Low-power test of the 1.5 GHz TM020-type harmonic cavity for the future synchrotron light sources

The TM020-type RF cavity has advantages of mitigating bunch-gap transient effects and enabling to introduce a compact parasitic-mode damping mechanism. We have suggested the use of this cavity as 1.5-GHz bunch-lengthening harmonic cavity for the future synchrotron light sources and fabricated its low-power model. Three frequency tuners are employed in order to improve the rotational symmetry of this cavity. For the power-coupling between a coaxial line and this cavity, we adopted a unique fan-shaped input coupler in order to reduce the perturbation to the accelerating field. To damp the harmful parasitic modes, the coaxial slots were installed at the node of the TM020 magnetic field. In this paper, we present the results of the low-power tests: the principal properties of the TM020 accelerating mode and the damping performance of the parasitic modes. (author)