Speaker
Description
In the framework of the development of the HBS HiCANS project in Jülich, a 1-dimensional cryogenic moderator based on liquid para-hydrogen has been designed, constructed, and tested. Para-hydrogen is hydrogen with antiparallel arrangement of the nuclear spins in the molecule. The mean free paths for thermal and cold neutrons in liquid para-hydrogen differ by about one order of magnitude. This makes it possible to develop a 1-dimensional cold moderator where the extraction happens along the extended dimension while the feeding with thermal neutrons is done along the other two dimensions, which are small in comparison.
The moderator cryostat was designed such that the hydrogen volume is completely enclosed and that hydrogen serves as coolant as well as moderator material. In a closed loop the heat is removed by a cryocooler outside the target-moderator shielding and the hydrogen is circulated by a pump for cryogenic fluids. A paramagnetic catalyst inside the liquid hydrogen loop is used to ensure the conversion into the para-hydrogen low-temperature ground state.
This system has been built to fit into a beamport plug of the JULIC Neutron Platform, the technology demonstrator of the HBS project in Jülich. The system successfully was brought into continuous operation for weeks and we measured the neutron spectrum emitted from this cold source. The presentation will focus on technology and first operation experience.