LBNL, Berkeley, California, USA
PNPI, Gatchina, Leningrad District, Russia
NPS, Monterey, California, USA
APEX the Advanced Photo-injector EXperiment at LBNL is devoted to the development of a MHz-class repetition rate high-brightness electron injector for X-ray FELs. APEX is based on a novel room-temperature 186 MHz RF gun operating in CW mode in conjunction with high quantum efficiency photocathodes capable of the required repetition rates with commercial lasers. APEX is organized in 3 phases. Phase 0 includes the demonstration of several important milestones for the project. The gun must be conditioned at full RF power in CW mode; the vacuum performance, directly impacting the lifetime of photocathodes, needs to be characterized; and different photocathodes will be tested at full repetition rate at the nominal gun energy of 750 keV. In Phase I, a new suite of beam diagnostics will be 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 at ~30 MeV to reduce space charge effects and measure the 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.
THOAI01
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
Current and planned X-ray FELs produce pulses with sub-10fs duration, requiring comparable timing stability to enable pump/probe experiments. We describe methods of achieving stability on this time scale, for FEL facilities hundreds of meters long. Our approach is based on CW and amplitude modulated optical signals delivered over fiber to pulsed lasers. A comprehensive design approach includes control of modelocked laser oscillators, amplifiers, propagation paths, arrival time diagnostics and finally cross-correlation between pump and probe signals at the experiment. Design options depend on global FEL parameters such as repetition rate. We show that current laser technology is capable of supporting performance at the few-femtosecond level using these techniques. High precision is achieved by leveraging recently developed, frequency stable spectroscopic lasers and optical clocks, as well as the mature field of fiber interferometry. Current experimental results using pulsed and CW lasers are described.