Heat loads measurements at the XFEL cold linac

Abstract

Abstract The European X-Ray Free Electron Laser (EuXFEL) at DESY is in operation since the beginning of 2017. The free electron laser is based on a superconducting linear accelerator that delivers electrons to the undulator section with beam energy up to 17.5 GeV. The linear accelerator consists of 96 cryomodules; each 12 m long module is an assembly of 8 superconducting cavities and one superconducting magnet. This paper focusses on the measurement of the static and dynamic heat loads of the cryomodules assembled in the linac. Heat loads are an important parameter to evaluate the efficiency of the refrigerator system, the quality of the cryomodule assembly and installation and the accelerating cavity performances, being the dynamic heat loads proportional to the cavity quality factor (Q0, the ratio of the stored energy to the dissipated energy). The paper describes at first the procedure to measure the static heat load without beam energy and the dynamic heat loads at different beam energy levels. The measurement results are then summarized and compared with the XFEL design values.