Results 1 - 10 of 14793
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[en] This year saw the completion of three accelerator improvement projects (AIP) and two capital equipment projects pertaining to the Tevatron cryogenic system. The projects result in the ability to operate the Tevatron at lower temperature, and thus higher energy. Each project improves a subsystem by expanding capabilities (refrigerator controls), ensuring reliability (valve box, subatmospheric hardware, and compressor D), or enhancing performance (cold compressors and coldbox II). In January of 1994, the Tevatron operated at an energy of 975 GeV for the first time. This was the culmination, of many years of R ampersand D, power testing in a sector (one sixth) of the Tevatron, and final system installation during the summer of 1993. Although this is a modest increase in energy, the discovery potential for the Top quark is considerably improved
[en] At temperatures below 50 mK Praseodymium metal develops antiferromagnetic order characterized by a narrow satellite reflection, accompanied by a broader 'central' peak, the nature of which is not understood. Neutron scattering experiments were carried out at low temperatures, and it was shown that at 8 mK the intensities are almost saturated. Whereas the width of the satellite corresponds to long-range magnetic order, the 'central' peak remains much broader. (orig.)
[en] We investigate experimentally the entropy transfer between two distinguishable atomic quantum gases at ultralow temperatures. Exploiting a species-selective trapping potential, we are able to control the entropy of one target gas in presence of a second auxiliary gas. With this method, we drive the target gas into the degenerate regime in conditions of controlled temperature by transferring entropy to the auxiliary gas. We envision that our method could be useful both to achieve the low entropies required to realize new quantum phases and to measure the temperature of atoms in deep optical lattices. We verified the thermalization of the two species in a 1D lattice.
[en] A new pair potential for helium in bulk iron was developed using a method based on the Chen-Moebius lattice inversion in order to study the effect of He in irradiated iron. By means of molecular dynamic (MD), we have examined this interatomic potential. Comparing with the ab initio calculation results, the stability of He-vacancy clusters at zero temperature and migration energy was well reproduced by this potential.
[en] Adsorption isotherms of 3He on cesium substrates have been measured in the temperature range from 0.2 K to 1.5 K. At liquid-vapor coexistence 3He wets cesium at all temperatures studied. Step-like features are found in the isotherms which are similar to the prewetting transitions of 4He on Cs substrates, but the width of these steps is ∼ 20 times wider for 3He than for 4He. In the case of 3He on Cs, the steps are located at a chemical potential about 0.6 K below liquid-vapor coexistence. If the low temperature behavior is interpreted to be first order prewetting, the prewetting critical point temperature is 0.6 ± 0.1 K
[en] We propose a new scheme aimed at cooling nanostructures to microkelvin temperature based on the well established technique of adiabatic nuclear demagnetization: we attach each device measurement lead to an individual nuclear refrigerator, allowing efficient thermal contact to a microkelvin bath. On a prototype consisting of a parallel network of nuclear refrigerators, temperatures of ∼1 mK simultaneously on ten measurement leads have been reached upon demagnetization, thus completing the first steps toward ultracold nanostructures.
[en] The authors report progress on a measurement of the specific heat of 4He-filled Vycor glass near 2K. It has been suggested that due to the reduced superfluid density in the 4He-Vycor system, the heat capacity signature will be diminished by a factor of 104 over the bulk value and will occur at the superflow onset temperature of Tc = 1.955 K. This is supported by observations of thin films of 4He in Vycor which show reduced heat capacity peaks coincident with superflow onset. The adiabetic heat capacity technique the authors are currently implementing should have resolution of 1 part in 106 and is expected to determine the presence of the predicted peak in Cv