Peak current reduction in presence of RF phase modulation in the dual RF system

High harmonic cavities are widely used in electron storage rings to lengthen the bunch, lower the bunch peak current, thereby reducing the IBS effect, enhancing the Touschek lifetime, as well as providing Landau damping, which is particularly important for storage rings operating with ultra-low emittance or at low beam energy.

To further increase the bunch length without additional hardware costs, the phase modulation in a dual-RF system is considered.

In this paper, turn-by-turn simulations incorporating random synchrotron radiation excitation are conducted, and a brief analysis is presented to explain the bunch lengthening mechanism.

Simulation results reveal that the peak current can be further reduced, thereby mitigating IBS effects and enhancing the Touschek lifetime. Although the energy spread increases, which tends to reduce the brightness of higher-harmonic radiation from the undulator, the brightness of the fundamental harmonic can, in fact, be improved.