Abstract
Simulations of charged particle beams in accelerator cavities show that a two-dimensional photonic crystal can be used to create a three-dimensional hybrid cavity with a single operating mode and no significant higher order modes, greatly reducing long-range wakefields. Optimizing the photonic crystal cavity to reduce radiation leakage in the desired mode (of a finite-sized structure) yields even lower wakefields. Wakefields in photonic crystal cavities are compared to those in metal pillbox cavities.
Highlights
The band gap of a photonic crystal (PhC) can be exploited to confine electromagnetic fields, as in an rf resonant accelerator cavity [1,2,3,4]
We measure the extent to which various modes can be excited by computing the wakefields of a small bunch of relativistic electrons in different cavities without beam tubes: a metal pillbox cavity, a hybrid cavity based on a 2D PhC, and a hybrid cavity based on a similar optimized structure
Having examined the accelerating mode by considering the 2D PhC cavity, we explore what other modes in the 3D hybrid cavity might be excited by a charged beam
Summary
The band gap of a photonic crystal (PhC) can be exploited to confine electromagnetic fields, as in an rf resonant accelerator cavity [1,2,3,4]. We measure the extent to which various modes can be excited by computing the wakefields of a small bunch of relativistic electrons in different cavities without beam tubes: a metal pillbox (cylindrical) cavity, a hybrid cavity based on a 2D PhC, and a hybrid cavity based on a similar optimized structure. In this paper we aim to calculate general properties regarding wakefields of hybrid cavities (that trap fields in two dimensions using a 2D PhC, and in the third dimension using metal boundaries); we have stripped the cavities of details such as beam tubes and rf input couplers. Practical designs for PhC cavities similar to those considered here, but with input couplers, beam tubes, and/or multiple cells (so the structure can be operated in a traveling-wave mode) can be found in [3,4,7], which describe actual experiments. A review of a different type of PhC accelerating cavity—intended to be driven by pulsed lasers at optical frequencies—can be found in Ref. [8]
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