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

Area of Science:

• Materials Science
• Particle Accelerator Technology

Background:

• Superconducting radio frequency (SRF) cavities are crucial for particle accelerators.
• Traditional bulk niobium cavities are expensive and have thermal management challenges.
• Depositing niobium films on copper offers a cost-effective alternative but faces challenges in film adhesion and uniformity.

Purpose of the Study:

• To develop a novel deposition technique for uniform niobium films on copper SRF cavity interiors.
• To address the challenge of achieving conformal superconducting films with excellent adhesive properties on complex geometries.
• To engineer the niobium-copper interface for improved superconducting performance.

Main Methods:

• Utilized a high-power impulse magnetron re-sputtering/sputtering (HiPIMRS) system for niobium film deposition.
• Implemented a re-sputtering process on copper substrates before niobium deposition to ensure an oxide-free interface.
• Characterized the niobium films using energy-dispersive x-ray spectroscopy, atomic force microscopy, electrical transport measurements, and X-ray diffraction (XRD).

Main Results:

• Achieved uniform niobium film deposition on 1.3 GHz copper cavity interiors.
• Confirmed an atomic-scale, oxide-free Nb/Cu interface, eliminating interfacial degradation.
• Observed ultra-smooth niobium surfaces (Ra < 20 nm for 3 μm films) and a critical temperature of 8.5 K.
• Demonstrated a (110)-oriented crystalline structure in the deposited niobium films.

Conclusions:

• The HiPIMRS system is a viable method for producing next-generation SRF cavities.
• Interfacial engineering protocols significantly enhance film conformity and superconducting performance.
• This approach offers a pathway to cost-effective and high-performance SRF cavity fabrication.