A field emission cathode is a prospective electron source for various space applications such as electricpropulsion, electrodynamic tethers, charging control of spacecraft, and scientific instruments. The field emissioncathode is especially suitable for small-sized space systems because the device can be small, simple, and lowpowered.In the Japan Aerospace Exploration Agency (JAXA), we have been developing carbon-nanotube fieldemission cathodes in which carbon nanotubes are used as electron emission materials. Performance of the fieldemission cathode is specified by the extraction voltage, emission current density, electron extraction efficiency,emission stability, and durability. While some laboratory-model cathodes have been tested in JAXA, thecharacteristics have not been sufficient to apply the cathodes to practical applications. The purpose of this study is toimprove these fundamental characteristics of the carbon nanotube cathode. A new laboratory-model cathode wasdesigned and fabricated based on our previous models. In order to suppress high-voltage-breakdowns at a narrowelectrode gap, surface flatness of the carbon-nanotube emitter was improved in the new model. Another majorchange was the insertion of a high resistance material between the electrodes to keep the close gap more stably. Thenominal emission current was designed as 3.0 mA based on electric field calculation. Results of the experimentsshowed that the cathode can emit electrons stably up to 4.0 mA without fatal breakdowns. The extraction voltagerequired for the 4-mA emission was approximately 550 V and the extraction efficiency was around 98%. Thesecharacteristics were superior to ones of our previous models.
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