Rutherford Backscattering Spectroscopy Analysis of MTW Debris Shields

A set of debris shields used at the multiterawatt (MTW) laser at the Laboratory for Laser Energetics was analyzed using Rutherford Backscattering Spectroscopy (RBS). The debris shields consist of microscope cover slips that were placed over an objective in the MTW target chamber. The debris shields were positioned directly behind copper and tin target foils that were irradiated by the MTW laser. The irradiation of the target caused target material to be accelerated from the rear side of the foil and strike the debris shields at normal incidence. RBS analysis of the debris shields was carried out using ion beams from the SUNY Geneseo accelerator. The ion beams had energies of up to 3.0 MeV for protons and 4.5 MeV for alpha particles. The ions struck the debris shields and the energy spectrum of the backscattered ions was measured. A peak consistent with a thin layer of target material on the debris shields was observed in the central portion of the debris shields. The ion beam was focused so that it struck different positions on the debris shield, and the intensity of the peak was measured as a function of position. RBS allows the concentration and depth of the target material in the debris shield to be measured, which can be used to infer information about the energy and intensity of the target ions accelerated by the laser in the MTW experiments.