Benchmarking of Energetic Electron Beam Transport in Nail and Wire Targets

The current generation of high-power (1015 Watt) lasers have been successfully used to produce energetic electron beams with enormous currents (10’s of mega-amperes). In the fast ignition (FI) concept for inertial confinement fusion energy (IFE) it is envisaged that such energetic electron beams could initiate nuclear fusion burn. This FI approach has the potential for significantly increased efficiency relative to conventional central hot spot ignition.

Recently, there has been extensive research into generation and transport of energetic particles in dense plasmas. These are the critical issues for FI applications. In this talk, experimental investigation of electron beam transport in long thin “nail”/wire targets irradiated by a picosecond ultra-high intensity (~ 2 ✗ 1020 Wcm-2) laser, will be presented. Various novel diagnostics, for example, K? and XUV imaging, have been fielded to diagnose the energetic electron production and transport through observations of x-ray fluorescence and target heating.

The “nail”/wire target experiments were specifically designed to test components of the relevant modeling codes. Three codes (PICLS, LSP and e-PLAS) incorporating either explicit PIC or implicit/hybrid PIC algorithms have been employed to model the experiments. Low mass “nail” and wire targets are excellent for benchmarking purpose as most of the laser and target parameters can be incorporated into the simulations. Strong similarities in electron beam transport and energy deposition have been found between the numerical results from the three codes and the experimental observations. Some recognizable discrepancies will also be discussed. It is hoped that this benchmarking effort will result in an increased level of confidence in the FI specific calculations that are to be performed in connection with large-scale IFE relevant experimental studies on the upcoming generation of high power laser systems such as Omega-EP and NIF-ARC.