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TY - UNPB AU - Penco, G. ED - Liu, Lin ED - Byrd, John M. ED - Neuenschwander, Regis T. ED - Picoreti, Renan ED - Schaa, Volker R. W. TI - Enhanced Seeded Free Electron Laser Performance with a "Cold" Electron Beam J2 - Proc. of IPAC2021, Campinas, SP, Brazil, 24-28 May 2021 CY - Campinas, SP, Brazil T2 - International Particle Accelerator Conference T3 - 12 LA - english AB - In a seeded free-electron laser operating in high gain harmonic generation (HGHG) as FERMI, the harmonic conversion efficiency decreases at high harmonics and the quality of the pulses is increasingly affected by the electron beam phase space distortions. The lower the electron time-slice energy spread the higher harmonic of the seed is efficiently obtained. The optimization of the FERMI photoinjector and of some linac parameters has allowed a reduction of the relative slice energy spread to the level of few times of 10⁵. With these new conditions, the FEL can be operated without the need for a laser heater to suppress micro-bunching instabilities and this "cold" beam has allowed the generation of extreme UV pulses with pulse energy exceeding 1 mJ, and with peak power of about 10 GW. We describe the electron beam characterization and the FEL performance improvement, including the extension of the range of harmonics of the seed which can be amplified, up to the twenty-fifth harmonic, i.e., 10 nm. PB - JACoW Publishing CP - Geneva, Switzerland ER -