Magnetized relativistic electron-ion plasma expansion
NASA Astrophysics Data System (ADS)
Benkhelifa, El-Amine; Djebli, Mourad
2016-03-01
The dynamics of relativistic laser-produced plasma expansion across a transverse magnetic field is investigated. Based on a one dimensional two-fluid model that includes pressure, enthalpy, and rest mass energy, the expansion is studied in the limit of λD (Debye length) ≤RL (Larmor radius) for magnetized electrons and ions. Numerical investigation conducted for a quasi-neutral plasma showed that the σ parameter describing the initial plasma magnetization, and the plasma β parameter, which is the ratio of kinetic to magnetic pressure are the key parameters governing the expansion dynamics. For σ ≪ 1, ion's front shows oscillations associated to the break-down of quasi-neutrality. This is due to the strong constraining effect and confinement of the magnetic field, which acts as a retarding medium slowing the plasma expansion.
Electromagnetic solitary pulses in a magnetized electron-positron plasma
Shukla, P. K.; Eliasson, B.; Stenflo, L.
2011-03-15
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.
Electron energy distributions in a magnetized inductively coupled plasma
Song, Sang-Heon E-mail: Sang-Heon.Song@us.tel.com; Yang, Yang; Kushner, Mark J.
2014-09-15
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.
The influence of magnetic field on electron beam generated plasmas
NASA Astrophysics Data System (ADS)
Petrov, G. M.; Boris, D. R.; Lock, E. H.; Petrova, Tz B.; Fernsler, R. F.; Walton, S. G.
2015-06-01
Magnetically confined argon plasma in a long cylindrical tube driven by an electron beam is studied experimentally and theoretically. Langmuir probes are used to measure the electron energy distribution function, electron density and temperature in plasmas generated by 2 keV, 10 mA electron beams in a 25 mTorr argon background for magnetic field strengths of up to 200 Gauss. The experimental results agree with simulations done using a spatially averaged Boltzmann model adapted to treat an electron beam generated plasma immersed in a constant magnetic field. The confining effect of the magnetic field is studied theoretically using fluid and kinetic approaches. The fluid approach leads to two regimes of operation: weakly and strongly magnetized. The former is similar to the magnetic field-free case, while in the latter the ambipolar diffusion coefficient and electron density depend quadratically on the magnetic field strength. Finally, a more rigorous kinetic treatment, which accounts for the impact of the magnetic field over the whole distribution of electrons, is used for accurate description of the plasma.
Studies of cryogenic electron plasmas in magnetic mirror fields
NASA Astrophysics Data System (ADS)
Gopalan, Ramesh
This thesis considers the properties of pure electron plasmas in Penning traps which have an axially varying magnetic field. Our theory of the thermal equilibrium of such plasmas in magnetic mirror fields indicates that their behavior may be characterized by the ratio of their temperature to their central density T/n. For cold, dense plasmas the density along the plasma axis scales linearly with the magnetic field, while for hot, tenuous plasmas, at the opposite limit of the parameter range, the density is constant along the axis, similar to the behavior of a neutral plasma in a magnetic mirror. We are able to conclude from this that the electrostatic potential varies along the field lines, in equilibrium. As the plasma charge and potential distribution must be consistent with the grounded potential on the trap walls, the plasma profile does not follow the geometry of the magnetic field lines; the plasma radius in the high-field region is smaller than would be obtained by mapping the field lines from the radial edge of the low-field region. Another interesting feature of these mirror equilibria is that there are trapped populations of particles both in the low-field and high-field regions. Our experiments on the Cryogenic Electron Trap have confirmed many of these theoretical results over a wide parameter range. We have been able to sample the volume charge density at various points on the axis. We have also measured the line-charge distribution of the plasma. Both these experiments are in general agreement with our theory of the global thermal equilibrium in the mirror- field. A surprising observation has been the unexpectedly long- life of the m = 1 diocotron mode in these traps where the magnetic field varies by ~100% across its length. We report these observations, along with plausible explanations for them. The trap we have constructed is intended for the eventual study of very cold electron plasmas in strong magnetic fields, where the plasma electrons are
Solitary and shock waves in magnetized electron-positron plasma
Lu, Ding; Li, Zi-Liang; Abdukerim, Nuriman; Xie, Bai-Song
2014-02-15
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 Alfvén 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 Alfvén speed. For a hot EP plasma, the existence range depends on the Alfvén 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.
Anomalous skin effects in a weakly magnetized degenerate electron plasma
Abbas, G. Sarfraz, M.; Shah, H. A.
2014-09-15
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].
Anomalous skin effects in a weakly magnetized degenerate electron plasma
NASA Astrophysics Data System (ADS)
Abbas, G.; Sarfraz, M.; Shah, H. A.
2014-09-01
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].
Magnetic insulation of secondary electrons in plasma source ion implantation
Rej, D.J.; Wood, B.P.; Faehl, R.J.; Fleischmann, H.H.
1993-09-01
The uncontrolled loss of accelerated secondary electrons in plasma source ion implantation (PSII) can significantly reduce system efficiency and poses a potential x-ray hazard. This loss might be reduced by a magnetic field applied near the workpiece. The concept of magnetically-insulated PSII is proposed, in which secondary electrons are trapped to form a virtual cathode layer near the workpiece surface where the local electric field is essentially eliminated. Subsequent electrons that are emitted can then be reabsorbed by the workpiece. Estimates of anomalous electron transport from microinstabilities are made. Insight into the process is gained with multi-dimensional particle-in-cell simulations.
Electron current extraction from a permanent magnet waveguide plasma cathode
Weatherford, B. R.; Foster, J. E.; Kamhawi, H.
2011-09-15
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.
Electron vortex magnetic holes: A nonlinear coherent plasma structure
Haynes, Christopher T. Burgess, David; Sundberg, Torbjorn; Camporeale, Enrico
2015-01-15
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.
Electron vortex magnetic holes: A nonlinear coherent plasma structure
NASA Astrophysics Data System (ADS)
Haynes, Christopher T.; Burgess, David; Camporeale, Enrico; Sundberg, Torbjorn
2015-01-01
We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.
Nonlocal electron transport in magnetized plasmas with arbitrary atomic number
Bennaceur-Doumaz, D.; Bendib, A.
2006-09-15
The numerical solution of the steady-state electron Fokker-Planck equation perturbed with respect to a global equilibrium is presented in magnetized plasmas with arbitrary atomic number Z. The magnetic field is assumed to be constant and the electron-electron collisions are described by the Landau collision operator. The solution is derived in the Fourier space and in the framework of the diffusive approximation which captures the spatial nonlocal effects. The transport coefficients are deduced and used to close a complete set of nonlocal electron fluid equations. This work improves the results of A. Bendib et al. [Phys. Plasmas 9, 1555 (2002)] and of A. V. Brantov et al. [Phys. Plasmas 10, 4633 (2003)] restricted to the local and nonlocal high-Z plasma approximations, respectively. The influence of the magnetic field on the nonlocal effects is discussed. We propose also accurate numerical fits of the relevant transport coefficients with respect to the collisionality parameter {lambda}{sub ei}/L and the atomic number Z, where L is the typical scale length and {lambda}{sub ei} is the electron-ion mean-free-path.
Electron series resonance plasma discharges: Unmagnetized and magnetized
NASA Astrophysics Data System (ADS)
Qiu, Weiguang
2001-08-01
This thesis explores high frequency electron series resonance in unmagnetized and magnetized bounded plasmas. Special interest is focused on low temperature plasmas in planar systems as such are useful for material processing and fusion devices. Chapter 1, Chapter 2 and Chapter 3 describe simulation studies of unmagnetized electron series resonance (ESR) sustained discharges with comparisons to theory and experiment. These plasmas have many desirable characteristics. The input resistance is small and the drive voltage and current are in phase. The drive voltage is small (˜Te) and the time average plasma potential is low (˜10Te). A strong kinetic phase space bunching process is shown to provide electrons of sufficient energy for ionization, which allows discharge operation at low neutral pressure and low electron temperatures. At low pressure, the ion flux to the wall has a narrow angular spread about the normal and the ion bombarding energy distribution has a sharp peak at the plasma potential. Scaling laws at fixed pressure nr∝w3RF ,s¯∝w -1RF are shown to hold when RF frequency is varied smoothly ("chirping") demonstrating continuous density control. Research on magnetized electron series resonance (MESR) discharges is described in Chapter 4, Chapter 5 and Chapter 6. The resonant frequency is derived from cold plasma theory and shows two resonant modes. Simulations verify these modes to be the natural oscillatory frequencies of weakly magnetized plasmas in a planar plasma diode. A global model is established for magnetized resonant discharges. The interrelations among the plasma parameters and the drive terms are formulated for both resonant modes. The initiation of a MESR discharge and its steady state properties are discussed and compared to the unmagnetized case. Weak lock-on of MESR frequency to the drive frequency is observed in simulation. Similar V - I characteristics as those in ESR are found both in theory and in simulation. Different from the ESR
Magnetically Controlled Optical Plasma Waveguide for Electron Acceleration
Pollock, B. B.; Davis, P.; Divol, L.; Glenzer, S. H.; Palastro, J. P.; Price, D.; Froula, D. H.; Tynan, G. R.
2009-01-22
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 5x10{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.
Magnetically Controlled Optical Plasma Waveguide for Electron Acceleration
Pollock, B B; Froula, D H; Tynan, G R; Divol, L; Davis, P; Palastro, J P; Price, D; Glenzer, S H
2008-08-28
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.
Electron Energization During m=0 Magnetic Bursts in MST plasmas
NASA Astrophysics Data System (ADS)
Young, W. C.; den Hartog, D. J.; Morton, L. A.; MST Team
2015-11-01
MST reversed-field pinch plasmas develop magnetic modes with both a core-resonant poloidal mode m=1 structure and edge-resonant m=0 structure on the reversal surface. The impact of the m=0 modes on electron energization has been observed with Thomson scattering under plasma conditions with suppressed m=1 modes. Under such conditions, the m=0 modes undergo brief (~100 μs) bursts of localized magnetic activity. These bursts show a localized 4% heating of electrons above a 600-900 eV background temperature, associated with a reduction of magnetic energy. An inward propagating cold pulse follows after the heating as a result of reduced confinement. Ensembles of hundreds of bursts are required to measure small relative heating, however single-shot results from MST's high repetition Thomson scattering diagnostic support the ensemble results. Analysis of Thomson scattering data also provides constraints on non-Maxwellian distributions and upcoming upgrades will improve the ability to resolve electron currents associated with the magnetic bursts. This work is supported by the US DOE and NSF.
NASA Astrophysics Data System (ADS)
Zhu, Zhenni; Wu, Zhengwei; Li, Chunhua; Yang, Weihong
2014-11-01
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.
Surface waves in magnetized quantum electron-positron plasmas
NASA Astrophysics Data System (ADS)
Misra, A. P.; Ghosh, N. K.; Shukla, P. K.
2010-02-01
The dispersion properties of electrostatic surface waves propagating along the interface between a quantum magnetoplasma composed of electrons and positrons, and vacuum are studied by using a quantum magnetohydrodynamic plasma model. The general dispersion relation for arbitrary orientation of the magnetic field and the propagation vector is derived and analyzed in some special cases of interest (viz. when the magnetic field is directed parallel and perpendicular to the boundary surface). It is found that the quantum effects facilitate the propagation of electrostatic surface modes in a dense magnetoplasma. The effect of the external magnetic field is found to increase the frequency of the quantum surface wave. The existence of a singular wave on the boundary surface is also proved, and its properties are analyzed numerically. It is shown that the new wave characteristics appear due to the Rayleigh type of the wave.
NASA Astrophysics Data System (ADS)
Singh, S. V.; Devanandhan, S.; Lakhina, G. S.; Bharuthram, R.
2016-08-01
A theoretical investigation is carried out to study the obliquely propagating electron acoustic solitary waves having nonthermal hot electrons, cold and beam electrons, and ions in a magnetized plasma. We have employed reductive perturbation theory to derive the Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) equation describing the nonlinear evolution of these waves. The two-dimensional plane wave solution of KdV-ZK equation is analyzed to study the effects of nonthermal and beam electrons on the characteristics of the solitons. Theoretical results predict negative potential solitary structures. We emphasize that the inclusion of finite temperature effects reduces the soliton amplitudes and the width of the solitons increases by an increase in the obliquity of the wave propagation. The numerical analysis is presented for the parameters corresponding to the observations of "burst a" event by Viking satellite on the auroral field lines.
Magnetic field measurements for study of fast electron transport in magnetized HED plasma
NASA Astrophysics Data System (ADS)
Sawada, Hiroshi; Griffin, Brandon; Presura, Radu; Haque, Showera; Sentoku, Yasuhiko
2014-10-01
Interaction of megagauss magnetic fields with high energy density (HED) plasma is of great interest in the field of magnetized plasma. The field changes fundamental properties of the HED plasma such as thermal and magnetic diffusion. A coupled capability utilizing the 1.0 MA Zebra pulsed power generator and the 50 TW Leopard laser at Nevada Terawatt Facility enables to create such a condition for studies of magnetized plasma properties. We have conducted an experiment to measure magnetic fields generated by a 1.0 MA, 100 ns Zebra pulsed current in stainless steel coils. Using a 532 nm continuous laser from a single longitudinal mode laser system, the temporal change in the magnetic field was measured with the Faraday rotation in F2 glass. The probe laser passing through the 1.5 mm in radius and 1.75 mm thick glass placed in the vicinity of the inductive coils was split with a Glan-Taylor prism to measure vertical and horizontal polarization components with photodiodes. We will present the analysis of the experimental result and a design of a coupled experiment for study of fast electron transport in the magnetized plasma.
NASA Astrophysics Data System (ADS)
Rafalskyi, Dmytro; Aanesland, Ane
2015-09-01
We present a plasma diagnostics method based on impedance measurements of a short matched dipole placed in the plasma. This allows measuring the local electron density in the range from 1012-1015 m-3 with a magnetic field of at least 0-50 mT. The magnetic field strength is not directly influencing the data analysis and requires only that the dipole probe is oriented perpendicularly to the magnetic field. As a result, the magnetic field can be non-homogeneous or even non-defined within the probe length without any effect on the final tolerance of the measurements. The method can be applied to plasmas of relatively small dimensions (< 10 cm) and doesn't require any special boundary conditions. The high sensitivity of the impedance measurements is achieved by using a miniature matching system installed close to the probe tip, which also allows to suppress sheath resonance effects. We experimentally show here that the tolerance of the electron density measurements reaches values lower than 1%, both with and without the magnetic field. The method is successfully validated by both analytical modeling and experimental comparison with Langmuir probes. The validation experiments are conducted in a low pressure (1 mTorr) Ar discharge sustained in a 10 cm size plasma chamber with and without a transversal magnetic field of about 20 mT. This work was supported by a Marie Curie International Incoming Fellowships within FP7 (NEPTUNE PIIF-GA-2012-326054).
Induced Compton Scattering by Relativistic Electrons in Magnetized Astrophysical Plasmas.
NASA Astrophysics Data System (ADS)
Sincell, Mark William
1994-01-01
The effects of stimulated scattering on high brightness temperature radiation are studied in two important contexts. In the first case, we assume that the radiation is confined to a collimated beam traversing a relativistically streaming magnetized plasma. When the plasma is cold in the bulk frame, stimulated scattering is only significant if the angle between the photon motion and the plasma velocity is less than gamma^{-1} , where gamma is the bulk Lorentz factor. Under the assumption that the center of the photon beam is parallel to the bulk motion, we calculate the scattering rate as a function of the angular spread of the beam and gamma. Magnetization changes the photon recoil, without which stimulated scattering has no effect. It also introduces a strong dependence on frequency and polarization: if the photon frequency matches the electron cyclotron frequency, the scattering rate of photons polarized perpendicular to the magnetic field can be substantially enhanced relative to Thomson, and if the photon frequency is much less than the cyclotron frequency the scattering is suppressed. Applying these calculations to pulsars, we find that stimulated scattering of the radio beam in the magnetized wind believed to exist outside the light cylinder can substantially alter the spectrum and polarization state of the radio signal. We suggest that the scattering rate is so high in some pulsars that the ability of the radio signal to penetrate the pulsar magnetosphere requires modification of either the conventional model of the magnetosphere or assumptions about the effects of stimulated scattering upon a beam. In the second case, we present a model of the radio emission from synchrotron self-absorbed sources, including the effects of induced Compton scattering by the relativistic electrons in the source. Order of magnitude estimates show that stimulated scattering becomes the dominant absorption process when (kTB/m ec^2)tau_{T }_sp{~}> 0.1. Numerical simulations
NASA Astrophysics Data System (ADS)
Vafin, S.; Schlickeiser, R.; Yoon, P. H.
2016-09-01
The general electromagnetic fluctuation theory is a powerful tool to analyze the magnetic fluctuation spectrum of a plasma. Recent works utilizing this theory for a magnetized non-relativistic isotropic Maxwellian electron-proton plasma have demonstrated that the equilibrium ratio of | δ B| /{B}0 can be as high as 10-12. This value results from the balance between spontaneous emission of fluctuations and their damping, and it is considerably smaller than the observed value | δ B| /{B}0 in the solar wind at 1 au, where {10}-3≲ | δ B| /{B}0≲ {10}-1. In the present manuscript, we consider an anisotropic bi-Maxwellian distribution function to investigate the effect of plasma instabilities on the magnetic field fluctuations. We demonstrate that these instabilities strongly amplify the magnetic field fluctuations and provide a sufficient mechanism to explain the observed value of | δ B| /{B}0 in the solar wind at 1 au.
Sustenance of inhomogeneous electron temperature in a magnetized plasma column
Karkari, S. K. Mishra, S. K.; Kaw, P. K.
2015-09-15
This paper presents the equilibrium properties of a magnetized plasma column sustained by direct-current (dc) operated hollow cathode discharge in conjunction with a conducting end-plate, acting as the anode. The survey of radial plasma characteristics, performed in argon plasma, shows hotter plasma in the periphery as compared to the central plasma region; whereas the plasma density peaks at the center. The off-centered peak in radial temperature is attributed due to inhomogeneous power deposition in the discharge volume in conjunction with short-circuiting effect by the conducting end plate. A theoretical model based on particle flux and energy balance is given to explain the observed characteristics of the plasma column.
Alinejad, H.
2012-05-15
The linear and nonlinear propagation of ion-acoustic waves are investigated in a magnetized electron-positron-ion (e-p-i) plasma with nonthermal electrons. In the linear regime, the propagation of two possible modes and their evolution are studied via a dispersion relation. In the cases of parallel and perpendicular propagation, it is shown that these two possible modes are always stable. Then, the Korteweg-de Vries equation describing the dynamics of ion-acoustic solitary waves is derived from a weakly nonlinear analysis. The influence on the solitary wave characteristics of relevant physical parameters such as nonthermal electrons, magnetic field, obliqueness, positron concentration, and temperature ratio is examined. It is observed that the increasing nonthermal electrons parameter makes the solitary structures much taller and narrower. Also, it is revealed that the magnetic field strength makes the solitary waves more spiky. The present investigation contributes to the physics of the nonlinear electrostatic ion-acoustic waves in space and laboratory e-p-i plasmas in which wave damping produces an electron tail.
The electron density distribution and field profile in underdense magnetized plasma
Sadighi-Bonabi, R.; Etehadi-Abari, M.
2010-03-15
In this work propagation of a high frequency electromagnetic wave in underdense plasma in presence of an external magnetic field is investigated. When a constant magnetic field perpendicular to the motion of electrons is applied, then the electrons rotate around the magnetic field lines and generate electromagnetic part in the wake with a nonzero group velocity. By using of the Maxwell equations and nonlinear differential equation for the electric field a direct one-dimensional (1D) procedure for calculating hydrodynamic equations are developed and the electric and magnetic field profiles in the plasma are investigated. It is shown that by using the external (dc) magnetic field in constant laser intensity, the magnetic field profile in plasma deviates from the sinusoidal structure. It is found that the wavelength of electric and magnetic field oscillations increases by increasing the external magnetic field and the density distribution of electrons also increases in comparison to the unmagnetized underdense plasma. We noticed that by the increase in electron temperature in the unmagnetized and magnetized plasmas the electron density distribution ratio deltan/n{sub 0e} increases and the wavelength of electric and magnetic fields increase where in the magnetized system it becomes positive in some regions.
Ponderomotive acceleration of electrons by a laser pulse in magnetized plasma
Sharma, Anamika; Tripathi, V. K.
2009-04-15
Electron acceleration by a circularly polarized Gaussian laser pulse in magnetized plasma is investigated in the limit of frozen refractive index. The electron acceleration depends on the ratio of laser frequency to electron cyclotron frequency, amplitude of the laser pulse and plasma density. Near Doppler shifted cyclotron resonance the electron acquires maximum energy. In this scheme, 0.10 MeV electrons can be effectively accelerated to 1-100 MeV using moderate intensity laser pulse.
Effect of electron reflection on magnetized plasma sheath in an oblique magnetic field
Wang, Ting-Ting; Ma, J. X. Wei, Zi-An
2015-09-15
Magnetized plasma sheaths in an oblique magnetic field were extensively investigated by conventionally assuming Boltzmann relation for electron density. This article presents the study of the magnetized sheath without using the Boltzmann relation but by considering the electron reflection along the magnetic field lines caused by the negative sheath potential. A generalized Bohm criterion is analytically derived, and sheath profiles are numerically obtained, which are compared with the results of the conventional model. The results show that the ion Mach number at the sheath edge normal to the wall has a strong dependence on the wall potential, which differs significantly from the conventional model in which the Mach number is independent of the wall potential. The floating wall potential is lower in the present model than that in the conventional model. Furthermore, the sheath profiles are appreciably narrower in the present model when the wall bias is low, but approach the result of the conventional model when the wall bias is high. The sheath thickness decreases with the increase of ion-to-electron temperature ratio and magnetic field strength but has a complex relationship with the angle of the magnetic field.
Electron acceleration in a warm magnetized plasma-filled cylindrical waveguide
Kumar, S.; Yoon, M.
2008-10-01
The effect of plasma-electron collision and their thermal motion is investigated on the externally injected electron in a warm magnetized plasma-filled cylindrical waveguide of cross section of 13.68 cm{sup 2}. The numerical results are presented for the external electron-energy gain and its trajectory in a nonrelativistic {gamma}{sub e}=1 and stationary v{sub 0}=0 warm magnetized plasma-filled waveguide. Results shows that for an electron-cyclotron frequency {omega}{sub c} greater than the electron-plasma frequency {omega}{sub p}, a 100 keV electron acquires a 1.74 MeV energy in a 2.5 cm distance for plasma density n{sub 0}=1.08x10{sup 17}/m{sup 3}, magnetic field B{sub 0}=0.193 T, microwave frequency f=7.64 GHz, plasma-electron thermal velocity v{sub th}=0.2c, and plasma-electron collision frequency {nu}=4 GHz, which is lower than the 7 MeV electron energy in a cold magnetized plasma-waveguide case. Space-charge effects and other nonlinear effects are assumed to be negligible in this model.
Fast electron generation and transport in a turbulent, magnetized plasma
Stoneking, W.R.
1994-05-01
The nature of fast electron generation and transport in the Madison Symmetric Torus (MST) reversed field pinch (RFP) is investigated using two electron energy analyzer (EEA) probes and a thermocouple calorimeter. The parallel velocity distribution of the fast electron population is well fit by a drifted Maxwellian distribution with temperature of about 100 eV and drift velocity of about 2 {times} 10{sup 6} m/s. Cross-calibration of the EEA with the calorimeter provides a measurement of the fast electron perpendicular temperature of 30 eV, much lower than the parallel temperature, and is evidence that the kinetic dynamo mechanism (KDT) is not operative in MST. The fast electron current is found to match to the parallel current at the edge, and the fast electron density is about 4 {times} 10{sup 11} cm{sup {minus}3} independent of the ratio of the applied toroidal electric field to the critical electric field for runaways. First time measurements of magnetic fluctuation induced particle transport are reported. By correlating electron current fluctuations with radial magnetic fluctuations the transported flux of electrons is found to be negligible outside r/a{approximately}0.9, but rises the level of the expected total particle losses inside r/a{approximately}0.85. A comparison of the measured diffusion coefficient is made with the ausilinear stochastic diffusion coefficient. Evidence exists that the reduction of the transport is due to the presence of a radial ambipolar electric field of magnitude 500 V/m, that acts to equilibrate the ion and electron transport rates. The convective energy transport associated with the measured particle transport is large enough to account for the observed magnetic fluctuation induced energy transport in MST.
Reduced electron temperature in a magnetized inductively-coupled plasma with internal coil
Arancibia Monreal, J.; Chabert, P.; Godyak, V.
2013-10-15
The effect of magnetic filtering on the electron energy distribution function is studied in an inductive discharge with internal coil coupling. The coil is placed inside the plasma and driven by a low-frequency power supply (5.8 MHz) which leads to a very high power transfer efficiency. A permanent dipole magnet may be placed inside the internal coil to produce a static magnetic field around 100 Gauss. The coil and the matching system are designed to minimize the capacitive coupling to the plasma. Capacitive coupling is quantified by measuring the radiofrequency (rf) plasma potential with a capacitive probe. Without the permanent magnet, the rf plasma potential is significantly smaller than the electron temperature. When the magnet is present, the rf plasma potential increases. The electron energy distribution function is measured as a function of space with and without the permanent magnet. When the magnet is present, electrons are cooled down to low temperature in the downstream region. This region of low electron temperature may be useful for plasma processing applications, as well as for efficient negative ion production.
Reduced electron temperature in a magnetized inductively-coupled plasma with internal coil
NASA Astrophysics Data System (ADS)
Arancibia Monreal, J.; Chabert, P.; Godyak, V.
2013-10-01
The effect of magnetic filtering on the electron energy distribution function is studied in an inductive discharge with internal coil coupling. The coil is placed inside the plasma and driven by a low-frequency power supply (5.8 MHz) which leads to a very high power transfer efficiency. A permanent dipole magnet may be placed inside the internal coil to produce a static magnetic field around 100 Gauss. The coil and the matching system are designed to minimize the capacitive coupling to the plasma. Capacitive coupling is quantified by measuring the radiofrequency (rf) plasma potential with a capacitive probe. Without the permanent magnet, the rf plasma potential is significantly smaller than the electron temperature. When the magnet is present, the rf plasma potential increases. The electron energy distribution function is measured as a function of space with and without the permanent magnet. When the magnet is present, electrons are cooled down to low temperature in the downstream region. This region of low electron temperature may be useful for plasma processing applications, as well as for efficient negative ion production.
Magnetic mirror trap with electron-cyclotron plasma heating as a source of multiply charged ions
Golovanivskii, K.S.
1986-03-01
This paper presents the physical operating principles of sources of multiply charged ions using electron cyclotron resonance. It is shown that the conditions that must be satisfied for multiple ionization are well matched to the conditions of effective plasma confinement in a magnetic mirror trap when a collision mode of confinement is provided. Plasma stability with hot electrons in the mirror magnetic trap and the mechanisms of plasma heating by highfrequency fields are analyzed. Two sources of multiply charged ions with ECR plasma heating are examined. Evaluations of the future of this area are given.
Two-dimensional plasma expansion in a magnetic nozzle: Separation due to electron inertia
Ahedo, Eduardo; Merino, Mario
2012-08-15
A previous axisymmetric model of the supersonic expansion of a collisionless, hot plasma in a divergent magnetic nozzle is extended here in order to include electron-inertia effects. Up to dominant order on all components of the electron velocity, electron momentum equations still reduce to three conservation laws. Electron inertia leads to outward electron separation from the magnetic streamtubes. The progressive plasma filling of the adjacent vacuum region is consistent with electron-inertia being part of finite electron Larmor radius effects, which increase downstream and eventually demagnetize the plasma. Current ambipolarity is not fulfilled and ion separation can be either outwards or inwards of magnetic streamtubes, depending on their magnetization. Electron separation penalizes slightly the plume efficiency and is larger for plasma beams injected with large pressure gradients. An alternative nonzero electron-inertia model [E. Hooper, J. Propul. Power 9, 757 (1993)] based on cold plasmas and current ambipolarity, which predicts inwards electron separation, is discussed critically. A possible competition of the gyroviscous force with electron-inertia effects is commented briefly.
Small amplitude nonlinear electron acoustic solitary waves in weakly magnetized plasma
Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Roychoudhury, Rajkumar; Chakrabarti, Nikhil
2013-01-15
Nonlinear propagation of electron acoustic waves in homogeneous, dispersive plasma medium with two temperature electron species is studied in presence of externally applied magnetic field. The linear dispersion relation is found to be modified by the externally applied magnetic field. Lagrangian transformation technique is applied to carry out nonlinear analysis. For small amplitude limit, a modified KdV equation is obtained, the modification arising due to presence of magnetic field. For weakly magnetized plasma, the modified KdV equation possesses stable solitary solutions with speed and amplitude increasing temporally. The solutions are valid upto some finite time period beyond which the nonlinear wave tends to wave breaking.
Huang, C. C.; Chou, S. F.; Chang, T. H.; Chao, H. W.; Chen, C. C.
2013-07-15
This study extensively measured the uniformity of an electron cyclotron resonance (ECR) plasma versus the magnetic field distribution. The influence of magnetic field distribution on the generation of uniform ECR plasma was examined. It is suggested that in addition to the uniformity of the magnetic field distribution at ECR zone and at the downstream zone near the substrate, the transition of the magnetic field between these two zones is also crucial. A uniform ECR plasma with the electron density uniformity of ±7.7% over 500 × 500 mm{sup 2} was measured at the downstream. The idea of generating uniform ECR plasma can be scaled up to a much larger area by using an n × n microwave input array and a well-designed magnetic system.
Mahmood, S.; Sadiq, Safeer; Haque, Q.
2013-12-15
Linear and nonlinear electrostatic waves in magnetized dense electron-ion plasmas are studied with nonrelativistic and ultra-relativistic degenerate and singly, doubly charged helium (He{sup +}, He{sup ++}) and hydrogen (H{sup +}) ions, respectively. The dispersion relation of electrostatic waves in magnetized dense plasmas is obtained under both the energy limits of degenerate electrons. Using reductive perturbation method, the Zakharov-Kuznetsov equation for nonlinear propagation of electrostatic solitons in magnetized dense plasmas is derived for both nonrelativistic and ultra-relativistic degenerate electrons. It is found that variations in plasma density, magnetic field intensity, different mass, and charge number of ions play significant role in the formation of electrostatic solitons in magnetized dense plasmas. The numerical plots are also presented for illustration using the parameters of dense astrophysical plasma situations such as white dwarfs and neutron stars exist in the literature. The present investigation is important for understanding the electrostatic waves propagation in the outer periphery of compact stars which mostly consists of hydrogen and helium ions with degenerate electrons in dense magnetized plasmas.
Alinejad, H.; Mamun, A. A.
2011-11-15
A theoretical investigation is carried out to understand the basic features of linear and nonlinear propagation of ion-acoustic (IA) waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized ion fluid, Boltzmann distributed positrons, and superthermal electrons. In the linear regime, the propagation of two possible modes (fast and slow) and their evolution are investigated. It is shown that the electron superthermality and the relative fraction of positrons cause both modes to propagate with smaller phase velocities. Also, two special cases of dispersion relation are found, which are related to the direction of the wave propagation. In the nonlinear regime, the Korteweg-de Vries (KdV) equation describing the propagation of fast and slow IA waves is derived. The latter admits a solitary wave solution with only negative potential in the weak amplitude limit. It is found that the effects of external magnetic field (obliqueness), superthermal electrons, positron concentration, and temperature ratio significantly modify the basic features of solitary waves.
NASA Astrophysics Data System (ADS)
Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2015-05-01
Obliquely propagating positron-acoustic solitary waves (PASWs) in a magnetized electron-positron-ion plasma (containing nonthermal hot positrons and electrons, inertial cold positrons, and immobile positive ions) are precisely investigated by deriving the Zakharov-Kuznetsov equation. It is found that the characteristics of the PASWs are significantly modified by the effects of external magnetic field, obliqueness, nonthermality of hot positrons and electrons, temperature ratio of hot positrons and electrons, and respective number densities of hot positrons and electrons. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of PASWs in various space and laboratory plasmas.
Magnetic field-aligned electrons escaping from plasma density minima in the cusp
NASA Astrophysics Data System (ADS)
Pedersen, A.; Lybekk, B.; Haaland, S.; Svenes, K.; Dandouras, I.; Fazakerley, A. N.
2012-04-01
On Cluster the plasma density in very tenuous plasmas can be estimated based on spacecraft potential measurements. This has made it possible to detect plasma density minima of 0.01-0.1 cm-3 in the cusp poleward of the main precipitation of electrons and ions. Electron data from PEACE show that some of these minima have magnetic field-aligned outflow of electrons with energies of several hundred eV. Ion data from CIS will be used to look for possible related ion field-aligned flow. In this study the locations and the extents of plasma density minima, with electron outflow, will be determined for the northern and the southern cusp. Information about extent across the magnetic field can be obtained by using data from all four Cluster satellites, and electric field data can be used to detect plasma drift and wave activity. Possible connections to solar wind conditions and magnetosphere disturbance level will be presented
Weakly nonlinear ion-sound waves in inhomogeneous electron temperature, magnetized plasmas
NASA Astrophysics Data System (ADS)
Pecseli, H. L.; Guio, P.
2009-12-01
Low frequency electrostatic waves are studied in magnetized plasmas for the case where the electron temperature varies with position in a direction perpendicular to the magnetic field. We analyze guided waves with characteristic frequencies below the ion cyclotron and ion plasma frequencies. A Korteweg-deVries equation is derived for the weakly nonlinear waves, and the results compared to numerical simulations. We study two different models for the electron distribution: one where the electrons are assumed to be in local Boltzmann equilibrium at all times, while the other model assumes a nonthermal-distribution for the electrons. The nonlinear space-time evolution of the electrostatic potential differs for the two cases.
Karpman-Washimi magnetization with electron-exchange effects in quantum plasmas
Hong, Woo-Pyo; Jamil, M.; Rasheed, A.; Jung, Young-Dae
2015-07-15
The influence of quantum electron-exchange on the Karpman-Washimi ponderomotive magnetization is investigated in quantum plasmas. The ponderomotive magnetization and the total radiation power due to the non-stationary Karpman-Washimi interaction related to the time-varying field intensity are obtained as functions of the de Broglie wave length, Debye length, and electron-exchange parameter. The result shows that the electron-exchange effect enhances the cyclotron frequency due to the ponderomotive interactions in quantum plasmas. It is also shown that the electron-exchange effect on the Karpman-Washimi magnetization increases with increasing wave number. In addition, the Karpman-Washimi magnetization and the total radiation power increase with an increase in the ratio of the Debye length to the de Broglie wave length. In streaming quantum plasmas, it is shown that the electron-exchange effect enhances the ponderomotive magnetization below the resonant wave number and, however, suppresses the ponderomotive magnetization above the resonant wave number. The variation of the Karpman-Washimi magnetization and the radiation power due to the variation of the electron-exchange effect and plasma parameters is also discussed.
NASA Astrophysics Data System (ADS)
Haas, Fernando; Mahmood, Shahzad
2016-09-01
Nonlinear ion-acoustic waves are analyzed in a nonrelativistic magnetized quantum plasma with arbitrary degeneracy of electrons. Quantum statistics is taken into account by means of the equation of state for ideal fermions at arbitrary temperature. Quantum diffraction is described by a modified Bohm potential consistent with finite-temperature quantum kinetic theory in the long-wavelength limit. The dispersion relation of the obliquely propagating electrostatic waves in magnetized quantum plasma with arbitrary degeneracy of electrons is obtained. Using the reductive perturbation method, the corresponding Zakharov-Kuznetsov equation is derived, describing obliquely propagating two-dimensional ion-acoustic solitons in a magnetized quantum plasma with degenerate electrons having an arbitrary electron temperature. It is found that in the dilute plasma case only electrostatic potential hump structures are possible, while in dense quantum plasma, in principle, both hump and dip soliton structures are obtainable, depending on the electron plasma density and its temperature. The results are validated by comparison with the quantum hydrodynamic model including electron inertia and magnetization effects. Suitable physical parameters for observations are identified.
Acoustic double layer structures in dense magnetized electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Akhtar, N.; Mahmood, S.
2011-11-01
The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.
Acoustic double layer structures in dense magnetized electron-positron-ion plasmas
Akhtar, N.; Mahmood, S.
2011-11-15
The acoustic double layer structures are studied using quantum hydrodynamic model in dense magnetized electron-positron-ion plasmas. The extended Korteweg-de Vries is derived using reductive perturbation method. It is found that increase in the ion concentration in dense magnetized electron-positron plasmas increases the amplitude as well as the steepness of the double layer structure. However, increase in the magnetic field strength and decrease in the obliqueness of the nonlinear acoustic wave enhances only the steepness of the double layer structures. The numerical results have also been shown by using the data of the outer layer regions of white dwarfs given in the literature.
NASA Astrophysics Data System (ADS)
Ruan, Shi-Sen; Wu, Shan; Raissan, Majid; Cheng, Ze
2013-08-01
This article presents the first study of the head-on collision between two magnetoacoustic solitary waves (MASWs) in magnetized quantum plasma consisting of electrons, positrons, and ions, using the extended Poincaré-Lighthill-Kou (PLK) method. The effects of the magnetic field intensity, the positron to ion number density ratio, the quantum parameter, the Fermi temperature ratio, and plasma number density on the solitary wave collisions are investigated. It is shown that these factors significantly modify the phase shift.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
NASA Astrophysics Data System (ADS)
Tinakiche, Nouara; Annou, R.
2015-04-01
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
Oscillating two-stream instability in a magnetized electron-positron-ion plasma
Tinakiche, Nouara; Annou, R.
2015-04-15
Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.
Measurement of hot electron transport in overdense plasma VIA self induced giant magnetic pulses
NASA Astrophysics Data System (ADS)
Mondal, S.; Narayanan, V.; Lad, Amit D.; Ahmed, Saima; Sengupta, S.; Das, A.; Sheng, Z. M.; Kaw, P. K.; Kumar, G. Ravindra
2010-08-01
Spatial and temporal resolved ultrashort(8ps) multimegagauss(65 MG) magnetic field has been measured in plasma produced on Al-coated BK-7 glass by the interaction of a relativististic intensity laser(4x1018W/cm2, 30 fs) using pump-probe polarimetry. The 2D profile of magnetic field is captured using a CCD camera. Mapping of this magnetic field maps the transport of relativistic electrons in the plasma. The magnetic field profiles indicate filamentary behavior (Weibel-like instability). Particle in cell simulation are used to explain the result obtained.
Sadiq, Safeer; Mahmood, S.; Haque, Q.; Ali, Munazza Zulfiqar
2014-09-20
The propagation of electrostatic waves in a dense magnetized electron-positron-ion (EPI) plasma with nonrelativistic and ultrarelativistic degenerate electrons and positrons is investigated. The linear dispersion relation is obtained for slow and fast electrostatic waves in the EPI plasma. The limiting cases for ion acoustic wave (slow) and ion cyclotron wave (fast) are also discussed. Using the reductive perturbation method, two-dimensional propagation of ion acoustic solitons is found for both the nonrelativistic and ultrarelativistic degenerate electrons and positrons. The effects of positron concentration, magnetic field, and mass of ions on ion acoustic solitons are shown in numerical plots. The proper form of Fermi temperature for nonrelativistic and ultrarelativistic degenerate electrons and positrons is employed, which has not been used in earlier published work. The present investigation is useful for the understanding of linear and nonlinear electrostatic wave propagation in the dense magnetized EPI plasma of compact stars. For illustration purposes, we have applied our results to a pulsar magnetosphere.
Experimental study of the hot electron plasma equilibrium in a minimum-B magnetic mirror
NASA Astrophysics Data System (ADS)
Chen, Xing; Lane, B. G.; Smatlak, D. L.; Post, R. S.; Hokin, S. A.
1989-03-01
The Constance B mirror [in Plasma Physics and Controlled Nuclear Fusion Research 1984 (IAEA, Vienna, 1985), Vol. II, p. 285] is a single cell quadrupole magnetic mirror in which high-beta (typically 0.3), hot electron plasmas (Te≂400 keV) are created with up to 4 kW of fundamental electron cyclotron resonance heating (ECRH). Details of the plasma equilibrium profile are quantitatively determined by fitting model plasma pressure profiles to the data from four complementary measurements: diamagnetic loops and magnetic probes, x-ray pinhole cameras, visible light TV cameras, and thermocouple probes. The experimental analysis shows that the equilibrium pressure profile of an ECRH generated plasma in a baseball magnetic mirror is hollow and the plasma is concentrated along a baseball-seam-shaped curve. The hollowness of the hot electron density profile is 50%±10%. The baseball-seam-shaped equilibrium profile coincides with the drift orbit of deeply trapped electrons in the quadrupole mirror field. Particle drift reversal is predicted to occur for the model pressure profile that best fits the experimental data under the typical operating conditions. When the ECRH resonance is just above the magnetic minimum, the plasma pressure closely approaches the mirror mode beta limit.
Tribeche, Mouloud; Bacha, Mustapha
2012-12-15
The combined effects of an oblique magnetic field and electron suprathermality on weak dust-acoustic (DA) waves in a charge varying electronegative dusty plasmas with application to the Halley Comet are investigated. The correct suprathermal electron charging current is derived based on the orbit-motion limited approach. A weakly nonlinear analysis is carried out to derive a Korteweg-de Vries-Burger equation. The electron suprathermality, the obliqueness, and magnitude of the magnetic field are found to modify the dispersive properties of the DA shock structure. Our results may aid to explain and interpret the nonlinear oscillations that may occur in the Halley Comet plasma.
MM-wave emission by magnetized plasma during sub-relativistic electron beam relaxation
Ivanov, I. A. Arzhannikov, A. V.; Burmasov, V. S.; Popov, S. S.; Postupaev, V. V.; Sklyarov, V. F.; Vyacheslavov, L. N.; Burdakov, A. V.; Sorokina, N. V.; Gavrilenko, D. E.; Kasatov, A. A.; Kandaurov, I. V.; Mekler, K. I.; Rovenskikh, A. F.; Trunev, Yu. A.; Kurkuchekov, V. V.; Kuznetsov, S. A.; Polosatkin, S. V.
2015-12-15
There are described electromagnetic spectra of radiation emitted by magnetized plasma during sub-relativistic electron beam in a double plasma frequency band. Experimental studies were performed at the multiple-mirror trap GOL-3. The electron beam had the following parameters: 70–110 keV for the electron energy, 1–10 MW for the beam power and 30–300 μs for its duration. The spectrum was measured in 75–230 GHz frequency band. The frequency of the emission follows variations in electron plasma density and magnetic field strength. The specific emission power on the length of the plasma column is estimated on the level 0.75 kW/cm.
Instability due to trapped electrons in magnetized multi-ion dusty plasmas
NASA Astrophysics Data System (ADS)
Haider, M. M.; Ferdous, T.; Duha, S. S.
2015-05-01
An attempt has been made to find out the effects of trapped electrons in dust-ion-acoustic solitary waves in magnetized multi-ion plasmas, as in most space plasmas, the hot electrons follow the trapped/vortex-like distribution. To do so, we have derived modified Zakharov-Kuznetsov equation using reductive perturbation method and its solution. A small- perturbation technique was employed to find out the instability criterion and growth rate of such a wave.
Wave breaking of nonlinear electron oscillations in a warm magnetized plasma
Pramanik, Sourav; Maity, Chandan; Chakrabarti, Nikhil
2014-02-15
Wave breaking phenomena of nonlinear electron oscillations around a homogeneous background of massive ions have been studied in a warm magnetized plasma by using Lagrangian variables. An inhomogeneity in the background magnetic field is shown to induce phase mixing and thus breaking of the oscillations. A nonlinear analysis in Lagrangian variables predicts that wave breaking may disappear above a critical value of the electron temperature. An estimate for the critical temperature has been provided.
Classical electron-ion scattering in strongly magnetized plasmas. I. A generalized Coulomb logarithm
Geller, D.K.; Weisheit, J.C.
1997-12-01
In a strongly magnetized plasma, where the electron cyclotron radius is less than the Debye length, the Rutherford scattering formula is expected to break down. In this paper, analytic expressions are developed for classical, small-angle scattering of electrons and ions in strong magnetic fields. Numerical evaluation of these expressions shows quantitatively how strong B fields can significantly inhibit electron deflections. The influence of the field on transport phenomena is then explored{emdash}in particular, a generalized Coulomb logarithm which includes the effects of a magnetic field is formulated and computed for a wide range of trajectory pitch angles. This generalized Coulomb logarithm is used to illustrate how a strong field influences the effective electron-ion cross section, the electron velocity diffusion coefficient, and the (parallel) electrical and thermal resistivity in a variety of astrophysical and terrestrial plasmas. {copyright} {ital 1997 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Ruan, Shi-Sen; Cheng, Ze
2013-07-01
In this paper, we study the head-on collision between two electron acoustic solitary waves (EASWs) in magnetized quantum electron-positron-ion plasma. Using the extended Poincaré-Lighthill-Kuo perturbation method, we obtain the Korteweg-de Vries equations, the phase shifts and the trajectories after the head-on collision of the two EASWs. It is found that the phase shifts are significantly affected by the values of the quantum parameter H, the ion to electron number density ratio δ, the electron cyclotron to electron plasma frequency ratio α and the obliqueness θ (propagation angle).
Shikama, T. Hasuo, M.; Kitaoka, H.
2014-07-15
Anisotropy in the electron energy distribution function (EEDF) in an electron cyclotron resonance plasma with magnetized electrons and weakly magnetized ions is experimentally investigated using a directional Langmuir probe. Under an assumption of independent EEDFs in the directions parallel and perpendicular to the magnetic field, the directional variation of the EEDF is evaluated. In the measured EEDFs, a significantly large population density of electrons with energies larger than 30 eV is found in one of the cross-field directions depending on the magnetic field direction. With the aid of an electron trajectory calculation, it is suggested that the observed anisotropic electrons originate from the EEDF anisotropy and the cross-field electron drift.
NASA Astrophysics Data System (ADS)
Mahmood, S.; Sadiq, Safeer; Haque, Q.; Ali, Munazza Z.
2016-06-01
The obliquely propagating arbitrary amplitude electrostatic wave is studied in a dense magnetized plasma having singly and doubly charged helium ions with nonrelativistic and ultrarelativistic degenerate electrons pressures. The Fermi temperature for ultrarelativistic degenerate electrons described by N. M. Vernet [(Cambridge University Press, Cambridge, 2007), p. 57] is used to define ion acoustic speed in ultra-dense plasmas. The pseudo-potential approach is used to solve the fully nonlinear set of dynamic equations for obliquely propagating electrostatic waves in a dense magnetized plasma containing helium ions. The upper and lower Mach number ranges for the existence of electrostatic solitons are found which depends on the obliqueness of the wave propagation with respect to applied magnetic field and charge number of the helium ions. It is found that only compressive (hump) soliton structures are formed in all the cases and only subsonic solitons are formed for a singly charged helium ions plasma case with nonrelativistic degenerate electrons. Both subsonic and supersonic soliton hump structures are formed for doubly charged helium ions with nonrelativistic degenerate electrons and ultrarelativistic degenerate electrons plasma case containing singly as well as doubly charged helium ions. The effect of propagation direction on the soliton amplitude and width of the electrostatic waves is also presented. The numerical plots are also shown for illustration using dense plasma parameters of a compact star (white dwarf) from literature.
Haque, Q.
2015-08-15
The plasma density non-uniformity gives rise to the coupling of transverse magnetic electron drift vortex (MEDV) mode with the longitudinal perturbations in dissipative and non-dissipative electron plasmas. This coupling produces partially transverse and partially longitudinal low frequency instabilities in classical un-magnetized laser plasmas. The MEDV mode couples with the ion acoustic wave, when the ion dynamics is also included. Both the modes have frequencies of the same order of magnitude and couple to give rise to electromagnetic instabilities in un-magnetized plasmas.
Electromagnetic drift waves in nonuniform quantum magnetized electron positron ion plasmas
NASA Astrophysics Data System (ADS)
Ren, Haijun; Wu, Zhengwei; Cao, Jintao; Chu, Paul K.
2008-03-01
Electromagnetic drift waves in a nonuniform quantum magnetized electron positron ion (EPI) plasma are studied. By using the quantum hydrodynamic equations with magnetic fields of the Wigner Maxwell system, we obtained a new dispersion relation in which ions' motions are not considered. The positrons component (featured by the parameter ξ), density gradient of electrons, and of positrons are shown to have a significant impact on the dispersion relation. Our results should be relevant to dense astrophysical objects, e.g. white dwarf and pulsar magnetospheres, as well as low-temperature laboratory EPI plasmas.
Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma
Li, Xiaocan; Guo, Fan; Li, Hui; Li, Gang
2015-09-24
By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.
Nonthermally dominated electron acceleration during magnetic reconnection in a low-β plasma
Li, Xiaocan; Guo, Fan; Li, Hui; Li, Gang
2015-09-24
By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization.more » We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. Thus, the nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.« less
NONTHERMALLY DOMINATED ELECTRON ACCELERATION DURING MAGNETIC RECONNECTION IN A LOW-β PLASMA
Li, Xiaocan; Li, Gang; Guo, Fan; Li, Hui
2015-10-01
By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton–electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-β regime but not in the high-β regime, where β is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-β regime. A guiding-center current description is used to reveal the role of electron drift motions during the bulk nonthermal energization. We find that the main acceleration mechanism is a Fermi-type acceleration accomplished by the particle curvature drift motion along the electric field induced by the reconnection outflows. Although the acceleration mechanism is similar for different plasma β, low-β reconnection drives fast acceleration on Alfvénic timescales and develops power laws out of thermal distribution. The nonthermally dominated acceleration resulting from magnetic reconnection in low-β plasma may have strong implications for the highly efficient electron acceleration in solar flares and other astrophysical systems.
NASA Astrophysics Data System (ADS)
Rafat, A.; Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2016-08-01
Obliquely propagating electron-acoustic solitary waves (EASWs) in a magnetized electron-positron-ion plasma (containing nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions) are precisely investigated by deriving the Zakharov-Kuznetsov equation. It is found that the basic features (viz. polarity, amplitude, width, phase speed, etc.) of the EASWs are significantly modified by the effects of the external magnetic field, obliqueness of the system, nonextensivity of hot positrons and electrons, ratio of the hot electron temperature to the hot positron temperature, and ratio of the cold electron number density to the hot positron number density. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of EASWs in various astrophysical plasmas.
NASA Astrophysics Data System (ADS)
Khan, Shahab Ullah; Adnan, Muhammad; Qamar, Anisa; Mahmood, Shahzad
2016-07-01
The propagation of linear and nonlinear electrostatic waves is investigated in magnetized dusty plasma with stationary negatively or positively charged dust, cold mobile ions and non-extensive electrons. Two normal modes are predicted in the linear regime, whose characteristics are investigated parametrically, focusing on the effect of electrons non-extensivity, dust charge polarity, concentration of dust and magnetic field strength. Using the reductive perturbation technique, a Zakharov-Kuznetsov (ZK) type equation is derived which governs the dynamics of small-amplitude solitary waves in magnetized dusty plasma. The properties of the solitary wave structures are analyzed numerically with the system parameters i.e. electrons non-extensivity, concentration of dust, polarity of dust and magnetic field strength. Following Allen and Rowlands (J. Plasma Phys. 53:63, 1995), we have shown that the pulse soliton solution of the ZK equation is unstable, and have analytically traced the dependence of the instability growth rate on the nonextensive parameter q for electrons, dust charge polarity and magnetic field strength. The results should be useful for understanding the nonlinear propagation of DIA solitary waves in laboratory and space plasmas.
Experimental study of the hot electron plasma equilibrium in a minimum-B magnetic mirror
Chen, X.; Lane, B.G.; Smatlak, D.L.; Post, R.S.; Hokin, S.A.
1989-03-01
The Constance B mirror (in Plasma Physics and Controlled Nuclear Fusion Research 1984 (IAEA, Vienna, 1985), Vol. II, p. 285) is a single cell quadrupole magnetic mirror in which high-beta (typically 0.3), hot electron plasmas (T/sub e/approx. =400 keV) are created with up to 4 kW of fundamental electron cyclotron resonance heating (ECRH). Details of the plasma equilibrium profile are quantitatively determined by fitting model plasma pressure profiles to the data from four complementary measurements: diamagnetic loops and magnetic probes, x-ray pinhole cameras, visible light TV cameras, and thermocouple probes. The experimental analysis shows that the equilibrium pressure profile of an ECRH generated plasma in a baseball magnetic mirror is hollow and the plasma is concentrated along a baseball-seam-shaped curve. The hollowness of the hot electron density profile is 50% +- 10%. The baseball-seam-shaped equilibrium profile coincides with the drift orbit of deeply trapped electrons in the quadrupole mirror field. Particle drift reversal is predicted to occur for the model pressure profile that best fits the experimental data under the typical operating conditions.
Electron dynamics and acceleration study in a magnetized plasma-filled cylindrical waveguide
Kumar, Sandeep; Yoon, Moohyun
2008-01-15
In this article, EH{sub 01} field components are evaluated in a cylindrical waveguide filled with plasma in the presence of external static magnetic field applied along the direction of the mode propagation. The electron acceleration inside the plasma-filled cylindrical waveguide is investigated numerically for a single-electron model. It is found that the electron acceleration is very sensitive to the initial phase of mode-field components, external static magnetic field, plasma density, point of injection of the electron, and microwave power density. The maximum amplitude of the EH{sub 01} mode's field components is approximately 100 times greater than the vacuum-waveguide case for operating microwave frequency f=7.64 GHz, plasma density n{sub 0}=1.08x10{sup 17} m{sup -3}, initial phase angle {phi}{sub 0}=60 deg., and microwave power {approx}14 MW in a cylindrical waveguide with a radius of 2.1 cm. An electron with 100 keV gets 27 MeV energy gain in 2.5 cm along the waveguide length in the presence of external power {approx}14 MW with a microwave frequency of 7.64 GHz. The electron trajectory is also analyzed under the effects of magnetic field when the electron is injected in the waveguide at r=R/2.
Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field
Bobrov, A. A.; Bronin, S. Ya.; Zelener, B. B.; Zelener, B. V.; Manykin, E. A.; Khikhlukha, D. R.
2013-07-15
The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100-50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the 'bottleneck' of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient {alpha}{sub B} has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in {alpha}{sub B} and this decrease can be several orders of magnitude.
Bains, A. S.; Saini, N. S.; Gill, T. S.; Tribeche, Mouloud
2011-10-15
By using the reductive perturbation method (RPM), a nonlinear Zakharov-Kuznetsov (ZK) equation for ion-acoustic solitary waves (IASWs) is derived for a magnetized plasma in which the electrons are nonextensively distributed. The combined effects of electron nonextensivity, strength of magnetic field, and obliqueness on the ion acoustic (IA) solitary profile are analyzed. Three different ranges of the nonextensive q-parameter are considered. It is observed that the system may support both compressive as well as rarefactive solitons. The magnetic field has no effect on the amplitude of solitary waves whereas the obliqueness affects both the amplitude as well as the width of the solitary wave structures.
Oblique shock waves in a two electron temperature superthermally magnetized plasma
NASA Astrophysics Data System (ADS)
Bains, A. S.; Panwar, A.; Ryu, C. M.
2015-11-01
A study is presented for the oblique propagation of low-frequency ion acoustic ( IA) shock waves in a magnetized plasma consisting of cold ions and two temperature superthermally distributed electrons. A nonlinear Korteweg de-Vries-Burger ( KdV-Burger) equation is obtained by using the reductive perturbation method (RPM) which governs the dynamics of the IA shock wave. Using the solution of KdV-Burger equation, the characteristics of the IA shock wave have been studied for various plasma parameters. The combined effects of the cold to hot electron temperature ratio (σ), the density ratio of hot electrons to ions (f), the superthermality of cold and hot electrons (κc, κh), the strength of the magnetic field (ω_{ci}), and the obliqueness (θ), significantly influence the profile of the shock wave. The findings in the present study could be important for the electrostatic wave structures in the Saturn's magnetosphere, where two temperature electrons exist with a kappa distribution.
Emamuddin, M.; Yasmin, S.; Asaduzzaman, M.; Mamun, A. A.
2013-08-15
The nonlinear propagation of dust-acoustic (DA) waves in an obliquely propagating magnetized dusty plasma, containing nonextensively distributed electrons of distinct temperatures (namely lower and higher temperature nonextensive electrons), negatively charged mobile dust grains, and Maxwellian ions, is rigorously studied and analyzed by deriving the Zakharov-Kuznetsov equation. It is found that the characteristics of the DA solitary waves (DASWs) are significantly modified by the external magnetic field, obliqueness of the system, nonextensivity of the electrons, electron temperature-ratios, and the respective number densities of two species of electrons. The results obtained from this analysis can be employed in understanding and treating the structures and the characteristics of DASWs both in laboratory and astrophysical plasma system.
Effects of Anomalous Electron Cross-Field Transport in a Low Temperature Magnetized Plasma
NASA Astrophysics Data System (ADS)
Raitses, Yevgeny
2014-10-01
The application of the magnetic field in a low pressure plasma can cause a spatial separation of low and high energy electrons. This so-called magnetic filter effect is used for many plasma applications, including ion and neutral beam sources, plasma processing of semiconductors and nanomaterials, and plasma thrusters. In spite of successful practical applications, the magnetic filter effect is not well understood. In this work, we explore this effect by characterizing the electron and ion energy distribution functions in a plasma column with crossed electric and magnetic fields. Experimental results revealed a strong dependence of spatial variations of plasma properties on the gas pressure. For xenon and argon gases, below ~ 1 mtorr, the increase of the magnetic field leads to a more uniform profile of the electron temperature. This surprising result is due to anomalously high electron cross-field transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Theory and simulations describing this rotating structure has been developed and points to ionization and electrostatic instabilities as their possible cause. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the large fraction of the cross-field current. The use of segmented electrodes with an electrical feedback control is shown to mitigate these oscillations. Finally, a new feature of the spoke phenomenon that has been discovered, namely a sensitive dependence of the rotating oscillations on the gas pressure, can be important for many applications. This work was supported by DOE Contract DE-AC02-09CH11466.
Soliton Reflection in a Magnetized Cold Plasma having Dust Grains and Trapped Electrons
NASA Astrophysics Data System (ADS)
Malik, Hitendra K.; Singh, Omveer; Dahiya, Raj P.
2012-10-01
A solitary wave is said to be a soliton if it retains its shape after collision with another solitary wave. The solitons get reflected from a boundary or the density gradient present in the plasma. In the present work, the reflection of a soliton is studied in a magnetized cold plasma having dust grains and trapped electrons. Considering the density inhomogeneity in the plasma, we derive relevant modified Korteweg-deVries (mKdV) equations for the right and left going solitary waves and then after coupling these equations at the point of reflection we solve the coupled equation for obtaining the expression for the reflection coefficient based on which the soliton reflection is examined under the effect of magnetic field, dust grain density, and the temperature of trapped electrons. Specifically the role of trapped electrons and dust grains is uncovered for the excitation of solitary waves and their reflection.
Robiche, J.; Rax, J.-M.; Bonnaud, G.; Gremillet, L.
2010-03-15
The collisional dynamics of a relativistic electron jet in a magnetized plasma are investigated within the framework of kinetic theory. The relativistic Fokker-Planck equation describing slowing down, pitch angle scattering, and cyclotron rotation is derived and solved. Based on the solution of this Fokker-Planck equation, an analytical formula for the root mean square spot size transverse to the magnetic field is derived and this result predicts a reduction in radial transport. Some comparisons with particle-in-cell simulation are made and confirm striking agreement between the theory and the simulation. For fast electron with 1 MeV typical kinetic energy interacting with a solid density hydrogen plasma, the energy deposition density in the transverse direction increases by a factor 2 for magnetic field of the order of 1 T. Along the magnetic field, the energy deposition profile is unaltered compared with the field-free case.
NASA Astrophysics Data System (ADS)
Popov, Tsv K.; Dimitrova, M.; Ivanova, P.; Kovačič, J.; Gyergyek, T.; Dejarnac, R.; Stöckel, J.; Pedrosa, M. A.; López-Bruna, D.; Hidalgo, C.
2016-06-01
Advanced Langmuir probe techniques for evaluating the plasma potential and electron-energy distribution function (EEDF) in magnetized plasma are reviewed. It is shown that when the magnetic field applied is very weak and the electrons reach the probe without collisions in the probe sheath the second-derivative Druyvesteyn formula can be used for EEDF evaluation. At low values of the magnetic field, an extended second-derivative Druyvesteyn formula yields reliable results, while at higher values of the magnetic field, the first-derivative probe technique is applicable for precise evaluation of the plasma potential and the EEDF. There is an interval of intermediate values of the magnetic field when both techniques—the extended second-derivative and the first-derivative one—can be used. Experimental results from probe measurements in different ranges of magnetic field are reviewed and discussed: low-pressure argon gas discharges in the presence of a magnetic field in the range from 0.01 to 0.08 T, probe measurements in circular hydrogen plasmas for high-temperature fusion (magnetic fields from 0.45 T to 1.3 T) in small ISTTOK and CASTOR tokamaks, D-shape COMPASS tokamak plasmas, as well as in the TJ-II stellarator. In the vicinity of the last closed flux surface (LCFS) in tokamaks and in the TJ-II stellarator, the EEDF obtained is found to be bi-Maxwellian, while close to the tokamak chamber wall it is Maxwellian. The mechanism of the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is discussed. Comparison of the results from probe measurements with those obtained from calculations using the ASTRA and EIRENE codes shows that the main reason for the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is the ionization of the neutral atoms.
Matched dipole probe for magnetized low electron density laboratory plasma diagnostics
Rafalskyi, Dmytro; Aanesland, Ane
2015-07-15
In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (10{sup 12}–10{sup 15 }m{sup −3}), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10 cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B ∼ 170 G) and unmagnetized (B = 0) low density (7 × 10{sup 12 }m{sup −3}–7 × 10{sup 13 }m{sup −3}) low pressure (1 mTorr) 10 cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7 × 10{sup 12 }m{sup −3}–7 × 10{sup 13 }m{sup −3} show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2 × 10{sup 13 }m{sup −3}. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling.
Matched dipole probe for magnetized low electron density laboratory plasma diagnostics
NASA Astrophysics Data System (ADS)
Rafalskyi, Dmytro; Aanesland, Ane
2015-07-01
In this paper, a diagnostic method for magnetized and unmagnetized laboratory plasma is proposed, based on impedance measurements of a short matched dipole. The range of the measured electron densities is limited to low density plasmas (1012-1015 m-3), where other diagnostic methods have strong limitations on the magnetic field strength and topology, plasma dimensions, and boundary conditions. The method is designed for use in both large- and small-dimension plasma (<10 cm) without or with strong non-homogeneous magnetic field, which can be undefined within the probe size. The design of a matched dipole probe allows to suppress the sheath resonance effects and to reach high sensitivity at relatively small probe dimensions. Validation experiments are conducted in both magnetized (B ˜ 170 G) and unmagnetized (B = 0) low density (7 × 1012 m-3-7 × 1013 m-3) low pressure (1 mTorr) 10 cm scale plasmas. The experimentally measured data show very good agreement with an analytical theory both for a non-magnetized and a magnetized case. The electron density measured by the matched dipole and Langmuir probes in the range of 7 × 1012 m-3-7 × 1013 m-3 show less than 30% difference. An experimentally measured tolerance/uncertainty of the dipole probe method is estimated to ±1% for plasma densities above 2 × 1013 m-3. A spatial resolution is estimated from the experiments to be about 3d, where d is the dipole diameter. The diagnostic method is also validated by comparing the measured plasma impedance curves with results of analytical modelling.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
Khan, S. A.; Masood, W.
2008-06-15
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
Linear and nonlinear quantum ion-acoustic waves in dense magnetized electron-positron-ion plasmas
NASA Astrophysics Data System (ADS)
Khan, S. A.; Masood, W.
2008-06-01
The linear and nonlinear quantum ion-acoustic waves propagating obliquely in two dimensions in superdense, magnetized electron-positron-ion quantum plasma are investigated on the basis of quantum hydrodynamic model. It is found in linear analysis that the quantum corrections of diffraction are important in the very short wavelength regime that may be found in dense astrophysical plasmas. To investigate the solitary waves, the Zakharov-Kuznetsov equation is derived and the solution is presented in the small amplitude limit. By numerical analysis, it is found that the soliton structure of the ion acoustic wave depends upon quantum pressure, concentration of positrons, strength of magnetic field, and the propagation angle.
NASA Astrophysics Data System (ADS)
Thomas, M. B.; Rafalskyi, D.; Lafleur, T.; Aanesland, A.
2016-08-01
In this paper we experimentally investigate the \\mathbf{E}× \\mathbf{B} drift of electrons in low temperature plasmas containing a magnetic field barrier; a plasma configuration commonly used in gridded negative ion sources. A planar Langmuir probe array is developed to quantify the \\mathbf{E}× \\mathbf{B} drift of electrons over the cross-section of the ion-extraction region of an ion–ion plasma source. The drift is studied as a function of pressure using both electropositive plasmas (Ar), as well electronegative plasmas (Ar and SF6 mixtures), and is demonstrated to result from an interaction of the applied magnetic field and the electric fields in the sheath and pre-sheath near the transverse boundaries. The drift enhances electron transport across the magnetic field by more than two orders of magnitude compared with simple collisional transport, and is found to be strongly dependant on pressure. The lowest pressure resulted in the highest influence of the drift across the extraction area and is found to be 30%.
NASA Astrophysics Data System (ADS)
Thomas, M. B.; Rafalskyi, D.; Lafleur, T.; Aanesland, A.
2016-08-01
In this paper we experimentally investigate the \\mathbf{E}× \\mathbf{B} drift of electrons in low temperature plasmas containing a magnetic field barrier; a plasma configuration commonly used in gridded negative ion sources. A planar Langmuir probe array is developed to quantify the \\mathbf{E}× \\mathbf{B} drift of electrons over the cross-section of the ion-extraction region of an ion-ion plasma source. The drift is studied as a function of pressure using both electropositive plasmas (Ar), as well electronegative plasmas (Ar and SF6 mixtures), and is demonstrated to result from an interaction of the applied magnetic field and the electric fields in the sheath and pre-sheath near the transverse boundaries. The drift enhances electron transport across the magnetic field by more than two orders of magnitude compared with simple collisional transport, and is found to be strongly dependant on pressure. The lowest pressure resulted in the highest influence of the drift across the extraction area and is found to be 30%.
Nonthermal Electron Energization from Magnetic Reconnection in Laser-Driven Plasmas.
Totorica, Samuel R; Abel, Tom; Fiuza, Frederico
2016-03-01
The possibility of studying nonthermal electron energization in laser-driven plasma experiments of magnetic reconnection is studied using two- and three-dimensional particle-in-cell simulations. It is demonstrated that nonthermal electrons with energies more than an order of magnitude larger than the initial thermal energy can be produced in plasma conditions currently accessible in the laboratory. Electrons are accelerated by the reconnection electric field, being injected at varied distances from the X points, and in some cases trapped in plasmoids, before escaping the finite-sized system. Trapped electrons can be further energized by the electric field arising from the motion of the plasmoid. This acceleration gives rise to a nonthermal electron component that resembles a power-law spectrum, containing up to ∼8% of the initial energy of the interacting electrons and ∼24% of the initial magnetic energy. Estimates of the maximum electron energy and of the plasma conditions required to observe suprathermal electron acceleration are provided, paving the way for a new platform for the experimental study of particle acceleration induced by reconnection. PMID:26991182
Electron cooling and finite potential drop in a magnetized plasma expansion
Martinez-Sanchez, M.; Navarro-Cavallé, J.; Ahedo, E.
2015-05-15
The steady, collisionless, slender flow of a magnetized plasma into a surrounding vacuum is considered. The ion component is modeled as mono-energetic, while electrons are assumed Maxwellian upstream. The magnetic field has a convergent-divergent geometry, and attention is restricted to its paraxial region, so that 2D and drift effects are ignored. By using the conservation of energy and magnetic moment of particles and the quasi-neutrality condition, the ambipolar electric field and the distribution functions of both species are calculated self-consistently, paying attention to the existence of effective potential barriers associated to magnetic mirroring. The solution is used to find the total potential drop for a set of upstream conditions, plus the axial evolution of various moments of interest (density, temperatures, and heat fluxes). The results illuminate the behavior of magnetic nozzles, plasma jets, and other configurations of interest, showing, in particular, in the divergent plasma the collisionless cooling of electrons, and the generation of collisionless electron heat fluxes.
Low-Frequency Electrostatic Ion Surface Waves in Magnetized Electron-Positron Plasmas
NASA Astrophysics Data System (ADS)
Cho, Sang-Hoon; Lee, Hee J.
The dispersion relations of a surface ion wave propagating on the interface between a warm electron-positron plasma and vacuum when a static magnetic field is directed either normal to the interface (x-wave) or parallel to the wave vector (z-wave) are solved analytically, and the influence of the magnetic field on the ion surface wave is investigated in detail using some numerical work. It is shown that ion surface waves do not exist if the magnetic field is large enough to make the ion gyrofrequency greater than the ion plasma frequency. The attenuation constant of x-waves is more attenuated than that of z-waves and the x-wave is more attenuated as the parameter normalized ion gyrofrequency ζ increases toward 1, but this tendency is reversed for the z-wave. The z-wave does not exist for k2λD2< (ζ/(1-ζ))(p + 1) while the x-wave exists over the whole range of k, where the fractional number p is the ratio between the unperturbed positron and the electron number density. Additionally, we compare the ion surface wave properties of electron-positron plasma with conventional electron-ion plasma.
Ion-acoustic double-layers in a magnetized plasma with nonthermal electrons
Rios, L. A.; Galvão, R. M. O.
2013-11-15
In the present work we investigate the existence of obliquely propagating ion-acoustic double layers in magnetized two-electron plasmas. The fluid model is used to describe the ion dynamics, and the hot electron population is modeled via a κ distribution function, which has been proved to be appropriate for modeling non-Maxwellian plasmas. A quasineutral condition is assumed to investigate these nonlinear structures, which leads to the formation of double-layers propagating with slow ion-acoustic velocity. The problem is investigated numerically, and the influence of parameters such as nonthermality is discussed.
Propagation of a nonrelativistic electron beam in a plasma in a magnetic field
Okuda, H.; Horton, R.; Ono, M.; Ashour-Abdalla, M.
1986-10-01
Propagation of a nonrelativistic electron beam in a plasma in a strong magnetic field has been studied using electrostatic one-dimensional particle simulation models. Electron beams of finite pulse length and of continuous injection are followed in time to study the effects of beam-plasma interaction on the beam propagation. For the case of pulsed beam propagation, it is found that the beam distribution rapidly spreads in velocity space generating a plateaulike distribution with a high energy tail extending beyond the initial beam velocity.
Weening, R. H.
2012-06-15
In order to model the effects of small-scale current-driven magnetic fluctuations in a mean-field theoretical description of a large-scale plasma magnetic field B(x,t), a space and time dependent hyper-resistivity {Lambda}(x,t) can be incorporated into the Ohm's law for the parallel electric field E Dot-Operator B. Using Boozer coordinates, a theoretical method is presented that allows for a determination of the hyper-resistivity {Lambda}({psi}) functional dependence on the toroidal magnetic flux {psi} for arbitrary experimental steady-state Grad-Shafranov axisymmetric plasma equilibria, if values are given for the parallel plasma resistivity {eta}({psi}) and the local distribution of any auxiliary plasma current. Heat transport in regions of plasma magnetic surfaces destroyed by resistive tearing modes can then be modeled by an electron thermal conductivity k{sub e}({psi})=({epsilon}{sub 0}{sup 2}m{sub e}/e{sup 2}){Lambda}({psi}), where e and m{sub e} are the electron charge and mass, respectively, while {epsilon}{sub 0} is the permittivity of free space. An important result obtained for axisymmetric plasma equilibria is that the {psi}{psi}-component of the metric tensor of Boozer coordinates is given by the relation g{sup {psi}{psi}}({psi}){identical_to}{nabla}{psi} Dot-Operator {nabla}{psi}=[{mu}{sub 0}G({psi})][{mu}{sub 0}I({psi})]/{iota}({psi}), with {mu}{sub 0} the permeability of free space, G({psi}) the poloidal current outside a magnetic surface, I({psi}) the toroidal current inside a magnetic surface, and {iota}({psi}) the rotational transform.
Electronic transport of Lorentz plasma with collision and magnetic field effects
NASA Astrophysics Data System (ADS)
Lv, Chong; Wan, Feng; Jia, Mo-Ran; Li, Zi-Liang; Sang, Hai-Bo; Xie, Bai-Song
2016-10-01
The electronic transverse transport of Lorentz plasma with collision and magnetic field effects is studied by solving the Boltzmann equation for different electron density distributions. For the Maxwellian distribution, it is shown that transport coefficients decrease as Ω increases, Ω is the ratio of an electron’s magneto-cyclotron frequency to plasma collision frequency. It means that the electrons are possible to be highly collimated by a strong magnetic field. For the quasi-monoenergetic distribution with different widths, it is found that the transport coefficients decrease greatly as ɛ¯ decreases. In particular when the width approaches to zero the transverse transport coefficients are hardly affected by the magnetic field and the minimal one is obtained. Results imply that the strong magnetic field and quasi-monoenergetic distribution are both beneficial to reduce the electronic transverse transport. This study is also helpful to understand the relevant problems of plasma transport in the background of the inertial confinement fusion. Project supported by the National Natural Science Foundation of China (Grant Nos. 11475026 and 11305010) and the NSAF of China (Grant No. U1530153).
Effect of the q-nonextensive electron velocity distribution on a magnetized plasma sheath
Safa, N. Navab Ghomi, H.; Niknam, A. R.
2014-08-15
In this work, a sheath model has been developed to investigate the effect of the q-nonextensive electron velocity distribution on the different characteristics of a magnetized plasma. By using Segdeev potential method, a modified Bohm criterion for a magnetized plasma with the nonextensive electron velocity distribution is derived. The sheath model is then used to analyze numerically the sheath structure under different q, the parameter quantifying the nonextensivity degree of the system. The results show that as the q-parameter decreases, the floating potential becomes more negative. The sheath length increases at the lower values of the q-parameter due to the increase in the electron population at the high-energy tail of the distribution function. As q-parameter decreases, the effective temperature of the electrons increases which results in a more extended plasma sheath. The ion velocity and density profiles for the different nonextensivity degrees of the system reflect the gyro-motion of the ions in the presence of the magnetic field. Furthermore, the results coincide with those given by the Maxwellian electron distribution function, when q tends to 1.
Threefold Increase of the Bulk Electron Temperature of Plasma Discharges in a Magnetic Mirror Device
NASA Astrophysics Data System (ADS)
Bagryansky, P. A.; Shalashov, A. G.; Gospodchikov, E. D.; Lizunov, A. A.; Maximov, V. V.; Prikhodko, V. V.; Soldatkina, E. I.; Solomakhin, A. L.; Yakovlev, D. V.
2015-05-01
This Letter describes plasma discharges with a high temperature of bulk electrons in the axially symmetric high-mirror-ratio (R =35 ) open magnetic system gas dynamic trap (GDT) in the Budker Institute (Novosibirsk). According to Thomson scattering measurements, the on-axis electron temperature averaged over a number of sequential shots is 660 ±50 eV with the plasma density being 0.7 ×1 019 m-3 ; in few shots, electron temperature exceeds 900 eV. This corresponds to at least a threefold increase with respect to previous experiments both at GDT and at other comparable machines, thus, demonstrating the highest quasistationary (about 1 ms) electron temperature achieved in open traps. The breakthrough is made possible by application of a new 0.7 MW /54.5 GHz electron cyclotron resonance heating system in addition to standard 5 MW heating by neutral beams, and application of a radial electric field to mitigate the flute instability.
Rufai, O. R. Bharuthram, R.; Singh, S. V. Lakhina, G. S.
2014-08-15
Arbitrary amplitude, ion acoustic solitons, and supersolitons are studied in a magnetized plasma with two distinct groups of electrons at different temperatures. The plasma consists of a cold ion fluid, cool Boltzmann electrons, and nonthermal energetic hot electrons. Using the Sagdeev pseudo-potential technique, the effect of nonthermal hot electrons on soliton structures with other plasma parameters is studied. Our numerical computation shows that negative potential ion-acoustic solitons and double layers can exist both in the subsonic and supersonic Mach number regimes, unlike the case of an unmagnetized plasma where they can only exist in the supersonic Mach number regime. For the first time, it is reported here that in addition to solitions and double layers, the ion-acoustic supersoliton solutions are also obtained for certain range of parameters in a magnetized three-component plasma model. The results show good agreement with Viking satellite observations of the solitary structures with density depletions in the auroral region of the Earth's magnetosphere.
NASA Astrophysics Data System (ADS)
Adnan, Muhammad; Williams, Gina; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis
2014-09-01
The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.
Effects of dust contamination on the transverse dynamics of a magnetized electron plasma
Romé, M.; Cavaliere, F.; Maero, G.; Cavenago, M.; Chen, S.
2015-06-29
Complex (dusty) plasmas are characterized by the presence of a fraction of micrometric or sub-micrometric particles which may collect a surface charge up to the order of a few thousand electron charges. The dusty plasmas studied in the experiments generally satisfy a global neutrality condition. By contrast, we present here the investigation of a magnetized nonneutral plasma, i.e., a plasma with a single sign of charge (e.g. electrons) confined in a Penning-Malmberg trap, contaminated by a dust population. We simulate the two-dimensional transverse dynamics of this multi-component plasma with a particle-in-cell code implementing a mass-less fluid (drift-Poisson) approximation for the electrons and a kinetic description for the dust component (including gravity). Simulations with different initial dust distributions and densities have been performed in order to investigate the influence of the dust on the development of the diocotron instability in the electron plasma. In particular, the early stage of the growth of the diocotron modes has been analyzed by Fourier decomposition.
NASA Astrophysics Data System (ADS)
Singh, Satyavir; Bharuthram, Ramashwar
2016-07-01
Small amplitude electron acoustic solitary waves are studied in a magnetized plasma consisting of hot electrons following Cairn's type non-thermal distribution function and fluid cool electrons, cool ions and an electron beam. Using reductive perturbation technique, the Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) equation is derived to describe the nonlinear evolution of electron acoustic waves. It is observed that the presence of non-thermal electrons plays an important role in determining the existence region of solitary wave structures. Theoretical results of this work is used to model the electrostatic solitary structures observed by Viking satellite. Detailed investigation of physical parameters such as non-thermality of hot electrons, beam electron velocity and temperature, obliquity on the existence regime of solitons will be discussed.
Electron acoustic waves in a magnetized plasma with kappa distributed ions
Devanandhan, S.; Lakhina, G. S.; Singh, S. V.; Bharuthram, R.
2012-08-15
Electron acoustic solitary waves in a two component magnetized plasma consisting of fluid cold electrons and hot superthermal ions are considered. The linear dispersion relation for electron acoustic waves is derived. In the nonlinear regime, the energy integral is obtained by a Sagdeev pseudopotential analysis, which predicts negative solitary potential structures. The effects of superthermality, obliquity, temperature, and Mach number on solitary structures are studied in detail. The results show that the superthermal index {kappa} and electron to ion temperature ratio {sigma} alters the regime where solitary waves can exist. It is found that an increase in magnetic field value results in an enhancement of soliton electric field amplitude and a reduction in soliton width and pulse duration.
Zakharov-Kuznetsov equation in a magnetized plasma with two temperature superthermal electrons
Saini, N. S. Chahal, B. S.; Bains, A. S.; Bedi, C.
2014-02-15
A nonlinear Zakharov-Kuznetsov (ZK) equation for ion-acoustic solitary waves (IASWs) in a magnetized plasmas containing kappa distributed cold and hot electrons is derived by using reductive perturbation method. From the solution of ZK equation, the characteristics of IASWs have been studied under the influence of various plasma parameters. Existence domain of physical parameters is determined. It has been observed that the present plasma system supports the existence of both positive as well as negative potential solitons. The combined effects of cold to hot electron temperature ratio (σ), density ratio of cold electrons to ions (f), superthermality of cold and hot electrons (κ{sub c},κ{sub h}), strength of magnetic field (via Ω{sub i}), and obliqueness (θ) significantly influence the profile of IASWs. The physical parameters play a great role to modify the width and amplitude of the solitary structures. The stability analysis is also presented in this investigation and parametric range is determined to check the presence of stable and unstable solitons. The findings of this study are important to the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature electrons with kappa distribution exist.
Wang, Jian-Yong; Cheng, Xue-Ping; Tang, Xiao-Yan; Yang, Jian-Rong; Ren, Bo
2014-03-15
The oblique propagation of ion-acoustic soliton-cnoidal waves in a magnetized electron-positron-ion plasma with superthermal electrons is studied. Linear dispersion relations of the fast and slow ion-acoustic modes are discussed under the weak and strong magnetic field situations. By means of the reductive perturbation approach, Korteweg-de Vries equations governing ion-acoustic waves of fast and slow modes are derived, respectively. Explicit interacting soliton-cnoidal wave solutions are obtained by the generalized truncated Painlevé expansion. It is found that every peak of a cnoidal wave elastically interacts with a usual soliton except for some phase shifts. The influence of the electron superthermality, positron concentration, and magnetic field obliqueness on the soliton-cnoidal wave are investigated in detail.
Kinetic Alfven solitary waves in a magnetized plasma with superthermal electrons
Panwar, A. E-mail: ryu201@postech.ac.kr Ryu, C. M. E-mail: ryu201@postech.ac.kr; Bains, A. S. E-mail: ryu201@postech.ac.kr
2015-09-15
A study of the ion Larmor radius effects on the solitary kinetic Alfven waves (SKAWs) in a magnetized plasma with superthermal electrons is presented by employing the kinetic theory. The linear dispersion relation of SKAW is shown to depend on the superthermal parameter κ, ion to electron temperature ratio, and the angle of wave propagation. Using the Sagdeev potential approach, the energy balance equation has been derived to study the dynamics of SKAWs. The effects of various plasma parameters are investigated for the propagation of SKAWs. It is shown that only compressive solitons can exist and in the Maxwellian limit our results are in good agreement with previous studies. Further, the characteristics of small amplitude SKAWs are investigated. Present study could be useful for the understanding of SKAWs in a low β plasma in astrophysical environment, where particle distributions are superthermal in nature.
Bains, A. S.; Gill, T. S.; Misra, A. P.; Saini, N. S.
2010-01-15
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schroedinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (mu), the normalized ion-cyclotron frequency (omega{sub c}) as well as the ratio (H) of the 'plasmonic energy density' to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing mu or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
Oblique propagation of ion-acoustic solitary waves in a magnetized electron-positron-ion plasma
Ferdousi, M.; Sultana, S.; Mamun, A. A.
2015-03-15
The properties of obliquely propagating ion-acoustic solitary waves in the presence of ambient magnetic field have been investigated theoretically in an electron-positron-ion nonthermal plasma. The plasma nonthermality is introduced via the q-nonextensive distribution of electrons and positrons. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations are derived by adopting reductive perturbation method. The solution of K-dV and modified K-dV equation, which describes the solitary wave characteristics in the long wavelength limit, is obtained by steady state approach. It is seen that the electron and positron nonextensivity and external magnetic field (obliqueness) have significant effects on the characteristics of solitary waves. A critical value of nonextensivity is found for which solitary structures transit from positive to negative potential. The findings of this investigation may be used in understanding the wave propagation in laboratory and space plasmas where static external magnetic field is present.
Small amplitude electron acoustic solitary waves in a magnetized superthermal plasma
NASA Astrophysics Data System (ADS)
Devanandhan, S.; Singh, S. V.; Lakhina, G. S.; Bharuthram, R.
2015-05-01
The propagation of electron acoustic solitary waves in a magnetized plasma consisting of fluid cold electrons, electron beam and superthermal hot electrons (obeying kappa velocity distribution function) and ion is investigated in a small amplitude limit using reductive perturbation theory. The Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) equation governing the dynamics of electron acoustic solitary waves is derived. The solution of the KdV-ZK equation predicts the existence of negative potential solitary structures. The new results are: (1) increase of either the beam speed or temperature of beam electrons tends to reduce both the amplitude and width of the electron acoustic solitons, (2) the inclusion of beam speed and temperature pushes the allowed Mach number regime upwards and (3) the soliton width maximizes at certain angle of propagation (αm) and then decreases for α >αm . In addition, increasing the superthermality of the hot electrons also results in reduction of soliton amplitude and width. For auroral plasma parameters observed by Viking, the obliquely propagating electron-acoustic solitary waves have electric field amplitudes in the range (7.8-45) mV/m and pulse widths (0.29-0.44) ms. The Fourier transform of these electron acoustic solitons would result in a broadband frequency spectra with peaks near 2.3-3.5 kHz, thus providing a possible explanation of the broadband electrostatic noise observed during the Burst a.
Phase-mixing of electrostatic modes in a cold magnetized electron-positron plasma
Maity, Chandan; Chakrabarti, Nikhil
2013-08-15
In a fluid description, we study space-time evolution of electrostatic oscillations in a cold magnetized electron-positron plasma. Nonlinear results up to third order, obtained by employing a simple perturbation technique, indicate phase-mixing and thus breaking of excited oscillations, and provide an expression for the phase-mixing time. It is shown that an increase in the strength of ambient magnetic field results in an increase in the phase-mixing time. The results of our investigation will be of relevance to astrophysical environments as well as laboratory experiments.
Chu, T.K.
1987-12-01
The interplay of electron cross-field thermal conduction and the reconnection of magnetic field lines around an m = 1 magnetic island prior to a sawtooth crash can generate a large pressure gradient in a boundary layer adjacent to the reconnecting surface, leading to an enhanced gradient of poloidal beta to satisfy the threshold condition for ideal MHD modes. This narrow boundary layer and the short onset time of a sawtooth crash can be supported by fine-grained turbulent processes in a tokamak plasma. 11 refs.
Electron density and temperature measurements in a magnetized expanding hydrogen plasma
NASA Astrophysics Data System (ADS)
Leyte-González, R.; Palomares, J. M.; Schram, D. C.; Engeln, R.
2016-08-01
We report measurements of electron densities, ne, and temperatures, Te, in a magnetized expanding hydrogen plasma performed using Thomson scattering. The effects of applying an axial magnetic field and changing the background pressure in the plasma vessel on ne and Te along the expansion axis are reported. Magnetic field strengths (B field) up to 170 mT were applied, which are one order of magnitude larger than previously reported. The main effect of the applied B field is the plasma confinement, which leads to higher ne. At B fields larger than 88 mT the electron density along the expansion axis does not depend strongly on the magnetic field strength. However, Te is susceptible to the B field and reaches at 170 mT a maximum of 2.5 eV at a distance of 1.5 cm from the exit of the cascaded arc. To determine also the effect of the arc current through the arc, measurements were performed with arc currents of 45, 60, and 75 A at background pressures of 9.7 and 88.3 Pa. At constant magnetic field ne decreases from the exit of the arc along the expansion axis when the arc current is decreased. At 88.3 Pa ne shows a higher value close to the exit of the arc, but a faster decay along the expansion axis with respect to the 9.7 Pa case. Te is overall higher at lower pressure reaching a maximum of 3.2 eV at the lower arc current of 45 A. The results of this study complement our understanding and the characterization of expanding hydrogen plasmas.
Electron density and temperature measurements in a magnetized expanding hydrogen plasma.
Leyte-González, R; Palomares, J M; Schram, D C; Engeln, R
2016-08-01
We report measurements of electron densities, n_{e}, and temperatures, T_{e}, in a magnetized expanding hydrogen plasma performed using Thomson scattering. The effects of applying an axial magnetic field and changing the background pressure in the plasma vessel on n_{e} and T_{e} along the expansion axis are reported. Magnetic field strengths (B field) up to 170 mT were applied, which are one order of magnitude larger than previously reported. The main effect of the applied B field is the plasma confinement, which leads to higher n_{e}. At B fields larger than 88 mT the electron density along the expansion axis does not depend strongly on the magnetic field strength. However, T_{e} is susceptible to the B field and reaches at 170 mT a maximum of 2.5 eV at a distance of 1.5 cm from the exit of the cascaded arc. To determine also the effect of the arc current through the arc, measurements were performed with arc currents of 45, 60, and 75 A at background pressures of 9.7 and 88.3 Pa. At constant magnetic field n_{e} decreases from the exit of the arc along the expansion axis when the arc current is decreased. At 88.3 Pa n_{e} shows a higher value close to the exit of the arc, but a faster decay along the expansion axis with respect to the 9.7 Pa case. T_{e} is overall higher at lower pressure reaching a maximum of 3.2 eV at the lower arc current of 45 A. The results of this study complement our understanding and the characterization of expanding hydrogen plasmas. PMID:27627401
Sahu, Biswajit; Sinha, Anjana; Roychoudhury, Rajkumar
2015-09-15
A numerical study is presented of the nonlinear dynamics of a magnetized, cold, non-relativistic plasma, in the presence of electron-ion collisions. The ions are considered to be immobile while the electrons move with non-relativistic velocities. The primary interest is to study the effects of the collision parameter, external magnetic field strength, and the initial electromagnetic polarization on the evolution of the plasma system.
Fluctuations in electron cyclotron resonance plasma in a divergent magnetic field
NASA Astrophysics Data System (ADS)
Bhattacharjee, Sudeep; Fredriksen, Åshild; Chandra, Sayan
2016-02-01
The dependence of fluctuations on electron-neutral collision frequency (νen) and the radial location is investigated in an electron cyclotron resonance plasma in a divergent magnetic field region for a set of magnetic fields. Results indicate that the fluctuations depend strongly on the collision frequency. At lower magnetic fields and νen, the fluctuation levels are small and are observed to peak around 3-5 cm from the central plasma region. Coherent wave modes are found to contribute up to about 30% of the total fluctuation power, and two to three harmonics are present in the power spectra. There are two principal modes present in the discharge: one appears to be a dissipative mode associated with a collisional drift wave instability initiated at a lower pressure (collision frequencies) (˜0.5 mTorr) and is stabilized at a higher pressure (≳3 mTorr). The other mode appears at intermediate pressure (≳1.75 mTorr) and possesses the signature of a flute instability. The fluctuation levels indicate that flute modes are predominant in the discharge at higher pressures ( >1.75 mTorr) and at higher values of the magnetic field (˜540 Gauss).
NASA Astrophysics Data System (ADS)
Grishanov, N. I.; Azarenkov, N. A.
2016-08-01
> Dispersion characteristics have been analysed for field-aligned electron-cyclotron waves (also known as right-hand polarized waves, extraordinary waves or whistlers) in a cylindrical magnetic mirror plasma including electrons with anisotropic temperature. It is shown that the instability of these waves is possible only in the range below the minimal electron-cyclotron frequency, which is much lower than the gyrotron frequency used for electron-cyclotron resonance power input into the plasma, under the condition where the perpendicular temperature of the resonant electrons is larger than their parallel temperature. The growth rates of whistler instability in the two magnetized plasma models, where the stationary magnetic field is either uniform or has a non-uniform magnetic mirror configuration, are compared.
Lee, H. C.; Jiang, T. F.
2010-11-15
We analytically solve the relativistic equation of motion for an electron in ion plasma channels and calculate the corresponding trajectory as well as the synchrotron radiation. The relativistic effect on a trajectory is strong, i.e., many high-order harmonic terms in the trajectory, when the ratio of the initial transverse velocity (v{sub x0}) to the longitudinal velocity (v{sub z0}) of the electron injected to ion plasma channels is high. Interestingly, these high-order harmonic terms result in a quite broad and intense radiation spectrum, especially at an oblique angle, in contrast to an earlier understanding. As the initial velocity ratio (v{sub x0}:v{sub z0}) decreases, the relativistic effect becomes weak; only the first and second harmonic terms remain in the transverse and longitudinal trajectories, respectively, which coincides with the result of Esarey et al. [Phys. Rev. E 65, 056505 (2002)]. Our formalism also allows the description of electron's trajectory in the presence of an applied magnetic field. Critical magnetic fields for cyclotron motions are figured out and compared with semiclassical results. The cyclotron motion leads to more high-order harmonic terms than the trajectory without magnetic fields and causes an immensely broad spectrum with vastly large radiation amplitude for high initial velocity ratios (v{sub x0}:v{sub z0}). The radiation from hard x-ray to gamma-ray regions can be generated with a broad radiation angle, thus available for applications.
Low frequency solitons and double layers in a magnetized plasma with two temperature electrons
Rufai, O. R.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.
2012-12-15
Finite amplitude non-linear ion-acoustic solitary waves and double layers are studied in a magnetized plasma with cold ions fluid and two distinct groups of Boltzmann electrons, using the Sagdeev pseudo-potential technique. The conditions under which the solitary waves and double layers can exist are found both analytically and numerically. We have shown the existence of negative potential solitary waves and double layers for subsonic Mach numbers, whereas in the unmagnetized plasma they can only in the supersonic Mach number regime. For the plasma parameters in the auroral region, the electric field amplitude of the solitary structures comes out to be 49 mV/m which is in agreement of the Viking observations in this region.
Ren, Yang; Yamada, Masaaki; Ji, Hantao; Dorfman, Seth; Gerhardt, Stefan; Kulsrud, Russel
2008-07-02
The Hall effect during magnetic reconnection without an external guide field has been extensively studied in the laboratory plasma of the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)] by measuring its key signature, an out-of-plane quadrupole magnetic field, with magnetic probe arrays whose spatial resolution is on the order of the electron skin depth. The in-plane electron flow is deduced from out-of-plane magnetic field measurements. The measured in-plane electron flow and numerical results are in good agreement. The electron diffusion region is identified by measuring the electron outflow channel. The width of the electron diffusion region scales with the electron skin depth (~ 8c/ωpe) and the peak electron outflow velocity scales with the electron Alfven velocity (~ 0:11VeA), independent of ion mass. The measured width of the electron diffusion region is much wider and the observed electron outflow is much slower than those obtained in 2D numerical simulations. It is found that the classical and anomalous dissipation present in the experiment can broaden the electron diffusion region and slow the electron outflow. As a consequence, the electron outflow flux remain consistent with numerical simulations. The ions, as measured by a Mach probe, have a much wider outflow channel than the electrons, and their outflow is much slower than the electron outflow everywhere in the electron diffusion region.
Electrostatic wave structures in a magnetized superthermal plasma with two-temperature electrons
Shahmansouri, M.; Alinejad, H.
2013-08-15
The linear and nonlinear excitation of arbitrary amplitude ion-acoustic (IA) solitary waves in a magnetized plasma comprising two-temperature electrons and cold ions are studied. The oblique propagation properties of two possible modes (in the linear regime) are investigated. It is found that the electron superthermality reduces the phase velocities of both modes, whereas obliqueness leads to an increase in the separation between two modes. In the nonlinear regime, an energy-like equation describes the evolution of IA solitary waves in the present model. The combined effects of the electron superthermality, magnitude of magnetic field, obliqueness and electron population are incorporated in the study of the existence domain of solitary waves and the soliton characteristics. It is shown that the small values of the hot electron population shift the permitted interval of Mach number to the lower values. Both compressive and rarefactive solitary structures are found to exist in the presence of two temperature electrons. The present investigation contributes to the physics of electrostatic wave structures in Saturn's magnetosphere in which two temperature electrons with kappa distribution exist.
A hyperbolic-equation system approach for magnetized electron fluids in quasi-neutral plasmas
Kawashima, Rei; Komurasaki, Kimiya; Schönherr, Tony
2015-03-01
A new approach using a hyperbolic-equation system (HES) is proposed to solve for the electron fluids in quasi-neutral plasmas. The HES approach avoids treatments of cross-diffusion terms which cause numerical instabilities in conventional approaches using an elliptic equation (EE). A test calculation reveals that the HES approach can robustly solve problems of strong magnetic confinement by using an upwind method. The computation time of the HES approach is compared with that of the EE approach in terms of the size of the problem and the strength of magnetic confinement. The results indicate that the HES approach can be used to solve problems in a simple structured mesh without increasing computational time compared to the EE approach and that it features fast convergence in conditions of strong magnetic confinement.
Dynamics of ion acoustic double layers in a magnetized two-population electrons plasma
Shahmansouri, M.
2013-10-15
The obliquely propagating ion acoustic (IA) double-layers are investigated in a magnetized two population electron plasmas. The extended Korteweg–de Vries equation is derived by using the reductive perturbation technique. The effect of obliqueness (l{sub z}) and magnitude of the external magnetic field (ω{sub ci}), as well as the electron number density (β) on the double-layer profile, is studied, and then the ranges of parameters for which the double-layers exist are investigated in detail. We found that the combined effects of l{sub z}, ω{sub ci}, and β significantly modify the basic properties (viz. amplitude and width) of the IA double-layers.
Haakonsen, Christian Bernt Hutchinson, Ian H.
2015-10-15
Flow of magnetized plasma past an obstacle creates a traditional wake, but also a forewake region arising from shadowing of electrons. The electron forewakes resulting from supersonic flows past insulating and floating-potential obstacles are explored with 2D electrostatic particle-in-cell simulations, using a physical ion to electron mass ratio. Drift-energization is discovered to give rise to modifications to the electron velocity-distribution, including a slope-reversal, providing a novel drive of forewake instability. The slope-reversal is present at certain locations in all the simulations, and appears to be quite robustly generated. Wings of enhanced electron density are observed in some of the simulations, also associated with drift-energization. In the simulations with a floating-potential obstacle, the specific potential structure behind that obstacle allows fast electrons to cross the wake, giving rise to a more traditional shadowing-driven two-stream instability. Fluctuations associated with such instability are observed in the simulations, but this instability-mechanism is expected to be more sensitive to the plasma parameters than that associated with the slope-reversal.
NASA Astrophysics Data System (ADS)
Evstatiev, Evstati; Svidzinski, Vladimir; Spencer, Andy; Galkin, Sergei
2014-10-01
Full wave 3-D modeling of RF fields in hot magnetized nonuniform plasma requires calculation of nonlocal conductivity kernel describing the dielectric response of such plasma to the RF field. In many cases, the conductivity kernel is a localized function near the test point which significantly simplifies numerical solution of the full wave 3-D problem. Preliminary results of feasibility analysis of numerical calculation of the conductivity kernel in a 3-D hot nonuniform magnetized plasma in the electron cyclotron frequency range will be reported. This case is relevant to modeling of ECRH in ITER. The kernel is calculated by integrating the linearized Vlasov equation along the unperturbed particle's orbits. Particle's orbits in the nonuniform equilibrium magnetic field are calculated numerically by one of the Runge-Kutta methods. RF electric field is interpolated on a specified grid on which the conductivity kernel is discretized. The resulting integrals in the particle's initial velocity and time are then calculated numerically. Different optimization approaches of the integration are tested in this feasibility analysis. Work is supported by the U.S. DOE SBIR program.
NASA Astrophysics Data System (ADS)
Akhtar, N.; El-Taibany, W. F.; Mahmood, S.; Behery, E. E.; Khan, S. A.; Ali, S.; Hussain, S.
2015-10-01
> . The magnetic field has no effect on the amplitude of the IASW, whereas the obliqueness angle of the wave propagation, the ion-to-electron temperature ratio and positron-to-ion density concentration ratio affect both the amplitude and the width of the solitary wave structures. The transverse instability analysis illustrates that the one soliton solution has a constant growth rate, and it suffers from instability in the transverse direction. The relevance of the present study to astrophysical space plasmas is also discussed.
Nonlinear plasma wave in magnetized plasmas
NASA Astrophysics Data System (ADS)
Bulanov, Sergei V.; Zh. Esirkepov, Timur; Kando, Masaki; Koga, James K.; Hosokai, Tomonao; Zhidkov, Alexei G.; Kodama, Ryosuke
2013-08-01
Nonlinear axisymmetric cylindrical plasma oscillations in magnetized collisionless plasmas are a model for the electron fluid collapse on the axis behind an ultrashort relativisically intense laser pulse exciting a plasma wake wave. We present an analytical description of the strongly nonlinear oscillations showing that the magnetic field prevents closing of the cavity formed behind the laser pulse. This effect is demonstrated with 3D PIC simulations of the laser-plasma interaction. An analysis of the betatron oscillations of fast electrons in the presence of the magnetic field reveals a characteristic "Four-Ray Star" pattern.
Oblique ion-acoustic cnoidal waves in two temperature superthermal electrons magnetized plasma
Panwar, A. Ryu, C. M.; Bains, A. S.
2014-12-15
A study is presented for the oblique propagation of ion acoustic cnoidal waves in a magnetized plasma consisting of cold ions and two temperature superthermal electrons modelled by kappa-type distributions. Using the reductive perturbation method, the nonlinear Korteweg de-Vries equation is derived, which further gives the solutions with a special type of cnoidal elliptical functions. Both compressive and rarefactive structures are found for these cnoidal waves. Nonlinear periodic cnoidal waves are explained in terms of plasma parameters depicting the Sagdeev potential and the phase curves. It is found that the density ratio of hot electrons to ions μ significantly modifies compressive/refractive wave structures. Furthermore, the combined effects of superthermality of cold and hot electrons κ{sub c},κ{sub h}, cold to hot electron temperature ratio σ, angle of propagation and ion cyclotron frequency ω{sub ci} have been studied in detail to analyze the height and width of compressive/refractive cnoidal waves. The findings in the present study could have important implications in understanding the physics of electrostatic wave structures in the Saturn's magnetosphere where two temperature superthermal electrons are present.
Bagryansky, P A; Shalashov, A G; Gospodchikov, E D; Lizunov, A A; Maximov, V V; Prikhodko, V V; Soldatkina, E I; Solomakhin, A L; Yakovlev, D V
2015-05-22
This Letter describes plasma discharges with a high temperature of bulk electrons in the axially symmetric high-mirror-ratio (R=35) open magnetic system gas dynamic trap (GDT) in the Budker Institute (Novosibirsk). According to Thomson scattering measurements, the on-axis electron temperature averaged over a number of sequential shots is 660±50 eV with the plasma density being 0.7×10^{19} m^{-3}; in few shots, electron temperature exceeds 900 eV. This corresponds to at least a threefold increase with respect to previous experiments both at GDT and at other comparable machines, thus, demonstrating the highest quasistationary (about 1 ms) electron temperature achieved in open traps. The breakthrough is made possible by application of a new 0.7 MW/54.5 GHz electron cyclotron resonance heating system in addition to standard 5 MW heating by neutral beams, and application of a radial electric field to mitigate the flute instability. PMID:26047233
Plasma studies of the permanent magnet electron cyclotron resonance ion source at Peking University
Ren, H. T.; Peng, S. X. Xu, Y.; Zhao, J.; Lu, P. N.; Chen, J.; Zhang, A. L.; Zhang, T.; Guo, Z. Y.; Chen, J. E.
2014-02-15
At Peking University (PKU) we have developed several 2.45 GHz Permanent Magnet Electron Cyclotron Resonance ion sources for PKUNIFTY, SFRFQ, Coupled RFQ and SFRFQ, and Dielectric-Wall Accelerator (DWA) projects (respectively, 50 mA of D{sup +}, 10 mA of O{sup +}, 10 mA of He{sup +}, and 50 mA of H{sup +}). In order to improve performance of these ion sources, it is necessary to better understand the principal factors that influence the plasma density and the atomic ion fraction. Theoretical analysis about microwave transmission and cut-off inside the discharge chamber were carried out to study the influence of the discharge chamber diameters. As a consequence, experimental studies on plasma density and ion fraction with different discharge chamber sizes have been carried out. Due to the difficulties in measuring plasma density inside the discharge chamber, the output beam current was measured to reflect the plasma density. Experimental results show that the plasma density increases to the maximum and then decreases significantly as the diameter changed from 64 mm to 30 mm, and the atomic ion fraction has the same tendency. The maximum beam intensity was obtained with the diameter of 35 mm, but the maximum atomic ion fraction with a diameter of 40 mm. The experimental results are basically accordant with the theoretical calculation. Details are presented in this paper.
Plasma studies of the permanent magnet electron cyclotron resonance ion source at Peking University
NASA Astrophysics Data System (ADS)
Ren, H. T.; Peng, S. X.; Xu, Y.; Zhao, J.; Lu, P. N.; Chen, J.; Zhang, A. L.; Zhang, T.; Guo, Z. Y.; Chen, J. E.
2014-02-01
At Peking University (PKU) we have developed several 2.45 GHz Permanent Magnet Electron Cyclotron Resonance ion sources for PKUNIFTY, SFRFQ, Coupled RFQ&SFRFQ, and Dielectric-Wall Accelerator (DWA) projects (respectively, 50 mA of D+, 10 mA of O+, 10 mA of He+, and 50 mA of H+). In order to improve performance of these ion sources, it is necessary to better understand the principal factors that influence the plasma density and the atomic ion fraction. Theoretical analysis about microwave transmission and cut-off inside the discharge chamber were carried out to study the influence of the discharge chamber diameters. As a consequence, experimental studies on plasma density and ion fraction with different discharge chamber sizes have been carried out. Due to the difficulties in measuring plasma density inside the discharge chamber, the output beam current was measured to reflect the plasma density. Experimental results show that the plasma density increases to the maximum and then decreases significantly as the diameter changed from 64 mm to 30 mm, and the atomic ion fraction has the same tendency. The maximum beam intensity was obtained with the diameter of 35 mm, but the maximum atomic ion fraction with a diameter of 40 mm. The experimental results are basically accordant with the theoretical calculation. Details are presented in this paper.
Cho; Lee; Kim
2000-04-01
Nonrelativistic electromagnetic surface waves propagating on the plane interface between dusty electron-positron plasma and vacuum are investigated by specular reflection procedure. In the presence of an applied magnetic field (B(0)=B(0)yinsertion mark) directed perpendicular to both the interface normal and the wave vector, transverse electromagnetic modes are studied in terms of the dispersion relation. The analytic modes are derived and discussed with the aid of some numerical analysis. The cold electromagnetic surface wave dispersion relation considering the effect of dust particle shows that possible modes appear only when the normalized frequency (omega;) and the wave vector (&Kmacr;) satisfy the condition Omega;
Dust acoustic dromions in a magnetized dusty plasma with superthermal electrons and ions
NASA Astrophysics Data System (ADS)
Saini, N. S.; Ghai, Yashika; Kohli, Ripin
2016-06-01
An investigation of dust acoustic (DA) dromions in a magnetized dusty plasma consisting of inertial dust fluid, kappa-type distributed electrons, and ions is presented. Using reductive perturbation technique, we have derived coupled nonlinear evolution equations of (2 + 1) dimensions (called Davey-Stewartson (DS-I) equations). Hirota bilinear method has been employed to derive the analytical solution of DS-I equations. The solutions of such equations are exponentially localized and are called dromions. The combined effects of various physical parameters such as superthermality of charged particles, strength of magnetic field, and dust concentration have been studied on the existence regions and propagation properties of DA dromions in context with observations of POLAR satellite in the presence of superthermal particles in polar cap boundary layer region of Earth's atmosphere.
NASA Astrophysics Data System (ADS)
Akitsu, Tetsuya
1998-10-01
A plasma-enhanced reactive sputtering was developed for the deposition of oriented thin crustals of metallic-oxide compound. An oxygen plasma was excited with microwave, electron cyclotron resonance discharge at 2.45 GHz and a compact DC magnetron sputtering was combined. The discharge characteristics was compared in two types of magnetic field configurations.using the optical emission spectroscopy and the appearance potential mass-spectrometry. In a divergent magnetic field, the microwave was absorbed in a single electron-cyclotron resonance Layer, 30-45 mm apart from a crystallized ceramic vesse, and the deposition region was exposed to a freely expanding plasma. Next, the end of the magnetic field line was closed with a magnetic circuit and the source plasma was magnetically confined in the local mirror, thus only neutral oxygen was allowed to expand into the deposition region.
NASA Astrophysics Data System (ADS)
Bains, A. S.; Misra, A. P.; Saini, N. S.; Gill, T. S.
2010-01-01
The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schrödinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (μ), the normalized ion-cyclotron frequency (ωc) as well as the ratio (H) of the "plasmonic energy density" to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing μ or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.
Lopez, Rodrigo A.; Munoz, Victor; Asenjo, Felipe A.; Alejandro Valdivia, J.
2012-08-15
The nonlinear evolution of a circularly polarized electromagnetic wave in an electron-positron plasma propagating along a constant background magnetic field is considered, by studying its parametric decays. Relativistic effects, of the particle motion in the wave field and of the plasma temperature, are included to obtain the dispersion relation of the decays. The exact dispersion relation of the pump wave has been previously calculated within the context of a relativistic fluid theory and presents two branches: an electromagnetic and an Alfven one. We investigate the parametric decays for the pump wave in these two branches, including the anomalous dispersion zone of the Alfven branch where the group velocity is negative. We solve the nonlinear dispersion relation for different pump wave amplitudes and plasma temperatures, finding various resonant and nonresonant wave couplings. We are able to identify these couplings and study their behavior as we modify the plasma parameters. Some of these couplings are suppressed for larger amplitudes or temperatures. We also find two kinds of modulational instabilities, one involving two sideband daughter waves and another involving a forward-propagating electroacoustic mode and a sideband daughter wave.
El-Taibany, W. F. E-mail: eltaibany@hotmail.com; Selim, M. M.; Al-Abbasy, O. M.; El-Bedwehy, N. A.
2014-07-15
The propagation of both linear and nonlinear dust acoustic waves (DAWs) in an inhomogeneous magnetized collisional and warm dusty plasma (DP) consisting of Boltzmann ions, nonextensive electrons, and inertial dust particles is investigated. The number density gradients of all DP components besides the inhomogeneities of electrostatic potential and the initial dust fluid velocity are taken into account. The linear dispersion relation and a nonlinear modified Zakharov-Kusnetsov (MZK) equation governing the propagation of the three-dimensional DAWs are derived. The analytical solution of the MZK reveals the creation of both compressive and rarefactive DAW solitons in the proposed model. It is found that the inhomogeneity dimension parameter and the electron nonextensive parameter affect significantly the nonlinear DAW's amplitude, width, and Mach number. The relations of our findings with some astrophysical situations have been given.
Lee, Min-Hyong; Choi, Seong Wook
2008-12-01
We investigated the evolution of the electron energy distribution function (EEDF) in a solenoidal inductively coupled plasma surrounded by an axial dc magnetic field. The increase in the dc magnetic field caused the EEDF to evolve from a bi-Maxwellian to a Maxwellian distribution. At the discharge center, the number of low energy electrons was significantly reduced while the high energy electron population showed little change when a weak dc magnetic field was present. However, at the discharge radial boundary, the high energy electron population decreased significantly with the magnetic field while the change in low energy population was not prominent compared to the discharge boundary. These changes in EEDFs at the boundary and center of the discharge are due to the radial confinement and the restriction of radial transport of electrons by dc magnetic field.
NASA Astrophysics Data System (ADS)
Rafat, A.; Rahman, M. M.; Alam, M. S.; Mamun, A. A.
2016-08-01
Obliquely propagating electron-acoustic solitary waves (EASWs) in a magnetized electron-positron-ion plasma (containing nonextensive hot electrons and positrons, inertial cold electrons, and immobile positive ions) are precisely investigated by deriving the Zakharov-Kuznetsov equation. It is found that the basic features (viz. polarity, amplitude, width, phase speed, etc.) of the EASWs are significantly modified by the effects of the external magnetic field, obliqueness of the system, nonextensivity of hot positrons and electrons, ratio of the hot electron temperature to the hot positron temperature, and ratio of the cold electron number density to the hot positron number density. The findings of our results can be employed in understanding the localized electrostatic structures and the characteristics of EASWs in various astrophysical plasmas.
External magnetic field effect on the growth rate of a plasma-loaded free-electron laser
NASA Astrophysics Data System (ADS)
Esmaeildoost, N.; Jafari, S.; Abbasi, E.
2016-06-01
In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers' efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.
NASA Astrophysics Data System (ADS)
Andreev, V. V.; Novitsky, A. A.; Vinnichenko, L. A.; Umnov, A. M.; Ndong, D. O.
2016-03-01
The parameters of the injector of an axial plasma beam injected into a plasma accelerator operating on the basis of gyroresonance acceleration of electrons in the reverse magnetic field are determined. The trapping of the beam electrons into the regime of gyroresonance acceleration is numerically simulated by the particle- in-cell method. The optimal time of axial injection of the beam into a magnetic mirror trap is determined. The beam parameters satisfying the condition of efficient particle trapping into the gyromagnetic autoresonance regime are found.
Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.
Amin, M R
2015-09-01
Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.
Wave dispersion in a counterstreaming, cold, magnetized, electron-positron plasma.
Verdon, M W; Melrose, D B
2008-04-01
The dispersion equation is analyzed for waves in a strongly magnetized, electron-positron plasma in which counterstreaming electrons are cold in their respective rest frames. For propagation parallel to the magnetic field the dispersion equation factorizes into equations for two longitudinal modes and four transverse modes. Instabilities occur in both longitudinal and transverse modes, with the most notable being at low wave numbers where a longitudinal branch has purely imaginary frequency. For oblique propagation at small angles, the modes reconnect at points where the parallel modes intersect, either deviating away from each another, or being separated by a pair of complex modes. In addition, intrinsically oblique branches of the dispersion equation appear. The results are applied to an oscillating model for a pulsar magnetosphere, in which the oscillations are purely temporal with a frequency well below relevant wave frequencies, and in which the counterstreaming becomes highly relativistic. We assume that the medium may be treated as time stationary in treating the wave dispersion and wave growth. The wave properties, including the wave frequency, vary periodically with the phase of the oscillations. The fastest growing instability is when the counterstreaming is nonrelativistic or mildly relativistic. A given wave can experience bursts of growth over many oscillations. Mode coupling associated with the cyclotron resonance may be effective in generating the observed orthogonally polarized modes at phases of the oscillation where the (relativistic) cyclotron and wave frequencies are comparable. PMID:18517741
Kuwahata, A.; Igami, H.; Kawamori, E.; Kogi, Y.; Inomoto, M.; Ono, Y.
2014-10-15
We report the observation of electromagnetic radiation at high harmonics of the electron cyclotron frequency that was considered to be converted from electrostatic waves called electron Bernstein waves (EBWs) during magnetic reconnection in laboratory overdense plasmas. The excitation of EBWs was attributed to the thermalization of electrons accelerated by the reconnection electric field around the X-point. The radiative process discussed here is an acceptable explanation for observed radio waves pulsation associated with major flares.
B. Jones; G. Taylor; P.C. Efthimion; T. Munsat
2004-01-28
Measurement of the magnetic field in a spherical torus by observation of harmonic overlap frequencies in the electron Bernstein wave (EBW) spectrum has been previously suggested [V.F. Shevchenko, Plasma Phys. Reports 26 (2000) 1000]. EBW mode conversion to X-mode radiation has been studied in the Current Drive Experiment-Upgrade spherical torus, [T. Jones, Ph.D. thesis, Princeton University, 1995] with emission measured at blackbody levels [B. Jones et al., Phys. Rev. Lett. 90 (2003) article no. 165001]. Sharp transitions in the thermally emitted EBW spectrum have been observed for the first two harmonic overlaps. These transition frequencies are determined by the magnetic field and electron density at the mode conversion layer in accordance with hot-plasma wave theory. Prospects of extending this measurement to higher harmonics, necessary in order to determine the magnetic field profile, and high beta equilibria are discussed for this proposed magnetic field diagnostic.
Kumar, Ravinder; Malik, Hitendra K.
2013-03-15
This article aims at studying the reflection of solitons in an inhomogeneous magnetized warm plasma having dust grains with positive or negative charge and trapped electrons (low temperature nonisothermal electrons). In order to study the soliton reflection, a coupled modified Korteweg-de Vries equation is derived and solved along with the use of incident soliton solution. The expressions for the reflected soliton amplitude, width, and reflection coefficient are obtained, and examined under different parameter regimes. The combined effect of the dust grain density with their charge polarity and trapping of the electrons is largely studied on the soliton reflection characteristics under the influence of magnetic field.
Wavelet characterization of 2D turbulence and intermittency in magnetized electron plasmas
NASA Astrophysics Data System (ADS)
Romé, M.; Chen, S.; Maero, G.
2016-06-01
A study of the free relaxation of turbulence in a two-dimensional (2D) flow is presented, with a focus on the role of the initial vorticity conditions. Exploiting a well-known analogy with 2D inviscid incompressible fluids, the system investigated here is a magnetized pure electron plasma. The dynamics of this system are simulated by means of a 2D particle-in-cell code, starting from different spiral density (vorticity) distributions. A wavelet multiresolution analysis is adopted, which allows the coherent and incoherent parts of the flow to be separated. Comparison of the turbulent evolution in the different cases is based on the investigation of the time evolution of statistical properties, including the probability distribution functions and structure functions of the vorticity increments. It is also based on an analysis of the enstrophy evolution and its spectrum for the two components. In particular, while the statistical features assess the degree of flow intermittency, spectral analysis allows us not only to estimate the time required to reach a state of fully developed turbulence, but also estimate its dependence on the thickness of the initial spiral density distribution, accurately tracking the dynamics of both the coherent structures and the turbulent background. The results are compared with those relevant to annular initial vorticity distributions (Chen et al 2015 J. Plasma Phys. 81 495810511).
High frequency electromagnetic modes in a weakly magnetized relativistic electron plasma
NASA Astrophysics Data System (ADS)
Abbas, Gohar; Murtaza, G.; Kingham, R. J.
2010-07-01
Using the linearized Vlasov-Maxwell model, the polarization tensor for a weakly magnetized electron plasma is derived. For isotropic relativistic Maxwellian velocity distribution function, dispersion relations are obtained for both parallel and perpendicular propagations. The integrals (called Meijer G functions) that arise due to relativistic effects are examined in various limits and dispersion relations are derived for the nonrelativistic, weakly, strongly, and ultrarelativistic Maxwellian velocity distributions. It is generally observed that the propagation domains of the modes are enlarged as one proceeds from the nonrelativistic to the highly relativistic regime. Resultantly, due to the relativistic effects, the Whistler mode is suppressed in the R-wave, the nonpropagation band of X-mode is reduced, and the X-mode itself approaches the O-mode. Further, the results derived in the ultra- and nonrelativistic limits found to be in agreement with the earlier calculations [G. Abbas et al. Phys. Scr. 76, 649 (2007); F. F. Chen, Introduction to Plasma Physics and Controlled Fusion (Plenum, New York, 1984), Vol. 1].
Fast magnetic reconnection in low-density electron-positron plasmas
Bessho, Naoki; Bhattacharjee, A.
2010-10-15
Two-dimensional particle-in-cell simulations have been performed to study magnetic reconnection in low-density electron-positron plasmas without a guide magnetic field. Impulsive reconnection rates become of the order of unity when the background density is much smaller than 10% of the density in the initial current layer. It is demonstrated that the outflow speed is less than the upstream Alfven speed, and that the time derivative of the density must be taken into account in the definition of the reconnection rate. The reconnection electric fields in the low-density regime become much larger than the ones in the high-density regime, and it is possible to accelerate the particles to high energies more efficiently. The inertial term in the generalized Ohm's law is the most dominant term that supports a large reconnection electric field. An effective collisionless resistivity is produced and tracks the extension of the diffusion region in the late stage of the reconnection dynamics, and significant broadening of the diffusion region is observed. Because of the broadening of the diffusion region, no secondary islands, which have been considered to play a role to limit the diffusion region, are generated during the extension of the diffusion region in the outflow direction.
Investigation of particle diffusion and suprathermal electrons in a magnetized helium plasma column
Lefevre, T.; Escarguel, A.; Stamm, R.; Godbert-Mouret, L.; Rosmej, F. B.
2014-02-15
Studying radiative properties of magnetized helium plasma via high-resolution spectroscopy identified close correlations between the particle diffusion and suprathermal electrons for different modes of operation of the MISTRAL installation. The standard diagnostic emission lines in neutral helium (1s3d {sup 3}D-1s2p {sup 3}P, 1s3s {sup 3}S-1s2p {sup 3}P, 1s3d {sup 1}D-1s2p {sup 1}P, and 1s3s {sup 1}S-1s2p {sup 1}P) show anomalous ratios that are related to enhanced particle diffusion and suprathermal electron generation. The supplementary investigation of singlet/triplet Rydberg series (transitions 1snd {sup 3}D-1s2p {sup 3}P and 1s5p {sup 1}P-1s2s {sup 1}S) as well as ionic lines (HeII, transitions n = 3–4 at 469 nm and n = 4–6 at 656 nm) allowed quantitative characterization. Simulations carried out with the atomic physics code SOPHIA demonstrate that simultaneous implementation of diffusion processes and suprathermal electrons matches all experimental findings. Single consideration, however, of either diffusion or hot electrons is in contradiction to the proposed extended set of HeI and HeII emission lines. The high precision achieved with the LSJ-split level structure of SOPHIA coupled to Langmuir probe measurements allowed to conclude to a Bohm type diffusion in MISTRAL.
Andreev, Pavel A.
2015-06-15
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-06-01
We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.
NASA Astrophysics Data System (ADS)
Tang, C. L.; Zhou, M.; Yao, Z. H.; Shi, F.
2016-05-01
Using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations, we study electron acceleration (<30 keV) in the magnetic flux pileup regions (FPRs) in the near-Earth plasma sheet (X ~ -10 RE). We present three cases of FRPs associated with dipolarization fronts and substorm dipolarization. Based on the characteristics of the magnetic field, we defined the magnetic field enhancement region (MFER) as the magnetic field with significant ramp that is usually observed near the dipolarization front boundary layer. On the other side, the increased magnetic field without a significant ramp is the rest of a FPR. Our results show that betatron acceleration dominates for 10-30 keV electrons inside the MFER, whereas Fermi acceleration dominates for 10-30 keV electrons inside the rest of the FPR. Betatron acceleration is caused by the enhancement of the local magnetic field, whereas Fermi acceleration is related to the shrinking length of magnetic field line. These accelerated electrons inside the FPRs in the near-Earth tail play a potentially important role in the evolution of the Earth's electron radiation belt and substorms.
Electron beam guiding by external magnetic fields in imploded fuel plasma
NASA Astrophysics Data System (ADS)
Johzaki, T.; Sentoku, Y.; Nagatomo, H.; Sunahara, A.; Sakagami, H.; Fujioka, S.; Shiraga, H.; Endo, T.; FIREX project Group
2016-05-01
For enhancing the core heating efficiency in fast ignition laser fusion, we proposed the fast electron beam by externally-applied the kilo-tesla (kT) class longitudinal magnetic field. We evaluated the imploded core and the magnetic field profiles formed through the implosion dynamics by resistive MHD radiation hydro code. Using those profiles, the guiding effect was evaluated by fast electron transport simulations, which shows that in addition to the feasible field configuration (moderate mirror ratio), the kT-class magnetic field is required at the fast electron generation point. In this case, the significant enhancement in heating efficiency is expected.
NASA Astrophysics Data System (ADS)
Lachhvani, Lavkesh; Pahari, Sambaran; Goswami, Rajiv; Bajpai, Manu; Yeole, Yogesh; Chattopadhyay, P. K.
2016-06-01
A long confinement time of electron plasma, approaching magnetic pumping transport limit, has been observed in SMARTEX-C (a small aspect ratio partial torus with R o / a ˜ 1.59 ). Investigations of the growth rate reveal that they are governed by instabilities like resistive wall destabilization, ion driven instabilities, and electron-neutral collisions. Successful confinement of electron plasmas exceeding > 1 × 10 5 poloidal E → × B → rotations lasting for nearly 2.1 ± 0.1 s is achieved by suppressing these instabilities. The confinement time has been estimated in two ways: (a) from the frequency scaling of the linear diocotron mode launched from sections of the wall that are also used as capacitive probes and (b) by dumping the plasma onto a charge collector at different hold times.
Nonthermally Dominated Electron Acceleration during Magnetic Reconnection in a Low-beta Plasma
Li, Xiaocan
2015-07-21
This work was motivated by electron acceleration during solar flares. After some introductory remarks on proposed particle acceleration mechanisms and questions needing answers, dynamic simulations and simulation results are presented including energy spectra and the formation of the power law distribution. In summary, magnetic reconnection is highly efficient at converting the free magnetic energy stored in a magnetic shear and accelerating electrons to nonthermal energies in low-β regime. The nonthermal electrons have a dominant fraction and form power-law energy spectra with spectral index p ~ 1 in low-β regime. Electrons are preferentially accelerated along the curvature drift direction along the electric field induced by the reconnection outflow. The results can be applied to explain the observations of electron acceleration during solar flares.
Persistence of magnetic field driven by relativistic electrons in a plasma
NASA Astrophysics Data System (ADS)
Flacco, A.; Vieira, J.; Lifschitz, A.; Sylla, F.; Kahaly, S.; Veltcheva, M.; Silva, L. O.; Malka, V.
2015-05-01
The onset and evolution of magnetic fields in laboratory and astrophysical plasmas is determined by several mechanisms, including instabilities, dynamo effects and ultrahigh-energy particle flows through gas, plasma and interstellar media. These processes are relevant over a wide range of conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion in stars. The disparate temporal and spatial scales where each process operates can be reconciled by scaling parameters that enable one to emulate astrophysical conditions in the laboratory. Here we unveil a new mechanism by which the flow of ultra-energetic particles in a laser-wakefield accelerator strongly magnetizes the boundary between plasma and non-ionized gas. We demonstrate, from time-resolved large-scale magnetic-field measurements and full-scale particle-in-cell simulations, the generation of strong magnetic fields up to 10-100 tesla (corresponding to nT in astrophysical conditions). These results open new paths for the exploration and modelling of ultrahigh-energy particle-driven magnetic-field generation in the laboratory.
Rufai, O. R.; Bharuthram, R.; Singh, S. V. Lakhina, G. S.
2015-10-15
The effect of excess superthermal electrons is investigated on finite amplitude nonlinear ion-acoustic waves in a magnetized auroral plasma. The plasma model consists of a cold ion fluid, Boltzmann distribution of cool electrons, and kappa distributed hot electron species. The model predicts the evolution of negative potential solitons and supersolitons at subsonic Mach numbers region, whereas, in the case of Cairn's nonthermal distribution model for the hot electron species studied earlier, they can exist both in the subsonic and supersonic Mach number regimes. For the dayside auroral parameters, the model generates the super-acoustic electric field amplitude, speed, width, and pulse duration of about 18 mV/m, 25.4 km/s, 663 m, and 26 ms, respectively, which is in the range of the Viking spacecraft measurements.
NASA Astrophysics Data System (ADS)
Rufai, O. R.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.
2015-10-01
The effect of excess superthermal electrons is investigated on finite amplitude nonlinear ion-acoustic waves in a magnetized auroral plasma. The plasma model consists of a cold ion fluid, Boltzmann distribution of cool electrons, and kappa distributed hot electron species. The model predicts the evolution of negative potential solitons and supersolitons at subsonic Mach numbers region, whereas, in the case of Cairn's nonthermal distribution model for the hot electron species studied earlier, they can exist both in the subsonic and supersonic Mach number regimes. For the dayside auroral parameters, the model generates the super-acoustic electric field amplitude, speed, width, and pulse duration of about 18 mV/m, 25.4 km/s, 663 m, and 26 ms, respectively, which is in the range of the Viking spacecraft measurements.
Beta electron fluxes inside a magnetic plasma cavern: Calculation and comparison with experiment
NASA Astrophysics Data System (ADS)
Stupitskii, E. L.; Smirnov, E. V.; Kulikova, N. A.
2010-12-01
We study the possibility of electrostatic blanking of beta electrons in the expanding spherical blob of a radioactive plasma in a rarefied ionosphere. From numerical studies on the dynamics of beta electrons departing a cavern, we obtain the form of a function that determines the portion of departing electrons and calculate the flux density of beta electrons inside the cavern in relation to the Starfish Prime nuclear blast. We show that the flux density of electrons in geomagnetic flux tubes and inside the cavern depend on a correct allowance for the quantity of beta electrons returning to the cavern. On the basis of a physical analysis, we determine the approximate criterion for the return of electrons from a geomagnetic flux tube to the cavern. We compare calculation results in terms of the flux density of beta electrons inside the cavern with the recently published experimental results from operation Starfish Prime.
Kato, Yushi; Sakamoto, Naoki; Kiriyama, Ryutaro; Takenaka, Tomoya; Kurisu, Yosuke; Nozaki, Dai; Sato, Fuminobu; Iida, Toshiyuki
2012-02-15
In order to contribute to various applications of plasma and beams based on an electron cyclotron resonance, a new concept on magnetic field with all magnets on plasma production and confinement has been proposed with enhanced efficiency for broad and dense ion beam. The magnetic field configuration consists of a pair of comb-shaped magnet surrounding plasma chamber cylindrically. Resonance zones corresponding for 2.45 GHz and 11-13 GHz frequencies are positioned at spatially different positions. We launch simultaneously multiplex frequencies microwaves operated individually, try to control profiles of the plasma parameters and the extracted ion beams, and to measure them in detail.
Sepehri Javan, N.
2012-12-15
The aim of the present study is to investigate the problem of modulation instability of an intense laser beam in the hot magnetized electron-positron plasma. Propagation of the intense circularly polarized laser beam along the external magnetic field is studied using a relativistic fluid model. A nonlinear equation describing the interaction of the laser pulse with the magnetized hot pair plasma is derived based on the quasi-neutral approximation, which is valid for the hot plasma. Also, the nonlinear dispersion equation for the hot plasma is obtained. The growth rate of the instability is calculated and its dependence on temperature and external magnetic field are considered.
NASA Astrophysics Data System (ADS)
Bacha, Mustapha; Tribeche, Mouloud
2016-08-01
The combined effects of an oblique magnetic field and electron trapping on dissipative dust-acoustic waves are examined in varying charge electronegative dusty plasmas with application to the Halley Comet plasma (˜104 km from the nucleus). A weakly nonlinear analysis is carried out to derive a modified Korteweg-de Vries-Burger-like equation. Making use of the equilibrium current balance equation, the physically admissible values of the electron trapping parameter are first constrained. We then show that the Burger dissipative term is solely due to the dust charge variation process. It is found that an increase of the magnetic field obliqueness or a decrease of its magnitude renders the shock structure more dispersive.
Coupled modes in magnetized dense plasma with relativistic-degenerate electrons
Khan, S. A.
2012-01-15
Low frequency electrostatic and electromagnetic waves are investigated in ultra-dense quantum magnetoplasma with relativistic-degenerate electron and non-degenerate ion fluids. The dispersion relation is derived for mobile as well as immobile ions by employing hydrodynamic equations for such plasma under the influence of electromagnetic forces and pressure gradient of relativistic-degenerate Fermi gas of electrons. The result shows the coexistence of shear Alfven and ion modes with relativistically modified dispersive properties. The relevance of results to the dense degenerate plasmas of astrophysical origin (for instance, white dwarf stars) is pointed out with brief discussion on ultra-relativistic and non-relativistic limits.
Nonlinear behavior of electron acoustic waves in an un-magnetized plasma
Dutta, Manjistha; Khan, Manoranjan; Chakrabarti, Nikhil
2011-10-15
The nonlinear electron acoustic wave, which is found in the earth's magnetosphere by satellite observations, is studied analytically by Lagrangian fluid description. The basic linear mode is observed in a two temperature electron species plasma where ions form stationary charge neutral background. We have obtained nonlinear description of this mode, which depends on both time and space. A possible solution shows a soliton like structure, which is localized in space, and the amplitude increases with time in the absence of dispersion. Small dispersive correction, however, shows spread of the solution in space. This method can be generalized to study the nonlinear behavior of a general class of multispecies plasma.
NASA Astrophysics Data System (ADS)
Raitses, Yevgeny; Donnelly, Vincent; Kaganovich, Igor; Godyak, Valery
2013-09-01
The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the largest fraction of the cross-field current. This work was supported by the US DOE under Contract DE-AC02-09CH11466.
NASA Astrophysics Data System (ADS)
Raitses, Yevgeny; Donnelly, Vincent M.; Kaganovich, Igor D.; Godyak, Valery
2013-10-01
The application of the magnetic field in a low pressure plasma can cause a spatial separation of cold and hot electron groups. This so-called magnetic filter effect is not well understood and is the subject of our studies. In this work, we investigate electron energy distribution function in a DC-RF plasma discharge with crossed electric and magnetic field operating at sub-mtorr pressure range of xenon gas. Experimental studies showed that the increase of the magnetic field leads to a more uniform profile of the electron temperature across the magnetic field. This surprising result indicates the importance of anomalous electron transport that causes mixing of hot and cold electrons. High-speed imaging and probe measurements revealed a coherent structure rotating in E cross B direction with frequency of a few kHz. Similar to spoke oscillations reported for Hall thrusters, this rotating structure conducts the largest fraction of the cross-field current. This work was supported by DOE contract DE-AC02-09CH11466.
Shokri, B.; Khorashadizadeh, S.M.
2006-05-15
The possibility of the excitation of extraordinary and ordinary cyclotron waves by interaction of a rotating electron beam propagating parallel to the external magnetic field with a cold plasma medium is investigated. By obtaining the growth rates, the influence of dissipation on the development of extraordinary and ordinary cyclotron waves are studied. By comparing the development of the cyclotron instability with the dissipative instability in extraordinary and ordinary cyclotron waves excitation in the beam-plasma system, the dependency of the growth rates of these instabilities on the physical parameters is discussed.
Misra, Amar P; Chowdhury, A Roy
2004-11-01
The theory of electromagnetic surface modes propagating along the planar interface between dusty electron-positron plasma and vacuum is reexamined by the conventional matching method of boundary conditions. It is shown that in a magnetoplasma the direct use of specular reflection method is not appropriate and the derivations for the TM-mode dispersion relation [Phys. Rev. E 61, 4357 (2000)] are incorrect.
Soliton-like solutions in scattering of electrons by an ion in magnetized plasma
NASA Astrophysics Data System (ADS)
Novak, O.; Kholodov, R.
2015-04-01
Scattering of an electron on positive and negative ions has been studied. The transverse electron motion is assumed to be suppressed by a strong magnetic field. Transferred energy is greater for scattering on a negative ion and shows a sharp peak for the impact parameter equal to the distance of the closest approach. It has been found that the motion equations have a soliton-like solution in this case.
NASA Astrophysics Data System (ADS)
Gao, Dong-Ning; Wang, Cang-Long; Yang, Xue; Duan, Wen-Shan; Yang, Lei
2012-12-01
Theoretical and numerical studies are carried out for the stability of the electron acoustic waves under the transverse perturbation in a magnetized quantum plasma. The Zakharov-Kuznetsov (ZK) equation of the electron-acoustic waves (EAWs) is given by using the reductive perturbation technique. The cut-off frequency is obtained by applying a transverse sinusoidal perturbation to the plane soliton solution of the ZK equation. The propagation velocity of solitary waves, the real cut-off frequency, as well as the growth rate of the higher order perturbation to the traveling solitary wave are obtained.
Gao Dongning; Wang Canglong; Yang Xue; Duan Wenshan; Yang Lei
2012-12-15
Theoretical and numerical studies are carried out for the stability of the electron acoustic waves under the transverse perturbation in a magnetized quantum plasma. The Zakharov-Kuznetsov (ZK) equation of the electron-acoustic waves (EAWs) is given by using the reductive perturbation technique. The cut-off frequency is obtained by applying a transverse sinusoidal perturbation to the plane soliton solution of the ZK equation. The propagation velocity of solitary waves, the real cut-off frequency, as well as the growth rate of the higher order perturbation to the traveling solitary wave are obtained.
NASA Astrophysics Data System (ADS)
Hosseinpour, M.; Mohammadi, M. A.; Biabani, S.; Biabani
2013-10-01
Collisionless magnetic reconnection via tearing instability in non-relativistic electron-positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < r L ). This condition is satisfied when β > d 2 (d = c/ω p is the particle skin-depth with the electron/positron frequency ω p and β = 8πP (0)/B 0 2 << 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of dx. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτ A ) ~ d.
Parametric instabilities in weakly magnetized plasma
Weatherall, J.C.; Goldman, M.V.; Nicholson, D.R.
1981-05-15
Parametric instabilities in a weakly magnetized plasma are discussed. The results are applied to waves excited by electron streams which travel outward from the Sun along solar-wind magnetic field lines, as in a type III solar radio burst.
NASA Astrophysics Data System (ADS)
Iwamoto, D.; Sakuma, I.; Kitagawa, Y.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.
2012-10-01
In next step of fusion devices such as ITER, lifetime of plasma-facing materials (PFMs) is strongly affected by transient heat and particle loads during type I edge localized modes (ELMs) and disruption. To clarify damage characteristics of the PFMs, transient heat and particle loads have been simulated by using a plasma gun device. We have performed simulation experiments by using a magnetized coaxial plasma gun (MCPG) device at University of Hyogo. The line-averaged electron density measured by a He-Ne interferometer is 2x10^21 m-3 in a drift tube. The plasma velocity measured by a time of flight technique and ion Doppler spectrometer was 70 km/s, corresponding to the ion energy of 100 eV for helium. Thus, the ion flux density is 1.4x10^26 m-2s-1. On the other hand, the MCPG is connected to a target chamber for material irradiation experiments. It is important to measure plasma parameters in front of target materials in the target chamber. In particular, a vapor cloud layer in front of the target material produced by the pulsed plasma irradiation has to be characterized in order to understand surface damage of PFMs under ELM-like plasma bombardment. In the conference, preliminary results of application of the He-Ne laser interferometer for the above experiment will be shown.
Coupled ion acoustic and drift waves in magnetized superthermal electron-positron-ion plasmas
Adnan, Muhammad; Qamar, Anisa; Mahmood, S.
2014-09-15
Linear and nonlinear coupled drift-ion acoustic waves are investigated in a nonuniform magnetoplasma having kappa distributed electrons and positrons. In the linear regime, the role of kappa distribution and positron content on the dispersion relation has been highlighted; it is found that strong superthermality (low value of κ) and addition of positrons lowers the phase velocity via decreasing the fundamental scalelengths of the plasmas. In the nonlinear regime, first, coherent nonlinear structure in the form of dipoles and monopoles are obtained and the boundary conditions (boundedness) in the context of superthermality and positron concentrations are discussed. Second, in case of scalar nonlinearity, a Korteweg–de Vries-type equation is obtained, which admit solitary wave solution. It is found that both compressive and rarefactive solitons are formed in the present model. The present work may be useful to understand the low frequency electrostatic modes in inhomogeneous electron positron ion plasmas, which exist in astrophysical plasma situations such as those found in the pulsar magnetosphere.
NASA Astrophysics Data System (ADS)
Egedal, Jan; Le, Ari; Daughton, William
2013-06-01
From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, βe∞, the pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for
Bessho, Naoki; Bhattacharjee, A.
2012-05-10
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.
NASA Astrophysics Data System (ADS)
Sawlani, Kapil; Herzog, Joshua M.; Kwak, Joowon; Foster, John
2012-10-01
The electron energy distribution function (EEDF) plays a very important role in determining thruster efficiency as it determines various gas phase reaction rates. In Hall thrusters, secondary electron emission derived from the interaction of energetic electrons with ceramic channel surfaces influence the overall shape of the EEDF as well as determine the potential difference between the plasma and wall. The role of secondary electrons on the discharge operation of Hall thrusters is poorly understood. Experimentally, determining this effect is even more taxing as the secondary electron yield (SEY) varies drastically based on many parameters such as incident electron energies, flux and impact angle, and also on the surface properties such as temperature and roughness. The electron transport is also affected by the profile of the magnetic field, which is not uniform across the length of the accelerating channel. The goal of this work is to map out the variation of the EEDF and potential profile in response to the controlled introduction of secondary electrons. This data is expected to serve as a tool to validate and improve existing numerical models by providing boundary conditions and SEY for various situations that are encountered in Hall thrusters.
NASA Astrophysics Data System (ADS)
Oks, E.
2016-03-01
A general framework for calculating shapes of hydrogen (or deuterium) spectral lines in strongly-magnetized plasmas with the allowance for spiraling trajectories of perturbing electrons has been developed. It has been shown that in this situation the first order term Φ(1)(B) of the Dyson expansion of the electron broadening operator does not vanish - in distinction to the case of rectilinear trajectories, where the first non-vanishing term appeared only in the second order. An example of the Lyα line has been used to illustrate the effects of the spiraling trajectories. It has been shown that the shape of each of the two σ-components can become a doublet: in addition to the shifted component, there can appear also an unshifted component. Moreover, the shape of each of the two σ-components can also become a triplet: in addition to the shifted and unshifted component, there can appear also a component shifted to the opposite wing of the line. Both the positions and the intensities of the shifted components depend strongly on the magnitude of Φ(1)(B). The primary effect in the entire spectral line is a significant increase of the ratio of the intensity of the central peak to the intensity of any of the two lateral peaks. As practical examples, magnetic fusion plasmas and plasmas of DA white dwarfs have been considered. It is shown that for both of these, physically very different objects, the allowance for the spiraling trajectories of perturbing electrons can be important.
López, Rodrigo A.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, Juan A.
2015-09-15
We use a particle-in-cell simulation to study the propagation of localized structures in a magnetized electron-positron plasma with relativistic finite temperature. We use as initial condition for the simulation an envelope soliton solution of the nonlinear Schrödinger equation, derived from the relativistic two fluid equations in the strongly magnetized limit. This envelope soliton turns out not to be a stable solution for the simulation and splits in two localized structures propagating in opposite directions. However, these two localized structures exhibit a soliton-like behavior, as they keep their profile after they collide with each other due to the periodic boundary conditions. We also observe the formation of localized structures in the evolution of a spatially uniform circularly polarized Alfvén wave. In both cases, the localized structures propagate with an amplitude independent velocity.
Electron cyclotron resonance plasma photos
Racz, R.; Palinkas, J.; Biri, S.
2010-02-15
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.
Waves and Instabilities in AN Electron-Positron Plasma in AN Ultra-Strong Magnetic Field.
NASA Astrophysics Data System (ADS)
Pulsifer, Peter Emery
1987-09-01
Magnetic fields of up to 10^{13 } Gauss have been observed in pulsars. At these ultrastrong fields, the energy between Landau levels is comparable to the electron rest-mass, and the cyclotron radius is comparable to the Compton wavelength. To study the electromagnetic properties of an electron or positron gas in such ultrastrong fields, the polarization tensor Pi_{mu nu} is calculated. This response function is simply related to other functions like the dielectric and diamagnetic tensors. A dispersion relation is found involving Pi_{munu }, whose solution determines the frequency -wavenumber relation for propagating electromagnetic waves in the system. Damping of these waves is determined by the imaginary part of Pi_{mu nu}. A relativistic quantum-kinetic (Wigner function) technique is used. A relativistic treatment is needed partly because of the high magnetic field and partly because of the assumed high electron densities (of order 10 ^{29} cm^{ -3}). The quantum analog to the Vlasov equation is derived and linearized about a zero-temperature Fermi equilibrium, an approximation scheme equivalent to the random-phase-approximation (RPA). An integral equation is found for the four-current, which then determines the polarization tensor. The resulting dispersion is evaluated for propagation parallel to the magnetic field. In this case, solutions have one of three possible polarizations: longitudinal, right-circular and left-circular. Many acoustic-like waves are seen, arising from logarithmic peaks in Pi . The longitudinal plasmon oscillation, always undamped, is discussed. Generalizations of the cyclotron frequency and the whistler mode are considered. A previously unreported propagating wave, with frequency slightly above the pair-production energy, is discovered at all polarizations. Wave propagation and damping are analyzed in terms of two-body processes. Cutoffs and discontinuities in phase velocities of waves are noted and discussed in terms of the different
NASA Astrophysics Data System (ADS)
Goodrich, Katherine A.; Ergun, Robert E.; Stawarz, Julia E.
2016-06-01
We report observations of magnetic holes (MHs) in the near-Earth (8 RE to 12 RE) plasma sheet that have physical sizes perpendicular to the magnetic field (B) on the order of the ion Larmor radius (ρi) and, more importantly, have current layers less than ρi in thickness. Small-scale MHs can have >90% depletion in |B| and are commonly associated with the braking of bursty bulk flow events. The generation of MHs is often attributed to magnetohydrodynamic (MHD) instabilities, which requires a size greater than ρi; the depletion in |B| is from an ion current consistent with a pressure gradient. Electric field (E) observations indicate a negative potential inside of small-scale MHs that creates an outward E at the boundary, which drives an E × B electron current in a thin layer. These observations indicate that a Hall electron current is primarily responsible for the depletion of |B| in small-scale magnetic holes, rather than the ion pressure gradient.
Andreev, Pavel A. Kuz’menkov, L.S.
2015-10-15
We consider quantum plasmas of electrons and motionless ions. We describe separate evolution of spin-up and spin-down electrons. We present corresponding set of quantum hydrodynamic equations. We assume that plasmas are placed in an uniform external magnetic field. We account different occupation of spin-up and spin-down quantum states in equilibrium degenerate plasmas. This effect is included via equations of state for pressure of each species of electrons. We study oblique propagation of longitudinal waves. We show that instead of two well-known waves (the Langmuir wave and the Trivelpiece–Gould wave), plasmas reveal four wave solutions. New solutions exist due to both the separate consideration of spin-up and spin-down electrons and different occupation of spin-up and spin-down quantum states in equilibrium state of degenerate plasmas.
Rotation of a magnetized plasma
Annaratone, B. M.; Escarguel, A.; Lefevre, T.; Rebont, C.; Claire, N.; Doveil, F.
2011-03-15
The plasma rotation in the axial magnetic field of the linear machine Mistral [A. Escarguel, Eur. Phys. J. D 56, 209 (2010)] is well described by the assumption that the electrons injected from the source exit radially from the central column and are subject to the Lorentz force. Electrons and ions rotate together by ambipolarity. The solution of the momentum equations foresees correctly the observed radial dependence of the ionic radial velocity measured by laser induced fluorescence. The resolution of these equations is also in good agreement with the measured dependence of the rotation frequency on the applied magnetic field and on the background pressure.
Macroscopic magnetic islands and plasma energy transport
Cima, G; Porcelli, F; Rossi, E; Wootton, A J
1998-12-03
A model is presented, based on the combined effects of m=n=l magnetic island dynamics, localized heat sources, large heat diffusivity along magnetic field lines and plasma rotation, which may explain the multipeaked temperature profiles and transport barriers observed in tokamak plasmas heated by electron cyclotron resonant waves.
López, Rodrigo A.; Moya, Pablo S.; Muñoz, Víctor; Viñas, Adolfo F.; Valdivia, J. Alejandro
2014-09-15
We use a kinetic treatment to study the linear transverse dispersion relation for a magnetized isotropic relativistic electron-positron plasma with finite relativistic temperature. The explicit linear dispersion relation for electromagnetic waves propagating along a constant background magnetic field is presented, including an analytical continuation to the whole complex frequency plane for the case of Maxwell-Jüttner velocity distribution functions. This dispersion relation is studied numerically for various temperatures. For left-handed solutions, the system presents two branches, the electromagnetic ordinary mode and the Alfvén mode. In the low frequency regime, the Alfvén branch has two dispersive zones, the normal zone (where ∂ω/∂k > 0) and an anomalous zone (where ∂ω/∂k < 0). We find that in the anomalous zone of the Alfvén branch, the electromagnetic waves are damped, and there is a maximum wave number for which the Alfvén branch is suppressed. We also study the dependence of the Alfvén velocity and effective plasma frequency with the temperature. We complemented the analytical and numerical approaches with relativistic full particle simulations, which consistently agree with the analytical results.
Parametric analysis of a magnetized cylindrical plasma
Ahedo, Eduardo
2009-11-15
The relevant macroscopic model, the spatial structure, and the parametric regimes of a low-pressure plasma confined by a cylinder and an axial magnetic field is discussed for the small-Debye length limit, making use of asymptotic techniques. The plasma response is fully characterized by three-dimensionless parameters, related to the electron gyroradius, and the electron and ion collision mean-free-paths. There are the unmagnetized regime, the main magnetized regime, and, for a low electron-collisionality plasma, an intermediate-magnetization regime. In the magnetized regimes, electron azimuthal inertia is shown to be a dominant phenomenon in part of the quasineutral plasma region and to set up before ion radial inertia. In the main magnetized regime, the plasma structure consists of a bulk diffusive region, a thin layer governed by electron inertia, a thinner sublayer controlled by ion inertia, and the non-neutral Debye sheath. The solution of the main inertial layer yields that the electron azimuthal energy near the wall is larger than the electron thermal energy, making electron resistivity effects non-negligible. The electron Boltzmann relation is satisfied only in the very vicinity of the Debye sheath edge. Ion collisionality effects are irrelevant in the magnetized regime. Simple scaling laws for plasma production and particle and energy fluxes to the wall are derived.
NASA Astrophysics Data System (ADS)
Etemadpour, R.; Sepehri Javan, N.; Dorranian, D.
2016-05-01
The nonlinear dynamics of a circularly polarized laser pulse propagating in the magnetized plasmas whose constituents are superthermal ions and mixed nonthermal high-energy tail electrons is studied theoretically. A nonlinear equation which describes the dynamics of the slowly varying amplitude is obtained using a relativistic two-fluid model. Based on this nonlinear equation and taking into account some nonlinear phenomena such as modulational instability, self-focusing and soliton formation are investigated. Effect of the magnetized plasma with superthermal ions and mixed nonthermal high-energy tail electrons on these phenomena is considered. It is shown that the nonthermality and superthermality of particles can substantially change the nonlinearity of medium.
Peinetti, F.; Peano, F.; Coppa, G. . E-mail: gianni.coppa@polito.it; Wurtele, J.
2006-10-10
The present paper describes the numerical technique that has been developed, in the framework of the particle-in-cell (PIC) method, to study the dynamics of a nonneutral plasma along the magnetic field lines. In particular, the technique has been employed to simulate the formation and long-term evolution of large-amplitude electrostatic waves experimentally observed in electron plasmas confined in a Penning trap [W. Bertsche, J. Fajans, L. Friedland, Phys. Rev. Lett. 91 (2003) 265003]. Due to the peculiar features of the physical system, namely the existence of different time scales and the presence of a perturbative oscillating potential, ad hoc numerical techniques have been developed. In particular, with a suitable radial decomposition all important two-dimensional phenomena are fully taken into account while keeping the computational effort to that of a standard one-dimensional PIC codes. Moreover, a novel particle loading technique (ergodic loading) has been developed, which ensures a significant reduction of numerical noise. The results obtained with the present technique are in excellent agreement with the experiments [F. Peinetti, W. Bertsche, J. Fajans, J. Wurtele, L. Friedland, Phys. Plasmas 12 (2005) 062112]. Moreover, results presented here furnish clear evidences of the close relationship between the observed nonlinear structures and the Bernstein-Greene-Kruskal modes.
Plasma separation from magnetic field lines in a magnetic nozzle
NASA Technical Reports Server (NTRS)
Kaufman, D. A.; Goodwin, D. G.; Sercel, J. C.
1993-01-01
This paper discusses conditions for separation of a plasma from the magnetic field of a magnetic nozzle. The analysis assumes a collisionless, quasineutral plasma, and therefore the results represent a lower bound on the amount of detachment possible for a given set of plasma conditions. We show that collisionless separation can occur because finite electron mass inhibits the flow of azimuthal currents in the nozzle. Separation conditions are governed by a parameter G which depends on plasma and nozzle conditions. Several methods of improving plasma detachment are presented, including moving the plasma generation zone downstream from the region of strongest magnetic field and using dual magnets to focus the plasma beam. Plasma detachment can be enhanced by manipulation of the nozzle configuration.
NASA Astrophysics Data System (ADS)
Gashti, M. A.; Jafari, S.
2016-06-01
Electron acceleration based on a laser pulse propagating through plasma channel has been studied in the simultaneous presence of a helical magnetic wiggler and an obliquely applied external magnetic field. A numerical study of electron energy and electron trajectory has been made using the fourth-order Runge-kutta method. Numerical results indicate that electron energy increases with decreasing θ -angle of the obliquely external magnetic field. Besides, it increases with increasing the amplitude of the obliquely magnetic field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of the wiggler field Ωw . Therefore, employing a magnetic wiggler field is very beneficial for electron acceleration in short distances. Further new results reveal that in the absence of the wiggler field (Ωw=0) , the electron energy increases with increasing the laser intensity, whereas in the presence of the wiggler field (Ωwneq0) , the electron energy increases with decreasing the laser intensity. As a result, employing a wiggler magnetic field in the laser-based electron accelerators can be worthwhile in the design of table top accelerators and it can enhance the electron energy at lower laser intensities.
NASA Astrophysics Data System (ADS)
Willensdorfer, M.; Denk, S. S.; Strumberger, E.; Suttrop, W.; Vanovac, B.; Brida, D.; Cavedon, M.; Classen, I.; Dunne, M.; Fietz, S.; Fischer, R.; Kirk, A.; Laggner, F. M.; Liu, Y. Q.; Odstrčil, T.; Ryan, D. A.; Viezzer, E.; Zohm, H.; Luhmann, I. C.; The ASDEX Upgrade Team; The EUROfusion MST1 Team
2016-11-01
The plasma response from an external n = 2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement around the outboard midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the predictions from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components |m|>|nq| , whereas the poloidal mode structure of its displacement is almost resonant |m|≈ |nq| . This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response.
Production of a large, quiescent, magnetized plasma
NASA Technical Reports Server (NTRS)
Landt, D. L.; Ajmera, R. C.
1976-01-01
An experimental device is described which produces a large homogeneous quiescent magnetized plasma. In this device, the plasma is created in an evacuated brass cylinder by ionizing collisions between electrons emitted from a large-diameter electron gun and argon atoms in the chamber. Typical experimentally measured values of the electron temperature and density are presented which were obtained with a glass-insulated planar Langmuir probe. It is noted that the present device facilitates the study of phenomena such as waves and diffusion in magnetized plasmas.
Pulsed Plasma Electron Sources
NASA Astrophysics Data System (ADS)
Krasik, Yakov
2008-11-01
Pulsed (˜10-7 s) electron beams with high current density (>10^2 A/cm^2) are generated in diodes with electric field of E > 10^6 V/cm. The source of electrons in these diodes is explosive emission plasma, which limits pulse duration; in the case E < 10^5 V/cm this plasma is not uniform and there is a time delay in its formation. Thus, there is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E <= 10^5 V/cm. In the present report, several types of plasma electron source (PES) will be considered. The first type of PES is fiber-based cathodes, with and without CsI coating. The operation of these cathodes is governed by the formation of the flashover plasma which serves as a source of electrons. The second type of PES is the ferroelectric plasma source (FPS). The operation of FPS, characterized by the formation of dense surface flashover plasma is accompanied also by the generation of fast microparticles and energetic neutrals. The latter was explained by Coulomb micro-explosions of the ferroelectric surface due to an large time-varying electric field at the front of the expanding plasma. A short review of recent achievements in the operation of a multi-FPS-assisted hollow anode to generate a large area electron beam will be presented as well. Finally, parameters of the plasma produced by a multi-capillary cathode with FPS and velvet igniters will be discussed. Ya. E. Krasik, J. Z. Gleizer, D. Yarmolich, A. Krokhmal, V. Ts. Gurovich, S.Efimov, J. Felsteiner V. Bernshtam, and Yu. M. Saveliev, J. Appl. Phys. 98, 093308 (2005). Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner, Phys. Plasmas 8, 2466 (2001). D. Yarmolich, V. Vekselman, V. Tz. Gurovich, and Ya. E. Krasik, Phys. Rev. Lett. 100, 075004 (2008). J. Z. Gleizer, Y. Hadas and Ya. E. Krasik, Europhysics Lett. 82, 55001 (2008).
Kumar Samanta, Utpal; Saha, Asit; Chatterjee, Prasanta
2013-05-15
Bifurcations of nonlinear propagation of ion acoustic waves (IAWs) in a magnetized plasma whose constituents are cold ions and kappa distributed electron are investigated using a two component plasma model. The standard reductive perturbation technique is used to derive the Zakharov-Kuznetsov (ZK) equation for IAWs. By using the bifurcation theory of planar dynamical systems to this ZK equation, the existence of solitary wave solutions and periodic travelling wave solutions is established. All exact explicit solutions of these travelling waves are determined. The results may have relevance in dense space plasmas.
Yano, Keisuke Kurisu, Yosuke; Nozaki, Dai; Kimura, Daiju; Imai, Youta; Kumakura, Sho; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki
2014-02-15
Multi-charged ion source which has wide operating conditions is required in various application fields. We have constructed tandem type ECR ion source (ECRIS); one of the features of its main stage is an additional coil for controlling magnetic field distribution around the mirror bottom precisely. Here the effect of magnetic field variation caused by the additional coil is experimentally considered in terms of plasma parameters and beam current as the first investigation of the main stage plasma. Furthermore, behavior of magnetic lines of force flowing from the ECR zone is calculated, and is compared with measurement results aiming for better understanding of interrelationship between plasma production and ion beam generation on the ECRIS.
Anomalous Diffraction in Cold Magnetized Plasma.
Abelson, Z; Gad, R; Bar-Ad, S; Fisher, A
2015-10-01
Cold magnetized plasma possesses an anisotropic permittivity tensor with a unique dispersion relation that for adequate electron density and magnetic field results in anomalous diffraction of a right-hand circularly polarized beam. In this work, we demonstrate experimentally anomalous diffraction of a microwave beam in plasma. Additionally, decreasing the electron density enables observation of the transition of the material from a hyperbolic to a standard material. Manipulation of the control parameters will enable plasma to serve as a reconfigurable metamaterial-like medium. PMID:26551813
NASA Astrophysics Data System (ADS)
Rozhdestvensky, V. V.; Krikunov, S. V.; Lashkul, S. I.; Esipov, L. A.; Altukhov, A. B.; Kuprienko, D. V.
2014-03-01
Results of observation of anomalously intense microwave radiation (MR) in the electron plasma frequency range of 10-20 GHz that is generated continuously during ohmic heating of moderately dense plasma in the FT-2 tokamak are presented. Its appearance is associated with development of the "fan" plasma instability, and the presence of a large number of the local ripples of the toroidal magnetic field. It was found that MR is accompanied by the short gigantic and less intense flashes in the range of magnetic broadening of the first harmonic of the electron gyrofrequency (57-75 GHz). As is known, the latter occurs upon maser amplification of the synchrotron radiation of accelerated electrons interacting with the harmonics of local magnetic ripples in an autoresonance cyclotron mode. In our conditions, due to the nonlinear transformation of plasma waves into electromagnetic ones under the buildup of the fan instability, collective radiation (CR) is generated. Therefore, an abnormally high MR-intensity is probably due to CR maser amplification, whereas gigantic flashes occur during the self-excitation of maser amplifier under suitable conditions.
Permanent Magnet Ecr Plasma Source With Magnetic Field Optimization
Doughty, Frank C.; Spencer, John E.
2000-12-19
In a plasma-producing device, an optimized magnet field for electron cyclotron resonance plasma generation is provided by a shaped pole piece. The shaped pole piece adjusts spacing between the magnet and the resonance zone, creates a convex or concave resonance zone, and decreases stray fields between the resonance zone and the workpiece. For a cylindrical permanent magnet, the pole piece includes a disk adjacent the magnet together with an annular cylindrical sidewall structure axially aligned with the magnet and extending from the base around the permanent magnet. The pole piece directs magnetic field lines into the resonance zone, moving the resonance zone further from the face of the magnet. Additional permanent magnets or magnet arrays may be utilized to control field contours on a local scale. Rather than a permeable material, the sidewall structure may be composed of an annular cylindrical magnetic material having a polarity opposite that of the permanent magnet, creating convex regions in the resonance zone. An annular disk-shaped recurve section at the end of the sidewall structure forms magnetic mirrors keeping the plasma off the pole piece. A recurve section composed of magnetic material having a radial polarity forms convex regions and/or magnetic mirrors within the resonance zone.
NASA Astrophysics Data System (ADS)
Guo, Shimin; Mei, Liquan; He, Ya-Ling; Guo, Huaqi; Zhao, Yanjun
2016-04-01
The effect of trapped electrons featuring vortex-like distribution on the nonlinear behavior of a three-dimensional ion-acoustic shock wave is investigated in a magnetized ionic-pair plasma. In the long-wave approximation, the dynamics of the shock wave is governed by the (3{+}1) -dimensional Schamel-Zakharov-Kuznetsov-Burgers' equation due to the presence of trapped electrons and ion kinematic viscosity. By using the homogeneous balance principle and tanh function method, we obtain a novel exact shock wave solution of the equation. It is found for the first time that the trapped electrons can support a shock wave with only positive polarity.
NASA Astrophysics Data System (ADS)
Vinas, A. F.; Adrian, M. L.; Moya, P. S.; Wendel, D. E.
2015-12-01
The solar wind electron velocity distribution function (eVDF) displays a great variety of non-thermal features (e.g., core, halo and strahl electron populations; with superposition of different temperatures, thermal anisotropies, suprathermal tails, beam-like features, etc.) that deviate from thermal equilibrium. These electron nonthermal deviations provide a local source for whistler-cyclotron and firehose instabilities electromagnetic fluctuations that are commonly observed. We present clear observational evidence that the temperature anisotropy whistler instability threshold, of a nonthermal kappa distribution plasma, marginally bounds solar wind magnetic fluctuations — when the full electron distribution is considered, without regard of separation of the various electron components during slow solar wind periods. Analysis seems to suggest that during slow solar wind periods, collisional effects are dominant. During fast solar wind periods, magnetic fluctuations and solar wind anisotropies are enhanced above the parallel whistler anisotropic threshold boundary and collisional effects are drastically reduced. Preliminary calculations further show that the oblique electron whistler mirror anisotropic instability bounds both the slow and fast solar wind. Regardless of solar wind speed, the solar wind electron thermal anisotropy appears globally bounded by the parallel electron firehose instability for anisotropies Te⊥ / Te|| < 1 indicative of a firehose-stable electron plasma. Preliminary analysis suggests that skew-kappa nonthermal distributions also shows marginally stable threshold boundaries when considering electron heat flux instability thresholds. The results of our analysis suggests that the slow solar wind electron plasma, when considered globally as a single eVDF, is only marginally stable with respect to nonthermal skew kappa distributions and parallel propagating instabilities.
Magnetic insulation for plasma propulsion
NASA Technical Reports Server (NTRS)
Gonzalez, Dora E.
1990-01-01
The design parameters of effective magnetic insulation for plasma engines are discussed. An experimental model used to demonstrate the process of plasma acceleration and magnetic insulation is considered which consists of a copper strap that is wound around a glass tube and connected to a capacitor. In order to adequately model the magnetic insulation mechanisms, a computer algorithm is developed. Plasma engines, with their efficient utilization of the propellant mass, are expected to provide the next-generation advanced propulsion systems.
Nonlinear magnetohydrodynamics of electron-positron plasmas
NASA Astrophysics Data System (ADS)
Shukla, P. K.; Dasgupta, B.; Sakanaka, P. H.
2000-05-01
A set of nonlinear magnetohydrodynamic (MHD) equations for magnetized, nonrelativistic electron-positron plasmas is derived by employing a two fluid model that is supplemented by Ampère's and Faraday's laws. The nonlinear equations show how the baroclinic driver (the Biermann battery) generates the electron positron flows and how these flows give rise to plasma currents which act as a source for the magnetic fields. The newly derived nonlinear equations form a basis for investigating waves, instabilities, as well as coherent nonlinear structures, in addition to studying exact equilibria of electron-positron jets in a magnetoplasma.
Plasma lenses for focusing relativistic electron beams
Govil, R.; Wheeler, S.; Leemans, W.
1997-04-01
The next generation of colliders require tightly focused beams with high luminosity. To focus charged particle beams for such applications, a plasma focusing scheme has been proposed. Plasma lenses can be overdense (plasma density, n{sub p} much greater than electron beam density, n{sub b}) or underdense (n{sub p} less than 2 n{sub b}). In overdense lenses the space-charge force of the electron beam is canceled by the plasma and the remaining magnetic force causes the electron beam to self-pinch. The focusing gradient is nonlinear, resulting in spherical aberrations. In underdense lenses, the self-forces of the electron beam cancel, allowing the plasma ions to focus the beam. Although for a given beam density, a uniform underdense lens produces smaller focusing gradients than an overdense lens, it produces better beam quality since the focusing is done by plasma ions. The underdense lens can be improved by tapering the density of the plasma for optimal focusing. The underdense lens performance can be enhanced further by producing adiabatic plasma lenses to avoid the Oide limit on spot size due to synchrotron radiation by the electron beam. The plasma lens experiment at the Beam Test Facility (BTF) is designed to study the properties of plasma lenses in both overdense and underdense regimes. In particular, important issues such as electron beam matching, time response of the lens, lens aberrations and shot-to-shot reproducibility are being investigated.
Filamentation instability in a quantum magnetized plasma
Bret, A.
2008-02-15
The filamentation instability occurring when a nonrelativistic electron beam passes through a quantum magnetized plasma is investigated by means of a cold quantum magnetohydrodynamic model. It is proved that the instability can be completely suppressed by quantum effects if and only if a finite magnetic field is present. A dimensionless parameter is identified that measures the strength of quantum effects. Strong quantum effects allow for a much smaller magnetic field to suppress the instability than in the classical regime.
Plasma transport in mixed magnetic topologies
Hegna, C.C.; Callen, J.D.
1992-12-01
A simple model is introduced to illustrate some features concerning anomalous transport associated with magnetic turbulence. For magnetic topologies that are described as bands of stochasticity separated by regions with good flux surfaces, the transport coefficients deviate significantly from those describing completely stochastic magnetic fields. It is possible to have the electron heat diffusivity exceed a runaway electron diffusion coefficient, despite the existence of widespread magnetic stochasticity. Comparing the ratios of transport coefficients is not an accurate way to determine whether anomalous plasma transport is controlled by electrostatic or electromagnetic fluctuations.
NASA Astrophysics Data System (ADS)
Toncian, Toma; Hegelich, Bjorn Manuel; Willi, Oswald; Lehmann, Goetz
2014-10-01
First direct measurements of the electron transport along extended wire targets by Quinn et al. [PRL 102 (2009)] revealed a charging current and associated magnetic field moving close to the speed of light away from focal volume of the employed heating laser. The motion of the electrons is bound electrostatic to the proximity of the solid. A return current compensating the escaping charge is formed at the surface of the solid, the overall current loop sustaining kT magnetic fields, with traversal decay lengths of μm. In our study we show by means of numerical 2 dimensional particle in cell simulations that the motion of the hot electrons and dynamic of the charge compensating return current can be dramatically affected by a preformed μm scale length plasma gradient on the solid surface. In particularly the two velocities distribution and two antiparallel currents developing in the near critical plasma are unstable in respect of two stream and Kevin Helmholtz instability. The particle motion becomes locally magnetized resulting in current eddies trapping particles and localized magnetic and electric fields with values of tens of kT and TV/m sustained on μm scales and with characteristic decay times of ps.
NASA Astrophysics Data System (ADS)
Pramanik, Sourav; Kuznetsov, V. I.; Gerasimenko, A. B.; Chakrabarti, Nikhil
2016-10-01
An analytical study is presented on the steady states of a plasma diode that is uniformly occupied by infinitely massive ions of constant density and driven by a cold electron beam in the presence of an external transverse magnetic field. In contrast to our previous work [Pramanik et al., Phys. Plasmas 23, 062118 (2016)], here, we investigate the case when electrons are reflected back to the emitter by the magnetic field for arbitrary values of the neutralization parameter. Using the emitter electric field as a characteristic parameter, the steady-state solutions have been evaluated for the specific values of the diode gap, applied voltage, neutralization parameter, and magnetic field strength. It was found that unlike vacuum diodes (e.g., the Bursian diode), steady state solutions also exist for negative values of the emitter field strength. In case of the Bursian diode, only a single type of solutions (Bursian branches) was observed. However, for the Pierce diode, the new family of solutions appeared along with the Bursian ones. In the absence of the external magnetic field as well as when it is weak, the potential distribution shows a wavy nature. However, when the Larmor radius was ten times the beam Debye length, the wavy potential profile and non-Bursian branches disappeared. Based on this phenomenon, a non-neutral diode can be used to operate fast electronic switches.
Ceccolini, E; Rocchi, F; Mostacci, D; Sumini, M; Tartari, A
2011-08-01
The electron beam emitted from the back of plasma focus devices is being studied as a radiation source for intraoperative radiation therapy applications. A plasma focus device is being developed for this purpose, and there is a need for characterizing its electron beam, particularly, insofar as the energy spectrum is concerned. The instrument used is a magnetic spectrometer. To calibrate this spectrometer, a procedure relying on the energy-range relation in Mylar® has been devised and applied. By measuring the transmission through increasing thicknesses of the material, electron energies could be assessed and compared to the spectrometer readings. Thus, the original calibration of the instrument has been extended to higher energies and also to better accuracy. Methods and results are presented. PMID:21895271
Ceccolini, E.; Mostacci, D.; Sumini, M.; Rocchi, F.; Tartari, A.
2011-08-15
The electron beam emitted from the back of plasma focus devices is being studied as a radiation source for intraoperative radiation therapy applications. A plasma focus device is being developed for this purpose, and there is a need for characterizing its electron beam, particularly, insofar as the energy spectrum is concerned. The instrument used is a magnetic spectrometer. To calibrate this spectrometer, a procedure relying on the energy-range relation in Mylar has been devised and applied. By measuring the transmission through increasing thicknesses of the material, electron energies could be assessed and compared to the spectrometer readings. Thus, the original calibration of the instrument has been extended to higher energies and also to better accuracy. Methods and results are presented.
Forced Magnetic Reconnection In A Tokamak Plasma
NASA Astrophysics Data System (ADS)
Callen, J. D.; Hegna, C. C.
2015-11-01
The theory of forced magnetic field reconnection induced by an externally imposed resonant magnetic perturbation usually uses a sheared slab or cylindrical magnetic field model and often focuses on the potential time-asymptotic induced magnetic island state. However, tokamak plasmas have significant magnetic geometry and dynamical plasma toroidal rotation screening effects. Also, finite ion Larmor radius (FLR) and banana width (FBW) effects can damp and thus limit the width of a nascent magnetic island. A theory that is more applicable for tokamak plasmas is being developed. This new model of the dynamics of forced magnetic reconnection considers a single helicity magnetic perturbation in the tokamak magnetic field geometry, uses a kinetically-derived collisional parallel electron flow response, and employs a comprehensive dynamical equation for the plasma toroidal rotation frequency. It is being used to explore the dynamics of bifurcation into a magnetically reconnected state in the thin singular layer around the rational surface, evolution into a generalized Rutherford regime where the island width exceeds the singular layer width, and assess the island width limiting effects of FLR and FBW polarization currents. Support by DoE grants DE-FG02-86ER53218, DE-FG02-92ER54139.
Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device
NASA Astrophysics Data System (ADS)
Hu, Guanghai; Jin, Xiaoli; Yuan, Lin; Zhang, Qiaofeng; Xie, Jinlin; Li, Hong; Liu, Wandong
2016-09-01
Plasma source is the most important part of the laboratory plasma platform for fundamental plasma experimental research. Barium oxide coated cathode plasma source is well recognized as an effective technique due to its high electron emission current. An indirectly heated oxide coated cathode plasma source has been constructed on a linear magnetized plasma device. The electron emission current density can reach 2 A/cm2 to 6 A/cm2 in pulsed mode within pulse length 5-20 ms. A 10 cm diameter, 2 m long plasma column with density 1018 m-3 to 1019 m3 and electron temperature Te ≃ 3-7 eV is produced. The spatial uniformity of the emission ability is less than 4% and the discharge reproducibility is better than 97%. With a wide range of the plasma parameters, this kind of plasma source provides great flexibility for many basic plasma investigations. The detail of construction and initial characterization of oxide coated cathode are described in this paper. supported by National Natural Science Foundation of China (No. 11275200)
Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device
NASA Astrophysics Data System (ADS)
Hu, Guanghai; Jin, Xiaoli; Yuan, Lin; Zhang, Qiaofeng; Xie, Jinlin; Li, Hong; Liu, Wandong
2016-09-01
Plasma source is the most important part of the laboratory plasma platform for fundamental plasma experimental research. Barium oxide coated cathode plasma source is well recognized as an effective technique due to its high electron emission current. An indirectly heated oxide coated cathode plasma source has been constructed on a linear magnetized plasma device. The electron emission current density can reach 2 A/cm2 to 6 A/cm2 in pulsed mode within pulse length 5–20 ms. A 10 cm diameter, 2 m long plasma column with density 1018 m‑3 to 1019 m3 and electron temperature Te ≃ 3–7 eV is produced. The spatial uniformity of the emission ability is less than 4% and the discharge reproducibility is better than 97%. With a wide range of the plasma parameters, this kind of plasma source provides great flexibility for many basic plasma investigations. The detail of construction and initial characterization of oxide coated cathode are described in this paper. supported by National Natural Science Foundation of China (No. 11275200)
NASA Astrophysics Data System (ADS)
Das, Jayasree; Bandyopadhyay, Anup; Das, K. P.; Das
2014-02-01
Schamel's modified Korteweg-de Vries-Zakharov-Kuznetsov (S-ZK) equation, governing the behavior of long wavelength, weak nonlinear ion acoustic waves propagating obliquely to an external uniform static magnetic field in a plasma consisting of warm adiabatic ions and non-thermal electrons (due to the presence of fast energetic electrons) having vortex-like velocity distribution function (due to the presence of trapped electrons), immersed in a uniform (space-independent) and static (time-independent) magnetic field, admits solitary wave solutions having a sech 4 profile. The higher order stability of this solitary wave solution of the S-ZK equation has been analyzed with the help of multiple-scale perturbation expansion method of Allen and Rowlands (Allen, M. A. and Rowlands, G. 1993 J. Plasma Phys. 50, 413; 1995 J. Plasma Phys. 53, 63). The growth rate of instability is obtained correct to the order k 2, where k is the wave number of a long wavelength plane wave perturbation. It is found that the lowest order (at the order k) instability condition is strongly sensitive to the angle of propagation (δ) of the solitary wave with the external uniform static magnetic field, whereas at the next order (at the order k 2) the solitary wave solutions of the S-ZK equation are unstable irrespective of δ. It is also found that the growth rate of instability up to the order k 2 for the electrons having Boltzmann distribution is higher than that of the non-thermal electrons having vortex-like distribution for any fixed δ.
Vortices, Reconnection and Turbulence in High Electron-Beta Plasmas
Stenzel, R. L.
2004-08-31
Plasmas in which the kinetic energy exceeds the magnetic energy by a significant factor are common in space and in the laboratory. Such plasmas can convect magnetic fields and create null points in whose vicinity first the ions become unmagnetized, then the electrons. This project focuses on the detailed study of the transition regime of these plasmas.
Stoschus, H.; Schmitz, O.; Frerichs, H.; Unterberg, B.; Abdullaev, S. S.; Clever, M.; Coenen, J. W.; Kruezi, U.; Schega, D.; Samm, U.; Jakubowski, M. W.
2010-06-15
Measurements of the plasma edge electron density n{sub e} and temperature T{sub e} fields during application of a fast rotating, resonant magnetic perturbation (RMP) field show a characteristic modulation of both, n{sub e} and T{sub e} coherent to the rotation frequency of the RMP field. A phase delay PHI between the n{sub e}(t) and T{sub e}(t) waveforms is observed and it is demonstrated that this phase delay PHI is a function of the radius with PHI(r) depending on the relative rotation of the RMP field and the toroidal plasma rotation. This provides for the first time direct experimental evidence for a rotation dependent damping of the external RMP field in the edge layer of a resistive high-temperature plasma which breaks down at low rotation and high resonant field amplitudes.
Ramos, J. J.
2010-08-15
A closed theoretical model to describe slow, macroscopic plasma processes in a fusion-relevant collisionality regime is set forward. This formulation is a hybrid one, with fluid conservation equations for particle number, momentum and energy, and drift-kinetic closures. Intended for realistic application to the core of a high-temperature tokamak plasma, the proposed approach is unconventional in that the ion collisionality is ordered lower than in the ion banana regime of neoclassical theory. The present first part of a two-article series concerns the electron system, which is still equivalent to one based on neoclassical electron banana orderings. This system is derived such that it ensures the precise compatibility among the complementary fluid and drift-kinetic equations, and the rigorous treatment of the electric field and the Fokker-Planck-Landau collision operators. As an illustrative application, the special limit of an axisymmetric equilibrium is worked out in detail.
Electron trapping around a magnetic null
NASA Astrophysics Data System (ADS)
He, J.-S.; Zong, Q.-G.; Deng, X.-H.; Tu, C.-Y.; Xiao, C.-J.; Wang, X.-G.; Ma, Z.-W.; Pu, Z.-Y.; Lucek, E.; Pedersen, A.; Fazakerley, A.; Cornilleau-Wehrlin, N.; Dunlop, M. W.; Tian, H.; Yao, S.; Tan, B.; Fu, S.-Y.; Glassmeier, K.-H.; Reme, H.; Dandouras, I.; Escoubet, C. P.
2008-07-01
Magnetic reconnection is an important process in astrophysical, space and laboratory plasmas. The magnetic null pair structure is theoretically suggested to be a crucial feature of the three-dimensional magnetic reconnection. The physics around the null pair, however, has not been explored in combination with the magnetic field configuration deduced from in situ observations. Here, we report the identification of the configuration around a null pair and simultaneous electron dynamics near one null of the pair, observed by four Cluster spacecraft in the geo-magnetotail. Further, we propose a new scenario of electron dynamics in the null region, suggesting that electrons are temporarily trapped in the central reconnection region including electron diffusion region resulting in an electron density peak, accelerated possibly by parallel electric field and electron pressure gradient, and reflected from the magnetic cusp mirrors leading to the bi-directional energetic electron beams, which excite the observed high frequency electrostatic waves.
Magnetic confinement of a high-density cylindrical plasma
Ahedo, Eduardo
2011-10-15
The stationary structure of a weakly collisional plasma column, confined by an axial magnetic field and a cylindrical vessel, is studied for the high-density case, when the diamagnetic azimuthal current is large enough to demagnetize partially the plasma. The plasma response is characterized mainly by two dimensionless parameters: the ratios of the electron gyroradius and the electron skin-depth to the plasma radius, and each of them measures the independent influence of the applied magnetic field and the plasma density on the plasma response. The strong magnetic confinement regime, characterized by very small wall losses, is limited to the small gyroradius and large skin-depth ranges. In the high-density case, when the electron skin-depth is smaller than the electron gyroradius, the skin-depth turns out to be the magnetic screening length, so that the bulk of the plasma behaves as unmagnetized.
Runaway electrons and magnetic island confinement
NASA Astrophysics Data System (ADS)
Boozer, Allen H.
2016-08-01
The breakup of magnetic surfaces is a central feature of ITER planning for the avoidance of damage due to runaway electrons. Rapid thermal quenches, which lead to large accelerating voltages, are thought to be due to magnetic surface breakup. Impurity injection to avoid and to mitigate both halo and runaway electron currents utilizes massive gas injection or shattered pellets. The actual deposition is away from the plasma center, and the breakup of magnetic surfaces is thought to spread the effects of the impurities across the plasma cross section. The breakup of magnetic surfaces would prevent runaway electrons from reaching relativistic energies were it not for the persistence of non-intercepting flux tubes. These are tubes of magnetic field lines that do not intercept the walls. In simulations and in magnetic field models, non-intercepting flux tubes are found to persist near the magnetic axis and in the cores of magnetic islands even when a large scale magnetic surface breakup occurs. As long as a few magnetic surfaces reform before all of the non-intercepting flux tubes dissipate, energetic electrons confined and accelerated in these flux tubes can serve as the seed electrons for a transfer of the overall plasma current from thermal to relativistic carriers. The acceleration of electrons is particularly strong because of the sudden changes in the poloidal flux that naturally occur in a rapid magnetic relaxation. The physics of magnetic islands as non-intercepting flux tubes is studied. Expressions are derived for (1) the size of islands required to confine energetic runaway electrons, (2) the accelerating electric field in an island, (3) the increase or reduction in the size of an island by the runaway electron current, (4) the approximate magnitude of the runaway current in an island, and (5) the time scale for the evolution of an island.
NASA Astrophysics Data System (ADS)
Araghi, F.; Dorranian, D.
2016-02-01
Effect of dust electrical charge fluctuations on the nature of dust acoustic solitary waves (DASWs) in a four-species magnetized dusty plasma containing nonextensive electrons and two-temperature isothermal ions has been investigated. In this model, the negative dust electric charge is considered to be proportional to the plasma space potential. The nonlinear Zakharov-Kuznetsov (ZK) and modified Zakharov-Kuznetsov (mZK) equations are derived for DASWs by using the standard reductive perturbation method. The combined effects of electron nonextensivity and dust charge fluctuations on the DASW profile are analyzed. The different ranges of the nonextensive q-parameter are considered. The results show that solitary waves the amplitude and width of which depend sensitively on the nonextensive q-parameter can exist. Due to the electron nonextensivity and dust charge fluctuation rate, our dusty plasma model can admit both positive and negative potential solitons. The results show that the amplitude of the soliton increases with increasing electron nonextensivity, but its width decreases. Increasing the electrical charge fluctuations leads to a decrease in both the amplitude and width of DASWs.
Electron Diffraction Experiments using Laser Plasma Electrons
Fill, E E; Trushin, S; Tommasini, R; Bruch, R
2005-09-07
We demonstrate that electrons emitted from a laser plasma can be used to generate diffraction patterns in reflection and transmission. The electrons are emitted in the direction of laser polarization with energies up to 100 keV. The broad electron energy spectrum makes possible the generation of a ''streaked'' diffraction pattern which allows recording fast processes in a single run.
Spin solitons in magnetized pair plasmas
Brodin, G.; Marklund, M.
2007-11-15
A set of fluid equations, taking into account the spin properties of the electrons and positrons in a magnetoplasma, are derived. The magnetohydrodynamic limit of the pair plasma is investigated. It is shown that the microscopic spin properties of the electrons and positrons can lead to interesting macroscopic and collective effects in strongly magnetized plasmas. In particular, it is found that new Alfvenic solitary structures, governed by a modified Korteweg-de Vries equation, are allowed in such plasmas. These solitary structures vanish if the quantum spin effects are neglected. Our results should be of relevance for astrophysical plasmas, e.g., in pulsar magnetospheres, as well as for low-temperature laboratory plasmas.
NASA Astrophysics Data System (ADS)
Sayyar, M.; Zahed, H.; Pestehe, S. J.; Sobhanian, S.
2016-07-01
Using the Sagdeev pseudo-potential method, the oblique propagation of dust-ion acoustic solitary waves is studied in a magnetized dusty plasma. By considering non-thermal distribution of electrons, the related pseudo-potential is obtained using the Poisson equation. The behavior of the wave is investigated for some ranges of parameters. It is demonstrated that the increase in ion density, lz, β, and also δ1 can lead to the increases in the width and amplitude of the pseudo-potential, while any increase of a2, the coefficient that describes the first nonlinear term in the G ( ϕ ) , increases the amplitude of the V ( ϕ ) .
Dynamics of exploding plasmas in a large magnetized plasma
Niemann, C.; Gekelman, W.; Constantin, C. G.; Everson, E. T.; Schaeffer, D. B.; Clark, S. E.; Zylstra, A. B.; Pribyl, P.; Tripathi, S. K. P.; Bondarenko, A. S.; Winske, D.; Larson, D.; Glenzer, S. H.
2013-01-15
The dynamics of an exploding laser-produced plasma in a large ambient magneto-plasma was investigated with magnetic flux probes and Langmuir probes. Debris-ions expanding at super-Alfvenic velocity (up to M{sub A}=1.5) expel the ambient magnetic field, creating a large (>20 cm) diamagnetic cavity. We observe a field compression of up to B/B{sub 0}=1.5 as well as localized electron heating at the edge of the bubble. Two-dimensional hybrid simulations reproduce these measurements well and show that the majority of the ambient ions are energized by the magnetic piston and swept outside the bubble volume. Nonlinear shear-Alfven waves ({delta}B/B{sub 0}>25%) are radiated from the cavity with a coupling efficiency of 70% from magnetic energy in the bubble to the wave.
Electron plasma dynamics during autoresonant excitation of the diocotron mode
Baker, C. J. Danielson, J. R. Hurst, N. C. Surko, C. M.
2015-02-15
Chirped-frequency autoresonant excitation of the diocotron mode is used to move electron plasmas confined in a Penning-Malmberg trap across the magnetic field for advanced plasma and antimatter applications. Plasmas of 10{sup 8} electrons, with radii small compared to that of the confining electrodes, can be moved from the magnetic axis to ≥90% of the electrode radius with near unit efficiency and reliable angular positioning. Translations of ≥70% of the wall radius are possible for a wider range of plasma parameters. Details of this process, including phase and displacement oscillations in the plasma response and plasma expansion, are discussed, as well as possible extensions of the technique.
Strongly magnetized classical plasma models
NASA Technical Reports Server (NTRS)
Montgomery, D.; Peyraud, J.; Dewitt, C.
1974-01-01
Discrete particle processes in the presence of a strong external magnetic field were investigated. These processes include equations of state and other equilibrium thermodynamic relations, thermal relaxation phenomena, transport properties, and microscopic statistical fluctuations in such quantities as the electric field and the charge density. Results from the equilibrium statistical mechanics of two-dimensional plasmas are discussed, along with nonequilibrium statistical mechanics of the electrostatic guiding-center plasma (a two-dimensional plasma model).
Electron Beam Emission Characteristics from Plasma Focus Devices
NASA Astrophysics Data System (ADS)
Zhang, T.; Patran, A.; Wong, D.; Hassan, S. M.; Springham, S. V.; Tan, T. L.; Lee, P.; Lee, S.; Rawat, R. S.
2006-01-01
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.
Electron density measurements in highly electronegative plasmas
NASA Astrophysics Data System (ADS)
Rafalskyi, D.; Lafleur, T.; Aanesland, A.
2016-08-01
In this paper we present experimental measurements of the electron density in very electronegative ‘ion–ion’ Ar–SF6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than ±2 · 1013 m‑3. The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 1013 m‑3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF6 plasma, while adding only 6% SF6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources.
Electron density measurements in highly electronegative plasmas
NASA Astrophysics Data System (ADS)
Rafalskyi, D.; Lafleur, T.; Aanesland, A.
2016-08-01
In this paper we present experimental measurements of the electron density in very electronegative ‘ion-ion’ Ar-SF6 plasmas where previous investigations using Langmuir probes have observed electronegativities of up to 5000. The electron density is measured using a short matched dipole probe technique that provides a tolerance better than ±2 · 1013 m-3. The results demonstrate that the electron density in the low pressure plasma source (which contains a magnetic filter) can be reduced to around 2.7 · 1013 m-3 with a corresponding plasma electronegativity of about 4000; close to that from fluid simulation predictions. The highest electronegativity, and lowest electron density, is achieved with a pure SF6 plasma, while adding only 6% SF6 to Ar allows the electronegativity to be increased from 0 to a few hundred with a corresponding decrease in the electron density by more than a thousand. The impedance probe based on a short matched dipole appears to be a practical diagnostic that can be used for independent measurements of the electron density in very electronegative plasmas, and opens up the possibility to further investigate and optimize electronegative plasma sources.
Condensation modes in magnetized plasmas
NASA Technical Reports Server (NTRS)
An, Chang-Hyuk
1986-01-01
Condensation modes in magnetized cylindrical plasmas, with concentration on how magnetic field affects the stability were studied. It is found that the effects of magnetic field (shear, twist, and strength) on the condensation modes are different depending on the wave vector. For modes whose wave vector is not perpendicular to magnetic field lines the plasma motion is mainly along the field lines; the effects of magnetic field on the modes are negligible except on the heat flow parallel to the field line. For a mode which is localized near a surface where the wave vector is perpendicular to the field line, the plasma moves perpendicular to the line carrying the field line into the condensed region; magnetic field affects the mode by building up magnetic pressure in the condensed region. The stability of condensation modes strongly depends on how density and temperature vary with field twist. The stable nature of global quiescent prominence magnetic configurations implies that prominences form for low field twist for which ideal MHD modes are stable; plasma temperature should increase with field twist for stable prominence formation.
NASA Astrophysics Data System (ADS)
Hadjaz, Idir; Tribeche, Mouloud
2014-06-01
Alternative localized dust-ion acoustic waves are investigated in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution. The correct non-Maxwellian charging currents are obtained based on the well-known orbit limited motion theory. Following the standard reductive perturbation technique, a Schamel-Zakharov Kuznetsov Burgers (S-ZKB) equation is derived. It is shown that due to an interplay between trapping and nonthermality, our dusty plasma model may support solitary as well as shock waves the main quantities (phase velocity, amplitude and width) of which are drastically influenced by trapping, nonthermality and charge variation. Due to the flexibility provided by the outlined distribution function (two concepts of non isothermality), we stress that our model should provide a good fit of the space observations.
Kuppel, S.; Matsushita, D.; Hatayama, A.; Bacal, M.
2010-02-15
The physical mechanisms involved in the extraction of H{sup -} ions from the negative ion source are studied with a PIC 2D3V code. The effect of a weak magnetic field transverse to the extraction direction is taken into account, along with a variable bias voltage applied on the plasma electrode (PE). In addition to previous modeling works, the electron diffusion across the magnetic field is taken into account as a simple one-dimensional random-walk process. The results show that without PE bias, the value of the diffusion coefficient has a significant influence upon the value of the extracted H{sup -} current. However, the value of this coefficient does not affect qualitatively the mechanism leading to the peak of extracted H{sup -} ion current observed for an optimum value of the PE bias.
Electron cyclotron emission imaging in tokamak plasmas
Munsat, Tobin; Domier, Calvin W.; Kong, Xiangyu; Liang, Tianran; Luhmann, Jr.; Neville C.; Tobias, Benjamin J.; Lee, Woochang; Park, Hyeon K.; Yun, Gunsu; Classen, Ivo. G. J.; Donne, Anthony J. H.
2010-07-01
We discuss the recent history and latest developments of the electron cyclotron emission imaging diagnostic technique, wherein electron temperature is measured in magnetically confined plasmas with two-dimensional spatial resolution. The key enabling technologies for this technique are the large-aperture optical systems and the linear detector arrays sensitive to millimeter-wavelength radiation. We present the status and recent progress on existing instruments as well as new systems under development for future experiments. We also discuss data analysis techniques relevant to plasma imaging diagnostics and present recent temperature fluctuation results from the tokamak experiment for technology oriented research (TEXTOR).
Magnetic stochasticity in gyrokinetic simulations of plasma microturbulence
Nevins, W M; Wang, E; Candy, J
2010-02-12
Analysis of the magnetic field structure from electromagnetic simulations of tokamak ion temperature gradient turbulence demonstrates that the magnetic field can be stochastic even at very low plasma pressure. The degree of magnetic stochasticity is quantified by evaluating the magnetic diffusion coefficient. We find that the magnetic stochasticity fails to produce a dramatic increase in the electron heat conductivity because the magnetic diffusion coefficient remains small.
Conceptual Design of Electron-Beam Generated Plasma Tools
NASA Astrophysics Data System (ADS)
Agarwal, Ankur; Rauf, Shahid; Dorf, Leonid; Collins, Ken; Boris, David; Walton, Scott
2015-09-01
Realization of the next generation of high-density nanostructured devices is predicated on etching features with atomic layer resolution, no damage and high selectivity. High energy electron beams generate plasmas with unique features that make them attractive for applications requiring monolayer precision. In these plasmas, high energy beam electrons ionize the background gas and the resultant daughter electrons cool to low temperatures via collisions with gas molecules and lack of any accelerating fields. For example, an electron temperature of <0.6 eV with densities comparable to conventional plasma sources can be obtained in molecular gases. The chemistry in such plasmas can significantly differ from RF plasmas as the ions/radicals are produced primarily by beam electrons rather than those in the tail of a low energy distribution. In this work, we will discuss the conceptual design of an electron beam based plasma processing system. Plasma properties will be discussed for Ar, Ar/N2, and O2 plasmas using a computational plasma model, and comparisons made to experiments. The fluid plasma model is coupled to a Monte Carlo kinetic model for beam electrons which considers gas phase collisions and the effect of electric and magnetic fields on electron motion. The impact of critical operating parameters such as magnetic field, beam energy, and gas pressure on plasma characteristics in electron-beam plasma processing systems will be discussed. Partially supported by the NRL base program.
Guo, Shimin Mei, Liquan
2014-08-15
Dust-ion-acoustic (DIA) rogue waves are investigated in a three-dimensional magnetized plasma containing nonthermal electrons featuring Tsallis distribution, both positive and negative ions, and immobile dust grains having both positive and negative charges. Via the reductive perturbation method, a (3 + 1)-dimensional nonlinear Schrödinger (NLS) equation is derived to govern the dynamics of the DIA wave packets. The modulation instability of DIA waves described by the (3 + 1)-dimensional NLS equation is investigated. By means of the similarity transformation and symbolic computation, both the first- and second-order rogue wave solutions of the (3 + 1)-dimensional NLS equation are constructed in terms of rational functions. Moreover, the dynamics properties and the effects of plasma parameters on the nonlinear structures of rogue waves are discussed in detail. The results could be useful for understanding the physical mechanism of rogue waves in laboratory experiments where pair-ion plasmas with electrons and dust grains can be found.
NASA Astrophysics Data System (ADS)
Suvorova, A. V.; Huang, C.-M.; Dmitriev, A. V.; Kunitsyn, V. E.; Andreeva, E. S.; Nesterov, I. A.; Klimenko, M. V.; Klimenko, V. V.; Tumanova, Yu. S.
2016-06-01
The initial phase of a major geomagnetic storm on 14 December 2006 was selected in order to investigate the ionizing effect of energetic electrons in the ionosphere. The global network of GPS receivers was used to analyze the total electron content (TEC). A strong positive ionospheric storm of ~20 TEC units (TECU) with ~6 h duration was observed on the dayside during the interval of northward interplanetary magnetic field. At the same time, the NOAA/POES satellites observed long-lasting intense fluxes of >30 keV electrons in the topside ionosphere at middle and low latitudes, including a near-equatorial forbidden zone outside of the South Atlantic Anomaly (SAA). We found that the TEC increases overlapped well with the enhancements of energetic electrons. Modeling of the ionospheric response by using a Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere, based on the standard mechanisms of plasma transport, could only partially explain the ionospheric response and was unable to predict the long-duration increase of TEC. For the energetic electrons, we estimated the ionizing effect of ~45 TECU and ~23 TECU in the topside ionosphere, respectively, inside and outside of SAA. The ionizing effect contributed from 50% to 100% of TEC increases and provided the long duration and wide latitudinal extension of the positive ionospheric storm. This finding is a very important argument in supporting significant ionizing effect of energetic electrons in the storm time ionosphere both at middle and low latitudes.
Magnetic reconnection in space plasmas
Gosling, J.; Feldman, W.; Walthour, D.
1996-04-01
This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Magnetic reconnection produces fundamental changes in the magnetic field topology of plasmas and leads ultimately to substantial plasma heating and acceleration. The transfer of stored magnetic field energy to the plasma occurs primarily at thin conversion layers that extend outward from the reconnection site. We performed a comparative study of the structure and nature of these conversion layers as observed during reconnection at Earth`s magnetopause and in the geomagnetic tail. Our research utilized plasma and magnetic field data from the Earth-orbiting ISEE satellites during crossings of the conversion layers at the magnetopause and in the geomagnetic tail, as well as data obtained during a long-duration balloon flight in Antarctica and simultaneously from satellites in geosynchronous orbit. We have found that the reconnection layer at the magnetopause usually does not contain a slow mode shock, contrary to earlier theoretical expectations. Through a coordinated analysis of data obtained from balloon altitudes and at geosynchronous orbit, we obtained evidence that reconnection can occur simultaneously in both hemispheres at the magnetopause above the polar caps. The final year of our study was oriented primarily towards the question of determining the magnetic topology of disturbances in the solar wind associated with coronal mass ejections (CMEs) and understanding how that topology is affected by magnetic reconnection occurring near the Sun.
Localized whistlers in magnetized spin quantum plasmas
Misra, A. P.; Brodin, G.; Marklund, M.; Shukla, P. K.
2010-11-15
The nonlinear propagation of electromagnetic (EM) electron-cyclotron waves (whistlers) along an external magnetic field, and their modulation by electrostatic small but finite amplitude ion-acoustic density perturbations are investigated in a uniform quantum plasma with intrinsic spin of electrons. The effects of the quantum force associated with the Bohm potential and the combined effects of the classical as well as the spin-induced ponderomotive forces (CPF and SPF, respectively) are taken into consideration. The latter modify the local plasma density in a self-consistent manner. The coupled modes of wave propagation is shown to be governed by a modified set of nonlinear Schroedinger-Boussinesq-like equations which admit exact solutions in form of stationary localized envelopes. Numerical simulation reveals the existence of large-scale density fluctuations that are self-consistently created by the localized whistlers in a strongly magnetized high density plasma. The conditions for the modulational instability (MI) and the value of its growth rate are obtained. Possible applications of our results, e.g., in strongly magnetized dense plasmas and in the next generation laser-solid density plasma interaction experiments are discussed.
Magnetic Flux Compression in Plasmas
NASA Astrophysics Data System (ADS)
Velikovich, A. L.
2012-10-01
Magnetic flux compression (MFC) as a method for producing ultra-high pulsed magnetic fields had been originated in the 1950s by Sakharov et al. at Arzamas in the USSR (now VNIIEF, Russia) and by Fowler et al. at Los Alamos in the US. The highest magnetic field produced by explosively driven MFC generator, 28 MG, was reported by Boyko et al. of VNIIEF. The idea of using MFC to increase the magnetic field in a magnetically confined plasma to 3-10 MG, relaxing the strict requirements on the plasma density and Lawson time, gave rise to the research area known as MTF in the US and MAGO in Russia. To make a difference in ICF, a magnetic field of ˜100 MG should be generated via MFC by a plasma liner as a part of the capsule compression scenario on a laser or pulsed power facility. This approach was first suggested in mid-1980s by Liberman and Velikovich in the USSR and Felber in the US. It has not been obvious from the start that it could work at all, given that so many mechanisms exist for anomalously fast penetration of magnetic field through plasma. And yet, many experiments stimulated by this proposal since 1986, mostly using pulsed-power drivers, demonstrated reasonably good flux compression up to ˜42 MG, although diagnostics of magnetic fields of such magnitude in HED plasmas is still problematic. The new interest of MFC in plasmas emerged with the advancement of new drivers, diagnostic methods and simulation tools. Experiments on MFC in a deuterium plasma filling a cylindrical plastic liner imploded by OMEGA laser beam led by Knauer, Betti et al. at LLE produced peak fields of 36 MG. The novel MagLIF approach to low-cost, high-efficiency ICF pursued by Herrmann, Slutz, Vesey et al. at Sandia involves pulsed-power-driven MFC to a peak field of ˜130 MG in a DT plasma. A review of the progress, current status and future prospects of MFC in plasmas is presented.
Generating electron cyclotron resonance plasma using distributed scheme
Huang, C. C.; Chang, T. H.; Chen, N. C.; Chao, H. W.; Chen, C. C.; Chou, S. F.
2012-08-06
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.
Transparency of Magnetized Plasma at Cyclotron Frequency
G. Shvets; J.S. Wurtele
2002-03-14
Electromagnetic radiation is strongly absorbed by a magnetized plasma if the radiation frequency equals the cyclotron frequency of plasma electrons. It is demonstrated that absorption can be completely canceled in the presence of a magnetostatic field of an undulator or a second radiation beam, resulting in plasma transparency at the cyclotron frequency. This effect is reminiscent of the electromagnetically induced transparency (EIT) of the three-level atomic systems, except that it occurs in a completely classical plasma. Unlike the atomic systems, where all the excited levels required for EIT exist in each atom, this classical EIT requires the excitation of the nonlocal plasma oscillation. The complexity of the plasma system results in an index of refraction at the cyclotron frequency that differs from unity. Lagrangian description was used to elucidate the physics and enable numerical simulation of the plasma transparency and control of group and phase velocity. This control naturally leads to applications for electromagnetic pulse compression in the plasma and electron/ion acceleration.
Low-frequency fluctuations in plasma magnetic fields
Cable, S.; Tajima, T.
1992-02-01
It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.
Nonquasineutral electron vortices in nonuniform plasmas
Angus, J. R.; Richardson, A. S.; Swanekamp, S. B.; Schumer, J. W.; Ottinger, P. F.
2014-11-15
Electron vortices are observed in the numerical simulation of current carrying plasmas on fast time scales where the ion motion can be ignored. In plasmas with nonuniform density n, vortices drift in the B × ∇n direction with a speed that is on the order of the Hall speed. This provides a mechanism for magnetic field penetration into a plasma. Here, we consider strong vortices with rotation speeds V{sub ϕ} close to the speed of light c where the vortex size δ is on the order of the magnetic Debye length λ{sub B}=|B|/4πen and the vortex is thus nonquasineutral. Drifting vortices are typically studied using the electron magnetohydrodynamic model (EMHD), which ignores the displacement current and assumes quasineutrality. However, these assumptions are not strictly valid for drifting vortices when δ ≈ λ{sub B}. In this paper, 2D electron vortices in nonuniform plasmas are studied for the first time using a fully electromagnetic, collisionless fluid code. Relatively large amplitude oscillations with periods that correspond to high frequency extraordinary modes are observed in the average drift speed. The drift speed W is calculated by averaging the electron velocity field over the vorticity. Interestingly, the time-averaged W from these simulations matches very well with W from the much simpler EMHD simulations even for strong vortices with order unity charge density separation.
Electrostatic instabilities in circularly polarized microwave produced magnetized plasmas
Ghorbanalilu, M.; Shokri, B.
2009-12-15
The growth rate of electrostatic instabilities of electron oscillation and low-frequency (LF) ion oscillation are investigated for a plasma produced by a circularly polarized microwave field during the breakdown process. The plasma is magnetized by an external homogenous static magnetic field on the direction of microwave field propagation. Numerical calculations show that the electron and ion perturbations are unstable in such an anisotropic plasma. Electron perturbations have the maximum growth rate across the magnetic field. In addition, ion perturbation growth rate is minimum on this direction. The LF ion oscillation is excited by Cherenkov emission mechanism due to the nonequilibrium form of the electron velocity distribution function. Electron oscillation growth rate decreases by increasing the external magnetic field, while the LF ion oscillation increases smoothly and reaches a maximum when the electron oscillation is stopped.
Analysis of magnetic field plasma interactions using microparticles as probes.
Dropmann, Michael; Laufer, Rene; Herdrich, Georg; Matthews, Lorin S; Hyde, Truell W
2015-08-01
The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles. PMID:26382535
Analysis of magnetic field plasma interactions using microparticles as probes.
Dropmann, Michael; Laufer, Rene; Herdrich, Georg; Matthews, Lorin S; Hyde, Truell W
2015-08-01
The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles.
Harmonic generation in magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Kumar, Punit; Singh, Shiv; Singh, Abhisek Kumar
2016-05-01
A study of second harmonic generation by propagation of a linearly polarized electromagnetic wave through homogeneous high density quantum plasma in the presence of transverse magnetic field. The nonlinear current density and dispersion relations for the fundamental and second harmonic frequencies have been obtained using the recently developed quantum hydrodynamic (QHD) model. The effect of quantum Bohm potential, Fermi pressure and the electron spin have been taken into account. The second harmonic is found to be less dispersed than the first.
Electron holes in inhomogeneous magnetic field: Electron heating and electron hole evolution
NASA Astrophysics Data System (ADS)
Vasko, I. Y.; Agapitov, O. V.; Mozer, F. S.; Artemyev, A. V.; Drake, J. F.
2016-05-01
Electron holes are electrostatic non-linear structures widely observed in the space plasma. In the present paper, we analyze the process of energy exchange between electrons trapped within electron hole, untrapped electrons, and an electron hole propagating in a weakly inhomogeneous magnetic field. We show that as the electron hole propagates into the region with stronger magnetic field, trapped electrons are heated due to the conservation of the first adiabatic invariant. At the same time, the electron hole amplitude may increase or decrease in dependence on properties of distribution functions of trapped and untrapped resonant electrons. The energy gain of trapped electrons is due to the energy losses of untrapped electrons and/or decrease of the electron hole energy. We stress that taking into account the energy exchange with untrapped electrons increases the lifetime of electron holes in inhomogeneous magnetic field. We illustrate the suggested mechanism for small-amplitude Schamel's [Phys. Scr. T2, 228-237 (1982)] electron holes and show that during propagation along a positive magnetic field gradient their amplitude should grow. Neglect of the energy exchange with untrapped electrons would result in the electron hole dissipation with only modest heating factor of trapped electrons. The suggested mechanism may contribute to generation of suprathermal electron fluxes in the space plasma.
Kalita, B. C.; Barman, S. N.
2009-05-15
The propagation of ion-acoustic solitary waves in magnetized plasma with cold ions and ion-beams together with electron inertia has been investigated theoretically through the Korteweg-de Vries equation. Subject to the drift velocity of the ion beam, the existence of compressive solitons is found to become extinct as {alpha} (=cold ion mass/ion-beam mass) tends to 0.01 when {gamma}=0.985 ({gamma} is the beam velocity/phase velocity). Interestingly, a transitional direction of propagation of solitary waves has been unearthed for change over, from compressive solitons to rarefactive solitons based on {alpha} and {sigma}{sub {upsilon}}(=cosine of the angle {theta} made by the wave propagation direction {xi} with the direction of the magnetic field) for fixed Q(=electron mass/ion mass). Further, the direction of propagation of ion-acoustic waves is found to be the deterministic factor to admit compressive or rarefactive solitons subject to beam outsource.
Oblique Propagation of Ion Acoustic Solitons in Magnetized Superthermal Plasmas
NASA Astrophysics Data System (ADS)
Devanandhan, S.; Sreeraj, T.; Singh, S.; Lakhina, G. S.
2015-12-01
Small amplitude ion-acoustic solitons are studied in a magnetized plasma consisting of protons, doubly charged helium ions and superthermal electrons. The Korteweg-de-Vries-Zakharov-Kuznetsov (KdV-ZK) is derived to examine the properties of ion acoustic solitary structures observed in space plasmas. Our model is applicable for weakly magnetized plasmas. The results will be applied to the satellite observations in the solar wind at 1 AU where magnetized ion acoustic waves with superthermal electrons can exist. The effects of superthermality, temperature and densities on these solitary structures will be discussed.
Relativistic nonlinear plasma waves in a magnetic field
NASA Technical Reports Server (NTRS)
Kennel, C. F.; Pellat, R.
1975-01-01
Five relativistic plane nonlinear waves were investigated: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an 'electron-positron' plasma leads to equations which have the form of a one-dimensional potential well. The solutions indicate that a large-amplitude superluminous wave determines the average plasma properties.
NASA Astrophysics Data System (ADS)
Seadawy, Aly R.
2016-08-01
The nonlinear three-dimensional modified Korteweg-de Vries-Zakharov-Kuznetsov (mKdV-ZK) equation governs the behavior of weakly nonlinear ion-acoustic waves in magnetized electron-positron plasma which consists of equal hot and cool components of each species. By using the reductive perturbation procedure leads to a mKdV-ZK equation governing the oblique propagation of nonlinear electrostatic modes. The stability of solitary traveling wave solutions of the mKdV-ZK equation to three-dimensional long-wavelength perturbations is investigated. We found the electrostatic field potential and electric field in form traveling wave solutions for three-dimensional mKdV-ZK equation. The solutions for the mKdV-ZK equation are obtained precisely and efficiency of the method can be demonstrated.
Plasma acceleration above martian magnetic anomalies.
Lundin, R; Winningham, D; Barabash, S; Frahm, R; Holmström, M; Sauvaud, J-A; Fedorov, A; Asamura, K; Coates, A J; Soobiah, Y; Hsieh, K C; Grande, M; Koskinen, H; Kallio, E; Kozyra, J; Woch, J; Fraenz, M; Brain, D; Luhmann, J; McKenna-Lawler, S; Orsini, R S; Brandt, P; Wurz, P
2006-02-17
Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space. PMID:16484488
Plasma acceleration above martian magnetic anomalies.
Lundin, R; Winningham, D; Barabash, S; Frahm, R; Holmström, M; Sauvaud, J-A; Fedorov, A; Asamura, K; Coates, A J; Soobiah, Y; Hsieh, K C; Grande, M; Koskinen, H; Kallio, E; Kozyra, J; Woch, J; Fraenz, M; Brain, D; Luhmann, J; McKenna-Lawler, S; Orsini, R S; Brandt, P; Wurz, P
2006-02-17
Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space.
Movement of electron when recombining in hydrogen plasma
NASA Astrophysics Data System (ADS)
Vikhrev, V. V.
2015-11-01
An analytical model and the results of modeling are presented for movement of electrons in recombining hydrogen plasma. It is shown that in case of taking into account the magnetic moment and angular momentum as well as spin flip of electron in magnetic field the electron comes to the orbit with angular momentum ħ/2. If azimuthal and radial components of kinetic energy of electron are equal then the full energy of such the orbits is 13.6 eV.
Plasma enclosed in a magnetic field produced by flexible surface magnets.
Schott, L
1978-04-01
A homogeneous steady state plasma with a usable volume of approximately 200 l and with an electron temperature of 1-2 eV and a plasma density of approximately 10(9)-10(10) cm(-3) is produced in a discharge chamber the outside of whose walls is covered with flexible magnetic strips. This magnet arrangement can be built at a fraction of the cost of a conventional system using rigid surface magnets. The magnetic multipole field leads to an increase of the plasma density by one to two orders of magnitude and it is also found to cause trapping of high energy electrons originating from the discharge region.
Electron dynamics in a subproton-gyroscale magnetic hole
NASA Astrophysics Data System (ADS)
Gershman, Daniel J.; Dorelli, John C.; Viñas, Adolfo F.; Avanov, Levon A.; Gliese, Ulrik; Barrie, Alexander C.; Coffey, Victoria; Chandler, Michael; Dickson, Charles; MacDonald, Elizabeth A.; Salo, Chad; Holland, Matthew; Saito, Yoshifumi; Sauvaud, Jean-Andre; Lavraud, Benoit; Paterson, William R.; Torbert, Roy; Chen, Li-Jen; Goodrich, Katherine; Russell, Christopher T.; Strangeway, Robert J.; Giles, Barbara L.; Pollock, Craig J.; Moore, Thomas E.; Burch, James L.
2016-05-01
Magnetic holes are ubiquitous in space plasmas, occurring in the solar wind, downstream of planetary bow shocks, and inside the magnetosphere. Recently, kinetic-scale magnetic holes have been observed near Earth's central plasma sheet. The Fast Plasma Investigation on NASA's Magnetospheric Multiscale (MMS) mission enables measurement of both ions and electrons with 2 orders of magnitude increased temporal resolution over previous magnetospheric instruments. Here we present data from MMS taken in Earth's nightside plasma sheet and use high-resolution particle and magnetometer data to characterize the structure of a subproton-scale magnetic hole. Electrons with gyroradii above the thermal gyroradius but below the current layer thickness carry a current sufficient to account for a ~10-20% depression in magnetic field magnitude. These observations suggest that the size and magnetic depth of kinetic-scale magnetic holes is strongly dependent on the background plasma conditions.
Electrons Confined with an Axially Symmetric Magnetic Mirror Field
Higaki, H.; Ito, K.; Kira, K.; Okamoto, H.
2008-08-08
Low energy non-neutral electron plasmas were confined with an axially symmetric magnetic mirror field and an electrostatic potential to investigate the basic confinement properties of a simple magnetic mirror trap. As expected the confinement time became longer as a function of the mirror ratio. The axial electrostatic oscillations of a confined electron plasma were also observed. Obtained results suggested an improved scheme to accumulate low energy charged particles with the use of a magnetic mirror field, which would enable the investigation of electron-positron plasmas.
Strong electron heating in the near-Earth plasma sheet.
NASA Astrophysics Data System (ADS)
Grigorenko, Elena; Zelenyi, Lev; Kronberg, Elena; Daly, Patrick
2016-07-01
Strong perturbations of the Plasma Sheet (PS) magnetic field in the course of magnetic dipolarization are often followed by the generation of magnetic turbulence and plasma heating. Various plasma instabilities and waves can be excited during these processes, which may affect ion and electron velocity distributions in a different way. We have analyzed 70 crossings of the central PS by Cluster spacecraft (s/c) at -19 < X < -8 Re in 2001-2005. We have found that in 32 intervals the ratio of Tion/Tele dropped in the central PS down to <3.0, which denotes significant electron heating. The detailed analysis of these crossings showed that in majority of these events strong magnetic dipolarizations and magnetic turbulence were observed. In the present study we discuss possible mechanisms of such strong electron heating.
Apparatus for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl
2006-04-11
An apparatus and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Apparatus for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl
2013-06-11
An apparatus and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions ions are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Apparatus for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl
2006-10-31
An apparatus and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Apparatus for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl
2016-07-05
An apparatus and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions ions are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Fully magnetized plasma flow in a magnetic nozzle
NASA Astrophysics Data System (ADS)
Merino, Mario; Ahedo, Eduardo
2016-02-01
A model of the expansion of a plasma in a magnetic nozzle in the full magnetization limit is presented. The fully magnetized and the unmagnetized-ions limits are compared, recovering the whole range of variability in plasma properties, thrust, and plume efficiency, and revealing the differences in the physics of the two cases. The fully magnetized model is the natural limit of the general, 2D, two-fluid model of Ahedo and Merino [Phys. Plasmas 17, 073501 (2010)], and it is proposed as an analytical, conservative estimator of the propulsive figures of merit of partially magnetized plasma expansions in the near region of the magnetic nozzle.
High Magnetic field generation for laser-plasma experiments
Pollock, B B; Froula, D H; Davis, P F; Ross, J S; Fulkerson, S; Bower, J; Satariano, J; Price, D; Glenzer, S H
2006-05-01
An electromagnetic solenoid was developed to study the effect of magnetic fields on electron thermal transport in laser plasmas. The solenoid, which is driven by a pulsed power system suppling 30 kJ, achieves magnetic fields of 13 T. The field strength was measured on the solenoid axis with a magnetic probe and optical Zeeman splitting. The measurements agree well with analytical estimates. A method for optimizing the solenoid design to achieve magnetic fields exceeding 20 T is presented.
Yeliseyev, Y. N.
2009-03-30
The non-local stability problem of the plasma cylinder, filled with 'cold' magnetized rigidly rotating electrons, and a small density fraction of ions, is solved. The ions are supposed to be born at rest by ionization of background gas. The study is based on the kinetic description of ions. The equilibrium distribution function, taking into account the peculiarity of ions birth, is used. The radial electric field is caused by space charge of non-neutral plasma. The dispersion equation for plasma eigen frequencies is obtained analytically. It is valid within the total admissible range of values of electric and magnetic fields. Normalized eigen frequencies {omega}'/{omega}{sub i} are calculated for the basic azimuth mode m = 1({omega}' {omega}-m{omega}{sub i}{sup +}, {omega}{sub +} = (-{omega}{sub ci}+{omega}{sub i})/2, {omega}{sub i} ({omega}{sub ci}{sup 2}-4eE{sub r}/m{sub i}r){sup 1/2} is called the 'modified' ion cyclotron (MIC) frequency), for the density fraction of ions of atomic nitrogen f N{sub i}/n{sub e} = 0,01 and are presented in graphic form versus parameter 2{omega}{sub pe}{sup 2}/{omega}{sub ce}{sup 2}. The spectra of oscillations {omega}'/{omega}{sub i} consist of the family of electron Trivel-piece--Gould (TG) modes and of the families of MIC modes. The frequencies of MIC modes are located in a small vicinity of harmonics of the MIC frequency {omega}{sub i} above and below the harmonic. The TG modes in non-neutral plasma fall in the region of MIC frequencies {omega}{sub i} and interact strongly with MIC modes. The slow TG modes become unstable near the crossings with non-negative harmonics of MIC frequencies. The instabilities have a resonant character. The lowest radial TG mode has a maximum growth rate at crossing with a zero harmonic of {omega}{sub i} ((Im {omega}'/{omega}{sub i}){sub max}{approx_equal}0,074). The growth rates of MIC modes are much lower ((Im {omega}'/{omega}{sub i}){sub max} < or approx. 0,002). Their instability has a threshold
NASA Astrophysics Data System (ADS)
Yeliseyev, Y. N.
2009-03-01
The non-local stability problem of the plasma cylinder, filled with "cold" magnetized rigidly rotating electrons, and a small density fraction of ions, is solved. The ions are supposed to be born at rest by ionization of background gas. The study is based on the kinetic description of ions. The equilibrium distribution function, taking into account the peculiarity of ions birth, is used. The radial electric field is caused by space charge of non-neutral plasma. The dispersion equation for plasma eigen frequencies is obtained analytically. It is valid within the total admissible range of values of electric and magnetic fields. Normalized eigen frequencies ω'/Ωi are calculated for the basic azimuth mode m = 1 (ω' = ω-mωi+, ω+ = (-ωci+Ωi)/2, Ωi = (ωci2-4eEr/mir)1/2 is called the "modified" ion cyclotron (MIC) frequency), for the density fraction of ions of atomic nitrogen f = Ni/ne = 0,01 and are presented in graphic form versus parameter 2ωpe2/ωce2. The spectra of oscillations ω'/Ωi consist of the family of electron Trivel-piece—Gould (TG) modes and of the families of MIC modes. The frequencies of MIC modes are located in a small vicinity of harmonics of the MIC frequency Ωi above and below the harmonic. The TG modes in non-neutral plasma fall in the region of MIC frequencies Ωi and interact strongly with MIC modes. The slow TG modes become unstable near the crossings with non-negative harmonics of MIC frequencies. The instabilities have a resonant character. The lowest radial TG mode has a maximum growth rate at crossing with a zero harmonic of Ωi ((Im ω'/Ωi)max≈0,074). The growth rates of MIC modes are much lower ((Im ω'/Ωi)max≲0,002). Their instability has a threshold character. The instabilities of TG and MIC modes take place mainly at the values of parameter 2ωpe2/ωce2, corresponding to strong radial electric fields (ωci2≪|eEr/mir|), in which the ions are unmagnetized. The oscillations of small amplitude are seen on some frequency
Electron energy transport and magnetic curvature driven modes
Coppi, B.; Tang, W.M.
1984-10-01
A transport coefficient for anomalous electron thermal conduction is constructed on the basis of the so-called Principle of Profile Consistency. It is assumed that the relevant modes in plasma where a substantial fraction of the electron population is magnetically trapped produce magnetic reconnection at a microscopic level and are driven by the combined effects of the plasma pressure gradient and the magnetic field curvature. Consequently, the scaling for the electron energy confinement time exhibits a strongly favorable dependence on the radius of magnetic curvature.
Magnetic Bubble Expansion Experimental Investigation Using a Compact Coaxial Magnetized Plasma Gun
NASA Astrophysics Data System (ADS)
Zhang, Yue; Lynn, Alan; Hsu, Scott; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher
2009-11-01
The poster will first discuss the construction and improved design of a compact coaxial magnetized plasma gun. The plasma gun is used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, which as a model for extragalactic radio lobes and solar coronal mass ejections. In this experiment, the plasma bubble's density, electron temperature, and propagation speed are measured by using a multiple-tipped langmuir probe. Also a three axis B-dot probe array is used to measure the magnetic field in three dimensions during the expansion process. In this poster experiment setup and data will be provided. Finally the comparison with the simulation result will be made.
Two-Dimensional Turbulence in Magnetized Plasmas
ERIC Educational Resources Information Center
Kendl, A.
2008-01-01
In an inhomogeneous magnetized plasma the transport of energy and particles perpendicular to the magnetic field is in general mainly caused by quasi two-dimensional turbulent fluid mixing. The physics of turbulence and structure formation is of ubiquitous importance to every magnetically confined laboratory plasma for experimental or industrial…
Magnetic multipole redirector of moving plasmas
Crow, James T.; Mowrer, Gary R.
1999-01-01
A method and apparatus for redirecting moving plasma streams using a multiple array of magnetic field generators (e.g., permanent magnets or current bearing wires). Alternate rows of the array have opposite magnetic field directions. A fine wire mesh may be employed to focus as well as redirect the plasma.
Magnetic Detachment and Plume Control in Escaping Magnetized Plasma
P. F. Schmit and N. J. Fisch
2008-11-05
The model of two-fluid, axisymmetric, ambipolar magnetized plasma detachment from thruster guide fields is extended to include plasmas with non-zero injection angular velocity profiles. Certain plasma injection angular velocity profiles are shown to narrow the plasma plume, thereby increasing exhaust efficiency. As an example, we consider a magnetic guide field arising from a simple current ring and demonstrate plasma injection schemes that more than double the fraction of useful exhaust aperture area, more than halve the exhaust plume angle, and enhance magnetized plasma detachment.
Dust-Plasma Sheath in an Oblique Magnetic Field
Foroutan, G.; Mehdipour, H.
2008-09-07
Using numerical simulations of the multi fluid equations the structure of the magnetized sheath near a plasma boundary is studied in the presence of charged dust particles. The dependence of the electron, ion, and dust densities as well as the electrostatic potential, dust charge, and ion normal velocity, on the magnetic field strength and the edge dust number density is investigated.
Secondary-electrons-induced cathode plasma in a relativistic magnetron
Queller, T.; Gleizer, J. Z.; Krasik, Ya. E.
2012-11-19
Results of time- and space-resolved spectroscopic studies of cathode plasma during a S-band relativistic magnetron operation and a magnetically insulated diode having an identical interelectrode gap are presented. It was shown that in the case of the magnetron operation, one obtains an earlier, more uniform plasma formation due to energetic electrons' interaction with the cathode surface and ionization of desorbed surface monolayers. No differences were detected in the cathode's plasma temperature between the magnetron and the magnetically insulated diode operation, and no anomalous fast cathode plasma expansion was observed in the magnetron at rf power up to 350 MW.
Internal dynamics of a plasma propelled across a magnetic field
NASA Technical Reports Server (NTRS)
Buneman, Oscar
1992-01-01
When a plasma is pushed across a magnetic field by some nonelectromagnetic force, ions and electrons get turned in opposite directions by the magnetic field. An exact analysis of that process is presented here for the internal region of the plasma. The energy provided by the initial push is used, in part, to create the electric field and in part to create some gyrations inside the plasma. When the rest energy density of the plasma exceeds twice the magnetic energy density (or when the Alfven speed is less than c), there will be enough energy to spare for the plasma to continue across the magnetic field at half its initial momentum. Two cases are considered: an impulsive start and a gentle push such as provided by gravity. The amplitude of the resulting internal gyrations becomes small in the second case. The frequencies of the gyrations are those of extraordinary modes of very long spatial wavelength.
A plasma generator utilizing the high intensity ASTROMAG magnets
NASA Technical Reports Server (NTRS)
Sullivan, James D.; Post, R. S.; Lane, B. G.; Tarrh, J. M.
1986-01-01
The magnet configuration for the proposed particle astrophysics magnet facility (ASTROMAG) on the space station includes a cusp magnetic field with an intensity of a few tesla. With these large magnets (or others) located in the outer ionosphere, many quite interesting and unique plasma physics experiments become possible. First there are studies utilizing the magnet alone to examine the supersonic, sub-Alfvenic interaction with the ambient medium; the scale length for the magnet perturbation is approx. 20 m. The magnetic field geometry when combined with the Earth's and their relative motion will give rise to a host of plasma phenomena: ring nulls, x-points, ion-acoustic and lower-hybrid shocks, electron heating (possible shuttle glow without a surface) launching of Alfvenwaves, etc. Second, active experiments are possible for a controlled study of fundamental plasma phenomena. A controlled variable species plasma can be made by using an RF ion source; use of two soft iron rings placed about the line cusp would give an adequate resonance zone (ECH or ICH) and a confining volume suitable for gas efficiency. The emanating plasma can be used to study free expansion of plasma along and across field lines (polar wind), plasma flows around the space platform, turbulent mixing in the wake region, long wavelength spectrum of convecting modes, plasma-dust interactions, etc.
Magnetic reconnection in a weakly ionized plasma
Leake, James E.; Lukin, Vyacheslav S.; Linton, Mark G.
2013-06-15
Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.
Dust particle dynamics in magnetized plasma sheath
Davoudabadi, M.; Mashayek, F.
2005-07-15
In this paper, the structure of a plasma sheath in the presence of an oblique magnetic field is investigated, and dynamics of a dust particle embedded in the sheath is elaborated. To simulate the sheath, a weakly collisional two-fluid model is implemented. For various magnitudes and directions of the magnetic field and chamber pressures, different plasma parameters including the electron and ion densities, ion flow velocity, and electric potential are calculated. A complete set of forces acting on the dust particle originating from the electric field in the sheath, the static magnetic field, gravity, and ion and neutral drags is taken into account. Through the trapping potential energy, the particle stable and unstable equilibria are studied while the particle is stationary inside the sheath. Other features such as the possibility of the dust levitation and trapping in the sheath, and the effect of the Lorentz force on the charged dust particle motion are also examined. An interesting feature is captured for the variation of the particle charge as a function of the magnetic field magnitude.
Moon, Chanho; Kaneko, Toshiro; Tamura, Shuichi; Hatakeyama, Rikizo
2010-05-01
An electron temperature gradient (ETG) is formed perpendicular to the magnetic field lines by superimposing low-temperature thermionic electrons emitted from a tungsten hot plate upon high-temperature electrons of an electron cyclotron resonance plasma, which pass through two different-shaped mesh grids. The radial profile of the plasma space potential can be controlled independent of the ETG by changing the bias voltages of the hot plate.
Auroral electron beams near the magnetic equator
NASA Technical Reports Server (NTRS)
Mcilwain, C. E.
1975-01-01
Intense beams of electrons traveling parallel to the local magnetic field have been observed at a magnetic latitude of 11 deg and a radial distance of 6.6 earth radii. The distribution function for electrons traveling within 8 deg of the field line direction is typically flat or slightly rising up to a break point beyond which it decreases as inversely as the 5-10th power of v. The energy corresponding to the break point velocity is usually between 0.1 and 10 keV. These beams are found to occur on closed field lines at the inner edge of the plasma sheet and thus at the root of the earth's magnetotail. Beams with break point energies greater than 2 keV seem to occur only within the first 10 minutes after the onset of hot plasma injection associated with a magnetospheric substorm.
Initial Results from the Magnetized Dusty Plasma Experiment (MDPX)
NASA Astrophysics Data System (ADS)
Thomas, Edward; Konopka, Uwe; Lynch, Brian; Adams, Stephen; Leblanc, Spencer; Artis, Darrick; Dubois, Ami; Merlino, Robert; Rosenberg, Marlene
2014-10-01
The MDPX device is envisioned as a flexible, multi-user, research instrument that can perform a wide range of studies in fundamental and applied plasma physics. The MDPX device consists of two main components. The first is a four-coil, open bore, superconducting magnet system that is designed to produce uniform magnetic fields of up to 4 Tesla and non-uniform magnetic fields with gradients up to up to 2 T/m configurations. Within the warm bore of the magnet is placed an octagonal vacuum chamber that has a 46 cm outer diameter and is 22 cm tall. The primary missions of the MDPX device are to: (1) investigate the structural, thermal, charging, and collective properties of a plasma as the electrons, ions, and finally charged microparticles become magnetized; (2) study the evolution of a dusty plasma containing magnetic particles (paramagnetic, super-paramagnetic, or ferromagnetic particles) in the presence of uniform and non-uniform magnetic fields; and, (3) explore the fundamental properties of strongly magnetized plasmas (``i.e., dust-free'' plasmas). This presentation will summarize the initial characterization of the magnetic field structure, initial plasma parameter measurements, and the development of in-situ and optical diagnostics. This work is supported by funding from the NSF and the DOE.
Studies of Magnetic Reconnection in Colliding Laser-Produced Plasmas
NASA Astrophysics Data System (ADS)
Rosenberg, Michael
2013-10-01
Novel images of magnetic fields and measurements of electron and ion temperatures have been obtained in the magnetic reconnection region of high- β, laser-produced plasmas. Experiments using laser-irradiated foils produce expanding, hemispherical plasma plumes carrying MG Biermann-battery magnetic fields, which can be driven to interact and reconnect. Thomson-scattering measurements of electron and ion temperatures in the interaction region of two colliding, magnetized plasmas show no thermal enhancement due to reconnection, as expected for β ~ 8 plasmas. Two different proton radiography techniques used to image the magnetic field structures show deformation, pileup, and annihilation of magnetic flux. High-resolution images reveal unambiguously reconnection-induced jets emerging from the interaction region and show instabilities in the expanding plasma plumes and supersonic, hydrodynamic jets due to the plasma collision. Quantitative magnetic flux data show that reconnection in experiments with asymmetry in the scale size, density, temperature, and plasma flow across the reconnection region occurs less efficiently than in similar, symmetric experiments. This result is attributed to disruption of the Hall mechanism mediating collisionless reconnection. The collision of plasmas carrying parallel magnetic fields has also been probed, illustrating the deformation of magnetic field structures in high-energy-density plasmas in the absence of reconnection. These experiments are particularly relevant to high- β reconnection environments, such as the magnetopause. This work was performed in collaboration with C. Li, F. Séguin, A. Zylstra, H. Rinderknecht, H. Sio, J. Frenje, and R. Petrasso (MIT), I. Igumenshchev, V. Glebov, C. Stoeckl, and D. Froula (LLE), J. Ross and R. Town (LLNL), W. Fox (UNH), and A. Nikroo (GA), and was supported in part by the NLUF, FSC/UR, U.S. DOE, LLNL, and LLE.
Annular vortex merging processes in non-neutral electron plasmas
Kaga, Chikato Ito, Kiyokazu; Higaki, Hiroyuki; Okamoto, Hiromi
2015-06-29
Non-neutral electron plasmas in a uniform magnetic field are investigated experimentally as a two dimensional (2D) fluid. Previously, it was reported that 2D phase space volume increases during a vortex merging process with viscosity. However, the measurement was restricted to a plasma with a high density. Here, an alternative method is introduced to evaluate a similar process for a plasma with a low density.
Plasma actuator electron density measurement using microwave perturbation method
NASA Astrophysics Data System (ADS)
Mirhosseini, Farid; Colpitts, Bruce
2014-07-01
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.
Plasma actuator electron density measurement using microwave perturbation method
Mirhosseini, Farid; Colpitts, Bruce
2014-07-21
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.
Optical plasma torch electron bunch generation in plasma wakefield accelerators
NASA Astrophysics Data System (ADS)
Wittig, G.; Karger, O.; Knetsch, A.; Xi, Y.; Deng, A.; Rosenzweig, J. B.; Bruhwiler, D. L.; Smith, J.; Manahan, G. G.; Sheng, Z.-M.; Jaroszynski, D. A.; Hidding, B.
2015-08-01
A novel, flexible method of witness electron bunch generation in plasma wakefield accelerators is described. A quasistationary plasma region is ignited by a focused laser pulse prior to the arrival of the plasma wave. This localized, shapeable optical plasma torch causes a strong distortion of the plasma blowout during passage of the electron driver bunch, leading to collective alteration of plasma electron trajectories and to controlled injection. This optically steered injection is more flexible and faster when compared to hydrodynamically controlled gas density transition injection methods.
Generation of magnetic fields by a gravitomagnetic plasma battery
NASA Astrophysics Data System (ADS)
Khanna, Ramon
1998-03-01
The generation of magnetic fields by a battery, operating in an ion-electron plasma around a Kerr black hole, is studied in the 3 + 1 split of the Kerr metric. It is found that the gravitomagnetic contributions to the electron partial pressure are able to drive currents. The strength of the equilibrium magnetic field should be higher than for the classical Biermann battery, which is found to operate in this relativistic context as well, since the gravitomagnetic driving terms can less easily be quenched than the classical ones. In axisymmetry the battery can induce only toroidal magnetic fields. Once a toroidal magnetic field is present, however, the coupling of gravitomagnetic and electromagnetic fields generates a poloidal magnetic field even in axisymmetry. A rotating black hole, embedded in plasma, will therefore always generate toroidal and poloidal magnetic fields.
Plasma scale-length effects on electron energy spectra in high-irradiance laser plasmas.
Culfa, O; Tallents, G J; Rossall, A K; Wagenaars, E; Ridgers, C P; Murphy, C D; Dance, R J; Gray, R J; McKenna, P; Brown, C D R; James, S F; Hoarty, D J; Booth, N; Robinson, A P L; Lancaster, K L; Pikuz, S A; Faenov, A Ya; Kampfer, T; Schulze, K S; Uschmann, I; Woolsey, N C
2016-04-01
An analysis of an electron spectrometer used to characterize fast electrons generated by ultraintense (10^{20}Wcm^{-2}) laser interaction with a preformed plasma of scale length measured by shadowgraphy is presented. The effects of fringing magnetic fields on the electron spectral measurements and the accuracy of density scale-length measurements are evaluated. 2D EPOCH PIC code simulations are found to be in agreement with measurements of the electron energy spectra showing that laser filamentation in plasma preformed by a prepulse is important with longer plasma scale lengths (>8 μm). PMID:27176413
Adiabatic expansion of a strongly correlated pure electron plasma
Dubin, D.H.E.; O'Neil, T.M.
1986-02-17
Adiabatic expansion is proposed as a method of increasing the degree of correlation of a magnetically confined pure electron plasma. Quantum mechanical effects and correlation effects make the physics of the expansion quite different from that for a classical ideal gas. The proposed expansion may be useful in a current experimental effort to cool a pure electron plasma to the liquid and solid (crystalline) states.
Adiabatic expansion of a strongly correlated pure electron plasma
NASA Astrophysics Data System (ADS)
Dubin, D. H. E.; Oneil, T. M.
1986-02-01
Adiabatic expansion is proposed as a method of increasing the degree of correlation of a magnetically confined pure electron plasma. Quantum mechanical effects and correlation effects make the physics of the expansion quite different from that for a classical ideal gas. The proposed expansion may be useful in a current experimental effort to cool a pure electron plasma to the liquid and solid (crystalline) states.
Enhanced magnetic ionization in hydrogen reflex discharge plasma source
Toader, E.I.; Covlea, V.N.
2005-03-01
The effect of enhanced magnetic ionization on the external and internal parameters of a high-density, low pressure reflex plasma source operating in hydrogen is studied. The Langmuir probe method and Druyvesteyn procedure coupled with suitable software are used to measure the internal parameters. The bulk plasma region is free of an electric field and presents a high degree of uniformity. The electron energy distribution function is bi-Maxwellian with a dip/shoulder structure around 5.5 eV, independent of external parameters and radial position. Due to the enhanced hollow cathode effect by the magnetic trapping of electrons, the electron density n{sub e} is as high as 10{sup 18} m{sup -3}, and the electron temperature T{sub e} is as low as a few tens of an electron volt, for dissipated energy of tens of Watts. The bulk plasma density scales with the dissipated power.
NASA Technical Reports Server (NTRS)
Hershkowitz, Noah (Inventor); Longmier, Benjamin (Inventor); Baalrud, Scott (Inventor)
2009-01-01
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.
NASA Technical Reports Server (NTRS)
Hershkowitz, Noah (Inventor); Longmier, Benjamin (Inventor); Baalrud, Scott (Inventor)
2011-01-01
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; Longmier, Benjamin; Baalrud, Scott
2009-03-03
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.
Energy efficiency of electron plasma emitters
Zalesski, V. G.
2011-12-15
Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter supplies sources-the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission as a result can be realized: 'a probe measurements mode,' 'a transitive mode,' and 'a full switching mode.'.
Plasma response to electron energy filter in large volume plasma device
Sanyasi, A. K.; Awasthi, L. M.; Mattoo, S. K.; Srivastava, P. K.; Singh, S. K.; Singh, R.; Kaw, P. K.
2013-12-15
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.
Radio frequency line-plasma source using permanent magnets
Sakawa, Youichi; Yano, Kentaro; Shoji, Tatsuo
2004-09-01
A high-density and uniform line-plasma source is developed by an inductive rf discharge using a rectangular discharge chamber (200x100x20 mm) with a pair of permanent magnets placed on top and bottom of the chamber. Ion-saturation current-density J{sub is} profile is controlled by varying the width of the magnets and the distance between the antenna and the magnets. A 140-mm-wide plasma [plasma density {approx_equal}(1.8-2.5)x10{sup 12} cm{sup -3} for electron temperature =4-8 eV] of a uniformity variation within 90% is produced using a 140-mm-long antenna for an Ar pressure of 20 mTorr and a rf power of 3 kW. The measured J{sub is} profiles are explained by solving the equation of motion for electrons under a magnetic field structure of longitudinal line cusps.
A solvable blob-model for magnetized plasmas
NASA Astrophysics Data System (ADS)
Pécseli, H. L.; Sortland, D. S.; Garcia, O. E.
2016-11-01
A simple analytically solvable model for blobs in magnetized plasmas is proposed. The model gives results for a scaling of the blob velocity and acceleration with varying plasma parameters. Limiting cases are considered: one where the plasma motion is strictly perpendicular to an externally imposed toroidal magnetic field, and one where the electrons can move along magnetic field lines to compensate partly the collective electric fields. For these limiting cases, the model predicts scaling laws for the dependence of the blob velocities and accelerations with varying plasma density, temperature and magnetic field strength. Also the scaling with the dominant ion mass is derived. The analysis is completed by including the effects of collisions between ions and neutrals.
Resistive collimation of electron beams in relativistic and degenerate plasma
NASA Astrophysics Data System (ADS)
Mahdavi, M.; Khodadadi Azadboni, F.
2014-09-01
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 μm, 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.
Interaction of a neutral cloud moving through a magnetized plasma
NASA Technical Reports Server (NTRS)
Goertz, C. K.; Lu, G.
1990-01-01
Current collection by outgassing probes in motion relative to a magnetized plasma may be significantly affected by plasma processes that cause electron heating and cross field transport. Simulations of a neutral gas cloud moving across a static magnetic field are discussed. The authors treat a low-Beta plasma and use a 2-1/2 D electrostatic code linked with the authors' Plasma and Neutral Interaction Code (PANIC). This study emphasizes the understanding of the interface between the neutral gas cloud and the surrounding plasma where electrons are heated and can diffuse across field lines. When ionization or charge exchange collisions occur a sheath-like structure is formed at the surface of the neutral gas. In that region the crossfield component of the electric field causes the electron to E times B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating. The thermal electron current is significantly enhanced due to this heating.
Edge Plasma Structure with Rotating Resonant Magnetic Perturbations at TEXTOR
NASA Astrophysics Data System (ADS)
Stoschus, H.; Schmitz, O.; Frerichs, H.; Lehnen, M.; Reiser, D.; Unterberg, B.; Samm, U.; Textor Research Team
2011-10-01
Rotating Resonant Magnetic Perturbations impose a characteristic modulation to the electron density and temperature in the TEXTOR plasma edge (r / a > 0 . 9). The modulation matches the position of the magnetic topology modeled in vacuum approximation for low relative rotation of frel = - 0 . 2 kHz between RMP field and toroidal plasma rotation. With increasing relative rotation (frel = 1 . 8 kHz), the plasma structure at the outermost rational flux surface is shifted by π / 2 in counter-Bt direction due to internal plasma response. The shift is correlated to a smaller displacement of the plasma structure in front of the RMP coils of 0 . 1 π . This indicates a competition between the near-field of the RMP coils and the net magnetic field at the rational flux surface. Work supported in part by US DOE under DE-AC05-06OR23100.
Recent results from CHAMP plasma parameter and magnetic field observations
NASA Astrophysics Data System (ADS)
Stolle, Claudia; Luehr, Hermann; Park, Jaeheung; Xiong, Chao; Fejer, B. G.
The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contains an enormous potential to investigate the behaviour and the origin of currents in the F region. Very prominent phenomena are the post-sunset equatorial plasma irregularities (commonly known as "bubbles", or "Equatorial Spread-F" (ESF)) which cause also signatures in the total magnetic field due to diamagnetic currents. The continuous magnetic observations, available at a 1Hz rate, have allowed for the compilation of a comprehensive climatology of the magnetic signatures due to ESF. It reveals a distinct seasonal/longitudinal (S/L) distribution, and the occurrence rate reduces considerably with decreasing solar flux. The (S/L) distribution of bubbles has been found to correlate very well, up to 90 percent, with the pre-reversal enhancement vertical plasma drift peak. This provides strong evidence for the close relation between these phenomena. Since the amplitude of the diamagnetic effect depends on the ambient magnetic field strength and on the background electron density, the global distribution shows also slight differences to the ESF climatology based on plasma depletions. Although electron density readings are only available every 15s, CHAMP data suggest that the plasma irregularities are less structured at places where the ambient magnetic field is strong (e.g. East Asia, Indonesia). In these regions the bubble statistic based on magnetic signatures is systematically lower than that from plasma measurements.
Electron-scale measurements of magnetic reconnection in space.
Burch, J L; Torbert, R B; Phan, T D; Chen, L-J; Moore, T E; Ergun, R E; Eastwood, J P; Gershman, D J; Cassak, P A; Argall, M R; Wang, S; Hesse, M; Pollock, C J; Giles, B L; Nakamura, R; Mauk, B H; Fuselier, S A; Russell, C T; Strangeway, R J; Drake, J F; Shay, M A; Khotyaintsev, Yu V; Lindqvist, P-A; Marklund, G; Wilder, F D; Young, D T; Torkar, K; Goldstein, J; Dorelli, J C; Avanov, L A; Oka, M; Baker, D N; Jaynes, A N; Goodrich, K A; Cohen, I J; Turner, D L; Fennell, J F; Blake, J B; Clemmons, J; Goldman, M; Newman, D; Petrinec, S M; Trattner, K J; Lavraud, B; Reiff, P H; Baumjohann, W; Magnes, W; Steller, M; Lewis, W; Saito, Y; Coffey, V; Chandler, M
2016-06-01
Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region. PMID:27174677
Preliminary Experimental Result of Magnetic Reconnection in Laboratory Plasma
NASA Astrophysics Data System (ADS)
Zhang, S. B.; Xie, J. L.; Hu, G. H.; Li, H.; Huang, G. L.; Liu, W. D.
2011-05-01
Magnetic reconnection is one of the most important physical processes in astrophysical plasmas. Lots of theoretical works, numerical simulations and observations have been done. Some experimental programs have been activated to investigate the basic mechanisms of magnetic reconnection. In order to investigate the electron dynamic near the electron diffusion region in magnetic reconnection process, an upgrade is accomplished in the LMP (Linear magnetic plasmas) device at University of Science and Technology of China. The magnetic field of reconnection is produced by passing two identical currents axially through two copper plates. Magnetic field and parallel electric field are measured by magnetic probes and emissive probes, respectively. The existence of a large electric field related to the reconnection process is verified. The plasma is driven by electric field and magnetic field, so the magnetic reconnection appears. The magnitude of axial current is found to scale with the number of passing particles. In the configuration of current bars, passing particles are even more and our measured axial current is about 10 A. Magnetic flux doesn't pile up because of the parameter region in our case, which is consistent with the result of numerical simulation.
Thermodynamic Study on Plasma Expansion along a Divergent Magnetic Field
NASA Astrophysics Data System (ADS)
Zhang, Yunchao; Charles, Christine; Boswell, Rod
2016-01-01
Thermodynamic properties are revisited for electrons that are governed by nonlocal electron energy probability functions in a plasma of low collisionality. Measurements in a laboratory helicon double layer experiment have shown that the effective electron temperature and density show a polytropic correlation with an index of γe=1.17 ±0.02 along the divergent magnetic field, implying a nearly isothermal plasma (γe=1 ) with heat being brought into the system. However, the evolution of electrons along the divergent magnetic field is essentially an adiabatic process, which should have a γe=5/3 . The reason for this apparent contradiction is that the nearly collisionless plasma is very far from local thermodynamic equilibrium and the electrons behave nonlocally. The corresponding effective electron enthalpy has a conservation relation with the potential energy, which verifies that there is no heat transferred into the system during the electron evolution. The electrons are shown in nonlocal momentum equilibrium under the electric field and the gradient of the effective electron pressure. The convective momentum of ions, which can be assumed as a cold species, is determined by the effective electron pressure and the effective electron enthalpy is shown to be the source for ion acceleration. For these nearly collisionless plasmas, the use of traditional thermodynamic concepts can lead to very erroneous conclusions regarding the thermal conductivity.
Propagation of intense laser pulses in strongly magnetized plasmas
Yang, X. H. Ge, Z. Y.; Xu, B. B.; Zhuo, H. B.; Ma, Y. Y.; Shao, F. Q.; Yu, W.; Xu, H.; Yu, M. Y.; Borghesi, M.
2015-06-01
Propagation of intense circularly polarized laser pulses in strongly magnetized inhomogeneous plasmas is investigated. It is shown that a left-hand circularly polarized laser pulse propagating up the density gradient of the plasma along the magnetic field is reflected at the left-cutoff density. However, a right-hand circularly polarized laser can penetrate up the density gradient deep into the plasma without cutoff or resonance and turbulently heat the electrons trapped in its wake. Results from particle-in-cell simulations are in good agreement with that from the theory.
Kato, Tsunehiko N.; Takabe, Hideaki
2010-09-20
A two-dimensional particle-in-cell simulation is performed to investigate weakly magnetized perpendicular shocks with a magnetization parameter of {sigma} = 6 x 10{sup -5}, which is equivalent to a high Alfven Mach number M{sub A} of {approx}130. It is shown that current filaments form in the foot region of the shock due to the ion-beam-Weibel instability (or the ion filamentation instability) and that they generate a strong magnetic field there. In the downstream region, these current filaments also generate a tangled magnetic field that is typically 15 times stronger than the upstream magnetic field. The thermal energies of electrons and ions in the downstream region are not in equipartition and their temperature ratio is T{sub e}/T{sub i} {approx} 0.3-0.4. Efficient electron acceleration was not observed in our simulation, although a fraction of the ions are accelerated slightly on reflection at the shock. The simulation results agree very well with the Rankine-Hugoniot relations. It is also shown that electrons and ions are heated in the foot region by the Buneman instability (for electrons) and the ion-acoustic instability (for both electrons and ions). However, the growth rate of the Buneman instability is significantly reduced due to the relatively high temperature of the reflected ions. For the same reason, ion-ion streaming instability does not grow in the foot region.
Electron plasma orbits from competing diocotron drifts.
Hurst, N C; Danielson, J R; Baker, C J; Surko, C M
2014-07-11
The perpendicular dynamics of a pure electron plasma column are investigated when the plasma spans two Penning-Malmberg traps with noncoinciding axes. The plasma executes noncircular orbits described by competing image-charge electric-field (diocotron) drifts from the two traps. A simple model is presented that predicts a set of nested orbits in agreement with observed plasma trajectories.
Magnetic field structure evolution in rotating magnetic field plasmas
Petrov, Yuri; Yang Xiaokang; Huang, T.-S.
2008-07-15
A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80 cm long/40 cm diameter cylindrical chamber, in which a plasma current I{sub p}{approx_equal}2 kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial I{sub z} current. With a relatively small current (I{sub m} {<=} 600 A) in the middle coil, the plasma current is boosted up to 5 kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.
Magnetized Plasma Experiments Using Thermionic- Thermoelectronic Plasma Emitter
NASA Astrophysics Data System (ADS)
Kawamori, Eiichirou; Cheng, C. Z.; Fujikawa, Nobuko; Lee, Jyun-Yi; Peng, Albert
2008-11-01
We are developing a magnetic mirror device, which is the first magnetized plasma device in Taiwan, to explore basic plasma sciences relevant to fusion, space and astrophysical plasmas. Our research subjects include electromagnetically induced transparency (EIT), Alfven wave physics, and plasma turbulence. A large diameter (> 200 mm) plasma emitter1, which utilizes thermionic- thermoelectronic emission from a mixture of LaB6 (Lanthanum-hexaboride) and beta-eucryptite (lithium type aluminosylicate) powders, is employed as a plasma source because of its production ability of fully ionized plasma and controllability of plasma emission rate. The plasma emitter has been installed recently and investigation of its characteristics will be started. The employment of beta-eucryptite in plasma emitter is the first experimental test because such investigation of beta-eucryptite has previously been used only for Li+-ion source2. Our plan for magnetized plasma experiments and results of the plasma emitter investigation will be presented. 1. K. Saeki, S. Iizuka, N. Sato, and Y. Hatta, Appl. Phys. Lett., 37, 1980, pp. 37-38. 2. M. Ueda, R. R. Silva, R. M. Oliveira, H. Iguchi, J. Fujita and K. Kadota, J. Phys. D: Appl. Phys. 30 1997, pp. 2711--2716.
Magnetic control of particle injection in plasma based accelerators.
Vieira, J; Martins, S F; Pathak, V B; Fonseca, R A; Mori, W B; Silva, L O
2011-06-01
The use of an external transverse magnetic field to trigger and to control electron self-injection in laser- and particle-beam driven wakefield accelerators is examined analytically and through full-scale particle-in-cell simulations. A magnetic field can relax the injection threshold and can be used to control main output beam features such as charge, energy, and transverse dynamics in the ion channel associated with the plasma blowout. It is shown that this mechanism could be studied using state-of-the-art magnetic fields in next generation plasma accelerator experiments.
Localized electron heating during magnetic reconnection in MAST
NASA Astrophysics Data System (ADS)
Yamada, T.; Tanabe, H.; Watanabe, T. G.; Hayashi, Y.; Imazawa, R.; Inomoto, M.; Ono, Y.; Gryaznevich, M.; Scannell, R.; Michael, C.; The MAST Team
2016-10-01
Significant increase in the plasma temperature above 1 keV was measured during the kilogauss magnetic field reconnection of two merging toroidal plasmas under the high-guide field and collision-less conditions. The electron temperature was observed to peak significantly at the X-point inside the current sheet, indicating Joule heating caused by the toroidal electric field along the X-line. This peaked temperature increases significantly with the guide field, in agreement with the electron mean-free path calculation. The slow electron heating in the downstream suggests energy conversion from ions to electrons through ion-electron collisions in the bulk plasma as the second electron heating mechanism in the bulk plasma. The electron density profile clearly reveals the electron density pile-up / fast shock structures in the downstream of reconnection, suggesting energy conversion from ion flow energy to ion thermal energy as well as significant ion heating by reconnection outflow.
A review on ion-ion plasmas created in weakly magnetized electronegative plasmas
NASA Astrophysics Data System (ADS)
Aanesland, A.; Bredin, J.; Chabert, P.
2014-08-01
Ion-Ion plasmas are electronegative plasmas where the electron density is several orders of magnitude lower than the negative ion density. These plasmas have been scarcely observed and investigated since the 1960s and are formed as a transient state of pulsed plasmas or in separate regions in magnetized plasmas. In this review we focus on the latter case of continuous formation of ion-ion plasmas created at the periphery of magnetized plasma columns or downstream localized magnetic barriers. We bring together and review experimental results already published elsewhere and complement them with new results to illustrate the physics important in ion-ion plasma formation and highlight in particular unanswered questions. We show that with a good design the density in the ion-ion region is dropping only by a factor of 2-3 from the initial plasma density. These plasmas can therefore be well suited for various ion source applications when both fluxes or beams of positive and negative ions are desired, and when electrons can cause harmful effects.
Effect of magnetic and physical nozzles on plasma thruster performance
NASA Astrophysics Data System (ADS)
Takahashi, Kazunori; Charles, Christine; Boswell, Rod; Ando, Akira
2014-08-01
Plasma cross-field diffusion in a magnetic nozzle is inhibited by increasing the magnetic field strength in a helicon plasma thruster attached to a pendulum thrust balance, while maintaining constant plasma density and electron temperature in the source tube, i.e. a constant plasma injection into the magnetic nozzle, where the field strength near the radio frequency (rf) antenna is less than 210 G and the operating argon pressure in the vacuum chamber is 0.8 mTorr. Inhibition of the cross-field diffusion yields a higher electron pressure in the magnetic nozzle and a resultant larger thrust. The thrust component arising from the magnetic nozzle approaches the theoretical limit derived from an ideal magnetic nozzle approximation where no plasma is lost from the nozzle and there is an azimuthal plasma current originating from the electron diamagnetic drift. It is also shown that the momentum of the plasma lost from the magnetic nozzle is captured by a physical nozzle attached at the source exit resulting in a larger thrust. Two physical nozzles of different sizes (nozzle 1 : 10.5 cm in length with a maximum diameter of 20 cm, nozzle 2 : 26 cm in length with a maximum diameter of 36 cm) are tested. The maximum thrust of 20 ± 1 mN is obtained for 25 sccm argon propellant and 2 kW rf power with a reflection power less than 5 W, which gives a specific impulse of 2750 ± 165 s and a thrust efficiency of 13.5 ± 1.5%.
Kimura, Daiju Kurisu, Yosuke; Nozaki, Dai; Yano, Keisuke; Imai, Youta; Kumakura, Sho; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki
2014-02-15
We are constructing a tandem type ECRIS. The first stage is large-bore with cylindrically comb-shaped magnet. We optimize the ion beam current and ion saturation current by a mobile plate tuner. They change by the position of the plate tuner for 2.45 GHz, 11–13 GHz, and multi-frequencies. The peak positions of them are close to the position where the microwave mode forms standing wave between the plate tuner and the extractor. The absorbed powers are estimated for each mode. We show a new guiding principle, which the number of efficient microwave mode should be selected to fit to that of multipole of the comb-shaped magnets. We obtained the excitation of the selective modes using new mobile plate tuner to enhance ECR efficiency.
Magnetic field of a combined plasma trap
NASA Astrophysics Data System (ADS)
Kotenko, V. G.; Moiseenko, V. E.; Ågren, O.
2012-06-01
This paper presents numerical simulations performed on the structure of a magnetic field created by the magnetic system of a combined plasma trap. The magnetic system includes the stellarator-type magnetic system and one of the mirror-type. For the stellarator type magnetic system the numeric model contains a magnetic system of an l=2 torsatron with the coils of an additional toroidal magnetic field. The mirror-type magnetic system element is considered as being single current-carrying turn enveloping the region of existence of closed magnetic surfaces of the torsatron. The calculations indicate the existence of a vast area of the values of the additional magnetic field magnitude and magnetic field of the single turn where, in principle, the implementation of the closed magnetic surface configuration is quite feasible.
On the Physics of the Interaction of a Rotating Magnetic Field with a Magnetized Plasma
NASA Astrophysics Data System (ADS)
Karavaev, A. V.; Papadopoulos, K.; Shao, X.; Milikh, G.; Gekelman, W.; Gigliotti, A.; Vincena, S.
2007-12-01
The interaction of Rotating Magnetic Fields (RMF) with plasmas is a fundamental plasma physics problem with implications to fusion related Field-Reversed Configurations (FRC), space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of energetic population in the radiation belts and near zone processes in pulsar magnetospheres. An important but not yet explored application of RMF is as an efficient radiation source of MHD and whistler waves in space plasmas. Despite its importance the basic plasma physics understanding of the interaction of rotating magnetic fields with magneto-plasmas, the scaling laws that control it and the range of potential applications to space plasmas remains unexplored. To zero order a magnetic field rotating at a rate w in a plasma drives plasma currents due to the difference in mass between electrons and ions. The electrons quickly come to a co-rotation with RMF, generating a differential azimuthal current whose maximum is given by Jtheta = nwr . The RMF can be generated either by a pair of polyphase coils, superconducting or else, or a rotating permanent magnet. Key questions include the depth of penetration of the field in the plasma, the spatiotemporal structure of the induced magnetic field as a function of the RMF and plasma parameters and the spatial decay rate magnetic field. Flux conservation arguments indicate that the induced field will decay slower than 1/r**2 and 2D simulation studies indicate that depending on the plasma beta it falls as 1/r**n with n smaller than 1.5. Our preliminary simulations indicate that penetration lengths exceeding 20-30 collisionless skin depths can be reached. The paper will present a combination of analytic/computational results along with preliminary experiments conducted using the Large Plasma Device (LAPD) located at UCLA that emphasize the RMF properties for generating MHD and whistler waves. This work was sponsored by ONR MURI Grant 5-28828
Magnetic Field Effects on Plasma Plumes
NASA Technical Reports Server (NTRS)
Ebersohn, F.; Shebalin, J.; Girimaji, S.; Staack, D.
2012-01-01
Here, we will discuss our numerical studies of plasma jets and loops, of basic interest for plasma propulsion and plasma astrophysics. Space plasma propulsion systems require strong guiding magnetic fields known as magnetic nozzles to control plasma flow and produce thrust. Propulsion methods currently being developed that require magnetic nozzles include the VAriable Specific Impulse Magnetoplasma Rocket (VASIMR) [1] and magnetoplasmadynamic thrusters. Magnetic nozzles are functionally similar to de Laval nozzles, but are inherently more complex due to electromagnetic field interactions. The two crucial physical phenomenon are thrust production and plasma detachment. Thrust production encompasses the energy conversion within the nozzle and momentum transfer to a spacecraft. Plasma detachment through magnetic reconnection addresses the problem of the fluid separating efficiently from the magnetic field lines to produce maximum thrust. Plasma jets similar to those of VASIMR will be studied with particular interest in dual jet configurations, which begin as a plasma loops between two nozzles. This research strives to fulfill a need for computational study of these systems and should culminate with a greater understanding of the crucial physics of magnetic nozzles with dual jet plasma thrusters, as well as astrophysics problems such as magnetic reconnection and dynamics of coronal loops.[2] To study this problem a novel, hybrid kinetic theory and single fluid magnetohydrodynamic (MHD) solver known as the Magneto-Gas Kinetic Method is used.[3] The solver is comprised of a "hydrodynamic" portion based on the Gas Kinetic Method and a "magnetic" portion that accounts for the electromagnetic behaviour of the fluid through source terms based on the resistive MHD equations. This method is being further developed to include additional physics such as the Hall effect. Here, we will discuss the current level of code development, as well as numerical simulation results
Transport equations for partially ionized reactive plasma in magnetic field
NASA Astrophysics Data System (ADS)
Zhdanov, V. M.; Stepanenko, A. A.
2016-06-01
Transport equations for partially ionized reactive plasma in magnetic field taking into account the internal degrees of freedom and electronic excitation of plasma particles are derived. As a starting point of analysis the kinetic equation with a binary collision operator written in the Wang-Chang and Uhlenbeck form and with a reactive collision integral allowing for arbitrary chemical reactions is used. The linearized variant of Grad's moment method is applied to deduce the systems of moment equations for plasma and also full and reduced transport equations for plasma species nonequilibrium parameters.
NASA Technical Reports Server (NTRS)
Mallavarpu, R.; Roth, J. R.
1978-01-01
Microwave emission near the electron plasma frequency of the NASA Lewis Bumpy Torus plasma has been observed, and its relation to the average electron density and the dc toroidal magnetic field was examined. The emission was detected using a spectrum analyzer and a 50-ohm miniature coaxial probe. The radiation appeared as a broad amplitude peak that shifted in frequency as the plasma parameters were varied. The observed radiation scanned an average plasma density ranging from 20 billion to 800 billion per cu cm. A linear relation was observed between the density calculated from the emission frequency and the average plasma density measured with a microwave interferometer. With the aid of a relative density profile measurement of the plasma, it was determined that the emissions occurred from the outer periphery of the plasma.
Stochastic heating of electrons by a large-amplitude extraordinary wave in plasma
Krasovitskiy, V. B.; Turikov, V. A.
2010-12-15
Stochastic heating of plasma electrons by a large-amplitude electromagnetic wave propagating across a strong external magnetic field is studied theoretically and numerically. An analytic estimate of the threshold wave amplitude at which heating begins is obtained. The dependence of the average electron energy on the magnetic field and plasma density is investigated using particle-in-cell simulations.
Study on spatial distribution of plasma parameters in a magnetized inductively coupled plasma
Cheong, Hee-Woon; Lee, Woohyun; Kim, Ji-Won; Whang, Ki-Woong; Kim, Hyuk; Park, Wanjae
2015-07-15
Spatial distributions of various plasma parameters such as plasma density, electron temperature, and radical density in an inductively coupled plasma (ICP) and a magnetized inductively coupled plasma (M-ICP) were investigated and compared. Electron temperature in between the rf window and the substrate holder of M-ICP was higher than that of ICP, whereas the one just above the substrate holder of M-ICP was similar to that of ICP when a weak (<8 G) magnetic field was employed. As a result, radical densities in M-ICP were higher than those in ICP and the etch rate of oxide in M-ICP was faster than that in ICP without severe electron charging in 90 nm high aspect ratio contact hole etch.
Fast magnetic reconnection due to anisotropic electron pressure
Cassak, P. A.; Baylor, R. N.; Fermo, R. L.; Beidler, M. T.; Shay, M. A.; Swisdak, M.; Drake, J. F.; Karimabadi, H.
2015-02-15
A new regime of fast magnetic reconnection with an out-of-plane (guide) magnetic field is reported in which the key role is played by an electron pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations of state in the generalized Ohm's law, which even dominates the Hall term. A description of the physical cause of this behavior is provided and two-dimensional fluid simulations are used to confirm the results. The electron pressure anisotropy causes the out-of-plane magnetic field to develop a quadrupole structure of opposite polarity to the Hall magnetic field and gives rise to dispersive waves. In addition to being important for understanding what causes reconnection to be fast, this mechanism should dominate in plasmas with low plasma beta and a high in-plane plasma beta with electron temperature comparable to or larger than ion temperature, so it could be relevant in the solar wind and some tokamaks.
Fast magnetic reconnection due to anisotropic electron pressure
NASA Astrophysics Data System (ADS)
Cassak, Paul; Baylor, Robert; Fermo, Raymond; Beidler, Matthew; Shay, Michael; Swisdak, Marc; Drake, James; Karimabadi, Homa
2015-11-01
A new regime of fast magnetic reconnection with an out-of-plane (guide) magnetic field is reported in which the key role is played by an electron pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations of state in the generalized Ohm's law, which even dominates the Hall term. A description of the physical cause of this behavior is provided and two-dimensional fluid simulations are used to confirm the results. The electron pressure anisotropy causes the out-of-plane magnetic field to develop a quadrupole structure of opposite polarity to the Hall magnetic field and gives rise to dispersive waves. In addition to being important for understanding what causes reconnection to be fast, this mechanism should dominate in plasmas with low plasma beta and a high in-plane plasma beta with electron temperature comparable to or larger than ion temperature, so it could be relevant in the solar wind and some tokamaks.
Fast magnetic reconnection due to anisotropic electron pressure
NASA Astrophysics Data System (ADS)
Cassak, P. A.; Baylor, R. N.; Fermo, R. L.; Beidler, M. T.; Shay, M. A.; Swisdak, M.; Drake, J. F.; Karimabadi, H.
2015-02-01
A new regime of fast magnetic reconnection with an out-of-plane (guide) magnetic field is reported in which the key role is played by an electron pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations of state in the generalized Ohm's law, which even dominates the Hall term. A description of the physical cause of this behavior is provided and two-dimensional fluid simulations are used to confirm the results. The electron pressure anisotropy causes the out-of-plane magnetic field to develop a quadrupole structure of opposite polarity to the Hall magnetic field and gives rise to dispersive waves. In addition to being important for understanding what causes reconnection to be fast, this mechanism should dominate in plasmas with low plasma beta and a high in-plane plasma beta with electron temperature comparable to or larger than ion temperature, so it could be relevant in the solar wind and some tokamaks.
Directed Plasma Flow across Magnetic Field
NASA Astrophysics Data System (ADS)
Presura, R.; Stepanenko, Y.; Neff, S.; Sotnikov, V. I.
2008-04-01
The Hall effect plays a significant role in the penetration of plasma flows across magnetic field. For example, its effect may become dominant in the solar wind penetration into the magnetosphere, in the magnetic field advection in wire array z-pinch precursors, or in the arcing of magnetically insulated transmission lines. An experiment performed at the Nevada Terawatt Facility explored the penetration of plasma with large Hall parameter (˜10) across ambient magnetic field. The plasma was produced by ablation with the short pulse high intensity laser Leopard (0.35 ps, 10^17W/cm^2) and the magnetic field with the pulsed power generator Zebra (50 T). The expanding plasma assumed a jet configuration and propagated beyond a distance consistent with a diamagnetic bubble model. Without magnetic field, the plasma expansion was close to hemispherical. The ability to produce the plasma and the magnetic field with distinct generators allows a controlled, quasi-continuous variation of the Hall parameter and other plasma parameters making the experiments useful for benchmarking numerical simulations.
Collimation of laser-produced plasmas using axial magnetic field
Roy, Amitava; Harilal, Sivanandan S.; Hassan, Syed M.; Endo, Akira; Mocek, Tomas; Hassanein, A.
2015-06-01
We investigated the expansion dynamics of laser-produced plasmas expanding into an axial magnetic field. Plasmas were generated by focusing 1.064 µm Nd:YAG laser pulses onto a planar tin target in vacuum and allowed to expand into a 0.5 T magnetic-filed where field lines were aligned along the plume expansion direction. Gated images employing intensified CCD showed focusing of the plasma plume, which were also compared with results obtained using particle-in-cell modelling methods. The estimated density and temperature of the plasma plumes employing emission spectroscopy revealed significant changes in the presence and absence of the 0.5T magnetic field. In the presence of the field, the electron temperature is increased with distance from the target, while the density showed opposite effects.
Plasma expansion in the presence of a dipole magnetic field
Winske, D.; Omidi, N.
2005-07-15
Simulations of the initial expansion of a plasma injected into a stationary magnetized background plasma in the presence of a dipole magnetic field are carried out in two dimensions with a kinetic ion, massless fluid electron (hybrid) electromagnetic code. For small values of the magnetic dipole, the injected ions have large gyroradii compared to the scale length of the dipole field and are essentially unmagnetized. As a result, these ions expand, excluding the ambient magnetic field and plasma to form a diamagnetic cavity. However, for stronger magnetic dipoles, the ratio of the gyroradii of the injected ions to the dipole field scale length is small so that they remain magnetized, and hence trapped in the dipole field, as they expand. The trapping and expansion then lead to additional plasma currents and resulting magnetic fields that not only exclude the background field but also interact with the dipole field in a more complex manner that stretches the closed dipole field lines. A criterion to distinguish between the two regimes is derived and is then briefly discussed in the context of applying the results to the plasma sail scheme for the propulsion of small spacecraft in the solar wind.
Passive Spectroscopic Diagnostics for Magnetically-confined Fusion Plasmas
Stratton, B. C.; Biter, M.; Hill, K. W.; Hillis, D. L.; Hogan, J. T.
2007-07-18
Spectroscopy of radiation emitted by impurities and hydrogen isotopes plays an important role in the study of magnetically-confined fusion plasmas, both in determining the effects of impurities on plasma behavior and in measurements of plasma parameters such as electron and ion temperatures and densities, particle transport, and particle influx rates. This paper reviews spectroscopic diagnostics of plasma radiation that are excited by collisional processes in the plasma, which are termed 'passive' spectroscopic diagnostics to distinguish them from 'active' spectroscopic diagnostics involving injected particle and laser beams. A brief overview of the ionization balance in hot plasmas and the relevant line and continuum radiation excitation mechanisms is given. Instrumentation in the soft X-ray, vacuum ultraviolet, ultraviolet, visible, and near-infrared regions of the spectrum is described and examples of measurements are given. Paths for further development of these measurements and issues for their implementation in a burning plasma environment are discussed.
Magnetic circuit for hall effect plasma accelerator
NASA Technical Reports Server (NTRS)
Manzella, David H. (Inventor); Jacobson, David T. (Inventor); Jankovsky, Robert S. (Inventor); Hofer, Richard (Inventor); Peterson, Peter (Inventor)
2009-01-01
A Hall effect plasma accelerator includes inner and outer electromagnets, circumferentially surrounding the inner electromagnet along a thruster centerline axis and separated therefrom, inner and outer magnetic conductors, in physical connection with their respective inner and outer electromagnets, with the inner magnetic conductor having a mostly circular shape and the outer magnetic conductor having a mostly annular shape, a discharge chamber, located between the inner and outer magnetic conductors, a magnetically conducting back plate, in magnetic contact with the inner and outer magnetic conductors, and a combined anode electrode/gaseous propellant distributor, located at a bottom portion of the discharge chamber. The inner and outer electromagnets, the inner and outer magnetic conductors and the magnetically conducting back plate form a magnetic circuit that produces a magnetic field that is largely axial and radially symmetric with respect to the thruster centerline.
Electrostatic decay in a weakly magnetized plasma.
Layden, A; Cairns, Iver H; Li, B; Robinson, P A
2013-05-01
The kinematics of the electrostatic (ES) decay of a Langmuir wave into a Langmuir wave and an ion sound wave are generalized to a weakly magnetized plasma. Unlike the unmagnetized case, ES decay in a magnetized plasma is always kinematically permitted and can produce daughter Langmuir waves with very small wave numbers, which we demonstrate by quasilinear simulations. The simulations further show that ES decay in magnetized plasmas is consistent with STEREO spacecraft observations of transversely polarized Langmuir waves in the solar wind. PMID:23683206
Electrostatic solitary waves in a magnetized dusty plasma
Maharaj, S. K.; Bharuthram, R.; Singh, S. V.; Lakhina, G. S.; Pillay, S. R.
2008-11-15
The nonlinear evolution of driven low-frequency electrostatic waves is investigated in a three-component magnetized dusty plasma comprised of a warm dust fluid, electrons, and ions. Electrons as well as ions are considered to have Boltzmann distributions. The fluid equations for the dust along with the quasineutrality condition are used to obtain a single nonlinear differential equation for the electric field. Periodic solutions of the nonlinear differential equation yield sinusoidal, sawtooth and bipolar structures which are similar to nonlinear structures supported in electron-ion plasmas. Results of our findings are applied to Saturn's rings.
Tevatron electron lens magnetic system
Vladimir Shiltsev et al.
2001-07-12
In the framework of collaboration between IHEP and FNAL, a magnetic system of the Tevatron Electron Lens (TEL) has been designed and built. The TEL is currently installed in the superconducting ring of the Tevatron proton-antiproton collider and used for experimental studies of beam-beam compensation [1].
Anomalous electron mobility in a coaxial Hall discharge plasma.
Meezan, N B; Hargus, W A; Cappelli, M A
2001-02-01
A comprehensive analysis of measurements supporting the presence of anomalous cross-field electron mobility in Hall plasma accelerators is presented. Nonintrusive laser-induced fluorescence measurements of neutral xenon and ionized xenon velocities, and various electrostatic probe diagnostic measurements are used to locally determine the effective electron Hall parameter inside the accelerator channel. These values are then compared to the classical (collision-driven) Hall parameters expected for a quiescent magnetized plasma. The results indicate that in the vicinity of the anode, where there are fewer plasma instabilities, the electron-transport mechanism is likely elastic collisions with the background neutral xenon. However, we find that in the vicinity of the discharge channel exit, where the magnetic field is the strongest and where there are intense fluctuations in the plasma properties, the inferred Hall parameter departs from the classical value, and is close to the Bohm value of (omega(ce)tau)(eff) approximately 16. These results are used to support a simple model for the Hall parameter that is based on the scalar addition of the electron collision frequencies (elastic collision induced plus fluctuation induced), as proposed by Boeuf and Garrigues [J. Appl. Phys. 84, 3541 (1998)]. The results also draw attention to the possible role of fluctuations in enhancing electron transport in regions where the electrons are highly magnetized.
Magnetic field structure evolution in RMF plasmas
NASA Astrophysics Data System (ADS)
Petrov, Yuri; Yang, Xiaokang; Huang, Tian-Sen
2007-11-01
A study of magnetic field structure evolution during 40-ms plasma discharge had been performed in 80 cm long / 40 cm OD cylindrical chamber. Plasma current Ip˜2--3 kA is produced by applied 500 kHz rotating magnetic field. In experiments, the 2D profile of plasma current is changed by feeding a 10-ms pulse current to additional magnetic coil located at the midplane. Using newly developed magnetic field pick-up coils system, we scanned the magnetic field in cross-section of plasma. Two experimental regimes were studied: without external toroidal field (TF), and with TF produced by applied axial current. When a relatively small current (<0.5 kA) is applied to the midplane coil, in both cases the total plasma current measured with Rogowski coil experiences a jump (up to 100%), but the profile of current remains almost unchanged. When a larger current (1--2 kA) is applied to the midplane coil, the total plasma current drops; the magnetic structure changes differently in two regimes. In regime without TF, the magnetic field of plasma current is reversed at Rplasma current first extends along Z, and then two rings of current are formed at the edge. At smaller radii, the current layer is still approximately uniform along Z. We also show how the magnetic field evolves during initial 1--3 ms transitional period of plasma formation.
Plasma relaxation and topological aspects in electron magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Shivamoggi, B. K.
2016-07-01
Parker's formulation of isotopological plasma relaxation process toward minimum magnetics energy states in magnetohydrodynamics (MHD) is extended to electron MHD (EMHD). The lower bound on magnetic energy in EMHD is determined by both the magnetic field and the electron vorticity field topologies, and is shown to be reduced further in EMHD by an amount proportional to the sum of total electron-flow kinetic energy and total electron-flow enstrophy. The EMHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics, and the torsion coefficient α turns out to be proportional to potential vorticity. The winding pattern of the magnetic field lines appears to evolve, therefore, in the same way as potential vorticity lines in 2D hydrodynamics.
Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma
Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M.; Myers, Clayton E.
2014-09-10
Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first timemore » in a well defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step toward resolving one of the most important problems in plasma physics.« less
Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma
Yamada, Masaaki; Yoo, Jongsoo; Jara-Almonte, Jonathan; Ji, Hantao; Kulsrud, Russell M.; Myers, Clayton E.
2014-09-10
Magnetic reconnection, in which magnetic field lines break and reconnect to change their topology, occurs throughout the universe. The essential feature of reconnection is that it energizes plasma particles by converting magnetic energy. Despite the long history of reconnection research, how this energy conversion occurs remains a major unresolved problem in plasma physics. Here we report that the energy conversion in a laboratory reconnection layer occurs in a much larger region than previously considered. The mechanisms for energizing plasma particles in the reconnection layer are identified, and a quantitative inventory of the converted energy is presented for the first time in a well defined reconnection layer; 50% of the magnetic energy is converted to particle energy, 2/3 of which transferred to ions and 1/3 to electrons. Our results are compared with simulations and space measurements, for a key step toward resolving one of the most important problems in plasma physics.
Collapse of nonlinear electron plasma waves in a plasma layer
NASA Astrophysics Data System (ADS)
Grimalsky, V.; Koshevaya, S.; Rapoport, Yu; Kotsarenko, A.
2016-10-01
The excitation of nonlinear electron plasma waves in the plasma layer is investigated theoretically. This excitation is realized by means of initial oscillatory perturbations of the volume electron concentration or by initial oscillatory distributions of the longitudinal electron velocity. The amplitudes of the initial perturbations are small and the manifestation of the volume nonlinearity is absent. When the amplitudes of the initial perturbations exceed some thresholds, the values of the electron concentration near the plasma boundary increase catastrophically. The maxima of the electron concentration reach extremely high magnitudes, and sharp peaks in the electron concentration occur, which are localized both in the longitudinal and transverse directions. This effect is interpreted as wave collapse near the plasma boundary.
Thermal magnetic fluctuations of whistlers in a Maxwellian plasma
NASA Technical Reports Server (NTRS)
Golubyatnikov, G.; Stenzel, R. L.
1993-01-01
Thermal fluctuations were measured with a magnetic-loop antenna inside a large afterglow plasma in the whistler-wave regime. The magnetic fluctuations exhibit a 1/f-like spectrum for whistlers, no resonant enhancement at the electron cyclotron frequency, and a flat spectrum in the evanescent regime. The observed fluctuations are therefore described neither by blackbody radiation laws nor by cyclotron emission, but resemble the decaying Alfvenic fluctuations spectrum calculated by Cable and Tajima (1992).
Method for generating a plasma wave to accelerate electrons
Umstadter, D.; Esarey, E.; Kim, J.K.
1997-06-10
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.
Method for generating a plasma wave to accelerate electrons
Umstadter, Donald; Esarey, Eric; Kim, Joon K.
1997-01-01
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.
NASA Technical Reports Server (NTRS)
Mallavarpu, R.; Roth, J. R.
1978-01-01
Microwave emission near the electron plasma frequency was observed, and its relation to the average electron density and the dc toroidal magnetic field was examined. The emission was detected using a spectrum analyzer and a 50 omega miniature coaxial probe. The radiation appeared as a broad amplitude peak that shifted in frequency as the plasma parameters were varied. The observed radiation scanned an average plasma density ranging from 10 million/cu cm to 8 hundred million/cu cm. A linear relation was observed betweeen the density calculated from the emission frequency and the average plasma density measured with a microwave interferometer. With the aid of a relative density profile measurement of the plasma, it was determined that the emissions occurred from the outer periphery of the plasma.
Brenner, P. W.; Sunn Pedersen, T.
2012-05-15
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.
Ciaccio, G. Spizzo, G.; Schmitz, O. Frerichs, H.; Abdullaev, S. S.; Evans, T. E.; White, R. B.
2015-10-15
The electrostatic response of the edge plasma to a magnetic island induced by resonant magnetic perturbations to the plasma edge of the circular limiter tokamak TEXTOR is analyzed. Measurements of plasma potential are interpreted by simulations with the Hamiltonian guiding center code ORBIT. We find a strong correlation between the magnetic field topology and the poloidal modulation of the measured plasma potential. The ion and electron drifts yield a predominantly electron driven radial diffusion when approaching the island X-point while ion diffusivities are generally an order of magnitude smaller. This causes a strong radial electric field structure pointing outward from the island O-point. The good agreement found between measured and modeled plasma potential connected to the enhanced radial particle diffusivities supports that a magnetic island in the edge of a tokamak plasma can act as convective cell. We show in detail that the particular, non-ambipolar drifts of electrons and ions in a 3D magnetic topology account for these effects. An analytical model for the plasma potential is implemented in the code ORBIT, and analyses of ion and electron radial diffusion show that both ion- and electron-dominated transport regimes can exist, which are known as ion and electron root solutions in stellarators. This finding and comparison with reversed field pinch studies and stellarator literature suggest that the role of magnetic islands as convective cells and hence as major radial particle transport drivers could be a generic mechanism in 3D plasma boundary layers.
Atoms and plasmas in a high-magnetic-field trap
Raithel, G.; Knuffman, B.; Shah, M. H.; Hempel, C.; Paradis, E.; Mhaskar, R.; Zhang, X.; Choi, J.-H.; Povilus, A. P.; Guest, J. R.
2008-08-08
We investigate cold rubidium plasmas in a particle trap that has the unique capability to simultaneously laser-cool and trap neutral atoms as well as to confine plasmas in magnetic fields of about three Tesla. The atom trap is a high-field Ioffe-Pritchard laser trap, while the plasma trap is a Ioffe-Penning trap that traps electrons and ions in separate wells. The observed plasma dynamics is characterized by a breathing-mode oscillation of the positive (ionic) plasma component, which feeds back on the behavior of the negative (electron) component of the plasma. At higher densities, the observed oscillations become nonlinear. The electron component has been found to undergo rapid cooling. We further report on the recombination of magnetized plasmas into Rydberg atoms in transient traps and quasi-steady-state traps. In transient traps, large numbers of recombined Rydberg atoms in high-lying states are observed. In quasi-steady-state traps, the measured numbers of recombined atoms are lower and the binding energies higher.
Nonlinear electron oscillations in a warm plasma
Sarkar, Anwesa; Maity, Chandan; Chakrabarti, Nikhil
2013-12-15
A class of nonstationary solutions for the nonlinear electron oscillations of a warm plasma are presented using a Lagrangian fluid description. The solution illustrates the nonlinear steepening of an initial Gaussian electron density disturbance and also shows collapse behavior in time. The obtained solution may indicate a class of nonlinear transient structures in an unmagnetized warm plasma.
Microwave Reflectometry for Magnetically Confined Plasmas
Mazzucato, E.
1998-02-01
This paper is about microwave reflectometry -- a radar technique for plasma density measurements using the reflection of electromagnetic waves by a plasma cutoff. Both the theoretical foundations of reflectometry and its practical application to the study of magnetically confined plasmas are reviewed in this paper. In particular, the role of short-scale density fluctuations is discussed at length, both as a unique diagnostic tool for turbulence studies in thermonuclear plasmas and for the deleterious effects that fluctuations may have on the measurement of the average plasma density with microwave reflectometry.
NASA Astrophysics Data System (ADS)
Ghorui, Malay Kumar; Samanta, Utpal Kumar; Chatterjee, Prasanta
2013-06-01
The head-on collisions of ion-acoustic solitary waves (IASWs) in a dense magnetized quantum plasma are investigated. The two-sided Korteweg-de Vries (KdV) equations in generic case as well as the two-sided modified Korteweg-de Vries (mKdV) equations in a special case are obtained, the analytical phase shifts and the trajectories after the head-on collisions of two IASWs in a three species quantum plasma are derived by using the extended version of Poincaré-Lighthill-Kuo (PLK) method for both the situations. We provide the theoretical predictions about the existence of compressive and rarefactive IASWs in the model. We observe that in generic case collisions are possible among the same polarity solitons, whereas in the special case collisions are possible among the same or opposite polarities solitons. Moreover the colliding phase shifts are significantly affected by the quantum diffraction parameter, by the square of the ratio of ion gyrofrequency to ion plasma frequency and by obliqueness of propagation. The important observations of this manuscript are that the waves reach a maximum amplitude which is the superposition of the initial amplitudes and they suffer a time delay during their collision. The plasma parameter values for white dwarfs are taken for discussion.
Simulation of laser-plasma interactions and fast-electron transport in inhomogeneous plasma
Cohen, B.I. Kemp, A.J.; Divol, L.
2010-06-20
A new framework is introduced for kinetic simulation of laser-plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell's equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell's equations are solved using an Ohm's law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere's law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.
Hybrid Simulation of Laser-Plasma Interactions and Fast Electron Transport in Inhomogeneous Plasma
Cohen, B I; Kemp, A; Divol, L
2009-05-27
A new framework is introduced for kinetic simulation of laser-plasma interactions in an inhomogenous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell's equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell's equations are solved using an Ohm's law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere's law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.
Slot-Antenna/Permanent-Magnet Device for Generating Plasma
NASA Technical Reports Server (NTRS)
Foster, John E.
2007-01-01
A device that includes a rectangular-waveguide/slot-antenna structure and permanent magnets has been devised as a means of generating a substantially uniform plasma over a relatively large area, using relatively low input power and a low gas flow rate. The device utilizes electron cyclotron resonance (ECR) excited by microwave power to efficiently generate plasma in a manner that is completely electrodeless in the sense that, in principle, there is no electrical contact between the plasma and the antenna. Plasmas generated by devices like this one are suitable for use as sources of ions and/or electrons for diverse material-processing applications (e.g., etching or deposition) and for ion thrusters. The absence of plasma/electrode contact essentially prevents plasma-induced erosion of the antenna, thereby also helping to minimize contamination of the plasma and of objects exposed to the plasma. Consequently, the operational lifetime of the rectangular-waveguide/ slot-antenna structure is long and the lifetime of the plasma source is limited by the lifetime of the associated charged-particle-extraction grid (if used) or the lifetime of the microwave power source. The device includes a series of matched radiating slot pairs that are distributed along the length of a plasma-source discharge chamber (see figure). This arrangement enables the production of plasma in a distributed fashion, thereby giving rise to a uniform plasma profile. A uniform plasma profile is necessary for uniformity in any electron- or ion-extraction electrostatic optics. The slotted configuration of the waveguide/ antenna structure makes the device scalable to larger areas and higher powers. All that is needed for scaling up is the attachment of additional matched radiating slots along the length of the discharge chamber. If it is desired to make the power per slot remain constant in scaling up, then the input microwave power must be increased accordingly. Unlike in prior ECR microwave plasma
Magnetic Lens For Plasma Engine
NASA Technical Reports Server (NTRS)
Sercel, Joel C.
1992-01-01
Low-field electromagnet coils placed downstream of plasma engine, polarized oppositely to higher-field but smaller radius coil in nozzle of engine, reduces divergence of plasma jet, thereby increasing efficiency of engine. Concept tested by computer simulation based on simplified mathematical model of plasma, engine, and coils.
Accessibility of electron Bernstein modes in over-dense plasma
Carter, M. D.; Bigelow, T. S.; Batchelor, D. B.
1999-09-20
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 design can also be applied near the electron cyclotron frequency. In this paper, we investigate the 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. (c) 1999 American Institute of Physics.
Accessibillity of Electron Bernstein Modes in Over-Dense Plasma
Batchelor, D.B.; Bigelow, T.S.; Carter, M.D.
1999-04-12
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.
Self-effect in expanding electron beam plasma
Garcia, M
1999-05-07
An analytical model of plasma flow from a metal plate hit by an intense, pulsed, electron beam 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 work aims to model the spatial distribution of plasma speed, density, degree of ionization, and magnetization to inquire. The initial solid density, several eV plasma expands to 1 cm and 10{sup {minus}4} relative density by 2 {micro}s, beyond which numerical simulations are imprecise. Yet, a Faraday cup detector at the ETA-II facility is at 25 cm from the target and observes the flow after 50 {micro}s. The model helps bridge this gap. The expansion of the target plasma into vacuum is so rapid that the ionized portion of the flow departs from local thermodynamic equilibrium. When the temperature (in eV) in a parcel of fluid drops below V{sub i} x [(2{gamma} - 2)/(5{gamma} + 17)], where V{sub i} is the ionization potential of the target metal (7.8 eV for tantalum), and {gamma} is the ratio of specific heats (5/3 for atoms), then the fractional ionization and electron temperature in that parcel remain fixed during subsequent expansion. The freezing temperature as defined here is V{sub i}/19. The balance between the self-pinching force and the space charge repulsion of an electron beam changes on penetrating a flow: (i) the target plasma cancels the space-charge field, (ii) internal eddy currents arise to counter the magnetization of relativistic electrons, and (iii) electron beam heating alters the flow magnetization by changing the plasma density gradient and the magnitude of the conductivity.
APPARATUS FOR MINIMIZING ENERGY LOSSES FROM MAGNETICALLY CONFINED VOLUMES OF HOT PLASMA
Post, R.F.
1961-10-01
An apparatus is described for controlling electron temperature in plasma confined in a Pyrotron magnetic containment field. Basically the device comprises means for directing low temperature electrons to the plasma in controlled quantities to maintain a predetermined optimum equilibrium electron temperature whereat minimum losses of plasma ions due to ambipolar effects and energy damping of the ions due to dynamical friction with the electrons occur. (AEC)
Magnetic Nozzle and Plasma Detachment Experiment
NASA Technical Reports Server (NTRS)
Chavers, Gregory; Dobson, Chris; Jones, Jonathan; Martin, Adam; Bengtson, Roger D.; Briezman, Boris; Arefiev, Alexey; Cassibry, Jason; Shuttpelz, Branwen; Deline, Christopher
2006-01-01
High power plasma propulsion can move large payloads for orbit transfer (such as the ISS), lunar missions, and beyond with large savings in fuel consumption owing to the high specific impulse. At high power, lifetime of the thruster becomes an issue. Electrodeless devices with magnetically guided plasma offer the advantage of long life since magnetic fields confine the plasma radially and keep it from impacting the material surfaces. For decades, concerns have been raised about the plasma remaining attached to the magnetic field and returning to the vehicle along the closed magnetic field lines. Recent analysis suggests that this may not be an issue of the magnetic field is properly shaped in the nozzle region and the plasma has sufficient energy density to stretch the magnetic field downstream. An experiment was performed to test the theory regarding the Magneto-hydrodynamic (MHD) detachment scenario. Data from this experiment will be presented. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) being developed by the Ad Astra Rocket Company uses a magnetic nozzle as described above. The VASIMR is also a leading candidate for exploiting an electric propulsion test platform being considered for the ISS.
NASA Astrophysics Data System (ADS)
Noland, Jonathan David
2011-12-01
The goal of this dissertation was to gain an understanding on the relative importance of microwave power, neutral pressure, and magnetic field configuration on the behavior of the hot electrons within an Electron Cyclotron Resonance Ion Source (ECRIS) plasma. This was carried out through measurement of plasma bremsstrahlung with both NaI(Tl) (hv > 30 keV) and CdTe (2 keV < hv < 70 keV) x-ray detectors, and through measurement of the plasma energy density with a diamagnetic loop placed around the plasma chamber. We also examined the anisotropy in x-ray power by simultaneously measuring the x-ray spectra in two orthogonal directions: radially and axially, using NaI(Tl) detectors. We have seen that for a 6.4 GHz ECRIS, both the x-ray power produced by confined electrons and the plasma energy density behave logarithmically with microwave power. The x-ray flux created by electrons lost from the plasma, however, does not saturate. Thus, the small increase in plasma density that occurred at high microwave powers (> 150 W on a 6.4 GHz ECRIS) was accompanied by a large increase in total x-ray power. We suggest that the saturation of x-ray power and plasma energy density was due to rf-induced pitch-angle scattering of the electrons. X-ray power and plasma energy density were also shown to saturate with neutral pressure, and to increase nearly linearly as the gradient of the magnetic field in the resonance zone was decreased. All of these findings were in agreement with the theoretical models describing ECRIS plasmas. We have discussed the use of a diamagnetic loop as a means of exploring various plasma time scales on a relative basis. Specifically, we focused much of our attention on studying how changing ion source parameters, such as microwave power and neutral pressure, would effect the rise and decay of the integrated diamagnetic signal, which can be related to plasma energy density. We showed that increasing microwave power lowers the e-fold times at both the leading
Electron density and plasma dynamics of a colliding plasma experiment
NASA Astrophysics Data System (ADS)
Wiechula, J.; Schönlein, A.; Iberler, M.; Hock, C.; Manegold, T.; Bohlender, B.; Jacoby, J.
2016-07-01
We present experimental results of two head-on colliding plasma sheaths accelerated by pulsed-power-driven coaxial plasma accelerators. The measurements have been performed in a small vacuum chamber with a neutral-gas prefill of ArH2 at gas pressures between 17 Pa and 400 Pa and load voltages between 4 kV and 9 kV. As the plasma sheaths collide, the electron density is significantly increased. The electron density reaches maximum values of ≈8 ṡ 1015 cm-3 for a single accelerated plasma and a maximum value of ≈2.6 ṡ 1016 cm-3 for the plasma collision. Overall a raise of the plasma density by a factor of 1.3 to 3.8 has been achieved. A scaling behavior has been derived from the values of the electron density which shows a disproportionately high increase of the electron density of the collisional case for higher applied voltages in comparison to a single accelerated plasma. Sequences of the plasma collision have been taken, using a fast framing camera to study the plasma dynamics. These sequences indicate a maximum collision velocity of 34 km/s.
Alfvénic tornadoes in a magnetized plasma
NASA Astrophysics Data System (ADS)
Shukla, P. K.
2013-01-01
It is shown that three-dimensional (3D) modified-kinetic Alfvén waves (m-KAWs) in a magnetized plasma can propagate in the form of Alfvénic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum. By using the two-fluid model, together with Ampère's law, we derive the wave equation for 3D m-KAWs in a magnetoplasma with me/mi ≪ β ≪ 1, where me (mi) is the electron (ion) mass, β=4πn0kB (Te+Ti)/B02, n0 the unperturbed plasma number density, kB the Boltzmann constant, Te(Te) the electron (ion) temperature, and B0 the strength of the ambient magnetic field. The 3D m-KAW equation admits solutions in the form of a Laguerre-Gauss Alfvénic vortex beam or a twisted kinetic Alfvénic wave with plasma density whirls that support the dynamics of shear Alfvénic magnetic flux ropes in plasmas.
Stoerk, H.B.; Winter, J.; Ihde, J.; Esser, H.G.; Reimer, H.; Freisinger, M
2001-01-15
The TOroidal MAgnetized System (TOMAS) is a simple magnetized torus dedicated to the investigation of wall conditioning methods by microwave-induced plasmas. In the TOMAS facility, an electron cyclotron resonance plasma is produced by microwaves at a frequency of 2.45 GHz and the corresponding resonant magnetic field of 87.6 mT. The facility and the first operational experience of film deposition by means of methane plasmas are described.
Magnetic Flux Compression Experiments Using Plasma Armatures
NASA Technical Reports Server (NTRS)
Turner, M. W.; Hawk, C. W.; Litchford, R. J.
2003-01-01
Magnetic flux compression reaction chambers offer considerable promise for controlling the plasma flow associated with various micronuclear/chemical pulse propulsion and power schemes, primarily because they avoid thermalization with wall structures and permit multicycle operation modes. The major physical effects of concern are the diffusion of magnetic flux into the rapidly expanding plasma cloud and the development of Rayleigh-Taylor instabilities at the plasma surface, both of which can severely degrade reactor efficiency and lead to plasma-wall impact. A physical parameter of critical importance to these underlying magnetohydrodynamic (MHD) processes is the magnetic Reynolds number (R(sub m), the value of which depends upon the product of plasma electrical conductivity and velocity. Efficient flux compression requires R(sub m) less than 1, and a thorough understanding of MHD phenomena at high magnetic Reynolds numbers is essential to the reliable design and operation of practical reactors. As a means of improving this understanding, a simplified laboratory experiment has been constructed in which the plasma jet ejected from an ablative pulse plasma gun is used to investigate plasma armature interaction with magnetic fields. As a prelude to intensive study, exploratory experiments were carried out to quantify the magnetic Reynolds number characteristics of the plasma jet source. Jet velocity was deduced from time-of-flight measurements using optical probes, and electrical conductivity was measured using an inductive probing technique. Using air at 27-inHg vacuum, measured velocities approached 4.5 km/s and measured conductivities were in the range of 30 to 40 kS/m.
Experimental evidence of warm electron populations in magnetron sputtering plasmas
Sahu, B. B. Han, Jeon G.; Kim, Hye R.; Ishikawa, K.; Hori, M.
2015-01-21
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.
Plasma transport in a simulated magnetic-divertor configuration
Strawitch, C. M.
1981-03-01
The transport properties of plasma on magnetic field lines that intersect a conducting plate are studied experimentally in the Wisconsin internal ring D.C. machine. The magnetic geometry is intended to simulate certain aspects of plasma phenomena that may take place in a tokamak divertor. It is found by a variety of measurements that the cross field transport is non-ambipolar; this may have important implications in heat loading considerations in tokamak divertors. The undesirable effects of nonambipolar flow make it preferable to be able to eliminate it. However, we find that though the non-ambipolarity may be reduced, it is difficult to eliminate entirely. The plasma flow velocity parallel to the magnetic field is found to be near the ion acoustic velocity in all cases. The experimental density and electron temperature profiles are compared to the solutions to a one dimensional transport model that is commonly used in divertor theory.
Computational studies for plasma filamentation by magnetic field in atmospheric microwave discharge
Takahashi, Masayuki; Ohnishi, Naofumi
2014-12-01
Plasma filamentation is induced by an external magnetic field in an atmospheric discharge using intense microwaves. A discrete structure is obtained at low ambient pressure if a strong magnetic field of more than 1 T is applied, due to the suppression of electron diffusion, whereas a diffusive pattern is generated with no external field. Applying a magnetic field can slow the discharge front propagation due to magnetic confinement of the electron transport. If the resonance conditions are satisfied for electron cyclotron resonance and its higher harmonics, the propagation speed increases because the heated electrons easily ionize neutral particles. The streamer velocity and the pattern of the microwave plasma are positively controlled by adjusting two parameters—the electron diffusion coefficient and the ionization frequency—through the resonance process and magnetic confinement, and hot, dense filamentary plasma can be concentrated in a compact volume to reduce energy loss in a plasma device like a microwave rocket.
Thrust and efficiency model for electron-driven magnetic nozzles
Little, Justin M.; Choueiri, Edgar Y.
2013-10-15
A performance model is presented for magnetic nozzle plasmas driven by electron thermal expansion to investigate how the thrust coefficient and beam divergence efficiency scale with the incoming plasma flow and magnetic field geometry. Using a transformation from cylindrical to magnetic coordinates, an approximate analytical solution is derived to the axisymmetric two-fluid equations for a collisionless plasma flow along an applied magnetic field. This solution yields an expression for the half-width at half-maximum of the plasma density profile in the far-downstream region, from which simple scaling relations for the thrust coefficient and beam divergence efficiency are derived. It is found that the beam divergence efficiency is most sensitive to the density profile of the flow into the nozzle throat, with the highest efficiencies occurring for plasmas concentrated along the nozzle axis. Increasing the expansion ratio of the magnetic field leads to efficiency improvements that are more pronounced for incoming plasmas that are not concentrated along the axis. This implies that the additional magnet required to increase the expansion ratio may be worth the added complexity for plasma sources that exhibit poor confinement.
Injection of a coaxial-gun-produced magnetized plasma into a background helicon plasma
NASA Astrophysics Data System (ADS)
Zhang, Yue; Lynn, Alan; Gilmore, Mark; Hsu, Scott
2014-10-01
A compact coaxial plasma gun is employed for experimental investigation of plasma bubble relaxation into a lower density background plasma. Experiments are being conducted in the linear device HelCat at UNM. The gun is powered by a 120-uF ignitron-switched capacitor bank, which is operated in a range of 5 to 10 kV and 100 kA. Multiple diagnostics are employed to investigate the plasma relaxation process. Magnetized argon plasma bubbles with velocities 1.2Cs, densities 1020 m-3 and electron temperature 13eV have been achieved. The background helicon plasma has density 1013 m-3, magnetic field from 200 to 500 Gauss and electron temperature 1eV. Several distinct operational regimes with qualitatively different dynamics are identified by fast CCD camera images. Additionally a B-dot probe array has been employed to measure the spatial toroidal and poloidal magnetic flux evolution to identify plasma bubble configurations. Experimental data and analysis will be presented.
Effects of geometry in itinerant electron magnets
NASA Astrophysics Data System (ADS)
Nakamura, H.; Muro, Y.; Kohara, T.; Shiga, M.
2007-04-01
The magnetism of quasi-one-dimensional itinerant electron magnets RMn4Al8 is compared with that of the typical frustrated itinerant electron magnet YMn2. The possible formation and observation of the spin pseudogap are discussed in connection with the spin-liquid state in strongly correlated itinerant electron systems.
Electron/ion whistler instabilities and magnetic noise bursts
NASA Technical Reports Server (NTRS)
Akimoto, K.; Gary, S. Peter; Omidi, N.
1987-01-01
Two whistler instabilities are investigated by means of the linear Vlasov dispersion equation. They are called the electron/ion parallel and oblique whistler instabilities, and are driven by electron/ion relative drifts along the magnetic field. It is demonstrated that the enhanced fluctuations from these instabilities can explain several properties of magnetic noise bursts in and near the plasma sheet in the presence of ion beams and/or field-aligned currents. At sufficiently high plasma beta, these instabilities may affect the current system in the magnetotail.
Model of electron collecting plasma contactors
Davis, V.A.; Katz, I.; Mandell, M.J.; Parks, D.E. )
1991-06-01
In laboratory experiments, plasma contactors are observed to collect ampere-level electron currents with low impedance. In order to extend the laboratory experience to the low-earth-orbit environment, a model of plasma contactors is being developed. Laboratory results are being used to support and validate the model development. The important physical processes observed in the laboratory are that the source plasma is separated from the background plasma by a double layer and that ionization of the expellant gas by the collected electrons creates the bulk of the ions that leave the source plasma. The model, which uses Poisson's equation with a physical charge density that includes the ion and electron components of both the source and the ambient plasmas, reproduces this phenomenon for typical experimental parameters. The calculations, in agreement with the laboratory results, show little convergence of the accelerated electrons. The angular momentum of the incoming electrons dramatically reduces the peak electron density. These electrons ionize enough gas to generate the source plasma. Calculations show that the increase in ionization rate with potential produces a steep rise in collected current with increasing potential as seen in the laboratory. 26 refs.
Magnetized Target Fusion Driven by Plasma Liners
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Eskridge, Richard; Smith, James; Lee, Michael; Richeson, Jeff; Schmidt, George; Knapp, Charles E.; Kirkpatrick, Ronald C.; Turchi, Peter J.; Rodgers, Stephen L. (Technical Monitor)
2001-01-01
Magnetized target fusion (MTF) attempts to combine the favorable attributes of magnetic confinement fusion (MCF) for energy confinement with the attributes of inertial confinement fusion (ICF) for efficient compression heating and wall-free containment of the fusing plasma. It uses a material liner to compress and contain a magnetized plasma. For practical applications, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC). For the successful implementation of the scheme, plasma jets of the requisite momentum flux density need to be produced. Their transport over sufficiently large distances (a few meters) needs to be assured. When they collide and merge into a liner, relative differences in velocity, density and temperature of the jets could give rise to instabilities in the development of the liner. Variation in the jet properties must be controlled to ensure that the growth rate of the instabilities are not significant over the time scale of the liner formation before engaging with the target plasma. On impact with the target plasma, some plasma interpenetration might occur between the liner and the target. The operating parameter space needs to be identified to ensure that a reasonably robust and conducting contact surface is formed between the liner and the target. A mismatch in the "impedance" between the liner and the target plasma could give rise to undesirable shock heating of the liner leading to increased entropy (thermal losses) in the liner. Any irregularities in the liner will accentuate the Rayleigh-Taylor instabilities during the compression of the target plasma by the liner.
Electromagnetic response of dynamic magnetized plasma
NASA Astrophysics Data System (ADS)
Kalluri, Dikshitulu K.
2000-06-01
An electromagnetic wave is transformed in a remarkable way by a transient magnetoplasma medium. The main effect of the temporal change in the parameters of the medium is the splitting of the source wave into new waves whose frequencies are different from the incident wave frequency. Several transient problems [1] involving slow or fast creation or slow or fast collapse of the plasma medium in the presence of a static magnetic field will be discussed. Approximate perturbation solution for the case of rapid temporal change of the plasma medium, based on time-domain Green's function, will be presented. WKP or Adiabatic analysis for the problem of slow temporal change of the plasma medium will also be presented. Finite Difference Time Domain (FDTD) method of numerical solution will be developed. Several interesting results obtained by the author by using the approximate solutions and verified by the FDTD method will be discussed. The more important results are: (1) frequency upshifting with power intensification of a whistler wave by a collapsing plasma medium, (2) conversion of a whistler wave into a controllable helical wiggler magnetic field, (3) mode coupling due to a magnetized plasma in a cavity, and (4) frequency down-shifting due to switched plasma layers in the presence of a background magnetic field. A switched magentoplasma can act like a frequency transformer. The source wave can be generated in an available frequency band and the switched plasma device converts the source wave into a new wave in a frequency band not easily obtainable by other methods. Frequency shifting mechanism can be applied for plasma cloaking of satellites and aircraft and for producing short-chirped-pulses as ultra wide band signals. Recent proof of the principle experiments confirmed many theoretical results. Many more experiments need to be done to study the scalability of the results. Fast Switching of magnetized plasma is a challenging experimental task.
Plasma Jet Braking: Energy Dissipation and Nonadiabatic Electrons
Khotyaintsev, Yu. V.; Cully, C. M.; Vaivads, A.; Andre, M.; Owen, C. J.
2011-04-22
We report in situ observations by the Cluster spacecraft of wave-particle interactions in a magnetic flux pileup region created by a magnetic reconnection outflow jet in Earth's magnetotail. Two distinct regions of wave activity are identified: lower-hybrid drift waves at the front edge and whistler-mode waves inside the pileup region. The whistler-mode waves are locally generated by the electron temperature anisotropy, and provide evidence for ongoing betatron energization caused by magnetic flux pileup. The whistler-mode waves cause fast pitch-angle scattering of electrons and isotropization of the electron distribution, thus making the flow braking process nonadiabatic. The waves strongly affect the electron dynamics and thus play an important role in the energy conversion chain during plasma jet braking.
NASA Astrophysics Data System (ADS)
Saha, Saikat
It has been proposed to extract momentum from the solar wind for spacecraft propulsion in deep space. For this purpose, a magnetic bubble is inflated from the spacecraft. The magnetic bubble inflation is affected by the expansion of a dense warm plasma in the magnetic field created by a solenoid aboard the spacecraft. The interaction between the inflated magnetic field and solar wind is likely to affect the transfer of momentum for the purpose of propulsion. The aim of our research here is to study the feasibility of this propulsion scheme by means of numerical simulations. For this purpose, we developed a 3-D hybrid particle code to model (i) the expansion of plasma in an ambient magnetic field created by a solenoid and (ii) the interaction of a plasma stream with the inflated magnetic field. The code is hybrid in the sense that ions are treated as particles and electrons as an isothermal fluid. We solve the coupled set of Maxwell's equations and the electron momentum equation for the electromagnetic fields using a predictor-corrector method. Using the 3-D simulations, we have demonstrated that when a warm and high-density plasma is injected in solenoidal magnetic fields, the trapping of the plasma in a magnetic mirror creates a dense plasma. When the trapped plasma energy densities (thermal and dynamic) exceed the magnetic energy density, the expanding plasma inflates the magnetic field lines. The extent of field inflation is seen to be greatly dependent on the injection velocity of the thermal plasma. The higher the injection velocity, the larger is the size of the inflated magnetic bubble. It is seen that the original magnetic field, which decreases as R-3, is stretched to the extent where it falls as R-alpha, where R is the distance from the center of the solenoid and alpha is found in the range 1 ≤ alpha ≤ 2. We have also demonstrated that when a plasma stream resembling the solar wind interacts with the expanding magnetic bubble, a magnetopause or bow
MHD Simulations of the Plasma Flow in the Magnetic Nozzle
NASA Technical Reports Server (NTRS)
Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.
2013-01-01
The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the
Momentum transfer to rotating magnetized plasma from gun plasma injection
Shamim, Imran; Hassam, A. B.; Ellis, R. F.; Witherspoon, F. D.; Phillips, M. W.
2006-11-15
Numerical simulations are carried out to investigate the penetration and momentum coupling of a gun-injected plasma slug into a rotating magnetized plasma. An experiment along these lines is envisioned for the Maryland Centrifugal Experiment (MCX) [R. F. Ellis et al., Phys. Plasmas 8, 2057 (2001)] using a coaxial plasma accelerator gun developed by HyperV Technologies Corp. [F. D. Witherspoon et al., Bull. Am. Phys. Soc. 50, LP1 87 (2005)]. The plasma gun would be located in the axial midplane and fired off-axis into the rotating MCX plasma annulus. The numerical simulation is set up so that the initial momentum in the injected plasma slug is of the order of the initial momentum of the target plasma. Several numerical firings are done into the cylindrical rotating plasma. Axial symmetry is assumed. The slug is seen to penetrate readily and deform into a mushroom, characteristic of interchange deformations. It is found that up to 25% of the momentum in the slug can be transferred to the background plasma in one pass across a cylindrical chord. For the same initial momentum, a high-speed low density slug gives more momentum transfer than a low-speed high density slug. Details of the numerical simulations and a scaling study are presented.
Magnetic-Field Generation and Amplification in an Expanding Plasma
NASA Astrophysics Data System (ADS)
Schoeffler, K. M.; Loureiro, N. F.; Fonseca, R. A.; Silva, L. O.
2014-05-01
Particle-in-cell simulations are used to investigate the formation of magnetic fields B in plasmas with perpendicular electron density and temperature gradients. For system sizes L comparable to the ion skin depth di, it is shown that B˜di/L, consistent with the Biermann battery effect. However, for large L/di, it is found that the Weibel instability (due to electron temperature anisotropy) supersedes the Biermann battery as the main producer of B. The Weibel-produced fields saturate at a finite amplitude (plasma β≈100), independent of L. The magnetic energy spectra below the electron Larmor radius scale are well fitted by the power law with slope -16/3, as predicted by Schekochihin et al. [Astrophys. J. Suppl. Ser. 182, 310 (2009)].
Effect of radial plasma transport at the magnetic throat on axial ion beam formation
NASA Astrophysics Data System (ADS)
Zhang, Yunchao; Charles, Christine; Boswell, Rod
2016-08-01
Correlation between radial plasma transport and formation of an axial ion beam has been investigated in a helicon plasma reactor implemented with a convergent-divergent magnetic nozzle. The plasma discharge is sustained under a high magnetic field mode and a low magnetic field mode for which the electron energy probability function, the plasma density, the plasma potential, and the electron temperature are measured at the magnetic throat, and the two field modes show different radial parametric behaviors. Although an axial potential drop occurs in the plasma source for both field modes, an ion beam is only observed in the high field mode while not in the low field mode. The transport of energetic ions is characterized downstream of the plasma source using the delimited ion current and nonlocal ion current. A decay of ion beam strength is also observed in the diffusion chamber.
NASA Astrophysics Data System (ADS)
Takahashi, Kazunori; Chiba, Aiki; Komuro, Atsushi; Ando, Akira
2016-10-01
The azimuthal plasma current in a magnetic nozzle of a radiofrequency plasma thruster is experimentally identified by measuring the plasma-induced magnetic field. The axial plasma momentum increases over about 20 cm downstream of the thruster exit due to the Lorentz force arising from the azimuthal current. The measured current shows that the azimuthal current is given by the sum of the electron diamagnetic drift and \\mathbf{E}× \\mathbf{B} drift currents, where the latter component decreases with an increase in the magnetic field strength; hence the azimuthal current approaches the electron diamagnetic drift one for the strong magnetic field. The Lorentz force calculated from the measured azimuthal plasma current and the radial magnetic field is smaller than the directly measured force exerted to the magnetic field, which indicates the existence of a non-negligible Lorentz force in the source tube.
Integrity of the Plasma Magnetic Nozzle
NASA Technical Reports Server (NTRS)
Gerwin, Richard A.
2009-01-01
This report examines the physics governing certain aspects of plasma propellant flow through a magnetic nozzle, specifically the integrity of the interface between the plasma and the nozzle s magnetic field. The injection of 100s of eV plasma into a magnetic flux nozzle that converts thermal energy into directed thrust is fundamental to enabling 10 000s of seconds specific impulse and 10s of kW/kg specific power piloted interplanetary propulsion. An expression for the initial thickness of the interface is derived and found to be approx.10(exp -2) m. An algorithm is reviewed and applied to compare classical resistivity to gradient-driven microturbulent (anomalous) resistivity, in terms of the spatial rate and time integral of resistive interface broadening, which can then be related to the geometry of the nozzle. An algorithm characterizing plasma temperature, density, and velocity dependencies is derived and found to be comparable to classical resistivity at local plasma temperatures of approx. 200 eV. Macroscopic flute-mode instabilities in regions of "adverse magnetic curvature" are discussed; a growth rate formula is derived and found to be one to two e-foldings of the most unstable Rayleigh-Taylor (RT) mode. After establishing the necessity of incorporating the Hall effect into Ohm s law (allowing full Hall current to flow and concomitant plasma rotation), a critical nozzle length expression is derived in which the interface thickness is limited to about 1 ion gyroradius.
NASA Astrophysics Data System (ADS)
Bose, Sayak; Chattopadhyay, P. K.; Ghosh, J.; Sengupta, S.; Saxena, Y. C.; Pal, R.
2015-04-01
In a quasineutral plasma, electrons undergo collective oscillations, known as plasma oscillations, when perturbed locally. The oscillations propagate due to finite temperature effects. However, the wave can lose the phase coherence between constituting oscillators in an inhomogeneous plasma (phase mixing) because of the dependence of plasma oscillation frequency on plasma density. The longitudinal electric field associated with the wave may be used to accelerate electrons to high energies by exciting large amplitude wave. However when the maximum amplitude of the wave is reached that plasma can sustain, the wave breaks. The phenomena of wave breaking and phase mixing have applications in plasma heating and particle acceleration. For detailed experimental investigation of these phenomena a new device, inverse mirror plasma experimental device (IMPED), has been designed and fabricated. The detailed considerations taken before designing the device, so that different aspects of these phenomena can be studied in a controlled manner, are described. Specifications of different components of the IMPED machine and their flexibility aspects in upgrading, if necessary, are discussed. Initial results meeting the prerequisite condition of the plasma for such study, such as a quiescent, collisionless and uniform plasma, are presented. The machine produces δnnoise/n <= 1%, Luniform ~ 120 cm at argon filling pressure of ~10-4 mbar and axial magnetic field of B = 1090 G.
Energetic Electron Transport In An Inhomogeneous Plasma Medium
Das, Amita
2010-11-23
A review of the work carried out at IPR on energetic electron transport through an inhomogeneous plasma medium is presented in this article. A Generalized Electron Magnetohydrodynamic (G-EMHD) fluid model has been developed and employed for such studies. Novel observations such as (i) the trapping of electron current pulse structure in a high density plasma region, (ii) the formation of sharp magnetic field shock structures at the inhomogeneous plasma density layer (iii) and intense energy dissipation at the shock layer even in the collisionless limit are reported. The intense energy dissipation of the electron current pulse at the shock layer provides a mechanism whereby highly energetic electrons which are essentially collision-less can also successfully deposit their energy in a local region of the plasma. This is specially attractive as it opens up the possibility of heating a localized region of an overdense plasma (where lasers cannot penetrate) by highly energetic collision-less electrons. A direct application of this mechanism to Fast Ignition (FT) experiments is discussed.
Characterization of plasma in magnetic multidipole discharges
NASA Astrophysics Data System (ADS)
Guimaraesferreira, Julio
1988-09-01
A characterization of the discharge of the quiescent plasma machine of INPE, and an identification of the most relevant processes in the definition of its plasma properties, were achieved. Measurements of plasma potential, the floating potential, the temperature of the electrons, and the density of the plasma, for pressures ranging from 10(-3) to 10(-1) Pa and for discharge potentials for 45 V to 120 V were accomplished. These measurements were made with a Langmuir spherical probe with 1mm in diameter. In the whole range of operation the presence of two populations of electrons with distinct temperatures in the energy range from 1 to 10 eV was observed, although for pressures approaching 10(-1) Pa the plasma tended to a single population of electrons with temperature of 1eV. The difference between plasma and floating potentials was observed to become smaller as the pressure raised, and the potential difference between plasma and anode reached a value around 2 V when pressure raised above 10(-2) Pa. The plasma density increases approximately linearly with pressure, for values below 10(-2) Pa, but above 10(-1) Pa its increase with pressure is quite reduced. A study on the collision processes in the plasma volume and on loss processes to surfaces allowed to interpret qualitatively the observed plasma behavior and to estimate, by means of simple expressions, some of the plasma parameters. The loss areas for ions and primary electrons were estimated from experimental results. A simple quantitative model which allows the calculation of plasma density in the whole range of operation, reproduced the correct order of magnitude of experimental values. However, an additional work, both theoretical and experimental, is required to obtain better agreement between experimental and theoretical values.
Electron Temperature Modification in Gas Discharge Plasmas
NASA Astrophysics Data System (ADS)
Godyak, Valery
2011-10-01
In gas discharge plasma with a Maxwellian electron energy distribution function (EEDF), the ionization balance results in the electron temperature Te being solely a function of the product of gas pressure p and plasma characteristic size d, Te = Te(pd), independently on plasma density and electron heating mechanism. This common feature of gas discharge plasma takes place in self-sustained discharges where ionization is locally coupled with electron heating, usually in a uniform heating electric field. At such condition, there is no room for electron temperature change at fixed pd. Variety of non-equilibrium phenomena observed in self-organized dc and rf discharge structures, and in relaxation process therein suggests the way to EEDF and Te modification. At such conditions, the electron heating can be separated (in space or/and in time) from the ionization. Few examples of such discharge structures in well know stationary dc and rf discharges and in plasma transient processes, leading to considerable mean electron energy reduction, will be considered in the presentation together with abbreviated review of existing methods and experimental results on EEDF control in laboratory plasmas. This work was supported in part by the DOE OFES (Contract No DE-SC0001939).
Performance characterization of a permanent-magnet helicon plasma thruster
NASA Astrophysics Data System (ADS)
Takahashi, Kazunori; Charles, Christine; Boswell, Rod
2012-10-01
Helicon plasma thrusters operated at a few kWs of rf power is an active area of an international research. Recent experiments have clarified part of the thrust-generation mechanisms. Thrust components which have been identified include an electron pressure inside the source region and a Lorentz force due to an electron diamagnetic drift current and a radial component of the applied magnetic field. The use of permanent magnets (PMs) instead of solenoids is one of the solutions for improving the thruster efficiency because it does not require electricity for the magnetic nozzle formation. Here the thrust imparted from a permanent-magnet helicon plasma thruster is directly measured using a pendulum thrust balance. The source consists of permanent magnet (PM) arrays, a double turn rf loop antenna powered by a 13.56 MHz rf generator and a glass source tube. The PM arrays provide a magnetic nozzle near the open exit of the source and two configurations, which have maximum field strengths of about 100 and 270 G, are tested. A thrust of 15 mN, specific impulse of 2000 sec and a thrust efficiency of 8 percent are presently obtained for 2 kW of input power, 24 sccm flow rate of argon and the stronger magnetic field configuration.
Heat flux viscosity in collisional magnetized plasmas
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-15
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Heat flux viscosity in collisional magnetized plasmas
NASA Astrophysics Data System (ADS)
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-01
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a "heat flux viscosity," is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Magnetic curvature effects on plasma interchange turbulence
NASA Astrophysics Data System (ADS)
Li, B.; Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-01
The magnetic curvature effects on plasma interchange turbulence and transport in the Z-pinch and dipole-like systems are explored with two-fluid global simulations. By comparing the transport levels in the systems with a different magnetic curvature, we show that the interchange-mode driven transport strongly depends on the magnetic geometry. For the system with large magnetic curvature, the pressure and density profiles are strongly peaked in a marginally stable state and the nonlinear evolution of interchange modes produces the global convective cells in the azimuthal direction, which lead to the low level of turbulent convective transport.
Magnetic field measurements in tokamak plasmas
Feldman, U.; Seely, J.F.; Sheeley,Jr., N.R.; Suckewer, S.; Title, A.M.
1984-11-01
The measurement of the poloidal magnetic field in a tokamak plasma from the Zeeman splitting and polarization of the magnetic dipole radiation from heavy ions is discussed. When viewed from a direction perpendicular to the toroidal field, the effect of the poloidal field on the circularly polarized radiation is detectable using a photoelectric polarimeter. The Zeeman splittings for a number of magnetic dipole transitions with wavelengths in the range 2300--9300 A are presented. An imaging polarimeter is proposed that can measure the poloidal magnetic field with space and time resolution.
Emission current formation in plasma electron emitters
Gruzdev, V. A.; Zalesski, V. G.
2010-12-15
A model of the plasma electron emitter is considered, in which the current redistribution over electrodes of the emitter gas-discharge structure and weak electric field formation in plasma are taken into account as functions of the emission current. The calculated and experimental dependences of the switching parameters, extraction efficiency, and strength of the electric field in plasma on the accelerating voltage and geometrical sizes of the emission channel are presented.
Simulation of the nonlinear evolution of electron plasma waves
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Cairns, I. H.
1991-01-01
Electrostatic waves driven by an electron beam in an ambient magnetized plasma were studied using a quasi-1D PIC simulation of electron plasma waves (i.e., Langmuir waves). The results disclose the presence of a process for moving wave energy from frequencies and wavenumbers predicted by linear theory to the Langmuir-like frequencies during saturation of the instability. A decay process for producing backward propagating Langmuir-like waves, along with low-frequency waves, is observed. The simulation results, however, indicate that the backscattering process is not the conventional Langmuir wave decay. Electrostatic waves near multiples of the electron plasma frequency are generated by wave-wave coupling during the nonlinear stage of the simulations, confirming the suggestion of Klimas (1983).
Magnetically Controlled Plasma Waveguide For Laser Wakefield Acceleration
Froula, D H; Divol, L; Davis, P; Palastro, J; Michel, P; Leurent, V; Glenzer, S H; Pollock, B; Tynan, G
2008-05-14
An external magnetic field applied to a laser plasma is shown produce a plasma channel at densities relevant to creating GeV monoenergetic electrons through laser wakefield acceleration. Furthermore, the magnetic field also provides a pressure to help shape the channel to match the guiding conditions of an incident laser beam. Measured density channels suitable for guiding relativistic short-pulse laser beams are presented with a minimum density of 5 x 10{sup 17} cm{sup -3} which corresponds to a linear dephasing length of several centimeters suitable for multi-GeV electron acceleration. The experimental setup at the Jupiter Laser Facility, Lawrence Livermore National Laboratory, where a 1-ns, 150 J 1054 nm laser will produce a magnetically controlled channel to guide a < 75 fs, 10 J short-pulse laser beam through 5-cm of 5 x 10{sup 17} cm{sup -3} plasma is presented. Calculations presented show that electrons can be accelerated to 3 GeV with this system. Three-dimensional resistive magneto-hydrodynamic simulations are used to design the laser and plasma parameters and quasi-static kinetic simulations indicate that the channel will guide a 200 TW laser beam over 5-cm.
Viscosity and Shear Flows in Magnetized Dusty Plasmas
NASA Astrophysics Data System (ADS)
Romero-Talamas, C. A.; Bates, E. M.; Birmingham, W. J.; Rivera, W. F.; Takeno, J.; Knop, S.
2015-11-01
Magnetized dusty plasma experiments are planned at the Dusty Plasma Laboratory of the University of Maryland, Baltimore County (UMBC), to investigate E x B rotation with dust of at least 500 nm in diameter. At this size, individual particles can be tracked and viscosity, shear flow, and temperature can be measured directly using a methodology similar to that used for linear shear flow configurations [Feng et al. PRL 109, 185002 (2012)]. The experiments are planned with a specially designed Bitter-type magnet that can be configured to achieve up to 10 T for at least 10 seconds, to minutes, with much longer operation times at lower fields also possible. At the highest field, the dust will be fully magnetized and thus we aim to achieve direct E x B rotation of the dust (and not just by ion drag). The motivation for these experiments comes from observations of electron and ion temperatures in excess of 100 eV in E x B rotating plasmas [R. Reid et al. Phys. Plasmas 21, 063305 (2014)]. The experimental setup and planned diagnostics for the magnetized dusty plasma are presented.
Plasma production for electron acceleration by resonant plasma wave
NASA Astrophysics Data System (ADS)
Anania, M. P.; Biagioni, A.; Chiadroni, E.; Cianchi, A.; Croia, M.; Curcio, A.; Di Giovenale, D.; Di Pirro, G. P.; Filippi, F.; Ghigo, A.; Lollo, V.; Pella, S.; Pompili, R.; Romeo, S.; Ferrario, M.
2016-09-01
Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (10-100 GV/m), enabling acceleration of electrons to GeV energy in few centimeter. However, the quality of the electron bunches accelerated with this technique is still not comparable with that of conventional accelerators (large energy spread, low repetition rate, and large emittance); radiofrequency-based accelerators, in fact, are limited in accelerating field (10-100 MV/m) requiring therefore hundred of meters of distances to reach the GeV energies, but can provide very bright electron bunches. To combine high brightness electron bunches from conventional accelerators and high accelerating fields reachable with plasmas could be a good compromise allowing to further accelerate high brightness electron bunches coming from LINAC while preserving electron beam quality. Following the idea of plasma wave resonant excitation driven by a train of short bunches, we have started to study the requirements in terms of plasma for SPARC_LAB (Ferrario et al., 2013 [1]). In particular here we focus on hydrogen plasma discharge, and in particular on the theoretical and numerical estimates of the ionization process which are very useful to design the discharge circuit and to evaluate the current needed to be supplied to the gas in order to have full ionization. Eventually, the current supplied to the gas simulated will be compared to that measured experimentally.
Development of plasma cathode electron guns
NASA Astrophysics Data System (ADS)
Oks, Efim M.; Schanin, Peter M.
1999-05-01
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 E×B 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.
Nonlinear electron acoustic waves in presence of shear magnetic field
Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Chakrabarti, Nikhil
2013-12-15
Nonlinear electron acoustic waves are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic wave. Whereas, nonlinear wave dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear wave characteristics are well depicted by KdV equation. The wave dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere.
Laboratory study of avalanches in magnetized plasmas.
Van Compernolle, B; Morales, G J; Maggs, J E; Sydora, R D
2015-03-01
It is demonstrated that a novel heating configuration applied to a large and cold magnetized plasma allows the study of avalanche phenomena under controlled conditions. Intermittent collapses of the plasma pressure profile, associated with unstable drift-Alfvén waves, exhibit a two-slope power-law spectrum with exponents near -1 at lower frequencies and in the range of -2 to -4 at higher frequencies. A detailed mapping of the spatiotemporal evolution of a single avalanche event is presented.
Images of Complex Interactions of an Intense Ion Beam with Plasma Electrons
Igor D. Kaganovich; Edward Startsev; Ronald C. Davidson
2004-08-03
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.
Diagnostic techniques for measuring suprathermal electron dynamics in plasmas (invited)
Coda, S.
2008-10-15
Plasmas, both in the laboratory and in space, are often not in thermodynamic equilibrium, and the plasma electron distribution function is accordingly non-Maxwellian. Suprathermal electron tails can be generated by external drives, such as rf waves and electric fields, or internal ones, such as instabilities and magnetic reconnection. The variety and importance of the phenomena in which suprathermal electrons play a significant role explains an enduring interest in diagnostic techniques to investigate their properties and dynamics. X-ray bremsstrahlung emission has been studied in hot magnetized plasmas for well over two decades, flanked progressively by electron-cyclotron emission in geometries favoring the high-energy end of the distribution function (high-field-side, vertical, oblique emission), by electron-cyclotron absorption, by spectroscopic techniques, and at lower temperatures, by Langmuir probes and electrostatic analyzers. Continuous progress in detector technology and in measurement and analysis techniques, increasingly sophisticated layouts (multichannel and tomographic systems, imaging geometries), and highly controlled suprathermal generation methods (e.g., perturbative rf modulation) have all been brought to bear in recent years on an increasingly detailed, although far from complete, understanding of suprathermal electron dynamics.
Electron heating in capacitively coupled plasmas revisited
NASA Astrophysics Data System (ADS)
Lafleur, T.; Chabert, P.; Booth, J. P.
2014-06-01
We revisit the problem of electron heating in capacitively coupled plasmas (CCPs), and propose a method for quantifying the level of collisionless and collisional heating in plasma simulations. The proposed procedure, based on the electron mechanical energy conservation equation, is demonstrated with particle-in-cell simulations of a number of single and multi-frequency CCPs operated in regimes of research and industrial interest. In almost all cases tested, the total electron heating is comprised of collisional (ohmic) and pressure heating parts. This latter collisionless component is in qualitative agreement with the mechanism of electron heating predicted from the recent re-evaluation of theoretical models. Finally, in very electrically asymmetric plasmas produced in multi-frequency discharges, we observe an additional collisionless heating mechanism associated with electron inertia.
Li Liuhe; Wang Zhuo; Lu Qiuyuan; Fu, Ricky K. Y.; Chu, Paul K.; Pang Enjing; Dun Dandan; He Fushun; Li Fen
2011-01-10
A permanent annular magnet positioned at the grounded anode alters the discharge characteristics in enhanced glow discharge plasma immersion ion implantation (EGD-PIII). The nonuniform magnetic field increases the electron path length and confines electron motion due to the magnetic mirror effect and electron-neutral collisions thus occur more frequently. The plasma potential and ion density measured by a Langmuir probe corroborate that ionization is improved near the grounded anode. This hybrid magnetic field EGD-PIII method is suitable for implantation of gases with low ionization rates.
Exact solutions to magnetized plasma flow
Wang, Zhehui; Barnes, Cris W.
2001-03-01
Exact analytic solutions for steady-state magnetized plasma flow (MPF) using ideal magnetohydrodynamics formalism are presented. Several cases are considered. When plasma flow is included, a finite plasma pressure gradient {nabla}p can be maintained in a force-free state JxB=0 by the velocity gradient. Both incompressible and compressible MPF examples are discussed for a Taylor-state spheromak B field. A new magnetized nozzle solution is given for compressible plasma when U{parallel}B. Transition from a magnetized nozzle to a magnetic nozzle is possible when the B field is strong enough. No physical nozzle would be needed in the magnetic nozzle case. Diverging-, drum- and nozzle-shaped MPF solutions when U{perpendicular}B are also given. The electric field is needed to balance the UxB term in Ohm's law. The electric field can be generated in the laboratory with the proposed conducting electrodes. If such electric fields also exist in stars and galaxies, such as through a dynamo process, then these solutions can be candidates to explain single and double jets.
Scaling laws in magnetized plasma turbulence
Boldyrev, Stanislav
2015-06-28
Interactions of plasma motion with magnetic fields occur in nature and in the laboratory in an impressively broad range of scales, from megaparsecs in astrophysical systems to centimeters in fusion devices. The fact that such an enormous array of phenomena can be effectively studied lies in the existence of fundamental scaling laws in plasma turbulence, which allow one to scale the results of analytic and numerical modeling to the sized of galaxies, velocities of supernovae explosions, or magnetic fields in fusion devices. Magnetohydrodynamics (MHD) provides the simplest framework for describing magnetic plasma turbulence. Recently, a number of new features of MHD turbulence have been discovered and an impressive array of thought-provoking phenomenological theories have been put forward. However, these theories have conflicting predictions, and the currently available numerical simulations are not able to resolve the contradictions. MHD turbulence exhibits a variety of regimes unusual in regular hydrodynamic turbulence. Depending on the strength of the guide magnetic field it can be dominated by weakly interacting Alfv\\'en waves or strongly interacting wave packets. At small scales such turbulence is locally anisotropic and imbalanced (cross-helical). In a stark contrast with hydrodynamic turbulence, which tends to ``forget'' global constrains and become uniform and isotropic at small scales, MHD turbulence becomes progressively more anisotropic and unbalanced at small scales. Magnetic field plays a fundamental role in turbulent dynamics. Even when such a field is not imposed by external sources, it is self-consistently generated by the magnetic dynamo action. This project aims at a comprehensive study of universal regimes of magnetic plasma turbulence, combining the modern analytic approaches with the state of the art numerical simulations. The proposed study focuses on the three topics: weak MHD turbulence, which is relevant for laboratory devices, the solar
On zero frequency magnetic fluctuations in plasmas
Tajima, T.; Cable, S. . Inst. for Fusion Studies); Kulsrud, R.M. . Dept. of Astrophysical Sciences)
1992-01-01
A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy lost'' by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l angle}B{sup 2}{r angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.
On zero frequency magnetic fluctuations in plasmas
Tajima, T.; Cable, S.; Kulsrud, R.M.
1992-01-01
A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy ``lost`` by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l_angle}B{sup 2}{r_angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.
Electronic Broadening operator for relativistic plasmas
Meftah, M. T.; Naam, A.
2008-10-22
In this work we review some aspects of the semiclassical dipole impact approximation for isolated ion lines in relativistic plasma. Mainly we focuss our work on the collision operator for relativistic electrons. In this case, the electron trajectory around a positive charge in the plasma differs drastically from those known earlier as hyperbolic. The effect of this difference on the collision operator is discussed with respect the various plasma conditions. Some theoretical and practical aspects of lines -shape calculations are discussed. Detailed calculations are performed for the collision operator in the semiclassical (dipole) impact approximation.
Energetics of the magnetic reconnection in laboratory and space plasmas
NASA Astrophysics Data System (ADS)
Yamada, Masaaki
2014-10-01
The essential feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy. This talk addresses this key unresolved question; how is magnetic energy converted to plasma kinetic energy during reconnection? Our recent study on MRX demonstrates that more than half of the incoming magnetic energy is converted to particle energy at a remarkably fast speed (~ 0.2VA) in the reconnection layer. A question arises as to whether the present results should be applied to magnetic reconnection phenomena in the space astrophysical plasmas. In a reconnection region of effectively similar size in the Earth's magnetotail, the energy partition was carefully measured during multiple passages of the Cluster satellites. The half length of the tail reconnection layer (L) was estimated to be 2000-4000 km namely 3-6 di, (ion skin depth); the scale length of this measurement is very similar to the MRX case, L ~ 3di. Reconnection in the magneto-tail is driven by an external force, i.e., the solar wind, and the boundary conditions are very similar to the MRX setup. The observed energy partition is notably similar, namely, more than 50% of the magnetic energy flux is converted to the particle energy flux, which is dominated by the ion enthalpy flux, with smaller contributions from the electron enthalpy and heat flux. A broad implication will be discussed. Supported by DoE, NASA, NSF.
Collimated fast electron beam generation in critical density plasma
Iwawaki, T. Habara, H.; Morita, K.; Tanaka, K. A.; Baton, S.; Fuchs, J.; Chen, S.; Nakatsutsumi, M.; Rousseaux, C.; Filippi, F.; Nazarov, W.
2014-11-15
Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is observed when an ultra-intense laser pulse (I = 10{sup 14 }W/cm{sup 2}, 300 fs) irradiates a uniform critical density plasma. The uniform plasma is created through the ionization of an ultra-low density (5 mg/c.c.) plastic foam by X-ray burst from the interaction of intense laser (I = 10{sup 14 }W/cm{sup 2}, 600 ps) with a thin Cu foil. 2D Particle-In-Cell (PIC) simulation well reproduces the collimated electron beam with a strong magnetic field in the region of the laser pulse propagation. To understand the physical mechanism of the collimation, we calculate energetic electron motion in the magnetic field obtained from the 2D PIC simulation. As the results, the strong magnetic field (300 MG) collimates electrons with energy over a few MeV. This collimation mechanism may attract attention in many applications such as electron acceleration, electron microscope and fast ignition of laser fusion.
Location of the first plasma response to resonant magnetic perturbations in DIII-D H-mode plasmas
NASA Astrophysics Data System (ADS)
Xiao, W. W.; Evans, T. E.; Tynan, G. R.; Eldon, D.
2016-06-01
The resonant location of the first plasma response to periodic toroidal phase flips of a resonant magnetic perturbation (RMP) field is experimentally identified in the DIII-D tokamak using phase minima of the modulated plasma density and toroidal rotation relative to the RMP field. The plasma response coincides with the q = 3 rational surface and electron fluid velocity null, which is consistent with simulations of the plasma response to the RMP field from resistive magnetohydrodynamics (MHD) modeling. An asymmetric propagation of the particle and the momentum transport from the resonant location of the plasma response to the RMP into the core and into the plasma edge is observed.
Evolution of plasma parameters in a He - N2/Ar magnetic pole enhanced inductive plasma source
NASA Astrophysics Data System (ADS)
Younus, Maria; Rehman, N. U.; Shafiq, M.; Zakaullah, M.; Abrar, M.
2016-02-01
A magnetic pole enhanced inductively coupled H e - N2/A r plasma is studied at low pressure, to monitor the effects of helium mixing on plasma parameters like electron number density (ne) , electron temperature (Te) , plasma potential (Vp ) , and electron energy probability functions (EEPFs). An RF compensated Langmuir probe is employed to measure these plasma parameters. It is noted that electron number density increases with increasing RF power and helium concentration in the mixture, while it decreases with increase in filling gas pressure. On the other hand, electron temperature shows an increasing trend with helium concentration in the mixture. At low RF powers and low helium concentration in the mixture, EEPFs show a "bi-Maxwellian" distribution with pressure. While at RF powers greater than 50 W and higher helium concentration in the mixture, EEPFs evolve into "Maxwellian" distribution. The variation of skin depth with RF power and helium concentration in the mixture, and its relation with EEPF are also studied. The effect of helium concentrations on the temperatures of two electron groups ( Tb u l k and Tt a i l ) in the "bi-Maxwellian" EEPFs is also observed. The temperature of low energy electron group ( Tb u l k) shows significant increase with helium addition, while the temperature of tail electrons ( Tt a i l) increases smoothly as compared to ( Tb u l k).
Plasma-Jet Magnetized-Target Fusion Burn Dynamics
NASA Astrophysics Data System (ADS)
Santarius, John F.
2006-10-01
In magnetized-target fusion (MTF), an imploding, conducting liner compresses a magnetized plasmoid, such as a spheromak or field-reversed configuration (FRC). The increasing magnetic field of the target reduces thermal conduction and the liner's inertia provides transient plasma stability and confinement. This poster explores the burn dynamics of using plasma jets to form the liner [1]. The investigation uses the University of Wisconsin’s 1 D Lagrangian radiation hydrodynamics code, BUCKY, which solves single-fluid equations of motion with pressure contributions from electrons, ions, radiation, and fast charged particles, using either ideal-gas or table-lookup equations of state. BUCKY includes ion-electron interactions, PdV work, and fast-ion energy deposition. For this research, the code has been extended to include the magnetic field evolution as the plasmoid compresses plus the dependence of the thermal conductivity and fusion product energy deposition on the magnetic field.[1] Y.C. F. Thio, et al., ``Magnetized Target Fusion in a Spheroidal Geometry with Standoff Drivers,'' in Current Trends in International Fusion Research, E. Panarella, ed. (National Research Council of Canada, Ottawa, Canada, 1999), p. 113.* Research funded by the DOE Office of Fusion Energy Sciences, grant DE-FG02-04ER54751.
ELECTRON HEATING IN A RELATIVISTIC, WEIBEL-UNSTABLE PLASMA
Kumar, Rahul; Eichler, David; Gedalin, Michael
2015-06-20
The dynamics of two initially unmagnetized relativistic counter-streaming homogeneous ion–electron plasma beams are simulated in two dimensions (2D) 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. This field, which is partially inductive and partially electrostatic, is identified as the main source of net electron acceleration, greatly exceeding that due to magnetic field decay at later stages. The transverse electric field, although larger than the longitudinal field, is shown to play a smaller role in heating electrons, contrary to previous claims. It is found that in one dimension, the electrons become strongly magnetized and are not accelerated beyond their initial kinetic energy. Rather, the heating of the electrons is enhanced by the bending and break up of the filaments, which releases electrons that would otherwise be trapped within a single filament and slow the development of the Weibel instability (i.e., the magnetic field growth) via induction as per Lenz’s law. In 2D simulations, electrons are heated to about one quarter of the initial kinetic energy of ions. The magnetic energy at maximum is about 4%, decaying to less than 1% by the end of the simulation. The ions are found to gradually decelerate until the end of the simulation, by which time they retain a residual anisotropy of less than 10%.
Magnetized Target Fusion Driven by Plasma Liners
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Cassibry, Jason; Eskridge, Richard; Kirkpatrick, Ronald C.; Knapp, Charles E.; Lee, Michael; Martin, Adam; Smith, James; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)
2001-01-01
For practical applications of magnetized target fusion, standoff drivers to deliver the imploding momentum flux to the target plasma remotely are required. Quasi-spherically converging plasma jets have been proposed as standoff drivers for this purpose. The concept involves the dynamic formation of a quasi-spherical plasma liner by the merging of plasma jets, and the use of the liner so formed to compress a spheromak or a field reversed configuration (FRC). Theoretical analysis and computer modeling of the concept are presented. It is shown that, with the appropriate choice of the flow parameters in the liner and the target, the impact between the liner and the target plasma can be made to be shockless in the liner or to generate at most a very weak shock in the liner. Additional information is contained in the original extended abstract.
Plasma observations at the earth's magnetic equator
NASA Technical Reports Server (NTRS)
Olsen, R. C.; Shawhan, S. D.; Gallagher, D. L.; Chappell, C. R.; Green, J. L.
1987-01-01
New observations of particle and wave data from the magnetic equator from the DE 1 spacecraft are reported. The results demonstrate that the equatorial plasma population is predominantly hydrogen and that the enhanced ion fluxes observed at the equator occur without an increase in the total plasma density. Helium is occasionally found heated along with the protons, and forms about 10 percent of the equatorially trapped population at such times. The heated H(+) ions can be characterized by a bi-Maxwellian with kT(parallel) = 0.5-1.0 eV and kT = 5-50 eV, with a density of 10-100/cu cm. The total plasma density is relatively constant with latitude. First measurements of the equatorially trapped plasma and coincident UHR measurements show that the trapped plasma is found in conjunction with equatorial noise.
Dynamics of Exploding Plasma Within a Magnetized Plasma
Dimonte, G; Dipeso, G; Hewett, D
2002-02-01
This memo describes several possible laboratory experiments on the dynamics of an exploding plasma in a background magnetized plasma. These are interesting scientifically and the results are applicable to energetic explosions in the earth's ionosphere (DOE Campaign 7 at LLNL). These proposed experiments are difficult and can only be performed in the new LAPD device at UCLA. The purpose of these experiments would be to test numerical simulations, theory and reduced models for systems performance codes. The experiments are designed to investigate the affect of the background plasma on (1) the maximum diamagnetic bubble radius given by Eq. 9; and (2) the Alfven wave radiation efficiency produced by the induced current J{sub A} (Eqs. 10-12) These experiments involve measuring the bubble radius using a fast gated optical imager as in Ref [1] and the Alfven wave profile and intensity as in Ref [2] for different values of the exploding plasma energy, background plasma density and temperature, and background magnetic field. These experiments extend the previously successful experiments [2] on Alfven wave coupling. We anticipate that the proposed experiments would require 1-2 weeks of time on the LAPD. We would perform PIC simulations in support of these experiments in order to validate the codes. Once validated, the PIC simulations would then be able to be extended to realistic ionospheric conditions with various size explosions and altitudes. In addition to the Alfven wave coupling, we are interested in the magnetic containment and transport of the exploding ''debris'' plasma to see if the shorting of the radial electric field in the magnetic bubble would allow the ions to propagate further. This has important implications in an ionospheric explosion because it defines the satellite damage region. In these experiments, we would field fast gated optical cameras to obtain images of the plasma expansion, which could then be correlated with magnetic probe measurements. In
Double-layer shocks in a magnetized quantum plasma.
Misra, A P; Samanta, S
2010-09-01
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio δ . The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
Double-layer shocks in a magnetized quantum plasma
NASA Astrophysics Data System (ADS)
Misra, A. P.; Samanta, S.
2010-09-01
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio δ . The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
Double-layer shocks in a magnetized quantum plasma
Misra, A. P.; Samanta, S.
2010-09-15
The formation of small but finite amplitude electrostatic shocks in the propagation of quantum ion-acoustic waves obliquely to an external magnetic field is reported in a quantum electron-positron-ion plasma. Such shocks are seen to have double-layer (DL) structures composed of the compressive and accompanying rarefactive slow-wave fronts. Existence of such DL shocks depends critically on the quantum coupling parameter H associated with the Bohm potential and the positron to electron density ratio {delta}. The profiles may, however, steepen initially and reach a steady state with a number of solitary waves in front of the shocks. Such novel DL shocks could be a good candidate for particle acceleration in intense laser-solid density plasma interaction experiments as well as in compact astrophysical objects, e.g., magnetized white dwarfs.
Magnetic stochasticity in gyrokinetic simulations of plasma microturbulence
NASA Astrophysics Data System (ADS)
Wang, Eric
2010-11-01
One of the fundamental components of a steady state tokamak or stellerator fusion reactor is the structural integrity of nested magnetic surfaces. The consequences of losing this integrity can have very serious implications, ranging from sawtooth crashes to disruptions. In the present work, we use GYRO to examine the perturbed magnetic field structure generated by electromagnetic gyrokinetic simulations of the CYCLONE base case as β is varied from .1% to .7%, as first investigated in [J. Candy, Phys. Plasmas 12, 072307 (2005)]. By integrating the self-consistent magnetic field lines to produce Poincare surface of section plots, we demonstrate destruction of magnetic surfaces for all nonzero values of β. Despite widespread stochasticity of the perturbed magnetic fields, no significant increase in electron transport is observed. We can quantify the stochastic electron heat transport by using test particles to estimate the magnetic diffusion coefficient Dst [A.B. Rechester and M.N. Rosenbluth, PRL 40, 38 (1978)] for hundreds of time slices in each simulation and find the time-history of Dst to be highly correlated with the electron heat transport due to ``magnetic-flutter'' computed in the simulations. The mechanism that couples electromagnetic turbulence to the linearly damped high-n tearing modes that are responsible for reconnection will be discussed.
Electron Densities Near Io from Galileo Plasma Wave Observations
NASA Technical Reports Server (NTRS)
Gurnett, D. A.; Persoon, A. M.; Kurth, W. S.; Roux, A.; Bolton, S. J.
2001-01-01
This paper presents an overview of electron densities obtained near Io from the Galileo plasma wave instrument during the first four flybys of Io. These flybys were Io, which was a downstream wake pass that occurred on December 7, 1995; I24, which was an upstream pass that occurred on October 11, 1999; I25, which was a south polar pass that occurred on November 26, 1999; and I27, which was an upstream pass that occurred on February 22, 2000. Two methods were used to measure the electron density. The first was based on the frequency of upper hybrid resonance emissions, and the second was based on the low-frequency cutoff of electromagnetic radiation at the electron plasma frequency. For three of the flybys, Io, I25, and I27, large density enhancements were observed near the closest approach to Io. The peak electron densities ranged from 2.1 to 6.8 x 10(exp 4) per cubic centimeters. These densities are consistent with previous radio occultation measurements of Io's ionosphere. No density enhancement was observed during the I24 flyby, most likely because the spacecraft trajectory passed too far upstream to penetrate Io's ionosphere. During two of the flybys, I25 and I27, abrupt step-like changes were observed at the outer boundaries of the region of enhanced electron density. Comparisons with magnetic field models and energetic particle measurements show that the abrupt density steps occur as the spacecraft penetrated the boundary of the Io flux tube, with the region of high plasma density on the inside of the flux tube. Most likely the enhanced electron density within the Io flux tube is associated with magnetic field lines that are frozen to Io by the high conductivity of Io's atmosphere, thereby enhancing the escape of plasma along the magnetic field lines that pass through Io's ionosphere.
Magnetized Target Fusion Driven by Plasma Liners
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Kirkpatrick, Ronald C.; Knapp, Charles E.; Rodgers, Stephen L. (Technical Monitor)
2002-01-01
Magnetized target fusion is an emerging, relatively unexplored approach to fusion for electrical power and propulsion application. The physical principles of the concept are founded upon both inertial confinement fusion (ICF) and magnetic confinement fusion (MCF). It attempts to combine the favorable attributes of both these orthogonal approaches to fusion, but at the same time, avoiding the extreme technical challenges of both by exploiting a fusion regime intermediate between them. It uses a material liner to compress, heat and contain the fusion reacting plasma (the target plasma) mentally. By doing so, the fusion burn could be made to occur at plasma densities as high as six orders of magnitude higher than conventional MCF such as tokamak, thus leading to an approximately three orders of magnitude reduction in the plasma energy required for ignition. It also uses a transient magnetic field, compressed to extremely high intensity (100's T to 1000T) in the target plasma, to slow down the heat transport to the liner and to increase the energy deposition of charged-particle fusion products. This has several compounding beneficial effects. It leads to longer energy confinement time compared with conventional ICF without magnetized target, and thus permits the use of much lower plasma density to produce reasonable burn-up fraction. The compounding effects of lower plasma density and the magneto-insulation of the target lead to greatly reduced compressional heating power on the target. The increased energy deposition rate of charged-particle fusion products also helps to lower the energy threshold required for ignition and increasing the burn-up fraction. The reduction in ignition energy and the compressional power compound to lead to reduced system size, mass and R&D cost. It is a fusion approach that has an affordable R&D pathway, and appears attractive for propulsion application in the nearer term.
Simulation of electromagnetically and magnetically induced transparency in a magnetized plasma
NASA Astrophysics Data System (ADS)
Hur, M. S.; Wurtele, J. S.; Shvets, G.
2003-07-01
Electromagnetically induced transparency (EIT), a phenomenon well known in atomic systems, has a natural analogy in a classical magnetized plasma. The magnetized plasma has a resonance for right-hand polarized electromagnetic waves at the electron cyclotron frequency Ω0, so that a probe wave with frequency ω1=Ω0 cannot propagate through the plasma. The plasma can be made transparent to such a probe by the presence of a pump wave. The pump may be an electromagnetic wave or magnetostatic wiggler. Simulations and theory show that the physical reason for the transparency is that the beating of the probe wave with the pump wave sets up a plasma oscillation, and the upper sideband of the pump wave cancels the resonant plasma current due to the probe. The theory of plasma EIT derived here extends that found in the earlier work to include the effects of the lower sideband of the pump and renormalization of the plasma frequency and an analysis of the transient response. A detailed comparison of theory to one-dimensional particle-in-cell simulations is presented and estimates for the performance ion accelerator using the EIT interaction are given. The dispersion relation and estimates for the phase velocity and amplitude of the plasma wave are in good agreement with particle-in-cell simulations.
Electron Beam Diagnostics in Plasmas Based on Electron Beam Ionization
NASA Astrophysics Data System (ADS)
Leonhardt, Darrin; Leal-Quiros, Edbertho; Blackwell, David; Walton, Scott; Murphy, Donald; Fernsler, Richard; Meger, Robert
2001-10-01
Over the last few years, electron beam ionization has been shown to be a viable generator of high density plasmas with numerous applications in materials modification. To better understand these plasmas, we have fielded electron beam diagnostics to more clearly understand the propagation of the beam as it travels through the background gas and creates the plasma. These diagnostics vary greatly in sophistication, ranging from differentially pumped systems with energy selective elements to metal 'hockey pucks' covered with thin layers of insulation to electrically isolate the detector from the plasma but pass high energy beam electrons. Most importantly, absolute measurements of spatially resolved beam current densities are measured in a variety of pulsed and continuous beam sources. The energy distribution of the beam current(s) will be further discussed, through experiments incorporating various energy resolving elements such as simple grids and more sophisticated cylindrical lens geometries. The results are compared with other experiments of high energy electron beams through gases and appropriate disparities and caveats will be discussed. Finally, plasma parameters are correlated to the measured beam parameters for a more global picture of electron beam produced plasmas.
Electromagnetic wave propagation through an overdense magnetized collisional plasma layer
NASA Astrophysics Data System (ADS)
Thoma, C.; Rose, D. V.; Miller, C. L.; Clark, R. E.; Hughes, T. P.
2009-08-01
The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth's upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.
Electromagnetic wave propagation through an overdense magnetized collisional plasma layer
Thoma, C.; Rose, D. V.; Miller, C. L.; Clark, R. E.; Hughes, T. P.
2009-08-15
The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth's upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.
Experiments on beam plasma interactions and EM waves in magnetized plasmas
NASA Astrophysics Data System (ADS)
Phelps, Alan D. R.
2012-04-01
An energetic electron beam can exhibit several types of interesting behaviour when interacting with plasmas and/or magnetic fields. The focus in the present work is on electron cyclotron maser interactions. The instabilities that occur are also often observed in space as well as in the laboratory. Some of the high power sources of electromagnetic radiation, such as gyrodevices, make use of similar instability mechanisms. Laboratory experiments and numerical simulations have led to both a better understanding of natural phenomena and the development of high power electromagnetic radiation sources for several applications in fusion plasma physics. The gyrotron is one such device that is being used to provide auxiliary heating for large tokamaks via electron cyclotron resonance heating (ECRH). It is planned to use a number of gyrotrons supplied by several nations in the ITER experiment. In the ITER experiment these gyrotrons will not only be used for auxiliary heating but also for advanced tailoring of the tokamak plasma properties.
Magnetic reconnection in collisionless plasmas - Prescribed fields
NASA Technical Reports Server (NTRS)
Burkhart, G. R.; Drake, J. F.; Chen, J.
1990-01-01
The structure of the dissipation region during magnetic reconnection in collisionless plasma is investigated by examining a prescribed two-dimensional magnetic x line configuration with an imposed inductive electric field E(y). The calculations represent an extension of recent MHD simulations of steady state reconnection (Biskamp, 1986; Lee and Fu, 1986) to the collisionless kinetic regime. It is shown that the structure of the x line reconnection configuration depends on only two parameters: a normalized inductive field and a parameter R which represents the opening angle of the magnetic x lines.
Currents between tethered electrodes in a magnetized laboratory plasma
NASA Technical Reports Server (NTRS)
Stenzel, R. L.; Urrutia, J. M.
1989-01-01
Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed.
NASA Astrophysics Data System (ADS)
Zolghadr, S. H.; Jafari, S.; Raghavi, A.
2016-05-01
Significant progress has been made employing plasmas in the free-electron lasers (FELs) interaction region. In this regard, we study the output power and saturation length of the plasma whistler wave-pumped FEL in a magnetized plasma channel. The small wavelength of the whistler wave (in sub-μm range) in plasma allows obtaining higher radiation frequency than conventional wiggler FELs. This configuration has a higher tunability by adjusting the plasma density relative to the conventional ones. A set of coupled nonlinear differential equations is employed which governs on the self-consistent evolution of an electromagnetic wave. The electron bunching process of the whistler-pumped FEL has been investigated numerically. The result reveals that for a long wiggler length, the bunching factor can appreciably change as the electron beam propagates through the wiggler. The effects of plasma frequency (or plasma density) and cyclotron frequency on the output power and saturation length have been studied. Simulation results indicate that with increasing the plasma frequency, the power increases and the saturation length decreases. In addition, when density of background plasma is higher than the electron beam density (i.e., for a dense plasma channel), the plasma effects are more pronounced and the FEL-power is significantly high. It is also found that with increasing the strength of the external magnetic field frequency, the power decreases and the saturation length increases, noticeably.
Diagnosing laser-preheated magnetized plasmas relevant to magnetized liner inertial fusion
NASA Astrophysics Data System (ADS)
Harvey-Thompson, A. J.; Sefkow, A. B.; Nagayama, T. N.; Wei, M. S.; Campbell, E. M.; Fiksel, G.; Chang, P.-Y.; Davies, J. R.; Barnak, D. H.; Glebov, V. Y.; Fitzsimmons, P.; Fooks, J.; Blue, B. E.
2015-12-01
We present a platform on the OMEGA EP Laser Facility that creates and diagnoses the conditions present during the preheat stage of the MAGnetized Liner Inertial Fusion (MagLIF) concept. Experiments were conducted using 9 kJ of 3ω (355 nm) light to heat an underdense deuterium gas (electron density: 2.5 ×1020 cm-3=0.025 of critical density) magnetized with a 10 T axial field. Results show that the deuterium plasma reached a peak electron temperature of 670 ± 140 eV, diagnosed using streaked spectroscopy of an argon dopant. The results demonstrate that plasmas relevant to the preheat stage of MagLIF can be produced at multiple laser facilities, thereby enabling more rapid progress in understanding magnetized preheat. Results are compared with magneto-radiation-hydrodynamics simulations, and plans for future experiments are described.
Diagnosing laser-preheated magnetized plasmas relevant to magnetized liner inertial fusion
Harvey-Thompson, Adam James; Sefkow, Adam B.; Nagayama, Taisuke N.; Wei, Mingsheng; Campbell, Edward Michael; Fiksel, Gennady; Chang, Po -Yu; Davies, Jonathan R.; Barnak, Daniel H.; Glebov, Vladimir Y.; Fitzsimmons, Paul; Fooks, Julie; Blue, Brent E.
2015-12-22
In this paper, we present a platform on the OMEGA EP Laser Facility that creates and diagnoses the conditions present during the preheat stage of the MAGnetized Liner Inertial Fusion (MagLIF) concept. Experiments were conducted using 9 kJ of 3ω (355 nm) light to heat an underdense deuterium gas (electron density: 2.5 × 10^{20} cm^{-3} = 0.025 of critical density) magnetized with a 10 T axial field. Results show that the deuterium plasma reached a peak electron temperature of 670 ± 140 eV, diagnosed using streaked spectroscopy of an argon dopant. The results demonstrate that plasmas relevant to the preheat stage of MagLIF can be produced at multiple laser facilities, thereby enabling more rapid progress in understanding magnetized preheat. Results are compared with magneto-radiation-hydrodynamics simulations, and plans for future experiments are described.
Diagnosing laser-preheated magnetized plasmas relevant to magnetized liner inertial fusion
Harvey-Thompson, Adam James; Sefkow, Adam B.; Nagayama, Taisuke N.; Wei, Mingsheng; Campbell, Edward Michael; Fiksel, Gennady; Chang, Po -Yu; Davies, Jonathan R.; Barnak, Daniel H.; Glebov, Vladimir Y.; et al
2015-12-22
In this paper, we present a platform on the OMEGA EP Laser Facility that creates and diagnoses the conditions present during the preheat stage of the MAGnetized Liner Inertial Fusion (MagLIF) concept. Experiments were conducted using 9 kJ of 3ω (355 nm) light to heat an underdense deuterium gas (electron density: 2.5 × 1020 cm-3 = 0.025 of critical density) magnetized with a 10 T axial field. Results show that the deuterium plasma reached a peak electron temperature of 670 ± 140 eV, diagnosed using streaked spectroscopy of an argon dopant. The results demonstrate that plasmas relevant to the preheatmore » stage of MagLIF can be produced at multiple laser facilities, thereby enabling more rapid progress in understanding magnetized preheat. Results are compared with magneto-radiation-hydrodynamics simulations, and plans for future experiments are described.« less
Scaling of the beam plasma discharge for low magnetic fields
NASA Technical Reports Server (NTRS)
Papadopoulos, K.
1986-01-01
A theoretical analysis of the scaling law and the value of the threshold current for beam plasma discharge (BPD) is presented, based on the requirement for an absolute instability near the plasma frequency. It is shown that both the scaling law as well as the numerical values of Ic are consistent with the experimental data, in the low pressure regimes and for weak magnetic field experiments if the dominant particle loss mechanism is due to Bohm diffusion. The implications of the findings to electron injection in space are discussed.
Waves and instabilities in a magnetized plasma
NASA Technical Reports Server (NTRS)
Dawson, J. M.
1982-01-01
Work on computer simulation of waves and instabilities in magnetized plasmas is reviewed. Included are verification of linear theory. Particular emphasis is given to investigation of nonlinear processes involved in the saturation of instabilities and of wave damping; these include a nonlinear cyclotron resonance and particle trapping in intense waves.
A generalized plasma dispersion function for electron damping in tokamak plasmas
NASA Astrophysics Data System (ADS)
Berry, L. A.; Jaeger, E. F.; Phillips, C. K.; Lau, C. H.; Bertelli, N.; Green, D. L.
2016-10-01
Radio frequency wave propagation in finite temperature, magnetized plasmas exhibits a wide range of physics phenomena. The plasma response is nonlocal in space and time, and numerous modes are possible with the potential for mode conversions and transformations. In addition, diffraction effects are important due to finite wavelength and finite-size wave launchers. Multidimensional simulations are required to describe these phenomena, but even with this complexity, the fundamental plasma response is assumed to be the uniform plasma response with the assumption that the local plasma current for a Fourier mode can be described by the "Stix" conductivity. However, for plasmas with non-uniform magnetic fields, the wave vector itself is nonlocal. When resolved into components perpendicular (k⊥) and parallel (k||) to the magnetic field, locality of the parallel component can easily be violated when the wavelength is large. The impact of this inconsistency is that estimates of the wave damping can be incorrect (typically low) due to unresolved resonances. For the case of ion cyclotron damping, this issue has already been addressed by including the effect of parallel magnetic field gradients. In this case, a modified plasma response (Z function) allows resonance broadening even when k|| = 0, and this improves the convergence and accuracy of wave simulations. In this paper, we extend this formalism to include electron damping and find improved convergence and accuracy for parameters where electron damping is dominant, such as high harmonic fast wave heating in the NSTX-U tokamak, and helicon wave launch for off-axis current drive in the DIII-D tokamak.
Kinetic modelling of runaway electron avalanches in tokamak plasmas
NASA Astrophysics Data System (ADS)
Nilsson, E.; Decker, J.; Peysson, Y.; Granetz, R. S.; Saint-Laurent, F.; Vlainic, M.
2015-09-01
Runaway electrons can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force owing to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate runaway electrons mainly through knock-on collisions (Hender et al 2007 Nucl. Fusion 47 S128-202), where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of runaway electrons. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. For this purpose, a bounce-averaged knock-on source term is derived. The generation of runaway electrons from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3D linearized bounce-averaged relativistic electron Fokker-Planck equation (Decker and Peysson 2004 DKE: a fast numerical solver for the 3D drift kinetic equation Report EUR-CEA-FC-1736, Euratom-CEA), through the calculation of the response of the electron distribution function to a constant parallel electric field. The model, which has been successfully benchmarked against the standard Dreicer runaway theory now describes the runaway generation by knock-on collisions as proposed by Rosenbluth (Rosenbluth and Putvinski 1997 Nucl. Fusion 37 1355-62). This paper shows that the avalanche effect can be important even in non-disruptive scenarios. Runaway formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons can not contribute to the runaway electron population. Finally, the
Laboratory study of avalanches in a magnetized plasma
NASA Astrophysics Data System (ADS)
van Compernolle, Bart
2015-11-01
Results of a basic heat transport experiment [] involving an off-axis heat source are presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A ring-shaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a preexisting, large and cold plasma. The injected electrons are thermalized by Coulomb collisions within a short distance and provide an off-axis heat source that results in a long, hollow, cylindrical region of elevated electron temperature embedded in a colder plasma, and far from the machine walls. It is demonstrated that this heating configuration provides an ideal environment to study avalanche phenomena under controlled conditions. The avalanches are identified as sudden rearrangements of the pressure profile following the growth of fluctuations from ambient noise. The intermittent collapses of the plasma pressure profile are associated with unstable drift-Alfvén waves and exhibit both radial and azimuthal dynamics. After each collapse the plasma enters a quiescent phase in which the pressure profile slowly recovers and steepens until a threshold is exceeded, and the process repeats. The use of reference probes as time markers allows for the visualization of the 2D spatio-temporal evolution of the avalanche events. Avalanches are only observed for a limited combination of heating powers and magnetic fields. At higher heating powers the system transitions from the avalanche regime into a regime dominated by sustained drift-Alfvén wave activity. The pressure profile then transitions to a near steady-state in which anomalous transport balances the external pressure source. Performed at the Basic Plasma Science Facility at UCLA, supported jointly by DOE and NSF.
Behavior of moving plasma in solenoidal magnetic field in a laser ion source.
Ikeda, S; Takahashi, K; Okamura, M; Horioka, K
2016-02-01
In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons. PMID:26931973
Behavior of moving plasma in solenoidal magnetic field in a laser ion source.
Ikeda, S; Takahashi, K; Okamura, M; Horioka, K
2016-02-01
In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons.
Magnetic filter apparatus and method for generating cold plasma in semicoductor processing
Vella, Michael C.
1996-01-01
Disclosed herein is a system and method for providing a plasma flood having a low electron temperature to a semiconductor target region during an ion implantation process. The plasma generator providing the plasma is coupled to a magnetic filter which allows ions and low energy electrons to pass therethrough while retaining captive the primary or high energy electrons. The ions and low energy electrons form a "cold plasma" which is diffused in the region of the process surface while the ion implantation process takes place.
Magnetic filter apparatus and method for generating cold plasma in semiconductor processing
Vella, M.C.
1996-08-13
Disclosed herein is a system and method for providing a plasma flood having a low electron temperature to a semiconductor target region during an ion implantation process. The plasma generator providing the plasma is coupled to a magnetic filter which allows ions and low energy electrons to pass therethrough while retaining captive the primary or high energy electrons. The ions and low energy electrons form a ``cold plasma`` which is diffused in the region of the process surface while the ion implantation process takes place. 15 figs.
Relativistic laser pulse compression in magnetized plasmas
Liang, Yun; Sang, Hai-Bo Wan, Feng; Lv, Chong; Xie, Bai-Song
2015-07-15
The self-compression of a weak relativistic Gaussian laser pulse propagating in a magnetized plasma is investigated. The nonlinear Schrödinger equation, which describes the laser pulse amplitude evolution, is deduced and solved numerically. The pulse compression is observed in the cases of both left- and right-hand circular polarized lasers. It is found that the compressed velocity is increased for the left-hand circular polarized laser fields, while decreased for the right-hand ones, which is reinforced as the enhancement of the external magnetic field. We find a 100 fs left-hand circular polarized laser pulse is compressed in a magnetized (1757 T) plasma medium by more than ten times. The results in this paper indicate the possibility of generating particularly intense and short pulses.
Multi-ion Double Layers in a Magnetized Plasma
NASA Astrophysics Data System (ADS)
Shahmansouri, M.; Alinejad, H.; Tribeche, M.
2015-11-01
A theoretical investigation is carried out to study the existence, formation and basic properties of ion acoustic (IA) double layers (DLs) in a magnetized bi-ion plasma consisting of warm/cold ions and Boltzmann distributed electrons. Based on the reductive perturbation technique, an extended Korteweg de-Vries (KdV) equation is derived. The propagation of two possible modes (fast and slow), and their evolution are investigated. The effects of obliqueness, magnitude of the magnetic field, ion concentration, polarity of ions, and ion temperature on the IA DL profile are analyzed, and then the ranges of parameters for which the IA DLs exist are investigated in details.
Kim, Kihong; Lee, Dong-Hun
2006-04-15
A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized, and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances, and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obtained. The dependencies of mode conversion phenomena on the magnitude of the external magnetic field, the incident angle, and the wave frequency are explored in detail.
Radiative decay of keV-mass sterile neutrinos in a strongly magnetized plasma
NASA Astrophysics Data System (ADS)
Dobrynina, Alexandra A.; Mikheev, Nicolay V.; Raffelt, Georg G.
2014-12-01
The radiative decay of sterile neutrinos with typical masses of 10 keV is investigated in the presence of a strong magnetic field and degenerate plasma. A full account is taken of the strongly modified photon dispersion relation relative to vacuum. The limiting cases of relativistic and nonrelativistic plasma are analyzed. The decay rate in a strongly magnetized plasma as a function of the electron number density is compared with the unmagnetized case. We find that a strong magnetic field suppresses the catalyzing influence of the plasma on the decay rate.
Gyrokinetic stability theory of electron-positron plasmas
NASA Astrophysics Data System (ADS)
Helander, P.; Connor, J. W.
2016-06-01
> The linear gyrokinetic stability properties of magnetically confined electron-positron plasmas are investigated in the parameter regime most likely to be relevant for the first laboratory experiments involving such plasmas, where the density is small enough that collisions can be ignored and the Debye length substantially exceeds the gyroradius. Although the plasma beta is very small, electromagnetic effects are retained, but magnetic compressibility can be neglected. The work of a previous publication (Helander, Phys. Rev. Lett., vol. 113, 2014a, 135003) is thus extended to include electromagnetic instabilities, which are of importance in closed-field-line configurations, where such instabilities can occur at arbitrarily low pressure. It is found that gyrokinetic instabilities are completely absent if the magnetic field is homogeneous: any instability must involve magnetic curvature or shear. Furthermore, in dipole magnetic fields, the stability threshold for interchange modes with wavelengths exceeding the Debye radius coincides with that in ideal magnetohydrodynamics. Above this threshold, the quasilinear particle flux is directed inward if the temperature gradient is sufficiently large, leading to spontaneous peaking of the density profile.
Waves and negative refraction in magnetized plasma with ferrite grains
Mesfin, Belayneh; Mal'nev, V. N.; Martysh, E. V.; Rapoport, Yu. G.
2010-11-15
The propagation of high frequency electromagnetic waves in the low temperature magnetized plasma with ferrite grains (MPFG) is considered. The dispersion properties of MPFG are simultaneously characterized by the permittivity and permeability tensors. The dispersion of the permeability is caused by the high frequency magnetization of the grain subsystem and is important in the vicinity of the frequency of ferromagnetic resonance, which coincides with the electron cyclotron frequency {omega}{sub c}. The MPFG becomes transparent for the waves that cannot propagate in conventional electron-ion magnetized plasma. It is shown that the refractive index of the extraordinary wave propagating along and transversal to the external magnetic field with frequencies close to {omega}{sub c} can be negative as well as positive. For the typical parameters of MPFG, the group velocity of this wave is much smaller than the speed of light. The refractive index of MPFG matched with the free space is obtained for waves propagating at an arbitrary angle with respect to the applied constant magnetic field. The results obtained clearly shows that the dispersion properties of MPFG have all the known properties of left-handed media in the vicinity of {omega}{sub c}.
Runaway electron generation in a cooling plasma
Smith, H.; Helander, P.; Eriksson, L.-G.; Fueloep, T.
2005-12-15
The usual calculation of Dreicer [Phys. Rev. 115, 238 (1959); 117, 329 (1960)] generation of runaway electrons assumes that the plasma is in a steady state. In a tokamak disruption this is not necessarily true since the plasma cools down quickly and the collision time for electrons at the runaway threshold energy can be comparable to the cooling time. The electron distribution function then acquires a high-energy tail which can easily be converted to a burst of runaways by the rising electric field. This process is investigated and simple criteria for its importance are derived. If no rapid losses of fast electrons occur, this can be a more important source of runaway electrons than ordinary Dreicer generation in tokamak disruptions.
Magnetized Plasma Compression for Fusion Energy
NASA Astrophysics Data System (ADS)
Degnan, James; Grabowski, Christopher; Domonkos, Matthew; Amdahl, David
2013-10-01
Magnetized Plasma Compression (MPC) uses magnetic inhibition of thermal conduction and enhancement of charge particle product capture to greatly reduce the temporal and spatial compression required relative to un-magnetized inertial fusion (IFE)--to microseconds, centimeters vs nanoseconds, sub-millimeter. MPC greatly reduces the required confinement time relative to MFE--to microseconds vs minutes. Proof of principle can be demonstrated or refuted using high current pulsed power driven compression of magnetized plasmas using magnetic pressure driven implosions of metal shells, known as imploding liners. This can be done at a cost of a few tens of millions of dollars. If demonstrated, it becomes worthwhile to develop repetitive implosion drivers. One approach is to use arrays of heavy ion beams for energy production, though with much less temporal and spatial compression than that envisioned for un-magnetized IFE, with larger compression targets, and with much less ambitious compression ratios. A less expensive, repetitive pulsed power driver, if feasible, would require engineering development for transient, rapidly replaceable transmission lines such as envisioned by Sandia National Laboratories. Supported by DOE-OFES.
Long-Range Collisions in Magnetized Plasmas
NASA Astrophysics Data System (ADS)
Dubin, D.
2015-12-01
Astrophysical (and earthbound) plasmas in strong magnetic fields exhibit collisional effects that are not described by classical collision theory nor by the standard collision operators, such as the Landau or Balescu-Lenard operators. These theories implicitly neglect "long-range" collisions, i.e. collisions with impact parameters large compared to the cyclotron radius. This presentation will review several important physical effects such collisions have on various phenomena, including cross-magnetic field diffusion, heat conduction, and collisional slowing parallel to the magnetic field. Long-range collisions are analyzed as guiding-centers moving in one-dimension along the magnetic field, with parallel energy and momentum transferred to particles on separate field lines through the screened Coulomb interaction. This causes cross-field heat transport that is independent of magnetic field strength B (as opposed to the classical 1/B2 scaling), and enhances the rate of collisional slowing parallel to B. The Coulomb interaction between guiding centers on different field lines also produces random ExB drifts that enhance cross-magnetic field diffusion compared to the classical theory. The theory of long-range guiding center collisions must also include the novel effect of "collisional caging": plasma noise causes two colliding guiding centers to diffuse in relative parallel velocity, reversing their motion along B and colliding several times before becoming uncorrelated. This further enhances cross-field diffusion from long-range collisions by a factor of three, and enhances parallel slowing by a factor of approximately 1.5.
High-Energy Electron Confinement in a Magnetic Cusp Configuration
NASA Astrophysics Data System (ADS)
Park, Jaeyoung; Krall, Nicholas A.; Sieck, Paul E.; Offermann, Dustin T.; Skillicorn, Michael; Sanchez, Andrew; Davis, Kevin; Alderson, Eric; Lapenta, Giovanni
2015-04-01
We report experimental results validating the concept that plasma confinement is enhanced in a magnetic cusp configuration when β (plasma pressure/magnetic field pressure) is of order unity. This enhancement is required for a fusion power reactor based on cusp confinement to be feasible. The magnetic cusp configuration possesses a critical advantage: the plasma is stable to large scale perturbations. However, early work indicated that plasma loss rates in a reactor based on a cusp configuration were too large for net power production. Grad and others theorized that at high β a sharp boundary would form between the plasma and the magnetic field, leading to substantially smaller loss rates. While not able to confirm the details of Grad's work, the current experiment does validate, for the first time, the conjecture that confinement is substantially improved at high β . This represents critical progress toward an understanding of the plasma dynamics in a high-β cusp system. We hope that these results will stimulate a renewed interest in the cusp configuration as a fusion confinement candidate. In addition, the enhanced high-energy electron confinement resolves a key impediment to progress of the Polywell fusion concept, which combines a high-β cusp configuration with electrostatic fusion for a compact, power-producing nuclear fusion reactor.
Electron transport in one-dimensional plasmas
Wienke, B.R.
1983-11-01
A one-dimensional, multigroup, discrete ordinates technique for computing electron energy deposition in plasmas is detailed. The Fokker-Planck collision operator is employed in the continuous approximation and electric fields (considered external) are included in the equation. Bremsstrahlung processes are not treated. Comparisons with analytic and Monte Carlo results are given. Fits to deposition profiles and energy scaling are proposed and discussed for monoenergetic and Maxwellian sources in the range, 0 to 150 keV, with and without uniform fields. The techniques employed to track electrons are generally useful in situations where the background plasma temperature is an order of magnitude smaller than the electron energy and collective plasma effects are negligible. We have used the approach successfully in laser pellet implosion applications.
Relativistic thermal electron scale instabilities in sheared flow plasma
NASA Astrophysics Data System (ADS)
Miller, Evan D.; Rogers, Barrett N.
2016-04-01
> The linear dispersion relation obeyed by finite-temperature, non-magnetized, relativistic two-fluid plasmas is presented, in the special case of a discontinuous bulk velocity profile and parallel wave vectors. It is found that such flows become universally unstable at the collisionless electron skin-depth scale. Further analyses are performed in the limits of either free-streaming ions or ultra-hot plasmas. In these limits, the system is highly unstable in the parameter regimes associated with either the electron scale Kelvin-Helmholtz instability (ESKHI) or the relativistic electron scale sheared flow instability (RESI) recently highlighted by Gruzinov. Coupling between these modes provides further instability throughout the remaining parameter space, provided both shear flow and temperature are finite. An explicit parameter space bound on the highly unstable region is found.
Spatially resolved study of primary electron transport in magnetic cusps
Hubble, Aimee A.; Foster, John E.
2012-01-15
Spatially resolved primary electron current density profiles were measured using a planar Langmuir probe in the region above a magnetic cusp in a small ion thruster discharge chamber. The probe current maps obtained were used to study the electron collection mechanics in the cusp region in the limit of zero gas flow and no plasma production, and they allowed for the visualization of primary electron transport through the cusp. Attenuation coefficients and loss widths were calculated as a function of probe distance above the anode at various operating conditions. Finally, the collection mechanics between two magnetic cusps were studied and compared. It was found that primary electron collection was dominated by the upstream magnet ring.
Model of magnetic reconnection in space and astrophysical plasmas
NASA Astrophysics Data System (ADS)
Boozer, Allen H.
2013-03-01
Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.
Model of magnetic reconnection in space and astrophysical plasmas
Boozer, Allen H.
2013-03-15
Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.
Magnetic field generation during intense laser channelling in underdense plasma
NASA Astrophysics Data System (ADS)
Smyth, A. G.; Sarri, G.; Vranic, M.; Amano, Y.; Doria, D.; Guillaume, E.; Habara, H.; Heathcote, R.; Hicks, G.; Najmudin, Z.; Nakamura, H.; Norreys, P. A.; Kar, S.; Silva, L. O.; Tanaka, K. A.; Vieira, J.; Borghesi, M.
2016-06-01
Channel formation during the propagation of a high-energy (120 J) and long duration (30 ps) laser pulse through an underdense deuterium plasma has been spatially and temporally resolved via means of a proton imaging technique, with intrinsic resolutions of a few μm and a few ps, respectively. Conclusive proof is provided that strong azimuthally symmetric magnetic fields with a strength of around 0.5 MG are created inside the channel, consistent with the generation of a collimated beam of relativistic electrons. The inferred electron beam characteristics may have implications for the cone-free fast-ignition scheme of inertial confinement fusion.
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2015-04-01
The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter ( ωeτe≫1 ), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ωeτe as does the Bohm diffusion coefficient c T /(16 e B ) , which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
Velikovich, A. L.; Giuliani, J. L.; Zalesak, S. T.
2015-04-15
The magnetized liner inertial fusion (MagLIF) approach to inertial confinement fusion [Slutz et al., Phys. Plasmas 17, 056303 (2010); Cuneo et al., IEEE Trans. Plasma Sci. 40, 3222 (2012)] involves subsonic/isobaric compression and heating of a deuterium-tritium plasma with frozen-in magnetic flux by a heavy cylindrical liner. The losses of heat and magnetic flux from the plasma to the liner are thereby determined by plasma advection and gradient-driven transport processes, such as thermal conductivity, magnetic field diffusion, and thermomagnetic effects. Theoretical analysis based on obtaining exact self-similar solutions of the classical collisional Braginskii's plasma transport equations in one dimension demonstrates that the heat loss from the hot compressed magnetized plasma to the cold liner is dominated by transverse heat conduction and advection, and the corresponding loss of magnetic flux is dominated by advection and the Nernst effect. For a large electron Hall parameter (ω{sub e}τ{sub e}≫1), the effective diffusion coefficients determining the losses of heat and magnetic flux to the liner wall are both shown to decrease with ω{sub e}τ{sub e} as does the Bohm diffusion coefficient cT/(16eB), which is commonly associated with low collisionality and two-dimensional transport. We demonstrate how this family of exact solutions can be used for verification of codes that model the MagLIF plasma dynamics.
Equatorial plasma bubbles with enhanced ion and electron temperatures
NASA Astrophysics Data System (ADS)
Park, Jaeheung; Min, Kyoung Wook; Kim, Vitaly P.; Kil, Hyosub; Su, Shin-Yi; Chao, Chi Kuang; Lee, Jae-Jin
2008-09-01
While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period between 2000 and 2001. The oxygen ion fraction inside the BETs, which was no lower than that of the ambient ionosphere, was similar to the case of ordinary low-temperature EPBs. These observations indicate that the BETs and low-temperature EPBs detected on the topside were produced by the upward drift of low-density plasma from lower altitudes. The feature that distinguishes BETs from normal EPBs is the occurrence of an unusually fast poleward field-aligned plasma flow relative to the ambient plasma. The BETs occurred preferentially around geomagnetic latitudes of 10° in the summer hemisphere, where the ambient ion and electron temperatures are lower than those in the conjugate winter hemisphere. The occurrence of BETs did not show any notable dependence on geomagnetic activities. The characteristics of the BETs suggest that the BETs were produced by adiabatic plasma heating associated with a fast poleward oxygen ion transport along magnetic flux tubes.
Corrosion behavior of magnetic ferrite coating prepared by plasma spraying
Liu, Yi; Wei, Shicheng Tong, Hui; Tian, Haoliang; Liu, Ming; Xu, Binshi
2014-12-15
Graphical abstract: The saturation magnetization (M{sub s}) of the ferrite coating is 34.417 emu/g while the M{sub s} value of the ferrite powder is 71.916 emu/g. It can be seen that plasma spray process causes deterioration of the room temperature soft magnetic properties. - Highlights: • Spinel ferrite coatings have been prepared by plasma spraying. • The coating consists of nanocrystalline grains. • The saturation magnetization of the ferrite coating is 34.417 emu/g. • Corrosion behavior of the ferrite coating was examined in NaCl solution. - Abstract: In this study, spray dried spinel ferrite powders were deposited on the surface of mild steel substrate through plasma spraying. The structure and morphological studies on the ferrite coatings were carried out using X-ray diffraction, scanning electron microscope and Raman spectroscopy. It was showed that spray dried process was an effective method to prepare thermal spraying powders. The coating showed spinel structure with a second phase of LaFeO{sub 3}. The magnetic property of the ferrite samples were measured by vibrating sample magnetometer. The saturation magnetization (M{sub s}) of the ferrite coating was 34.417 emu/g. The corrosion behavior of coating samples was examined by electrochemical impedance spectroscopy. EIS diagrams showed three corrosion processes as the coating immersed in 3.5 wt.% NaCl solution. The results suggested that plasma spraying was a promising technology for the production of magnetic ferrite coatings.
Laboratory study of avalanches in magnetized plasmas.
Van Compernolle, B; Morales, G J; Maggs, J E; Sydora, R D
2015-03-01
It is demonstrated that a novel heating configuration applied to a large and cold magnetized plasma allows the study of avalanche phenomena under controlled conditions. Intermittent collapses of the plasma pressure profile, associated with unstable drift-Alfvén waves, exhibit a two-slope power-law spectrum with exponents near -1 at lower frequencies and in the range of -2 to -4 at higher frequencies. A detailed mapping of the spatiotemporal evolution of a single avalanche event is presented. PMID:25871044
Large-Area Permanent-Magnet ECR Plasma Source
NASA Technical Reports Server (NTRS)
Foster, John E.
2007-01-01
A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired
Drift-tearing magnetic islands in tokamak plasmas
Fitzpatrick, R.; Waelbroeck, F. L.
2008-01-15
A systematic fluid theory of nonlinear magnetic island dynamics in conventional low-{beta}, large aspect-ratio, circular cross-section tokamak plasmas is developed using an extended magnetohydrodynamics model that incorporates diamagnetic flows, ion gyroviscosity, fast parallel electron heat transport, the ion sound wave, the drift wave, and average magnetic field-line curvature. The model excludes the compressible Alfven wave, geodesic field-line curvature, neoclassical effects, and ion Landau damping. A collisional closure is used for plasma dynamics parallel to the magnetic field. Two distinct branches of island solutions are found, namely the 'sonic' and 'hypersonic' branches. Both branches are investigated analytically, using suitable ordering schemes, and in each case the problem is reduced to a relatively simple set of nonlinear differential equations that can be solved numerically via iteration. The solution determines the island phase velocity, relative to the plasma, and the effect of local currents on the island stability. Sonic islands are relatively wide, flatten both the temperature and density profiles, and tend to propagate close to the local ion fluid velocity. Hypersonic islands, on the other hand, are relatively narrow, only flatten the temperature profile, radiate drift-acoustic waves, and tend to propagate close to the local electron fluid velocity. The hypersonic solution branch ceases to exist above a critical island width. Under normal circumstances, both types of island are stabilized by local ion polarization currents.
Numerical simulation of cathode plasma dynamics in magnetically insulated vacuum transmission lines
Thoma, C.; Genoni, T. C.; Welch, D. R.; Rose, D. V.; Clark, R. E.; Miller, C. L.; Stygar, W. A.; Kiefer, M. L.
2015-03-15
A novel algorithm for the simulation of cathode plasmas in particle-in-cell codes is described and applied to investigate cathode plasma evolution in magnetically insulated transmission lines (MITLs). The MITL electron sheath is modeled by a fully kinetic electron species. Electron and ion macroparticles, both modeled as fluid species, form a dense plasma which is initially localized at the cathode surface. Energetic plasma electron particles can be converted to kinetic electrons to resupply the electron flux at the plasma edge (the “effective” cathode). Using this model, we compare results for the time evolution of the cathode plasma and MITL electron flow with a simplified (isothermal) diffusion model. Simulations in 1D show a slow diffusive expansion of the plasma from the cathode surface. But in multiple dimensions, the plasma can expand much more rapidly due to anomalous diffusion caused by an instability due to the strong coupling of a transverse magnetic mode in the electron sheath with the expanding resistive plasma layer.
Electron density measurements for plasma adaptive optics
NASA Astrophysics Data System (ADS)
Neiswander, Brian W.
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.
Kato, K.G.
1983-01-01
Prodigious quantities of microwave energy are observed uniformly across a very wide frequency band when a relativistic electron beam penetrates a plasma. Typically 20 MW total in the calibrated range is measured and estimate as high as 350 MW total in the full observational range for ..delta..f approx. = 100 GHz. An intense, annular, pulsed REB (1 approx. = 128 kA; r approx. = 3 cm; ..delta..r approx. = 1 cm; 50 ns FWHM; ..gamma.. approx. = 3) through an unmagnetized or weakly magnetized plasma column (n/sub plasma/ approx. = 10/sup 13/ cm/sup -3/). A 0.01 less than or equal to (n/sub beam)/(n/plasma) less than or equal to 2 is used, the higher values of this range being an unconsidered region for most previous theoretical and experimental efforts. For these high (n/sub b)/(n/sub p) values, the observed emission with >> Vertical Barsub p/ and weak harmonic structure is wholly unanticipated from Langmuir scattering or soliton collapse models. A model of Compton-like boosting by the beam electrons of ambient plasma waves, with the collateral emission of high frequency photons, qualitatively explains this observed spectra. Power emerges largely in an angle approx. =I/..gamma.., as required by Compton mechanisms. As n/sub b//n/sub p/ falls, Vertical Barsub p/ - 2Vertical Barsub p/ structure and harmonic power ratios consistent with soliton collapse theories are observed. With further reduction of (n/sub b/)/(n sub p/) only the Vertical Barsub p/ line persists. Thus a transition has been observed in spectral behavior from the weak to strong turbulence theories advocated for Type III solar burst radiation, and further into a regime characterized as super-strong REB-plasma interactions. The presence of radiation is observed for
Plasma Density and Magnetic Field Evolution in a 100-ns Plasma Opening Switch
NASA Astrophysics Data System (ADS)
Weingarten, A.; Maron, Y.; Krasik, Ya. E.; Weber, B. V.; Commisso, R. J.
1997-11-01
The electron density and magnetic field evolution in a 100-ns, 170-kA POS are investigated using emission spectroscopy. The plasma is doped by various elements using laser evaporation in order to obtain spatially resolved measurements. The prefilled plasma density, determined from Stark broadening and ionization times, is 1-2× 10^14 cm-3. The opening time was observed to depend on the prefilled plasma azimuthal uniformity. During the pulse, the plasma density drops substantially during 10-20 ns. The drop propagates mainly axially from the plasma generator side to the load side at a velocity of ≈ 2 × 10^8 cm/s. The drop is accompanied by penetration of the magnetic field, determined from the Zeeman effect. A mapping of the density and the magnetic field distributions in the r-z plane will be presented. Proton motion is probably important, but the axial velocities of heavy ions are low (≈ 10^6 cm/s << V_Alfven). These results will be compared with previous results obtained on Gamble I(B. V. Weber et. al.), Appl. Physc. Lett. 45, 1043, (1984).
Laser plasma in a magnetic field
Kondo,K.; Kanesue, T.; Tamura, J.; Dabrowski, R.; Okamura, M.
2009-09-20
Laser Ion Source (LIS) is a candidate among various heavy ion sources. A high density plasma produced by Nd:YAG laser with drift velocity realizes high current and high charge state ion beams. In order to obtain higher charged particle ions, we had test experiments of LIS with a magnetic field by which a connement effect can make higher charged beams. We measured total current by Faraday Cup (FC) and analyzed charge distribution by Electrostatic Ion Analyzer (EIA). It is shown that the ion beam charge state is higher by a permanent magnet.
Modeling Current Drive in Space Plasma with Rotating Magnetic Field (RMF)
NASA Astrophysics Data System (ADS)
Shao, X.; Papadopoulos, K.; Joyce, G.
2006-05-01
The interaction of rotating magnetic fields with plasmas is fundamental plasma physics problem with implications to fusion related Field-Reversed Configuration (FRC) configurations, space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of energetic population in the radiation belts and near zone processes in pulsar magnetospheres. Despite its importance the basic plasma physics understanding of the interaction of rotating magnetic fields with magneto-plasmas, the scaling laws that control it and the range of potential applications to space plasmas remains unexplored. In this study, we focus on studying current drive in Space Plasma with RMF rotation rates satisfying (electron gyro-frequency) > RMF rotation rate >> (ion gyro-frequency) so that ion dynamics can be neglected. The relevant physics in this regime can be described by the so-called EMHD equations. This description neglects displacement current and plasma oscillations by enforcing quasi-neutrality. An important ingredient of the description is the presence of the Hall current and retention of the electron inertia. A spherical-coordinate-based EMHD code is developed and applied to study current drive with rotating magnet in plasma with magnetic field strength B much larger than the ambient magnetic field Bo. The current will modify the B field dependence on the distance to B~1/r**n. This study will investigate the value of n and determine the resultant magnetic profile as a function of the rotating speed relatively to the particle gyro-frequencies and plasma parameters.
Cathode Plasma Formation in High Intensity Electron Beam Diodes
NASA Astrophysics Data System (ADS)
Johnston, Mark; Kiefer, Mark; Oliver, Bryan; Bennett, Nichelle; Droemer, Darryl; Bernshtam, V.; Doron, R.; Maron, Yitzhak
2013-10-01
This talk will detail the experimental results and conclusions obtained for cathode plasma formation on the Self-Magnetic Pinch (SMP) diode fielded on the RITS-6 accelerator (4-7.5 MeV) at Sandia National Laboratories. The SMP diode utilizes a hollowed metal cathode to produce high power (TW), focused electron beams (<3 mm diameter) which are used for flash x-ray radiography applications. Optical diagnostics include high speed (<10 ns) framing cameras, optical streak cameras, and spectroscopy. The cathode plasma in this high electric (MV/cm) and magnetic (>10 Tesla) field environment forms well-defined striations. These striations have been examined for a number of different cathode sizes, vacuum gap spacings, and diode voltages. Optical streak images have been taken to determine the time evolution of the plasma, and optical spectroscopy has been employed to determine its constituents as well as their densities and temperatures inferred from detailed time-dependent, collisional-radiative (CR) and radiation transport modelings. Comments will be made as to the overall effect of the cathode plasma in regards to the diode impedance and electron beam focusing. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Scaling of Magnetic Reconnection in Relativistic Collisionless Pair Plasmas
NASA Technical Reports Server (NTRS)
Liu, Yi-Hsin; Guo, Fan; Daughton, William; Li, Hui; Hesse, Michael
2015-01-01
Using fully kinetic simulations, we study the scaling of the inflow speed of collisionless magnetic reconnection in electron-positron plasmas from the non-relativistic to ultra-relativistic limit. In the anti-parallel configuration, the inflow speed increases with the upstream magnetization parameter sigma and approaches the speed of light when sigma is greater than O(100), leading to an enhanced reconnection rate. In all regimes, the divergence of the pressure tensor is the dominant term responsible for breaking the frozen-in condition at the x-line. The observed scaling agrees well with a simple model that accounts for the Lorentz contraction of the plasma passing through the diffusion region. The results demonstrate that the aspect ratio of the diffusion region, modified by the compression factor of proper density, remains approximately 0.1 in both the non-relativistic and relativistic limits.
Dressed ion-acoustic solitons in magnetized dusty plasmas
El-Labany, S. K.; El-Shamy, E. F.; El-Warraki, S. A.
2009-01-15
In the present research paper, the characteristics of ion acoustic solitary waves are investigated in hot magnetized dusty plasmas consisting of negatively charged dust grains, positively charged ion fluid, and isothermal electrons. Applying a reductive perturbation theory, a nonlinear Korteweg-de Vries (KdV) equation for the first-order perturbed potential and a linear inhomogeneous KdV-type equation for the second-order perturbed potentials are derived. Stationary solutions of these coupled equations are obtained using a renormalization method. The effects of the external oblique magnetic field, hot ion fluid, and higher-order nonlinearity on the nature of the ion acoustic solitary waves are discussed. The results complement and provide new insights into previously published results on this problem [R. S. Tiwari and M. K. Mishra, Phys. Plasmas 13, 062112 (2006)].
Magnetic-field-dependent plasma composition of a pulsed aluminum arc in an oxygen ambient
NASA Astrophysics Data System (ADS)
Schneider, Jochen M.; Anders, André; Yushkov, George Yu.
2001-01-01
A variety of plasma-based deposition techniques utilize magnetic fields to affect the degree of ionization as well as for focusing and guiding of plasma beams. Here we use time-of-flight charge-to-mass spectrometry to describe the effect of a magnetic field on the plasma composition of a pulsed Al plasma stream in an ambient containing intentionally introduced oxygen as well as for high vacuum conditions typical residual gas. The plasma composition evolution was found to be strongly dependent on the magnetic field strength and can be understood by invoking two electron impact ionization routes: ionization of the intentionally introduced gas as well as ionization of the residual gas. These results are characteristic of plasma-based techniques where magnetic fields are employed in a high-vacuum ambient. In effect, the impurity incorporation during reactive thin-film growth pertains to the present findings.
Yuan Chengxun; Zhou Zhongxiang; Sun Hongguo; Pu Shaozhi; Xiang Xiaoli
2010-11-15
The terahertz characteristics of a dense-magnetized-collisional-bounded plasma under normal incident are analyzed in this study, which is of practical significance in plasma diagnostics with electromagnetic waves. We theoretically calculate the reflection, absorption, and transmission coefficients for right- and left-handed polarized terahertz waves through a uniform, magnetized, and collisional plasma slab bounded by lossless transparent walls. The power absorption spectra in the frequency range of 0.1-2 THz are given with strong external magnetic fields and different plasma parameters such as plasma density and collisional frequency. Our numerical result is consistent with Jamison's experimental result. It is found that plasma absorption is mainly caused by the collisional absorption and electron cyclotron resonance. Furthermore, the absorption heavily depends on the polarization mode of the terahertz waves when the external magnetic field B is high enough that the election gyrofrequency is near the incident wave frequency. The relationships between the corresponding parameters of the problem are studied numerically.
NASA Astrophysics Data System (ADS)
Horton, W.; Ditmire, T.; Zakharov, Yu. P.
2010-06-01
Laboratory experiments using a plasma wind generated by laser-target interaction are proposed to investigate the creation of a shock in front of the magnetosphere and the dynamo mechanism for creating plasma currents and voltages. Preliminary experiments are shown where measurements of the electron density gradients surrounding the obstacles are recorded to infer the plasma winds. The proposed experiments are relevant to understanding the electron acceleration mechanisms taking place in shock-driven magnetic dipole confined plasmas surrounding compact magnetized stars and planets. Exploratory experiments have been published [P. Brady, T. Ditmire, W. Horton, et al., Phys. Plasmas 16, 043112 (2009)] with the one Joule Yoga laser and centimeter sized permanent magnets.
Finding Plasma Equilibria with Magnetic Islands
NASA Astrophysics Data System (ADS)
Miller, G.; Faber, V.; White, A. B., Jr.
1988-12-01
The traditional method of solving the helically symmetric plasma equilibrium equation, of the form L[ G] = F( G, r) where L is an elliptic linear operator, has been the simple iteration L[ Gn + 1 ]= F( Gn, r). A model of a Tokomak equilibrium is constructed and used to illustrate the divergence of the simple iteration for plasma equilibria with magnetic islands. Although the problem of equilibria with magnetic islands is two dimensional, for small islands the numerical stability of the simple iteration may be analyzed using a one-dimensional equation similar to the linearized equilibrium equation used to analyze physical (resistive) instability. This analysis is used to prove that any equilibria of the Tokamak type with small islands cannot be obtained by the simple iteration and to illustrate the superlinear convergence of Newton's method on these problems. The implementation of Newton's method is discussed and examples are given.
Non-Neutral Ion Plasma in a Toroidal Magnetic Field
NASA Astrophysics Data System (ADS)
Boyd, D. A.
1997-11-01
We propose to trap and study the equilibria of a non-neutral ion plasma in a toroidal magnetic field. Such equilibria have been described by O'Neil and Smith(T. M. O'Neil, R. A. Smith, Phys. Plasmas 1, 2430 (1994)). An electron plasma has been studied by Zaveri et al.(Puravi Zaveri, P. I. John, K. Avinash, and P. K. Kaw, Phys. Rev. Lett. 68, 3295 (1992)). Although single ions are not confined in such a trap, for plasmas there exists a large parameter space with radically different regimes for the trapped ions. This is a novel form of ion trap in which to study orbit dynamics, equilibria, and different thermodynamic states by cooling and manipulation of the ion distribution. Barium and Calcium ions produced by photo-ionization would be injected into the trap from a transient magnetic divertor with positively charged target plates. Ions permit a detailed study of their distribution function with non-perturbative techniques. Laser Induced Fluorescence and ion tagging techniques would be used to study the microscopic dynamics of the ions. Image charge probes would be used to study density fluctuations. In the longer term lasers would be used to cool the ions and the distribution altered by externally launched waves coupled to the plasma. A basic description and classification of the stable equilibria will be given as well as the parameters and design of a low cost, experimental trap.
Focusing intense electron beams using a positive space charge cloud plasma lens
NASA Astrophysics Data System (ADS)
Goncharov, A.; Dobrovolskiy, A.; Litovko, I.; Gushenets, V.; Oks, E.
2014-05-01
An original plasma-optical device for focusing and manipulating negatively charged particle beams by a dynamic cloud of non-magnetized free positive ions and magnetically isolated electrons produced by a toroidal plasma source such as an anode layer thruster has recently been proposed and explored. In such systems, the electrons are separated from the ions by the relatively strong magnetic field in the discharge channel. The accelerated ions are weakly affected by the magnetic field, owing to their mass. Here, we describe the current status of ongoing research and development of a wide-aperture electrostatic plasma lens with a positive space charge cloud for focusing and manipulating large-area, high-current electron beams. The new modified magnetic system was simulated, designed and tested for minimal aberrations. In this work, we present new simulation results of the further lens development.
Nishimura, Seiya
2014-12-15
Resonant magnetic perturbations (RMPs) produce magnetic islands in toroidal plasmas. Self-healing (annihilation) of RMP-induced magnetic islands has been observed in helical systems, where a possible mechanism of the self-healing is shielding of RMP penetration by plasma flows, which is well known in tokamaks. Thus, fundamental physics of RMP shielding is commonly investigated in both tokamaks and helical systems. In order to check this mechanism, detailed informations of magnetic island phases are necessary. In experiments, measurement of radial magnetic responses is relatively easy. In this study, based on a theoretical model of rotating magnetic islands, behavior of radial magnetic fields during the self-healing is investigated. It is confirmed that flips of radial magnetic fields are typically observed during the self-healing. Such behavior of radial magnetic responses is also observed in LHD experiments.
Toroidal dust motion in magnetized plasmas
Reichstein, Torben; Pilch, Iris; Piel, Alexander
2010-09-15
In a magnetized anodic plasma, dust particles can be confined in a torus-shaped cloud with a distinct dust-free region (void) in its center. The formation of these clouds and their dynamical behavior are experimentally studied with a new observation geometry. The particles rotate about the major axis of the torus. A refined model for the description of the particle dynamics is presented that accounts for inertia and many-body effects.
Landau Fluid Models for Magnetized Plasmas
Sulem, P. L.; Passot, T.; Marradi, L.
2008-10-15
A Landau fluid model for a magnetized plasma, that retains a linear description of low-frequency kinetic effects involving transverse scales significantly smaller than the ion Larmor radius, is discussed and validated in the context of nonlinear wave dynamics. Preliminary simulations of the turbulent regime are presented in one space dimension, as a first step towards more realistic three-dimensional computations, aimed to analyze the combined effect of dispersion and collisionless dissipation on the energy cascade.
Twisted electron-acoustic waves in plasmas
NASA Astrophysics Data System (ADS)
Aman-ur-Rehman, Ali, S.; Khan, S. A.; Shahzad, K.
2016-08-01
In the paraxial limit, a twisted electron-acoustic (EA) wave is studied in a collisionless unmagnetized plasma, whose constituents are the dynamical cold electrons and Boltzmannian hot electrons in the background of static positive ions. The analytical and numerical solutions of the plasma kinetic equation suggest that EA waves with finite amount of orbital angular momentum exhibit a twist in its behavior. The twisted wave particle resonance is also taken into consideration that has been appeared through the effective wave number qeff accounting for Laguerre-Gaussian mode profiles attributed to helical phase structures. Consequently, the dispersion relation and the damping rate of the EA waves are significantly modified with the twisted parameter η, and for η → ∞, the results coincide with the straight propagating plane EA waves. Numerically, new features of twisted EA waves are identified by considering various regimes of wavelength and the results might be useful for transport and trapping of plasma particles in a two-electron component plasma.
Low Energy Electrons in the Mars Plasma Environment
NASA Technical Reports Server (NTRS)
Link, Richard
2001-01-01
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.
Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl
2003-12-16
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Magnetic and electrostatic confinement of plasma with tuning of electrostatic field
Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang
2006-03-21
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Magnetic and electrostatic confinement of plasma with tuning of electrostatic field
Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang
2006-10-10
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Magnetic and electrostatic confinement of plasma with tuning of electrostatic field
Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang
2008-10-21
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang
2007-02-20
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma
Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang
2006-02-07
A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.
Non-linear plasma wake growth of electron holes
Hutchinson, I. H.; Haakonsen, C. B.; Zhou, C.
2015-03-15
An object's wake in a plasma with small Debye length that drifts across the magnetic field is subject to electrostatic electron instabilities. Such situations include, for example, the moon in the solar wind 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 size, beyond which their uncontrolled growth disrupts the ions. The hole growth calculations provide a quantitative prediction of hole profile and size evolution. Hole growth appears to explain the observations of recent particle-in-cell simulations.
Generalized Langmuir Waves in Magnetized Kinetic Plasmas
NASA Technical Reports Server (NTRS)
Willes, A. J.; Cairns, Iver H.
2000-01-01
The properties of unmagnetized Langmuir waves and cold plasma magnetoionic waves (x, o, z and whistler) are well known. However, the connections between these modes in a magnetized kinetic plasma have not been explored in detail. Here, wave properties are investigated by numerically solving the dispersion equation derived from the Vlasov equations both with and without a beam instability present. For omega(sub p)>Omega(sub e), it is shown that the generalized Langmuir mode at oblique propagation angles has magnetic z-mode characteristics at low wave numbers and thermal Langmuir mode characteristics at high wave numbers. For omega(sub p)
Plasma Braking Due to External Magnetic Perturbations
NASA Astrophysics Data System (ADS)
Frassinetti, L.; Olofsson, Kejo; Brunsell, P. R.; Khan, M. W. M.; Drake, J. R.
2010-11-01
The RFP EXTRAP T2R is equipped with a comprehensive active feedback system (128 active saddle coils in the full-coverage array) and active control of both resonant and non-resonant MHD modes has been demonstrated. The feedback algorithms, based on modern control methodology such as reference mode tracking (both amplitude and phase), are a useful tool to improve the ``state of the art'' of the MHD mode control. But this tool can be used also to improve the understanding and the characterization of other phenomena such as the ELM mitigation with a resonant magnetic perturbation or the plasma viscosity. The present work studies plasma and mode braking due to static RMPs. Results show that a static RMP produces a global braking of the flow profile. The study of the effect of RMPs characterized by different helicities will also give information on the plasma viscosity profile. Experimental results are finally compared to theoretical models.
Propagation of electron and positron beams in long, dense plasmas
NASA Astrophysics Data System (ADS)
Muggli, Patric; Blue, Brent; Clayton, Chris; Decker, Franz-Joseph; Hogan, Mark; Hunag, Chengkun; Joshi, Chan; Katsouleas, Tom; Lu, Wei; Mori, Warren; O'Connell, Caollionn; Siemann, Robert; Walz, Dieter; Zhou, Miaomiao
2008-04-01
Electron beams with density larger than the plasma density can propagate through plasmas without significant emittance growth. The electron beam expels the plasma electrons from the bunch volume and propagate in a pure, uniform ion column. In contrast, positron beams attract plasma electrons that flow through the positron bunch. As a result the plasma focusing force is nonlinear, a charge halo forms around the bunch, and the bunch emittance grows. After some distance into the plasma, the bunch emittance reaches an approximately constant value, and the beam and the plasma focusing force reach a steady state. Experimental results obtained with electron and positron bunches, as well as numerical simulation results will be presented.
Formation of high-{beta} plasma and stable confinement of toroidal electron plasma in Ring Trap 1
Saitoh, H.; Yoshida, Z.; Morikawa, J.; Furukawa, M.; Yano, Y.; Kawai, Y.; Kobayashi, M.; Vogel, G.; Mikami, H.
2011-05-15
Formation of high-{beta} 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 {beta} 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).].
Electron-temperature and energy-flow history in an imploding plasma.
Gregorian, L; Kroupp, E; Davara, G; Starobinets, A; Fisher, V I; Bernshtam, V A; Ralchenko, Yu V; Maron, Y; Fisher, A; Hoffmann, D H H
2005-05-01
The time-dependent radial distribution of the electron temperature in a 0.6 micros, 220-kA gas-puff z-pinch plasma is studied using spatially-resolved observations of line emission from singly to fivefold ionized oxygen ions during the plasma implosion, up to 50 ns before maximum compression. The temperature obtained, together with the previously determined radial distributions of the electron density, plasma radial velocity, and magnetic field, allows for studying the history of the magnetic-field energy coupling to the plasma by comparing the energy deposition and dissipation rates in the plasma. It is found that at this phase of the implosion, approximately 65% of the energy deposited in the plasma is imparted to the plasma radial flow, with the rest of the energy being converted into internal energy and radiation. PMID:16089655
Electron-temperature and energy-flow history in an imploding plasma.
Gregorian, L; Kroupp, E; Davara, G; Starobinets, A; Fisher, V I; Bernshtam, V A; Ralchenko, Yu V; Maron, Y; Fisher, A; Hoffmann, D H H
2005-05-01
The time-dependent radial distribution of the electron temperature in a 0.6 micros, 220-kA gas-puff z-pinch plasma is studied using spatially-resolved observations of line emission from singly to fivefold ionized oxygen ions during the plasma implosion, up to 50 ns before maximum compression. The temperature obtained, together with the previously determined radial distributions of the electron density, plasma radial velocity, and magnetic field, allows for studying the history of the magnetic-field energy coupling to the plasma by comparing the energy deposition and dissipation rates in the plasma. It is found that at this phase of the implosion, approximately 65% of the energy deposited in the plasma is imparted to the plasma radial flow, with the rest of the energy being converted into internal energy and radiation.
Electron dynamics in a plasma focus. [electron acceleration
NASA Technical Reports Server (NTRS)
Hohl, F.; Gary, S. P.; Winters, P. A.
1977-01-01
Results are presented of a numerical integration of the three-dimensional relativistic equations of motion of electrons subject to given electric and magnetic fields deduced from experiments. Fields due to two different models are investigated. For the first model, the fields are those due to a circular distribution of axial current filaments. As the current filaments collapse toward the axis, large azimuthal magnetic and axial electric fields are induced. These fields effectively heat the electrons to a temperature of approximately 8 keV and accelerate electrons within the radius of the filaments to high axial velocities. Similar results are obtained for the current-reduction phase of focus formation. For the second model, the fields are those due to a uniform current distribution. Both the current-reduction and the compression phases were studied. These is little heating or acceleration of electrons during the compression phase because the electrons are tied to the magnetic field. However, during the current-reduction phase, electrons near the axis are accelerated toward the center electrode and reach energies of 100 keV. A criterion is obtained which limits the runaway electron current to about 400 A.
Electron Temperature and Potential Measurements in a Helicon Plasma
NASA Astrophysics Data System (ADS)
Plank, J.; Hayes, T. R.; Gilmore, M.
2013-10-01
Measurements of plasma potential, floating potential, and electron temperature, Te, are notoriously difficult in RF-produced plasmas such as helicons. This work presents comparisons of potential and Te measurements made via swept and stepped compensated and uncompensated single and double Langmuir probes, emissive probes, and static triple probes. These measurements have been made in the HelCat (Helicon-Cathode) linear plasma device at the University of New Mexico using HelCat's helicon source. HelCat is a 4 m long, 0.5 m diameter device with magnetic field, B0 <2.2 kG, and typical densities n ~ 1018 - 1020 m-3. Comparisons between the measurements and expected theoretical differences will be presented. Supported by US National Science Foundation Award 1201995.
Tailoring of electron flow current in magnetically insulated transmission lines
NASA Astrophysics Data System (ADS)
Martin, J. P.; Savage, M. E.; Pointon, T. D.; Gilmore, M. A.
2009-03-01
It is desirable to optimize (minimizing both the inductance and electron flow) the magnetically insulated vacuum sections of low impedance pulsed-power drivers. The goal of low inductance is understandable from basic efficiency arguments. The goal of low electron flow results from two observations: (1) flowing electrons generally do not deliver energy to (or even reach) most loads, and thus constitute a loss mechanism; (2) energetic electrons deposited in a small area can cause anode damage and anode plasma formation. Low inductance and low electron flow are competing goals; an optimized system requires a balance of the two. While magnetically insulated systems are generally forgiving, there are times when optimization is crucial. For example, in large pulsed-power drivers used to energize high energy density physics loads, the electron flow as a fraction of total current is small, but that flow often reaches the anode in relatively small regions. If the anode temperature becomes high enough to desorb gas, the resulting plasma initiates a gap closure process that can impact system performance. Magnetic-pressure driven (z pinches and material equation of state) loads behave like a fixed inductor for much of the drive pulse. It is clear that neither fixed gap nor constant-impedance transmission lines are optimal for driving inductive loads. This work shows a technique for developing the optimal impedance profile for the magnetically insulated section of a high-current driver. Particle-in-cell calculations are used to validate the impedance profiles developed in a radial disk magnetically insulated transmission line geometry. The input parameters are the spacing and location of the minimum gap, the effective load inductance, and the desired electron flow profile. The radial electron flow profiles from these simulations are in good agreement with theoretical predictions when driven at relatively high voltage (i.e., V≥2MV).
New Electron Temperature Diagnostic for Low Temperature Plasmas
NASA Astrophysics Data System (ADS)
Boivin, Robert; Loch, Stuart
2004-11-01
A new line ratio diagnostic design to measure electron temperature in plasma is presented. Unlike previous diagnostics, this new technique features emission lines originating from levels with different principal quantum numbers. A significant advantage of this approach is that the line ratio varies considerably with temperature in the 1 to 20 eV range. Another advantage is that both transitions are optically thin even for plasma density up to 1 E 14 cm-3. The drawbacks are: a large difference in the line intensities and the significant difference in wavelength. The event of high sensitivity CCD camera combine with precise calibration can to a large extent minimize these latest two issues. The diagnostic is tested on the ASTRAL (Auburn Steady sTate Research fAciLity) helicon plasma source. ASTRAL is a 2.3 m long helicon source designed to investigate basic plasma and space plasma processes. The device produces plasmas with the following typical parameters ne = 1 E9 to 1 E13 cm-3, Te = 2 to 20 eV and Ti = 0.03 to 0.3 eV. A series of 8 large coils produce an axial magnetic field up to 1.2 kGauss. Operating pressure varies from 0.1 to 100 mTorr. A water cooled fractional helix antenna is used to introduce RF power up to 2 kwatt through a standard matching circuit. The line ratio temperatures are measured by means of a 0.33 m McPherson Criss-Cross Scanning monochromator instrumented with a SPH5 Apogee CCD camera. The line ratio temperatures are compared to electron temperatures measured by a rf compensated Langmuir Probe. To validate the diagnostic, a new collisional radiative model that makes use of the latest excitation cross-section values is presented. The model is also used to predict the potential range of this new diagnostic both in terms of electron temperature and plasma density.
Auroral electrostatic solitons and supersolitons in a magnetized nonthermal plasma
Rufai, O. R.
2015-05-15
Exploiting the spacecraft measurements in the auroral region, finite amplitude nonlinear low frequency electrostatic solitons and supersolitons in a magnetized plasma consisting of cold ions fluid, Boltzmann protons, and nonthermal hot electrons are studied by applying a pseudo-potential technique. The localized solution of the nonlinear structures is obtained through the charge neutrality condition. Further numerical investigation shows the existence of supersoliton solutions at supersonic Mach numbers regime. The amplitude of ion-acoustic structures decreased with an increase in nonthermal electrons and ion density ratio. For the plasma parameters relevant to the auroral zone of the Earth's magnetosphere, the electric field amplitude of supersolitons is found to be about 9 mV/m, which is in agreement with satellite observations.