US3031594A - Magnetron tube - Google Patents

Description

April 24, 1962 D. GLASER ET AL MAGNETRON TUBE 2 Sheets-Sheet 1 Filed Feb. 24. 1959 April 24, 1962 D.GLASER ETAL MAGNETRON TUBE Filed Feb. 24, 1959 2 Sheets-Sheet 2 F i Q- 7 JNVENTOR.

DAVAD GLAEP By ARFWD SOMMYODY we. fi

A Tram/E) United States Patent 3,031,594 MAGNETRON TUBE David Glaser, Middlesex, and Arpad Somlyody, Raritan, N.J., assignors to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Filed Feb. 24, 1959, Ser. No. 795,068 12 Claims. (Cl. 313-157) This invention relates to magnetron-type electron discharge tubes and to improvements in the construction of such tubes, particularly in the magnet used with such tubes.

One form of magnetron tube, to which the principles of the invention apply, includes an electrode assembly which comprises an elongated central cathode and a plurality of groups of elongated electrodes surrounding the cathode and secured together at their opposite ends by means of insulating end disks or plates. All of the electrodes are substantially parallel to each other. A cylindrical magnet surrounds the electrode assembly. In operation of this type of tube, current flows from the can tral cathode to one of the groups of electrodes at a time. It has been found that some of the electrons in the beam from the cathode tend to flow toward the ends of the electrode assembly where they strike the insulating end disks which support the electrodes. It has been found that this electron bombardment of the insulating disks causes them to become electrically charged, with the result that the electric field in the tube becomes distorted and electron flow is adversely afiected.

The objects of the present invention are concerned with an improved construction for a magnetron tube in which electron flow is controlled so that spurious effects on the magnetic and electric fields in the tube are minimized and tube operation is improved.

In brief, a magnetron-type electron tube embodying the invention includes, in a suitable envelope, an electrode assembly including a central longitudinally elongated cathode surrounded by groups of longitudinally elongated electrodes which are adapted to form and receive an electron beam from the cathode. The various electrodes are secured together parallel to each other by means of insulating end disks secured to the opposite ends of the electrodes. A cylindrical permanent magnet surrounds the tube envelope and the electrodes contained therein. The axis of the magnet is coaxial with the longitudinal axis of the envelope and the electrode assembly. 'The magnet provides a longitudinal magnetic field in the envelope which combines with the electric field therein to control the flow of electrons from the cathode to the groups of electrodes.

According to the invention, the magnet is adapted to control the flow of the electrons so that they strike the electrodes substantially at their centers and are substantially prevented from fanning out and striking the insulating end plates of the electrode assembly. Thus, the end plates do not become electrically charged and they do not adversely afiect electron flow. The desired result may be achieved in several ways. According to one aspect of the invention, the permanent magnet is modified by the provision of an auxiliary region of material which has high magnetic permeability but is not permanently magnetized. Thus, this region does not produce magnetic lines of force. The auxiliary region of non-magnetized material may be in the form of a ring and is positioned so that it surrounds substantially the center of the electrodes in the electrode assembly. The auxiliary ring modifies the magnetic field produced by the permanent magnet so that electrons tend to flow toward the centers of the electrodes and not to the ends thereof. In another arrangement, the magnet is physically shaped to provide the desired magnetic field con- Patented Apr. 24, 1962 figuration to prevent the electrons from flowing out toward the ends of the electrodes.

The invention is described in greater detail by reference to the drawing, wherein:

FIG. 1 is a perspective view of a magnetron beam switching tube embodying the invention;

FIG. 2 is a sectional view of the magnet shown in FIG. 1 and two of the magnetic flux lines generated thereby;

FIG. 3 is a sectional view of a magnet of the type used in the prior art andsome of the flux lines generated thereby;

FIG. 4 is an elevational view, partly in section, of the tube of FIG. 1 and a modified magnet embodying the invention;

FIG. 5 is an elevational view, partly in section, of the tube of FIG. 1 and another modification of the magnet of the invention;

FIG. 6 is an elevational view, partly in section, of the tube of FIG. 1 and another modification of the magnet of the invention; and

FIG. 7 is an elevational View, partly' in section, of the tube of FIG. 1 and another modification of the magnet of the invention.

The principles of the invention are applicable to magnetron tubes and, particularly, to a magnetron beam switching tube, type 6700. This type of tube is shown in FIG. 1 as tube 10 and includes, briefly, an envelope 12 which contains an electrode assembly 13 including a central longitudinally elongated cathode 14 and ten groups of electrodes spaced radially equidistantly from the cathode and surrounding the cathode and parallel to each other and to the cathode. Each group of electrodes includes a generally U-shaped elongated spade electrode 16 and a generally L-shaped target electrode 18 positioned so that each target occupies the space between adjacent spade electrodes. Each spade electrode serves to form and hold an electron beam on its associated target electrode. A generally rod-like switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. The Switching electrodes are known as switching grids. The electrodes of the cage 13 are secured together by means of top and bottom insulating end disks 22 and 24, respectively, of mica or the like, which have inner facing surfaces 26 and 28 that are accessible to electrons flowing from the cathode to the other electrodes. The mica disks are provided with suitable apertures 30 to receive and secure end portions of the electrodes, as is Well known in the art.

An open-ended cylindrical permanent magnet 32 is provided surrounding the tube envelope and coaxial therewith. The magnet is secured to the tube envelope, for example, by means of a layer 34 of a suitable plastic material. The magnet provides an axial magnetic field which is utilized in conjunction with electric fields within the tube to form and switch an electron beam from the cathode to each of the groups of electrodes. The direction in which the beam switches, that is clockwise or counter-clockwise, is always the same and is determined by the orientation of the electric and magnetic fields.

Briefly, in operation of the tube 10, electrons emitted by the cathode are retained at the cathode if each of the spades, targets and switching grids carries its normal operating electrical potential. When a spade or switching grid experiences a suitable lowering of its potential, an electron beam is formed and directed to the corresponding target electrode. Ordianrily with a cylindrical magnet, the electrons in the beam tend to flow out toward the ends of the electrode assembly 13 and, in addition, some electrons strike the mica disks 28 and 30. Such electron bombardment of the mica disks would ordinarily cause the disks to become electrically charged and then adversely affect electron flow in the tube.

According to the invention, the magnet 32 is constructed to provide a magnetic field within the tube of such configuration that the electrons in a beam are substantially' prevented from flowing toward the ends of the electrode assemby and are substantially limited to the central region of the tube electrodes between the end disks 2 8 and 30. Thus, electrons are substantially prevented from striking and charigng the end plates or other surfaces in the tube.

In one embodiment of the invention, referring to FIG. 1, the desired results are achieved with a magnet 32 having two end rings 36 and 38 of high reluctance, permanently magnetized material, which generate magnetic lines of force, and an intermediate ring 40 of comparatively high permeability material which, preferably, cannot be permanently magnetized and does not generate magnetic lines of force. The end rings 36 and 38 may be made of Alnico VI, for example, and the ring 40 may be made of soft iron. The ring 40 is positioned in the magnet so that it surrounds the region of the tube 10 in which it is desired to maintain the electron beam. Thus, in the present embodiment, the ring 40 is positioned so that it surrounds thte electrode assembly at about its longitudinal center.

The general shape of magnetic field provided by the magnet 32 is illustrated in FIG. 2 by flux lines 41, and the magnetic field generated by a similar cylindrical permanent magnet 42 of uniform construction and not having the ring 40 is illustrated by lines 43 in FIG. 3. The magnetic lines of flux generated by the magnet t2 shown in FIG. 3 are smoothly curved and bow outwardly from the body of the magnet toward the aXis of the magnet. Flux lines of this shape tend to cause some electrons to flow outwardly toward the ends of tthe elecrode assembly. In the magnet 32 of FIG. 2, the magnetic flux lines leave the ends of the magnet as they do in the magnet 44, but in the region of the ring 40 they bend outwardly toward the main body of the magnet. With this shape of magnetic field, all electrons tend to flow toward the ring 40. Thus, if the ring 40 is properly positioned with re spect to the tube electrodes, substantially all electrons can be directed to the desired region of the tube electrodes.

in a type 6700 tube, the electrodes have a length of about 1 inch, and the magnet has a total length of about 1% inches. The ring 40 has a length of about Mr inch. The magnet is also magnetized so that the end rings have a magnetic flux density of about 450 gausses. The rings 36 and 38 have a reluctance of about 10, and the ring 40 has a reluctance of about .01.

In a modification of the invention shown in FIG. 4, the tube '10 may employ a permanent magnet 44 of onepiece construction, for example, of the same material as the end pieces 36 and 38 of the magnet 32. A ring or band 45 of the same material as the ring 40 is provided surrounding the magnet 44 and slidably mounted thereon. The ring 45 is properly positioned on the magnet to orient the electron beam as desired.

If desired, a one-piece permanent magnet, suitably shaped, may be used to practice the invention. One such magnet as shown in FIG. is in the form of a cylinder having a concave inner Wall Thus, the magnet 4-6 has a thin central region and thick end portions 50, a construction which provides the desired magnetic field configuration. Alternatively, as shown in FIG. 6, the magnet 46 may have a flat, rather than concave, inner wall 52 as seen in cross-section. In addition, the desired result may be achieved in a magnet 54 (FIG. 7) having a concave outer wall 56.

The effect of the magnet construction of the invention was studied in type 6700 tubes in which the target elec trodes were divided into three separate portions, top, bottom, and central portions. Tubes having conventional magnets were compared with tubes having magnets of the invention, and it was found that in the conven-' tional tube the currents from the top, bottom, and cen-' tral portions of the targets were substantially the same with a typical value for each section being about milliamperes. Tubes using magnets embodying the inabout 3 .5 milliamperes.

in the tube substantially to the central portions of the target electrodes. With this orientation of the current, the mica end plates do not become charged and do not adversely affect the operation of the tube. Thus, tube operation is more uniform than heretofore.

What is claimed is:

1. A magnetron beam switching tube adapted to operate with crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an elec-- tron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its as' sociated target electrode, and a switching electrode which;

serves to switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of electrodes; said magnet having regions of different magnetic charac-' teristics whereby a magnetic field configuration is provided in said tube which substantially prevents electrons from flowing to the ends of said electrodes and directs them toward the centers of said electrodes.

2. A magnetron beam switching tube adapted to op rate with crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of electrodes; said magnet including means for directing the flow of electrons from said cathode toward the longitudinal center of the electrodes of the tube and preventing the flow of electrons toward the ends of said electrodes.

3. A magnetron beam switching tube adapted to operate with crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which servesto switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of elec-.- trodes; said magnet having a body of magnetic but unmagnetized material associated therewith to control the configuration of the magnetic field in said tube to direct electrons generally away from the ends of satid electrodes and toward their centers.

4. The tube defined in claim 3 wherein said magnet includes integral therewith a ring of material having high magnetic permeability but unmagnetized.

5. The tube defined in claim 3 wherein said magnet includes a ring of material having high magnetic permeability but unmagnetized substantially at the center thereof.

6. The tube defined in claim 3 wherein said magnet includes a ring of material having high magnetic permeability but unmagnetized, said ring being positioned between two rings of permanent magnet material.

7. The tube defined in claim 3 wherein said magnet consists of outer portions of permanent magnet material and an intermediate ring'of high-permeability unmagnetized material. 7

8. A magnetron beam switching tube adapted to operate with crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of electrodes; said magnet having a thin central region and thick end portions.

9. A magnetron beam switching tube adapted to operate With crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode Which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of electrodes; said magnet having a concave inner wall.

10. A magnetron beam switching tube adapted to operate with crossed electric and magnetic fields including a cathode and a plurality of groups of electrodes; each group including a target electrode which receives an electron beam and produces an output signal therefrom, a spade electrode which holds an electron beam on its associated target electrode, and a switching electrode which serves to switch an electron beam from one group of electrodes to the next; and a hollow cylindrical magnet surrounding said cathode and said groups of electrodes; said magnet having a concave outer wall.

11. The tube defined in claim 3 and including in operative relationship with said magnet a ring of material having high magnetic permeability.

12. A magnetron beam switching tube including an envelope, an electrode assembly in said envelope, said electrode assembly having a longitudinal orientation in said envelope and including a central cathode and a plurality of electron-receiving electrodes surrounding said cathode, permanent magnet means providing a longitudinal magnetic field in said envelope, said magnetic field operating with the electric field in said tube to control the flow of electrons from said cathode to said electronreceiving electrodes, and auxiliary magnetic means in operative relation with said permanent magnet means altering the shape of the longitudinal magnetic field produced thereby whereby the flow of electrons from said cathode is limited to a selected region of said electron-receiving electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,387,985 Hull Aug. 16, 1921 1,617,172 Smith Feb. 8, 1927 2,246,121 Blewett June 17, 1941 2,390,884 Jansky Dec. 11, 1945 2,418,469 Hagstrum Apr. 8, 1947 2,839,702 Fan June 17, 1958

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