Numerical calculation of ion runaway distributions

Abstract

Ions accelerated by electric fields (so-called runaway ions) in plasmas may explain observations in solar flares and fusion experiments, however limitations of previous analytic work have prevented definite conclusions. In this work we describe a numerical solver of the 2D non-relativistic linearized Fokker-Planck equation for ions. It solves the initial value problem in velocity space with a spectral-Eulerian discretization scheme, allowing arbitrary plasma composition and time-varying electric fields and background plasma parameters. The numerical ion distribution function is then used to consider the conditions for runaway ion acceleration in solar flares and tokamak plasmas. Typical time scales and electric fields required for ion acceleration are determined for various plasma compositions, ion species and temperatures, and the potential for excitation of toroidal Alfvén eigenmodes during tokamak disruptions is considered.

25 pages, 8 figures

References in corpus (6)

• Electron fishbones: Theory and experimental evidence
• Linearized model Fokker-Planck collision operators for gyrokinetic simulations. I. Theory
• Effective Critical Electric Field for Runaway-Electron Generation
• Solar Flare Composition and Thermodynamics from RESIK X-ray Spectra
• Quasi-linear analysis of the extraordinary electron wave destabilized by runaway electrons
• Alfvénic instabilities driven by runaways in fusion plasmas