Ponderomotive barrier as a Maxwell demon

The possibility of efficient ponderomotive current drive in a magnetized plasma was reported recently in [N. J. Fisch, J. M. Rax, and I. Y. Dodin, Phys. Rev. Lett. 91, 205004 (2003)]. Precise limitations on the efficiency are now given through a comprehensive analytical and numerical study of single-particle dynamics under the action of a cyclotron-resonant rf drive in various field configurations. Expressions for the particle energy gain and acceleration along the dc magnetic field are obtained. The fundamental correlation between the two effects is described. A second fundamental quantity, namely, the ratio of the potential barrier to the energy gain, can be changed by altering the field configuration. The asymmetric ponderomotive current drive effect can be optimized, by minimizing the transverse heating.