Weld Qualification of the Cold Mass of the Superconducting Quadrupoles Magnets (MQXF) for the HL-LHC Project

The High Luminosity Large Hadron Collider (HL-LHC) is a major upgrade to the existing Large Hadron Collider (LHC) at CERN, aimed at increasing the integrated luminosity of the collider by a factor of ten [1]. A key component of the HL-LHC are the superconducting Nb3Sn quadrupole magnets, known as MQXF, whose purpose is to focus the particle beam [3]. In order to ensure the proper operation and structural reliability of the MQXF quadrupoles, it is essential to qualify the welds of their cold mass, used as a He container of the magnets. This paper describes the process of qualification of the welds involved in the closure of the cold mass, including the testing and inspection methods used to evaluate their strength and soundness. The results of the qualification process are used to ensure that the MQXF quadrupoles cold masses can withstand the high-stress operating conditions of the HL-LHC and operate as expected at cryogenic temperature. The qualification process has been used to implement a novel approach for quality control of the production parts using Phased Array Ultrasonic Testing (PAUT). This advanced testing method uses phased array ultrasonic probes to scan the welds and generate a detail 3D image of their internal structure. This allows for a more accurate and efficient inspection of the welds, compared to traditional ultrasonic testing methods. Overall, the welding qualification process for the cold mass of the MQXF quadrupoles is a crucial step in ensuring the safe and reliable operation of the HL-LHC.