Multipacting (MP) is a resonant electron discharge, often plaguing
radiofrequency structures, produced by the synchronization of emitted electrons
with the RF fields and by the electron multiplication at the impact point with
the surface of the structure. The current of re-emitted electrons grows via
true secondary re-emission when the secondary yield for the primary electron
impact energy is greater than one. A simple example (MP in short-gap
accelerating axial-symmetric cavities) allows an analytical solution of the
equation of motion, giving both the synchronization (kinematics) and
multiplication (impact energy) conditions as a function of the gap voltage (or
accelerating field). Starting from this example a thorough discussion of MP
discharges in axial-symmetric accelerating structures will be given and some
poor man's rules are given to estimate the critical cavity field levels to meet
the kinematic condition for resonance. The results of these poor man's rules
are compared with computer simulations of MP discharges obtained by a
statistical analysis of the re-emission yield for impinging electrons versus RF
field level in the accelerating structure.Comment: presented at the CERN Accelerator School CAS 2010: RF for
accelerators, Ebeltoft, 8-17 June 201