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TY - UNPB AU - Roussel, E. AU - Ferrari, E. ED - Schaa, Volker R.W. ED - Decking, Winfried ED - Sinn, Harald ED - Geloni, Gianluca ED - Schreiber, Siegfried ED - Marx, Michaela TI - Microbunching Instability and Laser Heater Usage in Seeded 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 - Seeded FELs are tremendous coherent sources in the EUV and soft X-rays domain. They are driven by high-quality electron beams produced in linear accelerators. However, spatio-temporal instabilities can develop in the magnetic compressor chicanes degrading the beam quality. The so-called microbunching instability is a major limitation for the generation of coherent pulses in the X-ray domain. Laser-heater systems are nowadays routinely used to control the electron beam energy spread in order to dump this instability. In the last years, there have proven to be also a powerful device to influence the FEL amplification process. We present here several LH usages in FELs with specific examples achieved on seeded FELs such as improving the harmonic up-conversion process in HGHG seeded FEL, generating short FEL pulses or also producing multi-color FEL pulses. We also report on microbunching instability issues and its effect on FEL spectral quality with strategies to benefit from that. Direct observation of the microbunching level in the electron beam remains also an open challenge. Innovative strategies to measure the electron beam and potentially its microbunching will be presented. PB - JACoW Publishing CP - Geneva, Switzerland ER -