Formation of ST Plasmas by ECH on LATE

摘要

Experiments on formation of spherical tokamak (ST) plasmas by electron cyclotron heating (ECH) alone without a central OH solenoid have been carried out on LATE (Low Aspect ratio Torus Experiments). By injecting a 2.45 GHz microwave pulse of 6.3 kW for 4 seconds, a plasma current is initiated and ramped up to Ip≌3 kA, and finally maintained for 1 second by adjusting the external vertical field. Magnetic measurements show that closed flux surfaces are formed and the last closed flux surface has an aspect ratio of A∽1.3 and an elongation ofκ∽1.3.The electron density measured by an interferometer is more than 1.5×10^11cm^-3 which exceeds twice of the plasma cut-off density, suggesting that electron cyclotron heating by mode-converted electron Bernstein waves may take place.