Medium-temperature furnace baking of 1.3 GHz 9-cell superconducting cavities at IHEP

Abstract

Abstract Recently, heat treatment in the range of 250 °C–500 °C has been attempted with the aim of improving the quality factor ( Q ) of superconducting radio-frequency (SRF) cavities worldwide. Herein, medium-temperature (mid-T) furnace baking experiments were conducted at the Institute of High Energy Physics to obtain higher Q values. First, 1.3 GHz 1-cell cavities received mid-T furnace baking at different temperatures, resulting in not only the improvement of Q but also an anti- Q -slope behavior. Furthermore, mid-T furnace baking was applied to six 1.3 GHz 9-cell cavities, all of which indicated higher Q and anti- Q -slope behavior. The average Q was 3.8 × 10 10 at 16 MV m −1 . The maximum gradients of the 9-cell cavities were 22.7–26.5 MV m −1 . Finally, the mid-T furnace baked 1.3 GHz 9-cell cavities were welded with helium vessel, with no degradation in the vertical tests. In addition, the mid-T furnace baking process was simplified in comparison with European X-ray Free Electron Laser and Linear Coherent Light Source because of the cancellation of light electro-polishing. This simplification is beneficial in the mass production of SRF cavities with high Q , which are widely adopted in free electron lasers and high-energy colliders.