CALCULATION OF AN UPPER LIMIT FOR AN EFFECTIVE FAST-ELECTRON DIFFUSION CONSTANT USING THE HARD X-RAY-CAMERA ON PBX-M

Fast electron localization and transport are important for tokamak current profile control schemes. The hard x-ray camera on PBX-M produces two-dimensional, time resolved tangential images of fast electron bremsstrahlung, from which a fast electron diffusion constant is calculated. Assuming a radially narrow lower hybrid power absorption profile, a momentum space absorption profile and a transport model [1], a model fast electron current density profile is calculated and compared to an experimentally derived profile, and the diffusion coefficient is adjusted until a good fit is found. Using this model, we compute an upper limit for an effective diffusion constant of D* less-than-or-equal-to 1.1 m2/sec to within a factor of two.