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Features of LLRF control systems in KEKB and SuperKEKB will be reviewed, and the evaluation of the bunch gap transient effect on beam phase will be presented for SuperKEKB. The RF systems of KEKB are being reinforced to handle triple as large beam power for upgrade to SuperKEKB. Furthermore, a new LLRF control system, which is based on a recent digital control technique, has been developed. For nine RF stations, among a total of thirty, the LLRF control system has been replaced with new ones. They were worked successfully in the Phase-1 commissioning. Bunch phase shift along the bunch train due to a bunch gap transient is a concern. In KEKB operation, a rapid phase change was observed at the leading part of the train, which was not predicted. Our new simulation study clarified that the rapid phase change is caused by a transient loading in the three-cavity system of ARES. And the new simulation shows that the phase change will be much large in SuperKEKB. The main issue is the difference in beam phase change between the two rings for the asymmetry colliding. The measures by means of mitigation of the relative beam phase difference between the two rings will be also suggested., Proceedings of the 58th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e^+e^- Colliders, eeFACT2016, Daresbury, UK

In the recent decades, Superconducting cavities have been widely used to accelerate electron, positron, and ions. Most SRF cavities are made from bulk niobi-um till now, which has developed fast in the past years and is hard to advance more. Take 1.3 GHz 9-cell cavi-ty for example, the quality factor (Q) can keep above 10¹⁰ when the accelerating field (Eacc) reach 40 MV/m, which nearly touch the theoretical limitation of Q and Eacc for bulk niobium. For large superconducting accelerators in future (FCC, CEPC, etc), Q and Eacc should be increased significantly compared to now, which can reduce the cryogenic power and use fewer cavities. So new cavity material and techniques are being studied at accelerator laboratories, while Nitro-gen doping (N-doping) and Nb3Sn have developed quickly and been paid attention to mostly [1]. N-doping can increase Q by one time for 1.3 GHz 9-cell cavity, which have been adopted by Linac Coherent Light Source II (LCLS-II) at SLAC [2]., Proceedings of the 58th ICFA Advanced Beam Dynamics Workshop on High Luminosity Circular e^+e^- Colliders, eeFACT2016, Daresbury, UK

The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada