Numerical simulation of current-free double layers created in a helicon plasma device

Journal Article · Sat Sep 15 04:00:00 EDT 2012 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4754598· OSTI ID:22086182

Rao, Sathyanarayan; Singh, Nagendra ^[1]

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1. Department of Electrical and Computer Engineering, University of Alabama, Huntsville, Alabama 35899 (United States)

Two-dimensional simulations reveal that when radially confined source plasma with magnetized electrons and unmagnetized ions expands into diverging magnetic field B, a current-free double layer (CFDL) embedded in a conical density structure forms, as experimentally measured in the Australian helicon plasma device (HPD). The magnetized electrons follow the diverging B while the unmagnetized ions tend to flow directly downstream of the source, resulting in a radial electric field (E{sub Up-Tack }) structure, which couples the ion and electron flows. Ions are transversely (radially) accelerated by E{sub Up-Tack} on the high potential side of the double layer in the CFDL. The accelerated ions are trapped near the conical surface, where E{sub Up-Tack} reverses direction. The potential structure of the CFDL is U-shaped and the plasma density is enhanced on the conical surface. The plasma density is severely depleted downstream of the parallel potential drop ({phi}{sub Double-Vertical-Line Double-Vertical-Line o}) in the CFDL; the density depletion and the potential drop are related by quasi-neutrality condition, including the divergence in the magnetic field and in the plasma flow in the conical structure. The potential and density structures, the CFDL spatial size, its electric field strengths and the electron and ion velocities and energy distributions in the CFDL are found to be in good agreements with those measured in the Australian experiment. The applicability of our results to measured axial potential profiles in magnetic nozzle experiments in HPDs is discussed.

• OSTI ID: 22086182
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 9 Vol. 19; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COMPUTERIZED SIMULATION
ELECTRIC FIELDS
ELECTRONS
ENERGY SPECTRA
HELICON WAVES
IONS
LAYERS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
PLASMA DENSITY
PLASMA GUNS
PLASMA SIMULATION
TWO-DIMENSIONAL CALCULATIONS