RF breakdown test of SiO2 coated copper electrodes

RF breakdown test results with copper and SiO/sub 2/-coated copper are presented. The interest was to investigate what improvement could be made in depressing the field emission and increasing the maximum field gradient by the SiO/sub 2/ coating. The results show that the breakdown started at a field level of 97-100 MV/m with the SiO/sub 2/-coated electrodes. The Kilpatrick limit at 471 MHz is 20 MV/m. This means that SiO/sub 2/ coating may provide a method for keeping the electrode surface free of damage during high field gradient operation. The SiO/sub 2/ coating can also reduce the field emission. Compared with the pure copper electrodes which were used for more than 100 h, the data show that the total normalized X-ray counts of the pure copper sample were about 20 times more than that of SiO/sub 2/-coated copper.<>