| Superconducting loops can be used to detect the passage of cosmic-ray magnetic monopoles by inductively coupling to the monopole field. A superconducting induction detector with three mutually orthogonal loops and 476 {dollar}{lcub}rm cm{rcub}sp2{dollar} sensing area averaged over solid angle was in operation at Stanford from 25 Jan. 1983 to 20 March 1986. It set a monopole flux limit of {dollar}4.4 times 10sp{lcub}-12{rcub}{dollar} {dollar}{lcub}rm cmsp{lcub}-2{rcub}{rcub}{dollar} {dollar}{lcub}rm ssp{lcub}-1{rcub}{rcub}{dollar} {dollar}{lcub}rm srsp{lcub}-1{rcub}{rcub}{dollar} at 90% confidence limit, the best limit to date with a superconducting detector. This work describes the three-loop detector in detail, provides theoretical analysis of the detector response to a flux of magnetic monopoles, and describes results obtained from the detector. The detector response is found from Monte Carlo simulation of monopole trajectories to determine the locus of possible monopole signals. In addition, a larger detector has been constructed with eight loops laid in octagonal fashion around a cylinder and 1.5 {dollar}{lcub}rm m{rcub}sp2{dollar} sensing area averaged over solid angle, a factor of 30 larger than the three-loop detector. General design aspects of the eight-loop detector are discussed and a similar theoretical analysis of this detector is provided. The detectors are found to be very discriminating against spurious signals. |
