Steady Inductive Helicity Injected Torus (HIT-SI, HIT-SI3)
The Helicity Injected Torus (HIT) program investigates helicity injection current drive in magnetized toroidal plasmas of interest to controlled nuclear fusion. The HIT-SI experiment utilizes Steady Inductive (SI) helicity injection to form and sustain a spheromak equilibrium. Steady inductive helicity injection is an inductive current drive method that injects helicity at a nearly constant rate, without open field lines, and without removing any helicity or magnetic energy from the plasma. The HIT-SI device includes the two non-axisymmetric injectors with a time varying toroidal flux and induced loop voltage. The upgraded HIT-SI3 device features three injectors on the same side of the spheromak volume. The injectors yield a constant rate of overall helicity injection with all applied power delivered into the plasma, rather than to the plasma facing surfaces. The lack of electrodes or other strong plasma-wall interactions make HIT-SI/HIT-SI3 an ideal platform for clean studies of helicity injection current drive and current-profile relaxation.