Within the conceptual design study for the Future Circular Hadron Collider (FCChh) it was shown, that a large part of the total cryogenic heat load falls into the temperature range between 40 to 60 K. Thus, additional cryogenic refrigerators for this temperature level are specified for each of the 10 foreseen cryoplants. Such a cryogenic system was developed at the TU Dresden and is based on a Brayton cycle working with a neon-helium mixture as refrigerant and using multistage centrifugal compressors. The duty requirements comprise a 6.2 MW total heat load at 40 to 60 K for beam screens and shielding, additional 2.7 MW at 300 to 40 K for the pre-cooling of the helium cycle and a turndown ratio of up to 3.8. The optimisation of the referenced system was performed in order to obtain a high efficiency of the cryogenic cycle and tolerable costs for system components at the same time. An analysis of the mixture composition influence on the components and on the total gas mass was performed. Restrictions for industrially existing hardware were taken into consideration. Updated cycle parameters are subsequently described.

The Cryogenic Moderator System (CMS) has been designed to cool high-energy neutrons down to cold neutrons in two cryogenic hydrogen moderators (four ones in the future) by forced flow of subcooled liquid hydrogen at 17 K and 1.0 MPa. At 5 MW proton beam power, an estimated nuclear heating of 6.7 kW (17.3 kW in the future) is generated in the moderators. The subcooled liquid hydrogen is circulated by two pumps arranged in series with a mass flow rate of 1 kg/s to maintain the average temperature rise over each moderator below 3 K and is cooled through a plate fin heat exchanger by a helium refrigerator with a cooling capacity of 30.3 kW at 15 K. The ESS moderator vessels are optimized for maximum cold neutron brightness and pure para-hydrogen, requiring a para concentration of > 99.5 %. An ortho-para-hydrogen convertor is integrated into the loop along with an online para-hydrogen measurement system. The pressure fluctuation caused by unpredictable abrupt changes of nuclear heating will be mitigated using a pressure control buffer with a volume of 65 l.

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100TeV. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.

Two trends can be found in current large-scale cryogenic projects. The first is the ever-increasing capacity requirements, while also a shift towards cooling demands at higher temperatures is observed. Conventional helium cycles require the use of oil flooded screw compressors, which are limited in efficiency, capacity, and reliability. Reverse-Brayton cycles with neon-helium mixtures deliver efficient refrigeration at a temperature above the dew point of neon, but cannot be applied to the cooling of conventional superconductors. This paper describes an approach where oxygen as a heavier gas allows the use of turbo-compressors viable. The oxygen is separated and used for providing refrigeration at higher temperature levels.

The use of superconductors in very long power transmission lines requires a reliable and effective cooling. Since the use of cryocoolers does not appear feasible for very long distances, a cryogenic refrigeration cycle needs to be developed. For cooling superconducting cables based on MgB2 (T-c = 39 K), liquid hydrogen (LH2) is the obvious cooling agent. For recooling LH2, one would need a refrigeration cycle providing temperatures at around 20 K. For this purpose, one could propose the use of a helium refrigeration cycle. But the very low molecular weight of helium restricts the use of turbo compressors, which limits the overall efficiency. In order to increase the molecular weight of the refrigerant a mixture of cryogens could be used, allowing the use of a turbo compressor. Temperatures below the triple point of neon are achieved by phase separation. This paper presents a possible layout of a refrigeration cycle utilizing a three component mixture of neon, hydrogen, and helium.

Following the update of the European strategy in particle physics, CERN has undertaken an international study of possible future circular colliders beyond the LHC. The study considers several options for very high-energy hadron-hadron, electron-positron and hadron-electron colliders. From the cryogenics point of view, the most challenging option is the hadron-hadron collider (FCC-hh) for which the conceptual design of the cryogenic system is progressing. The FCC-hh cryogenic system will have to produce up to 120 kW at 1.8 K for the superconducting magnet cooling, 6 MW between 40 and 60 K for the beam-screen and thermal-shield cooling as well as 850 g/s between 40 and 290 K for the HTS current-lead cooling. The corresponding total entropic load represents about 1 MW equivalent at 4.5 K and this cryogenic system will be by far the largest ever designed. In addition, the total mass to be cooled down is about 250’000 t and an innovative cool-down process must be proposed. This paper will present the proposed cryogenic layout and architecture, the cooling principles of the main components, the corresponding cooling schemes, as well as the cryogenic plant arrangement and proposed process cycles. The corresponding required development plan for such challenging cryogenic system will be highlighted.

High-energy neutrons are being decelerated by passing through supercritical parahydrogen circulated by pumps in a closed loop. Fluctuations in neutron heat load cause changes of the circuits' local and average temperature and hence significant pressure variations caused by the almost incompressible behavior of hydrogen. Solutions by adding a variable volume in form of a helium gas-backed metal bellow to mitigate pressure deviations are already in use. This paper presents an alternative approach by introducing a vertical storage vessel for supercritical hydrogen in a side branch of the moderator loop, with cold incompressible high density hydrogen at the bottom and warmer compressible lower density hydrogen at the top.

The European Spallation Sourcein Lund, Sweden, will be a 5 MW beam power neutron spallation research center. As subsystem of the target station the moderators play a vital role by slowing down high energy neutrons set free during the spallation process. To provide maximum neutron flux intensities with high availability for scattering experiments a conceptual liquid hydrogen moderator cooling circulation design proposal was developed. Supercritical hydrogen at 17 K will be utilized to absorb energy of the incoming neutrons in two parallel moderator vessels. A helium refrigerator provides the necessary cooling capacity by implementing an additional helium expansion turbine downstream the refrigerator coldbox. Strategies for the mitigation of pressure fluctuations due to beam trips are being presented. Solutions in form of electrical heaters and an accumulator or an expansion vessel are discussed. Different supercritical hydrogen circulator implementation scenarios are being matched to indicate the most reliable setup. For an efficient moderation process parahydrogen concentrations higher than 99% have to be guaranteed at the moderator inlet. Due to potential conversion of parahydrogen to orthohydrogen via irradiation processes the implementation of an ortho-parahydrogen catalyst bed is being evaluated. Methods for a continuous measurement of the apparent parahydrogen concentration at the moderator in- and outlet will be introduced. The arrangement and interaction of the components will be detailed in the paper.

In the course of the studies for the next generation particle accelerators, in this case the Future Circular Collider for hadron-hadron interaction (FCC-hh), different aspects are being investigated. One of these is the heat load on the beam screen, which results mainly from the synchrotron radiation. In case of the FCC-hh, a heat load of 6 MW is expected. The heat has to be absorbed at 40 to 60 K due to vacuum restrictions. In this range, refrigeration is possible with both helium and neon. Our investigations are focused on a mixed refrigerant of these two components, which combines the advantages of both. Especially promising is the possible substitution of the oil flooded screw compressors by more efficient turbo compressors. This paper investigates different flow schemes and mixture compositions with respect to complexity and efficiency. Furthermore, thermodynamic aspects, e.g. whether to use cold or warm secondary cycle compressors are discussed. Additionally, parameters of the main compressor are established.

The European Spallation Source (ESS) project is a neutron spallation source research facility currently being designed and built outside of Lund, Sweden. A linear accelerator delivers a 5 MW, 2.0 GeV, 62.5 mA proton beam to a spallation target to generate fast neutrons. Supercritical hydrogen circulates through two moderators surrounding the target, and transforms the fast neutrons emitted into slow neutrons, which are the final form of useful radiation. The supercritical hydrogen is in turn cooled from a helium cryogenic plant operating at 15-20 K. The supercritical cryogenic hydrogen circuit is a dynamic system, subject to significant changes in heat load. Proper pressure control of this system is critical to assure safe operation. The interaction between the hydrogen system and helium cryoplant poses unique challenges. This paper investigates the impact of the hydrogen system constraints on operation and control of the helium cryoplant, and suggests design options for the helium circuit.

In the search for the optimum process for the liquefaction of hydrogen, it was found that mixtures of helium and neon, called “Nelium”, allow processes with very high efficiency compared to pure helium or pure neon. This is demonstrated in the design of a 500 kW refrigerator between 40 and 60 K, whereby the composition is varied between pure helium and pure neon. It turns out that helium-rich mixtures have an advantage for the heat exchange, whereas the neon-rich mixtures are easier to compress in turbo compressors. In any case a process efficiency of over 44% is feasible.

In a future energy scenario, in which storage and transport of liquid hydrogen in large quantities will be used, the efficiency of the liquefaction of hydrogen will be of utmost importance. The goal of the IDEALHY working party is to identify the most promising process for a 50 t/d plant and to select the components, with which such a process can be realized. In the first stage the team has compared several processes, which have been proposed or realized in the past. Based on this information a process has been selected, which is thermodynamically most promising and for which it could be assumed that good components already exist or can be developed in the foreseeable future. Main features of the selected process are the compression of the feed stream to a relatively high pressure level, o-p conversion inside plate-fin heat exchangers and expansion turbines in the supercritical region. Precooling to a temperature between 150 and 100 K will be obtained from a mixed refrigerant cycle similar to the systems used successfully in natural gas liquefaction plants. The final cooling will be produced by two Brayton cycles, both having several expansion turbines in series. The selected overall process has still a number of parameters, which can be varied. The optimum, i.e. the final choice will depend mainly on the quality of the available components. Key components are the expansion turbines of the two Brayton cycles and the main recycle compressor, which may be common to both Brayton cycles. A six-stage turbo-compressor with intercooling between the stages is expected to be the optimum choice here. Each stage may consist of several wheels in series. To make such a high efficient and cost-effective compressor feasible, one has to choose a refrigerant, which has a higher molecular weight than helium. The present preferred choice is a mixture of helium and neon with a molecular weight of about 8 kg/kmol. Such an expensive refrigerant requires that the whole refrigeration loop is extremely tight.

In the framework of a collaboration, CRPP (Centre de Recherches en Physique des Plasmas) and WEKA AG have developed high-temperature superconductor (HTS) current leads for currents in the range of 3 to 30 kA, which are suitable for industrial fabrication. In the development project, two 10 kA HTS current leads, mainly distinguished by the design of the copper heat exchanger and the transition zone between the HTS module and the heat exchanger, have been manufactured by WEKA AG and tested at CRPP. The test of the current leads covered their behavior under normal operating conditions as well as in the case of a loss of flow. Furthermore, a quench of the current leads was initiated by increasing of the helium temperature by means of heaters immediately before the inlet. The measured quench temperatures provide an estimate of the operational limits of the 10 kA HTS current leads.

A broad acceptance of hydrogen as an alternative energy carrier requires cost-efficient production, transport and storage solutions. Liquid hydrogen can play an important role in these scenarios. But it is a necessity that the hydrogen liquefaction is performed in a very efficient way. The best liquefaction plants in operation today, have a power requirement of about 11 kWh/kg of liquid hydrogen. Several partners from industry and research institutes are presently working together in the IDEALHY project and are developing the conceptual design of a large capacity hydrogen liquefaction plant, which has a power consumption lower than 7 kWh/kg. In the paper the method of identification of the most promising liquefaction process will be described. The search for suitable components for a plant with a capacity of 50 t/d is under way and first results of this investigation will be reported.

This paper elaborates a concept for designing efficient large scale hydrogen liquefaction plants, based on dividing the process into 4 independent stages and finding the optimum solution for each stage. The main focus is put on the precooling stage. Not because of its power consumption, but because it is the stage with the most degrees of freedom in design. Several processes have been discussed, mentioning some of the main advantages and disadvantages. One of the main challenges in efficient hydrogen liquefaction is light gas compression. This is unavoidable, since only light gases can provide cooling at the required temperature levels, but should be minimized by using heavier fluids where possible. Due to the higher exergy efficiency of compression compared to refrigeration, the hydrogen feed pressure should be as high as possible, as long as the pressure reduction in the liquefaction stage is performed by expansion machines instead of throttling.

The goal of the IDEALHY project is to identify processes and components, which allow liquefying hydrogen with a power consumption much lower than with plants built so far. This requires comparing different possible processes concerning power efficiency, investment cost and compactness. The power consumption of a process depends on a number of boundary conditions. Without a clear overall definition of these boundary conditions, all statements and comparisons on the overall power consumption are questionable. So in the first step of the project the participants agreed on common boundary conditions.Then it turned out, that the choice of the high pressure of the feed hydrogen influences strongly the rest of the liquefaction process, especially the region below 80 K. For this region there is an option between helium, hydrogen and neon as refrigerants and their mixtures. For the final choice of the working fluid and the process one has to identify the maximum possible circumferential speed of turbo compressors.

For environmental reasons more and more cars, trucks and buses are using compressed natural gas (CNG) as fuel. This trend could be enlarged, if there were more CNG gas stations. Presently such stations can only be built near the distribution grid of natural gas. To build a station away from the grid, it would be necessary to transport the natural gas there in form of liquefied natural gas (LNG). Sometimes it is economical to transport the LNG from far away locations, but it would be beneficial, if gas companies could produce LNG within their own grid.An optimum location for such a small LNG production facility would be a place in the grid, where high pressure gas from the pipeline with a pressure higher than 40 bar is throttled to a medium pressure distribution grid with a pressure below 6 bar. Here one can efficiently liquefy a small part stream. The main stream is used to supply precooling due to the Joule-Thomson effect. It can act as heat sink for the heat given off by the liquefaction process and it also can absorb those components of the natural gas, which are separated upstream or during the liquefaction process like H2O, CO2, higher hydrocarbons and N-2.The liquefaction process is a Joule-Thomson process supported by precooling of a cascade with e.g. CO2 and ethylene as refrigerants. To improve the quality of the CNG for the use in internal combustion engines it is advisable to reduce the content in ethane below about 3 %. For this purpose one can include a small rectification column in the process, which can work at a pressure level between 10 and 40 bar.The concept is usable for plant sizes between 5 and 50 T/d. The power consumption is in the order of 0.2 to 0.22 kWh/kg, which is lower than the specific power needed in large bulk LNG facilities.

High temperature superconductor current leads have been demonstrated to provide cryogenic savings compared to conventional copper leads. The applicability of HTS current leads to industrial fabrication is now a possibility. CRPP and WEKA AG are collaborating in the development of current leads for currents in the range of 3 kA to 30 kA, which are suitable for industrial fabrication. The design of these leads is such that the architecture and construction can be easily scaled to the required current level. The main components of these current leads are an HTS module, a copper heat exchanger, and cold and warm end connections. Two 10 kA prototype current leads, mainly distinguished by different designs of the copper heat exchanger, will be constructed. They will be tested at CRPP to verify the manufacturing processes and the overall design.