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

Abstract

The future high luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC) at CERN will include eight (plus two spares) 8.4 m-long cryostatted cold masses which will be components of the triplets for two LHC insertion regions. Each cold mass will consist of two 4.2 m long Nb3Sn high gradient quadrupole magnets, designated MQXFA, with aperture 150 mm and operating gradient 132.6 T/m, for a total of twenty magnets. Before assembling and testing the final cold masses at Fermilab, the twenty component quadrupoles will be tested first at the vertical superconducting magnet test facility of the Superconducting Magnet Division at Brookhaven National Laboratory (BNL), in superfluid He at 1.9 K and to 18.0 kA, to meet LHC operational requirements. The first two full-length prototype quadrupole magnets, MQXFAP1 and MQXFAP2, have been tested at BNL. This paper reports on the quench test and training results of these magnets, and also the retest of the first prototype, rebuilt and designated as MQXFAP1b. The test results of these magnets will be important for validating the MQXFA design.

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

“…The test of the first MQXFA prototype (MQXFAP1) [8], performed at BNL Vertical Test Facility, was stopped after detection of a coil-to-ground short when magnet training had almost reached 17.5 kA. Test data analysis and autopsy [7] showed that this short had been caused by a series of issues, which we summarize in chronological order: 1) a coil (QXFP5) used in this magnet had an experimental S2-glass cloth (provided by a new vendor and with a denser fabric than all cloths previously used) on its outer surface that resulted in a non-conforming epoxy impregnation due to dry spots; 2) during the first quench, the test facility burst valve ruptured forcing a thermal cycle; 3) at room temperature heater-to-coil high-voltage withstand (Hipot) tests were performed at the pre-cooldown values (2.5 kV) and one heater of coil QXFP5 failed; 4) Hipot tests were repeated on the failed heater to assess its reduced insulation strength but ended up causing further degradation; 5) after cooldown the failed QXFP5 heater was found to be shorted to the coil and was disconnected from the heater firing unit and from ground.…”

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

“…MQXFAP1a was tested in the BNL vertical test facility and reported in [13] and [14]. The magnet experienced thermal cycles after the first and third quenches due to issues with the cryogenic system [13]. The magnet initially trained quicklyit had the highest first quench of the MQXF magnets to date, and took only 9 quenches to reach nominal current.…”

“…The magnet had a first quench at 13.3 kA and reached 15 kA in 10 quenches, which were followed by detraining quenches. The training performance of the magnet is reported in [13] and [14]. All coils participated in the quenches, but the magnet was not able to reach the nominal current.…”

“…However, with the exception of one more quench in 06, all subsequent quenches were located in Coil 03, previously tested in MQXFAP1. The maximum current reached was 17.69 kA after 15 quenches and several fall backs [13]. Weak epoxy properties may have contributed to the limited coil performance, and an extensive campaign to study the properties of the impregnated epoxy have begun.…”

Quench Protection of the First 4-m-Long Prototype of the HL-LHC Nb<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula>Sn Quadrupole Magnet

“…Extensive quench protection studies were performed on various 1.2 m long model magnets [18]- [25], which allowed defining protection parameters [26], [27]. The first 4.0 m long prototype magnet, named MQXFAP1, was tested at the Brookhaven National Laboratory (BNL) test facility in stand-alone configuration [28], [29].…”