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Among the components to be upgraded in LHC interaction regions for the HiLumi-LHC projects are the inner triplet (or low-β) quadrupole magnets, denoted as Q1, Q2a, Q2b, and Q3. The new quadrupole magnets, called MQXF, are based on Nb3Sn superconducting magnet technology and operate at a gradient of 132.6 T/m with a conductor peak field of 11.4 T. The Q1 and Q3 are composed by magnets (called MQXFA) fabricated by the US Accelerator Upgrade Project (AUP) with a magnetic length of 4.2 m. The Q2a and Q2b consists of magnets (called MQXFB) fabricated by CERN with a magnetic length of 7.15 m. After a series of short models, constructed in close collaboration by the US and CERN, the development program is now entering in the prototyping phase, with CERN on one side and BNL, FNAL, and LBNL on the other side assembling and testing their first long magnets. We provide in this paper a description of the status of the MQXF program, with a summary of the short model test results, including quench performance, and mechanics, and an update on the fabrication, assembly and test of the long prototypes.

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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.

The objective of this paper is to review recent advances in the sensors used to measure seismic linear vibrations at low frequencies. The main types of inertial sensors are reviewed: absolute displacement sensors, geophones, accelerometers, and seismometers. The working principle of each of them is explained, along with the general strategies to extend their bandwidth. Finally, the principle fundamental limitations of all inertial sensors are reviewed: tilt-to-horizontal coupling, zerolength springs, and sources of noise.