Evidence for Separatrix Formation and Sustainment with Steady Inductive Helicity Injection

The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI) has achieved a breakthrough in the development of a new, more efficient current drive method for magnetic confinement fusion. Results include the first sustainment of toroidal plasma current of over 50 kA at 3 times the injected currents added in quadrature, the ratio of current density to electron density exceeding $10^{-14}$ A$\cdot$m, and toroidal current persistence of 0.6 ms after injector shut off. Separatrix toroidal currents--currents not linking the helicity injectors--are sustained at up to 40 kA. Results are achieved in HIT-SI during deuterium operations immediately after helium operations. Toroidal mode measurements for these high performance deuterium shots have a three stage evolution: initial growth of an n=1 eigenstate, rapid transition to a weak toroidal current and toroidal current growth coupled to a decrease in the n=1 activity with near constant helicity injection.