High-Power Test of Two Prototype X-Band Accelerating Structures Based on SwissFEL Fabrication Technology
William Millar, Alexej Grudiev, Walter Wuensch, Nuria Catalán Lasheras, Gerard McMonagle, Riccardo Zennaro, P. Craievich, M. Bopp, Thomas G. Lucas, M. Volpi, Jan Paszkiewicz, A. Edwards, Rolf Wegner, Hikmet Bursali, Benjamin Woolley, Anastasiya Magazinik, Igor Syratchev, Anna Vnuchenko, S. Pitman, Veronica del Pozo Romano, David Ba non Caballero, Graeme Burt
Abstract
This article presents the design, construction, and high-power test of two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band radio frequency (RF) accelerating structures built as part of a collaboration between CERN and the Paul Scherrer Institute (PSI) for the compact linear collider (CLIC) study. The structures are a modified “tuning-free” variant of an existing CERN design and were assembled using Swiss free electron laser (SwissFEL) production methods. The purpose of the study is two-fold. The first objective is to validate the RF properties and high-power performance of the tuning-free, vacuum brazed PSI technology. The second objective is to study the structures’ high-gradient behavior to provide insight into the breakdown and conditioning phenomena as they apply to high-field devices in general. Low-power RF measurements showed that the structure field profiles were close to the design values, and both structures were conditioned to accelerating gradients in excess of 100 MV/m in CERN’s high-gradient test facility. Measurements performed during the second structure test suggest that the breakdown rate (BDR) scales strongly with the accelerating gradient, with the best fit being a power law relation with an exponent of 31.14. In both cases, the test results indicate that stable, high-gradient operation is possible with tuning-free, vacuum brazed structures of this kind.