Generalized collision operator for fast electrons interacting with partially ionized impurities
Journal article, 2018

Accurate modelling of the interaction between fast electrons and partially ionized atoms is important for evaluating tokamak disruption mitigation schemes based on material injection. This requires accounting for the effect of screening of the impurity nuclei by the cloud of bound electrons. In this paper, we generalize the Fokker–Planck operator in a fully ionized plasma by accounting for the effect of screening. We detail the derivation of this generalized operator, and calculate the effective ion length scales, needed in the components of the collision operator, for a number of ion species commonly appearing in fusion experiments. We show that for high electric fields, the secondary runaway growth rate can be substantially larger than in a fully ionized plasma with the same effective charge, although the growth rate is significantly reduced at near-critical electric fields. Furthermore, by comparison with the Boltzmann collision operator, we show that the Fokker–Planck formalism is accurate even for large impurity content.

runaway electrons

fusion plasma

Author

Linnea Hesslow

Chalmers, Physics, Subatomic and Plasma Physics

Ola Embréus

Chalmers, Physics, Subatomic and Plasma Physics

Mathias Hoppe

Chalmers, Physics, Subatomic and Plasma Physics

Timothy Dubois

Chalmers, Physics, Subatomic and Plasma Physics

Martin Rahm

Chalmers, Chemistry and Chemical Engineering, Chemistry and Biochemistry

Tünde Fülöp

Chalmers, Physics, Subatomic and Plasma Physics

Journal of Plasma Physics

0022-3778 (ISSN) 1469-7807 (eISSN)

Vol. 84 6 905840605-

Subject Categories

Atom and Molecular Physics and Optics

Fusion, Plasma and Space Physics

DOI

10.1017/S0022377818001113

More information

Created

12/14/2018