High-Power Test of Two Prototype X-band Accelerating Structures Based on SwissFEL Fabrication Technology

Millar, William L. and Grudiev, Alexej and Wuensch, Walter and Lasheras, Nuria Catalan and McMonagle, Gerard and Zennaro, Riccardo and Craievich, Paolo and Bopp, Markus and Lucas, Thomas G. and Volpi, Matteo and Paszkiewicz, Jan and Edwards, Amelia and Wegner, Rolf and Bursali, Hikmet and Woolley, Benjamin and Magazinik, Anastasiya and Syratchev, Igor and Vnuchenko, Anna and Pitman, Samantha and Romano, Veronica del Pozo and Caballero, David Banon and Burt, Graeme (2023) High-Power Test of Two Prototype X-band Accelerating Structures Based on SwissFEL Fabrication Technology. IEEE Transactions on Nuclear Science, 70 (1). pp. 1-19. ISSN 0018-9499

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Abstract

This article presents the design, construction, and high-power test of two $X$-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.