Mechanical robustness of HL-LHC collimator designs

Two new absorbing materials were developed as collimator inserts to fulfil the requirements of HL-LHC higher brightness beams: molybdenum-carbide graphite (MoGr) and copper-diamond (CuCD). These materials were tested under intense beam impacts at CERN HiRadMat facility in 2015, when full jaw prototypes were irradiated. Additional tests in HiRadMat were performed in 2017 on another series of material samples, including also improved grades of MoGr and CuCD, and different coating solutions. This paper summarizes the main results of the two experiments, with a main focus on the behaviour of the novel composite blocks, the metallic housing, as well as the cooling circuit. The experimental campaign confirmed the final choice for the materials and the design solutions for HL-LHC collimators, and constituted a unique chance of benchmarking numerical models. In particular, the tests validated the selection of MoGr for primary and secondary collimators, and CuCD as a valid solution for robust tertiary collimators

Innovative MoC - Graphite composite for thermal management and thermal shock applications

Innovative collimators are being investigated to handle the high energy particle beams foreseen in future upgrades of CERN Large Hadron Collider (LHC). This calls for the development of novel advanced materials, as no existing metal- or carbon-based material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by extreme collimator's working conditions. An ambitious research program has been undertaken at CERN and collaborating partners to investigate, process and characterize novel composite materials. A promising new family of materials has been identified in metal/ceramiccarbon composites: these are intended to combine optimum mechanical, thermal and electrical properties, such as mechanical strength, melting temperature, thermal shock resistance, electrical conductivity, and energy absorption. Besides High Energy Physics equipment, these materials are of particular interest for thermal management applications such as high power density electronic packaging, aerospace, automotive, nuclear fusion and solar energy. With that in mind, this paper aims at discussing the properties of investigated materials with respect to their relevance for the various application domains

Ultra-High Vacuum characterization of molybdenum-carbide graphite for HL-LHC collimators

Abstract. In view of the High-Luminosity upgrade of the Large Hadron Collider (LHC) collimation system, a family of novel molybdenum-carbide graphite (MoGr) composites was developed to meet the challenging requirements of HL-LHC beam-halo collimation, in particular the electrical conductivity and thermo-mechanical performances. The Ultra-High Vacuum (UHV) behaviour of this material was extensively characterized to assess its compatibility with the accelerator’s specifications. The results presented in this paper correlate the outgassing behaviour with the microscopic features of MoGr compared to other graphite-based materials. Residual gas analysis (RGA) was exploited to optimize post-production treatments

Mechanical robustness of HL-LHC collimator designs

Abstract Two new absorbing materials were developed as collimator inserts to fulfil the requirements of HL-LHC higher brightness beams: molybdenum-carbide graphite (MoGr) and copper-diamond (CuCD). These materials were tested under intense beam impacts at CERN HiRadMat facility in 2015, when full jaw prototypes were irradiated. Additional tests in HiRadMat were performed in 2017 on another series of material samples, including also improved grades of MoGr and CuCD, and different coating solutions. This paper summarizes the main results of the two experiments, with a main focus on the behaviour of the novel composite blocks, the metallic housing, as well as the cooling circuit. The experimental campaign confirmed the final choice for the materials and the design solutions for HL-LHC collimators, and constituted a unique chance of benchmarking numerical models. In particular, the tests validated the selection of MoGr for primary and secondary collimators, and CuCD as a valid solution for robust tertiary collimators.</jats:p

Quench Protection of Fusillo Subscale Curved CCT Magnet

The Fusillo project at CERN aims to design and build a demonstrator magnet with multi-harmonic corrected fields in a 90° curved CCT magnet. In the first stage, a subscale magnet is built with 30° bending, about 1/30 of the demonstrator conductor length, and increased current to reach coil stresses equivalent to the demonstrator. The subscale magnet enables qualification of the technology developments, fabrication methods, winding and assembly procedures, and magnetic and quench protection design and measurement setups. The subscale magnet comprises two tilted solenoids with an opposite inclination on curved aluminium formers. Each solenoid has two channel turns with 70 Nb-Ti/Cu wires. The magnet is protected by an active quench detection with energy extraction (EE). EE causes current decay, which induces eddy currents in the formers. As a result, the differential inductance of the magnet is reduced, and the formers heat up, with the potential to strongly influence the quench behaviour of the windings. Calculation of the eddy currents and heat propagation in the formers with simultaneous quench propagation in the magnet windings requires a three-dimensional (3D) simulation. A cooperative simulation approach has been developed to simulate transients in this magnet. It involves two software tools developed at CERN as part of the STEAM framework: a finite element-based tool called FiQuS and a finite difference-based tool called LEDET. FiQuS calculates eddy currents in the formers and the temperature of the formers, whereas LEDET calculates windings' temperature, current and voltage. This approach enables a 3D quench simulation with great geometrical detail while maintaining reasonable computational cost. The simulation results are compared to measurement results from the forced EE. The agreement between the measurements and simulations is presented, and the key factors that affect magnet quench behaviour are identified

Thermomechanical characterisation of copper diamond and benchmarking with the MultiMat experiment

The High-Luminosity Large Hadron Collider upgrade at CERN will result in an increase in the energy stored in the circulating particle beams, making it necessary to assess the thermomechanical performance of currently used and newly developed materials for use in beam intercepting devices such as collimators and absorbers. This study describes the thermomechanical characterisation of a novel copper diamond grade selected for use in tertiary collimators of the HL-LHC. The data obtained are used to build an elastoplastic material model and implemented in numerical simulations performed to benchmark experimental data obtained from the recently completed MultiMat experiment conducted at CERN's HiRadMat facility, where various materials shaped as slender rods were tested under particle beam impact. The analyses focus on the dynamic longitudinal and flexural response of the material, with results showing that the material model is capable of replicating the material behaviour to a satisfactory level in both thermal and structural domains, accurately matching experimental measurements in terms of temperature, frequency content, and amplitude

Curved-Canted-Cosine-Theta (CCCT) Dipole Prototype Development at CERN

Due to its flexibility in generating advanced field harmonic corrections and potential for low cost compared to traditional designs, the Canted Cosine Theta (CCT) configuration is particularly interesting for compact particle accelerators and gantries for medical applications. This article presents the design of a curved demonstrator named Fusillo, a Canted Cosine Theta Nb-Ti dipole magnet that is being developed at CERN, featuring a large aperture of 236 mm, a small bending radius of 1 m, a bending angle of 90$^{\circ }$, and multi-harmonic field correction, with a 3.61 T conductor peak field. We detail the magnetic coil design, incorporating high-order magnetic field correction of the errors produced by the heavily curved coil, peak field reduction at the coil ends, the development of a new rope type cable, and the mechanical design and the development of the former that supports the coil and provides the curved shape. We also present the first results of a subscale model used to qualify the coil's former manufacturing process, the rope cable, the coil winding optimization, and the coil impregnation system

Radiation-Induced Effects on LHC Collimator Materials under Extreme Beam Conditions

Over the last years, several samples of present and novel LHC collimator materials were irradiated under various beam conditions (using protons, fast neutrons, light and heavy ions at different energies and fluences) in different facilities around the world. This was achieved through an international collaboration including many companies and laboratories over the world. The main goal of the beam tests and the post-irradiation campaign is the definition of a threshold for radiation damage above which LHC collimators need to be replaced. In this paper, highlights of the measurements performed will be presented. First conclusions from the available data are also discussed

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10$^{20}$ p/cm$^2$ . We employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors

Beam-beam long range compensator mechanical demonstrator

Beam-Beam Long-Range Compensators employing current-carrying wires are considered as valuable options in hadron colliders to increase dynamic aperture at small crossing angles. This paper presents a simple design proposal for application at CERN LHC. The preliminary design allows for a certain scalability of the number of modules, current flowing in the wire, and dimensions. It complies with two key requirements: (a) the use of a thin, bare metal wire that allows for movement as near to the beam as necessary while minimising interactions with beam particles and meeting the specified DC current target; and (b) a wire support that is both an electrical insulator and a thermal conductor (ceramic).A molybdenum wire, vacuum brazed on an aluminium nitride support, is proposed, and the design is conceptually proved through the realisation and extensive test of a demonstrator device. The wire brazing validation, as well as the system's heat management, which are the most critical aspects, are given particular regard