The New Pegasus-III Experiment and Plans for RF Heating and Current Drive

Solenoid-free startup techniques such as helicity injection (HI) and radiofrequency (RF) wave injection offer the potential to simplify the cost and complexity of reactor-class devices by reducing the technical requirements of, or possibly the need for, a central solenoid. \textsc{P}\textsc{egasus}-III is the next generation of the \textsc{Pegasus} experiments, with increased $B_{T}$ to 0.6 T and extended pulse duration (\textless 100 ms). It is a solenoid-free, low aspect ratio ST that will serve as a dedicated US platform for comparative non-solenoidal tokamak startup studies. It will be equipped with a new local helicity injection (LHI) system capable of $I_{p}<0.3$ MA, a coaxial helicity injection (CHI) system, and an 8 GHz klystron-based system for sustained electron Bernstein wave (EBW) heating and current drive. While the RF system will be initially employed for heating HI-initiated plasmas, EBW modeling indicates that up to 50 kA of current can be driven near $\rho \sim 0.3$ near the fundamental EC resonance. RF on \textsc{P}\textsc{egasus}-III will provide a key enabling reactor relevant technology to directly test proposed plasma startup and ramp-up scenarios envisioned for NSTX-U, investigating methods to synergistically improve the target plasma for consequent bootstrap and NBI current sustainment.