The New Pegasus-III Experiment

Minimizing or eliminating 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 and RF wave injection offer the potential to simplify large-scale devices by reducing the requirements of the solenoid. The Pegasus-III Experiment is a new solenoid-free ST (A > 1.22, I_p < 0.3 MA, B_T < 0.6 T, pulse length ~ 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, sustained and transient coaxial helicity injection (CHI) systems, and a 28 GHz RF system for electron Bernstein wave and electron cyclotron heating. Initial experiments will establish high-I_p LHI scenarios, followed by deployment and tests of transient CHI, modest sustained CHI and low-power RF studies. Pegasus-III will provide key enabling fusion power plant relevant technology to directly test proposed plasma startup and ramp-up scenarios envisioned for larger scale ST devices and investigate methods to synergistically improve the target plasma for consequent bootstrap and NBI current sustainment.