Fast electron transport studies in Petawatt laser irradiation of solid dielectric and metallic target materials

During the interaction of high-intensity short-pulse lasers with solid target materials up to 30% of the laser energy is converted into so-called 'fast' electrons, that is electrons with relativistic kinetic energy, much higher than the thermal plasma electron energy. The study of the transport of the high-current fast electron beam through the underlying target material is an active research field due to its crucial importance for the fast ignition approach to inertial confinement fusion. In the fast ignitor scheme the fast electron beam is required to travel through the outer region of low-Z dense plasma to reach the compressed fuel core, where the electrons deposit their energy to rapidly heat the fuel to ignition. Here we report on a joint experiment carried out within the HiPER project, for a systematic study of fast electron transport phenomena from the irradiation of multi-layered targets with the VULCAN Petawatt laser beam. The targets consisted of a propagation layer and a tracer layer for the X-ray measurements. High resolution spectroscopy and monochromatic X-ray source imaging of line emission from the tracer layer have been performed in the experiment, thus giving information on the spectrum and on the spatial distribution of the fast electrons after their passage through the propagation layer. The experiment was designed to study transport phenomena depending on the material resistivity, such as return current issues, and Z-dependent phenomena. Therefore, metallic and low and medium Z dielectric target materials have been used as propagation layers. The observed differences of the X-ray emission features for the different target materials will be discussed. (author)