Correlation between high tension performances in vacuum and space charge characteristics

A high voltage device was built in order to test alumina insulators in vacuum (/spl sim/2.10/sup -8/ torr). With this experimental set up and a specific test procedure, it is possible to classify the different types and batches of the commercial ceramics which have been tested. Doping with manganese the alumina ceramics (oxide surface diffusion process), modifies their behaviour with regard to the space charge physics: at room temperature, it is possible to characterize according to the "mirror" method, the embedded space charge which has been generated by the electron gun of a SEM, while, before doping, such measurements were not possible (very low space charge, if any). With the help of this high-voltage set-up, it is possible to note the doping influence on the recorded characteristics: conditioned voltage, holdoff voltage and breakdown rate at a given voltage. Some space charge physics related explanations of the results are suggested. They should be validated by further tests on a greater number of samples.