Abstract Details
Abstracts
Author: Linjin Zheng
Requested Type: Poster
Submitted: 2017-03-17 14:42:56
Co-authors: M. T. Kotschenreuther, P. Valanju
Contact Info:
University of Texas at Austin
University of Texas at Austin
Austin, Texas 78712
USA
Abstract Text:
The MHD stability is critical for ITER. However, the numerical assessment of MHD stability contains some uncertain factors, depending on how much percentage of plasma column is retained for stability calculations. Exclusion of a certain part of plasma column at tokamak edge is a common practice in the MHD stability calculations. In this work we intend to examine how sensitive MHD stability is on this practice. It is well known that for tokamak free boundary equilibria with X-point included the magnetic shear tends to increase dramatically at plasma edge. This leads to a challenge both for MHD equilibrium and stability computations. The situation becomes even harder when the bootstrap current is taken into account. On one hand, the numerical equilibrium convergence for high q (safety factor) surfaces at edge is not easy to achieve; On the other hand, the edge q value determines the location of mode resonance surface to be inside or outside the last closed flux surface. Note that the external modes tend to be more unstable than internal modes, just like the stability condition for peeling modes are more stringent than interchanges. This motivates us to examine the sensitivity issue of MHD stability condition on the edge equilibrium. We use the ITER configuration for our studies. The CORSICA code is used to construct numerically the ITER equilibria with bootstrap current taken into account. As one can expect, the numerical convergence becomes worse and worse as the last closed flux surface is approached due to the presence of the X-point. Nevertheless, within the achievable numerical equilibrium accuracy we run the AEGIS stability code on the equilibria to determine the dependence of stability condition on the percentage of plasma column being retained for stability calculations. The numerical results will be detailed and discussed. Also, an adaptive shooting scheme for tokamak equilibrium calculation is presented.
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