Higher-Order-Mode Damping Coupler for Beam Instability Suppression

Abstract

The effects of a higher-order-mode damping coupler on coupled-bunch instabilities were studied in the Photon Factory storage ring. It was inserted in the RF accelerating cavity in order to suppress higher-order modes, especially the TM011-like mode excitation which causes a longitudinal coupled-bunch instability. Threshold currents of this beam instability were measured before and after insertion. The results showed the obvious damping effects: instability thresholds were largely improved. No practical problems, such as discharge or vacuum trouble were observed during operation with a high-current beam and a single-bunched beam.