European XFEL Superconducting Cryomodules Characterization Toward Modules Acceptance and Future LLRF Operation

This paper describes some achievements of the low-level radio frequency (LLRF) tests performed to evaluate the superconducting cryomodules in preparation of their installation in the European X-ray Free Electron Laser (XFEL) accelerator. The software developed to characterize the cryomodules tested at the Accelerator Module Test Facility (AMTF) will be presented. The purpose of these tests is to evaluate some of the key parameters of the eight Tera Electronvolt Superconducting Linear Accelerator cavities, housed in every cryomodule. These parameters include: cavity quench gradients, cavity fundamental resonant modes, performance of the slow and fast frequency tuners, and characteristics of the input power coupler. These results impact the final decision on the cryomodule acceptance and its installation inside the linear accelerator (linac). In this approach, the MicroTCA.4-based LLRF system is used to control and assess the cryomodule performance. Middle layer servers are developed to verify the tests initial conditions, carry the test, and log the results in a dedicated database. The tests results provide a basis for the cryomodule validation, but also serve as a reference useful during the commissioning and operating phase of the accelerator.