First results from plasma edge biasing on SPECTOR

TL;DR

This paper reports initial findings from plasma edge biasing on SPECTOR, showing increased electron temperature and CT lifetime, decreased density, and the effects of a transport barrier on fueling.

Contribution

It presents the first experimental results of plasma edge biasing on SPECTOR, demonstrating significant impacts on plasma parameters and fueling behavior.

Findings

Electron temperature increased by up to 2.4 times.

CT lifetime extended by up to 2.3 times.

Electron density decreased due to transport barrier effects.

Abstract

A description of an edge-biasing experiment conducted on the SPECTOR (Spherical Compact Toroid) plasma injector is presented, along with initial results. The insertion of a disc-shaped molybdenum electrode (probe), biased at up to +100V, into the edge of the CT (Compact Torus), resulted in up to 1kA radial current being drawn. Core electron temperature, as measured with a Thomson-scattering diagnostic, was found to increase by a factor of up to 2.4 in the optimal configuration tested. H_alpha intensity was observed to decrease, and CT lifetimes increased by a factor of up to 2.3. A significant reduction in electron density was observed; this is thought to be due to the effect of a transport barrier impeding CT fueling, where, as verified by MHD simulation, the fueling source is neutral gas that remains concentrated around the gas valves after CT formation.