Development of a new ionization gauge with Bessel Box type energy analyzer

Abstract

A new type of hot filament ionization gauge with an ion energy analyzer was developed for pressure measurement in ultrahigh and extremely high vacua. The new gauge has a Bayard-Alpert gauge type ionizer, a Bessel Box type energy analyzer, and a secondary electron multiplier of pulse counting mode for ion detection. The Bessel Box type energy analyzer is composed of a cylinder electrode with a center disc and two end plates. The center disc, which is placed perpendicularly to the cylinder axis, shields the ion collector from direct incidence of X-rays generated at the surface of the ionizer. The energy analyzer focuses the ions from the limited region in the grid cage, whose potential is about 30 V lower than that of the grid, on the ion collector. Therefore, the energy spectrum obtained by the energy analyzer showed that the two peaks of gas phase ions and electron stimulated desorption (ESD) ones were completely separated with an energy difference of 30 eV. The residual X-ray photocurrent was equivalent to a pressure about 4 × 10 −11 Pa (N 2 eq.). The sensitivities of the gauge for argon and hydrogen were constant between 5 × 10 −10 and ∼ 10 −6 Pa and were 8.2 × 10 −3 and 3.2 × 10 −3 Pa −1, respectively. The counting rate of the gas phase ions was 1200 counts s −1 at 2 × 10 −10 Pa (N 2 eq.) with 30 μA of emission current. The lower limit of pressure measurement of this new gauge is estimated to be 3 × 10 −12 Pa or less.