Preliminary experiments on the bias system with concentric electrodes in pilot GAMMA PDX-SC

In toroidal confinement systems, the scrape-off layer (SOL) magnetic field exhibits characteristics analogous to those of a magnetic mirror configuration, particularly in the edge plasma region. Therefore, linear plasma devices have advanced divertor simulation studies. To further promote divertor simulation studies, a new divertor simulator, ‘Pilot GAMMA PDX-SC (PGX-SC)’ has been developed, incorporating a pair of superconducting coils that generate a simple magnetic mirror configuration. An electrode-biasing system was installed on the PGX-SC to regulate the plasma potential. The system comprises three concentric basing plates installed at the east end of the main chamber of PGX-SC, in conjunction with a DC-stabilised power supplies for each basing plate. This system can also measure the floating potentials and electrode currents by connecting a resistor to each plate in the absence of an external power supply. Preliminary experiments were conducted to investigate the effect of plasma by applying a bias to the electrode plates. Applying a voltage to the inner electrode increased the plasma potential at the outer electrode. This result suggests the feasibility of controlling the peripheral plasma potential using concentric biasing plates. When voltage was applied to the outer electrode, the amplitude of the fluctuating current decreased. These results collectively indicate the capability of plasma control employing concentric biasing plates.