• R.A. Marsh, B.J. Munroe, M.A. Shapiro, R.J. Temkin
  MIT/PSFC, Cambridge, Massachusetts

Funding: Work supported by DOE HEP, under contract DE-FG02-91ER40648

The design of advanced photonic bandgap (PBG) accelerator structures is examined. PBG structures are chosen for their wakefield damping. A potential disadvantage of PBG structures, as well as damped detuned structures, is the increased wall currents at the structure surface due to the reduced surface area, leading to higher pulsed wall heating. Research is carried out to improve the pulsed heating performance of PBG structure concepts while maintaining higher order mode damping. Wakefield damping parameters are discussed and a quantitative figure of merit is expressed to evaluate and compare PBG concepts. Pulsed heating performance in PBG structures is improved by breaking perfect symmetry and allowing deformation of both rod and lattice geometry. A final design for an improved pulsed heating performance PBG structure for breakdown testing at 11.424 GHz is presented and discussed.

• B.J. Munroe, R.A. Marsh, M.A. Shapiro, R.J. Temkin
  MIT/PSFC, Cambridge, Massachusetts

Funding: Work supported by DOE HEP, under contract DE-FG02-91ER40648

The design of a new photonic bandgap (PBG) accelerator structure based on a pentagonal array of rods is presented. The goal of this structure is to damp the higher order modes (HOMs) present in the structure. By removing the bilateral symmetry present in the four and six rod PBG structures the five rod photonic quasi-crystal (PQC) structure is able to damp the symmetric dipole mode. The field pattern and mode Q factors for the fundamental and dipole modes are presented for various values of the ratio of rod radius to rod spacing. These results are compared to the equivalent results for the six rod structure. The ratio of the Q factors is also calculated, and found to show an optimal value near a rod radius to rod spacing ratio of 0.17 in both cases.