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Classical Cross-Field Self-Diffusion Due to Finite Larmor Radius

Tomonori TAKIZUKA, Satoshi TOGO¹⁾, Kenzo IBANO and Yuki HOMMA²⁾

Graduate School of Engineering, Osaka University, Suita 565-0871, Japan

1)

Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan

2)

National Institutes for Quantum Science and Technology, Rokkasho 039-3212, Japan

(Received 2 October 2023 / Accepted 12 November 2023 / Published 8 December 2023)

Abstract

It has been considered that the classical diffusion of plasma particles across the magnetic field is determined only by collisions between different species. Taking account of the finite Larmor radius ρ of an ion, the random walk of its guiding center (step size ρ per collision time τ) can result from collisions even with the same species. A resultant “self-diffusion” coefficient is D_⊥ ≈ ρ²/2τ. When there exists a radial electric field, the step size becomes asymmetric, and an “electric-field induced collisional displacement” of the guiding center is generated. In an inhomogeneous plasma, the collision time for an ion is varied during a gyration, and a “self-friction force” is induced. We propose these three collisional responses to be included to the ion fluid equations. We discuss that the ion cross-field self-diffusion becomes important in the edge plasma, where electrons are mainly lost along the magnetic field.

Copyright (c) 2023 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

classical cross-field diffusion, particle self-diffusion, finite Larmor radius, radial electric field, edge plasma

DOI: 10.1585/pfr.18.1203090

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Publisher's Note

This article has an erratum: Tomonori TAKIZUKA et al., Plasma Fusion Res. 19, 1903018 (2024).

References

• [1] K. Miyamoto, Fundamentals of Plasma Physics and Control. Fusion, sec. 7.1 (Iwanami Book Service Center, Tokyo, 1997).
• [2] S.I. Braginskii, Reviews of Plasma Physics vol.1, p.205 (Consultants Bureau, New York, 1965).
• [3] B.A. Trubnikov, Reviews of Plasma Physics vol.1, p.105 (Consultants Bureau, New York, 1965).