Studies of Runaway Electron Transport in Text

The transport of runaway electrons is studied by a plasma position shift experiment and by imposing an externally applied perturbing magnetic field on the edge. The perturbing magnetic field can produce either magnetic islands or, with overlapping islands, a stochastic field. Hard X-ray signals are then measured and compared with analytic and numerical model results. Diffusion coefficients in the edge, ~10^4 cm^2/sec, and inside the plasma, ~10^2 -10^3 cm^2/sec, are estimated. The averaged drift effects are small and the intrinsic magnetic fluctuations are estimated to be <(b_{r}/B_0) ^2 >~ 10^{-10} at the edge and decreasing inward. Runaway electrons are a good diagnostic of the magnetic fluctuations. It is concluded that the magnetic fluctuations have a negligible effect on electron thermal diffusion in the edge plasma. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253 -1690.).