US3392308A - Crossed field tube having a pair of permanent magnets of different magn etomotive force - Google Patents

Crossed field tube having a pair of permanent magnets of different magn etomotive force Download PDF

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Publication number
US3392308A
US3392308A US458617A US45861765A US3392308A US 3392308 A US3392308 A US 3392308A US 458617 A US458617 A US 458617A US 45861765 A US45861765 A US 45861765A US 3392308 A US3392308 A US 3392308A
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United States
Prior art keywords
circuit
pair
magnets
region
magnetic
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Expired - Lifetime
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US458617A
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English (en)
Inventor
Edward J Cook
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Varian Medical Systems Inc
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Varian Associates Inc
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Priority to US458617A priority Critical patent/US3392308A/en
Priority to DE19661541087 priority patent/DE1541087A1/de
Priority to FR62496A priority patent/FR1480771A/fr
Priority to GB22897/66A priority patent/GB1129254A/en
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Publication of US3392308A publication Critical patent/US3392308A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00—Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/50—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field
    • H01J25/52—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode
    • H01J25/54—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode having only one cavity or other resonator, e.g. neutrode tubes
    • H01J25/56—Magnetrons, i.e. tubes with a magnet system producing an H-field crossing the E-field with an electron space having a shape that does not prevent any electron from moving completely around the cathode or guide electrode having only one cavity or other resonator, e.g. neutrode tubes with interdigital arrangements of anodes, e.g. turbator tube
    • 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
    • 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
    • H01J23/10—Magnet systems for directing or deflecting the discharge along a desired path, e.g. a spiral path

Definitions

  • a crossed field microwave tube includes a cylindrical slow wave anode circuit structure concentrically surrounding a cathode electrode to define a magnetron interaction region therebetween.
  • An electron gun is disposed at one axial end of the tube for injecting a stream of electrons axially into the interaction region for interaction with the fields of the slow wave anode circuit to produce an output microwave signal.
  • a permanent magnet circuit produces an axial magnetic field through the magnetron interaction region and through the electron beam injection region to produce crossed electric and magnetic fields between the anode and cathode electrodes.
  • the magnet circuit includes a pair of conically shaped permanent magnets disposed at opposite axial ends of the microwave tube for producing the axially directed magnetic field within the tube.
  • a low reluctance magnetic shield encloses the magnets to provide a low reluctance return path for the magnetic field and also to shield the region outside of the magnet circuit from the intense magnetic field produced by the permanent magnets.
  • the magnets produce a magnetic field profile which has a maximum intensity in the electron injection region and which progressively decreases to a uniform magnetic field intensity throughout the interaction region.
  • the permanent magnets are made of platinum-cobalt material, whereby the size and the weight of the magnets are minimized.
  • the magnetic field profile is produced by causing the permanent magnet disposed nearest to the beam injection region to have a greater magnetomotive force than the magnet on the opposite end of the tube.
  • both magnets are of similar truncated conical shapes, except that the magnet producing the greater magnetomotive force has a longer axial length than the other magnet.
  • the optimum magnetic field required for a voltage tunable magnetron is characterized by a first region containing the electron injection gun within which the axial field intensity decreases in the axial direction taken toward the second region containing the anode to cathode interaction gap. Within the interaction gap the magnetic field should have relatively constant intensity.
  • Such a symmetric magnet circuit provides the desired shape inasmuch as the field intensity sags in the middle of the magnet gap to provide a first region of decreasing intensity followed by a relatively flat region of field in the center of the gap.
  • an unnecessary third region of field is produced wherein the field increases in the direction of the field.
  • This undesired field region can be minimized by use of specially shaped pole pieces at opposite ends of the magnet gap.
  • the pole pieces use up a substantial portion of the gap length thereby requiring the magnets to be larger than necessary.
  • the magnetic field may be shaped to conform to the optimum shape having substantially only the desired two regions, one flared and one substantially constant by making one of the magnets of substantially greater magnetomotive force than the other and properly shaping these magnets. In this manner the desired magnetic field is produced with a minimum of magnet material, whereby the size and weight of the magnetic circuit is substantially reduced.
  • the principal object of the present invention is the provision of an improved magnetic circuit for beam injected crossed field tubes and improved tubes using same.
  • One feature of the present invention is the provision of a magnetic field of the proper shape formed by a pair of magnets having substantially different magnetomotive forces, defining the magnetic gap therebetween and being surrounded by a low reluctance magnetic shield whereby size and weight of the magnetic circuit are minimized.
  • Another feature of the present invention is the sameas the preceding feature wherein the magnets are made of platinum cobalt whereby an intense field of high uniformity is obtained without the use of separate pole piece members.
  • Another feature of the present invention is the same as any one of the preceding features wherein the magnets are of truncated conical shape having substantially the same large and small diameters but being of substantially unequal length, the stronger magnet having the longer length whereby fabrication of the circuit is facilitated.
  • FIG. 1 is an enlarged longitudinal sectional view, partly schematic, of the tube and circuit employing features of the present invention
  • FIG. 2 is a graph of magnetic field intensity as a function of gap length for a prior art magnetic circuit using a pair of magnets of symmetric shape and equal magnitude
  • FIG. 3 is a plot similar to that of FIG. 2 showing the field intensity for a magnetic circuit of the present invention and having a pair of magnets of unequal magnetomotive force.
  • the tube 1 comprises an evacuated stacked ceramic vacuum envelope 2 having an external microwave cavity 3 disposed within the gap 4 of a magnetic circuit formed by a pair of trunca'ed conical magnets S and 6 enclosed within a cylindrical low reluctance shield 7 as of 0.150" thick cold rolled steel.
  • the magnetic circuit is more fully described below.
  • Output power is extracted from the tube 1 via an ouput coaxial line 8 coupled by an RF. magnetic coupling loop 9 to the fields of the microwave cavity 3.
  • the vacuum envelope 2 is formed of conventional stacked ceramic configuration formed by a stack of alternating metallized ceramic ring members 11, as of alumina, and conductive electrode members, having disk like flange portions, all brazed together to form a composite envelope with the electrode structures passing through the side walls of the ceramic vacuum envelope 2.
  • One end of the ceramic envelope 2 is closed by a ceramic plate 12 while the other end is closed by an electrode brazed into the end ring 11 of the envelope 2.
  • the tube electrodes Internally of the envelope 2, the tube electrodes include a bifilar coil filamentary emitter 13 as of thoriated tungsten emitter wire disposed at one end of the envelope 2.
  • emitter 13 includes a pair of leads 14 and 15 passing through and sealed into the end ceramic plate 12 in a vacuum tight manner.
  • a ring shaped beam injector anode electrode 16 as of copper surrounds the emitter 13 and includes a disk-like portion 17 passing out through the side wall of the envelope.
  • a cold cathode electrode 18 as of molybdenum is coaxially disposed of the envelope 2 in axially spaced relation from the emitter 13.
  • the cold cathode electrode 18 includes a cylindrical sole portion 19 and a flared end portion 21 which is sealed across the central opening in the end ring 11 of vacuum envelope 2.
  • An interdigital anode circuit 22 coaxially surrounds the sole portion 19 of the cold cathode electrode 18.
  • the interdigital anode circuit is formed by a-pair of slotted and interdigitated flared cylinder members 23 and 24 as of copper. More specifically the cylindrical portions of each of the members 23 and 24 are slotted with an array of axial slots 25 to form an array of conductive fingers 26 in each of the cylindrical portions of the electrodes 23 and 24. The finger arrays 26 are then angularly displaced relatively to each other and then interdigitated to form the interdigital line anode circuit 22.
  • the circuit 22 is supported by means of the disk-like flange portions 27 and 28 of the cylindrical members which flange portions extend outwardly of and through the envelope 2 to the external microwave circuit 3.
  • the external circuit is formed by an annular conductive channel 29 as of copper which is of generally toroidal shape.
  • the channel 29 is aflixed to the disk like flange portions as by silver soldering at the mating edges of the disk flange member portions 27 and 28 to form a rigid tube structure.
  • the channel 29 is apertured at 31 to receive the coaxial output line 8 and loop 9.
  • a small cathode heater voltage is derived from battery 33 and fed across the directly heated cathode emiiter filament 13 via leads 34 and 35, respectively, which include separate electrode portions 34' and 35' brazed across the ceramic end plate 12 of the envelope 2 which in turn connect to filament leads 14 and 15, respectively.
  • the negative potential side of the cathode filament 13 is also connected via insulated lead 36 to the cold cathode electrode 18.
  • the lead 36 passes between the outside wall of the toroidal microwave circuit 3 and the inside wall of the magnetic shield 7.
  • the toroidal microwave circuit 3 is made to have a slightly smaller outside diameter than the inside diameter of the shield to allow suflicient clearance for the lead 36.
  • An injector anode voltage supply 37 as of 525 volts positive with respect to the cathode emitter 13 and electrode 18 is connected to the injector electrode 17 via insulated lead 38.
  • a variable positive anode voltage supply 39 as of 1000 to 1800 volts relative to the injector voltage, is applied to the anode circuit 22 and interconnected mag netic circuit via grounded lead 41.
  • a pair of insulator sheet members 42 as of 0.015" thick Teflon are disposed between the magnets and 6 and the end electrode portions of the tube envelope 2 for holding off the applied anode to cathode voltage, as of 1500 to 2300 volts.
  • the tube envelope 2 with fixedly attached external microwave circuit 3 is fixedly held in position within the surrounding magnetic circuit by means of a solid epoxy potting material such as Stycast No. 1090 made by Emmerson Cummings and introduced, in fluid form, into the voids 44 between the tube envelope 2 and the enclosing magnetic circuit members 5, 6 and 7 via suitable holes, not shown, in the cylindrical shield 7.
  • the potting material is then allowed to set up to form a solid rigid tube structure.
  • electrons emitted from emitter 13 are formed into a tubular stream and injected axially into the annular electronic interaction region 45 via the combined action of the radial electric fields between the electrodes 13, 17, 18 and 22 and the axial magnetic field produced by the magnetic circuit.
  • the electrons circulate around the sole 19 of the cold, cathode electrode 18 cumulatively interacting with the RF. fields of the interdigital line to produce backward wave oscillation on the anode circuit 22.
  • Power is extracted from the circuit 22 and fed to a load via output loop 9 and terminal 8.
  • the output frequency depends upon the anode to cathode voltage and thus the tube 1 is electronically tuned by varying the voltage of voltage supply 39.
  • the optimum magnetic field in gap 4 is characterized by having a constant intensity in the electronic interaction gap 45 while flaring to increased intensity in the injector region 46.,This shape of field properly introduces the stream of electrons into the interaction region and yields optimum efliciency.
  • the prior method for obtaining the desired field shape in the injector and interaction regions is illustrated in FIG. 2 and comprised use of two magnets 5 and -6 polarized in the same direction and of equal magnetomotive force.
  • Such a magnetic circuit produced a satisfactory flared intensity in the injection region 46 but produce a variance of about gauss, at about 2000 gauss, over the length of the interaction region 45. This is a substantial variance from the desired constant intensity of fieldover the interaction region 45.
  • this prior magnetic circuit includes the second flared intensity region 47 which is as large as the injector flared region and which third region 47 is not serving any useful purpose.
  • the second flared region represents wasted magnetomotive force and thus requires more magnet weight and size than necessary.
  • FIG. 3 there is shown the magnetic field intensity plot for the magnetic circuit of FIG. 1 wherein the magnetomotive force of the injector magnet 5 is substantially greater than the magnetomotive force of the cold cathode magnet 6.
  • the desired shape of field is produced having the flared intensity injection region 46 and uniform intensity interaction region 45 without the necessity of producing the third flared intensity region as encountered in the prior art. Accordingly, in the improved field shaping circuit of FIGS. 1 and 3, the magnet gap length can be reduced to a minimum thereby conserving magnetomotive force and thereby reducing the size and weight of the magnetic circuit.
  • a magnetic circuit of the present invention as used for a voltage tunable magnetron tube 1 operable over the range from 2.6 to 3.7 gc. with power output of 12 watts the gap length is about 0.700", the magnets are of equal diameter for ease of construction having maximum diameters of 1.300" and minimum diameters of 0.875" with the larger magnet 5 having an axial length of 0.500” and the smaller magnet having a length of 0.310".
  • the magnets 5 and 6 were made of platinum-cobalt and provided a uniform magnetic intensity of 1950 gauss over the interaction region 45 which was 0.200 long with only a 40 gauss variance between maximum and minimum field intensities within the interaction region 45.
  • said magnetic circuit means including, a pair of permanent magnets spaced apart to define a magnetic gap therebetween which contains the DO magnetic field threading through both said regions of space, and said permanent magnet of said pair of permanent magnets which is closest to said region of most intense field having a substantially greater magnetomotive force than the other permanent magnet of said pair of magnets, whereby the size and weight of said magnetic circuit is minimized.
  • the apparatus according to claim 2 including means forming a magnetic shield of relatively low reluctance material surrounding said pair of magnets and said magnet gap therebetween and providing a relatively low reluctance return path for magnetic field lines between said magnets but oppositely directly to the field lines in the magnet gap.
  • a microwave tube apparatus including means forming a hollow cylindrical dielectric evacuated envelope, means forming a thermionic cathode emitter at one end of said envelope, means forming a cold cathode sole electrode projecting axially of and into said envelope from the other end thereof, means forming an anode circuit surrounding said sole electrode and passing through the cylindrical side portions of said envelope to define an internal anode circuit portion and an external anode circuit portion external of said vacuum envelope, means forming an injector anode electrode surrounding said cathode emitter, means forming a pair of spaced permanent magnets disposed at opposite ends of said cylindrical envelope and defining a magnetic gap therebetween with the magnetic field lines of said magnet gap being axially directed of and threading through said cylindrical envelope, said pair of permanent magnets being energized and shaped such that one permanent magnet produces substantially greater magnetomotive force than the other permanent magnet of said pair, and the magnet having the greater magnetomotive force being disposed at the emitter end of said vacuum envelope to produce a magnetic field shape having greater intensity in

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  • Microwave Tubes (AREA)
US458617A 1965-05-25 1965-05-25 Crossed field tube having a pair of permanent magnets of different magn etomotive force Expired - Lifetime US3392308A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US458617A US3392308A (en) 1965-05-25 1965-05-25 Crossed field tube having a pair of permanent magnets of different magn etomotive force
DE19661541087 DE1541087A1 (de) 1965-05-25 1966-05-20 Kreuzfeld-Mikrowellenroehre mit verbessertem Magnetkreis
FR62496A FR1480771A (fr) 1965-05-25 1966-05-23 Circuit magnétique perfectionné et tube à champs croisés en comportant application
GB22897/66A GB1129254A (en) 1965-05-25 1966-05-23 Improved magnetic circuit and crossed field tubes using same

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Application Number Priority Date Filing Date Title
US458617A US3392308A (en) 1965-05-25 1965-05-25 Crossed field tube having a pair of permanent magnets of different magn etomotive force

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DE (1) DE1541087A1 (de)
GB (1) GB1129254A (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3558970A (en) * 1968-05-14 1971-01-26 Philips Corp Resonant cavity magnetrons using cathode heater currents to intensify magnetic fields
US4048542A (en) * 1975-04-25 1977-09-13 Tokyo Shibaura Electric Co., Ltd. Permanent magnets of different magnetic materials for magnetrons
US4071804A (en) * 1975-01-31 1978-01-31 Tokyo Shibaura Electric Co., Ltd. Magnetron device having magnetic means for generating a uniform interaction field
US4104559A (en) * 1976-11-01 1978-08-01 Microwave Associates, Inc. Isopolar magnetron supported with rigid insulation in a remote housing
US5635798A (en) * 1993-12-24 1997-06-03 Hitachi, Ltd. Magnetron with reduced dark current
WO2005083735A2 (en) * 2004-02-27 2005-09-09 E2V Technologies (Uk) Limited Electron beam tubes

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1504344A (en) * 1974-08-03 1978-03-22 Matsushita Electric Ind Co Ltd Magnetron

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2473547A (en) * 1945-09-28 1949-06-21 Raytheon Mfg Co Electron discharge device
US2939046A (en) * 1958-06-16 1960-05-31 Gen Electric Electron beam control
US3229152A (en) * 1961-10-19 1966-01-11 Gen Electric Magnetron having evacuated discharge subassembly united with unevacuated magnetic andresonant cavity structure
US3302060A (en) * 1963-07-17 1967-01-31 Philips Corp Control system for regulating the current in a magnetron tube

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2473547A (en) * 1945-09-28 1949-06-21 Raytheon Mfg Co Electron discharge device
US2939046A (en) * 1958-06-16 1960-05-31 Gen Electric Electron beam control
US3229152A (en) * 1961-10-19 1966-01-11 Gen Electric Magnetron having evacuated discharge subassembly united with unevacuated magnetic andresonant cavity structure
US3302060A (en) * 1963-07-17 1967-01-31 Philips Corp Control system for regulating the current in a magnetron tube

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3558970A (en) * 1968-05-14 1971-01-26 Philips Corp Resonant cavity magnetrons using cathode heater currents to intensify magnetic fields
US4071804A (en) * 1975-01-31 1978-01-31 Tokyo Shibaura Electric Co., Ltd. Magnetron device having magnetic means for generating a uniform interaction field
US4048542A (en) * 1975-04-25 1977-09-13 Tokyo Shibaura Electric Co., Ltd. Permanent magnets of different magnetic materials for magnetrons
US4104559A (en) * 1976-11-01 1978-08-01 Microwave Associates, Inc. Isopolar magnetron supported with rigid insulation in a remote housing
US5635798A (en) * 1993-12-24 1997-06-03 Hitachi, Ltd. Magnetron with reduced dark current
WO2005083735A2 (en) * 2004-02-27 2005-09-09 E2V Technologies (Uk) Limited Electron beam tubes
US20050200283A1 (en) * 2004-02-27 2005-09-15 E2V Technologies Limited Electron beam tubes
WO2005083735A3 (en) * 2004-02-27 2005-10-20 E2V Tech Uk Ltd Electron beam tubes
US7187130B2 (en) 2004-02-27 2007-03-06 E2V Technologies (Uk) Limited Electron beam tubes including a vacuum envelope seal and having a metallized balance ring

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DE1541087A1 (de) 1969-09-11
GB1129254A (en) 1968-10-02

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