Coupling of lower-hybrid radiation at the plasma edge. Technical report

The mode‐conversion process encountered in the lower‐hybrid heating scheme at the edge of the plasma, where the frequency of the external radiation is comparable to the local value of the electron plasma frequency is considered. The problem is formulated in terms of a modulational representation of the electric field that permits the description of the full space‐time evolution of the process. The numerical study of the model equations confirms that a backward wave is excited at the edge and that it leads to a net energy flow directed toward the interior of the plasma. For small external power levels, the flow is characterized by the progagation of a leading‐edge pulse whose arrival at a given spatial location marks the onset of the steady state. At large external power levels, the self‐consistent modification of the density profile by the ponderomotive force is found to quench the mode‐conversion process, thus causing a significant reduction in the amount of rf energy that can be coupled from the externa...