Increasing the Single-Bunch Instability Threshold by Bunch Splitting Due to RF Phase Modulation

RF phase modulation at twice the synchrotron frequency can be used to split a stored electron bunch into two or more bunchlets orbiting each other. We report on time-resolved measurements at the KArlsruhe Research Accelerator (KARA), where this bunch splitting was used to increase the threshold current of the microbunching instability, happening in the short-bunch operation mode. Switching the modulation on and off, reproducibly influences the sawtooth behaviour of the emitted coherent synchrotron radiation.