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Helium, as an important strategic resource, is widely used in medical and sophisticated high-tech, but its distribution is seriously imbalanced, mainly concentrated in the USA, Qatar, Algeria and Russia. In this paper, based on th...
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Helium, as an important strategic resource, is widely used in medical and sophisticated high-tech, but its distribution is seriously imbalanced, mainly concentrated in the USA, Qatar, Algeria and Russia. In this paper, based on the systematic study of the global distribution and supply and demand of helium, the current situation and future trend of helium consumption in china were analyzed. In view of the shortage of helium resources in China and the high dependence on foreign countries, suggestions were put forward to strengthen the comprehensive research on domestic helium resources, enhance the investigation and utilization of associated helium resources, deepen the research on helium exploration and development technology, and promote the process of commercial exploration and development.
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Experiments with helium in thin films and small pores show that the bulk properties are greatly modified. With He-4, the onset of superfluidity is depressed and the specific heat anomaly is rounded and also depressed to lower temp...
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Experiments with helium in thin films and small pores show that the bulk properties are greatly modified. With He-4, the onset of superfluidity is depressed and the specific heat anomaly is rounded and also depressed to lower temperatures. With He-3 new features are found such as surface magnetism and free path effects.. Bulk superfluid He-4 is shown to have a sharp transition to turbulence, and bulk He-3 the characteristics of a Fermi fluid. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 16]
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Helium droplets are large helium clusters that are capable of picking up individual atoms and molecules and show promise as nano-reactors for the synthesis of unique nanoparticles. In particular, the sequential addition of materia...
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Helium droplets are large helium clusters that are capable of picking up individual atoms and molecules and show promise as nano-reactors for the synthesis of unique nanoparticles. In particular, the sequential addition of materials of different types offers opportunities for the fabrication of novel core– shell nanoparticles that cannot be synthesised by other methods. To exploit this potential, here we have carried out a mass spectrometry investigation on metal clusters in order to establish how to control the doping conditions for the fabrication of nanoparticles in superfluid helium droplets, and in particular to develop a recipe to control core and shell ratios in the case of core–shell nanoparticles. Several types of metal nanoparticles, including pure Ag, Au and Ni nanoparticles, and Ag/Au and Ni/Au core–shell systems, have been synthesised and then removed from the helium droplets by deposition on substrates for ex situ investigations using high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM imaging has been used to estimate the sizes of nanoparticles, which show a bimodel distribution under the conditions employed. We also present the first evidence that crystalline metal nanoparticles are formed by self-assembly of metal atoms in helium droplets. The XPS investigation of Ni/Au core–shell nanoparticles shows an absence of any Au 4f core-level shift that would occur on alloying of Au and Ni, which provides the first direct evidence for the successful formation of core–shell nanoparticles using superfluid helium droplets.
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Helium is a finite global resource, which is becoming vitally important to recover and reuse as it continually diminishes. The helium recovery process uses plant machinery that can consume significant amounts of power and generate...
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Helium is a finite global resource, which is becoming vitally important to recover and reuse as it continually diminishes. The helium recovery process uses plant machinery that can consume significant amounts of power and generate a large carbon footprint. Many organizations around the world are actively trying to reduce their carbon footprint and, therefore, lessen the impact of their operations on the climate. Here we have assessed the CO2 produced per litre of liquid helium, when processed by the ISIS helium recovery system, and compared it with the estimated carbon footprint of liquid helium that is supplied by the gas companies. The comparison clearly demonstrates that the carbon footprint of liquid helium from the recovery system is significantly smaller than that of liquid helium supplied by the gas companies.
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We studied the thermal conductivity of superfluid He-3 in a 2.5-mm effective diameter and 0.15-m-long channel connecting the two volumes of our experimental assembly. The main volume contained pure solid He-4, pure liquid He-3 and...
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We studied the thermal conductivity of superfluid He-3 in a 2.5-mm effective diameter and 0.15-m-long channel connecting the two volumes of our experimental assembly. The main volume contained pure solid He-4, pure liquid He-3 and saturated liquid He-3-He-4 mixture at varying proportions, while the separate heat-exchanger volume housed sinter and was filled by liquid He-3. The system was cooled externally by a copper nuclear demagnetization stage, and, as an option, internally by the adiabatic melting of solid He-4 in the main volume. The counterflow effect of superfluid just below the transition temperature T-c resulted in the highest observed conductivity about five times larger than that of the normal fluid at the T-c. Once the hydrodynamic contribution had practically vanished below 0.5T(c), we first observed almost constant conductivity nearly equal to the normal fluid value at the T-c. Finally, below about 0.3T(c), the conductivity rapidly falls off toward lower temperatures.
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The possibility of supersolid behavior in 4He was predicted many years ago, but negative experiments in the 1970's removed motivation for further experimental efforts to explore the possibility until the work of Goodkind's group r...
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The possibility of supersolid behavior in 4He was predicted many years ago, but negative experiments in the 1970's removed motivation for further experimental efforts to explore the possibility until the work of Goodkind's group renewed attention. Kim and Chan found unambiguous evidence for a period shift in a torsional oscillator filled with solid 4He and this observation and its interpretation have created substantial interest in the study of solid 4He. Here, recent work with an experimental design that allows for superfluid 4He to be in direct contact with solid 4He off the melting curve will be discussed and evidence for the flow of helium atoms through a cell filled with solid 4He, caused by an applied chemical potential difference will be briefly reviewed.
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We studied a novel cooling method, in which He-3 and He-4 are mixed at the He-4 crystallization pressure at temperatures below 0.5 mK. We describe the experimental setup in detail and present an analysis of its performance under v...
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We studied a novel cooling method, in which He-3 and He-4 are mixed at the He-4 crystallization pressure at temperatures below 0.5 mK. We describe the experimental setup in detail and present an analysis of its performance under varying isotope contents, temperatures, and operational modes. Further, we developed a computational model of the system, which was required to determine the lowest temperatures obtained, since our mechanical oscillator thermometers already became insensitive at the low end of the temperature range, extending down to (90 +/- 20) mu K approximate to T-c/(29 +/- 5) (T-c of pure He-3). We did not observe any indication of superfluidity of the He-3 component in the isotope mixture. The performance of the setup was limited by the background heat leak of the order of 30 pW at low melting rates, and by the heat leak caused by the flow of He-4 in the superleak line at high melting rates up to 500 mu mol/s. The optimal mixing rate between He-3 and He-4, with the heat leak taken into account, was found to be about 100..150 mu mol/s. We suggest improvements to the experimental design to reduce the ultimate achievable temperature further.
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The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak. Four low-temperature helium turbines are used in the 2 kW helium refrigeratio...
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The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak. Four low-temperature helium turbines are used in the 2 kW helium refrigeration system, and their performance and reliability are critical for the continuous operation of the tokamak. The turbines were made by the Helium Mechanics Company in Russia. The start-up process is very unstable, easily broken, and thus testing and improvements are needed. In this paper, we analyze the structure of the helium turbine, make improvements, and describe the testing process and results of the improved helium turbines. Some of the operational experiences during the start-up process and tests are also presented.
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In pure superfluid He-3-B at ultra-low temperatures, the quartz tuning fork oscillator response is expected to saturate when the dissipation caused by the superfluid medium becomes substantially smaller than the internal dissipati...
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In pure superfluid He-3-B at ultra-low temperatures, the quartz tuning fork oscillator response is expected to saturate when the dissipation caused by the superfluid medium becomes substantially smaller than the internal dissipation of the oscillator. However, even with a small amount of He-4 covering the surfaces, we have observed saturation already at significantly higher temperatures than anticipated, where we have other indicators to prove that the He-3 liquid is still cooling. We found that this anomalous behavior has a rather strong pressure dependence, and it practically disappears above the crystallization pressure of He-4. We also observed a maximum in the fork resonance frequency at temperatures where the transition in quasiparticle flow from the hydrodynamic to the ballistic regime is expected. We suggest that such anomalous features derive from the superfluid He-4 film on the oscillator surface.
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By injecting a neutral beam of 60 keV helium (He) atoms as central fueling of helium into the ELMy H-mode plasmas, helium exhaust has been studied in the W-shaped pumped divertor on JT-60U. Efficient He exhaust was realized by He ...
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By injecting a neutral beam of 60 keV helium (He) atoms as central fueling of helium into the ELMy H-mode plasmas, helium exhaust has been studied in the W-shaped pumped divertor on JT-60U. Efficient He exhaust was realized by He pumping using argon frosted cryopumps in the TJ-60U new divertor. The He fueling rate by He beam injection was balanced with He pumping. In steady state, good He exhaust capability was successfully demonstrated in attached ELMy H-mode plasmas. A global particle confinement time of #tau#_(He)~* = 0.7 s and #tau#_(He)~*/#tau#_E = 4 (#tau#_E: the energy confinement time) was achieved in attached plasmas, well within the range generally considered necessary for successful operation of a future fusion reactor, such as ITER. The enrichment factor of He was obtained to be about 1.0, which is five times larger than the ITER requirement of 0.2. Good He exhaust capability was also obtained in detached ELMy H-mode plasmas, which was comparable to one in attached plasmas. This result of the helium exhaust is sufficient to support a detached divertor operation on ITER.
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