Observation of Lower-Hybrid Current Drive at High Densities in the Alcator<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>C</mml:mi></mml:math>Tokamak

A quasi-steady-state lower-hybrid current-drive operation is demonstrated in the Alcator $C$ tokamak at densities up to ${\stackrel{-}{n}}_{e}\ensuremath{\simeq}1\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. 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.