摘要:

Experiments were conducted to determine the transverse stress sensitivity of the critical current (Ic) of jelly‐roll multifilamentary Nb3Al wires at 8 and 12 T. For comparison, similar experiments were conducted on bronze‐process (NbTi)3Sn wires. At 12 T and under a transverse compressive stress of 150 MPa−conditions expected in fusion magnets−theIcdegradation of the Nb3Al specimen was ∼20% vs ∼65% for the (NbTi)3Sn specimen. The intrinsic superiority of Nb3Al over (NbTi)3Sn with regard to transverse compressive stress is thus clear. There is optimism that Nb3Al will eventually become a useful superconductor for large‐scale, high‐field applications.

ISSN:0003-6951    

DOI:10.1063/1.104241

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It is demonstrated that polycrystalline thin films of highTcsuperconducting YBa2Cu3O7−xcan be grown with clean grain boundaries, i.e., without a boundary layer of segregation or different phase. In clean stoichiometric samples, angular misorientations of grains may be the origin of weak link behavior. High‐resolution scanning transmission electron microscope images of films grown on ZrO2and MgO by reactive evaporation, reactive sputtering, and laser ablation show atomic lattice images of clean grain boundaries. X‐ray microanalysis with a 10 A˚ spatial resolution also indicates no composition deviation at the grain boundaries. Grain sizes and epitaxial relations of samples prepared by different methods are characterized.

ISSN:0003-6951    

DOI:10.1063/1.104242

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

On lowering the chemical potential of diatomic oxygen, the compound YBa2Cu4O8was found to decompose into a mixture of YBa2Cu3O6+xand CuO. The equilibrium oxygen potential corresponding to this decomposition has been measured from 870 to 1150 K using a solid‐state cell incorporating yttria‐stabilized zirconia as the solid electrolyte and pure oxygen at a pressure of 1.01×105Pa as the reference electrode: Pt, O’2‖YBa2Cu4O8+YBa2Cu3O6+x+CuO∥(Y2O3) ZrO2∥O2(1.01×105 Pa), Pt. The low oxygen potential boundary for the stability of YBa2Cu4O8can be represented by &Dgr;&mgr;O2=−238 900+207.7 T(±800) J mol−1. At the standard pressure of oxygen (1.01×105Pa) the decomposition occurs at 1150 K.

ISSN:0003-6951    

DOI:10.1063/1.103635

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High surface electric fields have been obtained in the first tests of a superconducting rf quadrupole device. The rf quadrupole fields were generated between niobium vanes 6.5 cm in length, with an edge radius of 2 mm, and with a beam aperture of 6 mm diameter. In tests at 4.2 K, the 64 MHz device operated cw at peak surface electric fields of 128 MV/m. Virtually no electron loading was observed at fields below 100 MV/m. It was possible to operate at surface fields of 210 MV/m in pulses of 1 ms duration using a 2.5 kW rf source. For the vane geometry tested, more than 10 square centimeters of surface support a field greater than 90% of the peak field. The present result indicates that electric fields greater than 100 MV/m can be obtained over an appreciable area, sufficient for some accelerator applications. It also shows that superconducting rf technology may provide an extended range of options for rf quadrupole design.

ISSN:0003-6951    

DOI:10.1063/1.103636

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have measured for the first time the temperature‐dependent anisotropic resistivity of several Tl2Ca2Ba2Cu3Oxsingle crystals. The resistivity ratio between thecaxis and thea‐bplane orientations in the best crystals is approximately 60 at room temperature. Resistivity data indicate substantial differences in bothTcand the transition width of nominal Tl2Ca2Ba2Cu3Oxplates grown from two different melt compositions. A Tl‐O and CuO‐rich flux yielded approximately stoichiometric plates with sharp transitions beginning near 113 K, while a Tl‐O‐rich flux produced plates containing more Tl and less Ba with broad transitions starting near 103 K. These data demonstrate the extreme sensitivity of the superconductivity to cation site disorder in the Tl‐Ca‐Ba‐Cu‐O system.

ISSN:0003-6951    

DOI:10.1063/1.104243

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We demonstrate thatinsituoff‐axis sputtering from a composite target can reproducibly fabricate very high quality YBa2Cu3O7−&dgr;films over large areas of deposition. A significant reduction in the microwave surface resistance,Rs, compared to many previously reported values is found.Rsvalues at 10 GHz were found to be as low as 20 &mgr;&OHgr; at 4.2 K and 450 &mgr;&OHgr; at 77 K. A systematic variation of several properties including the transition temperature, critical current density at high magnetic fields, and thec‐axis lattice parameter across the 3.8 cm×3.8 cm (14.5 cm2) deposition area was found.

ISSN:0003-6951    

DOI:10.1063/1.104244

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Critical current densities (Jc) in YBa2Cu3O7−xfilms made at deposition rates from 0.1 to 14.5 nm/s (∼50 &mgr;m/h) were measured using a direct transport method. As the deposition rate was increased by two orders of magnitude, the films exhibited no marked degradation in current carrying capability withJcof ∼4×106A/cm2at 77 K and zero field.Jcfor all the films showed similar behavior under a magnetic field up to 8 T, although extra structural defects were found in the films deposited at the higher rates. The results from this experiment indicate the feasibility for coating wires, tapes, and other macroscopic shapes with highTcsuperconductors using proper vapor deposition techniques.

ISSN:0003-6951    

DOI:10.1063/1.104245

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0003-6951    

DOI:10.1063/1.103637

出版商:AIP    

年代:1990

数据来源: AIP