The Josephson microcircuit technology being developed for computers has also found numerous applications in analog measurements. These applications include high sensitive magnetic field detectors, voltage standards and microwave mixers. This paper focuses on the Josephson DC sampling technique and the Josephson pulse sampling technique. These techniques having advantages of high sensitivity and high time resolution are widely applicable for ultra-fast phenomena measurements. The Josephson switching signal in the circuit chips and packaging components, the vortex signal in the Josephson transmission line and SQUID resonances are typical measured examples. This report reviews the measurement principle, the circuit design and the automatic systems for two sampling techniques. Recent examples of applications are also presented.
A Nb-61.7at.%Ti-3at.%Hf alloy has been fabricated into multifilamentary wires and studied in terms of high field superconducting properties. First, effects of precipitation heat treatment at temperatures between 325 and 500°C and cold working up to 99% area reduction ratio after the heat treatment on the superconducting properties at 4.2K were examined. The heat treatment enhances the critical current density, Jc, in low fields below 8T, but not that inhigh fields above 10T. The cold working after heat treatment is identified as critical to increasing Jc in high fields. Jc increases with reduction ratios up to 95%. Thus, to obtain high Jc in high fields a process emerges where the heat treatment producing a maximum upper critical field, Bc2, is followed by severe cold working. The concept underlying this may be applicable to alloy superconductors other than NbTiHf. Second, the superconducting properties at 1.8K were investigated. The critical current density Jc vs. magnetic field B curves obtained for 4.2K are found to coincide with those for 1.8K when shifted along the B axis by 3.5T. The present NbTiHf superconductor has higher Jc and Bc2 at 1.8K than those of typical NbTi. For both 4.2 and 1.8K, maximum pinning forces in samples cold-worked after heat treatment appear at the same reduced field of about 0.5, indicating that the temperature scaling law may hold for this NbTiHf superconductor.
A small solenoid coil, which has an inner diameter of 20mm, an outer diameter of 146.5mm, a length of 100mm, has been wound by a fine filamentary Nb-Ti superconductor. A cryostat which generates superfluid helium at atmospheric pressure has been also constructed for the coil test at superfluid helium temperature. The coil has been successfully excited up to the magnetic field of 12.3T at 1.8K. The performances of the cryostat obtained of using a 140m3/h vacuum pump were: the lowest temperature reached was 1.45K and the effective cooling power was 1.9W at 1.8K.
The design, construction and testing of a liquid helium transfer tube installed with a carbon-resistor level indicator are reported. The position of the level indicator is adjustable and the alarm, which informs us the fill-up of liquid helium up to a pre-set level, is also provided.