First density profile measurements of high-performance plasmas in HIT-SI3 and progress on HIT-SIU*

The final run campaign of the HIT-SI3 experiment at the University of Washington produced discharges with record performance, including toroidal plasma current exceeding 100 kA and the first experimental observations of peaked plasma density profiles during sustainment as measured by a new multi-chord interferometer. Beginning in 2014, the HIT-SI3 program studied application of steady inductive helicity injection, using three independent injectors driven with frequencies in the 10’s of kHz, to form and sustain spheromak plasmas [1]. The recent results were enabled by switching power amplifier (SPA) and capacitor bank upgrades and improved control of the six driver circuits (two per injector), provided by a GPU-based feedback system [2]. Initial results from the new HIT-SIU experiment, which provides additional control over the applied mode spectrum and plasma density, will also be presented.

[1] A. Hossack et al., Nucl. Fusion 57, 076026 (2017)

[2] K. Morgan et al., Rev. Sci. Instrum. 92, 053530 (2021)