3D simulations of vertical displacement events in tokamaks: A benchmark of M3D-C$^1$, NIMROD and JOREK

TL;DR

This paper presents a comprehensive benchmark of three advanced 3D MHD codes—JOREK, M3D-C1, and NIMROD—in simulating vertical displacement events in tokamaks, demonstrating their agreement and highlighting differences in modeling approaches.

Contribution

It provides the first detailed comparison of these codes for VDEs, validating their use and exploring the impact of different physics models on simulation results.

Findings

Good agreement in wall forces and energy decay across codes

Differences observed due to physics model choices (full vs. reduced MHD)

Captured 3D features like halo currents and wall forces in NSTX simulations

Abstract

In recent years, the nonlinear 3D magnetohydrodynamic codes JOREK, M3D-C$^1$ and NIMROD developed the capability of modelling realistic 3D vertical displacement events (VDEs) including resistive walls. In this paper, a comprehensive 3D VDE benchmark is presented between these state of the art codes. The simulated case is based on an experimental NSTX plasma but with a simplified rectangular wall. In spite of pronounced differences between physics models and numerical methods, the comparison shows very good agreement in the relevant quantities used to characterize disruptions such as the 3D wall forces and energy decay. This benchmark does not only bring confidence regarding the use of the mentioned codes for disruption studies, but also shows differences with respect to the used models (e.g. reduced versus full MHD models). The simulations show important 3D features for a NSTX plasma such as the self-consistent evolution of the halo current and the origin of the wall forces. In contrast to other reduced MHD models based on an ordering in the aspect ratio, the ansatz based JOREK reduced MHD model allows capturing the 3D dynamics even in the spherical tokamak limit considered here.