Plasma and Fusion Research

Volume 21, 1403040 (2026)

Regular Articles

Approximate Formulae Representing Effective-Charge-Number Dependence of Collisional Relaxation Coefficients for Electron Fluid Moment Equations in Open Magnetic Field System
Tomonori TAKIZUKA1), Satoshi TOGO2)
1)
TFuEL, Tokai-mura 319-1112, Japan
2)
Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
(Received 15 March 2026 / Accepted 12 May 2026 / Published 2 September 2026)

Abstract

We study the collisional relaxation processes of electron fluid moments in open magnetic field systems, such as scrape-off layer and divertor plasmas, by using a simplified Fokker-Planck equation. Anisotropies in temperature and heat flux in directions parallel and perpendicular to the magnetic field are taken into account. The thermal force is not given by the temperature gradient but by the heat flux damping. The relaxation of heat-flux anisotropy is found to play a role in the heat flux transport. For the convenience of plasma fluid simulations, approximate formulae are devised to represent the dependence of relaxation coefficients on the effective charge number.

Keywords

plasma fluid simulation, SOL divertor, moment equation, collisional relaxation, electron heat flux, thermal force, anisotropic temperature, effective charge number

DOI: 10.1585/pfr.21.1403040

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References

  • [1] A. Loarte et al., Nucl. Fusion 47, S203 (2007).
  • [2] K. Krieger et al., Nucl. Fusion 65, 043001 (2025).
  • [3] H. Kawashima et al., Plasma Fusion Res. 1, 031 (2006).
  • [4] S.I. Braginskii, Reviews of Plasma Physics vol.1 (Consultants Bureau, New York, 1965), p.205.
  • [5] T. Takizuka et al., J. Nucl. Mater. 128–129, 104 (1984).
  • [6] A. Froese et al., Plasma Fusion Res. 5, 026 (2010).
  • [7] W. Fundamenski, Plasma Phys. Control. Fusion 47, R163 (2005).
  • [8] B.A. Trubnikov, Reviews of Plasma Physics vol.1 (Consultants Bureau, New York, 1965), p.105.
  • [9] P.C. Stangeby, The Plasma Boundary of Magnetic Fusion Devices (IoP Publishing, Bristol, 2000).
  • [10] S. Togo et al., Comput. Phys. 310, 109 (2016).
  • [11] S. Togo et al., Nucl. Fusion 59, 076041 (2019).