Dielectric assist accelerating (DAA) structures are being studied as an alternative to conventional disk-loaded copper structures. This paper investigates numerically an efficient X-band DAA structure operating in a higher order mode of TM02-π. This accelerating structure consists of dielectric disks with irises arranged periodically in a metallic enclosure. Through optimizations, the RF power loss on the metallic wall can be significantly reduced, resulting in an extremely high quality factor Q0 = 134525 and a very high shunt impedance rʹ = 781 MΩ/m. The RF-to-beam power efficiency reaches 51% which is significantly higher than previously-reported CLIC-G structures with an efficiency of only 33.5%. The optimum geometry of the regular and the end cells is described in detail. Due to the wide bandwidth from the dispersion relation of the accelerating mode, the DAA structure is allowed to have a maximum number of 72 regular cells with a frequency separation of 1.0 MHz, which is superior to that of conventional disk-loaded copper structures. In addition, the DAA structure is found to have a short-range transverse wakefield lower than that of the CLIC-G structure.

Numerical optimizations on couplers of the traveling-wave (TW) accelerating structures usually require lots of calculation resources. This paper proposes a new technique for matching couplers to an accelerating structure in a more efficient and accurate way. It combines improved Kroll method with improved Kyhl method, thereby simplifying simulation process while achieving a high accuracy. This paper also presents the detailed design on couplers for a C-band constant-gradient (CG) accelerating structure based on this new technique. Such a new technique can be widely used for any TW accelerating structures working at different frequencies of S-band, C-band, and X-band including CG, constant-impedance (CI), and other structures with either electric couplers or magnetic couplers. Published by the American Physical Society 2024

This paper presents the design, fabrication, and low-power rf measurement of an externally powered $X$-band dielectric-loaded accelerating (DLA) structure with a dielectric constant ${ϵ}_{\mathrm{r}}=16.66$ and a loss tangent $\tan \delta =3.43\times {10}^{-5}$. A dielectric matching section for coupling the rf power from a circular waveguide to an $X$-band DLA structure consists of a compact dielectric disk with a width of 2.035 mm and a tilt angle of 60°, resulting in a broadband coupling at a low rf field which has the potential to survive in the high-power environment. Based on simulation studies, a prototype of the DLA structure was fabricated. Results from low-power rf measurements and the comparison with simulated values are presented. A significant discrepancy was found between measurements and simulations. The detailed analysis on the fabrication errors which may cause the discrepancy is also discussed.