Resistive MHD Modelling of Quasi-Single Helicity State in the KTX Regimes

Abstract

The potential formation of the quasi-single-helicity (QSH) state in the Keda Torus eXperiment (KTX) is investigated in resistive MHD simulations using the NIMROD code. We focus on the effects of finite resistivity on the mode structure and characteristics of the dominant linear and nonlinear resistive tearing-mode in a finite $β$, cylindrical configuration of reversed field pinch model for KTX. In the typical resistive regimes of KTX where Lundquist number $S=5 \times 10^4$, the plasma transitions to a steady QSH state after evolving through an initial transient phase with multiple helicities. The dominant mode of the QSH state develops from the dominant linear tearing mode instability. In lower $β$ regime, the QSH state are intermittent and short in duration; in higher $β$ regime, the QSH state persists for a longer time and should be more observable in experiment.

The manuscript confirms that the MHD dynamics of RFP quasi-single helical states is based on the resistive-kink tearing modes, shows the spontaneous emergence of a QSH state during the RFP dynamics and studies the effect of a finite pressure on the system. The authors find that higher plasma pressure increases the persistence of QSH states