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(THP1/04) Internal Disruptions in Stellarators

  (This paper was rapporteured in lecture TH2/2)  

 
B. A. Carreras , V. E. Lynch , H. Zushi ¹, K. Ichiguchi ², M. Wakatani ³
 
Oak Ridge National Laboratory Oak Ridge, Tennessee 37831, U.S.A.
¹ Research Institute for Applied Mechanics, Kyushu University, Kasuga 816, Japan
² National Institute for Fusion Science, Toki 509-5292, Japan
³ Graduate School of Energy Science, Kyoto University, Kyoto, Japan

Abstract
Internal disruptions have been observed in different modes of stellarator  operation. In Heliotron E  shifted-in vacuum magnetic field configuration, the ideal modes  of the $m/n = 2/1$ helicity can be unstable. Their nonlinear evolution leads to a sudden crash of the pressure within the $r/a = 0.3$ radius (sawtooth oscillation). When beta is increased further, the $q = 2$ surface moves out of the plasma, and the ideal modes of the $m/n = 2/1$ helicity are effectively stabilized when $q(0) < 1.85$. As a result, the sawtooth oscillations are suppressed.

   

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