Author: John B O'Bryan
Requested Type: Poster
Submitted: 2016-02-15 19:42:02
Co-authors: C.A. Romero-Talamás, S. Woodruff
University of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250
Nonlinear, extended-MHD computation with the NIMROD code is used to explore spheromak formation and sustainment with multi-pulse coaxial helicity injection (CHI). The goal of this research is to find candidate modes of operation for future experimental studies by optimizing spheromak performance, particularly with respect to plasma temperature, lifetime, and poloidal flux amplification. We validate the numerical model by simulating multiple specific shots from the Sustained Spheromak Physics eXperiment (SSPX) and make direct quantitative comparisons between experimental and synthetic diagnostics. We are exploring a wide range of drive parameters, as even modest gains in poloidal flux amplification during the column mode have produced significant improvements to spheromak performance. Preliminary results show that the column mode instability produces poloidal flux amplification much more efficiently than that produced by subsequent current-driven instability. Both the threshold (in volt-seconds) for the onset of the column mode instability and the degree of poloidal amplification increase with peak injected current. Thermal confinement is very sensitive to the rate at which the injector current decreases after the column mode instability. Overall, our preliminary results suggest that more precise control of the injector drive allows for significant gains in spheromak performance without significantly affecting power demand.
This work is supported by DAPRA under grant no. N66001-14-1-4044.