The development of a low energy neutron accelerator for rebunching pulsed neutrons

Low energy neutrons can be accelerated or decelerated by the technique of AFP-NMR with RF in a gradient magnetic fields. The neutrons have magnetic moments, hence their potential energy are not cancelled before and after passage of magnetic fields and their kinetic energy change finally when their spins are flipped in the fields. Nowadays most measurements of the neutron electric dipole moment (nEDM) are carried out with ultra cold neutrons (UCN), whose kinetic energies are lower than about 300 neV, and with a small storage bottle to reduce the systematic errors. In such experiments highly dense UCNs are desired. The spallation neutron sources generate high-density neutrons at the target, however, the pulsed neutrons with spread velocities are diffused in guide tubes during long beam transport. It is necessary to concentrate UCN temporally upon the bottle by controlling their velocities for nEDM experiments at those facilities. We demonstrated such rebuncher and have been developed the advanced apparatus which makes it possible to handle broader energy range UCN. The design, measured specification of the new rebuncher is described in detail.