Effect of the magnetic field on the operation of ionisation gauges

Hot cathode ionisation gauges are the only reliable pressure measurement devices suitable for both high and ultra-high vacuum measurement. These devices are characterized by low accuracy that is hardly better than 20%. The sources of loss of accuracy are documented in the literature although their quantification and details are not fully understood. In the present work, simulations of Bayard-Alpert and extractor gauges were performed under the influence of uniform magnetic fields up to 30 Gs. Results are in qualitative agreement with measurements taken previously with the Bayard-Alpert gauge. Both gauges are sensitive to low intensity magnetic fields which may be present in vacuum chambers. However, the extractor gauge proved to be more stable in the presence of a magnetic field due to its ring-shaped cathode.