Recent results from the HIT-SI spheromak

Summary form only given. The Helicity Injected Torus (HIT-SI) is a "bow tie" spheromak formed and sustained by steady inductive helicity injection (SIHI) current drive. SIHI is implemented via two "helicity injectors". Each injector acts as a 180-degree segment of a reversed-field pinch (RFP), with a typical peak current of 11 kA and a peak flux of 0.5 mWb. The toroidal loop voltage, toroidal injector plasma current, and toroidal flux of a single injector all oscillate sinusoidally at a frequency of 5 kHz and nearly in phase, so the single injector helicity injection rate and power input to the plasma are always positive. Operating the two injectors 90/spl deg/ out of phase in time provides nearly constant power input and helicity injection rate. To date, plasmas have been sustained in this manner for over 5 ms. An internal magnetic probe array has been installed in one of the injectors. Observations of the injector fields are presented, illustrating the evolution of the field structure through the injector cycle.