![]() ![]() Thermionic cathodes come in various forms, and there are three major types of thermionic cathodes: metal cathodes, oxide cathodes, and dispense cathodes. 12,19–21 They are an integral part of the devices that provide strong and stable electron supplies. Thermionic cathodes are widely used in many applications such as x-ray machines in the medical field, microwave (and millimeter wave) traveling wave tubes (TWTs) for space communications, linear accelerators in high-energy physics, and florescent lamps and other gas electronics devices. In this study, we show the implementation of barium strontium oxide-coated CNTs on a rather complex filament structure and present a practical thermionic cathode based on this material. 17,18 Real thermionic devices often have more complex structures and the ability of an emissive coating to be incorporated into such structures is important. While their thermionic emission properties have been characterized and studied in detail they have not been implemented in practical thermionic devices. However, in our earlier work, barium strontium oxide-coated CNTs were grown and deposited on a flat surface. Measurements on thermionic emission and thermionic cooling of the cathode are also presented. Plasma enhanced chemical vapor deposition was used to grow CNTs, and magnetron sputtering deposition was used to deposit the barium strontium oxide functional coating details of the cathode fabrication are presented to illustrate both the versatility of the processing techniques and the adaptability of barium strontium oxide-coated CNTs as a functional coating. Strong thermionic emission and a large cooling effect obtained are the result of the combination of the low work function of barium strontium oxide (1.6 eV) and the large field effect induced by the CNTs. Temperature reduction as large as 90° was observed from the cathode surface when it was emitting electrons. Strong thermionic emissions from the cathode also lead to a large thermionic cooling effect. This level of emission is about three times as large as a conventional oxide cathode operating at similar temperature and field strength. At 1395 K and 2.5 V/ μm, the thermionic emission current of 0.87 A or current density of 2.9 A/cm 2 was obtained from this oxide-coated CNT cathode. The cathode produces a strong thermionic emission. It has the same coiled tungsten filament as a conventional oxide cathode but uses barium strontium oxide-coated CNTs instead of the traditional barium strontium calcium oxide powder mixture as an emissive coating. This cathode resembles conventional oxide cathodes in structure. Barium strontium oxide-coated carbon nanotubes (CNTs) were implemented as a work function lowering and field enhancing functional coating on a coiled tungsten filament to create a new thermionic cathode. ![]()
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