Hamiltonian analysis of fast wave current drive in tokamak plasmas

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Abstract
The Hamiltonian formalism is used to address the problem of the direct resonant interaction between the fast magnetosonic wave and the electrons in a tokamak plasma. The intrinsic stochasticity of the electron trajectories in phase space is first derived. Together with extrinsic decorrelation processes, it assesses the validity of the quasilinear approximation for the kinetic studies of fast wave current drive (FWCD). A full-wave solution of the Maxwell–Vlasov set of equations provides the exact pattern of the wave fields in the tokamak geometry, consistent with a realistic antenna spectrum. The local quasilinear diffusion tensor is then derived from the wave fields and the driven current density profile, the power deposition profile and the current drive efficiency are computed, including possible nonlinear effects in the kinetic equation. Several applications of FWCD on existing and future machines are given, and the combination of FWCD with other noninductive current drive methods is investigated. Finally, an analytical expression for the current drive efficiency is derived in the moderate to high single-pass absorption regime.