Introduction

The search for very high gradient acceleration has been driven to a large extent by the high energy physics community, for the construction of higher energy accelerators. But the needs of this community are more complex than just high gradient: the accelerator must carry relatively cheap. These requirements are not easily met with the high gradient mechanisms we now know. There are however other needs for high gradient that are less demanding and are thus more appropriate at this stage. For instance high brightness electron guns. Since the intent here is to explore the technology for such a gun, it is reasonable not to require a high repetition rate. Something of the order of 1 Hz would be sufficient. As will be seen this makes the demonstration a lot easier. It must be remembered however that for a real FEL or other application, rates of a few hundred Hz would be desirable. 1 ref