Optimizing current drive by electron cyclotron waves in the presence of trapped particles

Moving the absorption region to the inboard side of the magnetic surfaces and combining electron cyclotron waves and lower hybrid waves are investigated in order to solve problems caused by electron trapping in tokamak devices. The time dependent bounce averaged quasilinear Fokker Planck equation is solved in order to evaluate the current drive efficiency for realistic wave power levels. It is shown that moving the absorption region is ineffective in enhancing the current drive efficiency, because of the interplay of quasilinear and toroidal effects for high wave power. On the other hand, combination with lower hybrid waves can be quite efficient in minimizing the negative impact of electron trapping.