Physics design of the next-generation spallation neutron target-moderator-reflector-shield assembly at LANSCE

We discuss the physics design of the next-generation spallation neutron target-moderator-reflector-shield (TMRS) assembly for the Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) at the Los Alamos Neutron Science Center (LANSCE). We developed this TMRS to improve the neutronic performance of the Lujan Center in the intermediate energy range (keV-MeV) enabling a variety of new nuclear physics experiments, as well as increasing the quality of the ongoing experiments. The results of our Monte Carlo optimization study indicate that the new TMRS will generate keV-MeV neutrons with higher intensity and improved time resolution. At the same time, the new design largely maintains its current performance in the cold and thermal ranges supporting materials research. In this article we show that the new TMRS has the potential to enhance the Lujan Center's experimental capability in a wider interval of energies - cold to intermediate - after its scheduled installation in 2020.