Over the past several decades, superconducting radiofrequency (SRF) particle accelerators have helped researchers probe the fundamental structure of matter. Now, scientists at the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility are working to broaden their capabilities — and potentially reduce operating costs — by using niobium-tin coatings.
Credit: Jefferson Lab photo/Aileen Devlin
Members of the team who enabled the completion of Jefferson Lab’s Gray Enid I cryomodule.
Traditionally, SRF accelerators rely on cavities made from pure niobium, a metal that can conduct electricity without resistance when cooled to just a few degrees above absolute zero. While this approach has fueled advances in nuclear physics research, the technology is approaching its practical limits. Researchers are now looking to niobium alloys, especially niobium-tin (Nb₃Sn), to allow for higher superconducting temperatures and less demanding cryogenic systems.
In a new prototype named Gray Enid I, the Jefferson Lab team vaporized tin inside standard niobium cavities at temperatures above 1,100° C. This process allowed tin atoms to bind with the niobium surface, forming a thin Nb₃Sn layer. With a superconducting transition at around 18.3 Kelvin — nearly twice that of pure niobium — Nb₃Sn may enable cavities to run at higher temperatures and reduce the complexity and cost of cooling equipment.
Early attempts to coat older, previously used cavities revealed some challenges. Deforming cavities to tune their operating frequency after coating damaged the carefully prepared Nb₃Sn surface. To address this, the researchers refined their processes. They pre-tuned new cavities before coating, ensuring the Nb₃Sn layer remained intact and stable. According to Jefferson Lab SRF scientist Uttar Pudasaini, the updated approach improved performance, allowing the cavities to remain superconducting at higher temperatures and dissipate heat more effectively.
The coated cavities were then installed into a one-quarter cryomodule for further testing at Jefferson Lab’s Cryomodule Test Facility. The assembly successfully accelerated electrons beyond 10 million electron volts (MeV) at both 4.4 Kelvin and 2 Kelvin, results that closely matched earlier vertical tests. Achieving the 10 MeV benchmark is significant because it enables various applications beyond fundamental research, such as cancer treatment, medical device sterilization, and wastewater cleanup.
With these encouraging findings, the team will place Gray Enid I into Jefferson Lab’s Upgrade Injector Test Facility to evaluate how well it accelerates electron beams in a more realistic setting. If these tests confirm that Nb₃Sn-coated cavities can operate efficiently at temperatures closer to 4 Kelvin, it could reshape the design of future accelerators. Such a shift might lower energy consumption, simplify cryogenic systems, and pave the way for broader use of SRF accelerators in sectors like manufacturing and environmental remediation.
This progress builds on decades of SRF innovation at Jefferson Lab, supported by the DOE’s Office of Science. Although challenges remain, the Gray Enid I milestone suggests that with the right materials and assembly processes, researchers can enhance the versatility and efficiency of SRF technology and perhaps bring advanced accelerators into the mainstream.
Further Reading:
Award Enables Research for More Efficient Accelerators
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