Speaker
Description
Plasma disruption is one of the key factors limiting the stable and safe operation of future large tokamaks. It involves a sudden collapse of the plasma confinement and can cause severe heat loads and electromagnetic forces on surrounding structures. Understanding the chain of events leading to unintentional/natural disruptions remaining a critical goal in the pursuit of sustainable fusion energy [1]. The final phase of a disruption is commonly associated with the growth of magnetohydrodynamic (MHD) instabilities, particularly tearing modes. Recent studies indicated that the finite resistivity of the wall can modify the previously predicted stability boundaries of such modes [2], giving rise to what are termed as Resistive Wall Tearing Modes (RWTMs) [2,3]. If this is the main mechanism that triggers the termination of plasma, then predictions on the thermal quench duration must be revised and adjusted to the RWTM growth rates, which need to be studied in detail.
In order to investigate these effects, we developed a linear solver that accounts for wall resistivity, a feature typically omitted in classical tearing mode analysis. This implementation was based on the methodology shown in [4]. The solver was employed to scan for unstable RWTM scenarios, specifically by varying current profile shapes in large-aspect-ratio equilibria, providing a baseline for nonlinear studies. Subsequently, simulations were carried out using the three-dimensional non-linear MHD code JOREK, coupled with STARWALL. Notably, this work marks the first identification of RWTMs in JOREK–STARWALL simulations. Good agreement was found between the linear solver and the JOREK-STARWALL code results in terms of mode growth rates. Further benchmarking are being performed against the CASTOR3D MHD code. The applicability of these findings are also being tested in a more realistic and experimentally relevant setup. Specifically, the effect of wall resistivity on mode growth are being analyzed with JOREK-STARWALL for a JET disruption case previously studied by Hank Strauss using the M3D code [2]. The sensitivity of the mode growth rate to wall resistivity are being examined, and comparison with previous M3D simulations will be discussed.
Our findings offer new insight into the role of RWTMs in disruption dynamics and support the development of improved prediction and mitigation strategies, an essential step toward ensuring the stability and safety of next-generation fusion devices.
References
[1] G. Pucella et al., Nuclear Fusion 61 (2021): 046020
[2] H. Strauss et al., Physics of Plasmas 28 (2021): 032501
[3] H. Strauss et al., Plasma Physics and Controlled Fusion 65 (2023): 084002
[4] J.P. Graves et al., Plasma Physics and Controlled Fusion 64 (2021): 014001
