Diagnosis and Maintenance of Curetron Low Voltage Electron Beam Accelerator

Curetron is a self-shielded, curtain type cockroft-walton electron beam accelerator with a low operation voltage of 0.2 MeV. It was obtained in August 1991 through cooperation with Japanese Government under JICA programme. Curetron was mainly used to support research works in the field of radiation curing of surface coatings and some activities on radiation modification of polymers. Curetron encountered malfunctions somewhere in 2012 due to vacuum system breakdown. Maintenance work slowly started in 2016 focusing on the diagnosis of Curetron machine breakdown. It was found during diagnosis that Curetron breakdown was not only due to vacuum system failure, but it was more extensive than originally thought. Electron gun system which is the integral part of Curetron was unable to start due to several interlocks failure namely vacuum system, cooling water system and conveyer system. Vacuum system failed to create a minimum required high vacuum environment of 1 x 10^-5 Pascal in the vacuum chamber due to a number of factors which are oil backflow of rotary pump, turbo molecular pump (TMP) overheat, faulty vacuum valves and also the occurrence of vacuum leakages at window titanium foil and vacuum seals. Cooling water system encounter failures due to faulty contactor and disconnection of cooling water piping for TMP vacuum pump. Lastly, conveyer system failure was due to the breakage of pneumatic hoses, faulty switch buttons, and mainly due to programmable logic controller (PLC) failure. All of these failures contribute to Curetron machine malfunction and require extensive repair works. (author)