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TY - UNPB AU - Richard, C.J. AU - Cogan, S. AU - Lidia, S.M. ED - Tavares, Daniel ED - Picoreti, Renan ED - Bruno, Gustavo ED - Marques, Sergio ED - Schaa, Volker R.W. TI - Bunch Length Measurements Using Beam Position Monitors J2 - Proc. of IBIC2020, Santos, Brazil, 14-18 September 2020 CY - Santos, Brazil T2 - International Beam Instrumentation Conference T3 - 9 LA - english AB - Capacitive Beam Position Monitors (BPMs) are broadband pickups. For measurements of RF bunched beams, however, they typically use narrowband filters to measure one harmonic of the beam current to reduce noise and simplify the signal processing. If several harmonics are measured simultaneously, the longitudinal bunch shape, in principle, may also be measured. This can be accomplished by recording the waveforms from the BPMs with an oversampling measurement scheme before the narrowband analysis is applied. In order to reconstruct the bunch shape, the measured spectra should be corrected for non-relativistic effects, cable attenuation and filtering, and the geometry and impedance of the BPM pick up. These corrections are discussed as well as the procedure for calibrating the BPM system for measuring multiple harmonics. Measurements are presented that were taken in the medium energy beam transport line and the first linac section at the Facility for Rare Isotope Beams and are compared to simulations and measurements with a fast Faraday cup. Resolution and uncertainties of the reported bunch length measurements are described. PB - JACoW Publishing CP - Geneva, Switzerland ER -