High power test of low dark current accelerating structure

To achieve a lower impurity in single-bunch operation of the SPring-8, lower dark currents from injector linac are desired. We are developing a new accelerating structure to reduce dark currents emitted from cavity surface. Applied improvements are an ellipsoidal shape of iris cross-section and a single-feed waveguide coupler. A high power test for this accelerating structure was performed. The maximum field gradient was achieved up to 27.6MV/m and dark current intensity and energy spectrum were measured. (author)