RADIATION DAMAGES IN TRISTAN VACUUM-SYSTEMS

The TRISTAN e+ e- collider, the all aluminum (Al) alloy vacuum system, has been operated for 4 years at a beam energy between 27.5 and 32 GeV, with a characteristic energy of the synchrotron radiation between 187 and 295 keV. The radiation in the TRISTAN tunnel was measured using thermoluminescence dosimeters. Radiation damage in the aluminum vacuum system is mainly from HNO3 produced from NO(x). N2 and SO2 in atmosphere are oxidized, combined with H2O, and turned to HNO3 and H2SO4 in TRISTAN tunnel. Freon also turned to HCl and HF. Corroded materials on aluminum surface is amorphous Al(NO3)3.9H2O. To decrease corrosion due to the radiation, one or two of the components in the atmosphere must be removed. This can be realized by pumping with a rotary pump (RP) or a RP together with a turbomolecular pump, or supplying N2 or He with low dew point, to protect beryllium (Be) windows for internal targets and beam injection and extraction, and race track type bellows. SiO2 coating superior to almite coating is applied to protect bellows from radiation damage. Most organic materials are decomposed with the radiation. Halogens in the materials are decomposed and turned to acids combining with H2O. Connectors of distributed ion pumps and cables of beam position monitors were damaged by fluorine gas, resulting from the decomposition of Teflon insulators in cables and connectors. Polyimide and polystyrene are durable under radiation of about 10(10) rad. They however turned fragile and caused insulation failure in connectors. Rubbers and oils also received radiation damage. Organic materials must be exchanged to inorganic or metallic materials to avoid radiation damage. Mineral insulation cable is developed and is under test.