Cyclotron effects on double layer ion acceleration from laser-irradiated thin foils

Abstract

The effect of an axial magnetic field on laser driven ion acceleration from a thin overdense plasma slab is investigated. The magnetic field modifies the refractive index of the plasma and the axial ponderomotive force. The latter compresses the electrons until the space charge field thus created offsets it. When the foil thickness is just bigger than the length at which this happens, the compressed electrons and a thin ion layer detach from the foil forming a double layer that gets accelerated by the laser radiation pressure force. The optimum thickness of laser foil, Δs, for maximum acceleration is sensitive to the polarization of the laser pulse. For right circular polarization it increases, while for left circular polarization it decreases with the magnetic field. The ion energy gain is sensitive to a02ω2∕Δsωp2 (where a0 is the laser field strength, ωp is the plasma frequency, and ω is the laser frequency) and can be tuned by varying the magnetic field.