Cleaning stainless steel for use in accelerators—Phase 1

Particle accelerators such as the SRS at Daresbury Laboratory generally require pressures lower than 10−9 mbar for satisfactory stored electron beam lifetimes. To achieve this requires that particular attention be given to the cleanliness of the stainless-steel vacuum vessels and other components of the vacuum system. Pre-installation cleaning is an important step in the process.Currently, trichloroethylene is employed at Daresbury Laboratory as the primary cleaning solvent of choice, having been chosen as the outcome of earlier studies of the effects of various cleaning techniques on outgassing and electron- stimulated desorption from stainless steel [Herbert JD, Reid RJ, Groome AE. J Vac Sci Technol A 1994; 12(4): 1767; Herbert JD, Reid RJ. Vacuum 1996; 47(6–8): 693].However, in light of the re-classification of trichloroethylene by the European Union as a class two carcinogen, with consequent stringent and expensive safety precautions required in order to continue using it, a suitable, more economical, replacement is sought after.This paper, details the assessment of different cleaning agents against the two criteria important to particle accelerator vacuum systems. The criteria being room temperature thermal outgassing rates and electron-stimulated desorption yields. A variety of different cleaning agents, ranging from halogenated solvents to aqueous-based cleaning agents have been tested. A comparison of the performance of a selection of such cleaning agents is presented and a satisfactory alternative to trichloroethylene is proposed.