Cavity basics
  The fields in rectangular and circular waveguides are derived from Maxwell's equations by superposition of plane waves. Subsequently the results are applied to explain cavity modes. Interaction of the cavity modes with a charged particle beam leads to the fundamental parameters used to describe the performance of accelerating cavities. Finally an introduction to multi-gap cavities is given by the example of travelling-wave structures. 
E. Jensen (CERN)
physics.acc-ph