A potential alternative to conventional disk-loaded copper structures is dielectric-loaded accelerating (DLA) structures, which utilizes dielectrics to slow down the phase velocity of travelling wave in the vacuum channel. A DLA structure comprises a simple geometry where a dielectric tube is surrounded by a conducting cylinder. The simplicity of the DLA structure offers a great advantage for RF-driven accelerating structures as compared with conventional metal structures which demand extremely tight fabrication tolerances. This is of a great importance in the case of linear collider where tens of thousands accelerating structures have to be built.

This contribution numerically investigates a X-band dielectric disk accelerating (DDA) structure operating at a higher-order TM₀₂-π mode.This accelerating structure consists of dielectric disks with irises periodically arranged in a metallic enclosure. Through optimizations, the RF power loss on the metallic wall can be significantly reduced, thereby resulting in an extremely high quality factor  and a very high shunt impedance  MΩ/m. The RF-to-beam power efficiency reaches as high as 46.6% which is 63.5% higher than previous reported CLIC-G structures with an efficiency of 28.5%. The optimum geometry of the regular and end cells is described in detail. Due to the wide bandwidth from dispersion relation of the accelerating mode, the DDA structure is allowed to have a maximum number of regular cells of 73 with a frequency separation of 1.0 MHz, which is superior to those conventional RF accelerating structures. The DDA structure is also found to have a short-range transverse wakefield lower than that of the CLIC-G structure. In addition, a novel design of matching section for coupling the high power from a circular waveguide to an X-band dielectric-loaded accelerating structure is also presented in this talk. This matching section consists of a very compact dielectric disk with a tilted angle of 60°, resulting in a broadband coupling coefficient at a low RF field which has potential to go to very high power. Through optimizations, a reflection coefficient < -40 dB can be obtained, with the maximum electromagnetic fields located at a DLA structure.

Yelong Wei received his master degree in June 2012 from the University of Chinese Academy of Sciences (UCAS) with a major in electromagnetic fields and microwave technology, his bachelor degree was awarded in June 2009 from Nanjing University of Aeronautics and Astronautics with a major in electronics information science and technology. In July 2012, after graduation from UCAS, he joined Tektronix Inc. and worked as an RF Design Engineer. His work mainly focused on RF modules including passive/active circuits design in a 6 GHz RF signal generator.In March 2014, Yelong joined the University of Liverpool as a Marie Curie Fellow within the LA³NET project. His PhD project focused on the investigations into dielectric laser-driven accelerating structures.After successfully defended his PhD thesis, he joined CERN RF group as a CERN fellow since February 2020. His work focuses on the investigations into the X-band conventional accelerating structures and dielectric disk-loaded accelerating structures within CLIC project. So far, he has worked as first author to have 5 journal papers published within SCI and he obtained the best PhD thesis at University of Liverpool in 2018.