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

摘要

We present particle-in-cell (PIC) simulations of minority energetic protonsin deuterium plasmas, which demonstrate a collective instability responsiblefor emission near the lower hybrid frequency and its harmonics. The simulationscapture the lower hybrid drift instability in a regime relevant to tokamakfusion plasmas, and show further that the excited electromagnetic fieldscollectively and collisionlessly couple free energy from the protons todirected electron motion. This results in an asymmetric tail antiparallel tothe magnetic field. We focus on obliquely propagating modes under conditionsapproximating the outer mid-plane edge in a large tokamak, through which therepass confined centrally born fusion products on banana orbits that have largeradial excursions. A fully self-consistent electromagnetic relativistic PICcode representing all vector field quantities and particle velocities in threedimensions as functions of a single spatial dimension is used to model thissituation, by evolving the initial antiparallel travelling ring-beamdistribution of 3MeV protons in a background 10keV Maxwellian deuterium plasmawith realistic ion-electron mass ratio. The simulations thus demonstrate a keybuilding block of alpha channelling scenarios for burning fusion plasmas intokamaks.