Overview of the Helicity Injected Torus Program

The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI) spheromak experiment [Jarboe, Fus.Tech., v.36, p.85 (1999)] addresses critical research areas for spheromak formation and sustainment, including current drive, high-beta operation, confinement quality, and efficient steady-state operation. HIT-SI has a ``bow-tie'' shaped, axisymmetric confinement region with a major radius of 0.33 m, and an axial extent of 0.57 m. Attached to the confinement region are two half-torus helicity injectors, one mounted on each end of the flux conserver. HIT-SI has produced up to 30 kA of toroidal current in spheromaks generated using less than 4 MW of applied power, demonstrating that Steady Inductive Helicity Injection can create and sustain discharges with modest power requirements. HIT-SI has recently been repaired and upgraded, with an improved flux conserver, higher helicity and power injection, better diagnostic coverage, and an improved plasma-facing insulating surface. HIT-SI operational and diagnostic improvements, and corresponding physics studies, will be summarized.