A fully relativistic theory of electron cyclotron current drive (ECCD) efficiency based on Green's function techniques is considered. Numerical calculations of the current drive efficiency in a uniform magnetic field are performed. The numerical results with parameter regimes relevant to ITER operation are compared with those of two simplified models in which the electron-electron Coulomb collision operator is respectively approximated by its high-velocity limit and a semirelativistic form. Our results indicate that the semirelativistic approximation of the collision operator should be appropriate for modeling the ECCD efficiency under ITER conditions.
