The effect of shaping on turbulent dynamics in RFP simulations

TL;DR

This study investigates how the shape of the plasma container influences the turbulent dynamics in Reversed Field Pinch simulations, revealing shape-dependent mode excitation and flow characteristics that impact device performance.

Contribution

It provides the first detailed numerical analysis of how elliptical and circular geometries affect plasma turbulence and magnetic modes in RFP configurations.

Findings

Elliptical shapes excite different magnetic and dynamic modes.

Circular cross-section exhibits significant local poloidal angular momentum.

Pressure gradient fluctuations remain constant despite changes in Lundquist number.

Abstract

We study the influence of the shape of the plasma container on the dynamics of the Reversed Field Pinch (RFP). The geometries we consider are periodic cylinders with elliptical and circular-shaped cross-sections. Numerical simulations of fully nonlinear visco-resistive magnetohydrodynamics are carried out to illustrate how the plasma dynamics are affected by shaping. It is shown that independent of the plasma shape, the quantity $\beta$, comparing the hydrodynamic pressure to the magnetic pressure, decreases for increasing values of the Lundquist number, but the pressure gradient fluctuations remain roughly constant, when compared to the Lorentz force. Different elliptical shapes of the cross-section of the domain lead to the excitation of different toroidal (or axial) magnetic and dynamic modes. Furthermore, it is found that in a geometry with circular cross-section a significant local poloidal angular momentum is observed, absent in the geometries with elliptical cross-section. Since the confinement is dominantly determined by plasma movement, and the dynamics of the velocity and magnetic field are modified by the modification of the geometry, shaping can thus affect the performance of RFP-devices.