The development of ever advanced, high gradient accelerating structures is one of the leading activity of the accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability. Recent experiments showed that accelerating cavities made out of hard copper fabricated without hightemperature processes, can achieve better performance as compared with soft copper ones. The results of experiments showed that welding, a robust and low-cost alternative to brazing or diffusion bonding, is an optimal solution for high-gradient operation, providing, with a gradient of about 150 MV/m, in the X-band, a breakdown rate of 10 −3 /pulse/meter using a shaped pulse with a 150 ns flat part. Within this framework, we are involved in the design, construction and higher power experimental tests of three cells standing-wave (SW) 11.424 GHz (X-band) accelerating cavities fabricated with hard Cu/Ag materials in order to study the RF breakdown physics. Our aim is to fabricate the accelerating structures with innovative technologies easier to handle and cheaper; easier for surfaces inspection; easier for data elaboration and validation of joining techniques. The choice of these new technological approaches and design methods provides also the possibility of allocating the parasitic Higher Order Mode (HOM) dampers in case of regular multi-cells structure, both standing and traveling-wave accelerating structures, of advanced generation. This paper describes the design of an optimised cavity made with sectors that allows an increase of the frequency separation of longitudinal modes, and it provides a high longitudinal shunt impedance R sh of the operating mode. The cavity will be fabricated by using the Tungsten Inert Gas (TIG) process in order to realise a hard Cu/Ag structure. Two three-cells SW X-band accelerating cavities, to be operated in the π-mode and made out of hard Cu/Ag alloy, were already fabricated at INFN-LNF by means of clamping and welding by using the TIG approach. Finally, we also report the RF characterisation and low-power RF tests of a two-halves split hard Cu/Ag structure that will be consequently TIG welded and employed for high-gradient tests and for the study of the RF breakdown physics.
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