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Title: Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment

Abstract

Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization during multi-pulse coaxial helicity injection in the Sustained Spheromak Physics eXperiment. We describe multiple distinct phases of spheromak evolution, starting from vacuum magnetic fields and the formation of the initial magnetic flux bubble through multiple refluxing pulses and the eventual onset of the column mode instability. Experimental and computational magnetic diagnostics agree on the onset of the column mode instability, which first occurs during the second refluxing pulse of the simulated discharge. Our computations also reproduce the injector voltage traces, despite only specifying the injector current and not explicitly modeling the external capacitor bank circuit. Furthermore, the computations demonstrate that global magnetic evolution is fairly robust to different transport models and, therefore, that a single fluid-temperature model is sufficient for a broader, qualitative assessment of spheromak performance. Although discharges with similar traces of normalized injector current produce similar global spheromak evolution, details of the current distribution during the column mode instability impact the relative degree of poloidal flux amplification and magnetic helicity content.

Authors:
 [1]; ORCiD logo [2];  [3]
  1. Univ. of Maryland, Baltimore County, MD (United States). Dept. of Mechanical Engineering; Univ. of Washington, Seattle, WA (United States). Dept. of Aeronautics and Astronautics
  2. Univ. of Maryland, Baltimore County, MD (United States). Dept. of Mechanical Engineering
  3. Woodruff Scientific, Inc., Seattle, WA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1498097
Grant/Contract Number:  
AC52-07NA27344; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 3; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

O'Bryan, J. B., Romero-Talamás, C. A., and Woodruff, S. Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment. United States: N. p., 2018. Web. doi:10.1063/1.5018319.
O'Bryan, J. B., Romero-Talamás, C. A., & Woodruff, S. Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment. United States. doi:10.1063/1.5018319.
O'Bryan, J. B., Romero-Talamás, C. A., and Woodruff, S. Thu . "Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment". United States. doi:10.1063/1.5018319. https://www.osti.gov/servlets/purl/1498097.
@article{osti_1498097,
title = {Simulation of multi-pulse coaxial helicity injection in the Sustained Spheromak Physics Experiment},
author = {O'Bryan, J. B. and Romero-Talamás, C. A. and Woodruff, S.},
abstractNote = {Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization during multi-pulse coaxial helicity injection in the Sustained Spheromak Physics eXperiment. We describe multiple distinct phases of spheromak evolution, starting from vacuum magnetic fields and the formation of the initial magnetic flux bubble through multiple refluxing pulses and the eventual onset of the column mode instability. Experimental and computational magnetic diagnostics agree on the onset of the column mode instability, which first occurs during the second refluxing pulse of the simulated discharge. Our computations also reproduce the injector voltage traces, despite only specifying the injector current and not explicitly modeling the external capacitor bank circuit. Furthermore, the computations demonstrate that global magnetic evolution is fairly robust to different transport models and, therefore, that a single fluid-temperature model is sufficient for a broader, qualitative assessment of spheromak performance. Although discharges with similar traces of normalized injector current produce similar global spheromak evolution, details of the current distribution during the column mode instability impact the relative degree of poloidal flux amplification and magnetic helicity content.},
doi = {10.1063/1.5018319},
journal = {Physics of Plasmas},
number = 3,
volume = 25,
place = {United States},
year = {2018},
month = {3}
}

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Figures / Tables:

Figure 1 Figure 1: Our computations start from vacuum magnetic fields corresponding to specific experimental discharges in the SSPX spheromak. Color contours show the poloidal magnetic flux profile in units of mWb consistent with SSPX shot #19719, i.e., 40 mWb of nominal magnetic flux in the modified flux (MF) configuration. Black contourmore » lines are shown at equally spaced contour levels to highlight the flux profile shape in the injector region.« less

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