Design of high gradient S-band cavity and coupler

Studies on high gradient linear accelerators are among the new areas in the field of accelerators. The most important factor that limits the electric field gradient in linear accelerators is the radio frequency breakdown. Many studies have been conducted on the effect of the material and manufacturing method of cavities on the achievable gradient, which shows that rigid structures fabricated without high-temperature processes achieve a better high gradient performance. Employing the brazing method, as the most common method for construction of cavities, requires the use of high-temperature furnaces, which causes softening of the copper. Therefore, using non-brazing methods to construct high gradient cavities has been considered. Based on the experiences gained in the national electron linear accelerator project at the institute for research in fundamental science (IPM) and the shrinking fit method used to fabricate and assemble its acceleration cavities, the design and construction of high gradient S-band cavities are in progress with international cooperation. Radiofrequency design of cavity with vacuum breakdown consideration and coupler design are discussed. Achieving the appropriate shape and dimensions of the cavity and coupler for maximizing the axial electric field (134 MV/m) with a breakdown rate of less than  at 8 MW input power and S11 parameter -60 dB for the coupler are the results of this article.