RaDIATE set out to apply expertise in nuclear materials and accelerator beam intercepting devices to a broad range of high-power accelerator projects, with the ultimate goal of predicting operating lifetimes for a specified list of materials that are of particular interest for targets and beam windows.
In the framework of energy and intensity increase, new alternative materials for critical accelerator components, such as beam windows and secondary particle-production targets, are necessary to improve the performance, reliability and operation lifetimes of next-generation multi-megawatt accelerator target facilities.
The design of new materials in this context requires an understanding of how materials evolve and fail under high-energy radiation. Many of the phenomena controlling the evolution of target and window materials are analogous to those encountered during material irradiation in fusion and fission research, with a key difference being significantly higher (and continually increasing) particle energies used in accelerators.
Target materials
The following materials are of particular interest for use in beam-intercepting devices.
- Graphite and carbon-carbon composites
- Beryllium
- Titanium alloys
- Tungsten alloys
- Tantalum alloys
- Molybdenum alloys
- Austenitic stainless steels
- Ferritic-martensitic steels
- Aluminum alloys
- Nickel-based superalloys
- Silicon and silicon carbide
- Iridium
- Novel materials
- Other target, beam window and collimator candidate materials
The collaboration’s ultimate goal is to predict operating lifetimes for as many of these target materials as possible in terms of integrated proton fluence for the high-energy proton accelerator parameter space (e.g., temperature, dose rate, duty factor and dynamic stress), while accepting that such predictions are inherently challenging and may not be expected to be applied to safety-critical items.
A subset of the above list is identified as ripe for new experimental research, while examination of other materials may be accelerated through the application of research previously conducted, currently underway, or already planned as part of ongoing fission and fusion radiation damage R&D efforts.
For example, some of these materials, such as graphite and structural steels, have a long history of use in nuclear fission applications and a large body of research on irradiation effects, primarily due to low-energy neutrons.
Others, including beryllium and tungsten, have a more limited and recent body of work directed at fast neutron environments like fusion reactors. For example, Culham Centre for Fusion Energy has equipped the JET reactor with a tungsten/beryllium wall system.
Prioritization
Guidance provided by the high-power target community must prioritize previous or simultaneous experimental research because the current program may provide only enough resources to address one or two of these very dissimilar materials (depending on synergies with existing research). Thus, a key task is to assess and apply existing knowledge to new irradiation environments to determine each material’s effectiveness.
Materials not addressed by the initial program could be addressed in future or parallel collaborative activities.
Properties under evaluation
Some of the properties of interest include the following.
- Thermal diffusion (e.g., heat capacity and conduction)
- Tensile properties (yield and ultimate strength, elastic modulus and ductility)
- Fracture toughness
- Fatigue and creep-fatigue
- Thermal expansion
- Dimensional stability (swelling and void formation) and irradiation creep
- In-situ and post-irradiation annealing characteristics
- General corrosion characteristics (weight loss of material)
- Microstructural evaluation
Environments under evaluation
In the framework of the collaboration, the typical irradiation environments, as appropriate for each material and application under investigation, are as follows.
- Particle energy (1 MeV – 7 TeV)
- Irradiation temperature (100 – 2000° C)
- Atmosphere (inert, vacuum, low-humidity air and water)
- Displacement per atom (greater than 0.1 DPA)