Abstract Details
Abstracts
Author: Hank Strauss
Requested Type: Consider for Invited
Submitted: 2024-03-29 07:07:42
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HRS Fusiin
2 Januson Ct
West Orange, NJ 07052
USA
Abstract Text:
Resistive wall tearing mode (RWTM) disruptions can be prevented by feedback stabilization [1]. It was demonstrated in DIII-D and RFX - mod that disruptions caused by resistive wall modes (RWM) can be feedback stabilized. When the q = 2 surface is inside the plasma, the RWM becomes a RWTM. RWTMs can grow to large amplitude sufficient to cause a complete thermal quench, as shown in nonlinear simulations which compare well with experimental data. The q = 2 surface has to be close enough to the plasma edge so that the edge q is less than about 3.5, otherwise only a minor disruption occurs. This is demonstrated in nonlinear simulations of a sequence of model equilibria with different edge q. Feedback stabilization of RWTMs is demonstrated using the same equilibria. The gain requirement decreases as edge q increases. In the absence of feedback, the thermal quench time can be slowed passively by a resistive wall. If the resistive wall penetration time is sufficiently long, the thermal quench time is linearly proportional to the resistive wall penetration time. In ITER and MST, the thermal quench time could be of order of 100 ms, much longer than in JET and DIII-D. In the long resistive wall time regime, RWTMs and RWMs can satisfy the same linear dispersion relation. If the wall is too far from the plasma, the mode becomes a no wall tearing mode and wall stabilization is lost. RWTMs can be destabilized by edge cooling caused by impurity radiation or by localized tearing mode overlap, which causes the current to contract. Linear stability calculations of model equilibria show RWTM destabilization with contracted current profiles. RWTMs destabilized by current contraction might be a factor in density limit disruptions. The RWTMs considered here have low beta_N. High beta_N RWTMs will be studied in future work.
[1] H. R.Strauss, B. E. Chapman, B. C. Lyons,arXiv.2401.07133 (2024)
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