The "Multimat" experiment at CERN HiRadMat facility: advanced testing of novel materials and instrumentation for HL-LHC collimators

The increase of the stored beam energy in future particle accelerators, such as the HL-LHC and the FCC, calls for a radical upgrade in the design, materials and instrumentation of Beam Intercepting Devices (BID), such as collimators Following successful tests in 2015 that validated new composite materials and a novel jaw design conceived for the HL-LHC collimators, a new HiRadMat experiment, named “HRMT36-MultiMat”, is scheduled for autumn 2017. Its objective is to determine the behaviour under high intensity proton beams of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. The test bench features 16 separate target stations, each hosting various specimens, allowing the exploration of complex phenomena such as dynamic strength, internal damping, nonlinearities due to anisotropic inelasticity and inhomogeneity, effects of energy deposition and radiation on coatings. This paper details the main technical solutions and engineering calculations for the design of the test bench and of the specimens, the candidate target materials and the instrumentation system

Design and Construction of an Instrumentation System to Capture the Response of Advanced Materials Impacted by Intense Proton Pulses

In recent years, significant efforts were taken at CERN and other high-energy physics laboratories to study and predict the consequences of particle beam impacts on devices such as collimators, targets, and dumps. The quasi-instantaneous beam impact raises complex dynamic phenomena which may be simulated resorting to implicit codes, for what concerns the elastic or elastoplastic solid regime. However, when the velocity of the produced stress waves surpasses the speed of sound and we enter into the shock regime, highly nonlinear numerical tools, called Hydrocodes, are usually necessary. Such codes, adopting very extensive equations of state, are also able to well reproduce events such as changes of phase, spallation, and explosion of the target. In order to derive or validate constitutive numerical models, experiments were performed in the past years at CERN HiRadMat facility. This work describes the acquisition system appositely developed for such experiments, whose main goal is to verify, mostly in real time, the response of matter when impacted by highly energetic proton beams. Specific focus is given to one of the most comprehensive testing campaigns, named “HRMT-14.” In this experiment, energy densities with peaks up to 20 kJ/cm3 were achieved on targets of different materials (metallic alloys, graphite, and diamond composites), by means of power pulses with a population up to 3 × 1013 p at 450 GeV. The acquisition relied on embarked instrumentation (strain gauges, temperature probes, and vacuum sensors) and on remote acquisition devices (laser Doppler vibrometer and high-speed camera). Several studies have been performed to verify the dynamic behaviour of the standard strain gauges and the related cabling in the chosen range of acquisition frequency (few MHz). The strain gauge measurements were complemented by velocity measurements performed using a customised long-range laser Doppler vibrometer (LDV) operating in the amplitude range of 24 m/s; the LDV, together with the high-speed video camera (HSVC), has been placed at a distance of 40 m from the target to minimize radiation damage. In addition, due to the large number of measuring points, a radiation-hard multiplexer switch has been used during the experiment: this system was designed to fulfil the multiple requirements in terms of bandwidth, contact resistances, high channel reduction, and radiation resistance. Shockwave measurements and intense proton pulse effects on the instrumentation are described, and a brief overlook of the comparison of the results of the acquisition devices with simulations, performed with the finite element tool Autodyn, is given. Generally, the main goal of such experiments is to benchmark and improve material models adopted on the tested materials in explicit simulations of particle beam impact, a design scenario in particle accelerators, performed by means of Autodyn. Simulations based on simplified strain-dependent models, such as Johnson–Cook, are run prior to the experiment. The model parameters are then updated in order to fit the experimental response, under a number of load cases to ensure repeatability of the model. This paper, on the other hand, mostly focuses on the development of the DAQ for HiRadMat experiments, and in particular for HRMT-14. Such development, together with the test design and run, as well as postmortem examination, spanned over two years, and its fundamental results, mostly in terms of dedicated instrumentation, have been used in all successive HiRadMat experiments as of 2014. This experimental method can also find applications for materials undergoing similarly high strain rates and temperature changes (up to 106 s-1 and 10.000 K, respectively), for example, in the case of experiments involving fast and intense loadings on materials and structures

10 kA joints for HTS roebel cables

Future high temperature superconductor (HTS) high field magnets using multitape HTS cables need 10-kA low-resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide-operating temperature range, from 1.9-85 K. The EuCARD-WP10 Future Magnets collaboration aims at testing HTS-based Roebel cables in an accelerator magnet. Usually, low temperature superconductor (LTS) cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO-coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally, the test results as a function of current and temperature are presented

Dynamic Testing and Characterization of Advanced Materials in a New Experiment at CERN HiRadMat Facility

An innovative and comprehensive experiment (named "Multimat") was successfully carried out at CERN HiRadMat facility on 18 different materials relevant for Collimators and Beam Intercepting Devices. Material samples, tested under high intensity proton pulses of 440 GeV/c, exceeding the energy density expected in HL-LHC, ranged from very light carbon foams to tungsten heavy alloys, including novel composites as graphite/carbides and metal/diamond without and with thin-film coatings. Experimental data were acquired relying on extensive integrated instrumentation (strain gauges, temperature sensors, radiation-hard camera) and on laser Doppler vibrometer. This allows investigating relatively unexplored and fundamental phenomena as dynamic strength, internal energy dispersion, nonlinearities due to inelasticity and inhomogeneity, strength and delamination of coatings and surfaces. By benchmarking sophisticated numerical simulations against these results, it is possible to establish or update material constitutive models, which are of paramount importance for the design of devices exposed to interaction with particle beams in high-energy accelerators such as the HL-LHC or FCC-hh

Dynamic testing and characterization of advanced materials in a new experiment at CERN HiRadMat facility

An innovative and comprehensive experiment (named "Multimat") was successfully carried out at CERN HiRadMat facility on 18 different materials relevant for Collimators and Beam Intercepting Devices. Material samples, tested under high intensity proton pulses of 440 GeV/c, exceeding the energy density expected in HL-LHC, ranged from very light carbon foams to tungsten heavy alloys, including novel composites as graphite/carbides and metal/diamond without and with thin-film coatings. Experimental data were acquired relying on extensive integrated instrumentation (strain gauges, temperature sensors, radiation-hard camera) and on laser Doppler vibrometer. This allows investigating relatively unexplored and fundamental phenomena as dynamic strength, internal energy dispersion, nonlinearities due to inelasticity and inhomogeneity, strength and delamination of coatings and surfaces. By benchmarking sophisticated numerical simulations against these results, it is possible to establish or update material constitutive models, which are of paramount importance for the design of devices exposed to interaction with particle beams in high-energy accelerators such as the HL-LHC or FCC-hh

Beam-Impact Validation of HL-LHC Collimator Materials: the "MultiMat-2" Experiment

In 2017, a proton-impact test HL-LHC collimator materials was carried out in the HiRadMat facility at CERN. The experiment, called “MultiMat”, enabled the testing of bulk and coated materials developed at CERN for different beam collimation functionalities. Manufacturing of these materials was then passed to the industry, leading to a series production for use in the collimators installed in the LHC during Long Shutdown 2 (LS2). The industrial versions of bulk and coating materials were tested in HiRadMat in 2021 in the “MultiMat-2” experiment, that efficiently re-used of the same experimental test bench as for “MultiMat”. This new experiment proved the reliability of the absorbers installed in LS2, and confirmed the possible use of alternative materials and coatings for the next LS3 collimator production. This paper describes the preparation and beam parameters of “MultiMat-2”, the experimental and data-acquisition equipment and the main results of the experiment

Dynamic Testing and Characterization of Advanced Materials in a New Experiment at CERN HiRadMat Facility

An innovative and comprehensive experiment (named "Multimat") was successfully carried out at CERN HiRadMat facility on 18 different materials relevant for Collimators and Beam Intercepting Devices. Material samples, tested under high intensity proton pulses of 440 GeV/c, exceeding the energy density expected in HL-LHC, ranged from very light carbon foams to tungsten heavy alloys, including novel composites as graphite/carbides and metal/diamond without and with thin-film coatings. Experimental data were acquired relying on extensive integrated instrumentation (strain gauges, temperature sensors, radiation-hard camera) and on laser Doppler vibrometer. This allows investigating relatively unexplored and fundamental phenomena as dynamic strength, internal energy dispersion, nonlinearities due to inelasticity and inhomogeneity, strength and delamination of coatings and surfaces. By benchmarking sophisticated numerical simulations against these results, it is possible to establish or update material constitutive models, which are of paramount importance for the design of devices exposed to interaction with particle beams in high energy accelerators such as the HL-LHC or FCC-hh.An innovative and comprehensive experiment (named “Multimat”) was successfully carried out at CERN HiRadMat facility on 18 different materials relevant for Collimators and Beam Intercepting Devices. Material samples, tested under high intensity proton pulses of 440 GeV/c, exceeding the energy density expected in HL-LHC, ranged from very light carbon foams to tungsten heavy alloys, including novel composites as graphite/carbides and metal/diamond without and with thin-film coatings. Experimental data were acquired relying on extensive integrated instrumentation (strain gauges, temperature sensors, radiation-hard camera) and on laser Doppler vibrometer. This allows investigating relatively unexplored and fundamental phenomena as dynamic strength, internal energy dispersion, nonlinearities due to inelasticity and inhomogeneity, strength and delamination of coatings and surfaces. By benchmarking sophisticated numerical simulations against these results, it is possible to establish or update material constitutive models, which are of paramount importance for the design of devices exposed to interaction with particle beams in high-energy accelerators such as the HL-LHC or FCC-hh

Dynamic Response of Advanced Materials Impacted by Particle Beams:The MultiMat Experiment

The introduction at CERN of new extremely energetic particle accelerators, such as the high-luminosity large hadron collider (HL-LHC) or the proposed future circular collider (FCC), will increase the energy stored in the circulating particle beams by almost a factor of two (from 360 to 680 MJ) and of more than 20 (up to 8500 MJ), respectively. In this scenario, it is paramount to assess the dynamic thermomechanical response of materials presently used, or being developed for future use, in beam intercepting devices (such as collimators, targets, dumps, absorbers, spoilers, windows, etc.) exposed to potentially destructive events caused by the impact of energetic particle beams. For this reason, a new HiRadMat experiment, named “MultiMat”, was carried out in October 2017, with the goal of assessing the behaviour of samples exposed to high-intensity, high-energy proton pulses, made of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. This paper describes the experiment and its main results, collected online thanks to an extensive acquisition system and after the irradiation by non-destructive examination, as well as the numerical simulations performed to benchmark experimental data and extend materials constitutive models.peer-reviewe

Dynamic Response of Advanced Materials Impacted by Particle Beams: The MultiMat Experiment

The introduction at CERN of new extremely energetic particle accelerators, such as the high-luminosity large hadron collider (HL-LHC) or the proposed future circular collider (FCC), will increase the energy stored in the circulating particle beams by almost a factor of two (from 360 to 680 MJ) and of more than 20 (up to 8500 MJ), respectively. In this scenario, it is paramount to assess the dynamic thermomechanical response of materials presently used, or being developed for future use, in beam intercepting devices (such as collimators, targets, dumps, absorbers, spoilers, windows, etc.) exposed to potentially destructive events caused by the impact of energetic particle beams. For this reason, a new HiRadMat experiment, named “MultiMat”, was carried out in October 2017, with the goal of assessing the behaviour of samples exposed to high-intensity, high-energy proton pulses, made of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. This paper describes the experiment and its main results, collected online thanks to an extensive acquisition system and after the irradiation by non-destructive examination, as well as the numerical simulations performed to benchmark experimental data and extend materials constitutive models