Applied Metrology in the Production of Superconducting Model Magnets for Particle Accelerators

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The High Luminosity Large Hadron Collider (LHC) Project target is to reach an integrated luminosity of the LHC of 3000 fb −1 , corresponding to a factor 10 increase in collisions with respect to the current accelerator. One of the main components is the superconducting quadrupole called MQXF. It is based on Nb 3 Sn technology and has a 150 mm single aperture with a field gradient of 132.6 T m −1 . The MQXF magnets are currently in preseries production in a joint collaboration between CERN and the US-LHC Accelerator Upgrade Project. The first prototype magnet based on 7 m-long coils (MQXFBP1) was assembled and preloaded in 2019. The testing and disassembly was done in 2020. The coils were equipped with optical fiber Bragg grating (FBG) sensors. Some of the FBG values exhibited strain jumps during preload and their signals were lost during cool-down. The magnet did not reach the nominal current, quenching at 15.15 kA. At the time of writing three MQXFB magnets have been preloaded from which the second prototype is soon to be tested. The objective of this paper is to analyze the mechanical behavior of MQXFB magnets in the light of current knowledge, thanks to earlier short model experiments, as well as describe in detail the process of assembly and preload. We synthesize the mechanical theory of preload and present new considerations on symmetric/asymmetric bladder-key operations and their effects. An extensive comparison between long and short model magnets is presented. In our analysis and FE modeling we take into account the measured coil sizes that vary over position. We introduce a novel technique that allows preload homogenization over the length of the magnet after preload has been done. We analyze the role of the stainless steel shell and show its mechanical behavior. Finally, the relevant data at cold is presented and analyzed.

Section: Coil Sizesmentioning

confidence: 99%

On the mechanics of MQXFB—the low-beta quadrupole for the HL-LHC

Takala

Ferracin

Lackner

et al. 2021

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“…These models were implemented in ANSYS by the creation of two user elements. This approach integrates the desired effects at the point of element matrix generation, no longer requiring manual updating of superconducting properties between a stop and restart of the solver as implemented in previous work [11,12]. The thermal model follows directly from ANSYS (see documentation in [17]), with extended capabilities of programmable material property fits and automatic quench checking and heat generation.…”

Section: The Finite Element Modelmentioning

confidence: 99%

“…With this assumption, the contribution to the resistive voltage is determined by the fractional area of stabilizer and the amount of current assumed to be flowing in this region. Adjusting equation (12) to account for these assumptions, the resistive voltage drop is given by…”

Section: R Lmentioning

confidence: 99%

“…We present a new approach using only the commercial finite element software ANSYS [9]. It has previously been demonstrated that ANSYS has the capability to simulate some aspects of the complete problem, such as quench propagation [10][11][12] and the effect of eddy currents in mechanical structures on the current decay of a circuit coupled magnet [13]. We show user defined elements replicating these features and adding the additional missing capabilities of: (1) modeling magnetization of the conductor due to coupling currents and (2) combining all the effects into a single, coupled simulation with field and temperature dependent material properties.…”

Section: Introductionmentioning

confidence: 99%

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User defined elements in ANSYS for 2D multiphysics modeling of superconducting magnets

Brouwer¹,

Arbelaez²,

Auchmann³

et al. 2019

Dynamic simulation of superconducting magnets is critical for the design of quench protection systems to prevent potentially damaging temperatures and high voltage from developing after magnet quench. Modeling these scenarios is challenging due to the many multiscale phenomena which impact magnet behavior. These range from conductor scale effects of quench and interfilament coupling currents up to the behavior of the magnet in its powering and protection circuit. In addition, a strong coupling between electromagnetic and thermal domains is required to capture temperature and field dependent material properties and quench behavior. We present a finite element approach which integrates the various effects into the commercial software ANSYS by means of programming new element types. This is shown capable of simulating the strongly coupled transient electromagnetic, thermal, and circuit behavior of superconducting magnets required for quench protection studies. A benchmarking study is presented which shows close agreement between the new ANSYS elements and a COMSOL Multiphysics implementation developed at CERN for dump resistor and Coupling Loss Induced Quench (CLIQ) based magnet protection of a Nb 3 Sn block dipole. Following this, the ANSYS implementation is shown reproducing strongly coupled quench back behavior observed during the test of a Nb 3 Sn superconducting undulator prototype at Lawrence Berkeley National Laboratory.

“…Finally, the coils are impregnated with epoxy CTD-101K resin. The arc length and radial dimension of the coils are measured every 100 mm using a coordinate measurement machine (CMM) [22]. The deviation of the azimuthal dimensions with respect to the nominal values is estimated by aligning the data on the nominal outer radius (60.8 mm).…”

Section: Magnet Designmentioning

confidence: 99%

Mechanical analysis of the Nb₃Sn 11 T dipole short models for the High Luminosity Large Hadron Collider

Bermúdez

Nilsson

Bottura

et al. 2019

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For the Large Hadron Collider luminosity upgrade, two of the NbTi 8.3 T main bending dipoles will be replaced by two shorter Nb 3 Sn 11.2 T dipoles to create space for the installation of collimators in the dispersion suppression region. With the aim to verify the design features, several 2 m long 11 T models have been constructed and tested at CERN. During the fabrication and assembly of, so far, seven single and two double aperture short model magnets, several challenges were identified and tackled. These include reproducibility in coil fabrication and assembly procedure, as well as control of mechanical stresses in the conductor and surrounding structure. In order to limit coil over-compression and improve reproducibility, the cable insulation was re-optimized. In addition, a review of the collaring procedure of the 11 T magnet was launched with the goal of reducing the risk of conductor degradation due to excessive stress. In this paper, the main fabrication and assembly steps are described, including the description of the actions taken to resolve the identified weakness.