Design, Fabrication, and Cold Test of a High-Efficiency C-Band Traveling-Wave Accelerating Structure

To implement the linear injector for the proposed Jinhua light source (JHLS) project, a 1-m C-band constant gradient (CG) traveling-wave (TW) accelerating structure is developed with the aim of generating a gradient of $\geq 40$ MV/m. This C-band structure works at a mode of $3\pi $ /4 with a relatively low group velocity varying from $0.016c$ to $0.009c$ to increase the accelerating gradient at a given input power. It employs a cell shape with elliptical irises and circular arc tops to reduce the surface electric and magnetic fields and to achieve an average shunt impedance of 94 M $\Omega $ /m through optimizations. This results in an accelerating gradient of 40 MV/m with an input power of 29.6 MW, which means this structure can convert the input power into the accelerating gradient with a high efficiency. Moreover, a new technique is utilized for the design of couplers, significantly simplifying the whole optimization process and achieving high accuracy. After fabrication, the structure was precisely tuned, and results from low-power radio frequency (RF) measurements and the comparison with simulated values are also presented in this article.