MEASUREMENT OF SUPRATHERMAL ELECTRONS IN TOKAMAKS VIA ELECTRON-CYCLOTRON TRANSMISSION

The momentum distribution of the current carrying suprathermal electrons is determined from the measurement of X-mode transmission near the fundamental of the cyclotron frequency during inductive and radiofrequency current drive in the Versator II tokamak. Measurement of the differential attenuation of radiation of two beams with finite and opposite parallel index of refraction N(allows the separation of the wave attenuation due to cyclotron absorption from that due to non-resonant mechanisms. It is shown that such transmission measurements can be used to determine the part of the parallel momentum distribution which is antisymmetric in p1 i.e. Fa(p1) ≡ ½ (F(−p1) − F(pi)). Measurements of Fa(p1) and its time evolution generally agree with expectations, although the parallel temperature is found to be lower than predicted by collisional theory in the inductively driven case. © 1990 IOP Publishing Ltd.