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1

Runaway electrons in plasma current sheets  

SciTech Connect

It is shown that a runaway electron population accelerates along the main magnetic field in a Sweet-Parker current sheet. After a characteristic distance the entire current is carried by runaways. The thickness of this runaway sheet is much smaller than the original Ohmic sheet. The influence of microinstabilities is discussed.

Gurevich, A.V.; Sudan, R.N. (Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States))

1994-01-31

2

Quantitative Comparison of Measured Plasma Sheet Electron Energy Flux and Remotely Sensed Auroral Electron Energy Flux  

NASA Astrophysics Data System (ADS)

In situ plasma sheet observations and auroral images give us two views of magnetospheric dynamics. With in situ observations, we get a detailed point measurement; auroral images give us a global view. Previous studies have shown an excellent correlation between dynamic plasma behavior in the plasma sheet and auroral activity. Here we extend the previous work with quantitative comparisons between the two regions. We directly compare the electron energy flux measured in the plasma sheet with the electron energy flux into the ionosphere inferred from auroral images. We find that during quiet times, the plasma sheet is able to supply the aurora with nearly all of the observed energy flux. During intervals of intense auroral emission, the electron spectrum in the conjugate region of the plasma sheet changes, increasing the amount of energy flux incident on the ionosphere. However, the increases in the plasma sheet energy flux is not enough to account for the inferred energy flux into the ionosphere from the images by nearly an order of magnitude. This implies that additional energy flux must be entering the loss cone through pitch angle diffusion or through the presence of parallel electric fields between the plasma sheet and the ionosphere during intervals of intense auroral emission. A likely source of this additional energy flux is the low altitude auroral acceleration region. >http://www.ess.washington.edu/People/Students/matt/AGU2001/

Fillingim, M. O.; Parks, G. K.; Chua, D.; Germany, G. A.; Lin, R. P.; McCarthy, M.

2001-12-01

3

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 and the solar wind, as well as >2 MeV geosynchronous electrons, is investigated using plasma sheet measurements from Cluster (2001­2005) and Geotail (1998­2005) and concurrent solar wind measurements from ACE

Li, Xinlin

4

Experimental investigation of a 1 kA/cm(2) sheet beam plasma cathode electron gun.  

PubMed

In this paper, a cold cathode based sheet-beam plasma cathode electron gun is reported with achieved sheet-beam current density ?1 kA/cm(2) from pseudospark based argon plasma for pulse length of ?200 ns in a single shot experiment. For the qualitative assessment of the sheet-beam, an arrangement of three isolated metallic-sheets is proposed. The actual shape and size of the sheet-electron-beam are obtained through a non-conventional method by proposing a dielectric charging technique and scanning electron microscope based imaging. As distinct from the earlier developed sheet beam sources, the generated sheet-beam has been propagated more than 190 mm distance in a drift space region maintaining sheet structure without assistance of any external magnetic field. PMID:25638082

Kumar, Niraj; Narayan Pal, Udit; Kumar Pal, Dharmendra; Prajesh, Rahul; Prakash, Ram

2015-01-01

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

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 on the magnetopause result in higher (lower) energetic electron fluxes in the CPS with a time delay of about 1 hour, while the influence of solar wind ion density on the energetic electrons fluxes is insignificant

Li, Xinlin

7

Electron distributions observed with Langmuir waves in the plasma sheet boundary layer  

SciTech Connect

The present paper investigates the Langmuir turbulence driven by counter-streaming electron beams and its plausible association with observed features in the Earth's plasma sheet boundary layer region. A one-dimensional electrostatic particle-in-cell simulation code is employed in order to simulate broadband electrostatic waves with characteristic frequency in the vicinity of the electron plasma frequency ?/?{sub pe}?1.0. The present simulation confirms that the broadband electrostatic waves may indeed be generated by the counter-streaming electron beams. It is also found that the observed feature associated with low energy electrons, namely quasi-symmetric velocity space plateaus, are replicated according to the present simulation. However, the present investigation only partially succeeds in generating the suprathermal tails such that the origin of observed quasi power-law energetic population formation remains outstanding.

Hwang, Junga [Solar and Space Weather Research Group, Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Department of Astronomy and Space Science, University of Science and Technology, Daejeon (Korea, Republic of); Rha, Kicheol [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of); Seough, Jungjoon [Solar and Space Weather Research Group, Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Yoon, Peter H. [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)

2014-09-15

8

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

9

Hybrid Simulation of Space Plasmas: Models with Massless Fluid Representation of Electrons. VI. Magnetotail Current Sheets  

Microsoft Academic Search

This is a survey of literature on hybrid simulation of magnetotail current sheets. The traditional electromagnetic hybrid model (with ions as particles and electrons as a massless fluid) is briefly described together with its main numerical schemes. This is followed by a description of the modified hybrid model in which the generalized Ohm's law includes both electron inertia and evolution

D. S. Filippychev

2004-01-01

10

Sheet electron beam tester  

NASA Astrophysics Data System (ADS)

The DARPA HiFIVE project uses a pulsed electron sheet beam gun to power a traveling wave tube amplifier operating at 220 GHz. Presented is a method for characterizing the high current density 0.1 mm by 1 mm sheet electron beam. A tungsten tipped probe was scanned through the cross section of the sheet electron beam inside of a vacuum vessel. The probe was controlled with sub-micron precision using stepper motors and LabView computer control while boxcar averaging hardware sampled the pulsed beam. Matlab algorithms were used to interpret the data, calculate beam dimensions and current density, and create 2-dimensional cross section images. Full characterization of two separate HiFIVE sheet electron guns was accomplished and is also presented.

Spear, Alexander Grenbeaux

11

Average plasma properties in the central plasma sheet  

SciTech Connect

Using four months of tail data obtained by the three-dimensional plasma instrument on board the AMPTE/IRM satellite in 1986, the authors have done a statistical survey on the behavior of ion and electron moments in the central plasma sheet. Almost 80,000 spin averages of plasma density, ion bulk velocity, ion and electron temperature, and plasma {beta} were analyzed with respect to differences between their values in the inner and outer central plasma sheet as well as their dependence on magnetic activity. The ion temperature increases with increasing magnetic activity while the ion density decreases during disturbed intervals, except in the neutral sheet neighborhood at smaller radial distances. The ion and electron temperatures in the central plasma sheet are highly correlated, with T{sub i}/T{sub e} being constant over a wide range of temperatures and about twice as large as in the distant tail. The average ion flow speeds in the central plasma sheet are below 100 km/s and nearly identical to those found in the plasma sheet boundary layer, although the distribution functions usually are quite different. High-speed flows do occur, but in bursts of most often less than 1 min duration with intermittent intervals of nearly stagnant plasma. The distribution of flow directions strongly favors sunward flow for velocities above 300 km/s, indicating that a near-earth neutral line is rarely, if ever, located inside of X{sub GSM} = {minus} 19 R{sub E}.

Baumjohann, W.; Paschmann, G. (Max-Planck-Institut fuer Physik und Astrophysik, Garching (West Germany)); Cattell, C.A. (Univ. of California, Berkeley (USA))

1989-06-01

12

Study of magnetic configuration effects on plasma boundary and measurement of edge electron density in the spherical tokamak compact plasma wall interaction experimental device using Li sheet beam  

SciTech Connect

Two-dimensional lithium beam imaging technique has been applied in the spherical tokamak CPD (compact plasma wall interaction experimental device) to study the effects of magnetic field configurations on rf plasma boundary in the absence of any plasma current, and also for the measurement of a two-dimensional edge electron density profile. With the present working condition of the diagnostics, the minimum measured electron density can be {approx}1.0x10{sup 16} m{sup -3}; this is considered to be the definition for the plasma boundary. The performance of the lithium sheet beam is absolutely calibrated using a quartz crystal monitor. Experimental results reveal that magnetic field configuration, either mirror or so-called null, critically affects the rf plasma boundary. A sharp lower boundary is found to exist in magnetic null configuration, which is quite different from that in the weak mirror configuration. Theoretical calculations of particle drift orbit and magnetic connection length (wall-to-wall) suggest that only mirror trapped particles are confined within a region where the magnetic connection length is {approx}4.0 m or more. A two-dimensional edge electron density profile is obtained from the observed Li I intensity profile. Overdense plasma formation is discussed from the viewpoint of mode conversion of rf wave into electron Bernstein wave and its dependence on the electron density profile.

Bhattacharyay, R.; Inada, Y.; Kikukawa, T.; Watanabe, S.; Sasaki, K.; Ryoukai, T. [Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka 816 8580 (Japan); Zushi, H.; Hasegawa, M.; Hanada, K.; Sato, K. N.; Nakamura, K.; Sakamoto, M.; Idei, H.; Yoshinaga, T.; Kawasaki, S.; Nakashima, H.; Higashijima, A. [Research Institute of Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816 8580 (Japan); Morisaki, T. [National Institute for Fusion Science, Toki 509 5292 (Japan)

2008-02-15

13

Quiet-time convection electric field properties derived from keV electron measurements at the inner edge of the plasma sheet by means of GEOS2  

Microsoft Academic Search

Results are given of an analysis of the electron upper energy limit local time distribution reached by the GEOS-2 satellite, in cutting through the innermost element of the electron plasma sheet during quiet conditions. It is found that an electric field model whose dusk singular point of the forbidden region lies at 1500 rather than 1800 M.L.T. is in agreement

B. Hultqvist; H. Borg; L.-A. Holmgren; H. Reme; A. Bahnsen; M. Jespersen; G. Kremser

1982-01-01

14

Observations of energetic electrons /E no less than about 200 keV/ in the earth's magnetotail - Plasma sheet and fireball observations  

NASA Technical Reports Server (NTRS)

An earlier paper by the authors (1976) has reported on energetic electron anisotropies observed in conjunction with the acceleration regions identified by Frank et al., (1976). The present paper gives more detailed analyses of observations in the distant plasma sheet, including specific features of intensities, energy spectra, and pitch angle distributions of the very energetic electrons associated with intense plasma particle events, with energies ranging between 50 eV and 45 keV, detected with an electron/isotope spectrometer aboard the earth-orbiting spacecraft Imp 8. Two domains are considered: the plasma sheet and the regions near and within the localized magnetotail acceleration regions known as the fireball regions. The instrumentation used offered a number of observational advantages over many previous studies, including inherently low background, large geometric factors, excellent species identification, good angular distribution measurement capability, and availability of high resolution of differential intensities.

Baker, D. N.; Stone, E. C.

1977-01-01

15

Plasma sheet behavior during substorms  

SciTech Connect

Auroral or magnetic substorms are periods of enhanced auroral and geomagnetic activity lasting one to a few hours that signify increased dissipation of energy from the magnetosphere to the earth. Data acquired during the past decade from satellites in the near-earth sector of the magnetotail have suggested that during a substorm part of the plasma sheet is severed from earth by magnetic reconnection, forming a plasmoid, i.e., a body of plasma and closed magnetic loops, that flows out of the tail into the solar wind, thus returning plasma and energy that have earlier been accumulated from the solar wind. Very recently this picture has been dramatically confirmed by observations, with the ISEE 3 spacecraft in the magnetotail 220 R/sub E/ from earth, of plasmoids passing that location in clear delayed response to substorms. It now appears that plasmoid release is a fundamental process whereby the magnetosphere gives up excess stored energy and plasma, much like comets are seen to do, and that the phenomena of the substorm seen at earth are a by-product of that fundamental process.

Hones, E.W. Jr.

1983-01-01

16

Energetic ion composition of the plasma sheet  

Microsoft Academic Search

Data obtained from the energetic ion mass spectrometer experiment on Isee 1 in the distant plasma sheet are presented. These data show that (1) the plasma sheet has a significant and variable ionospheric component (H\\/sup +\\/ and O\\/sup +\\/) representing from 10% to more than 50% of the total number density and (2) there is more than one process responsible

W.K. Peterson; R. D. Sharp; E. G. Shelley; R. G. Johnson; H. Balsiger

1981-01-01

17

The Effects of Non-adiabatic Processes on Near-Earth Plasma Sheet Electrons for Different Substorm-Related Magnetotail Conditions  

NASA Astrophysics Data System (ADS)

We investigate the spatial evolution of energetic electron distribution functions in the near-Earth plasma sheet associated with earthward propagating dipolarization fronts by using in situ observations as well as magnetohydrodynamic (MHD) and large scale kinetic (LSK) simulations. We have investigated two substorms, one on February 15, 2008 and the other on August 15, 2001. The February 15 event was observed by one of the THEMIS spacecraft at X_{GSM} -10RE, while the August 15 event was observed by Cluster at X -18RE. Both the MHD and LSK simulation results are compared to these spacecraft observations. Earthward propagating dipolarization fronts are found in both the observations and the MHD simulations, which exhibit very different magnetotail configurations, with contrasting flows, magnetic reconnection configuration, and plasma sheet structure. Electron LSK simulations were performed by using the time-varying magnetic and electric fields from the global MHD simulations. For the February 15, 2008 event, the electrons were launched near X = -20 RE with a thermal energy of 1 keV and for August 15, 2001 event, they were launched at 4 keV near X = -22 RE. These electrons undergo both non-adiabatic acceleration near the magnetotail reconnection region and adiabatic acceleration as they propagate earthward from the launch region. We compute the electron distribution functions parallel and perpendicular to the magnetic field at different locations between X = -18 RE and X = -10 RE in the plasma sheet. We find that for the February 15, 2008 event, reconnection is localized with a narrow region of high-speed flows ( 300 km/s). For this event the distribution functions show mainly f(v_perp) > f(v_par) ("par" and "perp" correspond to parallel and perpendicular to magnetic field). On August 15, 2001, there is a neutral line extending across the tail with relatively low-speed flows ( 100 km/s). For this event the distribution functions show mainly f(v_par) > f(v_perp). The different magnetotail configurations result in different amounts of non-adiabatic acceleration, leading to different electron distribution functions.

Liang, H.; Ashour-Abdalla, M.; Richard, R. L.; Schriver, D.; El-Alaoui, M.; Walker, R. J.

2013-12-01

18

The driving of the plasma sheet by the solar wind  

Microsoft Academic Search

The coupling of the plasma sheet to the solar wind is studied statistically using measurements from various satellite pairs: one satellite in the solar wind and one in either the magnetotail central plasma sheet or the near-Earth plasma sheet. It is found that the properties of the plasma sheet are highly correlated with the properties of the solar wind: specifically

Joseph E. Borovsky; Michelle F. Thomsen; Richard C. Elphic

1998-01-01

19

Azimuthal plasma pressure gradient in quiet time plasma sheet  

Microsoft Academic Search

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

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

2009-01-01

20

Structure of plasma sheet in magnetotail: Double-peaked electric current sheet  

Microsoft Academic Search

The structure of the plasma sheet in the distant magnetotail observed by the Geotail satellite is examined. We found that the observed structure of the plasma sheet is often different from the standard Harris-type plasma sheet [Harris, 1962]. The observed structure can be expressed as a double-peaked current sheet which has a pair of localized electric currents away from the

M. Hoshino; A. Nishida; T. Mukai; Y. Saito; T. Yamamoto; S. Kokubun

1996-01-01

21

Electric field generation in the plasma sheet  

NASA Astrophysics Data System (ADS)

The plasma sheet is considered as a thin electrically conducting layer with a prescribe flow across the magnetic field lines at the equatorial plane of the magnetotail. Electric field resulting from the geomagnetic field diffusion into the solar wind is also added to the model. This gives a defined electric potential distribution at the flanks of the plasma sheet. The calculated electric potential from the plasma sheet and from the diffusive magnetopause is projected to the ionosphere along the magnetic field lines. At the ionospheric level they map to an oval strip at the polar cap boundary. Electric potential in the regions of the ionosphere both poleward and equatorward of this region is obtained by numerical solving of the problem of electric conductivity in the ionosphere. The patterns of electric potential contours in the ionosphere are similar to that known from observations. The positive and negative peaks of electric potential located at dawn and dusk sides of the polar oval correspond to the same peaks in the far plasma sheet at distance of about 150 RE. The influence of the flow in the plasma sheet and other parameters of the model on the electric potential distribution in the ionosphere is discussed. The total potential drop across the polar cap is equal to 100 kV that exceed observed value. A conclusion is made that resistance to the field-aligned currents in the tail lobes should be taken into account.

Denissenko, Valery V.; Kitaev, Anatoly V.

2002-02-01

22

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

23

Plasma sheet turbulence observed by Cluster II  

NASA Technical Reports Server (NTRS)

Cluster fluxgate magnetometer (FGM) and ion spectrometer (CIS) data are employed to analyze magnetic field fluctuations within the plasma sheet during passages through the magnetotail region in the summers of 2001 and 2002 and, in particular, to look for characteristics of magnetohydrodynamic (MHD) turbulence. Power spectral indices determined from power spectral density functions are on average larger than Kolmogorov's theoretical value for fluid turbulence as well as Kraichnan's theoretical value for MHD plasma turbulence. Probability distribution functions of the magnetic fluctuations show a scaling law over a large range of temporal scales with non-Gaussian distributions at small dissipative scales and inertial scales and more Gaussian distribution at large driving scales. Furthermore, a multifractal analysis of the magnetic field components shows scaling behavior in the inertial range of the fluctuations from about 20 s to 13 min for moments through the fifth order. Both the scaling behavior of the probability distribution functions and the multifractal structure function suggest that intermittent turbulence is present within the plasma sheet. The unique multispacecraft aspect and fortuitous spacecraft spacing allow us to examine the turbulent eddy scale sizes. Dynamic autocorrelation and cross correlation analysis of the magnetic field components allow us to determine that eddy scale sizes fit within the plasma sheet. These results suggest that magnetic field turbulence is occurring within the plasma sheet resulting in turbulent energy dissipation.

Weygand, James M.; Kivelson, M. G.; Khurana, K. K.; Schwarzl, H. K.; Thompson, S. M.; McPherron, R. L.; Balogh, A.; Kistler, L. M.; Goldstein, M. L.; Borovsky, J.

2005-01-01

24

Plasma Synthesis of Nitrogen Clusters on Carbon Nanotube Sheets  

NASA Astrophysics Data System (ADS)

The radio frequency plasma synthesis of nitrogen clusters stabilized on carbon nanotube sheets has been demonstrated under various conditions. Characterization of the samples produced has been carried out using micro-Raman and attenuated total reflectance-Fourier transform infrared spectroscopy. Initial investigations of the sample morphologies and compositions have also been performed using scanning electron microscopy combined with energy-dispersive x-ray analysis and transmission electron microscopy. The spectroscopic results, together with density functional theory calculations, suggest that a linear chain nitrogen cluster is formed under the plasma conditions employed and is stabilized most likely inside the walls of the carbon nanotubes that are used as substrates during the synthesis.

Benchafia, El Mostafa; Yu, Chi; Sosnowski, Marek; Ravindra, N. M.; Iqbal, Zafar

2014-04-01

25

Thermomechanical processing of plasma sprayed intermetallic sheets  

DOEpatents

A powder metallurgical process of preparing a sheet from a powder having an intermetallic alloy composition such as an iron, nickel or titanium aluminide. The sheet can be manufactured into electrical resistance heating elements having improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The iron aluminide has an entirely ferritic microstructure which is free of austenite and can include, in weight %, 4 to 32% Al, and optional additions such as .ltoreq.1% Cr, .gtoreq.0.05% Zr .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Ni, .ltoreq.0.75% C, .ltoreq.0.1% B, .ltoreq.1% submicron oxide particles and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, and/or .ltoreq.3% Cu. The process includes forming a non-densified metal sheet by consolidating a powder having an intermetallic alloy composition such as by roll compaction, tape casting or plasma spraying, forming a cold rolled sheet by cold rolling the non-densified metal sheet so as to increase the density and reduce the thickness thereof and annealing the cold rolled sheet. The powder can be a water, polymer or gas atomized powder which is subjecting to sieving and/or blending with a binder prior to the consolidation step. After the consolidation step, the sheet can be partially sintered. The cold rolling and/or annealing steps can be repeated to achieve the desired sheet thickness and properties. The annealing can be carried out in a vacuum furnace with a vacuum or inert atmosphere. During final annealing, the cold rolled sheet recrystallizes to an average grain size of about 10 to 30 .mu.m. Final stress relief annealing can be carried out in the B2 phase temperature range.

Hajaligol, Mohammad R. (Midlothian, VA); Scorey, Clive (Cheshire, CT); Sikka, Vinod K. (Oak Ridge, TN); Deevi, Seetharama C. (Midlothian, VA); Fleischhauer, Grier (Midlothian, VA); Lilly, Jr., A. Clifton (Chesterfield, VA); German, Randall M. (State College, PA)

2001-01-01

26

Scales in a thinning plasma sheet  

SciTech Connect

With Cluster observations in the magnetotail, we study the dynamics of plasma sheet thinning and stretching in a typical growth phase event of September 12, 2001. The thinning and stretching proceed in parallel, with transient variations. The pre-onset value is B{sub z}{approx}1.5 nT, J{approx}8 nA/m{sup 2}. The current density increase is not accompanied with a corresponding number density increase. A large (>5 nT) guide field along the cross-tail current direction was registered. An embedded current sheet structure was detected and, therefore, caution is required if making thickness estimations.

Petrukovich, A. A. [Space Research Institute, Russian Academy of Sciences, Moscow (Russian Federation); Baumjohann, W.; Nakamura, R.; Runov, A. [Space Research Institute, Austrian Academy of Sciences, Graz (Austria); Balogh, A. [Imperial College, London (United Kingdom); Reme, H. [Centre d'Etude Spatiale des Rayonnements, Toulouse (France)

2009-06-16

27

Thin sheets of energetic electrons upstream from the earth's bow shock  

NASA Technical Reports Server (NTRS)

ISEE spacecraft observations show that energetic (not less than 16 keV) electrons are injected into the region upstream from the earth's bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface. Lower energy electrons leave the shock over a much broader region. Although the energetic electron intensity varies, the sheet is nearly always present and may be a quasi-steady state feature of the bow shock. The electron velocity distribution in the thin sheet is strongly peaked and is responsible for excitation of electron plasma waves.

Anderson, K. A.; Lin, R. P.; Martel, F.; Lin, C. S.; Parks, G. K.; Reme, H.

1979-01-01

28

A pincer-shaped plasma sheet at Uranus  

SciTech Connect

A model from Voigt et al. (1987) and an MHD simulation from Walker et al. (1989) both show that the curvature of the plasma sheet at Uranus changes as the dipole tilt varies between 38{degree} and 22{degree}. The models suggest that one of the two partial traversals of the uranian plasma sheet made during the outbound trajectory of Voyager 2 can be explained as an entry into the highly curved plasma sheet that develops when Uranus is near the maximum dipole tilt value of 38{degree}; previously both partial traversals have been explained as anomalous. The spacecraft would have reversed its motion relative to the plasma sheet as the continued rotation diminished the dipole tilt and the retreating plasma sheet uncurled. As the dipole tilt approached its minimum value, spacecraft motion towards the neutral sheet resumed and the traversal of the plasma sheet was completed. Evidence from the PWS plasma wave detector suggests that the spacecraft trajectory skimmed the plasma sheet boundary layer for several hours prior to the partial immersion. The plasma sheet of the Voigt et al. model was not located near the spacecraft during this time interval. On the other hand, the MHD simulation reveals a plasma sheet that is more curved than in the Boigt et al. model; near maximum dipole tilt, the plasma sheet is pincer-shaped. The unusual geometry implies that Voyager 2 remained near the plasma sheet boundary layer during the period suggested by the PWS data. Thus the simulation accounts easily for the first of the plasma sheet encounters previously called anomalous. The second partial immersion remains anomalous, having previously been related to substorm activity, and thus is not discussed here. The stagnation distances of the earth and Uranus at the nose of the magnetopause were used to scale the Walker et al. (1989) simulation of the terrestrial magnetosphere to represent the uranian magnetosphere.

Hammond, C.M.; Walker, R.J.; Kivelson, M.G. (Univ. of California, Los Angeles (USA))

1990-09-01

29

Solar wind control of plasma number density in the near Earth plasma sheet: three- dimensional structure  

NASA Astrophysics Data System (ADS)

Plasma number density in the near-Earth plasma sheet depends strongly on solar wind and IMF: (1) plasma sheet number density positively correlates with solar wind number density [Borovsky et al., 1998]. (2) plasma sheet number density positively correlates with theta angle of IMF with time lag of several-hours [Terasawa et al., 1997]. Recently, Nagata et al. [JGR in press] shows two-dimensional structure of such dependences in the near- Earth central plasma sheet (X<0, 9

Nagata, D.; Machida, S.; Ohtani, S.; Saito, Y.; Mukai, T.

2007-12-01

30

Birkeland currents in the plasma sheet  

SciTech Connect

A search was conducted for the signatures of Birkeland currents in the Earth`s magnetic tail, using observed values of B{sub x} and B{sub y} from large sets of spacecraft data. The data were binned by x and y for {minus}10 > x{sub GSM} > {minus}35 and {vert_bar}y{sub GSM}{vert_bar} {<=} 20 R{sub E} ({<=}30 R{sub E} for x{sub GSM} {<=} {minus}25 R{sub E}) and in each bin their distribution in the (B{sub x}, B{sub y}) plane was fitted by least squares to a piecewise linear function. That gave average x-y distributions of the flaring angle between B{sub xy} and the x direction, as well as that angle`s variation across the thickness of the plasma sheet. Angles obtained in the central plasma sheet differed from those derived near the lobe boundary. That is the expected signature if earthward or tailward Birkeland current sheets are embedded in the plasma sheet, and from this difference the authors derived the dawn-dusk profiles of the tail Birkeland currents for several x{sub GMS} intervals. It was found that (1) the Birkeland currents have the sense of region 1 currents, when mapped to the ionosphere; (2) both the linear current density (kiloamperes/R{sub E}) and the net magnitude of the field-aligned currents decrease rapidly down the tail; (3) the total Birkeland current x{approximately} {minus}10 R{sub E} equals {approximately}500-700 kA, which is {approx}30% of the net region 1 current observed at ionospheric altitudes, in agreement with model mapping results; and (4) the B{sub z} and B{sub y} components of the interplanetary magnetic field influence the distribution of Birkeland currents in the tail. 27 refs., 11 figs.

Tsyganeko, N.A.; Stern, D.P. [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Kaymaz, Z. [Univ. of California, Los Angeles, CA (United States)

1993-11-01

31

Design principles for a sheet-beam electron gun for a quasi-optical gyrotron  

SciTech Connect

This paper examines the design considerations for a magnetized sheet beam for which the electrons have energy both perpendicular and parallel to the magnetic field. The application envisioned for the sheet beam is the driving of a quasi-optical gyrotron for electron cyclotron resonance heating and current drive in fusion plasmas.

Manheimer, W.M.; Fliflet, A.W. (Naval Research Lab., Washington, DC (USA). Plasma Physics Div.); Lee, R. (JAYCOR, Vienna, VA (USA))

1990-03-01

32

Origins of the plasma in the distant plasma sheet  

Microsoft Academic Search

A statistical study of the composition of the plasma sheet at geocentric radial distances between 10 and 23 R\\/sub E\\/ has been conducted utilizing data from the energetic ion mass spectrometer experiment on ISEE 1. The composition of the ions in the energy per charge range 0.1< or =Elq< or =16 keV\\/e was found to be dependent on substorm activity.

R. D. Sharp; W. Lennartsson; W.K. Peterson; E. G. Shelley

1982-01-01

33

Bright subcycle extreme ultraviolet bursts from a single dense relativistic electron sheet.  

PubMed

Double-foil targets separated by a low density plasma and irradiated by a petawatt-class laser are shown to be a copious source of coherent broadband radiation. Simulations show that a dense sheet of relativistic electrons is formed during the interaction of the laser with the tenuous plasma between the two foils. The coherent motion of the electron sheet as it transits the second foil results in strong broadband emission in the extreme ultraviolet, consistent with our experimental observations. PMID:25526132

Ma, W J; Bin, J H; Wang, H Y; Yeung, M; Kreuzer, C; Streeter, M; Foster, P S; Cousens, S; Kiefer, D; Dromey, B; Yan, X Q; Meyer-Ter-Vehn, J; Zepf, M; Schreiber, J

2014-12-01

34

Periodic magnetic focusing of sheet electron beams  

SciTech Connect

Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low-frequency velocity-shear instabilities (such as the diocotron mode). This is in contrast to the more familiar unstable behavior in uniform solenoidal magnetic fields. A period-averaged analytic model shows that a PCM-focused beam is stabilized by ponderomotive forces for short PCM periods. Numerical particle simulations for a semi-infinite sheet beam verify this prediction and also indicate diocotron stability for long PCM periods is less constraining than providing for space-charge confinement and trajectory stability in the PCM focusing system. In this article the issue of beam matching and side focusing for sheet beams of finite width is also discussed. A review of past and present theoretical and experimental investigations of sheet-beam transport is presented.

Booske, J.H.; Basten, M.A.; Kumbasar, A.H. (Electrical and Computer Engineering, University of Wisconsin---Madison, Madison, Wisconsin 53706 (United States)); Antonsen, T.M. Jr.; Bidwell, S.W.; Carmel, Y.; Destler, W.W.; Granatstein, V.L.; Radack, D.J. (Laboratory for Plasma Research, University of Maryland, College Park, Maryland 20742-3511 (United States))

1994-05-01

35

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

36

Absence of the plasma sheet at lunar distance during geomagnetically quiet times.  

NASA Technical Reports Server (NTRS)

Evaluation of plasma data from the Apollo 14 charge particle lunar environment experiment showing that, contrary to previously published analyses, the plasma sheet does not extend to the lunar orbit with a thickness of 8 earth radii. Two electron spectral types are observed: (1) low-energy photoelectrons with no statistically significant medium and high energy fluxes, and (2) double-peaked medium- and high-energy electrons. The second type is observed either coincident with auroral substorms or at the center of the tail during quiet times. These spectra are one to several orders of magnitude less intense than plasma sheet spectra measured near 20 earth radii.

Burke, W. J.; Reasoner, D. L.

1972-01-01

37

A pincer-shaped plasma sheet at Uranus  

NASA Technical Reports Server (NTRS)

An MHD simulation of the terrestrial magnetosphere, rescaled to represent the Uranian magnetotail, is carried out. The 3p immersion can be explained in terms of possible extreme departures from average plasma sheet shapes in the Uranian magnetosphere. The orientation of the Uranian dipole and rotation axes produce a dynamically curved plasma sheet which is an unusual feature of the Uranian magnetosphere.

Hammond, C. Max; Walker, Raymond J.; Kivelson, Margaret G.

1990-01-01

38

Quiet time plasma sheet ion pressure contribution to Birkeland currents  

Microsoft Academic Search

Birkeland currents transport magnetic tangential stress resulting from JB forces, which,in the plasma sheet, are balanced by the pressure gradient, p. However, derivation of nightside Birkeland currents from p observationally has not been possible because pressure must be known everywhere in the plasma sheet at high resolution, which in situ satellites have been unable to provide. Recently, a method of

Simon Wing; Patrick T. Newell

2000-01-01

39

Geomagnetic activity effects on plasma sheet energy conversion  

Microsoft Academic Search

In this article we use three years (2001, 2002, and 2004) of Cluster plasma sheet data to investigate what happens to localized energy conversion regions (ECRs) in the plasma sheet during times of high magnetospheric activity. By examining variations in the power density, EJ, where E is the electric field and J is the current density obtained by Cluster, we

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

2010-01-01

40

A two satellite study of nightside flux transfer events in the plasma sheet  

NASA Technical Reports Server (NTRS)

The short-term (about 1 min) events during two consecutive substorms on March 23 1979 have been studied using high time resolution measurements of magnetic and electric fields and of the kiloelectronvolt electron flux at X about -21 R(e). Data obtained make it possible to describe the localized magnetic structures transported or propagated within the plasma sheet and to identify these events as plasma sheet nightside magnetic flux transfer events (NFTEs). The best examples of the NFTEs found so far are all observed in a thin portion of plasma sheet where the contraction of the reconnected field lines dominates over the oppositely directed pressure gradient force. Systematic differences in the magnetic variations observed at ISEE-1 and 2 indicate current concentration at the outer plasma sheet boundary during the passage of a NFTE.

Sergeev, V. A.; Elphic, R. C.; Mozer, F. S.; Saint-Marc, A.; Sauvaud, J. A.

1992-01-01

41

Azimuthal plasma pressure gradient in quiet time plasma sheet L. R. Lyons,1  

E-print Network

Azimuthal plasma pressure gradient in quiet time plasma sheet X. Xing,1 L. R. Lyons,1 V 2 June 2009; accepted 16 June 2009; published 28 July 2009. [1] We have investigated the quiet-time. Runov, and U. Auster (2009), Azimuthal plasma pressure gradient in quiet time plasma sheet, Geophys. Res

California at Berkeley, University of

42

Modeling the quiet-time inner plasma sheet protons  

Microsoft Academic Search

Abstract. In order to understand the characteristics of the quiet-time inner plasma sheet protons, weuse,a modified version of the Magnetospheric Specification Model to simulate ,the bounce averaged electric and magnetic drift of isotropic plasma sheet protons in an ,approximately self- consistent magnetic field. Proton differential fluxes are assigned to the model,boundary,to mimic a mixed tail source consisting of hot plasma

Chih-Ping Wang; R. Lyons; Margaret W. Chen; Richard A. Wolf

2000-01-01

43

Shape and postion of the plasma sheet in earth's magnetotail  

SciTech Connect

The configuration of the tail plasma sheet in earth's magnetotail has been calculated in connection with a three-dimensional magnetospheric B field modle. This model is based on the idea that thermal plasma, tail currents, and magnetic field be in magnetohydrostatic equilibrium during time periods of magnetically quiet conditions. The tail configuration is generated by a separation method assuming a cylindrical magnetotail boundary with constant radius. The separation method restricts self-consistency to planes perpendicular to the tail axis. The computed tail plasma sheet is flexible and reacts to changes of the earth's dipole tilt angle and changes of the solar wind pressure. Consequences for the plasma sheet configuration with respect to the assumed tail magnetopause shape and the separation method are the following: (1) the plasma sheet thickness increases in Y/sub GSM/ direction toward the flanks of the tail; (2) the plasma sheet becomes thicker and more diffuse with increasing distance from the earth; (3) during the northern hemisphere summer, the neutral sheet is raised above the magnetospheric equatorial plane around local midnight but crosses this plane and is depressed below it near the flanks of the tail. The latter result agrees qualitatively with Fairfield's empirical neutral sheet model which he derived from spacecraft measurements of the tail field polarity. This agreement between theory and observational material provides a further piece of evidence that the magnetohydrostatic theory is an appropriate level for describing quantitatively the quiet state of the magnetosphere.

Voigt, G.

1984-04-01

44

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

45

Electrons, Ions and Plasma  

NSDL National Science Digital Library

This explanation of the factors that produce the polar aurora, (northern lights) discusses the role of electrons in the ionosphere, positive ions in the solar wind, and the mixing of the two to create plasma. The work of Kristian Birkeland of Norway in exploring the cause of the aurora is cited and a link leads to in-depth information on auroras, including some dramatic photographs.

David Stern

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

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  

Microsoft Academic Search

The use of a small period wiggler (lw < 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 20

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

1989-01-01

48

Camera data sheet for pictorial electronic still cameras  

Microsoft Academic Search

A data sheet is presented outlining the performance and characteristics of a Kodak DCS 200mi camera. In addition to providing information on this camera, the format and content of the data sheet could serve as a guide in the organization and display of pertinent information on electronic still cameras in general. Such data sheets are already common in silver halide

Sabine Susstrunk; Jack M. Holm

1995-01-01

49

Cold plasma heating in the plasma sheet boundary layer - Theory and simulations  

NASA Technical Reports Server (NTRS)

Satellite observations in recent years have confirmed that the plasma sheet boundary layer is a permanent feature of the earth's magnetotail located between the lobe and central plasma sheet during both quiet and active magnetic periods. Distinct features of the boundary layer include field aligned ion beams and intense electrostatic emissions known as broadband electrostatic noise. Since the plasma sheet boundary layer is a spatial feature of the magnetotail, within it will occur thermal mixing of the resident warm boundary layer plasma with inflowing (convecting) cold ionospheric plasma. A theoretical study involving linear theory and nonlinear numerical particle simulations is presented which examines ion beam instabilities in the presence of a thermally mixed hot and cold background plasma. It is found that the free energy in the ion beams can heat the cool ionospheric plasma to ambient plasma sheet boundary layer temperatures via broadband electrostatic noise. These results, along with recent observational reports that ionospheric outflow can account for measured plasma sheet densities, suggest that the ionospheric role in plasma sheet dynamics and content may be as large as the solar wind.

Schriver, David; Ashour-Abdalla, Maha

1990-01-01

50

Space Charge Effect in the Sheet and Solid Electron Beam  

NASA Astrophysics Data System (ADS)

We analyze the space charge effect of two different types of electron beam ; sheet and solid electron beam. Electron gun simulations are carried out using shadow and control grids for high and low perveance. Rectangular and cylindrical geometries are used for sheet and solid electron beam in planar and disk type cathode. The E-gun code is used to study the limiting current and space charge loading in each geometries.

Song, Ho Young; Kim, Hyoung Suk; Ahn, Saeyoung

1998-11-01

51

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

52

ADBD plasma surface treatment of PES fabric sheets  

NASA Astrophysics Data System (ADS)

Plasma treatment of textile fabrics is investigated as an alternative to the environmentally hazardous wet chemical fabric treatment and pretreatment processes. Plasma treatment usually results in modification of the uppermost atomic layers of a material surface and leaves the bulk characteristics unaffected. It may result in desirable surface modifications, e.g. surface etching, surface activation, cross-linking, chain scission and oxidation. Presented paper contains results of the applicability study of the atmospheric pressure dielectric discharge (ADBD), i.e. dielectric barrier discharge sustaining in air at atmospheric pressure and ambient temperature for synchronous treatment of several sheets of fabric. For tests sheets of polyester fabric were used. Effectivity of the modification process was determined with hydrophilicity measurements evaluated by means of the drop test. Hydrophilicity of individual sheets of fabric has distinctly increased after plasma treatment. Plasma induced surface changes of textiles were also proven by identification of new functional groups at the modified polyester fabric surface. Existence of new functional groups was detected by ESCA scans. For verification of surface changes we also applied high-resolution microphotography. It has shown distinct variation of the textile surface after plasma treatment. Important aspect for practical application of the plasma treatment is the modification effect time-stability, i.e. time stability of acquired surface changes of the fabric. The recovery of hydrophobicity was fastest in first days after treatment, later gradually diminished until reached almost original untreated state.

Pchal, J.; Klenko, Y.

2009-08-01

53

Plasma Sheets and Cylinders Generated From Aluminum Wire Fabric  

Microsoft Academic Search

Low-temperature nonequilibrium plasma has been produced within the microcavities of a single sheet of aluminum wire fabric. The fabric is composed of two sets of interwoven, orthogonally oriented Al wires and each of the sets serves as an electrode for the array of dielectric barrier devices. Carefully controlled anodization of the fabric electrically and chemically isolates the two sets of

Andrew J. Price; Sung-Jin Park; J. Gary Eden

2008-01-01

54

An Equilibrium in Negative Hydrogen Ion Production Process Related to the Sheet Plasma Experiment  

NASA Astrophysics Data System (ADS)

In the sheet plasma experiment, plasma potentials decreased but negative hydrogen ion currents increased toward the outside. The negative hydrogen ions are pushed inside by the electric field and are not coming out from the plasma unless an equilibrium exists somehow. A relation between negative hydrogen ion currents and plasma potentials is well explained by the one-dimensional Saha equation, from which the electron temperature 1.3 eV is obtained. This value is very close to the electron temperature 1 eV of the Langmuir method. A reasonable negative hydrogen ion density is also calculated from the equation. We conclude that electrons, hydrogen atoms and negative hydrogen ions are in equilibrium.

Jimbo, Kouichi

1996-08-01

55

Contribution of low-energy ionospheric protons to the plasma sheet  

NASA Technical Reports Server (NTRS)

The magnetospheric transport of low-energy ionospheric ions is examined by means of three-dimensional particle codes. Emphasis is placed on the behavior of polar wind and cleft originating protons. It is demonstrated that, via nonadiabatic motion inside the neutral sheet, these ions can significantly contribute to the populations of the plasma sheet. The importance of this contribution is found to depend critically upon the dynamics of particles originating from the highest latitudes, as these possibly have access to the distant tail. Hence it is shown that polar wind H(+) expelled into the magnetosphere at very low energies (in the electron volt range) preferentially feed the plasma sheet during quiet times, experiencing accelerations up to several kiloelectron volts upon return into the inner magnetosphere. In contrast, during disturbed times, the intensifying magnetospheric convection confines this population to low L shells where it travels in a nearly adiabatic manner. As for the protons originating from the cleft fountain, the simulations reveal that they can be transported up to the vicinity of the distant neutral line in the nightside sector. Via interaction with the neutral sheet, these ionospheric ions are rapidly raised to the characteristic plasma sheet energy range. The density levels contributed by these populations are quite substantial when compared to those measured in situ. These simulations establish an active role of low-energy ionospheric ions in the overall magnetospheric dynamics.

Delcourt, D. C.; Moore, T. E.; Chappell, C. R.

1994-01-01

56

Kinetic theory of the electron bounce instability in two dimensional current sheetsFull electromagnetic treatment  

SciTech Connect

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 ??=?B{sub z}/B{sub lobes}, 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 instabilityelectromagnetic electron-bounce instabilitymay explain fast and global scale destabilization of current sheets as required to describe substorm phenomena.

Tur, A.; Fruit, G.; Louarn, P. [Institut de Recherche en Astrophysique et Plantologie (IRAP), CNRS UMR5277/Universit Paul Sabatier, Toulouse (France)] [Institut de Recherche en Astrophysique et Plantologie (IRAP), CNRS UMR5277/Universit Paul Sabatier, Toulouse (France); Yanovsky, V. [Institute for Single Crystals, National Academy of Sciences of Ukraine, Kharkov 61001 (Ukraine)] [Institute for Single Crystals, National Academy of Sciences of Ukraine, Kharkov 61001 (Ukraine)

2014-03-15

57

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

58

Electron velocity distributions and plasma waves associated with the injection of an electron beam into the ionosphere  

NASA Astrophysics Data System (ADS)

An electron beam was injected into earth's ionosphere on August 1, 1985, during the flight of the Space Shuttle Challenger as part of the objectives of the Spacelab 2 mission. In the wake of the Space Shuttle a magnetically aligned sheet of electrons returning from the direction of propagation of the beam was detected with the free-flying Plasma Diagnostics Package. The thickness of this sheet of returning electrons was about 20 m. Large intensifications of broadband electrostatic noise were also observed within this sheet of electrons. A numerical simulation of the interaction of the electron beam with the ambient ionospheric plasmas is employed to show that the electron beam excites electron plasma oscillations and that it is possible for the ion acoustic instability to provide a returning flux of hot electrons by means of quasi-linear diffusion.

Frank, L. A.; Paterson, W. R.; Kurth, W. S.; Ashour-Abdalla, M.; Schriver, D.

1989-06-01

59

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

60

Cluster Observations of Energy Conversion Regions in the Plasma Sheet  

Microsoft Academic Search

\\u000a Cluster allows for the first time a systematic examination of energy conversion, by the evaluation of the power density, E J, with E the electric field and J the current density. Following a careful inspection of the Cluster plasma sheet data from the summer and fall of 2001, we\\u000a selected 43 energy conversion regions (ECRs), out of which 26

O. Marghitu; M. Hamrin; B. Klecker; K. Rnnmark; S. Buchert; L. M. Kistler; M. Andr; H. Rme

2010-01-01

61

Electronic Rotator For Sheet Of Laser Light  

NASA Technical Reports Server (NTRS)

Primary flow-visualization system in Basic Aerodynamic Research Tunnel (BART) at NASA Langley Research Center is sheet of laser light generated by 5-W argon-ion laser and two-axis mirror galvanometer scanner. Generates single and multiple sheets of light, which remain stationary or driven to sweep out volume. Sine/cosine potentiometer used to orient two galvanometer/mirror devices simultaneously and yields desired result at reasonable cost and incorporated into prototype in 1 day.

Franke, John M.; Rhodes, David B.; Leighty, Bradley D.; Jones, Stephen B.

1989-01-01

62

Propagation of wiggler focused relativistic sheet electron beams  

SciTech Connect

A recent design concept for millimeter-wave free-electron lasers (J. Appl. Phys. 60, 521 (1986)) would require the stable propagation of a sheet electron beam through a narrow waveguide channel. Experimental results reported in this article support the feasibility of such a configuration by demonstrating the stable propagation of relativistic sheet electron beams through a narrow waveguide gap (3.2 mm) using focusing by a short-period electromagnet wiggler. 90% of the electron current in a 100-keV sheet electron beam was transmitted through a 5-cm-long channel with peak wiggler fields of 800 G. Almost 80% of a 400-keV beam was similarly confined with a 1600-G wiggler field. The data were consistent with single electron trajectory models, indicating that space-charge effects were minimal. No evidence of beam breakup or filamentation instabilities was observed.

Booske, J.H.; Destler, W.W.; Segalov, Z.; Radack, D.J.; Rosenbury, E.T.; Rodgers, J.; Antonsen T.M. Jr.; Granatstein, V.L.; Mayergoyz, I.D.

1988-07-01

63

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

64

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

65

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

66

Electron velocity distributions and plasma waves associated with the injection of an electron beam into the ionosphere  

SciTech Connect

An electron beam was injected into Earth's ionosphere on August 1, 1985, the flight of the space shuttle /ital Challenger/ as part of the objectives of the Spacelab 2 mission. In the wake of the space shuttle a magnetically aligned sheet of electrons returning from the direction of propagation of the beam was detected with the free-flying plasma Diagnostics Package. The thickness of this sheet of returning electrons was about 20 m. Large intensifications of broadband electrostatic noise were also observed within this sheet of electrons. A numerical simulation of the interaction of the electron beam with the ambient ionospheric plasmas is employed to show that the electron beam excites electron plasma oscillations and that it is possible for the ion ascoustic instability to provide a returning flux of hot electorns by means of quasi-linear diffusion. /copyright/ American Geophysical Union 1989

Frank, L. A.; Paterson, W. R.; Ashour-Abdalla, M.; Schriver, D.; Kurth, W. S.; Gurnett, D. A.

1989-06-01

67

Electron cyclotron resonance plasma photos  

SciTech Connect

In order to observe and study systematically the plasma of electron cyclotron resonance (ECR) ion sources (ECRIS) we made a high number of high-resolution visible light plasma photos and movies in the ATOMKI ECRIS Laboratory. This required building the ECR ion source into an open ECR plasma device, temporarily. An 8MP digital camera was used to record photos of plasmas made from Ne, Ar, and Kr gases and from their mixtures. We studied and recorded the effect of ion source setting parameters (gas pressure, gas composition, magnetic field, and microwave power) to the shape, color, and structure of the plasma. The analysis of the photo series gave us many qualitative and numerous valuable physical information on the nature of ECR plasmas.

Racz, R.; Palinkas, J. [Institute of Nuclear Research (ATOMKI), H-4026 Debrecen, Bem ter 18/c (Hungary); University of Debrecen, H-4010 Debrecen, Egyetem ter 1 (Hungary); Biri, S. [Institute of Nuclear Research (ATOMKI), H-4026 Debrecen, Bem ter 18/c (Hungary)

2010-02-15

68

Cluster Observations of Energy Conversion Regions in the Plasma Sheet  

NASA Astrophysics Data System (ADS)

Cluster allows for the first time a systematic examination of energy conversion, by the evaluation of the power density, E J, with E the electric field and J the current density. Following a careful inspection of the Cluster plasma sheet data from the summer and fall of 2001, we selected 43 energy conversion regions (ECRs), out of which 26 concentrated load regions (CLRs, E J > 0) and 17 concentrated generator regions (CGRs, E J < 0). As expected in the tail, at about 19 RE geocentric distance, the energy conversion is more intense for CLRs, on average some 25 pW/m3, compared to some 5 pW/m3 for CGRs. The CLRs are located closer to the neutral sheet and dominated by E and J in the GSE y direction, unlike the CGRs, that prefer locations towards the plasma sheet boundary layer, where the deviations of E and J from the GSE y direction can be significant. The ECRs are often associated with high speed bulk flows, on average faster and hotter for CLRs. The CLRs appear to be associated also with density drop and sometimes with temperature anisotropy, T? > T?, features which are observed less frequently for CGRs.

Marghitu, O.; Hamrin, M.; Klecker, B.; Rnnmark, K.; Buchert, S.; Kistler, L. M.; Andr, M.; Rme, H.

69

Heating of the plasma sheet by broadband electromagnetic waves  

NASA Astrophysics Data System (ADS)

demonstrate that broadband low-frequency electromagnetic field fluctuations embedded within fast flows throughout the Earth's plasma sheet may drive significant ion heating. This heating is nearly entirely in the direction perpendicular to the background magnetic field and is estimated to occur at an average rate of ~1 eV/s with rates in excess of 10 eV/s within one standard deviation of the average value over all observed events. For an Earthward flow the total change in temperature along a flow path may exceed one keV and for "wave-rich" flows can be comparable to that expected due to conservation of the first adiabatic invariant. The consequent increase in plasma pressure and flux tube entropy may lead to braking of inward motion and the suppression of plasma interchange.

Chaston, C. C.; Bonnell, J. W.; Salem, C.

2014-12-01

70

Electronic structures of graphane sheets with foreign atom substitutions  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we investigate the electronic structures of the recently synthesized hydrogenated graphene, called graphane, with substitutional B, N, P, and Al atoms. We find that both the n-type and p-type substitutions can cause the semiconductor-to-metal transitions in graphane sheets. The substitutional B and Al atoms induce magnetic moments of nearby carbon atoms. Moreover, the B-substituted graphane sheets have the concentration-dependent magnetic properties, while the Al-substituted ones exhibit robust half-metallic behaviors. Our studies demonstrate that the substituted graphane sheets have potential applications in nanoelectronics and spintronics.

Wang, Yanli; Ding, Yi; Shi, Siqi; Tang, Weihua

2011-04-01

71

The origins of the plasma in the distant plasma sheet  

Microsoft Academic Search

It is pointed out that ion mass spectrometers operating in the keV range have recently begun to provide a new class of information on magnetospheric processes. One of the principal motivations for the development of energetic ion mass spectrometers has been to investigate the origins of the hot plasma populations of the magnetosphere. Peterson et al. (1981) were able to

R. D. Sharp; W. Lennartsson; W. K. Peterson; E. G. Shelley

1982-01-01

72

Formation and transport of PCM-focused sheet electron beams  

SciTech Connect

Sheet electron beams have the potential to make possible higher power sources of coherent millimeter-wave radiation. Recent studies indicate the feasibility of stable focusing of low-emittance sheet beams using periodically-cusped magnetic (PCM) fields. The authors will discuss progress on the preparation of experiments to study the stability and transport of PCM-focused sheet electron beams. This includes a laboratory method to form sheet beams using magnetic quadrupole lenses, a commercially relevant strip-beam thermionic electron gun design, and a PCM configuration to confine the beam in both transverse dimensions. The experiments will involve a 10 kV, 2 A, 1.6 mm X 36 mm elliptical sheet beam and a PCM array with a 3.5 cm spatial period. Peak midplane magnetic fields of 1.0 kG should be adequate for stable beam focusing. The experimental studies will be complemented by numerical simulations using the MAGIC particle-in-cell code and the TOSCA 3-D magnetic design code.

Basten, M.A.; Booske, J.H.; Anderson, J.; Scharer, J.E. [Univ. of Wisconsin, Madison, WI (United States). Electrical and Computer Engineering Dept.; True, R. [Litton Electron Devices, San Carlos, CA (United States)

1994-12-31

73

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

74

Dense attosecond electron sheets from laser wakefields using an up-ramp density transition.  

PubMed

Controlled electron injection into a laser-driven wakefield at a well defined space and time is reported based on particle-in-cell simulations. Key novel ingredients are an underdense plasma target with an up-ramp density profile followed by a plateau and a fairly large laser focus diameter that leads to an essentially one-dimensional (1D) regime of laser wakefield, which is different from the bubble (complete blowout) regime occurring for tightly focused drive beams. The up-ramp profile causes 1D wave breaking to occur sharply at the up-ramp-plateau transition. As a result, it generates an ultrathin (few nanometer, corresponding to attosecond duration), strongly overdense relativistic electron sheet that is injected and accelerated in the wakefield. A peaked electron energy spectrum and high charge (?nC) distinguish the final sheet. PMID:23581329

Li, F Y; Sheng, Z M; Liu, Y; Meyer-ter-Vehn, J; Mori, W B; Lu, W; Zhang, J

2013-03-29

75

Observational determination of the adiabatic index in the quiet time plasma sheet  

NASA Technical Reports Server (NTRS)

An anticorrelation in the plasma density and temperature in the quiet time (AE of less than 100 nT) central plasma sheet has been demonstrated. The present results suggest that the adiabatic index is less than 1, and that earthward convecting plasma cools as it is compressed. It is pointed out that there are no observations which can presently account for the heat loss noted for the earthward convecting flux tubes of the central plasma sheet.

Huang, C. Y.; Goertz, C. K.; Frank, L. A.; Rostoker, G.

1989-01-01

76

On the cause of plasma-sheet thinning during magnetospheric substorms  

NASA Technical Reports Server (NTRS)

It is proposed that the thinning of the plasma sheet during magnetospheric substorms is caused by an earthward gradient of the rate of magnetic merging (field annihilation) in the tail current sheet, which is in turn caused by the velocity-dependent access of plasma mantle particles to the current sheet. A simple model calculation based on this effect predicts a thinning time constant of the order of 1 hour, consistent with observations. The mechanism is also consistent with the observed correlation between plasma-sheet thinning and southward-directed magnetic field components in the solar wind.

Hill, T. W.; Reiff, P. H.

1980-01-01

77

A statistical analysis of heliospheric plasma sheets, heliospheric current sheets, and sector boundaries observed in situ by STEREO  

NASA Astrophysics Data System (ADS)

heliocentric orbits of STEREO A and B with a separation in longitude increasing by about 45 per year provide the unique opportunity to study the evolution of the heliospheric plasma sheet (HPS) on a time scale of up to ~2 days and to investigate the relative locations of HPSs and heliospheric current sheets (HCSs). Previous work usually determined the HCS locations based only on the interplanetary magnetic field. A recent study showed that a HCS can be taken as a global structure only when it matches with a sector boundary (SB). Using magnetic field and suprathermal electron data, it was also shown that the relative location of HCS and SB can be classified into five different types of configurations. However, only for two out of these five configurations, the HCS and SB are located at the same position and only these will therefore be used for our study of the HCS/HPS relative location. We find that out of 37 SBs in our data set, there are 10 suitable HPS/HCS event pairs. We find that an HPS can either straddle or border the related HCS. Comparing the corresponding HPS observations between STEREO A and B, we find that the relative HCS/HPS locations are mostly similar. In addition, the time difference of the HPSs observations between STEREO A and B match well with the predicted time delay for the solar wind coming out of a similar region of the Sun. We therefore conclude that HPSs are stationary structures originating at the Sun.

Liu, Y. C.-M.; Huang, J.; Wang, C.; Klecker, B.; Galvin, A. B.; Simunac, K. D. C.; Popecki, M. A.; Kistler, L.; Farrugia, C.; Lee, M. A.; Kucharek, H.; Opitz, A.; Luhmann, J. G.; Jian, Lan

2014-11-01

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

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

Microsoft Academic Search

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

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

2001-01-01

80

An Equilibrium in Negative Hydrogen Ion Production Process Related to the Sheet Plasma Experiment  

Microsoft Academic Search

In the sheet plasma experiment, plasma potentials decreased but negative hydrogen ion currents increased toward the outside. The negative hydrogen ions are pushed inside by the electric field and are not coming out from the plasma unless an equilibrium exists somehow. A relation between negative hydrogen ion currents and plasma potentials is well explained by the one-dimensional Saha equation, from

Kouichi Jimbo

1996-01-01

81

Transient field-aligned electric fields inside the plasma sheet inferred from measurements of energetic particles  

NASA Astrophysics Data System (ADS)

The presence of transient electric fields inside the plasma sheet of the earth's magnetotail is inferred from observations of proton-electron counterstreaming under certain well determined conditions. Measurements of the angular distributions and the energy spectra of the proton (Ep = 300 keV or greater) and electron (Ee = 220 keV or greater) intensities by IMP-7 and 8 S/C provide the means to compute the amplitude of the transient fields. Estimates of the 'effective' potential along the magnetic field were obtained independently for the energetic proton and electron populations. After Compton-Getting correction of the proton intensities to the frame of reference moving with the translation velocity of the ambient energetic proton population, the two independent estimates were found to be in good agreement, yielding energy gains along the B-field of about 30-100 keV.

Sarafopoulos, D. V.; Sarris, E. T.

1987-08-01

82

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

NASA Astrophysics Data System (ADS)

We developed a novel approach to the fabrication of three-dimensional, nanoporous graphene sheets featuring a high specific surface area of 734.9 m2 g?1 and an ultrahigh pore volume of 4.1 cm3 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.

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

2014-12-01

83

A reflector antenna for electron plasma waves  

Microsoft Academic Search

Summary form only given. A linear antenna with a mesh reflector immersed in a plasma was studied in the frequency range where electron plasma waves can propagate. The electron plasma wave appears to be difficult to excite and to be buried in the noise level because it is damped by Landau damping except in a very small region of frequency

Y. Morita; R. Kurati; S. Egashira

1992-01-01

84

Bursty bulk flows in the inner central plasma sheet  

SciTech Connect

High speed flow in the inner central plasma sheet are studied, together with the concurrent behavior of the plasma and magnetic field, by using AMPTE/IRM data from {approx} 9 to 19 R{sub E} in the Earth's magnetotail. The conclusions drawn from the detailed analysis of a representative event are reinforced by a superposed epoch analysis on 2 years of data. The high-speed flows organize themselves in 10-min time scale flow enhancements which they call 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 temperatures 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 {times} 10{sup 19} ergs/R{sub E}{sup 2}.

Angelopoulos, V.; Kennel, C.F.; Coroniti, F.V.; Kivelson, M.G.; Pellat, R.; Walker, R.J. (Univ. of California, Los Angeles (United States)); Baumjohann, W.; Paschmann, G. (Max-Planck-Inst. fuer extraterrestrische Physik, Garching (West Germany)); Luehr, H. (Univ. Braunschweig (West Germany))

1992-04-01

85

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

86

Interaction of an interplanetary shock with the heliospheric plasma sheet  

NASA Technical Reports Server (NTRS)

Interplanetary shocks often propagate along the heliospheric plasma sheet (HPS) where the interplanetary magnetic field (IMF) changes its polarity. This problem is investigated by the time-dependent 2.5-D MHD numerical model in the meridional plane. An example of computation is shown in the figure using density (log) contours and IMF vectors. Values of plasma parameters along the HPS fluctuate in time due to the Kelvin-Helmholtz instability. The HPS with its decreased intensity of the IMF as well as with its increased mass density causes a dimple in the shock structure (relatively weak for the forward shock, significant for the reverse shock, and very large for the contact discontinuity). Beyond the forward shock, the HPS is slightly compressed due to the post-shock increase of the azimuthal IMF component. Then follows expansion of the HPS surrounded by the highly-deformed contact discontinuity. A significant draping of IMF lines occurs around this structure that increases the meridional component of the IMF. This can cause a favorable condition for initiation of a geomagnetic storm.

Odstrcil, D.; Dryer, M.; Smith, Z.

1995-01-01

87

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

88

Observational determination of the adiabatic index in the quiet time plasma sheet  

Microsoft Academic Search

The authors show that in the quiet time (AE<100nT) central plasma sheet the plasma density and temperature are, in general, anticorrelated. This indicates that the adiabatic index is less than 1 and that earthward convecting plasma cools as it is compressed. They do not have a satisfactory explanation for this surprising result.

C. Y. Huang; C. K. Goertz; L. A. Frank; G. Rostoker

1989-01-01

89

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

90

Cluster observations of sub-proton scale magnetic holes in Earth's plasma sheet  

NASA Astrophysics Data System (ADS)

Spacecraft observations from Earth's plasma sheet have shown that magnetic holes with high electron perpendicular temperature anisotropy can develop when the magnetotail is in a relaxed (dipolarized) state. As these appear in environments that are stable to the mirror-mode instability and they often have cross-field scale-sizes equivalent to or shorter than the local proton gyro radius, these magnetic holes cannot exclusively be explained in terms of a standard mirror-mode growth from an anisotropic proton distribution. We here investigate a series of such events observed by the Cluster spacecraft and assess whether they may in be explained in terms of electron-vortex magnetic holes (EVMH) - a formation scenario where turbulent depressions in the magnetic field interact with the local electron population, leading to a self-consistent growth of magnetic holes by trapped or quasi-trapped electrons with high energies and large pitch angles. Some of the observable features of EVMH are that they should be close to circularly symmetric with non-gyrotropic electron distributions, and there should be a clear relation between the characteristic electron energy and their cross-field scale-size. In addition to evaluating these criteria, we also attempt to constrain the scale-size of the observed magnetic holes, and we show that they in fact can be highly localized in both the direction parallel and perpendicular to the local magnetic field.

Sundberg, Torbjorn; Burgess, David; Haynes, Christopher T.

2014-05-01

91

Plasma Sheet and Ring Current Formation from Solar and Polar Wind Sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and quiet ring current in the framework of collisionless test particle motions in 3D magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft, during 2001 and 2002. Many particles were initiated in two regions representative of the solar wind

T. E. Moore; M. C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2004-01-01

92

Plasma Sheet and (non-storm) Ring Current Formation from Solar and Polar Wind Sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and geosynchronous region (non-storm) ring current in the framework of collisionless test particle motions in 3D magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft, during 2001 and 2002. Many particles were initiated in two regions representative of the

T. E. Moore; M. C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2004-01-01

93

Plasma sheet and (nonstorm) ring current formation from solar and polar wind sources  

Microsoft Academic Search

We consider the formation of the plasma sheet and geosynchronous region (nonstorm) ring current in the framework of collisionless test particle motions in three-dimensional magnetospheric fields obtained from self-consistent MHD simulations. Simulation results are compared with observations of the near-Earth plasma sheet from the Polar spacecraft during 2001 and 2002. Many particles were initiated in two regions representative of the

T. E. Moore; M.-C. Fok; M. O. Chandler; C. R. Chappell; S. P. Christon; D. C. Delcourt; J. Fedder; M. Huddleston; M. Liemohn; W. K. Peterson; S. Slinker

2005-01-01

94

Substorm Evolution in the Near-Earth Plasma Sheet  

NASA Technical Reports Server (NTRS)

The goal of this project is to determine precursors and signatures of local substorm onset and how they evolve in the plasma sheet using the Geotail near-Earth database. This project is part of an ongoing investigation involving this PI, Nelson Maynard (Mission Research Corporation), and William Burke (AFRL) toward an empirical understanding of the onset and evolution of substorms. The first year began with dissemination of our CRRES findings, which included an invited presentation and major publication. The Geotail investigation began with a partial survey of onset signature types at distances X less than 15 R(sub E) for the first five months (March-July 1995) of the Geotail near-Earth mission. During the second year, Geotail data from March 1995 to present were plotted. Various signatures at local onset were catalogued for the period through 1997. During this past year we performed a survey of current-disruption-like (CD-like) signatures at distances X less than or equal to 14 R(sub E) for the three years 1995-1997.

Erickson, Gary M.

2003-01-01

95

High current density sheet-like electron beam generator  

NASA Astrophysics Data System (ADS)

Sheet electron beams are very desirable for coupling to the evanescent waves in small millimeter wave slow-wave circuits to achieve higher powers. In particular, they are critical for operation of the free-electron-laser-like Orotron. The program was a systematic effort to establish a solid technology base for such a sheet-like electron emitter system that will facilitate the detailed studies of beam propagation stability. Specifically, the effort involved the design and test of a novel electron gun using Lanthanum hexaboride (LaB6) as the thermionic cathode material. Three sets of experiments were performed to measure beam propagation as a function of collector current, beam voltage, and heating power. The design demonstrated its reliability by delivering 386.5 hours of operation throughout the weeks of experimentation. In addition, the cathode survived two venting and pump down cycles without being poisoned or losing its emission characteristics. A current density of 10.7 A/sq cm. was measured while operating at 50 W of ohmic heating power. Preliminary results indicate that the nearby presence of a metal plate can stabilize the beam.

Chow-Miller, Cora; Korevaar, Eric; Schuster, John

96

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

97

Negative potentials above the day-side lunar surface in the terrestrial plasma sheet: Evidence of non-monotonic potentials  

NASA Astrophysics Data System (ADS)

The Lunar Prospector (LP) Electron Reflectometer (ER) instrument conducted a series of measurements of the lunar surface potential in a variety of conditions. Occasionally, when the Moon was exposed to the terrestrial plasma sheet and in daylight, large, unexpected negative potentials (-500 V) were measured. In this paper, we compare LP ER measurements with one-dimensional particle-in-cell simulations of the potential above the lunar surface when the Moon is exposed to both solar UV radiation and the terrestrial plasma sheet. The simulations show that large negative potentials will be measured by LP ER due to the presence of stable, non-monotonic potentials. Implications of these measurements to other airless bodies in the solar system are also discussed.

Poppe, Andrew; Halekas, Jasper S.; Hornyi, Mihly

2011-01-01

98

Low sheet resistance titanium nitride films by low-temperature plasma-enhanced atomic layer deposition using design of experiments methodology  

SciTech Connect

A design of experiments methodology was used to optimize the sheet resistance of titanium nitride (TiN) films produced by plasma-enhanced atomic layer deposition (PE-ALD) using a tetrakis(dimethylamino)titanium precursor in a N{sub 2}/H{sub 2} plasma at low temperature (250?C). At fixed chamber pressure (300 mTorr) and plasma power (300?W), the plasma duration and N{sub 2} flow rate were the most significant factors. The lowest sheet resistance values (163??/sq. for a 20?nm TiN film) were obtained using plasma durations ?40?s, N{sub 2} flow rates >60 standard cubic centimeters per minute, and purge times ?60?s. Time of flight secondary ion mass spectroscopy data revealed reduced levels of carbon contaminants in the TiN films with lowest sheet resistance (163??/sq.), compared to films with higher sheet resistance (400600??/sq.) while transmission electron microscopy data showed a higher density of nanocrystallites in the low-resistance films. Further significant reductions in sheet resistance, from 163??/sq. to 70??/sq. for a 20?nm TiN film (corresponding resistivity ?145 ??cm), were achieved by addition of a postcycle Ar/N{sub 2} plasma step in the PE-ALD process.

Burke, Micheal, E-mail: micheal.burke@tyndall.ie; Blake, Alan; Povey, Ian M.; Schmidt, Michael; Petkov, Nikolay; Carolan, Patrick; Quinn, Aidan J., E-mail: aidan.quinn@tyndall.ie [Tyndall National Institute, University College Cork, Cork (Ireland)

2014-05-15

99

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

100

Plasma sources for electrons and ion beams  

SciTech Connect

Plasma devices are commonly used for the production of ion beams. It has been demonstrated that the multicusp generator can produce very low energy ion beams for ion projection lithography applications. The multicusp source has also found important applications in focused ion beam systems. With its high and uniform plasma density, attempts have been made to extract high brightness electron beams from this type of plasma source, making it also useful for electron beam lithography applications. (c) 1999 American Vacuum Society.

Leung, Ka-Ngo [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)] [Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720 (United States)

1999-11-01

101

Average patterns of precipitation and plasma flow in the plasma sheet flux tubes during steady magnetospheric convection  

NASA Technical Reports Server (NTRS)

Average patterns of plasma drifts and auroral precipitation in the nightside auroral zone were constructed during a steady magnetospheric convection (SMC) event on February 19, 1978. By comparing these patterns with the measurements in the midtail plasma sheet made by ISEE-1, and using the corresponding magnetic field model, the following features are inferred: (1) the concentration of the earthward convection in the midnight portion of the plasma sheet (convection jet); (2) the depleted plasma energy content of the flux tubes in the convection jet region; and (3) the Region-1 field-aligned currents generated in the midtail plasma sheet. It is argued that these three elements are mutually consistent features appearing in the process of ionosphere-magnetosphere interaction during SMC periods. These configurational characteristics resemble the corresponding features of substorm expansions (enhanced convection and 'dipolarized' magnetic field within the substorm current wedge) and appear to play the same role in regulating the plasma flow in the flux tubes connected to the plasma sheet.

Sergeev, V. A.; Lennartsson, W.; Pellinen, R.; Vallinkoski, M.; Fedorova, N. I.

1990-01-01

102

Resonant laser plasma interactions and electron acceleration  

NASA Astrophysics Data System (ADS)

The interaction between intense laser radiation and a plasma is often dominated by the generation of large amplitude plasma waves. These plasma waves can drastically affect both the plasma particles of which they are composed and the laser radiation by which they are driven. This dissertation addresses two facets of these processes. In part I, the acceleration of electrons by highly nonlinear plasma waves is addressed. It is shown experimentally that energy gains exceeding the dephasing limit of linear theory are possible. In part II, the recent theory of electromagnetically induced transparency in a plasma is examined. It is found that the requirements of causality do not allow for the transmission of electromagnetic radiation through an overdense plasma as conceived in the original theory. However, it is possible for radiation below the cutoff frequency to be generated by a plasma. Also, a Raman-type instability is found to afflict electromagnetic waves in a plasma even when the density exceeds quarter-critical.

Gordon, Daniel Francis

1999-10-01

103

Thin sheets of energetic electrons upstream from the earth's bow shock  

Microsoft Academic Search

ISEE spacecraft observations show that energetic, > or =16 keV electrons are injected into the region upstream from the Earth's bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface. Lower energy electrons leave the shock over a much broader region. Although the energetic electron intensity

K. A. Anderson; R. P. Lin; F. Martel; C. S. Lin; G. K. Parks; H. Reme

1979-01-01

104

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

105

Creating standardized electronic data sheets for applications and devices  

NASA Astrophysics Data System (ADS)

The Air Force Research Laboratory (AFRL) continues to develop infrastructure to enable the modular construction of satellites using an open network architecture and off-the-shelf avionics for space systems. Recent efforts have included the refinement of an ontology to formalize a standard language for the exchange of data and commands between components, including hardware and software, which is still evolving. AFRL is also focusing effort on creating standard interfaces using electronic data sheets based on this recently defined ontology. This paper will describe the development of standard interfaces that are documented in terms of an electronic datasheet for a specific application. The datasheet will identify the standard interfaces between hardware devices and software applications that are needed for a specific satellite function, in this case, a spacecraft guidance, navigation, and control (GN& C) application for Sun pointing. Finally, the benefits of using standardized interfaces will be discussed.

Hansen, L. J.; Lanza, D.

106

Low-frequency waves in the near-Earth plasma sheet  

SciTech Connect

The authors present an analysis of plasma wave measurements in the plasma sheet in the frequency range from 0.1 mHz to 8 Hz. They compute power spectra in several different bands, and look at this data against location in the plasma sheet, magnetic field, and magnetospheric activity. In general the power spectra increase with decreasing frequency over the full range. Wave power is enhanced during periods of enhanced activity, or substorms. Fluctuations are in the range of nanotesla, and tend to be stronger along X{sub GSM} as opposed to the two orthogonal directions.

Bauer, T.M.; Baumjohann, W.; Treumann, R.A. [Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany)] [and others] [Max-Planck-Institut fuer Extraterrestrische Physik, Garching (Germany); and others

1995-06-01

107

An electron conductivity model for dense plasmas  

NASA Astrophysics Data System (ADS)

An electron conductivity model for dense plasmas is described which gives a consistent and complete set of transport coefficients including not only electrical conductivity and thermal conductivity, but also thermoelectric power, and Hall, Nernst, Ettinghausen, and Leduc-Righi coefficients. The model is useful for simulating plasma experiments with strong magnetic fields. The coefficients apply over a wide range of plasma temperature and density and are expressed in a computationally simple form. Different formulas are used for the electron relaxation time in plasma, liquid, and solid phases. Comparisons with recent calculations and available experimental measurement show the model gives results which are sufficiently accurate for many practical applications.

Lee, Y. T.; More, R. M.

1984-05-01

108

Plasma Jet Diagnostic for Runaway Electron Beam-Plasma Interaction  

NASA Astrophysics Data System (ADS)

FAR-TECH's recently developed C60/C plasma jet has the potential to rapidly and significantly increase electron density, deep into tokamak plasma, hence to change the `critical electric field' as well as the runaway electrons (REs) collisional drag, during different phases of REs dynamics. Suitably chosen visible/UV lines emitted by the injected C ions can then be used for line intensity quantitative spectroscopy, allowing the diagnostic of the RE beam-plasma interaction. The C60 delivered in 1 ms by the prototype plasma jet system, estimated to be 75 mg, carries 4x10^21 C atoms and 2.4x10^22 electrons, and would lead to an electron density ne2.4x10^21 m-3, i.e. 60 times larger than typical DIII-D pre-disruption value (ne0 4x10^19 m-3). While the prototype's C60/C plasma jet mass is not sufficient to achieve the Rosenbluth electron density in DIII-D, it delivers a total number of electrons 5 times larger than that of the Ar pellet, with the advantage of a much faster response and precisely chosen delivery time. We will present several proposed diagnostic schemes using rapid C60/C plasma jet injection capability in different phases of the discharge in DIII-D.

Bogatu, I. N.; Thompson, J. R.; Galkin, S. A.; Kim, J. S.; Brockington, S.; Case, A.; Messer, S. J.; Witherspoon, F. D.

2012-10-01

109

Wiggler focused relativistic sheet beam propagation in a planar free-electron laser configuration  

SciTech Connect

The propagation of a relativistic sheet electron beam through a spatially periodic magnetic field (wiggler) has been studied experimentally. The wiggler serves two purposes; it provides beam focusing as well as the magnetostatic pump for the free-electron laser (FEL) interaction. Experiments conducted to study sheet beam generation and propagation in a short-period (1 cm) planar wiggler are presented. A 500 keV, 7 A sheet electron beam was propagated through a 3.2 mm waveguide with negligible losses due to intercepted current. In addition, the first observation of wiggler-induced radiation was obtained from the sheet beam FEL in a short-period wiggler oscillator configuration.

Radack, D.J.; Booske, J.H.; Carmel, Y.; Destler, W.W. (Laboratory for Plasma Research, University of Maryland, College Park, Maryland 20742-3511 (US))

1989-11-13

110

Vortex and ULF wave structures in the plasma sheet of the Earth magnetosphere  

NASA Astrophysics Data System (ADS)

We studied the ULF wave packet propagation in the Earth plasma sheet making use of the magnetic field measurements from FGM detector and plasma properties from CORRAL detector aboard the Interball-Tail spacecraft. The MHD vortex structures were observed simultaneously with the Pc5 ULF waves. The vortex spatial scale was found to be about 1200-3600 km and the velocity is 4-16 km/s transverse to the background magnetic field. We studied numerically the dynamics of the initial vortex perturbations in the plasma system with parameters observed in the Earth plasma sheet. The system with the vector nonlinearity was processed making use of the full reduction scheme. The good agreement of the experimental value of the vortex structure velocity with numerical results was obtained. The velocity was found to be close to the local plasma drift velocity.

Saliuk, D. A.; Agapitov, O. V.

2013-08-01

111

The motion and magnetic structure of the plasma sheet near 30 earth radii  

NASA Technical Reports Server (NTRS)

Data taken by the NASA-GSFC magnetometer aboard the Explorer 34 satellite are analyzed in an effort to ascertain the average motion and magnetic field structure of the plasma sheet near 30 earth radii. It is found that the flapping motion of the plasma sheet in the solar ecliptic Z-coordinate is characterized by a typical speed of 90 km/sec and an amplitude of plus or minus 2 earth radii. Results suggest that there exists a layer of nearly uniform cross-tail current density in the central region of the plasma sheet approximately 2.3-2.6 earth radii thick within which the solar-magnetospheric X-component of the magnetic field changes from 10 gamma to -10 gamma.

Bowling, S. B.; Wolf, R. A.

1974-01-01

112

Magnetic quadrupole formation of elliptical sheet electron beams for high-power microwave devices  

Microsoft Academic Search

Sheet electron beams are attractive for high-power microwave sources due to their ability to transport high current, at reduced current density, through thin clearance apertures and in close proximity to walls or RF structures. This paper reports on the theoretical investigation of magnetic quadrupole formation of elliptical sheet electron beams for use in high-power microwave devices. The beam envelope equations

M. A. Basten; J. H. Booske; J. Anderson

1994-01-01

113

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

114

Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis  

NASA Astrophysics Data System (ADS)

Multiple-harmonic electromagnetic waves in the ULF band have occasionally been observed in Earth's magnetosphere, both near the magnetic equator in the outer plasmasphere and in the plasma sheet boundary layer (PSBL) in Earth's magnetotail. Observations by the Cluster spacecraft of multiple-harmonic electromagnetic waves with fundamental frequency near the local proton cyclotron frequency, ?cp, were recently reported in the plasma sheet boundary layer by Broughton et al. (2008). A companion paper surveys the entire magnetotail passage of Cluster during 2003, and reports 35 such events, all in the PSBL, and all associated with elevated fluxes of counterstreaming ions and electrons. In this study we use observed pitch angle distributions of ions and electrons during a wave event observed by Cluster on 9 September 2003 to perform an instability analysis. We use a semiautomatic procedure for developing model distributions composed of bi-Maxwellian components that minimizes the difference between modeled and observed distribution functions. Analysis of wave instability using the WHAMP electromagnetic plasma wave dispersion code and these model distributions reveals an instability near ?cp and its harmonics. The observed and model ion distributions exhibit both beam-like and ring-like features which might lead to instability. Further instability analysis with simple beam-like and ring-like model distribution functions indicates that the instability is due to the ring-like feature. Our analysis indicates that this instability persists over an enormous range in the effective ion beta (based on a best fit for the observed distribution function using a single Maxwellian distribution), ?', but that the character of the instability changes with ?'. For ?' of order unity (for instance, the observed case with ?' 0.4), the instability is predominantly electromagnetic; the fluctuating magnetic field has components in both the perpendicular and parallel directions, but the perpendicular fluctuations are larger. If ?' is greatly decreased to about 5 10-4 (by increasing the magnetic field), the instability becomes electrostatic. On the other hand, if ?' is increased (by decreasing the magnetic field), the instability remains electromagnetic, but becomes predominantly compressional (magnetic fluctuations predominantly parallel) at ?' 2. The ?' dependence we observe here may connect various waves at harmonics of the proton gyrofrequency found in different regions of space.

Denton, R. E.; Engebretson, M. J.; Keiling, A.; Walsh, A. P.; Gary, S. P.; DCrAu, P. M. E.; Cattell, C. A.; RMe, H.

2010-12-01

115

Turbulence, currents sheets, and shock waves in the cosmic plasma  

NASA Astrophysics Data System (ADS)

Recent advances in the theory of turbulence are first discussed, including the dynamics of magnetic fields in space (e.g., dynamo theory) and processes of fast energy transformation. The physics of current sheets is then discussed in some detail; it is noted that current sheets appear as the result of the loss of equilibriunm of magnetic configurations, particularly in the solar corona, leading to heating of the upper parts of the solar atmosphere, solar flares, and other active phenomena. Also considered are the generation and propagation of shock waves in the interplanetary and interstellar media.

Vainshtein, Samuil I.; Bykov, Andrei M.; Toptygin, Igor'n.

116

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

117

Amplitude modulation of electron plasma waves in a quantum plasma  

SciTech Connect

Using the one dimensional quantum hydrodynamic model for a two-component electron-ion dense quantum plasma the linear and nonlinear properties of electron plasma waves are studied including ion motion. By using the standard method of multiple scales perturbation technique a nonlinear Schroedinger equation containing quantum effects is derived. From this equation it is shown that with immobile ions an electron plasma wave becomes modulationally unstable in two distinct regions of the wavenumber. Numerical calculation shows that the stability domain of the wavevector shrinks with the increase in quantum diffraction effect. It is also found that the growth rate of instability in the high wavenumber region increases with the increase in quantum effect. Ion motion is found to have significant effect in changing the stability/instability domains of the wavenumber in the low k-region.

Ghosh, Basudev; Chandra, Swarniv [Department of Physics, Jadavpur University, Kolkata 700032 (India); Paul, S. N. [Swami Vivekananda Institute of Science and Technology, Dakshin Gobindapur, P.S.-Sonarpur, Kolkata 700145 (India)

2011-01-15

118

Survey of 0. 1- to 16-keV/e plasma sheet ion composition  

SciTech Connect

A large statistical survey of the 0.1- to 16-keV/e plasma sheet ion composition has been carried out using data obtained by the Plasma Composition Experiment on ISEE 1 between 10 and 23 R/sub E/ during 1978 and 1979. This survey includes more than 10 times the quantity of data used in earlier studies of the same topic and makes it possible to investigate in finer detail the relationship between the ion composition and the substorm activity. The larger data base also makes it possible for the first time to study the spatial distribution of the principal ion species. As found in previous studies, the ion composition has a large variance at any given value of the AE index, but a number of distinct trends emerge when the data are averaged at each activity level. During quiet conditions the plasma sheet is dominated by ions of solar origin (H/sup +/ and He/sup + +/), as found in earlier studies, and these ions are most numerous during extended periods of very low activity (AE< or approx. =30 ..gamma..). The quiet time density of these ions is particularly large in the flanks of the plasma sheet (GSM Yapprox. +- 10 R/sub E/), where it is about twice as large as it is near the central axis of the plasma sheet (Y = Z = 0). In contrast, the energy of these ions peaks near the central axis.

Lennartsson, W.; Shelley, E.G.

1986-03-01

119

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

120

Thermal Structure of Supra-arcade Downflows and Flare Plasma Sheets  

NASA Astrophysics Data System (ADS)

We use Hinode/XRT and SDO/AIA data to determine the thermal structure of supra arcade downflows as well as the surrounding plasma sheet. Using the multiple filters and broad temperature coverage provided by the combination of these two telescopes, we construct DEMs in the fan plasma and the supra-arcade downflows. Several models have indicated that the plasma inside the supra-arcade downflows should be significantly hotter than the surrounding plasma, but about an order of magnitude less dense. However, we find that the temperatures of the plasma within the downflows are either roughly the same as or lower than the surrounding fan plasma, with only one exception. We also compare the thermal structure of the supra-arcade plasma with calculations of the divergence of the velocity of the plasma in the sheet in order to locate evidence of adiabatic cooling and heating. The velocity fields are calculated using local correlation tracking applied to high-resolution sequences of AIA images. We find preliminary evidence that diverging velocity fields are cooler and less dense than the surrounding plasma.

Reeves, Kathy; Hanneman, W.; McKenzie, D. E.

2013-07-01

121

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

122

Energy Storage and Release at the Inner Edge of the Plasma Sheet  

Microsoft Academic Search

The inner edge of the plasma sheet, as a region of transition from the dipolar to stretched magnetic field topology, may stay in the equilibrium for long lasting periods. At the same time, relatively slow energy storage, and its release at pseudo-breakups and substorm onsets, occur in this region. We use three complimentary MHD models, full nonlinear MHD, Lagrangian approach,

I. O. Voronkov; V. I. Prosolin; P. Dobias; J. C. Samson

2003-01-01

123

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

124

Laser-Plasma Acceleration of Electrons and Plasma Diagnostics  

E-print Network

to miniaturize proton cancer therapy. Laser MeV protons Target H-rich film e $6 B $0.5 B $0.2 B Laser-plasma proton accelerators are poised. Special Topics - Accel. & Beams 10, 061301 (2007) "Generating multi-GeV electron bunches using single

Shvets, Gennady

125

Electron Bernstein waves in spherical torus plasmas  

SciTech Connect

Propagation and absorption of the electron Bernstein waves (EBWs) in spherical tokamaks (STs) have been intensively discussed in recent years because the EBWs coupled with an externally launched electromagnetic beam seem to be the only opportunity for microwave plasma heating and current drive in the electron cyclotron (EC) frequency range in the STs. The whole problem of the electron Bernstein heating and current drive (EBWHCD) in spherical plasmas is naturally divided into three major parts: coupling of incident electromagnetic waves (EMWs) to the EBWs near the upper hybrid resonance (UHR) surface, propagation and absorption of the EBWs in the plasma interior and generation of noninductive current driven by the EBWs. The present paper is a brief survey of the most important theoretical and numerical results on the issue of EBWs.

Saveliev, A. N. [A.F.Ioffe Physico-Technical Institute, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation)

2006-11-30

126

Electronic transport properties of BN sheet on adsorption of ammonia (NH3) gas.  

PubMed

We report the detection of ammonia gas through electronic and transport properties analysis of boron nitride sheet. The density functional theory (DFT) based ab initio approach has been used to calculate the electronic and transport properties of BN sheet in presence of ammonia gas. Analysis confirms that the band gap of the sheet increases due to presence of ammonia. Out of different positions, the bridge site is the most favorable position for adsorption of ammonia and the mechanism of interaction falls between weak electrostatic interaction and chemisorption. On relaxation, change in the bond angles of the ammonia molecule in various configurations has been reported with the distance between NH3 and the sheet. An increase in the transmission of electrons has been observed on increasing the bias voltage and I-V relationship. This confirms that, the current increases on applying the bias when ammonia is introduced while a very small current flows for pure BN sheet. PMID:25666919

Srivastava, Anurag; Bhat, Chetan; Jain, Sumit Kumar; Mishra, Pankaj Kumar; Brajpuriya, Ranjeet

2015-03-01

127

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

128

30-cm electron cyclotron plasma generator  

NASA Technical Reports Server (NTRS)

Experimental results on the development of a 30-cm-diam electron cyclotron resonance plasma generator are presented. This plasma source utilizes samarium-cobalt magnets and microwave power at a frequency of 4.9 GHz to produce a uniform plasma with densities of up to 3 x 10 to the 11th/cu cm in a continuous fashion. The plasma generator contains no internal structures, and is thus inherently simple in construction and operation and inherently durable. The generator was operated with two different magnetic geometries. One used the rare-earth magnets arranged in an axial line cusp configuration, which directly showed plasma production taking place near the walls of the generator where the electron temperature was highest but with the plasma density peaking in the central low B-field regions. The second configuration had magnets arranged to form azimuthal line cusps with approximately closed electron drift surfaces; this configuration showed an improved electrical efficiency of about 135 eV/ion.

Goede, Hank

1987-01-01

129

Ballooning Instability Induced Plasmoid Formation in Near-Earth Plasma Sheet*  

NASA Astrophysics Data System (ADS)

The formation of plasmoids in the near-Earth magnetotail is believed to be a key element of the substorm onset process. The physical mechanism of plasmoid formation in the plasma sheet has remained a subject of considerable interests and investigations. Previous work has identified a new scenario in MHD simulations where the nonlinear evolution of a ballooning instability is able to induce the formation of plasmoids in a generalized Harris sheet with finite normal magnetic component [1]. In present work, we further examine this novel mechanism for plasmoid formation and explore its implications in the context of substorm onset trigger problem. For that purpose, we adopt the generalized Harris sheet as a model proxy to the near-Earth region of magnetotail during the substorm growth phase. In this region the magnetic component normal to the neutral sheet Bn is weak but nonzero. The magnetic field lines are closed and there are no X-lines. Simulation results indicate that in the higher Lundquist number regime, the linear axial tail mode, which is also known as ``two-dimensional resistive tearing mode'', is stabilized by the finite Bn, hence cannot give rise to the formation of X-lines or plasmoids by itself. On the other hand, the linear ballooning mode is unstable in the same regime, and in its nonlinear stage, the tailward stretching of the plasma sheet in the closed field line region due to the growing ballooning finger structures tends to accelerate the thinning of the near-Earth current sheet. This eventually leads to the formation of a series of plasmoid structures in the near-Earth and middle magnetotail regions of plasma sheet. This new scenario of plasmoid formation suggests a critical role of ballooning instability in the near-Earth plasma sheet in triggering the onset of a substorm expansion. [1] P. Zhu and J. Raeder, Plasmoid formation in current sheet with finite normal magnetic component, Phys. Rev. Lett. 110, 235005 (2013). *Supported by NSF grants AGS-0902360 and PHY-0821899.

Zhu, P.; Raeder, J.

2013-12-01

130

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

131

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

132

First IBEX observations of the terrestrial plasma sheet and a possible disconnection event  

NASA Astrophysics Data System (ADS)

The Interstellar Boundary Explorer (IBEX) mission has recently provided the first all-sky maps of energetic neutral atoms (ENAs) emitted from the edge of the heliosphere as well as the first observations of ENAs from the Moon and from the magnetosheath stagnation region at the nose of the magnetosphere. This study provides the first IBEX images of the ENA emissions from the nightside magnetosphere and plasma sheet. We show images from two IBEX orbits: one that displays typical plasma sheet emissions, which correlate reasonably well with a model magnetic field, and a second that shows a significant intensification that may indicate a near-Earth (10 RE behind the Earth) disconnection event. IBEX observations from 0.5-6 keV indicate the simultaneous addition of both a hot (several keV) and colder (700 eV) component during the intensification; if IBEX directly observed magnetic reconnection in the magnetotail, the hot component may signify the plasma energization.

McComas, D. J.; Dayeh, M. A.; Funsten, H. O.; Fuselier, S. A.; Goldstein, J.; Jahn, J.-M.; Janzen, P.; Mitchell, D. G.; Petrinec, S. M.; Reisenfeld, D. B.; Schwadron, N. A.

2011-02-01

133

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.

134

Electron acoustic blow up solitary waves and periodic waves in an unmagnetized plasma with kappa distributed hot electrons  

NASA Astrophysics Data System (ADS)

Electron acoustic blow up solitary waves and periodic waves are studied in a classical unmagnetized plasma containing cold electron fluid, kappa distributed hot electrons and stationary ions. We obtain Korteweg-de Vries (KdV) equation for electron acoustic waves (EAWs) using the reductive perturbation technique (RPT). Applying bifurcation theory of planar dynamical systems to the obtained KdV equation, we prove the existence of electron acoustic blowup solitary and periodic wave solutions. Depending on different physical parameters, two types of exact explicit solutions of the mentioned waves are derived. Our model may be applied to explain blow up solitary and periodic wave features that may occur in the planetary magnetosphere and the plasma sheet boundary layer.

Saha, Asit; Chatterjee, Prasanta

2014-09-01

135

Electronic and magnetic properties of Fe and Mn doped two dimensional hexagonal germanium sheets  

SciTech Connect

Using first principles density functional theory calculations, the present paper reports systematic total energy calculations of the electronic properties such as density of states and magnetic moment of pristine and iron and manganese doped two dimensional hexagonal germanium sheets.

Soni, Himadri R., E-mail: himadri.soni@gmail.com; Jha, Prafulla K., E-mail: himadri.soni@gmail.com [Department of Physics, Maharaja Krishnakumarsinhji Bhavnagar University, Bhavnagar-364001 (India)

2014-04-24

136

Etching with electron beam generated plasmas  

Microsoft Academic Search

A modulated electron beam generated plasma has been used to dry etch standard photoresist materials and silicon. Oxygen-argon mixtures were used to etch organic resist material and sulfur hexafluoride mixed with argon or oxygen was used for the silicon etching. Etch rates and anisotropy were determined with respect to gas compositions, incident ion energy (from an applied rf bias) and

D. Leonhardt; S. G. Walton; C. Muratore; R. F. Fernsler; R. A. Meger

2004-01-01

137

Near-millimeter free electron lasers with small period wigglers and sheet electron beams  

Microsoft Academic Search

Electron cyclotron resonance heating (ECRH) of plasmas in magnetic fusion research and space-borne radar systems are both projected to require high power radiation sources at wavelength lambda ~ 1 mm. For ECRH, a premium is placed on cw operation combined with high efficiency and moderate voltage in order to meet budgetary contraints. The space-borne radar sources must be compatible with

V. L. Granatstein; T. M. Antonsen; J. H. Booske; W. W. Destler; P. E. Latham; B. Levush; I. D. Mayergoyz; D. J. Radack; Z. Segalov; A. Serbeto

1988-01-01

138

Structural and electronic properties of monolayer hydrogenated honeycomb III-V sheets from first-principles  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we investigate the structural and electronic properties of monolayer hydrogenated honeycomb III-V sheets. The lattice constants and cohesive energies of the hydrogenated III-V (XY H 2, X=B, Al, Ga, and Y =N, P, As) sheets depend on the III-V elements and follow the same trend as the atomic radii of the elements. We find that the short lattice constants correspond to the large cohesive energies of the hydrogenated III-V sheets. Similar to the graphane sheet, the hydrogenated BP and BAs sheets prefer the chair conformation. While for the hydrogenated BN, AlN, AlP, and GaN sheets, the boat conformation is favored. For the hydrogenated AlAs, GaP, and GaAs sheets, the chair and boat conformations are degenerate structures. We obtain that all the hydrogenated III-V sheets are wide-gap semiconductors. With GW corrections, the band gaps of hydrogenated III-V sheets follow the order of nitrogen > phosphorous > arsenic compounds for both the chair and boat conformations.

Wang, Yanli; Shi, Siqi

2010-08-01

139

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

140

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

141

GEOTAIL observation of ring-shaped ion distribution functions in the plasma sheet-lobe boundary  

SciTech Connect

The authors present an analysis of the observations made of ring shaped distribution functions of ion velocities observed in the boundary between the plasma sheet and lobe in regions near X{sub GSM} approximately {minus}70 or {minus} 170 R{sub E}. Data was collected by a particle analyzer configured to observe distribution functions, and the magnetic field instrumentation. The ions were observed to be moving tailward, and the normal to the ring was almost parallel with the magnetic field vector.

Saito, Yoshifumi; Mukai, Toshifumi; Nishida, Atsuhiro; Yamamoto, Tatsundo [Institute of Space and Astronautical Science, Kanagawa (Japan)] [Institute of Space and Astronautical Science, Kanagawa (Japan); Hirahara, Masafumi; Terasawa, Toshio [Univ. of Tokyo (Japan)] [Univ. of Tokyo (Japan); Machida, Shinobu [Kyoto Univ. (Japan)] [Kyoto Univ. (Japan); Kokubun, Susumu [Nagoya Univ. (Japan)] [Nagoya Univ. (Japan)

1994-12-15

142

Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma  

E-print Network

Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma by Erik Peter Gilson B;Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma Copyright Fall 2001 by Erik Peter Gilson #12;1 Abstract Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma by Erik

Gilson, Erik

143

Plasma sheet ion composition at various levels of geomagnetic and solar activity  

NASA Technical Reports Server (NTRS)

The data obtained in the earth's plasma sheet by the Plasma Composition Experiment on the ISEE-1 spacecraft are briefly reexamined. The data are shown in the form of statistically averaged bulk parameters for the four major ions H(+), He(2+), He(+), and O(+) to illustrate the apparent mixture of solar and terrestrial ions, a mixture that varies with geomagnetic and other conditions. Some major differences in the statistical properties of different ions, which may have a bearing on the physics of the solar wind-magnetosphere interaction, are highlighted.

Lennartsson, W.

1987-01-01

144

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

145

Quantum condensation in electron-hole plasmas  

SciTech Connect

We consider quantum condensation in the electron-hole plasma of highly excited semiconductors. A theoretical approach applying the concept of time long-range order in the framework of real time Green's functions is presented and generalizations of the basic equations of quantum condensation are derived. For the quasiequilibrium case, we solve the coupled system of number and gap equations in ladder approximation for a statically screened Coulomb potential. The resulting phase boundary shows a smooth crossover from the Bose-Einstein condensation (BEC) of excitons to a BCS state of electron-hole pairs.

Kremp, D.; Semkat, D.; Henneberger, K. [Universitaet Rostock, Institut fuer Physik, D-18051 Rostock (Germany)

2008-09-15

146

Spatial relaxation of electrons in inert and molecular gas plasmas  

SciTech Connect

The electron kinetics in spatially inhomogeneous plasma regions is a subject of growing interest with respect to the microscopic treatment of real discharge plasmas. In order to improve the understanding of the complex electron behaviour in inhomogeneous plasma regions an efficient approach for solving the one-dimensional inhomogeneous electron Boltzmann equation in weakly ionized, collision dominated plasmas has been recently developed. The kinetic equation includes elastic and inelastic collisions of electrons and the action of an inhomogeneous electric field. This method is used to investigate now the relaxation of the electrons to homogeneous states in different inert and molecular gas plasmas under the action of various constant electric fields.

Sigeneger, F.; Winkler, R. [Institut fuer Niedertemperatur-Plasmaphysik, Greifswald (Germany)

1995-12-31

147

Graphene electron cannon: High-current edge emission from aligned graphene sheets  

SciTech Connect

High-current field emitters are made by graphene paper consist of aligned graphene sheets. Field emission luminance pattern shows that their electron beams can be controlled by rolling the graphene paper from sheet to cylinder. These specific electron beams would be useful to vacuum devices and electron beam lithograph. To get high-current emission, the graphene paper is rolled to array and form graphene cannon. Due to aligned emission array, graphene cannon have high emission current. Besides high emission current, the graphene cannon is also tolerable with excellent emission stability. With good field emission properties, these aligned graphene emitters bring application insight.

Liu, Jianlong; Li, Nannan; Guo, Jing; Fang, Yong; Deng, Jiang [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); Zeng, Baoqing, E-mail: bqzeng@uestc.edu.cn [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); State Key Laboratory of Electronic Thin Films and Integrated Devices Zhongshan Lab, Department of Electronic Engineering, University of Electronic Science and Technology of China Zhongshan Institute, Zhongshan 528402 (China); Wang, Wenzhong; Li, Jiangnan; Hao, Chenchun [School of Science, Minzu University of China, Beijing 100081 (China)

2014-01-13

148

Electronic properties of nano-graphene sheets calculated using quantum chemical DFT  

Microsoft Academic Search

Electronic properties of nano-graphene with hydrogen terminated edges are significantly different from infinite graphene sheets without any defined edge. Structure of edges of 2D graphene sheets are either in trans (zig-zag) or cis (arm-chair) forms and these edges are known to spontaneously reduced by hydrogen to neutralize the valancies of all the carbons at the edges. Recent experiments revealed different

Sangam Banerjee; Dhananjay Bhattacharyya

2008-01-01

149

Stable transport and side-focusing of sheet electron beams in periodically cusped magnetic field configurations  

SciTech Connect

Sheet electron beams and configurations with multiple 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. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, grating TWT`s, and planar FELs. Historically, implementation of sheet beams in microwave devices has been discouraged by their susceptibility to the diocotron instability in solenoidal focusing systems. However, recent theoretical and numerical studies have shown that stable transport of sheet beams is possible in periodically cusped magnetic (PCM) fields. The use of an offset-pole PCM configuration has been shown analytically to provide side-fields for 2-D focusing of the beam, and this has been recently verified with PIC code simulations. The authors present further theoretical studies of sheet and multi-beam transport and discuss experimental measurements of an offset-pole PCM array which is currently being constructed.

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

1995-12-31

150

Laser-Plasma Acceleration of Electrons and Plasma Diagnostics at High Laser Fields  

E-print Network

Laser-Plasma Acceleration of Electrons and Plasma Diagnostics at High Laser Fields Mike Downer: Laser-plasma acceleration is now entering an era of petawatt lasers, tenuous plasmas and multi.5395) Plasma diagnostics 1. Introduction 30 years ago, Tajima and Dawson proposed the idea of accelerating

Shvets, Gennady

151

Three-dimensional particle simulation of plasma instabilities and collisionless reconnection in a current sheet  

NASA Astrophysics Data System (ADS)

Generation of anomalous resistivity and dynamical development of collisionless reconnection in the vicinity of a magnetically neutral sheet are investigated by means of a three-dimensional particle simulation. For no external driving source, two different types of plasma instabilities are excited in the current layer. The lower hybrid drift instability (LHDI) is observed to grow in the periphery of current layer in an early period, while a drift kink instability (DKI) is triggered at the neutral sheet in a late period as a result of the nonlinear deformation of the current sheet by the LHDI. A reconnection electric field grows at the neutral sheet in accordance with the excitation of the DKI. When an external driving field exists, the convective electric field penetrates into the current layer through the particle kinetic effect and collisionless reconnection is triggered by the convective electric field earlier than the DKI is excited. It is also found that the anisotropic ion distribution is formed through the anomalous ion heating by the DKI.

Horiuchi, Ritoku; Sato, Tetsuya

1999-12-01

152

On the identification of plasma sheet flapping waves observed by Cluster  

NASA Astrophysics Data System (ADS)

Runov et al. [2003] and Sergeev et al. [2003, 2004] have reported on low-frequency oscillations of the plasma sheet generated by some impulsive source in the center of the magnetospheric tail and propagating toward the flanks, with velocities that range from a few tens to a few hundreds of km/s. To interpret the finding, a number of wave modes have been invoked and then discarded, for either the group velocities or propagation directions were inconsistent with the observations. In the present paper we examine the MHD ballooning-type waves first described by Safargaleev and Maltsev [1986] who termed them internal ``gravitational'' waves, as a possible candidate to match the observed flapping motions. The role of gravity is played by the centrifugal force, acting on hot plasma in a curved magnetic field. The corresponding dispersion relation indicates propagation in the positive/negative azimuthal direction with a group velocity dependent on the wave number across the magnetic field, half-thickness of the current sheet, and thermal velocity of ions in the neutral sheet. The calculated group velocity ranges from 40 to 400 km/s, being consistent with the observations.

Golovchanskaya, I. V.; Maltsev, Y. P.

2005-01-01

153

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

154

Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma  

E-print Network

Quadrupole Induced Resonant Particle Transport in a Pure Electron Plasma E. Gilson1 and J. Fajans2 that a certain class of resonant electrons follows trajectories that take them out of the plasma. Even though are o® resonance, the lifetime of the plasma is not greatly a®ected by the quadrupole ¯eld, but near

Gilson, Erik

155

Electron-hose instability in an annular plasma sheath  

E-print Network

electron beams through plasma. Stability against transverse beam break-up1 is critical in such applications of an annular plasma sheath with inner radius b1, and outer radius b2, contained within a perfectly conducting 4 and (2) an electron- beam formed channel in a pre-formed plasma.13 In the case of t h e laser

156

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

157

Magnetic quadrupole formation of low-voltage 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. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, grating TWT`s, and planar FELs. One difficulty with the experimental investigation and implementation of sheet beams is the lack of a satisfactory source for large aspect-ratio beams. An attractive solution is the use of magnetic quadrupoles to transform an initially round beam from a conventional Pierce gun into a highly eccentric elliptical beam. Both 2-D envelope simulations and 3-D envelope and PIC code simulations indicate that this is a viable method of sheet beam formation, particularly for experimental investigations where flexibility and low-cost fabrication is desired. The authors are currently constructing a system to experimentally test this method. Features of the experiment include a low-cost commercially available Pierce gun, a four quadrupole sheet beam-forming system, and a highly elliptical output beam. Results of the 3-D PIC simulations of the beam and 3-D magnetostatic finite-element simulations of the quadrupole fringe fields will be discussed. Details of the experimental design and initial experimental measurements are presented.

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

1995-12-31

158

The model of plasma-electronic technology of producing electricity from electron beams  

NASA Astrophysics Data System (ADS)

The article obtains the main results of the research on plasma- electronic technology for producing electricity from electronic beams, based on the electrical properties of electrons and their combination in the form of electron beams. The functional diagram of the experimental setup implementing plasma-electronic technology that proves the possibility of electricity generation by electrical installations, based on plasma-electronic technology is described.

Ryzhov, D. R.; Kazmin, B. N.; Trifanov, I. V.

2015-01-01

159

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

SciTech Connect

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. [South African National Space Agency (SANSA) Space Science, P.O. Box 32, Hermanus 7200, Republic of South Africa (South Africa); University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Republic of South Africa (South Africa); Maharaj, S. K. [South African National Space Agency (SANSA) Space Science, P.O. Box 32, Hermanus 7200, Republic of South Africa (South Africa); Bharuthram, R. [University of the Western Cape, Robert Sobukwe Road, Bellville 7535, Republic of South Africa (South Africa)

2014-05-15

160

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

161

Electron Recombination in a Dense Hydrogen Plasma  

SciTech Connect

A high pressure hydrogen gas filled RF cavity was subjected to an intense proton beam to study the evolution of the beam induced plasma inside the cavity. Varying beam intensities, gas pressures and electric fields were tested. Beam induced ionized electrons load the cavity, thereby decreasing the accelerating gradient. The extent and duration of this degradation has been measured. A model of the recombination between ionized electrons and ions is presented, with the intent of producing a baseline for the physics inside such a cavity used in a muon accelerator. Analysis of the data taken during the summer of 2011 shows that self recombination takes place in pure hydrogen gas. The decay of the number of electrons in the cavity once the beam is turned off indicates self recombination rather than attachment to electronegative dopants or impurities. The cross section of electron recombination grows for larger clusters of hydrogen and so at the equilibrium of electron production and recombination in the cavity, processes involving H{sub 5}{sup +} or larger clusters must be taking place. The measured recombination rates during this time match or exceed the analytic predicted values. The accelerating gradient in the cavity recovers fully in time for the next beam pulse of a muon collider. Exactly what the recombination rate is and how much the gradient degrades during the 60 ns muon collider beam pulse will be extrapolated from data taken during the spring of 2012.

Jana, M.R.; Johnstone, C.; Kobilarcik, T.; Koizumi, G.M.; Moretti, A.; Popovic, M.; Tollestrup, A.V.; Yonehara, K.; /Fermilab; Leonova, M.A.; Schwarz, T.A.; /Fermilab; Chung, M.; /Unlisted /IIT, Chicago /Fermilab /MUONS Inc., Batavia /Turin Polytechnic

2012-05-01

162

Possible role of ionospheric oxygen in the initiation and development of plasma sheet instabilities  

SciTech Connect

We relate measurements made during substorm growth and expansion to available plasma compositional observations and propose that asymmetries in the distribution of enhanced densities of O/sup +/ (of ionospheric origin) may define regions of the plasma sheet in which tearing mode growth rates are increased and the instability threshold is lowered. We make qualitative estimates of the growth rates of the linear ion tearing mode using statistical models of the dusk-dawn and earthward-tailward distributions of O/sup +/. The theoretical results predict maximum ion tearing growth rate in the range X/sub GSM/ = -10 to -15 R/sub E/ and Y/sub GSM/approx.5 R/sub E/. These values are in reasonable accord with substorm observations since many asymmetries in particle and field phenomena associated with substorms favor the interpretation that substorm onset occurs in the dusk sector of the near-earth plasma sheet. Present results therefore suggest that substorm initiation and development may be closely related to distribution patterns of ionospheric ions.

Baker, D.N.; Hones, E.W. Jr.; Young, D.T.; Birn, J.

1982-12-01

163

First IBEX Observations of the Terrestrial Plasma Sheet and a Likely Disconnection Event  

NASA Astrophysics Data System (ADS)

The Interstellar Boundary Explorer (IBEX) mission has recently provided the first all-sky maps of Energetic Neutral Atoms (ENAs) from the edge of the heliosphere as well as the first observations of ENAs from the Moon and from the nose of the magnetosphere. This study provides the first IBEX images of the night side magnetosphere and plasma sheet, as viewed from the side. We show images from two IBEX orbits - one that shows the plasma sheet mapping to a model magnetic field and a second that shows a significant intensification that can most likely be explained as a near-Earth disconnection event (see image). This event followed ~30 minutes of moderately southward IMF (Bz ~ -5nT) and occurred at a time when the IMF turned abruptly northward while the solar wind dynamic pressure simultaneously doubled. The ENA intensification indicates the simultaneous addition of both a hot (several keV) and colder component (~700 eV); the hot component may be a direct observation of the energization of plasma via reconnection.

McComas, D. J.; Dayeh, M. A.; Funsten, H. O.; Fuselier, S. A.; Goldstein, J.; Jahn, J.; Janzen, P. H.; Petrinec, S. M.; Reisenfeld, D. B.; Schwadron, N. A.

2010-12-01

164

Spatial variation in the plasma sheet composition: Dependence on geomagnetic and solar activity  

NASA Astrophysics Data System (ADS)

study the spatial distribution of plasma sheet O+ and H+ ions using data from the COmposition and DIstribution Function (CODIF) instrument on board the Cluster spacecraft from 2001 to 2005. The densities are mapped along magnetic field lines to produce bidimensional density maps at the magnetospheric equatorial plane for various geomagnetic and solar activity levels (represented by the Kp and F10.7 indexes). We analyze the correlation of the O+ and H+ density with Kp and F10.7 in the midtail region at geocentric distances between 15 and 20 RE and in the near-Earth regions at radial distances between 7 and 8 RE. Near Earth the H+ density slightly increases with Kp and F10.7 while in the midtail region it is not correlated with Kp and F10.7. On the contrary, the amount of O+ ions significantly increases with Kp and F10.7 independently of the region. In the near-Earth region, the effects of solar EUV and geomagnetic activity on the O+ density are comparable. In the midtail region, the O+ density increases at a lower rate with solar EUV flux but strongly increases with geomagnetic activity although the effect is modulated by the solar EUV flux level. We also evidence a strong increase of the proportion of O+ ions with decreasing geocentric distance below ~10 RE. These results confirm the direct entry of O+ ions into the near-Earth plasma sheet and suggest that both energetic outflows from the auroral zone and cold outflow from the high-latitude ionosphere may contribute to feed the near-Earth plasma sheet with ionospheric ions.

Maggiolo, R.; Kistler, L. M.

2014-04-01

165

Distribution of O+ ions in the plasma sheet and locations of substorm onsets  

NASA Astrophysics Data System (ADS)

We discuss the effect of O+ ions on substorm onsets by examining the relation between the substorm onset location and the distribution of the O+/H+ number density ratio before the onset in the various regions within the plasma sheet (-8 RE > XGSM > -32 RE). We use 9-212 keV/e ion flux data observed by Geotail/Energetic Particles and Ion Composition (EPIC)/Suprathermal Ion Composition Spectrometer (STICS) instrument and the IMAGE/Far Ultra-Violet (FUV) substorm onset list presented by Frey et al. [Frey, H. U., S. B. Mende, V. Angelopoulos, and E. F. Donovan (2004), Substorm onset observations by IMAGE-FUV, J. Geophys. Res., 109, A10304, doi:10.1029/2004JA010607]. The results are summarized as follows. Substorm onsets, which we identify by auroral initial brightenings, are likely to occur in the more dusk-(dawn-)ward region when the O+/H+ number density ratio is high in the dusk (dawn) side. This property is observed only in the near-Earth plasma sheet (at -8 RE > XGSM > -14 RE). The above-mentioned property holds in each of two groups: substorm events due to internal instability of the magnetosphere (i.e., internally triggered substorms) and events due to external changes in the solar wind or the interplanetary magnetic field (i.e., externally triggered substorms). Thus, we conclude that the substorm onset location depends on the density of O+ ions in the near-Earth plasma sheet prior to onset, whether the substorm is triggered internally or externally.

Ono, Y.; Christon, S. P.; Frey, H. U.; Lui, A. T. Y.

2010-09-01

166

Electron Beam Emission Characteristics from Plasma Focus Devices  

SciTech Connect

In this paper we observed the characteristics of the electron beam emission from our plasma focus machine filling neon, argon, helium and hydrogen. Rogowski coil and CCD based magnetic spectrometer were used to obtain temporal and energy distribution of electron emission. And the preliminary results of deposited FeCo thin film using electron beam from our plasma focus device were presented.

Zhang, T.; Patran, A.; Wong, D.; Hassan, S.M.; Springham, S.V.; Tan, T.L.; Lee, P.; Lee, S.; Rawat, R.S. [Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University (Singapore)

2006-01-05

167

Weibel instability in positron-electron plasma  

NASA Astrophysics Data System (ADS)

The Weibel or filamentation instability of counter-flowing beams described by a recent model is investigated. The model combined computer simulations and an analytic one-particle distribution function for the quasi-equilibrium of a positron-electron plasma. An electron-ion plasma is not considered. This instability is conjectured to give rise to turbulent magnetic fields in collisionless shocks. The linear growth rate and time dependence of the instability is determined from the Vlasov-Maxwell equations and confirms that the dominant mode for the magnetic field has the spatial dependence of the initial perturbed magnetic field as found by the simulations. The quasi-equilibrium distribution function is expanded in Hermite polynomials varying in two spatial variables, a generalization of earlier results for nonlinear transverse waves. The quasi-equilibrium in reference 1 is further constrained by the conservation of particle number and total energy. That quasi-equilibrium agrees only qualitatively with the simulation results. A nonlinear model is proposed with the sinh-Poisson equation. An analytic form for the vector potential is found for this nonlinear model in terms of Jacobian elliptic functions. A. Suzuki and T. Shigeyama, Astrophys. J. 695, 1550-1558 (2009). B. Abraham-Shrauner, Phys. Fluids, 11, 1162-1167 (1968).

Shrauner, Barbara

2009-11-01

168

Current-sheet kink instability at ion-electron hybrid scale  

NASA Astrophysics Data System (ADS)

Current sheet instabilities having wavenumber vectors parallel to the current direction are studied as a linear eigenvalue problem in a two-fluid system where electrons are treated as a finite-mass charge neutralizing component. Focusing on ion-scale current sheets, we show that a hybrid scale current sheet kink instability (CSKI) is one of the major instabilities to appear. The hybrid scale CSKI in a magnetotail-like situation has a wavelength much shorter than the well-studied drift-kink instability (DKI). While most of the previous studies have focused on the long-wavelength range, a full-particle simulation with much larger ion-to-electron mass ratio ( RM = 400) shows the growth of the hybrid scale CSKI as predicted by linear analyses. We also show that the CSKI has large growth rates in a magnetopause-like situation.

Suzuki, H.; Fujimoto, M.; Shinohara, I.

169

PHYSICAL REVIEW B 87, 035404 (2013) Electronic structure of boron nitride sheets doped with carbon from first-principles calculations  

E-print Network

PHYSICAL REVIEW B 87, 035404 (2013) Electronic structure of boron nitride sheets doped with carbon quasiparticle (GW) approach, we study the electronic structure of hexagonal boron nitride (h-BN) sheets, both and doped h-BN and should further help to optimize the postsynthesis doping of boron nitride nanostructures

Krasheninnikov, Arkady V.

170

Observations of a nonthermal ion layer at the plasma sheet boundary during substorm recovery  

NASA Technical Reports Server (NTRS)

Measurements of the energy and angular distributions of energetic protons and alpha particles (not less than 30 keV/charge) in the geomagnetic tail are presented. The measurements were made during the recovery phase of a geomagnetic substorm on Apr. 19, 1978, with the Max-Planck-Institut/University of Maryland sensor system on the Isee 1 satellite. The measurements were also correlated with plasma observations made by the LASL/MPE instrument on Isee 1. The data reveal the presence of a thin nonthermal layer of protons and alpha particles at the plasma sheet boundary. The particles have their maximum flux at 60 keV/charge and are streaming highly collimated in the earthward direction. The alpha particle layer is confined within the proton layer. Many aspects of the observations are in agreement with an acceleration model near the neutral line proposed by Jaeger and Speiser (1974)

Moebius, E.; Scholer, M.; Hovestadt, D.; Klecker, B.; Ipavich, F. M.; Gloeckler, G.

1980-01-01

171

Nonlinear interaction of quantum electron plasma waves with quantum electron acoustic waves in plasmas.  

PubMed

An analysis of the interaction between modes involving two species with different pressures in the presence of a static-neutralizing ion background is presented using a quantum hydrodynamic model. It is shown that quantum electron plasma waves can nonlinearly interact with quantum electron acoustic waves in a time scale much longer than electron plasma oscillation response time. A set of coupled nonlinear differential equations is obtained that is similar to the Zakharov equations but includes quantum correction terms. These equations are solved in a moving frame, showing that solitary-wave-like solutions may also be possible in quantum Zakharov equations. It is also shown that quantum effects can reduce the growth rate of the usual caviton instability. Possible applications of the theory are also outlined. PMID:21405781

Chakrabarti, Nikhil; Mylavarapu, Janaki Sita; Dutta, Manjistha; Khan, Manoranjan

2011-01-01

172

Nonlinear interaction of quantum electron plasma waves with quantum electron acoustic waves in plasmas  

SciTech Connect

An analysis of the interaction between modes involving two species with different pressures in the presence of a static-neutralizing ion background is presented using a quantum hydrodynamic model. It is shown that quantum electron plasma waves can nonlinearly interact with quantum electron acoustic waves in a time scale much longer than electron plasma oscillation response time. A set of coupled nonlinear differential equations is obtained that is similar to the Zakharov equations but includes quantum correction terms. These equations are solved in a moving frame, showing that solitary-wave-like solutions may also be possible in quantum Zakharov equations. It is also shown that quantum effects can reduce the growth rate of the usual caviton instability. Possible applications of the theory are also outlined.

Chakrabarti, Nikhil; Mylavarapu, Janaki Sita; Dutta, Manjistha; Khan, Manoranjan [Saha Institute of Nuclear Physics, 1/AF Bidhannagar Calcutta-700 064 (India); Department of Instrumentation Science, Jadavpur University, Calcutta-700 032 (India)

2011-01-15

173

In situ observations of the plasma sheet at high latitudes in conjunction with a transpolar arc  

NASA Astrophysics Data System (ADS)

Transpolar arcs are auroral features which extend from the night side of the Earth's main auroral oval into the polar cap. Recent statistical studies have shown that they are formed by the closure of magnetic flux in the magnetotail during intervals when the IMF is northward and there is a cross-tail (BY ) component of the lobe magnetic field (due to the earlier IMF conditions). Under these circumstances, newly closed flux in the midnight sector has northern and southern hemisphere footprints that straddle the midnight meridian; this prevents the closed flux from returning to the day side in a simple manner. As tail reconnection continues, the footprints of closed field lines protrude into the polar cap, and the auroral emissions on these footprints form the transpolar arc. This mechanism predicts that closed flux should build up on the night side, embedded within the lobe. We present in situ observations of this phenomenon, taken by the Cluster spacecraft on 15th September 2005. Cluster was located at high latitudes in the southern hemisphere lobe (far from the typical location of the plasma sheet), and a transpolar arc was observed by the FUV cameras on the IMAGE satellite. Cluster periodically observed plasma similar to a typical plasma sheet distribution, but at much higher latitudes - indicative of closed flux embedded within the high latitude lobe. Each time that this plasma distribution was observed, the footprint of the spacecraft mapped to the transpolar arc (significantly poleward of the main auroral oval). These observations are consistent with closed flux being trapped in the magnetotail and embedded within the lobe, and provide further evidence for transpolar arcs being formed by magnetotail reconnection.

Fear, Robert; Milan, Steve; Maggiolo, Romain

2013-04-01

174

Nonlinear stability of the near-Earth plasma sheet during substorms: 9 February 1995 event  

NASA Astrophysics Data System (ADS)

It has been previously demonstrated that several minutes prior to an onset of a magnetospheric substorm the near-Earth plasma sheet becomes unstable to resonance-type perturbations. The next logical step, examined here, is an assumption that the velocity shear in the resonance would lead to a development of a Kelvin-Helmholtz (KH) instability. Using a Grad-Shafranov equilibrium constrained by CANOPUS data, we analyze the stability properties of the near-Earth plasma sheet in the presence of a field-line resonance-generated KH instability at around 10 Earth radii. The results of the analysis are in general agreement with observations and computer modeling of substorms. As a part of the analysis, we discuss the importance of the proper distinction between the stability properties of the magnetotail, and the trigger mechanism responsible for the instability. While these two aspects of a substorm may be (and likely are) related, it is possible that they involve different types of processes that work in a complementary fashion.

Dobias, P.; Wanliss, J. A.; Samson, J. C.

2006-12-01

175

Multiscale Auroral Emission Statistics as Evidence of Turbulent Reconnection in Earth's Midtail Plasma Sheet  

NASA Technical Reports Server (NTRS)

We provide indirect evidence for turbulent reconnection in Earth's midtail plasma sheet by reexamining the statistical properties of bright, nightside auroral emission events as observed by the UVI experiment on the Polar spacecraft and discussed previously by Uritsky et al. The events are divided into two groups: (1) those that map to absolute value of (X(sub GSM)) < 12 R(sub E) in the magnetotail and do not show scale-free statistics and (2) those that map to absolute value of (X(sub GSM)) > 12 R(sub E) and do show scale-free statistics. The absolute value of (X(sub GSM)) dependence is shown to most effectively organize the events into these two groups. Power law exponents obtained for group 2 are shown to validate the conclusions of Uritsky et al. concerning the existence of critical dynamics in the auroral emissions. It is suggested that the auroral dynamics is a reflection of a critical state in the magnetotail that is based on the dynamics of turbulent reconnection in the midtail plasma sheet.

Klimas, Alex; Uritsky, Vadim; Donovan, Eric

2010-01-01

176

Electron diffraction study on ironzinc ? 1 intermetallic phase in a galvannealed IF steel sheet  

Microsoft Academic Search

A series map of selected area electron diffraction patterns(SADPs) of ?1 phase in commercial galvannealed IF steel sheet were investigated by transmission electron microscopy(TEM). The cross-sectional TEM specimen was prepared using focused ion beam (FIB) technique which was also introduced briefly. The results show that there exist superlattice reflections in the SADPs of ?1 phase which indicate that ?1 phase

Jinshan Yu; Junliang Liu; Jinxu Zhang; Jiansheng Wu

2005-01-01

177

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

178

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

179

Etching with electron beam generated plasmas  

SciTech Connect

A modulated electron beam generated plasma has been used to dry etch standard photoresist materials and silicon. Oxygen-argon mixtures were used to etch organic resist material and sulfur hexafluoride mixed with argon or oxygen was used for the silicon etching. Etch rates and anisotropy were determined with respect to gas compositions, incident ion energy (from an applied rf bias) and plasma duty factor. For 1818 negative resist and i-line resists the removal rate increased nearly linearly with ion energy (up to 220 nm/min at 100 eV), with reasonable anisotropic pattern transfer above 50 eV. Little change in etch rate was seen as gas composition went from pure oxygen to 70% argon, implying the resist removal mechanism in this system required the additional energy supplied by the ions. With silicon substrates at room temperature, mixtures of argon and sulfur hexafluoride etched approximately seven times faster (1375 nm/min) than mixtures of oxygen and sulfur hexafluoride ({approx}200 nm/min) with 200 eV ions, the difference is attributed to the passivation of the silicon by involatile silicon oxyfluoride (SiO{sub x}F{sub y}) compounds. At low incident ion energies, the Ar-SF{sub 6} mixtures showed a strong chemical (lateral) etch component before an ion-assisted regime, which started at {approx}75 eV. Etch rates were independent of the 0.5%-50% duty factors studied in this work.

Leonhardt, D.; Walton, S.G.; Muratore, C.; Fernsler, R.F.; Meger, R.A. [U.S. Naval Research Laboratory, Plasma Physics Division, Washington, DC 20375 (United States)

2004-11-01

180

Influence of the renormalization plasma screening on the electron-atom collision in partially ionized plasmas  

SciTech Connect

The renormalization plasma screening effects on the elastic electron-atom collision are investigated in partially ionized dense hydrogen plasmas using the eikonal method. It is found that the renormalization plasma screening suppresses the eikonal phase shift and cross section for the elastic electron-atom collision in partially ionized plasmas. It is also found that the renormalization plasma screening effect on the elastic electron-atom collision process increases with an increasing impact parameter. In addition, it is found that the maximum position of the differential cross section is receded from the center of the atom with an increase of the Debye length.

Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2012-02-13

181

Generating electron cyclotron resonance plasma using distributed scheme  

SciTech Connect

This study employs a distributed microwave input system and permanent magnets to generate large-area electron cyclotron resonance (ECR) plasma. ECR plasmas were generated with nitrogen gas, and the plasma density was measured by Langmuir probe. A uniform ECR plasma with the electron density fluctuation of {+-}9.8% over 500 mm Multiplication-Sign 500 mm was reported. The proposed idea of generating uniform ECR plasma can be scaled to a much larger area by using n Multiplication-Sign n microwave input array system together with well-designed permanent magnets.

Huang, C. C. [Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan (China); Chung-Shan Institute of Science and Technology, Lung-Tan, Taoyuan, Taiwan (China); Chang, T. H.; Chen, N. C.; Chao, H. W. [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China); Chen, C. C. [Chung-Shan Institute of Science and Technology, Lung-Tan, Taoyuan, Taiwan (China); Chou, S. F. [Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan (China)

2012-08-06

182

Pulse propagation and electron acceleration in a corrugated plasma channel.  

PubMed

A preformed plasma channel provides a guiding structure for laser pulses unbound by the intensity thresholds of standard waveguides. The recently realized corrugated plasma channel [Layer, Phys. Rev. Lett. 99, 035001 (2007)] allows for the guiding of laser pulses with subluminal spatial harmonics. These spatial harmonics can be phase matched to high energy electrons, making the corrugated plasma channel ideal for the acceleration of electrons. We present a simple analytic model of pulse propagation in a corrugated plasma channel and examine the laser-electron beam interaction. Simulations show accelerating gradients of several hundred MeV/cm for laser powers much lower than required by standard laser wakefield schemes. PMID:18517531

Palastro, J P; Antonsen, T M; Morshed, S; York, A G; Milchberg, H M

2008-03-01

183

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

184

Reception Characteristics of Monopole Antennas for Electron Plasma Waves  

Microsoft Academic Search

The radiation patterns of a longitudinal electron plasma wave excited in a warm unbounded plasma by a grid and parallel plane grids and the reception patterns for wire antennas and the grid having a grounded plate were measured experimentally. The results agreed well with theoretically predicted radiation patterns based on a fluid model description for electrons. The dependence of the

Yoshiharu Nakamura; Masaharu Nakamura; Tomizo Itoh

1973-01-01

185

Loaded two-element ring antenna for electron plasma waves  

Microsoft Academic Search

A short, coil-loaded two-element ring antenna including a transmission line, immersed in a warm, isotropic plasma, is investigated as a boundary value problem in the frequency range where electron plasma waves exist. The wave potential of electron plasma waves launched from a two-element ring antenna has been enhanced by a factor of 4-6 in comparison with the case of an

Y. Morita; S. Egashira; M. Honjoh

1989-01-01

186

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

187

Slant Slot Antenna-Type Electron Cyclotron Resonance Plasma Source  

Microsoft Academic Search

A new compact electron cyclotron resonance (ECR) plasma source, which is termed slant-slot antenna-type ECR plasma source, is presented. Using this plasma source an ion saturation current density Iis of 6.2 mA\\/cm25.2% was obtained over a diameter of 300 mm under ambient conditions of Cl2 gas at 0.7 Pa. The features of the plasma source are an independent circular TM011

Seiichi Watanabe; Hitoshi Tamura; Masahiro Sumiya; Muneo Furuse; Sunao Kawasaki

1998-01-01

188

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

189

Experimental evidence of warm electron populations in magnetron sputtering plasmas  

NASA Astrophysics Data System (ADS)

This work report on the results obtained using the Langmuir probe (LP) measurements in high-power dc magnetron sputtering discharges. Data show clear evidence of two electron components, such as warm and bulk electrons, in the sputtering plasma in a magnetic trap. We have also used optical emission spectroscopy diagnostic method along with LP to investigate the plasma production. Data show that there is a presence of low-frequency oscillations in the 2-3 MHz range, which are expected to be generated by high-frequency waves. Analysis also suggests that the warm electrons, in the plasmas, can be formed due to the collisionless Landau damping of the bulk electrons.

Sahu, B. B.; Han, Jeon G.; Kim, Hye R.; Ishikawa, K.; Hori, M.

2015-01-01

190

Correction to ``Three-dimensional analyses of electric currents and pressure anisotropies in the plasma sheet'' by Richard L. Kaufmann,  

E-print Network

Correction to ``Three-dimensional analyses of electric currents and pressure anisotropies. Paterson, and L. A. Frank, Correction to ``Three-dimensional analyses of electric currents and pressure] In the paper ``Three-dimensional analyses of electric currents and pressure anisotropies in the plasma sheet

Kaufmann, Richard L.

191

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

SciTech Connect

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.; Russel, C.T.; Cattell, C.A.; Takahashi, K.; Bame, S.J.

1986-07-01

192

One-step synthesis of N-doped graphene quantum sheets from monolayer graphene by nitrogen plasma.  

PubMed

High-quality N-doped graphene quantum sheets are successfully fabricated from as-grown monolayer graphene on Cu using nitrogen plasma, which can be transferred as a film-like layer or easily dispersed in an organic solvent for further optoelectronic or photoelectrochemical applications. PMID:24664667

Moon, Joonhee; An, Junghyun; Sim, Uk; Cho, Sung-Pyo; Kang, Jin Hyoun; Chung, Chul; Seo, Jung-Hye; Lee, Jouhahn; Nam, Ki Tae; Hong, Byung Hee

2014-06-01

193

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

194

Dynamical features of the plasma-sheet ion composition, density, and energy  

NASA Technical Reports Server (NTRS)

The effects of changes in solar and geomagnetic activity on the major plasma-sheet ions are investigated on the basis of a statistical analysis of 1500 h of data obtained at distances 10-23 earth radii and energy/charge ratios 0.1-16 keV/e by the ISEE-1 energetic-ion mass spectrometer. The results are presented in extensive graphs and discussed in detail. It is found that substorm activity is accompanied by a significant decrease in the density of solar-origin H(+) ions, a sharp increase in the energy per nucleon of both H(+) and He(+) ions, and an increase in the density of terrestrial O(+) ions. A factor-of-three increase in the overall O(+) density over the observation period is attributed to an increase in the solar EUV flux.

Lennartsson, W.

1987-01-01

195

Formation and transport of sheet electron beams and multi-beam configurations for high-power microwave devices  

SciTech Connect

Sheet electron beams and configurations with multiple 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 RF interaction circuit. Possible microwave device applications using sheet electron beams include sheet-beam klystrons, rectangular grating circuits, and planar FELS. Historically, implementation of sheet beams in microwave devices has been discouraged by their susceptibility to the diocotron instability in solenoidal focusing systems. However, recent theoretical and numerical studies have shown that stable transport of sheet beams is possible, in periodically cusped magnetic (PCM) fields. The use of an offset-pole PCM configuration has been shown analytically to provide side-fields for 2-D focusing of the beam, and this has been recently verified with PIC code simulations. The authors will present further theoretical studies of sheet and multi-beam transport and discuss results from an experimental investigation of the formation, stability and transport of PCM-focused sheet electron beams. This includes a laboratory method of forming an elliptical sheet beam using a magnetic quadrupole pair and a round-beam Pierce gun.

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

1995-11-01

196

Electron beam emission characteristics from plasma focus devices  

Microsoft Academic Search

In this paper we observed the characteristics of the electron beam\\u000a emission from our plasma focus machine filling neon, argon, helium and\\u000a hydrogen. Rogowski coil and CCD based magnetic spectrometer were used to\\u000a obtain temporal and energy distribution of electron emission. And the\\u000a preliminary results of deposited FeCo thin film using electron beam from\\u000a our plasma focus device were presented.

T. Zhang; A. Patran; D. Wong; S. M. Hassan; S. V. Springham; T. L. Tan; P Lee; S. Lee; R. S. Rawat

2006-01-01

197

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

198

Heat treatment effect on the electronic and magnetic structures of nanographene sheets investigated through electron spectroscopy and conductance measurements.  

PubMed

The heat treatment effect on the electronic and magnetic structures of a disordered network of nanographene sheets has been investigated by in situ measurements of X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure (NEXAFS), and electrical conductance, together with temperature-programmed desorption measurements. Oxygen-containing functional groups bonded to nanographene edges in the pristine sample are almost completely decomposed under heat treatment up to 1300-1500 K, resulting in the formation of edges primarily terminated by hydrogen. The removal of the oxygen-containing groups enhances the conductance owing to the decrease in the electron transport barriers between nanographene sheets. Heat treatment above 1500 K removes also the hydrogen atoms from the edges, promoting the successive fusion of nanographene sheets at the expense of edges. The decrease in the ?* peak width in NEXAFS indicates the progress of the fusion reaction, that is, the extension of the ?-conjugation, which agrees with the increase in the orbital susceptibility previously reported. The fusion leads to the formation of local ?/sp(2) bridges between nanographene sheets and brings about an insulator-to-metal transition at 1500-1600 K, at which the bridge network becomes infinite. As for the magnetism, the intensity of the edge state peak in NEXAFS, which corresponds to the number of the spin-polarized edge states, decreases above 1500 K, though the effective edge-state spin density per edge state starts decreasing at approximately 200 K lower than the temperature of the edge state peak change. This disagreement indicates the development of antiferromagnetic short range ordering as a precursor of a spin glass state near the insulator-metal transition, at which the random network of inter-nanographene-sheet exchange interactions strengthened with the formation of the ?/sp(2) bridges becomes infinite. PMID:24618730

Takashiro, Jun-ichi; Kudo, Yasuhiko; Kaneko, Satoshi; Takai, Kazuyuki; Ishii, Takafumi; Kyotani, Takashi; Enoki, Toshiaki; Kiguchi, Manabu

2014-04-28

199

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

200

Magnetic quadrupole formation of elliptical sheet electron beams for high-power microwave devices  

SciTech Connect

Sheet electron beams are attractive for high-power microwave sources due to their ability to transport high current, at reduced current density, through thin clearance apertures and in close proximity to walls or RF structures. This paper reports on the theoretical investigation of magnetic quadrupole formation of elliptical sheet electron beams for use in high-power microwave devices. The beam envelope equations for an initially round beam passing through a physical non-symmetric quadrupole pair in the presence of space-charge, finite beam emittance, and under the effects of third-order field components and longitudinal velocity variations are presented. The presence of space-charge compensates for over-focusing in the thin beam-dimension and allows for the formation of highly elliptic sheet electron beams. As an example, the results of the study were applied to an existing Pierce gun source with a beam radius of 0.6 cm, beam energy of 10 keV and current density of 2.0 A/cm[sup 2]. The authors find that an elliptical beam with major radius r[sub a] = 3.61 cm, minor radius r[sub b] = 0.16 cm and ellipticity (r[sub a]/r[sub b]) of 22.5 can be produced with only modest quadrupole gradients of 64 G/cm and 18 G/cm. Quadrupole formation of elliptical sheet-beams may be particularly suited for experimental research applications since existing round-beam electron guns may be used and changes in beam ellipticity may be made without breaking the vacuum system.

Basten, M.A.; Booske, J.H.; Anderson, J. (Univ. of Wisconsin, Madison, WI (United States). Electrical and Computer Engineering Dept.)

1994-10-01

201

Nonlinear Interactions between Electromagnetic Waves and Electron Plasma Oscillations in Quantum Plasmas  

Microsoft Academic Search

We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schrdinger

P. K. Shukla; B. Eliasson

2007-01-01

202

Determination of Absolute Plasma Electron Density and Electron Neutral Collision Frequency from Plasma Impedance Probe Measurements.  

NASA Astrophysics Data System (ADS)

A plasma fluid finite difference (PFFDTD) simulation of an antenna immersed in a magneto-plasma is used to determine the absolute electron density ne and the electron neutral collision frequency ?en from RF impedance probe data. The Sudden Atomic layer (SAL) mission was launched as a part of the COQUI II campaign from Puerto Rico on 19th February, 1998 at 2009 LT. The impedance data analyzed here was obtained as the SAL rocket travelled through the lower sporadic sodium layer that occured between 90 to 94 km altitude. The impedance data is analyzed at 92.37 Km, 92.40 Km, 92.44 Km altitudes on the upleg and downleg. Analytical fits obtained from a cold collisional magnetoplasma model by Balmain is compared to the PFFDTD results. The Balmain fits are in reasonable agreement to the data but over predict the electron neutral collision frequency compared to the simulation fits. The values of ne obtained from the simulation are also compared to the values obtained from IRI model.Collision frequency ?en values are compared with the Schunk and Nagy(2000) model values. The simulation results are found to be in close agreement with the models.

Patra, S.; Spencer, E. A.; Andriyas, T.; Swenson, C. M.; Ward, J. D.

2007-12-01

203

Nonthermal Plasma Processing of VOCs with Electric Discharges: Gaseous Electronics and Plasma Chemistry Considerations  

Microsoft Academic Search

Electrical discharges in gases can be used to create nonthermal (or nonequilibrium) plasmas having energetic electrons (order few to several eV) at near-ambient background gas temperature. These low-temperature plasmas are an excellent source of free radicals and other active species useful for chemical conversion and synthesis: O(^3P), OH, N, H, NH, CH, O_3, O_2(^1Delta), plasma electrons. Interactions of the active

Louis A. Rosocha

1997-01-01

204

Level shifts and inelastic electron scattering in dense plasmas  

NASA Technical Reports Server (NTRS)

A completely quantum mechanical formalism has been developed to describe the high density plasma effects on fundamental atomic parameters. Both the bound and free electrons are treated by a method which in principle is similar to Hartree's self-consistent field method. The free plasma electrons' wavefunction is obtained from the Schroedinger equation with the effective potential representing the spherically averaged Coulomb interaction with bound and free electrons. Results are given for level shifts, coefficients of transition probabilities, and electron collision cross sections of Ne(9+) for temperatures of 200 and 500 eV for an electron density range of 1-6 x 10 to the 24th per cu cm.

Davis, J.; Blaha, M.

1982-01-01

205

Electron acoustic shock waves in a collisional plasma.  

PubMed

A nonlinear analysis for the finite amplitude electron acoustic wave (EAW) is considered in a collisional plasma. The fluid model is used to describe the two-temperature electron species in a fixed ion background. In general, in electron-ion plasma, the presence of wave nonlinearity, dispersion, and dissipation (arising from fluid viscosity) give rise to the Korteweg-de Vries Burgers (KdVB) equation which exhibits shock wave. In this work, it is shown that the dissipation due to the collision between electron and ion in the presence of collective phenomena (plasma current) can also introduce an anomalous dissipation that causes the Burgers term and thus leads to the generation of electron acoustic shock wave. Both analytical and numerical analysis show the formation of transient shock wave. Relevance of the results are discussed in the context of space plasma. PMID:23368060

Dutta, Manjistha; Ghosh, Samiran; Chakrabarti, Nikhil

2012-12-01

206

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW-6 event of March 22, 1979  

NASA Technical Reports Server (NTRS)

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near Earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the Earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.; Amata, E.; Candidi, M.; Balsiger, H.; Stokholm, M.; Huang, C. Y.; Lennartsson, W.; Lindqvist, P. A.

1983-01-01

207

Energy loss of fast electrons and positrons in a plasma.  

NASA Technical Reports Server (NTRS)

Calculation of the stopping power of a plasma for fast electrons and positrons. First the classical limit is considered where beta = v/c is much less than alpha is the fine structure constant. Then the nonrelativistic Born-approximation formulas are derived; this domain corresponds to alpha much less than beta much less than 1. Finally, the general case of relativistic electrons and positrons is treated; in the relativistic case the scattering cross sections of Moller (electron-electron) and Bhabha (positron-electron) are used in the calculation. In all three energy domains the problem is broken up into cases of small and large momentum transfers. For large q, scattering off individual plasma electrons is considered, while in the limit of very small q for the quantum-mechanical domain, excitation of quantized plasma oscillations contributes to dE/dx; in the classical limit for small q the polarizability of the plasma provides the effective cutoff. The formulas for the stopping power differ slightly from those for a heavy ion going through a plasma because there are exchange effects and the fast electrons and positrons can lose a large fraction of their energy in one scattering off a plasma electron.

Gould, R. J.

1972-01-01

208

Solitary and shock waves in magnetized electron-positron plasma  

SciTech Connect

An Ohm's law for electron-positron (EP) plasma is obtained. In the framework of EP magnetohydrodynamics, we investigate nonrelativistic nonlinear waves' solutions in a magnetized EP plasma. In the collisionless limit, quasistationary propagating solitary wave structures for the magnetic field and the plasma density are obtained. It is found that the wave amplitude increases with the Mach number and the Alfvn speed. However, the dependence on the plasma temperature is just the opposite. Moreover, for a cold EP plasma, the existence range of the solitary waves depends only on the Alfvn speed. For a hot EP plasma, the existence range depends on the Alfvn speed as well as the plasma temperature. In the presence of collision, the electromagnetic fields and the plasma density can appear as oscillatory shock structures because of the dissipation caused by the collisions. As the collision frequency increases, the oscillatory shock structure becomes more and more monotonic.

Lu, Ding; Li, Zi-Liang; Abdukerim, Nuriman; Xie, Bai-Song, E-mail: bsxie@bnu.edu.cn [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, and College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China)] [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, and College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China)

2014-02-15

209

Self-effect in expanding electron beam plasma  

Microsoft Academic Search

Summary form only given. An analytical model of plasma flow from metal plates hit by intense, pulsed, electron beams aims to bridge the gap between radiation-hydrodynamics simulations and experiments, and to quantify the self-effect of the electron beam penetrating the flow. Does the flow disrupt the tight focus of the initial electron bunch, or later pulses in a train? This

M. Garcia

1999-01-01

210

Electron-ion collisions in intensely illuminated plasmas G. Shvetsa)  

E-print Network

Electron-ion collisions in intensely illuminated plasmas G. Shvetsa) and N. J. Fisch Princeton, the collisions of electrons with ions can be made more frequent or less frequent, depending on the polarization 00802-1 I. INTRODUCTION The presence of an electromagnetic wave alters electron- ion collisions, thereby

211

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

212

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

NASA Astrophysics Data System (ADS)

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 , 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 TM111 modes still takes place at the midpoint even for a low-laser power of 0.01?J/pulse , although the number of TE111 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.; Nishimura, T.; Kido, Y.

2009-10-01

213

Effect of plasma-? on the onset of plasmoid instability in Sweet-Parker current sheets  

NASA Astrophysics Data System (ADS)

A numerical study of magnetic reconnection in two-dimensional resistive magnetohydrodynamics for Sweet-Parker current sheets that are subject to plasmoid instability is carried out. The effect of the initial upstream plasma-? on the critical Lundquist number Sc for the onset of plasmoid instability is studied. Our results indicate a weak dependence, with a value of Sc ~= 1.5 104 in the limit of zero ?, and a value of Sc ~= 1 104 in the opposite high ? regime (? >> 1). A similar dependence was previously obtained (Ni et al. 2012 Phys. Plasm. 19, 072902), but with a somewhat much larger variation, that can be largely attributed to the different configuration setup used in their study, and also to the definition of the Lundquist number. This conclusion does not depend significantly on the equilibrium used, i.e. both initial configurations with either plasma density or temperature spatial variations lead to very similar results. Finally, we show that the inner plasmoid structure appears as an under-dense hotted magnetic island, with a local temperature increase that is noticeably strengthened for low ? cases.

Baty, H.

2014-10-01

214

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

215

Electron surface waves in a nonuniform plasma slab  

NASA Astrophysics Data System (ADS)

Electron surface waves in a nonuniform, metal bound, thermal plasma slab have been analyzed and detected. Measurements of the dispersion relations of these waves, as well as the eigenstructure of the perturbed electron density, reveal a spectrum of waves with frequencies above and below the peak electron plasma frequency in the slab. These waves are analogous to the Gould-Trivelpiece and Tonks-Dattner waves found in dielectric bound plasma columns. Measurements have been made using particle-in-cell simulation of an argon plasma and are compared with linear fluid theory in which the adiabatic approximation is made for the perturbed pressure. The presence of the metal boundary leads to regions near the plasma sheaths in which the fluid theory breaks down; we explore the differences between theory and measurement in this region.

Cooperberg, D. J.

1998-04-01

216

The Role of Secondary Electron Emission on the Ecr Plasma  

NASA Astrophysics Data System (ADS)

The role of secondary electron emission from a metal dielectric structure introduced in the plasma chamber of an ECRIS is presented. Experiments at the Institute fur Kernphysik in Frankfurt/Main-Germany and Kernfysisch Versneller Instituut in Groningen, The Netherlands, demonstrated the high capabilities of these structures to enhance the high-charge-state ion production. The Ar16+ production was enhanced by two orders of magnitude as compared with the standard stainless steel plasma chamber without the metal dielectric structure. The influence on the main characteristics of the ECR plasma (plasma potential, electron temperature and electron density) was studied. Preliminary results obtained with a metal dielectric structure introduced in the plasma chamber of the ECR source SERSE at LNS - Catania are also presented.

Schachter, L.; Stiebing, K. E.; Dobrescu, S.; Drentje, A. G.; Gammino, S.; Ciavola, G.; Celona, L.; Consoli, F.; Galat, A.

2004-10-01

217

Electron current extraction from a permanent magnet waveguide plasma cathode  

SciTech Connect

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. [University of Michigan, Ann Arbor, Michigan 48109 (United States); Kamhawi, H. [NASA Glenn Research Center, Cleveland, Ohio 44135 (United States)

2011-09-15

218

Relativistic electromagnetic waves in an electron-ion plasma  

NASA Astrophysics Data System (ADS)

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.

1987-09-01

219

Probing the electronic structure of graphene sheets with various thicknesses by scanning transmission X-ray microscopy  

SciTech Connect

The electronic structure of an aggregation of graphene sheets with various thicknesses was probed by scanning transmission X-ray microscopy. A uniform oxidation of the graphene sheets in the flat area was observed regardless of the thickness, while in the folded area the result could be strongly affected by the geometry. Moreover, thick parts of the aggregation showed strong angle-dependence to the incident X-ray, while thin parts showed less angle-dependence, which might be related to the surface wrinkles and ripples. The electronic structure differences due to the geometry and thickness suggest a complicated situation in the aggregation of graphene sheets.

Bai, Lili; Liu, Jinyin; Zhao, Guanqi; Gao, Jing; Sun, Xuhui, E-mail: xhsun@suda.edu.cn, E-mail: jzhong@suda.edu.cn; Zhong, Jun, E-mail: xhsun@suda.edu.cn, E-mail: jzhong@suda.edu.cn [Soochow University-Western University Centre for Synchrotron Radiation Research, Institute of Functional Nano and Soft Materials Laboratory (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123 (China)] [Soochow University-Western University Centre for Synchrotron Radiation Research, Institute of Functional Nano and Soft Materials Laboratory (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123 (China)

2013-12-16

220

Ultracold Plasma Electron Temperature Measurements using Collective Mode Diagnostics  

NASA Astrophysics Data System (ADS)

Applying a radio-frequency electric field to an expanding ultracold neutral plasma leads to the observation of Tonks- Dattner resonances, electron sound waves propagating in a finite, inhomogeneous plasma. These TD resonances have strong dependence on the boundary conditions of the plasma; while earlier studies were done using plasmas confined in cylindrical chambers, our freely expanding spherical plasmas have no clear outer turning points for the TD electron waves. Choosing an outer turning point where the local Debye length equals the plasma size, a WKB approximation yields good agreement with the mode frequencies, extracting a temperature consistent with other measurements. We note that the outer turning point used is similar to the location of an ion shock wave predicted in simulations, which may play a role in establishing the boundary conditions for the TD resonances. The determination of a well- defined turning point for the sound waves will allow accurate temperature measurements using TD resonance frequencies.

Fletcher, Robert; Zhang, Xianli; Rolston, Steven

2006-10-01

221

3-D Phase space dynamics for pencil-to-sheet-electron-beam transformation in highly-non-paraxial quadrupole lens system  

NASA Astrophysics Data System (ADS)

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 structure. Previous investigations have indicated the feasibility for laboratory formation of an elliptical sheet beam using magnetic quadrupoles and a Pierce gun pencil-beam source.(M.A. Basten, J.H. Booske, and J. Anderson, IEEE Trans. Plasma Sci., vol. 22, 960 (1994))In addition to its practical utility, this configuration provides an excellent test case to examine and compare the accuracy of various 3-D beam optics simulation tools. Similarly, the configuration exhibits several unique physical features of phase space evolution not observed in more conventional, paraxial beam transport systems. We discuss and compare the results of numerical simulations using WARP, TRACE3-D, and MAGIC3-D codes.

McNeely, M. J.; Booske, J. H.; Scharer, J. E.; Basten, M. A.

1998-11-01

222

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

SciTech Connect

The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2014-08-15

223

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

NASA Astrophysics Data System (ADS)

The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

Hong, Woo-Pyo; Jung, Young-Dae

2014-08-01

224

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 94, NO. A6, PAGES 6995-7001, JUNE 1, 1989 Electron Velocity Distributions and Plasma Waves Associated With  

E-print Network

and inclination 49.5ø on the space shuttle Challenger on July 29, 1985.During August 1the Plasma.In the wake of the space shuttle a magneticallyaligned sheet of electrons returning from the direction, andthe ambientionosphere. The PDP provided observationsout to a distanceof--·400 m from the space shuttle

Gurnett, Donald A.

225

Plasma actuator electron density measurement using microwave perturbation method  

NASA Astrophysics Data System (ADS)

A cylindrical dielectric barrier discharge plasma under five different pressures is generated in an evacuated glass tube. This plasma volume is located at the center of a rectangular copper waveguide cavity, where the electric field is maximum for the first mode and the magnetic field is very close to zero. The microwave perturbation method is used to measure electron density and plasma frequency for these five pressures. Simulations by a commercial microwave simulator are comparable to the experimental results.

Mirhosseini, Farid; Colpitts, Bruce

2014-07-01

226

Electromagnetic Oscillations in Cylindrical Plasmas with Electron Beams Interactions  

NASA Astrophysics Data System (ADS)

The dispersion relation for a radial inhomogeneous cylindrical plasma in a strong magnetic field is studied. In order to determine the fundamental transversal magnetic mode (TM_01), we used a numerical algorithm based in expanded Fourier-Bessel functions. Both the effect of the electron beam-plasma interaction and the resonances for a finite transversal cylinder conductor are studied. We used different density profiles and temperatures for the plasma and the beam.

Devia, A.; Arango, P. J.; Barco, H.

227

Electron Bernstein wave current drive modeling in toroidal plasma confinement  

E-print Network

The steady-state confinement of tokamak plasmas in a fusion reactor requires non-inductively driven toroidal currents. Radio frequency waves in the electron cyclotron (EC) range of frequencies can drive localized currents ...

Decker, Joan, 1977-

2005-01-01

228

Controlling electron injection in laser plasma accelerators using multiple pulses  

SciTech Connect

Use of counter-propagating pulses to control electron injection in laser-plasma accelerators promises to be an important ingredient in the development of stable devices. We discuss the colliding pulse scheme and associated diagnostics.

Matlis, N. H.; Geddes, C. G. R.; Plateau, G. R.; Esarey, E.; Schroeder, C.; Bruhwiler, D.; Cormier-Michel, E.; Chen, M.; Yu, L.; Leemans, W. P. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Tech-X Corporation, 5621 Arapahoe Ave, Suite A, Boulder CO 80303 (United States); Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240 (China); Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States) and University of California, Berkeley, CA 94720 (United States)

2012-12-21

229

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

230

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

231

Picosecond electron deflectometry of laser-induced plasmas  

NASA Astrophysics Data System (ADS)

We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a CCD camera. The electric and magnetic fields are reconstructed by comparing the recorded patterns with numerical simulations. We have observed a cloud of hot electrons expanding away from a central core of positively charged ions, and the appearance of strong magnetic fields near the boundaries of the gas jet. In the case of a plasma generated in low density nitrogen (10^13 cm-3), we observed that even low energy electrons can escape from the plasma volume.

Centurion, Martin; Reckenthaeler, Peter; Apolonskiy, Alexander; Krausz, Ferenc; Fill, Ernst

2008-11-01

232

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

233

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

234

Accessibillity of Electron Bernstein Modes in Over-Dense Plasma  

SciTech Connect

Mode-conversion between the ordinary, extraordinary and electron Bernstein modes near the plasma edge may allow signals generated by electrons in an over-dense plasma to be detected. Alternatively, high frequency power may gain accessibility to the core plasma through this mode conversion process. Many of the tools used for ion cyclotron antenna de-sign can also be applied near the electron cyclotron frequency. In this paper, we investigate the possibilities for an antenna that may couple to electron Bernstein modes inside an over-dense plasma. The optimum values for wavelengths that undergo mode-conversion are found by scanning the poloidal and toroidal response of the plasma using a warm plasma slab approximation with a sheared magnetic field. Only a very narrow region of the edge can be examined in this manner; however, ray tracing may be used to follow the mode converted power in a more general geometry. It is eventually hoped that the methods can be extended to a hot plasma representation. Using antenna design codes, some basic antenna shapes will be considered to see what types of antennas might be used to detect or launch modes that penetrate the cutoff layer in the edge plasma.

Batchelor, D.B.; Bigelow, T.S.; Carter, M.D.

1999-04-12

235

Electron transport in a collisional plasma with multiple ion species  

SciTech Connect

A generalization of the Braginskii electron fluid description [S. I. Braginskii, Sov. Phys. JETP 6, 358 (1958)] to the case of an unmagnetized collisional plasma with multiple ion species is presented. A description of the plasma ions with disparate masses is also discussed.

Simakov, Andrei N., E-mail: simakov@lanl.gov; Molvig, Kim [Computational Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Computational Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2014-02-15

236

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

237

Low-frequency mobility response functions for the central plasma sheet with application to tearing modes  

NASA Technical Reports Server (NTRS)

Consideration is given to the effect of constant cross-tail magnetic field By on the collisionless conductivity produced by chaotic scattering and stochastic diffusion of particles in the current sheet for a parabolic geometry. It is shown that the correlation time scales as (By/Bz)-squared, and from this strong By scaling a strong tendency toward stabilization of the linear tearing modes with increasing values of By is inferred. This effect of increased dawn-dusk mobility is particularly dramatic when electrons are introduced in the calculation, and is in agreement with the results of kinetic particle simulations. The collisionless conductivity is expressed in terms of the ensemble-averaged power spectrum of the single particle trajectories, which makes it possible to calculate directly the linear conductivity instead of deriving it from the calculation of the irreversible heating rates.

Hernandez, J.; Horton, W.; Tajima, T.

1993-01-01

238

Picosecond electron deflectometry of laser-induced plasmas  

Microsoft Academic Search

We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a

Martin Centurion; Peter Reckenthaeler; Alexander Apolonskiy; Ferenc Krausz; Ernst Fill

2008-01-01

239

Linear analysis of a rectangular waveguide cyclotron maser with a sheet electron beam  

SciTech Connect

A linear theory for a rectangular waveguide cyclotron maser with a sheet electron beam is developed by using the Laplace transformation approach. This theory can be applied to any TE{sub mn} rectangular waveguide mode. The corresponding equations for the TM{sub mn} mode in the rectangular waveguide are also derived as a useful reference. Especially, the effect from the coupling between degenerate modes, which is induced by the nonideal rectangular waveguide walls, on the dispersion relation is considered in order to provide a more accurate model for the real devices. Through numerical calculations, the linear growth rate, launching loss, and spontaneous oscillations (caused by the absolute instability and backward wave oscillation) of this new structure can be analyzed in detail. It is worthwhile to point out that the operation at higher power levels of the rectangular waveguide sheet beam system is possible.

Zhao Ding; Ding Yaogen; Wang Yong; Ruan Cunjun [Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)

2010-11-15

240

Azimuthal Pressure Gradient and Associated Auroral Development in the Near-Earth Plasma Sheet 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 pre-midnight region of the near-earth plasma sheet during the substorm growth phase due 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 FACs variations associated with the substorm growth phase and thus may setup a plasma sheet pre-condition for the substorm onset being triggered near this region. We take advantage of two of the THEMIS spacecraft separated azimuthally near the orbit apogee and investigate the azimuthal plasma pressure gradient in the R~10-12 RE region. Equatorial plasma pressure is estimated by removing the curvature force effect. Four events with the spacecraft footprints mapped very close to the aurora onset region were selected. Two of them showed substantial duskward pressure gradient enhancement 2-5 min before onset. A late-growth-phase auroral arc, which became the substorm onset arc, was found to intensify simultaneously with the pressure gradient enhancement. The other two vents showed almost no change of azimuthal pressure gradient before onset, at the same time neither growth-phase auroral arc intensification was found near the spacecraft footprints, nor did onset occur along an observable arc. These results indicate that the duskward azimuthal pressure gradient enhancement associated with enhanced upward FACs during the late-growth-phase may provide important energy redistribution for the intensification of the growth-phase auroral arc soon before it breaks up and set up conditions for substorm onset to occur along such an arc.

Xing, X.; Lyons, L. R.; Nishimura, Y.; Angelopoulos, V.; Donovan, E. F.; Larson, D. E.; Carlson, C. W.; Auster, H.

2010-12-01

241

Plasma parameters and electron energy distribution functions in a magnetically focused plasma  

SciTech Connect

Spatially resolved measurements of ion density, electron temperature, floating potential, and the electron energy distribution function (EEDF) are presented for a magnetically focused plasma. The measurements identify a central plasma column displaying Maxwellian EEDFs at an electron temperature of about 5 eV indicating the presence of a significant fraction of electrons in the inelastic energy range (energies above 15 eV). It is observed that the EEDF remains Maxwellian along the axis of the discharge with an increase in density, at constant electron temperature, observed in the region of highest magnetic field strength. Both electron density and temperature decrease at the plasma radial edge. Electron temperature isotherms measured in the downstream region are found to coincide with the magnetic field lines.

Samuell, C. M.; Blackwell, B. D.; Howard, J.; Corr, C. S. [Plasma Research Laboratory, Research School of Physics and Engineering, Australian National University, Canberra (Australia)

2013-03-15

242

Measuring ionospheric electron density using the plasma frequency probe  

SciTech Connect

During the past decade, the plasma frequency probe (PFP) has evolved into an accurate, proven method of measuring electron density in the ionosphere above about 90 km. The instrument uses an electrically short antenna mounted on a sounding rocket that is immersed in the plasma and notes the frequency where the antenna impedance is large and nonreactive. This frequency is closely related to the plasma frequency, which is a direct function of free electron concentration. The probe uses phase-locked loop technology to follow a changing electron density. Several sections of the plasma frequency probe circuitry are unique, especially the voltage-controlled oscillator that uses both an electronically tuned capacitor and inductor to give the wide tuning range needed for electron density measurements. The results from two recent sounding rocket flights (Thunderstorm II and CRIT II) under vastly different plasma conditions demonstrate the capabilities of the PFP and show the importance of in situ electron density measurements of understanding plasma processes. 9 refs.

Jensen, M.D.; Baker, K.D. (Utah State University, Logan (United States))

1992-02-01

243

Oscillating plasma bubbles. III. Internal electron sources and sinks  

SciTech Connect

An internal electron source has been used to neutralize ions injected from an ambient plasma into a spherical grid. The resultant plasma is termed a plasma 'bubble.' When the electron supply from the filament is reduced, the sheath inside the bubble becomes unstable. The plasma potential of the bubble oscillates near but below the ion plasma frequency. Different modes of oscillations have been observed as well as a subharmonic and multiple harmonics. The frequency increases with ion density and decreases with electron density. The peak amplitude occurs for an optimum current and the instability is quenched at large electron densities. The frequency also increases if Langmuir probes inside the bubble draw electrons. Allowing electrons from the ambient plasma to enter, the bubble changes the frequency dependence on grid voltage. It is concluded that the net space charge density in the sheath determines the oscillation frequency. It is suggested that the sheath instability is caused by ion inertia in an oscillating sheath electric field which is created by ion bunching.

Stenzel, R. L.; Urrutia, J. M. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

2012-08-15

244

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

245

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

SciTech Connect

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 =d{sub e}=c/?{sub 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?d{sub e}), 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 [Max Planck/Princeton Center for Plasma Physics, Gttingen (Germany); Max Planck Institute for Solar System Research, Justus-Von-Liebig-Weg-3, Gttingen (Germany)

2014-07-15

246

Nonlocal collisionless and collisional electron transport in low temperature plasmas  

NASA Astrophysics Data System (ADS)

The purpose of the talk is to describe recent advances in nonlocal electron kinetics in low-pressure plasmas. A distinctive property of partially ionized plasmas is that such plasmas are always in a non-equilibrium state: the electrons are not in thermal equilibrium with the neutral species and ions, and the electrons are also not in thermodynamic equilibrium within their own ensemble, which results in a significant departure of the electron velocity distribution function from a Maxwellian. These non-equilibrium conditions provide considerable freedom to choose optimal plasma parameters for applications, which make gas discharge plasmas remarkable tools for a variety of plasma applications, including plasma processing, discharge lighting, plasma propulsion, particle beam sources, and nanotechnology. Typical phenomena in such discharges include nonlocal electron kinetics, nonlocal electrodynamics with collisionless electron heating, and nonlinear processes in the sheaths and in the bounded plasmas. Significant progress in understanding the interaction of electromagnetic fields with real bounded plasma created by this field and the resulting changes in the structure of the applied electromagnetic field has been one of the major achievements of the last decade in this area of research [1-3]. We show on specific examples that this progress was made possible by synergy between full scale particle-in-cell simulations, analytical models, and experiments. In collaboration with Y. Raitses, A.V. Khrabrov, Princeton Plasma Physics Laboratory, Princeton, NJ, USA; V.I. Demidov, UES, Inc., 4401 Dayton-Xenia Rd., Beavercreek, OH 45322, USA and AFRL, Wright-Patterson AFB, OH 45433, USA; and D. Sydorenko, University of Alberta, Edmonton, Canada. [4pt] [1] D. Sydorenko, A. Smolyakov, I. Kaganovich, and Y. Raitses, IEEE Trans. Plasma Science 34, 895 (2006); Phys. Plasmas 13, 014501 (2006); 14 013508 (2007); 15, 053506 (2008). [0pt] [2] I. D. Kaganovich, Y. Raitses, D. Sydorenko, and A. Smolyakov, Phys. Plasmas 14, 057104 (2007). [0pt] [3] V.I. Demidov, C.A. DeJoseph, and A.A. Kudryavtsev, Phys. Rev. Lett. 95, 215002 (2005); V.I. Demidov, C.A. DeJoseph, J. Blessington, and M.E. Koepke, Europhysics News, 38, 21 (2007).

Kaganovich, Igor

2009-10-01

247

Femtosecond laser-induced electronic plasma at metal surface  

SciTech Connect

We develop a theoretical analysis to model plasma initiation at the early stage of femtosecond laser irradiation of metal surfaces. The calculation reveals that there is a threshold intensity for the formation of a microscale electronic plasma at the laser-irradidated metal surface. As the full width at half maximum of a laser pulse increases from 15 to 200 fs, the plasma formation threshold decreases by merely about 20%. The dependence of the threshold intensity on laser pulse width can be attributed to laser-induced surface electron emission, in particular due to the effect of photoelectric effect.

Chen Zhaoyang; Mao, Samuel S. [Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California 94720 (United States)

2008-08-04

248

A plasma-cathode electron source designed for industrial use  

NASA Astrophysics Data System (ADS)

The article presents a description of the principle of operation, the design, and the performance data of a plasma-cathode electron source. Plasma is produced in a hollow-cathode reflex discharge operating in an axial magnetic field. The discharge unit is filamentless. Air is used as the working gas. The electron source generates a focused continuous electron beam of current up to 0.3 A at an accelerating voltage of up to 60 kV. Owing to the absence of hot electrodes, the system operates reliably under severe gas conditions with a long lifetime. The electron source is currently used as a component of electron-beam welding flow lines. The use of the electron source for electron-beam facing of composite powdered materials is also discussed.

Osipov, Igor; Rempe, Nikolai

2000-04-01

249

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

250

Formation of high-? plasma and stable confinement of toroidal electron plasma in Ring Trap 1a)  

NASA Astrophysics Data System (ADS)

Formation of high-? electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local ? value has exceeded 70%. Hot electrons are major component of electron populations, and its particle confinement time is 0.5 s. Plasma has a peaked density profile in strong field region [H. Saitoh et al., 23rd IAEA Fusion Energy Conference EXC/9-4Rb (2010)]. In pure electron plasma experiment, inward particle diffusion is realized, and electrons are stably trapped for more than 300 s. When the plasma is in turbulent state during beam injection, plasma flow has a shear, which activates the diocotron (Kelvin-Helmholtz) instability. The canonical angular momentum of the particle is not conserved in this phase, realizing the radial diffusion of charged particles across closed magnetic surfaces. [Z. Yoshida et al., Phys Rev. Lett. 104, 235004 (2010); H. Saitoh et al., Phys. Plasmas 17, 112111 (2010).].

Saitoh, H.; Yoshida, Z.; Morikawa, J.; Furukawa, M.; Yano, Y.; Kawai, Y.; Kobayashi, M.; Vogel, G.; Mikami, H.

2011-05-01

251

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

252

Laser Wakefield Acceleration of Electrons in Tapered Plasma Channels  

NASA Astrophysics Data System (ADS)

Electron energy gain in channel-guided laser wakefield accelerators can be limited by instabilities which disrupt the laser pulse and by electron dephasing. Pulse disruption due to Raman and modulational instabilities can be avoided by using pulses shorter than a plasma wavelength. The dephasing limited energy gain can be overcome by tapering the plasma channel, i.e., allowing the plasma density to vary longitudinally. For a channel in which the density is increasing, the wake can have a phase velocity equal to the speed of light at some point behind the pulse. The longitudinal density variation can be constructed such that this luminous point remains at a constant phase (a fixed number of plasma wavelengths behind the laser) as the pulse propagates. Test particle calculations show that electrons injected near the luminous point can achieve energies well beyond the dephasing limited energy associated with untapered channels. Simulation results exploring pulse propagation in tapered channels will also be presented.

Penano, J. R.; Sprangle, P.; Hafizi, B.; Hubbard, R. F.; Gordon, D. F.; Antonsen, T. M.

2000-10-01

253

Electron energy distributions in a magnetized inductively coupled plasma  

SciTech Connect

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, E-mail: ssongs@umich.edu, E-mail: Sang-Heon.Song@us.tel.com [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, Michigan 48109-2104 (United States); Yang, Yang, E-mail: yang-yang@amat.com [Applied Materials Inc., 974 E. Arques Avenue, M/S 81312, Sunnyvale, California 94085 (United States); Chabert, Pascal, E-mail: pascal.chabert@lpp.polytechnique.fr [LPP, CNRS, Ecole Polytechnique, UPMC, Paris XI, 91128 Palaiseau (France); Kushner, Mark J., E-mail: mjkush@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan 48109-2122 (United States)

2014-09-15

254

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

255

Cluster electric current density measurements within a magnetic flux rope in the plasma sheet  

NASA Technical Reports Server (NTRS)

On August 22, 2001 all 4 Cluster spacecraft nearly simultaneously penetrated a magnetic flux rope in the tail. The flux rope encounter took place in the central plasma sheet, Beta(sub i) approx. 1-2, near the leading edge of a bursty bulk flow. The "time-of-flight" of the flux rope across the 4 spacecraft yielded V(sub x) approx. 700 km/s and a diameter of approx.1 R(sub e). The speed at which the flux rope moved over the spacecraft is in close agreement with the Cluster plasma measurements. The magnetic field profiles measured at each spacecraft were first modeled separately using the Lepping-Burlaga force-free flux rope model. The results indicated that the center of the flux rope passed northward (above) s/c 3, but southward (below) of s/c 1, 2 and 4. The peak electric currents along the central axis of the flux rope predicted by these single-s/c models were approx.15-19 nA/sq m. The 4-spacecraft Cluster magnetic field measurements provide a second means to determine the electric current density without any assumption regarding flux rope structure. The current profile determined using the curlometer technique was qualitatively similar to those determined by modeling the individual spacecraft magnetic field observations and yielded a peak current density of 17 nA/m2 near the central axis of the rope. However, the curlometer results also showed that the flux rope was not force-free with the component of the current density perpendicular to the magnetic field exceeding the parallel component over the forward half of the rope, perhaps due to the pressure gradients generated by the collision of the BBF with the inner magnetosphere. Hence, while the single-spacecraft models are very successful in fitting flux rope magnetic field and current variations, they do not provide a stringent test of the force-free condition.

Slavin, J. A.; Lepping, R. P.; Gjerloev, J.; Goldstein, M. L.; Fairfield, D. H.; Acuna, M. H.; Balogh, A.; Dunlop, M.; Kivelson, M. G.; Khurana, K.

2003-01-01

256

Ion composition of the near-Earth plasma sheet in storm and quiet intervals: Geotail\\/EPIC measurements  

Microsoft Academic Search

We investigate the ion composition of the near-Earth plasma sheet in storm and quiet intervals, using energetic (9-210 keV) particle flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on the Geotail spacecraft. In 1998 four magnetic storms (minimum Dst=-10RE). For each of the storms, we have selected a

M. Nos; S. Ohtani; K. Takahashi; A. T. Y. Lui; R. W. McEntire; D. J. Williams; S. P. Christon; K. Yumoto

2001-01-01

257

The effect of electron beam on the electron hole in a plasma  

SciTech Connect

An electron hole is discussed theoretically in an electron beam--plasma system. The nonlinear dispersion relation for the electron hole along with the conditions on the existence of the electron hole is investigated numerically. It is found that depending upon the beam parameters and radial boundary there are two regions where the electron hole can be formed. It is also seen that the upper limit on Mach number of the electron hole does not vanish even in the presence of the electron beam. The electron holes of high Mach number are possible only in the presence of an electron beam.

Sayal, V.K.; Jain, S.L.; Sharma, S.R. (Department of Physics, University of Rajasthan, Jaipur (India))

1994-11-01

258

Multi electron species and shielding potentials in plasmas  

SciTech Connect

The phenomenon of Debye shielding is investigated in electron ion plasmas using the approach of two temperature electrons. We get different profiles of potential for different parameters and observe that the potentials fall very slowly than the standard Coulomb and Debye potentials. The importance of work is pointed out in the introduction.

Khan, Arroj A.; Murtaza, G. [Salam Chair in Physics, Government College University, Lahore 54000 (Pakistan); Rasheed, A.; Jamil, M. [Department of Physics, Government College University, Faisalabad 38000 (Pakistan)

2012-11-15

259

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

260

Plasma Wakefield Accelerator Driven by a Train of Electron Bunches  

Microsoft Academic Search

We study experimentally the physics of the interaction between a train of electron bunches and a plasma whose density can be varied. The train of electron bunches consists of equidistant (300 microns) drive bunches followed by a witness bunch (450 microns from the last drive bunch). Each bunch length is about half the drive bunch spacing (150 microns). The bunch

Patric Muggli; Brian Allen; Vitaly Yakimenko; Karl Kusche; Marcus Babzien

2009-01-01

261

Numerical model of the plasma formation at electron beam welding  

NASA Astrophysics Data System (ADS)

The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analysis by the diffusion equation for a multicomponent mixture. The electrostatic field is calculated using the Poisson equation. Thermionic electron emission is calculated for the keyhole wall. The ionization intensity of the vapors due to beam electrons and high-energy secondary and backscattered electrons is calibrated using the plasma parameters when there is no polarized collector electrode above the welding zone. The calculated data are in good agreement with experimental data. Results for the plasma parameters for excitation of a non-independent discharge are given. It is shown that there is a need to take into account the effect of a strong electric field near the keyhole walls on electron emission (the Schottky effect) in the calculation of the current for a non-independent discharge (hot cathode gas discharge). The calculated electron drift velocities are much bigger than the velocity at which current instabilities arise. This confirms the hypothesis for ion-acoustic instabilities, observed experimentally in previous research.

Trushnikov, D. N.; Mladenov, G. M.

2015-01-01

262

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

263

Method for generating a plasma wave to accelerate electrons  

DOEpatents

The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, with its pulse-shaping subsystem; the electron gun system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention.

Umstadter, Donald (Ann Arbor, MI); Esarey, Eric (Chevy Chase, MD); Kim, Joon K. (Ann Arbor, MI)

1997-01-01

264

Method for generating a plasma wave to accelerate electrons  

DOEpatents

The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, with its pulse-shaping subsystem; the electron gun system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode triggering system; the electron diagnostics; and the feedback system between the electron diagnostics and the laser system. The system also includes plasma source including vacuum chamber, magnetic lens, and magnetic field means. The laser system produces a train of pulses that has been optimized to maximize the axial electric field amplitude of the plasma wave, and thus the electron acceleration, using the method of the invention. 21 figs.

Umstadter, D.; Esarey, E.; Kim, J.K.

1997-06-10

265

Demonstration via simulation of stable confinement of sheet electron beams using periodic magnetic focusing  

Microsoft Academic Search

Using a two and one-half dimensional (two-dimensional for fields, three-dimensional for particle velocities) particle-in-cell (PIC) code we simulate the dynamics of a highly-elliptic sheet electron beam focused by a periodically-cusped-magnetic (PCM) field array. For edge-focusing, a periodic-quadrupole-magnetic (PQM) array is placed along the sides. Very high-space-charge, low-voltage beams may be focused in this way, without disruptive diocotron instability. The PCM-PQM

John H. Booske; Mark A. Basten

1999-01-01

266

Electron-transfer reactions at the plasma-liquid interface.  

PubMed

Electrochemical reactions are normally initiated in solution by metal electrodes such as Pt, which are expensive and limited in supply. In this Communication, we demonstrate that an atmospheric-pressure microplasma can act as a gaseous, metal-free electrode to mediate electron-transfer reactions in aqueous solutions. Ferricyanide is reduced to ferrocyanide by plasma electrons, and the reduction rate is found to depend on discharge current. The ability to initiate and control electrochemical reactions at the plasma-liquid interface opens a new direction for electrochemistry based on interactions between gas-phase electrons and ionic solutions. PMID:21985430

Richmonds, Carolyn; Witzke, Megan; Bartling, Brandon; Lee, Seung Whan; Wainright, Jesse; Liu, Chung-Chiun; Sankaran, R Mohan

2011-11-01

267

Nonlinear electron oscillations in a viscous and resistive plasma.  

PubMed

Nonlinear, spatially periodic, long-wavelength electrostatic modes of an electron fluid oscillating against a motionless ion fluid (Langmuir waves) are given, with viscous and resistive effects included. The cold plasma approximation is adopted, which requires the wavelength to be sufficiently large. The pertinent requirement valid for large amplitude waves is determined. The general nonlinear solution of the continuity and momentum transfer equations for the electron fluid along with Poisson's equation is obtained in simple parametric form. It is shown that in all typical hydrogen plasmas, the influence of plasma resistivity on the modes in question is negligible. Within the limitations of the solution found, the nonlinear time evolution of any (periodic) initial electron number density profile ne(x,t=0) can be determined (examples). For the modes in question, an idealized model of a strictly cold and collisionless plasma is shown to be applicable to any real plasma, provided that the wavelength ?>?min(n(0),Te) , where n(0)=const and Te are the equilibrium values of the electron number density and electron temperature. Within this idealized model, the minimum of the initial electron density n(e)(xmin,t=0) must be larger than half its equilibrium value, n(0)/2 . Otherwise, the corresponding maximum n(e)(xmax,t=?(p)/2) , obtained after half a period of the plasma oscillation blows up. Relaxation of this restriction on n(e)(x,t=0) as one decreases ? , due to the increase of the electron viscosity effects, is examined in detail. Strong plasma viscosity is shown to change considerably the density profile during the time evolution, e.g., by splitting the largest maximum in two. PMID:20866343

Skorupski, A A; Infeld, E

2010-05-01

268

Diagnostics of electron beams and plasma wave in laser-plasma accelerators  

NASA Astrophysics Data System (ADS)

Relevant techniques for temporal characterization of laser-driven electron bunches as well as accelerating plasma waves are discussed. Emphasis is placed on a combination of two state-of-the-art approaches providing unique temporal information about laser plasma acceleration process and on its applicability to conventional lasers.

Veisz, Laszlo; Buck, Alexander; Nicolai, Maria; Schmid, Karl; Sears, Chris M. S.; Svert, Alexander; Mikhailova, Julia M.; Kaluza, Malte C.; Krausz, Ferenc

2012-12-01

269

Two-dimensional-spatial distribution measurement of electron temperature and plasma density in low temperature plasmas  

SciTech Connect

A real-time measurement method for two-dimensional (2D) spatial distribution of the electron temperature and plasma density was developed. The method is based on the floating harmonic method and the real time measurement is achieved with little plasma perturbation. 2D arrays of the sensors on a 300 mm diameter wafer-shaped printed circuit board with a high speed multiplexer circuit were used. Experiments were performed in an inductive discharge under various external conditions, such as powers, gas pressures, and different gas mixing ratios. The results are consistent with theoretical prediction. Our method can measure the 2D spatial distribution of plasma parameters on a wafer-level in real-time. This method can be applied to plasma diagnostics to improve the plasma uniformity of plasma reactors for plasma processing.

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

2013-05-15

270

Detailed determination of the orientation and motion of the plasma sheet boundary layer using energetic protons on ISEE 1 and 2: Waves, curves, and flapping  

SciTech Connect

During a geomagnetic substorm on April 12, 1979, the ISEE 1 and 2 spacecraft entered the plasma sheet, crossing the boundary layer several times. The spacecraft were located approximately 21 Earth radii from the Earth on the nightside. Using the time delay between the two satellites, one can determine the speed of the plasma sheet surface only by making assumptions about its orientation. By contrast, in this work, the plasma sheet boundary is investigated with the method of remote sensing using energetic proton data from the medium energy particle experiment (MEPE) to measure the speed and the orientation simultaneously. It is shown that, in this case, the plasma sheet boundary is oriented more than 45 {degree} to the GSM equator and has a speed normal to its surface of the order of tens of kilometers per second in the dawn direction. The ion flux gradient scale length at the boundary is estimated to be some hundred kilometers. The orientations of the subsequent exit and reentry are such as to indicate curvature of the plasma sheet surface on the order of several thousand kilometers, the whole surface structure moving in the dawn direction at speeds of about 70 km s{sup {minus}1}. In addition, close analysis of the data suggests that the plasma sheet boundary may be locally aligned nearly perpendicular to the magnetic equator. These dawnward moving surface structures are possibly related to eastward moving auroral features observed on the ground.

Kettmann, G.; Daly, P.W. (Max-Planck-Inst. fuer Aeronomie, Katlenburg-Lindau (Germany))

1988-07-01

271

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

272

Radio-frequency detection of electron oscillations in ultracold plasmas  

NASA Astrophysics Data System (ADS)

Electron oscillations in ultracold plasmas were previously observed through the enhanced electron emission from the plasma due to resonant rf heating. Both simple Langmuir and Tonks-Dattner resonances were detected in this manner. Recent theoretical work [1] predicts that the resonant energy absorption occurs primarily at the edge of the electron distribution and thus the resonant frequency depends on the charge imbalance of the plasma. To aid in investigating this claim, we have developed a new technique to observe electron resonances by directly monitoring the amplitude and phase changes of the rf field capacitively coupled onto a grid located near the plasma. This technique provides a direct measure of the rf absorption that does not depend on the dynamics of electron evaporation, and can be used in experiments where electron detection is not possible. In addition to studying Langmuir waves, we have also excited and observed an upper hybrid oscillation of the electrons in the presence of a perpendicular magnetic field.[4pt] [1] A. Lyubonko, T. Pohl, and J.-M. Rost, arXiv:1011.5937 (2010). Supported by NSF PHY-1004242.

Twedt, K. A.; Rolston, S. L.

2011-06-01

273

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

274

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

275

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

276

Electron backscatter diffraction applied to lithium sheets prepared by broad ion beam milling.  

PubMed

Due to its very low hardness and atomic number, pure lithium cannot be prepared by conventional methods prior to scanning electron microscopy analysis. Here, we report on the characterization of pure lithium metallic sheets used as base electrodes in the lithium-ion battery technology using electron backscatter diffraction (EBSD) and X-ray microanalysis using energy dispersive spectroscopy (EDS) after the sheet surface was polished by broad argon ion milling (IM). No grinding and polishing were necessary to achieve the sufficiently damage free necessary for surface analysis. Based on EDS results the impurities could be characterized and EBSD revealed the microsctructure and microtexture of this material with accuracy. The beam damage and oxidation/hydration resulting from the intensive use of IM and the transfer of the sample into the microscope chamber was estimated to be <50 nm. Despite the fact that the IM process generates an increase of temperature at the specimen surface, it was assumed that the milling parameters were sufficient to minimize the heating effect on the surface temperature. However, a cryo-stage should be used if available during milling to guaranty a heating artefact free surface after the milling process. Microsc. Res. Tech., 78:30?39, 2015. 2014 Wiley Periodicals, Inc. PMID:25280344

Brodusch, Nicolas; Zaghib, Karim; Gauvin, Raynald

2015-01-01

277

Direct Acceleration of Electrons in a Corrugated Plasma Channel  

SciTech Connect

Direct laser acceleration of electrons provides a low power tabletop alternative to laser wakefield accelerators. Until recently, however, direct acceleration has been limited by diffraction, phase matching, and material damage thresholds. The development of the corrugated plasma channel [B. Layer et al., Phys. Rev. Lett. 99, 035001 (2007)] has removed all of these limitations and promises to allow direct acceleration of electrons over many centimeters at high gradients using femtosecond lasers [A. G. York et al., Phys Rev. Lett 100, 195001 (2008), J. P. Palastro et al., Phys. Rev. E 77, 036405 (2008)]. We present a simple analytic model of laser propagation in a corrugated plasma channel and examine the laser-electron beam interaction. Simulations show accelerating gradients of several hundred MeV/cm for laser powers much lower than required by standard laser wakefield schemes. In addition, the laser provides a transverse force that confines the high energy electrons on axis, while expelling low energy electrons.

Palastro, J. P. [Institute for Research in Electrical and Applied Physics, University of Maryland, College Park, MD 20740 (United States); Lawrence Livermore National Laboratory Livermore, CA 94550 (United States); Antonsen, T. M.; Morshed, S.; York, A. G.; Layer, B.; Aubuchon, M.; Milchberg, H. M. [Institute for Research in Electrical and Applied Physics, University of Maryland, College Park, MD 20740 (United States); Froula, D. H. [Lawrence Livermore National Laboratory Livermore, CA 94550 (United States)

2009-01-22

278

Effect of electron extraction from a grid plasma cathode on the generation of emission plasma  

NASA Astrophysics Data System (ADS)

The paper describes the operating mode of a plasma electron source based on a low- pressure arc discharge with grid stabilization of the plasma emission boundary which provides a considerable (up to twofold) increase in discharge and beam currents at an Ar pressure in the vacuum chamber p = 0.02-0.05 Pa, accelerating voltages of up to U = 10 kV, and longitudinal magnetic field of up to Bz = 0.1 T. The discharge and beam currents are increased on electron extraction from the emission plasma through meshes of a fine metal grid due to the energy of a high-voltage power supply which ensures electron emission and acceleration. The electron emission from the plasma cathode and arrival of ions from the acceleration gap in the discharge changes the discharge plasma parameters near the emission grid, thus changing the potential of the emission grid electrode with respect to the discharge cathode. The load is not typical and changes the voltage polarity of the electrode gap connected to the discharge power supply, which is to be taken into account in its calculation and design. The effect of electron emission from the plasma cathode on the discharge system can not only change the discharge and beam current pulse shapes but can also lead to a breakdown of the acceleration gap and failure of semiconductor elements in the discharge power supply unit.

Devyatkov, V. N.; Koval, N. N.

2014-11-01

279

Cluster observations of the plasma sheet at very high latitudes: The in situ signature of a transpolar arc  

NASA Astrophysics Data System (ADS)

Transpolar arcs are auroral features which extend into the polar cap, which is the dim region poleward of the main auroral oval. Several case and statistical studies have shown that they are formed by the closure of lobe magnetic flux by magnetotail reconnection, and that the transpolar arc forms at the footprints of the newly-closed field lines which are embedded within the open flux of the polar cap. Therefore, when transpolar arcs occur, the magnetotail should contain closed magnetic field lines even at high latitudes (but in a localised sector), embedded within the open lobe flux. We present in situ observations of this phenomenon, taken by the Cluster spacecraft on 15th September 2005. Cluster was located at high latitudes in the southern hemisphere lobe (far from the typical location of the plasma sheet), and a transpolar arc was observed by the FUV cameras on the IMAGE satellite. An initial analysis reveals that Cluster periodically observed plasma similar to a typical plasma sheet distribution, but at much higher latitudes - indicative of closed flux embedded within the high latitude lobe. Each time that this plasma distribution was observed, the footprint of the spacecraft mapped to the transpolar arc (significantly poleward of the main auroral oval). These observations are consistent with closed flux being trapped in the magnetotail and embedded within the lobe, and provide further evidence for transpolar arcs being formed by magnetotail reconnection.

Fear, R. C.; Milan, S. E.; Maggiolo, R.

2013-12-01

280

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

PubMed

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 = 10-100 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 N2 revealed the increase of electron density at distinct tube regions by one order to attain 10(13)?cm(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 N2 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. PMID:24007055

Haleem, N A; El Fiki, S A; Nouh, S A; El Disoki, T M; Ragheb, M S; Zakhary, S G

2013-08-01

281

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

NASA Astrophysics Data System (ADS)

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 = 10-100 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 N2 revealed the increase of electron density at distinct tube regions by one order to attain 1013/cm3. 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 N2 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.; El Fiki, S. A.; Nouh, S. A.; El Disoki, T. M.; Ragheb, M. S.; Zakhary, S. G.

2013-08-01

282

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

283

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

284

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

285

Anomalous skin effects in a weakly magnetized degenerate electron plasma  

SciTech Connect

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., E-mail: gohar.abbas@gcu.edu.pk; Sarfraz, M. [Department of Physics, GC University Lahore, Katchery Road, Lahore 54000 (Pakistan); Shah, H. A. [Forman Christian College University, Farozpur Road, Lahore 54600 (Pakistan)

2014-09-15

286

Strongly turbulent stabilization of electron beam-plasma interactions  

NASA Technical Reports Server (NTRS)

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.

1980-01-01

287

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

288

Improved plasma uniformity in a discharge system with electron injection  

NASA Astrophysics Data System (ADS)

We present the results of experiments leading to improvement in bulk plasma uniformity of a constricted-arc discharge system with electron injection. The steady-state discharge was in argon, at a gas pressure of 0.5 mTorr, and operated with a main discharge voltage between 20 and 100 V and current between 3 and 15 A. The radial plasma distribution was measured with a movable Langmuir probe. We find that geometric modification of the intermediate electrode exit aperture and the main discharge cathode add little to the plasma uniformity. Improved bulk plasma uniformity is observed when a special distributing grid electrode is used and the main discharge voltage is less than 20-30 V. The application of a weakly divergent magnetic field in the region of the intermediate electrode exit aperture decreases the plasma nonuniformity from 20% to 14% over a radial distance of 30 cm. The plasma uniformity was further improved by compensating the magnetic self-field of the injected electron beam by a reverse magnetic field produced with a special electrode compensator. It is shown that an increase in discharge current causes a proportional increase in back current in the distributing electrode. The approach allows a decrease in plasma nonuniformity from 20% to 13% over a radial distance of 30 cm.

Vizir, A. V.; Tyunkov, A. V.; Shandrikov, M. V.

2009-02-01

289

Nonlinear perpendicular propagation of ordinary mode electromagnetic wave packets in pair plasmas and electron-positron-ion plasmas  

Microsoft Academic Search

The nonlinear amplitude modulation of electromagnetic waves propagating in pair plasmas, e.g., electron-positron or fullerene pair-ion plasmas, as well as three-component pair plasmas, e.g., electron-positron-ion plasmas or doped (dusty) fullerene pair-ion plasmas, assuming wave propagation in a direction perpendicular to the ambient magnetic field, obeying the ordinary (O-) mode dispersion characteristics. Adopting a multiple scales (reductive perturbation) technique, a nonlinear

I. Kourakis; F. Verheest; N. F. Cramer

2007-01-01

290

Plasma Heating by an Electron Beam in Corrugated Magnetic Field  

E-print Network

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 heating by the electron beam results in peak electron temperature ~2 keV. To this time the ions are also collectively heated by gradients of electron pressure in the cells of the trap. Ion temperature increases above 1 keV and confines at the high level for ~1 ms. Dense hot plasma in GOL-3 trap emits D-D neutrons for ~1 ms. Details of collective plasma heating by the beam in the corrugated magnetic field will be presented in the paper. New physical mechanism of effective heating of plasma ions, substantially dependent on the corrugation of the magnetic field, is discussed. Experiments with complete multimirror...

Postupaev, V V; Astrelin, V T; Averkov, A M; Beklemishev, A D; Burdakov, A V; Ivanov, I A; Ivantsivsky, M V; Koidan, V S; Mekler, K I; Polosatkin, S V; Rovenskikh, A F; Sinitsky, S L; Sulyaev, Y S; Zubairov, E R; Sulyaev, Yu.S.

2004-01-01

291

High-frequency microinstabilities in hot-electron plasmas  

SciTech Connect

Instabilities with frequencies in the neighborhood of the electron cyclotron frequency are of interest in determining stable operating regimes of hot-electron plasmas in EBT devices and in tandem mirrors. Previous work used model distributions significantly different than those suggested by recent Fokker-Planck studies. We use much more realistic model distributions in a computer code that solves the full electromagnetic dispersion relation governing longitudinal and transverse waves in a uniform plasma. We allow for an arbitrary direction of wave propagation. Results for the whistler and upper-hybrid loss-cone instabilities are presented.

Chen, Y.J.; Nevins, W.M.; Smith, G.R.

1981-11-24

292

Plasma membrane electron transport in frog blood vessels.  

PubMed

In an attempt to see if frog blood vessels possess a plasma membrane electron transport system, the postcaval vein and aorta isolated from Rana tigrina were tested for their ability to reduce ferricyanide, methylene blue, and 2,6-dichloroindophenol. While the dyes remained unchanged, ferricyanide was reduced to ferrocyanide. This reduction was resistant to inhibition by cyanide and azide. Heptane extraction or formalin fixation of the tissues markedly reduced the capability to reduce ferricyanide. Denuded aortas retained only 30% of the activity of intact tissue. Our results indicate that the amphibian postcaval vein and aorta exhibit plasma membrane electron transport. PMID:20093738

Rao, Rashmi P; Nalini, K; Rao, J Prakasa

2009-12-01

293

New Longitudinal Waves in Electron-Positron-Ion Quantum Plasmas  

Microsoft Academic Search

A general quantum dispersion equation for electron-positron(hole)-ion quantum\\u000aplasmas is derived and studied for some interesting cases. In an\\u000aelectron-positron degenerate Fermi gas, with or without the Madelung term, a\\u000anew type of zero sound waves are found. Whereas in an electron-hole plasmas a\\u000anew longitudinal quantum waves are revealed, which have no analogies in quantum\\u000aelectron-ion plasmas. The excitation

Nodar L. Tsintsadze; Levan N. Tsintsadze; A. Rehman; G. Murtaza

2010-01-01

294

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

295

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

296

Kelvin-Helmholtz vortices around the magnetotail and cold plasma sheet formation: Insight as a multiscale phenomenon  

NASA Astrophysics Data System (ADS)

The magnetopause of the Earth's magnetosphere is a key region in magnetospheric physics, especially in the sense of multiscale coupling from global large-scale phenomena to microscale physics. The velocity shear across the magnetopause is believed to cause Kelvin-Helmholtz instability (KHI) on both the dawn and dusk sides when the interplanetary magnetic field (IMF) points northward; magnetic reconnection and some secondary instabilities are likely to occur in the vortical structure induced by KHI and to play a significant role in solar wind entry across the magnetopause as well as plasma mixing there. This is a manifestation of multiscale coupling; that is, large-scale KH instability may induce micro-scale phenomenon in the rolled-up vortices and resultant formation of the cold plasma sheet in a wide region of the near-Earth magnetotail. Here we show a nice simultaneous measurement of solar wind entry associated with KHI on both sides of the magnetosphere under prolonged northward IMF. In the event that we have found, Cluster on the dawnside and Geotail on the duskside had an opportunity to stay around the magnetopause simultaneously on the opposite side to each other for more than several hours. Proton distribution function on the magnetosphere side of the magnetopause presents dawn-dusk asymmetry, which means that different plasma mixing processes are actually taking place on both sides. Using the Grad-Shafranov reconstruction (GSR) technique that can visualize ambient plasma and field around spacecraft, we clarify that vortical structures due to KHI indeed developed on both sides. These observations and reconstruction analysis suggest that vortical structures induced by KHI result in dawn-dusk asymmetry of plasma mixing around the magnetopause and formation of the cold plasma sheet in a wide region of the near-Earth magnetotail.

Nishino, Masaki N.; Hasegawa, Hiroshi; Fujimoto, Masaki; Mukai, Toshifumi; Saito, Yoshifumi; Reme, Henri; Retino, Alessandro; Nakamura, Rumi; Lucek, Elizabeth

297

Mechanisms of plasma disruption and runaway electron losses in tokamaks  

E-print Network

Based on the analysis of data from the numerous dedicated experiments on plasma disruptions in the TEXTOR tokamak mechanisms of the formation of runaway electron beams and their losses are proposed. The plasma disruption is caused by strong stochastic magnetic field formed due to nonlinearly excited low-mode number MHD modes. It is hypothesized that the runaway electron beam is formed in the central plasma region confined inside the intact magnetic surface located between $q=1$ and the closest low--order rational [$q=4/3$ or $q=3/2$] magnetic surfaces. The thermal quench time caused by the fast electron transport in a stochastic magnetic field is calculated using the collisional transport model. The current decay stage is due to the ambipolar particle transport in a stochastic magnetic field. The runaway electron beam in the confined plasma region is formed due to their acceleration the inductive toroidal electric field. The runaway electron beam current is modeled as a sum of toroidally symmetric part and a ...

Abdullaev, S S; Wongrach, K; Tokar, M; Koslowski, H R; Willi, O; Zeng, L

2015-01-01

298

Hot Electron Instability in a Dipole Confined Plasma  

NASA Astrophysics Data System (ADS)

In plasma containing energetic electrons, two interacting collective modes, an MHD-like mode and a hot electron interchange (HEI) modeootnotetextN. A. Krall, Phys. Fluids, 9, 820 (1966)., may be present. The linear stability of interchange modes in a z-pinch at arbitrary beta, including a bulk and hot electron species was recently studiedootnotetextN. Krasheninnikova, P. J. Catto, Phys. Plasmas, 12, 32101 (2005).. Using the dispersion relation derived in this reference we show that when necessary conditions are satisfied the two modes may be present or absent in a closed-field line magnetic confinement geometry such as a hard core z-pinch or a dipole. The HEI instability and the MHD-like centrifugally-driven mode have been studied previouslyootnotetextB. Levitt, et al., Phys. Plasmas, 9, 2507 (2002), and 12, 055703 (2005)., including a comparison between the measured mode structure and the predictions of a global low-beta simulation. The radial eigenmode is seen to effect the saturation level of the mode. In the Levitated Dipole Experimenthttp://psfcwww2.psfc.mit.edu/ldx/ electron cyclotron resonance heating produces high beta plasmas containing hot electrons, and instability observations will be discussed and compared with theoretical predictions.

Kesner, J.; Mauel, M. E.

2005-10-01

299

Electron-acoustic solitary waves in a magnetized plasma with hot electrons featuring Tsallis distribution  

NASA Astrophysics Data System (ADS)

Nonlinear dynamics of electron-acoustic solitary waves in a magnetized plasma whose constituents are cold magnetized electron fluid, hot electrons featuring Tsallis distribution, and stationary ions are examined. The nonlinear evolution equation (i.e., Zakharov-Kuznetsov (ZK) equation), governing the propagation of EAS waves in such plasma is derived and investigated analytically and numerically, for parameter regimes relevant to the dayside auroral zone. It is revealed that the amplitude, strength and nature of the nonlinear EAS waves are extremely sensitive to the degree of the hot electron nonextensivity. Furthermore, the obtained results are in good agreement with the observations made by the Viking satellite.

Tribeche, Mouloud; Sabry, Refaat

2012-10-01

300

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

301

Effect of electron thermal motion on plasma heating in a magnetized inductively coupled plasma  

NASA Astrophysics Data System (ADS)

Power absorbed inside the magnetized inductively coupled plasma (MICP) is calculated using three different warm MICP models and is then compared with the result of the cold MICP model. The comparison shows that in the propagating region (?plasma heating Swarm is significantly less than the cold plasma heating Scold, unless the distance traveled by the electrons due to their thermal motion, during the effective wave period, becomes significantly less than the wavelength of the cavity wave. Furthermore, in the propagating region, when ? ???e?, there appears a valley on the plot of ?(? )=Swarm/Scold versus ? showing the negative effect of electron thermal motion on plasma heating. This valley widens and gets smoother with an increase in the plasma length. In the nonpropagating region (?>??e?), the maximum value of ?(? ) exists when ? -??e??vth/?, showing that, in the presence of the external magnetic field, the thermal motion of the electrons leads to a Doppler shift of the frequencies, at which collisionless heating is the dominant mode of electron heating. Furthermore, in the nonpropagating region, when ? ???e?, the skin depth of the right circularly polarized electric field decreases with magnetic field. This decrease in the skin depth results in an increase of collisionless heating under the Doppler-shifted wave particle resonant condition of ? -??e??vth/?. It is also observed that, for large plasma length, the results of all the three warm MICP models are consistent with each other.

Aman-ur-Rehman, Pu, Yi-Kang

2007-06-01

302

Electron Acoustic Solitary Waves in Magnetized Quantum Plasma with Relativistic Degenerated Electrons  

NASA Astrophysics Data System (ADS)

A model for the nonlinear properties of obliquely propagating electron acoustic solitary waves in a two-electron populated relativistically quantum magnetized plasma is presented. By using the standard reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived and this equation gives the solitary wave solution. It is observed that the relativistic effects, the ratio of the cold to hot electron unperturbed number density and the magnetic field normalized by electron cyclotron frequency significantly influence the solitary structures.

Zhu, Zhenni; Wu, Zhengwei; Li, Chunhua; Yang, Weihong

2014-11-01

303

Double tearing mode induced by parallel electron viscosity in tokamak plasmas  

SciTech Connect

The linear behaviors of the double tearing mode (DTM) mediated by parallel electron viscosity in cylindrical plasmas with reversed magnetic shear and thus two resonant rational flux surfaces is numerically investigated. The distance between the two surfaces is found to play an important role for modes with poloidal mode number m>1. Two modes, one of which is centered at the inner rational surface and the other is located between the two surfaces, are simultaneously unstable and the growth rates show the standard single tearing mode (STM) scaling as {gamma}{proportional_to}R{sup -1/3} when the distance is large (here, the Reynolds number R{identical_to}{tau}{sub {upsilon}/{tau}h}, {tau}{sub {upsilon},} and {tau}{sub h} are, respectively, the viscosity penetration time of the magnetic field and the Alfven time for a plasma sheet of width a). The latter is unstable only and the growth rate transits to the standard DTM scaling as {gamma}{proportional_to}R{sup -1/5} for low-m (e.g., m<4) modes and keeps the STM scaling {gamma}{proportional_to}R{sup -1/3} for high-m (e.g., m{approx}10) modes, which are found dominant, when the distance is decreased. In contrast, two unstable modes extending from plasma center to the two rational surfaces, respectively, coexist and the growth rates always show the scaling of {gamma}{proportional_to}R{sup -1/5}, independent of the distance, when the poloidal mode number m=1. The DTMs mediated by electron viscosity are enhanced by plasma resistivity of the range where the growth rate of the mode induced by the latter alone is comparable with that mediated by the former alone and vice versa. Otherwise, the growth rate of the mode is equal to the higher of the modes mediated by resistivity or electron viscosity alone when both of them are taken into account.

He Zhixiong [Southwestern Institute of Physics, Chengdu, Sichuan 610041 (China); Department of Engineering Physics, Tsinghua University, Beijing (China); Dong, J. Q. [Southwestern Institute of Physics, Chengdu, Sichuan 610041 (China); Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou (China); Long, Y. X.; Mou, Z. Z.; He, H. D.; Liu, F.; Shen, Y. [Southwestern Institute of Physics, Chengdu, Sichuan 610041 (China); Gao Zhe [Department of Engineering Physics, Tsinghua University, Beijing (China)

2010-11-15

304

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

305

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

306

Beam-Driven Plasma Wakefield Acceleration of Electrons in Lithium and Rubidium Plasmas  

NASA Astrophysics Data System (ADS)

We report on the plasma wakefield experiments performed at the newly commissioned FACET facility at the SLAC National Laboratory. A beam of 2x10^10 20.5 GeV electrons was focused through a 20-40 cm long vapor column of lithium or rubidium produced in a heat-pipe oven. The electron beam tunnel-ionized the metal vapor and then drove a large amplitude plasma wake. The resulting interaction was investigated for different plasma densities and beam parameters. The primary diagnostic was the energy gain and loss features observed using an imaging magnetic spectrometer. Preliminary data and a comparison between acceleration in rubidium and lithium plasmas will be presented.

Vafaei-Najafabadi, Navid; Marsh, Kenneth; Clayton, Christopher; Joshi, Chandrasekhar; Adli, Erik; Corde, Sebastien; Litos, Michael; Li, Selina; Gessner, Spencer; Frederico, Joel; Hogan, Mark; Walz, Dieter; England, Joel; An, Weiming; Lu, Wei; Mori, Warren; Muggli, Patric; Delahaye, Jean-Pierre

2012-10-01

307

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

308

Fizeau interferometer for measurement of plasma electron current  

SciTech Connect

A high-resolution, vertically viewing far-infrared polarimeter-interferometer system is currently used on the Madison symmetric torus (MST) reversed-field pinch (RFP) to measure the plasma electron density and toroidal current density via Faraday rotation. In this article, we propose a scheme to measure the well-known Fizeau effect, whereby through modest modification of the existing apparatus, the line-integrated poloidal current density can also be directly measured. This parameter is important, since the RFP toroidal magnetic field is largely determined by currents flowing within the plasma. The Fizeau effect is a phase shift of an electromagnetic wave associated with movement of a dielectric medium. This motion can be related directly to the plasma electron current. Determining the Fizeau effect involves measurement of the phase shift between two collinear, orthogonally polarized, counterpropagating laser beams. Estimates indicate a phase shift of {approx}2 deg. is expected for typical MST parameters, well within the existing system resolution.

Brower, D.L.; Ding, W.X.; Deng, B.H.; Mahdavi, M.A.; Mirnov, V.; Prager, S.C. [Electrical Engineering Department, University of California, Los Angeles, Los Angeles, California 90095 (United States); General Atomics, San Diego, California 92121 (United States); Physics Department, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2004-10-01

309

Nonlinear Electron Oscillations in a Viscous and Resistive Plasma  

E-print Network

New nonlinear one dimensional modes of electron oscillations in a viscous and resistive two component plasma are given. This extends the results given in Phys. Rev. Lett. 102, 145005 (2009). We assume that ions (of Z=1 and number density n_0 = const) are motionless, the electron temperature T_e = const and the electron pressure force is negligible as compared to the electric force ("cold" plasma approximation). The nonlinear solution of the continuity, momentum transfer and Poisson's equations are obtained in a convenient parametric form which contains only trigonometric and exponential functions. This simple form can be used to plot the solution in the physical variables, n_e(x, t), etc., while anlytical formulas for these quantities are much more complicated. We are able to describe the time evolution of any (periodic) initial electron density profile n_e(x, t=0) (examples). It turns out that our "cold" plasma approximation for the oscillations in question is in fact satisfied in any real plasma, both space...

Skorupski, A A

2009-01-01

310

Radiation fields of helical antenna in compressible electron plasma  

Microsoft Academic Search

Expressions for the radiation fields in a compressible electron plasma medium are derived pertaining to the helical antenna of finite size immersed in it. The current distribution on the helical antenna is assumed to be an out-going travelling wave with an arbitrary phase propagation constant. From these general expressions fields of circular loop and linear antennas can be deduced as

V. L. TALEKAR; K. R. SONI

1974-01-01

311

Design of high-average-power near-millimeter free electron laser oscillators using short period wigglers and sheet electron beams  

Microsoft Academic Search

The design and feasibility of a 1-MW continuous-wave (CW) free electron laser (FEL) oscillator are reviewed. The proposed configuration includes a short-period (Iw~ 1 cm) planar wiggler, a sheet electron beam, a 0.5-1.0-MV thermionic electron gun, a hybrid waveguide\\/quasi-optical resonator, commercial DC power supplies, and a depressed collector. Cavity ohmic RF losses are estimated to be extremely low (⩽10-100 W\\/cm2)

JOHN H. BOOSKE; DANIEL J. RADACK; THOMAS M. ANTONSEN; STEVEN W. BIDWELL; YUVAL CARMEL; WILLIAM W. DESTLER; HENRY P. FREUND; VICTOR L. GRANATSTEIN; PETER E. LATHAM; BARUCH LEVUSH; ISAAK D. MAYERGOYZ; A. Serbeto

1990-01-01

312

Collisional Damping Of Plasma Waves On A Pure Electron Plasma Column  

NASA Astrophysics Data System (ADS)

The collisional damping of electron plasma waves (or, more precisely, Trivelpiece-Gould waves) on a pure electron plasma column is discussed. The damping in a pure electron plasma differs from that in a neutral plasma, since there are no ions to provide collisional drag. A dispersion equation for the complex wave frequency is derived from Poisson's equation and the drift-kinetic equation with the Dougherty collision operatora Fokker-Planck operator that conserves particle number, momentum, and energy yet is analytically tractable. In the limit of weak collisionality, for phase velocity comparable to the thermal velocity, Landau damping is recovered. For larger phase velocity, where Landau damping is negligible, the dispersion equation can be solved analytically, yielding the complex frequency ? = (kz?p/k)[1+(3/2)(k?D)2(1+10i?/9)(1+2i?)-1], where ?p is the plasma frequency, kz is the axial wavenumber, k is the total wavenumber, ?D is the Debye length, ? is the collision frequency, and ???k/?pkz. This expression spans from the weakly collisional regime (??1)) to the strongly collisional regime (??1), matching onto fluid results in the latter limit. Note that in the weakly collisional regime the damping rate is given by Im(?)?-4?(k?D)2/3, which is suppressed from the damping rate in a neutral plasma [Im(?)?-?/2] by the factor (k?D)2?1; this suppression reflects the conservation of electron momentum in the pure electron plasma. In the limit of strong collisionality, the damping is enhanced by cross-field transport resulting from long-range collisions. These collisions are neglected in the kinetic treatment, but their contribution to the damping is estimated from fluid theory.

Anderson, M. W.; O'Neil, T. M.

2009-03-01

313

Anti-bias voltage electron-Kondo transport in a quantum dot device driven by a graphene sheet  

NASA Astrophysics Data System (ADS)

We theoretically investigate the manipulation of electron-Kondo transport through a single-quantum dot (QD) two-electrode device by introducing a side-coupled graphene sheet. It is shown that with increase of coupling strength between the QD and the zero-potential graphene sheet, the anti-bias voltage capability of the QD-electrode Kondo resonance is improved obviously. This causes a high-conductance QD-electrode channel to be opened up for electron transport within a wide bias voltage range. Moreover, the conductance/current of the Kondo channel can be accurately controlled by adjusting the potential of the graphene sheet. These results may be useful for the observation of nonequilibrium Kondo effect and the design of high-conductance control device.

Chen, Xiongwen; Shi, Zhengang; Zhang, Shunru; Song, Kehui; Zhou, Guanghui

2015-01-01

314

High-Brightness Electron Emission from Flexible Carbon Nanotube/Elastomer Nanocomposite Sheets  

NASA Astrophysics Data System (ADS)

Carbon nanotube (CNT)/elastomer nanocomposites (CECs) are flexible and easy to fabricate accordng to the required size and form. We succeeded in realizing a uniform dispersion of CNTs in the elastomer matrices of natural rubber (NR). Intense electron emission from the CEC sheets has been confirmed; the threshold electric field is about 1 V/?m, and the saturation current density reaches 10 mA/cm2. We discuss composite structures consisting of electrically conductive CNT networks dispersed in the insulating NR matrix. Local electric field is enhanced at the CEC surface, and the low threshold field is attributed to the sharp tips and side walls of bent CNTs that appeared on the surface.

Kita, Takashi; Hayashi, Yosuke; Wada, Osamu; Yanagi, Hisao; Kawai, Yasufumi; Magario, Akira; Noguchi, Toru

2006-11-01

315

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

316

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

317

Turbulent transport of trapped-electron modes in collisionless plasmas.  

PubMed

Global gyrokinetic particle simulations of collisionless trapped-electron mode turbulence in toroidal plasmas find that electron heat transport exhibits a device size scaling with a gradual transition from Bohm to gyro-Bohm scaling. A comprehensive analysis of spatial and temporal scales shows that the turbulence eddies are predominantly microscopic because of zonal flow shearing, but the presence of mesoscale structures drives a nondiffusive component in the electron heat flux due to the weak nonlinear detuning of the precessional resonance that excites the linear instability. PMID:19792734

Xiao, Yong; Lin, Zhihong

2009-08-21

318

Turbulent Transport of Trapped-Electron Modes in Collisionless Plasmas  

SciTech Connect

Global gyrokinetic particle simulations of collisionless trapped-electron mode turbulence in toroidal plasmas find that electron heat transport exhibits a device size scaling with a gradual transition from Bohm to gyro-Bohm scaling. A comprehensive analysis of spatial and temporal scales shows that the turbulence eddies are predominantly microscopic because of zonal flow shearing, but the presence of mesoscale structures drives a nondiffusive component in the electron heat flux due to the weak nonlinear detuning of the precessional resonance that excites the linear instability.

Xiao Yong; Lin Zhihong [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States)

2009-08-21

319

Electron-acoustic plasma waves: oblique modulation and envelope solitons.  

PubMed

Theoretical and numerical studies are presented of the amplitude modulation of electron-acoustic waves (EAWs) propagating in space plasmas whose constituents are inertial cold electrons, Boltzmann distributed hot electrons, and stationary ions. Perturbations oblique to the carrier EAW propagation direction have been considered. The stability analysis, based on a nonlinear Schrdinger equation, reveals that the EAW may become unstable; the stability criteria depend on the angle theta between the modulation and propagation directions. Different types of localized EA excitations are shown to exist. PMID:15089419

Kourakis, I; Shukla, P K

2004-03-01

320

Tunable Electron Multibunch Production in Plasma Wakefield Accelerators  

E-print Network

Synchronized, independently tunable and focused $\\mu$J-class laser pulses are used to release multiple electron populations via photo-ionization inside an electron-beam driven plasma wave. By varying the laser foci in the laboratory frame and the position of the underdense photocathodes in the co-moving frame, the delays between the produced bunches and their energies are adjusted. The resulting multibunches have ultra-high quality and brightness, allowing for hitherto impossible bunch configurations such as spatially overlapping bunch populations with strictly separated energies, which opens up a new regime for light sources such as free-electron-lasers.

Hidding, B; Wittig, G; Aniculaesei, C; Jaroszynski, D; McNeil, B W J; Campbell, L T; Islam, M R; Ersfeld, B; Sheng, Z -M; Xi, Y; Deng, A; Rosenzweig, J B; Andonian, G; Murokh, A; Hogan, M J; Bruhwiler, D L; Cormier, E

2014-01-01

321

Sporadic plasma sheet ion injections into the high-altitude auroral bulge: Satellite observations  

NASA Astrophysics Data System (ADS)

We report on a new feature of auroral substorms, namely, the sporadic though recurrent injections of magnetospheric ions throughout the auroral bulge. These injections are interpreted as time of flight dispersed ion structures (TDIS). Our analysis builds on a combination of measurements from Interball-Auroral, from UV imagery onboard Polar, from ground magnetometers, and also from observations on Geotail and from geostationary spacecraft. Backward tracing of ion trajectories from Interball-Auroral orbit using realistic three-dimensional magnetic and electric field models indicates that the injection region can extend over a wide range of radial distances, from ~7-40RE in the nearly equatorial magnetosphere. Both hydrogen and oxygen ions are shown to be injected toward the Earth's upper ionosphere. At Interball altitudes we find that ion injections are associated with two types of low-frequency torsional oscillations of the magnetic field: (1) shear Alfvn waves with a period of a few minutes with the highest amplitude near the bulge front and decreasing amplitude at lower latitudes and (2) higher-frequency shear Alfvn waves of the P1B type, strictly restricted to the poleward boundary of the surge, with a characteristic period of ~40 s. The systematic observation of sporadic TDIS during the auroral bulge expansion leads us to conclude that the same physical process is at work throughout the midtail. We also show that ion injections are detected well inside the bulge, which suggests that the injection fronts propagate from the outer to the inner magnetosphere over large distances. This topic is more extensively studied by V. Sergeev et al. (Plasma sheet ion injections into the auroral bulge: Correlative study of spacecraft and ground observations, submitted to Journal of Geophysical Research, 1999). We also show that the poleward boundary of the surge is associated with a prominent outflow of ionospheric H+ and O+. These ions in the hundred of eV to the keV range are heated perpendicularly to the local magnetic field and subsequently transported into the magnetotail. The expanding auroral bulge thus forms a significant source of ionospheric ions for the midtail magnetosphere.

Sauvaud, J.-A.; Popescu, D.; Delcourt, D. C.; Parks, G. K.; Brittnacher, M.; Sergeev, V.; Kovrazhkin, R. A.; Mukai, T.; Kokubun, S.

322

Electron energy spectrum in circularly polarized laser irradiated overdense plasma  

SciTech Connect

A circularly polarized laser normally impinged on an overdense plasma thin foil target is shown to accelerate the electrons in the skin layer towards the rear, converting the quiver energy into streaming energy exactly if one ignores the space charge field. The energy distribution of electrons is close to Maxwellian with an upper cutoff ?{sub max}=mc{sup 2}[(1+a{sub 0}{sup 2}){sup 1/2}?1], where a{sub 0}{sup 2}=(1+(2?{sup 2}/?{sub p}{sup 2})|a{sub in}|{sup 2}){sup 2}?1, |a{sub in}| is the normalized amplitude of the incident laser of frequency ?, and ?{sub p} is the plasma frequency. The energetic electrons create an electrostatic sheath at the rear and cause target normal sheath acceleration of protons. The energy gain by the accelerated ions is of the order of ?{sub max}.

Liu, C. S.; Tripathi, V. K.; Shao, Xi [Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742 (United States); Kumar, Pawan, E-mail: kumarpawan-30@yahoo.co.in [Department of Physics, Raj Kumar Goel Institute of Technology, Ghaziabad 201003, UP (India)

2014-10-15

323

Positron creation and annihilation in tokamak plasmas with runaway electrons.  

PubMed

It is shown that electron-positron pair production is expected to occur in post-disruption plasmas in large tokamaks, including JET and JT-60U, where up to about 10(14) positrons may be created in collisions between multi-MeV runaway electrons and thermal particles. If the loop voltage is large enough, they are accelerated and form a beam of long-lived runaway positrons in the direction opposite to that of the electrons; if the loop voltage is smaller, the positrons have a lifetime of a few hundred ms, in which they are slowed down to energies comparable to that of the cool ( less, similar 10 eV) background plasma before being annihilated. PMID:12689298

Helander, P; Ward, D J

2003-04-01

324

Electron energy spectrum in circularly polarized laser irradiated overdense plasma  

NASA Astrophysics Data System (ADS)

A circularly polarized laser normally impinged on an overdense plasma thin foil target is shown to accelerate the electrons in the skin layer towards the rear, converting the quiver energy into streaming energy exactly if one ignores the space charge field. The energy distribution of electrons is close to Maxwellian with an upper cutoff ?max=m c2(1 +a02) 1 /2-1 ] , where a02=(1 +(2 ?2/?p2)|ai n|2) 2-1 , |ai n| is the normalized amplitude of the incident laser of frequency ?, and ?p is the plasma frequency. The energetic electrons create an electrostatic sheath at the rear and cause target normal sheath acceleration of protons. The energy gain by the accelerated ions is of the order of ?max .

Liu, C. S.; Tripathi, V. K.; Shao, Xi; Kumar, Pawan

2014-10-01

325

Electron Heating in a Relativistic, Weibel-Unstable Plasma  

E-print Network

The dynamics of two initially unmagnetized relativistic counter-streaming homogeneous ion-electron plasma beams are simulated in two dimensions using the particle-in-cell (PIC) method. It is shown that current filaments, which form due to the Weibel instability, develop a large scale longitudinal electric field in the direction opposite to the current carried by the filaments as predicted by theory. Fast moving ions in the current filaments decelerate due to this longitudinal electric field. The same longitudinal electric field, which is partially inductive and partially electrostatic, is identified as the main source of acceleration of electrons in the current filaments. The transverse electric field, though larger than the longitudinal one, is shown to play a smaller role in heating electrons, contrary to previous claims. It is found that, in 1D, the electrons become strongly magnetized and are \\textit{not} accelerated beyond their initial kinetic energy. Rather, the heating of the electrons is enhanced by ...

Kumar, Rahul; Gedalin, Michael

2015-01-01

326

Atomic and Electronic Structure of Graphene-Oxide  

Microsoft Academic Search

ABSTRACT We elucidate the atomic and electronic structure of graphene oxide (GO) using annular dark field imaging of single and multilayer sheets and electron energy loss spectroscopy for measuring the fine structure of C and O K-edges in a scanning transmission electron microscope. Partial density of states and electronic plasma excitations are also measured for these GO sheets showing unusual

K. Andre Mkhoyan; Alexander W. Contryman; John Silcox; Derek A. Stewart; Goki Eda; Cecilia Mattevi; Steve Miller; Manish Chhowalla

2010-01-01

327

Radiation field in a superstrong magnetoactive electron plasma.  

PubMed

Using the language of quantum field theory, we present a concise derivation for the electromagnetic vector potential A(mu), which is valid for an anisotropic superstrong magnetoactive electron plasma. It is shown that the expression for the vector potential A(mu) can be reduced to various known limits. Applications to important problems in astrophysics are briefly discussed. The relevance of our result to the recent development of the collective interaction between intense neutrino fluxes and stellar plasmas is briefly stressed. PMID:11970505

Chou, C K

1999-11-01

328

Lissajous Electron Plasma (LEP) Generation for Dry Etching  

NASA Astrophysics Data System (ADS)

A new concept for plasma generation which enhances plasma density at low pressures through the use of a high-frequency rotating electric field is introduced. A 50-MHz electric power was applied to three electrodes which are positioned with a triangular symmetry. A phase shift of 120 between the electrodes brought about uniform and high plasma density at a pressure of 1 Pa. The nonuniformity of Ar gas plasma generated was within 10% over a 6'' wafer using a tuned Langmuir probe electron density measurement. Polysilicon etchings were made by both SF6/O2 and Cl2/O2 plasmas. The achieved polysilicon etch-rate was over 200 nm/min for both kinds of plasmas at an electric power of 90 W along with a 13.56 MHz RF bias power of 30 W applied to the substrate. High etch-rate selectivity between polysilicon and oxide of 45 for SF6/O2 and 152 for Cl2/O2 was realized. A very low etch-rate nonuniformity of 1.5% was attained for Cl2/O2.

Nomura, Noboru; Ohkuni, Mitsuhiro; Tamaki, Tokuhiko; Nakayama, Ichiro; Harafuji, Kenji; Sivaram, Srinivasan; Kubota, Masafumi

1992-12-01

329

Requirement for Coenzyme Q in Plasma Membrane Electron Transport  

NASA Astrophysics Data System (ADS)

Coenzyme Q is required in the electron transport system of rat hepatocyte and human erythrocyte plasma membranes. Extraction of coenzyme Q from the membrane decreases NADH dehydrogenase and NADH:oxygen oxidoreductase activity. Addition of coenzyme Q to the extracted membrane restores the activity. Partial restoration of activity is also found with ?-tocopherylquinone, but not with vitamin K_1. Analogs of coenzyme Q inhibit NADH dehydrogenase and oxidase activity and the inhibition is reversed by added coenzyme Q. Ferricyanide reduction by transmembrane electron transport from HeLa cells is inhibited by coenzyme Q analogs and restored with added coenzyme Q10. Reduction of external ferricyanide and diferric transferrin by HeLa cells is accompanied by proton release from the cells. Inhibition of the reduction by coenzyme Q analogs also inhibits the proton release, and coenzyme Q10 restores the proton release activity. Trans-plasma membrane electron transport stimulates growth of serum-deficient cells, and added coenzyme Q10 increases growth of HeLa (human adenocarcinoma) and BALB/3T3 (mouse fibroblast) cells. The evidence is consistent with a function for coenzyme Q in a trans-plasma membrane electron transport system which influences cell growth.

Sun, I. L.; Sun, E. E.; Crane, F. L.; Morre, D. J.; Lindgren, A.; Low, H.

1992-12-01

330

Self-consistent electron transport in collisional plasmas  

SciTech Connect

A self-consistent scheme has been developed to model electron transport in evolving plasmas of arbitrary classical collisionality. The electrons and ions are treated as either multiple donor-cell fluids, or collisional particles-in-cell. Particle suprathermal electrons scatter off ions, and drag against fluid background thermal electrons. The background electrons undergo ion friction, thermal coupling, and bremsstrahlung. The components move in self-consistent advanced E-fields, obtained by the Implicit Moment Method, which permits ..delta..t >> ..omega../sub p//sup -1/ and ..delta..x >> lambda/sub D/ - offering a 10/sup 2/ - 10/sup 3/-fold speed-up over older explicit techniques. The fluid description for the background plasma components permits the modeling of transport in systems spanning more than a 10/sup 7/-fold change in density, and encompassing contiguous collisional and collisionless regions. Results are presented from application of the scheme to the modeling of CO/sub 2/ laser-generated suprathermal electron transport in expanding thin foils, and in multi-foil target configurations.

Mason, R.J.

1982-01-01

331

Polar cap electron densities from DE 1 plasma wave observations  

NASA Technical Reports Server (NTRS)

Electric-field-spectum measurements from the plasma-wave instrument on the Dynamics Explorer 1 spacecraft are used to study the local electron density at high altitudes in the northern polar-cap region. The electron density is determined from the upper cutoff of whistler-mode radiation at the electron plasma frequency. Median density values over the polar cap at L greater than 10 are found to vary from 35.2 + or - 8.5 cu cm at 2.1 earth radii to 0.99 + or - 0.51 cu cm at 4.66 earth radii. The steady-state radial-outflow model is examined for consistency with the observed density profile. A power-law fit to the radial variation of the electron density yields an exponent of - 3.85 + or - 0.32, which for the radial-outflow model implies a flow velocity increasing nearly linearly with incresing radial distance. Comparison of the observed electron densities with theoretical polar-wind densities yields consistent results up to 2.8 earth radii. A comparison of the observed electron densities with low-altitude density profiles from the Alouette II and ISIS 1 spacecraft illustrates transitions in the slope of the profile at 1.16 earth radii and between 1.55 and 2.0 earth radii. The changes in the density profile suggest that changes occur in the basic radial-transport processes at these altitudes.

Persoon, A. M.; Gurnett, D. A.; Shawhan, S. D.

1983-01-01

332

Synchrotron radiation from electron beams in plasma-focusing channels.  

PubMed

Spontaneous radiation emitted from relativistic electrons undergoing betatron motion in a plasma-focusing channel is analyzed, and applications to plasma wake-field 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 a(beta), which plays a role similar to that of the wiggler strength parameter in a conventional FEL. For a(beta) > or approximately 1, radiation is emitted in numerous harmonics. Furthermore, a(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. PMID:12059723

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

2002-05-01

333

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

334

Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma in Semiconductor Quantum Wells  

E-print Network

Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma in Semiconductor Quantum provides insight into the cooperative be- havior of dense electron-hole (e-h) plasmas in quantum June 2006) We investigate photoluminescence from a high-density electron-hole plasma in semiconductor

Kono, Junichiro

335

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

336

Parametric generation of low-frequency waves by plasma electrons accelerated under electron cyclotron resonance conditions  

NASA Astrophysics Data System (ADS)

It has been shown experimentally that the diamagnetic effect appearing when electrons of a magnetized plasma in the antenna near field are accelerated under electron cyclotron resonance conditions can be used to generate low-frequency waves. The amplitude modulation of a signal supplied to the antenna is accompanied by the modulation of the diamagnetic effect and leads to the emission of waves at the modulation frequency to the surrounding plasma. In this process, the extended plasma region containing accelerated electrons serves as a parametric bodiless antenna. The results of the model laboratory experiments make it possible to propose a method for the parametric generation of low-frequency whistler waves in the Earths ionosphere by a powerful amplitude-modulated signal supplied to the satellite-borne antenna.

Gushchin, M. E.; Korobkov, S. V.; Kostrov, A. V.; Odzerikho, D. A.; Priver, S. E.; Strikovskii, A. V.

2010-07-01

337

Electron acoustic solitons in magneto-rotating electron-positron-ion plasma with nonthermal electrons and positrons  

NASA Astrophysics Data System (ADS)

The propagation of electron acoustic solitary waves (EASWs) in a magneto-rotating electron-positron-ion (epi) plasma containing cold dynamical electrons, nonthermal electrons and positrons obeying Cairns' distribution have been explored in the stationary background of massive positive ions. Through the linear dispersion relation (LDR) the effects of nonthermal components, magnetic field and rotation have been analyzed, wherein, various limiting cases have been deduced from the LDR. For nonlinear analysis, Korteweg-de Vries (KdV) equation is obtained using the reductive perturbation technique. It is found that in the presence of nonthermal positrons both hump and dip type solitons appear to excite, the structural properties of these solitary waves change drastically with magneto-rotating effects. The present work may be employed to explore and to understand the formation of electron acoustic solitary structures in the space and laboratory plasmas with nonthermal electrons and positrons under magneto-rotating effects.

Jilani, K.; Mirza, Arshad M.; Iqbal, J.

2015-02-01

338

Electron gas oscillations in plasma. Theory and applications  

E-print Network

We analyze the obtained solutions of the non-linear Shr{"o}dinger equation for spherically and axially symmetrical electrons density oscillations in plasma. The conditions of the oscillations process existence are examined. It is shown that in the center or on the axis of symmetry of the systems the static density of electrons enhances. This process results in the increasing of density and pressure of the ion gas. We suggest that this mechanism could occur in nature as rare phenomenon called the 'fireball' and could be used in carrying out the research concerning controlled fusion. The description of the experiments, carried out for the purpose to generate long-lived spherical plasma structures, is presented.

Dvornikov, M S; Dvornikov, Maxim; Dvornikov, Sergey

2003-01-01

339

A novel electron density reconstruction method for asymmetrical toroidal plasmas  

SciTech Connect

A novel reconstruction method is developed for acquiring the electron density profile from multi-channel interferometric measurements of strongly asymmetrical toroidal plasmas. It is based on a regularization technique, and a generalized cross-validation function is used to optimize the regularization parameter with the aid of singular value decomposition. The feasibility of method could be testified by simulated measurements based on a magnetic configuration of the flexible helical-axis heliotron device, Heliotron J, which has an asymmetrical poloidal cross section. And the successful reconstruction makes possible to construct a multi-channel Far-infrared laser interferometry on this device. The advantages of this method are demonstrated by comparison with a conventional method. The factors which may affect the accuracy of the results are investigated, and an error analysis is carried out. Based on the obtained results, the proposed method is highly promising for accurately reconstructing the electron density in the asymmetrical toroidal plasma.

Shi, N.; Ohshima, S.; Minami, T.; Nagasaki, K.; Yamamoto, S.; Mizuuchi, T.; Okada, H.; Kado, S.; Kobayashi, S.; Konoshima, S.; Sano, F. [Institute of Advanced Energy, Kyoto University, Gokasyo, Uji (Japan)] [Institute of Advanced Energy, Kyoto University, Gokasyo, Uji (Japan); Tanaka, K. [National Institute for Fusion Science, Toki (Japan)] [National Institute for Fusion Science, Toki (Japan); Ohtani, Y.; Zang, L.; Kenmochi, N. [Graduate School of Energy Science, Kyoto University, Uji (Japan)] [Graduate School of Energy Science, Kyoto University, Uji (Japan)

2014-05-15

340

Plasma expansion into vacuum assuming a steplike electron energy distribution  

NASA Astrophysics Data System (ADS)

The expansion of a semi-infinite plasma slab into vacuum is analyzed with a hydrodynamic model implying a steplike electron energy distribution function. Analytic expressions for the maximum ion energy and the related ion distribution function are derived and compared with one-dimensional numerical simulations. The choice of the specific non-Maxwellian initial electron energy distribution automatically ensures the conservation of the total energy of the system. The estimated ion energies may differ by an order of magnitude from the values obtained with an adiabatic expansion model supposing a Maxwellian electron distribution. Furthermore, good agreement with data from experiments using laser pulses of ultrashort durations ?L?80fs is found, while this is not the case when a hot Maxwellian electron distribution is assumed.

Kiefer, Thomas; Schlegel, Theodor; Kaluza, Malte C.

2013-04-01

341

Plasma expansion into vacuum assuming a steplike electron energy distribution.  

PubMed

The expansion of a semi-infinite plasma slab into vacuum is analyzed with a hydrodynamic model implying a steplike electron energy distribution function. Analytic expressions for the maximum ion energy and the related ion distribution function are derived and compared with one-dimensional numerical simulations. The choice of the specific non-Maxwellian initial electron energy distribution automatically ensures the conservation of the total energy of the system. The estimated ion energies may differ by an order of magnitude from the values obtained with an adiabatic expansion model supposing a Maxwellian electron distribution. Furthermore, good agreement with data from experiments using laser pulses of ultrashort durations ?(L)electron distribution is assumed. PMID:23679533

Kiefer, Thomas; Schlegel, Theodor; Kaluza, Malte C

2013-04-01

342

Electron trajectories and growth rates of the plasma wave pumped free-electron laser  

NASA Astrophysics Data System (ADS)

A theory for a plasma wave wiggler has been described which employs the plasma whistler wave for producing laser radiation in a free-electron laser (FEL). While electromagnetically pumped FELs have been proven to be an effective means generating short wavelengths, practical difficulties occur in the design of these wigglers. For this reason, it is found that a plasma wave wiggler can be employed in concept with an electromagnetic wave wiggler due to both higher tunability and holding the focus of pump wave and e-beam over a significant distance to achieve a suitable amplification. Plasma in the presence of static magnetic field supports a plasma whistler wave. The plasma wiggler period can be tuned by varying the plasma density and/or ambient magnetic field. Electron trajectories have been analyzed using single particle dynamics and regimes of orbital stability have been demonstrated. A polynomial dispersion relation for electromagnetic and space-charge waves has then been derived, analytically. Numerical studies of the dispersion relation reveal that the growth rates are sensitive functions of the cyclotron frequency. It has been shown that by increasing the axial magnetic field strength (or cyclotron frequency), the growth rate for groups I and III orbits increases, while a growth decrement has been obtained for groups II and IV orbits.

Jafari, S.; Jafarinia, F.; Nilkar, M.; Amiri, M.

2014-12-01

343

Dressed solitons in quantum electron-positron-ion plasmas  

SciTech Connect

Nonlinear propagation of quantum ion acoustic waves in a dense quantum plasma whose constituents are electrons, positrons, and positive ions is investigated using a quantum hydrodynamic model. The Korteweg-de Vries equation is derived using reductive perturbation technique. The higher order inhomogeneous differential equation is obtained for the dressed soliton. The dynamical equation for dressed soliton is solved using the renormalization method. The conditions for the validity of the higher order correction are described. The effects of quantum parameter, positron concentration, electron to positron Fermi temperature ratio, and soliton velocity on the amplitude and width of the dressed soliton are studied.

Chatterjee, Prasanta; Muniandy, S. V.; Yap, S. L.; Wong, C. S. [Plasma Research Laboratory, Department of Physics, University of Malaya, 50603 Kuala Lumpur (Malaysia); Roy, Kaushik [Department of Mathematics, Siksha Bhavana, Visva Bharati University, Santiketan 731235 (India); Mondal, Ganesh [Department of Mathematics, Siksha Satra, Visva Bharati University, Sriniketan 731236 (India)

2009-12-15

344

Ultrafast Diagnostics for Electron Beams from Laser Plasma Accelerators  

SciTech Connect

We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g., diverse forms of electromagnetic emission) and difficulties (e.g., shot-to-shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly-variable electron bunches from LPAs.

Matlis, N. H.; Bakeman, M.; Geddes, C. G. R.; Gonsalves, T.; Lin, C.; Nakamura, K.; Osterhoff, J.; Plateau, G. R.; Schroeder, C. B.; Shiraishi, S.; Sokollik, T.; van Tilborg, J.; Toth, Cs.; Leemans, W. P.

2010-06-01

345

Approximate Solutions of Quantum Equations for Electron Gas in Plasma  

E-print Network

We have obtained the solutions of linearized Shr{\\"o}dinger equation for spherically and axially symmetrical electrons density oscillations in plasma in the approximation of the self-consistent field. It was shown that in the center or on the axis of symmetry of such a system the static density of electrons can enhance, which leads to the increasing of density and pressure of ion gas. We suggest that this mechanism could be realized in nature as rare phenomenon called the 'fireball' and could be used in carrying out the research concerning controlled fusion.

M. Dvornikov; S. Dvornikov; G. Smirnov

2002-03-14

346

Angular momenta creation in relativistic electron-positron plasma.  

PubMed

Creation of angular momentum in a relativistic electron-positron plasma is explored. It is shown that a chain of angular momentum carrying vortices is a robust asymptotic state sustained by the generalized nonlinear Schrdinger equation characteristic to the system. The results may suggest a possible electromagnetic origin of angular momenta when it is applied to the MeV epoch of the early Universe. PMID:12935260

Tatsuno, T; Berezhiani, V I; Pekker, M; Mahajan, S M

2003-07-01

347

Electron temperature in a sodium-iodide lighting plasma  

NASA Astrophysics Data System (ADS)

The time-dependent electron temperature at the axis of an ac mercury-sodium-iodide arc discharge is determined experimentally. It modulates in phase with the discharge voltage and differs in modulation and magnitude from the temperature obtained assuming thermodynamic equilibrium. The method used is independent of plasma equilibrium assumptions as well as of line-transition probabilities, and since it is based on relative emission measurements, it can, in principle, be applied to discharges contained within translucent envelopes.

Karabourniotis, D.; Drakakis, E.

2002-09-01

348

Helicity Injection by Knotted Antennas into Electron Magnetohydrodynamical Plasmas  

Microsoft Academic Search

A fully three-dimensional computer simulation of an ideal electron magnetohydrodynamical plasma is performed. By introducing various pulsed inductive antenna sources, magnetic helicity ( H = A˙B dV) injection is studied. Confirming experimental results, a simple loop provides no net helicity injection. Linked and knotted antennas, however, do inject helicity and preferentially radiate whistler wave packets parallel or antiparallel to the

C. L. Rousculp; R. L. Stenzel

1997-01-01

349

Perpendicular dynamics of runaway electrons in tokamak plasmas  

NASA Astrophysics Data System (ADS)

In this paper, it will be shown that the runaway phenomenon in tokamak plasmas cannot be reduced to a one-dimensional problem, based on the competence between electric field acceleration and collisional friction losses in the parallel direction. A Langevin approach, including collisional diffusion in velocity space, will be used to analyze the two-dimensional runaway electron dynamics. An investigation of the runaway probability in velocity space will yield a criterion for runaway, which will be shown to be consistent with the results provided by the more simple test particle description of the runaway dynamics [Fuchs et al., Phys. Fluids 29, 2931 (1986)]. Electron perpendicular collisional scattering will be found to play an important role, relaxing the conditions for runaway. Moreover, electron pitch angle scattering perpendicularly broadens the runaway distribution function, increasing the electron population in the runaway plateau region in comparison with what it should be expected from electron acceleration in the parallel direction only. The perpendicular broadening of the runaway distribution function, its dependence on the plasma parameters, and the resulting enhancement of the runaway production rate will be discussed.

Fernndez-Gmez, I.; Martn-Sols, J. R.; Snchez, R.

2012-10-01

350

Analysis of electron transport in the plasma of thermionic converters  

SciTech Connect

Electron transport coefficients of a gaseous ensemble are expressed analytically as function of density, and are expressed analytically as function of temperature up to an unknown function which has to be evaluated for each specific electron-neutral atom cross section. In order to complete the analytical temperature dependence one may introduce a polynomial expansion of the function or one may derive the temperature dependence of a set of coefficients, numbering thirteen for a third approximation transport evaluation, which completely determine the transport coefficients. The latter approach is used for determining the electron transport coefficients of a cesium plasma for any ion neutral composition and any temperature between 500/sup 0/K and 3500/sup 0/K. The relation between the transport coefficients of a fully and partly ionized gas is readily available and shows that, in the classical formalism, electron-ion and electron-neutral resistivities are not additive. The present form of the transport coefficients makes possible an accurate numerical integration of transport equations eliminating lengthy computations which are frequently inaccessible. It thus provides a detailed knowledge of spatial distribution of particle and energy transport and makes possible the determination of one of the three internal voltage drops, surface barrier, sheath and plasma, which are linked together experimentally by current density versus voltage characteristics of thermionic converters.

Stoenescu, M.L.; Heinicke, P.H.

1980-03-01

351

Fast electron energy transport in solid density and compressed plasma  

NASA Astrophysics Data System (ADS)

We provide a review of selected experiments on fast electron transport in solids and plasmas following laser-matter interaction at relativistic intensities. Particular attention is given to precise measurements of intense laser pulses, fast electron energy transfer and the mean kinetic energy of the fast electrons. We discuss in detail mechanism of fast electron energy loss in solid and warm dense targets. We show that stopping due to resistive electric field and collimation due to resistive magnetic field play significant roles in fast electron dynamics. It has also been shown that reducing the size of the target can significantly affect the K? production from the targets. The use of reduced-mass target can also increase temperature up to 1 keV level, which provides an excellent platform for fast electron transport without assembling the fuel. The pre-pulse is a significant issue in fast ignition for fast electron coupling to the compressed core. Indeed, we have shown using a variety of targets that the laser pre-pulse can significantly reduce transfer of energy farther into the target. In this article, we show that a significant progress has been made in understanding the critical issues of fast electron transport pertinent to fast ignition (FI). This understanding will facilitate a better target design for large scale FI integrated experiments when laser facilities become available.

Norreys, P.; Batani, D.; Baton, S.; Beg, F. N.; Kodama, R.; Nilson, P. M.; Patel, P.; Prez, F.; Santos, J. J.; Scott, R. H. H.; Tikhonchuk, V. T.; Wei, M.; Zhang, J.

2014-05-01

352

Non-linear Plasma Wake Growth of Electron Holes  

E-print Network

An object's wake in a plasma with small Debye length that drifts \\emph{across} the magnetic field is subject to electrostatic electron instabilities. Such situations include, for example, the moon in the solar wind wake and probes in magnetized laboratory plasmas. The instability drive mechanism can equivalently be considered drift down the potential-energy gradient or drift up the density-gradient. The gradients arise because the plasma wake has a region of depressed density and electrostatic potential into which ions are attracted along the field. The non-linear consequences of the instability are analysed in this paper. At physical ratios of electron to ion mass, neither linear nor quasilinear treatment can explain the observation of large-amplitude perturbations that disrupt the ion streams well before they become ion-ion unstable. We show here, however, that electron holes, once formed, continue to grow, driven by the drift mechanism, and if they remain in the wake may reach a maximum non-linearly stable...

Hutchinson, I H; Zhou, C

2015-01-01

353

Ion boundary conditions in semi-infinite fluid models of electron beam-plasma interaction  

SciTech Connect

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 beamplasma 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 [LAPLACE (Laboratoire Plasma et Conversion d'Energie), Universite de Toulouse, UPS, INPT Toulouse, 118 route de Narbonne, F-31062 Toulouse cedex 9 (France)

2014-10-15

354

Collisional damping of plasma waves on a pure electron plasma column  

SciTech Connect

The collisional damping of electron plasma waves (or Trivelpiece-Gould waves) on a pure electron plasma column is discussed. The damping in a pure electron plasma differs from that in a neutral plasma, since there are no ions to provide collisional drag. A dispersion relation for the complex wave frequency is derived from Poisson's equation and the drift-kinetic equation with the Dougherty collision operator--a Fokker-Planck operator that conserves particle number, momentum, and energy. For large phase velocity, where Landau damping is negligible, the dispersion relation yields the complex frequency {omega}=(k{sub z}{omega}{sub p}/k)[1+(3/2)(k{lambda}{sub D}){sup 2}(1+10i{alpha}/9)(1+2i{alpha}){sup -}{sup 1}], where {omega}{sub p} is the plasma frequency, k{sub z} is the axial wavenumber, k is the total wavenumber, {lambda}{sub D} is the Debye length, {nu} is the collision frequency, and {alpha}{identical_to}{nu}k/{omega}{sub p}k{sub z}. This expression spans from the weakly collisional regime ({alpha}<<1) to the moderately collisional regime ({alpha}{approx}1) and in the weakly collisional limit yields a damping rate which is smaller than that for a neutral plasma by the factor k{sup 2}{lambda}{sub D}{sup 2}<<1. In the strongly collisional limit ({alpha}>>1), the damping is enhanced by long-range interactions that are not present in the kinetic theory (which assumes pointlike interactions); the effect of these long-range collisions on the damping is discussed.

Anderson, M. W.; O'Neil, T. M. [Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States)

2007-11-15

355

Fast electron studies in the ZT-40M edge plasma  

SciTech Connect

Measurements of the edge plasma on the ZT-40M Reversed Field Pinch (RFP) show the presence of a dilute (1 to 10 per cent of the edge density), fast (T{sub H} {approx equal} (2 {minus} 3)T{sub {epsilon}0}) electron tail with a nearly unidirectional flow along B in a toroidal sense that is against the external applied electric field force. These studies have been extended over a wide range of operating conditions including high density and krypton-injected radiation-dominated (P{sub RAD} {approx equal} 0.9 P{sub IN}) discharges. In all cases the current density of the fast electrons is sufficient to account for the current density required to maintain the RFP. For low current 60 kA discharges this result has been confirmed in to a depth 20 mm inside of the reversal surface suggesting that the source of the fast electrons is the core of the discharge. The fast electrons also carry a large power flux parallel to B (several hundreds of MW/m{sup 2}, typically), and radial transport measurements of the fast electrons in the shadow of a movable limiter for 120 kA standard discharges indicate that the fast electrons are the primary electron energy loss channel. The fast electrons are a significant energy loss channel for a broad range of other cases as well. The collisionality of the fast electrons varies widely over the range of cases studied and it is noted that a small backflowing component of fast electrons increases in relative size as the collisionality increases. An estimate of the magnetic field stochastic diffusivity at the edge is made from the fast electron limiter shadow measurements and shows that the stochasticity of the magnetic field is low at the edge relative to the core, in agreement with magnetic fluctuation diffusivity measurements and MHD simulations. 35 refs., 10 figs.

Ingraham, J.C.; Ellis, R.F.; Downing, J.N.; Miller, G.; Munson, C.P.; Pickrell, M.M.; Schoenberg, K.F.; Weber, P.G.; Wurden, G.A.

1990-01-01

356

The behavior of the electron plasma boundary in ultraintense laser-highly overdense plasma interaction  

NASA Astrophysics Data System (ADS)

The structural stability of the laser/plasma interaction is discussed, for the case of a linearly polarized laser beam interacting with a solid at normal incidence. Using a semi-analytical cold fluid model, the dynamics of the electron plasma boundary (EPB), usually related to the high-order harmonic generation and laser absorption, are presented. While the well-known J B plasma oscillations at two times the laser frequency are recovered by the model, several other periodic in time stable solutions exist for exactly the same value of the physical parameters. This novel behavior highlights the importance of the laser pulse history among other factors. Some important features, such as the synchronization between the incident laser and the EPB oscillation, depend on the solution under consideration. A description of the possible types of stable oscillations in a parametric plane involving plasma density and laser amplitude is presented. The semi-analytical model is compared with particle-in-cell and semi-Lagrangian Vlasov simulations. They show that, among all the stable solutions, the plasma preferentially evolves to a state with the EPB oscillating twice faster than the laser. The effect of the plasma temperature and the existence of a ramp in the ion density profile are also discussed.

Snchez-Arriaga, G.; Sanz, J.; Debayle, A.; Lehmann, G.

2014-12-01

357

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

358

Study of Electron-scale Dissipation near the X-line During Magnetic Reconnection in a Laboratory Plasma  

NASA Astrophysics Data System (ADS)

Despite its disruptive influences on the large-scale structures of space and solar plasmas, the crucial topological changes and associated dissipation during magnetic reconnection take place only near an X-line within thin singular layers. In the modern collisionless models where electrons and ions are allowed to move separately, it has been predicted that ions exhaust efficiently through a thicker, ion-scale dissipative layer while mobile electrons can evacuate through a thinner, electron-scale dissipation layer, allowing for efficient release of magnetic energy. While ion dissipation layers have been frequently detected, the existence of election layers near the X-line and the associated dissipation structures and mechanisms are still an open question, and will be a main subject of the coming MMS mission. In this presentation, we will summarize our efforts in the past a few years to study electron-scale dissipation in a well-controlled and well-diagnosed reconnecting current sheet in a laboratory plasma, with close comparisons with the state-of-the-art, 2D and 3D fully kinetic simulations. Key results include: (1) positive identification of electromagnetic waves detected at the current sheet center as long wave-length, lower-hybrid drift instabilities (EM-LHDI), (2) however, there is strong evidence that this EM-LHDI cannot provide the required force to support the reconnection electric field, (3) detection of 3D flux-rope-like magnetic structures during impulsive reconnection events, and (4) electrons are heated through non-classical mechanisms near the X-line with a small but clear temperature anisotropy. These results, unfortunately, do not resolve the outstanding discrepancies on electron layer thickness between best available experiments and fully kinetic simulations. To make further progress, we are continuously pushing in the both experimental and numerical frontiers. Experimentally, we started investigations on EM-LHDI and electron heating as a function of guide field strength and symmetry of reconnection geometry, with new attempts to measure non-thermal electrons and higher frequency fluctuations. Numerically, we started investigations of kinetic simulations at realistic ratios of electron plasma frequency to cyclotron frequency, and also at realistic ratios of ion mass to electron mass. The most updated results of these new projects will be presented with discussions on the relevance to space observations.

Ji, H.; Yoo, J.; Dorfman, S. E.; Jara-Almonte, J.; Yamada, M.; Swanson, C.; Daughton, W. S.; Roytershteyn, V.; Kuwahata, A.; Ii, T.; Inomoto, M.; Ono, Y.; von Stechow, A.; Grulke, O.; Phan, T.; Mozer, F.; Bale, S. D.

2013-12-01

359

Large-amplitude electron-acoustic solitons in a dusty plasma with kappa-distributed electrons  

SciTech Connect

The Sagdeev pseudopotential method is used to investigate the occurrence and the dynamics of fully nonlinear electrostatic solitary structures in a plasma containing suprathermal hot electrons, in the presence of massive charged dust particles in the background. The soliton existence domain is delineated, and its parametric dependence on different physical parameters is clarified.

Saini, N. S. [Department of Physics, Guru Nanak Dev University, Amritsar-143005 (India); Danehkar, A. [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Hellberg, M. A. [School of Physics, University of KwaZulu-Natal, Durban 4000 (South Africa); Kourakis, I. [Centre for Plasma Physics, Queen's University Belfast, BT7 1 NN, Northern Ireland (United Kingdom)

2011-11-29

360

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

361

Determining electron temperature and electron density in moderate pressure H2/CH4 microwave plasma  

NASA Astrophysics Data System (ADS)

The electron temperature and electron density are measured in a microwave (MW) plasma-assisted chemical vapour diamond deposition reactor for different experimental conditions by varying the substrate temperature, methane content and MW power density. Optical emission spectroscopy (OES) and MW interferometry are used to probe the discharge generated in a stainless steel resonant cavity excited at a frequency of 2.45 GHz. Changing the substrate temperature from 630 to 900 C does not show any significant influence on the electron temperature or on the electron density. Increasing the methane content from 0 to 10% does not lead to any modification of the electron temperature or density. However between 10% and 20% CH, a decrease of the electron density is observed which may be attributed to soot particle formation. The electron density increases in the range of (1.2-10) 1011 cm-3 from moderate power density conditions (50 hPa/1000 W) to high power density conditions (250 hPa/3500 W). OES measurements show that the electron temperature exhibits a flat axial profile in the plasma bulk and ranges from 14?000 K at (25 hPa/600 W) to 10 500 K at (400 hPa/3000 W).

Derkaoui, N.; Rond, C.; Gries, T.; Henrion, G.; Gicquel, A.

2014-05-01

362

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

363

To the problem of electron temperature control in plasma  

SciTech Connect

One of the main problems in low temperature plasma is control plasma parameters at fixed values of current and gas pressure in the discharge. It is known that an increase in the intensity of sound wave directed along the positive column to values in excess of a definite threshold leads to essential rise of the temperature of electrons. However, no less important is the reduction of electron temperature in the discharge down to the value less than that in plasma in the absence external influence. It is known that to reduce the electron temperature in the plasma of CO{sub 2} laser, easily ionizable admixture are usually introduced in the discharge area with the view of increasing the overpopulation. In the present work we shall show that the value of electron temperature can be reduced by varying of sound wave intensity at its lower values. The experiment was performed on an experimental setup consisted of the tube with length 52 cm and diameter 9.8 cm, two electrodes placed at the distance of 27 cm from each other. An electrodynamical radiator of sound wave was fastened to one of tube ends. Fastened to the flange at the opposite end was a microphone for the control of sound wave parameters. The studies were performed in range of pressures from 40 to 180 Torr and discharge currents from 40 to 110 mA. The intensity of sound wave was varied from 74 to 92 dB. The measurement made at the first resonance frequency f = 150 Hz of sound in the discharge tube, at which a quarter of wave length keep within the length of the tube. The measurement of longitudinal electric field voltage in plasma of positive column was conducted with the help of two probes according to the compensation method. Besides, the measurement of gas temperature in the discharge were taken. Two thermocouple sensors were arranged at the distance of 8 cm from the anode, one of them being installed on the discharge tube axis, the second-fixed the tube wall.

Galechyan, G.A. [Institute of Applied Problem of Physics, Yerevan (Armenia); Anna, P.R. [Raritan Valley Community College, Somerville, NJ (United States)

1995-12-31

364

Beam loading by electrons in nonlinear plasma wakes  

SciTech Connect

An analytical theory for the interaction of an electron bunch with a nonlinear plasma wave is developed to make it possible to design efficient laser- and/or beam-driven accelerators that generate high quality monoenergetic electron beams. This theory shows how to choose the charge, the shape, and the placing of the bunch so that the conversion efficiency from the fields of the bubble to the accelerating electrons reaches nearly 100% and the beam quality is optimized. For intense drivers the nonlinear wake is described by the shape of the bubble and beam loading arises when the radial space-charge force of the beam acts back on the electron sheath surrounding the ion channel. The modification of the wake due to the presence of flat-top electron bunches is studied and it is shown that the energy spread of an externally injected flat-top electron bunch can be kept low. The bunch profile that leads to zero energy spread is also derived.

Tzoufras, M. [Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Lu, W. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Tsung, F. S.; Huang, C. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Mori, W. B. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Katsouleas, T. [Pratt School of Engineering, Duke University, Durham, North Carolina 27708 (United States); Vieira, J.; Fonseca, R. A.; Silva, L. O. [GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

2009-05-15

365

A high-average-power tapered FEL amplifier at submillimeter frequencies using sheet electron beams and short-period wigglers  

Microsoft Academic Search

A high-average-power FEL amplifier operating at submillimeter frequencies is under development at the University of Maryland. Program goals are to produce a cw, ~1 MW, FEL amplifier source at frequencies between 280 and 560 GHz. To this end, a high-gain, high-efficiency, tapered FEL amplifier using a sheet electron beam and a short-period (superconducting) wiggler has been chosen. Development of this

S. W. Bidwell; D. J. Radack; T. M. Antonsen; J. H. Booske; Y. Carmel; W. W. Destler; V. L. Granatstein; B. Levush; P. E. Latham; I. D. Mayergoyz; Z. X. Zhang

1991-01-01

366

One-year follow-up of epithelial corneal cell sheet allografts mounted on platelet poor plasma in rabbits  

PubMed Central

Purpose To evaluate the usefulness of epithelial corneal sheets mounted on platelet poor plasma (PPP) for allograft transplantation of rabbits with total limbal stem cell deficiency (LSCD) and to prove its efficacy at 1 year after surgery. Methods LSCD was induced in 21 female rabbits by mechanical keratectomy. To configure the grafts, limbal biopsies were taken from male rabbits and cells were cultured on a fibroblast feeder layer grown on clotted autologous PPP. After keratectomy, grafts were sutured over the stroma. Control groups consisted of no implant or an implant of clotted PPP. Rabbits were euthanized at 3 and 12 months. Corneas and cultured sheets were processed for histopathology and immunohistochemistry (K3/12 and K19). Gender analysis was performed at 4 and 7 months. Results One rabbit had endophthalmitis, and another died of no apparent cause. The rest of the animals treated had no inflammation, showed a stratified epithelium, keratin 3/12 expression, and no expression of keratin 19. At 1 year, seven of eight rabbits showed no LSCD or corneal rejection signs. Y chromosomes were detected at 4 and 7 months postoperatively. All controls showed LSCD signs, erratic epithelium, and minimal cell differentiation; they revealed a slight expression of K3/12 and an expression of K19 in patchy patterns. Conclusions Allografts contributed to restoring a healthy eye surface without signs of graft rejection. This technique seems to be a promising procedure for bilateral ocular surface diseases and may be useful for new therapeutic strategies. PMID:20019875

Gimeno, Federico Luengo; Lavigne, Victoria; Gatto, Silvia; Croxatto, J. Oscar; Correa, Laura

2009-01-01

367

Design of high-average-power near-millimeter free electron laser oscillators using short-period wigglers and sheet electron beams  

SciTech Connect

The design and feasibility of a 1-MW continuous wave (CW) free electron laser (FEL) oscillator are reviewed. The proposed configuration will include a short-period planar wiggler, a sheet electron beam, a 0.5--1.0 MV thermionic electron gun, a hybrid waveguide/quasi-optical resonator, commercial dc power supplies, and a depressed collector. Cavity ohmic RF losses are estimated to be extremely low ({approx lt} 10--100 W/cm{sup 2}) at 1-MW output power, while thermal heat transfer studies conservatively indicate that wall cooling up to 1500 W/cm{sup 2} should be possible.

Booske, J.H. (Wisconsin Univ., Madison, WI (USA). Dept. of Electrical and Computer Engineering); Radack, D.J.; Antonsen, T.M.; Bidwell, S.W.; Carmel, Y.; Destler, W.W.; Granatstein, V.L.; Latham, P.E.; Levush, B.; Mayergonoz, I.D.; Serbeto, A. (Maryland Univ., College Park, MD (USA). Lab. for Plasma Research)

1990-06-01

368

Oscillatory screening and quantum interference effects on electron collisions in quantum plasmas  

Microsoft Academic Search

The oscillatory screening and collision-induced quantum interference effects on electronelectron collisions are investigated in dense quantum plasmas. The modified DebyeHckel potential with the total spin states of the system is considered to obtain the differential electronelectron scattering cross section in quantum plasmas. It is shown that the electronelectron scattering cross section decreases with an increase of the quantum wave number.

Sang-Chul Na; Young-Dae Jung

2008-01-01

369

Wakefields generated by collisional neutrinos in neutral-electron-positron plasma  

SciTech Connect

A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.

Tinakiche, Nouara [Faculty of Physics, U.S.T.H.B., Algiers 16111 (Algeria)

2013-02-15

370

Temperature and anisotropic-temperature relaxation measurements in cold, pure-electron plasmas  

E-print Network

Temperature and anisotropic-temperature relaxation measurements in cold, pure-electron plasmas B. R; accepted 3 January 1996 Plasma temperatures in the range 25 to 2 106 K have been measured using a cryogenic, ultra-high vacuum, pure-electron plasma trap. The rate at which the temperatures parallel

California at San Diego, University of

371

Counter-Propagation of Electron and CO2 Laser Beams in a Plasma Channel  

NASA Astrophysics Data System (ADS)

A high-energy CO2 laser is channeled in a capillary discharge. Occurrence of guiding conditions at a relatively low plasma density (<1018 cm-3) is confirmed by MHD simulations. Divergence of relativistic electron beam changes depending on the plasma density. Counter-propagation of the electron and laser beams inside the plasma channel results in intense x-ray generation.

Hirose, T.; Pogorelsky, I. V.; Ben-Zvi, I.; Yakimenko, V.; Kusche, K.; Siddons, P.; Kumita, T.; Kamiya, Y.; Zigler, A.; Greenberg, B.; Kaganovich, D.; Pavlishin, I. V.; Diublov, A.; Bobrova, N.; Sasorov, P.

2003-08-01

372

Fluid aspects of electron streaming instability in electron-ion plasmas  

SciTech Connect

Electrons streaming in a background electron and ion plasma may lead to the formation of electrostatic solitary wave (ESW) and hole structure which have been observed in various space plasma environments. Past studies on the formation of ESW are mostly based on the particle simulations due to the necessity of incorporating particle's trapping effects. In this study, the fluid aspects and thermodynamics of streaming instabilities in electron-ion plasmas including bi-streaming and bump-on-tail instabilities are addressed based on the comparison between fluid theory and the results from particle-in-cell simulations. The energy closure adopted in the fluid model is the polytropic law of d(p?{sup ??})/dt=0 with ? being a free parameter. Two unstable modes are identified for the bump-on-tail instability and the growth rates as well as the dispersion relation of the streaming instabilities derived from the linear theory are found to be in good agreement with the particle simulations for both bi-streaming and bump-on-tail instabilities. At the nonlinear saturation, 70% of the electrons are trapped inside the potential well for the drift velocity being 20 times of the thermal velocity and the p?{sup ??} value is significantly increased. Effects of ion to electron mass ratio on the linear fluid theory and nonlinear simulations are also examined.

Jao, C.-S. [Institute of Space Science, National Central University, Jhongli, Taiwan (China)] [Institute of Space Science, National Central University, Jhongli, Taiwan (China); Hau, L.-N. [Institute of Space Science, National Central University, Jhongli, Taiwan (China) [Institute of Space Science, National Central University, Jhongli, Taiwan (China); Department of Physics, National Central University, Jhongli, Taiwan (China)

2014-02-15

373

FAST MAGNETIC RECONNECTION AND PARTICLE ACCELERATION IN RELATIVISTIC LOW-DENSITY ELECTRON-POSITRON PLASMAS WITHOUT GUIDE FIELD  

SciTech Connect

Magnetic reconnection and particle acceleration in relativistic Harris sheets in low-density electron-positron plasmas with no guide field have been studied by means of two-dimensional particle-in-cell simulations. Reconnection rates are of the order of one when the background density in a Harris sheet is of the order of 1% of the density in the current sheet, which is consistent with previous results in the non-relativistic regime. It has been demonstrated that the increase of the Lorentz factors of accelerated particles significantly enhances the collisionless resistivity needed to sustain a large reconnection electric field. It is shown analytically and numerically that the energy spectrum of accelerated particles near the X-line is the product of a power law and an exponential function of energy, {gamma}{sup -1/4}exp (- a{gamma}{sup 1/2}), where {gamma} is the Lorentz factor and a is a constant. However, in the low-density regime, while the most energetic particles are produced near X-lines, many more particles are energized within magnetic islands. Particles are energized in contracting islands by multiple reflection, but the mechanism is different from Fermi acceleration in magnetic islands for magnetized particles in the presence of a guide field. In magnetic islands, strong core fields are generated and plasma beta values are reduced. As a consequence, the fire-hose instability condition is not satisfied in most of the island region, and island contraction and particle acceleration can continue. In island coalescence, reconnection between two islands can accelerate some particles, however, many particles are decelerated and cooled, which is contrary to what has been discussed in the literature on particle acceleration due to reconnection in non-relativistic hydrogen plasmas.

Bessho, Naoki; Bhattacharjee, A., E-mail: naoki.bessho@unh.edu [Center for Integrated Computation and Analysis of Reconnection and Turbulence, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824 (United States)

2012-05-10

374

Diagnosis of gas temperature, electron temperature, and electron density in helium atmospheric pressure plasma jet  

SciTech Connect

The optical emission spectra of helium atmospheric pressure plasma jet (APPJ) are captured with a three grating spectrometer. The grating primary spectrum covers the whole wavelength range from 200 nm to 900 nm, with the overlapped grating secondary spectrum appearing from 500 nm to 900 nm, which has a higher resolution than that of the grating primary spectrum. So the grating secondary spectrum of OH (A{sup 2}{Sigma} {sup +}({upsilon} Prime = 0) {yields} X{sup 2}{Pi}({upsilon} Double-Prime = 0)) is employed to calculate the gas temperature (T{sub g}) of helium APPJ. Moreover, the electron temperature (T{sub e}) is deduced from the Maxwellian electron energy distribution combining with T{sub g}, and the electron density (n{sub e}) is extracted from the plasma absorbed power. The results are helpful for understanding the physical property of APPJs.

Chang Zhengshi; Zhang Guanjun; Shao Xianjun; Zhang Zenghui [State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China)

2012-07-15

375

Electron Impact Dissociation of Molecular Ions for Thermonuclear Plasmas  

NASA Astrophysics Data System (ADS)

Absolute cross sections for electron impact dissociative excitation and ionization of ions of interest in thermonuclear fusion are reported for energies ranging from the respective reaction thresholds up to 2.5 keV. The animated crossed-beams method is used. Results have been measured both for heavy targets like the methane family CDn+(n = 1-4) and for light targets like H2+, D2+, D3+ and D2H+. Kinetic energy release distributions are deduced from the analysis of ionic product velocity distributions obtained for each ionic fragment, at selected electron energies. The comparison of the present energy thresholds and kinetic energy release with available published data allows the identification of initial or intermediate states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product, which are of significant interest in fusion plasma applications. Present experimental data for electron impact dissociative excitation and ionization processes are represented by three-parameter analytic fitting functions appropriate for plasma modeling. Isotope ratios are estimated in the study of the D2H+ target to check for isotope effects.

Defrance, P.; Lecointre, J.; Jureta, J. J.; Belic, D. S.; Janev, R. K.

2011-10-01

376

Modeling of the Convection and Interaction of Ring Current, Plasmaspheric and Plasma Sheet Plasmas in the Inner Magnetosphere  

NASA Technical Reports Server (NTRS)

Distinctive sources of ions reside in the plasmasphere, plasmasheet, and ring current regions at discrete energies constitute the major plasma populations in the inner/middle magnetosphere. They contribute to the electrodynamics of the ionosphere-magnetosphere system as important carriers of the global current system, in triggering; geomagnetic storm and substorms, as well as critical components of plasma instabilities such as reconnection and Kelvin-Helmholtz instability at the magnetospheric boundaries. Our preliminary analysis of in-situ measurements shoves the complexity of the plasmas pitch angle distributions at particularly the cold and warm plasmas, vary dramatically at different local times and radial distances from the Earth in response to changes in solar wind condition and Dst index. Using an MHD-ring current coupled code, we model the convection and interaction of cold, warm and energetic ions of plasmaspheric, plasmasheet, and ring current origins in the inner magnetosphere. We compare our simulation results with in-situ and remotely sensed measurements from recent instrumentation on Geotail, Cluster, THEMIS, and TWINS spacecraft.

Fok, Mei-Ching; Chen, Sheng-Hsien; Buzulukova, Natalia; Glocer, Alex

2010-01-01

377

Characterization and in situ monitoring of a novel compact electron cyclotron resonance plasma source  

Microsoft Academic Search

For plasma-assisted processing of future semiconductor devices, a new compact electron cyclotron resonance (ECR) plasma source has been specifically designed. The source is novel in that the magnets required for the production of ECR plasma are movable even in vacuum, and insitu monitoring of the discharge zone is also possible. Typical plasma characteristics were evaluated for nitrogen gas using Langmuir

Patrick O'Keeffe; S. den; Y. Hayashi; S. Komuro; T. Morikawa

1995-01-01

378

Results on Plasma Focusing of High Energy Density Electron and Positron Beams  

Microsoft Academic Search

The authors present results from the SLAC E-150 experiment on plasma focusing of high energy density electron and, for the first time, positron beams. They also discuss measurements on plasma lens-induced synchrotron radiation, longitudinal dynamics of plasma focusing, and laser- and beam-plasma interactions.

J. S. T. Ng; P. Chen; W. Craddock; F. J. Decker; R. C. Field; M. J. Hogan; R. Iverson; R. King; T. Kirby; T. Kotseroglou; P. Raimondi; D. Walz; H. A. Baldis; P. Bolton; D. Cline; Y. Fukui; V. Kumar; C. Crawford; R. Noble; K. Nakajima; A. Ogata; A. W. Weidemann

2000-01-01

379

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

380

Modulational instability of electron-acoustic waves in a plasma with Cairns-Tsallis distributed electrons  

NASA Astrophysics Data System (ADS)

The problem of the modulational instability (MI) of electron-acoustic waves (EAWs) in a plasma with Cairns-Tsallis distributed electrons is addressed. Using the standard multiple scale method, we derive a nonlinear Schrdinger-like equation. Electron nonextensivity and nonthermality are found to significantly influence the region stability of the EAWs. In particular, it is found that the critical value kc, beyond which the instability sets in, is slightly lowered as the electrons evolve far away from their Maxwellian thermodynamic equilibrium. Electron nonthermality renders more effective and more important the influence and role of nonextensivity. Moreover, the effect of the unperturbed hot electron and cold electron number density imbalance ? on the onset of the MI is analyzed. Although both dark and bright excitations are obtained, the trend is in contrast to our earlier observations. Our results should be of relevance in wave propagation stability. Nonthermal nonextensive models may play an increasingly important role in predicting complex plasma behavior, and understanding the underlying physical processes.

Merriche, Abderrzak; Tribeche, Mouloud

2015-03-01

381

Calculation of distribution of potential and electron concentration in the dust-electron thermal plasma with the axial geometry particles  

NASA Astrophysics Data System (ADS)

We obtained the equation, which describes the distribution of the potential and the electron density in an equilibrium dust-electron plasma taking into account parameters of the electron gas inside the axial geomtry dust particles. The inclusion of these parameters performed on the basis of the model of "solid-state plasma," considering the condensed particle system as the ion core and the free electron gas.

Dautov, G.; Fayrushin, I.; Kashapov, N.

2014-11-01

382

Plasma and ion barrier for electron beam spot stability  

SciTech Connect

The concept of a self-biased target to spatially confine the ions generated by the bombardment of intense electron beams on bremsstrahlung conversion targets has been predicted by computer simulation and further verified by experiments at the Integrated Test Stand for DARHT at Los Alamos National Laboratory. This technical article reports an alternative method of containing the plasmas and ions from the bremsstrahlung conversion target if the energy density of the electron beam is below a certain threshold. With the proposed changes of the electron beam parameters of the second axis of DARHT, the authors are able to show that a thin (0.5 mm) metallic barrier such as pure beryllium, or boron carbide with desirable thermal properties, is sufficiently transparent to the 20 MeV DARHT beam and at the same time able to confine the ions between the target and the barrier foil. The temperature rise in the foil due to energy deposited by the electron beam is expected to be below the melting point of the materials for the first three pulses. More important, they have shown in their time dependent particle-in-cell simulations that the deployment of a barrier situated 1 to 2 cm away from the converter target can achieve the ion confinement needed for the stability of the electron beam spot.

Kwan, T.J.T.; Snell, C.M.

1999-04-01

383

Radiation generated by bunched electron beams in corrugated plasma channels  

SciTech Connect

The excitation of radiation by bunched electron beams propagating in miniature corrugated plasma channels is considered. It is shown that the rate at which power is radiated by a beam is characterized by impedance that depends on the properties of the channel. For experimentally obtainable parameters radiation bursts of multiple millijoules can be achieved. The spectrum of the radiation can be made narrow and controlled through the properties of the channel. The effects of spatial variations in the channel parameters on the spectrum are also described.

Antonsen, Thomas M. Jr. [Centre de Physique Theorique, Ecole Polytechnique, CNRS, Palaiseau 91128 (France) and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)

2010-07-15

384

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

385

Beam Model for Energetic Electron Transport in Laser Produced Plasmas  

NASA Astrophysics Data System (ADS)

Energetic electron transport,in laser target implosion codes, is generally handled with a phenominological flux limit . Other techniques include nonlocal transport algorithms (1), although issues have been raised about both their numerical stability and accuracy (2). We have explored a different approach, a beam deposition model. It reduces to Spitzer thermal conduction in the short mean free path limit, is intuitively reasonable, and with suitable approximations, can be economically incorporated into existing implicit numerical algorithms for the electron heat conduction. While our first formulation is for one dimensional plasmas, the model extends easily to two or three dinensions. Initial results appear to be reasonable, and will be presented. 1. Luciani et al, Phys. Rev. Let., 51, 1664, 1983 2.Prasad and Kershaw, Phys. Fluids. B 1, 2430, 1989, and B3, 3087, 1991

Manheimer, Wallace; Colombant, Denis

2002-11-01

386

Suprathermal electron transport in laser-produced plasmas  

SciTech Connect

A self-consistent, collisional, particle-in-cell scheme has been developed to model the one dimensional transport of suprathermal electrons in laser produced plasmas. This full Monte Carlo approach was taken, since earlier, simpler models have failed to explain an experimentally almost universal anomalous inhibition of thermal transport. The Monte Carlo scheme allows for free-streaming, ion scatter, and self thermalization of the electrons, which are moved in self-consistent E-fields computed with the aid of implicit fluid moments. PIC hydrodynamics for the ions, ponderomotive forces, and resonance and inverse-bremsstrahlung absorption of the light are all accommodated. In application to the anomalous inhibition problem, use of the scheme demonstrates that intrinsic differences in the Monte Carlo, and conventional flux-limited diffusion modelling of the transport results in apparent and real inhibition, explaining the need for strong flux-limiting in the simpler diffusion modelling of experiments.

Mason, R.J.

1981-01-01

387

Electron state density and electron diffusion coefficient in energy space in nonideal nonequilibrium plasmas  

SciTech Connect

We suggest a model for a hydrogenic low-temperature nonequilibrium nonideal plasma that allows the kinetic parameters of the plasma to be calculated by the method of molecular dynamics by taking into account the interparticle interaction. The charges interact according to Coulomb's law; for unlike charges, the interaction is assumed to be equal to a constant at a distance smaller than several Bohr radii. For a system of particles, we solve the classical equations of motion under periodic boundary conditions. The initial conditions are specified in such a way that the electrons have a positive total energy. We consider the temperatures 1-50 K and densities n = 10{sup 9}-10{sup 10} cm{sup -3} produced in an experiment through laser cooling and resonant excitation. We calculate the electron state density as a function of the plasma coupling parameter and the electron diffusion coefficient in energy space for highly excited (Rydberg) electron states close to the boundary of the discrete and continuum spectra.

Bobrov, A. A. [Moscow Engineering Physics Institute (State University) (Russian Federation); Bronin, S. Ya. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation); Zelener, B. B. [Moscow Engineering Physics Institute (State University) (Russian Federation)], E-mail: bobozel@mail.ru; Zelener, B. V. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation); Manykin, E. A. [Moscow Engineering Physics Institute (State University) (Russian Federation)

2008-07-15

388

PRODUCTION OF A LARGE DIAMETER ECR PLASMA WITH LOW ELECTRON TEMPERATURE  

E-print Network

. However, the electron temperature in ECR plasma is relatively high so that the charge up damage is often microwaves [6]. Itagaki et al. succeeded in decreasing the electron temperature by using the mirror magneticPRODUCTION OF A LARGE DIAMETER ECR PLASMA WITH LOW ELECTRON TEMPERATURE Mayuko Koga* , Yasuhiro

Paris-Sud XI, Université de

389

Coupling between nonlinear Langmuir waves and electron holes in quantum plasmas  

Microsoft Academic Search

The nonlinear effects on a slow timescale, compared with the electron plasma frequency, are studied using the WignerPoisson system, in the plasma regimes characterized by the overlapping of the wavefunctions of individual electrons, by the presence of a large amplitude Langmuir pump wave, and whose temperature is higher than the Fermi temperature. It is shown that the electron trapping on

Dusan Jovanovic; Renato Fedele

2007-01-01

390

Saturn's E, G, and F rings - Modulated by the plasma sheet?  

NASA Technical Reports Server (NTRS)

Saturn's broad E ring, the narrow G ring, and the structured and apparently time-variable F ring(s) contain many micron and submicron-sized particles, which make up the 'visible' component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. In addition, Coulomb drag forces may be important, in particular for the E ring. The possibility that electromagnetic effects may play a role in determining the F ring structure and its possible time variations is critically examined. Sputtering of micron-sized dust particles in the E ring by magnetospheric ions yields lifetimes of 100 to 10,000 years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably Enceladus.

Morfill, G. E.; Gruen, E.; Johnson, T. V.

1983-01-01

391

Integration issues of a plasma contactor Power Electronics Unit  

NASA Technical Reports Server (NTRS)

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. Originally, a DC cathode heater converter was baselined for a continuous operation mode because only a few ignitions of the hollow cathode were expected. However, for cyclic operation, a DC heater supply can potentially result in hollow cathode heater component failure due to the DC electrostatic field. This can prevent the heater from attaining the proper cathode tip temperature for reliable ignition of the hollow cathode. To mitigate this problem, an AC cathode heater supply was therefore designed, fabricated, and installed into a modified PEU. The PEU was tested using resistive loads and then integrated with an engineering model hollow cathode to demonstrate stable steady-state operation. Integration issues such as the effect of line and load impedance on the output of the AC cathode heater supply and the characterization of the temperature profile of the heater under AC excitation were investigated.

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

1995-01-01

392

Charging of a dust particle in a plasma with a non extensive electron distribution function  

SciTech Connect

We present a theoretical model for the electrostatic charging of a spherical dust particle in an electron-ion plasma with streaming ions and a nonextensive electron distribution function following a non-Maxwell-Boltzmann law. The non-extensive electron distribution function drastically affects the electron current to dust grain surface and, therefore, the electron charge on a dust particle is significantly reduced in a non-Maxwellian dusty plasma.

Tribeche, Mouloud; Shukla, Padma Kant [International Centre for Advanced Studies in Physical Sciences, Faculty of Physics and Astronomy, Ruhr-University Bochum, D-44780 Bochum (Germany)

2011-10-15

393

Observation of plasma instabilities related to dust particle growth mechanisms in electron cyclotron resonance plasmas  

SciTech Connect

Instabilities are observed in the self-bias voltage measured on a probe immersed in microwave plasma excited at Electron Cyclotron Resonance (ECR). Observed in the MHz range, they were systematically measured in dust-free or dusty plasmas (obtained for different conditions of applied microwave powers and acetylene flow rates). Two characteristic frequencies, well described as lower hybrid oscillations, can be defined. The first one, in the 6070 MHz range, appears as a sharp peak in the frequency spectra and is observed in every case. Attributed to ions, its position shift observed with the output power highlights that nucleation process takes place in the dusty plasma. Attributed to lower hybrid oscillation of powders, the second broad peak in the 1020 MHz range leads to the characterization of dust particles growth mechanisms: in the same way as in capacitively coupled plasmas, accumulation of nucleus confined near the probe in the magnetic field followed by aggregation takes place. Then, the measure of electrical instabilities on the self-bias voltage allows characterizing the discharge as well as the chemical processes that take place in the magnetic field region and their kinetics.

Drenik, A. [Joef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia) [Joef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia); CNRS, LAPLACE, 31062 Toulouse/Universit de Toulouse, UPS, INPT, LAPLACE, 118 rte de Narbonne, 31062 Toulouse Cedex 9 (France); Yuryev, P.; Clergereaux, R. [CNRS, LAPLACE, 31062 Toulouse/Universit de Toulouse, UPS, INPT, LAPLACE, 118 rte de Narbonne, 31062 Toulouse Cedex 9 (France)] [CNRS, LAPLACE, 31062 Toulouse/Universit de Toulouse, UPS, INPT, LAPLACE, 118 rte de Narbonne, 31062 Toulouse Cedex 9 (France); Vesel, A. [Joef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia)] [Joef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia); Margot, J. [Groupe de Physique des Plasmas, Dpartement de Physique, Universit de Montral, CP 6128, Succursale Centre-ville, Montral, Qubec H3C 3J7 (Canada)] [Groupe de Physique des Plasmas, Dpartement de Physique, Universit de Montral, CP 6128, Succursale Centre-ville, Montral, Qubec H3C 3J7 (Canada)

2013-10-15

394

Electron Beam Charge Diagnostics for Laser Plasma Accelerators  

SciTech Connect

A comprehensive study of charge diagnostics is conducted to verify their validity for measuring electron beams produced by laser plasma accelerators (LPAs). First, a scintillating screen (Lanex) was extensively studied using subnanosecond electron beams from the Advanced Light Source booster synchrotron, at the Lawrence Berkeley National Laboratory. The Lanex was cross calibrated with an integrating current transformer (ICT) for up to the electron energy of 1.5 GeV, and the linear response of the screen was confirmed for charge density and intensity up to 160 pC/mm{sup 2} and 0.4 pC/(ps mm{sup 2}), respectively. After the radio-frequency accelerator based cross calibration, a series of measurements was conducted using electron beams from an LPA. Cross calibrations were carried out using an activation-based measurement that is immune to electromagnetic pulse noise, ICT, and Lanex. The diagnostics agreed within {+-}8%, showing that they all can provide accurate charge measurements for LPAs.

Nakamura, Kei; Gonsalves, Anthony; Lin, Chen; Smith, Alan; Rodgers, David; Donahue, Rich; Byrne, Warren; Leemans, Wim

2011-06-27

395

Nonlocal control of electron temperature in short direct current glow discharge plasma  

SciTech Connect

To demonstrate controlling the electron temperature in nonlocal plasma, experiments have been performed on a short (without positive column) dc glow discharge with a cold cathode by applying different voltages to the conducting discharge wall. The experiments have been performed for low-pressure noble gas discharges. The applied voltage can modify trapping the energetic electrons emitted from the cathode sheath and arising from the atomic and molecular processes in the plasma within the device volume. This phenomenon results in the energetic electrons heating the slow plasma electrons, which consequently modifies the electron temperature. Furthermore, a numerical model of the discharge has demonstrated the electron temperature modification for the above case.

Demidov, V. I. [Department of Optics and Spectroscopy, St. Petersburg State University, St. Petersburg 199034 (Russian Federation); International Laboratory Nonlocal Plasma in Nanotechnology and Medicine, ITMO University, Kronverkskiy pr. 49, St. Petersburg 197101 (Russian Federation); Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506 (United States); Kudryavtsev, A. A.; Stepanova, O. M. [Department of Optics and Spectroscopy, St. Petersburg State University, St. Petersburg 199034 (Russian Federation); Kurlyandskaya, I. P. [International Laboratory Nonlocal Plasma in Nanotechnology and Medicine, ITMO University, Kronverkskiy pr. 49, St. Petersburg 197101 (Russian Federation); St. Petersburg University of State Fire Service of EMERCOM RF, Murmansk Branch, Murmansk 183040 (Russian Federation)

2014-09-15

396

Collisionless conductivity and stochastic heating of the plasma sheet in the geomagnetic tail  

Microsoft Academic Search

The chaotic single particle orbits in the geomagnetic tail are used to calculate the collisionless conductivity. It is shown that the stochasticity from inhomogeneous magnetic fields leads to a power law decay of the single particle correlation function similar to an elastic collisional process. The height-integrated dissipative part of the collisionless conductivity governs the irreversible stochastic heating of the plasma

Wendell Horton; T. Tajima

1991-01-01

397

PIC-MCC Model for the Plasma Focused Electron Beam in the Pasotron  

Microsoft Academic Search

The plasma-assisted slow wave oscillator (Pasotron) employs a plasma lens for initial focusing of the driving electron beam, enabling operation without a magnetic field. In this study, the XOOPIC particle-in-cell code is used to model the beam interaction with an expanding background neutral gas. The 40 kV beam electrons impact-ionize the background gas, displacing the less energetic plasma electrons, and

J. P. Verboncoeur

2003-01-01

398

Ion-acoustic solitary waves in two-temperature electron plasmas  

SciTech Connect

By using the reductive perturbation technique, a modified Korteweg--deVries (KdV) equation aids in the study of the solitary wave solution in a nonisothermal two-temperature electron plasma. The results indicate the solitary wave solution in the plasma with isothermal electrons, and finally a link with the solitons existing in both cases is made. Moreover, general comparisons and conclusions are made on the ion-acoustic waves in the plasma with several ionic species and multiple electrons.

Das, G.C.; Paul, S.N.; Karmakar, B.

1986-07-01

399

Effects of initially energetic electrons on relativistic laser-driven electron plasma waves  

SciTech Connect

In this paper, using kinetic calculations and accurate 1D2V particle-in-cell simulations, we point out the important role of initially energetic electrons of the distribution tail in the behavior of high amplitude electron plasma waves (EPWs). In the presence of these electrons, the conventional warm fluid theory (WFT) breaks at very high wave amplitudes that are still noticeably lower than the wave breaking amplitude (WBA). The fluid breakdown results in electron super-heating with respect to the adiabatic laws. Indeed, a new kinetic regime of the relativistic EPWs appears below the WBA. It is argued that the mentioned super-heating results in WBA values lower than the corresponding WFT prediction.

Yazdanpanah, J., E-mail: jamal.yazdan@gmail.com; Anvari, A. [Department of Physics, Sharif University of Technology, P.O. Box 1155-4161, Tehran (Iran, Islamic Republic of)] [Department of Physics, Sharif University of Technology, P.O. Box 1155-4161, Tehran (Iran, Islamic Republic of)

2014-02-15

400

Increased Tensile Strength of Carbon Nanotube Yarns and Sheets through Chemical Modification and Electron Beam Irradiation  

NASA Technical Reports Server (NTRS)

The inherent strength of individual carbon nanotubes offers considerable opportunity for the development of advanced, lightweight composite structures. Recent work in the fabrication and application of carbon nanotube (CNT) forms such as yarns and sheets has addressed early nanocomposite limitations with respect to nanotube dispersion and loading; and has pushed the technology toward structural composite applications. However, the high tensile strength of an individual CNT has not directly translated to macro-scale CNT forms where bulk material strength is limited by inter-tube electrostatic attraction and slippage. The focus of this work was to assess post processing of CNT sheet and yarn to improve the macro-scale strength of these material forms. Both small molecule functionalization and e-beam irradiation was evaluated as a means to enhance tensile strength and Youngs modulus of the bulk CNT material. Mechanical testing results revealed a tensile strength increase in CNT sheets by 57 when functionalized, while an additional 48 increase in tensile strength was observed when functionalized sheets were irradiated; compared to unfunctionalized sheets. Similarly, small molecule functionalization increased yarn tensile strength up to 25, whereas irradiation of the functionalized yarns pushed the tensile strength to 88 beyond that of the baseline yarn.

Miller, Sandi G.; Williams, Tiffany S.; Baker, James S.; Sola, Francisco; Lebron-Colon, Marisabel; McCorkle, Linda S.; Wilmoth, Nathan G.; Gaier, James; Chen, Michelle; Meador, Michael A.

2014-01-01

401

Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons  

SciTech Connect

A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equation has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.

Alinejad, H.; Sobhanian, S.; Mahmoodi, J. [Faculty of Physics, Tabriz University, Tabriz 51664 (Iran, Islamic Republic of); Physics Department, University of Qom, Qom (Iran, Islamic Republic of)

2006-01-15

402

Nonlinear propagation of ion-acoustic waves in electron-positron-ion plasma with trapped electrons  

NASA Astrophysics Data System (ADS)

A theoretical investigation has been made for ion-acoustic waves in an unmagnetized electron-positron-ion plasma. A more realistic situation in which plasma consists of a negatively charged ion fluid, free positrons, and trapped as well as free electrons is considered. The properties of stationary structures are studied by the reductive perturbation method, which is valid for small but finite amplitude limit, and by pseudopotential approach, which is valid for large amplitude. With an appropriate modified form of the electron number density, two new equations for the ion dynamics have been found. When deviations from isothermality are finite, the modified Korteweg-deVries equation has been found, and for the case that deviations from isothermality are small, calculations lead to a generalized Korteweg-deVries equation. It is shown from both weakly and highly nonlinear analysis that the presence of the positrons may allow solitary waves to exist. It is found that the effect of the positron density changes the maximum value of the amplitude and M (Mach number) for which solitary waves can exist. The present theory is applicable to analyze arbitrary amplitude ion-acoustic waves associated with positrons which may occur in space plasma.

Alinejad, H.; Sobhanian, S.; Mahmoodi, J.

2006-01-01

403

Thomson scattering from near-solid density plasmas using soft x-ray free electron lasers  

SciTech Connect

We propose a collective Thomson scattering experiment at the VUV free electron laser facility at DESY (FLASH) which aims to diagnose warm dense matter at near-solid density. The plasma region of interest marks the transition from an ideal plasma to a correlated and degenerate many-particle system and is of current interest, e.g. in ICF experiments or laboratory astrophysics. Plasma diagnostic of such plasmas is a longstanding issue. The collective electron plasma mode (plasmon) is revealed in a pump-probe scattering experiment using the high-brilliant radiation to probe the plasma. The distinctive scattering features allow to infer basic plasma properties. For plasmas in thermal equilibrium the electron density and temperature is determined from scattering off the plasmon mode.

Holl, A; Bornath, T; Cao, L; Doppner, T; Dusterer, S; Forster, E; Fortmann, C; Glenzer, S H; Gregori, G; Laarmann, T; Meiwes-Broer, K H; Przystawik, A; Radcliffe, P; Redmer, R; Reinholz, H; Ropke, G; Thiele, R; Tiggesbaumker, J; Toleikis, S; Truong, N X; Tschentscher, T; Uschmann, I; Zastrau, U

2006-11-21

404

Collective acceleration of protons by the plasma waves in a counterstreaming electron beam  

SciTech Connect

A novel advanced accelerator is proposed. The counterstreaming electron beam accelerator relies on the same physical mechanism as that of the plasma accelerator but replaces the stationary plasma in the plasma accelerator by a magnetized relativistic electron beam, drifting antiparallel to the driving source and the driven particles, as the wave supporting medium. The plasma wave in a counterstreaming electron beam can be excited either by a density-ramped driving electron beam or by properly beating two laser beams. The fundamental advantages of the counterstreaming electron beam accelerator over the plasma accelerator are a longer and tunable plasma wavelength, a longer pump depletion length or a larger transformer ratio, and easier pulse shaping for the driving source and the driven beam. Thus the energy gain of the driven particles can be greatly enhanced whereas the trapping threshold can be dramatically reduced so as to admit the possibility for proton acceleration.

Yan, Y.T.

1987-03-01

405

Facile, noncovalent decoration of graphene oxide sheets with nanocrystals  

Microsoft Academic Search

Facile dry decoration of graphene oxide sheets with aerosol Ag nanocrystals synthesized from an arc plasma source has been\\u000a demonstrated using an electrostatic force directed assembly technique at room temperature. The Ag nanocrystal-graphene oxide\\u000a hybrid structure was characterized by transmission electron microscopy (TEM) and selected area diffraction. The ripening of\\u000a Ag nanocrystals on a graphene oxide sheet was studied by

Ganhua Lu; Shun Mao; Sungjin Park; Rodney S. Ruoff; Junhong Chen

2009-01-01

406

Electron beam-plasma interaction experiments with the Versatile Toroidal Facility (VTF)  

SciTech Connect

The laboratory investigation of electron beam-plasma interactions is motivated by the recent space shuttle experiments. Interesting but puzzling phenomena were observed in the shuttle experiments such as the bulk heating of background ionospheric plasmas by the injected electron beams and the excitation of plasma waves in the frequency range of ELF waves. The plasma machine, the Versatile Toroidal Facility (VTF) can generate a large magnetized plasma with the electron plasma frequency greater than the electron gyrofrequency by a factor of 3--5 similar to the plasma condition in the ionosphere. Short pulses of electron beams are injected into the VTF plasmas in order to simulate the beam injection from spacecrafts in the ionosphere. A Langmuir probe installed at a bottom port of VTF monitors the spatial variation of electron beams emitted from LaB6 filaments. An energy analyzer has been used to determine the particle energy distribution in the VTF plasmas. Several mechanisms will be tested as potential causes of the bulk heating of background plasmas by the injected electron beams as seen in the space shuttle experiments. It is speculated that the observed ELF emissions result from the excitation of purely growing modes detected by the space shuttle-borne detectors. Results of the laboratory experiments will be reported to corroborate this speculation.

Murphy, S.M.; Lee, M.C.; Moriarty, D.T.; Riddolls, R.J. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Plasma Fusion Center

1995-12-31

407

Excitation of surface plasma waves by a density modulated electron beam at a conductor-dusty plasma interface  

Microsoft Academic Search

A density modulated electron beam propagating through a conductor-dusty plasma interface drives electromagnetic surface plasma waves (SPWs) to instability via Cerenkov and cyclotron interaction. The SPWs propagate across an external magnetic field parallel to the interface. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the typical parameters of the SPWs. The frequency and

Ruby Gupta; Suresh C. Sharma; Ved Prakash

2011-01-01

408

Electromagnetic radiation and nonlinear energy flow in an electron beam-plasma system  

NASA Technical Reports Server (NTRS)

It is shown that the unstable electron-plasma waves of a beam-plasma system can generate electromagnetic radiation in a uniform plasma. The generation mechanism is a scattering of the unstable electron plasma waves off ion-acoustic waves, producing electromagnetic waves whose frequency is near the local plasma frequency. The wave vector and frequency matching conditions of the three-wave mode coupling are experimentally verified. The electromagnetic radiation is observed to be polarized with the electric field parallel to the beam direction, and its source region is shown to be localized to the unstable plasma wave region. The frequency spectrum shows negligible intensity near the second harmonic of the plasma frequency. These results suggest that the observed electromagnetic radiation of type III solar bursts may be generated near the local plasma frequency and observed downstream where the wave frequency is near the harmonic of the plasma frequency.

Whelan, D. A.; Stenzel, R. L.

1985-01-01

409

Energization of auroral electrons by electrostatic shock waves  

Microsoft Academic Search

Electrostatic shock waves are proposed as a possible mechanism for energizing electrons which are responsible for discrete auroras. It is shown that electrostatic shock solutions can exist in a Tt >> Te plasma carrying a field-aligned electron current if the plasma in the high-latitude plasma sheet has an earthward flow component. The model is formulated within the framework of the

Joseph R. Kan

1975-01-01

410

Numerical Simulation of the Self-Heating Effect Induced by Electron Beam Plasma in Atmosphere  

NASA Astrophysics Data System (ADS)

For exploiting advantages of electron beam air plasma in some unusual applications, a Monte Carlo (MC) model coupled with heat transfer model is established to simulate the characteristics of electron beam air plasma by considering the self-heating effect. Based on the model, the electron beam induced temperature field and the related plasma properties are investigated. The results indicate that a nonuniform temperature field is formed in the electron beam plasma region and the average temperature is of the order of 600 K. Moreover, much larger volume pear-shaped electron beam plasma is produced in hot state rather than in cold state. The beam ranges can, with beam energies of 75 keV and 80 keV, exceed 1.0 m and 1.2 m in air at pressure of 100 torr, respectively. Finally, a well verified formula is obtained for calculating the range of high energy electron beam in atmosphere.

Deng, Yongfeng; Tan, Chang; Han, Xianwei; Tan, Yonghua

2012-02-01

411

Plasma chemistry induced by low energy electron beams  

NASA Astrophysics Data System (ADS)

A table top setup for studying plasma chemical reactions is described. Low energy (15 keV) electrons are used to induce the chemical reactions. The experiments are performed with pure gases and gas mixtures at atmospheric pressure. The radiolysis of CO2 is studied as an example and a G-value of 3 was achieved for a gas flow of 14 ml/min. The experiments were performed with a total beam power of 450 mW sent into a gas cell with a volume of 40 mm3. Mass spectrometry and a spectroscopic study were used for diagnostics. A catalytic effect of xenon for the splitting of CO2 molecules was observed and supported by comparative measurements with Ar-CO2 and Ar-Xe-CO2 mixtures. The power deposition profiles in the target cell are discussed on the basis of a numerical model.

Himpsl, Andreas; Dandl, Thomas; Heindl, Thomas; Neumeier, Alexander; Wieser, Jochen; Ulrich, Andreas

2014-06-01

412

Weibel instabilities in relativistic electron-positron plasmas  

NASA Astrophysics Data System (ADS)

Wisps have long been observed in the Crab Nebula. Modern observations reveal a whole series of wisps to the northwest, and at least one much fainter wisp to the southeast. Recently, a conceptual model of the wisps in the Crab Nebula has been proposed based on the shock structure of a relativistic magnetosonic shock wave in a electron-positron-proton plasma. The ion overshoot, downstream compressional oscillations, and possibly the pair overshoot can be identified with the wisps. In this paper, we study the linear stability properties of the Weibel instability, which are collective electromagnetic oscillations driven by pitch-angle anisotropy of the distribution functions. This instability can cause pitch-angle scattering of the charged particles and the isotropization of the distribution functions.

Yang, T.-Y. B.; Gallant, Y.; Arons, J.; Langdon, A. B.

1992-07-01

413

Optimization of a plasma focus device as an electron beam source for thin film deposition  

Microsoft Academic Search

Electron beam emission characteristics from neon, argon, hydrogen and\\u000a helium in an NX2 dense plasma focus (DPF) device were investigated in\\u000a order to optimize the plasma focus device for deposition of thin films\\u000a using energetic electron beams. A Rogowski coil and CCD based magnetic\\u000a spectrometer were used to obtain temporal characteristics, total\\u000a electron charge and energy distributions of electron emission

T. Zhang; J. Lin; A. Patran; D. Wong; S. M. Hassan; S. Mahmood; T. White; T. L. Tan; S. V. Springham; S. Lee; P. Lee; R. S. Rawat

2007-01-01

414

Generation and transport of ultrashort phase-locked electron bunches to a plasma beatwave accelerator  

Microsoft Academic Search

The last five years have seen successful experimental efforts on ultrahigh gradient acceleration of electrons from laser- and electron-driven electron plasma waves. The challenges for future near-term experiments have now changed from proof-of-principle of high gradients to the production of a substantially high quality electron beam from a plasma accelerator. This paper discusses two aspects of this challenge, namely techniques

C. E. Clayton; Luca Serafini

1996-01-01

415

Effects of parallel electron dynamics on plasma blob transport  

SciTech Connect

The 3D effects on sheath connected plasma blobs that result from parallel electron dynamics are studied by allowing for the variation of blob density and potential along the magnetic field line and using collisional Ohm's law to model the parallel current density. The parallel current density from linear sheath theory, typically used in the 2D model, is implemented as parallel boundary conditions. This model includes electrostatic 3D effects, such as resistive drift waves and blob spinning, while retaining all of the fundamental 2D physics of sheath connected plasma blobs. If the growth time of unstable drift waves is comparable to the 2D advection time scale of the blob, then the blob's density gradient will be depleted resulting in a much more diffusive blob with little radial motion. Furthermore, blob profiles that are initially varying along the field line drive the potential to a Boltzmann relation that spins the blob and thereby acts as an addition sink of the 2D potential. Basic dimensionless parameters are presented to estimate the relative importance of these two 3D effects. The deviation of blob dynamics from that predicted by 2D theory in the appropriate limits of these parameters is demonstrated by a direct comparison of 2D and 3D seeded blob simulations.

Angus, Justin R.; Krasheninnikov, Sergei I. [University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093 (United States); Umansky, Maxim V. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550 (United States)

2012-08-15

416

High time-resolution correlation between the magnetic field behavior at 37 R sub E distance in the magnetotail plasma sheet and ground phenomena during substorm expansive phase  

NASA Astrophysics Data System (ADS)

A detailed study is made of the magnetic field response at a distance of 37 earth radii in the vicinity of the magnetotail plasma sheet to the discrete time structure of a substorm expansive phase. The magnetic field changes were detected by the IMP-8 satellite during six successive well-defined substorms on March 3, 1976 and combined with similar results which had been obtained for distances of 10-20 earth radii (Pytte et al. 1976, 1978; Sergeev, 1977); these were used to infer the pattern of magnetic field variations and its changes during the successive events in the whole expansion phase. Both successive Pi2 onsets and moments of abrupt changes in their regime, along with the corresponding auroral phenomena, are shown to be simultaneous with the impulsive magnetic field variations in the plasma sheet. The pattern of these variations at 37 earth radii was found to change typically in a sequence of microsubstorms, constituting the whole expansive phase.

Sergeev, V. A.

417

Quantitative analysis of steel sheet surfaces using computer-aided electron probe microanalysis  

Microsoft Academic Search

Generally, the classic methods such as Auger, ESCA or SIMS are used for the analysis of surfaces. With the use of these methods there has been increasing recognition of the great importance of surface composition for the manufacture, further processing and application of materials. But such methods, when used for the analysis of steel-sheet surfaces, also leave gaps if it

S. Baumgartl; P. Busch

1989-01-01

418

Expansion Rate Measurements at Moderate Pressure of Nonneutral Electron Plasmas in the Electron Diffusion Gauge (EDG) Experiment  

SciTech Connect

Measurements of the expansion rate of pure-electron plasmas have been performed on the Electron Diffusion Gauge (EDG) device at background helium gas pressures in the 5 x 10(superscript -8) Torr to 1 x 10(superscript -5) Torr range, where plasma expansion due to electron-neutral collisions dominates over plasma expansion due to trap asymmetries. It is found that the expansion rate, defined as the time rate of change of the particles' mean-square radius, scales approximately linearly with pressure and inversely as the square of the magnetic field strength in this regime, in agreement with classical predictions.

Morrison, Kyle A.; Davidson, Ronald C.; Paul, Stephen F.; Belli, Emily A.; and Chao, Edward H.

2001-05-18

419

IN-SITU ELECTRON CYCLOTRON RESONANCE (ECR) PLASMA POTENTIAL DETERMINATION USING AN EMISSIVE PROBE*  

E-print Network

scale and the high heat flux from its large population of hot electrons. In the present measurements must be small in comparison to the plasma length scale in order not to perturb the global state of the plasma, and at the same time be able to withstand the heat load from the plasma without damage

420

Images of Complex Interactions of an Intense Ion Beam with Plasma Electrons  

SciTech Connect

Ion beam propagation in a background plasma is an important scientific issue for many practical applications. The process of ion beam charge and current neutralization is complex because plasma electrons move in strong electric and magnetic fields of the beam. Computer simulation images of plasma interaction with an intense ion beam pulse are presented.

Igor D. Kaganovich; Edward Startsev; Ronald C. Davidson

2004-08-03

421

Estimation method for electron-hole pair density in plasma columns  

Microsoft Academic Search

A simple method to estimate the electron-hole pair density in plasma columns created by heavy ions is described. The volume of plasma column is described in a ratio to the one of cone with the same range and bottom radius of the plasma column. The volume ratio is expressed by second polynomials of the energy per unit mass of the

I. Kanno

1999-01-01

422

Electron shear-flow-driven instability in magnetized plasmas with magnetic field gradient  

SciTech Connect

It is found that the zero-order current associated with electron shear flow produces a drift wave in magnetized plasmas, which can become unstable under certain conditions. This wave will be particularly important in low density and low temperature plasmas of heavy ions. As an example, numerical estimates are presented for a barium plasma with parameters compatible with experiments.

Saleem, Hamid [National Centre for Physics (NCP), Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Eliasson, Bengt [Faculty of Physics and Astronomy, Ruhr-University Bochum, Bochum 44780 (Germany)

2011-05-15

423

FAST TRACK COMMUNICATION: Electron collision ionized plasma waves in the positive column of a fine discharge tube  

Microsoft Academic Search

In fluorescent lamp tubes, a few millimetres in radius, operating at several tens of kilohertz, the initiation of light radiation is characterized by the propagation of an electron plasma wave, accompanied by ionization caused by electron collision. Due to the effects of the ionization collision of electrons on the dispersion behaviour of the plasma waves, the electron plasma waves generated

Junghyun Kim; Jongmun Jeong; Hachung Hwang; Dongjun Jin; Jehuan Koo; Gichung Kwon; Eunha Choi; Guangsup Cho; Han Sup Uhm

2009-01-01

424

Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet  

NASA Technical Reports Server (NTRS)

Using data from 41 substorm events in the near-Earth magnetotail, we have combined plasma, energetic ion, and magnetic field data from the AMPTE/IRM spacecraft to perform a superposed epoch analysis of changes in the total pressure and in the magnetic field configuration as a function of time relative to substorm onset. Unloading is evident in the total pressure profile; the pressure decreases by about 20 percent. Pressure changes during the growth phase are not as uniform for the different substorms as the pressure changes during the expansion phase. To study changes in the magnetic field configuration, we have determined the development of the plasma pressure profiles in z for an average of data from 15 to 19 R(E). At substorm onset, the field line dipolarization begins on the innermost field lines and then progresses to the outer field lines. The field lines map the closest to the Earth about 45 min after substorm onset, and then begin to stretch out again during the recovery phase of the substorm.

Kistler, L. M.; Baumjohann, W.; Nagai, T.; Mobius, E.

1993-01-01

425

Superposed Epoch Analysis of Ring Current Geoeffectiveness Related to Solar Wind and Plasma Sheet Drivers  

NASA Technical Reports Server (NTRS)

The goal of that proposal was to examine the relationship between solar wind drivers and ring current dynamics through data analysis and numerical simulations. The data analysis study was a statistical examination (via superposed epoch analyses) of a solar cycle's worth of storm data. Solar wind data, geophysical indices, and geosynchronous plasma data were collected for every time period with Dst< -50 nT from 1989 through 2002, and the storm list now exceeds 400 entries. This work was first conducted by a summer undergraduate student, Mr. John Vann (University of Kansas), with funding from the NSF Research Experience for Undergraduates program. It was then continued by a University of Michigan graduate student, Mr.