Speaker
Description
Ultracold neutrons (UCN) are extremely cold neutrons with energies below ~ 300 neV and can be confined in a material vessel. Toward the neutron fundamental physics experiments like a neutron electric dipole moment (nEDM) measurement, we developed a new intense UCN source using superfluid helium (He-II) at the Research Center for Nuclear Physics (RCNP), in Japan. In He-II, cold neutrons are down-scattered by phonons to the UCN energy range efficiently. We coupled a lead spallation neutron source with 300 K and 10 K heavy water (D$_2$O) moderators to produce cold neutrons. The cold neutrons were then converted to UCN in He-II, and then, extracted from the He-II to an experimental apparatus. At the exit of the UCN source, a UCN density of 26 UCN/cm$^3$ at 90 neV critical energy was achieved with the 400 W proton beam of the ring cyclotron of RCNP in 2011. This was a world competitive value.
In 2016, this He-II UCN source was transported from RCNP to TRIUMF. The UCN source is to be installed above a tungsten spallation target on the beamline 1U in the Meson hall. Before the installation on the beamline 1U, we were doing cold tests of the cryostat.
We have succeeded in cooling down the UCN cryostat to 20 K using a Gifford-McMahon (GM) refrigerator. For the full cooling test using liquid helium planned in March 2017, we are building up the helium-3 circulation system, the isopure helium circulation system, the 4K liquid helium auto-filling system and radiation shielding.
In this talk, the present status of this apparatus will be discussed.
