HighNESS successfully completed- Conceptual Design Report published
The European Spallation Source, currently under construction in Lund, Sweden, is a multidisciplinary international laboratory. Once completed to full specifications, it will operate the world's most powerful pulsed neutron source. Supported by a 3 million Euro Research and Innovation Action within the EU Horizon 2020 program, a design study (HighNESS) has been completed to develop a second neutron source located below the spallation target. Compared to the first source, designed for high cold and thermal brightness, the new source has been optimized to deliver higher intensity, and a shift to longer wavelengths in the spectral regions of cold (CN) very cold (VCN) and ultracold (UCN) neutrons.
The second source comprises a large liquid deuterium moderator designed to produce CN and support secondary VCN and UCN sources. Various options have been explored in the proposed designs, aiming for world-leading performance in neutronics. These designs will enable the development of several new instrument concepts and facilitate the implementation of a high-sensitivity neutron-antineutron oscillation experiment (NNBAR).
ZEA-1 was work package leader "Enginnering", focusing on the Deuterium moderator engineering design, the UCN source design and the advanced reflectors for VCN.
The ZEA-1 Input can be found in various capters of the paper, like Design of the ESS Ultra Cold Source for He-II in MCB (6.8.1), the The NNBAR detector (9.11) and the Engineering of the experimental setup of the campaign with advanced reflectors (11.2). And mainley in capter 3 "Engineering design of the liquid deuterium moderator".
Here the major engineering challenge here was to handle the enormous heat load into the LD2 moderator of around 60 kW resulting from the spallation process of a 5 MW accelerator-driven neutron source. The moderator vessel consists of high-strength Aluminum alloy EN AW-6061 T6, which allows local stresses up to 87 MPa and will be filled with approximately 30 L of liquid deuterium. The cold moderator is surrounded by a vacuum jacket followed by a light water premoderator and a warm beryllium reflector. In addition, one cold beryllium filter (≤ 80 K) is installed inside the cold moderator vessel on the NNBAR side serving the large beam port.
It was demonstrated that a volume moderator, including all necessary process lines, can be integrated into the existing twister structure under the given restrictions. Furthermore, the detailed design shows that the moderator system can withstand all mechanical loads and that the manufacturing and welding, although very complex, is feasible.
The conceptual design for the cooling process describes all the additional infrastructure needed to realize such a moderator upgrade. A key point is to reduce the deuterium inventory as much as possible. On one hand, this can be accomplished by choosing a location for the cryostat as close as possible to the moderator and, on the other hand, by reducing the heat load.
The reduction of the heat load is also decisive from a thermo-mechanical point of view in order to be able to use the moderator at full beam power of 5 MW. Without further optimization, the proton beam power is currently limited to 2 MW. However, the first optimizations have already shown that the separation of the cold beryllium filter already leads to significant improvements. In contrast to the demonstrated box-shaped moderator (worst case), slightly shaped vessel walls would allow for a reduc- tion in the wall thickness, which means in turn that less heat is generated and the neutronic performance of the moderator is improved as well.
The complete Conceptual Design Report for the HighNESS its the projects final deliverable.