Experimental and Theoretical Investigation of Synergy Between Ion Bernstein and Lower Hybrid Waves in PBX-M
Authors: F. Paoletti, A. Cardinali, S. Bernabei, A. Post Zwicker, W. Tighe, and S. Von Goeler
The synergistic behavior of lower hybrid and ion Bernstein waves on the Princeton Beta Experiment-Modified tokamak [Phys. Fluids B 2, 1271 (1990)] is experimentally studied using a 2-D hard X-ray camera. The hard X-ray bremsstrahlung emission from suprathermal electrons, generated with lower hybrid current drive, is enhanced during ion Bernstein wave power injection. This enhancement is observed in limited regions of space suggesting the formation of localized current channels. The effects on plasma electrons during combined application of these two types of waves are theoretically investigated using a quasilinear model. The numerical code simultaneously solves the 3-D (R, Z, "capital phi") toroidal wave equation for the electric field (in the WKBJ approximation) and the Fokker-Planck equation for the distribution function in two dimensions (vparallel, vperpendicular) with an added quasilinear diffusion coefficient. The radial profile of the non-inductively generated current density, the transmitted power traces and the total power damping curve are calculated. The beneficial effects of a combined utilization of ion Bernstein and lower hybrid waves on the current drive are emphasized. The numerical results are compared with the experimental observations.