Use of radio-frequency waves in the formation of transport barrier in a stellarator

The effect of radio-frequency (RF) waves on negative-energy perturbations (NEPs) is investigated in a straight stellarator within the framework of the Maxwell and drift kinetic theories. It is found that the ponderomotive force and its radial gradient can modify the conditions for the existence of perpendicular NEPs, which are found to be the most important perturbations. It is shown that, if the profile of the RF field energy is properly chosen, the RF wave will have a stabilizing effect on the electron NEPs so that the fraction of active particles associated with the perpendicular NEPs decreases from the plasma interior to the edge. This result might have important implications with respect to whether the use of RF waves can create a transport barrier to reduce the loss of particles and energy in a stellarator.