Initial Results from the New Pegasus-III Experiment

Reducing the need for induction from a central solenoid during startup, ramp-up and sustainment of a tokamak plasma is a critical challenge in magnetic fusion. Solenoid-free startup techniques such as helicity injection (HI) and radiofrequency (RF) wave injection offer the potential to simplify the cost and complexity of fusion energy systems by reducing the requirements of, or need for, a central solenoid. Pegasus-III is a new solenoid-free, extremely low aspect ratio ST (A > 1.2, I_p < 0.3 MA, B_T < 0.6 T, t ~ 100 ms) focused on studying innovative non-solenoidal tokamak startup techniques. Pegasus-III will be equipped with a new local helicity injection (LHI) system capable of I_p < 0.3 MA, coaxial helicity injection (CHI) system, and a 28 GHz gyrotron-based system for initial electron Bernstein wave and electron cyclotron heating. Initial experiments are establishing high- I_p LHI scenarios, followed by tests of CHI, and low-power RF studies. Pegasus-III will provide key enabling fusion power plant relevant technology to directly test proposed plasma startup, ramp-up scenarios envisioned for larger scale devices, investigating methods to synergistically improve the target plasma for consequent bootstrap and NBI current sustainment.