Special Delivery from Germany
The elemental Target Station component the Moderator & Reflector System (so called Twister) will be delivered soon from Jülich to the ESS in Lund. The Twister is the biggest ZEA-1 deliverable for the ESS Target Station. In addition, important components have already been delivered like the liquid Hydrogen Cryostat, the Target Monitoring Plug and the first three Neutron Beam Port Inserts. In total more than 36 tons of engineering masterpieces which have been designed, analysed, produced and commissioned left Jülich as planned– despite the corona pandemic.
At the Moderator and Reflector system the high energy neutrons need to be slowed down to energy levels required by the scientific instruments. This is the task of the Moderator and Reflector plug consisting of the beryllium reflector, two hydrogen moderators and a thermal moderator – a kind of huge brake block for tiny particles. This constitutes the heart of the neutron source of the ESS, according to the shape of the cold moderator. “The design of the target system components has a direct impact on the effectivity of neutron production that can be released, and is therefore of utmost importance for the future scientific capabilities of the ESS facility” says Ghaleb Natour, Director of the Central Institute of Engineering, Electronics and Analytics – Engineering and Technology (ZEA-1).
The ESS ‘butterfly 2’ moderator design consists of two opposing hydrogen moderator cans, separated by an ‘X’ shaped thermal moderator with a disc shaped vessel underneath, acting as pre-moderator. The water flows first through the pre-moderator and then through the thermal moderator. The water is used to thermalize the fast neutrons and to remove the deposited radiation heat.
All this comes together in the so-called Twister, containing the moderator & reflector plug and the active cooled support & lifting structure. While the twister is 6.5 metres high and weighs 13 tons, the diameter of the neutrons is about one trillion times smaller than that of a grain of sand. For the sheathing of the twister frame, a total of nine plates – each of them one and a half metres long and one meter wide – have been milled in-house at a new five-axis machining centre, which has been in operation at ZEA-1 since mid-2020 and is worldwide one of the best of its kind.
Ten tons of specially manufactured stainless steel have been used. The sheathing shields the high-energy particles directly at the point of origin. “In order for this not to go wrong, the individual components must fit extremely accurately,” explains Yannick Beßler, leading Scientist at the ZEA-1. In addition, very different three-dimensional geometries, such as fine cooling channels, are being milled. The production of one single component takes weeks.
Made in Jülich
Already in Lund is the Hydrogen Cryostat. The 4 m tall cryostat is part of the Cryogenic Moderator System (CMS) and is designed and manufactured by ZEA-1 in Jülich. It provides 3.6 tons per hour of liquid parahydrogen to the cold neutron moderators located in the Twister at a temperature of 17 K and a pressure of 10 bar.
In addition to the cryogenic moderator system components of the first generation, the ZEA-1 has already started to work on the next generations of ESS Moderators. Object of Yannick Beßlers PhD was the fluid dynamic design and experimental validation of the second generation. And we already have started to work on the third generation as that is part of the ongoing H2020-Projekt HighNESS.
Another finished Masterpiece is the Target Monitoring Plug (TMP), an actively cooled system to monitor the behaviour of the spallation target wheel during operation. The X, Y and Z position of the target wheel and shaft as well as the vibrations of the target shaft must be measured in detail. In addition, the temperature of the returning cooling fluid (He) and the rim temperature will be measured for each of the 36 sectors. Furthermore, a gamma imaging insert is required. The scope of the project includes the selection and verification of measuring equipment, the detailed design, the manufacture and the testing of the system.
Last but not least prototypes of the Neutron Beam Port Insert and the Light Shutter System are the last puzzle of the target parts. Each of the planed instruments require a 3.5 m long Neutron Beam Port Insert (NBPI) containing an instrument unique Neutron Beam Optical Assembly (NBOA). The NBPIs form the first section of the neutron guide to the instruments and must be precisely aligned within the monolith to ensure efficient extraction of the neutrons. Each insert is customised to exactly position its instrument specific NBOA. The NBPIs contains a separated helium atmosphere and are also water cooled to prevent damages over planned 20 year lifetime. “The sealing for the water and helium cooling systems was quite challenging”, confirmed Project manager Chris Hall, “particularly the approximately 7 m long seal required for the upper lid”. Metal seals like a copper wire seal for the upper lid are used to meet all requirements. “The reliability, leak rate and precision of alignment was successfully verified on a prototype” says Hall.
All these key technical parts are important German in-kind contribution that has been designed, manufactured and delivered or commissioned by the Forschungszentrum Jülich.
With some 6,400 employees, FZJ is one of Europe's large research centres. At the Central Institute of Engineering, Electronics and Analytics - Engineering and Technology (ZEA-1) engineering at its finest and complex production technologies are combined. “By providing interdisciplinary, turn-key solutions – like done here: from the idea to the product – we enable excellent research to acquire new ground-breaking insights in many scientific areas,” says Ghaleb Natour. “And we are not done yet- next up we continue focusing on the engineering and technology of the three scattering instruments DREAM, T-REX and SKADI”.