[en] Recent advances in the technology of infrared detectors have made possible a wide range of scientific measurements and investigations. One of the requirements for the use of sensitive IR detectors is that the entire instrument be cooled to temperatures approaching absolute zero. The cryogenic cooling system for these instruments is commonly designed as a large dewar containing liquid helium which completely surrounds the apparatus. Thus, there is a need for a remotely controlled, motorized cryovalve that is simple, reliable, and compact and can operate over extended periods of time in cryo-vac conditions. The design, development, and test of a motorized cryovalve with application to a variety of cryogenic systems currently under development is described

[en] Weak-link devices were fabricated from polycrystalline thin films of YBaCuO and BiSrCaCuO. Two distinct types of weak links have been found in these devices. The first type, found in all of the YBaCuO and most of the BiSrCaCuO devices, has relatively low dynamic resistances and critical currents with nearly linear temperature dependences. The second type of weak links, found in some BiSrCaCuO films, has much larger dynamic resistances and critical current temperature dependences similar to that of a tunnel junction. Superconductivity quantum interference devices (SQUID's) fabricated from BiSrCaCuO showed a periodic response to applied fields that is consistent with the magnitude of the flux enclosed by the SQUID loop. Significant hysteresis was found in the SQUID response, apparently indicating flux penetration into the films at relatively low fields

[en] To improve the energy resolution of sensors used by NASA in its astrophysics and earth science research the agency has embarked on a cryogenic cooler research program. The coolers currently being developed by the agency include radiative coolers, surface tension confined liquid cryogen coolers, mechanical coolers, liquid helium dewars, He³ adsorption coolers, and adiabatic demagnetization and dilution refrigerators. The design and development of these coolers and their applications for specific missions are described

[en] Magnet cryosystem options utilizing the thermomechanical effect of He II and the mechano-caloric effect for refrigeration (referred to as vortex refrigeration) are examined. The performance of the existing He II magnet refrigeration system is briefly reviewed, with attention given to superleak properties, vortex shedding, heat input, and thermodynamic cycle. It is concluded that the possibilities of magnet heat leak use for energetics and stability improvements are promising when He II is selected as magnet coolant. 7 references

[en] Focused ion beam (FIB) processes have been developed for Y--Ba--Cu--O superconductor films. A Y--Cu liquid metal ion source has been fabricated, using a Y₆₇ --Cu₃₃ eutectic alloy as the ion source. As-sputtered Y--Ba--Cu--O film etch rate ratios to GaAs(100) and Si(100) substrates are 0.28 and 1.4 for 130-keV Au⁺ FIB ion etching, respectively. Y--Ba--Cu--O submicron patterns have been demonstrated by using FIB lithography and Cl₂ reactive ion beam etching. Moreover, a Y--Ba--Cu--O superconducting line with 4-μm linewidth has been fabricated by annealing an as-sputtered Y--Ba--Cu--O line pattern. T/sub c/ control of Y--Ba--Cu--O film has been achieved by 200-keV Ne⁺, using conventional ion implantation and 300 keV Si⁺⁺ FIB ion implantation

[en] A superconducting (SC) rf cavity has been operated in the presence of an external magnetic field up to 2.4 kG. Measurements on the 48.5-MHz cavity were performed at 4.2 K. The external field was produced by an unshielded 60-kG superconducting solenoid 5.8 cm from the cavity. No degradation of cavity Q was observed for fields on the outer surface of the cavity up to 1240 G. This result is consistent with no flux penetration of the cavity surface for fields up to the first critical field of niobium at 4.2 K, and shows that strong focusing elements with large fringing magnetic fields may be placed immediately next to Nb SC accelerating structures without causing performance degradation

[en] A process for producing a superconducting wire having a metal molybdenum chalcogenide superconductive phase is described comprising: introducing a powered superconductive phase or initial components for forming such superconductive phase of a grain size of less than 1 μm into a vacuum tight molybdenum shell, extruding the unit at temperatures between about 1000⁰ and 1600⁰C; reducing the cross sectional dimension of the unit to less than one-tenth its original size, and subjecting the unit to additional extruding and/or hot drawing

[en] At temperatures below about 1 K, a series of dc superconducting quantum interference devices (SQUID's) exhibited an apparent flux noise with a spectral density scaling as 1/f/sup //sup α/, where 0.58<α<0.80. Typically, the magnitude of the noise increased as the temperature was lowered below 1 K, tending to flatten out at low temperatures with a value of 7 +- 3 μPhi₀Hz^-1/sup //² at 1 Hz that was nearly independent of the parameters and materials of the SQUID's. Although a large number of hypothetical sources of the noise have been eliminated, the origin remains unidentified

[en] The effect of mechanical power control on the transient stability of a superconducting alternator for symmetrical and unsymmetrical fault conditions is studied. A detailed governor-turbine model, with electrohydraulic governors and fast valving is considered

[en] Al films deposited on Nb can be oxidized and used to make Josephson junction devices. We studied the structure of Al films deposited under ''warm'' (estimated to be near 200 ⁰C) and ''cold'' (near room temperature) conditions because the cold films produced better Josephson junction devices. For the warm case, the Al film was composed of islands with open channels between them, which we attribute to a high mobility of the Al atoms that lowers the island nucleation density. The Nb surface was extremely flat, which we ascribe to the high surface atom mobility at the higher deposition temperature. The cold Al film was of uniform thickness which can be explained by a high island nucleation density. The cold Nb films had an undulating surface, caused by the lack of surface atom mobility during deposition. There was no evidence of Al-Nb interdiffusion, even after postdeposition heating to 300 ⁰C. Auger spectroscopy, transmission electron microscopy, and scanning electron microscopy were needed to obtain these definitive conclusions