We describe the superconducting readout system to be used for resolving 0.001 arc second changes in the gyroscope spin direction in the Relativity Gyroscope (GP-B) experiment. This system couples the London magnetic moment flux of the spinning gyro to a low noise superconducting quantum interference device (SQUID) detector. Resolution limits and noise performance of the detection system will be discussed, and improvements obtained and expected with advanced SQUIDs will be presented. We also describe the novel use of superconducting magnetic shielding techniques to obtain a 250 dB attenuation of the Earth's magnetic field at the location of the gyroscopes. In this approach, expanded superconducting foil shields (as developed by Cabrera') are coupled with fixed cylindrical superconducting shields and special geometric considerations to obtain the extremely high attenuation factor required. With these shielding techniques, it appears that the 0.5 Gauss Earth field (which appears to the gyroscopes as an AC field at the satellite roll rate) can be reduced to the 10-13 G level required by the experiment. We present recent results concerning improvements in the performance of the superconducting foil technique obtained with the use of a new computer-controlled cooling system.
James M. Lockhart,
"Squid Readout And Ultra-Low Magnetic Fields For Gravity Probe-B (Gp-B)", Proc. SPIE 0619, Cryogenic Optical Systems and Instruments II, (18 July 1986); doi: 10.1117/12.966648; https://doi.org/10.1117/12.966648