Fast-wave ion cyclotron resonance heating experiments on the Alcator C tokamak

Abstract

In this paper, minority regime fast-wave ICRF (Ion cyclotron range of frequency) heating experiments conducted on the Alcator C tokamak [Nucl. Fusion 26, 1665 (1986)] are described. Up to 450 kW of rf (radio frequency) power at frequency f=180 MHz was injected into plasmas composed of deuterium majority and hydrogen minority ion species at magnetic fields of B0≂12 T, densities 0.8≤n̄e≤5×1020 m−3, and minority concentrations 0.25≲ηH≤8%. Typical ion temperatures were TD(0)∼1 keV, while, depending on density, typical electron temperatures were in the range Te(0)∼1.5–2.5 keV. Central deuterium ion temperature increases of ΔTD(0)=400 eV were observed at n̄e=1×1020 m−3, while significantly smaller ion temperature increases were observed at higher densities. At the highest densities, ion heating became insignificant due in part to a limitation on power handling by the antenna that became more severe with increasing density. Significant electron heating was not observed at any density. Heating of the minority species at low densities indicated severe losses, but at higher densities it was consistent with efficient collisional coupling of the rf power from the hydrogen minority species to the deuterium majority species. Analysis of the deuterium power balance indicated no significant change in the deuterium thermal transport properties as a function of rf power. This may be consistent with the fact that the rf power never exceeded the Ohmic heating (OH) contribution. However, a very strong dependence of the deuterium transport properties on density was observed, and appears to be the dominant process limiting the effectiveness of ICRF heating at high density.