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TY - UNPB AU - Chen, Y. AU - Krasilnikov, M. AU - Qian, H.J. AU - Stephan, F. ED - Schaa, Volker R.W. ED - Decking, Winfried ED - Sinn, Harald ED - Geloni, Gianluca ED - Schreiber, Siegfried ED - Marx, Michaela TI - Emittance Budget in the Transition Regime Between Linear Emission and Space Charge Dominated Photoemission J2 - Proc. of FEL2019, Hamburg, Germany, 26-30 August 2019 CY - Hamburg, Germany T2 - Free Electron Laser Conference T3 - 39 LA - english AB - Free electron laser based X-ray facilities require high brightness accelerators which entails minimization of the beam emittance in all planes for a fixed bunch charge. Since the lowest achievable emittance of linac based accelerators is set at the injectors already, emittance optimization at the injector exit needs to carefully budget the contributions from the space charge and rf forces as well as the intrinsic cathode contribution. The optimization of normalized transverse emittance at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) has routinely found the smallest possible emittance for a fixed bunch charge in a so-called transition regime of photoemission. In such a regime, high space charge density of the beam significantly contributes to the phase space formation. Strong space charge fields during the emission process alter the cathode physics thereby changing the emittance budget distribution. Based on an advanced beam dynamics modeling approach, we analyze each decomposed contribution of the measured emittance for understanding the optimization scheme in the transition regime between linear and space charge dominated emission. Obtained results will be presented. PB - JACoW Publishing CP - Geneva, Switzerland ER -