Start-up and formation of ST plasmas by ECH on the LATE device

Experiments on start-up and formation of spherical tokamak (ST) plasmas by electron cyclotron heating (ECH) alone without ohmic heating (OH) have been performed in the LATE (Low Aspect ratio Torus Experiment) device. By injecting a 2 GHz/0.1 s microwave pulse at the power range of 20 - 50 kW and increasing the vertical field with time, the plasma current increases up to 5 kA. The magnetic measurements show that closed flux surfaces are formed and the outer most one has the aspect ratio A ∼ 1.4 and the elongation κ ∼ 1.2. The electron density is higher than the plasma cutoff density, suggesting that ECH by mode converted electron Bernstein waves (EBW) occurs. (author)