Investigation of noise sources in SQUID electronics

The performance of SQUID (superconducting quantum interference device)-based electronics may be degraded from that found in laboratory operation. Investigations on superconducting tubes, wires, and sheets have been conducted to identify contributions to such noise. Results have been obtained for bulk and thin-film samples utilizing both the conventional low-temperature materials and the new high temperature oxide materials. Experiments have been conducted to quantify flux redistribution and flux motion in superconducting samples subjected to temperature changes, temperature gradients, and magnetic field gradients. These investigations have been conducted for magnetic fields typical of many SQUID applications, with field intensities much smaller than the critical values H/sub c1/. Penetration-depth, flux-pinning, and flux-motion effects have been observed. The various types of experiments conducted along with specific results are described.< >