Calculation of the ultracold neutron yield from a superfluid helium source in the WWR-M reactor

A new high-intensity source of ultracold neutrons (UCNs) is being developed on the WWR-M reactor at the Petersburg Nuclear Physics Institute. In this source, superfluid helium will be used, which will make it possible to attain the UCN density 2 to 3 orders of magnitude higher than in available sources in the world. With the most intense UCN source, the WWR-M reactor will become an international center of fundamental studies with UCNs. As a result of optimization of parameters of this source, the UCN density in the main trap is estimated as $\rho_{351}$ = 1.3 $\times$ 10$^4$ neutrons/cm$^3$ (for a trap with a volume of 351) and $\rho_{3501}$ = 8.4 $\times$ 10$^3$ neutrons/cm$^3$ (for a trap with a volume of 3501). For an auxiliary trap located on the platform, the calculated UCN densities are $\rho_{351}$ = 150 neutrons/cm$^3$ and $\rho_{3501}$ = 120 neutrons/cm$^3$. The ratio of UCN densities amounts to 2 orders of magnitude and indicates the effectiveness of the method of UCN extraction in the case of accumulation in superfluid helium.