The influence of the magnetic field strength upon the characteristic curve of a cold cathode ionization gauge

Cold cathode discharge gauges use crossed electric and magnetic fields to trap electrons and thus obtain a long ionizing path. For many inverted magnetron type gauges, the magnet is cylindrical, located concentrically about the discharge cell, and the peak field is about 1000 G. The slope of the gauge current versus pressure characteristic curve on a log–log plot for gauges reported in the literature usually falls in the range of 1.0 to 1.2 for pressures above 10−9 Torr, and may be steeper at lower pressures. Using an inverted magnetron gauge, gauge characteristic curves have been obtained for fields from 770 to 2330 G. Both the slope and low pressure gauge currents were found to be dependent upon the field. The slope decreases with increasing field, becoming unity by 2240 G for pressures greater than 10−8 Torr, but remains steeper than unity at lower pressures.