Current Rampup by Lower-Hybrid Waves in the PLT Tokamak

Recent lower-hybrid current-drive experiments have clearly demonstrated that the current in a tokamak discharge can be maintained by rf drive alone. We have extended the operating regime of such plasmas to include ramping up of the current. We find that at densities of \ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ approximately 20% of the launched rf power is converted to magnetic field energy.