Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Medium-temperature (mid-T) furnace baking was conducted at 650 MHz superconducting radio-frequency (SRF) cavity for circular electron positron collider (CEPC), which enhanced the cavity unloaded quality factor (Q0) significantly. In the vertical test (2.0 K), Q0 of 650 MHz cavity reached 6.4 × 1010 at 30 MV/m, which is remarkably high at this unexplored frequency. Additionally, the cavity quenched at 31.2 MV/m finally. There was no anti-Q-slope behavior after mid-T furnace baking, which is characteristic of 1.3 GHz cavities. The microwave surface resistance (RS) was also studied, which indicated both very low Bardeen–Cooper–Schrieffer (BCS) and residual resistance. The recipe of cavity process in this paper is simplified and easy to duplicate, which may benefit the SRF community.

Design of Fundamental Power Coupler of 5 Cell Elliptical SRF Cavity Using CST Microwave Studio

A 5 cell elliptical cavity prototype has been build to accelerate the 100 MeV high beam of protons [1]. For cavity = 0.61 β g at 650 MHz in which the cavity structure is optimized by using the code from SUPERFISH [2]. The Q value of the cavity measured is 0.61x109 for 4.2 K. In the frequency range 2 – 5 GHz with CST MICROWAVE STUDIO [3]. It has been designed taking into account the advantages of both the waveguide type and coaxial type coupler This paper explains the current design of the cavity with a different angle of aperture and wall which have better mechanical stability and flatness, consisting of facilities for surface processing and less loss of beam. In this paper, the fundamental power coupler of a 5-cell 650MHz elliptical SRF cavity has been designed using CST MICROWAVE STUDIO. Here we have considered the ceramic window matching and co-axial to rectangular waveguide matching for the power coupler.