Diamond Neutron Monochromator

Neutron research is critical to materials innovation, life sciences, physics, and, as such, the competitiveness of American industries. Current and future nuclear reactors and spallation sources require advanced neutron monochromators with improved energy selection and resolution. A diamond crystal with an appropriate mosaic distribution and dimensions would theoretically be the ultimate neutron monochromator, thanks to its ideal crystalline and nuclear properties. At present, diamond has limited usage in neutron optics components due to availability, cost, and size limitations, despite recent progress in lab-grown diamond growth that is shifting these barriers. Currently, there are no domestic suppliers of neutron diamond optics components in the United States to support this rapidly developing field. Plastically deformed perfect single crystals are ideally suited for focusing neutron beams because of the deterministic nature of their "mosaic" structure. While silicon and germanium monochromators have been developed based on this principle, sufficiently thick diamond plates cannot be bent under normal conditions due to their brittleness. Euclid Beamlabs, in collaboration with the Neutron Sciences Directorate at ORNL, proposes to overcome this limitation by bending diamond plates under extreme high-pressure, high-temperature (HPHT) conditions where plasticity is significantly improved. We will use Euclid's HPHT diamond growth apparatus, modified for pressure gradient diamond substrate bending. Unique total environmental control and material characterization of all processing steps will be utilized to achieve the required radius of curvature for neutron monochromator specifications. We will design a novel high-pressure (HP) cell to create an appropriate pressure gradient distribution inside. We will optimize the pressure cell components' geometries and materials for effective diamond plate bending using 3D finite element modeling. Several iterations of experiments with varied ambient conditions (pressure, temperature), HP cell parameters, and diamond substrate dimensions (up to 12x12x1 mm3) will be carried out to achieve controllable crystal bendings. Extensive material characterization (sequential rocking curve imaging, induced strain analysis, high-resolution X-ray, and neutron diffraction) will be performed before and after each experiment. These results and other optical and material characterizations will be analyzed and summarized in the final Phase 1 report. The project's long-term goal is to establish the first USA-based HPHT diamond neutron optics facility capable of producing monochromators that meet neutron source requirements. The diamond bending technology developed here is required to utilize neutron beams at current and future upgrades of nuclear reactors and spallation sources to their maximum potential. Diamond single crystals are potentially the best material for neutron monochromators at short wavelengths. If a manufacturing technology for large-size HPHT-bent diamond substrates is established, diamond-based neutron optical elements will supersede the current silicon and beryllium alternatives, which have lower performance and severe health and safety concerns. The diamond bending technology will also benefit X-ray optics, quantum computing, defense, medical, and other industrial applications.