LONG LIFETIME HIGH BRIGHTNESS PHOTOCATHODES

THE FREE ELECTRON LASER (FEL) REQUIRES A HIGH BRIGHTNESS, HIGH DUTY CYCLE ELECTRON BEAM. USE OF A PHOTOCATHODE, WHICH ELIMINATES BOTH GRIDAND BUNCHER AND ALLOWS HIGH GRADIENT RADIO FREQUENCY FIELDS AT THE ELECTRON SOURCE, CAN SUBSTANTIALLY IMPROVE THE BEAM BRIGHTNESS. FEL PHOTOCATHODES INVESTIGATED TO DATE (PRIMARILY CS:F:GAAS AND CS3SB) HAVE A SHORT EMISSION LIFETIME WHEN DRIVEN TO HIGH CURRENT AND CANNOT BE SCALED TO HIGH AVERAGE POWER. A LONG LIFETIME ALTERNATIVE TO CS3SBWHICH IS SCALEABLE IS BEING DEVELOPED AND ITS OPERATION IN AN OPERATING FEL IS BEING DEMONSTRATED. IN THIS STUDY, THE LASERS AND ULTRA HIGH VACUUM CHAMBER, THE QUANTUM EFFICIENCY IS BEING MEASURED OF A RANGE OF CANDIDATE MATERIALS SUCH AS LAB6, WHICH HAS EXCELLENT SCALINGCHARACTERISTICS, AS A FUNCTION OF WAVELENGTH AND TEMPERATURE. IN A LATER EFFORT, A LASER DRIVEN PHOTOCATHODE SYSTEM COULD BE CONSTRUCTED AND TESTED ON AN OPERATING FEL. WHEN SUCCESSFUL, THE IDENTIFICATION AND DEMONSTRATION OF A NEW PHOTOCATHODE FOR HIGH BRIGHTNESS ACCELERATORS WOULD BE ACHIEVED WITH HIGH POWER CAPABILITY AND RESISTANCE TO POISONING WITH APPLICATIONS IN FREE ELECTRON LASERS, LITHOGRAPHY, AND HIGH ENERGY ACCELERATORS.