[en] For the underlying task to cool the Wendelstein 7-X (W7-X) superconducting coil conductors and the divertor cryo-pumps, an extended cryo-system is required. Besides the magnet coils and cryo-pumps proper, the coil housings and supports, the thermal shields of the cryostat and cryo-pumps, and the current leads (CL) have to be cooled. This is achieved by a refrigeration plant including coolant transfer lines and distribution boxes, and a widespread pipework within the cryostat. All these components are finally defined, and purchase actions are under way

[en] The refrigeration system for the W7-X superconducting magnet and the divertor cryo-vacuum pumps is presented. In total, five main helium cooling circuits have to be supplied by the refrigerator-four for the magnet including auxiliary equipment like support structure, thermal shield and current leads, and one for the cryo-pumps. For the shields of the latter, an additional LN₂-cooling circuit is required. The lowest operating temperature is 3.3 K. It will be provided by evacuating a sub-cooler bath using a cold or warm compressor. Three of the helium cooling circuits use altogether four identical cold circulators. Apart from the current leads which are supplied with the coolant from a LHe storage tank, the peak reserve power required is equal to 7 kW at 4.5 K entropy equivalent. However, this potential maximal demand occurs continuously for periods of only a few hours at most, and altogether for less than 1% of annual time. The refrigerator thus will be designed for 5 kW continuous power at 4.5 K_equiv. corresponding to 1.5 MW compressor connected rating. The reserve peak power will be covered, if necessary, by using the latent heat and vapour enthalpy of LHe from a storage tank. This supporting LHe stream is added to the phase separator and fed subsequently to the low pressure return stream at the cold end of the cold box. LN₂-pre-cooling equipment of the cold box - which is installed for W7-X cool-down anyway - can also be used to increase refrigeration power. The LHe required for maintaining reserve refrigeration power as well as for running the current leads is generally produced overnight when W7-X is in idle current mode. (author)

[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] 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. (paper)

[en] The thermodynamic properties of the carbon dioxide clathrate hydrate as well as hexagonal ice Ih have been calculated using Quasiharmonic Lattice Dynamic framework in connection with Molecular Dynamic methods in order to show the existence of the self-preservation effect in the carbon dioxide hydrates. The statistical thermodynamics theory has been applied to calculate the thermal expansion coefficients for hydrate and ice systems. The calculations clearly show that because the thermal expansion of the hydrate phase is limited by the thermal expansion of ice it is possible to keep the hydrate in a stable region within the phase diagram. The differences in thermal expansion should lead to the self-preservation effect with the application of additional pressure on the hydrate phase. This effect allows using the self-preservation effect for the storage and transportation of gas in the hydrate form. (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] Using the original approach that utilizes statistical thermodynamic theory that has been developed in our group the phase p-T diagram and hydrate phase composition have been calculated for “CO₂ + H₂ + H₂O”. Depending on the CO₂ content in the gas phase two hydrates types can be formed: CS-I and CS-II. It has been found that increasing CO₂ content in the gas phase drastically reduces hydrate formation pressure and in the same time reduces hydrogen uptake by the hydrate. While pure H₂ hydrates have CS-II structure, addition of more than 2 mol.% of CO₂ into the gas phase makes CS-I hydrate structure more stable, that displays worse maximum hydrogen content. These results could be helpful for practical use of hydrates for efficient CO₂ utilization and H₂ transportation. (paper)

[en] The European XFEL is a new research facility currently under construction at DESY in the Hamburg area in Germany. From 2015 on, it will generate extremely intense X-ray flashes that will be used by researchers from all over the world. The superconducting XFEL linear accelerator consists of 100 accelerator modules with more than 800 RF-cavities inside. The accelerator modules, superconducting magnets and cavities will be tested in the accelerator module test facility (AMTF). This paper gives an overview of the design parameters and the commissioning of the vertical insert, used in two cryostats (XATC) of the AMTF-hall. The Insert serves as a holder for 4 nine-cell cavities. This gives the possibility to cool down 4 cavities to 2K in parallel and, consequently, to reduce the testing time. The following RF measurement, selected as quality check, will be done separately for each cavity. Afterwards the cavities will be warmed up again and will be sent to the accelerator module assembly

[en] The European X-ray Free Electron Laser (XFEL), now under construction at DESY in Hamburg, will make an extensive use of 1.3 GHz superconducting cavities aimed at accelerating the electrons to the energy of 17.5 GeV. The cavities will be operated at 2 K with the use of saturated HeII. Prior to their assembly in accelerator cryomodules, the RF performance of the cavities will be cold-tested in two dedicated vertical cryostats. Each cryostat allows a simultaneous testing of 4 cavities mounted on a dedicated insert. The cryostats are equipped with external lines allowing their supply with liquid helium and further conversion of the helium into superfluid He II. The paper describes the test stand flow scheme, the technical key elements, including a recuperative heat exchanger, and the cold commissioning. The thermodynamic analysis of the cryostat cool down and steady-state operation is given. A Second Law of Thermodynamics based theoretical model of the heat exchanger performance, and the model experimental validation, is presented

[en] Using a combination of Quasiharmonic Lattice Dynamic and Molecular Dynamic Simulation methods in conjunction with well developed statistical thermodynamics theory the thermodynamic properties of nitrogen gas hydrates has been calculated, with the main focus on the thermal expansion coefficient. It is shown that nitrogen gas hydrate displays larger value of the thermal expansion coefficient in comparison with hexagonal ice Ih and empty gas hydrate lattice, moreover this value is very close to one of the carbon dioxide and to other hydrates that have self-preservation effect. Exactly because of this difference in the thermal expansion coefficient it is possible to confirm existence of the self-preservation effect. The self-preservation effect can be used for creation of low-cost technology of hydrates storage and transportation technology applicable for many gas types. (paper)