Examining the Role of Cross-Beam Energy Transfer in National Ignition Facility Direct-Drive Exploding-Pusher Experiments

Direct-drive exploding-pusher experiments at the National Ignition Facility (NIF) have been shown to comprise a robust target platform producing a wide range of yields, from 1 ´ 1012 up to current levels of 1 ´ 1016. Inherent in these polar-drive implosions is the presence of cross-beam energy transfer (CBET), which has been shown to alter and degrade absorption of the incoming laser beams. Mitigation strategies are currently underway on several fronts, including capsule contouring, dedicated phase plates, wavelength detuning, and pulse shaping. However, comparisons of experimental data, at a constant target diameter, indicate improving differences in target shape as the laser energy is increased. Understanding this trend is imperative in our pursuit of remedying CBET in not only these high-yield experiments but also in eventual direct-drive–ignition designs. This observation could be influenced by several factors, particularly including CBET and thermal conduction. This presentation will numerically examine the underlying physics that determines shape for several NIF implosions, attempting to understand the relevant mechanisms behind the experimental trend. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.