Particle-in-cell studies of fast-ion slowing-down rates in cool tenuous magnetized plasma

TL;DR

This study uses 3D particle-in-cell simulations to analyze how fast ions lose energy in cold, weakly-magnetized plasmas, confirming theoretical scaling laws and exploring implications for magnetic fusion devices.

Contribution

It provides detailed simulation results of fast-ion slowing-down in a specific plasma regime, validating scaling laws and examining magnetic field effects.

Findings

Scaling of slowing-down time matches unmagnetized theory.

No clear anisotropy in slowing-down times with magnetic field.

Charge scaling reduces computational requirements.

Abstract

We report on 3D-3V particle-in-cell simulations of fast-ion energy-loss rates in cold, weakly-magnetized, weakly-coupled plasma where the electron gyroradius, $\rho_{e}$, is comparable to or less than the Debye length, $\lambda_{De}$, and the fast-ion velocity exceeds the electron thermal velocity, a regime in which the electron response may be impeded. These simulations use explicit algorithms, spatially resolve $\rho_{e}$ and $\lambda_{De}$, and temporally resolve the electron cyclotron and plasma frequencies. For mono-energetic dilute fast ions with isotropic velocity distributions, these scaling studies of the slowing-down time, $\tau_{s}$, \versus fast-ion charge are in agreement with unmagnetized slowing-down theory; with an applied magnetic field, no consistent anisotropy between $\tau_{s}$ in the cross-field and field-parallel directions could be resolved. Scaling the fast-ion charge is confirmed as a viable way to reduce the required computational time for each simulation. The implications of these slowing down processes are described for one magnetic-confinement fusion concept, the small, advanced-fuel, field-reversed configuration device.