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For the Compact Linear Collider Test Facility (CTF) at CERN a new rf gun with a laser driven photocathode is under construction. The new rf gun will replace the present 11/2 cell gun and will consist of 21/2 cells accelerating the beam to a momentum of 7.0 MeV/c with an electric field strength of 100 MV/m. The strong space-charge forces at low beam energy caused by the high charge density of the electron bunches are contained by radial and longitudinal rf focusing in the gun. The rf gun under construction has been optimized by MAFIA beam simulations for an injector assembly comprising a second accelerating rf structure and an intermediate solenoid magnet correcting the beam divergence of the 21/2 cell gun. The beam loading of the rf gun, by a train of 48 bunches with 21 nC charge each, causes a strong energy decay accompanied by an increase of the flight time for the bunches with lower energy. These effects can be corrected by slightly shifting the acceleration frequency of the gun. The experimental results obtained with the 11/2 cell gun and booster section presently in operation are reported.

The large electron positron storage ring (LEP) preinjector will provide the particles to be stored in the LEP. It is composed of a high‐intensity linear accelerator (linac) providing 200‐MeV electrons for the production of positrons, a low‐intensity linac (LIL) for the acceleration of electrons and positrons to 600 MeV (LIL), and an electron positron accumulator (EPA) ring to collect dense bunches of electrons and positrons at 600 MeV (EPA). The LIL rf accelerating cavities and waveguides are typical of severely conductance limited vacuum systems with high rf induced gas loads, in which a low hydrocarbon free residual pressure has to be maintained (5×10−8 mbar). For the EPA ring, subjected to synchrotron radiation induced gas desorption, considerations of beam lifetime require a base pressure in the 10−9 mbar range, achievable without in situ bakeout in the shortest possible time. The design features with particular emphasis on conceptual choices, cleanliness and special treatments, new hardware, low outg...