This disclosure generally relates to thermionic emission and more specifically to emitter structures for enhanced thermionic emission.
Thermionic emitters are critical components of cathodes that are used, for example, in electron sources, plasma sources, and electric propulsion devices for spacecraft (e.g., ion thrusters). High heat (e.g., over 1600 degrees Celsius) is applied to thermionic emitters in order to emit electrons from surfaces of the thermionic emitter. The total current emitted by a thermionic emitter is determined by the temperature of the emitter and the surface area. Higher temperatures and larger surface area thermionic emitters lead to more emitted current. However, higher temperatures add significant thermal challenges, and larger thermionic emitters are not desirable or compatible with certain applications.
In one embodiment, a system includes a cathode and a thermionic emitter installed at least partially within the cathode tube of the cathode. The thermionic emitter is in a shape of a hollow cylinder. The hollow cylinder includes an outer surface and an unsmooth inner surface. The outer surface is configured to contact an inner surface of the cathode tube. The unsmooth inner surface includes a plurality of structures that provide an increase in surface area over a smooth surface.
In another embodiment, a system includes a cathode and a thermionic emitter installed at least partially within the cathode tube of the cathode. The thermionic emitter is in a shape of a hollow cylinder. The hollow cylinder includes an outer surface and an inner surface. The inner surface includes a plurality of structures extending below or above the inner surface.
In another embodiment, a thermionic emitter includes a first surface and a second surface that is opposite the first surface. The thermionic emitter further includes a plurality of structures that each extend below or above the first surface.
The present disclosure provides numerous technical advantages over typical systems. As one example, the disclosed systems include thermionic emitters that each have a emitting surface that includes structures that each extend below or above the emitting surface. The structures, which for example may be ridges and/or troughs, function to increase the surface area of the emitting surface, thereby increasing the amount of electrons emitted by the emitting surface. This may permit a thermionic emitter to be operated at colder temperatures than a typical thermionic emitter of identical size but still produce the same current. As a result, the functional lifetime of the thermionic emitter may be extended. In addition, a thermionic emitter with the disclosed surface structures will produce more current than a typical thermionic emitter of identical size that is operated at the same temperature. As a result, the performance of devices that utilize such thermionic emitters may be increased without having to increase the temperature of the devices. In some embodiments, the surface structures also intercept radiated power from other nearby surfaces which may improve performance compared to non-structured surfaces with similar surface area. Surface structures may also be designed to produce a more uniform emitted current as the thermionic emitter evaporates and the inner surface shape alters.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated herein, various embodiments may include all, some, or none of the enumerated advantages.
Thermionic emitters are used to emit electron currents critical for many different plasma devices. For example, thermionic emitters are critical components of cathodes that are used in electron sources, plasma sources, and electric propulsion devices for spacecraft (e.g., ion thrusters). Thermionic emitters must be heated to extremely high temperature (e.g., ˜1600 degrees Celsius) in order to emit sufficient electron currents. Higher temperatures lead to more electron emission, higher achievable currents, and better plasma device performance. However, increasing the amount of temperature of a thermionic emitter is not always desirable or feasible in order to increase electron emission.
To address these and other challenges with typical thermionic emitters, the disclosure provides various embodiments of thermionic emitters that each include structures that each extend below or above the emitting surface of the thermionic emitter. The structures, which for example may be ridges and/or troughs, function to increase the surface area of the emitting surface, thereby increasing the amount of electrons emitted by the emitting surface. This may permit a thermionic emitter with the disclosed structures to be operated at colder temperatures than a typical thermionic emitter of identical size but still obtain the same current. As a result, the functional lifetime of the thermionic emitter may be extended. In addition, a thermionic emitter with the disclosed surface structures will produce more current than a typical thermionic emitter of identical size that is operated at the same temperature. As a result, the performance of devices that utilize such thermionic emitters may be increased. In certain embodiments, the surface structures also may have the added benefit of intercepting radiated power from other nearby surface structures, reducing some of the heat lost. Surface structures may also be designed to give a certain current emission profile as the emitter surface evaporates during the lifetime of the thermionic emitter.
To facilitate a better understanding of the present disclosure, the following examples of certain embodiments are given. In no way should the following examples be read to limit, or define, the scope of the disclosure. Embodiments of the present disclosure and its advantages may be best understood by referring to the included FIGURES, where like numbers are used to indicate like and corresponding parts.
In general, cathode 100 may be used in a device such as an electron source, plasma source, or electric propulsion device for a spacecraft (e.g., an ion thruster). Heater 110 heats thermionic emitter 130 in order to create electron currents from thermionic emitter 130 to be used in a plasma devices such as an ion thruster. As described in more detail below, thermionic emitter 130, unlike typical thermionic emitters, includes an emitting surface with structures that function to increase the surface area of the emitting surface. By increasing the surface are of the emitting surface, the structures enable thermionic emitter 130 to emit a greater amount of electrons than an identical thermionic emitter with a smooth emitting surface.
In general, outer heated surface 131 of some embodiments of thermionic emitter 130 is configured to contact an inner surface of cathode tube 120. Outer heated surface 131 is heated by an external heat source such as heater 110 in order to cause thermionic emitter 130 to emit electrons from inner emitter surface 132. Inner emitter surface 132, which is unsmooth is some embodiments, includes structures 136. Any number, arrangement, size, and shape of structures 136 may be utilized on inner emitter surface 132 in order to provide an increase in surface area to inner emitter surface 132 over a typical thermionic emitter that utilizes a smooth emitter surface (i.e., without structures 136). Various embodiments of structures 136 are discussed further below in reference to
In the illustrated embodiments of
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Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context.
The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.
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