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The effect of ion motion on rotating magnetic field current drive

The effect of ion motion on rotating magnetic field (RMF) current drive in field reversed configurations is studied using a fully two-dimensional numerical code that solves the two fluid equations with massless electrons and constant uniform temperature. The ion momentum equation includes viscosity and collisions with neutrals, which remain fixed. The electrons are described with an Ohm's law that includes the Hall and pressure gradient terms. For full penetration of the RMF, ion spin-up due to collisions with electrons reduces the current drive efficiency and a large fraction of neutrals is needed to prevent the ions from acquiring high azimuthal velocities. For conditions that would result in incomplete penetration with the fixed ion model, ion rotation and variable density can facilitate the penetration of the RMF, thus increasing the efficiency. The rotation modifies the density profile and can trigger rotational instabilities.