Azimuthal coil size and field quality in the main CERN Large Hadron Collider dipoles

Abstract-The US LHC Accelerator Research Program (LARP)and CERN are combining efforts for the HiLumi-LHC upgrade to design and fabricate 150 mm aperture, interaction region quadrupoles with a nominal gradient of 130 T/m using Nb3Sn. To successfully produce the necessary long MQXF triplets, the HiLumi-LHC collaboration is systematically reducing risk and design modification by heavily relying upon the experience gained from the successful 120 mm aperture LARP HQ program. First generation MQXF short (MQXFS) coils were predominately a scaling up of the HQ quadrupole design allowing comparable cable expansion during Nb3Sn formation heat treatment and increased insulation fraction for electrical robustness. A total of 13 first generation MQXFS coils were fabricated between LARP and CERN. Systematic differences in coil size, coil alignment symmetry, and coil length contraction during heat treatment are observed and likely due to slight variances in tooling and insulation/cable systems. Analysis of coil cross sections indicate that field-shaping wedges and adjacent coil turns are systematically displaced from the nominal location and the cable is expanding less than nominally designed. A second generation MQXF coil design seeks to correct the expansion and displacement discrepancies by increasing insulation and adding adjustable shims at the coil pole and midplanes to correct allowed magnetic field harmonics.

Section: Fabricated Coil Size and Symmetrymentioning

confidence: 99%

Fabrication and Analysis of 150 mm Aperture Nb<sub>3</sub>Sn LARP MQXF Coils

Holik

Ferracin

Krave

et al. 2016

“…A mechanical model of the dipole cross-section, previously developed and validated with experimental data [3], was used to evaluate the influence of coil pre-stress on field quality. At the nominal pre-stress of 70 MPa, a loss of 10 MPa would give +0.5 units of b3, +0.12 units of b5, -0.015 units of b7.…”

Section: Field Harmonicsmentioning

confidence: 99%

Long Term Stability of the LHC Superconducting Cryodipoles After Outdoor Storage

Seyvet

Izquierdo

Bertarelli

et al. 2006

Self Cite

The main superconducting dipoles for the LHC are being stored outdoors for periods from a few weeks to several years after conditioning with dry nitrogen gas. Such a storage before installation in the 27 km circumference tunnel may affect not only the mechanical and cryogenic functionality of the cryodipoles but also their quench and field performance. A dedicated task force was established to study all aspects of long term behaviour of the stored cryodipoles, with particular emphasis on electrical and vacuum integrity, quench training behaviour, magnetic field quality, performance of the thermal insulation, mechanical stability of magnet shape and of the interface between cold mass and cryostat, degradation of materials and welds. In particular, one specifically selected cryodipole stored outdoors for more than one year, was re-tested at cold. In addition, various tests have been carried out on the cryodipole assembly and on the most critical subcomponents to study aspects such as the hygrothermal behaviour of the supporting system and the possible oxidation of the Multi Layer Insulation reflective films. This paper summarizes the main investigations carried out and their results. MOA06PO021 Abstract-The main superconducting dipoles for the LHC are being stored outdoors for periods from a few weeks to several years after conditioning with dry nitrogen gas. Such a storage before installation in the 27 km circumference tunnel may affect not only the mechanical and cryogenic functionality of the cryodipoles but also their quench and field performance. A dedicated task force was established to study all aspects of long term behaviour of the stored cryodipoles, with particular emphasis on electrical and vacuum integrity, quench training behaviour, magnetic field quality, performance of the thermal insulation, mechanical stability of magnet shape and of the interface between cold mass and cryostat, degradation of materials and welds. In particular, one specifically selected cryodipole stored outdoors for more than one year, was re-tested at cold. In addition, various tests have been carried out on the cryodipole assembly and on the most critical subcomponents to study aspects such as the hygrothermal behaviour of the supporting system and the possible oxidation of the Multi Layer Insulation reflective films. This paper summarizes the main investigations carried out and their results.

“…3, solid lines). Therefore, the elastic modulus of the coil to be input in the model is neither the loading nor the unloading, but an "equivalent" modulus taking into account the peak pre-stress [11]. The equivalent stress-displacement curve is shown for the inner coil in Fig.…”

Section: Modeling Coil Elasticity At 300 Kmentioning

confidence: 99%

Modeling of coil pre-stress loss during cool-down in the main dipoles of the Large Hadron Collider

Ferracin

Scandale

Todesco

et al. 2002

Self Cite

Abstract-We describe a finite element mechanical model of the main LHC dipole, based on the geometry and on the properties of its components; coil characteristics are derived from measurements on stacks of conductors. We show how to define equivalent properties of cable blocks that take into account the collaring procedure when it is not explicitly modeled. Numerical results are then compared to experimental measurements of loads and deformations in dipole prototypes. At cryogenic temperature, equivalent properties are used to implement in the model a pressuredependent thermal contraction factor observed in stack measurements. This allows to forecast the large pre-stress loss during the cool-down observed in the LHC dipole prototypes.