US2871406A

US2871406A - Injection magnetrons

Info

Publication number: US2871406A
Application number: US687441A
Authority: US
Inventors: Dunsmuir Robert
Original assignee: British Thomson Houston Co Ltd
Current assignee: British Thomson Houston Co Ltd
Priority date: 1956-10-16
Filing date: 1957-10-01
Publication date: 1959-01-27
Anticipated expiration: 1976-01-27
Also published as: GB869603A

Description

Jan. 27, 1959 R. DUNSMUIR INJECTION MAGNEITRONS 2 Sheets-Sheet 1 Filed Oct. l, 1957 Jan. 27; 1959 R. DUNSMUIR INJECTION MAGNETRONS 2 Sheets-Sheet 2 Filed Oct. l,v 195'? M. Wl w m m m 4,1m f

//v vfw rox? n hrz-omver United States Patent-O INJECTION MAGNETRONS Robert Dunsmuir, Rugby, England, assignor to The yBritish Thomson-Houston Company Limited, London, England, a British company Application October 1, 1957, Serial No. 687,441

Claims priority, application Great Britain October 16, 1956 4 lClaims. (Cl. 315--39.63)

This invention relates to multi-cavity magnetron oscillators and amplifiers of the injection type and has for its object to provide an improved electrode arrangement for such devices.

Magnetrons are known in which an yannular beam of electrons is injected from one end of, andinto an annular interaction space between a cavity anode and an electrode coaxial therewith and maintained at a negative potential with respect to the anode. In such known types of magnetron, however, the electrons in the beam enterthe interaction space with widely varying angular velocities, resulting, in part, from the dispersion of the electron emittingfsurface with relation to the remaining electrodes'.

It is a further object of the invention to provide irn- Vproved means for injecting the electron beam so that all lor a majority of, the electrons in the beam have almost a uniform angular velocity `on injection. f e

A magnetron in accordance with the invention yhas an 4electrode system arranged to produce, in an .annular space, a wall of whichis formed to provide resonant cavities, a radial electrostatic field, into one end of which space a cylindrical beam of electrons is injected, the electrons v injected into said space being caused to proceed in substantially helical paths by means of an axial magnetic field produced therein whereby to induce or amplify os. cillations in said cavities.

In carrying out the invention a short cylindrical cathode, preferably of the emission-limited type, is mounted at one end of the magnetron co-axial with the annular lspace in which a radial electric field is developed, the cathode being surrounded by an annular anode concenrice Theinvention will be more readily understood from a consideration of the 4vfollowing description of an embodinent shown in the accompanying drawings, in which Fig. 1 is a diagrammatic representation of the electrode "structure of the magnetron indicating the electron paths,

Fig. 2 is a plan view away, and

Fig. 3 is a cross-section on the line 3,3, of Fig. 2.

Referring to Fig. 1, the main cavity anode is shown at 10; concentrically located within it and shown in interrupted lines is a cylindrical post electrode 11, maintained at a negative" potentialr with respect to the main anode and to the cathode 12. The cathode 12 and its asso; ciated electrodes are designed to inject into the annular interaction space between the main anode 10 and the cylindrical electrode 11 a hollow cylindrical beam -of elec trons, indicated at13. The electron beam, as well as being projected axially into the annular space between the main anode l10 and the cylindrical electrode 11, is in-i fluenced by a magnetic held produced axially of the elecvtrode structure (not shown) as indicated by the arrowed lines, so that the electrons are given a continuous circumferential component of motion resulting in the elec: trons in the beam proceeding in a helical path, indicated at 14. The annular beam of electrons is produced of the magnetron, partly broken by forming the cathode 12 with an annular emissive sur,l

face 15- from which the electrons emerge, the electrons being omitted initially in a radial direction by the electrostatic field produced between the cathode 12 and a' first annular anode 16,shown in interrupted lines,and maintained4 at a positive potential with Vrespect to the cathode. The annular beam of electrons is injected into the annular interaction spaceby means of an annular de'-l fiecting electrode 17 maintained at a high negative po? tentialwith respect to the cathode. The arrangement of the electrodes'and the potentials applied to them are such that the electronskin the annular beam are rotating in a helicalipath when theylv enter the inteaction space with l an angular velocity synchronous with the wave which propagates von the anode circuit.

trically disposed and at a positive potential with respect to the cathode. Electrons are emitted by the cylindrical 4surface of the cathode when it is heated, and travel t wards the annular anode, but they are deflected in an axial direction by an annular electrode at negative potential, situated adjacent the annular gap between" the cathvv ode and the annular anode.

Partly shaded from the cathode by the annular anode is Ya main anode which forms a wall of the annular! space.

The main anode is of larger diameter thanv the annular anode, has the resonant cavities formed therein, and is mounted co-axial with the annular anode. The main an rode is axially displaced with respect to the annular anode and is at a more positive potential. Concentrically within it is located a cylindrical electrode `at a negative potential with respect to the main anode and to the cathode. There is thus developed in the `annular interaction `space between the main anode andthe -cylindrical elec-` trode within it an electric field into which the 4annular beam of electrons originating at the cathode is injected,-

The spatial arrangement of the electrodes is shown more clearly in the cross-section of the magnetron 'ilJ lustrated inFig. 3, in which similar reference numerals have been used to indicate corresponding parts referred ,to in connection with Fig.v 1.

The vcathode* l12 is preferably ofthe emission-limited type; i. e, emissionis temperature limited, i. e. itis determined bythe temperature and not by the space charge, and may consist, for instance, of a disc Vof tantalum. lItis heated by radiation from a filament 18 to which heating current is applied through a lead-in conductor 19, the other end 'of the heating filament being connected to the V"stern 20 which ksupports the cathode disc.

` Thestem 20 is secured to cover plate 21 which, toa

20 by means of an insulating collar *25, and is connected electrically to an insulated bushing 32.

Coaxial with the cathode is mounted the cylindrical electrode 25 between which and the anode 10 is formed the annular interaction space into which the electron beam is injected. Electrode 26 is mounted upon a stem 27 insulatingly supported from the cover plate 22. Electrode 26 is in the form of a hollow cylinder having a central web 28 by which it is mounted upon the stern 27, the innerend of thestem 27 supporting a heat shield 29. Anode is supported on Vthree insulated conductors 30, angularly disposed at 120 and passing through glass-to-metal seals 31. I l Y The annular anode, which is maintained. at a positive potential with respect to the cathode to induce an initially radial flow of electrons therefrom, `is shown at i6. lt is insulatingly Supported upon bushing 32 led through the cover plate 21 and insulated therefrom by a glass-tometal seal 33, and two other` similar posts angularly disposed at 120, to one of which it is electrically connected.

After the electron beam has traversed the annular interaction space, it is received by aucollector electrodeV 34, insulatingly supported from the cover plate 22 which in the specific example described is of steel.l

The magnet poles 34 between which the axial magnetic field is produced to cause the electrons injected into the annular interaction space, are centered on the

cover plates

21 and 22 by locating shoulders shown at 35.

Oscillatory energy is withdrawn Vfrom the main cavity anode 10 by means of an output coupling lead 36 which extends through an aperture in the wall of the main anode to end in a coupling loop of the usual type located within one of the anode cavities. The cavities may be coupled together by the customary strapping.

Assuming that the magnetron is subjected in the normal manner to an axial magnetic field, the electron beam, as well as being projected axially by the electric field provided by the annular deflecting electrode, is also influenced by a continuous circumferential component of force, tending to rotate the electrons in the beam in a circular orbit about the axis of the device.

Under the influence of the electric and the magnetic fields, the electrons enter the annular interaction space projected on spiral orbits, and as electrons are emitted by the Whole cylindrical surface of the cathode, there is a cylindrical Wall of electrons enteringthe interaction space all set on a helical course.

It will be understood that after the electrons enter the interaction space they are influenced also by the high frequency wave, and generate or amplify oscillationsV in the resonant circuit according to well-known magnetron principles.

ln a typical arrangement the potentials applied to the electrodes would be as follows r' Main anode 1o kv +415 First anode 16 kv-- `|1.4l vPos1: electrode 11 kv 1.3 Cathode 12 0 Deflecting electrode 17 kv -5 Magnetic eld gauss 570 The main anode has an internal diameter of 2.65

and a length 1.45. and the post electrode external diameter is 1.68. The power output is 5 kw. for a wavelength of l0 cm.

Whilst in the above description the main 'anode is referred to as containing resonant cavities, it is clear that a segmental type lof construction may be adopted for `the main anode and that in speaking of resonant cavities it is desired to include such a construction Within this term.

What I claim is: v

l. An injection type magnetron comprising an'evacuated chamber containing a cathode providingan annular electron emissive surface, a first anode of annular shape vsurrounding said cathode, a main anode coaxial with said cathode and formed to provide resonant cavities in which oscillations are adapted to be produced, a post electrode coaxial with said cathode and said main anode and forming with said main anode an annular interaction space into which an annular electron beam from said cathode is adapted to be injected, said annular interaction space being axially displaced from said cathode, an annular electrode disposed on the opposite side of said cathode from said interaction space and adapted to deflect electrons initially emitted from said cathode towards said first anode in an'axial direction towards said interaction space, and means for producing a magnetic eld axially of said cathode and said main anode whereby to impart to the electrons in said beam as they enter said interaction space an angular velocity synchronous with waves propagated in said anode.

2. An injection type magnetron comprising an evacuated chamber containing a cathode providing an annular electron emissive surface, heating means for said cathode, a first anode of annular shape surrounding said cathode, a main anode coaxial with said cathodeand formed to provide resonant cavities in which oscillations are adapted to be produced, a post electrode coaxial with said'cathode and said main anode and forming with said main anode an .annular interaction space into which an annular electron beam from said cathode is adapted to be injected, said annular interaction space being axially displaced lfrom said cathode, an annular electrode substantially enclosing said heating means disposed on the opposite side of saidv cathode from said interaction space and 4adapted to be charged negatively with respect to said cathode whereby to deiiect electrons initially emitted from said cathode towards said first anode in an axial direction towards said interaction space, and means for producing a magnetic field axially of said cathode and main anode whereby to impart to the electrons in said beam as they enter said interaction space an angular velocity synchronous with waves propagated in said anode cavities. v

3. An injection type magnetron comprising an evacuated chamber containing a cathode providing :an annular electron emissive surface, means for heating said cathode, a rst anode of annular shape surrounding said cathode, a main anode coaxial with said cathode and formed to Aprovide resonant cavities in which oscillations are adapted to be produced, a post electrode coaxial with said cathode and said main anode and forming -said lmain anode an annular interaction space into which an annular electron beam from said cathode is adapted to be injected, said annular interaction space being axially displaced from lsaid cathode,Y an annular electrode disposed on the opposite side of said cathode from said interaction space and adapted to be charged negatively with respect to lsaid 'cathode whereby to deflect electrons initially emitted from said cathode towards said iirst fanode in la radial direction towards said interaction space, saidannular electrode being constructed to form a heat shielding enclosure around said cathode heating means, Vmeans for producing `a magnetic field axially of said cathode and main anode whereby to impart to the electrons in said hea'm as they enter said interaction space `an kangular .velocity synchronous 'with waves propagated in :said yanode cavities, and electrode means for receiving elec trons from said annular Vinteraction'space after they have completed their passage therethrough.

4. An injection type magnetron comprising an evacuated chamber containing a cathode providing an annular electron emissive surface,`heating means for saidcathode, a 'main 'anode coaxial with Asaid cathode and formed to klprovide resonant cavities in which oscillations areadapted to be produced, a post electrode coaxial with said cathode `and-said main anode Aa'nd lforming with said main anode an annular interaction space into which `anannular :electron beam from said cathode is adapted to be injected, a

first anode of annular shape surrounding said cathode and co-operating therewith to provide an electron beam initially proceeding in radial paths to said rst anode, said first anode extending into said interaction space, an electrode substantially enclosing said heating means and formed to provide an annular rim extending towards said interaction space, said electrode being disposed on the opposite side of said cathode from said interaction space and adapted to be changed negatively with respect to said cathode, whereby to deect electrons emitted from said cathode towards said lirst anode in an axial direction towards said interaction space, and means for producing 6 a magnetic eld axially of said cathode and said main anode whereby to impart to the electrons in said beam as they enter said interaction space an angular velocity synchronous with waves propagated in said anode cavities.

References Cited in the file of this patent UNITED STATES PATENTS 2,534,503 Donal et al Dec. 19, 1950 2,538,597 Steele Jan. 16, 1951 2,542,797 Cuccia Feb. 20, 1951 2,602,156 Donal et a1. July 1, 1952