The plasma current start-up experiment is conducted through electron cyclotron (EC) heating in the QUEST spherical tokamak. During the EC heating, the application of a toroidal electric field in the opposite direction to the plasma current effectively inhibits the growth of energetic electrons. Observations show rapid increases in plasma current and hard x-ray count immediately following the cancellation of the retarding electric field. When a compact tokamak configuration maintains equilibrium on the high field side, along with the retarding field, it leads to effective bulk electron heating. This heating achieved an electron temperature of Te ≈ 1 keV at electron density ne > 1.0 × 1018 m−3. Ray tracing of the EC wave verifies that more power absorption into plasma through a single-pass occurs around the second resonance layer with higher values of electron density and temperature.
This paper describes how the researchers used electron cyclotron (EC) heating to start up the plasma current in the QUEST spherical tokamak. They applied a retarding electric field during the EC heating, which inhibited the growth of energetic electrons. After cancelling the retarding field, they observed rapid increases in plasma current and hard x-ray count, achieving an electron temperature of 1 keV at a density over 1e18 m-3.