Design Considerations for the Implementation of a High-Field-Side Transient CHI System on QUEST

Transient coaxial helicity injection (T-CHI), a method first developed on the small injected torus (HIT-II) experiment and then validated much larger National Spherical Torus Experiment (NSTX) device, is to initiate an inductive-like tokamak plasma discharge without reliance central solenoid. A CHI initiated by driving current along magnetic flux that connects inner outer divertor plates one end of tokamak. To permit this, both HIT-II NSTX, toroidal ceramic insulators were used electrically separate vessel components. The use such large vacuum may not be easy implement in reactors. address this issue, Q-shu University experiments with steady-state spherical (ST) (QUEST) developing reactor-relevant configuration which insulated from rest vessel. application T-CHI QUEST biased electrode While discharges could easily generated, it was found as filled vessel, separation distance between injector footprints widened, condition favorable for generation closed surfaces. Biasing wall similar NSTX HIT-II, but initial testing has proved challenging. design described here overcomes present limitation locating closer coil using NSTX-like gas manifold enable high-field-side startup QUEST. concepts article should also benefit future implementation systems other tokamaks tokamaks.