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TY - UNPB AU - Weise, H. ED - Schaa, Volker R.W. ED - Decking, Winfried ED - Sinn, Harald ED - Geloni, Gianluca ED - Schreiber, Siegfried ED - Marx, Michaela TI - Overview on Future Continuous Wave X-Ray Free Electron Lasers J2 - Proc. of FEL2019, Hamburg, Germany, 26-30 August 2019 CY - Hamburg, Germany T2 - Free Electron Laser Conference T3 - 39 LA - english AB - FELs based on superconducting accelerators offer a photon beam time structure being flexible in pulse pattern, with the electron bunch properties tailored to effectively meet user requirements. While DESY’s long time operated FLASH facility as well as the in 2017 commissioned European XFEL in the Hamburg region, Germany, are operated in pulsed mode with bunch trains of up to 600 µs and bunch repetition rates of up to 4.5 MHz, new facilities aim for continuous wave (cw) RF operation allowing bunch repetition rates of typically 100 kHz to 1 MHz. The used accelerator modules are still using the so-called TESLA technology. Minor but essential modifications in the accelerating structure design bring the cryogenic load to a reasonable and acceptable level. The upcoming LCLS-II, being under construction at SLAC, U.S., uses so-called Nitrogen doped accelerating structures. The recently started SHINE project at Shanghai, China, will adopt similar ideas. For a possible European XFEL upgrade towards cw, also so-called large grain Niobium is an option. The presentation will give an overview about R&D towards the great future of X-ray FELs. Activities in all three regions will be described. PB - JACoW Publishing CP - Geneva, Switzerland ER -