Recharging of the ohmic-heating transformer by means of lower-hybrid current drive in the ASDEX tokamak

Recharging of the Ohmic-heating transformer of a tokamak by means of lower-hybrid waves is demonstrated experimentally in ASDEX. The results are analyzed on the basis of a simple transformer circuit. A recharging efficiency is defined and found to depend on rf power, plasma density, and plasma resistivity modified by the applied rf power. Up to now, we achieved in our recharging experiments in ASDEX a flux swing of FI${̇}_{\mathrm{OH}\mathrm{Mdt}=0.24\mathrm{}}$ V sec, at an rf power of $P_{\mathrm{RF}}$=690 kW, with a pulse duration of 1 sec, while maintaining a plasma with n${¯}_e$=4×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and $I_p$=290 kA.