OA13276A - Thermionic electric converter. - Google Patents

Description

ThexuiQcon.s Inc 1 3276

THERMIONIC ELECTRIC CONVERTER

FIELD OF THE INVENTION

The présent invention relates generally to the field of converting heat energydirectly to electrical energy. More particularly, a thermionic electric converter 5 is provided.

BACKGROUND OF THE INVENTION

Heretofore, there hâve been known thermionic converters such as thoseshown in U.S. Pat Nos. 3,519,854, 3,328,611,4,303,845, 4,323,808, 10 5,459,367, 5,780,954 and 5,942,834 (ail to the inventor of the présent invention and ail hereby incorporated by référencé), which disclose variousapparatus and méthode for the direct conversion of thermal energy toelectrical energy. In U S. Pat. No. 3,519,854, there is described a converterusing Hall effect techniques as the output current collection means. The '854 15 patent teaches use of a stream of électrons boiled off of an emissive cathode surface as the source of électrons. The électrons are accelerated toward an anode positioned beyond the Hall effect transducer. The anode of the '854patent is a simple metallic plate, which has a heavily static charged membercircling the plate and insulated from it. 20 U.S. Pat. No. 3,328,611 discloses a spherically configured thermionicconverter, wherein a spherical emissive cathode is supplied with heat, therebyemitting électrons to a concentrically positioned, spherical anode under theinfluence of a control member, the spherical anode having a high positive -1- 1 3276 potential thereon and insulated from the control member. As with the '854patent, the anode of the '611 patent is simply a metallic surface. U.S. Pat. No. 4,303,845 discloses a thermionic converter wherein the électron 5 stream from the cathode passes through an air core induction coil located within a transverse magnetic field, thereby generating an EMF in the inductioncoil by interaction of the électron stream with the transveree magnetic field.The anode of the '845 patent also comprises a metallic plate which has aheavily static charged member circling the plate and insulated from it. 10 U.S. Pat. No. 4,323,808 discloses a laser-excited thermionic converter that isvery similar to the thermionic converter disclosed in the '845 patent. The maindifférence is that the '808 patent discloses using a laser which is applied to agrid on which électrons are collected at the same time the potential to the grid 15 is removed, thereby creating électron boluses that are accelerated toward theanode through an air core induction coil located within a transverse magneticfield. The anode of the '808 patent is the same as that disclosed in the '845patent, i.e., simply a metallic plate which has a heavily static charged membercircling the plate and insulated from it. 20 U.S. Pat. No. 5,459,367 advantageously uses an improved collector elementwith an anode having copper wool fibers and copper sulfate gel instead of ametallic plate. Additionally, the collector element has a highly charged (i.e.,static electricity) member surrounding the anode and insulated from it. -2- 1 3276 U.S. Patent Nos. 5,780,954 and 5,942,834 are directed to the provision of acathode that is constructed as a wire grid, with the cathode being of a non-planar shape to increase its emissive surface area. These patents alsodisclose the technique of using a laser to hit the stream of électrons before 5 they reach the anode, as a measure of providing quantum interférence suchthat the electronics may be more readily captured by the anode.

Another prior design has an anode and cathode which are relatively closetogether such as two microns apart within a vacuum chamber. Such a prior 10 design uses no attractive force to attract électrons emitted from the cathode tothe anode other than induction of césium into the chamber housing the anodeand cathode. The césium coats the anode with a positive charge to keep theélectrons flowing. With the cathode and anode so close together, it is difficultto maintain the températures of the cathode and anode at substantially 15 different températures. For example, one would normally hâve the cathode at1800 degrees Kelvin and the anode at 800 degrees Kelvin. A heat source isprovided to heat the cathode and a codant circulation System is provided atthe anode in order to maintain it at the desired température. Even though thechamber is maintained at a vacuum (other than the césium source), heat from 20 the cathode goes to the anode and it takes a significant amount of energy tomaintain the high température différentiel between the closely spaced cathodeand anode. This in tum lowers the efficiency of the System substantially.

QBJECTS AND SUMMARY OF THE INVENTION 25 Accordingly, an object of the présent invention is to provide a thermionic -3- 1 3276 converter having enhanced and/or improved features over those previouslydesigned or developed. A further principal object of the présent invention is provide a thermionic 5 electric converter with improved conversion efficiency.

Another object ot the présent invention is to provide an improved cathode fora thermionic electric converter having an increased cathode output. 10 Yet another object of the présent invention is to provide a thermionic electricconverter in which the cathode is bombarded by a laser to increase theemissivity of the cathode. A further object of the invention is to provide an anode or target designed to 15 capture électrons emitted from the cathode, while also accommodating a lasercathode enhancer.

The above and other objecte of the présent invention, which will be apparentas the description proceeds, are realized by a thermionic electric converter 20 having a casing member, a cathode within the casing member opérable whenheated to serve as a source of électrons, and an anode within the casingmember opérable to receive électrons emitted from the cathode. The cathodemav be a wire grid having wires going in at least two directions that aretransverse to each other. A charged first focusing ring is in the casing 25 member, between the cathode and the anode, and is opérable to direct -4- 1 3276 électrons emitted by the cathode through the first focusing ring on theirway tothe anode. A charged second focusing ring is in the casing member, betweenthe first focusing ring and the anode, and is opérable to direct électronsemitted by the cathode through the second focusing ring on their way to theanode. Additional focusing rings may be necessary. The cathode is preferablyseparated from the anode at a distance between about 4 microns to about fivecentimeters. More preferably, the cathode is separated from the anode by adistance of one to three centimeters. A laser opérable to hit électrons (i.e.,apply a laser beam to the électrons) is positioned between the cathode andanode. The laser hits the électrons just before they reach the anode. Thelaser is opérable to provide quantum interférence with the électrons such thatélectrons are more readily captured by the anode.

The cathode may be either a solid matériel orformed of a wire grid. When thewire grid construction is used, the wire grid preferably includes at least fourlayers of wires. Further, each of the wire layers has wîres extending in adifferent direction from each of the other of the wire layers, the wire grid of thecathode thus including wires extending in at least four different directions.

This is designed to greatly increase the emissive surface of the cathode.

The présent invention may altemately be described as a thermionic electricconverter having a casing member, a cathode within the casing memberopérable when heated to serve as a source of électrons, an anode within thecasing member opérable to receive électrons emitted from the cathode; and alaser opérable to hit électrons between the cathode and anode. The laser thus -5- 1 3276 provides quantum interférence with the électrons such that électrons are morereadily captured by the anode. The laser is opérable to hit électrons justbefore they reach the anode. The laser is opérable to hit électrons within 2microns of when they reach the anode. The cathode is a wire grid having 5 wires going in at least two directions that are transverse to each other. Thecathode is separated from the anode at a distance of about 4 microns to about five centimeters.

The présent invention may altemately be described as a thermionic electric 10 converter having a casing member, a cathode within the casing member opérable when heated to serve as a source of électrons, and an anode withinthe casing member opérable to receive électrons emitted from the cathodeand which proceed generally along a movement direction defining thedirection from the cathode to the anode. The cathode has a planar cross 15 section area normal to the movement direction, the cathode has an électronémission surface area for électron émission towards the anode, and the électron émission surface area is at least 30 percent greater than the planarcross section area. The cathode is a wire grid having wires going in at leasttwo directions that are transverse to each other. Altemately, or additionally, 20 the cathode is curved in at least one direction perpendicular to the movementdirection. A laser is positioned so as to be opérable to hit électrons betweenthe cathode and anode just before they reach the anode. Preferably, theelectren émission surface area is at least double the planar cross sectionarea. More preferably, the électron émission surface area is at least double -6- 1 3276 the planar cross section area. The smaller the diameter of the wire, the largerthe emissive area. This is an expotential relationship.

The présent invention also involves the use of a laser positioned to impinge5 upon the cathode while being rastered or stepped along the cathode emissive surface, for the purpose of enhancing the output of électrons emitted from thecathode. The laser may be positioned behind the anode or target and aimedat the cathode, and the laser beam may be emitted through an opening in thetarget to impinge on the cathode. A target or anode specially designed to 10 hâve an opening therein, preferably through the center thereof, is provided toaccommodate the operation of the laser.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail herein with référencé to the following15 figures in which like référencé numérale dénoté like éléments, and wherein: FIG. 1 is a schematic diagram of a prior art thermionic electric converter; FIG. 2 is a schematic diagram of a prior art laser-excited thermionic electricconverter; FIG. 3 is a side view with parts in cross section and schematic diagram of a20 thermionic electric converter according to the présent invention; FIG. 4 is a top view of a wire grid structure used for a cathode; FIG. 5 is a side view of a part of the wire grid structure; FIG. 6 is a side view of a part of an altemate wire grid structure; FIG. 7 is a side schematic diagram illustrating multiple layers in a wire grid -7-

structure; and FIG. 8 is a simplified side view of an altemate cathode structure. FIG. 9 is a side view with parts in cross-section and schematic diagranr» of athermionic converter according to another preferred embodiment of the 5 présent invention. FIG. 10 is a substantially schematic front élévation view of the targetsubassembly employed in the FIG. 9 embodiment FIG. 11 is a substantially schematic side view of the target subassembly of FIG. 10. 10

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show prior art thermionic electric converters as shown anddescribed in U.S. Pat. Nos. 4,303,845 and 4,323,808, respectively, both toEdwin D. Davis, the inventor ofthe présent invention, the disclosures of which 15 are incorporated by référencé herein in their entirety. While the operation ofboth thermionic converters is described in detail in the incorporated patents, ageneral operational overview is presented herein with référencé to FIGS. 1and 2. This may provide background useful in understanding the présent invention. 20 FIG. 1 shows a basic thermionic electric converter. FIG. 2 shows a laser-exdted thermionic converter. The operation of both converters is very simitar.

With référencé to the figures, a basic thermionic electric converter 10 is -8- 1 3276 shown. The converter 10 has an elongated, cylindrically shaped outer housing12 fitted with a pair of end walls 14 and 16, thereby forming a closed chamber 18. The housing 12 is made of any of a number of known strong, electricallynon-conductive matériels, such as, for example, high-temperature plastics or 5 ceramics, while the end walls 14,16 are metallic plates to which electricalconnections may be made. The éléments are mechanically bonded togetherand henmetically sealed such that the chamber 18 may support a vacuum,and a moderately high electrical potentiel may be applied and maintained across the end walls 14 and 16. 10

The first end wall 14 contains a shaped cathode région 20 having an électronemissive coating disposed on its interior surface, while the second end wall 16is formed as a circular, slightly convex surface which is first mounted in aninsulating ring 21 to form an assembly, ail of which is then mated to the 15 housing 12. In use, the end walls 14 and 16 function respectively as the cathode terminal and the collecting plate of the converter 10. Between thesetwo walls, an électron stream 22 will flow substantially along the axis ofsymmetry of the cylindrical chamber 18, originating at the cathode région 20and terminating at the collecting plate 16. 20

An annular focusing element 24 is concentrically positioned within thechamber 18 at a location adjacent to the cathode 20. A baffle element 26 isconcentrically positioned within the chamber 18 at a location adjacent to thecollecting plate 16. -9- 1 3276

Disposed between these two éléments is an induction assembly 28 comprisedof a helical induction coil 30 and an elongated annular magnet 32. The coil 30and the magnet 32 are concentrically disposed within, and occupy the centralrégion of, the chamber 18. Referring briefly to the schematic view of FIG. 2,the relative radial positioning of the various éléments and assemblies may beseen. For clarity of présentation, the mechanical retaining means for theseinteriorly located éléments hâve not been induded in either figure. Focusingelement 24 is electrically connected by means of a lead 34 and a hermeticallysealed feed through 36 to an extemal source of static potential (not shown).The induction coil 30 is similarly connected via a pair of leads 38 and 40 and apair of feed-throughs 42 and 44 to an extemal load element shown simply as a resistor 46.

The potentiels applied to the various éléments are not explicltly shown nordiscussed in detail as they constitute well known and conventional means forimplementing related électron stream devices. Briefly, considering(conventionally) the cathode région 20 as a voltage référencé level, a high,positive static charge is applied to the collecting plate 16 and the extemalcircuit containing this voltage source is completed by connection of itsnégative side to the cathode 20. This applied high, positive static chargecauses the électron stream 22 which originated at the cathode région 20 to beaccelerated towards the collecting plate 16 with a magnitude directlydépendent upon the magnitude of the high static charge applied. Theélectrons impinge upon the collecting plate 16 at a velocity sufficient to causea certain amount of ricochet. The baffle element 26 is configured and -10- 1 3276 positioned to prevent these ricochet électrons fram reaching the main sectionof the converter, and electrical connections (not shown) are applied thereto asrequired. A négative voltage of low to moderate levai is applied to the focusingelement 24 for focusing the électron stream 22 into a narrow beam. In 5 operation, a heat source 48 (which could be derived from diverse sourcessuch as combustion of fossil fuels, solar devices, atomic devices, atomicwaste or heat exchangers from existing atomic operations) is used to heat theélectron emissive coating on the cathode 20, thereby boiling off quantities ofélectrons. The released électrons are focused into a narrow beam by focusing 10 element 24 and are accelerated towards the collecting plate 16. While transiting the induction assembly 28, the électrons corne under the influenceof the magnetic field produced by the magnet 32 and execute an interactivemotion which causes an EM F to be induced in the tums of the induction coil 30. Actually, this induced EM F is the sum of a large number of individual 15 électrons executing small circular current loops thereby developing a correspond!ngly large number of minute EMFs in each winding of the coil 30.

Taken as a whole, the output voltage of the converter is proportional to thevelodty of the électrons in transit, and the output current is dépendent on thesize and température of the électron source. The mechanism for the induced 20 EMF may be explained in terms of the Lorentz force acting on an électronhaving an initial linear velodty as it enters a substantially uniform magneticfield orthogonally disposed to the électron velodty. In a properly configureddevice, a spiral électron path (not shown) résulte, which produces the desirednet rate of change of flux as required by Faraday's law to produce an induced 25 EMF. -11- 13276

This spiral électron path resultsfrom a combination ofthe lineartranslationalpath (longitudinal) due to the accélération action of collecting plate 16 and acirculer path (transverse) due to the interaction of the initial électron velodty 5 and the transverse magnetic field of magnet 32. Depending on the relativemagnitude ofthe high voltage applied to the collecting plate 16 and thestrength and orientation of the magnetic field produced by the magnet 32,other mechanisms for producing a voltage directly in the induction coil 30 maybe possible. The mechanism outlined above is suggested as an illustrative 10 one only, and is not considered as the only operating mode available. Ailmechanisms, however, would resuit from various combinations oftheapplicable Lorentz and Faraday considérations.

The basic différence between the basic converter shown in U.S. Pat. No. 15 4,303,845 and the laser-excited converter shown in U.S. Pat. No. 4,323,808, is that the laser-excited converter collects électrons boiled off the surface of the cathode on a grid 176 having a small négative potential applied thereonby a négative potential source 178 through lead 180, which traps the électronflow and mass of électrons. The electrical potential imposed on the grid is 20 removed, while the grid is simultaneously exposed to a laser puise dischargefrom laser assembly 170,173,174,20 causing a bolus of électrons 22 to bereieased. The électron bolus 22 is then electricaliy focused and directedthrough the interior of the air core induction colis located within a transversemagnetic field, thereby generating an EMF in the induction coil which is 25 applied to an extemal circuit to perform work, as set forth above with respect -12- to the basic thermionic converter. 1 3276

As set forth the présent inventons prior U.S. Pat. No. 5,459,367, there arenumerous attendant disadvantages usually associated with having a 5 côllecting element simply made up of a conductive métal plate. Therefore, thecollecting element of that design includes a conductive layer of copper sulfategel impregnated with copper wool fibers. The présent invention may use suchan anode. However, the présent invention also may use a conductive métalplate anode as other aspects of the présent invention will minimize or avoid i 0 some of the disadvantages that such a plate anode might otherwise cause.

Basically then, the spécifies of the anode are not central tothe preferreddesign of the présent invention.

With référencé now to FIG. 3, a thermionic electric converter 200 according to 15 the présent invention includes a casing member 202 in which a vacuum wouldbe maintained by vacuum apparatus (not shown) in known fashion. Thecasing member 202 is preferably cylindrical about a central axis 202A whichserves as an axis of symmetry of the member 202 and the componentstherein except where otherwise noted. 20

The collecter 204 may include a fiat anode drcular plate 206 (made of copperfor example) surrounded by a statically charged ring 208 (charged to 1000Coulombs for exemple) having insulating rings 210 concentric therewith. Thering 208 and rings 210 may be constructed and opérable as discussed in the 25 U.S. Pat. No. 5,459,367. A cooling member 212 is thermally coupled to the -13- '” 13276 plate 206 such that coolant from coolant source 214 is redrculatedtherethrough by coolant circuit 216. The cooling member 212 maintains theanode plate at a desired température. The cooling member 212 mayaltemately be the same as the anode plate 206 (in other words coolant wouldcirculate through plate 206). A feedback arrangement (not shown) using oneor more sensors (not shown) could be used to stabilize the température of anode 206.

The cathode assembly 218 of the présent invention includes a cathode 220heated by a heat source such that it emits électrons which generally movealong movement direction 202A towards the anode 206. (As in the U.S. Pat.No. 5,459,367, the charged ring 208 helps attract the électrons towards theanode.) Although the heat source is shown as a source 222 of heating fluid(liquid or gas) flowing to heating member 224 (which is thenmally coupled tothe cathode 220) via heating circuit 226, alternats energy sources such as alaser applied to the cathode 224 might be used. The energy input into source222 could be fossil fuel, solar, laser, microwave, or radioactive matériels.Further, used nuclearfuel that would otherwise simply be stored at greatexpense and without benefit might be used to provide the heat to source 222.

Electrons energized to the Fermi level in cathode 220 escape from thesurface thereof and, attracted by static charge ring 208, travel alongmovement direction 202A through tiret and second focussing rings orcylinders 228 and 230, which may be constructed and opérable in simiiarfashion focussing element 24 of the prior art arrangement discussed above. In -14· 1 3276 order to help the électrons move in the proper direction a shield 232 maysurround the cathode 224. The shield 232 may be cyiindrical or conical or, asshown, include a cylindrical portion dosest the cathode 224 and a conicalportion furtherfrom the cathode 224. In any case, the shield tends to keepélectron movement in direction 202A. The électrons will tend to be repelledfrom the shield 232 since the shield will be at a relatively high température(from its proximity to the relatively high température cathode 220). Alternately,or additionally, to being repelled by the high température of the shield, theshield 232 could hâve a négative charge applied to it. In the latter case,insulation (not shown) could be used between the shield 232 and cathode 220.

The electrical energy produced corresponding to électron fiow from cathode220 to anode 206 is supplied via cathode wire 234 and anode wire 236 to an extemal circuit 238.

Tuming from the overall operation of the converter 200 to spécifieadvantageous aspects thereof, électrons such as électron 240 tend to hâve ahigh energy level as they approach the anode 206. Therefore, the normaltendency would be for some to bounce off the surface and not be capturedtherein. This normally results in électron scatter and diminishes theconversion effidency of a converter. in order to avoid or greatly reduce thistendency, the présent invention uses a laser 242 which hits the électrons(e.g., hits them with a laser beam 244) just before they hit the anode 206. Thequantum interférence between the photons of the laser beam 244 and the -15- 1 3276 électrons 240 drops the energy State of the électrons such that they are morereadily captured by the surface of anode 206.

As will be understood from the dual wave-partide theory of physics, theélectrons hit by the laser beam may be exhibiting properties of waves and/orpartides. Of course, the scope of the daims of the présent invention are notlimited to any particular theory of operation unless and except where a daimexpressly référencés such a theory of operation, such as quantum interférence.

As used herein, when référencé is made to the laser 242 hitting the électronswith beam 244 "just before" the électrons reach the anode 206 means that theélectrons which hâve been hit do not pass through any other components(such as a focusing member) as they continue to the anode 206. Morespecifically, the électrons are preferably hit within 2 microns of when theyreach the anode 206. Even more preferably, the électrons are hit by the laserwith 1 micron of reaching the anode 206. Indeed, the distance from thesecond focusing element 230 to the anode 206 may be 1 micron and the lasermay hit électrons doser to the anode 206. In thatfashion (i.e., hitting theélectrons just before they reach the anode), the energy of the électrons isreduced at a point where reduced energy is most appropriate and useful.

Although casing member 202 may be opaque, such as a meta! member, alaser window 246 is made of transparent matériel such that the laser beam244 can travel from laser 242 into the chamber within member 202. -16- 1 3276

Altemately, the laser 242 could be disposée! in the chamber.

In addition to improving conversion efficiency by using the laser 242 to reducethe energy level of électrons just before they reach the anode 205, the 5 cathode 220 of the présent invention is spedficalîy designed to improveefficiency by increasing the électron émission area of the cathode 220.

With référencé to FIG. 4, the cathode 220 is shown as a circular grid of wires248. Wires 250 of a top or first layer of parallel wires extend in direction 252, 10 whereas wires 254 of a second layer of parallel wires extend in direction 256,transverse to direction 252 and preferably perpendicular to direction 252. Athird layer of parallel wires (only one wire 258 shown for ease of illustration)extend in direction 260 (45 degrees from directions 252 and 256. A fourthlayer of parallel wires (only one wire 262 shown for ease of illustration) extend 15 in direction 264 (90 degrees from direction 260).

It should also be noted that FIG. 4 shows the wires with relatively largeséparation distances between them but this is also for ease of illustration.Preferably, the wires are finely extruded wires and the séparation distances 20 between parallel wires in the same layer would be similar to the diameter ofthe wires. Preferably, the wires hâve diameters of 2 mm ôr less to finefilament size. The wires may be tungsten or other metals used in cathodes.

With référencé to FIG. 5, the wires 250 and 254 may be offset from each 25 other with ail wires 250 (only one shown in FIG. 5) disposed in a common -17- 1 3276 plane offset from a different common plane in which ail wires 254 aredisposed. An altemate arrangement shown in FIG. 6 has wires 250' (only onevisible) and 254' which are interwoven in the manner of fâbric.

With référencé to FIG. 7, an altemate cathode 220' may hâve three portions266, 268, and 270. Each of portions 266, 268, and 270 may hâve twoperpendicular layers of wires (not shown in FIG. 7) such as 250 and 254 (or250' and 254'). Portion 266 would hâve wires going into the plane of view ofFIG. 7 and wires parailel to the plane of FIG. 7. Portion 268 has two layers ofwires, each having wires extending in a direction 30 degrees from one of thedirections of the wires for portion 266. Portion 270 has two layers of wires,each layer having wires extending in a direction 60 degrees from one of thedirections of the wires for portion 266.

It will be appreciated that FIG. 7 is illustrative of the point that multiple layersof wires extending in different directions could be used.

The various wire grid structures for the cathode increase the effective électronémission surface area by way of the shape of the wires and their multiplelayers. An alternative way of increasing the surface area is illustrated in FIG. 8. FIG. 8 shows a side cross section view of a parabolic cathode 280 opérableto émit électrons for movement generally along movement direction 220A*.

The cathode 28Q has a planar cross section area A normal to the movementdirection 202A. Significantly, the cathode 280 has an électron émissionsurface area EA (from the curvature of the cathode) for électron émission -18- 1 3276 towards the anode which is at least 30 percent greater than the planar crosssection area A. Thus, a greater density of électrons are generated for a givensize cathode. Although the cathode 280 is shown as a parabola, other curvedsurfaces may be used. The cathode 280 may be made of a solid member ormay also incorporate multiple layer wire grid structures like described forFIGS. 4-7 except that each layer would be curved and not planar.

Although the curved cathode arrangement of FIG. 8 provides an électronémission surface area EA that is at least 30 percent greater than the sidecross section area A, the various wire grid arrangements such as FIG. 4provide an électron émission surface area that is at least double the sidecross section area (i.e., defined as shown for FIG. 8). Indeed, the électronémission surface area in the grid arrangements should be at least ten times the side cross section area.

Advantageously, the présent invention allows the cathode 220 and anode 206to be offset from each other by from 4 microns to 5 cm. More specifically, thatoffset or séparation distance will be from 1 to 3 cm. Thus, the cathode andanode are sufficiently far apart that heat from the cathode is less likely to beconveyed to the anode than in the arrangements where the cathode andanode must be in close proximity. Therefore, the coolant source 214 can be arelatively low coolant demand arrangement since less cooling is required thanin many prior designs.

Tuming now to FIGS. 9-11, a further embodiment of the thermionic electric -19- 13276 convertér of the présent invention is illustrated. This embodiment is designedto further increase the output of électrons from the cathode, thereby furtherincreasing the conversion efficiency and electrical current génération of the converter. 5 The thermionic electric converter 300 according to the embodiment shown inFIGS. 9-11 may preferably employ many of the same or similar componentsto the converter 200 illustrated and described with respect to FIGS. 3-8. Inparticular, the converter 300 preferably includes a casing member 302, whichmay preferably be cylindrical along at least a portion of its longitudinal extent. 10 The converter 300 further includes an électron target subassembly or collector304, the constructional details of which will be discussed later. Acoolingmember 312 is provided to maintain the target subassembly 304, or spécifiecomponents thereof, at a desired température, generally lower than anoperating température of cathode subassembly 318. The cathode 15 subassembly 318 preferably includes a cathode 320 having a cathode emitter321, the cathode being heated by a heat source 322 thermal ly coupled to thecathode such that the heating of the cathode will cause électrons to becomeenergized and escape from the surface of the cathode emitter 321. 20 The heat source 322, as illustrated, includes a heating member 324 coupledto the cathode, and a heating circuit 326 which delivers a heating fluid (liquidor gas) to cathode 320. As with the embodiments disclosed in FIGS. 3-8, itwill be recognized by persons of ordinary skill in the art that the source ofthermal energy for heating the cathode from an extemal source may take the -20- 13276 form of solar energy, fossil fuel, laser energy, microwave energy, or thermalenergy derived from radioactive materials, such as radioactive waste or spentradioactive materials. Used nudear fuel that would otherwise be required tobe stored at great expense could be used to provide thermal energy for beatsource 322. The construction of basic Systems or subassemblies forproviding the various types of thermal energy will be readily apparent topersons of ordinary skill in the art.

Converter 300 may also preferably employ first and second focusing rings328, 330, in a manner similar to that shown in FIG. 3. A shield 332 may alsobe provided to surround cathode 320, to perform essentially the same function as does shield 232 in the FIG. 3 embodiment

Electrical energy produced corresponding to an électron flow from cathodeemitter 321 to anode 306 of target subassembly 304 is supplied via cathodewire 334 and anode wire 336 to an extemal circuit 338. Circuit 338 thus receives energy in electrical form, which energy is produced or generatedfrom thermal energy by converter 300. Circuit 338 may preferably include atransistor 337 connected in the circuit return line (shown as cathode wire 334in FIG. 9), so that the current in the circuit is restricted to flowing in only onedirection, Le,, in the direction back to cathode emitter 321, via a feedthrough339 in casing member 302.

The converter 300 further preferably indudes an électron interférence laser342, which opérâtes to lower the energy State of the électrons as they reach -21- 13276 anode 306, as by quantum interférence or other particie interactionphenomena. Laser beam 344 passes through laser window 346 andintersects the path of, or “hits”, the incoming électrons to reduce the energystored in the électrons. Référencé may be had to the discussion of this 5 aspect of the invention in connection with laser 242 and laser beam 244, andFIG. 3 herein, insofar as the theory of operation is concemed. The réductionin the energy level of the électrons immediately prior to contacting anode 306decreases the tendency of électrons to hit anode 306 and to bounce off andscatter because of the collision. Anode 306 will thus capture a larger 10 percentage of the incoming électrons.

Target subassembly or collecter 304 is preferably constructed so as to hâve acentral opening 370 sized and adapted to allow a cathode output enhancingdevice or auxiliary cathode enhancer 372, in the form or a laser 374, to émit a 15 laser beam 376 in the direction 376a of the emitting surface 321 of cathode320. Altematively, target subassembly may hâve such an opening in an off-center location, or, altematively, may be sized and positioned within casingmember 302 such that laser 374 can direct laser beam 376 from a positionoutside the periphery of the target subassembly. 20

Referring to ail of FIGS. 9-1 i, target subassembly 304 may preferablycomprise an anode 306 having opening 370 therethrough, shown centrally inthe drawing figures, for the sake of convenience. An insulafing (electricallyinsulating) ring 378 is positioned at an edge of opening 370, and is preferably 25 secured to anode 306 at that edge. An électron repulsion ring 380 is -22- 13276 disposed at an inner periphery of insulating ring 378. This repulsion ring 380is provided in orderto substantially prevent électrons emanating from cathode320 and traveling along path 302a from passing into and through the openingdefined by repulsion ring 380, or to minimize the number of électrons passingtherethrough. Electron répulsion ring 380 is preferably provided with anégative charge imposed by an extemal source (not shown) coupled to therépulsion ring at feedthrough 379, or may operate in a different manner torepel électrons. Preferably, the ring 380 will operate to deflect at least portionof the électrons into a path that will resuit in the électrons colliding with anode306 of target subassembly 304.

Anode 306 may be formed as a fiat circular plate, as illustrated, or mayaltematively be curved in either a direction toward or away from cathode 324,or otherwise shaped in a manner designed to effectively capture électronstraveling along paths from the cathode 320 into contact with the anode.

Anode 306 preferably has, at its outer periphery, a highly statically charged, orFaraday, ring 308 bounded by inner and outer insulating rings 310. Thisportion of the target subassembly will be essentially the same as thatdisclosed with respect to the FIG. 3 embodiment, and will operate in generallythe same manner, to aid in attracting the électrons toward anode 306, wherethe électrons can be collected in order to generate an electrical current. Afeedthrough connecter, shown schematically in FIG. 11 at 382, is employed tocouple the Faraday ring 308 to a means for imparting the desired high staticcharge. Insulating rings 310 operate to electrically insulate anode 306 andthe main electrical circuit 338 from the static charge imposed on ring 308. -23- 13276

The plate anode 306 may be constructed of the same matériels as is theanode 206 in FIG. 3, or may be of any other type known in the art to besuitable for this use. Cathode 320 may also be constructed of the same 5 matériels and in the same manner as is cathode 220 discussed and illustratedwith respect to FIGS. 3*8, or any other cathode structure disclosed in the priorpatents discussed in the Background section herein.

In the embodiment of FIGS. 9-11, the output of the cathode is greatly 10 increased over that obtained in the embodiment shown in FIGS. 3-8. As noted previously, an auxiliary cathode enhancer 372, in the form of laser 374,is provided to direct a laser beam 376 at the emissive surface 321 of thecathode, which further excites the électrons on that surface, over and abovethe excitation obtained by the thermal energy supplied by heating source 322. 15

In the illustrated preferred embodiment, the laser 374 is positioned inside ofcasing member 302 and on a side of anode 306 opposite the side at whichcathode 320 is positioned. Laser 374 is aimed to direct laser beam 376 suchthat the photons travel along path 376a in essentially the opposite direction of 20 the path 302a of the électrons traveling from cathode 320 to anode 306.

Laser beam 376 preferably strikes the emissive surface 321 of the cathodeeither orthogonally to that surface, or at a small angle of incidence thereto, tomaximize the energy transfer to the électrons. -24- 13276

The laser 374 will preferably be controlled by controller 400 to émit “shots” orpuises having, for example, a duration on the order of one to severalpicoseconds, ata frequencyof about 10-100 MHz. Otheroperational régimesmay also be adopted, and it should be recognized that these parameters are 5 provided primarily for illustrative purposes.

The auxiliary cathode enhancer 372 will also preferably include a rasteringdevice, shown schematically at 382 in FIG. 11. The rastering device 382 willbe controlled, preferably also by controller 400, to cause the laser beam 376 10 to sweep in both latéral (side-to-side) and vertical (up-to-down, or vice versa)directions, in a manner that will be readily apparent to persons skilled in theart upon reading this description. The rastering device 382 is used so as toprevent érosion of the emissive surface of the cathode 320 at régions wherethe laser beam might otherwise constantly orfrequently impinge, thus 15 prolonging the life of the cathode. The rastering device will preferably complété a sweep from side-to-side and from top to bottom of the cathode ata frequency on the order of one to several nanoseconde. Again, this periodmay differ from the stated preferred range, and may be coordinated with thefrequency and duration of the laser puises to provide different desired 20 degrees of auxiliary excitation of the électrons at the cathode surface.

It is expected that the use of an auxiliary cathode enhancer of the typedisciosed will increase the output of the cathode by appraximately 20-25 timesthe output of the cathode in FIGS. 3-8, for example, when that converter is 25 operated withoutthe auxiliary enhancer. Again, the operating parameters of -25- 1 3276 the enhancer may be varied as desired to either increase or decrease thelevai of enhancement to the cathode output.

In FIG. 10, possible alternative positions for the laser 374 of the auxiliarycathode enhancer 372 are shown at A, B and C. These désignations areintended to show that the laser 374 may be mounted off-center, relative totarget subassembly 304, whereby the opening in the anode 306 would be off-center, or may be mounted outside the outer periphery of target subassembly304. In this latter case, there would be no need to provide an opening in theanode, nor would an électron repulsion ring be necessary. As notedpreviously, it is desired to maintain a relatively small angle of incidence of thelaser beam relative to the emlssive surface 321 of the cathode, in order tomaintain an efficient transfer of energy. The off-center positionings couldpossibly resuit in a less-effident enhancement of cathode output, however,other design considération may be simplified using such positions, whichcould compensais for the slightly lower efficiency.

Further, to this point, the discussion of the positioning of the laser has focusedon positioning the laser at the back side of the target subassembly 304,opposite the side at which the cathode is positioned. While such positioningtends to maintain a smaller angle of incidence of the laser beam with respectto the cathode surface, it would be possible to position the laser 374 forwardof the anode 306 (i.e., longitudinally between the anode and cathode),provided it is positioned radiaily outside the path of the électrons travelingfrom the cathode to the anode. -26- 1 3276 A further feature of the invention illustrated in FIG. 11 is the provision of aplurality of electrets 398 around the inner periphery of casing member 302, toaid in scavenging any stray électrons that may bounce off of anode 306 or 5 otherwise fail to be captured by the anode. Such stray électrons can create aspace charge within the vacuum chamber. The electrets 398 will beconnected to ground, so as to substantially prevent any space charge buildup. 10 While the invention has been described in conjunction with spécifie embodiments thereof, it is évident that many alternatives, modifications andvariations will be apparent to those skilled in the art. Accordingly, thepreferred embodiments of the invention, as set forth herein, are intended to beillustrative, not limiting. Various changes may be made without departing from 15 the spirit and scope of the invention as defined herein and in the foilowing daims. -27-

Claims (21)

1. WHATIS CLAIMED1S: 1 3276

   1. A thermionic electric converter comprising:a casing member; a cathode within said casing member having a cathode emitter opérable, when heated, to serve as a source of électrons; 5 a target structure within the casing member comprising an anode opérableto reçoive électrons emitted from the cathode emitter; and a cathode output enhancing device opérable to increase an excitationenergy of électrons disposed at said cathode emitter.
2. 2. A theromionic electric converter as set forth in Claim 1 wherein said 10 cathode output enhancing device comprises a cathode enhancing laserpositioned to direct a laser beam to strike an emissive surface of said cathode emitter.
3. 3. A thermionic electric converter as set forth in Claim 2, wherein said cathode enhancing laser is positioned in the interior of said casing member. 15
4. 4. A therimionic electric converter as set forth in Claim 3, wherein saidcathode enhancing laser is controlled by a rastering device opérable to causethe laser beam to sweep across said emissive surface of said cathode.
5. 5. A thermionic electric converter as set forth in Claim 4, wherein saidrastering device is opérable to cause the laser beam to sweep across 20 substantially the entire emissive surface of said cathode. -28- 1 3276
6. 6. A thenmionic electric converter as set forth in Claim 2 wherein said cathode is positioned at a first side of said anode, and said cathodeenhancing laser is positioned at a second side of said anode opposite said first side.
7. 7. A thenmionic electric converter as set forth in Claim 6, wherein said anode 5 has an opening therein to allow a laser beam emanating from said cathodeenhancing laser to pass therethrough.
8. 8. A thermionic electric converter as set forth in Claim 7, wherein saidopening in said anode is located substantially in a center of said anode.
9. 9. A thermionic electric converter as set forth in Claim 7, wherein said targetlû structure further comprises an électron repulsion ring positioned in theopening in said anode, said électron repulsion ring having an openingtherethrough.
10. 10. A thermionic electric converter as set forth in Claim 9, wherein said électron repulsion ring is joined to said anode by an electrically insulating ring 15 positioned at an edge of said opening in said anode.
11. 11. A thermionic electric converter as set forth in Claim 10, wherein saidélectron repulsion ring Is operatively coupled to a source opérable to impose anégative charge on said électron repulsion ring. -29- 1 3276
12. 12. A thermionic electric converter as set forth in Claim 7 wherein said targetstructure further comprises a highly statically charged ring disposed at anouter periphery of said anode.
13. 13. A thermionic electric converter as set forth in Claim 12 wherein said 5 anode and said highly statically charged ring are joined together via an inner insulating ring, and wherein said highly statically charged ring has an outerinsulating ring adapted to mount said target structure inside said casing member.
14. 14. A thermionic electric converter as set forth in Claim 1, wherein said 10 cathode emitter comprises a wire grid having wires going in at least two directions that are transverse to each other.
15. 15. A thermionic electric converter as set forth in Claim 1, wherein said anodeis a substantially planar plate anode.
16. 16. A thermionic electric converter as set forth in Claim 1, further comprising 15 an électron interférence laser opérable to hit électrons between the cathode and anode.
17. 17. A thermionic electric converter as set forth in Claim 2, further comprisingan électron interférence laser opérable to hit électrons between the cathode and anode. -30- vn 1 3276
18. 18. A thermionic electric converter as set forth in Claim 1 further comprising atleast one electret positioned within said casing member and being opérable toscavenge stray électrons présent within said casing member.
19. 19. A thermionic electric converter comprising:a casing member; a cathode within said casing member having a cathode emitter opérable,when heated, to serve as a source of électrons, a target structure within the casing member comprising an anodeopérable to reçoive électrons emitted from the cathode emitter; a cathode enhancing laser positioned to direct a laser beam to strike an 10 emissive surface of said cathode emitter; and a contrôler opérable to rester said laser beam across said emissive surface of said cathode emitter.
20. 20. A thermionic electric converter as set forth in Claim 19, wherein said cathode and said cathode enhancing laser are positioned on opposite sides of 15 said target structure, and wherein said anode has an opening therein to allow a laser beamemanating from said cathode enhancing laser to pass therethrough; and wherein said target structure further comprises an électron repulsion ringpositioned at said opening in said anode, and a highly statically charged ring 20 extending around an outer periphery of said anode, opérable to aid inattracting électrons in said casing member toward said anode. -31- ' 13276
21. 21. A thermionic electric converter as set forth in Claim 20, further comprisingan électron interférence laser opérable to hit électrons between the cathode and anode. -32-