Electron cyclotron power absorption and current drive in the lower hybrid heating regime

The power deposition and the current drive by electron cyclotron waves interacting at the downshifted cyclotron resonance with the suprathermal electrons in a lower hybrid heating tokamak regime is analyzed. The power absorption is evaluated in the framework of the relativistic linear theory, using a suitable model electron distribution to describe the lower hybrid sustained plasma; the driven current is computed by means of the adjoint method. Top and equatorial launch have been explored for a wide range of plasma parameters and propagation angles. A favorable scaling of the driven current with the magnetic field is found with a proper choice of launching conditions. The results are interpreted in terms of single-particle efficiencies for absorption and current drive, location of resonant regions in momentum and physical space, and characteristics of the ray trajectories.