Abstract
An extremely overdense special Tokamak plasma has been non-inductively formed and maintained by electron Bernstein (EB) wave heating and current drive in the Low Aspect ratio Torus Experiment (LATE) device. The plasma current reaches 12 kA and the line-averaged electron density exceeds 7 times the plasma cut off density by injecting a 2.45 GHz microwave power of 60 kW. Such a highly overdense plasma is obtained when the upper hybrid resonance layer lies to the higher field side of the 2nd harmonic ECR layer, which may realize a good coupling to EB waves at their first propagation band. The effect of the injection polarization on the mode conversion rate to EB waves at the extremely overdense regime has been investigated and an improvement in the plasma current is observed.
Highlights
There has been a considerable interest in noninductive start-up of Tokamak plasma without the use of the central solenoid (CS)
Electron cyclotron heating and current drive (ECH/ECCD) is an attractive candidate for this purpose since the microwave power can be injected through a simple small launcher located far from the plasma surface
In this paper we report a non-inductive start-up and formation of an extremely overdense spherical Tokamak (ST) plasmas by electron Bernstein (EB) waves
Summary
There has been a considerable interest in noninductive start-up of Tokamak plasma without the use of the central solenoid (CS). If the plasma current can be non-inductively started up, the CS could be reduced or eliminated from the Tokamak device. These provide a major technical advantage for designing a future compact reactor, such as VECTOR [1] and Slim-CS [2]. Once the incident waves are mode-converted to electron Bernstein (EB) waves they can propagate into and cyclotron-heat the core plasma without the limit of the plasma cutoff density. This is suitable for STs since they are essentially overdense
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