Abstract
The next-generation neutron spallation target station, the Target-Moderator-Reflector System (TMRS) Mk. IV, will be installed in 2021. This iteration features an unprecedented, water-cooled, third internal target aptly named the Upper Target. With the Upper Target designed completely by analysis, a complementary empirical investigation was undertaken to ascertain target conformance to those computational results which deemed the cooling efficacious. Three facets of the target were designated for verification: displacement under hydraulic load, critical fluid velocities, and the characteristic heat transfer coefficient. With the potential for flow maldistribution under excessive displacements, static pressure testing was performed. Discrepancies of an order of magnitude became evident between empirical and simulated displacements, 1.499 mm vs. 0.203 mm, respectively. A closed water flow loop reproducing the flow parameters intrinsic to the TMRS Mk. IV was constructed. Utilizing particle image velocimetry, global fluid dynamics were observed to be analogous to computer simulation. Furthermore, crucial velocities such as those at the point of beam impingement were met or exceeded, thus satisfying cooling requirements by preponderance. A graphite susceptor mirroring nominal beam geometry was coupled to a solenoid coil to replicate a prodigious peak heat flux of 169 W/cm2 via induction heating. Matching peak heat flux within 3% engendered a heat transfer coefficient 80% that of simulation. Consistent with analysis, the local heat transfer coefficient sufficiently mitigated nucleate/flow boiling. In summary, the analytically-derived Upper Target design empirically demonstrated sufficient cooling despite quixotic beam conditions and unforeseen displacements.
Design of the third-generation lead-based neutron spallation target for the neutron time-of-flight facility at CERN
