Showing papers by "David R. Smith published in 1997"

Recent progress on photonic band gap accelerator cavities

Abstract: We report on the current status of our program to apply Photonic Band Gap (PBG) concepts to produce novel high-energy, high-intensity accelerator cavities. The PBG design on which we have concentrated our inital efforts consists of a square array of metal cylinders, terminated by conducting or superconducting sheets, and surrounded by microwave absorber on the periphery of the structure. A removed cylinder from the center of the array constitutes a site defect where a localized electromagnetic mode can occur. In previous work, we have proposed that this structure could be utilized as an accelerator cavity, with advantageous properties over conventional cavity designs. In the present work, we present further studies, including MAFIA-based numerical calculations and experimental measurements, demonstrating the feasibility of using the proposed structure in a real accelerator application.

Wake-field studies on photonic band gap accelerator cavities

Abstract: We have studied the wake-field of several metal Photonic Band Gap (PBG) cavities which consist of either a square or a hexagonal array of metal cylinders, bounded on top and bottom by conducting or superconducting sheets, surrounded by placing microwave absorber at the periphery or by replacing outer rows of metal cylinders with lossy dielectric ones, or by metallic walls. A removed cylinder from the center of the array constitutes a site defect where a localized electromagnetic mode can occur. While both monopole and dipole wake-fields have been studied, we confine our attention here mainly to the dipole case. The dipole wake-field is produced by modes in the propagation bands which tend to fill the entire cavity more or less uniformly and are thus easy to damp selectively. MAFIA time domain simulation of the transverse wake-field has been compared with that of a cylindrical pill-box comparison cavity. Even without damping the wake-field of the metal PBG cavity is substantially smaller than that of the p...

Improved form of backfire bifilar helix conical beam antenna

Abstract: The nonresonant-length backfire bifilar helix is often used as a vehicle satcom antenna, as it has a circularly polarized conical beam with azimuthal symmetry. Some antenna configurations, however, exhibit poor back-lobe levels. It is shown that radiation patterns can be significantly improved by correct termination of the helix. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 14:278–280, 1997.