The first goal of any accelerator project is to reach the design energy. This battle is usually won rather quickly, only to be replaced by a longer struggle to reach the highest intensity possible. This latter phase can last for the whole of the accelerator's working life and, for the most part, will end up as a struggle against coherent instabilities. Both theoretically and experimentally the study of coherent instabilities is too advanced to be covered exhaustively in this book, but in line with the extreme importance of this subject an introduction is given in this chapter. More emphasis is put on physical description than the mathematical treatment and the latter is restricted to coasting beams. For more complete analyses, including bunched beams, the reader can refer to Hofmann, Zotter and Sacherer, Laclare and Chao. Many of the same phenomena were already known in electron tubes, where they were of interest as amplification mechanisms. A good account of the early work in this field can be found in Beck. For those readers interested in the historical aspects, Maxwell had already analysed the stability of a ring of weakly interacting particles in a prize-winning essay on Saturn's rings in 1856.

GENERAL DESCRIPTION

In all accelerators the beams are surrounded by cavities, pipes, plates, grids, etc., which for the most part are metal.