Slow Formation of Spherical Tokamak by ECH on LATE

Abstract

The main objective of LATE is to demonstrate the formation of Spherical Tokamak (ST) by electron cyclotron heating (ECH) alone without the center solenoid. In the last year, as a result of the extended microwave power from 10 to 30kW and introducing the vertical plasma position control system, the achievable plasma current has been raised substantially compared with the results reported previously(1). With a two-seconds pulse of 2.45GHz microwave power up to 30kW, a plasma current of 2.0kA have been spontaneously initiated under the steady vertical field, then ramped-up slowly to 7.2kA with a slow ramp-up of the vertical field strength (Bv) for the equilibrium of the plasma current loop. The Bv decay index is temporally-controlled during the discharge to successfully increase the plasma elongation with the aid of the active control of the vertical plasma position. This increase in elongation has lead to an effective increase in the plasma current. Magnetic analysis shows that an ST equilibrium, having the last closed flux surface with an aspect ratio of R0 / a = 20.5cm/14.8cm 1.4, an elongation of κ 1.6 and qedge 34, has been finally formed and maintained steady until the end of the microwave pulse.