US2569517A - Magnet for cathode-ray tube ion traps - Google Patents

Description

Oct. 2, 1951 J. DE LEON 2,569,517

MAGNET FOR CATHODE-RAY TUBE ION TRAPS Filed Sept. 9, 1949 INVEN TOR. JOHN DE LEON B P fVp ja Patented Oct. 2, 1951 2,569,517 MAGNET FOR CATHODE-RAY TUBE ION TR APS John de Leon, Ridgewood, N. 1., minor to Allen B. Du Mont Laboratories, Inc., Pasaaic, N. J., a corporation of Delaware Application September 9, 1949, Serial No. 114,722

8 Claims. 1

This invention relates to cathode ray tubes such as are used in television apparatus and to means for preventing ion blemishes in the fluorescent screens thereof.

Although in the manufacture of cathode ray tubes for television, great care is exercised to obtain a high vacuum, nevertheless during use negative ions often appear in minute quantities. In an electrostatic deflection cathode ray tube these ions are deflected with the negative electrons and hence do not concentrate in one spot. In a magnetically deflected cathode ray tube, however, since the negative ions are considerably heavier than the electrons, the former are not appreciabl deflected, and hence often concentrate in one portion of the fluorescent screen, causing a blemish to appear.

An object of this invention is to provide a magnetic structure particularly adapted to be used as a part of an ion trap.

Another object is to provide a magnetic structure which can readily and adequately compensate for structural variations in the electron gun of a cathode ray tube.

Another object is to provide a magnetic structure not requiring electrical connections.

Other objects can best be understood by referring to the accompanying drawings in which:

Fig. 1 shows in perspective one embodiment of my invention;

Fig. 2 shows in perspective another embodiment of my invention;

Fig. 3 shows the structure of Fig. 1 is use to prevent ion blemishes in a cathode ray tube, parts being broken away for clarity of illustration.

Referring to Fig. 1, a permanent magnet I2 is fastened to two soft iron pole pieces i3 and H by means of non-magnetic sheets l5 and I5. By peening or spreading the tips I! of these sheets l5 and I6 after assembly, the entire structure is held together. The other ends of the pole pieces 13 and I 4 are held together in a manner known to the art by a brass screw 23 and a thumb nut 24, forming a clamp that holds the structure to the neck of a cathode ray tube. The word soft here is being used to denote the property of being readily magnetized, such as is characteristic of soft iron, cold rolled steel, and silicon steel, distinguishing thereby from "hard or permanent magnetic materials which resist magnetization and demagnetization, examples being cobalt steels and Alnico.

A magnetic shunt member ll of soft magnetic material is attached at its center to one of the 2 sheets is by means of a rivet I 9 so as to be rotatable, a spring 22 providing friction therefor,

The operation of the magnetic structure is as follows: Magnetic flux, having as its source the permanent magnet, extends along the pole pieces in the direction of the clamping screw 23 and extends across the space between the pole pieces l3 and H as shown by the dotted line 25. Although a single dotted line is shown for illustrative purposes, the flux actually is distributed quite uniformly over the area between the pole pieces, this area being occupied by the neck of a cathode ray tube.

In addition, some of the flux from the permanent magnet I 2 extends along the pole pieces in the other direction and bridges the short distance to the shunt member I8 as shown by a second dotted line 26. By rotating the shunt member I8, the reluctance of the second flux path 26 can be controlled. If the reluctance of this second path is low, more flux will pass therethrough and less flux will pass along the first path 25 through the neck of the cathode ray tube.

A second embodiment of my invention, similar to that shown in Fig. 1, is shown in Fig. 2. However, in contrast to that embodiment shown in Fig. l, the magnetic shunt member 21 comprises magnetic material in a cylindrical form having a threaded opening extending longitudinally along its axis. The shunt member?! is supported on a magnetic clamping screw 3| having corresponding threads. This screw 3| is provided with a bridging structure 28, the tips 29 of which fit into slots 32 on the edges of the pole piece I3. A hole 33 in the pole piece l3 provides clearance for the shunt 21.

In Fig. 3, a cathode ray television picture tube is shown with the magnetic structure H of Fig. 1 in place of the neck of the tube, part of one of the pole pieces being broken away, however, so that the electron gun structure of the tube is clearly visible. This gun consists of a thermionic cathode 34, providing a source of electrons, a control electrode 35 controlling the intensity of the beam, and a bent anode structure 36 providing acceleration of the beam 3'1. The gun parts are contained in an evacuated envelope 38, preferably glass, along with a fluorescent screen 39, these parts being well known to the art.

The magnetic structure H, which has already been described in detail in connection with Fig. 1, provides a magnetic field 25 at right angles to the axis of the tube, the strength of the field being adjustable by means of the magnetic shunt l8.

The action of the magnet is to deflect the electrons in the region designated by the reference numeral 43. The electrons are emitted from the cathode 34 and are accelerated in a path forming an angle with the axis of the tube. In the region 43 the electrons are bent by the magnetic field into a beam 37 which is parallel to the axis of the tube and centered therewith. Being thus bent the electrons pass through a small hole 44 in the end of the accelerating anode 36. The negative ions, following the same path from the cathode, are not appreciably deflected by the magnet because of their far greater mass and follow a straight course 45 so that instead of being emitted from the hole 44 they are trapped" within the accelerating anode structure 35 and do not strike the fluorescent screen 39.

Because of the variations in the mechanical and electrical properties of the electron gun and associated portions of the cathode ray tube structure in production, it is desirable that the magnetic field 25 be adjustable. In this way the ion trap magnet can be adjusted for each tube so that the beam is centered properly on the hole 44. In this invention this adjustment can be made by the adjustable magnetic shunt provided for the purpose.

Although the specific embodiments of my invention have been shown and described the scope of my invention can best be understood by the following claims.

What is claimed is:

1. A magnetic structure for producing a magnetic field in an area containing an electron beam, comprising a source of magnetic flux, pole pieces of soft magnetic material and respective opposite polarity attached thereto, extending respectively along opposite sides of and beyond said area,

and lying substantially in a plane normal to said beam and an adjustable magnetic shunt member positioned between and bridging a portion of the distance between said pole pieces outside said area.

2. A magnetic structure for deflecting the beam of a cathode ray tube comprising two pole pieces of soft magnetic material and respective opposite polarity, shaped to fit about and extend beyond the neck of said cathod ray tube on respective opposite sides thereof and lying in a plane normal to the longitudinal axis of said beam. a source of magnetic flux attached to and extending between said pole pieces, and a magnetic shunt of soft magnetic material positioned between and bridging a portion of the space between, the extension of said pole pieces.

3. An electron beam deflecting structure comprising two pole pieces of respective opposite polarity and of soft magnetic material, lying in a plane normal to the longitudinal axis of said beam, having complementary semi annular portions and laterally extending portions, a permanent magnet connected to and extending between said pole pieces, and a magnetic shunt of soft magnetic material positioned between said laterally extending portions of said pole pieces to bridge a portion of the space therebetween.

4. An electron beam deflecting structure comprising two pole pieces of soft magnetic material of respective opposite polarity lying in a plane normal to the longitudinal axis of said beam, having semi annularly shaped portions and laterally extending portions, a source of magnetic flux extending between said pole pieces and a pivotally mounted shunt of soft magnetic material bridging by an adjustable amount the space between said laterally extending portions of said pole pieces.

5. An electron beam deflecting structure for a cathode ray tube comprising two pole pieces of soft magnetic material shaped to flt about and extend beyond the neck of a cathode ray tube, a source of magnetic flux extending between said pole pieces, a bridge of non-magnetic material extending between the extension of said pole pieces, and a magnetic shunt of soft magnetic material afiixed to said bridge.

6. An electron beam deflecting structure comprising two pole pieces of soft magnetic material having complementary semi annular portions and laterally extending portions, a source of magnetic flux attached to and extending between said pole pieces, a bridge of non-magnetic material extending between said laterally extending portions of said pole pieces, and a magnetic shunt of soft magnetic material secured rotatably to said br dge.

7. An electron beam deflecting structure comprsing two pole pieces of soft magnetic material having complementary semi annular portions and laterally extending portions, a permanent magnet attached to and extending between said pole pieces, a threaded screw of non-magnetic material extending between and connecting said laterally extending portions of said pole pieces and a sleeve of magnetic material mounted on said screw and positioned between said pole pieces.

8. An electron beam deflecting structure for a cathode ray tube comprising two pole pieces of soft magnetic material shaped to fit about and extend beyond the neck of a cathode ray tube, a permanent magnet attached to and extending between said pole pieces, a threaded screw of nonmagnetic material connecting the extension of said pole pieces providing means for clamping said magnet to said neck, and a sleeve of magnetic material mounted on said screw, said sleeve being threaded internally and extending at least partially through one of said pole pieces.

JOHN M: LEON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,181,850 Nlcoll Nov. 28, 1939 2,211,613 Bowie Aug. 13, 1940 2,234,720 De Tar Mar. 11, 1941 2,274,586 Branson Feb. 24, 1942 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,431,113 Glyptis et al Nov. 18, 1947 2,456,474 Wainwright Dec. 14, 1948 2,460,609 Torsch Feb. 1, 1949 2,472,766 Woodbridge June 7, 1949 2,499,065 Heppner Feb. 28, 1950 2,500,455 Fisher Mar. 14, 1950 2,513,929 Gethmann' July 4, 1950 2,522,872 Heppner Sept. 19, 1950 2,539,156 Ostreicher Jan. 23, 1951 2,542,924 Heppner Feb. 20, 1951 FOREIGN PATENTS Number Country Date 464,637 Great Britain Apr. 21, 1937

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