Heat Flux in the Storage Plant of Ultracold Neutrons

The realization of the idea of producing of ultracold neutrons through their interaction with superfluid helium can lead to increase in the density of created ultracold neutrons by several orders of magnitude. It will significantly expand the capabilities of neutron physics. However, it is fundamentally important to cool superfluid helium to temperatures below 1.0 K in the design of such a facility. The expected heat fluxes with reasonable sizes of the cooling system (>0.2 W/cm²) significantly exceed the regimes of transition of a vortex system of superfluid helium to the turbulent state. The article describes heat transfer regimes in superfluid helium, estimates the thermal resistance at different temperatures, and discusses the problems of scaling the results of test measurements that need to be carried out to answer the question of the performance of the proposed scheme for producing ultracold neutrons. It is shown that at temperatures below 1.0 K testing must be carried out on capillaries of several diameters (1, 2, and 10 mm) for correct scaling to the assumed dimensions of the cooling system.