Plasma and Fusion Research

Volume 5, 026 (2010)

Regular Articles

Kinetic Particle Simulation Study of Parallel Heat Transport in Scrape-off Layer Plasmas over a Wide Range of Collisionalities

Aaron FROESE, Tomonori TAKIZUKA¹⁾ and Masatoshi YAGI²⁾

: IGSES, Kyushu University, Kasuga 816-8580, Japan
1): Japan Atomic Energy Agency, Naka 311-0193, Japan
2): RIAM, Kyushu University, Kasuga 816-8580, Japan

(Received 15 March 2010 / Accepted 10 June 2010 / Published 2 August 2010)

Abstract

Fluid models are not generally applicable to fusion edge plasmas without external provision of kinetic factors: closure parameters and boundary conditions inside the sheath region. We explain the PARASOL-1D simulation, a particle-in-cell code with a binary collision Monte-Carlo model, and use it to determine four kinetic factors commonly needed in fluid codes. These are the electron and ion heat flux limiting factors, α_e and α_i, the ion adiabatic index, γ_A, and the electron and ion temperature anisotropy, T_∥/T_⊥. We survey these factors over a wide range of collisionalities and find that, as predicted, the conductive heat flux is accurately described by the Spitzer-Härm expression in the collisional limit and asymptotes to a constant value in the collisionless limit. However, unique behavior occurs in the weakly collisional regime when the ratio of the mean free path to connection length is 0.1 < λ_mfp/L_∥< 10, when the SOL is between the conduction- and sheath-limited regimes. We find that α_e can peak, becoming larger than the collisionless limit, γ_A is less than unity, and only the ions are anisotropic. The effects of electron energy radiation and Langevin heating are explored. Finally, the strong deviations of the energy distribution function from Maxwellian in the weakly collisional and collisionless regimes are explained.

Keywords

scrape-off layer, particle-in-cell simulation, heat flux limiting factor, adiabatic index

DOI: 10.1585/pfr.5.026

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This paper may be cited as follows:

Aaron FROESE, Tomonori TAKIZUKA and Masatoshi YAGI, Plasma Fusion Res. 5, 026 (2010).