A Theoretical Study of Electrostatic Potential in the SOL plasma and a Computational Model for NBI in LTX-β*

The Lithium Tokamak eXperiment (LTX) is a spherical tokamak device designed to study the effects of low recycling lithium plasma PFCs on tokamak confinement & equilibria. The lithium coated wall of LTX has been demonstrated to allow for a low density, high temperature, and hence low collisionality plasma edge. The low collisionality region extends into the scrape-off layer (SOL). With a high mirror ratio near the LCFS, the majority of particles in the SOL will be mirror-trapped, and will modify the physics of the SOL plasma. Here we present a theoretical study of the formation of ambipolar potential in the collisionless SOL via differential loss of the electrons and ions. Progress towards an analytical model and preliminary numerical results will be presented. 

The recent upgrade to LTX-β includes a 17 keV NBI system, which provides further fueling and heating of the plasma. A 3D computational model is implemented to study particle deposition and first orbit losses. Beam-particle penetration is simulated via a Monte Carlo model, with hot ion trajectories integrated with both full orbit and guiding center equations.