Accessibility enhanced ECCD for plasma current start-up and ramp-up *

An efficient low-field-side launched X-mode ECH current start-up and ramp-up regime was identified. By choosing an appropriate operational density range, it is possible to access the EC resonance for the LFS X-mode. In this regime, the current drive is particularly efficient due to the strong cyclotron interaction with unidirectional passing electrons aided by the wave accessibility. The accessible density goes up with the square of frequency or magnetic field which favors high field devices including compact fusion pilot plant. This concept can now be tested in the higher field ST experimental devices becoming available such as NSTX-U, MAST, and ST-40.