Performance of LHC Main Dipoles for Beam Operation

At present about 90% of the main dipoles for the LHC have been manufactured and one of the three cold mass assemblers has already completed the production. 85% of the 1232 dipoles needed for the tunnel have been tested and accepted. In this paper we mainly deal with the performance results: the quench behaviour, the magnetic field quality, the electrical integrity quality and the geometry features will be summarized

Compilation of latest progress on the installation of the HL-LHC IT String in SM18

This photo collection shows the works that have been carried out in recent months at SM18 (CERN). These include, in addition to cleaning and painting, the removal of the old crane and the installation of a new one, the refurbishment of the Control Room, the installation of the racks for the electronics and the installation of the metallic structure where the string equipment will be located

Chapter 16: IT string and hardware commissioning

The HL-LHC IT string (IT string) is a test stand for the HL-LHC, whose goal is to validate the collective behaviour of the IT magnets and circuits in conditions as near as possible to the operational ones. Each individual magnet circuit will be powered through a SC link and its associated current leads up to the ultimate operational current while cooled to 1.9 K in liquid helium. The test stand will be installed in the building 2173 (SM18) and will use magnets, superconducting (SC) link, current leads, power converters and protection equipment designed for the HL-LHC with their final design, and usable for the HL-LHC. The test bench will allow a real size training for the installation and alignment, the validation of the electrical circuits, the protection scheme of the magnets, and the SC link. At this occasion, all subsystem owners will be able to fine- tune their set up and to complement or change when necessary, before they are finally installed into the HL- LHC. The powering procedures will be written and validated during the tests. These tests will also improve our knowledge of every single component and will give us the opportunity to optimize the installation and hardware commissioning procedures

Quench propagation velocity and hot spot temperature models in Nb3_{3}Sn racetrack coils

Since 2010 to present, several subsize magnet assemblies, designed as test beds for the validation of impregnated Nb$_{3}$Sn-based coil technology, have been tested at the Superconducting Magnet Test Facility (SM18) at CERN. These short model coils and racetrack model coils have been used to study two types of Rutherford cables foreseen for the coils of the Nb$_{3}$Sn magnets in the framework of the HL-LHC upgrade and High Field Magnet program of CERN. During several test campaigns, the Rod Restack Process and the Powder-In-Tube conductors have been characterized in terms of performance and quench propagation velocity (QPV). Moreover, hot spot temperature (HST) increase during quenches has been estimated from the analysis of the registered voltage and current signals. In this paper, the multiphysics problem of quench propagation in Nb$_{3}$Sn cables is addressed under adiabatic conditions by means of a set of analytical formulae and several finite element models with different level of complexity in ANSYS APDL, COMSOL Multiphysics, and MATLAB. These models are aimed at describing the conductor behavior in terms of HST and QPV observed during the training of racetrack coils at SM18

The Cryogenic System and Planned Cryogenic Tests For the Future High Luminosity LHC IT Magnet String

The high luminosity upgrade of the Large Hadron Collider will require the replacement of the triplet of final focusing superconducting magnets at interaction points 1 and 5 with a new set of helium II cooled magnets. To validate the technologies and assembly procedures and to investigate the collective effects, a string of magnets representative of the final HL-LHC configuration, will be installed in the SM18 test facility at CERN in 2021. The local cryogenic distribution connected to the string of magnets will also be representative of the final configuration. This paper first describes the cryogenic configuration of the magnet string and the functional cryogenic requirements for the operation and test program. The cryogenic parameters for the different circuits and operation phases are presented. The paper details the cryogenic test program foreseen to investigate the specific challenges of cooling Nb3Sn magnets and their beam screens during high heat load (several hundred watts at 1.9 K), steady state, and transient operation. The paper presents the complete cryogenic system planned for the string, its integration into the SM18 facility, the required adaptation of the SM18 cryogenic infrastructure, and the conceptual design of the main components

The Characterization of Optical Fibers for Distributed Cryogenic Temperature Monitoring

Thanks to their characteristics, optical fiber sensors are an ideal solution for sensing applications at cryogenic temperatures, such as the monitoring of superconducting devices. Their applicability at such temperatures, however, is not immediate as optical fibers exhibit a non-linear thermal response which becomes rapidly negligible below 50 K. A thorough analysis of such a response down to cryogenic temperatures then becomes necessary to correctly translate the optical interrogation readings into the actual fiber temperature. Moreover, to increase the fiber sensitivity down to a few kelvin, special coatings can be used. In this manuscript we described the thermal responses experimental characterization of four commercially available optical fiber samples with different polymeric coatings in the temperature range from 5 K to 300 K: two with acrylate coatings of different thickness, one with a polyimide coating and one with a polyether-ether-ketone (PEEK) coating. Multiple thermal cycles were performed consecutively to guarantee the quality of the results and a proper estimate of the sensitivity of the various samples. Finally, we experimentally validated the quality of the measured thermal responses by monitoring the cool down of a dummy superconducting link from room temperature to approximately 50 K using two fibers coated, respectively, in acrylate and PEEK. The temperatures measured with the fibers agreed and matched those obtained by standard electronic sensors, providing, at the same time, further insight in to the cool-down evolution along the cryostat

Advanced Nb3_{3}Sn conductors tested in a racetrack coil configuration for the 11T dipole project

Within the 11T dipole magnet conductor development for the High Luminosity LHC Upgrade, two types of Nb3Sn cable based on the Powder-in-tube (PIT) and Rod and Restack (RRP) processes are tested in racetrack configuration in the Short Model Coil (SMC) magnets. In 2016 and 2017, the performances of three different coils wound with 40-strand cables, one made of OST RRP 132/169 and two of PIT 120 strands have been measured using SMC structure. This paper reports on the main design parameters of the SMC-11T-3 (RRP), the SMC-11T-4 and SMC-11T-5 (PIT) magnets including details on the instrumentation, applied pre-load, maximum expected performances, Residual Resistivity Ratio, splice resistances and inductances. For SMC-11T-3, eight runs have been performed varying the azimuthal pre-stress from 150 to 200 MPa with the aim to study the impact of transverse pressure on the magnet stability and degradation. Only two runs were done for SMC-11T-4 and 5. For the three magnets, the training behavior at both 4.2 and 1.9 K is analyzed in terms of training rate, quench location, maximum quench current and dependence to the Helium bath temperature, level of transverse pre-stress and current ramp rate. The main tests outcome about the coil performances are here discussed.Within the 11T dipole magnet conductor development for the high-luminosity LHC upgrade, two types of Nb3 Sn cable based on the powder-in-tube (PIT) and the Rod and Restack processes (RRP) are tested in racetrack configuration in the short model coil (SMC) magnets. In 2016 and 2017, the performances of three different coils wound with 40-strand cables, one made of OST RRP 132/169 and two of PIT 120 strands have been measured using the SMC structure. This paper reports on the main design parameters of the SMC-11T-3 (RRP), and the SMC-11T-4 and SMC-11T-5 (PIT) magnets including details on the instrumentation, applied preload, maximum expected performances, residual resistivity ratio, splice resistances, and inductances. For SMC-11T-3, eight consecutive runs have been performed varying the azimuthal prestress from 150 to 200 MPa with the aim to study the impact of the transverse pressure on the magnet stability and degradation. Only two runs were done for SMC-11T-4 and SMC-11T-5. For the three magnets, the training behavior at both 4.2 and 1.9 K is analyzed in terms of training rate, quench location, maximum quench current and its dependence to the helium bath temperature, the level of transverse prestress, and current ramp rate. The main outcome of the tests on the coil performance is given as conclusion

Cryogenic-temperature profiling of high-power superconducting lines using local and distributed optical-fiber sensors

This contribution presents distributed and multi-point fiber-optic monitoring of cryogenic temperatures along a superconducting power transmission line down to 30 K and over 20 m distance. Multi-point measurements were conducted using fiber Bragg gratings sensors coated with two different functional overlays (epoxy and PMMA) demonstrating cryogenic operation in the range 300 – 4.2 K. Distributed measurements exploited optical frequency-domain reflectometry to analyze the Rayleigh scattering along two concatenated fibers with different coatings (acrylate and polyimide). The integrated system has been placed along the 20 m long cryostat of a superconducting power transmission line, which is currently being tested at the European Organization for Nuclear Research (CERN). Cool-down events from 300 K to 30 K have been successfully measured in space and time, confirming the viability of these approaches to the monitoring of cryogenic temperatures along a superconducting transmission line

Quench protection study of a 11 T Nb3_3Sn model dipole for the High Luminosity LHC

The planned upgrade of the Large Hadron Collider collimation system requires the installation of 11 T Nb$_3$Sn dipole magnets in the dispersion suppressor areas. Due to the large stored energy density and the low copper stabilizer section, the quench protection of these magnets is particularly challenging. The baseline protection scheme after installation in the main dipole circuit is based on quench heaters and a bypass diode. The maximum allowable temperature during quench has a primary importance. In one of the latest short model magnets, full protection studies were performed up to a quench integral and hot spot temperatures well beyond the design value in order to understand the limits. Measurements are compared to electro-transient and thermo-mechanical models to evaluate quench propagation, temperature rise in the conductor, and thermal stress due to temperature gradients in the coil and surrounding structure