Understanding how minority relativistic electron populations may dominate charge state balance and radiative cooling of a post-thermal quench tokamak plasma

Abstract

Minority relativistic electron populations can occur in a range of complex plasmas. Of specific interest is when runaway electrons form among the presence of high-atomic-number ion species in a tokamak plasma discharge. It has been recently demonstrated that ion charge state distributions and radiation losses at low bulk electron temperatures can be dominated by relativistic electrons, even though their density is orders of magnitude lower. This was attributed to the relativistic enhancement of electron impact inelastic cross sections. In this work, we provide a closer inspection of the atomic physics underpinning this effect. We also demonstrate the consequences of runaway enhanced scattering on post-disruption tokamak fusion discharges with neon and argon impurities present. Effects on charge state distributions, radiation and spectral characteristics, and reduced-order modeling considerations are discussed.

Maxwellian and non-Maxwellian rate coefficients of the tungsten ions: W46+–W55+

“…Hansen and Shlyaptseva studied the effects of EEDF on collisional rates with two-temperature distribution [26]. Garland et al demonstrated that minority hot electron populations can dominate the charge states distributions and radiation losses by Ne and Ar impurities [27]. Recently, Dilmi and Boumali reported the effect of the types of EEDF and the ratio of hot electrons on the rate coefficients of Li [28].…”

The constraint of plasma power balance on runaway avoidance

“…For the Ohmic root, this leads to the familiar expression P η ≡ ηj 2 ∥ . For the RE root, this leads to an estimate of the net energy transferred to the plasma being given by P RE = E av j ∥ , though some of this energy will be lost via radiative losses in the channels of synchrotron radiation [18,19], bremsstrahlung [20], and line emission [21,22]. Thus, at steady state the heating of the bulk electrons will be bounded from above by P RE = E av j ∥ when on the RE root.…”