Proton and Ion Radiography for High Energy Density Physics Experiments

High Energy Density (HED) experiments at the HHT experimental site of the GSI Plasma Physics Group employ intense, energetic uranium beams in order to study new regimes of the equation of state (EOS) of matter under extreme conditions. A key parameter to be determined in these experiments is the density distribution in the irradiated and heated target. Determining the spatial and density distribution with good time resolution is a demanding task, since it changes dramatically on short time scales during heating, expansion and eventually compression. To cope with short time scales and high line densities targets, radiography with energetic protons and ions [1] turns out to be a promising method to be applied. Protons can be made available at high intensities and energies by accelerators and feature high penetration depth and sensitivity to different target materials due to the mass number dependency of the interaction cross section. One can distinguish two types of radiography methods: attenuation radiography and energy loss radiography. Protons are practical in the first case. Due to nuclear collisions and large-angle scattering, proton beams are attenuated in the material. The intensity of the remaining proton beam reflects the density distribution within the target. The second radiography method uses the energy loss of the projectiles. This scales with density and material type as well. The density distribution can be thus reconstructed via the projectiles’ energy distribution after the target. Adjusting the projectile energy appropriately maximizes projectile energy deposition in the detector and provides for high contrast images. Radiography is planned to be incorporated in future HED experiments at FAIR to determine density distributions via a diagnostic beam delivered by SIS-18. The first steps in the development of this diagnostic facility are briefly described in this report. A series of experiments on 800 MeV proton attenuation and 214 AMeV C energy loss radiography have been carried out in collaboration with ITEP Moscow at the TWAC accelerator facility. Teflon discs embedded in plexiglas have been used for the attenuation radiography experiments. These experiments show clear separation between the two materials but also stress the need for a specifically designed and optimized ion optical system [2] for an improved quality of the images. Several wires of different materials and widths heve been employed for the energy loss radiography experiments. An image obtained by this method is shown in Fig. 1(a). It (a) experiment (b) simulation (c) profile