Method for detection of weak links in the current path of electrically continuous superconductors

A method for detecting weak links in a current path of an electrically continuous superconducting sample comprising:

• (a) providing the electrically continuous superconducting sample;
• (b) imposing a magnetic field in the range of 1G to 5KG on the sample;
• (c) modulating the imposed magnetic field, in the range >0-5G and at a frequency in the range of 5-100 KHz, in such a fashion that the total magnetic field is always of the same polarity;
• (d) sequentially changing the temperature of the sample, recording the temperature at each change and producing first signals;
• (e) applying a current in the range of 0.1 .mu.A-1 A to the sample, measuring the resulting voltage at each temperature change and producing second signals;
• (f) comparing the second signals to the modulation frequency by phase detection and producing third signals;
• (g) plotting a series of coordinate points where one axis represents said first signals and the other axis represents said third signals;
• and
• (h) measuring the dc resistance of the sample as a function of the temperature to obtain a dc resistance curve;
• wherein the T.sub.c of the superconducting sample is indicated by the presence of a first peak formed by the series of coordinate points and a corresponding precipitous drop in resistance on the resistance curve and further wherein the existence of weak links in the superconducting sample is indicated by the presence of a second peak formed by the series of coordinate points at a lower temperature than the first peak and a corresponding tail on the low temperature end of the resistance curve.

A method for detecting weak links in a current path of an electrically continuous superconducting sample comprising:

• providing the electrically continuous superconducting sample;
• imposing a magnetic field of 30 G on the sample;
• modulating the imposed magnetic field at 5 G and at a frequency of 10 KHz, in such a fashion that the total magnetic field is always of the same polarity;
• sequentially changing the temperature of the sample, recording the temperature at each change and producing first signals;
• applying a current of 5 ma to the sample, measuring the resulting voltage at each temperature change and producing second signals;
• comparing the second signals to the modulation frequency by phase detection and producing third signals;
• plotting a series of coordinate points where one axis represents said first signals and the other axis represents said third signals;
• and
• measuring the dc resistance of the sample as a function of the temperature to obtain a dc resistance curve;
• wherein the T.sub.c of the superconducting sample is indicated by the presence of a first peak formed by the series of coordinate points and a corresponding precipitous drop in resistance on the resistance curve and further wherein the existence of weak links in the superconducting sample is indicated by the presence of a second peak formed by the series of coordinate points at a lower temperature than the first peak and a corresponding tail on the low temperature end of the resistance curve.