Dramatic Reduction of Dc Field Emission from Large Area Electrodes by Plasma-source Ion Implantation*

Field emission is one of the principal phenomena limiting the operating voltage of practical electron guns. There is interest in developing photoemission cathode based DC electron guns employing cathode field strengths and cathode-anode voltages well above the present stateof-the-art. Such electron sources could provide high brightness, high average current beams for energy recovered superconducting linear accelerators, for applications in next generation light sources, electron cooling, and electron-ion colliders. We have studied the effect of plasma-source ion implantation on the field emission behavior of large area stainless steel electrodes. Our apparatus allows operation of disc-shaped electrode pairs with 100 cm uniform field area to 125 kV. The cathode electrode is biased at high voltage, and the anode is electrically isolated, allowing measurement of the field emission current. Electrodes were either mechanically polished, or implanted with nitrogen ions. Two separate ion implanted electrodes have shown negligible field emission at 20 MV/m, and emission between 0.5 and 1.8 pA/cm during multi-hour runs at 30 MV/m. These electrodes show very little conditioning effect.