During the run 1998/1999 a new injector based on a laser-driven RF gun was
brought in operation at the TESLA Test Facility (TTF) linac at DESY, in ord
er to produce the beam structure and quality required either by TeV collide
r and SASE FEL experiments. High quantum efficiency cesium telluride photoc
athodes, prepared at Milano and transferred to DESY, have been successfully
operated in the RF gun. A bunch charge of 50 nC, only limited by space cha
rge effects, was achieved. The photocathodes have shown an operative lifeti
me of several months. A new cathode surface finishing has showed a promisin
g decrease of the photocathode dark current. Measurements of dark current,
quantum efficiency and lifetime are reported. (C) 2000 Elsevier Science B.V
. All rights reserved.