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For the High Luminosity Upgrade project (HL-LHC) of the CERN Large Hadron Collider (LHC), lower $\beta$ * quadrupole magnets based on advanced Nb $_\text{3}$ Sn conductors will be installed on each side of the ATLAS and CMS interaction points. To quantify the endurance and technological limits of these magnets, beyond their maximum operational conditions, two short length model magnets have been extensively tested at the CERN SM18 test facility. Both magnets were subjected to eight thermal cycles. One of them was trained beyond its ultimate current (17.89 kA, corresponding to 143 T/m field gradient and 12.2 T peak field), reaching a maximum of 19.57 kA at 1.9 K (corresponding to 155 T/m, 13.4 T peak field and 95.4% of the short sample limit) in a 150 mm diameter bore. This magnet currently has the record highest field gradient of this quadrupole magnet class. The second short model had zero re-training quenches up to nominal (16.47 kA) and ultimate current at 1.9 K during the thermal cycles; more than 1000 current cycles to nominal current; and provoked quenches to simulate the most severe failure scenarios of the protection system. After all these tests, both magnets continue to perform beyond requirements for operating current and temperature. In this paper, the tests performed on the two magnets are discussed.

In the context of CERN's high-luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC), a new double aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These 2.2 m long NbTi dipoles are built with the canted cosine theta (CCT) technique. The two independently powered apertures are oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A full-length double aperture prototype was built and tested at CERN in the SM18 test facility. Here we present the results of powering tests at 1.9 and 4.5 K: training of each aperture, magnetic field quality and cross-talk effects, quench detection system effectiveness, quench protection performance and quench-back with several energy extraction systems.

Author(s): Mangiarotti, F; Bajas, H; Ambrosio, G; Bajko, M; Bordini, B; Bourcey, N; Duda, M; Desbiolles, V; Feuvrier, J; Fleiter, J; Bermudez, SI; Chiuchiolo, A; Devred, A; Ferracin, P; Fiscarelli, L; Mentink, M; Nobrega, A; Pepitone, K; Ravaioli, E; Schmalzle, J; Todesco, E; Perez, JC; Vallone, G; Willering, G; Yu, M | Abstract: For the high luminosity upgrade of the CERN large hadron collider, lower β∗ quadrupole magnets based on advanced Nb3Sn conductors will be installed on each side of the ATLAS and compact muon solenoid (CMS) experiment insertion zones. As part of the technological developments needed to achieve the required field gradient of 132.6 T/m within a 150-mm aperture, short length model magnets, named MQXFS, are tested both at the CERN SM18 and Fermilab test facilities. The model magnets rely on two types of Nb3Sn conductors (restack rod process (RRP) and powder-in-tube (PIT)) and on an innovative bladders and keys design to provide mechanical support against the Lorentz forces. In 2016 and 2017, the powering tests of the first two models MQXFS3 (RRP) and MQXFS5 (PIT) proved that nominal performance (16.5 kA) could be reached with excellent memory of the quench current after thermal cycle. However both magnets showed a slow training behavior with clear observations of voltage disturbances before the quench. Besides, only MQXFS5 could reach ultimate current (17.9 kA) whereas erratic behavior was observed on MQXFS3 due to conductor local degradation at the head of one of the coils. In 2018, this limiting coil was changed and the applied azimuthal prestress increased. While ultimate current could then be reached, no stable current could be maintained due to identified defect on the outer layer of the new coil. Finally the outcome of the test of the new model MQXFS4, featuring the final RRP conductors that will be used for the series production and variation on the inner layer quench heater designs are here reported in details.

In the frame of the high-luminosity upgrade project for the large hadron collider, new twin aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long canted cosine theta NbTi dipoles, with two independently powered apertures oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A 0.5 m model magnet in single and double aperture configuration and a full-length double aperture prototype were built and tested at CERN. In this paper, the performance of these magnets at 1.9 K in terms of training behavior, quench detection and protection, and other tests is discussed. In addition, the thermal response of the magnet to a hypothetical beam discharge is simulated and analyzed.

In the frame of the compact linear collider project, a high-field short-period superconducting damping wigglers will be required to reduce the emittance of the electron and positron beams. The use of Nb 3 Sn as superconducting material is being investigated, as a valid option for its smaller size and increased working margin. At CERN, Geneva, Switzerland, a second Nb 3 Sn damping wiggler short model has been developed, assembled, and tested. In this paper, the cold power test of that magnet is discussed in terms of training, quench detection, protection, endurance, and other tests.

Author(s): Ravaioli, E; Bajas, H; Datskov, VI; Desbiolles, V; Feuvrier, J; Kirby, G; Maciejewski, M; Ten Kate, HHJ; Verweij, AP; Willering, G | Abstract: The coupling-loss induced quench system (CLIQ) is an innovative method for the protection of high-field superconducting magnets. With respect to the conventional method based on quench heaters, it offers significant advantages in terms of electrical robustness and energy-deposition velocity. Its effective intrawire heating mechanism targets a fast and homogeneous transition to the normal state of the winding pack, hence assuring a quick magnet discharge and avoiding overheating of the coil's hot spot. Furthermore, it is possible to implement CLIQ as a time- and cost-effective repair solution for the protection of existing magnets with broken quench heaters. After being successfully tested on model magnets of different geometries and made of different types of superconductor, CLIQ is now applied for the first time for the protection of a full-scale quadrupole magnet at the CERN magnet test facility. One aperture of a 3.4-m-long LHC matching quadrupole magnet is equipped with dedicated terminals to allow the connection of a CLIQ system. Experimental results convincingly show that CLIQ can protect this coil over the entire range of operating conditions. The complex electrothermal transients during a CLIQ discharge are successfully reproduced by means of a 2-D model. The test is part of the RD program of CLIQ quench protection systems, which has convincingly demonstrated the maturity of this technology and its effectiveness also for large-scale magnet systems. The proposed CLIQ-based solution for the quench protection of the LHC matching quadrupole magnet is now ready to be implemented in the LHC machine if needed.