A spherical ionization gauge for use in a high magnetic field

This paper describes a new type of hot filament ionization gauge for measurement of neutral gas density in a high magnetic field. The notable feature of the gauge is its spherical symmetry. The ion current varies linearly with the pressure from 10−4 to 1 Pa for N2 and Ar. The sensitivity changes by no more than +20% in a magnetic field of up to 1.2 T. The main reasons for this small change in the sensitivity are as follows: (i) The probability of ionization of gas molecules is almost independent of a high magnetic field, because the spherical symmetry causes electrons to be emitted from the filament to the region in which the electric field is almost parallel to the magnetic field; (ii) the probability of ion collection is independent of a magnetic field.