Bent belt-beam gauge: Extending low-pressure measurement limits in a hot-cathode ionization vacuum gauge by combining multiple methods

Abstract

A commercially viable, extremely high vacuum hot-cathode ionization gauge that can measure pressures as low as 5.4×10−12 Pa, by reducing the limits imposed by soft x rays, electron-stimulated desorption (ESD), and outgassing, is reported. The gauge construction includes a cylindrical grid, which is closed at both ends; ions are drawn from the grid through a long, axial slit made in the cylindrical surface. Thus, the ion beam that emerges forms a “belt.” This beltlike ion beam is guided on a curved path by a cylindrical sector deflector and terminates on a plate collector arranged after a beam trajectory rotation of 230°. These elements are embedded in a solid cylinder of 0.2% BeCu alloy, which has a low emissivity (radiation factor) and high thermal conductivity. As a result, the effects of heat radiation and outgassing (caused by the hot-cathode filament) and soft x-ray photoemission (the grid is the soft x-ray source) are reduced in the deflector/collector region. This electrode arrangement can also greatly decrease the flux of soft x rays and ESD in the direction of the belt ion beam because it sets to 90° the angle between the extracted gas-phase ion beam and the maximum flux of soft x rays and ESD. In addition, it achieves an extremely low-pressure measurement limit by minimizing loss in the ion transport, and because the collector is well hidden, being located after the large deflection of the ion beam.