A road map to extreme high vacuum

Abstract

Ultimate pressure of a well-designed vacuum system very much depends on pretreatments, processing and procedures [1, 2]. Until now much attention has been paid to minimizing hydrogen outgassing from the vacuum chamber wall materials, however, procedures and processing deserve further scrutiny. For reducing the gas load, high sensitivity helium leak detection techniques with sensitivities better than 1×10−12 Torr l/sec should be used. Effects that are induced by vacuum instrumentation need to be reduced in order to obtain accurate pressure measurements. This paper presents the current status of the CEBAF DC photogun. This state of the art technology is driving the need for Extreme High Vacuum (XHV). We also present sensitive helium leak detection techniques with RGA's, vacuum gauge and RGA calibration procedures, metal sponges for cryosorption pumping of hydrogen to XHV, low cost surface diffusion barriers for reducing the hydrogen gas load and clean assembly procedures. Further, alternative backing pump systems based on active NEGs [3] for turbo molecular pumps are also discussed.