Self-consistent kinetic simulations of lower hybrid drift instability resulting in electron current driven by fusion products in tokamak plasmas

TL;DR

This paper uses particle-in-cell simulations to demonstrate how energetic fusion protons in tokamak plasmas excite lower hybrid drift instabilities, leading to electron currents that could enhance fusion efficiency.

Contribution

It provides the first self-consistent 3D electromagnetic PIC simulation of the lower hybrid drift instability driven by fusion products in tokamaks.

Findings

Fusion protons excite lower hybrid waves near the frequency and harmonics.

Electromagnetic fields transfer energy from protons to electrons, creating an antiparallel tail.

Results support alpha channelling concepts for improved fusion plasma control.

Abstract

We present particle-in-cell (PIC) simulations of minority energetic protons in deuterium plasmas, which demonstrate a collective instability responsible for emission near the lower hybrid frequency and its harmonics. The simulations capture the lower hybrid drift instability in a regime relevant to tokamak fusion plasmas, and show further that the excited electromagnetic fields collectively and collisionlessly couple free energy from the protons to directed electron motion. This results in an asymmetric tail antiparallel to the magnetic field. We focus on obliquely propagating modes under conditions approximating the outer mid-plane edge in a large tokamak, through which there pass confined centrally born fusion products on banana orbits that have large radial excursions. A fully self-consistent electromagnetic relativistic PIC code representing all vector field quantities and particle velocities in three dimensions as functions of a single spatial dimension is used to model this situation, by evolving the initial antiparallel travelling ring-beam distribution of 3MeV protons in a background 10keV Maxwellian deuterium plasma with realistic ion-electron mass ratio. The simulations thus demonstrate a key building block of alpha channelling scenarios for burning fusion plasmas in tokamaks.