Academy of Sciences. 1. Frank A.G., Bogdanov S.Yu., Markov V.S. et al. // Phys. Plasmas 2005. 12, 052316(1-11). 2. Frank A.G., Bugrov S.G., Markov V.S. // Phys. Plasmas 2008. 15, 092102 (1-10). 3. Frank A.G., Bogdanov S.Yu., Dreiden G.V. et al. // Phys. Lett. A 2006. 348, 318-325. 4. Frank A.G., Kyrie N.P., Satunin S.N. // Phys. Plasmas 2011. 18, 111209 (1-9). 5. Kyrie N.P., Markov V.S., Frank A.G. // Plasma Phys. Reports 2010. 36, 357-364; JETP Lett. 2012. 95, 14-19. 6. Ostrovskaya G.V., Frank A.G. // Plasma Phys. Reports 2014. 40, 21-33.

Frank, Anna

269

Ion-acoustic solitons in electron-positron-ion plasmas  

Microsoft Academic Search

The ion-acoustic solitons are investigated in three-component plasmas, whose constituents are electrons, positrons, and singly charged ions. It is found that the presence of the positron component in such a multispecies plasma can result in reduction of the ion-acoustic soliton amplitudes.

S. I. Popel; S. V. Vladimirov; P. K. Shukla

1995-01-01

270

Rarefaction ion acoustic solitons in two-electron-temperature plasma  

Microsoft Academic Search

This paper shows that rarefaction ion acoustic solitons appear in a two-electron-temperature plasma. It also presents general conditions and physical mechanism for existence of the rarefaction solitons. It is found that finite amplitude rarefaction and compression solitons coexist in a plasma within a certain parameter region.

Katsunobu Nishihara; Masayoshi Tajiri

1981-01-01

271

Particle behaviour in an electron cyclotron resonance plasma etch tool  

Microsoft Academic Search

Sources of particles in a closed-coupled electron cyclotron resonance plasma source used for polysilicon etch included flaking of a residual film deposited on chamber surfaces and shedding of material from the electrostatic wafer chuck. A large, episodic increase in the number of particles added to a wafer in a clean system is observed more frequently for a plasma-on than for

M. G. Blain; G. D. Tipton; W. M. Holber; G. S. Selwyn; P. L. Westerfield; K. L. Maxwell

1994-01-01

272

Alfvenic Solitons in Ultrarelativistic Electron-Position Plasmas  

NASA Technical Reports Server (NTRS)

In electron-positron plasmas some of the plasma modes are decoupled due to the equal charge-to-mass ratio of both species. We derive the dispersion law for a low-frequency, generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field.

Verheest, G. S. Lakhina F.

1997-01-01

273

Probing Plasma Turbulence by Modulating the Electron Temperature Gradient  

Microsoft Academic Search

Validating transport models is an essential step toward accurate predictive capability of plasma transport in tokamak plasmas. Experiments with a single key parameter varied and the turbulence response measured provide excellent data sets for model validation studies. One such experiment on DIII-D will be discussed where the electron temperature gradient was systematically varied and the turbulence response documented and compared

J. C. Deboo

2009-01-01

274

A PLASMA CHANNEL BEAM CONDITIONER FOR A FREE ELECTRON LASER  

E-print Network

and at a reasonable cost [2, 3, 4]. A more recent proposal for a conditioner involves manipulating the electron beam within magnetic wigglers using lasers [5]. There is a strong motivation to continue the search for novel a plasma channel. We concede that a plasma device will add com- plexity to accelerator operation

Wurtele, Jonathan

275

Equatorial plasma bubbles with enhanced ion and electron temperatures  

Microsoft Academic Search

While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological

Kyoung Wook Min; Vitaly P. Kim; Hyosub Kil; Shin-Yi Su; Chi Kuang Chao; Jae-Jin Lee

2008-01-01

276

Modeling the Self-organized Critical Behavior of the Plasma Sheet Reconnection Dynamics  

NASA Technical Reports Server (NTRS)

Analyses of Polar UVI auroral image data reviewed in our other presentation at this meeting (V. Uritsky, A. Klimas) show that bright night-side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality (SOC) that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

Klimas, Alex; Uritsky, Vadim; Baker, Daniel

2006-01-01

277

Modeling the Self-organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics  

NASA Technical Reports Server (NTRS)

Analyses of Polar UVI auroral image data show that bright night-side high-latitude W emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. These analyses will be reviewed. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the magnetotail plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques (and more) that have been applied to the auroral image data have also been applied to this Poynting flux. New results will be presented showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. A strong correlation between these key properties of the model and those of the auroral UV emissions will be demonstrated. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

Klimas, Alexander J.

2006-01-01

278

Modeling the Self-Organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics  

NASA Astrophysics Data System (ADS)

Analyses of Polar UVI auroral image data (Uritsky et al. JGR, 2002; GRL, 2003, 2006) show that bright night- side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study (Klimas et al. JGR, 2004; GRL 2005). The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.

Klimas, A.; Uritsky, V.; Baker, D.

2006-05-01

279

Study on electron beam in a low energy plasma focus  

NASA Astrophysics Data System (ADS)

Electron beam emission was investigated in a low energy plasma focus device (2.2 kJ) using copper hollow anode. Faraday cup was used to estimate the energy of the electron beam. XR100CR X-ray spectrometer was used to explore the impact of the electron beam on the target observed from top-on and side-on position. Experiments were carried out at optimized pressure of argon gas. The impact of electron beam is exceptionally notable with two different approaches using lead target inside hollow anode in our plasma focus device.

Khan, Muhammad Zubair; Ling, Yap Seong; San, Wong Chiow

2014-03-01

280

Properties of Trapped Electron Bunches in a Plasma Wakefield Accelerator  

SciTech Connect

Plasma-based accelerators use the propagation of a drive bunch through plasma to create large electric fields. Recent plasma wakefield accelerator (PWFA) experiments, carried out at the Stanford Linear Accelerator Center (SLAC), successfully doubled the energy for some of the 42 GeV drive bunch electrons in less than a meter; this feat would have required 3 km in the SLAC linac. This dissertation covers one phenomenon associated with the PWFA, electron trapping. Recently it was shown that PWFAs, operated in the nonlinear bubble regime, can trap electrons that are released by ionization inside the plasma wake and accelerate them to high energies. These trapped electrons occupy and can degrade the accelerating portion of the plasma wake, so it is important to understand their origins and how to remove them. Here, the onset of electron trapping is connected to the drive bunch properties. Additionally, the trapped electron bunches are observed with normalized transverse emittance divided by peak current, {epsilon}{sub N,x}/I{sub t}, below the level of 0.2 {micro}m/kA. A theoretical model of the trapped electron emittance, developed here, indicates that the emittance scales inversely with the square root of the plasma density in the non-linear 'bubble' regime of the PWFA. This model and simulations indicate that the observed values of {epsilon}{sub N,x}/I{sub t} result from multi-GeV trapped electron bunches with emittances of a few {micro}m and multi-kA peak currents. These properties make the trapped electrons a possible particle source for next generation light sources. This dissertation is organized as follows. The first chapter is an overview of the PWFA, which includes a review of the accelerating and focusing fields and a survey of the remaining issues for a plasma-based particle collider. Then, the second chapter examines the physics of electron trapping in the PWFA. The third chapter uses theory and simulations to analyze the properties of the trapped electron bunches. Chapters four and five present the experimental diagnostics and measurements for the trapped electrons. Next, the sixth chapter introduces suggestions for future trapped electron experiments. Then, Chapter seven contains the conclusions. In addition, there is an appendix chapter that covers a topic which is extraneous to electron trapping, but relevant to the PWFA. This chapter explores the feasibility of one idea for the production of a hollow channel plasma, which if produced could solve some of the remaining issues for a plasma-based collider.

Kirby, Neil; /SLAC

2009-10-30

281

Plasma wave undulator for laser-accelerated electrons  

SciTech Connect

Laser-plasma accelerators have become compact sources of ultrashort electron bunches at energies up to the gigaelectronvolt range thanks to the remarkable progress made over the past decade. A direct application of these electron bunches is the production of short pulse x-ray radiation sources. In this letter, we study a fully optically driven x-ray source based on the combination of a laser-plasma accelerator and a plasma wave undulator. The longitudinal electric field of a laser-generated plasma wave is used to wiggle electrons transversally. The period of this plasma undulator being equal to the plasma wavelength, tunable photon energies in the 10 keV range can be achieved with electron energies in the 100-200 MeV range. Considering a 10s TW class femtosecond laser system, undulators with a strength parameter K{approx}0.5 and with about ten periods can be combined with a laser-plasma accelerator, resulting in several 10{sup -2} emitted x-ray photons per electron.

Corde, S.; Ta Phuoc, K. [Laboratoire d'Optique Appliquee, ENSTA ParisTech--CNRS UMR7639--Ecole Polytechnique, Chemin de la Huniere, 91761 Palaiseau (France)

2011-03-15

282

Dynamic focusing of an electron beam through a long plasma  

NASA Astrophysics Data System (ADS)

The focusing effects of a 1.4m long, (0-2)1014 cm-3 plasma on a single 28.5GeV electron bunch are studied experimentally in the underdense or blowout regime, where the beam density is much greater than the plasma density. As the beam propagates through the plasma, the density of plasma electrons along the incoming bunch drops from the ambient density to zero leaving a pure ion channel for the bulk of the beam. Thus, from the head of the beam up to the point where all plasma electrons are blown out, each successive longitudinal slice of the bunch experiences a different focusing force due to the plasma ions. The time-changing focusing force results in a different number of betatron oscillations for each slice depending upon its location within the bunch. By using an electron beam that has a correlated energy spread, this time-dependent focusing of the electron bunch has been observed by measuring the beam spot size in the image plane of a magnetic energy spectrometer placed at the plasma exit.

O'Connell, C.; Decker, F.-J.; Hogan, M. J.; Iverson, R.; Raimondi, P.; Siemann, R. H.; Walz, D.; Blue, B.; Clayton, C. E.; Joshi, C.; Marsh, K. A.; Mori, W. B.; Wang, S.; Katsouleas, T.; Lee, S.; Muggli, P.

2002-12-01

283

Energetic O+ and H+ Ions in the Plasma Sheet: Implications for the Transport of Ionospheric Ions  

NASA Technical Reports Server (NTRS)

The present study statistically examines the characteristics of energetic ions in the plasma sheet using the Geotail/Energetic Particle and Ion Composition data. An emphasis is placed on the O+ ions, and the characteristics of the H+ ions are used as references. The following is a summary of the results. (1) The average O+ energy is lower during solar maximum and higher during solar minimum. A similar tendency is also found for the average H+ energy, but only for geomagnetically active times; (2) The O+ -to -H+ ratios of number and energy densities are several times higher during solar maximum than during solar minimum; (3) The average H+ and O+ energies and the O+ -to -H+ ratios of number and energy densities all increase with geomagnetic activity. The differences among different solar phases not only persist but also increase with increasing geomagnetic activity; (4) Whereas the average H+ energy increases toward Earth, the average O+ energy decreases toward Earth. The average energy increases toward dusk for both the H+ and O+ ions; (5) The O+ -to -H+ ratios of number and energy densities increase toward Earth during all solar phases, but most clearly during solar maximum. These results suggest that the solar illumination enhances the ionospheric outflow more effectively with increasing geomagnetic activity and that a significant portion of the O+ ions is transported directly from the ionosphere to the near ]Earth region rather than through the distant tail.

Ohtani, S.; Nose, M.; Christon, S. P.; Lui, A. T.

2011-01-01

284

The Heliospheric Plasma Sheet Observed in situ by Three Spacecraft over Four Solar Rotations  

NASA Astrophysics Data System (ADS)

In this paper we present in situ observations of the heliospheric plasma sheet (HPS) from STEREO-A, Wind, and STEREO-B over four solar rotations in the declining phase of Solar Cycle 23, covering late March through late June 2007. During this time period the three spacecraft were located in the ecliptic plane, and were gradually separating in heliographic longitude from about 3 degrees to 14 degrees. Crossings of the HPS were identified using the following criteria: reversal of the interplanetary magnetic field sector, enhanced proton density, and local minima in both the proton specific entropy argument and in the alpha particle-to-proton number density ratio ( N a/ N p). Two interplanetary coronal mass ejections (ICMEs) were observed during the third solar rotation of our study period, which disrupted the HPS from its quasi-stationary state. We find differences in the in situ proton parameters at the HPS between the three spacecraft despite temporal separations of less than one day. We attribute these differences to both small separations in heliographic latitude and radial evolution of the solar wind leading to the development of compression regions associated with stream interaction regions (SIRs). We also observed a modest enhancement in the density of iron ions at the HPS.

Simunac, K. D. C.; Galvin, A. B.; Farrugia, C. J.; Kistler, L. M.; Kucharek, H.; Lavraud, B.; Liu, Y. C.-M.; Luhmann, J. G.; Ogilvie, K. W.; Opitz, A.; Popecki, M. A.; Sauvaud, J.-A.; Wang, S.

2012-11-01

285

The Role of MHD Turbulence on Plasma Sheet Structure and Dynamics  

NASA Astrophysics Data System (ADS)

There is a growing body of evidence that transport in the plasma sheet may be turbulent. In this study we use an enhanced resolution version of our global magnetohydrodynamic (MHD) simulation code to investigate the global aspects of turbulence in the tail. We examine the overall convection system that results and how it influences magnetospheric and ionospheric convection. As first step we consider the effects of turbulence for southward IMF when reconnection drives flows and vorticity in the tail. This will allow us to investigate the relationship between reconnection-driven convection and turbulence. The grid spacing and the resistivity are the two parameters that can be adjusted to influence the magnetic Reynolds number in the global MHD simulation. Explicit resistivity is necessary in our code for reconnection to occur. We set the resistivity to the smallest value that gives us a reconnecting magnetosphere. Then we investigated the effects of grid spacing on the nature of convection in the tail by carrying out simulations with different grids. We will present three cases: one with our present grid spacing (0.2 RE), one with intermediate resolution and one with grid resolution on the ion Larmor radius scale (0.05 RE).

El-Alaoui, M.; Ashour-Abdalla, M.; Goldstein, M. L.; Walker, R. J.

2006-12-01

286

Electron productions from short-pulse laser plasma interactions  

Microsoft Academic Search

Characterization of hot electrons produced by ultra-intense laser-matter interactions is important not only to the understanding of laser plasma physics, but also to applications making use of the temporally short, broad spectrum of electrons. Using our newly built fiber-array-based compact electron spectrometer, we performed systematic measurements of electron production from various solid targets using the high intensity (10^17 to 10^21

H. Chen; A. B. Langdon; B. F. Lasinski; H. McLean; P. K. Patel; D. F. Price; C. H. Still; B. K. Young

2002-01-01

287

Electron beam transport analysis of W-band sheet beam klystron  

NASA Astrophysics Data System (ADS)

The formation and transport of high-current density electron beams are of critical importance for the success of a number of millimeter wave and terahertz vacuum devices. To elucidate design issues and constraints, the electron gun and periodically cusped magnet stack of the original Stanford Linear Accelerator Center designed W-band sheet beam klystron circuit, which exhibited poor beam transmission (?55%), have been carefully investigated through theoretical and numerical analyses taking advantage of three-dimensional particle tracking solvers. The re-designed transport system is predicted to exhibit 99.76% (cold) and 97.38% (thermal) beam transmission, respectively, under space-charge-limited emission simulations. The optimized design produces the required high aspect ratio (10:1) sheet beam with 3.2 A emission current with highly stable propagation. In the completely redesigned model containing all the circuit elements, more than 99% beam transmission is experimentally observed at the collector located about 160 mm distant from the cathode surface. Results are in agreement of the predictions of two ray-tracing simulators, CST PARTICLE STUDIO and OMNITRAK which also predict the observed poor transmission in the original design. The quantitative analysis presents practical factors in the modeling process to design a magnetic lens structure to stably transport the elliptical beam along the long drift tube.

Wang, Jian-Xun; Barnett, Larry R.; Luhmann, Neville C.; Shin, Young-Min; Humphries, Stanley

2010-04-01

288

Electron Beam Transport in Advanced Plasma Wave Accelerators  

SciTech Connect

The primary goal of this grant was to develop a diagnostic for relativistic plasma wave accelerators based on injecting a low energy electron beam (5-50keV) perpendicular to the plasma wave and observing the distortion of the electron beam's cross section due to the plasma wave's electrostatic fields. The amount of distortion would be proportional to the plasma wave amplitude, and is the basis for the diagnostic. The beat-wave scheme for producing plasma waves, using two CO2 laser beam, was modeled using a leap-frog integration scheme to solve the equations of motion. Single electron trajectories and corresponding phase space diagrams were generated in order to study and understand the details of the interaction dynamics. The electron beam was simulated by combining thousands of single electrons, whose initial positions and momenta were selected by random number generators. The model was extended by including the interactions of the electrons with the CO2 laser fields of the beat wave, superimposed with the plasma wave fields. The results of the model were used to guide the design and construction of a small laboratory experiment that may be used to test the diagnostic idea.

Williams, Ronald L

2013-01-31

289

Simulation of laser-plasma interactions and fast-electron transport in inhomogeneous plasma  

SciTech Connect

A new framework is introduced for kinetic simulation of laser-plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell's equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell's equations are solved using an Ohm's law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere's law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.

Cohen, B.I. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551 (United States)], E-mail: bcohen@llnl.gov; Kemp, A.J.; Divol, L. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551 (United States)

2010-06-20

290

Transition of electron kinetics in weakly magnetized inductively coupled plasmas  

SciTech Connect

Transition of the electron kinetics from nonlocal to local regime was studied in weakly magnetized solenoidal inductively coupled plasma from the measurement of the electron energy probability function (EEPF). Without DC magnetic field, the discharge property was governed by nonlocal electron kinetics at low gas pressure. The electron temperatures were almost same in radial position, and the EEPFs in total electron energy scale were radially coincided. However, when the DC magnetic field was applied, radial non-coincidence of the EEPFs in total electron energy scale was observed. The electrons were cooled at the discharge center where the electron heating is absent, while the electron temperature was rarely changed at the discharge boundary with the magnetic field. These changes show the transition from nonlocal to local electron kinetics and the transition is occurred when the electron gyration diameter was smaller than the skin depth. The nonlocal to local transition point almost coincided with the calculation results by using nonlocal parameter and collision parameter.

Kim, Jin-Yong; Lee, Hyo-Chang; Kim, Young-Do; Chung, Chin-Wook [Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)] [Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of); Kim, Young-Cheol [Department of Nanoscale Semiconductor Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)] [Department of Nanoscale Semiconductor Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

2013-10-15

291

Cryo-electron microscopy of extracellular vesicles in fresh plasma  

PubMed Central

Introduction Extracellular vesicles (EV) are phospholipid bilayer-enclosed vesicles recognized as new mediators in intercellular communication and potential biomarkers of disease. They are found in many body fluids and mainly studied in fractions isolated from blood plasma in view of their potential in medicine. Due to the limitations of available analytical methods, morphological information on EV in fresh plasma is still rather limited. Objectives To image EV and determine the morphology, structure and size distribution in fresh plasma by cryo-electron microscopy (cryo-EM). Methods Fresh citrate- and ethylenediaminetetraacetic acid (EDTA)-anticoagulated plasma or EV isolated from these plasmas were rapidly cryo-immobilized by vitrification and visualized by cryo-EM. Results EV isolated from fresh plasma were highly heterogeneous in morphology and size and mostly contain a discernible lipid bilayer (lipid vesicles). In fresh plasma there were 2 types of particles with a median diameter of 30 nm (25260 nm). The majority of these particles are electron dense particles which most likely represent lipoproteins. The minority are lipid vesicles, either electron dense or electron lucent, which most likely represent EV. Lipid vesicles were occasionally observed in close proximity of platelets in citrate and EDTA-anticoagulated platelet-rich plasma. Cryo-electron tomography (cryo-ET) was employed to determine the 3D structure of platelet secretory granules. Conclusions Cryo-EM is a powerful technique that enables the characterization of EV in fresh plasma revealing structural details and considerable morphological heterogeneity. Only a small proportion of the submicron structures in fresh plasma are lipid vesicles representing EV. PMID:24455109

Yuana, Yuana; Koning, Roman I.; Kuil, Maxim E.; Rensen, Patrick C. N.; Koster, Abraham J.; Bertina, Rogier M; Osanto, Susanne

2013-01-01

292

Influence of electron velocity distribution on the plasma expansion features  

SciTech Connect

Collisionless plasma expansion into vacuum is addressed emphasizing on the kinetic effects associated with the plasma electrons. It is an important issue since there are situations in which the plasmas are in nonequilibrium state. Thus, the electron distribution function (DF) that is generally non-Maxwellian has to be modeled. For this purpose, the generalized Lorentzian (kappa) DF is used to simulate the electron DF. The Maxwellian and kappa distributions differ substantially in a high-energy tail. Thus, the electron dynamics is studied by the Vlasov equation. Neglecting the ion temperatures, fluid equations are used for them. It is shown that by increasing the population of energetic electrons, the expansion takes place faster, the resulting electric field is stronger, and the ions are accelerated to higher energy.

Shokoohi, R.; Abbasi, H. [Faculty of Physics, Amirkabir University of Technology, P. O. Box 15875-4413, Tehran (Iran, Islamic Republic of)

2009-08-01

293

Simulations of turbulent plasma heating by powerful electron beams  

SciTech Connect

Basic mechanisms of turbulent plasma heating by powerful electron beams are studied using numerical simulations. Both particle-in-cell and hybrid codes are used to investigate how beam-plasma instability evolves and saturates in the case of continuously injected electron beam. For sufficiently high plasma temperature beam driven turbulence is found to operate in the regime of the constant pump, when the saturation level of heating power is determined solely by the nonlinear interaction of beam particles with resonant waves and does not depend on the turbulence structure in the nonresonant part of the spectrum.

Timofeev, I. V.; Terekhov, A. V. [Budker Institute of Nuclear Physics, 630090 Novosibirsk (Russian Federation); Institute of Computational Mathematics and Mathematical Geophysics, 630090 Novosibirsk (Russian Federation) and Novosibirsk State University, 630090 Novosibirsk (Russian Federation)

2010-08-15

294

Pure electron plasmas confined for 90 ms in a stellarator without electron sources or internal objects  

SciTech Connect

We report on the creation and up to 90 ms sustainment of pure electron plasmas confined in a stellarator without internal objects. Injection of positrons into such plasmas is expected to lead to the creation of the first electron-positron plasma experiments. These newly created plasmas will also allow a study of pure electron plasmas without the perturbing presence of internal objects. The plasmas were created by thermionic emission of electrons from a heated, biased filament that was retracted in 20 ms. The confinement of these transient plasmas is different from that of steady state plasmas with internal objects and emissive filaments, and is generally shorter, limited by ion buildup. The decay time is increased by lowering the neutral pressure, lowering the electron plasma temperature, or operating with neutrals with high ionization energies (helium). These findings are all consistent with ion accumulation being the cause for the shorter than expected confinement times. The magnetic field strength also moderately increases the decay times. The deleterious effect of ions is not expected to imply a similar deleterious effect when introducing positrons, but it implies that ion accumulation must be avoided also in an electron-positron experiment.

Brenner, P. W.; Sunn Pedersen, T.

2012-05-15

295

Electron inertia effects on the planar plasma sheath problem  

SciTech Connect

The steady one-dimensional planar plasma sheath problem, originally considered by Tonks and Langmuir, is revisited. Assuming continuously generated free-falling ions and isothermal electrons and taking into account electron inertia, it is possible to describe the problem in terms of three coupled integro-differential equations that can be numerically integrated. The inclusion of electron inertia in the model allows us to obtain the value of the plasma floating potential as resulting from an electron density discontinuity at the walls, where the electrons attain sound velocity and the electric potential is continuous. Results from numerical computation are presented in terms of plots for densities, electric potential, and particles velocities. Comparison with results from literature, corresponding to electron Maxwell-Boltzmann distribution (neglecting electron inertia), is also shown.

Duarte, V. N.; Clemente, R. A. [Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, Cidade Universitaria Zeferino Vaz, Campinas SP 13083-859 (Brazil)

2011-04-15

296

Control of electron temperature and space potential gradients by superposition of thermionic electrons on electron cyclotron resonance plasmas.  

PubMed

An electron temperature gradient (ETG) is formed perpendicular to the magnetic field lines by superimposing low-temperature thermionic electrons emitted from a tungsten hot plate upon high-temperature electrons of an electron cyclotron resonance plasma, which pass through two different-shaped mesh grids. The radial profile of the plasma space potential can be controlled independent of the ETG by changing the bias voltages of the hot plate. PMID:20515138

Moon, Chanho; Kaneko, Toshiro; Tamura, Shuichi; Hatakeyama, Rikizo

2010-05-01

297

Geotail observations of plasma sheet ion composition over 16 years: On variations of average plasma ion mass and O+ triggering substorm model  

Microsoft Academic Search

We examined long-term variations of ion composition in the plasma sheet, using energetic (9.4212.1 keV\\/e) ion flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on board the Geotail spacecraft. EPIC\\/STICS observations are available from 17 October 1992 for more than 16 years, covering the declining phase of solar

M. Nos; A. Ieda; S. P. Christon

2009-01-01

298

New aspects of plasma sheet dynamics MHD and kinetic theory Institut fu r Astronomie und Astrophysik, Ludwig-Maximilians-Universita t Mu nchen, Scheinerstr. 1, D-81679 Munich, Germany  

E-print Network

). There are several microscopic processes discussed in the literature which may yield non-idealness on macroscopic reconnection is a process of funda- mental importance for the dynamics of the Earth's plasma sheet. In this context, the development of thin current sheets in the near-Earth plasma sheet is a topic of special

Boyer, Edmond

299

Secondary-electrons-induced cathode plasma in a relativistic magnetron  

SciTech Connect

Results of time- and space-resolved spectroscopic studies of cathode plasma during a S-band relativistic magnetron operation and a magnetically insulated diode having an identical interelectrode gap are presented. It was shown that in the case of the magnetron operation, one obtains an earlier, more uniform plasma formation due to energetic electrons' interaction with the cathode surface and ionization of desorbed surface monolayers. No differences were detected in the cathode's plasma temperature between the magnetron and the magnetically insulated diode operation, and no anomalous fast cathode plasma expansion was observed in the magnetron at rf power up to 350 MW.

Queller, T.; Gleizer, J. Z.; Krasik, Ya. E. [Physics Department, Technion, Haifa 32000 (Israel)

2012-11-19

300

Ionization-Induced Electron Trapping inUltrarelativistic Plasma Wakes  

SciTech Connect

The onset of trapping of electrons born inside a highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions of a Li plasma confined by He gas. Li plasma electrons support the wake, and higher ionization potential He atoms are ionized as the beam is focused by Li ions and can be trapped. As the wake amplitude is increased, the onset of trapping is observed. Some electrons gain up to 7.6 GeV in a 30.5 cm plasma. The experimentally inferred trapping threshold is at a wake amplitude of 36 GV/m, in good agreement with an analytical model and PIC simulations.

Oz, E.; Deng, S.; Katsouleas, T.; Muggli, P.; /UCLA; Barnes, C.D.; Blumenfeld, I.; Decker, F.J.; Emma, P.; Hogan, M.J.; Ischebeck, R.; Iverson, R.H.; Kirby, N.; Krejcik,; O'Connell, C.; Siemann, R.H.; Walz, D.; /SLAC; Auerbach, D.; Clayton, C.E.; Huang, C.; Johnson, D.K.; Joshi, C.; /UCLA

2007-04-06

301

Electron energy distributions in a magnetized inductively coupled plasma  

NASA Astrophysics Data System (ADS)

Optimizing and controlling electron energy distributions (EEDs) is a continuing goal in plasma materials processing as EEDs determine the rate coefficients for electron impact processes. There are many strategies to customize EEDs in low pressure inductively coupled plasmas (ICPs), for example, pulsing and choice of frequency, to produce the desired plasma properties. Recent experiments have shown that EEDs in low pressure ICPs can be manipulated through the use of static magnetic fields of sufficient magnitudes to magnetize the electrons and confine them to the electromagnetic skin depth. The EED is then a function of the local magnetic field as opposed to having non-local properties in the absence of the magnetic field. In this paper, EEDs in a magnetized inductively coupled plasma (mICP) sustained in Ar are discussed with results from a two-dimensional plasma hydrodynamics model. Results are compared with experimental measurements. We found that the character of the EED transitions from non-local to local with application of the static magnetic field. The reduction in cross-field mobility increases local electron heating in the skin depth and decreases the transport of these hot electrons to larger radii. The tail of the EED is therefore enhanced in the skin depth and depressed at large radii. Plasmas densities are non-monotonic with increasing pressure with the external magnetic field due to transitions between local and non-local kinetics.

Song, Sang-Heon; Yang, Yang; Chabert, Pascal; Kushner, Mark J.

2014-09-01

302

Electron Acceleration by Plasma Waves in the Io Flux Tube  

Microsoft Academic Search

Io's interaction with the jovian magnetosphere generates auroral and radio emissions. The underlying electron acceleration process is not well understood and only few observations exist to constrain the theoretical models. The Galileo spacecraft made a number of low altitudes passes near Io and the plasma wave\\/particle instruments have collected new information. The source of energy for the electron acceleration is

T. Chust; A. Roux; W. S. Kurth; D. A. Gurnett

2001-01-01

303

Electron-hose instability in an annular plasma sheath  

E-print Network

such as ion-hose5 and resistive hose.6 Until recently less attention has been given to the transverse two-stream Center Stanford University, Stanford CA 94309 (Received ) A relativistic electron beam propagating electron beams through plasma. Stability against transverse beam break-up1 is critical in such applications

304

Determination of Jupiter's electron density profile from plasma wave observations  

Microsoft Academic Search

This paper summarizes the electron density measurements obtained in the Jovian magnetosphere from the plasma wave instruments on the Voyager 1 and 2 spacecraft. Three basic techniques are discussed for determining the electron density: (1) local measurements from the low-frequency cutoff of continuum radiation, (2) local measurements from the frequency of upper hybrid resonance emissions, and (3) integral measurements from

D. A. Gurnett; F.L. Scarf; W. S. Kurth; R. R. Shaw; R. L. Poynter

1981-01-01

305

Decay instability of an electron plasma wave in a dusty plasma  

SciTech Connect

The parametric decay instability of an electron plasma wave in a homogeneous, unmagnetized, hot and collisionless dusty plasma has been investigated analytically. The Vlasov equation has been solved perturbatively to find the nonlinear response of the plasma particles. The presence of the charged dust grains introduces a background inhomogeneous electric field that significantly influences the dispersive properties of the plasma and the decay process. The growth rate of the decay instability through the usual ion-acoustic mode is modified, and depends upon the dust perturbation parameter {mu}{sub {ital i}}, dust correlation length {ital q}{sub 0}, and the related ion motion. However, the decay process of the electron plasma wave through the ultralow frequency dust mode, excited due to the presence of the dust particles, is more efficient than the decay through the usual ion-acoustic mode in the dusty plasma. {copyright} {ital 1996 The American Physical Society.}

Amin, M.R.; Ferdous, T.; Salimullah, M. [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)] [Department of Physics, Jahangirnagar University, Savar, Dhaka 1342 (Bangladesh)

1996-03-01

306

Cluster observations of the electric field structure of the reconnection region in the plasma sheet: an electrostatic nozzle  

NASA Astrophysics Data System (ADS)

Measurements from the Cluster spacecraft of electric fields, magnetic fields, and ions at distances of 18 Re in the geomagnetic tail are used to study the structure and dynamics of the reconnection region during a major geomagnetic storm on October 1, 2001. The paper focuses on the structure of the normal component of the electric field at the current sheet. Evidence is presented at "thin" current sheet crossings with widths of 1-2 c/?pe for a +/- 60 mV/m symmetric bipolar electric field structure in the normal component of the electric field. The bipolar structure spatially coincides spatially with the bifurcated cross tail current sheet and reverses at the current sheet midplane with the vectors pointing towards the current sheet mid plane. The associated intE\\cdotdl is 2 kV between the outer boundary of the current and the mid-plane. The data is consistent at these thin current sheet crossings with a picture in which the normal component of the electric field drives an EB drift of the magnetized electrons which provides the cross tail current. Over these scales, 100 eV ions from the tail lobes should be largely un-magnetized and accelerated nearly ballistically through the 2 kV potential drop . A heuristic model is presented in which the normal component of the electric field spatially coincide with planar current sheet in an X line geometry forming a potential well creating a two dimensional "quasi-electrostatic nozzle". In this model, low energy ions accelerated into this nozzle gain a kinetic energy of 1/2 mV_A^2 (2 keV) and bounce several times between opposing walls. Each bounce converts ion velocity normal to the current sheet to that parallel to the x gse axis forming in ion jets with velocity V_A flowing away from the separatrix region in a manner consistent with fluid pictures of reconnection. Measurements are also presented from thicker tail current sheet crossings (1000-2000 km1-2 c/?pi) with normal components of the electric field of 5-20 mV/m and potential drops of 4-30 kV. It is expected that only higher energy ions are non- adiabatic in this portion of the current sheet structure. The bipolar electric field structure correlates with the magnetic field perturbations due to the Hall magnetic field perturbation. The associated Poynting flux provides a non-negligible contribution to the outgoing energy flux.

Wygant, J.; Dombeck, J.; Lysak, R.; McFadden, J.; Carlson, C.; Mozer, F.; Reme, H.; Lucek, E.; Balogh, A.; Andre, M.

2003-04-01

307

Energetic Electron Transport In An Inhomogeneous Plasma Medium  

SciTech Connect

A review of the work carried out at IPR on energetic electron transport through an inhomogeneous plasma medium is presented in this article. A Generalized Electron Magnetohydrodynamic (G-EMHD) fluid model has been developed and employed for such studies. Novel observations such as (i) the trapping of electron current pulse structure in a high density plasma region, (ii) the formation of sharp magnetic field shock structures at the inhomogeneous plasma density layer (iii) and intense energy dissipation at the shock layer even in the collisionless limit are reported. The intense energy dissipation of the electron current pulse at the shock layer provides a mechanism whereby highly energetic electrons which are essentially collision-less can also successfully deposit their energy in a local region of the plasma. This is specially attractive as it opens up the possibility of heating a localized region of an overdense plasma (where lasers cannot penetrate) by highly energetic collision-less electrons. A direct application of this mechanism to Fast Ignition (FT) experiments is discussed.

Das, Amita [Institute for Plasma Research, Bhat Gandhinagar-382428 (India)

2010-11-23

308

Energetic Electron Transport In An Inhomogeneous Plasma Medium  

NASA Astrophysics Data System (ADS)

A review of the work carried out at IPR on energetic electron transport through an inhomogeneous plasma medium is presented in this article. A Generalized Electron Magnetohydrody-namic (G-EMHD) fluid model has been developed and employed for such studies. Novel observations such as (i) the trapping of electron current pulse structure in a high density plasma region, (ii) the formation of sharp magnetic field shock structures at the inhomogeneous plasma density layer (iii) and intense energy dissipation at the shock layer even in the collisionless limit are reported. The intense energy dissipation of the electron current pulse at the shock layer provides a mechanism whereby highly energetic electrons which are essentially collisionless can also successfully deposit their energy in a local region of the plasma. This is specially attractive as it opens up the possibility of heating a localized region of an overdense plasma (where lasers cannot penetrate) by highly energetic collisionless electrons. A direct application of this mechanism to Fast Ignition (FT) experiments is discussed.

Das, Amita

2010-11-01

309

Formation and transport of low-voltage, space-charge dominated sheet electron beams for high-power microwave devices  

SciTech Connect

Sheet electron beams have the potential to make possible higher power sources of microwave radiation due to their ability to transport high currents, at reduced current densities, through a single narrow RF interaction circuit. The authors will discuss experimental investigations of the formation of an elliptical sheet beam using magnet quadrupoles and a round-beam electron gun. Features of this configuration include a low-cost, commercially available Pierce gun and a lens system consisting of four tunable magnetic quadrupoles with modest field gradients. Three-dimensional envelope and particle-in-cell simulations indicate that this method can generate highly elliptic output beams, with variability in final beam size, for laboratory experiments on sheet beam transport. They also will present the results of particle-in-cell simulations of the transport of sheet beams in long-period offset-pole periodic magnet arrays. While the stability of sheet beams in short-period arrays has previously been established, the extension to longer magnet periods indicate that side-focusing of space-charge dominated sheet beams is more problematic than beam stability. However, long-term (> 20 periods) stable transport is demonstrated for {lambda}{sub m} = 1 cm for a 2 A, 10 kV elliptical beam with a = 2.7 cm and b = 0.05 cm.

Basten, M.A.; Booske, J.H.; Louis, L.J.; Joe, J.; Scharer, J.E. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Electrical and Computer Engineering

1996-12-31

310

Dynamical Casimir effect for TE and TM modes in a resonant cavity bisected by a plasma sheet  

SciTech Connect

Parametric photon creation via the dynamical Casimir effect (DCE) is evaluated numerically, in a three-dimensional rectangular resonant cavity bisected by a semiconductor diaphragm (SD), which is irradiated by a pulsed laser with frequency of GHz order. The aim of this paper is to determine some of the optimum conditions required to detect DCE photons relevant to an experimental detection system. We expand upon the thin plasma sheet model [M. Crocce et al., Phys. Rev. A 70, 033811 (2004)] to estimate the number of photons for both transverse electric (TE) and transverse magnetic (TM) modes at any given SD position. Numerical calculations are performed considering up to 51 intermode couplings by varying the SD location, driving period and laser power without any perturbations. It is found that the number of photons created for TE modes strongly depends on SD position, where the strongest enhancement occurs at the midpoint (not near the cavity wall); while TM modes have weak dependence on SD position. Another important finding is the fact that significant photon production for TM{sub 111} modes still takes place at the midpoint even for a low-laser power of 0.01 {mu}J/pulse, although the number of TE{sub 111} photons decreases almost proportionately with laser power. We also find a relatively wide tuning range for both TE and TM modes that is correlated with the frequency variation in the instantaneous mode functions caused by the interaction between the cavity photons and conduction electrons in the SD excited by a pulsed laser.

Naylor, W.; Matsuki, S.; Kido, Y. [Department of Physics, Ritsumeikan University, Kusatsu, Shiga 525-8577 (Japan); Nishimura, T. [Research Center of Ion Beam Technology, Hosei University, Koganei, Tokyo 184-8584 (Japan)

2009-10-15

311

Suprathermal electrons produced by beam-plasma-discharge  

NASA Technical Reports Server (NTRS)

Experiments conducted with a low energy plasma lens, HARP, in the electron beam of the large vacuum chamber at Johnson Space Center indicate that an enhanced population of 50 to 300 volt electrons appear when the beam goes into the Beam-Plasma Discharge (BPD) mode. Below the BPD instability the electron distribution appears to be characterized as non-energized single particle scattering and energy loss. At 100 cm from the beam core in the BPD mode the fluxes parallel to the beam are reduced by a factor of 20 with respect to the fluxes at 25 cm. Some evidence for isotropy near the beam core is presented.

Sharp, W. E.

1982-01-01

312

Suprathermal electrons produced by Beam-Plasma-Discharge  

SciTech Connect

Experiments conducted with a low energy plasma lens, HARP, in the electron beam of the large vacuum chamber at Johnson Space Center indicate that an enhanced population of 50 to 300 volt electrons appear when the beam goes into the Beam-Plasma Discharge (BPD) mode. Below the BPD instability the electron distribution appears to be characterized as non-energized single particle scattering and energy loss. At 100 cm from the beam core in the BPD mode the fluxes parallel to the beam are reduced by a factor of 20 with respect to the fluxes at 25 cm. Some evidence for isotropy near the beam core is presented.

Sharp, W.E.

1982-08-01

313

Kinetic description of electron plasma waves with orbital angular momentum  

SciTech Connect

We describe the kinetic theory of electron plasma waves with orbital angular momentum or twisted plasmons. The conditions for a twisted Landau resonance to exist are established, and this concept is introduced for the first time. Expressions for the kinetic dispersion relation and for the electron Landau damping are derived. The particular case of a Maxwellian plasma is examined in detail. The new contributions to wave dispersion and damping due the orbital angular momentum are discussed. It is shown that twisted plasmons can be excited by rotating electron beams.

Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

2012-11-15

314

Synchrotron radiation from electron beams in plasma focusing channels  

SciTech Connect

Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma focusing channel is analyzed and application to plasma wakefield accelerator experiments and to the ion channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter alpha-beta, which plays a similar role to that of the wiggler strength parameter in a conventional FEL. For alpha-beta > 1, radiation is emitted in numerous harmonics. Furthermore, alpha-beta is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. The radiation spectrum emitted from an electron beam is calculated by averaging the single electron spectrum over the electron distribution. This leads to a frequency broadening of the radiation spectrum, which places serious limits on the possibility of realizing an ICL.

Esarey, E.; Shadwick, B.A.; Catravas, P.; Leemans, W.P.

2001-12-06

315

dc-plasma-sprayed electronic-tube device  

DOEpatents

An electronic tube and associated circuitry which is produced by dc plasma arc spraying techniques is described. The process is carried out in a single step automated process whereby both active and passive devices are produced at very low cost. The circuitry is extremely reliable and is capable of functioning in both high radiation and high temperature environments. The size of the electronic tubes produced are more than an order of magnitude smaller than conventional electronic tubes.

Meek, T.T.

1982-01-29

316

Classification of fast flows in central plasma sheet: Superposed epoch analysis based on THEMIS observations  

NASA Astrophysics Data System (ADS)

A statistical survey of 560 fast flows in midnight central plasma sheet is performed based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations during its first two tail phases. From superposed epoch analysis, no significant substorm activities are found to be associated with the occurrence of fast flows beyond X=-15 Re. Considering the associations with substorm activities, the fast flows inside of X=-15 Re can be classified into two obvious classes: short duration (< 2.0 min) and long duration (> 4.0 min). Substorm breakups are shown to be more closely correlated to short-duration fast flows. Furthermore, the onset of short-duration fast flows in the dipolarization region (X=-9 to -11 Re) is almost simultaneous with the onset of substorm breakups and dipolarizations. On the other hand, time delays of 2-4 min are both found in the near-Earth region (X=-7 to -9 Re) and in the near-tail region (X=-11 to -15 Re). Assuming that short-duration fast flows are generated by the force imbalance caused by cross-tail current disruption, these features are consistent with the predictions made by the cowling electrojet current loop and the cross-tail current disruption substorm models. In comparison, although more magnetic flux is transported toward Earth for long-duration fast flows, no clear substorm breakup is closely associated with them. The analysis of 2-D ion velocity distribution further shows some differences. For short-duration fast flows, multiple crescent-shaped ion populations are found. However, for long-duration fast flows, there exists only a single crescent-shaped ion population. The difference may be an important signature for distinguishing these two classes of fast flows.

Li, H.; Wang, C.; Fu, S. Y.

2014-09-01

317

Spatiotemporal relaxation of electrons in non-isothermal plasmas  

NASA Astrophysics Data System (ADS)

A powerful method for the study of time-dependent electron kinetics in spatially one-dimensional plasmas is presented. The method is based on the solution of the space- and time-dependent kinetic equation for the electron velocity distribution function in two-term approximation. The resulting three-dimensional partial differential equation for the isotropic part of the velocity distribution function is numerically solved as an initial-boundary value problem over the space of the spatial coordinate and the total energy proceeding in time. As an application, the spatiotemporal relaxation of electrons in the column-anode plasma of a glow discharge in krypton, acted upon by a space-independent electric field and initiated by a constant electron influx at the cathode side of the plasma, is studied. The electron relaxation process is traced up to the establishment into a spatially structured, time-independent state. A detailed analysis of the spatiotemporal behaviour of the velocity distribution function and relevant macroscopic quantities of the electrons is given for different electric field strengths and boundary conditions. In particular, a significant increase in the relaxation time of the spatiotemporal electron relaxation compared with the relaxation time to approach steady state in spatially homogeneous plasmas has been found.

Loffhagen, D.; Winkler, R.

2001-05-01

318

Electron emission and plasma generation in a modulator electron gun using ferroelectric cathode  

Microsoft Academic Search

Strong electron emission and dense plasma generation have been observed in a modulator electron gun with a Ba0.67Sr0.33TiO3 ferroelectric cathode. Parameter of the modulator electron gun and lifetime of the ferroelectric cathode were investigated. It was shown that electron emission from Ba0.67Sr0.33TiO3 cathode with a positive triggering pulse is a sort of plasma emission. Electrons were emitted by the co-effect

Shutao Chen; Shuxin Zheng; Ziqiu Zhu; Xianlin Dong; Chuanxiang Tang

2006-01-01

319

Multiple-satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral-zone activity  

NASA Technical Reports Server (NTRS)

Particle observations from pairs of satellites (Ogo 5, Vela 4A and 5B, Imp 3) during the recovery of plasma sheet thickness late in substorms were examined. Six of the nine events occurred within about 5 min in locations near the estimated position of the neutral sheet, but over wide ranges of east-west and radial separations. The time of occurrence and spatial extent of the recovery were related to the onset (defined by ground Pi 2 pulsations) and approximate location (estimated from ground mid-latitude magnetic signatures) of substorm expansions. It was found that the plasma sheet recovery occurred 10 - 30 min after the last in a series of Pi bursts, which were interpreted to indicate that the recovery was not due directly to a late, high latitude substorm expansion. The recovery was also observed to occur after the substorm current wedge had moved into the evening sector and to extend far to the east of the center of the last preceding substorm expansion.

Pytte, T.; Mcpherron, R. L.; Kivelson, M. G.; West, H. I., Jr.; Hones, E. W., Jr.

1977-01-01

320

Dense laser-driven electron sheets as relativistic mirrors for coherent production of brilliant X-ray and ?-ray beams  

NASA Astrophysics Data System (ADS)

Several techniques exist to obtain brilliant X-ray beams by coherent reflection from relativistic electrons ( E e= ? mc 2) with Doppler frequency upshift of 4 ? 2. We describe a new approach starting with an ultra-thin solid target. Larger driver-laser intensities with high contrast are required to produce dense electron sheets. Their acceleration in vacuum results in a transverse momentum component besides the dominant longitudinal momentum component. The counter-propagating production laser for optimum Doppler boost in X-ray production by reflection has to be injected opposite to the electron direction and not opposite to the driver laser. Different measures to increase the reflectivity of the electron sheet via laser trapping or free-electron-laser-like micro-bunching are discussed, extending the photon energy into the MeV range. Here, first-order estimates are given.

Habs, D.; Hegelich, M.; Schreiber, J.; Gross, M.; Henig, A.; Kiefer, D.; Jung, D.

2008-11-01

321

Separation of finite electron temperature effect on plasma polarimetry  

SciTech Connect

This study demonstrates the separation of the finite electron temperature on the plasma polarimetry in the magnetic confined fusion plasma for the first time. Approximate solutions of the transformed Stokes equation, including the relativistic effect, suggest that the orientation angle, {theta}, and ellipticity angle, {epsilon}, of polarization state have different dependency on the electron density, n{sub e}, and the electron temperature, T{sub e}, and that the separation of n{sub e} and T{sub e} from {theta} and {epsilon} is possible in principle. We carry out the equilibrium and kinetic reconstruction of tokamak plasma when the central electron density was 10{sup 20} m{sup -3}, and the central electron temperatures were 5, 10, 20, and 30 keV. For both cases when a total plasma current, I{sub p}, is known and when I{sub p} is unknown, the profiles of plasma current density, j{sub {phi}}, n{sub e}, and T{sub e} are successfully reconstructed. The reconstruction of j{sub {phi}} without the information of I{sub p} indicates the new method of I{sub p} measurement applicable to steady state operation of tokamak.

Imazawa, Ryota; Kawano, Yasunori; Kusama, Yoshinori [Japan Atomic Energy Agency, 801-1 Mukoyama, Naka, Ibaraki (Japan)

2012-12-15

322

Sheet resistance of LiNbO3 wafers processed in radio-frequency plasma of hydrogen  

NASA Astrophysics Data System (ADS)

Radio-frequency discharge of 13.56MHz in hydrogen was used for processing single domain crystalline LiNbO3 wafers under an electrodeless capacitive coupling. At a pressure of 0.5 torr and RF input power of 250 W a surface layer of approx. 0.5 ?m on the LiNbO3 wafers was created in which the niobate structure was strongly injured. The Li concentration dropped almost to zero at the very surface and only niobium oxides remained there. After the surface modification the wafers lost their insulating properties and became electrically conducting. The sheet resistance was measured and revealed a semiconducting character. We discuss possible mechanisms of the charge carriers creation in the material during the plasma processing. The nuclear method NDP (Neutron Depth Profiling) has been used for the lithium depth profiling and the four-point probe technique for the sheet resistanace measurements.

Tur?i?ov, H.; Pracha?ov, J.; ?erven, J.; Vack, J.

2000-03-01

323

Heating of the solar flare plasma by high energy electrons.  

NASA Technical Reports Server (NTRS)

Discussion of the heating of the ambient plasma by high-energy electrons in solar flares. It is shown that for large flares the heating is enough to produce a thermal plasma with a temperature up to 10 to the 7th K rapidly in the initial phase of the flares. Thus thermal bremsstrahlung in addition to nonthermal bremsstrahlung should be considered for the X-ray emission of solar flares in the initial phase.-

Cheng, C.-C.

1972-01-01

324

Interaction of a modulated electron beam with a magnetoactive plasma  

Microsoft Academic Search

Experimental results concerning the interaction of a modulated electron beam with a magnetoactive plasma in the whistler frequency\\u000a range are reported. It was shown experimentally that when a beam is injected into the plasma, waves can be generated by two\\u000a possible mechanisms: Cherenkov emission of whistlers by the modulated beam, and transition radiation from the beam injection\\u000a point. In the

A. V. Kostrov; M. V. Starodubtsev; C. Krafft; G. Matthieussent; A. S. Volokitin

1998-01-01

325

Electron cyclotron heating correlation with tokamak toroidal plasma rotation  

Microsoft Academic Search

Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak (in Plasma Physics and Controlled Nuclear Fusion Research 1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131). Measurements were made using a curved-crystal Bragg x-ray spectrometer with spectral resolution of lambda\\/..delta..lambda

A. J. Lieber; R. T. Snider; Ping Lee; S. S. Wojtowicz

1988-01-01

326

Electron cyclotron heating correlation with tokamak toroidal plasma rotation  

Microsoft Academic Search

Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak [in PlasmaPhysicsandControlledNuclearFusionResearch 1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131]. Measurements were made using a curved-crystal Bragg x-ray spectrometer with spectral resolution of ?\\/?? of greater than 19 000 and

A. J. Lieber; R. T. Snider; Ping Lee; S. S. Wojtowicz

1988-01-01

327

Strongly turbulent stabilization of electron beam-plasma interactions  

NASA Astrophysics Data System (ADS)

The stabilization of electron beam interactions due to strongly turbulent nonlinearities is studied analytically and numerically for a wide range of plasma parameters. A fluid mode coupling code is described in which the effects of electron and ion Landau damping and linear growth due to the energetic electron beam are included in a phenomenological manner. Stabilization of the instability is found to occur when the amplitudes of the unstable modes exceed the threshold of the oscillating two-stream instability. The coordinate space structure of the turbulent spectrum which results clearly shows that soliton-like structures are formed by this process. Phenomenological models of both the initial stabilization and the asymptotic states are developed. Scaling laws between the beam-plasma growth rate and the fluctuations in the fields and plasma density are found in both cases, and shown to be in good agreement with the results of the simulation.

Freund, H. P.; Haber, I.; Palmadesso, P.; Papadopoulos, K.

1980-03-01

328

Anomalous skin effects in a weakly magnetized degenerate electron plasma  

NASA Astrophysics Data System (ADS)

Fully relativistic analysis of anomalous skin effects for parallel propagating waves in a weakly magnetized degenerate electron plasma is presented and a graphical comparison is made with the results obtained using relativistic Maxwellian distribution function [G. Abbas, M. F. Bashir, and G. Murtaza, Phys. Plasmas 18, 102115 (2011)]. It is found that the penetration depth for R- and L-waves for degenerate case is qualitatively small in comparison with the Maxwellian plasma case. The quantitative reduction due to weak magnetic field in the skin depth in R-wave for degenerate plasma is large as compared to the non-degenerate one. By ignoring the ambient magnetic field, previous results for degenerate field free case are salvaged [A. F. Alexandrov, A. S. Bogdankevich, and A. A. Rukhadze, Principles of Plasma Electrodynamics (Springer-Verlag, Berlin/Heidelberg, 1984), p. 90].

Abbas, G.; Sarfraz, M.; Shah, H. A.

2014-09-01

329

Electron-cyclotron-resonance (ECR) plasma thruster research  

NASA Technical Reports Server (NTRS)

An experimental apparatus to scientifically investigate the process of Electron-Cyclotron-Resonance (ECR) plasma acceleration has been tested. The apparatus consists of a vacuum facility, a 20 kW microwave power supply, and an argon ECR plasma thruster. Present instrumentation allows measurement of microwave input power, reflected power, propellant flow rate, and static pressure in the vacuum tank. In initial tests, an argon ECR plasma has been initiated repeatably at power levels ranging from 0.3 to 7.0 kW. The ECR plasma appears to diverge and separate from the applied magnetic field as predicted by theory. These tests suggest that the ECR plasma acceleration concept can be studied scientifically in the new apparatus.

Sercel, Joel C.

1988-01-01

330

Numerical study of a dust-contaminated electron plasma  

NASA Astrophysics Data System (ADS)

The collective behaviour of dusty plasmas is heavily affected by the presence of a small fraction of micrometric or sub-micrometric dust particles which collect a large surface charge. While dusty plasmas under study are usually quasi-neutral, we propose here an investigation on a magnetized nonneutral plasma (a situation found for example in Penning traps) where a conventional plasma with a single sign of charge (e.g. electrons) is contaminated by a dust population. We simulate the two-dimensional dynamics of such a plasma in the plane orthogonal to a homogeneous magnetic field with a tailored Particle-In-Cell code implementing a mass-less fluid (drift-Poisson) approximation for electrons and a kinetic description for the dust component, including gravity effects. Simulations with a range of initial conditions are performed to observe the influence of dust on the diocotron instability developing in the electron plasma. The early stage of the growth of diocotron modes is analyzed by Fourier decomposition. The fully non-linear evolution is studied by means of a statistical analysis of probability density functions and flatness of spatial vorticity increments in order to characterize the intermittency properties of the turbulence. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.

Maero, Giancarlo; Rom, Massimiliano; Lepreti, Fabio; Cavenago, Marco

2014-10-01

331

Plasma-beta dependence of the fast reconnection mechanism in an initially force-free current sheet  

SciTech Connect

The present paper systematically studies the spontaneous fast reconnection mechanism in an initially force-free current sheet in a wide range of plasma beta ({beta}); in our previous work it was studied for a special case of {beta} = 0.15. In each case, the evolution as well as the resulting structure of the fast reconnection is qualitatively similar to the one that was already reported for the case of {beta} = 0.15. Quantitatively, the fast reconnection evolution becomes more rapid and drastic for the lower plasma beta. For the cases of very low plasma beta ({beta} = 0.01 or 0.02), the plasma temperature is extremely enhanced to the value almost 1/{beta} times larger than its initial value in the resulting fast reconnection jet and large-scale plasmoid regions. Once the fast reconnection mechanism is ignited in a local spot-like region, its basic structure eventually established is sustained almost steadily, giving rise to the plasmoid swelling with time and propagating outwards. Accordingly, the characteristic reconnection regions, where plasma thermodynamic quantities are remarkably enhanced, rapidly expand in all (x, y, and z) directions in Alfven time scales, which may be responsible for the explosive expansion of large flares as well as for the distinct plasma heating observed in the solar corona.

Ugai, M. [Research Center for Space and Cosmic Evolution, Ehime University, Matsuyama 790-8577 (Japan)

2011-10-15

332

Influence of electron injection into 27 cm audio plasma cell on the plasma diagnostics  

SciTech Connect

In this article, the plasma is created in a Pyrex tube (L = 27 cm, ?= 4 cm) as a single cell, by a capacitive audio frequency (AF) discharge (f = 10100 kHz), at a definite pressure of ?0.2 Torr. A couple of tube linear and deviating arrangements show plasma characteristic conformity. The applied AF plasma and the injection of electrons into two gas mediums Ar and N{sub 2} revealed the increase of electron density at distinct tube regions by one order to attain 10{sup 13}/cm{sup 3}. The electrons temperature and density strengths are in contrast to each other. While their distributions differ along the plasma tube length, they show a decaying sinusoidal shape where their peaks position varies by the gas type. The electrons injection moderates electron temperature and expands their density. The later highest peak holds for the N{sub 2} gas, at electrons injection it changes to hold for the Ar. The sinusoidal decaying density behavior generates electric fields depending on the gas used and independent of tube geometry. The effect of the injected electrons performs a responsive impact on electrons density not attributed to the gas discharge. Analytical tools investigate the interaction of the plasma, the discharge current, and the gas used on the electrodes. It points to the emigration of atoms from each one but for greater majority they behave to a preferred direction. Meanwhile, only in the linear regime, small percentage of atoms still moves in reverse direction. Traces of gas atoms revealed on both electrodes due to sheath regions denote lack of their participation in the discharge current. In addition, atoms travel from one electrode to the other by overcoming the sheaths regions occurring transportation of particles agglomeration from one electrode to the other. The electrons injection has contributed to increase the plasma electron density peaks. These electrons populations have raised the generated electrostatic fields assisting the elemental ions emigration to a preferred electrode direction. Regardless of plasma electrodes positions and plasma shape, ions can be departed from one electrode to deposit on the other one. In consequence, as an application the AF plasma type can enhance the metal deposition from one electrode to the other.

Haleem, N. A.; Ragheb, M. S.; Zakhary, S. G. [Accelerators Department, Nuclear Research Center, AEA, Cairo 13759 (Egypt)] [Accelerators Department, Nuclear Research Center, AEA, Cairo 13759 (Egypt); El Fiki, S. A.; Nouh, S. A. [Faculty of Science, Ain Shams University, Cairo 11566 (Egypt)] [Faculty of Science, Ain Shams University, Cairo 11566 (Egypt); El Disoki, T. M. [Faculty of Girls, Ain Shams University, Cairo 11566 (Egypt)] [Faculty of Girls, Ain Shams University, Cairo 11566 (Egypt)

2013-08-15

333

Measurement of cold electrons in a pulsed inductively coupled plasma  

NASA Astrophysics Data System (ADS)

During the afterglow of a low pressure pulsed plasma, energetic electrons are rapidly lost to the walls while low energy electrons remain trapped within the ambipolar potential well, resulting in the fast cooling of the electron ensemble. In time, a collapse of the ambipolar potential occurs which depletes the electron energy distribution function in the high-energy range. Late in the afterglow, elastic electron-atom collisions are the only electron heating mechanism remaining. For a gas with poor thermal contact between gas atoms and electrons, diffusive cooling can cool electrons to temperatures around the gas temperature, and, in principle, even below that. We report direct measurements of cold electrons in the late afterglow that have been performed using a cylindrical Langmuir probe. The Laframboise model^1 has been employed to determine the electron temperatures. This work is supported by DOE under grant No. ER-54554. ^1 J. Laframboise, Theory of cylindrical and spherical Langmuir probes in a collisionless plasma at rest, in: Rarefied Gas Dynamics: P. 4th Int. Symp. Toronto/Canada 1964, vol.2, 22-43.

Hebert, Michael; Kortshagen, Uwe; Uhrlandt, Dirk

2003-10-01

334

Nonlinear electron-acoustic rogue waves in electron-beam plasma system with non-thermal hot electrons  

NASA Astrophysics Data System (ADS)

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, non-thermal hot electrons obeying a non-thermal distribution, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles on the electron beam and energetic population parameter are discussed. The results of the present investigation may be applicable in auroral zone plasma.

Elwakil, S. A.; El-hanbaly, A. M.; Elgarayh, A.; El-Shewy, E. K.; Kassem, A. I.

2014-11-01

335

Non-adiabatic Bouncing Ion Clusters in the Plasma Sheet Boundary Layer Observed by Cluster-CIS  

NASA Astrophysics Data System (ADS)

We report on ion beams injected into the plasma sheet boundary layer (at or near the separatrix) at distances greater than 39 Re and up to 169 Re that bounced several times back and forth (up to three echoes) while remaining in coherent bunches before thermalizing in the central plasma sheet (CPS). These bouncing ion clusters (BIC) interacted with the far-tail current sheet with a possible curvature parameter, kappa, of less than 2. The existence of these BIC shows that ion beams can interact several times non-adiabatically with the far-tail current sheet and still remain coherent. Owing to the large-scale ExB drift, echoes also appeared in the CPS after several bounces. The echoes had higher energies compared to the initially injected ion cluster which can be attributed to additional non-adiabatic acceleration during their second and third interaction with the tail current sheet. After multiple bounces, the ion cluster became thermalized isotropic plasma mixing with the CPS. BIC events were identified on the basis of the energy dispersion slopes associated with the ions. Simple model calculations showed, however, that in the case of these far-tail ion injections the 1:3:5:etc.-ratios of travel distances for echoes, used as diagnostics for near-Earth adiabatic BIC, are not valid. This is largely due to a significant shortening of the tail field lines, caused by Earthward convection, during the large ion travel times. The model calculations also reproduced newly observed properties such as concave dispersion slopes for the echoes. Furthermore, we argue here that the energy dispersion of the BIC was dominated by a time-of-flight effect. The injection region for BIC events, determined on the basis of this time-of-flight interpretation, covered a broad range of X (GSE)=26-40 Re. BIC events were dominantly observed during the substorm recovery phase and during quiet geomagnetic activity. We conclude that these nonadiabatic BIC are different from the adiabatic BIC that are routinely reported in the CPS.

Keiling, A.; Parks, G.; Reme, H.; Dandouras, I.; Bosqued, J.; Wilber, M.; McCarthy, M.; Kistler, L.; Mouikis, C.; Klecker, B.; Korth, A.; Lundin, R.; Frey, H.

2005-12-01

336

Analysis of electron beam damage of exfoliated MoS2 sheets and quantitative HAADF-STEM imaging.  

PubMed

In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200kV. Structural damage of the MoS2 sheets has been controlled at 80kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron-matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers. PMID:24929924

Garcia, Alejandra; Raya, Andres M; Mariscal, Marcelo M; Esparza, Rodrigo; Herrera, Miriam; Molina, Sergio I; Scavello, Giovanni; Galindo, Pedro L; Jose-Yacaman, Miguel; Ponce, Arturo

2014-11-01

337

Electron cooling in decaying low-pressure plasmas  

NASA Astrophysics Data System (ADS)

A simple analytical fluid dynamic model is developed for evaporative electron cooling in a low-pressure decaying plasma and compared to a two-dimensional simulation and experimental data for the particular case of argon. Measured electron temperature and density developments are fully reproduced by the ab initio model and the simulation. Further, it is shown that in the late afterglow thermalization of electrons occurs by coupling to the ion fluid via Coulomb collisions at sufficiently high electron densities and not by coupling to the neutral background.

Celik, Yusuf; Tsankov, Tsanko V.; Aramaki, Mitsutoshi; Yoshimura, Shinji; Luggenhlscher, Dirk; Czarnetzki, Uwe

2012-04-01

338

Propagation of energetic electrons in a hollow plasma fiber  

SciTech Connect

Transport of energetic electrons in a hollow plasma fiber is investigated. The high-current electron beam induces in the fiber strong radial electric fields and azimuthal magnetic fields on the inner and outer surfaces of the hollow fiber. The hot electrons are pushed out by the surface magnetic field and returned into the fiber by the sheath electric field. Imbalance of the latter fields can drive chaotic oscillations of electrons around the fiber wall. Intense thin return-current layers inside both the inner and outer wall surfaces are observed. This enhances local joule heating around both surfaces by the return current.

Zhou, C. T.; He, X. T. [Institute of Applied Physics and Computational Mathematics, Beijing 100094 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Chew, L. Y. [Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Nanyang Avenue, Singapore 639798 (Singapore)

2010-08-02

339

Relativistic electron-beam generation in a plasma-filled diode and its interaction with plasma  

NASA Astrophysics Data System (ADS)

A relativistic electron beam of 150-300 keV, 1-2 kA, and 40-80 ns generated in a plasma-filled diode is injected into a magnetized hydrogen plasma of density 10 to the 11th to 10 to the 14th/cu cm. Beam-plasma interaction was observed to be strong when the plasma density in the diode and interaction region was about 10 to the 12th/cu cm. The effective collision frequency was estimated to be around 0.01 times the ion plasma frequency. The plasma heating levels of about 10 to the 16th eV/cu cm/microsec were inferred. The observed net current multiplication was explained by two-stream instability.

Rao, G. Venugopala; Paithankar, A. S.; Iyyengar, S. K.

1991-03-01

340

Time evolution of nonplanar electron acoustic shock waves in a plasma with superthermal electrons  

NASA Astrophysics Data System (ADS)

The propagation of cylindrical and spherical electron acoustic (EA) shock waves in unmagnetized plasmas consisting of cold fluid electrons, hot electrons obeying a superthermal distribution and stationary ions, has been investigated. The standard reductive perturbation method (RPM) has been employed to derive the cylindrical/spherical Korteweg-de-Vries-Burger (KdVB) equation which governs the dynamics of the EA shock structures. The effects of nonplanar geometry, plasma kinematic viscosity and electron suprathermality on the temporal evolution of the cylindrical and spherical EA shock waves are numerically examined.

Pakzad, Hamid Reza; Javidan, Kurosh; Tribeche, Mouloud

2014-07-01

341

Influence of electron evaporative cooling on ultracold plasma expansion  

SciTech Connect

The expansion of ultracold neutral plasmas (UCP) is driven primarily by the thermal pressure of the electron component and is therefore sensitive to the electron temperature. For typical UCP spatial extents, evaporative cooling has a significant influence on the UCP expansion rate at lower densities (less than 10{sup 8}/cm{sup 3}). We studied the effect of electron evaporation in this density range. Owing to the low density, the effects of three-body recombination were negligible. We modeled the expansion by taking into account the change in electron temperature owing to evaporation as well as adiabatic expansion and found good agreement with our data. We also developed a simple model for initial evaporation over a range of ultracold plasma densities, sizes, and electron temperatures to determine over what parameter range electron evaporation is expected to have a significant effect. We also report on a signal calibration technique, which relates the signal at our detector to the total number of ions and electrons in the ultracold plasma.

Wilson, Truman; Chen, Wei-Ting; Roberts, Jacob [Department of Physics, Colorado State University, Fort Collins, Colorado 80523 (United States)] [Department of Physics, Colorado State University, Fort Collins, Colorado 80523 (United States)

2013-07-15

342

Electron collision cross-section data for plasma modeling  

SciTech Connect

Electron collisions provide the driving mechanism behind the plasma processes employed in semiconductor manufacturing and related industries. The radicals and ions produced by the collisions of electrons with the feed gas interact with the surface through a series of complex chemical reactions, leading to etching, deposition, or cleaning. Thus electron collision data are just as important as data on heterogeneous surface reactions in understanding and controlling such processes. Here, an overview of the current status in electron collision cross section databases for plasma modeling is presented. Emphasis is on dissociation, ionization, and dissociative ionization. The effect of the operating conditions on the relative importance of different collision mechanisms is discussed. For high density plasmas with low gas pressure, a second collision with electrons becomes likely and metastable states may play a role in the dissociation and ionization processes. A number of outstanding theoretical and experimental issues in the cross-section data are discussed. For the total ionization cross section, a four=parameter fitting formulate is found to represent the numerical data well and the parameters for some molecules used in plasma modeling are presented.

Huo, W.M.; Kim, Y.K.

1999-10-01

343

CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES  

SciTech Connect

We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60 Degree-Sign ) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio bursts and accompanied by wide (>212 Degree-Sign ) and fast (>1400 km s{sup -1}) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in situ by the spacecraft to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.

Agueda, N.; Sanahuja, B. [Departament d'Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki (Finland); Dalla, S. [Jeremiah Horrocks Institute, University of Central Lancashire (United Kingdom); Lario, D. [Applied Physics Laboratory, Johns Hopkins University (United States)

2013-03-10

344

High current, low pressure plasma cathode electron gun  

Microsoft Academic Search

A plasma-cathode electron gun based on a moderate pressure (>5 mTorr) cold-cathode discharge and a high perveance, multiaperture accelerator was previously developed at Hughes Research Laboratories and produced electron beam currents of up to 1 kA at voltages of over 200 kV for pulse lengths of 100 mus. This gun was limited in pulse repetition frequency and duty by the

Dan M. Goebel; Ron M. Watkins

2000-01-01

345

Spectral line broadening by relativistic electrons in plasmas: Collision operator  

NASA Astrophysics Data System (ADS)

In the present work we compute the real part of the impact collision operator for the electron broadening of ion lines in plasmas, taking into account relativistic effects in the dynamics of the perturbing electron. Specifically two relativistic effects are included: The modification of the trajectory due to non-Newtonian mechanics and the modification of the velocity distribution (Maxwell-Juttner). The results are compared to the non-relativistic case.

Naam, A.; Meftah, M. T.; Douis, S.; Alexiou, S.

2014-10-01

346

Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument  

NASA Astrophysics Data System (ADS)

We present the observations of energetic neutral atoms (ENAs) produced at the lunar surface in the Earth's magnetotail. When the Moon was located in the terrestrial plasma sheet, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) detected hydrogen ENAs from the Moon. Analysis of the data from CENA together with the Solar Wind Monitor (SWIM) onboard Chandrayaan-1 reveals the characteristic energy of the observed ENA energy spectrum (the e-folding energy of the distribution function) 100 eV and the ENA backscattering ratio (defined as the ratio of upward ENA flux to downward proton flux) <0.1. These characteristics are similar to those of the backscattered ENAs in the solar wind, suggesting that CENA detected plasma sheet particles backscattered as ENAs from the lunar surface. The observed ENA backscattering ratio in the plasma sheet exhibits no significant difference in the Southern Hemisphere, where a large and strong magnetized region exists, compared with that in the Northern Hemisphere. This is contrary to the CENA observations in the solar wind, when the backscattering ratio drops by 50% in the Southern Hemisphere. Our analysis and test particle simulations suggest that magnetic shielding of the lunar surface in the plasma sheet is less effective than in the solar wind due to the broad velocity distributions of the plasma sheet protons.

Harada, Yuki; Futaana, Yoshifumi; Barabash, Stas; Wieser, Martin; Wurz, Peter; Bhardwaj, Anil; Asamura, Kazushi; Saito, Yoshifumi; Yokota, Shoichiro; Tsunakawa, Hideo; Machida, Shinobu

2014-05-01

347

Low Energy Electrons in the Mars Plasma Environment  

NASA Astrophysics Data System (ADS)

The ionosphere of Mars is rather poorly understood. The only direct measurements were performed by the Viking 1 and 2 landers in 1976, both of which carried a Retarding Potential Analyzer. The RPA was designed to measure ion properties during the descent, although electron fluxes were estimated from changes in the ion currents. Using these derived low-energy electron fluxes, Mantas and Hanson studied the photoelectron and the solar wind electron interactions with the atmosphere and ionosphere of Mars. Unanswered questions remain regarding the origin of the low-energy electron fluxes in the vicinity of the Mars plasma boundary. Crider, in an analysis of Mars Global Surveyor Magnetometer/Electron Reflectometer measurements, has attributed the formation of the magnetic pile-up boundary to electron impact ionization of exospheric neutral species by solar wind electrons. However, the role of photoelectrons escaping from the lower ionosphere was not determined. In the proposed work, we will examine the role of solar wind and ionospheric photoelectrons in producing ionization in the upper ionosphere of Mars. Low-energy (< 4 keV) electrons will be modeled using the two-stream electron transport code of Link. The code models both external (solar wind) and internal (photoelectron) sources of ionization, and accounts for Auger electron production. The code will be used to analyze Mars Global Surveyor measurements of solar wind and photoelectrons down to altitudes below 200 km in the Mars ionosphere, in order to determine the relative roles of solar wind and escaping photoelectrons in maintaining plasma densities in the region of the Mars plasma boundary.

Link, Richard

2001-05-01

348

Low Energy Electrons in the Mars Plasma Environment  

NASA Technical Reports Server (NTRS)

The ionosphere of Mars is rather poorly understood. The only direct measurements were performed by the Viking 1 and 2 landers in 1976, both of which carried a Retarding Potential Analyzer. The RPA was designed to measure ion properties during the descent, although electron fluxes were estimated from changes in the ion currents. Using these derived low-energy electron fluxes, Mantas and Hanson studied the photoelectron and the solar wind electron interactions with the atmosphere and ionosphere of Mars. Unanswered questions remain regarding the origin of the low-energy electron fluxes in the vicinity of the Mars plasma boundary. Crider, in an analysis of Mars Global Surveyor Magnetometer/Electron Reflectometer measurements, has attributed the formation of the magnetic pile-up boundary to electron impact ionization of exospheric neutral species by solar wind electrons. However, the role of photoelectrons escaping from the lower ionosphere was not determined. In the proposed work, we will examine the role of solar wind and ionospheric photoelectrons in producing ionization in the upper ionosphere of Mars. Low-energy (< 4 keV) electrons will be modeled using the two-stream electron transport code of Link. The code models both external (solar wind) and internal (photoelectron) sources of ionization, and accounts for Auger electron production. The code will be used to analyze Mars Global Surveyor measurements of solar wind and photoelectrons down to altitudes below 200 km in the Mars ionosphere, in order to determine the relative roles of solar wind and escaping photoelectrons in maintaining plasma densities in the region of the Mars plasma boundary.

Link, Richard

2001-01-01

349

Collisionless forced magnetic reconnection in an electron-positron plasma  

SciTech Connect

Collisionless forced magnetic reconnection in an electron-positron plasma, where the mechanism of the magnetic field breaking is inertia of plasma particles, is considered. The model under analytical investigation is the so-called Taylor problem: a tearing stable slab plasma equilibrium with a magnetic field reversal is subjected to a small-amplitude boundary perturbation that drives magnetic reconnection at the neutral surface within the plasma. It is shown that forced collisionless reconnection has a direct analogy with its collisional (resistive) counterpart investigated by T. S. Hahm and R. M. Kulsrud [Phys. Fluids 28, 2412 (1985)], with the role of the inverse Lundquist number S{sup -1}<<1 of the resistive magnetohydrodynamics now being played by the normalized inertia skin depth d{identical_to}(c/{omega}{sub p}a)<<1 ({omega}{sub p} is the electron-positron plasma frequency, and a is a width of the plasma slab). The transition between the collisionless and resistive regimes of forced reconnection is also considered.

Hosseinpour, M.; Vekstein, G. [Jodrel Bank Center for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

2008-02-15

350

Strong plasma screening in thermonuclear reactions: Electron drop model  

E-print Network

We analyze enhancement of thermonuclear fusion reactions due to strong plasma screening in dense matter using a simple electron drop model. The model assumes fusion in a potential that is screened by an effective electron cloud around colliding nuclei (extended Salpeter ion-sphere model). We calculate the mean field screened Coulomb potentials for atomic nuclei with equal and nonequal charges, appropriate astrophysical S factors, and enhancement factors of reaction rates. As a byproduct, we study analytic behavior of the screening potential at small separations between the reactants. In this model, astrophysical S factors depend not only on nuclear physics but on plasma screening as well. The enhancement factors are in good agreement with calculations by other methods. This allows us to formulate the combined, pure analytic model of strong plasma screening in thermonuclear reactions. The results can be useful for simulating nuclear burning in white dwarfs and neutron stars.

P. A. Kravchuk; D. G. Yakovlev

2014-01-11

351

Strong plasma screening in thermonuclear reactions: Electron drop model  

NASA Astrophysics Data System (ADS)

We analyze enhancement of thermonuclear fusion reactions due to strong plasma screening in dense matter using a simple electron drop model. In the model we assume fusion in a potential that is screened by an effective electron cloud around colliding nuclei (extended Salpeter ion-sphere model). We calculate the mean-field screened Coulomb potentials for atomic nuclei with equal and nonequal charges, appropriate astrophysical S factors, and enhancement factors of reaction rates. As a byproduct, we study the analytic behavior of the screening potential at small separations between the reactants. In this model, astrophysical S factors depend not only on nuclear physics but on plasma screening as well. The enhancement factors are in good agreement with calculations by other methods. This allows us to formulate a combined, pure analytic model of strong plasma screening in thermonuclear reactions. The results can be useful for simulating nuclear burning in white dwarfs and neutron stars.

Kravchuk, P. A.; Yakovlev, D. G.

2014-01-01

352

Strong plasma screening in thermonuclear reactions: Electron drop model  

E-print Network

We analyze enhancement of thermonuclear fusion reactions due to strong plasma screening in dense matter using a simple electron drop model. The model assumes fusion in a potential that is screened by an effective electron cloud around colliding nuclei (extended Salpeter ion-sphere model). We calculate the mean field screened Coulomb potentials for atomic nuclei with equal and nonequal charges, appropriate astrophysical S factors, and enhancement factors of reaction rates. As a byproduct, we study analytic behavior of the screening potential at small separations between the reactants. In this model, astrophysical S factors depend not only on nuclear physics but on plasma screening as well. The enhancement factors are in good agreement with calculations by other methods. This allows us to formulate the combined, pure analytic model of strong plasma screening in thermonuclear reactions. The results can be useful for simulating nuclear burning in white dwarfs and neutron stars.

Kravchuk, P A

2014-01-01

353

Thermalization of a nonequilibrium electron-positron-photon plasma  

E-print Network

Starting from a nonequilibrium configuration we analyse the essential role of the direct and the inverse binary and triple interactions in reaching an asymptotic thermal equilibrium in a homogeneous isotropic electron-positron-photon plasma. We focus on energies in the range 0.1--10 MeV. We numerically integrate the integro-partial differential relativistic Boltzmann equation with the exact QED collisional integrals taking into account all binary and triple interactions in the plasma. We show that first, when detailed balance is reached for all binary interactions on a timescale $t_{k}\\lesssim10^{-14}$sec, photons and electron-positron pairs establish kinetic equilibrium. Successively, when triple interactions fulfill the detailed balance on a timescale $t_{eq}\\lesssim10^{-12}$sec, the plasma reaches thermal equilibrium. It is shown that neglecting the inverse triple interactions prevents reaching thermal equilibrium. Our results obtained in the theoretical physics domain also find application in astrophysics and cosmology.

A. G. Aksenov; R. Ruffini; G. V. Vereshchagin

2007-07-22

354

Magnetically Controlled Optical Plasma Waveguide for Electron Acceleration  

SciTech Connect

In order to produce multi-Gev electrons from Laser Wakefield Accelerators, we present a technique to guide high power laser beams through underdense plasma. Experimental results from the Jupiter Laser Facility at the Lawrence Livermore National Laboratory that show density channels with minimum plasma densities below 5 x 10{sup 17} cm{sup -3} are presented. These results are obtained using an external magnetic field (<5 T) to limit the radial heat flux from a pre-forming laser beam. The resulting increased plasma pressure gradient produces a parabolic density gradient which is tunable by changing the external magnetic field strength. These results are compared with 1-D hydrodynamic simulations, while quasi-static kinetic simulations show that for these channel conditions 90% of the energy in a 150 TW short pulse beam is guided over 5 cm and predict electron energy gains of 3 GeV.

Pollock, B B; Froula, D H; Tynan, G R; Divol, L; Davis, P; Palastro, J P; Price, D; Glenzer, S H

2008-08-28

355

Plasma oscillations of massless Dirac electrons in a planar superlattice  

NASA Astrophysics Data System (ADS)

The spectrum of plasma oscillations in a lateral superlattice of massless Dirac electrons has been calculated in the weak coupling approximation. The intensity of absorption of electromagnetic waves by plasmons of the superlattice at frequencies near the edges of band gaps has been found.

Chaplik, A. V.

2014-10-01

356

Experimental Studies of Self Organization with Electron Plasmas  

SciTech Connect

During the period of this grant we had a very active research effort in our group on the topic of 2D electron plasmas, relaxation, 2D Navier Stokes turbulence, and related issues. The project also motivated other studies we carried out such as a study of 2D turbulence with two-species vorticity.

Matthaeus, William H. [University of Delaware] [University of Delaware

2011-04-11

357

Gamma flashes from relativistic electron-positron plasma droplets  

E-print Network

Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes

Munshi G. Mustafa; B. Kampfer

2008-09-15

358

Electron densities near Io from Galileo plasma wave observations  

Microsoft Academic Search

This paper presents an overview of electron densities obtained near Io from the Galileo plasma wave instrument during the first four flybys of Io. These flybys were 10, which was a downstream wake pass that occurred on December 7, 1995; I24, which was an upstream pass that occurred on October 11, 1999; I25 which was a south polar pass that

D. A. Gurnett; A. M. Persoon; W. S. Kurth; A. Roux; S. J. Bolton

2001-01-01

359

Plasma heating, plasma flow and wave production around an electron beam injected into the ionosphere  

NASA Technical Reports Server (NTRS)

A brief historical summary of the Minnesota ECHO series and other relevant electron beam experiments is given. The primary purpose of the ECHO experiments is the use of conjugate echoes as probes of the magnetosphere, but beam-plasma and wave studies were also made. The measurement of quasi-dc electric fields and ion streaming during the ECHO 6 experiment has given a pattern for the plasma flow in the hot plasma region extending to 60m radius about the ECHO 6 electron beam. The sheath and potential well caused by ion orbits is discussed with the aid of a model which fits the observations. ELF wave production in the plasma sheath around the beam is briefly discussed. The new ECHO 7 mission to be launched from the Poker Flat range in November 1987 is described.

Winckler, J. R.; Erickson, K. N.

1986-01-01

360

Langmuir oscillations in a nonextensive electron-positron plasma.  

PubMed

The Langmuir oscillations, Landau damping, and growing unstable modes in an electron-positron (EP) plasma are studied by using the Vlasov and Poisson's equations in the context of the Tsallis's nonextensive statistics. Logically, the properties of the Langmuir oscillations in a nonextensive EP plasma are remarkably modified in comparison with that of discussed in the Boltzmann-Gibbs statistics, i.e., the Maxwellian plasmas, because of the system under consideration is essentially a plasma system in a nonequilibrium stationary state with inhomogeneous temperature. It is found that by decreasing the nonextensivity index q which corresponds to a plasma with excess superthermal particles, the phase velocity of the Langmuir waves increases. In particular, depend on the degree of nonextensivity, both of damped and growing oscillations are predicted in a collisionless EP plasma, arise from a resonance phenomena between the wave and the nonthermal particles of the system. Here, the mechanism leads to the unstable modes is established in the context of the nonextensive formalism yet the damping mechanism is the same developed by Landau. Furthermore, our results have the flexibility to reduce to the solutions of an equilibrium Maxwellian EP plasma (extensive limit q?1), in which the Langmuir waves are only the Landau damped modes. PMID:23767648

Saberian, E; Esfandyari-Kalejahi, A

2013-05-01

361

Ion and electron-acoustic solitons in two-electron temperature space plasmas  

Microsoft Academic Search

Properties of ion- and electron-acoustic solitons are investigated in an unmagnetized multicomponent plasma system consisting of cold and hot electrons and hot ions using the Sagdeev pseudopotential technique. The analysis is based on fluid equations and the Poisson equation. Solitary wave solutions are found when the Mach numbers exceed some critical values. The critical Mach numbers for the ion-acoustic solitons

G. S. Lakhina; A. P. Kakad; S. V. Singh; F. Verheest

2008-01-01

362

Electron densities in the upper ionosphere of Mars from the excitation of electron plasma oscillations  

E-print Network

spacecraft, which was placed in a highly eccentric orbit around Mars on 25 December 2003 [Chicarro et alElectron densities in the upper ionosphere of Mars from the excitation of electron plasma to remote radio sounding of the ionosphere of Mars, the MARSIS (Mars Advanced Radar for Subsurface

Gurnett, Donald A.

363

Feedback control of plasma electron density and ion energy in an inductively coupled plasma etcher  

SciTech Connect

Here the authors report the development of a fuzzy logic based feedback control of the plasma electron density and ion energy for high density plasma etch process. The plasma electron density was measured using their recently developed transmission line microstrip microwave interferometer mounted on the chamber wall, and the rf voltage was measured by a commercial impedance meter connected to the wafer stage. The actuators were two 13.56 MHz rf power generators which provided the inductively coupled plasma power and bias power, respectively. The control system adopted the fuzzy logic control algorithm to reduce frequent actuator action resulting from measurement noise. The experimental results show that the first wafer effect can be eliminated using closed-loop control for both poly-Si and HfO{sub 2} etching. In particular, for the HfO2 etch, the controlled variables in this work were much more effective than the previous one where ion current was controlled, instead of the electron density. However, the pressure disturbance effect cannot be reduced using plasma electron density feedback.

Lin Chaung; Leou, K.-C.; Huang, H.-M.; Hsieh, C.-H. [Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan 30043 (China)

2009-01-15

364

Betatron radiation from electron beams in plasma focusing channels  

SciTech Connect

Spontaneous radiation emitted from an electron undergoing betatron motion is a plasma focusing channel is analyzed and applications to plasma wakefield accelerator experiments and to the ion channel laser (ICL) are discussed. Important similarities and differences between a free electron laser (FEL) and in an ICL are delineated. It is shown that the frequency of spontaneous radiation is a strong function of the betatron strength parameter a{sub {beta}}, which plays a similar role to that of the wiggler strength parameter in a conventional FEL. For a{sub {beta}} {approx_gt} 1, radiation is emitted in numerous harmonics. Furthermore, a{sub {beta}} is proportional to the amplitude of the betatron orbit, which varies for every electron in the beam. This places serious limits on the possibility of realizing an ICL.

Esarey, E.; Catravas, P.; Leemans, W.P.

2000-06-01

365

Electron Densities Near Io from Galileo Plasma Wave Observations  

NASA Technical Reports Server (NTRS)

This paper presents an overview of electron densities obtained near Io from the Galileo plasma wave instrument during the first four flybys of Io. These flybys were Io, which was a downstream wake pass that occurred on December 7, 1995; I24, which was an upstream pass that occurred on October 11, 1999; I25, which was a south polar pass that occurred on November 26, 1999; and I27, which was an upstream pass that occurred on February 22, 2000. Two methods were used to measure the electron density. The first was based on the frequency of upper hybrid resonance emissions, and the second was based on the low-frequency cutoff of electromagnetic radiation at the electron plasma frequency. For three of the flybys, Io, I25, and I27, large density enhancements were observed near the closest approach to Io. The peak electron densities ranged from 2.1 to 6.8 x 10(exp 4) per cubic centimeters. These densities are consistent with previous radio occultation measurements of Io's ionosphere. No density enhancement was observed during the I24 flyby, most likely because the spacecraft trajectory passed too far upstream to penetrate Io's ionosphere. During two of the flybys, I25 and I27, abrupt step-like changes were observed at the outer boundaries of the region of enhanced electron density. Comparisons with magnetic field models and energetic particle measurements show that the abrupt density steps occur as the spacecraft penetrated the boundary of the Io flux tube, with the region of high plasma density on the inside of the flux tube. Most likely the enhanced electron density within the Io flux tube is associated with magnetic field lines that are frozen to Io by the high conductivity of Io's atmosphere, thereby enhancing the escape of plasma along the magnetic field lines that pass through Io's ionosphere.

Gurnett, D. A.; Persoon, A. M.; Kurth, W. S.; Roux, A.; Bolton, S. J.

2001-01-01

366

Growth in Electron Plasma Radius Caused By Fast Proton Beam*  

NASA Astrophysics Data System (ADS)

A slightly warmed nonneutral electron plasma is stabilized in a long-lived state with slow particle loss to the trap wall balanced by weak ionization of background gas. Sub-nanowatt power is input by noise, or a line source tuned below a resonance, while a rotating electric field provides compressional torque. From line charge density, extracted from the diocotron frequency, and plasma potential, extracted from a G-T mode frequency, a non-destructive measure of the plasma radius is obtained. When the plasma is bombarded by 0.2 GeV protons in the IUCF storage ring, this radius is observed to increase with proton current. The effect is insensitive to changes in beam position or angle relative to the plasma symmetry axis. Torque estimated from proton-electron Coulomb scatter is orders of magnitude too small to explain the observations. The mechanism for beam-induced radial growth remains unexplained. Progress toward torque calibration, and containment with higher magnetic field, will be described. *Work supported by US DOE (DE FG0297 ER 54433) & US NSF (PHY 96-02872, 94-23896).

Pollock, R. E.; Ellsworth, Jennifer; Muterspaugh, M. W.; Todd, D. S.

1999-11-01

367

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

Microsoft Academic Search

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

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

2010-01-01

368

Thermal equilibrium of a cryogenic magnetized pure electron plasma  

NASA Technical Reports Server (NTRS)

The thermal equilibrium correlation properties of a magnetically confined pure electron plasma (McPEP) are related to those of a one-component plasma (OCP). The N-particle spatial distribution rho sub s and the Helmholtz free energy F are evaluated for the McPEP to O(lambda sub d-squared/a-squared), where lambda sub d is the thermal de Broglie wavelength and is an interparticle spacing. The electron gyromotion is allowed to be fully quantized while the guiding center motion is quasi-classical. The distribution rho sub s is shown to be identical to that of a classical OCP with a slightly modified potential. To O(lambda sub d-squared/a-squared) this modification does not affect that part of F that is caused by correlations, as long as certain requirements concerning the size of the plasma are met. This theory is motivated by a current series of experiments that involve the cooling of a magnetically confined pure electron plasma to the cryogenic temperature range.

Dubin, D. H. E.; Oneil, T. M.

1986-01-01

369

Probing with PIC simulations the plasma dynamics of solar wind in a vicinity of the Heliospheric Current Sheet at various distances from the Sun  

NASA Astrophysics Data System (ADS)

There are number of peculiarities in the solar wind plasma dynamics observed around the sector boundaries at 1 AU which are shown to be most likely resulted from a quasi-continuous magnetic reconnection at the Heliocentric Current Sheet (HCS) (Zharkova, Khabarova, ApJ, 2012). In the current study we explore further a transformation of physical conditions in the HCS and compare the dynamics of observed characteristics of magnetic field, electrons and protons' in the HCS vicinity at different distances from the Sun and different times of the satellites' passing. By using different spacecraft's data gathered over the entire space era we analyze the radial and longitudinal transformation of the HCS shape and strength at different phases of the solar cycle. We carry out a comparison of the observed solar wind plasma parameters with those derived for particle and electro-magnetic fields dynamics from 3D PIC modeling and evaluate the level of turbulence inside the HCS occurring at different distances from the Sun.

Zharkova, Valentina; Khabarova, Olga; Kuznetsov, Vladimir; Dobranskis, Rytis

2014-05-01

370

Electron productions from short-pulse laser plasma interactions  

NASA Astrophysics Data System (ADS)

Characterization of hot electrons produced by ultra-intense laser-matter interactions is important not only to the understanding of laser plasma physics, but also to applications making use of the temporally short, broad spectrum of electrons. Using our newly built fiber-array-based compact electron spectrometer, we performed systematic measurements of electron production from various solid targets using the high intensity (10^17 to 10^21 W/cm^2) short pulse (< 100 fs) laser JanUSP at Lawrence Livermore National laboratory. The electron distributions obtained at various laser energies for different target materials and observation angles will be presented, together with a comparison with theoretical simulations using the Particle-in-cell(PIC) code. This work was performed under the auspices of DOE by UC-LLNL under contract W-7405-Eng-48. This project was funded by Laboratory Directed Research and Development (LDRD) Program (01-ER-100).

Chen, H.; Langdon, A. B.; Lasinski, B. F.; McLean, H.; Patel, P. K.; Price, D. F.; Still, C. H.; Young, B. K.

2002-11-01

371

Plasma Heating by an Electron Beam in Corrugated Magnetic Field  

Microsoft Academic Search

New experimental results from the multimirror trap GOL-3 are presented. Deuterium plasma of $~10^21 m^-3$ density is heated by a high power relativistic electron beam (peak parameters are ~1 MeV, ~25 kA, ~8 $\\\\mu$s, ~120 kJ). Magnetic system of the facility is a 12-meter-long axisymmetrical solenoid with corrugated magnetic field, which consists of 55 cells with $B_max\\/B_min$=4.8\\/3.2 T. Collective plasma

V. V. Postupaev; A. V. Arzhannikov; V. T. Astrelin; A. M. Averkov; A. D. Beklemishev; A. V. Burdakov; I. A. Ivanov; M. V. Ivantsivsky; V. S. Koidan; K. I. Mekler; S. V. Polosatkin; A. F. Rovenskikh; S. L. Sinitsky; Yu. S. Sulyaev; E. R. Zubairov

2004-01-01

372

Electron emission and plasma generation in a modulator electron gun using ferroelectric cathode  

NASA Astrophysics Data System (ADS)

Strong electron emission and dense plasma generation have been observed in a modulator electron gun with a Ba 0.67Sr 0.33TiO 3 ferroelectric cathode. Parameter of the modulator electron gun and lifetime of the ferroelectric cathode were investigated. It was shown that electron emission from Ba 0.67Sr 0.33TiO 3 cathode with a positive triggering pulse is a sort of plasma emission. Electrons were emitted by the co-effect of surface plasma and non-compensated negative polarization charges at the surface of the ferroelectric. The element analyses of the graphite collector after emission process was performed to show the ingredient of the plasma consist of Ba, Ti and Cu heavy cations of the ceramic compound and electrode. It was demonstrated the validity of the Child-Langmuir law by introducing the decrease of vacuum gap and increase of emission area caused by the expansion of the surface plasma.

Chen, Shutao; Zheng, Shuxin; Zhu, Ziqiu; Dong, Xianlin; Tang, Chuanxiang

2006-10-01

373

Beat wave excitation of electron plasma waves in a toroidal magnetized plasma  

SciTech Connect

Electrostatic waves are driven in a toroidal plasma by counterpropagating microwave beams with a difference in frequency approximately equal to the electron plasma frequency. Energetic electrons are detected when the phase velocity of the electrostatic waves are 3{ital v}{sub {ital e}}{lt} {ital v}{sub ph} {lt} 7{ital v}{sub {ital e}}, where {ital v}{sub {ital e}} is the electron thermal velocity. Experiments are performed in the Davis Diverted Torus (DDT) (Bull. Am. Phys. Soc. {bold 33}, 2049 (1988)) operating in a high repetition rate (15 Hz), low-density (7{times}10{sup 7}--2{times}10{sup 9} cm{sup {minus}3}) mode with only a toroidal magnetic field ({similar to}110 G). The microwaves are triggered 30 {mu}sec after the pulsed discharge ends. At this time the energetic electrons have left the system and the velocity distribution is Maxwellian ({ital T}{sub {ital e}} {similar to} 1 eV). The microwaves have tunable frequencies over the range 8.5--9.5 GHz, and peak powers {similar to}180 kW (400 nsec). Bounded plasma modes are excited when the electron cyclotron frequency is larger than the electron plasma frequency. Direct measurements of the wave vector have been made with a double probe antenna, from which the dispersion relation of the electrostatic wave can be obtained. The electron distribution is measured with an electrostatic energy analyzer. The electron velocity distribution function is found to be constant over an interval that extends well beyond the phase velocity of the wave.

Rogers, J.H.; Hwang, D.Q.; Thomas, J.C.; Horton, R.L.; Killeen, J. (Department of Applied Science, University of California, Davis and Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)); Dimonte, G. (Lawrence Livermore National Laboratory, Livermore, California 94550 (United States))

1992-07-01

374

Graphene sheets via microwave chemical vapor deposition  

Microsoft Academic Search

High-quality graphene sheets (GS) were synthesized on stainless steel substrates at ?500C by microwave plasma chemical vapor deposition (CVD) in an atmosphere of methane\\/hydrogen mixture. The GS product was characterized to contain mostly 1- or 23-layers using scanning electron microscopy, transmission electron microscopy\\/selective area electron diffraction, atomic force microscopy, and Raman spectroscopy. The present CVD approach is capable of producing

G. D. Yuan; W. J. Zhang; Y. Yang; Y. B. Tang; Y. Q. Li; J. X. Wang; X. M. Meng; Z. B. He; C. M. L. Wu; I. Bello; C. S. Lee; S. T. Lee

2009-01-01

375

Longitudinal modulation of hot electrons in the Io plasma torus  

NASA Astrophysics Data System (ADS)

The longitudinal modulation in the Io torus has been an open question for decades. A major clue was provided by the discovery of the key modulation of the hot electron population, at both the System III and System IV periods. However, very little progress has been made in explaining the origin of these hot electron modulations. We propose that the hot electrons population is powered by the inward motion of empty flux tubes (i.e. related to the outward transport of the Iogenic plasma), which has been observed in the torus. We propose that the System IV and System III modulation of the hot electron population corresponds to modulation of the intensity of the current system and of the efficiency of the electron acceleration, respectively. We build on the latest models of the Io current system to describe the current system associated with the motion of the empty flux tubes, and the associated electron acceleration. The System III modulation of the hot electron population, due to the modulation of the efficiency of the electron acceleration, can then be related to the topology of the magnetic field. We show through calculation and simulation that the electron acceleration related to the inward motion of the empty flux tube may explain the observations. We discuss the energy budget and show that it is in favor of our hypothesis.

Hess, S. L. G.; Delamere, P. A.; Bagenal, F.; Schneider, N.; Steffl, A. J.

2011-11-01

376

Thomson-scattering measurements of high electron temperature hohlraum plasmas for laser-plasma interaction studies  

SciTech Connect

Accurate measurements of the plasma conditions in laser-produced high-temperature plasmas have been achieved using the recently activated 4{omega} Thomson-scattering diagnostic at the Omega Laser Facility, Soures et al., Laser Part. Beams 11 (1993). These diagnostic measurements were performed in a new hohlraum target platform that will be used to study laser-plasma interaction in a strongly damped regime comparable to those occurring in indirect drive inertial confinement fusion plasmas. The Thomson-scattering spectra show the collective ion-acoustic features that fit the theory for two ion species plasmas allowing us to accurately and independently determine both the electron and ion temperatures. The electron temperature was found to range from 2 to 4 keV as the total heater beam energy deposited into the hohlraum was increased from 8 to 17 kJ. The results are compared to 2D hydrodynamic simulations using flux limited diffusion and nonlocal heat flux models. The target platform presented provides a novel test bed to investigate laser-plasma interaction physics in the strongly damped backscatter regime.

Froula, D.H.; Ross, J.S.; Divol, L.; Meezan, N.; MacKinnon, A.J.; Wallace, R.; Glenzer, S.H. [L-399, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)

2006-05-15

377

Characteristics of InGaP/InGaAs pseudomorphic high electron mobility transistors with triple delta-doped sheets  

SciTech Connect

Fundamental and insightful characteristics of InGaP/InGaAs double channel pseudomorphic high electron mobility transistors (DCPHEMTs) with graded and uniform triple {delta}-doped sheets are coomprehensively studied and demonstrated. To gain physical insight, band diagrams, carrier densities, and direct current characteristics of devices are compared and investigated based on the 2D semiconductor simulator, Atlas. Due to uniform carrier distribution and high electron density in the double InGaAs channel, the DCPHEMT with graded triple {delta}-doped sheets exhibits better transport properties, higher and linear transconductance, and better drain current capability as compared with the uniformly triple {delta}-doped counterpart. The DCPHEMT with graded triple {delta}-doped structure is fabricated and tested, and the experimental data are found to be in good agreement with simulated results.

Chu, Kuei-Yi [National Cheng-Kung University, Institute of Microelectronics, Department of Electrical Engineering (China); Chiang, Meng-Hsueh, E-mail: mhchiang@niu.edu.tw; Cheng, Shiou-Ying, E-mail: sycheng@niu.edu.tw [National II an University, Department of Electronic Engineering (China); Liu, Wen-Chau [National Cheng-Kung University, Institute of Microelectronics, Department of Electrical Engineering (China)

2012-02-15

378

Electron temperature and average density in spherical laser-produced plasmas - Ultraviolet plasma spectroscopy  

NASA Technical Reports Server (NTRS)

The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high-Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 microns) and the frequency-tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15-200 A. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency-tripled laser irradiation, Te = 2600 + or - 600 eV and Ne is greater than 6 x 10 to the 20th/cu cm. This is consistent with a 'flux limit' smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 micron) irradiation.

Goldsmith, S.; Seely, J. F.; Feldman, U.; Behring, W. E.; Cohen, L.

1985-01-01

379

Observations of underdense plasma lens focusing of relativistic electron beams  

SciTech Connect

Focusing of a 15 MeV, 19 nC electron bunch by an underdense plasma lens operated just beyond the threshold of the underdense condition has been demonstrated in experiments at the Fermilab NICADD Photoinjector Laboratory (FNPL). The strong 1.9 cm focal-length plasma-lens focused both transverse directions simultaneously and reduced the minimum area of the beam spot by a factor of 23. Analysis of the beam-envelope evolution observed near the beam waist shows that the spherical aberrations of this underdense lens are lower than those of an overdense plasma lens, as predicted by theory. Correlations between the beam charge and the properties of the beam focus corroborate this conclusion.

Thompson, M.C.; /UCLA /LLNL, Livermore; Badakov, H.; Rosenzweig, J.B.; Travish, G.; /UCLA; Fliller, R.; Kazakevich, G.M.; Piot, P.; Santucci, J.; /Fermilab; Li, J.; Tikhoplav, R.; /Rochester U.

2007-06-01

380

Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams  

DOEpatents

An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

Hershkowitz, Noah (Madison, WI); Longmier, Benjamin (Madison, WI); Baalrud, Scott (Madison, WI)

2009-03-03

381

Simulation of ultrashort electron pulse generation from optical injection into wake-field plasma waves  

E-print Network

Simulation of ultrashort electron pulse generation from optical injection into wake-field plasma are focused in a plasma, one exciting a wake-field electron plasma wave while another locally alters some was proposed [1]. These wake-field accelerators seek to take advantage of the ultra-high electron acceleration

Umstadter, Donald

382

Generation of Alfven waves by high power pulse at the electron plasma frequency  

E-print Network

Generation of Alfve´n waves by high power pulse at the electron plasma frequency B. Van Compernolle 2005; published 19 April 2005. [1] The interaction of a short high power pulse at the electron plasma of Alfve´n waves by high power pulse at the electron plasma frequency, Geophys. Res. Lett., 32, L08101, doi

California at Los Angles, University of

383

Non-Local Effects in a Bounded Afterglow Plasma with Fast Electrons  

E-print Network

Non-Local Effects in a Bounded Afterglow Plasma with Fast Electrons V. I. Demidov UES, inc. and WVU Electron Temperature and Density in the Afterglow (Post-Discharge) #12;UES Plasma Models · Fluid (continuum-local kinetic models At low pressure, when the plasma scale L is less than electron energy relaxation length

Kaganovich, Igor

384

Plasma electron temperature and the entropy effect on hydrogen production  

NASA Astrophysics Data System (ADS)

The thesis is that the interaction between the microwave induced electric field and a conductive material will produce plasma with high effective temperature such that it is thermodynamically and kinetically possible to produce small molecules from large molecules. The high effective temperature increases the potency of the entropy term such that small molecules are produced from large molecules even though the enthalpy for the process is positive. This hypothesis will be tested in several reactions for which the entropy change is positive. The plasma enhanced chemical reactions examined here may also be important in the practical application of alternative fuel production. The specific reactions of interest to this thesis are: (1) H 2O?H2 + 1/2 O2; DeltaGo ( kJ) = 247.5--0.056T, (2) 1/2 N2 + H2O? H2 + NO; DeltaGo (kJ) = 338.45--0.069T, (3) C + H2O ?Fe H2 + CO; Delta Go(kJ) = 135.8--0.143 T, (4) C6H 10O5 ? 5H2 + C + 5CO; DeltaGo( kJ) = 711.3--2.48T. Experiments are carried out to examine the chemical species present within the plasma by the optical emission spectrometer (OES) and in the resultant gas outflow by the flue gas analyzer as a function of incoming gas composition and composition of the solid materials at the point of plasma initiation. The chemical and plasma reactions observed experimentally will be compared to thermodynamic calculations as a method to test the hypothesis. In addition, hydrogen production from water and from water and nitrogen at elevated effective temperature produces products, which recombine with negative free energy change at lower temperatures. Based on our initial results, it is also necessary to hypothesize that spatiotemporal plasma discharges can produce molecular hydrogen and an associated oxidant at an elevated effective temperature such that the mixture is 'quenched' to a lower temperature where said mixture is kinetically stabilized against spontaneous recombination. In all experiments, the results from OES show that atomic hydrogen is produced in the plasma, and the results from flue-gas analyzer show that H 2 is a product from the reaction in the plasma. From the experimental results, the yield of H2 is increased with the increasing of the electron temperature in gas/gas plasma reactions having positive entropy. For solid/gas plasma reactions which DeltaSo is either positive or negative, there is no correlation between H2 yield and electron temperature. However, H2 yield from all plasma reactions is lower than the prediction from the van't Hoff equation. Based on an analysis of the Saha equation, the effective temperature of the chemical species in the plasma may be lower than the electron temperature, thus rationalizing our observation of reduced H2 yield. An alternative hypothesis is that the quenching rates of the products from the plasma are not fast enough to avoid recombination of the reaction products at low temperature, where the enthalpy term dominates.

Chakartnarodom, Parinya

385

Optical Spectroscopy of High Intensity Electron Beam Plasmas^1  

NASA Astrophysics Data System (ADS)

This talk will be an overview of spectroscopic results obtained on the RITS-6 accelerator at Sandia National Laboratories on the Self-Magnetic Pinch (SMP) electron beam diode. The SMP diode produces a focused (<3mm diameter), e-beam at 7MeV and 150kA, which is used as an intense, flash x-ray source. During the 45ns electron beam pulse, plasmas are generated on the electrode surfaces which propagate into the A-K vacuum gap, affecting the diode impedance, x-ray spectrum, and pulse-width. These plasmas are measured using a series of optical diagnostics including: streak cameras, ICCD cameras, and avalanche photodetectors. Visible spectroscopy is used to gather time and space information on these plasmas. Density and temperature calculations are made using detailed, time-dependent, collisional-radiative (CR) and radiation transport modelings. The results are then used in conjunction with hybrid PIC/fluid simulations to model the overall plasma behavior. Details regarding the data collection, system calibration, analyses, and interpretation of results will be presented. [4pt] ^1Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Johnston, Mark; Oliver, Bryan; Bruner, Nichelle; Welch, Dale; Maron, Yitzhak

2012-10-01

386

Temperature diagnostics of ECR plasma by measurement of electron bremsstrahlung  

SciTech Connect

The x-ray bremsstrahlung spectrum emitted by the electron population in a 14.5 GHz ECR plasma source has been measured using a NaI(Tl) detector, and hence the electron temperature of the higher energy electron population in the plasma has been determined. The x-ray spectra for Ne and Ar gases have been systematically studied as a function of inlet gas pressure from 7 Multiplication-Sign 10{sup -7} mbar to 7 Multiplication-Sign 10{sup -5} mbar and for input microwave power {approx}1 W to {approx}300 W. At the highest input power and optimum pressure conditions, the end point bremsstrahlung energies are seen to reach {approx}700 keV. The estimated electron temperatures (T{sub e}) were found to be in the range 20 keV-80 keV. The T{sub e} is found to be peaking at a pressure of 1 Multiplication-Sign 10{sup -5} mbar for both gases. The T{sub e} is seen to increase with increasing input power in the intermediate power region, i.e., between 100 and 200 W, but shows different behaviour for different gases in the low and high power regions. Both gases show very weak dependence of electron temperature on inlet gas pressure, but the trends in each gas are different.

Kasthurirangan, S. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Colaba, Mumbai 400005 (India); Department of Physics, Institute of Chemical Technology, Matunga, Mumbai 400019 (India); Agnihotri, A. N.; Desai, C. A.; Tribedi, L. C. [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Colaba, Mumbai 400005 (India)

2012-07-15

387

Temperature diagnostics of ECR plasma by measurement of electron bremsstrahlung  

NASA Astrophysics Data System (ADS)

The x-ray bremsstrahlung spectrum emitted by the electron population in a 14.5 GHz ECR plasma source has been measured using a NaI(Tl) detector, and hence the electron temperature of the higher energy electron population in the plasma has been determined. The x-ray spectra for Ne and Ar gases have been systematically studied as a function of inlet gas pressure from 7 10-7 mbar to 7 10-5 mbar and for input microwave power 1 W to 300 W. At the highest input power and optimum pressure conditions, the end point bremsstrahlung energies are seen to reach 700 keV. The estimated electron temperatures (Te) were found to be in the range 20 keV-80 keV. The Te is found to be peaking at a pressure of 1 10-5 mbar for both gases. The Te is seen to increase with increasing input power in the intermediate power region, i.e., between 100 and 200 W, but shows different behaviour for different gases in the low and high power regions. Both gases show very weak dependence of electron temperature on inlet gas pressure, but the trends in each gas are different.

Kasthurirangan, S.; Agnihotri, A. N.; Desai, C. A.; Tribedi, L. C.

2012-07-01

388

Modulation of continuous electron beams in plasma wake-fields  

SciTech Connect

In this paper we discuss the interaction of a continuous electron beam with wake-field generated plasma waves. Using a one-dimensional two fluid model, a fully nonlinear analytical description of the interaction is obtained. The phenomena of continuous beam modulation and wave period shortening are discussed. The relationship between these effects and the two-stream instability is also examined. 12 refs., 1 fig.

Rosenzweig, J.B.

1988-09-08

389

Electron cyclotron heating correlation with tokamak toroidal plasma rotation  

NASA Astrophysics Data System (ADS)

Toroidal rotation of the central plasma core has been observed prior to and during electron cyclotron heating (ECH) in the Doublet III tokamak [in Plasma Physics and Controlled Nuclear Fusion Research 1984, Proceedings of the Tenth International Conference, London (IAEA, Vienna, 1985), Vol. 1, p. 131]. Measurements were made using a curved-crystal Bragg x-ray spectrometer with spectral resolution of ?/?? of greater than 19 000 and temporal resolution of 20 msec. Ion rotation velocity was determined from the Doppler shift of x rays emitted from the plasma impurity Ti XXI resonance line. Ion temperatures were determined from the Doppler broadening of this line. A study of purely Ohmic discharges suggests that nonrotating discharges exhibit magnetohydrodynamic activity other than sawtooth oscillations, while those that rotate exhibit sawteeth. Discharges with plasma rotation prior to the appliction of ECH appear to heat more effectively than those that do not. Velocity and temperature histories show that there are temporal characteristics corresponding to whether the plasma was or was not effectively heated.

Lieber, A. J.; Snider, R. T.; Lee, Ping; Wojtowicz, S. S.

1988-03-01

390

Nonlocal effect of plasma resonances on the electron energy-distribution function in microwave plasma columns.  

PubMed

Spatially resolved trace rare gases optical emission spectroscopy was used to analyze the electron energy-distribution function (EEDF) in low-pressure argon plasma columns sustained by surface waves. At frequencies >1 GHz, in the microwave-sustained region, the EEDF departs from a Maxwellian, characterized by a depletion of low-energy electrons and a high-energy tail, whereas in the field-free zone, the EEDF is Maxwellian. Abnormal behavior of the EEDF results from the acceleration of low-energy electrons due to the conversion of surface waves into volume plasmons at the resonance point where the plasma frequency equals the wave frequency and their absorption by either collisional or Landau damping. PMID:23005484

Boudreault, O; Mattei, S; Stafford, L; Margot, J; Moisan, M; Khare, R; Donnelly, V M

2012-07-01

391

Nonlocal effect of plasma resonances on the electron energy-distribution function in microwave plasma columns  

NASA Astrophysics Data System (ADS)

Spatially resolved trace rare gases optical emission spectroscopy was used to analyze the electron energy-distribution function (EEDF) in low-pressure argon plasma columns sustained by surface waves. At frequencies >1 GHz, in the microwave-sustained region, the EEDF departs from a Maxwellian, characterized by a depletion of low-energy electrons and a high-energy tail, whereas in the field-free zone, the EEDF is Maxwellian. Abnormal behavior of the EEDF results from the acceleration of low-energy electrons due to the conversion of surface waves into volume plasmons at the resonance point where the plasma frequency equals the wave frequency and their absorption by either collisional or Landau damping.

Boudreault, O.; Mattei, S.; Stafford, L.; Margot, J.; Moisan, M.; Khare, R.; Donnelly, V. M.

2012-07-01

392

Electron distribution function of a weakly ionized plasma in homogeneous and stationary external fields  

NASA Astrophysics Data System (ADS)

An analytical expression is obtained for the electron distribution function of a weakly ionized plasma in external homogeneous and stationary electric and magnetic fields, with allowance for the ionization of atoms due to electron impact and electron escape from the plasma. The electron distribution function is then used to find the mobility tensor components of the plasma electrons. The frequency and increment of the oscillations are determined through an expansion in plane waves.

Avtiushkov, A. P.; Stekolnikov, A. F.

393

Cutoff effects of electron velocity distribution to the properties of plasma parameters near the plasma-sheath boundary  

SciTech Connect

The plasma properties under high thermodynamic non-equilibrium condition, established due to the presence of electrically biased electrode, are investigated. Assumption of electron cut-off velocity distribution function (VDF), as done by Andrews and Varey in their investigations of the sheath region [J. Phys. A 3, 413 (1970)], has been extended here to both plasma and sheath regions. Analytic expressions for the moments of electron VDF, as well as for the electron screening temperature function dependence on the plasma-sheath local potential are derived. In deriving the ion velocity distribution the ''standard'' assumption of strict plasma quasineutrality, or equivalently vanishing of the plasma Debye length, is employed, whereas the ions are assumed to be generated at rest over the plasma region. However, unlike the standard approach of solving the plasma equation, where pure Boltzmann electron density profile is used, here we employ modified Boltzmann's electron density profile, due to cutoff effect of the electron velocity distribution. It is shown that under these conditions the quasineutrality equation solution is characterised by the electric field singularity for any negative value of the electrode bias potential as measured with respect to the plasma potential. The point of singularity i.e., the plasma length and its dependence on the electrode bias and sheath potential is established for the particular case of ionization profile mechanism proportional to the local electron density. Relevant parameters for the kinetic Bohm criterion are explicitly calculated for both ions and electrons, for arbitrary electrode bias.

Jelic, N. [Association EURATOM-OeAW, Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)

2011-11-15

394

Multidimensional instability of electron-acoustic solitary waves in a magnetized plasma with vortexlike electron distribution  

SciTech Connect

The basic features of obliquely propagating electron-acoustic (EA) solitary waves and their multidimensional instability in a magnetized plasma containing cold electrons, hot electrons obeying a vortexlike distribution, and stationary ions have been theoretically investigated by the reductive perturbation method and small-k perturbation expansion technique. The combined effects of external magnetic field (obliqueness) and trapped electron distribution, which are found to significantly modify the basic properties (amplitude and width) of small but finite-amplitude EA solitary waves, are explicitly examined. It is also found that the instability criterion and the growth rate are significantly modified by the external magnetic field and the propagation directions of both the nonlinear waves and their perturbation modes. The implications of our results in space plasmas are briefly discussed.

Anowar, M. G. M.; Mamun, A. A. [Department of Physics, Jahangirnagar University, Savar, Dhaka-1342 (Bangladesh)

2008-10-15

395

Observation of electron plasma waves inside large amplitude electromagnetic pulses in a temporally growing plasma  

SciTech Connect

Observation of electron plasma waves excited inside high power ({approx}10 kW) short pulse ({approx}20 {mu}s) electromagnetic (em) waves interacting with a gaseous medium (argon) in the pressure range 0.2-2.5 mTorr is reported. The waves have long wavelength ({approx}13 cm) and get damped at time scales slower ({approx}3 {mu}s) than the plasma period (0.1-0.3 {mu}s), the energy conveyed to the medium lead to intense ionization (ion density n{sub i} {approx} 10{sup 11} cm{sup -3} and electron temperature T{sub e} {approx} 6-8 eV) and rapid growth of the plasma ({approx}10{sup 5} s{sup -1}) beyond the waves. Time frequency analysis of the generated oscillations indicate the presence of two principal frequencies centered around 3.8 MHz and 13.0 MHz with a spread {Delta}f {approx} 4 MHz, representing primarily two population of electrons in the plasma wave. The experimental results are in reasonable agreement with a model that considers spatiotemporal forces of the em wave on the medium, space charges and diffusion.

Pandey, Shail; Bhattacharjee, Sudeep; Sahu, Debaprasad [Department of Physics, Indian Institute of Technology, Kanpur-208016 (India)

2012-01-15

396

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

Microsoft Academic Search

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

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

2006-01-01

397

Ion boundary conditions in semi-infinite fluid models of electron beam-plasma interaction  

NASA Astrophysics Data System (ADS)

The modified Bohm criterion is derived for the plasma consisting of the monoenergetic electron beam and thermal electrons. This criterion allows us to define the accurate ion boundary conditions for semi-infinite collisionless fluid models of electron beam-plasma interaction. In the absence of electron beam, these boundary conditions give the classical sheath parameters. When the monoenergetic electron beam propagates through the plasma, the fluid model with proposed boundary conditions gives the results, which are in qualitative agreement with the results obtained earlier in M. Sharifian and B. Shokri, Phys. Plasmas 14, 093503 (2007). However, dynamics and parameters of the plasma sheath are different.

Levko, Dmitry

2014-10-01

398

Spatial measurements of electron energy distribution and plasma parameters in a weakly magnetized inductive discharge  

SciTech Connect

Spatial characteristics of plasma parameters such as electron temperature, plasma density, plasma potential, and electron energy distribution (EED) were studied in inductively coupled plasma with an axial dc magnetic field. With dc magnetic field, the measured EEDs in the total electron energy scale are spatially coincided except cutting of the low electron energy part indicating the conserved non-local electron kinetics in an axial direction, even though the dc magnetic field is applied. Spatial distributions of the plasma densities at axial positions have almost same trends with various magnetic field strengths. We also discuss the reduction of the ambipolar potential along the axial direction as the applied magnetic field increased.

Kim, Young-Do; Lee, Young-Kwang; Lee, Hyo-Chang; Chung, Chin-Wook [Department of Electrical Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791 (Korea, Republic of)

2013-02-15

399

Effect of graded triple delta-doped sheets on the performance of GaAs based dual channel pseudomorphic high electron mobility transistors  

Microsoft Academic Search

The characteristics of InGaP\\/InGaAs\\/GaAs dual channel pseudomorphic high electron mobility transistors (DCPHEMTs) with different graded triple delta-doped sheets are investigated and experimentally demonstrated. Based on a two-dimensional simulator of ATLAS, the band diagrams, electron densities and DC characteristics of studied devices are comprehensively analyzed. Due to the use of properly graded triple delta-doped sheets, good pinch-off and saturation characteristics, improved

Kuei-Yi Chu; Shiou-Ying Cheng; Meng-Hsueh Chiang; Yi-Jung Liu; Chien-Chang Huang; Tai-You Chen; Chi-Shiang Hsu; Wen-Chau Liu; Wen-Yu Cheng; Bin-Cian Lin

2011-01-01

400

Excitation of forced ion acoustic waves, large plasma sheets, and magnetic field fluctuations over Gakona, Alaska  

E-print Network

Two research subjects: (1) excitation of "forced ion acoustic waves", and (2) "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" are reported in my M.S. thesis. The data was acquired ...

Cohen, Joel (Joel A.)

2009-01-01

401

Dust particle charge in plasma with ion flow and electron depletion near plasma boundaries  

SciTech Connect

The charge on micrometer-sized dust particles suspended in plasma above the powered electrode of radio-frequency discharges is studied. Using a self-consistent fluid model, the plasma profiles above the electrode are calculated and the electron depletion towards the electrode, as well as the increasing flow speed of ions toward the electrode are considered in the calculation of the dust particle floating potential. The results are compared with those reported in literature and the importance of the spatial dust charge variation is investigated.

Douglass, Angela; Land, Victor; Matthews, Lorin; Hyde, Truell [Center for Astrophysics, Space Physics, and Engineering Research, Baylor University, Waco, Texas 76798-7310 (United States)

2011-08-15

402

Generation of suprathermal electrons and Alfvn waves by a high power pulse at the electron plasma frequency  

E-print Network

Generation of suprathermal electrons and Alfvén waves by a high power pulse at the electron plasma; published online 15 September 2006 The interaction of a short high power pulse at the electron plasma frequency f =9 GHz, pulse length =0.5 s or 2.5 s, input power P 80 kW and a magnetized plasma n0 2 1012 cm-3

California at Los Angles, University of

403

NO EVIDENCE FOR HEATING OF THE SOLAR WIND AT STRONG CURRENT SHEETS  

SciTech Connect

It has been conjectured that strong current sheets are the sites of proton heating in the solar wind. For the present study, a strong current sheet is defined by a >45{sup 0} rotation of the solar-wind magnetic-field direction in 128 s. A total of 194,070 strong current sheets at 1 AU are analyzed in the 1998-2010 ACE solar-wind data set. The proton temperature, proton specific entropy, and electron temperature at each current sheet are compared with the same quantities in the plasmas adjacent to the current sheet. Statistically, the plasma at the current sheets is not hotter or of higher entropy than the plasmas just outside the current sheets. This is taken as evidence that there is no significant localized heating of the solar-wind protons or electrons at strong current sheets. Current sheets are, however, found to be more prevalent in hotter solar-wind plasma. This is because more current sheets are counted in the fast solar wind than in the slow solar wind, and the fast solar wind is hotter than the slow solar wind.

Borovsky, Joseph E. [Los Alamos National Laboratory, Los Alamos, NM (United States); Denton, Michael H. [Department of Physics, Lancaster University, Lancaster (United Kingdom)

2011-10-01

404

Evolution of the electron energy distribution and plasma parameters in a pulsed magnetron discharge  

Microsoft Academic Search

We demonstrate the creation of high-density plasma in a pulsed magnetron discharge. A 2.4 MW pulse, 100 mus wide, with a repetition frequency of 50 Hz is applied to a planar magnetron discharge to study the temporal behavior of the plasma parameters: the electron energy distribution function, the electron density, and the average electron energy. The electron density in the

J. T. Gudmundsson; J. Alami; U. Helmersson

2001-01-01

405

Development of Plasma Electron Guns to Produce Narrow Focusing Beams Under the Higher Operation Pressure  

Microsoft Academic Search

Summary form only given. One of the main advantages of the plasma cathode electron guns is its ability to produce electron beam under the higher operation pressure up to fore-pump pressure range. Present work is devoted to