ECCD studies for EU-DEMO plasmas

The possibility of driving a large fraction of the plasma current in a tokamak reactor employing electron cyclotron waves is investigated for scenarios as envisaged in the European DEMO through beamtracing calculations performed with the TORBEAM code, which assumes a linear regime for power absorption and employs an adjoint method for the determination of the driven current. Comparatively high ECCD efficiency in the inner half of the plasma column can be achieved by injecting the wave from an elevated position. On
the other hand, the efficiency deteriorates in the colder, outer part of the plasma, so that a prohibitive amount of power would be needed to sustain the plasma current non-inductively by ECCD only in the considered scenarios. As an alternative scheme, the injection of slow extraordinary wave below the fundamental resonance is considered. The basic physics features of this scenario are discussed.