Observation of persistent edge current driven by coaxial helicity Injection

Coaxial Helicity Injection (CHI) has been used on the National Spherical Torus Experiment [Ono et al., Nucl. Fusion 40, 557 (2000)], the Helicity Injected Torus (HIT) [Nelson et al., Phys. Rev. Lett. 72, 3666 (1994)] and HIT-II [Jarboe et al., Phys. Plasmas 5, 1807 (1998)] to initiate plasma and to drive up to 400 kA of toroidal current. On HIT-II, CHI initiated discharges have been successfully coupled to Ohmic sustainment [Raman et al., Phys. Plasmas 11, 2565 (2004)]. This paper presents the first results on the use of CHI to demonstrate the persistence of edge current drive in a pre-established single null diverted inductive discharge. Edge current drive has the potential to improve plasma stability limits [Menard et al., Nucl. Fusion 37, 595 (1997)]. While most current drive methods drive current in the interior of the plasma, CHI is well suited for driving current in the edge plasma