Prevention of resistuve wall tearing modes with feedback*

Disruptions are considered a major problem in large tokamaks such as ITER. Disruptions are caused by resistive wall modes (RWM) or  resistive wall tearing modes (RWTM). These can be passively slowed by a resistive wall with a long magnetic penetration time, and actively stabilized using feedback.  

Resistve wall tearing modes have been shown to produce disruptions in low beta, low edge q tokamaks,  This has been demonstrated in simulations and comparison with experimental data of locked mode disruptions in JET [1] and  DIII-D [2], which have a short resistive wall penetration time. Simulations have also been done of  ITER [3] and Madison Symetric Torus (MST) [4] , which have much longer wall times.  The predicted time scale of a major disruption is much longer in ITER and MST than in JET and DIII-D. Simulations using a sequence of MST - like equilibria  indicate that it is possible to prevent major disruptions with feedback.  The results are consistent with an experiment [5] in RFX - mod, in which feedback wa applied to stabillize equilibria with edge q > 2.

[1]  H. Strauss and JET Contributors, Effect of Resistive Wall on Thermal Quench in JET Disruptions, Phys. Plasmas  28, 032501 (2021)

[2] H. Strauss, B. C. Lyons, M. Knolker, Locked mode disruptions in DIII-D and application to ITER, Phys. Plasmas 29,  112508 (2022).

[3] H. Strauss, Thermal quench in ITER disruptions, Phys. Plasmas 28, 072507 (2021)

[4] H. R. Strauss,  B. E. Chapman, N. C. Hurst, MST Resistive Wall Tearing Mode Simulations, PPCF 65, 084002 (2023)

[5] P. Zanca, R. Paccagnella, et.al.,  Nucl. Fusion 55 043020 (2015)