US2462137A

US2462137A - Electron discharge device

Info

Publication number: US2462137A
Application number: US650358A
Authority: US
Inventors: William V Smith
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1946-02-26
Filing date: 1946-02-26
Publication date: 1949-02-22
Anticipated expiration: 1966-02-22
Also published as: DE968094C

Description

Feb. 22, 1949.

w. v'. SMITH ELECTRON DISCHARGE DEVICE Filed Feb. 26, 1946 2 Shets-Sheet 1 F/Gi/ {g so Feb. 22, 1949. V w. v. SMITH 2,462,137

ELECTRON DISCHARGE DEVICE Filed Feb. 26, 1946 2 Sheets-Sheet 2 F/GZ.

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Patented Feb. 22, 1949 I ELECTRON DISCHARGE DEVICE William V. Smith, Medford, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application February 26, 1946, Serial No. 650,358

6 Claims.

This invention relates to electron-discharge devices, and more particularly to such devices as are known as magnetrons.

This invention is particularly suitable for tuning or frequency modulation magnetrons which are adapted to generate microwaves having a wavelength of the order of several centimeters or less.

An object of this invention is to produce such a device in which the frequency of the oscillations may be modulated over an extremely wide band, for example, megacycles or more.

Another object is to devise such an arrangement in which the energy required to produce the frequency modulation is reduced to a small value.

A further object is to devise such an arrangement in which the current flow in the modulating circuit is very small.

The foregoing and other objects of this invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings wherein:

Fig. 1 is a fragmentary, longitudinal section of an electron-discharge device incorporating the invention;

Fig. 2 is a fragmentary, transverse section taken along line 2-2 of Fig. 1.

Fig. 3 is a fragmentary, perspective view with certain parts broken away showing the relationship of one of the modulating electrodes with respect to the anode arms; and

Figs. 4 and 5 are circuit diagrams representing two typical modulating circuits.

The arrangement as shown in Figs. 1 and 2, illustrates a magnetron indicated generally by the reference numeral I. This magnetron includes an anode structure 2, a cathode structure 3, a magnetic means 4 for establishing a magnetic field in a direction generally perpendicular to the electron path between said cathode and anode structures and a pair of modulating elec- The anode structure 2 preferably comprises a cylindrical body I made of a highly conductive material such as copper and provided with a plurality of anode members in the form of interiorly extending, radially disposed vanes 8. The cylindrical body 1 is closed at its end by plates 9 and ill, the junction between said body and said plates'being hermetically sealed as by silver solderin The c lindrical body 1 is of such diameter and the number, size and relative spacing of the vanes 8 are so chosen that each pair -2 of adjacent vanes, together with that portion of said cylindrical body lying therebetween, defines a cavity resonator adapted to oscillate in the desired frequency range.

The cathode structure 3, which is coaxial with the anode structure 2, preferably comprises an elongated sleeve I l, conventionally made of nickel or the like, and having a reduced portion I2 which is substantially coextensive with the vertical dimension of the vanes 8 and provided with a highly electron-emissive coating, for example, of the well known alkaline earth metal oxide type. In order to support the cathode sleeve ll with respect to the anode members 8, said sleeve may be reduced at its lower end to fit into a tubular conducting member l3 adapted to be supported from a tubular pole piece I hermetically sealed into the end plate 9. The pole piece M is provided with a bore Illa through which the cathode structure may enter the device. A sleeve l5 of a metal which seals well with glass is sealed in the lower end of the pole piece M. A glass sleeve I6 is sealed to the lower end of the sleeve l5 and in turn is sealed to and carries av metal sleeve H. The lower end of the tubular member [3 is electrically connected and supported by the sleeve I! in any desired manner not shown. The cathode sleeve H may be heated by a filament not shown connected at one end [8 to said sleeve and at the other end to a lead-in conductor l9 suitably entering said device through a glass seal not shown in the lower end of the sleeve l1.

Current may be conveyed to the heating filament by connecting an appropriate source of Voltage between the member I! and the lead-in conductor l9.

Another pole piece 20 is hermetically sealed. into the end plate ill. The pole piece 20 is likewise provided with a bore 20a terminating in a tubular member 2! sealed in the upper end thereof. The device is adapted to be evacuated through said tubular member which is then sealed at its upper end. The pole pieces 20 and I l are fixed, for example, at the opposite ends of a horseshoe magnet not shown, the two Dole pieces and the horseshoe magnet constituting the above-mentioned magnetic means 4 for establishing a magnetic field transverse to the electron path between the cathode and anode structures of the device.

The modulating electrodes 5 and 6 are supported adjacent the upper and lower open ends of the cavity resonators. The surfaces facing these open ends are preferably so constituted as to be good secondary electron emitters. For exductor 22 passing out of the device through a.-

pipe 23 threaded and hermetically sealed in the cylindrical body l. The outer :end of the. conductor 22 passes through a glass seal 24-carriedc by the outer end of said pipe 23. Likewise; the electrode 6 is supported by a conductor 25.which passes out through a pipe 26 and a glass sleeve 21 similar to those described in connecti0n-with-- the electrode 5.

When the device is generating oscillations, these oscillations may be let out therefrom by means of a loop 28 introduced into one of. the cavity resonators, said loop being supported by apipe 29 threaded and hermetically sealed in the cylindrical body 1. One end of the loop 28 is-connected' to the inner end of said pipe and the other end passes out through a glass sleeve Elli-supported at the outer end of said p pe.

As illustrated in Fig. 4, the cathode 3 may be maintained at the proper negative potential by a source of such potential illustrated diagrammatically as a battery 3!. Pursuant to this in-,- vention it is desirable that the electrodes 5 and 6- be' biased negatively with respect to the anode :2

structure 2. For this purpose biasing sources of potential illustrated diagrammatically as

batteries

32 and 33 may be interposed between the electrodes 5 and 6 and the anode structure 2. In series with one of the sources of biasing potential may be placed a suitable source of modulating voltage 34. The maximum amplitude of this modulating voltage is preferably related to the biasvoltage 33 so that the electrode 6 never becomes appreciably positive during operation. In a particular embodiment in which the voltage 3| was about 1200 volts, the voltage 32 about 500 volts, the voltage 33 about 250 volts and the modulation voltage having an amplitude between its maximum positive and negative peaks of about 500volts, the frequency at which the device oscillated could be varied through a range of about 15 megacycles.

In accordance with my present understanding of the theory of operation of this device, I believe that the operation is substantially as follows. In the space immediately adjacent either of the electrodes 5 and 6, will be found some free electrons whether due to the emission from the oathode 3 or from some other source. These electrons will be impelled under the voltage existing between the electrode 5 for example and the anode 2"in a direction toward the open ends of the cavity resonators. The device which under these conditions will be generating oscillations will have produced between the outer ends of the vanes 8 a high voltage, high frequency electrical field. Therefore, as the electrons enter this region they will be subjected to the action of the longitudinal magnetic field as well as the action of the transverse high frequency electrical field. Under these conditions, the electrons will travel in a variable spiral path toward the lower open end of the the electrons from being captured by the surfaces of the vanes 8. As the electrons in a particular cavity emerge from the lower end thereof, those electrons which are in proper phase relation with respect to the high frequency electrical field will have imparted thereto a considerable acceleration. If there were no electrode such as 6, interposed in their path, these electrons would be quickly captured, for example, by the pole piece [4 or by the cover 9. However, the electrode 6 which is interposed in the path of these electrons will intercept them. The acceleration to which these electrons are subjected by the high frequency electrical field :will be suflicient to cause them to liberate large numbers of secondary electrons from the electrode 6. These secondary electrons will .be impelled by the bias voltage existing between the electrode and the anode structure-in adirection to reenter the cavity resonator. Those electrons which are not in proper phase with respectto the high frequency electrical field,

as they tend to emerge. from thelower end of, the

cavity resonator, will be deceleratedand willjree enter the cavity resonator. thus joining with the .1 secondary electrons emitted from theelectrodefi.

in their travel through the cavity resonator in an upward direction toward the electrode 5. At the upper end of the anode structure a similar action occurs as the electrons emerge from the; cavity resonators thus producing a large amount of secondary emission from the electrode 5. Under; these conditions, an electron multiplying action-is.

created between the electrodes 5 and 6 which reeach of the cavity resonators.

the space within each of' the cavity resonators and thus, by varying-the density of this electron.

population, the frequency at which the cavity trolled.

oscillating circuit thus imparting to the device a 1 relatively high efiiciency.

By varying the extent to which the electrons between either or both of the

electrodes

5 and 8 and the anode 2 are reflected into the cavity resonators, the densityof'the electron concentration in the cavity resonators readily may be controlled. Thus, for example, by interposing the modulation voltage 34 in the connection extending to the electrode 5, the frequency modulation described above may be obtained.

Electrons which pass directly from either of the electrodes 5 and B to the upper ends of the vanes 3 constitute an ineffective flow of current and thus it is desired that such flow be reduced to a minimum. For this purpose, electrodes 5 andfi may'each be provided with an electrical shielding member 35 supported by each of said electrodes. This shielding member 35 is provided with a plurality of inwardly extending radial arms which are closely spaced" from and substantially cover those upper surfaces of the vanes 8 which tend to intercept the electrons. In this way the electron flow is constrained to pass between the anode arms 81 Although both of the electrodes 5 and 6 have been described as being electron emissive, in some instances one of these electrodes may be thus constituted, the other electrode serving sole- 1y as an electron reflecting member. However,

under these conditions, a substantial amount of frequency modulation may likewise be obtained Instead of modulating the voltage on but one of the electrodes 5 and 6, various other circuit arrangements may be devised. For example, in Fig. 5 there is illustrated an arrangement in which the voltage on both of these electrodes is modulated. The electrodes 5 and 6 may be connected together and a connection extending from the common lead to the anode structure may include a biasing battery 36 and a source of modulation voltage 31. In this instance likewise the biasing battery 36 is so polarized as to tend to maintain the electrodes 5'and 6 negative with respect to the anode structure 2. Such an arrangement likewise produces the desirable frequency modulation.

Although the electrodes 5 and 6 have been indicated as being sources of secondary electrons, other types of electron sources may be utilized.

For example, either one Or both of the electrodes 5 and 6 may be heated to temperature of thermionic emission. Under these conditions also the shielding member 35 effectively reduces the current flow and driving power required in the modulating circuit.

Of course it is to be understood that this invention is not limited to the particular details as described above inasmuch as many equivalents will suggest themselves to those skilled in the art.

What is claimed is:

1. An electron-discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a source of electrons facing one of said open ends, an electron-reflecting electrode facing the other of said open ends, and means adjacent said source of electrons for shielding the surfaces of the anode arms from electrons emitted from said source.

2. An electron-discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a pair of electrodes facing said open ends, one of said electrodes being electron emissive during operation, and means adjacent last-named electrode for shielding the surfaces of the anode arms from electrons emitted from said last-named electrode.

3. An electron-discharge device comprising a 6 cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together With that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a pair of electrodes facing said open ends, one of said electrodes having a secondary electron-emissive surface, and means adjacent said last-named electrode for shielding the surfaces of the anode arms from electrons emitted from said last-named electrode.

4. An electron-discharge device comprising a cathode, an anode structure spaced from said cathode and including a cavity resonator open at its ends, a source of electrons facing one of said open ends, an electron-reflecting electrode facing the other of said open ends, and means intermediate said source of electrons and said anode structure for shielding the surfaces of said anode structure facing said source of electrons from electrons emitted from said source.

5. An electron-discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms Which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a source of electrons facing one of said open ends, an electronreflecting electrode facing the other of said open ends, and a pair of metallic fingers depending from said source of electrons and interposed between said source and the adjacent surfaces of said anode arms.

6. An electron-discharge device comprising a cathode, an anode structure spaced from said cathode and including a pair of anode arms which, together with that portion of the anode structure lying therebetween, defines a cavity resonator open at both ends, a source of electrons facing one of said open ends, an electronreflecting electrode facing the other of said open ends, and a shielding member supported intermediate said source of electrons and the adjacent surfaces of said anode arms for shielding the latter from electrons emitted from the former.

WILLIAM V. SMITH.

REFERENCES CITED Name Date Schmidt Dec. 31, 1946 Number