  The CLIC Test Facility (CTF3) is an intermediate step to demonstrate the
technical feasibility of the key concepts of the new RF power source for CLIC.
CTF3 will use electron beams with an energy range adjustable from 170 MeV (3.5
A) to 380 MeV (with low current). The injector is based on a thermionic gun
followed by a classical bunching system embedded in a long solenoidal field. As
an alternative, an RF photo-injector is also being studied. The beam dynamics
studies on how to reach the stringent beam parameters at the exit of the
injector are presented. Simulations performed with the EGUN code showed that a
current of 7 A can be obtained with an emittance less than 10 mm.mrad at the
gun exit. PARMELA results are presented and compared to the requested beam
performance at the injector exit. Sub-Harmonic Bunchers (SHB) are foreseen, to
switch the phase of the bunch trains by 180 degrees from even to odd RF
buckets. Specific issues of the thermionic gun and of the SHB with fast phase
switch are discussed.
