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Electron cyclotron resonance heating (ECRH) experiments have began on Tokamak à Configuration Variable (TCV) using the 2nd harmonic in X-mode at 83.7 GHz with power of up to 1 Mw of two gyrotrons and a large geometrical flexibility in plasma heating. The heating powers exceed ohmic powers by up to 14 times and electron energy increases up to factor of 3 over ohmic. The experiments have revealed several interesting phenomena. For example during injection of ECW, various central magnetohydrodynamic (MHD) activities (Humpback Sawteeth, Saturated Sawteeth and Inverted Sawteeth) have been observed. The transition between these different activity types depends on the power deposition location, heating power, plasma shape, and safety factor.

Unlike normal sawteeth in which the changes in intensity can be explained by temperature variation, humpback sawteeth cannot be explained solely on the basis of temperature-X-ray intensity are higher than expected in part of a humpback. The density, being almost constant during this process, does not contribute to the X-ray variation. There are several possible interpretations of the different sawtooth behaviours; these will be discussed and evaluated. .

Additional information

Authors: PIETRZYK Z A ET AL, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne Association EURATOM � Confédération Suisse, Lausanne (CH)
Bibliographic Reference: Article: 1998 International Congress on Plasma Physics, 25th EPS Conference on Controlled Fusion and Plasma Physics, Prague (CZ), June 29 � July 3, 1998
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