Non-Inductive Startup Via a Plasma Gun DC Helicity Source on the Pegasus Experiment

Developing a non-inductive startup technique is important for the ultralow-A Pegasus ST experiment, and the ST concept in general. Two low impurity, high I ($\sim $1 kA) plasma guns have been installed in the lower divertor region of Pegasus to test toroidal current drive via DC helicity injection during plasma startup. Aided by a high magnetic stacking factor, the dual gun array provides a toroidal current of 15-20 kA. A transition from discrete helical current streams to a uniform reconnected plasma is observed, with a doubling of the net toroidal current. Relaxation to a tokamak-like plasma state was not observed at this low current, but is expected as the net current is raised to provide a poloidal field greater than the vacuum vertical field. Experimental attempts to attain a relaxed tokamak-like configuration are concentrating on optimizing a 2-3 gun assembly at very low field strengths. Design requirements are presented for a 12 gun array to be installed in Pegasus next year, which is projected to provide I$_{p} \quad >$ 0.1 MA.