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A compact HOM-damping beam-accelerating rf cavity was developed to mitigate coupled-bunch instabilities in electron storage rings. This cavity operates in the TM020 mode, characterized by a high Q -value and a high shunt impedance. The new HOM-damping mechanism leverages the unique field distributions of the TM020 mode, allowing direct embedding of rf absorbing materials into the cavity body. This novel structure underwent validation through rf simulations and measurements using a model cavity resonating at 508.58 MHz in the TM020 mode with a shunt impedance of 6.8 MΩ and designed to have HOM impedances of less than 0.1 MΩ longitudinally and 0.5 MΩ/m transversely. We also fabricated and tested a prototype cavity, showcasing its HOM-damping efficacy and high-power functionality at 120 kW, generating an accelerating voltage of 900 kV. This prototype operated successfully at full power, confirming the viability of both the damping structure and its high-power application. [ABSTRACT FROM AUTHOR]

Abstract: In a storage ring with a high-current beam, RF coupling between an RF acceleration cavity and a waveguide is usually fixed to high overcoupling. In operation at a low beam current, this overcoupling becomes discrepant and a large amount of RF power is reflected from the cavity. In order to dissolve the coupling discrepancy, a new RF input coupler with a coupling tuner has been developed for SPring-8 accelerator. Its coupling factor can be tuned from 1 to 100 or more according to beam loading. This paper describes the ideal RF input coupler by RF simulations and low RF-power tests. [Copyright &y& Elsevier]

A newly designed RF accelerating cavity resonating 508.58 MHz is proposed for reinforcement of beam current in the SPring-8 storage ring. Since an increase in beam current induces coupled-bunch instabilities arising from coupling impedances of higher-order modes in RF cavities, the new RF cavity is provided with three ways for damping the higher-order modes: a re-entrant quasi-half-cell structure, ports skewing the field distributions of the higher-order modes and a grooved beam pipe terminated by materials absorbing RF power. The RF properties of the higher-order modes in the RF cavity were examined by the MAFIA frequency-domain simulation. The measured RF properties of the higher-order modes in an aluminum model cavity were consistent with the simulations and verified the performance of damping the higher-order modes in the RF cavity. [Copyright &y& Elsevier]