Materials research for hydrogen-cooled superconducting power transmission lines. Sixth quarterly report, April 1, 1981-June 30, 1981

The objectives of this three-year program are to: perform dielectric breakdown and loss measurements in liquid hydrogen and liquid-hydrogen-impregnatd synthetic dielectrics at temperatures between 14 and 20/sup 0/K and at hydrostatic pressures up to 5 atmospheres and to determine the effects of dissolved impurities/additives in the liquid; and characterize the self-field and low-field superconducting properties of high-critical temperature materials at temperatures between approximately 14 and 20/sup 0/K. During the current reporting period, the following was accomplished. The construction of the dielectric test apparatus continued and the system of small electrodes was completed. Difficulties were encountered in the construction of the LH/sub 2/ vessels and the junction box, which have retarded their completion. Other work to be performed at the Westinghouse R and D Center on the dielectrics part of this project has been postponed indefinitely due to the shortage of funding

STABILIZATION OF HIGH-Tc Nb3Ge

Les résultats d'analyses physiques nous font croire que la croissance de Nb3Ge stoechiométrique se fait par homoépitaxie sur une phase A15 de Nb-Ge qui se forme près de l'interface avec le substrat et a une constante de réseau augmentée grâce à la présence des impuretés.From analytical results we hypothesize that stoichiometric Nb3Ge is formed through a homoepitaxial process form an A15 Nb-Ge phase having an impurity expanded lattice formed near the interface

Effect of HTS Superconductors on the Homogeneity of Measurement Field in Low Field NMR Detection

In recent years, superconducting quantum interference devices (SQUIDs) have been demonstrated to be useful in the low field nuclear magnetic resonance (NMR) measurements. The high temperature superconducting (HTS) SQUID used in our experiments has a frequency-independent sensitivity of 40-50 fT/Hz(1/2). When a liquid nitrogen cooled LC circuit is employed to form a tuned circuit with the SQUID, the sensitivity of the system can be further enhanced. The LC circuit consists of a capacitor and a coil made of copper wire or HTS tape, which is inductively coupled to the SQUID. However, the homogeneity of the measurement field deteriorates because of the HTS tape coil in the proximity of the sample. In contrast, the thin film SQUID with a washer area of 1 cm(2) has no effect on the NMR signal. Therefore, the impairment of the measurement field homogeneity in the case of different superconducting elements nearby is discussed by examining the free induction decay signals at 9 kHz. It is found that a square superconducting film with an area of 1 cm(2) may compensate for the inhomogeneity of the measurement field after the adjustment of its position

Lineare und nichtlineare Bauelemente aus HTSL fuer den Einsatz in kryoelektronischen Systemen Abschlussbericht

SIGLEAvailable from TIB Hannover: F97B2276+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y\u3csub\u3e1\u3c/sub\u3eBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e χ \u3c/sub\u3e

Measurements of the transport critical-current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3O χ from several different laboratories indicate that the transport Jc is limited by weak-link regions between high Jc regions. The weak-link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain-boundary region in Y1Ba2Cu3O χ shows no observable impurities or second phases to the scale of the [001] lattice planes (~12 Å). The effect of intrinsic conduction anisotropy is discussed. A current-transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors

An approach to optimization of the superconducting quantum interference bootstrap circuit

Recently, we demonstrated and analysed the superconducting quantum interference device (SQUID) bootstrap circuit (SBC). It is a direct readout scheme for dc SQUID in the voltage bias mode, permitting one to suppress the preamplifier noise. The SBC enables us to control the two key parameters of a voltage-biased SQUID: the flux-to-current transfer coefficient and the dynamic resistance. The flux-to-current, I-Phi, characteristics of SBC are made asymmetric by introducing the additional current feedback. Depending upon the choice of the working point, this feedback can be positive (working point W-2 on the steeper I-Phi slope) or negative (W-1 on the less steep slope). The dynamic resistance is controlled by the additional voltage feedback. In our publications to date we presented only the SBC operation at W-2, while in this paper we demonstrate operation at W-1 and show that also in this regime the preamplifier noise suppression is possible. We used a liquid-helium-cooled Nb SQUID with a loop inductance of 350 pH and attained white flux noise of 2.5 mu Phi(0) Hz(-1/2) both at W-2 and at W-1. In the latter case, the linear flux range exceeded one half-flux quantum Phi(0). This large linear range should lead to a significantly improved stability and slew rate of the system and also make the tolerable spread in circuit parameters much wider than in all SQUID direct readout schemes known to date. Consequently, operation in this regime opens a new path to possible SBC optimization