Ultracold-Neutron Source Based on Superfluid Helium for the PIK Reactor

A high-density ultracold-neutron source based on superfluid helium is being developed at the Petersburg Nuclear Physics Institute (PNPI) of the National Research Center “Kurchatov Institute” for fundamental physics research. This ultracold-neutron source is intended for installation in the largest experimental channel of the PIK reactor complex: the horizontal experimental channel (HEC-4). Calculations indicate that the thermal-neutron flux density at the channel output is 3 × 10¹⁰ cm^–2 s^–1. The new ultracold-neutron source aims to achieve an ultracold neutron density of 3.5 × 10³ cm^–3 at the reactor-chamber output and 200 cm^–3 in the spectrometer designated for measuring the neutron electric dipole moment. The neutron-guide system for ultracold neutrons is designed to support five experimental facilities alternately. Initially, the ultracold-neutron source will be equipped with existing experimental setups: a neutron electric-dipole-moment spectrometer and two setups for measuring the neutron lifetime (utilizing gravitational and magnetic traps). For this ultracold-neutron source, a unique technological cryogenic complex has been designed and implemented to work with superfluid helium under reactor-installation conditions. This complex includes equipment capable of achieving temperatures down to 1 K and removing heat from superfluid helium at a rate of up to 60 W.