Results from a Three-Model Frequency Scan of HIT-SI3 in NIMROD

The Helicity Injected Torus – Steady Inductive 3 (HIT-SI3) was a spheromak experiment that used three AC transformer and solenoid pairs, known as helicity injectors, to form and sustain a spheromak with DC toroidal current in a process known as Steady Inductive Helicity Injection (SIHI). Changing the injector frequency and temporal phasing between injectors changes the toroidal Fourier spectrum of the applied perturbations, which may have substantial effects on the sustained spheromaks. To examine the effects of different injector frequencies without extensive experimental campaigns, the NIMROD xMHD code is used to run simulations with constant, single and two-temperature models at a range of injector frequencies from 5 to 75 kHz, with the injector fields modeled as boundary conditions on tangential electric and normal magnetic fields at the injector locations. In particular, the presence of plasma-generated n=2 at each injector frequency will be examined, along with effects of temperature and density. Results from a new multichord interferometer brought online in 2021 will be compared to applicable shots from the simulations. Trends HIT-SI3 simulations, and the prior HIT-SI device, will be reviewed and compared to determine trends for SIHI-driven spheromak devices.