Sharples, Emmy and Letizia, Rosa (2016) Artificial engineered materials for novel accelerator applications. PhD thesis, School of Engineering.
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Abstract
This thesis presents the design of a metamaterial loaded waveguide for accelerator applications, the metamaterial comprises of sheets of Complementary Split Ring Resonators (CSRRs). These CSRRs act as a left handed medium at certain frequencies allowing the structure to be used for the generation of reverse Cherenkov radiation. The proposed initial design exhibits a left handed TM31-like mode at 5.5 GHz with a R/Q of 6.6 kΩ/m and a shunt impedance of 10.9 MΩ/m, indicating strong beam coupling, this is verified by the strong longitudinal wake impedance of 13 kΩ. Design considerations are discussed to alleviate typical issues of metamaterials in high-power environments and make the structure more suitable for a proof-of-concept beam test at the Cockcroft Institute. The objectives of this study have been to increase fabrication suitability, reduce the number of hybrid modes and improve resistance to damage from high power, while maintaining the electromagnetic performance. Designs with increased sheet thickness, ring spacing and curvature are discussed via electromagnetic and wakefield analysis. The final chosen design with 1mm thick metasurfaces exhibits a suitable TM31-like mode at 5.86 GHz. This mode exhibits a R/Q of 4.5 kΩ/m, a shunt impedance of 22.6 MΩ/m and a longitudinal wake impedance of 10.6 kΩ, indicating that the modified geometry does not significantly affect the electromagnetic interaction of the structure with charged particles. To understand the wave-beam interactions in the structure, particle in cell simulations were performed for a commercial beam, a very high intensity beam and the current beam available on the Versatile Electron Linear Accelerator (VELA) which the structure is designed for. Through these studies the VELA beam is confirmed as the most suitable for reverse Cherenkov applications. The CSRR loaded structure can lead to novel designs of particle detectors, coherent sources and acceleration schemes, leading to compact novel accelerator applications.