EMISSION PROPERTIES OF TOP-LAYER SCANDATE CATHODES PREPARED BY LAD

In the first part an overview of scandate cathode types, their histori cal development and the current status of research is given. Then rece nt improvements obtained by our group are elucidated: A new type of to p-layer scandate cathode has been prepared with the aid of laser ablat ion deposition. Emission current characteristics have been measured as a function of voltage and temperature. Zero field emission i(10%) is determined as 10% deviation from space-charge law. At 965 degrees CMo- Br i(10%) of about 400 A/cm(2) and at 760 degrees CMo-Br of 32 A/cm(2) were achieved, which is more than a factor of 3 higher than the best values for other scandate type cathodes given in literature. it corres ponds to a work-function of about 1.16 eV with a Richardson constant o f 7.8 A cm(-2) K-2. Other emission properties such as uniformity and c athode life are discussed. A description of I/U characteristics via th e superposition model is given.