Dielectric assist accelerating structure

Abstract

A higher-order TM 02n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 MΩ=m at room temperature.

Fabrication and cold test of dielectric assist accelerating structure

“…The optimization method of the DAA structure is as follows. Reference [34] has shown that the resonant frequency f 0 is sensitive to b 1 . Therefore, the four geometrical parameters (l 1 , r 1 , a 1 , c 1 ), except for b 1 , were changed in a down-hill simplex algorithm and the resonant frequency of the prototype was tuned to the desired f 0 by adjusting the b 1 on each simplex point.…”

“…Among many dielectric based accelerating structures, a dielectric assist accelerating (DAA) structure [34] appears to be very promising in terms of power efficiency. A conceptual illustration of a multicell DAA structure is shown in Fig.…”

“…It is a higher-order TM 02n mode standing-wave accelerating structure, which consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. The advantage of DAA structure is that it has an extremely high quality factor and a high shunt impedance at room temperature since the electromagnetic field distribution of the accelerating mode can be controlled by dielectric parts which greatly reduces the wall loss on metallic surface [34]. A simulation result of a five-cell DAA structure with an existing alumina ceramic indicated an unloaded Q factor of the accelerating mode over 120,000 and a shunt impedance exceeding 650 MΩ=m at room temperature [34].…”

“…The advantage of DAA structure is that it has an extremely high quality factor and a high shunt impedance at room temperature since the electromagnetic field distribution of the accelerating mode can be controlled by dielectric parts which greatly reduces the wall loss on metallic surface [34]. A simulation result of a five-cell DAA structure with an existing alumina ceramic indicated an unloaded Q factor of the accelerating mode over 120,000 and a shunt impedance exceeding 650 MΩ=m at room temperature [34]. This paper provides a detailed description of the design, fabrication, and cold tests of a series of multicell DAA structures.…”

Hybrid metal-dielectric, slow wave structure with magnetic coupling and compensation

“…More recently a modified dielectric loaded, periodic structure has been introduced to enhance coupling impedance [8]. However, that dielectric-structured approach seems to be difficult to apply for fabrication of a long, multi-cell, strongly tapered MicroLinac.…”