Direct Quartz Crystal Control of a Low-Level Pound-Knight-Watkins Spin Magnetometer

Abstract

A quartz crystal is placed in the feedback path of the marginal oscillator, between the cathodes of the oscillator tubes. This change results both in greatly improved frequency stability (2 parts in 107 per hour at 30 Mc with the simplest unthermostatted crystal) and a useful increase of signal-to-noise ratio (although not necessarily of noise figure) owing to the rf filtering action of the crystal. Magnetometer operation at an rf level as low as 100 μv across the sample coil, equivalent to an rf field of about 5 μgauss, has been obtained. A magnet servo based on the crystal-controlled magnetometer is discussed.