Is the classical two-term approximation of electron kinetic theory satisfactory for swarms and plasmas?

White, R.D., Robson, R.E., Schmidt, B., and Morrison, Michael A. (2003) Is the classical two-term approximation of electron kinetic theory satisfactory for swarms and plasmas? Journal of Physics D: applied physics, 36 (24). pp. 3125-3131.

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Abstract

The 'two-term' approximation (representation of the electron distribution by the first two terms of an expansion in spherical harmonics in velocity space) continues to occupy a central role in the low-temperature plasma physics literature, in spite of the mass of evidence illustrating its inadequacy in the swarm (free diffusion) limit for many molecular gases. Part of the problem lies in the failure of many authors to specify quantitatively what they mean when they say that the two-term approximation is 'acceptable'. Thus for example, an error of 10% in transport coefficients may well be acceptable in many plasma applications, but for analysis of highly accurate swarm experiments to compare with ab initio and beam-derived cross-sections, 0.1% or less is required, making 'multi-term' analysis mandatory. While reconciliation of the swarm and plasma literature along the lines of two different accuracy regimes may thus be possible, we dispute claims that the two-term approximation is generally satisfactory for inversion of swarm experiment data to obtain electron impact cross-sections. The unsatisfactory nature of other assumptions implicit in much of the modern plasma kinetic theory literature is also discussed.

Item ID: 879
Item Type: Article (Research - C1)
ISSN: 1361-6463
Keywords: plasma discharges, swarms, electron, two-term approximation
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© Institute of Physics and IOP Publishing Limited 2003.

Date Deposited: 25 Oct 2006
FoR Codes: 02 PHYSICAL SCIENCES > 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics > 020201 Atomic and Molecular Physics @ 51%
02 PHYSICAL SCIENCES > 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics > 020204 Plasma Physics; Fusion Plasmas; Electrical Discharges @ 49%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970102 Expanding Knowledge in the Physical Sciences @ 100%
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