3D non-linear MHD simulations of core density collapse event in LHD plasma

TL;DR

This paper introduces a new 3D non-linear MHD simulation model for LHD plasma, capturing core density collapse events and their underlying instability mechanisms.

Contribution

The development and benchmarking of a 3D non-linear MHD model with heat diffusivity extension for simulating core density collapse in LHD plasma.

Findings

Model captures destabilization by high-n ballooning modes.

Simulation shows pressure and density collapse with magnetic stochastization.

Core shift to low-n modes observed after non-linear coupling.

Abstract

A new three-dimensional, non-linear Magnetohydrodynamics (MHD) model has been extended in MIPS code, incorporating parallel heat diffusivity. The model has been benchmarked against the former MHD model used in MIPS code. A preliminary study of the core density collapse event (CDC) observed in the Large Helical Device (LHD) plasma has been performed using the developed model. The equilibrium has been constructed using HINT code for a typical super dense core discharge in LHD, with vacuum magnetic axis configuration RaxV = 3.85 m and magnetic axis beta \beta0 = 4% plasma. This configuration corresponds to a plasma with a steep pressure gradient and strong Shafranov shift, which makes the plasma potentially unstable in the LHD. The model shows preliminary characteristics of the CDC event. The plasma is destabilized by high-n ballooning modes in the low-field side region during the linear regime, eventually leading to the collapse of the pressure and density profiles, together with the stochastization of the magnetic field and a shift to low-n modes centered at the core of the plasma after the non-linear coupling at the relaxation regime.