Commissioning the CLIO injection system

The CLIO (Collaboration pour un laser infra-rouge à Orsay) project involves an FEL and a dedicated 50 MeV rf linac being built at Orsay. We have completed its 4 MeV injector. It consists of a pulsed thermionic gun, a 500 MHz subharmonic prebuncher and a standing-wave (3 GHz) buncher. The gun emits 1 ns wide pulses of 1 A at frequencies ranging from 31.25 to 500 MHz. These pulses are compressed by the injector to 100 A × 8 ps. The injector includes “wall current” type intensity and position monitors. For commissioning temporary diagnostic equipment has been added: a dipole magnet followed by a slit to analyse the energy distribution and a translating wire profile monitor to measure the emittance by varying the magnetic lenses focal length. Also an optical transition radiation foil can be inserted in the beam to measure the longitudinal distribution of the microbunches with a streak camera. The results of the first measurements characterizing the beam are presented.