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The ITER Thermal Shields (TS) consist of actively cooled stainless steel panels. Their role is to minimise the radiation heat load from warm components, such as the Vacuum Vessel (VV) and the cryostat, hence contributing to insulating the magnet system operating at 4.5 K. The panels, cooled by 304L stainless steel pipes stitch welded to 10 mm to 20 mm thick 304LN plates, were coated by a low emissivity silver layer following welding of the pipes and bending operations. Pressurised He gas flows in the pipes at a temperature of 80 K and a pressure of 1.8 MPa at the inlet. These components have been manufactured and delivered to IO and their assembly had been started. Three leaks were detected in Helium leak tests during site acceptance test of the TS. A failure analysis was carried out based on advanced non-destructive and destructive examination techniques, including X-ray microtomography and Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM), confirming crack initiations of different severities, in particular presence of multi-branched “lightning bolt” transgranular cracks through the thickness of the pipes and of corrosion residues featuring high chlorine content. The root cause of the leakages has been univocally associated to Stress Corrosion Cracking (SCC), initiated by halide residues from the silver coating process in combination with the stress induced by the attachment, by welding, of the pipes to the plates. The paper summarises the results of these investigations and the lessons learned, the remedial actions implemented and the planned repair/replacement solutions.

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.

The design and production of Nb3Sn-based dipole and quadrupole magnets is critical for the realization of the High-Luminosity Large Hadron Collider (HL-LHC) at the European Organization for Nuclear Research (CERN). Nb3Sn superconducting coils are aimed at enhancing the bending and focusing strengths of accelerator magnets for HL-LHC and beyond. Due to the brittle nature of Nb3Sn, the coil fabrication steps are very challenging and require very careful QA/QC. Flaws in the Nb3Sn filaments may lead to quenches, and eventually, performance limitation below nominal during magnet testing. A novel inspection method, including advanced non-destructive and destructive techniques, was developed to explore the root-causes of quenches occurring in performance-limiting coils. The most relevant results obtained for MQXF coils through this innovative inspection method are presented. This approach allows for precise assessment of the physical events associated with the quenches experienced by magnet coils, mainly occurring in the form of damaged strands with transversely broken sub-elements. Coil-slice preparation, micro-optical observations of transverse and longitudinal cross-sections, and a deep etching technique of copper will be illustrated in the present work, with a focus on the results achieved for a CERN coil from a non-conforming quadrupole magnet prototype, and two coils fabricated in the US, in the framework of the Accelerator Upgrade Project (AUP) collaboration, from two different non-conforming quadrupole magnets, respectively. The results obtained through the proposed inspection method will be illustrated.

The cold powering test of the first two prototypes of the MQXFB quadrupoles (MQXFBP1, now disassembled, and MQXFBP2), the Nb3Sn inner triplet magnets to be installed in the HL-LHC, has validated many features of the design, such as field quality and quench protection, but has found performance limitations. In fact, both magnets showed a similar phenomenology, characterized by reproducible quenches in the straight part inner layer pole turn, with absence of training and limiting the performance at 93% (MQXFBP1) and 98% (MQXFBP2) of the nominal current at 1.9 K, required for HL-LHC operation at 7 TeV. Microstructural inspections of the quenching section of the limiting coil in MQXFBP1 have identified fractured Nb3Sn sub-elements in strands located at one specific position of the inner layer pole turn, allowing to determine the precise origin of the performance limitation. In this paper we outline the strategy that has been defined to address the possible sources of performance limitation, namely coil manufacturing, magnet assembly and integration in the cold mass.

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.

Following a decision made at the ITER Council in November 2013, two types of in-vessel coils (IVCs), namely, edge-localized mode (ELM) coils to mitigate ELMs and vertical stability (VS) coils to provide vertical stabilization of the plasma, have been incorporated in the ITER baseline design. The in-vessel environment is severe, characterized by large transient electromagnetic fields, high radiation flux, and high temperature. To withstand this environment and provide the required functionality, a “mineral insulated conductor” (MIC) technology has been selected for the IVC conductor. It consists of an axially water-cooled copper conductor surrounded by magnesium oxide insulation and a stainless steel jacket. A major advantage of the coil design is the choice of the same conductor material and dimensions for both VS and ELM coils, long conductor length which eliminates the need for any internal joints, and Cu welding for the joints between coils and feeders. In situ winding of the VS coils is asking for the development of a creative solution for the unspooling, straightening, precise winding tools, bending, forming, and metrology processes in a tight and congested environment. Mock-ups for design verification and manufacturing feasibility have been produced, in particular, for the bracket manufacture and to perform thermal and mechanical fatigue testing on an ELM control coil winding pack assembly. Installation trials of a half-size ELM control coil have been performed to verify the feasibility of the assembly procedure. This article will give an overview of the IVC design status and the progress of ITER IVC conductor manufacturing.

In many industrial applications, like high precision weighing and positioning, the elastic and dimensional stability of materials is required at a nanometric scale. High-resolution laser interferometry and mechanical spectroscopy have been employed to measure low-temperature anelastic creep of the short-fiber-reinforced composite Al-4 wt pct Cu-Al2O3. The typical strain resolution of the laser interferometer is 10-10. Fiber reinforcement has been found to increase the dislocation density in the metal matrix; in parallel, damping and anelastic creep are enhanced. This behavior has been explained on the basis of the structure of interparticle dislocations and θ′ relaxation.