US3275923A

US3275923A - Thermionic converters

Info

Publication number: US3275923A
Application number: US462384A
Authority: US
Inventors: Robert L Laing; Carol D Feemster
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-06-08
Filing date: 1965-06-08
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27

Description

Sept. 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERS 4 Sheets-Sheet 1 Filed June e, 1965 Sept. 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERS Filed lJun@ e, 1965 4 Sheets-Sheet 2 L, l l J wwf N www i m r. mi@ A T Sept 27, 1966 R. L. LAING ETAL THERMIONIC CONVERTERS Filed June 8, 1965 4 Sheets-Sheet 3 Sept. 27, 1966 R. l.. LAlNG ETAL 3,275,923

THERMIONIC CONVERTEBS Filed June 8, 1965 4 Sheets-Sheet 4.

MAXIMUM POWER POINT 165 SPACE CHG. LIMITED CURRENT INVENTORS 20322? L LAING,

622m J2 Fuws'zz MAX. POSSIBLE COLLECTOR CURRENT I I l 25 5o 75 loo BY MAX. POSSIBLE COLLECTOR VOLTAGE THERMIONIC GENERATOR COLLECTOR VOLTAGE VS LOAD CURRENT United States Patent Gfiice 3,275,923- Patented Sept. 27, 1966 3,275,923 THERMIONIC CONVERTERS Robert L. Laing, 3527 Aquila Ave. S., St. Louis Park, Minn., and Carol D. Feemster, 444 W. Duarte Road, Apt. E-3, Arcadia, Calif.

Filed June 8, 1965, Ser. No. 462,384 19 Claims. (Cl. 322-2) This application is a continuation-impart of 'our prior application, Serial No. 222,426, filed September l0, 1962, now abandoned.

The present invention relates to thermionic converters in Iwhich heat energy is converted into electrical energy, the heat energy being applied to thermionic 'cathodes or electron emissive elements. The electrons emitted are collected on a second surface, termed a collector, producing a negative voltage on this second surface. If a load is connected between the collector and the thermionic cathode, an electron current will flow through the load producing usable electrical energy.

The present invention is specifically concerned with an improved form of such ya thermionic converter. It is obvious that if heat is applied to a thermionic cathode, there is some tendency for the heat to be transferred to the collector with the resultant loss of efficiency, particularly if the collector is in close proximity to the cathode, as is the common practice with previous thermionic converters. This heat transfer may occur by reason of radiation or by conduction through any plasma present in the tube. One of the objects of our invention is to reduce su-ch heat transfer. Broadly, this is accomplished by employing an accelerating anode between the thermionic cathode and the collector for the purpose of drawing the electrons a relatively long distance away from the cathode, thus making it possible to have a substantial spacing between the collector and the electron emissive surface. Such increase in spacing tends to reduce any heat loss by reason of radiation from the thermionic emissive surface to the collector.

Because yof the presence of the accelerating anode in our device, the space charge adjacent to the electron emissive surface is reduced and therefore the device is maintained at a high vacuum. Hence, Iit becomes unnecessary to use an ionizing gas such as is often used in present thermionic converters. Such ionizing gas, `in many cases, may be quite corrosive, ce-sium being one example. The elimination of the ionizing gas not only eliminates the corrosive effect but also reduces the heat loss through the plasma.

It is also an object of your invention to provide a thermionic converter in which the electrons travel in a generally linear path in moving between the electron emissive surface and the 'collector surface. It has been proposed inthe prior art to use thermionic converters of the crossed field type in which there is magnetic field which is parallel to the surface of the electron emissive surface and which bends the electron projectory into a cycloidal or trochoidal path. In our converter, an accelerating anode has an aperture therethrough, through which the beam of electrons passes. Where a magnetic field is employed, this magnetic field is employed for focusing purposes in- -stead of for deflecting the beam.

A further very important feature of our invention is the fact that a hollow collect-or is preferably employed. This hollow collector is comparable to the hollow collector of a Van de Graaff generator. As has been demonstrated in connection with Van de Graaff generators, the interior of such a hollow collector is at a substantially Iuniform potential at all points therein. The electrons injected into t-he hollow collector will go to the surface of the collector due to their mutual repulsion. This has the advantage that the electrons ejected into the collector tend to reach the surface Iof the collector so a-s to be collected in the load circuit, rather than being repelled away from the collector surface due to the negative potential thereof. Thus the usual power output is greatly increased. This also makes possible the attainment of much higher collect-or potentials than has hitherto been possible.

Because of the fact that the need for an ionizing gas is eliminated `and due to the much greater spacing between the electron emissive surface and the collector, it becomes unnecessary to use any means for cooling the collector as has been done in connection with previous thermionic converters. This further increases the efiiciency of our device.

Referring to the drawings,

FIGURE 1 is a sectional view of one form of our thermionic converter in which an electromagnet is employed to produce a parallel electron flow into a hollow collector and in which the heat source of the cathode is a flame;

FIGURE 2 is a partial view showing a modification of the thermionic converter of FIGURE 1;

FIGURE 3 is a form of a thermionic converter employing an electron gun in combination with a permanent focusing magnet for `directing the beam of electrons into a hollow collector, the disposition of the electrodes being similar to that of a Pierce type gun `and again with the heat source of the cathode being a fiame;

FIGURE 4 is a sectional view of another form of our thermionic converter in which, for :purposes of illustration, the electron emissive surface is heated by a coil through which hot gases flow;

FIGURE 5 is a view similar t-o that of FIGURE 4, but in which the section is taken at right angles to the plane of section of FIGURE 4;

FIGURE 6 is a view yof a further modification of our gun in which the electron emissive surface is also shown for purposes of illustration as being heated by radioactive material;

FIGURE 7 is a partial view of a modification of the collector in which pointed projections within the collector .alter the voltage gradient within the collector; and

FIGURE 8 is a chart showing the relationship between the current through the load and the collector voltage as the load resistance i-s increased.

Referring specifically to FIGURE 1, our thermionic converter is housed within an envelope including a cylindrical neck portion 11 and a hollow spherical collector port-ion 12. The neck portion 11 houses the elements of the electron gun including a cathode assembly having a thermionic emissive cathode surface 13, a control grid 14, an accelerating anode 15, and an electrostatic electrode 16. An electromagnet 17 surrounds the neck portion 11 and serves to concentrate the electron beam as will be presently described. A collector 12 is shown in FIGURE l, as comprising an outer portion 19 of glass or similar nonconductive material, to the interior of which is applied a coating 20 of suitable conductive material such as metal. The collector portion 12 and neck portion 11 may be either integral with each other, as shown, or joined to each other by any conventional method providing a vacuum-tight seal therebetween.

Referring more specifically to the elements of the gun, the cathode assembly is in the form of an inverted cylindrical cup 22. The cathode may be formed of nickel with the upper electron emissive surface 13 coated with equimolar proportions of barium and strontium oxides. It is, of course, understood that any of various other electron emissive surfaces may be employed. The cylindrical cup member 22 of the cathode 13 is supported in -a disc 23 of ceramic or other suitable material and suitable vacuum-tight seals are provided between the cylinder 22, the disc 23, and the neck portion 11 of our converter. The entire assemblage including the neck portion 11 yand the collector are evacuated to a vacuum of -10 to 10-6 torr. This p-ressure may be held by means of a pump or -by the use of a suitable getter within the envelope.

The electron emissive surface 13, which in the particular example shown may have a diameter from 1 to 5 centimeters, is shown as heated by a iiame 25 issuing from a burner 26. It is to be understood that the flame 25 represents a source of heat which is to be converted into electrical energy. Any of various sources of such heat may be employed and in some of the other modifications, we have shown other sources of heat. It is to be understood that the invention is not limited to any particular source of heat, and that in connection with any of the modifications, different sources of heat may be employed.

The control grid 14, in the particular example illustrated, is located about .060E inch above the cathode surface 13. This control grid has an aperture 27 therethrough, which aperture may have a diameter of from .5 to 2.5 centimeters. The aperture 27 is located concentrically with respect to the beam 28 of electrons emitted by the cathode surface 13.

The accelerating anode is shown in the form of a cylinder having an inside diameter slightly less than the aperture 27 of the control grid. This accelerating anode may be located from about one-fourth to two inches above the control grid 14.

The electrostatic electrode 16 acts to modify the field between the anode and collector to reduce the tendency of the electrons to return to the anode and thus increases electron flow into the collector 12. The electrode 16 also aids in focusing the electron beam. This electrode 16 may be located concentrically around the accelerating anode, 4as shown, or about .080 inch above it. As shown, the electrostatic electrode 16 surrounds the upper end of anode 15, being insulated therefrom by an annular memfber 30' of ceramic or other suitable material. The electrostatic electrode 16, located slightly above the anode 15, may have an interior diameter only slightly larger than the interior diameter of the anode 15.

The control grid 14, the anode 15 and the electrostatic electrode 16 may be made of molybdenum, 304r stainless steel or any other suitable high melting point, low gas emitting conductive material. The material forming the coating may be copper, gold or other similar material having relatively low secondary emission.

During the construction of the tube, the entire assembly is baked at 300 to 450 C. while being vacuum pumped to drive the gases out of the various parts. The cathodes may be initially coated with barium and strontium carbonatos in a nitrocellulose binder and the cathode is heated to about ll50 C. to convert these to the barium and strontium oxides referred to previously. While not shown, the entire envelope may be immersed in transformer oil to prevent external arcing of the electrode feed-throughs and to remove heat from any local hot areas.

Referring speciiically to the electrical connections, the

cathode assembly 22 is connected to a suitable ground connection 32. Connected between the control grid 14 and the cathode assembly 22 is a suitable source 33 of control vol-tage wh-ich is connected across a resistor 34, which in turn is connected between the cathode 13 and the accelerating grid 14. The source 33 of control voltage may provide any of various types of voltages such as an alternating voltage to modulate the beam 28 to produce an alternating component lin the output volt- `age. Thus, the control voltage may vary, for example, between ninety volts negative and thirty volts positive so as to turn the beam of electrons 28 on and off alternately. It is to be understood, however, the control voltage may be merely a voltage of any desired magnitude 4 to introduce a control effect in accordance with a desired condition. It is to be understood, of course, that the control voltage is not necessary in many applications of our device.

The anode 15 has the function of pulling the electrons away from the cathode and has a relatively high voltage applied thereto. In a typical case, the voltage applied to the anode 15 may be from 5 to 10 kilovolts. While it is to be understood that any suitable source of voltage capable of generating voltages of this magnitude may be employed between the anode 15 and the cathode, we have shown a rbattery 35 for this purpose. It is understood, however, that the battery is intended to be merely illustrative of a suitable power supply.

The electrostatic electrode 16 is maintained at a po tential somewhat negative with respect to the cathode. This potential should preferably be selected to provide for the maximum ratio of collector current and anode current. For purposes of illustration, we have shown a battery 36 for applying this potential.

A further battery 37 is shown as connected across the terminals of the electromagnet winding 17. This battery is selected to have a voltage output of a magnitude to produce a current to the electromagnet winding sufficient to produce the desired focusing of the beam 28. A field of 600 to 1200 gauss is typical of that employed. The magnitude of this voltage, of course, depends upon the nature of the electromagnet 17 The -overall operation of our thermionic converter, as `shown in FIGURE 1, Will now be described. The source of heat to be converted into electricity, such as fla-me 25, is effective to heat the electron emissive surface of cathode 13 thus causing a stream of e'lectrons to issue therefrom. The stream of electrons is focused by the electromagnet 1-7 so as to cause it to pass through the opening 27 in grid 14 Where the stream is affected by the voltage produced by the source 33 of control voltage where such a control voltage is employed. Where it is not employed, resistor 34 provides a grid return to maintain 4the grid 14 :at a desired voltage. The beam 28 is held in a concen- -trated stream by the magnetic field produced by electro'- magnet `17 so as to cause it to pass through the opening in accelerating electrode 15 to which the beam is accelerated as the result of thevrelatively high vo'l-tage applied to .the accelerating anode 15. By sufficiently concentrating the beam 28 of electrons and by applying a sufficiently high voltage to anode [15, the acceleration of the electrons will be sufficiently high to cause substantially `all of them to pass through the anode 15 so as to cause negligible drain on the anode power source, shown as battery 35. lDue to the electrostatic electrode 16, which as previously explained, is maintained ata negative potential with respect to the cathode, the iield between the anode and collector is modified so as t-o reduce the tendency of the electrons to return to the anode 15. If it were not for this electrode, there would be a high positive field in this region and the electrons would have difficulty in passing through this field. Partially because of this electrode 16, most of the electrons tend to enter the collector. The potential at which electrode I16 is maintained is, as previously pointed out, selected 4to provide the maximum ratio of collector current to anode current.

When the electrons enter the collector 12, they are no longer under the effect of the field focusing electromagnet I17, and are free to move apart due to their mutual repulsion. Since the potential within the spherical collector l1-2 is substantially equal throughout, the electrons will be moved substantially uniformly to the interior conductive coating 20 of the collector. This movement of the electrons takes place despite the negative potential on the interior conductive coating for several reasons. In the firs-t place, as pointed out above, the electrons, once they enter the ho'llow collector 12, are mutually repelled from each other. They hence tend .to force themselvesapart causing them to accelerate and thus acquiring additional velocity. This additional velocity enables the electrons to move into engagement with the conductive surface 20 vdespite its negative potential. Furthermore, due to the presence of the load circuit, including load 38 (presently to be referred to), the electrons are removed from the collector throu-gh the load. The load 38 is connected between the conductive coating of the collector and the cathode to form a utilization circuit so that, as mentioned above, as the electrons collect -on the conductive surface 20 of the cathode 12, they flow through this utilization circuit back to the cathode. This current flow through load 38 results in a useful electrical output. Due to the construction of our device, very substantial voltages may be produced between the collector 12 and the cathode 13. In actual experimental work, voltages as high as minus 18 volts have Ibeen obtained on the collector 12 when the load 38 was connected, and voltages as high as minus 180` volts when the load circuit was disconnected. It is obviously very desirable to have an appreciable vol-tage between the collector 12 and the cathode |13 since such voltages are of greater utility than the relatively low voltages of present thermionic converters.

Modification of FIGURE 2 In the modifie-ation of FIGURE 2, the thermionic converter is basically the same as that of FIGURE l except for the Iaddition of two pre-accelerator electrodes.

In FIGURE 2, only the gun portion of the thermionic converter has been shown since the collector is exactly the same as in FIGURE 1. Except for the pre-accelerator electrodes, the same reference characters have been applied as in FIGURE 1 to facilitate a comparison of the two figures. The two pre-accelerator electrodes are designated 4by the reference numerals 401 and 41. These electrodes are spaced be-tween the lgrid 14 .and the accelerator anode 15. Electrode 40 is provided with an aperture 42 and electrode 41 with an aperture 43. These apertures 42 and 43 are substantially the same in diameter as the aperture 27 of grid 14 and are coaxial with respect to .the stream 28 of electrons. Electrodes 40 and 41 are connected to taps 44 and 45 of the voltage source 35 for applying a voltage to the accelerator anode '15. The taps 44 and 45 are so selected that the voltage between the cathode 13 and the pre-accelerator electrode 40 is approximately equal to that between pre-accelerator electrodes 40 and 41 and between pre-accelerator electrode 41 and yanode '15.

The effect of the pre-accelerator electrodes 40` and 41 is to cause a gradual increase in acceleration of the bea-m of elec-trous 28 so that the stream of electrons is reaching a more parallel path when it passes through the opening in accelerating anode 15.

Modification of FIGURE 3 In the thermionic converter of FIGURE 3, we have employed a gun construction in which the electrodes are arranged in a manner similar to that in the Pierce type gun. The inverted cup-shaped cathode assembly designated in this ligure by the reference numeral 504 is provided with an electron emissive surface or layer 51 which, by way of example, may be sintered tungsten impregnated with lbarium and strontium oxide, commonly referred to as a Phillips or L-type cathode. Any of various other common electron emissive surfaces or layers may be employed. As shown in the drawing, the cathode is flat on top but this cathode may have a concave spherical shape or other concave shapes, the emissive surface having a diameter from one to ten centimeters. As pointed out, the emissive surface 51 is shown as iiat in FIGURE 3 and in this case, it is surrounded by a focusing electrode 53 suitably insulated by an insulating spacer 52 from the cathode 50. The focusing electrode is conical and the surfaces thereof form an angle of about 67.5 with respect to the beam axis. If the cathode 51 has a `spherical surface, the focusing electrode is` a continuation of the cir- 6 cumference of the spherical surface. The focusing electrode 53 may tbe electrically connected with the cathode `50 and at the same potential as the cathode. On the other hand, where it is insulated therefrom, as shown, it may be maintained at a somewhat negative potential with re- -spect to the cathode by a suitable source of .power supply such as battery 54. The lfocusing electrode 53 is shown as sealed to the tubular neck 55 of the gun, this seal being of any well known type which maintains a vacuum type seal between the focusing electrode 53 and the neck 55. The neck 55 is of suitable insulating material such as glass or ceramic. Located above the cathode is an accelerating anode 56 which has a function similar to that of accelerating anode 15 of the species of FIGURES 1 Iand 2. In one particular embodiment of our invention, the accelerating anode may be located at a distance of from .060 to .500 inch above the cathode. This accelerating anode is 4shown as having an aperture 57 concentric to the beam of electrons, which aperture is slightly less in the diameter than the diameter of the cathode. The `anode 56 is maintained by a suitable source of voltage 59 -at a potential which may range from about 1000 to 10,000 volts. Secured to the tubular neck 55 of the gun is a collector 60. In this particular case, the collector `is shown as being formed of metal, it being understood that in any of the embodiments it is possible to employ either a metal collector such as collector 60 or an envelope of insulating material such as envelope 19 having a conductive coating 20 therein, as illustrated in connection with FIGURE 1. The collector 60` has an aperture 6\1 therein, which `is slightly larger than the aperture 57 of the anode 56. In this particular embodiment, the aperture 611 is in a re-entrant frusto-conical flange 62 wlhich acts to .trap the electrons after they have passed through the collector aperture 61.

In FIGURE 3, we have shown a permanent magnet 63 as being employed to magnetically focus the beam. The magnet 63 is shown in section. This magnet comprises two generally U-shaped portions at their upper and lower extremities. At its upper extremity, the legs 64 abut along the line 65. The legs 64 are shown in dotted lines in the yligure and join the main portions of the magnets 63 along a diagonal line 66 conforming generally to the contour of the collector 60. It is to be understood that there are two such similar legs 64 for each ha'lf of the magnet and that these legs surround the collector 60. At their lower end, each section of the magnet 63 is provided with a pair of legs 67 which abut along the line 68 and which closely surround the neck portion 55 of the gun. The effect -of the ma-gnet 63 is to focus the beam of electron-s and to closely confine the same so that it passes through the aperture 57 of the anode 56 vand the opening 6:1 of Ithe collector 60 without appreciable spreading of the beam and thus without any substantial losses due to anode current. It is to be understood that in place of a yoke type magnet such .as magnet 63, it is possible to employ a hollow cylindrical magnet with a magnetic field direction parallel to the axis of the electron beam. It is also contemplated that the electron 'beam could be foculsed by electrostatic fields only, in which case no magnet need -be employed.

The collector 60 which may be 1 to 10 inches in diameter, in the particular embodiment being discussed, is sealed in a suitable manner to the neck portion 55 to form a vacuum type seal therewith. The entire unit including collector 60 and neck 55 is highly evacuated as in the case of the thermionic converter of FIGURES 1 and 2.

The cathode 50 is shown as bein-g heated by the flame 70 of a burner 71, this being merely one particular way of heating the cathode as was pointed out above.

In connection with the modification of FIGURE 3, a suitable load 7B is connected between the collector 60l and aground connection 74 which in turn is connected to the cathode 50.

The operation of the gun of FIGURE 3, as far as its broad function of converting thermal energy to electrical energy is generally similar to that of the modications of FIGURES 1 and 2. This beam of electrons emitted from cathode 51 is focused by the focusing electrode 53 and by the magnet 63 so that the beam of electr-ons enters the interior of hollow collector 60 in which the electrons are repelled from one another` to engage the surface of the collector 60. Due to the spherical nature of the collector, these electrons are repelled to the surface of collector 60, despite the high negative charge produced thereon, and flow through the load device 73 back to the cathode 50. In this way, the thermal energy of the llame 70 is converted into electrical energy.

Modification of FIGURES 4 and 5 The thermionic converter of FIGURES 4 and 5 is similar in electrode disposition to the so-called Hiel gun. This gun is provided with a concave cathode member 76 provided with a suitable electr-on emissive coating on the upper face thereof. An electrostatic focusing electrode 77 has an interior spherically concave surface which forms `a continuation of the concave electron emissive surface of cathode 76. Electrostatic focusing electrode 77 is sealed to the cathode 76 by an insulating annular ring 78 which Iforms an inwardly extending collar of an insulating sleeve 79. The collar 78 is sealed to the cathode 76 and the electrostatic focusing electrode 77 in a suitable vacuum type manner. The sleeve 79 for-ms a chamber around the under surface of cathode 76 and this cathode may be suitably heated in any desired manner. We have showna coil 80 having an inlet 81 and an outlet y82 and a plurality of coil turns 83 through which a hot fluid may be circulated. For example, this may be hot exhaust gas which it is desired to convert into useful electrical energy. Instead of employing a coil 80, the lower end of the cylindrical chamber 79 may be sealed and the hot gas may ybe simply passed through this chamber coming -in contact with the under surface of cathode 76. It is, of course, to be understood that any other means may be employed for heating the cathode 76 by a suitable source of heat which it is desired to convert into electrical energy Located above the electrostatic electrode 77 is an anode 90 having an interior spherical surface which is shaped to constitute a continuation of the spherical surface of electrostatic electrode 77. The anode 90 is sealed to the electrostatic electr-ode 77 by an annular member 91 of dielectric material. Interposed between the anode 90 and a spherical collector 92 is an insulating ring 93 which is curved so as to form a curved entrance throat to the collector 92. It is understood, of course, that the ring 93 of dielectric material is suitably sealed in a vacuum type'manner to the accelerating anode 90 yand to the collector 92. We have shown sweep coils 94 and 95 as disposed at right angles to the axis of the beam of electrons. These sweep coils are connected to a suitable source of alternating voltage 96.

A voltage which may vary from zero to 50 volts negative is applied between the electrostatic electrode 77 and the cathode 76 by a suitable source of voltage 98. A relatively high voltage which may range from 10,000 to 100,000 volts positive is maintained between the anode 90 and the cathode 76 by a suitable source of voltage 99.

In the operation of the modification of FIGURES 4 and 5, the electron beam emitted lby the electron emis` sive surface of anode 76 is caused to converge due to the concave spherical surface of thecathode 76 so that it passes through the anode 90 as a relatively narrow beam. The focusing of this beam is aided by the electrostatic focusing electrode 77 which is maintained lat a negative potential for this purpose. Upon entering the collector 92, the electrons are mutually repelled to engage the interior conducting surface of the collector 92. The electrons can then pass from the collector 92 through 8 a suitable load device back to the cathode 76, thus causing a current ilow through the load 100.

Referring for the moment to FIGURE 5, it will be noted that the coils 94 and 95 (only coil 95 being shown in FIGURE 5) and the polarity of the current therethrough are in such a direction that the magnetic field produced thereby tends to cause the electr-ons to be dellected to one side of the collector 92. Due to the alternating current applied to electron coils 94 and 95, this effect is periodically reversed so that the beam of electrons yare swept from side to side within the hollow collector 92 to aid `in dispersing the electrons throughout the interior surface of collector 92. Instead of coils such as coils 94 and 95, electrostatic deflection plates can be similarily employed and in this case an alternating source of voltage will be applied to these plates. The feature of the deflection means, such as that provided by coils 94 and 95, is an optional feature which may be employed where it is desired to secure even better distribution of the electrons over the inner surface of collector 92 than is possible without such a sweep means. It is to be understood that an arrangement such as coils 94 and 95 may be employed with other embodiments of the invention.

Modification of FIGURE 6 In FIGURE 6, we have shown a modification in which a very high current, high beam intensity gun is employed in which the electrons expand after leaving the anode land in which a magnet is employed to cause the beam of electrons to reconverge.

Referring specifically to the drawing, the electron emissive surface is indicated by the reference numeral 105. It will be noted that this surface is spherically concave and it will be understood that it is coated with a suitable electron emissive material. The electron emissive surface is supported by a chamberlike cathode structure 106 having a hollow interior for the reception of radioactive material 107 for heating the electron emissive surface 105. It is to be understood, of course, that any other suitable means may be employed for heating the cathode by any source of heat which it is desired to convert into electricity. The cathode structure 106 is provided with a closure member 108 for the insertion of the radioactive material. This closure may be of heat insulating material and where radioactive material is employed, the closure and the cathode structure 106 would be covered by material acting as a barrier to the transmission of radioactivity. Where a source of heat, such as a flame, is employed, it will be understood that the cover member 108 would be omitted or would beprovided with an opening for the reception of a burner member.

Surrounding the electron emissive surface 105 is an annular focusing electrode 110 which has a spherically concave inner surface which constitutes a continuation of the spherically concave electron emissive surface 105. This annular focusing electrode 110, which is shown as being at cathode potential, serves to concentrate the electrons leaving the electron emissive surface 105.

Secured to the cathode structure 106 but spaced therefrom by an insulating annular member 112 is an anode structure 113 comprising a disc member 114 at the lower end thereof which disc member has a passage 115 therethrough, through which the electron beam passes. The opening 115 is preferably slightly smaller in diameter than that of the electron emissive surface 105. Upon passing into the interior of the anode structure 113, the electrons in the beam 117 drift apart as shown in the drawing. In order to reconverge these electrons, a cylindrical magnet 118 surrounds the upper portion of the anode structure. This magnet is provided with a magnetic field the direction of which is parallel to the axis of the electron beam and serves to cause the beam to reconverge in the manner shown. The anode structure 113 has an annular flange 120 at the upper end thereof terminating in a downwardly turned flange 121 which is sealed by a suitable sealing and insulating seal 122 t-o a cylindrical casing 123 constituting the collector of our device. This chamber 123 may be formed of metal or other suitable conductive material. It will be, of course, understood that the chamber 123 may likewise be formed of nonconductive material with an interior conductive coating, as shown in lconnection with FIGURES l and 2. Secured within the lower por-tion of the cylindrical chamber 123 is a post-accelerator electrode 125 having an opening 126 therethrough, this opening being bounded by a flanged portion surrounding the opening. As will be explained, this post-accelerator electrode 125 is maintained at a somewhat higher potential than the anode structure 113. The electron stream, while passing through the opening 126, is thus further accelerated as it is converging due to the action of magnet 118. The electrode 125 is provided with a lead-in terminal member 128 suitably sealed within and insulated from the wall of the cylindrical chamber 123.

Supported above the post-accelerator electrode 125 is a decelerating electrode 130 having an aperture 131 therethrough which is concentric with aperture 126 and slightly larger. The decelerating electrode 130 is secured to a lead-in terminal 132 which extends through the Wall of chamber 123 and is suitably sealed and insulated therefrom. The decelerating electrode 130 is maintained at a lower potential than anode 113 and the post-accelerator electrode 125 and serves to reduce the positive field that would otherwise be present due vto the anode 113 and the post-accelerator electrode 125.

Secured above the decelerating electrode 130 is a still further electrode 135 which functions as a pusher electrode. This electrode has an aperture 136 therethrough which aperture may be slightly concial with the wider part of the aperture at the upper surface of the electrode. This aperture 136 is preferably somewhat larger than the aperture 131. The electrode 136 is secured to a lead-in terminal 138 extending through and sealed in an insulating manner from the wall of chamber 123. This pusher electrode 135 is connected so as to be negative with respect to the cathode and acts to repel the electrons into the collector 123 to facilitate the electrons moving to the interior of the cylindrical wall of chamber 123. Secured to the upper end of the collector 123 is an exhaust conduit 140 to which is connected an electronic ion pump 141. This pump includes a magnet 142 and the pump and magnet are shielded by a casing 143 of magnetic material so that the action of the beam 117 of electrons will not be interfered with.

A predetermined relatively high potential is maintained between the anode structure 113 and the cathode structure 106 by a suitable source of voltage `such as a battery 145'. This voltage may be of a magnitude from one to ten thousand volts. Connected in series with battery 145 is a further battery 146 to maintain the positive potential between the post-accelerator electrode 125 and the anode structure 113, the lead-in terminal 128 -of post-accelerator electrode 125 Abeing connected to the positive terminal of battery 146, the negative terminal yof which is connected to the positive terminal of battery 145. The decelerating electrode 130 is connected through lead-in terminal 132 and conductor y148` to an intermediate tap 149 of battery 145. This intermediate tap 149 is at a potential substantially lower than the anode potential 113 and acts so that the decelerating electrode 130 is maintained at a much lower potential than anode structure 113 and at a still lower potential than that at which the postaccelerator electrode 125 is maintained The pusher electrode 135 is connected through its lead-in terminal 138` and a conductor 149 to the negative terminal of a suitable source of power supply, such as battery 150, the positive terminal of which is connected to the cathode structure 106. The pusher electrode is thus -maintained at a potential negative with respect to the cathode structure, as poined out previously.

A suitable load 151 has its upper or negative terminal connected through a conduct-or 152 to the wall of cylindrical chamber 123, which as previously pointed out, acts as the collector. The lower positive terminal of resistor 151 is connected to ground at 153, this ground connection being in turn connected to the cathode structure 106. A further power supply, shown in the form of a battery 154, is connected between the wall of the collector 123 and the terminal 156 of the lion pump. The purpose of this power supply 154 is to provide a source of energy for operation of the ion pump.

Referring now to the operation of FIGURE 6, the beam of electrons produced bythe electron emissive surface is focused lby the annular focusing electrode 110 and passes through the aperture of anode disc 114, being accelerated as they approach the anode disc. The beam of electrons then enters the drift chamber Within the cylindrical anode structure 113 and due to the mutual repulsion between the electrons diverges outwardly until it reaches the area in which the eld of magnet 118 is effective. Thereafter, the beam begins to converge until it reaches a point above the aperture 126 of the postaccelerator electrode 125. The distance between this point at which the beam is again fully converged from the point of maximum divergence of the beam 117 is substantially equal to the distance between the point of maximum divergence and the electron emissive surface 105.

As the beam of electrons approaches the opening 126 in the post-accelerator electrode 125, it is further accelerated so that it enters the aperture 131 of the decelerating electrode at a relatively high speed. Due to the fact that the decelerator electrode 130' is maintained at a potential substantially lower than the potential of anode 113 and even lower with respect to the post-accelerator electrode 125, the positive field which would otherwise exist in this area is reduced so as to tend to retard or substantially prevent the return of electrons to the postaccelerator anode 125 and the anode 113.

The beam Iof electrons then passes through the opening 136 of the pusher electrode 135 which, as previously pointed out, is maintained at a potential negative with respect to the cathode 105. The effect of this electrode is to repel the electrons so as to force them into the interior of the collector chamber 123 ywhere they move rapidly apart. Due to the effect of the pusher electrode and to the mutual repulsion of the electrons, these electrons move apart and engage a major portion of the interior wall of the cylindrical chamber 123 above the pusher electrode 135. These electrons, as they engage the interior of this wall are drawn off through the load 151 back to the cathode 106.

The function of the ion pump 141 is to draw off any ions that may be formed in the converter construction so as to maintain the entire structure at a very high vacuum to an even greater extent than is possible with the use of getter material. It is to be understood that an ion pump such as ion pump 141 may be employed with any of the other modifications which we have shown where it is desired to maintain the apparatus at a very high vacuum.

Modification of FIGURE 7 The modification of FIGURE 7 shows an expedient which may be employed in connection with any of the collectors. In this case, the collector generally is designated yby the reference numeral 160. Located on the interior of the collector wall are a plurality of projections 161 which are spaced uniformly around the interior of the wall in a circular row. These projections act as pickup probes, tending to attract the electrons to them and thus reducing the field gradient adjacent the aperture of lthe collector. This helps to insure collection of the electrons on the interior wall of the collector 160 and to aid in the movement of the electrons to the interior of the FIGURE 8 shows the chart illustrating the relationship between the percentage of maximum possible collector current and maximum possible collector voltage. It will be noted that as the collector voltage is increased to its maximum value, the maximum possible collector current remains substantially constant up to a point 165 identiiied yby the legend Maximum Power Point. Thereafter, as the collector voltage is increased, the collector current decreases since the value thereof is limited Iby the space charge. When the collector voltage reaches its maximum possible value, the current will be substantially zero. It is to be understood that the current depicted is somewhat schematic and will vary with different types of converter structures. Generally in all of the various versions of our device, the current due to the load limited voltage tends to remain relatively constant until the collector voltage reaches a predetermined point at which it begins to fall `E as the collector voltage increases.

It will be obvious from the diagram of FIGURE S that where one desires the maximum power output, the load 151 should be so selected that the lsystem operates at approximately the point indicated by numeral 165. It is at this point that the collector voltage is at the maximum point possible without substantial reduction in the collector current.

Summary It will he seen that We have provided a thermionic converter in which the collector is substantially spaced from the electron emissive su-rface and in which it is unnecessary to employ any ionizing gases. As a result, much higher collector voltages may be used than have hitherto been possible. Furthermore, it is possible to obtain a relatively high degree of efficiency.

While We have shown various methods of heating the electron emissive surface of the cathode, it is to be understood that these have been fo-r illustrative purposes only and that the electron emissive surface may be heated by any source of heat which it is desired to convert into electricity.

While we have shown several types of guns for producing a stream of electrons, it is to be understood that other suitable types of guns may be employed.

It is also to -be understood that while We have shown batteries as the voltage sources, this is again merely for purposes of illustration. In actual practice, it would usually Ibe desirable to derive voltages from the voltage appearing across the load and apply these voltages to the various electrodes .so that no exterior power source would he necessary.

It is also to be understood that various features shown specifically in connection with one embodiment may be employed in connection with other embodiments. Thus, the beam may be electrostatically focused, it may be focused by an electromagnet as in FIGURES 1 and 2, by a yoke type magnet as in FIGURE 3, by an electrostatic electrode such as electrode 77 of FIGURE 4, or by an annular magnet such as magnet 118 of FIGURE 6.

Similarly, it is possible to employ a control voltage operating in connection with a control grid as in FIG- URES 1 and 2 but such a voltage need not be employed where no control of the electron beam in this manner is desirable.

Various expedients can be employed in vany of the modifications for more thoroughly distributing the electrons on the collector surface. Thus, sweep coils such as sweep coils 94 and 95 may be employed. Likewise, a pusher electrode such as electrode 135 of FIGURE 6 may be employed. Again, the probes of FIGURE 7 may be employed in connection with any of the modifications. Likewise, the anode voltage may be pulsed -t-o cause the electrons to be subjected to a pumping action.

1'2 In general, while we have shown certain' specific ernbodiments of our invention for purposes of illustration, it is to be understood that our invention is limited solely by the scope of the appended claims.

We claim as our invention:

1. A thermionic converter for converting heat energy to electrical energy comprising an enclosure including means for producing a beam of electrons including a thermionic cathode, adapted to be heated by a source of heat,

means for accelerating said beam of electrons comprising an anode having an aperture therethrough,

and a collector having a conductive surface within said enclosure,

a source of heat for heating said cathode and of a magnitude such that it constitutes the primary source of external energy applied to said converter,

means for applying a positive voltage between said anode and said cathode to accelerate the passage of said electrons through the aperture in said anode to cause said electrons to engage the conductive surface of said collector,

and means operative to withdraw the electrical energy from said generator resulting from the heat applied to said cathode,

said means including a utilization circuit connected between said collector and said cathode to withdraw the energy from the collector due to the electrons engaging the conductive surface thereof, said utilization circuit being free of any external electrical source of power.

2. A thermionic converter for converting heat energy to electrical energy comprising an enclosure including means for producing a beam of electrons including a thermionic cathode adapted to be heated -by a source of heat,

and a collector having an extended conductive surface within said enclosure which is much greater in area than the electron emissive surface of said cathode,

means for causing said beam of electrons to engage said extended conductive surface of said collector,

said means 'including a utilization circuit connected between said collector and said cathode to withdraw the energy from the collector due to the electrons being repelled from each other as they approach said collector and engage the extended conductive surface thereof, said utilization circuit being free of any external electrical source of power of the same order of 1magnitude of energy as that of said source o-f eat.

3. A thermionic converter for converting heat energy to electrical energy comprising an enclosure including means for producing a beam of electrons including a thermionic cathode adapted to be heated by a source of heat,

means for accelerating said beam of electrons,

and a collector hav-ing an extended conductive surface within said enclosure which is much greater in area than the electron emissive surface of said cathode,

a source of heat for heating said cathode and of a magnitude such that it constitutes the primary source of external energy applied t-o said converter,

means for applying a positive voltage between said accelerating means and said cathode to accelerate the passage of said electrons to cause said beam of electrons to engage said extended conductive sur- -face of said collector,

said means including a utilization circuit 4connected between said collector and said cathode to withdraw the energy from the collector due to the electrons being repelled from each other as they approach said collector and engage the extended conductive surface thereof, said utilizati-on circuit being free of any external electrical source of power of the same order of magnitude of energy as that of said source of heat.

4. A thermionic converter for converting heat energy to electrical energy comprising an enclosure including means for producing a beam `of electrons including a thermionic cathode adapted to be heated by a source of heat,

and a hollow collector having a conductive surface within said enclosure,

means for causing said beam of electrons to enter into said hollow collector,

said means including a utilization circuit connected between said collector and said cathode to withdraw the energy from the collector due to the electrons being repelled from each other within said collector and engaging the conductive surface thereof, said utilization circuit being `free of any external electrical source of power.

5. A thermionic converter for converting heat energy to electrical energy comprising an enclosure including means for producing a beam of electrons including a thermionic cathode adapted to be heated by a source of heat,

means for accelerating said beam of electrons,

and a hollow collector havin-g a conductive surface within said enclosure,

means for applying a positive voltage between said accelerating means and said cathode to accelerate the passage of said electrons to tend to cause said electrons to enter said hollow collector,

and means operative to withdraw the electrical energy from said converter resulting from the heat applied to said cathode,

said means including a utilization circuit connected between said collector and said cathode to withdraw the energy from the collector due to the electrons being repelled from each other with said collector and engaging the conductive surface thereof, said utilization circuit being free of any external electrical source of power of the same order of magnitude as that of said source of heat.

6. The thermionic converter of claim 2 in which electromagnetic means are employed for controlling and directing the beam of electrons.

7. The thermionic converter of claim 2 in which a permanent magnet is employed for controlling and directing the beam of electrons.

8. The thermionic converter of claim 2 in which an electrostatic focusing electrode is employed for focusing the beam of electrons.

9. The thermionic converter of claim 2 in which beam sweeping means are employed for dispersing the beam of electrons on the conductive surface of the collector.

10. The thermionic converter of claim 2 in which a control grid is provided to regulate the amount of beam current or to modulate the output voltage.

11. The thermionic converter of claim 1 yin which the interior of the collect-or has at least one pickup probe therein to facilitate collection of electrons.

12. The thermionic converter of claim 1 in which the electrons are allowed to diverge and are then reconverged by suitable focusing means so that they are substantially fully converged as they enter the collector region.

13. The thermionic converter of claim 5 in which an electrode is disposed adjacent to the entrance to the collector and is maintained at a volt-age negative with respect to the cathode to alter the positive eld produced by the accelerating means and hence to minimize the tendency of the electrons to return to the accelerating means.

14. The thermionic converter of claim 5 in which the cathode is designed to receive a burner for heating the cathode emissive surface thereof.

. 15. The thermionic converter of claim 5 in which the cathode is designed to retain radioactive material in heat transfer relation with the electron emissive surface of the cathode.

16. The thermionic converter of claim 5 in which the cathode is designed to have a hot fluid circulated in heat transfer relation with the electron emissive surface of the cathode.

17. The thermionic converter of claim 3 in which the accelerating means is an anode having an aperture therethrough through which the beam passes.

18. The thermionic converter of claim 5 in which the accelerating means is an anode and in which said anode and the hollow collector have aligned apertures through which the beam of electrons passes to enter the interior of said collector.

19. The thermionic converter of claim 18 in which there is at least one further electrode maintained at a diiferent potential than said anode for affecting the beam of electrons in a desired manner.

References Cited by the Examiner UNITED STATES PATENTS 2,907,908 10/ 1959 Bryan S13-84 2,915,652 12/1959 Hatsopulos et al. 310-4 2,953,706 9/ 1960 Gallet 310-4 JOHN F. COUCH, Primary Examiner. LLOYD MCCOLLUM, Examiner.

W. H. BEHA, Assistant Examiner.

Claims

1. A THERMIONIC CONVERTER FOR CONVERTING HEAT ENERGY TO ELECTRICAL ENERGY COMPRISING AN ENCLOSURE INCLUDING MEANS FOR PRODUCING A BEAM OF ELECTRONS INCLUDING A THERMIONIC CATHODE, ADAPTED TO BE HEATED BY A SOURCE OF HEAT, MEANS FOR ACCELERATING SAID BEAM OF ELECTRONS COMPRISING AN ANODE HAVING AN APERTURE THERETHROUGH, AND A COLLECTOR HAVING A CONDUCTIVE SURFACE WITHIN SAID ENCLOSURE, A SOURCE OF HEAT FOR HEATING SAID CATHODE AND OF A MAGNITUDE SUCH THAT IT CONSTITUTES THE PRIMARY SOURCE OF EXTERNAL ENERGY APPLIED TO SAID CONVERTER, MEANS FOR APPLYING A POSITIVE VOLTAGE BETWEEN SAID ANODE AND SAID CATHODE TO ACCELERATE THE PASSAGE OF SAID ELECTRONS THROUGH THE APERTURE IN SAID ANODE TO CAUSE SAID ELECTRONS TO ENGAGE THE CONDUCTIVE SURFACE OF SAID COLLECTOR, AND MEANS OPERATIVE TO WITHDRAW THE ELECTRICAL ENERGY FROM SAID GENERATOR RESULTING FROM THE HEAT APPLIED TO SAID CATHODE, SAID MEANS INCLUDING A UTILIZATION CIRCUIT CONNECTED BETWEEN SAID COLLECTOR AND SAID CATHODE TO WITHDRAW THE ENERGY FROM THE COLLECTOR DUE TO THE ELECTRONS ENGAGING THE CONDUCTIVE SURFACE THEREOF, SAID UTILIZATION CIRCUIT BEING FREE OF ANY EXTERNAL ELECTRICAL SOURCE OF POWER.