Design and manufacture of coaxial symmetric input coupler

In order to avoid emittance growth due to field asymmetries，a symmetric input coupler is designed. The symmetric coupler is designed as a coaxial input coupler that couples to the cavity on the cavity axis. Asymmetric mode configurations are strongly suppressed since the symmetry of the cavity is not disturbed. In addition the construction of the cooling channels is facilitated since the coupler connects to the gun at an area of low heat deposition. In this paper the design of the parts of coupler is given. The size of the coupler is gained correctly and some experiments have been done. The voltage standing wave ratio of 1.357 is got. The coupler is proved to be practical and feasible.