Taylor State Merging at SSX: Experiment and Simulation

Michael Brown,Kaitlin Gelber,Matiwos Mebratu

doi:10.3390/plasma3010004

Abstract

We describe experiments and simulations of dynamical merging with two Taylor state plasmas in a Swarthmore Spheromak Experiment (SSX) device. Taylor states are formed by magnetized plasma guns at opposite ends of the device. We performed experiments with Taylor states of both senses of magnetic helicity (right-handed twist or left-handed twist). We present results of both counter-helicity merging (one side left-handed, the other right-handed) and co-helicity merging (both sides left-handed). Experiments show significant ion heating, consistent with magnetic reconnection. We suggest that the merged, warm state could be a suitable target for future magneto-inertial fusion experiments. Magnetohydrodynamic simulations of these experiments reveal the structure of the final relaxed, merged state.

Highlights

A Taylor state [1,2] is the term for a relaxed magnetic plasma structure with a large aspect ratio (`/R 1)
If reconnection occurs at the midplane, we might expect the newly merged structure to retain the original twist of the two Taylor state plasmas in the case of co-helicity merging
Merging of Taylor states is considerably more complex than earlier experiments performed at Swarthmore Spheromak Experiment (SSX) with axisymmetric spheromaks [17,29]

Summary

Introduction

A Taylor state [1,2] is the term for a relaxed magnetic plasma structure with a large aspect ratio (`/R 1). It is the minimum energy state of magnetized plasma. The key benefit of Taylor states is that they are stable; they have already undergone the instabilities that plague other configurations. Taylor states were first studied in the SSX device at Swarthmore [3,4]. We have since accelerated and compressed Taylor state plasmas while measuring local proton temperature Ti , plasma density ne , and magnetic field B. A particular equation of state (EOS) was identified in these experiments [5,6,7]

Methods

Results

Conclusion