ISSN:0021-8979    

DOI:10.1063/1.1659532

出版商:AIP    

年代:1971

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1659565

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The design of an electromagnetic balance using superconducting coils is reported. Both dc and ac coils are used to support aerodynamic models in a supersonic (Mach 3) wind tunnel and to simultaneously measure the forces acting on them along 3 orthogonal axes. Major design characteristics include: adoption of symmetrical coil arrangement to provide maximum space for the wind tunnel; 3 gradient‐coil pairs capable of being driven between 0 and 350 A at a frequency of 30 Hz by specially designed power supplies; a vertical wind tunnel with a 6‐in. test section located in the axial room‐temperature access of a 250‐liter liquid‐helium Dewar. Results on ac losses for prototype gradient coils wound of three different superconducting materials are reported.

ISSN:0021-8979    

DOI:10.1063/1.1659586

出版商:AIP    

年代:1971

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1659645

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An isolated, isochoric Dewar and superconducting ring, operable up to 130 000 ampere turns, has been installed in the Princeton Spherator, and plasma physics experiments have been performed with the ring levitated and stabilized by means of a system similar to that discussed previously. The evolution of this device has progressed through three stages. Initially the poloidal field coil was a conventional copper conductor ring within a vacuum jacket supported within the reaction chamber from top and bottom by four thin bars. In its second stage of development, the conventional coil was replaced by a superconducting coil and Dewar, supported by thin wire‐like hangars. The present mode eliminates the need for mechanical supports of any sort.

ISSN:0021-8979    

DOI:10.1063/1.1659654

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A wattmeter technique is described which advances the measurement of alternating field losses in superconducting materials. In particular, it allows realistic experiments on strip conductors, the geometric form most promising for application to electrical power engineering. Uniform current distribution is achieved, contact problems are eliminated, and sample preparation is minimal. It is shown how the alternating field measurements can be interpreted to yield values for several properties of the material studied. Critical fields, the surface shielding currents, and the bulk critical currents can all be determined. When these quantities are inserted into expressions derived from a modified critical state model, a good match to the experimental results is obtained. Comparison of the measured alternating field dissipation with the area enclosed by magnetization curves, derived in slowly varying fields, confirms the validity of the technique and the applicability of critical state models to results obtained at audiofrequencies.

ISSN:0021-8979    

DOI:10.1063/1.1659533

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Low‐frequency (350 Hz) permeability measurements at 4.2°K using phase‐sensitive techniques were carried out on a Nb sample irradiated in the Oak Ridge Research Reactor at 40°C to several fast neutron doses up to 6×1019neutrons/cm2(E> 1 MeV). In the mixed‐state region a signal proportional to the electromagnetic loss in the sample is observed which decreases with increasing fast neutron dose. Quantitative estimates of the power dissipation in irradiated Nb are given which are then related to the magnetic field dependence of the critical current densityJc(H).

ISSN:0021-8979    

DOI:10.1063/1.1659554

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An electrical technique is described for measuring the audio frequency power dissipation in superconducting thin films as a function of the ac current density, frequency, and applied dc magnetic field. This system has been used to study the ac losses in thin films of Nb and NbN, and also the ac and dc critical current densities in these materials. The results can be explained by assuming that both hysteresis and eddy current losses contribute.

ISSN:0021-8979    

DOI:10.1063/1.1659568

出版商:AIP    

年代:1971

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1659579

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

We describe the adaption and use of superconducting quantum interference magnetometers for the measurement of voltage, resistance, and inductance. The instrument which we discuss achieves the Nyquist noise limit, about 10−22W of noise power in a 1‐Hz bandwidth, over a wide range of conditions. This permits resistance measurements down to this power level and a voltage sensitivity of a few femtovolts for low impedance sources. Using a 10‐&mgr;A measuring current, inductance changes of 0.1 pH have been measured. We discuss in detail the noise limitations of the device and the design criteria for optimum performance. Circuit and construction designs are presented which allow the device to be used, with minimal changes, for measurements over a wide range of parameters.

ISSN:0021-8979    

DOI:10.1063/1.1659582

出版商:AIP    

年代:1971

数据来源: AIP