Anomalous absorption of electromagnetic radiation

Summary form only given. A fully nonlinear electromagnetic fluid simulation code has been used to study the interaction of electromagnetic waves with a plasma at the critical layer. The code is two-and-one-half-D (two spatial dimensions and three velocities) and represents the electrons and ions each as a fluid. For the case of a smoothly varying density gradient in a collisionless plasma, the classical absorption curve with a maximum loss of 50% of the incoming radiation is obtained. This occurs for only a relatively narrow band of angles between the radiation and the density gradient. It is seen that the presence of large amplitude transverse density variations (plasma structure) at the critical layer leads to an increased coupling between the electromagnetic radiation and electrostatic modes and greater absorption and scattering of the radiation. Absorption of over 90% of the radiation has been observed. The interaction with the rippled surface can also lead to strong side scattering of the radiation. The amount of energy in the backward reflected wave has been reduced by two orders of magnitude. A simple model of the absorption has been developed which is in good agreement with the scalings observed in the simulations. The interaction of the electromagnetic plane wave with the rippled surface is shown to be a two step process-absorption and then scattering