Measuring the evolution of canonical vorticity vectors during RFP relaxation*

Recent theoretical work provides a picture of plasma relaxation as conversion between twisted magnetic flux tubes and twisted ion flow vorticity flux tubes, while conserving their total twist. We are developing a canonical vorticity probe to measure these fluxes simultaneously in a relaxing plasma, which has not been done previously. The probe will consist of clusters of B-dot and Mach probes, each measuring the local 3D vectors of magnetic field and ion flow. The 3D Mach vector is determined by a matrix inversion that includes the 3D angles of the tips. The clusters will be arranged in a finite difference stencil so that the curl of these vectors can be determined in the center. A prototype of a single cluster has been constructed [1] and is to be fielded on the Madison Symmetric Torus during sawtooth relaxation. Traditionally, plasma relaxation is described in terms of single fluid models as constrained by magnetic helicity alone. This work will help to generalize our understanding to a canonical-helicity-constrained relaxation explaining multi-scale dynamics.

[1] A. M. Sellner et al. Session 10.02 Undergraduate Research.