FIELD STABILIZATION OF A SUPERCONDUCTING MAGNET BY HELIUM PRESSURE CONTROL

Fluctuations and drifts of the magnetic field of superconducting solenoids are at present the main limitation in the precision of Penning ion trap mass spectrometers. Stabilities up to 10(-11) h(-1) are required to exploit fully the inherent possibilities of the method. Here we discuss possible reasons for these instabilities and demonstrate substantial improvement in stability upon stabilizing the temperature of the cryostat by helium gas pressure control. The improvement is about two orders in magnitude relative to the case of an unstabilized magnet.