CTF3 Injector Profile Monitor

The electron gun of the CLIC Test Facility 3 (CTF3) produces 15.6µs long pulses with an energy of 140keV and a current that can be as high as 9A. For the nominal beam operation a 5.4A beam current is generated and sent downstream into the bunching system and the rest of the accelerator. The corresponding beam charge will induce a thermal load that most of the materials, considered as radiators, would not withstand. With this problem in mind, we have built a beam imaging system, installed just after the gun and equipped with two screens. The first one is a phosphorescent screen which yields a high signal and can be for low beam currents. The second screen, a thin graphite foil, is used as a forward OTR radiator and can stand the full beam intensity. Moreover, the time resolution of OTR is very good, in the femtosecond range. This allows the observation of the evolution in time of the beam size during the pulse by using a gated camera. We present in this paper the first results obtained using this system.