Development of X-band single-cell dielectric disk accelerating structures

Abstract

Short-pulse two-beam acceleration (TBA) is a promising advanced accelerator concept that may meet the luminosity and cost requirements of future large-scale linear colliders. Accelerating structures with high group velocity (on the order of 0.1c) are required in this scheme to reduce the filling time so as to efficiently accelerate the main beam with multiple bunches. In conventional accelerating structures such as metallic disk-loaded and dielectric-loaded, high group velocity usually implies low shunt impedance, which limits the rf-to-main-beam efficiency and causes a bottleneck in the overall wall-plug-to-main-beam efficiency. A dielectric disk accelerator (DDA) is a hybrid structure, which has geometry similar to metallic disk-loaded accelerators, but replaces the metal disks with dielectric disks to form the cells. Such a configuration could achieve simultaneous high group velocity and high shunt impedance, making a DDA a very attractive candidate for the short-pulse TBA approach by significantly improving power efficiency. In this manuscript, we present the start-to-end development of two X-band single-cell DDA prototypes, including the rf and mechanical design, fabrication, cold test, high power beam test, and post-test inspection. Of the two, a clamped structure performed better, achieving 102 MV/m accelerating gradient from 320-MW input power.