Effects of Toroidally Distributed Divertor Biasing on Scrape-Off-Layer Plasma in the QUEST Spherical Tokamak

A novel divertor biasing using four plates that are arranged toroidally every 90◦ on the upper plate is applied to low-density plasmas of QUEST spherical tokamak. When some these biased in-phase by applying a sawtooth waveform voltage 85-V amplitude and 50-Hz repetition, up approximately 35% reduction particle flux observed during positive biasing. The input power for 0.2 kW tokamak produced ∼130-kW electron cyclotron wave injection. Additionally, signal probe placed in low-field side mid-plane vacuum vessel indicates enhanced losses fast electrons loss attributed small resonant magnetic perturbations bias-driven currents scrape-off layer. This expected provide new experimental tool studying heat load control confinement device.