MHD simulations of inductive helicity injection in HIT-SIU using realistic low-impedance circuit boundary conditions

Due to the complexity of current drive mechanisms in inductive helicity injection, numerical simulations are vital to understanding present results and extrapolating to future devices. Numerical simulations of the HIT-SI(3) experiments using Hall-MHD models in the NIMROD and PSI-Tet [1] codes have produced good agreement with experimental observations. However, differences remain in several important quantities (eg. mean current and magnetic profiles). Prior simulations used a “high-impedance” boundary condition for some circuits in contrast to their experimental properties. This difference is important as significant feedback between plasma dynamics and driven circuit waveforms is observed, with increased coupling present in the newly commissioned HIT-SIU experiment. Improvements to the injector boundary conditions have been developed to enable “low-impedance” boundary conditions for all injector coils to provide a more complete circuit-to-plasma model. Development of this model and results from simulations of HIT-SI3 and HIT-SIU will be presented, focusing on experimental comparison and validation.

1- C. Hansen et al. Phys. Plasmas 22, 042505 (2015)