MEASUREMENT OF FAST-ELECTRON VELOCITY DISTRIBUTION FUNCTION IN A REVERSED-FIELD PINCH PLASMA

Fast electrons in the edge region of the reversed field pinch (RFP) de vice, TPE-1RM20 are studied using an a electron energy analyzer (EEA) in the energy range below 1 keV. Results show that the fast electron v elocity distribution function can be approximated either by a drift Ma xwellian distribution function or two asymmetric half-Maxwellian distr ibution functions. The fast electron temperature is comparable to or s lightly less than the central electron temperature depending on the fi tting functions. The temperature obtained using the EEA is more than o ne order of magnitude lower than the characteristic fast electron ener gy estimated from soft X-ray emissions from the inserted materials at 2-8 keV. These observations indicate that fast electrons mainly have a Maxwellian distribution function with a temperature comparable to the central electron temperature-and that the distribution function may h ave a higher energy tail in the keV region.