A PULSED ELECTRON INJECTOR USING A METAL PHOTOCATHODE IRRADIATED BY AN EXCIMER LASER

laser-drij(p; source. This paper describes experiments using an 800-mJ, 20-ns pulse width, KrF excimer laser to generate an electron beam in a full-scale electron 8;~. The gun is a stan- dard PHERMEX hot cathode source that has a spheri- cal Pierce geometry. The 100-nun-diam dispenser cathode is replaced with a simple metal cathode that is illu- minated at a 45O angle. Because the cathode can be heated, a hybrid (hot/photocathode) source was also studied. The electron beam produced by the photo- cathode has the temporal shape of the laser pulse and iS independent of the voltage source. The eventual photo-cathode application is an injector for PHERMEX that can produce a train of electron beam pulses, synchronized with the 50-MHz rf accelerating fields. This new injector could minimize energy dispersion between micropulses, maximize beam transport, and simplify pulse power requirements for multipulse generation (i.e.. electron bursts separated by greater than the characteristic cavity accelerating cycle of 20 ns). Experiment