In-situ reactive glow discharge cleaning of NSLS distributed ion pumps

Abstract

Based on our experience with the in‐situ cleaning of optical systems by reactive r. f. glow discharges [1,2] and the conditioning and preparation of distributed ion pump (DIP) elements [3], we have sought to develop strategies for recovering from severe vacuum accidents by restoring DIP elements of storage rings such as those at the NSLS in‐situ. In this paper we will describe a series of experiments conducted in a test apparatus to condition a so called ‘egg‐crate’ DIP in‐situ, (this type element is common in older storage rings). A new untreated element, which was unable to pump below 5×10−8 Torr in its initial condition, was treated in oxygen and subsequent argon r.f. discharges, utilizing the pump element as the discharge electrode, resulting in a nitrogen pumping speed of 168 l/s at 2×10−8 Torr. A light bake at 75°C increased this to nearly 500 l/s at 5×10−8 Torr. After exposure to atmosphere the speed was reduced to nil at these pressures but subsequently recovered, without bakeout, by glow discharge cleaning.