New RF Design of Externally Powered Dielectric-Based Accelerating Structures

In order to provide high gradient acceleration demonstration experiments, a broadband coupling section will be needed for the high-gradient dielectric-loaded accelerator (DLA). This project will develop a coaxial-type coupler that can provide the required mode conversion and the impedance matching transition simultaneously, without using a tapered dielectric. The coupler design will avoid vacuum gaps between the dielectric sections and thus eliminate any points for potential radio frequency (RF) breakdown. The coupler will allow for the construction of a new type of dielectric-based accelerator structure, which will provide accelerating gradients exceeding 100 MV/m. Phase I fabricated and experimentally tested an X-band, traveling wave, gapless DLA structure using a coaxial type RF coupler. An X-band power combiner, integrated into the coaxial type RF coupler, was designed and fabricated. The overall structure, including the RF input/output coupler and the dielectric-loaded accelerating section, was characterized. In Phase II, a coaxial, RF-coupler-based, gapless, dielectric-based accelerating structure, loaded with alumina, will be experimentally tested at high power. A high-gradient dielectric accelerating structure will be developed, and its breakdown field strength will be determined. Commercial Applications and Other Benefits as described by the awardee: The coaxial-type, ceramic-based coupling section for the dielectric based accelerator should become a key enabling technology for high-gradient DLA operation. The coupler section should remove a major roadblock to the development of a high-gradient accelerator that can sustain accelerating gradients on the scale of 100 MV/m.