Results from the HIT-II coaxial helicity injection spherical tokamak

Summary form only given. The Helicity Injection Tokamak (HIT) has been upgraded to the "HIT-II" configuration. HIT-II extends coaxial helicity injection (CHI) to time scales longer than the wall resistive diffusion time. Previous results on HIT include production and sustainment of up to 250 kA of toroidal plasma current by CHI, without a transformer. HIT-II has approximately the same shape as HIT; major radius R=0.3 m, minor radius a=0.2 m with an co-axis toroidal field of up to 0.67 T. The 1 cm copper shell of HIT is replaced in HIT-II by a 6 mm stainless steel shell. Equilibrium fields are provided by 28 feedback controlled poloidal fields coils. These coils also provide programmable control of the magnetic flux boundary conditions for CHI current drive and are capable of 100 mWb of transformer flux swing. HIT-II has a graphite inner electrode and uses boronization and helium discharge cleaning for wall conditioning.