Numerical study and optimization of the formation and sustainment of a coaxial helicity injection spheromak

Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization during the formation, sustainment, and relaxation of a spheromak with coaxial helicity injection. The formation process is largely insensitive to the local current distribution in the annular current...

Full description

Saved in:
Bibliographic Details
Published in:Physics of plasmas 2018-11, Vol.25 (11)
Main Authors: O'Bryan, J. B., Romero-Talamás, C. A., Woodruff, S.
Format: Article
Language:English
Subjects:
Bias
Current distribution
Helicity
Injectors
Local current
Numerical analysis
Plasma physics
Poloidal flux
Robustness (mathematics)
Spheromaks
Stability
Citations: Items that this one cites
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization during the formation, sustainment, and relaxation of a spheromak with coaxial helicity injection. The formation process is largely insensitive to the local current distribution in the annular current column and details of the injector current trace, instead depending on the peak injected current (specifically λinj/λeig) and the bias flux Ψbias. The injected flux Φinj needed to trigger the column mode instability, the resulting local poloidal flux amplification AΨ, the amount of injected energy retained in the plasma as magnetic energy ηM, and the magnetic helicity per unit of injected energy ηK all scale with λinj/λeig. Both Φinj and ηK scale with the bias flux Ψbias, and ηM and ηK scale inversely with the pre-fill density. Sustained relaxation occurs when the injector current is maintained between two threshold values, 0.8 
ISSN:1070-664X
1089-7674
DOI:10.1063/1.5043299