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The technical properties of helium II ("superfluid" helium) are presented from the user point of view. Its applications to the cooling of superconducting devices, particularly in accelerators and colliders are discussed in terms of heat transfer capability and limitations in conductive and convective modes. Large-capacity refrigeration techniques b...
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Context 1
... e.g. for power heat transport over macroscop intimate stabilization of superconductors, they require elaborate the cooling circuits, conductor, insulation and coil assemblies. This o technical or economic requirements of the projects and acceptable trad 2. PRESSURIZED VERSUS SATURATED SUPERFLUID HELIUM A look at the phase diagram of helium (Fig. 3) clearly shows the saturated helium II, reached by gradually lowering the pressure down t saturation line, and pressurized helium II, obtained by subcooling li saturation, and in particular at atmospheric pressure (100 kPa). Although requiring one more level of heat transfer and additional particular a pressurized-to-saturated helium II ...
Context 2
... properties of helium at saturation (Fig. 3) impose to mainta below 1.6 kPa on the heat sink of a 1.8 K cryogenic system. Bringing to atmospheric pressure thus requires compression with a pressure rat times that of refrigeration cycles for "normal" helium at 4.2 K. For e.g. in small laboratory cryostats, this is achieved by means of stan vacuum pumps, handling the very-low ...
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The pressurized superfluid cooling system has been completed a final adjustment with the 920 MHz NMR in 2002. The superfluid cooling system used this time had been using for the 920 MHz NMR from 2002 to 2007. The first cooling system was able to automatically control the cooling of the superconducting coil to 1.55 K +/- 5 mK, and it was possible to...
Operation scenario for half-wave resonator (HWR1) cryomodule is made to produce PLC and EPICS. P&ID is shown for HWR1 cryomodule, which is operated at 2.1 K. Superfluid helium properties of viscosity, thermal conductivity and Stokes’ drag are introduced. Operation scenario includes cool-down procedure, operation with beam, warm-up procedure, interl...
The technical properties of helium II ("superfluid" helium) are presented from the user point of view. Its applications to the cooling of superconducting devices, particularly in accelerators, are discussed in terms of heat transfer capability and limitations in conductive and convective modes. Large-capacity refrigeration techniques below 2 K are...
Citations
... However, at the end, the capacity of the recovery compressor limits the increment of the pump units. Then against more heat loads, say more than about 300 W at 2 K, another kind of superfluid helium cryogenic system, which introduces cold compressors, should be considered and constructed [3]. ...
Recent accelerator projects at KEK, such as the Superconducting RF Test Facility (STF) for R&D of the International Linear Collider (ILC) project and the compact Energy Recovery Linac (cERL), employ superconducting RF cavities made of pure niobium, which can generate high gradient acceleration field. Since the operation temperature of these cavities is selected to be 2 K, we have developed two 2 K superfluid
helium
cryogenic systems for stable operation of superconducting RF cavities for each of STF and cERL. These two 2 K superfluid
helium
cryogenic systems are identical in principle. Since the operation mode of the cavities is different for STF and cERL, i.e. the pulse mode for STF and the continuous wave mode for cERL, the heat loads from the cavities are quite different. The 2 K superfluid
helium
cryogenic systems mainly consists of ordinary helium liquefiers/refrigerators, 2 K refrigerator cold boxes, helium gas pumping systems and high-performance transfer lines. The 2 K refrigerators and the high-performance transfer lines are designed by KEK. Some superconducting RF cavity cryomodules have been already connected to the 2 K superfluid
helium
cryogenic systems for STF and cERL respectively, and cooled down to 2 K successfully.
... applications such as superconducting RF acceleration cavities, lowering the operating temperature drastically reduces the BCS term of the surface resistance and thus the dynamic losses, particularly at high frequency. While the primary justification of He II cooling is the lower operating temperature, the excellent transport properties of the fluid can also be exploited to improve the stabilization of the superconductors, simplify the cooling scheme -a particularly acute technological challenge in extended systems with limited access such as large particle accelerators -, avoid boiling instabilities in two-phase cooling, and even enable precision calorimetry for diagnostics [3]. ...
Superfluid
helium is increasingly used as a coolant for superconducting devices in particle accelerators: the lower temperature enhances the performance of superconductors in high-field magnets and reduces BCS losses in RF acceleration cavities, while the excellent transport properties of superfluid
helium can be put to work in efficient distributed cooling systems. The thermodynamic penalty of operating at lower temperature however requires careful management of the heat loads, achieved inter alia through proper design and construction of the cryostats. A recurrent question appears to be that of the need and practical feasibility of an additional screen cooled by normal helium at around 4.5 K surrounding the cold mass at about 2 K, in such cryostats equipped with a standard 80 K screen. We introduce the issue in terms of first principles applied to the configuration of the cryostats, discuss technical constraints and economical limitations, and illustrate the argumentation with examples taken from large projects confronted with this issue, i.e. CEBAF, SPL, ESS, LHC, TESLA, European X-FEL, ILC.
... applications such as superconducting RF acceleration cavities, lowering the operating temperature drastically reduces the BCS term of the surface resistance and thus the dynamic losses, particularly at high frequency. While the primary justification of He II cooling is the lower operating temperature, the excellent transport properties of the fluid can also be exploited to improve the stabilization of the superconductors, simplify the cooling scheme -a particularly acute technological challenge in extended systems with limited access such as large particle accelerators -, avoid boiling instabilities in two-phase cooling, and even enable precision calorimetry for diagnostics [3]. ...
Cryogenics has become a key ancillary technology of particle accelerators and detectors, contributing to their sustained development over the last fifty years. Conversely, this development has produced new challenges and markets for cryogenics, resulting in a fruitful symbiotic relation which materialized in significant technology transfer and technical progress. This began with the use of liquid hydrogen and deuterium in the targets and bubble chambers of the 1950s, 1960s and 1970s. It developed more recently with increasing amounts of liquefied noble gases - mainly argon, but also krypton and even today xenon - in calorimeters. In parallel with these applications, the availability of practical type II superconductors from the early 1960s triggered the use of superconductivity in large spectrometer magnets - mostly driven by considerations of energy savings - and the corresponding development of helium cryogenics. It is however the generalized application of superconductivity in particle accelerators - RF acceleration cavities and high-field bending and focusing magnets - which has led to the present expansion of cryogenics, with kilometer-long strings of helium-cooled devices, powerful and efficient refrigerators and superfluid helium used in high tonnage as cooling medium. This situation was well reflected over the last decades by the topical courses of the CERN Accelerator School (CAS). In 1988, CAS and DESY jointly organized the first school on Superconductivity in Particle Accelerators, held at Haus Rissen in Hamburg, where I shared the h. and duty of lecturing on cryogenics with Professor J.L. Olsen of ETH Z rich, while P. Seyfert of CEA Grenoble delivered an evening seminar on superfluidity. This successful school was reiterated in 1995, with cryogenics being addressed by Professor W.F. Vinen of University of Birmingham (superfluidity), as well as J. Schmid (thermodynamics and refrigeration) and myself (superfluid helium technology) of CERN. In the CAS School on Superconductivity and Cryogenics for Particle Accelerators and Detectors held in May 2002 in Erice, Sicily, I am particularly pleased to see a more complete syllabus in cryogenics, most of which is covered by CERN colleagues and published in this report. This is in my view, another sign of the development and vitality of this discipline at CERN, primarily in the LHC division which, by virtue of its mandate and competence, is presently building the largest helium cryogenic system in the world for the Large Hadron Collider and its experiments. I hope this report constitutes a useful source of information and updated reference for our staff dedicated to this formidable endeavour.
