A Superconducting System for High Sensitivity Measurements of Pc 1 Geomagnetic Pulsations

Geomagnetic pulsations are a class of fluctuations of the earth's magnetic field in the ultra-lowfrequency (ULF) band (i. e. .001 Hz to 5 Hz). Pulsation amplitudes in this band range from milligammas to tens of gammas (1 gamma = 10-5 gauss). Pc 1 pulsations occur in the upper part of this band (.2 Hz to 5 Hz). Until the recent availability of superconducting magnetometers, Pc 1 measurement instrumentation had been internally noise limited. This paper briefly describes conventional Pc 1 instrumentation, and then goes on to describe a working measurement system incorporating a superconducting magnetometer. A good conventional system is compared experimentally to the superconducting system, and the noise of the latter system is seen to be significantly lower. Further, measurements taken with the superconducting system show that the noise in the conventional system can obscure weaker events in the Pc 1 band.