Segmented undulator operation at the SPARC-FEL test facility Franco Ciocci a , Maria Pia Anania b , Marcello Artioli a , Marco Bellaveglia b , Mariano Carpanese a , Enrica Chiadroni b , Alessandro Cianchi c , Giuseppe Dattoli a , Domenico Di Giovenale b , Emanuele Di Palma a , Giampiero Di Pirro b , Massimo Ferrario b , Andrea Mostacci d , Alberto Petralia a , Vittoria Petrillo e , Riccardo Pompili b , Elio Sabia a , Ivan Spassovsky a , Vincenzo Surrenti a , Cristina Vaccarezza b , Fabio Villa b . a ENEA Centro Ricerche Frascati, Via Enrico Fermi, 45 00044 Frascati, Roma, Italy; b INFN-LNF, Via Enrico Fermi, 40 00044 Frascati, Roma, Italy; c INFN-Roma Tor Vergata and Universita` di Roma Tor Vergata, Via della Ricerca Scientifica, 1 00133 Roma, Italy; d Universita` La Sapienza di Roma, Via Antonio Scarpa 14, Roma, Italy; e INFN-Milano and Universita` di Milano, Via Celoria, 16 20133 Milano, Italy ABSTRACT A short period undulator (1.4 cm) has been designed for the SPARC-FEL test facility and has been realized in collaboration with KYMA Srl. It has been installed on the undulator line at SPARC. The undulator, operating in a delta like mode, has been used as radiator in a segmented configuration. The first stage being provided by the five undulators of the SPARC FEL source “old” chain, with period 2.8 cm. The KYMA undulator has a quatrefoil structure, a high magnetic field homogeneity and focuses both in vertical and radial directions. The two sections, namely the bunching and radiating parts, are arranged in such a way that the second is adjusted on a harmonic of the first. Laser action occurring in the second part, is due to the bunching acquired in the first. Simulations of the temporal and spectral profiles in different electron beam operating conditions are reported, as well as the evolution of the longitudinal phase space. The agreement with the experimental results is discussed The importance of this experiment is at least threefold: 1) It proves that the segmented undulator can successfully be operated 2) It proves that the laser emission in the last undulator is entirely due to the bunching mechanism, being no second harmonic signal present in the first segment 3) Encourages various improvements of the configuration itself, as e.g. the use of a further undulator with variable magnetic field configuration in order to obtain a laser field with adjustable polarization. Keywords: SPARC, FEL, SASE, segmented undulator, harmonic generation 1. INTRODUCTION Free Electron Laser (FEL) devices are, for many of their aspects, very well established devices, currently exploited in applications. They cover a wide range of frequency interval and can be operated in either Self Amplified Spontaneous Emission (SASE) and oscillator configurations. The FEL devices themselves are the subject of an intensive experimentation and new operating schemes are proposed and tested. The SPARC facility 1 has been conceived as a benchmark for testing new aspects of the FEL physics and new operating configurations as well. It has provided, during the last years, important contributions to the understanding of the Physics of Free Electron Lasers and to its operation in non-conventional modes. Observations of FEL radiation in the SASE 2 , Seeded 3 and HHG 4 modes have been performed from 500 nm down to 40 nm wavelength Advances in X-ray Free-Electron Lasers Instrumentation III, edited by Sandra G. Biedron Proc. of SPIE Vol. 9512, 951203 · © 2015 SPIE · CCC code: 0277-786X/15/$18 doi: 10.1117/12.2185099 Proc. of SPIE Vol. 9512 951203-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/15/2015 Terms of Use: http://spiedl.org/terms