May 4 2022Reviewed by Alex Smith
Researchers have designed a new theoretical model for preparing niobium metal particle accelerator structures. The model predicts how oxygen moves deeper into the niobium metal from the thin oxide layer on its surface.
This occurs as the oxide layer dissolves as a result of gentle heating. This heating is part of how a particle accelerator is created and prepared for use. Tests reveal that the model precisely elucidates the concentration profile of oxygen in niobium samples after the process of heat treatment. The tests also reveal that the treatment enhances the performance of the accelerator structure.
Engineers and scientists liken the process of creating world-class particle accelerator structures to that of perfecting a recipe — it takes a lot of trial and error. For the first time, by using a new theoretical model, designers would be able to customize the accelerator structure preparation “recipe” without wasting time on trial-and-error testing.
The model allows for the fine-tuning of impurity inclusion near the surface. This fine-tuning can now be done in a more straightforward manner with fewer steps. The model could aid accelerator designers in determining the best “recipe” for their needs.
Particle accelerators are used by researchers and industry for a variety of tasks, including scientific research, cancer treatment and oil exploration. As a result, improving the efficiency of accelerators can benefit a wide range of industries.
Today’s most sophisticated particle accelerators are powered by niobium metal structures, and the finest accelerator structures were once produced of the purest niobium. According to recent research, adding small amounts of nitrogen to these structures can improve their efficiency. The performance of accelerator structures can also be improved by carefully heating them using a simpler process.
In the current study, a niobium heat treatment process that leads to improved performance has been closely characterized by researchers from the Jefferson Lab, Virginia Polytechnic Institute and State University, and North Carolina State University. The major impurity in the enhancement was oxygen.
The investigators also devised a theory to explain how oxygen moves into the niobium surface — explaining how the native niobium oxide layer dissolves during heating. They showed that the theory can predict oxygen profiles in test samples with a high degree of accuracy.
The oxygen-alloyed niobium was as efficient as the nitrogen-alloyed niobium, with a 70% increase in efficiency. Furthermore, the oxygen-alloying heat treatment process is easier, less expensive and compatible with any accelerator cavity design. Since the process has very few complicated steps and less stringent requirements, it should be easier to replicate at other facilities.
The study was supported by the Department of Energy (DOE) Office of Nuclear Physics and the DOE Office of Science, Office of High Energy Physics.
Lechner, E. M., et al. (2022) RF surface resistance tuning of superconducting niobium via thermal diffusion of native oxide. Applied Physics Letters. doi.org/10.1063/5.0059464.