MEASUREMENT OF THE RELAXATION OF ELECTRON PARALLEL MOMENTUM IN A TOKAMAK

Measurements of the momentum relaxation rate of suprathermal electrons in the VERSATOR II tokamak have been made using a novel cyclotron resonance technique. Attenuation of probe beams of X-mode radiation is interpreted as cyclotron absorption, yielding a measure of the distribution of current carriers. Differential measurements of two counter-propagating beams eliminate non-resonant effects. A distribution of electrons is produced by lower hybrid current drive and is observed to relax in the absence of wave power. The rate of momentum relaxation is anomalous but consistent with the observed current drive efficiency.