Current-free double layers: A review

Singh, Nagendra

doi:doi:10.1063/1.3664321

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The dynamics of ion with electrostatic waves in a sheared magnetic field

The interaction between an ion and multiple electrostatic waves propagating perpendicularly to an ambient magnetic field with shear is investigated. Based on the Lie transformation method, with the wave amplitude and the magnetic shear both as the perturbation parameters, the analytical formulas for the reduced Hamiltonian is derived and results are compared with numerical calculations of the complete equations of motion for the case of two on-resonance waves and the case of two off-resonance w...

A new mode and its interaction through ponderomotive force in electron-positron-ion plasmas

A new mode is found in e-p-i plasma in the presence of density and temperature difference of lighter particles. The electron beam induced Cherenkov instability condition for the excitation of positron sound wave is obtained for the system under consideration. Zakharov’s equation with sign modification due to negative Ponderomotive pressure is obtained. Nonlinear Schrödinger wave equation for the envelope type solitary waves is derived. Both stationary and nonstationary solutions are found and t...

During the last decade, there has been an upsurge in the research on current-free DLs (CFDLs). Research includes theory, laboratory measurements, and various applications of CFDLs ranging from plasma thrusters to acceleration of charged particles in space and astrophysical plasmas. The purpose of this review is to present a unified understanding of the basic plasma processes, which lead to the formation of CFDLs. The review starts with the discussion on early research on electric fields and double layers (DLs) and ion acceleration in planar plasma expansion. The review continues with the formation of DLs and rarefaction shocks (RFS) in expanding plasma with two electron populations with different temperatures. The basic theory mitigating the formation of a CFDL by two-electron temperature population is reviewed; we refer to such CFDLs as double layers structures formation by two-temperature electron populations (TET-CFDLs). Application of TET-CFDLS to ion acceleration in laboratory and space plasmas was discussed including the formation of stationary steady-state DLs. A quite different type of CFDLs forms in a helicon plasma device (HPD), in which plasma abruptly expands from a narrow plasma source tube into a wide diffusion tube with abruptly diverging magnetic fields. The formation mechanism of the CFDL in HPD, referred here as current free double layer structure in helicon plasma device (HPD-CFDL), and its applications are reviewed. The formation of a TET-CFDL is due to the self-consistent separation of the two electron populations parallel to the ambient magnetic field. In contrast, a HPD-CFDL forms due to self-consistent separation of electrons and ion perpendicular to the abruptly diverging magnetic field in conjunction with the conducting wall of the expansion chamber in the HPD. One-dimensional theoretical models of CFDLs based on steady-state solution of Vlasov-Poisson system of equations are briefly discussed. Applications of CFDLs ranging from helicon double-layer thrusters (HDLTs) to the accelerations of ions in space and astrophysical plasmas are summarized.

Article Outline

INTRODUCTION
PLASMA EXPANSION, ELECTRIC FIELDS, AND DLS
CURRENT-FREE DLS IN PLASMA EXPANSION WITH TWO TEMPERATURE ELECTRON POPULATIONS
1. Theory of TET-CFDL formation
2. Current-free DLs in terrestrial polar wind expansion
3. CFDLs at the bottom of the auroral density cavity in the upward current region
4. Small-scale time-dependent Vlasov simulations of RFS-CFDL formation
5. Mesoscale flux tube PIC simulation of RFS-CFDL
6. Laboratory experiments on TET-CFDLs
  1. TET-CFDL experiments at the University of Wisconsin (UW)
  2. UCLA experiments
EXPERIMENTS IN HELICON PLASMA DEVICES
1. Two-dimensional HPD-CFDLS
2. Pitch angles of ions accelerated by HPD-CFDLs
3. Currents and HPD-CFDLs
4. Instabilities in HPD-CFDL experiments
THEORETICAL DEVELOPMENTS ON CFDLS
APPLICATION OF CFDLS
1. Plasma thrusters
2. Acceleration of ions by CFDLs
3. Auroral acceleration process
CONCLUSION AND DISCUSSIONS

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KEYWORDS and PACS

Keywords

astrophysical plasma, plasma devices, plasma sheaths, plasma shock waves, plasma sources, plasma temperature, plasma transport processes, Poisson equation, Vlasov equation

PACS

52.40.Kh

Plasma sheaths
52.25.Fi

Transport properties
52.35.Tc

Shock waves and discontinuities
52.72.+v

Laboratory studies of space- and astrophysical-plasma processes
52.50.Dg

Plasma sources

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3664321

PUBLICATION DATA

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1070-664X (print)

1089-7674 (online)

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American Institute of Physics

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