Start-Up of Spherical Torus by ECH without Central Solenoid in the LATE Device

Abstract

Spherical torus plasma is started-up by electron cyclotron heating alone without Ohmic heating in the LATE (Low Aspect ratio Torus Experiment) device. By injecting a 2.45 GHz microwave pulse up to 10 kW for 4 seconds, a plasma current is initiated and ramped up to I_p≈4 kA by adjusting the external vertical field for the equilibrium of the plasma loop. Magnetic measurements show that the last closed flux surface has an aspect ratio of A˜1.4 and an elongation of κ˜1.3. The line-averaged electron density is 1.3×10¹¹ cm^-3 which is almost twice the plasma cutoff density, suggesting that electron cyclotron heating by mode-converted electron Bernstein waves may take place.