Characteristics of Different Materials on High-Gradient Experiments

RF breakdown is one of the major problems encountered in the development of accelerating structures that operate at high fields since the acceleration field is limited by the damage caused to metal surfaces. We examine electrical discharge characteristics such as breakdown rates and conduct surface observations of various materials in order to investigate the possibility of the stable operation of accelerating structures for highfield accelerations; a similar fundamental research has also been conducted at CERN and SLAC [1, 2,]. Highgradient RF breakdown studies have been in progress at Nextef (New X-band Test Facility at KEK) since 2006 [3, 4, 5]. In order to investigate the characteristics of various materials at high-gradient RF breakdown, we have performed high-gradient experiments by using narrow waveguides having a field of around 200 MV/m at a power of 100 MW. Copper (OFC) and stainless-steel (AISI-316L) waveguides were tested in order to perform high-gradient experiments at Nextef. The result of the experiment conducted at XTF (Old X-band Test Facility at KEK) suggested that the stainless-steel waveguide had a better performance than the copper waveguide, and it exhibited a lesser number of RF breakdowns at a higher electric field. This paper reports the results of breakdown rates and observations of the surface of stainless-steel waveguide subjected to high-gradient experiments. HIGH-GRADIENT EXPERIENTS