Division of accelerators, cryogenics and magnetism

The recent update of the European Strategy for Particle Physics recommended a feasibility study for the future generation of collider. In this context, the Laboratory Directors Group, of which IRFU is a member, has been mandated by the CERN Council to oversee the development of an accelerator R&D roadmap. One of the objectives of this roadmap is the development of technologies for the manufacture of high-field superconducting magnets, essential for future colliders: this is the HFM (High Field Magnets) project.

The MADMAX project, which was launched in November 2016, is led by the Max Planck Institut für Physik in collaboration with several European institutes. The goal of the project is the discovery of axions with a mass of about 100 µeV, potential candidates for dark matter. To detect these axions, it is necessary to develop a specific detector consisting of an electromagnetic signal amplifier and a magnet proportional to the size of the amplifier and delivering a strong magnetic field. In order to validate the innovations in the fabrication of the magnet conductor, its cooling concept and the quench detection, a demonstrator has been designed, fabricated, integrated and tested between March 2020 and August 2021. It is named MACQU for MADMAX Coil for Quench Understanding. The entire design, from the conductor to the support structure, including the MACQU magnet, its thermal shield and the busbars, was carried out at the CEA. The demonstrator, manufactured by the industrial Bilfinger Noell GmbH, arrived in March 2021 and was successfully tested between May 18 and August 27, 2021. The analysis of the data now completed provides the desired answers and opens up unexpected new avenues of work. The feasibility of the cable concept, its cooling as well as the quench detection for the MADMAX magnet was demonstrated during these tests.

The LEAS (Laboratoire d'Etude des Aimants Supraconducteurs) at CEA Paris-Saclay has entirely manufactured a coil based on the superconductor Nb3Sn (niobium-tin), of the SMC (Short Model Coil) type. This coil is a short model intended to be assembled in a magnet structure, then to be tested at cryogenic temperature. Nb₃Sn is being considered for future accelerator magnets generating magnetic fields up to 16 T (teslas), which would double the performance of the best magnets currently in use. However, this requires a great deal of technological development. This type of short coil has been developed by Cern, in collaboration with the CEA, to allow the testing of new technologies and new manufacturing processes under conditions representative of future high-field magnets. The fabrication of the SMC-CEA coil took place at LEAS from May to October 2021, then the coil was delivered to Cern to be assembled in a structure, and finally tested in a liquid and superfluid helium bath, under high current, in a dedicated station. The tests delivered encouraging results, demonstrating that LEAS is one of the few European laboratories that now has all the capabilities to manufacture Nb3Sn superconducting coils. This proof of feasibility validates the first step of the development program of high field magnets for future accelerators.

The large aperture (90 mm) quadrupole superconducting electromagnet for the CERN HL-LHC project, manufactured and tested at 4.2 K by the IRFU teams, reached its nominal gradient of 120 T/m (defined for 1.9 K) the 5th of March, 2021. These very good results validate the design and manufacturing process proposed by the IRFU engineers and were the subject of a technology transfer to the industrial companies working on the European project QuaCo (QUAdrupoleCOrector). This magnet was produced as part of the LHC upgrade in luminosity project called HiLumi-LHC. These NbTi magnets are part of the insertion magnets. They may be placed upstream and downstream of detectors such as ATLAS and CMS at the center of which the 2 beams cross to make the collisions. They should ensure the compression of the beams before collisions and thus contribute to increasing the integrated luminosity of the HL-LHC (i.e. the total number of collisions), up to ten times greater than the initial nominal value of the LHC.

Since the restart of the LHC on 20 November, CMS has taken advantage of the excellent operating performance of the collider to record a large amount of useful data. This is now being used to check its correct operation and calibration. During this period, CMS has demonstrated the stability of the detectors' working conditions as well as the efficiency of the data analysis system, which sends data from the detector to analysis teams around the world, and this in spite of very rapidly changing beam conditions.