Influence of the parasitic-mode damper on the accelerating mode in the TM020-type harmonic cavity

In many next-generation synchrotron light sources, installations of bunch-lengthening harmonic cavities are considered in order to mitigate the influence of intrabeam scattering. We study the design of the TM020-type harmonic cavity which utilises not the fundamental TM010 resonant mode but the TM020 mode as the accelerating mode. This cavity has great advantages as a bunch-lengthening harmonic cavity such as (1) reduction of the bunch-gap transient beam loading, and (2) enabling to install compact parasitic-mode damper at the node of the magnetic field of the TM020 mode. In this paper, we report some problems which we have found in the design study, and present reasonable solutions. (author)