Speaker
Description
Edge cooling is frequently observed in tokamak plasmas prior to disruptions and can lead to significant changes in the current density profile, potentially destabilizing magnetohydrodynamic (MHD) activity [1]. Understanding whether such cooling can drive the plasma toward instability, and whether/how the presence of a resistive wall affects this process, is essential for interpreting pre-disruption dynamics and improving disruption prediction.
In this work, we first investigate linear MHD stability in the presence of a resistive wall using a newly developed linear solver [2], with particular emphasis on resistive wall tearing modes (RWTMs). These modes correspond to tearing instabilities that would be stable in the presence of an ideal wall but become unstable in the no-wall limit [3]. The results from this fast solver are benchmarked against extended MHD simulations using JOREK–STARWALL and CASTOR3D, providing cross-code validation and establishing confidence in the modeling of RWTMs. This framework enables a systematic study of the effect of current density profile and resistive wall on MHD stability.
Building on this, we further investigate a realistic JET plasma in which edge cooling was experimentally observed prior to a disruption [4] via simulations with the JOREK-STRAWALL code. The simulations are initialized by modeling the edge cooling via impurity radiation and subsequently track the evolution of the current density profile and the onset of MHD activity. Experimental measurements indicate the presence of unusual and intermittent MHD signatures prior to the disruption, motivating a detailed numerical investigation of the underlying dynamics. In this work, we aim to assess whether edge cooling can modify the current profile sufficiently to move the plasma into an unstable regime and to identify the role of the resistive wall in the resulting MHD activity. In particular, by comparing simulated behavior with experimental observations, this work seeks to clarify whether RWTMs provide a consistent interpretation of the observed pre-disruption dynamics in the JET discharge.
References
[1] G. Pucella et al., Nuclear Fusion 61 (2021): 046020
[2] L. Édes et al., EFTC 2025
[3] H. Strauss et al., PPCF 65 (2023): 084002
[4] H. Strauss et al., PoP 28 (2021): 032501