Emission properties of top-layer scandate cathodes prepared by LAD

In the first part an overview of scandate cathode types, their historical development and the current status of research is given. Then recent improvements obtained by our group are elucidated: A new type of top-layer scandate cathode has been prepared with the aid of laser ablation deposition. Emission current characteristics have been measured as a function of voltage and temperature. Zero field emission i10% is determined as 10% deviation from space-charge law. At 965°CMo-Br i10% of about 400 A/cm2 and at 760°CMo-Br of 32 A/cm2 were achieved, which is more than a factor of 3 higher than the best values for other scandate type cathodes given in literature. It corresponds to a work-function of about 1.16 eV with a Richardson constant of 7.8 A cm−2 K−2. Other emission properties such as uniformity and cathode life are discussed. A description of IU characteristics via the superposition model is given.