Fractured superadiabaticity for wave heating/current drive - Collisional

Superadiabatic particle behavior can limit the energy increase and appreciably reduce the contribution to wave heating and current drive of energetic particles of low collisionality such as are found near the hot center of large tokamaks or as a result of the injection of high energy neutral beams. Sweeping of the wave frequency has been previously put forward as a means not only of suppressing superadiabatic limitation via phase randomization but also of exploiting the phase recapture phenomena associated with the superadiabatic regime ("fractured" superadiabaticity). Optimized heating rates well in excess of those seen either without sweeping or with strong ad hoc phase randomization were found (minority heating of beam ions in the TEXTOR-94 tokamak was examined numerically). With wave-induced stochasticity, the sole physical randomizing mechanism considered to date, the present study adds a Monte Carlo collisional description, finding the advantage of optimized sweeping to be strongly diminished by collisions in TEXTOR. In view of this, second harmonic heating of a deuterium beam injected into an (H)D JET tokamak plasma is examined, as well as fundamental heating of a hydrogen beam. (Author)