Reduction of field emission current from stainless steel and copper surface.

The field emission dark currents from stainless steel and copper electrodes were measured under DC high field gradient condition. The stainless steel electrode was made from special material called Clean-Z and was polished by electro-chemical buffing. The electrodes achieved 34MV/m with the dark current of 90pA at the gap separation of 1 mm. The copper electrodes were treated by four different types of surface cleaning procedures. The best results were obtained by using the electrode rinsed with ultra-pure water after diamond turning. A field gradient of 47MV/m was achieved with dark current at the level of 1nA, and the microscopic field enhancement factor was estimated to be a very low value of 56. The dark current from this electrode was dependent only on the field gradient at the cathode and not affected by the total voltage applied to the gap. This fact suggests that the surface fabricated by diamond turning method with ultra-pure water rinsing creates few secondary ions by the electron bombardment. [ABSTRACT FROM AUTHOR]