Studies of LL-type 500MHz 5-cell superconducting cavity at SINAP

TL;DR

This paper reports the development and testing of a 500 MHz superconducting 5-cell cavity with optimized performance, achieving high accelerating voltage and quality factor, demonstrating promising results for accelerator applications.

Contribution

The study presents a successful design, fabrication, and surface treatment process for a low loss superconducting cavity with improved performance and damping of higher order modes.

Findings

Achieved over 7.5 MV accelerating voltage at 4.2 K

Quality factor exceeded 1E9

No significant multipacting or field emission observed

Abstract

A low loss (LL) type 500 MHz 5-cell superconducting niobium prototype cavity with large beam aperture has been developed successfully including the optimization, the deep drawing and electron beam welding, the surface treatment and the vertical testing. The performance of the fundamental mode was optimized and the higher order modes were damped by adopting an enlarged beam pipe for propagation. Surface preparation or treatment including mechanical polishing, buffered chemical polishing and high pressure rinsing with ultra-pure water and so on was carried out carefully to promise a perfect inner surface condition. The vertical testing results show that the accelerating voltage higher than 7.5 MV was obtained while the quality factor was better than 1E9 at 4.2 K. No obvious multipacting or field emission was found during the test. However, a quench happened while increasing the field a little higher than 7.5 MV that at present limited the cavity performance.