FIELD STABILIZATION OF A SUPERCONDUCTING MAGNET BY HELIUM PRESSURE CONTROL

Fluctuations and drifts of the magnetic field of superconducting solen oids are at present the main limitation in the precision of Penning io n trap mass spectrometers. Stabilities up to 10(-11) h(-1) are require d to exploit fully the inherent possibilities of the method. Here we d iscuss possible reasons for these instabilities and demonstrate substa ntial 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.