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 potentially simplifies the cost and complexity of reactor-class devices by reducing the technical requirements of, or the need for, a central solenoid. The PEGASUS-III Experiment is a new solenoid-free, low aspect ratio 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.  It is 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 an RF system for initial electron Bernstein wave (EBW) and electron cyclotron (EC) heating. Initial experiments will establish high-I_p LHI scenarios, followed by deployment of transient CHI, modest sustained CHI, and low-power RF studies. PEGASUS-III will provide key enabling reactor relevant technology to directly test proposed plasma startup, ramp-up scenarios envisioned for larger scale STs, investigating methods to synergistically improve the target plasma for consequent bootstrap and NBI current sustainment.