Unlocking the Continuum from Low-safety-factor Tokamak to RFP via Refined Inductive Control

Toroidal equilibria that have low- and ultra-low edge safety factors, i.e., q(a) < 2 and < 1, respectively, remain mostly unexplored given the relatively poor confinement and disruption events that appear in these regimes. In the Madison Symmetric Torus (MST), new programmable power supplies provide robust access to the span of safety factors from tokamak to RFP. A combination of MST's 5-cm-thick close-fitting conducting shell and the power supplies' high-bandwidth, high-voltage-capable feedback control enables operation in low-q(a), high-resistivity plasmas with infrequent disruption events. The power supplies' flexible control of the loop voltages and currents allows for the investigation of novel schemes for plasma start-up and inductive current drive for fusion-grade performance. Rigid flat-top, oscillating-current, and ramped-current waveforms are shown, demonstrating robust operation as the plasma resistance varies by a factor of ten. Examples illustrating the breadth of achievable safety factors, implications for confinement and current relaxation, and non-inductive sustainment are presented.