By J. Knobloch

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Here more is already known. , [21–23]) The breakdown event is associated with a discharge and its accompanying plasma. 2(a)). Yet, there are outstanding issues about emitter processing by discharge. Is the mechanism in rf cavities the same as that for dc gaps? What is the chain of events that take place between emission and voltage breakdown? What are the factors that govern the conditions for the formation of the discharge? For example, where does the gas for the 8 Chapter 1. Introduction discharge come from?

Our results with rf and helium processed emitters hence allow us to formulate a revised theory of the evolution of field emitters from steady state emission to the processing stage. Based on this theory, predictions on the processability of field emitters can be made. The description of the revised model also provides the introduction to Chapter 6. Numerical simulations of field emission and the early stages of rf processing with a specially modified version of the program mask are discussed in Chapter 6.

The experimental part of our work was designed to address many of these questions. Prior to these experiments, we assumed that the heating by the field emission current alone is responsible for initiating the explosion. Our experiments, though, proved this hypothesis to be wrong. Microscopy revealed new features of emission sites that help us to draw a more complete picture of how field emission progresses to discharge. The evidence suggests that a plasma can coexist with rf emission before the onset of the discharge, and that gases play an important role in the progression of an emitter from steady state emission to its explosion.

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