Modeling Coil-Pole Debonding in ${\rm Nb_{3}Sn}$ Superconducting Magnets for Particle Accelerators

Anderssen

et al. 2019

Self Cite

The Nb 3 Sn quadrupole MQXF is being developed as a part of the LHC High Luminosity upgrade. The magnet design was tested on 1.5 m long short models, sharing the same cross-section with the full-length magnets. Various azimuthal and longitudinal preloads were applied, studying the impact on the magnet training and on its mechanical performances. The experiments demonstrated the possibility to control the magnet prestress. However, various factors, coil size among the others, may affect the stress variation between and within each winding. This variation could prevent the magnet to reach the desired performances, for example as result of critical current degradation of the Nb 3 Sn strands. This paper analyzes the mechanical performances of the short models, studying in particular the stress variation on different coils. The measured coil size was used as input in the numerical simulations, and results were then compared with the strain gauge measurements. Finally, the short models experience was used to evaluate the feasibility of a loading operation that does not rely on the strain measurements.

Section: Mqxf Short Model Magnetsmentioning

confidence: 78%

Summary of the Mechanical Performances of the 1.5 m Long Models of the Nb<inline-formula> <tex-math notation="LaTeX">$_{3}$</tex-math> </inline-formula>Sn Low-<inline-formula> <tex-math notation="LaTeX">$\beta$</tex-math> </inline-formula> Quadrupole MQXF

Vallone

Anderssen

et al. 2019

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“…The signals show very small variations up to a certain current level, and then suddenly start to increase. It was shown in [15] that this slope variation can be explained by the detachment of the coil from the pole, as the one seen in the winding pole strain. In fact, the slope variation appears simultaneously on the shell and on the Fig.…”

Section: Magnet Poweringmentioning

confidence: 86%

“…After a certain level, different for all the magnets, the winding pole stress does not vary linearly anymore. This sudden change is considered an indication of prestress exhaustion and detachment of the coil from the winding pole [15].…”

Section: Magnet Poweringmentioning

confidence: 99%

“…Numerical models, including the detachment of the coil from the winding pole, demonstrated that at the maximum the pole is indeed experiencing tension, and that the stress is null at the end of the ramp. As a consequence, a maximum tension of 10 MPa has to be considered when computing the prestress [15]. The total azimuthal prestress in presence of unloading can be then computed as the maximum measured delta stress minus 10 MPa.…”

Section: Magnet Poweringmentioning

confidence: 99%

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Mechanical Analysis of the Short Model Magnets for the Nb $_{3}$Sn Low-$\beta$ Quadrupole MQXF

Vallone

Bajas

et al. 2018

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During the development of MQXF, the new Nb3Sn quadrupole to be used in the LHC inner triplets for the High Luminosity upgrade, three short models were tested: MQXFS1, MQXFS3 and MQXFS5. These models differ in the use of thin or thick laminations for the iron components, in the coil design and in the superconductive strands, RRP or PIT. In the MQXF design, the azimuthal prestress is provided at room temperature by means of the bladder-key technology, and it is further increased during the cooldown by the differential thermal contraction of the various components. Four aluminum rods provide the longitudinal prestress. Both systems allow for a flexible control of the amount of prestress applied. As a consequence, it was possible to test the models exploring different azimuthal and longitudinal prestress conditions, in an attempt to understand their impact on the magnet performances. This paper studies the mechanical behavior of these short models, also providing the strain and stresses measured by means of strain gauges installed on the aluminum shell, on the winding poles and on the rods. Finally, the paper compares the measures with the results from FE models.

“…The data for the tested magnets are shown in Fig. 8 (y axis) and compared with target values: the two horizontal lines indicate the levels of coil compression that, according to computations and strain gauge measurements [24], prevent at Inom and Iult an azimuthal unloading of the coil pole turns due to the electro-magnetic (e.m.) forces. In addition, the plot provides the total longitudinal pre-load given to the coils by the axial support system, and compare it with the axial e.m. forces (see Table IV) at Inom and Iult (vertical lines).…”

Section: Magnet Assembly and Loadingmentioning

confidence: 99%

The HL-LHC Low-β Quadrupole Magnet MQXF: From Short Models to Long Prototypes

Ferracin

Anerella

et al. 2019

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Among the components to be upgraded in LHC interaction regions for the HiLumi-LHC projects are the inner triplet (or low-β) quadrupole magnets, denoted as Q1, Q2a, Q2b, and Q3. The new quadrupole magnets, called MQXF, are based on Nb3Sn superconducting magnet technology and operate at a gradient of 132.6 T/m with a conductor peak field of 11.4 T. The Q1 and Q3 are composed by magnets (called MQXFA) fabricated by the US Accelerator Upgrade Project (AUP) with a magnetic length of 4.2 m. The Q2a and Q2b consists of magnets (called MQXFB) fabricated by CERN with a magnetic length of 7.15 m. After a series of short models, constructed in close collaboration by the US and CERN, the development program is now entering in the prototyping phase, with CERN on one side and BNL, FNAL, and LBNL on the other side assembling and testing their first long magnets. We provide in this paper a description of the status of the MQXF program, with a summary of the short model test results, including quench performance, and mechanics, and an update on the fabrication, assembly and test of the long prototypes.