Observation of Lower-Hybrid Current Drive at High Densities in the AlcatorCTokamak

A quasi-steady-state lower-hybrid current-drive operation is demonstrated in the Alcator $C$ tokamak at densities up to ${\bar{n}}_e\simeq 1\times {10}^{14}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The current-drive efficiency is measured experimentally over a wide range of densities and magnetic fields. The radial distribution of high-energy x rays indicates that the current-carrying electrons peak near the plasma axis.