Electron Temperature Evolution During Local Helicity Injection on the Pegasus Toroidal Experiment

Understanding the electron temperature ($T_{e} )$ evolution during local helicity injection (LHI) is critical for scaling up this non-solenoidal startup technique to MA-class devices. The first comprehensive $T_{e} $ measurements during LHI reveal centrally-peaked profiles with $T_{e} >100$ eV for plasma current $I_{p} >120$ kA, toroidal field $\sim 0.15$ T, and electron density $n_{e} \sim 10^{19}$ m$^{\mathrm{-3}}$. $T_{e} $ rises and is sustained from just after magnetic relaxation through the plasma decoupling from edge-localized injectors. Results are presented for two injector edge locations: outboard midplane and inboard divertor. Outboard midplane injection couples LHI with inductive drive from poloidal field ramps and radial compression during inward plasma growth. Comparisons of $T_{e} $ at different LHI-to-inductive drive ratios show some profile flattening for higher LHI drive fraction. The latter, constant-shape discharges were necessarily lower performance, with $I_{p} \sim 50$ kA and reduced $T_{e,max} $. Inboard divertor injection achieves higher $I_{p} $ using minimal inductive drive and thus isolates effects of LHI drive on $T_{e} $. Initial results in this configuration show $T_{e} $ rising rapidly at the injector location as the discharge grows, settling to a roughly flat profile $\sim 100$ eV. Thus far, both scenarios provide relatively stable discharges with moderate $n_{e} $ and high-$T_{e} $, suitable for coupling to auxiliary current drive. Detailed studies of confinement dynamics and discharge optimization are planned for the near future.