An integrated method for enhancing energy efficiency of modern large-scale cryogenic complexes (annual energy consumption more than 100 GWh) that allow operation of superconducting magnets of particle accelerators is analyzed. Two conventional loops, namely, "cold" and "warm" (compressor), with subsequent separate optimization of each loop, are marked out in the cryogenic complex cycle. Separate optimization helps simplify the choice of optimal cycle pressure as well as the choice of the most efficient helium vapor evacuation for providing the required cryogenic temperature of 2 K.The phenomenon of complete loss of electrical resistance of metals at low temperatures, discovered by Heike Kamerlingh Onnes in 1911, is currently used widely in many areas of science and technology. For instance, development of high-energy physics is inseparably linked with the introduction of modern physical instruments developed with application of superconductors. Superconducting magnets and resonator structures of superconductor particle accelerators are used in modern designs of charged-particle accelerators [1].At the current stage of development of devices for cryostatting large superconductor systems, enhancing energy efficiency is a pressing issue. For instance, the annual power consumption of the currently largest cryogenic system of CERN's Large Hadron Collider (LHC) in 2010-2012 did not drop below 230 GWh and was more than one-third of the total electric power consumed by all the systems of the LHC [2][3][4]. This index clearly shows the high energy capacity of modern cryogenic systems of large charged-particle accelerator complexes and makes it essential to enhance energy efficiency of such installations.
Methods of Enhancing Energy Efficiency of Cryogenic SystemsAt the current level of development of engineering and technology, energy efficiency of cryogenic systems is achieved primarily by deep optimization of cryogenic cycles, in which case modernization of individual components (heat exchangers, turboexpanders, etc.) do not exert much influence on the overall efficiency [5].
Cryogenics is now widely used in large accelerator projects using applied superconductivity. Economic considerations require an increase in the performance of superconducting devices. One way to achieve this is by lowering their operating temperature and cooling with superfluid helium. For this reason, large cryogenic systems operating at 1.8 K and capable of producing refrigeration capacity in the kW range have to be developed and implemented. These cryogenic systems require a large pumping capacity at very low pressure using integral cold compression or mixed cold-warm compression. This paper describes the different cooling methods using cold and hybrid cycles, describes the cycle operational capabilities, and reviews the low-pressure helium compression control strategy for these cycles developed at Fermi National Accelerator Laboratory.
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