Preliminary experiments with edge plasma biasing in tokamak castor

To study a role of radial electric field in the particle confinement, preli minary experiments with an edge plasma biasing have been carried out in tok amak CASTOR. For the biasing, an insulated graphite electrode with the surf ace 1500mm(2), injecting into the plasma current up to one hundred ampers, has been used. The first measurements proved an increase of the global part icle confinement time nearly two times, however, for the positive polarity of the biasing only. A regular modulation (up to 50%) of the injected curre nt with a frequency about 10kH z has been observed. Oscillations highly coh erent with those oscillations of the injected current, but having a still s tronger modulation (up to 80%), exhibits also ion saturated current of a La ngmuir probe placed in the limiter shadow.