Mid-Term Report Summary - COXINEL (COherent Xray source INferred from Electrons accelerated by Laser)
Since the first laser discovery in 1960 and the first Free Electron Laser (FEL) in 1977, Linac based fourth generation light sources provide intense coherent fs pulses in the X-ray range for multidisciplinary investigations of matter. In parallel, Laser Wakefield Accelerator (LWFA) by using intense laser beams interacting with cm long plasmas can now provide high quality electron beams of very short bunches (few fs) with high peak currents (few kA). COXINEL aims at qualifying these new types of acceleration concepts with a Free Electron Laser application. Undulator spontaneous emission from LWFA has already been observed, but the presently still rather large energy spread (1 %) and divergence (mrad) prevent from the FEL amplification and electron beam handling schemes are required. COXINEL aims at demonstrating an appropriate electron beam transport from the source to the undulator, followed the first lasing of an LWFA FEL. The key concept relies on an innovative electron beam longitudinal and transverse manipulation in the transport towards an undulator: a “demixing” chicane sorts the electrons in energy and reduces the spread from 1 % to a slice one of 0.1 % and the transverse density is maintained constant all along the undulator (supermatching). Simulations for the COXINEL baseline reference case with 1 % energy spread, 1 mm.mrad emittance, 34 pC, 1 µm length show that FEL amplification is possible with a 2 m long in-vacuum U20 undulator and down to 40 nm with an in-vacuum U15 undulators. The different equipments of the transfer and FEL line have been designed, built, characterised on mounted at the LOA site where the electrons are produced. The line has been installed in Salle Jaune at Laboratoire d’Optique Appliquée where the electrons are produced. During the first preliminary tests, the equipments commissioning started and the electron beam has been rapidly transported after the undulator when it was close, with a measured charge of 30 pC at the exit. Progresses are expected with next beamtimes.