Journal article

Electron-Cyclotron Resonance Heating on the Tca Tokamak

Electron cyclotron resonance heating (ECRH) experiments at 39 GHz with power levels similar to those of Ohmic heating have been conducted in the TCA tokamak, in either the X-mode or the O-mode. ECRH was observed to be more efficiently absorbed in low density and low q(a) discharges. At low density the central electron temperature increased by a factor of two over Ohmic values and the stored energy increased by 40% when up to 80% of the plasma energy was supplied by ECRH. During low density ECRH operation, the electron energy confinement time tau(Ee) was the same as during pure Ohmic heating, but at high density tau(Ee) degraded with ECRH power. The decrease in the loop voltage required to maintain a constant current during ECRH is a very reproducible quantity and can be attributed in almost all cases to the change in the electron temperature. Sawtooth stabilization occurred during ECRH, with a sawtooth period of up to ten times longer than that before ECRH. This stabilization depends on the ECRH toroidal injection angle and the total input power. High energy ions were observed and their production is attributed, as in earlier experiments, to a three-wave interaction process.


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