Preload Characterization of Short Models of MQXF the Nb₃Sn Low-β Quadrupole for the Hi-Lumi LHC

Abstract

MQXF is the Nb3Sn Low-β Quadrupole magnet that the HL-LHC project is planning to install in the LHC interaction regions in 2026 as part of an upgrade to increase the LHC integrated luminosity by about a factor of ten. The magnet will be fabricated in two different lengths: 4.2 m for MQXFA, built in the US by the Accelerator Upgrade Project (AUP), and 7.15 m for MQXFB, fabricated by CERN. In order to qualify the magnet design and characterize its performance with different conductors, cable geometries and pre-load configuration, five short model magnets, called MQXFS, were fabricated, assembled and tested. The latest model, MQXFS6, uses a new powder-in-tube (PIT) superconducting wire, featuring a bundle barrier surrounding the filaments. The coil and the support structure were equipped with strain gauges and optical fibres to monitor strain during assembly, cool-down and excitation. In this paper we further develop the conventional azimuthal preload analysis and introduce a new set of tools for MQXF coil pack characterization which we use to analyse the behaviour of MQXFS6 room temperature preload and to reanalyse all the short models tested at CERN. A comparison is made between all the studied magnets revealing new characterizing preload parameters.

Mechanical Comparison of Short Models of Nb3 Sn Low-β Quadrupole for the Hi-Lumi LHC

“…Thus they deform plastically when tested. The resulting shape resembles the so called dent in [11]: the radius is reduced near the MP whereas the opposite is true near the poles. According to FEM the coils take a similar shape when preloaded.…”

“…The MP-MP contact takes into account the coil shape on both sides and the MP shims. In [11] it was noted that the coil pack size determined in the TF-KP (transfer function -key plot) analysis yielded on average 100 µm lower value than the value calculated according to the shimming plan. There are two possibilities: 1. the coil is smaller than measured, thus additional 100 µm can be reduced from the coil-collar contact offset, or 2. the structure does not exactly match their design values and thus one can add 100 µm to the loading key size.…”

“…The coil sizes are added to the coil-collar interface and the MP-MP interfaces varying the contact element offset (gap or interference) as a function of position. The coil-collar contact offset takes into account the shape of the coil and the radial shimming (nominal shimming plan shown in [11]). The MP-MP contact takes into account the coil shape on both sides and the MP shims.…”

“…The MQXF modeling and theory development has been done using octant ANSYS R -models [5], [7]- [11]. It is a great tool for fast computations and can provide a good understanding of the mechanical behavior of the magnet.…”

Progress in the Development of the Nb3Sn MQXFB Quadrupole for the HiLumi Upgrade of the LHC

“…The azimuthal solution is in general preferred, as it allows to bring the four coils inner surface at the same radius, with beneficial effects on the field homogeneity [19]. Radially, the target is to have about 125 μm smaller shims in order to improve the coil-collar contact [20]. Figure 8 shows the final shimming lay-out for the two MQXFB Prototype magnets.…”