Recent Studies in Fast Electron Energy Transport Relevant to Fast Ignition Inertial Fusion

The first results of an experimental campaign are reported in which it is intended to demonstrate whether it is possible for the fast electron beam (produced at irradiances in excess of 1019 Wcm−2μm2) to be artificially collimated even when the beam enters the target with a large divergence angle. The artificial collimation occurs because of a pre-generated magnetic field that is produced by a laser pulse of 1018 Wcm−2μm2 that precedes the main pulse. The first experiment to examine the double pulse collimation concept has revealed evidence for single-pass heating for Ti foils of ≤ 25 μm thickness irradiated by the double pulse. This may be evidence for magnetic field generation in the dense plasma that prevents refluxing of the fast electrons from the rear surface. There was no evidence for collimation of the main pulse for these conditions. The most likely explanation for the lack of collimation is the generation of competing hollowing and focusing magnetic fields that arise as a result of the hydrodynamic shock induced by the low intensity pedestal of the laser pulse. The implications of these results are discussed and future directions outlined. In addition, a new analytic model is presented that reproduces the intensity scaling results of Beg et al. [F.N.Beg et al., Phys. Plasmas 4, 447 (1997)] and the new data at intensities up to 10 Wcm.