International Workshop on Higher Order Modes in Superconducting Cavities (HOMSC2025)

CW operation characteristics of the spare Eu-XFEL third harmonic cryomodule

8 Oct 2025, 11:30

30m

Seminar Room IV (first floor) (CFEL (bld. 99))

Oral contribution Operation of SRF Facilities Operation of SRF Facilities

Speaker

Karol Kasprzak (MSL (Supraleitende Beschleuniger Technologie))

Description

The study investigated the continuous-wave (CW) performance of the spare 3.9 GHz third harmonic cryomodule for the European XFEL. While pulse mode operation exceeded specifications with high accelerating gradients, CW tests revealed strong limitations. The main issue was overheating of the first HOM coupler. Additional challenges included tuner backlash and mechanical resonances at 18.6 Hz affecting LLRF stability. The results indicate that, although well suited for pulsed operation, the cryomodule requires design modifications to HOM couplers to achieve reliable CW performance.