Many Free Electron Lasers (FEL) are nowadays based on linear superconducting accelerators (linacs). The typical layout of such a linac consists of a number of cryomodules (CMs) arranged in strings. Each cryogenic circuit in a string is protected by safety valves (SVs) in case of failure of the system or a catastrophic event. A typical worst-case scenario considers the venting of the insulation vacuum, causing a fast and uncontrolled warm up of the cryogenic circuits. Such venting can for example take place across a pump port belonging to a string. The amount of heat deposited on each circuit is a very important parameter to correctly size the safety devices. This paper describes the tests performed at DESY on an EuXFEL cryomodule to evaluate the heat input to the three cryogenic circuits of the CM while venting the insulation vacuum. Test results are given with a particular focus of their application to long strings.

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.

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.

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.

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

In order to produce pulsed electron beam with the energy of 17.5 GeV, the European X-ray Free Electron Laser (XFEL) linear accelerator is under construction. The XFEL accelerator will contain the linear accelerator (linac) and the injector. The XFEL cryogenic distribution system supplies the linac and the injector with cooling helium. The cryogenic supply of the linac is separated in parallel cryogenic sections called 'strings'.Operation of the XFEL cryogenic distribution system is under the process control system for Experimental Physics and Industrial Control System (EPICS). A complementary component of EPICS is the Open Source software suit CSS (Control System Studio) providing an integrated engineering, maintenance and operating tools for EPICS as well as human machine interface.Cryogenic instrumentation used for operation and diagnostic is connected to PROFIBUS. More than 300 PROFIBUS nodes control the XFEL cryogenic system. DESY introduced the monitoring system based on Field Device Tool (FDT). FDT framework contains Data Tool Management (DTM) applications to examine the correct installation and configuration of all PROFIBUS nodes in real time.This paper describes the control system for the XFEL cryogenic distribution system including all steps from engineering to the pre-service tests.

Two accelerator cryomodules will be delivered for the XFEL injector-1. It comprises: an end cap of the 1.3GHz cryomodule, a feed cap with Joule-Thomson box of the 3.9GHz cryomodule, a feed box, a valve box and a transfer line connecting the feed cap with a feed box. The first injector will be located at the minus 7th level of XTIN. At this level the end cap, two accelerator cryomodules and the feed cap with the Joule-Thomson box are placed. The feed box and the injector valve box will be located at the minus 4th level. The cryogenic supply of the first injector‘s accelerator cryomodulesare separated from the supply of the second injector‘scryomodules and linac in the main tunnel.

The European XFEL is a 3.4 km long X-ray Free Electron Laser in the final construction and commissioning phase in Hamburg. It will produce 27000 bunches per second at 17.5 GeV. Early 2015 a first electron beam was produced in the RF-photo-injector and the

The superconducting accelerator module is the key component of the European X-ray Free Electron Laser (XFEL) project to be built at DESY Hamburg. The XFEL linear accelerator will consist of 100 accelerator modules in order to produce pulsed electron beam with the energy of 17.5 GeV. All accelerator modules have to be tested after the assembly and before being installed in the accelerator tunnel. The tests will take place in the Accelerator Module Test Facility (AMTF) being constructed at DESY. Besides test stands for testing superconducting cavities and magnets constituting the accelerator modules, AMTF will come with three test stands for testing the completed accelerator modules. This paper describes layout of the test stands within the AMTF, cryogenic design of the test stand, design issues of principal components and schedule.