MEASUREMENT OF FIELD EMISSION DARK CURRENT FROM THE TITANIUM, COPPER, AND STAINLESS STEEL ELECTRODES UNDER THE HIGH DC-FIELD GRADIENT CONDITION

We have continued a systematic study on the field emission dark current under the high DC-field gradient by using a compact test apparatus at KEK. The dark current have been already measured for the several sample electrodes with same figures but made of different materials of stainless steel (SUS), copper (Cu), and titanium (Ti). For the SUS, the field gradient of 36 MV/m was achieved with the dark current level of less than 1 nA, and the microscopic field enhancement factor β was estimated to be ~40. For the Cu, it was 47 MV/m with β of 56. These data were taken for the same gap length of 1 mm and the same maximum-field-applied area of ~7 mm 2 . At present, we have been testing the Ti electrode samples. It was expected that Ti should give the higher performance than SUS and Cu due to the lower secondary electron yield and sputtering rate. The preliminary results for the pure-Ti electrode showed the much higher field gradient of 88 MV/m for 1 nA dark current level and β of 30 under the same experimental conditions for SUS and Cu.