D. U. Gubser

Superconducting motors and generators for naval applications

The US Navy is planning for a transition to electric warships as future ship combatants. Superconducting motors for propulsion and superconducting generators for power conversion are under active development (motors) or strong consideration (generators). This article describes the fundamentals of motor technology, as it applies to the Navy, how superconductivity leads to advantages in power density and quietness, and how the technology issues faced in the development of full scale naval motors are being addressed. Finally, the status of the naval superconducting propulsion power projects will be presented.

Resistive and Magnetic Susceptibility Transitions in Superconducting (TMTSF)2C104

Abstract We report measurements of the ac magnetic susceptibility and dc resistive superconducting transitions in the organic superconductor (TMTSF)2C104. Inductive measurements show complete diamagnetic shielding below a broad transition and initial flux penetration at very low fields [Hc1(0) < 1 Oe]. The resistive transition is also broad, but occurs at a significantly higher temperature than the inductive transition, Tc = 1.0 K and 0.65 K respectively. Resistance measurements also show evidence of a phase transition in the vicinity of 24 K. Magnetic field induced transitions, measured both inductively and resistively, show marked anistropy both in magnitude and in breadth of the transition. Results suggest that (TMTSF)2C104 is a quasi ID or 2D superconductor at high temperatures and high magnetic fields and an anisotropic bulk superconductor at low temperatures and fields. Associated thermoelectric power measurements suggest that spin density waves coexist with the superconducting state.

Giant resistivity and X-ray diffraction anomalies in low-dimensional ZrTe5 and HfTe5

Abstract Two giant anomalies have been observed in single crystal samples of metallic ZrTe 5 and HfTe 5 : one is an extremely large maximum in the electrical resistivity at low temperature and the other is a correspondingly large maximum in the intensities of certain “forbidden” x-ray reflections, which correlate in temperature with the electrical anomaly.

Superconducting current leads of YBCO and Pb-BSCCO

The authors fabricated and measured cylindrical superconducting current leads composed of a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ (YBCO) and Bi/sub 2-x/Pb/sub x/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ (Pb-BSCCO) that were approximately 20 cm long and 1 cm/sup 2/ in cross section. A steady-state, DC, critical current of 170 (230) A at a temperature of 77 K was measured for YBCO (Pb-BSCCO) using a voltage criterion of 2*10/sup -7/ V ( rho =8*10/sup -10/ Omega -cm). This current was limited by the current-induced self-magnetic field. At a temperature of 63 K this current increased to approximately 390 (465) A. The character of the magnetic field dependence of the critical current and shape of the current-induced voltage curves are different for the two materials.

Multifilamentary V 3 Ga wire: A critical review

Initial studies of V 3 Ga conductors formed by the bronze technique coincided with early work on Nb 3 Sn conductors; however, due to several technological difficulties, emphasis to date has been on commercial production of Nb 3 Sn composites. The superior critical current density of V 3 Ga in high magnetic fields (H> 10T), however, favor this conductor in selected applications. Improvements in critical current density have been achieved by using a modified bronze technique whereby the filaments as well as the Cu matrix are alloyed with Ga. Recent studies of the temperature and magnetic field dependence of the critical current density as well as stress effects, and third element additions are presented. Superconducting applications which may benefit from the use of V 3 Ga wire will be emphasized.

Formation of the structure of the superconducting phase of La-Sr-Cu-O by DC sputtering

Abstract DC sputtered film samples of La-Sr-Cu are found to be noncrystalline. Annealing in air at temperatures as low as 350°C yields crystallization of the structure of the superconducting phase of La-Sr-Cu-O. We present X-ray spectra showing the continuous development of the La-Sr-Cu-O phase and a decrease in the c / a ratio upon further annealing in air for temperatures up to 600°C.

Synthesis and Study of Electrochemically Grown Salts of Organic II-Donors

Abstract The effects of purity and crystal perfection on the properties of (TMTSF)2ClO4 are examined via SEMs and transition temperatures. Careful electrochemical techniques using gradient sublimed TMTSF starting material and short term oxidation result in high quality crystals. Preliminary work on HMTSF salts of PF − 6 and AsF− 6 is also reported.

Fatigue of a Reinforced High Temperature Superconducting Tape

High-cycle fatigue-life behavior of commercial multifilamentary BSCCO 2223 powder-in-tube tape and reinforced tape was evaluated. Mechanical fatigue at room temperature and 77 K, and the onset of significant superconductivity degradation at 77 K were evaluated under tension perpendicular to the flat faces of the tapes. No fatigue behavior was observed in this transverse configuration for unreinforced tape, but fatigue-life behavior associated until delamination of the reinforcement was found for reinforced tape. Fatigue tolerance of the reinforced tape is very high, about 24 MPa, to at least 100 000 cycles.

Multilayer Nb 3 Sn superconducting shields

Multilayer Nb 3 Sn shields have been designed, fabricated, and tested for use in low field, e.g. superconducting electronics, applications. Magnetic field profiles, shielding factors, and thermal effects are reported for these shields. The quality of the shields depends strongly on the reaction temperature used to form the Nb 3 Sn layers with lower reaction temperatures forming better quality shields. Nearly ideal behavior was observed with a reaction temperature of 750°C.

Critical current properties of multifilament V 3 Ga wire at temperatures above 4.2 Kelvin

Studies of the superconducting properties of V 3 Ga formed in composite wires by solid state reaction are presented. Multifilament wires were fabricated containing nineteen V-6.1 at.%Ga filaments or thirty V-8.0 at. %Ga filaments in a Cu-17.5 at .%Ga matrix. A study of J c as a function of magnetic field and temperature on these wires is reported. At a temperature of 8.6 K, and in a magnetic field of 10 Tesla, a J c of 4.2 × 105amps/ cm2was measured for the thirty filament wire. This is significantly higher than the J c of commercially available V 3 Ga tape Or Nb 3 Sn wire, These studies indicate that not only does our V 3 Ga wire exhibit high magnetic field properties Superior to those for commercially available wire at 4.2 K, but it also retains its superior J c values at temperatures in excess of 11 K.