TMRS MK III engineering design

Background: The Target-Moderator-Reflector System (TMRS) is the neutron source for nuclear physics experiments in the Lujan Neutron Scattering Center user facility. The TMRS is an assembly consisting of tungsten targets plus a network of moderators, reflectors and flight paths that deliver neutrons of specified energies and fluxes to surrounding experiments and detector stations. The second-generation TMRS (MK II), operational for 5 years, is scheduled for replacement in 2010. While many features of MK II will remain unchanged this paper describes the engineering design of important new features: (1) The tungsten components of the targets will be clad in tantalum to minimize erosion and consequent contamination of the water cooling system, and (2) A new liquid hydrogen moderator with a beryllium reflector/filter that doubles the neutron flux.