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Author(s):
T. Hayashi, N. Mizuguchi, H. Miura and T. Sato
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Title:
Dynamics of Relaxation Phenomena in Spherical Tokamak
Date of publication:
Sep. 2000
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Key words:
IAEA, fusion energy conference, Sorrento
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Abstract:
Three-dimensional magnetohydrodynamic (MHD) simulations are executed to clarify the physical mechanisms of MHD relaxation activities, specifically the Internal Reconnection Event (IRE), which are observed in the spherical tokamak experiments. For a case of an initial equilibrium with q(0) less than one, tunnel-like plasma jet flow is formed by the occurrence of the extemal magnetic reconnection accompanying the growth of localized deformation of torus. When initial q(0) is slightly greater than one, upon increase of beta multiple mode number of finer-scale ballooning type instabilities is triggered, where the typical toroidal mode nurnber n is 11 . In the nonlinear stage, the surface of the torus is deformed due to growth of those medium-n modes, and a part of heat energy is lost into the extemal region through occurrence of external reconnection. Interestingly, low n modes, particularly n=2, are enhanced presumably by nonlinear coupling among the unstable mediurn-n modes, and the n=2 type deformation of the torus becomes dominant in the later stage.
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