High-power impulse magnetron re-sputtering/sputtering apparatus for Nb–Cu 1.3 GHz RF cavities

Journal article

Superconducting radio frequency (SRF) cavities constitute the cornerstone of high-efficiency particle accelerators. While traditional bulk niobium cavities have dominated the field, copper substrates with niobium films deposited inside the cavity represent a transformative approach for cost reduction and thermal management. However, achieving conformal superconducting films on complex cavity geometries remains a fundamental challenge, especially on the adhesive behavior of the film. Here, we present a breakthrough high-power impulse magnetron re-sputtering/sputtering (HiPIMRS) system engineered for uniform Nb film depositions on 1.3 GHz copper cavity interiors. Through a re-sputtering process on the copper substrates prior to deposition, we achieve atomic-scale interfacial integrity and eliminate interfacial oxides or degradation. Energy-dispersive x-ray spectroscopy confirms an oxide-free Nb/Cu interface, and atomic force microscopy reveals ultra-smooth surfaces (R_a < 20 nm for 3 μm films). Crucially, electrical transport measurements show that the niobium film has a critical temperature of 8.5 K throughout the cavity interior. XRD demonstrates a (110)-oriented crystalline structure. This work establishes HiPIMRS as a viable pathway for next-generation SRF cavity production, with interfacial engineering protocols offering generational advancements in film conformity and superconducting performance.

Authors: Dong, P; Wang, Y; Xiao, J; Bao, M; Liu, X

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Institute of Physics
• Journal: Review of Scientific Instruments
• Volume: 96
• Issue: 10
• Article number: 103901
• Publication date: 2025-10-20
• Acceptance date: 2025-09-28
• DOI: 10.1063/5.0287381
• EISSN: 1089-7623
• ISSN: 0034-6748
• Pmid: 41114626
• Language: English
• Keywords: superconducting films; engineering science; radiowave and microwave technology; crystal structure; energy dispersive x-ray spectroscopy; atomic force microscopy; thin film deposition; x-ray diffraction; particle accelerators; radiofrequency cavities