The APEX electron source at LBNL combines the high-repetition-rate with the high beam brightness typical of photoguns, delivering low emittance electron pulses at MHz frequency. Proving the high beam quality of the beam is an essential step for the success of the experiment, opening the doors of the high average power to brightness-hungry applications as X-Ray FELs, MHz ultrafast electron diffraction etc.. As first step, a complete characterization of the beam parameters is foreseen at the Gun beam energy of 750 keV. Diagnostics for low and high current measurements have been installed and tested, and measurements of cathode lifetime and thermal emittance in a RF environment with mA current performed. The recent installation of a double slit system, a deflecting cavity and a high precision spectrometer, allow the exploration of the full 6D phase space. Here we discuss the present layout of the machine and future upgrades, showing the latest results at low and high repetition rate, together with the tools and techniques used.
A fiber-optic RF distribution system has been developed for synchronizing lasers and RF plants in short pulse FELs.
Typical requirements are 50-100fs rms over time periods from 1ms to several hours. Our system amplitude modulates a
CW laser signal, senses fiber length using an interferometer, and feed-forward corrects the RF phase digitally at the
receiver. We demonstrate less than 15fs rms error over 12 hours, between two independent channels with a fiber path
length difference of 200m and transmitting S-band RF. The system is constructed using standard telecommunications
components, and uses regular telecom fiber.
An ultrafast x-ray streak camera is under development at LBNL for application primarily to studies of ultrafast magnetization dynamics. In initial work, a temporal resolution of 900fs in accumulative mode at 5 KHz has been achieved. These results and methods currently being developed to improve the resolution and repetition rate are resented. One of the primary limits to temporal resolution is caused by the finite energy width of the electron distribution from the photocathode. The positive time of flight dispersion with energy in the accelerating region of the camera can be countered by introduction of downstream optics that give negative time of flight dispersion with energy, leading to an approximate overall cancellation of this temporal aberration. Initial results of an end-to-end simulation model using the full photoelectron distribution are presented.