Model validation and numerical investigation of inductive helicity injection drivers for spheromak formation and sustainment

Numerical investigation of inductive helicity injection drivers, as developed on the HIT-SI family of experiments at the University of Washington, is underway with a focus on developing validated models of relevant driver physics to support exploration and optimization of possible injector configurations for sustainment of spheromak plasmas. Two extended MHD codes are being used: NIMROD [1], where the injectors are approximated through boundary conditions on an axisymmetric domain, and PSI-Tet [2], where the full multiply-connected plasma volume is simulated. Simulations will be benchmarked against experimental data from the HIT-SI (two injectors), HIT-SI3 (three injectors), and the future HIT-SIU (four mouth injector manifold) devices. Validated physical models will then be used to explore possible injector configurations to determine the effect of toroidal/poloidal mode content, frequency, phasing, and other parameters on resulting sustained spheromak equilibria.\\ {[1]} K. Morgan et al. Phys. of Plasmas 24, 122510 (2017)\\ {[2]} C. Hansen et al. Phys. of Plasmas 22, 042505 (2015)