The temporal helicon-wave echo in a plasma with steepened density profile

The hydrodynamic echo on the surface helicon-type modes radiated to vacuum in a magnetized plasma with steepened density profile is investigated. It is shown that perturbations induced by an initial pulse at the plasma boundary are modulated by a later applied second pulse of different wavelength, to yield a non-vanishing echo signal, which can be radiated to vacuum. The angle of the radiation and the density of the energy flow of this signal are determined.