Experimental demonstration of the stabilizing effect of a superthermal electron avalanche during electron cyclotron resonant heating

A.Lazaros, A.Shimizu1), Y.Yoshimura1), K.Matsuoka1), S.Okamura1), C.Suzuki1), and the CHS Group1)

Association EURATOM-Hellenic Republic, National Technical University of Athens, GREECE
1) National Institute for Fusion Science, Toki-shi, JAPAN

The stabilizing effect of the superthermal electrons [A.Lazaros, Phys. Plasmas 6, 148 (1999)], which are produced through the "avalanche" effect [A.Lazaros, Phys. Plasmas 8, 1263 (2001)] during electron cyclotron resonant heating (ECRH), is demonstrated by the suppression of the "fishbone" mode with ECRH in the "Compact Helical System" [S.Okamura, et al., Nucl. Fusion 39, 1337 (1999)], in an experimental arrangement which favors the development of a superthermal electron avalanche and
excludes any other stabilizing effect. In this experiment no direct measurement of the superthermal electron density was available. Our conclusions, however, are strongly supported by the finding that the decay time of the fishbone mode (during radial scans of the EC resonance and density scans) was consistent with the predicted scaling law of the superthermal density growth time, i.e. tse is proportional to (rEC/PEC)3ne5, where rEC is the radius of the EC resonance, PEC is the ECRH power, and ne is the electron density.

This paper has been published at Physics of Plasmas, Vol.9, pp.3007-3012 (2002)