摘要:

A simple model of the electrical characteristics of thin‐film‐bridge, point‐contact, and tunnel junction Josephson devices is given, along with some comments on their relative performance at very low and at very high frequencies. A particular example is the dcIVcharacteristic of a point contact at the center of a parallel‐disk microwave cavity. Some recent developments in devices and the application of a point‐contact loop (SQUID) device to magnetocardiography is described.

ISSN:0021-8979    

DOI:10.1063/1.1659587

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A system comprising a weakly connected superconducting ring inductively coupled to a resonantL‐Ccircuit has been studied using an analog computer. The weak link was characterized either by a current‐phase relation of the formI=Icsin&jgr; or by ``supercurrent breakdown,'' and the results were compared. The effects of a normal resistance shunting the junction were investigated, as well as the effects of thermal current noise in the ring. Some criteria for achieving optimum coupling to the superconducting ring are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659605

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Recent progress in our laboratory on permanently adjusted niobium point‐contact superconducting devices is reported. We describe an rf noise‐biased magnetometer obtained by appropriate tuning and adjustment of the point contact in a superconducting ring that is coupled to anLCtank circuit which provides an rf noise‐bias excitation at its resonant frequency. Thus, the rf oscillator normally used is eliminated although the magnetometer noise increases somewhat. In addition, mechanically stable, room‐temperature‐helium‐temperature‐cyclable insulated double and single point contacts have been obtained by use of an insulating glass with thermal expansion matching that of niobium. When two of these contacts are connected in parallel the resultant device works quite well as a cyclable dc‐biased magnetometer. Study of the temperature dependence of the critical current is facilitated by the stable configuration. Preliminary measurements showed sharp rises of the critical current with decreasing temperature similar to those observed withS‐N‐Ssandwiches. Properties of these devices are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659621

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Superconductors have been prepared by impregnating porous glass with low‐melting‐point alloys such as those in the Pb&sngbnd;Bi&sngbnd;Sb system. The critical fields of many alloys in porous glass with a pore diameter of 32 Å are in excess of 100 kOe at 4.2°K. Samples have been prepared having critical current densities near 105A/cm2in low (< 10 kOe) magnetic fields.

ISSN:0021-8979    

DOI:10.1063/1.1659624

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Thin films of aluminum have been produced in the thickness range of 1000–30 Å in small area samples with photoetched edges. The superconducting transition temperatureTc, the critical magnetic fieldHc, and the room‐temperature conductivity have been measured as a function of thicknessd. The results indicate that films as thin as 30 Å act essentially as uniform layers in which the crystal size is approximately equal to the film thickness. The transition temperature was found to vary linearly withd−1.Hc(T) was measured fromTcto 0.4°K. For thickness from 1000 to 200 Å,Hc∼d−3/2, as expected from the Ginzburg‐Landau theory. Ford<200 Å,Hcis paramagnetically limited to about 49 kOe = 19.6Tc, slightly above the Clogston limit.

ISSN:0021-8979    

DOI:10.1063/1.1659648

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Previous results indicated that NbN thin films possess critical current and field characteristics significantly superior to that of bulk NbN having a similarTc. Further measurements made on NbN films, with thicknesses between 50 Å and 8 &mgr;, now show that, at 4.2°K, certain of these films exhibit the highest current densities of any presently known superconductor in all fields from zero up to the limit of our measurement capability (210 kOe). In addition, anomalously high current and field values have been measured in very thin (<300 Å) films. These thinner films show no depressions inJc(measured at 4.2°K) or inHc2(O) values despite decreases inTcfrom almost 16°K (in the thicker films) down to 11°K.

ISSN:0021-8979    

DOI:10.1063/1.1659649

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Intermetallic compounds of the binary systems Ta&sngbnd;Sn and Nb&sngbnd;Ge were formed on Ta or Nb wires by the method of vapor phase diffusion at elevated temperatures. Critical temperatureTc, critical magnetic fieldHc2at 4.2°K, and composition of these layers were measured as a function of heating conditions. Ta&sngbnd;Sn diffusion layers prepared at temperatures between 800° and 1200°C consisted predominantly of the A15 compound Ta3Sn with a lattice parameter ofa= 5.278 Å. The observed layer thickness was always less than 1 &mgr;. Simultaneous maxima inTc(7.0°K) andHc2(50 kOe) were measured on wires heated at 950°C for 3 days. On the other hand, in the Nb&sngbnd;Ge system the A15 compound Nb3Ge did not form in the same temperature range. The layers, of thickness from 1 to 20 &mgr;, consisted only of NbGe2for a diffusion temperature of 800°C, Nb3Ge2for 1200°C, and a mixture of the two at 1000°C. ConsequentlyHc2at 4.2°K for these samples did not exceed 12 kOe.

ISSN:0021-8979    

DOI:10.1063/1.1659650

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Previous measurements ofHc2versusTin selected Nb3Al1−xGexand Nb3Al alloys for dc magnetic fields to 200 kG and for 14 K ≤T≤Tchave now been extended to 4.2 K by means of pulsed magnetic fields and rf measurements. Long pulse (10 msec) multipalyer coils producing fields to 450 kG were employed for the measurements. At 4.2 K,Hc2≃410 kG andHc2≃320 kG for the highestTc, Nb3Al1−xGexand Nb3Al alloys, respectively. These values ofHc2are the highest measured for any superconductor. Measurements ofHc2in several related alloys with somewhat lower values ofTcandHc2will also be presented. The large values of Hc2(4.2 K) for all of these alloys permit great latitude of engineering design for practical wire materials. A summary of the physical properties of these high‐temperature superconductors, measurement techniques, present limits of highHc2materials, and a current appraisal of technical possibilities will be presented. A summary of some of the measurements has appeared.1

ISSN:0021-8979    

DOI:10.1063/1.1659652

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A 100‐kG, 8.26‐cm‐bore, 40‐kJ Nb3Sn magnet and a 75‐kG, 10.2‐cm‐bore, 95‐kJ twisted filament NbTi magnet have been constructed and tested. A number of other magnets of smaller size using both the Nb3Sn and twisted filament NbTi conductors will also be described. Material evaluation tests leading to these magnet designs will be reported. They include short sample tests with controlled surface cooling conditions and cusp coil tests in which an external field is applied perpendicular to the cusp coil axis. Finally, two successful stabilization techniques for Nb3Sn ribbon will be presented with coil performance data before and after the stabilization has been employed.

ISSN:0021-8979    

DOI:10.1063/1.1659653

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The superconducting magnet is a key component in various applications including high‐energy physics, fusion research, magnetohydrodynamics, and electrical rotating machinery. This paper presents the general characteristics of state of the art of superconducting magnets as far as design and performance are concerned. The properties of superconductors are briefly discussed, and the basis for design of stable conductors is set forth. Examples of conductors and magnet systems are given and discussed. The current state of affairs is summarized in three plots showing size versus field achieved, current density in coils as a function of magnetic field, and specific weight versus stored magnetic energy.

ISSN:0021-8979    

DOI:10.1063/1.1659655

出版商:AIP    

年代:1971

数据来源: AIP