CEPC 650 MHz Superconducting Cavities Achieve Ultrahigh Gradient

Two 650 MHz single-cell superconducting cavities (#1 and #2) for the Circular Electron Positron Collider (CEPC) received vertical tests (@ 2.0 K) at the Platform of Advanced Photon Source Technology R&D (PAPS) in June and July. The accelerating gradients of the cavities reached 41.0 MV/m and 41.6 MV/m, respectively. At the gradient of 40 MV/m, the unloaded quality factor (Q0) reached 1.7E9 for #1 and 2.5E10 for #2. Moreover, the field emission was very weak during the vertical tests. The results above indicate that the post-process and vertical tests of both cavities were very successful.

The gradients of large (frequency < 1 GHz) superconducting cavities had never previously reached 40 MV/m in China because of low frequency, large volume and surface area. Furthermore, few large cavities have been able to reach the gradient of 40 MV/m abroad either. This time, both 650 MHz single-cell cavities exceeded 40 MV/m at IHEP, which lays the foundation for high Q research in the future.


Fig. Vertical test results of CEPC 650 MHz single-cell cavities (Image by IHEP)

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Mr. GUO Lijun