Reviewed by Lexie CornerSep 19 2024
Researchers at Thomas Jefferson National Accelerator Facility have created a new set of tools to assist accelerator builders in better tracking and managing the properties of inner cavity surfaces. The study was published in Physical Review Accelerators and Beams.
Researchers have long thought pure niobium superconducting radiofrequency cavities were best for particle accelerators. Researchers are now using a toolkit to learn how to add impurities to the cavities to make them smoother—and more efficient. Image Credit: Thomas Jefferson National Accelerator Facility
Superconducting radiofrequency (SRF) cavities are essential components of advanced particle accelerators, generating the electromagnetic fields that accelerate subatomic particles. The performance of these cavities is affected by the cleanliness, shape, and smoothness of their inner surfaces. Scientists tested a new toolkit and found that smoother SRF cavities exhibit better performance, indicating that surface smoothness is a reliable predictor of cavity functionality. Additionally, by assessing the smoothness of a cavity's surface, the toolkit can accurately predict its performance.
The Impact
Niobium SRF cavities are the industry standard for efficient, high-power particle beam acceleration. Adding impurities like nitrogen or oxygen can increase their efficiency, but these enhanced cavities are less robust during high-power operations compared to pure niobium cavities.
This study investigated the surface roughness of cavities treated with additional nitrogen or oxygen, highlighting the crucial role of surface topography in performance. The findings suggest that the most cost-effective efficiency improvements can be achieved with oxygen. The toolkit developed through this research aims to help accelerator scientists optimize SRF cavities for future accelerators by controlling surface smoothness and impurities.
Summary
Particle accelerator scientists have developed a unique set of tools to study the topography of SRF cavities and its impact on performance. This toolkit is based on decades of empirical research in niobium SRF cavity surface processing. In this study, the team used the toolkit to analyze samples treated with the same methods used for cavities in upgrade projects at the DOE user facility, the Linac Coherent Light Source. These upgrades have recently expanded the DOE's fleet of SRF accelerators.
Their research revealed that performance is affected by grain boundaries formed during the manufacturing of niobium metal. These boundaries are lined with grooves resulting from the chemical processing of nitrogen-doped niobium. These grooves create a suppression factor of the superheating field, as predicted by an algorithm that uses differential surface geometry and atomic force microscope measurements. The grooves cause the doped surfaces to break down prematurely, reducing the performance of SRF cavities. Thus, achieving higher fields requires smoother surfaces.
The team also conducted new measurements on niobium samples using a simplified oxygen-doping process, which resulted in superior topography in these cavity samples.
This suggests that optimizing the impurity profile and surface smoothness could enhance performance in high fields and high efficiency, which would be beneficial for future DOE SRF accelerators like the Electron-Ion Collider (EIC).
Funding
This material is based on work funded by the DOE Office of Science Office of High Energy Physics and the Office of Nuclear Physics at the Department of Energy, as well as an Office of Nuclear Physics Early Career Award.
Journal Reference:
Eric, M. L., et al. (2024) Topographic evolution of heat-treated Nb upon electropolishing for superconducting rf applications. Physical Review Accelerators and Beams. doi.org/10.1103/physrevaccelbeams.26.103101