US2786957A - Emissive cathodes - Google Patents

Emissive cathodes Download PDF

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Publication number
US2786957A
US2786957A US420377A US42037754A US2786957A US 2786957 A US2786957 A US 2786957A US 420377 A US420377 A US 420377A US 42037754 A US42037754 A US 42037754A US 2786957 A US2786957 A US 2786957A
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Prior art keywords
tubes
cathode
emissive
cathodes
box
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Expired - Lifetime
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US420377A
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English (en)
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Huber Harry
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Thales SA
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CSF Compagnie Generale de Telegraphie sans Fil SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H01J1/28—Dispenser-type cathodes, e.g. L-cathode

Definitions

  • Ultrashort wave tubes of high power must be provided with cathodes capable of emitting high currents per unit .surface area and having a suiciently long life.
  • cathodes Many types have been proposed to this end.
  • One type of cathode in particular known as an oxidecoated cathode, has given excellent results in pulse operated tubes.
  • cathodes are formed usually of a metallic support on which is deposited an emitting material essentially comprising an alkaline-earth oxide, such as barium oxide or thorine.
  • the active element of these zcathodes is formed by the metal of the oxide.
  • the active metal may be destroyed by chemical reaction with the gases adsorbed by the electrodes of the tube and liberated by the electronic bombardment.
  • the barium, as well as barium oxide itself, is prone to evaporate in a vacuum, and this naturally contributes to limit the life of the ca thode.
  • cathodes are sensitive to the arcing effect. This results in the destruction of grains of oxide, which have a high electrical resistance and exist on the surface of the emitting cathode.
  • a metallic oxide cathode includes a metallic support, and this support is formed by at least one container in the shape of a cylinder.
  • This container is iilled with a mixture including 'at least one emissive metallic oxide, the free surface of the emissive material being flat and subjected to the extraction electric field.
  • the area of this free surface is small comparedwith the lateral areas of said cylindrical container, and the depth of the layer of emissive material is at least equal to one of the dimensions of said free surface, said dimension being of the order of 1/10 mm.
  • the thickness of the walls of the container mustl be of the order of 1/100 mm.
  • fa pure metal powder is incorporated in a homogeneous manner in said active materi-al.
  • Fig. l is a perspective view of one embodiment of the cathode according to the invention.
  • Fig. 2 is a fragmentary View from the top of the cathode shown in Fig. 1;
  • Fig. 3 is a sectional view of a detail of the cathode shown in Fig. l, showing the advantages of the cathodes according to the invention
  • Figs. 4 and 5 are diagrammatic views illustrating how a cathode such as that shown in Fig. l may be constructed.
  • Fig. 6 is a perspective view showing another embodiment of the invention.
  • Fig. 6a is a View of a detail of Fig. 6;
  • Fig. 7 is a diagrammatic view of an embodiment of the tube used in the cathode according to the invention.
  • Fig. 8 is a front view of the cathode using tubes of Fig. 7;
  • Figs. 9 and l0 are sectional Views of two embodiments of the cathodes according to Fig. 8;
  • Fig. 11 is a sectional view of another embodiment of the cathode according to the invention.
  • tubes 1 which may for example be of nickel. These tubes have a thin wall of the order of 1/100 mm. and a height of between 0.5 mm. and several millimeters. Their height is at least equal to their inside diameter.
  • the tubes 1 are grouped in a rectangular box, of nickel or molybdenum sheet, having side walls 2 and a base 4.
  • the tubes 1 are contiguous and are disposed to occupy the minimum of space.
  • the height of the walls 2 from the base 4 is equal to the height of the tubes.
  • the tubes 1 and the spaces between them are filled up to their upper edges with an emissive material 7. rThis material is composed, for example, of a mixture of alkaline-earth carbonates.
  • the heating filament 5 of the cathode is situated below the base 4 and is in direct contact with the latter. This filament rests on ⁇ a support 6.
  • the cathode 1 is seen from the top side, that is, the side corresponding to the emissive surface.
  • Like reference numerals denote like elements in Figs. l and 2.
  • the tubes 1 define therebetween spaces 20.
  • the longitudinal and transverse dimensions of the box are designated by a and b respectively.
  • the area of the emmissive surface is composed substantially of the areas of the upper ends of the cylinders and by the areas of the curvilinear triangles comprised between the upper sections.
  • Vlt Vlt can be seen, then, that the loss of emissive surface (represented by the total area of the upper ends or edges of the metallic walls of the tubes il) is relatively small. Further, it has been found that these metallic tube ends contribute to the electronic emission.
  • Fig. 3 shows a sectional View of one of the tubes 1 of the cathode shown in Fig. l, which is filled with emissive material 7, for example, alkaline-earth oxides.
  • emissive material 7 for example, alkaline-earth oxides.
  • the emissive material has a depth which is great compared to the diameter of the emissive surface of the cathode.
  • the surface of contact between the oxide and inner wall of the tube i. e., the lateral surface of this wall, is clearly more than twice as great as the surface of the end sections. Now, it is along this surface of contact that the reduction of the barium or other oxide by the metal of the tube occurs. There is, therefore, an improved generation of the active emissive element.
  • the stream of electric current inside the tube 1 is directed as shown at 100. It is known that this stream, due to electrolytic conduction, has for effect to separate the barium atoms from the top layer. It can be seen that this current is directed toward the wall of the tube 1 adjacent the emissive surface. VIt therefore does not interfere with the diffusion of the ⁇ barium towards the top layer, since the barium substantially does not separate from this layer.
  • the resistance of the tube to the arcing effect may, furthermore, be improved by incorporating a metallic powder, for example of nickel, in the emissive mixture.
  • Fig. 4 illustrates diagrammatically how the tubes may be stacked in regular manner, when these are of nickel.
  • the tubes 1 are thrown into a rectangular Plexiglas box 20.
  • One of the dimensions of this box is slightly greater than the height of the tubes.
  • This box is introduced between the poles of a magnet providing a uniform magnetic field and is so directed that the aforementioned dimension is parallel to this field.
  • the tubes therefore take up the same position, i. e., they arrange themselves parallel to this field, their bases resting on one of the side walls of the box which is then slightly shaken.
  • the box is then removed from the magnetic field and placed in such manner that the axes of the tubes are vertical (Fig. 5).
  • One lateral side of the box is then removed and the required number of tubes is removed in one go with the aid of pliers or tongs whose shape corresponds tothe shape of the emissive surface of the cathode.
  • a heating element 5 is introduced between the base 4 and the support 6 (Fig. l), and all the empty spaces are filled with a dry powder or a viscous paste of alkaline-earth carbonates, barium and strontium, for example, up to the edges of the tubes, by means of a spoon tool.
  • a thin coating of carbonate or a mixture of carbonate and metallic powder to a depth of 10 microns. This coating permits a ldecrease in the loss 0f the subjacent emissive material by evaporation; it serves as an absorptive and adsorptive coating for the active element.
  • the cathode thus prepared is heated slowly in the electronic tube in order to transform the carbonatos into oxides;
  • the carbonic gas escapes through the pores of the emissive surface.
  • the temperature is increased to about l,100 C.
  • the cathode emits electrons.
  • the temperature is then progressively decreased to 900 C. or 850 C. After a certain stabilizing period, the cathode is ready for use.
  • Fig. 6 shows a modification of the cathode illustrated in Fig. 1.
  • the tubes rest on the free surface of a reserve of emissive material 7 which is itself arranged on the base 4 of the box.
  • This reserve is an additional source of the active element. This element is capable of diffusing thermically through the oxides contained in the tubes.
  • This cathode of Fig. 6a combines the advantages of cathodes of Fig. l, with the advantages of cathodes having emissive material which are enclosed behind a p0- rous wall, such as for instance an L cathode.
  • Figs. 7, 8, 9, 10 there may be seen the various stages of another method of producing the cathode, which provides a cathode such as that shown in Fig. l (Fig. 9) or that shown in Fig. 6 (Fig. 10).
  • Fig. 7 there are shown long nickel tubes which are disposed on mandrels 8 of, for example, aluminum. These tubes are assembled in such manner as to form a bundle. This bundle is introduced in a cylindrical nickel tube 2 (Fig. 8). The whole is introduced in a drawing mill so as to press the tubes together. The pressed bundle of tubes is then cut into sections of required length.
  • the aluminum mandrels are then dissolved in caustic soda. In this way there is obtained a honey-comb-like structure having a series of cavities which are filled with emissive material.
  • the whole may be soldered in a vacuum to the support cylinder 20.
  • the cathode is then ready for use (Fig. 9). It may also include a reserve of emissive material (Fig. 10).
  • tubes of tantalum which are then disposed on nickel or iron mandrels. These mandrels are thereafter dissolved in a hydrochloric acid bath. The whole is then subjected to the aforementioned operations.
  • the tubes may then be filled with a thorine paste.
  • the cathode which is introduced in the electronic tube, is degassed at a temperature increasing progressively up to l600 or 1800o C. It is then ready for use.
  • cathode On account of the high operational temperature of such a cathode, it is advantageous to surround the whole of cathode, as shown in Fig. ll, with two cylindrical screens 30 and 40, both of these screens being of tantalum. Alternatively, the screen 30 may be of tantalum and the screen 40 of copper sheet.
  • the cathode is shown diagrammatically in the form of a cylinder of revolution. Such an arrangement enables the power necessary for heating to be reduced.
  • Such screens possess a high coefficient of reflection in the range of infrared light wavelengths comprised between 0.8 and 20 microns. It is in this range that the thermic radiation of the cathode attains its maximum energy.
  • thorine as the emissive material permits the manufacture of directly heated cathodes.
  • the cathodes obtained in accordance with the invention permit, when the emissive material is an alkalineearth material base, a continuous discharge of current densities of l A./cm.2 Thorine cathodes may attain current densities of 20 A./cm.2. Their life may exceed 1,000 hours in either case.
  • a cathode for electron discharge tubes of the type comprising a metallic cathode carrier', supporting an electron emitting material comprising metallic oxide: said metallic carrier comprising a box having ka base, and in said box, a plurality of identical metal tubes of equal length atleast equalto the diameter of the tube, said tubes projecting from said base of said box, the corresponding ends of said tubes lying in the same plane, said tubes being adjacent to each other, and the tubes and the spacings between them lled With said material, and a heater arranged under said base of said box.
  • a cathode for electron discharge tubes of the type comprising a metallic cathode carrier, supporting an elec tron emitting material comprising metallic oxide: said metallic carrier comprising a box having a base, and in said box a thick layer of said material, and projecting from said thick layer, a plurality of identical metal tubes of equal length at least equal to the diameter of the tube, the corresponding ends of said tubes lying in the same plane, said tubes being adjacent to each other, and

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  • Solid Thermionic Cathode (AREA)
  • Microwave Tubes (AREA)
US420377A 1953-04-02 1954-04-01 Emissive cathodes Expired - Lifetime US2786957A (en)

Applications Claiming Priority (1)

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FR1039140X 1953-04-02

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US (1) US2786957A (fr)
DE (1) DE1039140B (fr)
FR (1) FR1078606A (fr)
GB (1) GB756767A (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2939990A (en) * 1956-05-21 1960-06-07 Int Standard Electric Corp Oxide cathode for amplifier tubes
US3025428A (en) * 1959-10-15 1962-03-13 Kuthe Lab Inc Cathode structure
US3070719A (en) * 1957-07-24 1962-12-25 Varian Associates Cathodes for magnentically-confined glow discharge apparatus
US3441780A (en) * 1966-03-29 1969-04-29 Siemens Ag Indirectly heated dispenser cathode for electronic discharge devices
WO1984001664A1 (fr) * 1982-10-12 1984-04-26 Hughes Aircraft Co Cathode distributrice de porosite controlee
US4553063A (en) * 1982-09-10 1985-11-12 G. Rau Gmbh & Co. Electrical discharge electrode and method of production thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2452075A (en) * 1941-12-18 1948-10-26 Raytheon Mfg Co Velocity modulation electron discharge tube
US2459841A (en) * 1943-06-08 1949-01-25 Glenn F Rouse Cathode
US2488716A (en) * 1942-08-13 1949-11-22 Gen Electric Electric high-pressure discharge tube
US2499192A (en) * 1948-01-15 1950-02-28 Gen Electric Dispenser type cathode
US2624024A (en) * 1949-10-26 1952-12-30 Hartford Nat Bank & Trust Co Cathode for use in electron discharge tubes

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB207514A (en) * 1923-10-29 1924-05-01 Western Electric Co Ltd Improvements in electron discharge devices
NL24196C (fr) * 1928-04-10
DE663197C (de) * 1930-12-31 1938-08-01 Patra Patent Treuhand Elektrische Leuchtroehre mit Entladung durch die positive Saeule und mit kompakten, kalten Metallelektroden
GB437967A (en) * 1934-05-11 1935-11-08 Gen Electric Co Ltd Improvements in thermionic cathodes
GB495916A (en) * 1936-12-22 1938-11-22 Zeiss Ikon Ag Improvement in or relating to thermionic cathodes
FR945839A (fr) * 1947-04-18 1949-05-16 Radioelectriques Lab Perfectionnement aux cathodes des tubes à vide

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2452075A (en) * 1941-12-18 1948-10-26 Raytheon Mfg Co Velocity modulation electron discharge tube
US2488716A (en) * 1942-08-13 1949-11-22 Gen Electric Electric high-pressure discharge tube
US2459841A (en) * 1943-06-08 1949-01-25 Glenn F Rouse Cathode
US2499192A (en) * 1948-01-15 1950-02-28 Gen Electric Dispenser type cathode
US2624024A (en) * 1949-10-26 1952-12-30 Hartford Nat Bank & Trust Co Cathode for use in electron discharge tubes

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2939990A (en) * 1956-05-21 1960-06-07 Int Standard Electric Corp Oxide cathode for amplifier tubes
US3070719A (en) * 1957-07-24 1962-12-25 Varian Associates Cathodes for magnentically-confined glow discharge apparatus
US3025428A (en) * 1959-10-15 1962-03-13 Kuthe Lab Inc Cathode structure
US3441780A (en) * 1966-03-29 1969-04-29 Siemens Ag Indirectly heated dispenser cathode for electronic discharge devices
US4553063A (en) * 1982-09-10 1985-11-12 G. Rau Gmbh & Co. Electrical discharge electrode and method of production thereof
WO1984001664A1 (fr) * 1982-10-12 1984-04-26 Hughes Aircraft Co Cathode distributrice de porosite controlee

Also Published As

Publication number Publication date
FR1078606A (fr) 1954-11-19
DE1039140B (de) 1958-09-18
GB756767A (en) 1956-09-12

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