Lower hybrid heating, current drive and ion cyclotron heating experiments on Alcator C and Versator II tokamaks

Lower hybrid electron Landau heating experiments have been carried out on the Alcator C tokamak at densities 0.8x1014 < or approx. n-bar(cm-3) < or approx. 1.7x1014, and at B=7 to 11 T. With use of SiC-coated graphite limiters, on injection of 850 kW of power at a density of n-barsub(e) approx.= 1.3x1014cm-3 in deuterium, typical temperature increases of ΔTsub(i) approx.= 0.7 keV, ΔTsub(e) approx.= 1.0 keV were observed. Current drive and ramping experiments have also been carried out at densities 1013 < or approx. n-barsub(e)(cm-3) < or approx. 1014. The maximum current drive efficiency, defined as eta=n-bar(1014cm-3)I(MA)R(m)/P(MW), was eta approx.= 0.12 at B=10 T and eta approx.= 0.08 at B=8 T. Current ramping experiments have resulted in ramping rates of ΔI/Δt approx.= 400 kA/s with Psub(rf) approx.= 860 kW at a density of n-barsub(e) approx.= 3.0x1013cm-3. Initial results from the Alcator C 180 MHz, 0.5 MW ICRF heating programme are reported. Significant heating results were obtained in the hydrogen minority regime: on injection of 400 kW of radiofrequency power, the ion temperature rose by as much as 600 eV at a density of n-barsub(e) < or approx. 1.9x1014cm-3. In Versator II, during lower hybrid current drive experiments the global particle confinement increased by approximately a factor of two above the Ohmic discharge value when the Parail-Pogutse electron tail instability was stabilized. (author)