Description
Magnetohydrodynamic (MHD) instabilities such as (peeling-)ballooning, tearing and kink modes impose fundamental limits on the achievable plasma pressure and stable operation of magnetically confined fusion devices. The accurate prediction of their onset and characteristics is therefore essential for extrapolating stability limits in present experiments to future fusion reactors. While ideal or resistive MHD models capture the existence of many relevant instabilities, determining their precise onset and hence the true operational limit that these instabilities impose requires the inclusion of additional physical effects.
In this work, we present recent developments and applications of the linear extended MHD stability code CASTOR3D [1-3] for the analysis of three-dimensional tokamak and stellarator equilibria. CASTOR3D includes resistivity, parallel and gyro-viscosity, equilibrium flows and heat conductivity in the system of linearized MHD equations. Equilibrium flows are described by toroidal rotation or neoclassical flows (ExB and ion diamagnetic flows, Pfirsch-Schlüter flows and net parallel flows). We discuss the impact of these extended MHD effects on the growth rates and frequencies of relavant MHD instabilities and highlight their role in modifying MHD stability compared to the ideal MHD framework. It is shown that resistivity, gyro-viscosity and flow physics significantly affect growth rates and frequencies of MHD instabilities in both tokamaks and stellarators [3-6]. Frequencies of experimentally observed inter-ELM modes at ASDEX Upgrade [6] are demonstrated to be in good agreement with the frequencies of predicted MHD instabilities if extended MHD effects are taken into account. Recent numerical optimizations significantly improve the applicability of CASTOR3D to realistic three-dimensional plasma configurations. These developments provide a powerful framework for systematic and predictive MHD stability studies in both present and next-generation fusion devices.
[1] E. Strumberger & S. Günter 2017 NF 57 016032
[2] E. Strumberger et al 2023 JPP 89 905890309
[3] E. Strumberger et al 2026 JPP accepted
[4] J. Puchmayr et al 2023 NF 63 086008
[5] J. Puchmayr et al 2024 NF 64 086013
[6] B. Vanovac et al 2023 PPCF 65 095011