文档介绍：Introduction to Electrodynamics for
Microwave Linear Accelerators
David H. Whittum
Stanford Linear Accelerator Center, Stanford University,
Stanford, California 94309
This collection of notes and exercises is intended as a workbook to introduce the
principles of microwave linear accelerators, starting with the underlying foundation in
electrodynamics. We review Maxwell's equations, the Lorentz force law, and the
behavior of fields near a conducting boundary. We go on to develop the principles of
microwave electronics, including waveguide modes, circuit equivalence, shunt
admittance of an iris, and voltage standing-wave ratio. We construct an elementary
example of a waveguide coupled to a cavity, and examine its behavior during transient
filling of the cavity, and in steady-state. We go on to examine a periodic line. We then
turn to examine the problem of acceleration in detail, studying first the properties of a
single cavity-waveguide-beam system and developing the notions of wall Q, external Q,
[R/Q], shunt impedance, and transformer ratio. We examine the behavior of such a
system on and off resonance, on the bench, and under conditions of transient and steady-
state beam-loading. This work provides the foundation for monly employed
circuit equivalents and the basic scalings for such systems. Following this we examine
the coupling of two cavities, powered by a single feed, and go on to consider structures
constructed from multiple coupled cavities. The basic scalings for constant impedance
and constant gradient travelling-wave structures are derived, including features of steady-
state beam-loading, and the coupled-circuit model. Effects of uniform and random
detuning are derived. These notes conclude with a brief outline of some problems of
current interest in accelerator research.
Introduction
The accelerator is the instrument on which all intellectual life in high-energy
physics depends. Without accelerators,