[en] The Hadron-Electron-Ring-Accelerator (HERA) at the German Electron Synchrotron (DESY) in Hamburg, Germany, was in operation between 1990 and 2007. Due to the implementation of a successive research project, the European X-ray free electron laser (XFEL), the existing HERA refrigeration plant has to be adapted to the new heat load requirements. The turn-key project was awarded to Linde Kryotechnik AG in June 2011 and comprises the revamp, modification and extension of the existing HERA refrigeration plant. The main challenge of this project is the insertion of a 2 K cooling loop of approximately 2.6 kW including a string of four cold compressors into the existing refrigerator system. (author)

[en] A superconducting linac will provide electron bunches of 17.5 GeV beam energy for the operation of the European X-ray Free Electron Laser (XFEL) at DESY. 800 superconducting niobium 1.3 GHz nine cell cavities and 100 superconducting magnet packages will be cooled in a liquid helium II cooling bath at 2.0 K temperature. Liquid helium II bath cooling at 2.0 K is established by means of a 4 stages cold compressor system. For the stable operation of cold compressors sudden load changes should be avoided. Electrical heaters in the helium II bath will compensate dynamic heat load changes caused by the radio frequency (RF) operation of the cavities in the XFEL linac. The complementary load operation of electrical heaters is studied at the existing facilities at DESY. Measurements performed at Cryo Module Test Bench (CMTB), Accelerator Module Test Facility (AMTF) and FLASH accelerator are reported. (paper)

[en] The RF operation of the about 800 superconducting 1.3 GHz 9-cell cavities of the XFEL linac requires helium II bath cooling at 2 K, corresponding to a vapor pressure of 3100 Pa. After the first cool-down of the XFEL linac to 4 K in December, 27^th 2016 the operation of the 2 K cryogenic system was started in January, 2^nd 2017. The 2 K cryogenic system consist of a 4-stage set of cold compressors to compress helium vapor at a mass flow of up to 100 g/s from 2400 Pa to about 110 kPa and a full flow bypass with an arrangement of heat exchangers and control valves.

This paper describes the XFEL refrigerating plant, especially the 2 K cryogenic system, the tuning of the cold compressor regulation to adapt to the XFEL linac static and dynamic heat loads and experience of about 6 months of operation. (paper)

[en] Beam commissioning of the European X-ray Free Electron Laser (European XFEL project) is ongoing. Commissioning the XFEL cryogenic system has started by cooling down the XFEL injector section in December 2015. The stationary operation was continued until August 2016. After intermediate warming up of the complete XFEL cryogenic system, the commissioning of remaining components including the 1.5 km long superconducting XFEL linear accelerator (linac) has commenced and was completed in beginning of December 2016. After conclusive pressure and leak tests, and flushing the cooldown started on 11 December 2016. Stable 4.5 K operation both for the linac and injector was established on 28 December. In this paper the XFEL cryogenic system is introduced and the first cooldown of the XFEL linac is reported. The cooldown sequences are described and the measured cooldown evolution is presented. Thermal losses of single circuits are given. Preliminary conclusions with the review of critical points are drawn. (paper)

[en] The measurement of coolant flow is important operational parameter for reliable operation of cryogenic system with superconducting magnets or cavities as well as for the system diagnostics in case of non-steady-state operation, e.g. during cool-down/warm-up or other transients. Proper flowmeter is chosen according to the different parameters, e.g. turn-down, operating temperature range, leak-tightness, pressure losses, long-term stability, etc. For helium cryogenics, the Venturi tube or Orifice, as well as Coriolis flow meters are often applied. For the present time, the orifices are usually used due to their simplicity and low costs, however, low turn-down range, large pressure drop, restriction of flow area, susceptibility to thermoacoustic oscillations limit their useful operation range. Operational characteristics of Venturi tubes is substantially improved in comparison to orifices, however, relative high costs and susceptibility to thermoacoustic oscillations still limit their application to special cases. The Coriolis flow meters do not have typical drawbacks of Venturi tube and orifices, however long-term stability over many years was not demonstrated yet. This paper describes the long-term behaviour of Coriolis flow meters after many years of operation at AMTF and XMTS facilities. (paper)

[en] The European X-ray Free Electron Laser (XFEL) is a research facility and since December 2016 under commissioning at DESY in Hamburg. The XFEL superconducting accelerator is 1.5 km long and contains 96 superconducting accelerator modules. The control system EPICS (Experimental Physics and Industrial Control System) is used to control and operate the XFEL cryogenic system consisting of the XFEL refrigerator, cryogenic distribution systems and the XFEL accelerator. The PROFIBUS fieldbus technology is the key technology of the cryogenic instrumentation and the link to the control system. More than 650 PROFIBUS nodes are implemented in the different parts of the XFEL cryogenic facilities. The presentation will give an overview of PROFIBUS installation in these facilities regarding engineering, possibilities of diagnostics, commissioning and the first operating experience. (paper)

[en] In Hamburg, the European XFEL project was completed. The superconducting XFEL linear accelerator was commissioned in the course of 2017. The linear accelerator supplies electron bundles with an energy of up to 17.5 GeV and serves as the source of a free-electron laser (XFEL), which provides light with extreme intensity and brilliance with wavelengths in the X-ray range (0.2-0.05 nm). The active part of the linear accelerator consists of 96 cryomodules, each with 8 high-frequency resonators (cavities) and a superconducting magnet packet. The approx. 800 cavities made of high-purity niobium are operated at 1.3 GHz and cooled in a helium II bath at a temperature of 2.0 K. The cavities are surrounded by two thermal shields at temperatures of 5-8 K and 40-80 K. Parallel to the main accelerator, an injector is supplied with two cryogenic modules. The cryogenics of the XFEL linear accelerator includes a helium refrigeration system with design capacities of 2 KW at 2 K, 4 KW at 5/8 K and 24 KW at 40/80 K, various helium transfer lines, a branched distribution system and connection boxes between the module chains in the accelerator tunnel. It is reported on the commissioning of the components and first operating experience.

[en] In order to produce short pulsed electron beam of 17.5 GeV energy, the XFEL linear accelerator is being built at DESY in Hamburg. Before being installed in the accelerator tunnel, 103 accelerator modules have to be tested in Accelerator Module Test Facility (AMTF). Cavities and cryomodules are tested at two vertical cryostats and three horizontal test benches. Two valve boxes and a liquid helium (LHe) storage tank are installed to enable cryogenic operation of AMTF. This paper describes our experience of three years cryogenic operation of AMTF. All 800 cavities and almost all cryomodules have been tested. The test results and lessons learned are also summarized (paper)

[en] The European X-ray Free Electron Laser (XFEL) is in operation at DESY. The superconducting XFEL linac will produce pulsed electron beam at an energy of 17.5 GeV. The linac consists of 768 superconducting niobium 1.3 GHz nine cell cavities and 96 superconducting magnet packages assembled in 96 cryomodules. Each cryomodule is 12 m long and includes a 2 K helium II bath circuit for the cavities, and 5/8 and 40/80 K thermal radiation shields. Before being installed in the XFEL linac tunnel all cryomodules were tested in the Accelerator Module Test Facility (AMTF.)

In this paper methods and results of static and dynamic heat load measurements of all XFEL cryomodules are reported. A comparison with first integral heat load measurements in the XFEL linac is given. (paper)

[en] In order to produce pulsed electron beam with the energy of 17.5 GeV, the XFEL linear accelerator is under construction. After the assembly but before being installed in the accelerator tunnel, 100 accelerator modules have to be tested in Accelerator Module Test Facility (AMTF). Two vertical cryostats and three horizontal test benches are devoted to the testing of cavities and cryomodules as well as two other cold boxes and liquid helium (LHe) storage tank are installed to enable their operation. This paper describes our experience with cryogenic operation of AMTF after two years of operation. (paper)