WAKE-POTENTIAL FORMATION IN A THIN FOIL

The induced-potential distribution set up by a swift ion moving through a thin foil is studied in the Bloch hydrodynamic approximation. The material is approximated as a jellium in a rigid-slab geometry. The wake potential created by a charged-point particle traveling fully inside the bulk is characterized by oscillations whose wavelength is 2-pi-nu/omega(p), and it is only formed when the foil thickness is greater than that wavelength. The processes of wake formation and destruction are shown when the particle is traveling in both perpendicular and parallel directions with respect to the foil. The wake appears to be formed after the ion has traveled a distance of the order of the above wavelength from the entrance surface when the ion moves with velocity perpendicular to the surface. The destruction process begins when the particle arrives at the exit side.