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TY - UNPB AU - Shatilov, D.N. ED - Zhao, Ning ED - Poole, John ED - Schaa, Volker RW TI - Flip-flop Instability in FCC-ee at Low Energies J2 - Proc. of eeFACT2016, Daresbury, UK, October 24-27, 2016 C1 - Daresbury, UK T2 - ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e^+e^- Colliders T3 - 58 LA - english AB - At the energies of FCC-ee beam-beam effects get an extra dimension due to beamstrahlung - radiation in the field of the oncoming bunch. At high energies (175, 120 GeV) it limits the beam lifetime due to possible ingress of particles beyond the energy acceptance. At low energies (80, 45.5 GeV) beamstrahlung may lead to significant growth of the energy spread (and therefore the bunch length). We employed quasi-strong-strong tracking code Lifetrac to study the beam-beam effects in FCC-ee at 45.5 GeV. It was found that the collider performance here is limited by a peculiar flip-flop instability, which is triggered by the bunch lengthening due to beamstrahlung. We discuss how it depends on different parameters: RF voltage, horizontal emittance and beta-function, betatron coupling, asymmetry in the bunch currents. In order to achieve higher luminosity, it is proposed to decrease beta-x at the IP and to increase emittance-x. PB - JACoW CP - Geneva, Switzerland ER -