Plasma and Fusion Research

Volume 20, 1403033 (2025)

Regular Articles

Self-Consistent Establishment of the Bohm Criterion in Two-Ion-Species Plasmas Based on the Anisotropic-Ion-Pressure Plasma Fluid Scheme

Satoshi TOGO¹⁾, Tomonori TAKIZUKA²⁾, Hirohiko TANAKA³⁾, Ryuya IKEZOE⁴⁾, Naomichi EZUMI¹⁾, Kazuma EMOTO^1,a), Mizuki SAKAMOTO¹⁾

1): Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
2): TFuEL, Tokai 319-1112, Japan
3): Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya 464-8603, Japan
4): Research Institute for Applied Mechanics, Kyushu University, Fukuoka 816-8580, Japan
a): Present address: National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan

(Received 31 March 2025 / Accepted 7 May 2025 / Published 4 July 2025)

Abstract

The Bohm criterion for two-ion-species plasmas in a scrape-off layer–divertor system is investigated using the anisotropic-ion-pressure plasma fluid scheme and the virtual divertor model, which does not require the boundary condition of the incident flow speed at a divertor target. The flow velocities of the two ion species at the target obtained from our fluid simulations agree well with those obtained from earlier particle-in-cell simulations for both collisionless and collisional cases. The so-called Bohm criterion can be self-consistently established without direct treatment of the sheath region. Examining the time evolution of the flow velocity at the target, we infer that the Bohm criterion is not related to sheath potential formation but is the stability condition for an equilibrium solution of the quasi-neutral plasma region.

Keywords

scrape-off layer–divertor plasmas, fluid simulation, anisotropic-ion pressure, Bohm criterion, two-ion-species plasmas

DOI: 10.1585/pfr.20.1403033

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