US3899714A - Quick starting magnetron with shielded cathode - Google Patents

Quick starting magnetron with shielded cathode Download PDF

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Publication number
US3899714A
US3899714A US424358A US42435873A US3899714A US 3899714 A US3899714 A US 3899714A US 424358 A US424358 A US 424358A US 42435873 A US42435873 A US 42435873A US 3899714 A US3899714 A US 3899714A
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United States
Prior art keywords
magnetron
cathode structure
cathode
tube
quick starting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US424358A
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English (en)
Inventor
Maurice Esterson
Francis James Weaver
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Teledyne UK Ltd
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English Electric Valve Co Ltd
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Filing date
Publication date
Application filed by English Electric Valve Co Ltd filed Critical English Electric Valve Co Ltd
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Publication of US3899714A publication Critical patent/US3899714A/en
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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

  • ABSIRACT A quick starting magnetron having two cathodes, one of low heat inertia and thermally emissive for starting purposes and the second of high heat inertia positioned between the magnetron anode and the first cathode.
  • the second cathode is apertured to allow electrons to pass through from the first cathode and is arranged to partially shield the first cathode from electron bombardment during normal running of the magnetron.
  • cathode structure of such design It is well known to obtain quick starting qualities in a magnetron by making the cathode structure of such design that it will heat up very rapidly to emission temperature from cold.
  • known cathode structures of such design have the defect that because, after starting and during normal running of a magnetron, the cathode is subjected to considerable electron bombardment, the cathode temperature tends to rise substantially and this sets an undesirable limit to the power which can be safely handled. Indeed it is not uncommon to make magnetrons with heated cathodes the heaters of which are switched on only during starting, electron bombardment during running serving alone to maintain the cathode at normal operating temperature.
  • a magnetron To be quick starting a magnetron must have a thermionic cathode of low heat inertia and such a cathode is necessarily of poor heat dissipation properties usually through being of poor heat conductivity and accordingly, if, after starting, the cathode is subjected to too much additional heating by electron bombardment, the heat is unable to get away and the temperature rises to an unacceptably high level.
  • the present invention seeks to lift this limitation and to provide improved quick starting magnetrons of higher power capability than comparable quick starting magnetrons known to the applicants.
  • a quick starting magnetron has an anode, a first thermally emissive cathode structure of low heat inertia; and a second cathode structure of relatively high heat inertia positioned between said anode and said first cathode structure and apertured so as to allow electrons to pass therethrough from said first cathode structure into the space between the anode and the second cathode structure; said second cathode structure being positioned and dimensioned so as to at least partially screen the first cathode structure from electron bombardment during normal running of the magnetron.
  • the second cathode structure is given a sufficiently high secondary emission coefficient to ensure that practically all or the major part of the electron current required for magnetron operation is supplied by secondary electron emission.
  • the second cathode structure may be designed to be heated only by electron bombardment but,-if desired, it may also be arranged to be heated electrically.
  • the first cathode structure comprises a thin walled inner metal tube having a ring coating of thermionically emissive material thereon and said second cathode structure comprises, co-axial with said thin walled tube, a thick walled tubular structure apertured axially adjacent said ring coating.
  • Electrical heating of the thin walled tube may be effected in any of a variety of known ways but preferably it is accomplished directly by passing heating current through it.
  • a central axial rod is provided inside and spaced from the thin walled metal tube; said rod is fixed at its outer end to an outer end hat" of disc form which also locates the outer end of the thin walled tube and the outer end of the thick walled tubular structure; and an inner annular end hat" surrounds said rod and locates the inner end of the thick walled tubular structure, means being provided for feeding heating current through a circuit including the axial rod, the outer end hat and the thin walled tube.
  • the last mentioned means preferably includes said support rod and an additional support which is hollow, e.g., cylindrical, surrounds said rod and supports both the inner end hat and the inner end of the thin walled tube.
  • an additional support which is hollow, e.g., cylindrical, surrounds said rod and supports both the inner end hat and the inner end of the thin walled tube.
  • the thick walled tubular structure must not short circuit the thin walled tube and therefore there must be an insulating gap in the electrical path from one end hat to the other through the tubular structure. This could be done by insulating one end of the tubular structure from the associated end hat but preferably the tubular structure is formed by two cylindrical sections separated one from the other, with the gap therebetween forming the aperture for electrons from the thin walled first cathode structure.
  • the support rod and additional support provide good thermal conduction paths from the thick walled structure to the exterior of the magnetron.
  • the magnetron represented in the drawing is, except for the cathode arrangement, a multi-cavity magnetron of well known form. Accordingly only the said arrangement is shown in any detail, the rest of the magnetron being represented merely by the inner ends, of the radial vanes which are fixed to the inside of the anode cylinder to provide a plurality of resonant cavities in accordance with well known magnetron practice.
  • V are the inner ends of two of the vanes which project radially inwards from the cylindrical anode of the anode system of a multi-cavity magnetron.
  • a cathode arrangement which comprises a quick staring first cathode structure and a second main cathode structure which acts also as an electron shield to prevent overheating of the quick starting cathode and its support by bombardment by returning electrons when the magnetron is in normal running operation.
  • the quick starting cathode structure is constituted by a ring 1 of suitable thermionic emissive material on the outer surface of a thin-walled metal tube 2 at about the middle of the length thereof. Because of the thinness of the wall of the tube 2, the quick starting cathode is of low thermal inertia. For the same reason, however, it is unable to conduct heat away quickly for dissipation.
  • Co-axially surrounding the quick starting cathode is a combined main cathode structure and electron shield.
  • This consists of two similar thick walled metal tube portions 3, 4 on the outer surfaces of which are deposits 5, 6 of material capable of secondary electron emission. if desired material capable of primary electron emission may also be deposited over all or part of the surface.
  • end hats which locate the ends of the cathode structures and an axial metal rod 10 extends up to and is connected to the upper end hat 8.
  • 11 represents a main electrically conductive support for the cathode structure as a whole and the lower end hat 9 sits on this support. Heating of the quick starting cathode is effected electrically by passing heating current through a heating current circuit consisting of the rod 10, the upper end hat 8 the thin walled tube 1 and the support 11.
  • An arrangement as illustrated enables a quick starting magnetron of substantially high power capability to be obtained because, owing to the electron shielding of the thin walled cathode structure provided by the tube portions 3 and 4, over-heating of the thin walled tube 2 and the emissive cathode material 1 carried thereby will not now occur. Additionally the rod 10 and support 11 provide a good thermal conduction path for heat form the thick walled structure 3, 4 to the exterior of the magnetron so as to permit operation of the magnetron at levels of power which cause substantial back heating of the structure 3, 4 by electron bombardment.
  • the design may be such that the heating current is kept switched on after starting or it may be such that the heating current is switched on only for starting and then switched off.
  • the main cathode (3, 5 4, 6) is not provided with any heating means (other, of course, than by electron bombardment by returning electrons) but, if desired, electrical heating for this cathode may be arranged for in any convenient manner known per se and the design may be such that this electrical heating is switched on only during starting or, alternatively, is kept on after starting.
  • a quick starting magnetron including an anode; a first thermally emissive cathode structure of low heat inertia; and a second cathode structure of relatively high heat inertia positioned between said anode and said first cathode structure; a continuous circumferential aperture provided in said second cathode so that said second cathode is formed in two axially separated portions, the aperture permitting electrons to pass therethrough from said first cathode structure into the space between the anode and the second cathode structure; said second cathode structure being positioned and dimensioned so as to at least partially screen the first cathode structure from electron bombardment during normal running of the magnetron.
  • first cathode structure comprises a thin walled inner metal tube having a ring coating of thermionically emissive material thereon and said second cathode structure comprises, co-axial with said thin walled tube, a thick walled tubular structure apertured axially adjacent said ring coating.
  • a quick starting magnetron according to claim 6 wherein a central axial rod is provided inside and spaced from the thin walled metal tube; said rod is fixed at its outer end to an outer end hat of disc form which also locates the outer end of the thin walled tube and the outer end of the thick walled tubular structure; and an inner annular end hat surrounds said rod and locates the inner end of the thick walled tubular structure, means being provided for feeding heating current through a circuit including the axial rod, the outer and hat and the thin walled tube.
  • a quick quick starting magnetron according to claim 7 wherein the means for feeding heating current includes said support rod and an additional support which is hollow cylindrical, surrounds said rod and supports both the inner end hat and the inner end of the thin walled tube and wherein there is an insulating gap in the electrical path from one end hat to the other through the tubular structure.
  • a first cathode structure disposed within said anode space and comprising a thin wall tube having a ring of thermally emissive material on its outer surface;
  • a second cathode structure surrounding and spaced from said tube and having aperture means aligned with said ring of thermally emissive material to allow electrons to pass into said anode space
  • said second cathode structure including thick wall tube portions on either side of said aperture means shielding said thin wall tube from bombardment from returning electrons, said conductor means engaging said tube portions for conducting heat therefrom to the exterior of the magnetron, and said tube portions being provided with exterior coatings of secondary emission material.

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  • Microwave Tubes (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
US424358A 1972-12-21 1973-12-13 Quick starting magnetron with shielded cathode Expired - Lifetime US3899714A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB5913672A GB1399260A (en) 1972-12-21 1972-12-21 Magnetrons

Publications (1)

Publication Number Publication Date
US3899714A true US3899714A (en) 1975-08-12

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US424358A Expired - Lifetime US3899714A (en) 1972-12-21 1973-12-13 Quick starting magnetron with shielded cathode

Country Status (6)

Country Link
US (1) US3899714A (enrdf_load_stackoverflow)
JP (1) JPS4998168A (enrdf_load_stackoverflow)
CA (1) CA1003964A (enrdf_load_stackoverflow)
FR (1) FR2211746A1 (enrdf_load_stackoverflow)
GB (1) GB1399260A (enrdf_load_stackoverflow)
NL (1) NL7317243A (enrdf_load_stackoverflow)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5242067A (en) * 1975-09-29 1977-04-01 New Japan Radio Co Ltd Magnetron cathode construction
US5280218A (en) * 1991-09-24 1994-01-18 Raytheon Company Electrodes with primary and secondary emitters for use in cross-field tubes
FR2699325A1 (fr) * 1992-12-11 1994-06-17 Litton Systems Inc Suppression de l'instabilité dans un amplificateur à champs croisés à l'aide d'un émetteur de champ.
US5412281A (en) * 1993-03-31 1995-05-02 Litton Systems, Inc. Phase smoothing cathode for reduced noise crossed-field amplifier
EP0803899A4 (en) * 1995-10-30 1998-08-19 Seiko Epson Corp LAMP AND IMAGE READER USING THE SAME
US5874806A (en) * 1996-10-02 1999-02-23 Litton Systems, Inc. Passive jitter reduction in crossed-field amplifier with secondary emission material on anode vanes
US5977714A (en) * 1997-04-16 1999-11-02 Adamovski; Victor Isaevich Magnetron anodes having refractory material and cooled by fluid boiling
RU2150765C1 (ru) * 1999-04-07 2000-06-10 Санкт-Петербургский государственный технический университет Способ создания широкополосных квазишумовых сверхвысокочастотных сигналов большой мощности и устройство для его осуществления
US6329753B1 (en) 1998-01-08 2001-12-11 Litton Systems, Inc. M-type microwave device with slanted field emitter
US6388379B1 (en) 1998-01-08 2002-05-14 Northrop Grumman Corporation Magnetron having a secondary electron emitter isolated from an end shield
US6485346B1 (en) 2000-05-26 2002-11-26 Litton Systems, Inc. Field emitter for microwave devices and the method of its production
US20040104679A1 (en) * 2002-11-13 2004-06-03 New Japan Radio Co., Ltd. Pulse magnetron

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2317741B (en) * 1995-12-12 1999-02-17 Lg Electronics Inc Magnetron

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2736838A (en) * 1951-04-03 1956-02-28 Richard B Nelson Starting apparatus for a cold cathode electron discharge device
US2818528A (en) * 1956-09-17 1957-12-31 Bell Telephone Labor Inc Electron discharge device
US2822499A (en) * 1955-02-17 1958-02-04 Bell Telephone Labor Inc Cathodes for electron discharge devices
US3297901A (en) * 1964-06-05 1967-01-10 Litton Industries Inc Dispenser cathode for use in high power magnetron devices
US3403281A (en) * 1965-08-16 1968-09-24 English Electric Valve Co Ltd Magnetron having rapid starting property when cold
US3505557A (en) * 1966-12-14 1970-04-07 Philips Corp Indirectly heated cathode having portions with different thermal relations with a heater

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2736838A (en) * 1951-04-03 1956-02-28 Richard B Nelson Starting apparatus for a cold cathode electron discharge device
US2822499A (en) * 1955-02-17 1958-02-04 Bell Telephone Labor Inc Cathodes for electron discharge devices
US2818528A (en) * 1956-09-17 1957-12-31 Bell Telephone Labor Inc Electron discharge device
US3297901A (en) * 1964-06-05 1967-01-10 Litton Industries Inc Dispenser cathode for use in high power magnetron devices
US3403281A (en) * 1965-08-16 1968-09-24 English Electric Valve Co Ltd Magnetron having rapid starting property when cold
US3505557A (en) * 1966-12-14 1970-04-07 Philips Corp Indirectly heated cathode having portions with different thermal relations with a heater

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5242067A (en) * 1975-09-29 1977-04-01 New Japan Radio Co Ltd Magnetron cathode construction
US5280218A (en) * 1991-09-24 1994-01-18 Raytheon Company Electrodes with primary and secondary emitters for use in cross-field tubes
FR2699325A1 (fr) * 1992-12-11 1994-06-17 Litton Systems Inc Suppression de l'instabilité dans un amplificateur à champs croisés à l'aide d'un émetteur de champ.
GB2274198A (en) * 1992-12-11 1994-07-13 Litton Systems Inc Cross field amplifier
GB2274198B (en) * 1992-12-11 1997-01-08 Litton Systems Inc Cross-field amplifier
US5412281A (en) * 1993-03-31 1995-05-02 Litton Systems, Inc. Phase smoothing cathode for reduced noise crossed-field amplifier
US6222647B1 (en) 1995-10-30 2001-04-24 Seiko Epson Corporation Lamp unit and image reading apparatus using the same
EP0803899A4 (en) * 1995-10-30 1998-08-19 Seiko Epson Corp LAMP AND IMAGE READER USING THE SAME
EP0989588A1 (en) * 1995-10-30 2000-03-29 Seiko Epson Corporation Lamp unit and image reading apparatus using the same
US5874806A (en) * 1996-10-02 1999-02-23 Litton Systems, Inc. Passive jitter reduction in crossed-field amplifier with secondary emission material on anode vanes
US5977714A (en) * 1997-04-16 1999-11-02 Adamovski; Victor Isaevich Magnetron anodes having refractory material and cooled by fluid boiling
US6329753B1 (en) 1998-01-08 2001-12-11 Litton Systems, Inc. M-type microwave device with slanted field emitter
US6388379B1 (en) 1998-01-08 2002-05-14 Northrop Grumman Corporation Magnetron having a secondary electron emitter isolated from an end shield
RU2150765C1 (ru) * 1999-04-07 2000-06-10 Санкт-Петербургский государственный технический университет Способ создания широкополосных квазишумовых сверхвысокочастотных сигналов большой мощности и устройство для его осуществления
US6485346B1 (en) 2000-05-26 2002-11-26 Litton Systems, Inc. Field emitter for microwave devices and the method of its production
US6646367B2 (en) 2000-05-26 2003-11-11 L-3 Communications Corporation Field emitter for microwave devices and the method of its production
US20040104679A1 (en) * 2002-11-13 2004-06-03 New Japan Radio Co., Ltd. Pulse magnetron
US7038387B2 (en) * 2002-11-13 2006-05-02 New Japan Radio Co., Ltd. Pulse magnetron with different anode and cathode radiuses
GB2396959B (en) * 2002-11-13 2007-05-09 New Japan Radio Co Ltd Pulse magnetron

Also Published As

Publication number Publication date
GB1399260A (en) 1975-07-02
NL7317243A (enrdf_load_stackoverflow) 1974-06-25
CA1003964A (en) 1977-01-18
FR2211746A1 (enrdf_load_stackoverflow) 1974-07-19
JPS4998168A (enrdf_load_stackoverflow) 1974-09-17

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