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Author(s):
S. Sakakibara et al.
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Title:
Stability in High-Beta Plasmas of LHD
Date of publication:
Oct. 2006
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Key words:
21 IAEA Fusion Energy Conference , EX/7-5
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Abstract:
In Large Helical Device (LHD), the volume averaged beta value <beta_dia> of 4.5 %, which is the highest value in all of heliotron/stellarators, was achieved by optimizing the magnetic configuration from a virepoint of MHD characterisitcs, transport and heating efficiency of neutral beam. In this study, characteristics of MHD activities in extended <beta_dia> range over 4 % and the configuration dependence have been investigated. The dominant MHD modes moved from inner region to outer one when <beta_dia> increases, and the mode excited in the outermost resonance near plasma edge are enhanced in the <beta_dia> range over 4 %. The dependence of saturated amplitude of the mode on magnetic Reynolds number is close to that of linear growth rate of resistive interhcnage mode. When the magnetic shear was decreased and the plasma is close to m/n = 1/1 ideal stability boundary, the m/n = 1/1 mode suddenly growed and led to a minor collapse in the core region. The results suggest the significance of magnetic shear and a validity of a linear thory on ideal interchange mode. The mode can be stabilized easily by using external resonant field.
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