In a seeded FEL machine as FERMI, the interplay between the electrons energy curvature and the seed laser frequency chirp has a relevant impact on the output FEL spectrum. It is therefore crucial controlling and manipulating the electron beam longitudinal phase space at the undulator entrance. In case of very short bunches, i.e. high compression scheme, the longitudinal wakefields generated in the linac induce a positive quadratic curvature in the electrons longitudinal phase space that is hard to compensate by tuning the phase of the main RF sections or the possible high harmonic cavity. At FERMI we have experimentally exploited a longitudinal ramp current distribution at the cathode, obtained with an adhoc photoinjector laser pulse shaping, to linearize the longitudinal wakefields in the downstream linac and flatten the electrons energy distribution, as theoretical foreseen in [1]. Longitudinal phase space measurements in this novel configuration are here presented, providing a comparison with the typical longitudinal flat-top profile. Copyright © 2013 CC-BY-3.0 and by the respective authors.

Electron beam longitudinal phase space manipulation by means of an ad-hoc photoinjector laser pulse shaping

Giannessi, L.
2013

Abstract

In a seeded FEL machine as FERMI, the interplay between the electrons energy curvature and the seed laser frequency chirp has a relevant impact on the output FEL spectrum. It is therefore crucial controlling and manipulating the electron beam longitudinal phase space at the undulator entrance. In case of very short bunches, i.e. high compression scheme, the longitudinal wakefields generated in the linac induce a positive quadratic curvature in the electrons longitudinal phase space that is hard to compensate by tuning the phase of the main RF sections or the possible high harmonic cavity. At FERMI we have experimentally exploited a longitudinal ramp current distribution at the cathode, obtained with an adhoc photoinjector laser pulse shaping, to linearize the longitudinal wakefields in the downstream linac and flatten the electrons energy distribution, as theoretical foreseen in [1]. Longitudinal phase space measurements in this novel configuration are here presented, providing a comparison with the typical longitudinal flat-top profile. Copyright © 2013 CC-BY-3.0 and by the respective authors.
9783954501267
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12079/4408
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