Characterization of T$_{\mathrm{e}}$ and n$_{\mathrm{e\thinspace }}$Profiles of Discharges Driven Purely by Helicity Injection in the \textsc{Pegasus} Toroidal Experiment

Understanding the electron confinement and transport in plasmas driven purely by local helicity injection (LHI) is critical to the demonstration of high-performance discharges. Given the proper operating conditions, purely LHI-driven discharges can feature peaked $T_{e}$ profiles with $T_{e,0}\sim 150$ eV. Ohmic discharges in \textsc{Pegasus} at the same field level, $B_{T}\sim 0.15$ T exhibit similar $T_{e}$ profiles albeit with higher $n_{e}$. At lower levels of $B_{T}$, LHI discharges feature hollow $T_{e}$ profiles that increase in \textless $T_{e}$\textgreater $\thinspace $ as the effective loop voltage, $V_{LHI}$, is increased. The increase in \textless $T_{e}$\textgreater $\thinspace $ scales with $V_{LHI}$ rather than the injector electrode voltage, $V_{inj}$, contrary to predictions from open field line theory. The hollowing of the $T_{e}$ profile is hypothesized to be a combination of low $\eta j^{2}$ heating power due to the hollow current profile and low-Z impurity radiation losses. Approximations of $Z_{eff}$ in LHI discharges from voltage balance assuming purely Spitzer and neoclassical resistivity are $\sim 3$ and $\sim 1$, respectively. Thomson scattering and magnetic probe measurements indicate a pressure-free region between the kinetic and magnetic boundaries, possibly indicative of separate Ohmic and stochastic confinement regions. Overall scaling of $I_{p}$ with $V_{LHI\thinspace }$ appears to be consistent with linear Ohmic confinement scaling assuming auxiliary ion and electron heating from magnetic reconnection.