Abstract
A full test of the cavity package concept under realistic operating condition was a necessary step before the assembly of the European XFEL (EXFEL) 3.9 GHz superconducting system and its installation in the accelerator. One cavity, equipped with magnetic shielding, power coupler and frequency tuner has been tested in a specially designed single cavity cryostat in one of the test benches of the DESY Accelerator Module Test Facility (AMTF). The cavity was operated at high pulsed power up to an accelerating field of $24\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, above the quench accelerating field of $21\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ achieved during the continuous wave (CW) vertical qualification test and with a large margin with respect to the EXFEL maximum operating specification of $15\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ for the 3.9 GHz system. All subsystems under test---coupler, tuner, waveguide tuners, low level radio-frequency (LLRF) system---were qualified to their design performances.
Highlights
A full test of the cavity package concept under realistic operating condition was a necessary step before the assembly of the European XFEL (EXFEL) 3.9 GHz superconducting system and its installation in the accelerator
The cavity was operated at high pulsed power up to an accelerating field of 24 MV=m, above the quench accelerating field of 21 MV=m achieved during the continuous wave (CW) vertical qualification test and with a large margin with respect to the EXFEL maximum operating specification of 15 MV=m for the 3.9 GHz system
The third harmonic system was technically commissioned and characterized by means of rf measurements performed directly in the injector building after installation. This was decided to limit the infrastructure work needed for adapting the Accelerator Module Test Facility (AMTF) for the testing of 3.9 GHz modules, to avoid slowing down the test schedule of the 101 1.3 GHz modules needed for the EXFEL linac, and considering the moderate performances needed by the 3.9 GHz cavities [5]
Summary
The correct operation of a superconducting cavity in an accelerator under nominal conditions requires a number of active and passive subcomponents. In order to validate the complete design of the cavity package in its operating environment a complete test of a cavity dressed with all its ancillary components is performed in a short horizontal cryostat, which preferably provides a mechanical environment similar to that of the cryomodules in the accelerator [1,2]. Such an activity took place at the DESY AMTF facility, in joint collaboration between DESY and INFN, for the characterization of the EXFEL 3.9 GHz cavity package. Coupling radio frequency antennas for the field pick-up probe and HOMs, and the magnetic shield (the top half of the parts connecting the cavities and the support structure of the module have been blanked for clarity)
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