Abstract
A modified Nuclear Thermionic Avalanche Cell (NTAC) to reduce back-scatter losses of avalanche electrons emitted by a NTAC. The present invention provides a novel topological surface configuration for electron collector layers in NTAC devices. Sawtooth configurations of the surface configurations of electron collector layers allow for the recapture of back-scattered electrons, increasing the efficiency of NTAC devices as well as reducing thermal loading and increasing NTAC efficiency.
Claims
1. Means for minimizing electron back-scatter losses in nuclear thermal avalanche cells, the means comprising electrons emitted from a nuclear thermal avalanche cell emitter, crossing a vacuum gap, and striking one or more electron collector surfaces disposed within a nuclear thermal avalanche cell, and disposing topological surface designs on the one or more electron collector surfaces, the topological surface designs capturing back-scattered electrons.
2. The means of claim 1 wherein the topological surface designs are not co-planar with the plane of the one or more electron collector surfaces.
3. The means of claim 2 wherein the topological surface designs are sawtooth configurations.
4. The means of claim 1 wherein the captured back-scattered electrons are forward-scattered.
5. A device for minimizing electron back-scatter losses in nuclear thermal avalanche cells, the device comprising: one or more nuclear thermal cell emitters; one or more electron collector surfaces separated from the one or more nuclear thermal cell emitters by one or more vacuum gaps; the one or more electron collector surfaces having topological surface designs that are not co-planar with the plane of the one or more electron.
6. The device of claim 4 wherein the topological surface designs are sawtooth designs.
7. Means for maximizing electron forward-scatter emission in nuclear thermal avalanche cells, the means comprising electrons emitted from a nuclear thermal avalanche cell emitter, crossing a vacuum gap, and striking one or more electron collector surfaces disposed within a nuclear thermal avalanche cell, and disposing topological surface designs on the one or more electron collector surfaces, the topological surface designs capturing back-scattered electrons and causing them to be forward-scattered.
8. The means of claim 1 wherein the topological surface designs are not co-planar with the plane of the one or more electron collector surfaces.
9. The means of claim 2 wherein the topological surface designs are sawtooth configurations.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows the forward-scattering and back-scattering of electrons on the surface of a conducting collector in a NTAC.
[0016] FIG. 2 shows an illustration of the interaction of high-energy electrons across an insulator surface.
[0017] FIG. 3 demonstrates a simulation of back-scattered electrons impinging on an iron-rich material.
[0018] FIG. 4 is an illustration of the back-scattering of electrons at the collector surface of a NTAC.
[0019] FIG. 5 shows a novel topological collector surface design in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention provides a means for minimizing electron back-scatter losses in Nuclear Thermal Avalanche Cells (“NTACs”) through a novel topological surface design for collector surfaces in NTACs.
[0021] Referring now to FIG. 1, the forward-scattering and back-scattering of electrons on the surface of a conducting collector 101 in a NTAC of electrons striking a typical conducting electron collector is shown. The electron beam 102 (in the case of a NTAC the stream of electrons emitted from a NTAC emitter) projects one or more electrons 103 which strike the surface 104 of a conducting collector 101, producing the desired forward-scattering electrons into the conducting collector 101 as shown 105. However, a portion of the one or more electrons 103 striking the surface 104 will interact with the surface 104 in a manner that causes the emission of back-scattering electrons 106. These liberated back-scattering electrons 106 cause a net loss of energy. In addition, as the energy of the one or more electrons 103 increases, the greater the number of back-scattering electrons 106, thereby carrying away a larger portion of the energy imparted by the one or more electrons 103 and decreasing the efficiency of the NTAC device.
[0022] FIG. 2 illustrates the effect of a high-energy primary electron 201 from an emitter source 102 striking the surface 202 of an insulator material 203. This process is referred to as “surface flashover” where the primary electron 201 strikes the surface 202, which then emits secondary electrons 204 which are of lower energy than the primary electron 201 but are more numerous. The secondary electrons 204 also strike the surface 202, emitting tertiary electrons 205 which are more numerous than the secondary electrons 204. This behavior is similar to the behavior of electrons striking a surface under an electric field such as exists in collectors disposed within a NTAC device.
[0023] FIG. 3 illustrates an application of a Monte-Carlo simulation of the effect of electrons striking a ferrous or other conducting material. A Monte Carlo simulation of a 15 keV electron beam impinges on the surface of Fayalite (an iron-rich material with the formula Fe.sub.2SiO.sub.4) is shown. A similar back-scattering occurs on a collector surface. And with an increase in both the number and energy of electrons impinging upon a collector surface, the incidence of back-scattered electrons increases as well. So the higher the power (electron) output of a NTAC emitter, the higher the proportional losses will be due to back-scattering. At some theoretical limit, therefore, additional increases in emitter output will result in no corresponding increase in electron capture at the collector. The 15 keV electrons 302 strike the surface 303 of the Fayalite material 301, and result in the production of forward-scattering electrons shown by their scatter trajectories 304. The simulation also shows the back-scattering electrons 305. As the number and energy of the electrons 302 increase, so too does the energy and number of back-scattering electrons 305. The high output of avalanche electrons in a NTAC increase this effect significantly. FIG. 4 illustrates this effect. Because a NTAC layer 401 consists of a collector 402, insulator 403, and emitter 404, the emitted electrons 407 caused to be emitted from the emitter 406 by a γ-ray source 405 strike the surface 408 of the collector 402, and result is a large number of back-scattered electrons 407 in comparison to the transmission of energy through the NTAC layer 401 and the resulting γ-ray emission 410 from the emitter layer 404.
[0024] Referring now to FIG. 5, an embodiment of the present invention is shown. The emitter layer 404 and the collector layer 402 are separated by a vacuum gap 502. In a typical configuration, emitter spikes 501 are utilized to direct emission of electrons 503 from the emitter layer 404 to the collector layer 402. However, due to Coulomb scattering, the paths of the emitted electrons 503 are not consistently perpendicular to the surfaces of the emitter layer 404 and the collector layer 402. This inconsistency increases the backscattering effect the present invention ameliorates. Rather than a flat surface, the surface 408 of the collector layer 402 is modified topologically into a sawtooth configuration with spikes 504. As the electrons 503 strike the surface 408 of the collector layer 402, the sawtooth spikes 504 allow for both the forward-scattering of electrons as shown by the forward-scattering paths 506 but also allow for the recapture of the back-scattering electrons 507 as a result of the non-planar or non-flat surface structure of the collector layer 402. This novel non-planar surface configuration allows for the capture of energy lost due to backscatter present in current NTAC designs.
[0025] The invention described herein is intended to be an exemplar of configurations in accordance with the invention and should not be construed to be limiting except as required to achieve the purposes of the invention.
