US2668929A - Magnetron - Google Patents

Description

Feb. 9, 1954 E. D. MGARTHUR MAGNETRON Filed April 3, 1952 Fig.6.

Inventor: Elmer D. McArthur,

His Attorney.

Patented Feb. 9, 1954 MAGNETRON Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 3, 1952, Serial No. 280,245

6 Claims. 1

My invention relates to electric discharge devices of the magnetron type.

Numerous magnetron constructions employing an array of anode segments about a centrally located cathode have been employed. as high frequency oscillation generators, the anode segments being interconnected in an anode block or by external circuits to provide a resonant output circuit. One of the problems arising in the design and operation of such devices is caused by the return of high velocity electrons from the magnetron space charge to the cathode. Largely contributing to this undesired effect are the outof-phase electrons which do not do useful work in exciting the resonant output circuits associated with the magnetron anode, and it is accordingly desirable to remove these electrons from the interaction space between the cathode and anode segments to prevent overheating of the cathode.

It is an object of my invention to provide a magnetron discharge device in which cathode backheating is reduced.

It is another object of my invention to provide a magnetron anode gap configuration for improved magnetron operation.

It is a further object of my invention to provide means for removing the non-useful electrons from a magnetron space charge chamber.

According to my invention, the anode segments defining the cylindrical space charge chamber through which an electron-emitting cathode extends are shaped to provide interaction gaps between adjacent segments whose center portions nearer the ends of the anode segments with respect to the desired direction of rotation of the space charge around the cathode. The space charge rotation is established by conventional orthogonally aligned static electric and magnetic fields. When the anode segments are interconnected to provide resonant circuits between them, the alternating electric fields established across the gaps during operation of themagnetron have a component parallel to the axis of the space charge chamber. This component produces a corresponding axial force on the in-phase useful electrons which is directed inwardly from the ends of the anode towards the center portion, thus bunching the useful space charge so that it traverses the leading center portions of the gaps. The out-of-phase electrons are subjected to oppositely directed axial forces, thus. throwing them to the ends of the space charge chamber. of-phase electrons would otherwise cause cathode Due to their high kinetic energy the out- 2 backheating if they remained in the space charge chamber. At the same time, the useful in-phase portion of the space charge is retained for efficient operation.

The features of my invention which I believe to be novel are described with particularity in the appended claims. The invention itself, however, both as to its method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a perspective view of a magnetron discharge device embodying my invention; Fig. 2 is an enlarged view of the anode segment arrangement of Fig. 1; Fig. 3 is a sectional view of another magnetron embodying my invention; Fig. 4 is an end view of the anode of Fig. 3; Fig. 5 is a development of the anode segments illustrating the configuration of the interaction gaps of Fig. 4; and Fig. 6 is a similar development illustrating a modified gap configuration.

Referring now to Fig. 1, I have shown my invention embodied in a magnetron device having a generally cylindrical evacuated glass envelope I having its open end sealed to a metallic base or header member 2. An anode structure 3, which may suitably take the form of a rectangular copper block, has its base conductively secured to the header. A central opening 4 through the thickness of the block and communicating with the upper surface of the block defines the resonant circuit. Thus conductive side portions 5 and 6 of the anode block on diametrically opposite sides of the opening 4 are spaced from each other at the upper portion of the block and are connected in circuit by the base portion of the block.

The facing portions of the anode segments 5 and 6 are shaped to define a cylindrical space charge chamber 1 between them commensurate in length with the block thickness together with interaction gaps 8 and 9 between the facing segments of portions 5 and 6 on diametrically oppo site sides of the space charge chamber 1. An elongated cathode III, which may suitably comprise a wire helix coated with electron-emitting alkaline earth oxides, is centrally disposed within the space charge chamber 1 and coaxial therewith. The ends of the cathode extend beyond the ends of the-space charge chamber so that the cathode is conductively supported between the ends of a pair of upright cathode support rods II which are insulatingly sealed through the metal header 2. The cathode is entirely conventional and is adapted to provide electrons for the magnetron space charge when it is suitably heated, as by applying a heating current voltage across the ends of the support rods ll extending through the header. A pair of conductive cathode end shields or collector electrodes 12 are respectively positioned near the opposite ends of the space charge chamber and are suitably supported by the cathode ends and by auxiliary support members l3 each connected between a support rod II and an adjacent end shield l2. The shields are preferably shaped as disks of a diameter somewhat larger than that of the space charge chamber in order that electrons expelled from the chamber may be collected thereon.

An output coupling means 14 is employed to transfer the high frequency output ener y to a desired load. As shown in the drawing the outer conductor l of a concentric transmissionline coupling section is conductively secured to the header 2 and the inner conductor" lit is insulatingly sealed through the header 2 and the base of anode block 3 in order to provide an inductive pickup loop within the anode opening 4.

In accordance with myinvention, as may be seen more clearly in Fig. 2, the interaction gaps '8 and 9 between the opposing faces or segments of the anode portions '5 and 5 are not provided with straight gap-defining edges but instead have a chevron shape. As oriented in Figs. 1 and 2, the apex of each chevron, a viewed from the cathode, is positioned midway along the length of the gap and is directed in a counterclockwise direction of rotation about the cham- 9 her. Thus, it may be seen that with respect to a given direction of space charge rotation around the cathode, the ends of each gap lag its center portion. This direction of space charge rotation is provided in operation when a static magnetic field, such as may be supplied by the sole noid schematically represented by the coil il in l, is supplied through the space charge chamber 1 and coaxial therewith, and a radial electric field is supplied between the cathode and the anode by applying a positive voltage to the anode block A with respect to the cathode. This space charge excites the resonant anode circuit in a conventional manner in that electrons in phase with the alternating electric field induced between the anode segments on opposite sides of gaps 8 and 9 give up part of their kinetic energy to the field.

Referring again to Fig. 2 where the chevron configuration of the gaps 3 may be more clearly viewed, it is apparent that the alternating electric field between the facing segments of the anode portions 5 and 6 on opposite sides of the gap 8 has a substantial component parallel to the space charge chamber axis. The relative magnitude of this axial component as compared with the component in planes transverse to the space charge chamber axis depends upon the chevron apex angle. Thus in the construction shown in the drawing where the apex angle is approximately l50-, the half-lengths of the gap edges on either side of the midpoint of the gap are at an angle of with respect to the cathode axis and; the axial component of the total electric field is proportional to the sine of that angle. While the magnitude of the angle may vary, it is desirably less than in order that-a major proportion of the alternating electric field may b tangential to the. cathode axis for efiective ex- --citati'on of the output circuit.

' center.

Whether this axial component of the alternating electric field is directed inwardly towards the center of the gaps or outwardly from the gap apex towards the end spaces depends upon the phase of the electrons crossing the gap. Thus, when the electrons cross the interaction gap substantially in phase with the electric field, that is, when the electrons travel from a positively charged edge of the gap to the negatively charged edge, the electrons must work against the field and give up part of their kinetic energy to the resonant output circuit of the magnetron. For these in-phase or useful electrons there is an electric field force directed inwardly from the end portions of the gap towards the Accordingly, the useful electrons are bunched near the center of the space charge chamber and do not tend to stray towards the end spaces beyond the thickness of the anode block.

Conversely, out-of-phase electrons which arrive at gap 8 or 9 with a velocity component opposing the alternating' electric field across the gap are subject to an axial force directed towards the end spaces beyond the space charge chamber where they may be easily collected by collector electrodes l3 and I4. Removal of these electrons is especially desirable since they subtract energy from the resonant output system and, because of the increased velocity thereby gained, normally tend to return to the cathode Where they cause backheating.

Obviously, of course, an additional number of anode segments and hence additional number of chevron-shaped gaps may be employed without departing from the spirit of my invention, so long as the central portions of the gaps lead the end portions with respect to the desired direction of rotation of magnetron space charge in order to provide the axial component of the like anode block assembly it preferably made of superposed upper and lower disk members [9 and It. A central opening 20 in the anode assembly provides a cylindrical space charge chamber in which a cathode 2 i, which may suitably take the form of an electron emitting cylindrical sleeve containing a thermionic heater within, is centrally disposed. A plurality of hole and slot cavity resonators 22 are incorporated into the anode assembly which communicate through excitation slots within the central opening 20.

Thus, as viewed from the cathode or space charge chamber axis, a series of anode segments 23 are spaced from each other by interaction gaps 24. In the specific embodiment illustrated, eight cavity resonators are employed, but of course, a greater or lesser number may be alternatively be employed.

In accordance with my invention the edges of each anode segment 23 are shaped to define chevron-shaped interaction gaps 24. The central portion oi each gap, that is, the mid-length portion, comprises the apex of the chevron which leads the end portions of the. gap with respect to a given direction of electron space charge. rotation around the space charge chamher 20. This configuration, which corresponds with that of the interaction gaps in the embodiment shown in Figs. 1 and 2, is further illustrated in Fig. 5 which is a developed view of the anode segment 23 and interaction gaps 24 as viewed from the cathode. This construction is facilitated by the laminated anode assembly, th hole and slot resonators 22 of the separate anode members It and ZEI being separately machined or otherwise formed with their radial center planes at an angle, preferably less than 30 from a vertical center plane. As described in relation to the embodiment of Figs. 1 and 2 an axial static magnetic field and a radial static electric field are established in the space charge chamber of the magnetron to provide the desired direction of space charge rotation. Due to the particular configuration of the gaps in which the central portion leads the end portions with respect to the direction of space charge velocity, an axial component of the induced alternating electric field is established. This results in bunching of the in-phase or useful electrons near the center of the space charge member and the expulsion of out-oi-phase or non-useful electrons into the anode end spaces. Cathode end shields 25, shown in Fig. 3 and corresponding to the end shields I2 of Fig. 1, may be suitably employed to collect the unwanted electrons.

It is not necessary that the gap configuration referred to herein as chevron-shaped be one in which the apex of the chevron is sharply defined. For example, as shown in the development view of Fig. 6 whose layout corresponds with that of Fig. 5, the gaps 24 between the anode segments 23 may be more generally curved. It is important, however, that the curves all have their central portions leading their end portions with respect to the space charge direction, and hence may be considered as convex in that direction.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetron anode structure comprising a plurality of anode segments of given length defining a cylindrical space charge chamber with adjacent edges of adjacent segments defining chevron-shaped interaction gaps.

2. A magnetron anode structure comprising a plurality of anode segments of given length defining a cylindrical space charge chamber with the segment edges defining chevron-shaped interaction gaps between adjacent segments, the apex of the gaps being midway between ends of the segments.

3. A magnetron discharge device comprising an elongated electron-emitting cathode extending along a given axis, a plurality of anode segments surrounding said cathode and defining a cylindrical. space charge chamber coaxial therewith with adjacent segments spaced from each other, and resonant circuit means interconnecting said segments, said segments defining chevron-shaped interaction gaps between adjacent segments.

4. A magnetron discharge device comprising an elongated electron-emitting cathode extending along a given axis, an anode structure comprising a plurality of spaced anode segments surrounding said cathode and defining a cylindrical space charge chamber coaxial therewith, resonant circuit means interconnecting said segments, said segments defining chevron-shaped interaction gaps between adjacent segments, and collector shields positioned near the ends of said space charge chamber.

5. A magnetron discharge device comprising an elongated electron-emitting cathode extending along a given axis, an anode block surrounding said cathode and defining a cylindrical space charge chamber coaxial therewith, said anode block incorporating a plurality of cavity resonators communicating with said space charge chamber and with the anode segments between said resonators defining a plurality of chevronshaped interaction gaps.

6. A magnetron discharge device comprising an elongated electron emitting cathode extending along a given axis, a plurality of anode segments surrounding said cathode and defining a cylindrical space charg chamber coaxial therewith, and resonant circuit means interconnecting said segments, said segments defining aligned chevron-shaped interaction gaps between adjacent segments with the apex of each chevron-shaped gap directed in a given direction around a circumference of the space charge chamber.

ELMER D. McARTl-IUR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,233,482 Linder Mar. 4, 1941 2,412,772 Hansell Dec. 17, 1946 2,477,122 Garner July 26, 1949

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