Electron cyclotron heating of currentless plasmas in stellarators

A review is presented of experiments on the production and heating of currentless plasmas by electron cyclotron (EC) waves in the Heliotron-E, Wendelstein VII-A, and L-2 stellarators, in wide ranges of the magnetic field (1.0 - 2.5 T), frequency (28 - 70 GHz) and microwave power (100 - 500 kW). EC heating of low and high-density currentless plasmas as well as of ohmically heated (OH) plasmas is discussed. Nonlinear ion heating and plasma current generation were observed to accompany EC plasma heating. It was found that a high efficiency of microwave absorption, a high electron temperature (1 - 1.5 keV) and a considerable energy confinement time are characteristic of EC plasma heating. (author)