Inductively driven helicity injection with non-axisymmetric perturbation control*

The HIT-SI (2005-2013), HIT-SI3 (2013-2021), and HIT-SIU (2021-present) devices use sets of inductively driven helicity injectors to form and sustain spheromak plasma equilibria.  Each injector is a semi-toroid connected to the main confinement volume and is operated by two sets of coils oscillating in phase to inductively inject magnetic energy and helicity.  The HIT-SIU device additionally features a toroidal geometry connecting the four injectors to provide additional control over operation.  The toroidal spectrum of the imposed perturbation depends primarily on the geometry of the helicity injectors and the relative temporal phase of the helicity injection waveforms, with a variety of spectra involving n=1, n=2, and n=3 perturbations [1].  Experimental results from the three injector configurations are compared with Taylor state equilibria (PSI-Tet) and dynamic extended MHD models (NIMROD) of the plasma.

[1] Morgan et al, Physics of Plasmas. 92, 052305 (2022)