TRANSITION PHENOMENA OBSERVED DURING EDGE ELECTRON-CYCLOTRON HEATING IN THE HELIOTRON-E HELICAL DEVICE

An edge electron cyclotron heating (ECH) experiment has been performed on the Heliotron-E helical device using 35 GHz and 53 GHz gyrotrons. Transition phenomena have been observed during the 53 GHz edge ECH. Th e H alpha emission and the outflux to the wall dropped, and then the c ore electron density increased by 20%-60%. The electron stored energy seems to be improved up to 20% after the transition. This phenomenon i s found to depend strongly on the edge heating power, the target plasm a density and the limiter position. A possible mechanism is discussed in terms of high energy electrons produced by the edge ECH.