LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) is a project of advanced and compact Free Electron Laser (FEL). It aims at investigating the production of short, intense, coherent Free Electron Laser (FEL) pulses in the 40-4 nm spectral range (on the first, third and fifth harmonics). It is a collaboration of different partners : Synchrotron SOLEIL, LOA (CNRS/Palaiseau), PhLAM (Univ. de Lille-CNRS), LAL (CNRS-IN2P3, Orsay), CEA/IRAMIS and IRFU, LCPMR (Univ. Paris VI/CNRS, Paris) and ESRF.
It comprises two different types of accelerators. A 400 MeV superconducting linac (SC) with 2-3 modified XFEL type cromodules at 1.3 GHz (fed with solid state amplifiers) will enable a CW operation for high repetition rate (10 kHz) and multiple users. The electron bunch is compressed thanks to a dogleg with sextupoles, enabling phase space linearization and cancellation of the second order dispersion. The gun will be either superconducting or APEX type. In addition, using a LWFA for FEL will be explored, requiring a specific beam transfer line to handle the divergence (1 mrad) and energy spread (1 %). The superconducting linear accelerator is adapted for studies of advanced FEL schemes. A Laser Wakefield Accelerator (0.4 -1 GeV) is also considered as an advance compact accelerating concept, to be qualified by the FEL application.
The single FEL line with different cryo-ready undulator segments of 15 mm (radiators) and modulators of 30 mm period will allow Echo Enable Harmonic Generation (echo) and HHG seeding to be compared for further handling of the spectral and temporal properties. SC linac based FEL calculations anticipate more than 1011 photons/pulse and 1027 peak brightness on the fundamental wavelength. Two pilot user experiments in gas phase and condensed matter will qualify the FEL performance in the different cases.
After the completion of the LUNEX5 Conceptual design Report at the end of 2011, complementary studies and R&D are under way. In the frame of two ERC Advanced Grants COXINEL and X-Five, test experiment for the demonstration of 180 MeV LWFA based FEL amplification at 200 nm is under preparation, thanks to a proper electron beam manipulation enabling to handle the large divergence and energy spread of LWFA beam : electrons are first strongly focused thanks to a variable permanent magnet quadrupole of variable strength. The electrons are sorted in energy thanks to a magnetic chicane, and the focus of the electron bunch slices, where correlation between position and energy has been introduced, is synchronised with the advance of the optical wave.
Specific hardware is also under development such as a cryo-ready 3 m long undulator of 15 mm period and 1.65 T at 3 mm gap (under the frame of the SOLEIL/VR collaboration), the permanent magnet quadrupole of variables strength (200 T / m) which concept was patented (QUAPEVA program-Triangle de la Physique, SOLEIL/Sigmaphi collaboration). The study and test of an elementary RF unit with sc cavity, low level RF and solid state amplifier for CW operation is launched (SESAME Ile de France, partners : SOLEIL, LAL, IFRU, ALSYOM, Thal├Ęs, Sigmaphi Electronics).
The photonic time-stretch strategy combined to usual electron bunch length measurement technique based on the spectrally encoded electro-optic sampling detection enables single-shot recordings up to 88 MHz, as tested experimentally with the Coherent Synchrotron Radiation pulses on the AILES beamline at SOLEIL and to be applied for LUNEX5. A new method for characterizing the temporal properties of the radiation emitted by LUNEX5 even in the presence of partial longitudinal coherence has been developed. The measurement scheme relies on laser-dressed XUV photoionization: the evolution of the shot-averaged photoelectron spectrum with the laser/XUV delay provides a two-dimensional spectrogram. The statistical properties of the XUV pulses accumulated during the measurement are then extracted from this spectrogram using a phase-retrieval algorithm.