On the efficacy of cold-bore vacuum system in TRISTAN

Possibility of cold bore vacuum system is discussed for the proton storage accelerator (Ring LLL) of TRISTAN project. Main problem in this vacuum system is the adsorption of hydrogen and helium on the wall of the cold bore section, because accumulation of such adsorbed molecules induces pressure bumps by energetic particle bombardments. The tolerable surface coverages of adsorbed hydrogen and helium molecules are estimated, and it is concluded that both the expected flowing rate of hydrogen into the cold bore section and the remaining helium leak from the helium reservoir of cryostat can be made small enough for one year operation of the cold bore system without any pressure bump. (author)