Design and Fabrication of the 1.9 K Magnet Test Facility at BNL, and Test of the First 4-m-Long MQXF Coil

The future high luminosity upgrade of the Large Hadron Collider (LHC) at CERN will include 20 4.2-m-long Nb$_3$Sn high gradient quadrupole magnets, which will be components of the triplets for two LHC insertion regions. In order to test these and four preproduction models, the vertical superconducting magnet test facility of the Superconducting Magnet Division (SMD) at Brookhaven National Laboratory (BNL) has been upgraded to perform testing in superfluid He at 1.9 K and 1 bar, the operational condition at the LHC. This has involved extensive modification of the 4.5 K cryogenics plant, including piping, compressors, and other upgraded components; a new vertical test cryostat, which can accept larger diameter magnets; a modernized power supply system upgraded with IGBT switches and fast shutoff capability, and that can supply 24 kA to test high field Nb$_3$Sn magnets; and completely new data acquisition, signal analysis, and control software and hardware, allowing for fast, high precision, large volume data collection. This paper reports on the design, assembly, and commissioning of this upgraded test facility, and presents results of the first magnet test performed.