US3421039A - Thermionic cathode having emissive material and metallic paths which sputter away at the same rate - Google Patents

Thermionic cathode having emissive material and metallic paths which sputter away at the same rate Download PDF

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Publication number
US3421039A
US3421039A US518081A US3421039DA US3421039A US 3421039 A US3421039 A US 3421039A US 518081 A US518081 A US 518081A US 3421039D A US3421039D A US 3421039DA US 3421039 A US3421039 A US 3421039A
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Prior art keywords
oxide
cathode
metal
disks
thermionic cathode
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US518081A
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English (en)
Inventor
Wolfgang Knauer
Hayden E Gallagher
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Raytheon Co
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Hughes Aircraft Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J17/00—Gas-filled discharge tubes with solid cathode
    • H01J17/02—Details
    • H01J17/04—Electrodes; Screens
    • H01J17/06—Cathodes
    • H01J17/063—Indirectly heated cathodes, e.g. by the discharge itself
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J17/00—Gas-filled discharge tubes with solid cathode
    • H01J17/02—Details
    • H01J17/04—Electrodes; Screens
    • H01J17/06—Cathodes

Definitions

  • the emissive material is sufliciently thin to prevent excessive resistive heating from current flowing through the metallic paths and thence through the emissive material to the emissive surface. Furthermore, the metallic paths are sufficiently thin that they are sputtered away under ion bombardment at substantially the same rate as the emissive material.
  • This invention relates to thermionic cathode structures for use in gaseous discharges and plasmas and more particularly to improvements therein.
  • Another object of this invention is the provision of a novel thermionic cathode structure which is capable of withstanding heavy ion bombardment for long periods of operation.
  • Yet another object of the presentinvention is the provision of a novel structure for a thermionic cathode wherein the oxide layer is physically thick and yet electrically and thermally thin.
  • the cathode may have the form of a stack of alternate, oxide and conductive metal disks which are heated from a filament source at their centers. Another form may be a stack of alternate metal and oxide disks which are heated by a filament disposed around their peripheries. A cone may be cut into the centers of the disks whereby electrons are emitted from the centers. Still other arrangements are to fill a heated cup with either felt metal impregnated with oxide material or oxide grains encapsulated in metal.
  • the conductive material must also provide suflicient thermal conductivity so that the heat energy passed from the heating element to the emitting surface is substantially transported by the conductive material.
  • the thickness of the individual cell walls of the conductive structure must be so small that under ion bombardment it is sputtered away at substantially the same rate as the oxide.
  • the size of the individual cells of the conductive structure has to be so dimensioned that the oxide within each cell does not :become Joule heated when it is utilized as an emission site.
  • FIGURE 1 is a cross-sectional View of one embodiment of the invention
  • FIGURE 2 is a cross-sectional view of another embodiment of the invention.
  • FIGURE 3 is a cross-section of a disk which may be used in an embodiment of the invention of the type shown in FIGURE 1 or FIGURE 2;
  • FIGURE 4 is a cross-section of another disk which may be used in an embodiment of the invention of the type shown in FIGURE 1 or FIGURE 2;
  • FIGURE 5 is an enlarged cross-section of a cathode structure in accordance with this invention.
  • FIGURES 6 and 7 respectively are cross-sectional views of two other embodiments of this invention.
  • FIGURE 8 is an enlarged cross-sectional view of one of the elements of the cathode structure shown in FIGURE 7.
  • the cathode structure comprises a core or central hub 10 of a pyroceramic material having wound therein heater filament windings 12. Electrical current is applied to the filament windings to generate the heat required for causing the oxide cathode to liberate electrons.
  • the central core 10 hasa flange 14 in order to hold a plurality of disks which are alternately composed of oxide emitting material 16 and conductive metal 18.
  • the oxide material may be barium oxide, or calcium oxide, or strontium oxide
  • the conductive metal may be nickel.
  • another flange 20 On top of the stack of disks is another flange 20 which may be threaded or fastened through the hub 10 by any suitable means.
  • FIGURE 2 is a crosssection of another embodiment of the invention wherein, instead of the heater being at the center surrounded by the oxide-metal disks, the heater structure 22 is cupshaped and the alternate oxide disks 24, conductive metal disks 26 are disposed within the cup. In addition, a conical opening 28 having its axis aligned with the axis of the disks is cut into the disks and extends from the uppermost disk down to the lowest disk.
  • This cathode emits electrons axially and has the virtue that the entire cathode is shielded except for the emitting region.
  • FIGURE 3 is an enlarged cross-section illustrative of a disk which may be used in FIGURE 1 or FIGURE 2 instead of alternate nickel-oxide layers wherein the center 32 is a conductive metal, such as nickel, and the outer surfaces are coated with a suitable oxide layer 34, 36.
  • FIGURE 4 is a cross-sectional view of an oxide coated metal disk wherein the metal disk 38 has holes therein so that the amount of oxide 40 available for producing electrons is increased by virtue of the fact that it fills the holes in the disk.
  • the dimensions of the cell structures in the cathode as described depends substantially upon the type of plasma used. To indicate the procedure by which the pertinent dimensions are determined, a specific situation is analyzed below.
  • the cell wall thickness can be determined. With cell size and wall thickness known, both electrical and thermal impedance can be computed and it can be seen whether both satisfy the requirements for low voltage and low temperature gradients.
  • the maximum electron current density r becomes 1 A./cm.
  • the sputtering rates are 6CE1O 4 atoms/ ion, 6 510 atoms/ion.
  • the cell walls have to be approximately 5 X 10- cm. thick.
  • FIGURE 5 is an enlarged end view in cross-section of several coated conductive disks.
  • the coating may be barium oxide and the conductive metal upon which the barium is coated may be nickel. It will be seen that the upper and lower surfaces of the nickel disk 44 are coated by the respective oxide coatings 42, 46. There is a small space left between adjacent oxide coatings. The plasma sheath 48 established between the plasma 50 and the surface of the layers of the cathode does not penetrate into the spaces between the oxide coatings since these are smaller than the Debye length. It will be noted that the metal disks extend beyond the termination of the oxide coatings thereon.
  • both the barium oxide and nickel which are used in these disks are gradually sputtered under ion bombardment.
  • a suitable ratio of the layer thicknesses must be chosen. For an estimate of this ratio, the following assumptions are made.
  • the nickel layer is permitted to stand out over the barium oxide layer by a distance d which is approximately equal to the width b of the barium oxide layer. With a Debye length x smaller than the width of the oxide layer, the plasma sheath will follow the contour of the emitter surface and thus provide the fields necessary to draw current from the recessed barium oxide surfaces. Furthermore, the ions impinge with equal rates on the barium oxide and nickel surfaces.
  • FIGURE 6 is a cross-sectional view of another embodiment of the invention.
  • a cupshaped heating structure 52 wherein the cup is filled with felt metal strands 54, preferably made of nickel, which have been impregnated with oxide.
  • Felt metal is the designation given to porous metal strands which are made by compressing powdered metal or by sintering metal and then grinding it into slivers.
  • the felt metal has microporous openings.
  • the dissolved oxide is mixed with the porous metal and the microporous openings absorb the oxide material.
  • the metal impregnated with the oxide is placed in the cup-shaped structure 52 and heated.
  • the conductive metal provides both the thermal and electrical paths necessary to avoid undue loss of the oxide material.
  • the oxide material emits electrons. The effects of the ion bombardment are minimized by virtue of the structure provided.
  • FIGURE 7 Another variation of the arrangement in FIGURE 6 is shown in FIGURE 7.
  • the cup-shaped heating structure 56 is loaded with small spheres 58.
  • Each of the spheres is shown in FIGURE 8 and comprises a central gain 60 of oxide material surrounded by a metal coating 62, such as nickel.
  • the oxide material is encapsulated in the metal coating.
  • the metal coating is not perfect, there are sufiicient cracks so that upon heating, the oxide material can emit electrons which will pass through these cracks. Undue heating of the oxide is avoided by the conductive metal encapsulating material.
  • a thermionic cathode structure comprising heating means, and cathode means having one surface to which heat from said heating means is applied for emitting electrons from another surface thereof, said cathode means including a body of material having the property that when it is heated it emits electrons, said body of material having one surface disposed to receive heat from said heating means and another surface disposed to emit electrons, and metal conductive material means in contact and substantially coextensive with said body of material for conducting a substantial amount of the emission currents and heat from the surface of said body which is exposed to said heating means to the surface which emits electrons, the improvement comprising: said body of material and said metal conductive material means having relative thicknesses such as to be sputtered away under ion bombardment at substantially the same rate.
  • a thermionic cathode structure comprising heating means, alternate layers of material for emitting electrons in response to heat energy and metal conductive material, means for applying heat energy from said heating means to one layered surface of said alternate layers whereby electrons are emitted from said material for emitting electrons at the opposite layered surface, the improvement comprising: said material for emitting electrons and said metal conductive material having a relative thickness to prevent ohmic heating of said material for emitting electrons due to current flow and to sputter away said material for emitting electrons and said conductive material at substantially equal rates under ion bombardment.
  • a thermionic cathode structure comprising a disk of material having the property that it will emit electrons in response to heat, metal conductive disk means in contact with said disk of material, for protecting said disk of material from adverse effects due to emission currents and temperature, the thickness of said disk of material and said metal conductive disk means being established to provide substantially the same sputtering rate to ion bombardment, and means for applying heat to one edge of said disk of material for causing electrons to be emitted from the other edge thereof.
  • a thermionic cathode structure as recited in claim 4 wherein said cathode structure comprises a plurality of said disks of material and metal conductive material means disposed adjacent one another, said plurality of disks having an opening in the center thereof and said means for heating being disposed within said central openmg.
  • a thermionic cathode structure as recited in claim 4 wherein said cathode structure comprises a stack of said disks of metal conductive material means and material for emitting electrons responsive to the application of heat, said heating means comprises means for applying heat to the outer edges of said stack of disks, and said stack of disks have a conical shaped hole formed therein with the base of said conical shaped hole being adjacent one end of said stack of disks and the axis of said conical shaped hole being coincident to the axis of said stack of disks.
  • a thermionic cathode comprising a cup-shaped means for generating heat and a plurality of means within the cup of said cup-shaped means for emitting electrons responsive thereto to said heat, each of said plurality of means comprising material for emitting electrons and metal conductive material in contact therewith, the thickness of said material for emitting electrons and the thickness of said conductive material being established to provide substantially the same sputtering rate under ion bombardment.
  • each of said plurality of means comprises a nucleus of said material for emitting electrons encapsulated in a metal conductive material shell having openings therethrough.
  • each of said plurality of means comprises a porous strand of said metal conductive material with said material for emitting electrons within the pores thereof.

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  • Solid Thermionic Cathode (AREA)
US518081A 1966-01-03 1966-01-03 Thermionic cathode having emissive material and metallic paths which sputter away at the same rate Expired - Lifetime US3421039A (en)

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US51808166A 1966-01-03 1966-01-03

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US (1) US3421039A (de)
CH (1) CH452711A (de)
DE (1) DE1564100A1 (de)
GB (1) GB1122840A (de)
SE (1) SE329445B (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3495121A (en) * 1967-04-10 1970-02-10 Siemens Ag Indirectly heated dispenser cathode for electrical discharge vessels

Citations (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1416623A (en) * 1914-10-01 1922-05-16 Donath Bruno Electric discharging tube
US1701356A (en) * 1923-06-09 1929-02-05 Gen Electric Electrical discharge device
US1891074A (en) * 1931-02-19 1932-12-13 Gen Electric Cathode for electric discharge devices
US2014539A (en) * 1933-04-15 1935-09-17 Cutler Hammer Inc Electron tube
US2107945A (en) * 1934-11-20 1938-02-08 Gen Electric Cathode structure
US2173208A (en) * 1935-05-07 1939-09-19 Ets Claude Paz & Silva Electrode
US2177703A (en) * 1936-11-25 1939-10-31 Gen Electric Electric gaseous discharge device
US2420014A (en) * 1944-04-18 1947-05-06 Eitel Mccullough Inc Cathode
US2459841A (en) * 1943-06-08 1949-01-25 Glenn F Rouse Cathode
DE952543C (de) * 1954-02-27 1956-11-15 Siemens Ag Indirekt geheitzte Kathode fuer elektrische Entladungsgefaesse
US2888592A (en) * 1954-07-22 1959-05-26 Gen Electric Cathode structure
US2937304A (en) * 1957-09-25 1960-05-17 Edgerton Germeshausen & Grier Electric-discharge device and cathode
US3147362A (en) * 1960-08-01 1964-09-01 Smith Corp A O Composite consumable electrode containing emissive compounds and method of manufacture
US3149253A (en) * 1962-01-03 1964-09-15 Gen Electric Electrode structure from magnetohydrodynamic device
US3210575A (en) * 1961-03-07 1965-10-05 Podolsky Leon Thermoelectron engine having composite emitter

Patent Citations (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1416623A (en) * 1914-10-01 1922-05-16 Donath Bruno Electric discharging tube
US1701356A (en) * 1923-06-09 1929-02-05 Gen Electric Electrical discharge device
US1891074A (en) * 1931-02-19 1932-12-13 Gen Electric Cathode for electric discharge devices
US2014539A (en) * 1933-04-15 1935-09-17 Cutler Hammer Inc Electron tube
US2107945A (en) * 1934-11-20 1938-02-08 Gen Electric Cathode structure
US2173208A (en) * 1935-05-07 1939-09-19 Ets Claude Paz & Silva Electrode
US2177703A (en) * 1936-11-25 1939-10-31 Gen Electric Electric gaseous discharge device
US2459841A (en) * 1943-06-08 1949-01-25 Glenn F Rouse Cathode
US2420014A (en) * 1944-04-18 1947-05-06 Eitel Mccullough Inc Cathode
DE952543C (de) * 1954-02-27 1956-11-15 Siemens Ag Indirekt geheitzte Kathode fuer elektrische Entladungsgefaesse
US2888592A (en) * 1954-07-22 1959-05-26 Gen Electric Cathode structure
US2937304A (en) * 1957-09-25 1960-05-17 Edgerton Germeshausen & Grier Electric-discharge device and cathode
US3147362A (en) * 1960-08-01 1964-09-01 Smith Corp A O Composite consumable electrode containing emissive compounds and method of manufacture
US3210575A (en) * 1961-03-07 1965-10-05 Podolsky Leon Thermoelectron engine having composite emitter
US3149253A (en) * 1962-01-03 1964-09-15 Gen Electric Electrode structure from magnetohydrodynamic device

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3495121A (en) * 1967-04-10 1970-02-10 Siemens Ag Indirectly heated dispenser cathode for electrical discharge vessels

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DE1564100A1 (de) 1970-03-19
GB1122840A (en) 1968-08-07
SE329445B (de) 1970-10-12
CH452711A (de) 1968-03-15

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