%0 Conference Proceedings
%4 sid.inpe.br/mtc-m17@80/2007/12.17.14.59
%2 sid.inpe.br/mtc-m17@80/2007/12.17.14.59.43
%T Ion bmbardment comparative studies for hollow cathode started by anode and keeper pulse voltage
%D 2007
%A Gonçalves, José Américo Neves,
%A Sandonato, Gilberto Marrega,
%A Irita, Ricardo Toshiyuki,
%@affiliation Instituto Nacional de Pesquisas Espaciais (INPE)
%@affiliation Instituto Nacional de Pesquisas Espaciais (INPE)
%@affiliation Instituto Nacional de Pesquisas Espaciais (INPE)
%B Encontro Brasileiro de Física dos Plasmas, 9.
%C São Pedro, SP
%8 25-28 Nov.
%X Hollow cathodes have been studied extensively since the early 1930s due to their wide range of applications in vacuum microelectronic devices, microwave tubes, lasers, and materials processing. Over the past two decades hollow cathodes have also become critical components in many °ight electric propulsion systems such as Kaufman-type and Hall-e®ect thrusters. Cathodes made of either porous tungsten inserts or tantalum rolled foils, impregnated with barium aluminates or barium oxides are potential candidates to meet the performance and lifetime requirements for both space and ground based applications. Empirical studies of impregnated cathodes in diodes and traveling-wave tubes were carried out in the late 1970s. These studies showed that lifetime is largely determined by the rate at which the emitting material is depleted by ion bombardment over the cathode surface. The hollow cathode developed and investigated in the Associated Plasma Laboratory at INPE, consists of components mechanically assembled and rolled tantalum foil oxide emitters. A 5mm outside- diameter Ta tube, 40mm long and 0:3mm thick, having in one end a small Molybdenum tip disk (mechanically pressed) with an ori¯ce of 1:2mm diameter comprises the body of the hollow cathode. The emitter was built using a Ta foil painted with (Ba; Sr;Ca)CO3 and rolled into an approximately ¯ve-turns insert, with an outside- diameter of 4:7mm, an inside-diameter of 3mm and a length of 12mm. This work will show the harmful e®ects of the ion impacts on the insert surface, when the hollow cathode is started up by turning on both voltages at the keeper and anode at the same time. The tantalum foil is melted close to the molybdenum tip and sprayed through the ori¯ce, reducing its life time to only few hours. However, when the hollow cathode is started up only by the keeper and the discharge set to the anode afterwards, there are no signi¯cant damages. These results were investigated by Scanning Electron Microscopy with X-ray microanalysis.
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