Apex initial commissioning results

APEX, the Advanced Photo-injector Experiment at the Lawrence Berkeley National Laboratory, is devoted to the development of a MHz-class repetition rate high-brightness electron injector for X-ray FEL applications. The injector is based on a new concept photocathode gun utilizing a room-temperature 186 MHz RF cavity operating in CW mode in conjunction with high quantum efficiency semiconductor photocathodes capable of delivering the required charge at repetition rates consistent with commercially available laser technology. APEX is organized in three main phases. Phase 0 demonstrates several important milestones for the project: gun cavity conditioning to full RF power in CW mode to demonstrate the required field at the cathode; the gun vacuum performance impacting the lifetime of photo-cathodes; and tests of several different photocathodes at full repetition rate at the nominal gun energy of 750 keV. Phase I, continues cathode studies with a new suite of beam diagnostics added to characterize the electron beam at the gun energy and at full repetition rate. In Phase II, a pulsed linac will be added for accelerating the beam to several tens of MeV to reduce space charge effects and measure the high-brightness performance of the gun when integrated in an injector scheme. Phase 0 is presently under commissioning, and the first experimental results from this phase are presented.