It has recently been shown that the principle of time focusing and F.L. Shapiro’s idea of pulsed filling of a UCN trap make it possible to create a sufficiently intense UCN source at a pulsed reactor of medium power. For a time-dependent effect on the neutron velocity, providing focusing in time, it was proposed to use the phenomenon of nonstationary neutron diffraction on a moving diffraction structure. Subsequent analysis has shown that the creation of a time lens based on this principle is associated with hardly surmountable difficulties. This forces us to turn to an alternative focusing approach based on the principle of nonstationary spin flip in a magnetic field.

The report will consider both approaches to time focusing and analyze the advantages and disadvantages of each of them. The results of conceptual calculations of a UCN source with magnetic focusing in the conditions of the IBR-2 and Neptun reactors will be presented, as well as the main problems encountered in the creation of such a source will be formulated.