For particle
physics at the TeV energy scale, CERN is developing an ambitious two-beam
accelerator concept for the construction of a linear collider, CLIC.
This scheme is based on acceleration of the beam by 30 GHz cavities
for which the RF power would be provided by the deceleration of a secondary
electron beam at high intensity but low energy. To test issues in this
scheme, an accelerator, the CLIC Test Facility (CTF3) is under development
at CERN. LAL-Orsay is responsible for the construction of two photo-injectors
for two different linacs of CTF3. The specifications for the photo-gun
which will be used to produce the 30 GHz RF power are very demanding.
The RF gun must provide a high quality beam composed of more than 2,000
bunches each containing 2.33 nC of charge at a repetition rate of 3
GHz. The model adopted is inspired from the CERN 2-1/2 cell type IV
RF gun. It has been modified according to the results of experiments
at CERN which showed a dramatic exponential growth of the residual pressure
in the gun with the extracted charge. We will summarize all the studies
performed on the RF design and on the beam dynamics. A comparison with
RF measurements will be also shown. The constraints on the second photo-injector
are less severe since it must be operated with one or 64 bunches of
0.5 nC each. It will also be a 2.5 cell gun at 3 GHz but its design
will be substantially different with respect to the former. This last
project has only recently begun and therefore we will limit ourselves
to the presentation of the results of the RF and beam dynamics simulations.