This paper presents the analysis of some quench tests addressed to study the dynamic effects in the 1-m-long 120-mm-aperture Nb3Sn quadrupole magnet, i.e., HQ02b, designed, fabricated, and tested by the LHC Accelerator Research Program. The magnet has a short sample gradient of 205 T/m at 1.9 K and a peak field of 14.2 T. The test campaign has been performed at CERN in April 2014. In the specific tests, which were dedicated to the measurements of the dynamic inductance of the magnet during the rapid current discharge for a quench, the protection heaters were activated only in some windings, in order to obtain the measure of the resistive and inductive voltages separately. The analysis of the results confirms a very low value of the dynamic inductance at the beginning of the discharge, which later approaches the nominal value. Indications of dynamic inductance variation were already found from the analysis of current decay during quenches in the previous magnets HQ02a and HQ02a2; however, with this dedicated test of HQ02b, a quantitative measurement and assessment has been possible. An analytical model using interfilament coupling current influence for the inductance lowering has been implemented in the quench calculation code QLASA, and the comparison with experimental data is given. The agreement of the model with the experimental results is very good and allows predicting more accurately the critical parameters in quench analysis (MIITs, hot spot temperature) for the MQXF Nb3Sn quadrupoles, which will be installed in the High Luminosity LHC.

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. Q1 and Q3 are composed of magnets (called MQXFA) fabricated by the U.S. Accelerator Upgrade Project (AUP), with a magnetic length of 4.2 m. Q2a and Q2b consist 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.

A next step of energy increase of hadron colliders beyond the LHC requires high-field superconducting magnets capable of providing a dipolar field in the range of 16 T in a 50-mm aperture with accelerator quality. These characteristics could meet the requirements for an upgrade of the LHC to twice the present beam energy or for a 100-TeV center of mass energy future circular collider. This paper summarizes the activities and plans for the development of these magnets, in particular within the 16 T Magnet Technology Program, the WP5 of the EuroCirCol, and the U.S. Magnet Development Program.

By the end of October 2022, the US HL-LHC Accelerator Upgrade Project (AUP) had completed fabrication of ten MQXFA magnets and tested eight of them. The MQXFA magnets are the low-beta quadrupole magnets to be used in the Q1 and Q3 Inner Triplet elements of the High Luminosity LHC. This AUP effort is shared by BNL, Fermilab, and LBNL, with strand verification tests at NHMFL. An important step of the AUP QA plan is the testing of MQXFA magnets in a vertical cryostat at BNL. The acceptance criteria that could be tested at BNL were all met by the first four production magnets (MQXFA03-MQXFA06). Subsequently, two magnets (MQXFA07 and MQXFA08) did not meet some of the criteria and were disassembled. Lessons learned during the disassembly of MQXFA07 caused a revision to the assembly specifications that were used for MQXFA10 and subsequent magnets. In this article, we present a summary of: 1) the fabrication and test data for all the MQXFA magnets; 2) the analysis of MQXFA07/A08 test results with characterization of the limiting mechanism; 3) the outcome of the investigation, including the lessons learned during MQXFA07 disassembly; and 4) the finite element analysis correlating observations with test performance.