Characterization of an impregnated scandate cathode using a semiconductor model

A scandate cathode was tested inside a gun-structure. Suitable for a high power traveling-wave tube, with a water cooled anode. Its work function was about 0.25 eV lower than that of a Re-coated impregnated cathode. Its emission performance at high duty ratios was encouraging. Based on the evidence of possible reactions between tungsten and its oxides with Sc/sub 2/O/sub 3/, and also, on the results from similar cathodes studied using Auger electron spectroscope (AES), scanning electron microscope (SEM) and energy dispersive analysis of X-rays (EDAX), the emission characteristics of the present cathode were analyzed using a semiconductor model in a manner which is an extension to that of oxide cathodes. Excellent agreement was found between theoretical and experimental results over a wide range of anode voltages. Application of patch field treatment showed that the nonsaturation of current-voltage characteristic was not primarily due to inherent patchy behavior. In order for semiconductor model to be applicable. The active material must have a depth substantially greater than that of a mature B-type cathode and the analysis to be presented indicates how the depth and doping density together affect the calculated field enhancement. Finally, using the present model, the real and apparent work function distributions were evaluated and mere compared with those of B-type cathode.<
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