This structure is a charged particle beam deflector. Only 1/8 of the model is shown, as it has three planes of geometric and electromagnetic symmetry. The full structure has a beampipe down the centerline that intersects three circular cavities connected with complex coupling regions. The structure operates using a resonant mode at 2.82 GHz that produces a transverse electric field on the beampipe axis.
Depending on the amplitude of the resonant mode (its field strength), and also the secondary emission characteristics of the metal walls, the structure supports resonant electron orbits that can bleed power from the cavity and potentially result in damage to cavity walls. The development of resonant orbits is computed using Analyst, and an animation of the results shows the electron positions over several RF periods given initial random positions and velocities. Most of the initial particles are swept away by the field in the first RF period, but some impact the walls with favorable energies such that one or more secondary particles are emitted. These new particles are also tracked by Analyst, and they can in turn cause more secondary particles to be created on subsequent impacts, resulting in a resonant condition in which the total particle counts increase with each RF period. This phenomenon is called “multipacting”, and it is evident late in the animation in a particular region of the cavity.