Novel ionisation vacuum gauge suitable as a reference standard: Influence of primary electron trajectories on the operation

Abstract

A detailed study of the operation of a novel ionisation gauge, recently proposed as a reference standard by the consortium of the European project 16NRM05, is performed with focus on the influence of electron trajectories and the interaction of electrons with electrode surfaces. The strategy behind the gauge design was to provide well defined primary electron trajectories that form an electron beam. This investigation seeks to correlate experimental investigations of improper primary beam focusing, electron beam profiling, electron stimulated desorption and outgassing, with charged particle optics simulations that include space charge effects, and a detailed study of secondary electron emission. The main outcome of the research is that control of the primary electron trajectories, quantified by electron transmission efficiency, is essential for its proper operation mainly as a pressure measurement device but also as a vacuum gauge sensitivity reference standard. Once all primary electrons end their trajectories in a Faraday cup, being one of the gauge electrodes, two additional problems are identified: escape of a very small fraction of electrons from the Faraday cup and electron stimulated desorption of neutrals. Their contribution is of low significance when using this device as a sensitivity reference standard in the high vacuum range, which meets the major goal of the 16NRM05 project. However, these effects might represent an obstacle for the gauge application, mainly as a measurement device, at lower pressures. Approaches to mitigate the mentioned potential problems are discussed.