Development of Longitudinal-Gradient Magnet for Time Focusing of Ultra-Cold Neutron With Anisotropic Inter-Pole

Ultra-cold neutron (UCN) is attractive for a search of the neutron electric dipole moment (nEDM). It is crucial to store UCNs with high density in a bottle for nEDM measurement apparatus. To increase the density, time focusing technique can be useful, where slow neutrons are accelerated and fast neutrons are decelerated by using magnetic potential. This device is called “rebuncher.” The rebuncher consists of a gradient magnet, RF coil, and neutron guide. The magnet generates a field gradient of 3.5 T/m (from 1 T to 0.2 T within 24 cm) in the longitudinal direction. By using anisotropic inter-poles, the magnet is compact and keeps the gradient uniform. The fabricated magnet showed good performance as designed.