Heated and Lithium-coated Marshall Gun CHI performance on SLiC Spherical Tokamak

The SLiC device produces small scale (R=12 cm, a = 7cm) spherical tokamak plasmas using fast Coaxial Helicity Injection (CHI) with external formation current (500 kA peak) applied for a duration of 50 ms followed by Ohmic decay of internal plasma currents (up to 350 kA peak) over a lifetime of 1.5 ms. The small volume/surface-area ratio of SLiC makes plasma lifetime very sensitive to wall conditions and works well as a testbed for studying liquid Li as a plasma facing surface. We have recently added 4 new lithium input ports to the Marshall gun section and increased the heating capacity to enable plasma formation with the gun up to 250 C and with a liquid Li layer on the center and outer electrodes. These conditions are similar to what would occur in the Marshall gun of our CHI-formed Magnetized Target Fusion reactor concepts. Traditionally, most experiments with Marshall guns do not operate at sustained elevated temperatures because of the technical complications that adds, with SLiC being the first to also operate with liquid Li on the high-current electrode surfaces. Preliminary results to date show no decrease in performance when running with gun electrodes that are wetted with liquid Li. Latest results will be shown along with a summary of efforts to control Li surface quality in situ, implementation of plasma diagnostics in a lithium-vapor environment, and simulations of free surface motion of liquid Li in the SLiC system performed with in-house MHD solver