نتایج جستجو برای: liquid helium
تعداد نتایج: 230724 فیلتر نتایج به سال:
Neutron inelastic scattering studies of the elementary excitations in con ned super uid He are reviewed. Both recent work on helium in porous silica glass (aerogel, Vycor, etc.) and earlier work on helium lms on graphite surfaces are discussed. The global picture emerging from these studies is that the three-dimensional excitations are essentially the same as in bulk helium. The characteristic ...
Helium has a unique phase diagram and below 25 bar it does not form a solid even at the lowest temperatures. Electrostriction leads to the formation of a solid layer of helium around charged impurities at much lower pressures in liquid and superfluid helium. These so-called 'Atkins snowballs' have been investigated for several simple ions. Here we form HenC60+ complexes with n exceeding 100 via...
We evaluate speculation about the possibility of a dangerous release of energy within the liquid Helium of the Large Hadron Collider (LHC) cryogenic system due to the occurrence of a " Bose-Nova ". Bose-Novae are radial bursts of rapidly moving atoms which can occur when a Bose-Einstein Condensate (BEC) undergoes a collapse due the interatomic potential being deliberately made attractive using ...
A new search for a permanent electric dipole moment (EDM) of the neutron is underway using ultracold neutrons produced and held in a bath of superfluid helium. Attaining the target sensitivity requires maintaining an electric field of several tens of kilovolts per centimeter across the experimental cell, which is nominally 7.5 cm wide and will contain about 4 liters of superfluid. The electrica...
Early measurements of the specific heat of liquid helium confined in all three spatial dimensions suggest a coupling of individual regions of superfluid via connecting channels. Preliminary measurements have been made to investigate this apparent coupling. Although more data need to be collected before anything conclusive can be said, the available data support the idea that behavior of helium ...
We have investigated the adsorption and desorption of helium near its liquid-vapor critical point in silica aerogels with porosities between 95% and 98%. We used a capacitive measurement technique which allowed us to probe the helium density inside the aerogel directly, even though the samples were surrounded by bulk helium. The aerogel’s very low thermal conductivity resulted in long equilibra...
The magnet system of the VENUS ECR Ion Source at LBNL has two 1.5-watt cryocoolers suspended in the cryostat vacuum. Helium vapor from the liquid reservoir is admitted to a finned condenser bolted to the cryocooler 2 stage and returns as liquid via gravity. Small-diameter flexible tubes allow the cryocoolers to be located remotely from the reservoir. With 3.1 watts load, the helium reservoir is...
Liquid hydrogen is used as a powerful and efficient propellant in spacecraft industries. This paper first presents the main principles of hydrogen liquefaction. Then, different methods for hydrogen liquefaction, including four general categories: precooled Linde-Hampson process, Claude process, helium-precooled Claude process and liquefaction by small cryo-coolers, are expressed along with thei...
The use of liquid helium and neon as scintillators for neutrino detection is investigated. Several unique properties of these cryogens make them promising candidates for real-time solar neutrino spectroscopy: large ultraviolet scintillation yields from ionizing radiation, transparency to their own scintillation light, and low levels of radioactive impurities. When neutrinos scatter from electro...
We have constructed a versatile current to voltage (I-V ) converter operating at liquid helium temperature, using a commercially available all-CMOS OPamp. It is valuable for cryogenic measurements of electrical current of nano-pico amperes, for example, in scanning probe microscopy. The I-V converter is thermally linked to liquid helium bath and self-heated up to 10.7 K. We have confirmed its c...
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