Spreading of Wave-Driven Currents in a Tokamak
Author: D.W. Ignat, R. Kaita, S.C. Jardin, and M. Okabayashi
Lower hybrid current (LHCD) in the tokamak Princeton Beta Experiment-Modification (PBX-M) is computed with a dynamic model in order to understand an actual discharge aimed at obtaining central q above unity. Such configurations offer advantages for steady-state operation and calculation found that singular profiles of plasma current density J and safety factor q develop after LHCD begins in a time of order 0.1 second. Smoothing the lower hybrid-driven current and power using a diffusion-like equation and a velocity-independent diffusivity for fast-electron current brought the model into reasonable agreement with the measurements if Dfast 1.0 m2/s. Such a value for Dfast is in the range suggested by other work.