Magnetic Relaxation and Energy Transport in Reversed-Field Pinch (RFP) Computations

The role of pressure-gradient driven dynamics in magnetic relaxation and global thermal transport of RFPs is studied with nonlinear 3D MHD computations. It is well known that average magnetic curvature in RFPs is unfavorable, so pressure can contribute to both tearing and interchange dynamics. Several non-linear computations have been performed with the NIMROD code to span the parameter space from low to high current density. High current, low beta cases produce a tearing dominant reversed final state that resembles RFPs. Linear stability analysis of equilibrium profiles extracted from the saturated states of these computations is being applied to understand the balance of drives for different modes. Initial results show that the highest energy, low-n tearing modes may be both pressure-driven and current-driven. Also, thermal transport from second-order correlations of parallel heat flux density with magnetic fluctuations is dominated by thermal conduction, as expected. However, higher-order correlation terms significantly reduce the contribution of parallel thermal conduction in the net global thermal transport. Further analysis of linear stability and thermal transport constitutes ongoing work to better characterize the effects of pressure in RFP dynamics.