Influence of the beam-beam collisions on the energetic particle distribution in large helical device

Abstract

The influence of Coulomb collisions between energetic particles in a neutral beam injection (NBI)-heated plasma is numerically investigated utilizing the improved collision operator for the orbit-following type of Monte Carlo codes. This nonlinear collision operator enables the collisional effect by non-Maxwellian plasmas including energetic particles to be taken into account. We have implemented it into GNET, one of the orbit-following Monte Carlo codes solving drift kinetic equation in the 5D phase-space, and performed simulations for tangentially injected NBI cases (beam energy: 180 keV), taking account of beam–beam Coulomb collisions. It is found that the beam–beam collisions cause energetic particle orbits to transition from passing to trapped and enhance the collisional transport, which results in the deterioration of the energetic particle confinement.

Degradation of fast-ion confinement depending on the neutral beam power in MHD quiescent LHD plasmas

“…Non-linear Coulomb collision effect and beam-particle self-interaction (BPSI) are some of them. Because non-linear Coulomb collision between fast-ions can enhance the pitch angle scattering, much radial particle flux is induced due to the neo-classical transport [39]. It is known that the BPSI effect, which is based on the charge exchange loss between beam neutrals and fast-ions, can enhance the beam-stopping cross-section [40].…”