SEEDING SCHEMES ON THE FRENCH FEL PROJECT LUNEX5 C. Evain, M. Labat, M.E. Couprie, F. Briquez, A. Loulergue Synchrotron SOLEIL, Saint Aubin, France V. Malka, Laboratoire d’Optique Appliqu´ ee, Palaiseau, France Abstract LUNEX5 is a single pass FEL project aims at produc- ing coherent synchrotron radiation with, in a first step, an electron bunch accelerated in conventional RF cavities up to 300 MeV [1]. It is planned to work in a seeded con- figuration where the longitudinal coherence of the emitted light is improved and the gain length reduced [2], compared to the SASE configuration (Self-Amplified Spontaneous Emission). Two seeding schemes are considered: High order Harmonics in Gas (HHG) seeding [3] and EEHG scheme (Echo Enabled Harmonic Generation) [4]. Prelimi- nary simulation results indicate that these two schemes per- mit to reach the saturation below a wavelength of 7 nm, and with less undulator periods for the EEHG scheme. HHG seeding with plasma acceleration based FEL is also con- sidered. GENERAL PARAMETERS AND LAYOUT Electron Bunch Parameters After acceleration in a 3 GHz warm Radio-Frequency gun and linac up to 300 MeV, the 1 nC bunches are com- pressed. Their main characteristics are: Table 1: Electron Bunch Parameters Energy (MeV) 300 Slice relative energy spread 2 × 10 -4 Emittance ǫ x,y (π.mm.mrad) 2 Peak current (A) 400 Charge (nC) 1 RMS Length (ps) 1 FODO Lattice and Undulators The electron-bunch is guided along the undulators in a FODO lattice. The parameters are given in the Table 2. Each section is composed of a 3 meter undulator and of a horizontal focusing quadrupole (Fig. 2). Focusing in the vertical plane is achieved by the undulators. Figure 1 shows typical transverse beam-size along the FODO lattice. The RMS width is about 100 μm in the horizontal and vertical planes. It is planned to use 15 mm period in vacuum undu- lators with a magnetic field standing between 0.3 and 1.5 T [1], i.e. fundamental resonant wavelength stands be- tween 24 nm and 70 nm. We study here two seeding schemes (direct seeding with HHG source [3] and EEHG scheme [4]) to get FEL ra- horizontal plane vertical plane 0.06 0.08 0.1 0.12 0 4 8 12 16 20 RMS beam-s i zes [mm] z [m] Figure 1: Horizontal σ x and vertical σ y beam sizes along the FODO lattice from GENESIS simulation. Table 2: FODO Lattice and Undulators Parameters Undulator period (mm) 15 Number of undulator periods 200 Magnetic field (T) 0.3-1.5 Undulator parameter K 0.45-2.1 Resonant wavelength (nm) 24-70 Number of sections 5 Length of quadrupole (m) 0.15 Typical quadrupole field (T/m) 4 diation at short-wavelength with good coherence proper- ties [2, 5]. To compare the two schemes, we focus on the emission at 38 nm and on its third and fifth harmonic (12.76 nm and 7.6 nm respectively). SEEDING WITH HARMONICS IN GAS SOURCE The first studied seeding scheme is direct seeding, i.e. FEL amplification of a harmonics generated in gas source (Fig. 2) [3, 5]. Figure 2: Layout of the FEL amplifier scheme with Har- monic in Gas Source. Distance in mm. HHG pulses at 38 nm are obtained using the 21 th har- monic of a 800 nm of the Ti:Sa laser. Parameters of the seed pulse are presented in Table 3 [6]. To estimate the output power, GENESIS simulations in TUPA06 Proceedings of FEL2011, Shanghai, China ISBN 978-3-95450-117-5 198 Copyright c ○ 2012 by the respective authors/CC BY 3.0 — cc Creative Commons Attribution 3.0 (CC BY 3.0) FEL Experiments and Projects