Development of MQXF: The Nb&lt;sub&gt;3&lt;/sub&gt;Sn Low-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\beta$&lt;/tex-math&gt;&lt;/inline-formula&gt; Quadrupole for the HiLumi LHC

High-performance Nb 3 Sn superconducting wires have become one of the key technologies for the development of next generation accelerator magnets. While their large critical current densities enable the design of compact accelerator-quality magnets for their operation above 10 T, the noticeable reduction of the conductor performance due to mechanical strain appears as a new essential characteristic in magnet design.In this work, we extensively investigate the effect of transverse loads, up to 250 MPa, in state-of-the-art Nb 3 Sn Restacked-Rod-Process round superconducting wires. The tests are performed using a compressive Walters spring device, where the force is applied to the resin-impregnated wire, and the critical current is measured under magnetic fields ranging from 16 to 19 T. As a complement, critical current measurements under axial strain are also performed using a standard Walters spring. Interestingly, the study shows that the wire's electro-mechanical response under transverse stress depends on the initial axial strain condition. Nonetheless, when the main direction load becomes predominant, all tested wires converge to a common behavior. This observation allowed us to combine the results from critical current measurements under the loads exerted in both directions (axial and transverse), shedding some new light on the mechanisms behind critical current degradation.

Section: Experimental Campaign Descriptionmentioning

confidence: 99%

Effects of the initial axial strain state on the response to transverse stress of high-performance RRP Nb₃Sn wires

Troitino

Bagni

Barth

et al. 2021

“…The mechanical development of MQXF magnets started with successful tests of the support structures for short models (MQXFS) housing dummy coils [4,5,22]. The studies hinted at the critical role of the pole key in the azimuthal preload.…”

Section: The Transfer Function and The Role Of The Pole Keymentioning

confidence: 99%

“…One of the main components in this project is the so called inner * Author to whom any correspondence should be addressed. triplet that consists of MQXF [2][3][4][5][6] superconducting Nb 3 Sn low-β quadrupole magnets. There are MQXFA and MQXFB variants that are mainly different in length (4.2 and 7.5 m, respectively).…”

Section: Introductionmentioning

confidence: 99%

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

Takala

Ferracin

Lackner

et al. 2021

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.

“…The new magnets, designed under the name of MQXF [53,54] and based on Nb 3 Sn technology, will replace their today's present NbTi counterparts with the objective of producing a gradient of 132.6 T m −1 in a 150 mm single aperture. As a part of the triplet circuit, they will operate at 1.9 K, and will be powered with a nominal current value of 16.47 kA.…”

Section: The Mqxf Magnetmentioning

confidence: 99%

A methodology for the analysis of the three-dimensional mechanical behavior of a Nb₃Sn superconducting accelerator magnet during a quench

Troitino

Bajas

Bianchi

et al. 2021

The fast thermal and electromagnetic transients that occur in a superconducting magnet in case of a quench have the potential of generating large mechanical stresses both in the superconducting coils and in the magnet structure. While the investigation of such quench loads should generally be conducted to ensure a safe operation of the system, its importance is greatly enlarged in the case of high-field magnets based on strain sensitive superconductors. For these, a rigorous analysis of the magnet mechanics during a quench becomes critical. The scope of this work is hence to bring, for the first time, a detailed understanding of the three-dimensional mechanical behavior of a Nb 3 Sn accelerator magnet during a quench discharge. The study relies on the use of finite element models, where various multi-domain simulations are employed together to solve the coupled physics of the problem. Our analysis elaborates on the case study of the new MQXF quadrupole magnet, currently being developed for the high-luminosity upgrade of the LHC. Notably, we could find a very good agreement between the results of the simulation and experimental data from full-scale magnet tests. The validated model confirms the appearance of new peak stresses in the superconducting coils. An increase in the most relevant transverse coil stresses of 20-40 MPa with respect to the values after magnet cool-down has been found for the examined case.