Abstract
Photonic band gap (PBG) dielectric fibers with hollow cores are being studied both theoretically and experimentally for use as laser driven accelerator structures. The hollow core functions as both a longitudinal waveguide for the transverse-magnetic (TM) accelerating fields and a channel for the charged particles. The dielectric surrounding the core is permeated by a periodic array of smaller holes to confine the mode, forming a photonic crystal fiber in which modes exist in frequency passbands, separated by band gaps. The hollow core acts as a defect which breaks the crystal symmetry, and so-called defect, or trapped modes having frequencies in the band gap will only propagate near the defect. We describe the design of 2D hollow-core PBG fibers to support TM defect modes with high longitudinal fields and high characteristic impedance. Using as-built dimensions of industrially made fibers, we perform a simulation analysis of prototype PBG fibers with dimensions appropriate for speed-of-light TM modes.
Highlights
Because of electrical breakdown of metals in the presence of high electric fields, conventional particle accelerators, which consist of metal cavities driven by high-power microwaves, typically operate with accelerating fields of 20 to 40 megavolts=meter (MV=m)
In this paper we have focused on the basic electromagnetic properties of the accelerating modes in 2D hollowcore Photonic band gap (PBG) fibers and to the geometry changes that will improve both the characteristic impedance and the ratio of acceleration gradient to maximum field
Wherever possible we provided physical insight into accelerating mode behavior based on the surface mode nature and the distinction with core defect modes
Summary
Because of electrical breakdown of metals in the presence of high electric fields, conventional particle accelerators, which consist of metal cavities driven by high-power microwaves, typically operate with accelerating fields of 20 to 40 megavolts=meter (MV=m). Light waves travel as Bloch waves, characterized as a product of a periodic function and a plane wave with characteristic wave vector These Bloch waves have a dispersion relation similar to free photons, but modified by the Fourier components of the variation of the dielectric structure, near the Brillouin zone boundaries (given by half of the unit reciprocal lattice vectors). A summary of the results is given in the last section
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