$V_{eff} $ Scaling of $T_{e} $ and $n_{e} $ Measurements During Local Helicity Injection on the Pegasus Toroidal Experiment

Understanding the electron confinement of local helicity injection (LHI) is critical in order to evaluate its scalability as a startup technique to MA-class devices. Electron confinement in the Pegasus Toroidal Experiment is investigated using multi-point Thomson scattering (TS). The Pegasus TS system utilizes a set of high-throughput transmission gratings and intensified CCDs to measure $T_{e} $ and $n_{e} $ profiles. Previous TS measurements indicated peaked $T_{e}_{\mathrm{\thinspace }}$profiles $\sim 120$ eV in outboard injector discharges characterized by strong inductive drive and low LHI drive. Injectors designed to have dominant non-inductive drive have recently been installed in the divertor region of Pegasus to understand the relationship between effective drive voltage, $V_{eff} $, and plasma performance. At low $V_{eff} $ and reduced plasma current, $I_{p} \sim 60$ kA, TS measurements reveal a flat $T_{e} $ profile $\sim 50$ eV, with a peaked $n_{e} $ profile $\sim 1\times 10^{19}$ m$^{\mathrm{-3}}$, resulting in a slightly peaked $p_{e} $ profile. As current drive is increased, the $T_{e} $ profiles become hollow with a core $T_{e} \sim 50$ eV and an edge $T_{e} \sim 120$--150 eV. These hollow profiles appear after the start of the $I_{p} $ flattop and are sustained until the discharge terminates. The $n_{e} $ profiles drop in magnitude to $<1\times 10^{19}$ m$^{\mathrm{-3}}$ but remain somewhat peaked. Initial results suggest a weak scaling between input power and core $T_{e} $. Additional studies are planned to identify the mechanisms behind the anomalous profile features.