Scientists have developed a new theoretical model for preparing particle accelerator structures made of niobium metal. The model predicts how oxygen in the thin oxide layer on the surface of the niobium metal moves deeper into the metal. This happens as the oxide layer dissolves during gentle heating. This heating is part of how a particle accelerator is made and prepared for use. Tests show that the model accurately describes the concentration profile of oxygen in niobium samples after the heat treatment. The tests also indicate that the treatment improves accelerator structure performance.
Engineers and researchers compare the tradition of crafting world-class particle accelerator structures to perfecting a recipe – it takes trial and error. Using this new theoretical model would, for the first time, allow designers to customize the accelerator structure preparation ‘recipe’ without losing time to trial-and-error testing. The model offers a way to fine-tune the inclusion of impurities near the surface. Now this fine-tuning can be done in a simpler process with fewer steps. The model may help accelerator builders predict the optimum ‘recipe’ for their needs.
Researchers and industry use particle accelerators for a wide range of tasks, such as cancer treatment, scientific research, and searching for oil. Building more efficient accelerators can therefore benefit many different industries. Niobium metal structures power today’s most advanced particle accelerators, and the best accelerator structures were once made of the purest niobium. Recent studies show that adding small amounts of nitrogen to these structures can make them more efficient. Careful heating of accelerator structures using a simpler process can similarly enhance their performance.
In this study, scientists from the Thomas Jefferson National Accelerator Facility (Jefferson Lab), Virginia Polytechnic Institute and State University, and North Carolina State University closely characterized a niobium heat treatment process that leads to enhanced performance. Oxygen was the key impurity in the enhancement. The researchers also developed a theory describing how the native niobium oxide layer dissolves during heating to describe how oxygen migrates into the niobium surface. They demonstrated that the theory reliably predicts oxygen profiles in test samples. The oxygen-alloyed niobium performed as well as nitrogen-alloyed niobium, increasing efficiency by 70 percent. In addition, the oxygen-alloying heat treatment process is simpler, cheaper and works on any accelerator cavity design. Because the process has less stringent requirements and fewer complicated steps, it should also be more easily reproduced at other facilities.
This material is based on work 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., RF surface resistance tuning of superconducting niobium via thermal diffusion of native oxide. Applied Physics Letters 119, 082601 (2021). [DOI: 10.1063/5.0059464]
Accelerators May Get a Boost from Oxygen, Jefferson Lab news release
Cooking Up a New Theory for Better Accelerators, Jefferson Lab news release
Reaching New Heights in Accelerator Technology, Jefferson Lab news release
How Particle Accelerators Work, DOE web article/infographic