CERN Accelerating science

High thermal performance materials

Figure 1. (CERN)

CERN, GSI, POLITO and POLIMI  carry out an extensive characterization campaign of a broad range of advanced materials for applications in future particle accelerators, as well as high-technology industrial domains. The collaboration characterized both novel materials, currently under development, as well as commercially available carbon-based materials, including thin-film coatings. This work has been developed in the context of the H2020 project ARIES.

The development and use of high thermal performance materials, with low mass density and excellent resistance to thermal shocks, is increasingly becoming an enabling technology in a broad range of industrial and research applications.

In industry, these materials are appealing in a number of fields, such as high power electronics, avionics, energy production, aerospace, nuclear engineering, and luxury sports automotive. Researchers and engineers working in these domains require materials with efficient thermal management, high temperature resistance and mechanical robustness. In the field of fundamental research, some components of the high-energy particle accelerators largely share these requirements. In fact, beam-intercepting devices (BID), such as collimators, beam absorbers, catchers, dumps and targets, are routinely exposed to the impact of highly energetic and intense particle beams, making the selection of key materials extremely important.

This is especially true for the next-generation of accelerator facilities like the High-Luminosity upgrade of LHC (HL-LHC) at CERN, the Facility for Antiproton and Ion Research (FAIR) at GSI, or the proposed Future Circular Collider (FCC). They will exhibit increased beam intensities (in some cases by orders of magnitude). In combination with the shorter pulse lengths and greater particle densities requested by physics experiments, this leads to significantly higher transient thermo-mechanical loads in all beam-intercepting devices. Additionally, materials for some of these components must possess high electric conductivity to limit the destabilizing effects they may induce on particle beams circulating in their close vicinity.

Unfortunately, no existing material possesses the combination of physical, thermal, electrical and mechanical properties, imposed by such extreme working conditions. For instance, the material currently employed for the absorbers of LHC Collimator jaws (a two-dimensional carbon-fibre-reinforced carbon composite – CFC – ) is predicted not to satisfy the full set of requirements imposed by the severe working conditions expected in the HL-LHC from 2026. In particular, numerical simulations indicate that the limited electrical conductivity of CFC may induce electro-magnetic instabilities in the particle beam.

In recent years, CERN has collaborated with international laboratories, universities and industries to address these issues. After having commenced in the framework of EuCARD and EuCARD-2 projects, this partnership is continuing within H2020 ARIES collaboration, Work Package 17 (PowerMat), a Joint Research Activity, in cooperation with Work Package 14 (Promoting Innovation).

Carbon-based materials have a long history of applications in beam intercepting devices and their harsh radiation environments, thanks to their low activation, high radiation-hardness, thermal stability in combination with improved strength at high temperatures and low density. PowerMat focuses on the exploration of advanced types of carbons, such as various grades of isotropic graphite, thermal pyrolytic graphite, CFC and carbon foams. It has also targeted the development of novel composite materials based on the combination of graphite and diamond with metals or high performance ceramics.

In this context, a family of new graphite-matrix composites, reinforced with molybdenum carbides (Molybdenum Carbide – Graphite, MoGr) has been co-developed by CERN and Brevetti Bizz, an Italian SME, with the goal of increasing the electrical conductivity of the materials for the primary and secondary collimator jaws, while maintaining or improving the beam impact robustness of CFC. To further enhance the electrical conductivity of the jaw surface exposed to the beam, a thin film of electrically conductive metals or ceramics can be applied to the MoGr bulk material. Solutions under development are, for example, molybdenum, copper and titanium nitride coatings.

In order to assess the performance of these materials and gain a deeper understanding of their response to beam-induced dynamic thermal shocks, dedicated experiments are carried out at facilities like CERN’s High-Radiation to Materials (HiRadMat), GSI’s UNILAC and SIS 18 accelerators, with short-pulse, high-intensity beams.

 

 

Figure 2. (CERN)

WP17 partners have performed an extensive characterization of both commercially available advanced materials and newly developed composites. The characterization performed included the study of materials morphology and microstructure, the measurement of their thermal, electrical and mechanical properties, as well as their behaviour in ultra-high vacuum, and the study of application of thin films on the surfaces of the bulk materials. This campaign has allowed quantifying the advantages of novel composites, compared to commercial materials and has laid the ground for further optimizations and improvements in the development of advanced thermal management materials. It will be complemented in the course of the projects by additional characterization campaigns, including examination after long-term irradiation and experiments under high intensity particle pulses.

During the course of this work, the ARIES Consortium also plans to engage experts from space, aviation, car and electronic industry to exchange ideas on the latest developments in design, manufacture, testing and applications of novel thermal management materials. These industries could consider the novel materials developed in this WP for advanced engineering solutions, efficient energy solutions and thermal management, given their excellent thermal conductivity and high mechanical and shock resistance.

Rama Calaga (CERN)
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Workshop for extreme thermal management materials

 

The ARIES project organised its first workshop for Work Package 17 (WP17) “PowerMat” in Turin, Italy over 27-28 October 2017. The event hosted 30 participants from several Laboratories, Universities, and small companies.

The main objective of WP17 is the development and investigation (through both simulations and experiments) of novel materials for extreme thermal management related to particle accelerators and other challenging applications.

Many lively discussions and fruitful exchanges took place during the five sessions of the workshop. Each session was dedicated to a specific task of WP17, with special input regarding ARIES WP14 “Promoting Innovation”, which operates synergistically with PowerMat to provide material specimens and samples to be characterized and tested.

The main goal of the workshop was the presentation and discussion of results related to the latest developments of novel and advanced materials based on carbon and diamond. Besides excellent thermomechanical properties, these materials are required to resist the long-term effects of radiation, in the harsh accelerator environment. In this respect, material characterization campaigns are performed both on pristine and irradiated samples.

The first session of talks considered the investigation of metal carbide-reinforced graphite and fibre-reinforced graphite, with specific regard to their thermomechanical, microstructural and ultra-high vacuum characteristics. These materials are used in Collimators and Beam Intercepting Devices (BID), and must be optimized for the challenges of future high-energy particle accelerators.

The workshop also dedicated talks to the discussion of dynamic tests of advanced materials, with specific attention to experiments performed at the CERN HiRadMat facility. Several experiments were presented, including preliminary results from the MultiMat experiment, which took place in October 2017. The reusable, rotatable barrel hosted in the test bench allowed the testing of 18 different materials, ranging from very low-density carbon foams to high-density tungsten alloy, and three thin-film coatings under the most intense and energetic proton pulses available from CERN Super Proton Synchrotron (SPS).

The target stations were equipped with strain gauges, pressure sensors and thermal probes in order to acquire the dynamic response of the materials and benchmark the numerical results of the simulations. The experiment was concluded with more than 2·1015 protons delivered on target. All the carbon-based materials survived the maximum intensities, with energy densities exceeding those expected in the HL-LHC. The online instrumentations worked very reliably, providing a wealth of data for post-processing. The first analyses indicate a good agreement with the numerical and analytical predictions.

Workshop attendees also reviewed recent results of radiation damage studies from GSI, CERN and Polimi; and to agree on a plan for future simulations and experiments at various facilities in Europe and USA.


Importantly, PowerMat aims to explore the possible societal applications of novel materials in challenging domains, such as advanced engineering, medical imaging, quantum computing, energy efficiency, aerospace, and thermal management. In this context, researchers discussed the development of diamond-reinforced composites for luminescence screens, as well as optimization paths and experiments.


The visit of the DYNLab in Politecnico of Turin (Image: M. Scapin/Polito)

Attendees were also able to visit Polito’s DYNLab, a comprehensive facility for material testing in quasi-static and dynamic conditions, which will characterize materials for PowerMat. In addition, the programme featured a visit to Polito’s Additive Manufacturing facilities and invited talks on several inspiring topics, including Advanced Joining Technologies.

The presentations and interaction during these two days allowed participants to plan a large number of future activities as well as strengthen or launch new collaborations. Partners will report on the progress of their activities at the next WP17 meeting, to be held at the ARIES 2018 Annual Meeting in Riga, Latvia.

Special thanks go to Lorenzo Peroni and Martina Scapin at Polito, for their organisation of an inspiring venue with a unique context and atmosphere.

***

Header image: Participants of the Workshop of ARIES WP17 PowerMat, 27-28th November 2017, Politecnico of Turin, Italy (Image: M. Scapin/Polito)

Panos Charitos (CERN)
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