Hideo Nuga

Fokker-Planck simulation of runaway electron generation in disruptions with the hot-tail effect

To study runaway electron generation in disruptions, we have extended the three-dimensional (two-dimensional in momentum space; one-dimensional in the radial direction) Fokker-Planck code, which describes the evolution of the relativistic momentum distribution function of electrons and the induced toroidal electric field in a self-consistent manner. A particular focus is placed on the hot-tail effect in two-dimensional momentum space. The effect appears if the drop of the background plasma temperature is sufficiently rapid compared with the electron-electron slowing down time for a few times of the pre-quench thermal velocity. It contributes to not only the enhancement of the primary runaway electron generation but also the broadening of the runaway electron distribution in the pitch angle direction. If the thermal energy loss during the major disruption is assumed to be isotropic, there are hot-tail electrons that have sufficiently large perpendicular momentum, and the runaway electron distribution becom...

Kinetic Transport Simulation of ICRF Heating in Tokamak Plasmas

The deviation of the distribution functions from the Maxwellian due to the interaction with waves affects the propagation and absorption of the wave itself. Therefore self-consistent analysis including the modification of the momentum distribution function is required for quantitative analysis of wave heating and current drive. The modeling code TASK was updated to describe the momentum distribution function of multi-species and the wave dielectric tensor for arbitrary momentum distribution function. Numerical results of ICRF heating in tokamak plasmas which generates energetic tail of distribution function are reported.