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TCV [1] is a moderate-size tokamak (R=0.88 m, a = 0.25 m) with a highly elongated vacuum vessel allowing the creation of plasmas up to K~ 3 (K=2.8, achieved). The sole auxiliary heating system on TCV is ECH, consisting of 6 X2 (82.7GHz) gyrotrons and 3 X3 ( 118GHz) gyrotrons. The complete X2 system has been in operation since 1999 and the first of the 3 X3 gyrotrons was used for absorption experiments for the first time in 2000 by installing a microwave switch in one of the X2 evacuated transmission lines. Thus, either X2 or X3 power can be launched from the X2 antenna of that line (i.e. the frequency from that antenna can be changed from shot to shot).

All X3 power is intended to be launched from one antenna at the top of the machine in order to take advantage of the increased optical depth resulting from propagation along the elongated length of the resonance in high elongation plasmas. The standard low field side (LFS) launch used for the X2 power would, for a Maxwellian electron distribution function, result in only-60% X3 absorption for even the hottest TCV plasmas. Nevertheless, LFS launch of the X3 has resulted in up to 100% absorption when the plasmas are pre-heated with X2 ECCD. A vertically-viewing 14 chord hard X-ray camera and 21-channel high field side (HFS) electron cyclotron emission (ECE) diagnostic provide evidence of the strong non-maxwellian nature of electron distribution function during both X2 ECCD pre-heating and later, additional, X3 heating. This suggests that the excess X3 absorption is on the non- Maxwellian part of the electron distribution. .

Additional information

Authors: GOODMAN ET AL, Centre de Recherches en Physique des Plasmas, EURATOM Association-Confederation Suisse, Ecole Polytechnique Federale de Lausanne (CH)
Bibliographic Reference: An oral report given at: The 28th EPS Conference of Controlled Fusion and Plasma Physics. Held in: Madeira (PT) June 2001
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