Fabrication and cold test of photonic band gap resonators and accelerator structures

Evgenya I Smirnova,Ivan Mastovsky,Randall L Edwards,Lawrence M Earley,Richard J Temkin,Michael A Shapiro

doi:10.1103/physrevstab.8.091302

Abstract

We present the detailed description of the successful design and cold test of photonic band gap (PBG) resonators and traveling-wave accelerator structures. Those tests provided the essential basis for later hot test demonstration of the first PBG accelerator structure at 17.140 GHz [E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).]. The advantage of PBG resonators is that they were built to support only the main, ${\mathrm{TM}}_{01}$-like, accelerator mode while not confining the higher-order modes (HOM) or wakefields. The design of the PBG resonators was based on a triangular lattice of rods, with a missing rod at the center. Following theoretical analysis, the rod radius divided by the rod spacing was held to a value of about 0.15 to avoid supporting HOM. For a single-cell test the PBG structure was fabricated in X-band (11 GHz) and brazed. The mode spectrum and $Q$ factor ($Q=5\text{ }000$) agreed well with theory. Excellent HOM suppression was evident from the cold test. A six-cell copper PBG accelerator traveling-wave structure with reduced long-range wakefields was designed and was built by electroforming at Ku-band (17.140 GHz). The structure was tuned by etching the rods. Cold test of the structure yielded excellent agreement with the theoretical design. Successful results of the hot test of the structure demonstrating the acceleration of the electron beam were published in E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).

Highlights

Two-dimensional (2D) metallic photonic band gap (PBG) structures [1] have received considerable attention recently, because of their possible applications in accelerators [2,3]
We experimentally demonstrate that the use of PBG structures is a promising approach to long-range wakefield suppression
The design and construction of a PBG accelerator with long-range wakefield suppression became possible after the success of a single-mode 2D PBG resonator demonstration

Summary

INTRODUCTION

Two-dimensional (2D) metallic photonic band gap (PBG) structures [1] have received considerable attention recently, because of their possible applications in accelerators [2,3]. The design and construction of a PBG accelerator with long-range wakefield suppression became possible after the success of a single-mode 2D PBG resonator demonstration. This paper provides a detailed description of the design, fabrication, and cold test of a series of photonic band gap (PBG) test resonators and of a six-cell, 17 GHz PBG traveling-wave accelerator structure. We design a single-mode 2D PBG resonator based on the global band gap picture from [7] and our computations using high frequency structure simulator (HFSS) code [10]. We found that the mode with frequency in the band gap was confined in a PBG structure with only three rows of rods (Fig. 1) For this geometry, the diffraction Q factor was found to be of the order of 105, which is much higher than the computed Ohmic Q factor of about 5000. A wave with a frequency to the right of the solid black curve cannot propagate through the PBG structure, while a wave with a frequency to the left of the black curve can propagate

MODE CONFINEMENT IN 2D PBG RESONATORS

Brass PBG resonator testing

High Q PBG resonator fabrication and testing

PBG ACCELERATOR DESIGN

PBG ACCELERATOR CONSTRUCTION AND COLD TESTS

CONCLUSION