Modeling of Formation of Helical Structures in Reversed-Field Pinch

Abstract

Nonlinear three-dimensional magnetohydrodynamic(MHD) simulations were applied to a reversed-field pinch(RFP) plasma to reveal the physical mechanism of the formation of helical structures such as the so-called quasi-single helicity and single helical axis states. The simulations were executed using the MHD Infrastructure for Plasma Simulation (MIPS) code in a realistic experimental geometry of the REversed field pinch of Low-Aspect ratio eXperiment (RELAX) device with reconstructed initial equilibria calculated by the RELAXFit code. Long-term evolutions showed remarkable formation of n = 4 structures as a result of the dominant growth of resistive modes. The resultant relaxed helical state consists of a bean-shaped, hollow pressure profile in the poloidal cross section for both the cases of resonant and non-resonant triggering instabilities.

First Experimental Monitoring of the Three-Dimensional Structure of Toroidal Plasmas Using Multiple Soft X-Ray Imaging Techniques

“…The toroidal mode number n may be four. Previous research using nonlinear MHD simulations indicated that the plasma would deform into helical structures with (m, n) = (1, −4) [9], which is consistent with the magnetic field measurements. While more detailed investigations are required, the obtained profiles show periodicity, which may be correlated to magnetic field fluctuations.…”

The effect of toroidicity on reversed field pinch dynamics

“…Ideal MHD equilibrium solvers allow the reproduction of QSH equilibria [26], but need experimental input such as the position of the helical axis, pressure profile and safetyfactor profile. Three-dimensional codes solving the MHD equations in toroidal geometries without a priori definition of pressure and safety-factor profiles exist, [24,27,28] but there is not yet, to our knowledge, a study which systematically investigates the influence of curvature on the dynamics of a toroidal magnetofluid in the RFP context. This motivates the present study which compares, using exactly the same numerical code and governing equations, the dynamics of a viscoresistive magnetofluid in a toroidal domain to those in a cylindrical domain.…”

Effect of shaping on turbulent dynamics in reversed-field pinch simulations

“…Indeed, in some recent RFP investigations, the pressure is retained (Mizuguchi et al. 2012) and recently we focused on the importance of the pressure dynamics (Chahine & Bos 2018). In particular, we illustrated in MHD simulations in cylindrical geometry that, to understand the dynamics of the plasma, the important quantity to monitor is not the pressure but its gradient.…”