DEVELOPMENT OF A NEW IONIZATION GAUGE WITH BESSEL-BOX TYPE ENERGY ANALYZER

A new type of hot filament ionization gauge with an ion energy analyze r was developed for pressure measurement in ultrahigh and extremely hi gh vacua. The new gauge has a Bayard-Alpert gauge type ionizer, a Bess el Box type energy analyzer, and a secondary electron multiplier of pu lse counting mode for ion detection. The Bessel Box type energy analyz er is composed of a cylinder electrode with a center disc and two end plates. The center disc, which is placed perpendicularly to the cylind er axis, shields the ion collector from direct incidence of X-rays gen erated at the surface of the ionizer. The energy analyzer focuses the ions from the limited region in the grid cage, whose potential is abou t 30 V lower than that of the grid, on the ion collector. Therefore, t he 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 res idual X-ray photocurrent was equivalent to a pressure about 4 x 10(-11 ) Pa (N-2 eq.). The sensitivities of the gauge for argon and hydrogen were constant between 5 x 10(-10) and similar to 10(-6) Pa and were 8. 2 x 10(-3) and 3.2 x 10(-3) Pa-1, respectively. The counting rate of t he gas phase ions was 1200 counts s(-1) at 2 x 10(-10) Pa(N-2 eq.) wit h 30 mu A of emission current. The lower limit of pressure measurement of this new gauge is estimated to be 3 x 10(-12) Pa or less.