Development and applications of the tunnel junction dc SQUID
The development of a cylindrical dc SQUID made with shunted Nb-NbOx-Pb Josephson tunnel junctions is described. The SQUID is current biased at a non-zero voltage, and modulated with a 100 KHz flux. The 100 KHz signal across the SQUID drives a cooled tank circuit that optimally matches the SQUID impedance to the input of a room-temperature FET preamplifier. The SQUID is operated in a flux-locked loop with a dynamic range of +- 3 x 10/sup 6/ (in a 1-Hz bandwidth), a bandwidth of 0 to 2 KHz, and a slewing rate of 2 x 10/sup 4/ phi/sub o/sec/sup -1/. A flux noise power spectrum for a SQUID in a superconducting shield at 4.2 K is shown. Above 2 x 10/sup -2/ Hz the spectrum is white with an rms value of 10/sup -5/ phi/sub o/Hz/sup -1/2/. At lower frequencies the spectrum is approximately 10/sup -10/ (1 Hz/f) phi/sub o//sup 2/Hz/sup -1/, where f is the frequency. Factors contributing to the long term drift of the SQUID are discussed. A drift rate of 2 x 10/sup -5/ phi/sub o/h/sup -1/ over a 20-h period is achieved by regulating the temperature of the helium bath. A detailed description is given of the coupling of various input coils to the SQUID. The energy resolution of the SQUID with respect to a current in a 24-turn input coil is 7 x 10/sup -30/ J Hz/sup -1/ in the white noise region. The energy resolution in the l/f noise region and the long term drift performance are better than for any other SQUID.
- Research Organization:
- California Univ., Berkeley (USA)
- OSTI ID:
- 6156902
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ELECTRON DRIFT
ELECTRONIC EQUIPMENT
EQUIPMENT
FLUXMETERS
JOSEPHSON JUNCTIONS
JUNCTIONS
MEASURING INSTRUMENTS
MICROWAVE EQUIPMENT
NOISE
PERFORMANCE
SQUID DEVICES
SUPERCONDUCTING DEVICES
SUPERCONDUCTING JUNCTIONS