First Operation of a High Duty Factor Photoinjector*

Tests of the Boeing Average Power Laser Experiment (APLE) injector have demonstrated first-time operation of a photocathode RF gun electron accelerator at 25 % duty factor. The multi-alkali photocathode was illuminated by a frequency-doubled, mode-locked Nd:YLF laser. The cathode was placed in the first cell of four single-cell cavities resonant at 433 MHz. The 4 cavities accelerated the beam to 5 MeV. The pulse duration was 8.3 ms and the repetition rate was 30 Hz. True average beam currents of up to 35 mA have been accelerated to 5 MeV for an average beam power of 170 kilowatts. The 35 mA beam current exceeded previous photocathode p rformance by a factor of 1000. I