Estimating the runaway diffusion coefficient in the TEXT tokamak from shift and externally applied resonant magnetic-field experiments

Two techniques are employed on the TEXT tokamak [Nucl. Fusion 29, 547 (1989); 30, 167 (1990)] to measure the runaway diffusion coefficient D: (i) displacing the plasma column, and (ii) externally applying resonant magnetic fields. Model diffusion equations for the experiments are solved to obtain analytic predictions which then can be used to interpret the measurements. The initial transient response of the x-ray flux to the perturbing shift or applied magnetic field is used to measure a D of order 1 m2 sec−1 near the edge that decreases inward.