GB1336126A - Ion gauges - Google Patents

Abstract

1336126 Ionization manometers MULLARD Ltd 16 Oct 1970 [29 Oct 1969] 53007/69 Heading H1D In an ion gauge having an electron source 21 and an ion collector 30 both external to an electrically conductive equipotential enclosure 23 surrounding an ionization space 13, the wall of said enclosure has an end region 26 substantially opaque to the passage of soft X-rays provided with an ion extraction aperture 27 and an electron transparent region 24 forming an electron accelerating grid having apertures the size and shape of which are such as to prevent the penetration of the accelerating field into the enclosure. A substantially continuous equipotential boundary is formed adjacent the inner surface of region 24 within which, owing to space charge, a more negative region is formed, which causes ions to be drawn to the central region on the axis of the aperture 27. Cathodes 21, 22 of rhenium coated with lanthanum hexaboride are supported by leads 41 on either side of the grid 24, 25 of closely woven tungsten wire mesh. End wall 26 may be of stainless steel and has a cylindrical extension 47 surrounding the aperture 27. An extractor electrode 49 and reflector electrode 51 may also be of stainless steel. The electrode assembly is surrounded by a conducting cylinder 44 to which is welded a flange 43 for attachment to a vacuum system. Alternatively the assembly may be enclosed in an envelope. The extension 47, extractor electrode 49 and reflector electrode 51 together form two converging electrostatic tenses having focal points F1 and F2 respectively which direct ions to the collector 30 which is shielded by the wall 26 from X-rays and described ions produced by electron bombardment of the wall 24. The portion of collector 30 and lead 54 outside the reflector 52 are shielded by a glass tube 56. Alternative embodiments (Figs. 3 to 5, not shown) comprise an arrangement in which the extractor and reflector electrodes are omitted, and other arrangements having modified extraction electrode constructions. The gauge may be provided with a modulation electrode projecting axially into the space 13 from the end opposite the aperture 27 (Fig. 6, not shown). Reference has been directed by the Comptroller to Specification 1,173,354.