AN ALKALI DISPENSER PHOTOCATHODE (AL-LI)- AG-O-LI

We propose a new Li-actived metallic photocathode that could be used i n high-current photo-injectors for linear accelerators. An Ag thin fil m is evaporated in UHV on the surface of a piece of (Al-Li) alloy. Aft er treating at 380-degrees-C Li diffuses through Ag and decreases the surface work function to 2.7 eV. The emission yields Q(e), in electron s per incident photon, are higher than those measured with (Al-Li) alo ne. Oxidation of the surface allows one to increase again Q(e) which r eaches Q(e) congruent-to 10(-3) and Q(e) congruent-to 1.7.10(-3) for p hoton energies of 3.5 and 4.6 eV respectively (energies corresponding to photons delivered by a frequency tripled - or quadrupled - YAG lase r).