Mechanical Performance of the First Two Prototype 4.5 m Long Nb₃Sn Low-β Quadrupole Magnets for the Hi-Lumi LHC Upgrade

Abstract

The U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) team is collaborating with CERN in the design and fabrication of the first 4.5 m long MQXFA magnets, a 150 mm aperture high-field Nb3Sn quadrupole magnet that uses the aluminum shell-based bladder-and-key technology. The first two prototype magnets, MQXFAP1 and MQXFAP2, were assembled and tested while the first pre-series structure (MQXFA03) was in fabrication. This paper summarizes the mechanical performance of these prototype structures based on the comparison of measured strain gauge data with finite element model analyses from all load steps to powering. The MQXFAP1 magnet almost reached ultimate current before a short to ground was detected and the test was stopped. The MQXFAP2 magnet experienced a low training performance due to a fractured aluminum shell. MQXFAP1b was rebuilt with a new replacement coil, but an old coil limited the magnet from achieving the ultimate current. The mitigations and analyses of these prototype magnets are discussed in the context of the transition to pre-series production.

Field Quality Measurement of a 4.2-m-Long Prototype Low-<inline-formula> <tex-math notation="LaTeX">$\beta$</tex-math> </inline-formula> Nb<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula>Sn Quadrupole Magnet During the Assembly Stage for the High-Luminosity LHC Accelerator Upgrade Project

“…This was demonstrated by using the piecewise reference axis which considered the fiducials on the magnet. Dedicated survey measurements on the assembly table showed that the table deformed with the magnet [34]. This contributed to the magnet deformation and will be corrected [34].…”

“…It has nominally the same mechanical structure as the first prototype magnet featuring eight separate aluminum shells [3]. No mid-plane shim or asymmetric radial shim was used thanks to the relatively uniform coil size [34].…”

Lessons Learned From the Prototypes of the MQXFA Low-Beta Quadrupoles for HL-LHC and Status of Production in the US

“…The second prototype (MQXFAP2) demonstrated poor training and limited performance because of a fractured aluminum shell. MQXFAP2 test data were presented in [7], [20] and a detailed analysis of fracture causes and preventive actions was published in [21]. Here we present a short list of the causes, which lead to this issue: 1) the design of the MQXFAP2 aluminum shells included small rounding (3 mm radius) at cutout corners, 2) a vendor made an error during fabrication resulting in "sharp corners" on one side of an end shell, 3) this non-conformity was accepted based on past LARP experience, 4) a small design change, successfully used on some short models, increased the end shell pre-load during cooldown.…”

Test Results of the First Two Full-Length Prototype Quadrupole Magnets for the LHC Hi-Lumi Upgrade

“…This paper is concerned with quench test results only; other testing operations and results are reported in [7]- [9]. Therefore, the instrumentation most relevant to this discussion are the voltage taps and signals produced by them during quenches.…”

“…b. Shell alignment cut-outs are now to have 10 -15 mm radius at the corners to minimize stress there [7], [12]. 3) MQXFAP1b Coil P03 failure:…”