Speaker
Description
Longitudinal higher-order modes (HOMs) trapped in vacuum components such as gate valves are a potential source of coupled-bunch instabilities in the HALF storage ring. Using macroparticle tracking simulations, we study these instabilities under bunch lengthening provided by a passive third-harmonic cavity. Two distinct instability types are identified: a centroid-oscillation mode and an energy-spread-growth mode. The former can be suppressed by a longitudinal feedback system, while the latter cannot. Quantitative thresholds as a function of HOM frequency with different bunch distributions are obtained to guide the impedance optimization of HALF vacuum components.
Funding Agency
National Natural Science Foundation of China (No. 12475158, No. 12341501 and No. 12375324)
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