US2113422A

US2113422A - Electron discharge device

Info

Publication number: US2113422A
Application number: US543992A
Authority: US
Inventors: William D Coolidge
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1931-06-12
Filing date: 1931-06-12
Publication date: 1938-04-05
Anticipated expiration: 1955-04-05
Also published as: NL35143C; GB404299A; DE629214C

Description

Ap 1933- w. D. COOLIDGE. 7 2,113,422

ELECTRON DISCHARGE DEVICE I Filed June 12, 1931 IIIIIIIIIIIIII/If;

Inventor: I William D. Coolidge, by MW His Attorney.

Patented Apr. 5, 1938 PATENT OFFICE ELECTRON DISCHARGE DEVICE William D. Coolidge, Schenectady, N. 2., assignor to General Electric Company, a corporation of New York Application June 12, 1931, Serial No. 543,992

18 Claims.

The present invention comprises an improvement in the construction of electron devices in which a beam of electrons (otherwise known as cathode rays) is produced. For example, my invention may be utilized in cathode ray tubes and X-ray tubes. It is particularly applicable to the construction of such devices in which a plurality of discharge members are operated in cascade, that is, in which the cathode rays are given successive cumulative accelerations in their passage through the tube. Such a device is described in my prior application Serial No. 244,014, filed December 31, 1927 (British Patent 322,662),

The device described in this prior application provides one or more apertured electrodes located intermediate the main electrodes. The electrons in their passage from the main cathode to the main anode pass through apertures in the intermediate electrodes. It has been found diflicult to construct such a cascade discharge device with sufiicient accuracy to cause the cathode ray beam to traverse the discharge space without striking the intermediate electrodes and to some extent being discharged thereon. It is desirable to have the cathode ray beam pass through the device along its axis without being discharged even partially upon an intermediate electrode.

In accordance with my present invention, I have provided a construction whereby the direction and diameter of a beam of cathode rays may be varied by changing the position of the parts of the cathode structure with respect to one another-from the exterior of an operating discharge device without disturbing the assembly of parts a or disturbing the evacuated condition of the device. In order to carry out the desired adjustments, I have provided a cathode construction which by employment of extensible and compressible members between the parts of the oathode and the envelope provides for the variation of the spatial relations of .the cathode members so as to produce the desired changes.

The novel features of my invention will be described in greater detail in the accompanying specification taken in connection with the accompanying drawing in which Fig. 1 is a side elevation of an electron discharge device embodying my invention; Fig. 2 is a longitudinal section on a larger scale of the cathode structure; and Fig. 3 is a fragmental sectional view of part of the anode.

The device shown in Fig. 1 of the drawing comprises an envelope consisting of bulbs l and 2, ordinarily consisting of glass, connected by a conductive coupling 3. In Fig. 1 of the drawing,

the coupling 3 is shown surrounded by a rounded corona guard. The number of bulbs is not limited to the number shown herein. The bulb I contains a. cathode structure 4 (to be hereinafter more fully described) from which a beam of electrons, or "cathode rays is projected through a tubular intermediate electrode 5 which is mounted upon and electrically connected to the coupling 3. The electrode 5 extends from the bulb i into the bulb 2 of the envelope, the righte hand part of the electrode 5 being of greater diameter than the left-hand part. The cathode beam emerging from the tubular electrode 5 enters a second tubular electrode 6 which is joined to an anode member I by a coupling 8. The anode l, as shown in Fig. 3, comprises a hollow metal tube consisting of brass, or other suitable metal. To the inner surface of the closed outer end of the anode (see Fig. 3) is attached a thin plate 9 of tungsten on the back of which has been cast a layer of copper, preferably in a vacuum. To this layer of copper is attached a brass cell provided with passages II! for the circulation of water, or other cooling fluid. The connection between these passages and the supply tubes for the cooling fluid are not shown to avoid complication of the drawing. Inlet and outlet tubes for the cooling fluid are indicated externally at H, in Fig. 1. Surrounding the tubular electrode 6 is a magnetic coil I2, whereby the cathode beam may be focussed. This coil is supported by brackets 13 from a wall member through which the anode projects. This wall may be made of material impervious to X-rays. The coupling 8 is grounded and as indicated is connected to a suitable vacuum system through a tube I 4.

As shown in Fig. 2, the cathode structure 4 of Fig. 1 comprises a filament l5 which is surrounded by a hollow molybdenum cylinder and is connected to the current-conveying conductors l6, l5. Surrounding the filament I5 is a toroidshaped focussing member ll, which may be made of copper having rounded surfaces to reduce cold cathode effect. The filament I5 is located near the bottom of the depressed or dished portion of the focussing member ll thereby causing the electrons emanating from the filament to be iocussed to form a beam, due to the distribution of the electrostatic field. This circumscribed beam traverses the tube passing through the eleco trodes 5 and 6, finally reaching the anode where either X-rays are produced or where part of the cathode rays pass through the anode to the exterior of the discharge tube, depending on the character of the anode, as well known.

The focussing device I! is mounted upon three rods of which two, 20, 2|, are shown. These rods are connected to the plate It by three extensible and compressible bellows members, two of which, 22 and 23, are shown. Such bellows members are commonly made of copper and commonly are termed sylphons. As is apparent from the drawing, the rotation of the nut 24 upon the threaded end of the rod 20 will shorten or lengthen the portion of the rod 20 intermediate the members I and I8, depending on the direction of its rotation. The sylphon member 22 will be either compressed or extended, thereby tilting the focussing ring or, in other words, changingthe position of the focussing member with respect to the tube axis and causing the beam of cathode rays to be correspondingly tilted. When the rod 20 is lengthened to tilt the focussing member I! forward at the top, then the cathode ray beam is moved in a downward direction, and conversely pushing forward of the lower portion of the member |1 directs the beam upwardly. The other two rods may be similarly adjusted. For convenience the rods 20 and 2| are made of several sections. Surrounding the supporting rods is a large cylindrical metal tube 26, which may be made of brass, and which is joined by screws to a base plate 21 to which the bulb is sealed by cement or otherwise as indicated at 28. It is the function of the tube 26 to shield the cathode supply wires and other parts within the same from deleterious electrical discharges during the operation of the device and to support a plate 29 provided for guiding and supporting the rods 20 and 2|, as indicated.

My invention also provides means for varying the axial position of the filament IS with respect to the focussing member I1. In other words, the filament |5 may be either drawn further into the hole or cavity of the focussing member or pushed further out.

The cathode supply wires I6, l5 pass through a tube 3| which is connected by a sylphon 32 to a threaded closure plug 33 for the plate l8. The wires l6, l6 are spaced at the end of the tube nearest the filament |l5 by passing through apertures in an insulating plug 34. At the outer or left-hand end of the tube 3|, which projects beyond the plate 18 the wires I6 and I6 pass through and are rigidly held in

insulators

35 and 36, which are embedded in a metal plug 31. This metal plug is connected to the sylphon 32. Upon the plug 31 is mounted a rod 38 which projects through a housing 39 for the sylphon member 32. By moving the nut 40 upon the threaded portion of the rod 38, the cathode filament with its, surrounding molybdenum tube can be moved longitudinally with respect to the focussing member When the cathode filament I5 is drawn into the passage of the focussing member the focussing is made sharper, that is, the beam of cathode rays becomes more circumscribed and conversely when the filament is moved outwardly the focus of the cathode ray beam is broadened.

Although the electrical circuit connections form no part of my present invention, they have been shown for illustrative purposes. Referring to Fig.1, the cathode filament I5 is connected by circuit conductors 43, 44, to a suitable source of heating current, such as a battery 45 in series with an adjustable resistance 46 and a switch 41. The main cathode of the tube and the grounded anode are connected by the conductor 48 and the grounded conductors 49, 43' to the high tension terminals of the secondary of an induction coil 5|]. The middle point of the secondary of this coil is connected to the intermediate electrode 5 by a conductor 5|. The primary of the coil 50 is connected to the secondary winding of a transformer 52 in series with an interrupter 53, including a condenser shunting the make and break device. In circuit with the primary of the transformer 52 is an auto-transformer 54 which is employed for regulating purposes.

With the proper adjustment of the electrostatic focussing member none of the cathode rays strike the intermediate electrodes as may be shown by the fact when a milliammeter is placed in series with the conductor 5| leading to the electrode 5 it indicates no current while the device is operating. The focal spot may be brought to the exact position desired on the target or anode face by slightly tilting the elec- 'trostatic focussing member IT as above described.

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

1. An electron discharge device comprising the combination of a sealed envelope constituted in part of an anode, a focussing member and a movable cathode in said envelope, leading-in conductors connected to said cathode, said envelope including an extensible member rigidly mounted with respect to said conductors and adapted to move the cathode with respect to all of the remaining electrodes.

2. An X-ray tube comprising the combination of a sealed evacuated envelope, electrodes therein including a cathode, a focussing member and a target, mechanical means operable from the exterior of the envelope for adjusting the longitudinal position of the focussing member with respect to said target, said means including a mechanical connection to the focussing member.

3. An electron discharge device comprising the combination of a sealed evacuated envelope comprising a plurality of sections joined end to end, a cathode located at one extremity of said envelope, an anode located at the opposite extremity and at least one tubular intermediate electrode through which an electrical discharge from said cathode to said anode passes, said electrode having a length several times greater than the diameter thereof, a focussing member surrounding said cathode, supports for said member passing through said envelope to the exterior, and connections between said supports and said envelope permitting movement of said supports and focussing member relative to the envelope, wherebythe discharge is constrained to a bundle of rays which passes through the entire length of said tubular electrode in a focussed condition.

4. A cathode structure for electric discharge tubes comprising the combination of a filament,

va focussing member surrounding said filament,

a support for said filament, a compressible and extensible link secured to said support and manually operable mechanical means for changing the position of said filament with respect to the focussing member through the intermediary of said link.

5. An electron discharge device comprising an evacuated envelope containing a movable cathode, and a focusing device surrounding the cathode, an anode positioned at the opposite end of the envelope from said cathode, a support for said cathode, said support including a compressible and extensible member which constitutes part of the envelope, and means'mounted on the exterior of the envelope for compressing and extending said member whereby the cathode may be moved with respect to the focusing device.

6. An X-ray tube comprising an evacuated envelope containing a movable filamentary cathode, and a movable focusing device surrounding the filament, a stationary anode positioned at the opposite end of the envelope from said cathode, a support for said focusing device including a compressible and extensible member, a support for said filament including a compressible and extensible member, both of said members constituting part of the envelope, and means mounted on the exterior of the envelope for compressing and extending said members whereby the focusing device and the filament may be moved with respect to one another and with respect to the anode.

7. An electron discharge device comprising the combination oi. a sealed evacuated envelope comprising a plurality of sections joined end to end,

an electron-emitting cathode located at one extremity of said envelope, an anode located at the opposite extremity and at least one tubular intermediate electrode through which a discharge from said cathode to said anode passes, a focusing member surrounding the cathode for constraining the electrons to a bundle of rays having a diametral size less than the interior diameter of the tubular electrode, and means for adjusting the focusing member with respect to the tubular electrode whereby the bundle of rays may be caused to pass through said electrode without striking.

8. An electron discharge device comprising the combination of a sealed evacuated envelope comprising a plurality of sections joined end to end, a cathode structure located at one extremity of said envelope, an anode located at the opposite extremity and at least one tubular intermediate electrode through which an electrical discharge from said cathode to said anode passes, said cathode structure comprising a thermionic electron emitter, a surrounding focussing member, a supporting structure for said focussing member and a supporting structure for said electron emitter, said structures passing through the envelope to the exterior and being separately movable with respect to the envelope whereby the cathode and the focusing member respectively are movable with respect to one another and with respect to the envelope.

9. An electron discharge device comprising an evacuated envelope containing a cathode and a focussing device surrounding the cathode, an anode positioned at the opposite end of the envelope from said cathode, a plurality of supports equidistantly spaced about said focussing device, said supports including compressible and extensible members which constitute part of the envelope, and means mounted on the exterior of the envelope for compressing one of said members and extending another of said members whereby the focussing device may be tilted with respect to the axis of the envelope.

10. An electron discharge device comprising an evacuated envelope containing a cathode and a focussing member surrounding the cathode, an anode positioned at the opposite end of the envelope from said cathode, a plurality of supports equidistantly spaced about the focussing device, said supports including compressible and extensible members which constitute part of the envelope, asupport for said cathode, said support including a compressible and extensible member which constitutes part of the envelope, and means mounted on the exterior of the envelope for ex-v tending one of said members which constitutes part of the focussing device supports and for compressing another of said members which constitutes part of the focussing device supports, and means mounted on the exterior of the en-' velope for compressing and extending said member which constitutes part of the cathode support, whereby the focussing device may be tilted with respect to the axis of the envelope and the cathode may be moved with respect to the focussing device.

11. An electron discharge device comprising the combination of a sealed evacuated envelope comprising a plurality of sections joined end to end, an electron-emitting cathode located at one ex tremity of said envelope, an anode located at the opposite extremity, and at least one tubular intermediate electrode through which a discharge from said cathode to said anode passes, a focussing member surrounding the cathode for'constraining the electrons to a bundle of rays having a dlametral size less than the interior diameter of the tubular electrode, and means operable from the exterior of the envelope for adjusting the focussing member with respect to the tubular electrode whereby the bundle of rays may be caused to pass through said electrode without striking. Y

12. An electron discharge device comprising an evacuated envelope containing a cathode and a focussing member surrounding the cathode, an anode positioned at a remote end of the envelope from the cathode, said cathode being movable toward and away from said anode, and means including mechanically operated elements extending from the interior to the exterior of the envelope for selectively adjusting the position of the cathode with respect to the anode during operation of the device.

13. An electron discharge device comprising an evacuated envelope containing a cathode, an anode and a focussing member surrounding the cathode, said cathode being adjustably movable with respect to said member, and means including mechanically operated elements extending from the interior to the exterior of the envelope for moving the cathode with respect to said focussing member during operation of the device.

14. An electron discharge device comprising an evacuated envelope containing a cathode, an anode and a focussing member surrounding the cathode, said cathode being adjustably movable with respect to said member, and cathode-adjusting means manually operable from the exterior of the envlope for moving the cathode with respect to said focussing'member during operation of the device, said means including a compressible and extensible link forming part of the envelope.

15. The combination in an X-ray tube of an evacuated envelope having an aperture leading from the exterior to the evacuated interior thereof, a flexible metallic vacuum-tight closure for said aperture, a target, an electron-emissive cathode in operative relation to said target for the production of X-rays, adjustably variable focussing means for concentrating the stream of electrons from said cathode into a beam impinging upon said target, and a mechanism operable upon said focussing means for adjustably varying the size of the focal spot, said mechanism being also operable to direct said beam to each of a plurality of target areas successively whereby to vary the position of the focal spot thereon,

said mechanism including said closure,'said target, cathode and focusing means being disposed within said envelope.

16. In an X-ray tube, a cathode head comprising, in combination, a cathode, an adjustably variable focussing device operatively associated with saidcathode, a mechanism including links for operating said focussing device, a flexible closure element, said mechanism being connected with said closure element, and an operating member connected to and carried by said closure element, said operating member being accessible for manipulation fromthe exterior of the tube.

1'7. An X-ray tube comprising, in combination, an evacuated envelope including a stem having apertures leading into the evacuated interior thereof, a target, a cathode head in operative relation to said target for the production of X-rays, said cathode head including an electron-emissive cathode, flexible metallic diaphragms sealed to said stemand forming vacuum-tight closures for said apertures, an adjustably variable focussing device and mechanism operable through said diaphragms for actuating said i'ocussing device to vary the size 01 the focal-spot, said cathode head being supported by said stem, said target and cathode head being disposed within said envelope.

18. In an adjustable-focus X-ray tube, an evacuated envelope, a target, an electron-emissive cathode, focussing means situated adjacent said cathode, said cathode and i'ocussing means being relativeLv movable for varying the area of the focal spot, a focuss-adju'sting mechanism partly' within said envelope for effecting relative movement between said cathode and tocussing means, said focuss-adjusting mechanism including an operating member extending outside the evacuated interior of said envelope, said operating member being arranged for manipulation by the operator for effecting focal spot adjustments, and means for holding said i'ocuas-adjusting mechanism in any operating position to which it 20 happens to be adjusted.

WILLIAM D. COOLIDGE.