title: PRESTO, the on-line photon energy spectrometer at FERMI: design, features and commissioning results.
abstract: Measurement of the emission wavelength and the spectral content of the photon radiation is essential information for both machine and experimental physicists at a free-electron laser (FEL) user facility. Knowledge of the photon beam spectral properties is needed during the machine optimization and for performing machine studies (i.e. monitoring the change of the FEL output as a function of the machine parameters). The experimentalists, on the other hand, need to know the photon beam spectral distribution of the source, shot to shot, to discriminate the acquired data. Consequently, the main requirement for the instrument, supposed to obtain this information, is the capability of working on-line and shot-to-shot, with minimal perturbation of the beam delivered to the experimental stations. Starting from the grating fundamental equations, the conceptual design of the FERMI Pulse-Resolved Energy Spectrometer: Transparent and On-line (PRESTO) is presented, explaining the optical design in detail. The performance of PRESTO, in terms of resolving power, efficiency and spectral response, is also discussed. Finally, some useful features beyond the usual measurement of the energy spectrum are reported, as they have been routinely used by both machine and experimental physicists.
authors.affiliation: Elettra-Sincrotrone Trieste SCpA, SS 14 km, 163.5 in Area Science Park, Basovizza 34149, Italy.
authors.forename: Cristian
authors.initials: C
authors.lastname: Svetina
authors.affiliation: SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA.
authors.forename: Daniele
authors.initials: D
authors.lastname: Cocco
authors.affiliation: Elettra-Sincrotrone Trieste SCpA, SS 14 km, 163.5 in Area Science Park, Basovizza 34149, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Mahne
authors.affiliation: Elettra-Sincrotrone Trieste SCpA, SS 14 km, 163.5 in Area Science Park, Basovizza 34149, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Raimondi
authors.affiliation: Elettra-Sincrotrone Trieste SCpA, SS 14 km, 163.5 in Area Science Park, Basovizza 34149, Italy.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Ferrari
authors.affiliation: Elettra-Sincrotrone Trieste SCpA, SS 14 km, 163.5 in Area Science Park, Basovizza 34149, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Zangrando
keywords: PRESTO; free-electron lasers; photon energy spectrometer