Current drive by synergy of slow modes in tokamaks

Enhancement of lower-hybrid current drive in the presence of wave converted ion-ion slow modes is discussed using the one-dimensional quasilinear equation. The special case where the slow mode resulting from conversion in a deuterium-hydrogen mixture is absorbed by low energy electrons, is considered in detail. In this scheme, the effect of the ion-ion modes is to increase the electron tail density and the current enhancement is given by the ratio of the parallel velocity distributions with and without mode converted slow modes, calculated at the lower p'' limit of the lower-hybrid tail. The synergy method is well suited for a remote control of the lower-hybrid fast tail population, and is useful for current drive optimization. Some insights on current drive by ion-ion slow modes in the absence of lower hybrid waves, are also given