Mode conversion and electron damping of the fast Alfvén wave in a tokamak at the ion–ion hybrid frequency

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Abstract
Mode conversion of the fast Alfvén wave (FAW) at the ion‐hybrid frequency in the ion cyclotron range of frequencies (ICRF) is studied in the presence of ion cyclotron absorption and direct electron damping in a tokamak plasma. The usual Budden model is extended to include the effect of electron damping and of the high‐field‐side cutoff, and is solved analytically and numerically. The mode‐conversion efficiency is given as a function of the Budden transmission coefficient and of a phase integral, which describes interference between the incoming and outgoing waves. In incidence from the low‐field side, a discrete spectrum of phases exists for which complete absorption (i.e., combined mode conversion and direct electron damping) of the FAW for a single transit of the resonance region can be achieved. This permits efficient electron heating and/or current drive via mode conversion of FAWs.