By injecting microwave power (120 kW, 35.6 GHz) into the WT-2 device, a toroidal plasma is produced by electron cyclotron heating near the upper-hybrid resonance. (1) The production mechanism is interpreted as the result of damping of electron Bernstein waves and described by a ray-tracing code. (2) The production mechanism of high-energy electrons in such a plasma is studied and interpreted as a competition between electron acceleration by the incident wave and deceleration by collisions. These electrons interact resonantly with the lower hybrid wave during the startup of an RF tokamak discharge. (3) The first experimental observation, in an ECR plasma, of the resulting macroinstability, consistent with a theory suggested by Peng et al., is reported. (4) This instability is suppressed by the lower-hybrid driven current, the required rotational transform being produced by this current.
Plasma dynamics with second and third-harmonic ECRH and access to quasi-stationary ELM-free H-mode on TCV