2007 Volume 2 Pages 003
Multi MeV proton beam is generated via target normal sheath acceleration when the target is irradiated with an ultra-intense laser pulse. In addition, a unique structure, “zonal pattern”, of energetic protons is observed in the perpendicular directions of the target edges using triangular targets. The sheath field production on the target edges may be responsible for this zonal pattern. Two dimensional particle-in-cell simulations show that the electrostatic field initially produced at around the cross point at the laser axis and the rear surface expands on the target surface in time. The field enhancement occurs at the target edges when the sheath field reaches there. The enhanced field can accelerate protons in a zonal pattern.
