Resonant absorption by a step-like density profile

A numerical investigation is reported of resonant absorption by a plasma density profile with a step. It is shown that the resonance curve is affected not only by the inhomogeneity length at the point with the critical density, but also by the density at the upper and lower boundaries of the step. An analytic solution is obtained for the resonant absorption coefficient on the assumption that a plasma region occupied by the step is thin.