  The buildup of low energy electrons in an accelerator, known as electron
cloud, can be severely detrimental to machine performance. Under certain beam
conditions, the beam can become resonant with the cloud dynamics, accelerating
the buildup of electrons. This paper will examine two such effects:
multipacting resonances, in which the cloud development time is resonant with
the bunch spacing, and cyclotron resonances, in which the cyclotron period of
electrons in a magnetic field is a multiple of bunch spacing. Both resonances
have been studied directly in dipole fields using retarding field analyzers
installed in the Cornell Electron Storage Ring (CESR). These measurements are
supported by both analytical models and computer simulations.
