CLIC drive beam generation by induction linac and FEL experimental studies for the CERN Linear Collider

Generation of the intense 30 GHz drive beam for the CERN Linear Collider project (CLIC) presents several interesting technological challenges. Following recent suggestions to generate this beam using a linear induction accelerator (LIA) and free electron laser (FEL), this option is now actively studied. Newly introduced schemes for harmonic acceleration of the CLIC drive beam, possibly including RF pulse compression, require four or more trains of many bunchlets at 30 GHz and these requirements are well matched to the known performance of the induction linac and FEL. A test facility is being set up at CESTA with the initial aim to generate and measure the properties of a low-energy bunched beam close to the needs of CLIC. An electron beam (1 MeV, 1 kA, 50 ns) created by the LELIA induction injector will be transported through a dipole wiggler in order to generate the low-energy beam bunched by FEL effects. This spatial modulation will be measured by using the Cerenkov radiation analysed by a high-speed streak camera in the picosecond regime. The experimental programme is supplemented by theoretical studies relating to the problems of post-acceleration without significant loss of the essential bunch structure and to the control of phase jitter