US2416315A - Electron discharge device - Google Patents

Description

Patented Feb. 25, 1 947 careers ELECTRON DISCHARGE DEVICE Paul L. Hartman, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application June 4, 1942, Serial No. 445,747

8 Claims. (Cl. 250-275) This invention relates to electron discharge devices and more particularly to such devices capable of generating a high power output in ultrahigh frequency systems.

In the usual high power discharge device, such as employed in transmitters for broadcasting and allied purposes, the power output is limited by space charge which is determined by cathode emission which in itself is governed by the heating current. Any attempt to increase the heating current to obtain higher emission necessarily accentuates the electrical and mechanical diiilculties in the device, such as electric and magnetic fields which complicate the electron trajectorles and a greater cathode area and a more involved heating source must be provided. Furthermore, the potential distribution of the heating source tends to lower the transconductance of the device. Some advantage in increased emission may be attained by employing a cathode of large area indirectly heated by conduction and radiation but such emission radiation is dependent on the heating radiator being large and operating at a temperature higher than the cathode emitter. This necessarily requires high current in the heating radiator.

These difficulties are overcome in accordance with this invention by heating the emission source or cathode by electron bombardment so that the heating source is of moderate current consuming character and interaction-between the source and emitter is substantially eliminated.

An object of this invention is to attain a high emission of electrons whereby higher output may be achieved in ultra-high frequency devices.

Another object of the invention is to eliminate end cooling effect in the electron emitting cathode.

A further object of the invention relates to the matching of the characteristic impedances of the device with a cooperating continuous coaxial circult having constant value over the whole length thereof.

These objects are attained, in accordance with this invention, in a high power electron discharge device operating in the ultra-high frequency range, said device having an external anode which forms part of the enclosing vessel, and the cooperating electrodes, such as a control electrode and an emission source, being mounted therein. The control electrode and emission source or cathode are concentrically arranged within the anode of the device and provided with integral flare ring portions which are sealed in the enclosing vessel and constitute coaxial conductors for applying suitable potentials to these electrodes.

A feature of this construction relates to the fabrication of the device wherein the cathode is provided with portions at opposite ends, of high thermal resistance, to reduce end cooling effect whereby uniform thermal conditions are maintained to increase the emissivity of the cathode.

A further feature relates to the provision of a primary emitting source within'the cathode structure to directly heat the cathode by electron bombardment to maintain the cathode at a high temperature for the copious emission of electrons in the discharge space of the device, the temperature of the primary emitter and the cathode being so chosen that excessive interaction between them is avoided.

Another feature relates to the construction of the cathode assembly to insure an efflcient emitter of composite layers intended to be self-activating whereby loss of activating material by normal diffusion during operation is renewed or replaced by adjacent environmental substances of the composite cathode. In this arrangement the cathode is formed of concentric layers or cylinders of carbon, thorium and tungsten or tantalum with a central spiral heater element within the composite structure. The intermediate thorium layer replenishes the thorium diffused from the outer cathode cylinder which supplies the electron emission to the discharge space and the inner carbon cylinder reactivates the heater element within the assembly. Furthermore, the

carbon cylinder maintains the cathode at a high emission temperature due to the bombardment thereof by the central heater.

Another feature of the invention relates to the utilization of the concentric disposition of the anode, cathode and control electrode rim conductors to directly connect a coaxial line thereto to form a unitary resonating amplifier or oscillator circuit having matched impedance and other electrical characteristics for eflicient operation in ultra-high frequency transmission systems.

In view of the high temperature involved in this power generating system, another feature of this construction is the provision of yieldable or expansion coupling members between the concentric conductors of the coaxial line and the related conductors of the electrodes of the device. A metallic bellows-type ring coupling member is connected through a capacitance to the adjacent termination of the coaxial line conductor and the electrode conductor to form an expansion joint to compensate for thermal differences between these elements in the assembly and also to isolate the cathode and anode from the control electrode in the resonator structure.

These and other features and advantages of the invention will be more clearly set forth in the following detailed specification and will be more apparent when considered with the accompanying drawing.

Fig. 1 shows in cross section one form of the invention in which the primary emitter is brought out through opposite ends of the device.

Fig. 2 illustrates another form of the invention, in cross section, in which all the connections project from one end of the device.

Fig. 3 is an enlarged view, partly broken away, of the composite cathode assembly which may be utilized in the structure of Figs. 1 and 2; and,

Fig. 4 shows a unitary assembly, partly in cross section, of the device of Fig. 2, coupled to a concentric line to form an eflicient amplifier circuit for high power ultra-high frequency communieating systems.

Referring to the drawing, one embodiment of the invention is shown in Fig. 1 in which the high power discharge device is formed of a cylindrical metallic anode portion l0, preferably of copper, having the opposite ends closed by vitreous cap portions II and ll, of borosilicate glass, and the anode is surrounded by an integral water jacket l3 provided with inlet and outlet ports M and I5, respectively, for the circulation of a cooling fluid therein to dissipate the heat energy generated in the external anode III of the device. A filamentary emitter I6, of tungsten or thoriated tungsten is centrally mounted along the axis of the device by leading-in conductors l1 sealed through the glass portions at opposite ends of the vessel, the filamentary emitter 16 being tensioned by a spring I8 at one end of the vessel adjacent the glass cap portion l2. The filamentary emitter adjacent the lower conductor l1 and the spring I8 at the opposite end is provided with elongated cup-shaped members I!) to form end shields so that the portions of the filamentary emitter within the cup shields are maintained at a uniform temperature by radiation from the inner surface of the shield so that end cooling effect is eliminated and the emitter is held at a uniform temperaturg throughout its length.

The filamentary emitter I6 is surrounded coaxially by a cathode cylinder 20, preferably of tungsten with a thoria coating applied thereto or thorium metal admixed in the cylindrical body portion thereof, the cathode cylinder being provided with an aperture adjacent the glass cap H to permit passage of the filament l6 and cup l9 while the opposite end is provided with a tapered outwardly extending wall 2|, which is sealed through the glass cap l2 to form an external ring conductor 22 extending radially from the glass cap portion l2 in a plane perpendicular to the axis of the device. The cathode shell is also provided with guard ring portions in the form of elongated slots 23 and 2d at opposite ends of the shell to form restricted or attenuated peripheral high resistance paths to reduce end cooling effect of the cathode shell, thereby maintaining the area of the cathode shell between the guard rings at a uniform temperature.

A control electrode 25 formed of a plurality of longitudinal wires surrounds the cathode shell 20, the wires being attached at one end to a cupshaped disc 26 having a central aperture which clears the cup shield 19 of the primary emitter filament l6 and the wires at the other end being attached to a metallic flared ring 21 having the cylindrical cathode 20, whereby the cathode 20 is heated to the required emission temperature, for the copious supply of electrons to the discharge space between the cathode and the anode by electron bombardment from the primary emitter I 6. This arrangement permits high temperature emission from the cylindrical cathode shell 20 by a heating source of moderate current consuming character, whereby maximum emissivity is attained in the cathode without expending enormous current in the heating radiator to obtain this result.

It is desirable to keep the ratio of the cathode cylinder diameter to primary emitter diameter from being too high, since if the filament becomes too small, then for even moderate voltages between it and the cathode cylinder, high fields are produced at its surface so that it operates as a temperature limited electron source and tends to be unstable when the two temperatures approach each other. This effect is produced by radiation from the primary emitter thereby raising the temperature of the cathode cylinder which then raises the temperature of the primary emitter and in turn more electrons are supplied with the result that the cathode temperature is raised and this cycle continues until the primary emitter becomes space charge limited. This effect may be overcome by operating the primary emitter at a much higher temperature than the cathode sleeve to prevent excessive interaction between them. Accordingly, if the primary emitter is formed of pure tungsten operating at approximately 2500 K. and the cathode sleeve is formed of thoriated tungsten or tantalum operating at a much lower temperature, interaction between them is easily controlled and reciprocal heating effect is avoided. In the event that tantalum is employed as the cathode sleeve, the flare portion 2| may be formed of copper or tungsten which will seal in the glass cap portion l2 of the device.

A modification of the invention is shown in Fig. 2 in which the external anode is formed of a tubular metallic portion 29 which is closed at one end and which merges at the other end into a reversely turned or spun portion 30. The turned edge of the latter portion is sealed to a glass cap portion 3!, which in combination with the anode forms a vacuum-tight container or vessel. The peripheral rim of the anode portion 30 is rigidly attached to a metallic ring member 32 to form a supporting surface for a water jacket to encase the anode of the device. The cathode cylinder 20 and the control electrode shown herein are substantially the same as described in connection with Fig. 1 except that these elements'extend into the tubular portion 29 of the external anode while the flare portions 2| and 21, respectively, are sealed radially through the wall of the glass cap portion 3|. Since the external anode 29 is closed at the lower end, the primary emitter conductors 33 and 34 may be sealed through the top of the glass cap portion 3! so that all the connections to the device are closely related at one end of the vessel. The primary emitter in this form of the invention consists of a spiral conductor 35 supported by a central standard 36 which extends along the axis of the cathode 20 and the terminations thereof form the external conductors 33 and 34 of the primary emitter. The cathode sleeve 20 is also provided with a carbon sleeve liner 3! to increase the temperature distribution in the cathode by the bombarding electrons striking it and also constitutes a source of carbonaceous vapor to reactivate the primary emitter 35 in which the active material is depletedby diffusion.

The cathode assembly shown in Fig. 3 is similar to the structure in Fig. 2 and may be substituted therefor or employed also in the device shown in Fig. 1. This view shows a composite assembly in which an intermediate layer 38, of conducting or semi-conducting material containing a thermionically active emitting substance, such as thorium or thorium and thorium oxide, is interposed between the carbon liner 3! and the cathode sleeve to form a reservoir to replenish active material diffused from the surface of the cathode 20, the carbon liner, reservoir layer and cathode sleeve lying in stratified relation in an outward direction from the internal'heater or primary emitter 35. This construction forms a substantially rigid and efficient composite assembly capable of emitting a copious supply of electrons in the discharge device of this invention over a considerable period of operation.

The power discharge device of this invention, particularly including the annular coaxial conductors of the main electrodes in the vessel, is especially suitable for continuous coaxial transmission systems operating in the ultra-high frequency range, since the device can be directly matched with a resonating circuit employed as an amplifier or oscillator in the system and the characteristic impedances of the line may be maintained at a substantially constant value over its entire length by simulating the impedances of the amplifier or oscillator circuit to coincide with the device. This is accomplished in aocordance with this invention by the unitary assembly of the structure, as shown in Fig. 4, which represents a grounded grid amplifier having a coaxial resonator chamber integrally associated with the discharge device. As shown the anode 29 of the device of Fig. 2 is enclosed in and supported by a water jacket container 39 having an inner partition 49 which extends partly within the boundary of the device as defined by the reversely turned wall 30 of the anode. The water jacket is electrically and mechanically connected to the ring 32 of the anode and a positive high voltage is ap-' plied to the jacket to maintain the anode at a high positive potential. A closed resonating chamber 4| formed of three concentric tubular ,membcrs 42, 43 and 44 of conductive material,

such as copper or brass, of increasing diameter and increasing length, respectively, from the inner tubular member 42 to the outer tubular member 44 is associated with the discharge device to form a unitary coaxial transmission system operating in the ultra-high frequency range. These tubular members are rigidly aflixed to a flat metallic disc or plate 45 at the top end with the tubular members equally spaced from each other and extending downwardly therefrom. The resonating chamber is of considerable mass so that it is necessary to support it in relation to the dis- Since the resonator 4| and the discharge deyice are separately and rigidly afllxed to perof the cathode and control electrode and the charge device from a Wall or standard by brackets 46, the complete chamber being grounded to maintain the grid or control electrode at grounded potential. The cathode 20 is maintained at a negative potential with respect to the anode 29 by connecting a conductor 41 to the rim conductor 22 of the device and the central terminals 33 and 34 of the primary emitter are connected to twisted insulated wires 48 to apply a suitable heating current to the primary emitter, the conductor 41 and wires 49 extending through apertures in the closure plate of the resonator.

flange 32 of the anode, respectively. This arrangement compensates for expansion and contraction of the separate units and materially reduces rupture strains on the coacting metallic parts of the resonator and discharge device.

In order to couple the tubular members of the resonating chamber to the various electrodes of the discharge device and at the same time main-' tain the cathode and anode at their respective negative and positive potentials, in relation to the control electrode, it is preferable to interpose the necessary blockingcondensers between the tubular members 42 and 44 and the respective electrodes. This type of blocking condenser may take the form of a channelled ring 52 soldered or sweated to an inwardly extending flange of the bellows ring, such as 49, so that the end of the tubular member 42 extends within the channel opening but is insulated therefrom by a suitable dielectric material 53 which is sealed in the channel opening and rigidly aflixes the end of the tubular member 42 therein. A similar annular channelled ring 54 is attached to the bellows expansion joint 5| of the anode to encase the free end of the outer tubular member 44 of the resonating chamber, said end being suitably embedded in a dielectric material in the channel ring to insulate the anode from the resonator housing. The intermediate tubular member 43 is electrically and mechanically secured to the bellows ring of the control electrode by soldering the end of the tubular member 43 within the confines of a channel ring 55 so that the control electrode is at ground potential through the conductive path provided by the metallic resonating chamber.

Since the spaces bounded by the walls of the tubular members form fields of resonance between-the cathode and control electrode and the control electrode and the anode for ultra-high frequency currents, these volumes can be utilized for impressing and taking out energy generated by the electron discharge device. Furthermore, the close coupling of these volumes to the discharge device eliminates inherent losses due to resistance and capacity which reduce the emciency of the transfer of energy particularly in the ultra-high frequency range. It is possible to construct the resonant chambers of such characteristic impedances to match the characteristic impedances of the internal electrodes in the dis- 0 intermediate member 43 and to adjust the relation of the contacts in a vertical direction so as to make the electrical distance from the contacts to the extreme ends of the cathode and grid one quarter wave-length, or stated differently, to make the impedance between the grid and cathode a maximum. The contacts are adjusted by rigid push rods 51 and 59 which are aflixed to a ring 59 exterior to the resonator 4|. The rod 58 is hollow to provide a coaxial channel for a central input conductor 99 which terminates in a loop 6| below one of the contacts 66 to inductively couple the input circuit of the amplifier to the input resonating chamber of the assembly, the loop 6| being attached to the end of the hollow rod 58 to form a coaxial termination.

Similarly the .space between the intermediate tubular member 43 and the outer coaxial member 44 may be tuned to the resonant frequency of the input by slidable contacts 62 attached to rods 63 and 64 connected exterior to the chamber by a ring support 65. The rod 64 is hollow and provided with a central output conductor 66 which terminates in a loop 61 inductively coupled to the resonating space and attached to the end of the hollow rod 64.

While the invention in its various aspects has been described in relation to an external anode discharge device, it is, of course, understood that the concepts of the invention may be employed in other types of discharge devices wherein high power output is not a predominating factor. Furthermore, various modifications in the rela tion of the electrodes and their constituent parts and also in the elimination or addition of one or more of the electrodes may be practiced in accordance with this invention without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. A cathode assembly comprising a tubular shell, an emitting source therein for heating said shell by electron bombardment, a carbon sleeve between said source and shell, and a thermionically active metal layer between said sleeve and shell, said sleeve layer and shell being in stratiform relation.

2. A cathode assembly comprising a central helical filament, a carbonaceous member surrounding said filament, a layer of thorium containing material in contact with said member, and a refractory metallic shell enclosing said layer and member.

3. A cathode assembly comprising a central helical filament, a carbonaceous member surrounding said filament, a layer of thorium containing material in contact with said member, and a refractory metallic shell enclosing said layer and member, said shell having a flare portion at one end and an attenuated guard ring portion between said member and said flare portion.

4. A high frequency unit comprising, an electron discharge device having a plurality of cooperating electrodes concentrically mounted in said device, said cooperating electrodes having coaxial ring conductors'extending from said device, a coaxial line unit of matched characteristic impedance comparable to that of said device including concentric conducting cylinders, said cylinders being coupled to said cooperating electrodes through said conductors, and capacitance elements interposed between said cylinders and said conductors, each of said capacitive elements being coupled between its respective cylinder and conductor.

5. A high frequency unit comprising an external anode discharge device having a plurality of cooperatin electrodes concentrically mounted within said anode, said cooperating electrodes and anode having coaxial ring conductors extending from said device, a coaxial line unit of matched characteristic impedance comparable to that of said device including concentric conductive cylinders, said cylinders being coupled to said anode and said cooperating electrodes, and yieldable connections between said cylinders and said anode and cooperating electrodes.

6. A high frequency unit comprising an external anode discharge device having a plurality of cooperating electrodes concentrically mounted within said anode, said cooperating electrodes and anode having coaxial ring conductors extending from said device, a coaxial line unit of matched characteristic impedance comparable to that of said device including concentric conductive cylinders, yieldable connections between said cylinders and said electrodes, and capacitive elements interposed between certain of said cylinders and the respective yieldable connections.

7. A high frequency unit comprising an electron discharge device having an external anode and a glass portion sealed thereto, a plurality of coaxial electrodes within said anode having annular portions sealed through the side walls of said glass portion, a plurality of concentric tubular metallic members coupled to said annular portions and said anode, and external input and output ring connectors having extensions slidably extending within and between adjacent members coupled to said electrodes and said anode, respectively.

8. An ultra-high frequency power generating unit comprising an external anode discharge device having concentric cathode and control electrodes in coaxial relation within said anode and rim conductors extendin from said electrodes and mounted in parallel planes, a coaxial line resonator of matched characteristic impedance directly coupled to said device including three concentric cylinders of varying length, the inner and outer cylinders being capacitatively coupled to said rim conductors of said cathode and anode respectively and the intermediate cylinder being conductively connected to the rim conductor of said'control electrode, a cover plate joined to and closing said resonator remote from said device, tuning elements adjustably movable in the spaces between said inner and intermediate cylinders and said intermediate and outer cylinders respectively, and coaxial input and output loops inductively coupled to said control electrode and anode respectively and movable with said tuning elements.

' PAUL L. HARTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,281,878 Heger May 5, 1942 1,712,402 Robinson May 7, 1929 1.947,179 Acheson Feb. 13, 1934 2,280,980 Samuel- Apr. 28, 1942 2,278,210 Morton Mar. 3, 1942 2,231,610 Becker Feb. 11, 1941 2,154,278 Mouromtsefi Apr. 11, 1939 2,107,945 Hull et 'al Feb. 8, 1938 2,272,374 Kallmann et al Feb. 10, 1942 2,287,845 Varian et a1 June 30, 1942 2,325,865 Litton Aug. 3, 1943 2,289,846 Litton July 14, 1942 FOREIGN PATENTS Number Country Date 211,551 British Feb. 18, 1934 164,175 British June 9, 1921

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