  The paper considers the concept of an ultracold neutron source (UCN) based on
the deceleration of very cold neutrons (VCN) by a local decelerating device. As
the latter, it is proposed to use a gradient spin flipper. It is shown that in
this case, the flux of VCNs, which after deceleration are converted into the
UCN, has a pulse structure. In this case, the duration of neutron bunches can
be significantly less than their repetition period. Accordingly, the density of
the neutron flux in the bunch will significantly exceed the average value. This
opens up the possibility of pulse filling of the UCN trap, without preliminary
time focusing
