Generation of rf-Driven Currents by Lower-Hybrid-Wave Injection in the Versator II Tokamak

Abstract

Experimental verification of lower-hybrid rf current drive in the Versator II tokamak is presented. The experiments show that efficient current drive exists only in low-density discharges (${\overline{n}}_{e}\ensuremath{\lesssim}6\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) in the "slide-away" regime where a preformed suprathermal electron tail exists prior to the application of the rf power.