Studies of proton generation and focusing for fast ignition applications

Summary form only given. The production of MeV protons by intense lasers is an area of great topical interest particularly with respect to the proposal to use protons to initiate burn in a fusion capsule. Following successful initial studies of focusing protons with hemishell targets, using a 10 J, 100 fs laser we extended the study to higher energy and longer pulses using PW class lasers at the RAL Vulcan, ILE Gekko facilities. Proton focusing was significantly aberrated in these experiments where a relatively small laser focal spot produced a central maximum in the sheath extension giving radial components to the acceleration. Experimental studies of this effect will be discussed and compared to 2D hybrid PIC modeling. In addition recent 1D numerical modeling of proton conversion efficiency with the hybrid PIC code LSP are beginning to show promising results, namely increased conversion of electron energy to proton energy. These theoretical predictions are currently being experimentally tested with targets that increase the proportion of protons on the target surface compared to heavy ions. Conclusions from these studies will be present and discussed in the context of fast ignition