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The initial experimental results of the Brookhaven measurement or beam matching for the experimental tines.There RF GUN CHARACTERIZATION AND ELECTRON EMISSION MEASUREMENTS

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The progress of various high-brightness electron source technologies, specially laser based electron sources, such as photocathode RF gun, DC and pulsed photo-gun, and laser plasma electron source, will be reviewed. The physics processes of those sources to realize best performance are clarified according to three basic ideas. They are transverse space charge emittance compensation, space charge compensation and longitudinal emittance compensation. The major progresses and issues of photoinjector are briefly reviewed. The performance of photocathode RF gun at the Brookhaven Accelerator Test Facility (ATF) is presented.

Electron beam bunch compression directly from photocathode RF gun injector was experimentally observed at the Brookhaven Accelerator Test Facility (ATF). The analysis is presented in this report shows that, the configuration of transverse space-charge emittance compensation photoinjecotor can also be operated in bunch length compression mode for modest amount charge (4.0 nc), i.e., longitudinal emittance compensation. For a constant laser energy, the electron beam bunch length almost linearly decrease with the RF gun phase, and the compression ratio as large as factor of 30 was experimentally observed for a 40 pC charge. We also discuss the effect of electron beam bunching inside the RF gun on the transverse emittance, and compared with experimental results. Fig. 1 is the schematic of the layout of space-charge emittance compensation photocathode RF gun injector. Though several authors [1,6,7,9] studied electron beam bunching process inside the RF gun, the roles of the solenoid magnet, drift distance and linac were not discussed. LONGITUDINAL EMTI'TANCE COMPENSATIONWhen the spacecharge emittance compensation photocathode RF gun injector operated in the small launch phases, the electron beam bunch length can be significantly shorter than the driving laser pulse length (for modest amount charge). The electron beam bunch lenghth compression process can be divided into four stages: