Three-dimensional magnetohydrodynamics simulations of counter-helicity spheromak merging in the Swarthmore Spheromak Experiment

Journal Article · Tue Nov 15 04:00:00 EST 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3660533· OSTI ID:22047074

Myers, C E; Belova, E V ^[1]; Brown, M R; Gray, T; Cothran, C D ^[2]; Schaffer, M J ^[3]

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1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
2. Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081 (United States)
3. General Atomics, San Diego, California 92186 (United States)

Recent counter-helicity spheromak merging experiments in the Swarthmore Spheromak Experiment (SSX) have produced a novel compact torus (CT) with unusual features. These include a persistent antisymmetric toroidal magnetic field profile and a slow, nonlinear emergence of the n = 1 tilt mode. Experimental measurements are inconclusive as to whether this unique CT is a fully merged field-reversed configuration (FRC) with strong toroidal field or a partially merged ''doublet CT'' configuration with both spheromak- and FRC-like characteristics. In this paper, the SSX merging process is studied in detail using three-dimensional resistive MHD simulations from the Hybrid Magnetohydrodynamics (HYM) code. These simulations show that merging plasmas in the SSX parameter regime only partially reconnect, leaving behind a doublet CT rather than an FRC. Through direct comparisons, we show that the magnetic structure in the simulations is highly consistent with the SSX experimental observations. We also find that the n = 1 tilt mode begins as a fast growing linear mode that evolves into a slower-growing nonlinear mode before being detected experimentally. A simulation parameter scan over resistivity, viscosity, and line-tying shows that these parameters can strongly affect the behavior of both the merging process and the tilt mode. In fact, merging in certain parameter regimes is found to produce a toroidal-field-free FRC rather than a doublet CT.

• OSTI ID: 22047074
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 11 Vol. 18; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
COMPARATIVE EVALUATIONS
COMPUTERIZED SIMULATION
FIELD-REVERSED THETA PINCH DEVICES
H CODES
HELICITY
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
NONLINEAR PROBLEMS
PLASMA
PLASMA SIMULATION
REVERSE-FIELD PINCH
REVERSED-FIELD PINCH DEVICES
SPHEROMAK DEVICES
THREE-DIMENSIONAL CALCULATIONS
VISCOSITY