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(EXP1/10) Progress in Long Sustainment and High Density Experiments with Potential Confinement on GAMMA 10

K. Yatsu¹⁾, T. Cho¹⁾, M. Hirata¹⁾, H. Hojo¹⁾, M. Ichimura¹⁾, K. Ishii¹⁾, A. Itakura¹⁾, I. Katanuma¹⁾, J. Kohagura¹⁾, Y. Nakashima¹⁾, T. Saito¹⁾, T. Tamano¹⁾, S. Tanaka¹⁾, Y. Tatematsu¹⁾, M. Yoshikawa^1)
 
1) Plasma Research Center, University of Tsukuba, Tsukuba, Japan

Abstract.  The improvement of potential confinement reported in the last IAEA meeting was attained by axisymmetrization of heating pattern of electron cyclotron resonance heating (ECRH). It was experimentally shown that the axisymmetrization of ECRH really produced axisymmetric potential profile. GAMMA 10 experiments have advanced in longer sustainment and high density operation of potential confinement. Experiments for long sustainment of potential confinement were carried out in order to study problems of steady state operation of a tandem mirror reactor. A confining potential was sustained for 150 ms by sequentially injecting two (ECRH) powers in the plug region. It was difficult before to increase the central cell density higher than about 2.5×10¹²cm^{- 3} with and/or without potential confinement due to some density limiting mechanism. In order to overcome this problem, a new higher frequency ion cyclotron range of frequency (ICRF) system (RF3: 36-76 MHz) has been installed. A higher density plasma has been produced with RF3. In addition to RF3, neutral beam injection (NBI) in the anchor cell became effective by reducing neutral gas from beam injectors. Potential confinement experiments have advanced to higher central cell densities up to 4×10¹²cm^{- 3} with RF3 and NBI. A 20% density increase due to the potential confinement was obtained in the high density experiments.

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