Mechanisms for the effect of residual pressure on field emission in vacuum

It has been widely reported that injection of gas into high voltage vacuum insulation systems is effective for the reduction of field emission; this technique is sometimes called gas conditioning 1 . While it is commonly thought that the responsible mechanism is ionic bombardment of microscopic field emitter structures, there still exists debate on this point. In this presentation, we will compare and contrast several competing ideas for the mechanism in light of measurements of field emission on the order of pA to µA in the presence of different gases over several orders of magnitude of pressure. These mechanisms include gas adsorption induced by high electric field, ionic bombardment leading to erosion of field emitters, and ionic bombardment leading to implantation of species within the cathode material. Implications of these issues on the design of certain accelerator structures will then be discussed.