Experimental studies of a high-gradient X-band welded hard-copper split accelerating structure

Abstract

Recent research on high-gradient radio frequency (RF) accelerating structures indicates that the use of hard copper alloys provides improvement in high gradient performance over annealed copper. Such structures are made by bonding individually manufactured parts. However, there are no well-established bonding techniques that preserve the hardness, surface finish and cleanliness required for high gradient operation. To preserve the copper hardness, RadiaBeam has developed a joining technique based on electron beam welding. This technique provides efficient bonding with strong, clean welds and minimal thermal loading, while maintaining a clean inner RF environment. Our RF design and fabrication methodology limits the small heat affected zone to the outer cavity envelop, with virtually no distortions or thermal loading of critical RF surfaces. It also incorporates provisions to precisely control the gap despite conventional issues with weld joint shrinkage. To date we have manufactured and validated an RF accelerating structure joined by electron-beam welding that incorporates a novel open split design to significantly reduce the assembly complexity and cost. In this paper, we will present the electromagnetic design of this structure, discuss bonding, and present the results of high-power tests, where the accelerating gradients of 140 MV/m with surface peak fields of 400 MV/m were achieved for flat-top pulse length of 600 ns with an RF breakdown rate of 10-4 1/(pulse∙m).

Design Criteria for High-Gradient Radio-Frequency Linacs

“…Practical applications of the hard, non-brazed, diffusion-bonded copper depend on the development of robust joining techniques, which preserve the vacuum and electrical properties of high-performance linacs. This work is ongoing with numerous experimental results [32,82,[84][85][86].…”

“…Simultaneously with these experiments, cell-joining technologies are being developed and tested that allow the fabrication of practical accelerating structures without hightemperature brazing or diffusion bonding [32,82,[84][85][86][87][88][89].…”

Hybrid actor-critic algorithm for quantum reinforcement learning at CERN beam lines

“…The ultimate goal for AWAKE is to reach a field gradient of 1 GV m −1 . These numbers are to be compared to conventional accelerating structures using radio-frequency (rf) cavities in the X-band regime, which are currently limited to accelerating field gradients of about 150 MV m −1 [41].…”

Quantum Fuzzy Inference Engine for Particle Accelerator Control

“…Ultimately, by the end of Run 2, the AWAKE scheme should start providing electron bunches for particle physics experiments [44]. The targeted field gradients are to be compared to conventional accelerating structures using radio-frequency (rf) cavities in the X-band regime, which are currently limited to about 150 MV/m [45]. The AWAKE electron source and electron beam line are particularly interesting for algorithm preparation and testing due to the high repetition rate and insignificant damage potential in case of losing the beam at accelerator components.…”