ALP Seminar: Brave Nuclear World: The role of Nuclear Physics in High Energy Density Plasmas

The National Ignition Facility (NIF) laser at Lawrence Livermore National Laboratory can produce a high energy density plasma with temperatures ~10 keV, particle densities ~10³² m^-3, and neutron fluxes of up to 10³⁴ m^-2 s^-1. These features, combined with the advanced x-ray, neutron and radiochemistry diagnostics that are available at the NIF, make it uniquely suitable for exploiting and investigating interactions between Plasma Physics and Nuclear Physics. Two particular aspects of these interactions will be surveyed in this seminar.

First, when plasmas are composed of deuterium or deuterium-tritium, as in the case of Inertial Confinement Fusion (ICF) experiments, nuclear reactions produce large amounts of fast neutrons. These neutrons can undergo nuclear scattering within in the plasma and induce secondary and tertiary nuclear reactions. Measurements of the spectra of neutrons emitted from the plasma can provide diagnostic information on quantities such as plasma density and temperature to give insights into the process of ignition in ICF experiments.

Secondly, hot plasma environments, such as those found in stars and created on the NIF, can cause nuclei to be excited from the ground state. The neutron capture cross section for excited state nuclei can differ significantly from those of ground state nuclei. This has implications for the rates at which different elements are produced in stars by the Astrophysical slow neutron capture process (“s process”). However, it is not possible to measure cross sections of excited state nuclei at conventional accelerator facilities. This seminar will outline how experiments on the NIF could make these measurements.