On self-consistent ray-tracing and Fokker–Planck modeling of the hard x-ray emission during lower-hybrid current drive in tokamaks

Abstract

A detailed investigation is presented on the ability of combined ray-tracing and Fokker–Planck calculations to predict the hard x-ray (HXR) emission during lower-hybrid (LH) current drive in tokamaks when toroidally induced ray stochasticity is important. A large number of rays is used and the electron distribution function is obtained by self-consistently iterating the appropriate power deposition and Fokker–Planck calculations. It is shown that effects due to radial diffusion of suprathermal electrons and to radiation scattering by the inner wall can be significant. The experimentally observed features of the HXR emission are fairly well predicted, thus confirming that combined ray-tracing and Fokker–Planck codes are capable of correctly modeling the physics of LH current drive in tokamaks.