US3403281A - Magnetron having rapid starting property when cold - Google Patents

Magnetron having rapid starting property when cold Download PDF

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Publication number
US3403281A
US3403281A US556663A US55666366A US3403281A US 3403281 A US3403281 A US 3403281A US 556663 A US556663 A US 556663A US 55666366 A US55666366 A US 55666366A US 3403281 A US3403281 A US 3403281A
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United States
Prior art keywords
magnetron
emission
cathode
filament
cold
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Expired - Lifetime
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US556663A
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English (en)
Inventor
Weaver Francis James
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Teledyne UK Ltd
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English Electric Valve Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00—Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02—Electrodes; Magnetic control means; Screens
    • H01J23/04—Cathodes
    • H01J23/05—Cathodes having a cylindrical emissive surface, e.g. cathodes for magnetrons

Definitions

  • cathode emission of a high powered magnetron is provided, when the magnetron is in normal operation, by secondary emission resulting from bombardment of the cathode by returning electrons of the electron cloud in the tube.
  • Normal present day high power magnetron practice is to Provide a massive thermionic cathode having the usual built-in heater which is switched on when the magnetron is required to be brought into use and which heats the cathode to cause it to emit primary electrons.
  • the cathode surface is suitably constructed so as to be of high secondary emission coefiicient and, some little time after switching on, electrons from the electron cloud in the tube bombard the cathode thus causing secondary emission which supplements the initial primary thermionic emission.
  • a mangetron is provided with a cathode structure comprising a secondary electron emissive cathode member adapted to provide at least the major part of the required electron emission by a secondary emission by electron bombardment when the magnetron is in normal operation, and a filamentary thermionic emitter adapted to provide emission for rapidly starting said magnetron into operation from cold.
  • the secondary emissive cathode member is an externally grooved body having an outer surface of high secondary electron emission coefficient and the filamentary thermionic emitter is constiuted by filament wire positioned in the grooving.
  • the secondary emissive cathode member is helically grooved on its external surface and thermionic emissive filamentary wire is positioned in the helical grooving.
  • the secondary emissive cathode member is formed with grooves distributed round it and running parallel to its axis and thermionic emissive filamentary wires are positioned in these grooves.
  • the secondary emissive cathode member is a massive solid body of beryllium alloy having an oxidised surface adapted to provide the required secondary emission at a relatively low temperature (below about 600 C.), said body being kept down to said low temperature, when the magnetron is in normal operation, with the aid of loss of heat by substantial heat conduction occurring through said body.
  • the secondary emissive cathode member is a barium aluminate impregnated sleeve adapted to provide the required primary and secondary emission at a temperature in the neighborhood of 950 to 1000 C. when the magnetron is in normal operation.
  • the filamentary thermionic emitter may be of any suitable material known per se e.g. tungsten wire.
  • the materials used in the above described secondary emissive cathode membersbaryllium alloy or barium -aluminate have quite good electrical conductivity and in such cases it is therefore necessary to prevent the occurrence of short-circuiting electrical contact between the filament or filaments and the secondary emissive cathode member. Such prevention may be achieved in some constructions solely by tensioning the filament material to hold it in spaced relation with the adjacent surfaces of the said member. In some cases however insulating material must be provided for this purpose e.g. the filament wire may be threaded through spaced insulating beads which space it from said member at required intervals along its length and/ or the surfaces of the said cathode member adjacent the filament or filaments may be provided with a layer of insulation e.g. alumina sintered thereon.
  • FIGURES 1 and 2 are mutually perpendicular views illustrating one embodiment
  • FIGURE 3 and 4 are mutually perpendicular views illustrating another embodiment.
  • the drawings are to a large extent diagrammatic, no attempt having been made to show close detail. Except for the cathode structure a magnetron in accordance with this invention may be as known per se and accordingly, in the drawings, only cathode structures are shown.
  • the cathode structure therein shown comprises a directly heated filament 1 supported in and insulated from a helical groove 2 formed in a solid cylindrical body 3 having a surface of high secondary emission co-efiicient.
  • the cathode body 3 may also be capable of significant thermionic primary emission and in practice probably will be, though this primary emission capability is not essential and will not, in normal practice, contribute to any very great extent to the total emission.
  • the body 3 may be of a beryllium alloy such as beryllium copper with an oxydized surface which, when the magnetron is in normal operation, operates at a relatively low temperature i.e. a temperature not exceeding about 600 C. This low temperature operation is maintained largely by loss of heat 'by massive thermal conduction through the body 3 to a suitable heat conducting and radiating support structure.
  • Such a structure appears at 4 in the sectioned part of FIGURE 1.
  • FIGURES 1 and 2 the filament 1 follows the helical groove and at its ends passes through holes 5 to an axial bore 6 formed in the body 3.
  • One of the connections to the filament 1 appears in FIGURES 1 at 7.
  • Beryllium copper is of good electrical conductivity so that it is necessary to insulate the filament from the body 3 so as to prevent its being short circuited by the body. Any convenient means (not shown) may be provided for this purpose.
  • the filament 1 may be spaced off from the walls of the groove and of the holes 5 by small spaced insulating beads threaded on the filament. This arrangement is, however, not preferred in the construction of FIGURES 1 and 2 because, owing to the helical shape of the filament, the beads would have to be fairly closely spaced along the filament and this is an obvious disadvantage.
  • FIGURES 1 and 2 it is therefore preferred in the construction of FIGURES 1 and 2 to insulate the filament from the body 3 by providing the latter with a layer of 3 V insulation suitably positioned on the walls of the groove and of the holes in the neighbourhood of the filament.
  • a layer of alumina insulation could be sintered on to the base of the groove and the walls of the holes 5 and the filament bedded on this.
  • the parts 8 are the normally provided nickel or molybdenum or similar end hats for localising the electron emission.
  • the secondary emissive part of the structure is provided by a barium aluminate impregnated sleeve of a general nature similar to that commonly used at present in magnetron cathode practice.
  • This sleeve is referenced 13.
  • the sleeve is provided with grooves 12 equiangularly spaced around it and running parallel to its axis. In these grooves are positioned lengths of filament 11 which are tensioned by means not shown between end connector rings 9.
  • the filaments 11 must be insulated from the sleeve 13 but since they are straight filaments it is not difficult by suitable design to secure the required insulation simply by tensioning the filament lengths 11 to hold them clear of the walls of the grooves in which they run. In the case of a long cathode structure it may be advisable to provide a few spaced insulating beads through which the filament lengths are threaded or, as before, layers of insulation may be provided in the grooves on the body 13. As in FIGURES 1 and 2, 4 represents part of the cathode support structure and 8 are the end hats. In FIGURE 4 the left hand connector 9 of FIGURE 3 is removed so as not to conceal the grooves 12 and filaments 11.
  • the barium aluminate impregnated sleeve structure of FIGURES 3 and 4 is so designed that, when the magnetron is in normal operation, it operates at a temperature at present customary in magnetron cathode practice i.e., at a temperature in the neighbourhood of 950 to 1000 C.
  • the filamentary primary electron emitter which may be made of any suitable known suitable material (for example tungsten) is of relatively small area and mass and is so arranged that, when switched on, it will rapidly reach a required high temperature. It has quite small thermal inertia and accordingly will rapidly provide the thermionic emission necessary for starting a cold magnetron. Because of its small area it will not appreciably limit the handling capacity of the cathode structure as a whole as respects back bombardment. Accordingly the desired advantage (as compared with a known comparable cathode structure) of rapid warm up without appreciable limitation of back bombardment power handling capacity is obtained. It is expected, moreover, that cathode structures as herein described will have superior long term secondary emission properties.
  • any suitable known suitable material for example tungsten
  • the characteristic feature distinguishing the present invention from usual known practice resides in the substantial separation of the functions of primary and secondary emission.
  • the non-filamentary part of the cathode structure may in practice contribute a certain amount of primary emission when the magnetron is in operation, this does not happen until after an initial starting period is over and, from the practical point of view, the filament may be fairly regarded as providing primary emission for quick starting and the secondary emissive cathode mememission, the electrons required to maintain the mag netron in normal operation.
  • the design may be and preferably is such that, in the case of a cathode surface providing both primary and secondary emissione.g. a barium aluminate impregnated surfacethe filamentary primary emitter may be switched off when normal operating conditions have been reached.
  • a magnetron having a cathode structure comprising a secondary electron emissive cathode member adapted to provide at least the major part of the required electron emission by secondary emission by electron bombardment when the magnetron is in normal operation, and a filamentary thermionic emitter adapted to provide emission for rapidly starting said magnetron into operation from cold.
  • a magnetron as claimed in claim 1 wherein the secondary emissive cathode member is a massive solid body of beryllium alloy having an oxidised surface adapted to provide the required secondary emission at a relatively low temperature, said body being kept down to said low temperature, when the magnetron is in normal operation, with the aid of loss of heat by substantial heat conduction occurring through said body.

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US556663A 1965-08-16 1966-06-10 Magnetron having rapid starting property when cold Expired - Lifetime US3403281A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB34961/65A GB1141495A (en) 1965-08-16 1965-08-16 Improvements in or relating to magnetrons

Publications (1)

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US3403281A true US3403281A (en) 1968-09-24

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US556663A Expired - Lifetime US3403281A (en) 1965-08-16 1966-06-10 Magnetron having rapid starting property when cold

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US (1) US3403281A (enrdf_load_stackoverflow)
CH (1) CH437542A (enrdf_load_stackoverflow)
DE (1) DE1541003B1 (enrdf_load_stackoverflow)
FR (1) FR1514978A (enrdf_load_stackoverflow)
GB (1) GB1141495A (enrdf_load_stackoverflow)
NL (2) NL6609353A (enrdf_load_stackoverflow)
SE (1) SE325082B (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS49120579A (enrdf_load_stackoverflow) * 1973-03-16 1974-11-18
US3896332A (en) * 1973-06-04 1975-07-22 M O Valve Co Ltd High power quick starting magnetron
US3899714A (en) * 1972-12-21 1975-08-12 English Electric Valve Co Ltd Quick starting magnetron with shielded cathode
US4687964A (en) * 1985-05-09 1987-08-18 The United States Of America As Represented By The Administrator National Aeronautics & Space Administration Apparatus for mounting a field emission cathode
US5130601A (en) * 1990-03-14 1992-07-14 Litton Systems, Inc. Quick warm-up cathode heater for high average power magnetrons
US6686696B2 (en) * 2001-03-08 2004-02-03 Genvac Aerospace Corporation Magnetron with diamond coated cathode

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4480235A (en) * 1983-01-18 1984-10-30 Varian Associates, Inc. Coaxial magnetron with improved starting
GB2214704B (en) * 1988-01-20 1992-05-06 English Electric Valve Co Ltd Magnetrons
US4975656A (en) * 1989-03-31 1990-12-04 Litton Systems, Inc. Enhanced secondary electron emitter
RU2115193C1 (ru) * 1994-03-22 1998-07-10 Владимир Ильич Махов Магнетрон

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2097302A (en) * 1935-11-09 1937-10-26 Telefunken Gmbh Cathode for discharge devices
DE940181C (de) * 1953-10-24 1956-03-15 Elektronik G M B H Deutsche Indirekt geheizte Hochleistungskathode mit dickwandigem metallischem Kathodentraeger und Verfahren zu seiner Herstellung

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2818528A (en) * 1956-09-17 1957-12-31 Bell Telephone Labor Inc Electron discharge device
US2928987A (en) * 1958-04-01 1960-03-15 Gen Electric Magnetron device and system
US2967264A (en) * 1959-01-29 1961-01-03 Raytheon Co Grid controlled magnetrons

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2097302A (en) * 1935-11-09 1937-10-26 Telefunken Gmbh Cathode for discharge devices
DE940181C (de) * 1953-10-24 1956-03-15 Elektronik G M B H Deutsche Indirekt geheizte Hochleistungskathode mit dickwandigem metallischem Kathodentraeger und Verfahren zu seiner Herstellung

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3899714A (en) * 1972-12-21 1975-08-12 English Electric Valve Co Ltd Quick starting magnetron with shielded cathode
JPS49120579A (enrdf_load_stackoverflow) * 1973-03-16 1974-11-18
US3896332A (en) * 1973-06-04 1975-07-22 M O Valve Co Ltd High power quick starting magnetron
US4687964A (en) * 1985-05-09 1987-08-18 The United States Of America As Represented By The Administrator National Aeronautics & Space Administration Apparatus for mounting a field emission cathode
US5130601A (en) * 1990-03-14 1992-07-14 Litton Systems, Inc. Quick warm-up cathode heater for high average power magnetrons
US6686696B2 (en) * 2001-03-08 2004-02-03 Genvac Aerospace Corporation Magnetron with diamond coated cathode

Also Published As

Publication number Publication date
NL6609353A (enrdf_load_stackoverflow) 1967-02-17
DE1541003B1 (de) 1971-07-08
FR1514978A (fr) 1968-03-01
SE325082B (enrdf_load_stackoverflow) 1970-06-22
GB1141495A (en) 1969-01-29
NL130735C (enrdf_load_stackoverflow) 1900-01-01
CH437542A (fr) 1967-06-15

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