Design, fabrication and low-power RF measurement of an X-band dielectric-loaded accelerating structure

TL;DR

This paper reports the design, fabrication, and low-power RF testing of an X-band dielectric-loaded accelerating structure aimed at high-gradient applications, including detailed analysis of fabrication errors and RF performance.

Contribution

It introduces a novel compact dielectric matching section and demonstrates successful fabrication and measurement of an X-band DLA structure with detailed error analysis.

Findings

Successful RF measurements closely match design simulations

The dielectric matching section enables broadband coupling at low RF fields

Fabrication errors are identified as key factors affecting performance

Abstract

Dielectric-loaded accelerating (DLA) structures are being studied as an alternative to conventional disk-loaded copper structures to produce the high accelerating gradient. This paper presents the design, fabrication and low-power RF measurement of an externally-powered X-band DLA structure with a dielectric constant epsilon_r=16.66 and a loss tangent tan_delta=0.0000343. A dielectric matching section for coupling the RF power from a circular waveguide to an X-band DLA structure consists of a very compact dielectric disk with a width of 2.035 mm and a tilt angle of 60 degree, resulting in a broadband coupling at a low RF field which has the potential to survive in the high-power environment. Based on simulation studies, a prototype of the DLA structure was fabricated. Results from bench measurements and their comparison with design values are presented. The detailed analysis on the fabrication error which may cause the discrepancy between the RF measurements and simulations is also discussed.