Design, fabrication and test of parallel-coupled slow-wave high-gradient structure for ultrashort input power pulses

TL;DR

This paper presents the design, fabrication, and testing of a parallel-coupled slow-wave high-gradient structure for ultrashort input power pulses, demonstrating high gradients and novel analysis of inter-cavity coupling effects.

Contribution

It introduces a redesigned 40-ns, 10-cell structure tailored for high-power ultrashort pulses and provides a detailed analysis of unexpected coupling effects during testing.

Findings

Achieved a maximum gradient of 130 MV/m after 11 million conditioning pulses.

Observed unexpected bead-pull results attributed to inter-cavity coupling.

Distributed power feeding system reduces conditioning time and enables higher gradients.

Abstract

Tsinghua University has designed an X-band (11.424 GHz) slow-wave parallel-coupling accelerating structure, and demonstrated the high performance of the over-coupled structure operating with ultrashort pulse. In this study, we redesigned a 40-ns structure with 10 cells, tailored to the specifications of a high-power experimental platform, and provided a detailed analysis of the experimental results. Unexpected bead-pull results were observed during the cold testing, which we attribute to inter-cavity coupling. To explain these results, a multi-cell coupling circuit model was proposed and analyzed. High-power testing was conducted on the TPOT-X platform, and the highest gradient achieved was 130 MV/m after $1.1*10^7$ conditioning pulses. Compared to conventional multi-cavity high-gradient structures, the distributed power feeding system offers a shorter conditioning period and demonstrates the potential to achieve higher accelerating gradients under short-pulse operation.