Singh, R. Forck, P. Klaproth, S. Reichert, T. Reiter, A. Rodrigues, G.O. JACoW Publishing Geneva, Switzerland 2673-5350 978-3-95450-241-7 10.18429/JACoW-IBIC2022-TUP25 English 286-290 electron simulation target heavy-ion coupling Contribution to a conference proceedings 2022 2022-12 https://doi.org/10.18429/JACoW-IBIC2022-TUP25 https://jacow.org/ibic2022/papers/tup25.pdf The longitudinal charge profiles of the high intensity heavy ion beam accelerated at the GSI UNILAC upto 11.4 MeV/u can differ significantly in consecutive macro-pulses. Variations in bunch shape and mean energy were also observed within a single macro-pulse. In order to have an accurate and fast determination of bunch shape and its evolution within a macro-pulse, a study of fast Faraday Cup designs is underway at GSI. In this contribution, we present CST particle in cell (PIC) simulations of radially coupled co-axial Fast Faraday Cup (RCFFC) and conventional axially coupled FFC (ACFFC) design. The simulation results are compared to the measurements performed under comparable beam conditions primarily with RCFFCs. A rather large impact of secondary electron emission is observed in simulations and experiments. The biasing of the FFC central electrode as a mitigation mechanism on the measured profiles is discussed.