US2356645A - X-ray tube - Google Patents

Description

z. J. ATLEE ET'AL X-RAY TUBE l Filed Feb. s, 1943 1NVENTR5;-. f Q Zed Jaa@ www @uw Nw Aug. 22, 1944.

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. f\ NN KEN @N Patented Aug. 22, 1944 UNITED STATES -PATENT OFFICE f X-RAY TUBE Zed' J. Atlee, lElmhurst, Ill., and Howard W.

Brackney, Washington, DI. C., assignors to General Electric X-Ray Corporation, Chicago, Illi. a corporation of New York Application February 8, 1943, Serial No. 475,075- claims. (o1. 25o- 87.)

This invention relates in general to electronics and has more particular reference to the construction of X-ray generators, more especially general purpose generators adapted for the application of X-rays for body cavity therapy, for supercial therapy and for radiography.

An important object of the invention is to provide a shockproof X-ray apparatus comprising a transformer and an X-ray generator having compact' arrangement of the generator and the transformer within an enclosing casing; a further object being to provide adjustable capacity means Within the casing and operable outwardly thereof to tune the generator energizing system for operation within a predetermined fre`- quency range.

Another important object is to provide an im'- proved cathode structure for electron now devices, such as X-ray generators.

Another important object is to provide an improved electrode configuration and relationship, including the immersion of the cathode in the anode, to insure complete shielding of the electron source at the cathode and the entire electron beam between the source and the anode target from the intense electrical charges that collect upon the walls of the generator envelope during operation, thereby completely eliminating `the biasing effect that would otherwise be irnposed by said wellcharges upon the electron beam.

Another important object is to provide a tubular anode structure of the character mentioned, including an anode target therein and W absorption means allowing X-rays generated at the target within the tube to escape thence in substantially unimpeded fashion for useful application outwardly of the tubular anode structure; a further object being to provide a low absorption window in the tubular anode, through which window the X-rays may pass without appreciable absorption.

Another object is to arrange the anode for substantially unimpeded X-ray emission there-v from in a direction radially of the tubular anode structure, such arrangement being particularly well suited to the application of X-rays in supercial therapy; a further objectebeing to provide an anode structure and target arrangement for the transmission of X-rays in an axial direction outwardly and at the end of the tubular anode structure.

Another important object is to utilize a beryllium disc as a low absorption window in the anode structure.

Among the numerous other important objects of the invention is Ato provide a safe X-ray generator-for contact and' cavity therapy and for radiography; to provide a generator of simplified design having an improveda'node structure, in combination with an immersed cathode, to improve the operating characteristics of the device lwith respect to the uniformity of' electron flow;

Ito provide a device of the character mentioned having a shockproof casing in which all high voltage parts, including` the generator operating transformer, are'oil immersed and thus safely insulated, the casing including novel means for tuning the generator'energizing system; and, in general, to provide 'an' extremely useful general 'purpose generator for radiography, as Well'as contact and cavity therapy purposes.

These and numerous other important objects, advantages, and inherent functions of the inven-Y tion will be fully understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment of the invention. f

Referring to the drawing: Figure l is a sectional view taken longitudinally through a generator and casingr embodying the present invention;

. Figure 2 is a sectional view taken substantially along the line 2-2 in Figure 1; Figure 3 is an enlarged sectional view taken substantially along the line 3 3 in Figure 1;

Figures 4 and Y5 are sectionalY views showing modified forms of the anode structure, Figure 4 illustrating an anode `structure particularly adapted for radiographic purposes 'and Figure 5 showing a preferred structure for contact and cavity therapy; and f `Figure 6 is a diagram of electrical connections.

To illustrate the invention the drawing shows an X-ray generator II comprising an anode I3, a cathode I5, and envelope means II enclosing the anode and cathode. The envelope means I'I comprises a preferably steel plate or disc I9 forming a frame having a central opening 2| in which is sealingly secured, as by welding or brazing, an'end of a preferably copper tube 23, said tube forming a part of the anode structure and carrying at its other end means carrying an anode target 25. The tube 23 projectsk on one side of the disc I9, which on its other side is formed with an annular shoulder providing a seat 21 for receiving the annular flanged end of la metal mounting sleeve 29 which forms a part of the envelope means I 'I. The sleeve v29 pref# erably comprises steel containing` appreciable quantities of nickel and yprovides an annular rim 3| remote from the seat 21. The generator envelope also comprises a glass cathode carrying portion 33 sealed onvthe rim 3| by a glass-tometal seal 35. The end of the envelope portion 33V remote from the seal 35 preferably forms a re-entrant sleeve portion 39 having an annular edge forming a, glass-to-metal seal 4| with the rim of a metallic cup-shaped end seal 43, which serves also as a support for the cathode structure I5.

The cathode structure l5 comprises a head 45 formed with a socket 4'| in alignment with and facing toward the end of the tube 23 in the open ing 2|. An electron'emitting element, preferably a filament 49, is supported in the head 45 adjacent the bottom of the socket 4l. The head 45, in turn, is supported, as by means of intermediate frames 5| and 53, on a stem 55 which Eprojects through and is sealed in a central Aopening formed in the bottom ofthe cup-shaped seal member 43." The head 45 and the support members 5| and 53 are hollow to accommodate electrical conductors 51 which are connected with the filament 49 and which extend thence through the 'head and the hollow support members and through seals 58 formed in the bottom of the seal member 43; The member 5| may also carry a cylindrical skirt 59 whichsurrounds and encloses the support memberp53, the seal member 43 andthe glass-to-metal seal 4| for the purpose of shielding the seal 4| against impingement of stray electrons. 'I'he skirt 59 also defines a chamber 6U in. whichjmay be disposed gettering means 6|, the s-ame preferablyy comprising a hollow metallic wire containing a gettering medium, lsuch as barium, one end of the wire being grounded on the frame member 53 and the other end. being connected to a conductor 63 which extends through a seal 64 in the member 43.

In conditioning theX-ray generator for op eration, it is necessary to Aremove all gas and other impurities present within 'the envelope, to-

barium and/or magnesium contained in the hollow wire 6|, may be volatilized by applying an electrical potentialrbetween the conductor 63 and the projecting end of the stem 55, thereby heating the wire 6| and vaporizing the gettering material contained therein, the wire having a weakened wall portion longitudinally thereof, through which weakened wall portion the vaporized gettering material may be expelled into the chamber 60.

It should be understood that an X-ray generator functions to produce X-rays at the target by the impingement thereon of electrons generated and emitted at the cathode filament 49 anddirected as an electron stream upon the target under the influence of electrical potential applied between the cathode filament and the anode target. The cathode is energized for electron emission by the application of filament energizing potential between the conductors 5T, while the emitted electrons are impelled toward the target 25 by electrical potential applied between the cathode and the target, as by connectgether with any gas occluded in the electrodes and in the material of the `envelope itself. If such occluded gases are not substantiallyV entirely removed, they will be gradually released within the envelope and will impair the exhausted condition in which the device is designed to operate.

After the envelope has been formed in hermetic fashion, removal of the gases therefrom is accomplished by heating the entire device at a temperature short of the Ysoftening temperature of the glass envelope portion33, while maintaining the envelope in connection with a suitable exhaust pump. At the same time the electrodes also are heated to a high temperature, either by electronic bombardment or by placing the electrodes in a magnetic field fluctuating at frequencies of the order of radio frequencies.

After all gas, including occluded gases and other impurities, have thus been removed from the envelope, the exhaust connection may be sealed ing to a suitable potential source one of Vthe cathode conductors 51 and the frame I9, to

which the target is electrically connected.

Although the operating potential applied between the cathode filament and anode target,

in conjunction with the shape of socket cathode head 45, serves to impel the electrons in a` stream focused upon'the target, various disturbances may .cause some of Vthe electrons to escape from the stream and become stray electrons within the envelope. Such stray electrons ultimately may impinge upon the en- Velope wall, and particularly on the glass portions of the envelope, thus building up charges having deleteriouseffects upon .the generator. Such charges may etchI and weaken the glass envelope Walls and may puncture Y the envelope, particularly at the end seals 35 and 4|. Furthermore, when operated at high voltage, the charges built up on the envelope walls, as a result of stray electron impingement, may exert electrostatic effects upon the electron stream and cause it to deviate from the desired flow path between the cathode filament and the target 25. In order to minimize the effects of such electrostatic forces, the head of the cathode is immersed within the anode by providing a sleeve forming a cylindrical shield 61 embracing and enclosing the electron emitting cathode portions, said shield Slat one end being secured, as by soldering or brazing the same on a mounting ring 69 which is fastened, as by means of screws 1|, upon the plate I9 adjacent the seat 2'|.` The shield 61 not only serves to minimize the occurrence of stray electrons within the envelope, vbut also aids in guarding the electron stream from the effects of electrostatic Vcl'iarges built up on the envelope walls during operation of the device.

It will be seen-from the foregoing that the inventionY contemplates the provision of an X-ray generator having an anode target forming an X-ray source arranged at the projecting end of the tube 23; the tube being of Vrelatively restricted diameter, allowing for insertion of the same, as in a body cavity, for the treatment of the tissues of the cavity, although, of course, the generator may be arranged for general radiographic purposes and for the therapeutic treatment of other than body Cavity tissues.V The arrangement of the target at the end of the relatively slender, elongated tube 23,

l the coils ofthe transformer.

sealed in the collar preferably by means of solder comprising copper and silver.

In order to develop X-rays at the disc ||3, it is necessary tovprovide 'a suitable target for the reception of electrons Vand capable of developing X-rays in response to electron impingement thereon. To this end the target may comprise any suitable target material, but gold is preferably employed for the purpose. Consequently the surface of the disc ||3 facing into the tube carries a layer of gold ||1 thereon for the purpose of providing an anode target.v The gold layer forming the target is preferably applied on the beryllium disc by electroplating the gold thereon to a thickness of the order of 2-.0 microns,

which is the thickness of gold capable of s topping substantially all electrons impinging thereon, at the voltage at which the tube is intended to operate, say 30-100 kv. p., thereby providing for the efficient generation of X-rays, substantially all of which may escape outwardly through the disc ||3.

The jacketing means 13 comprises inner and outer sleeves 91 and 99 similar to the sleeves employed in the structure shown in Figure 4 and similarly mounted at the target remote end of the anode structure` At the other end of the jacketing structure the sleeves 91 and 99 are secured in a support collar ||9 providing for the interconnection of the jacket channels |05 and in a manner causing iiow of cooling fluid behind the disc ||3. Said collar ||9 preferably comprises Monel metal or other material containing nickel in substantial proportions. The collar furthermore sealingly receives an end plate |2 preferably of beryllium, through which X-rays generated at the target layer l |1 may be projected substantially without absorption.

It will be noted that, for the sake of safety, the anode structure including the'tube 23, the jacketing means, the mounting plate I9 and the sealing rim 29 may be grounded. AThe ungrounded or high tension portions of the tube, which are supported on'the glass envelope portion 33, may be enclosed in a suitable casing |23 by securing the plate I9 in an opening |25 formed in the casing at one end thereof. The plate I9 is preferably secured on the casing in demountable yet liquid-tight fashiony as by means of readily -removable screw fasteners, AsoY that the tube may be easily removed from the casing for inspection or repair and replacement. The casing |23 preferably contains a suitableV insulating medium such as oil, in which the cathode carrying portions of the generator are immersed while the generator is in service. l Within the casing |23 also is preferably mounted a transformer |21 which preferably comprises a high frequency coreless transformer adapted for operation at frequencies ranging between five hundred and one thousand cycles per second. This transformer is of annular shape and is disposed in the casing in position encircling the glass cathode carrying portions of the generator, said portions occupying substantially onehalf the space within the coils of the transformer. Electrical apparatus for regulating lament current is disposed in a casing |29 occupying the remaining portions of the space within In order to provide for tuning the transformer and its control circuits for operation at any desired frequency within the range of the apparatus, the casing |23, in'its end remote from the generator receiving opening |25, is provided with a preferably screw threaded stem 3|, said stem Vthe casing |23, and the inner end of the stem |3| carries a plate |35 forming one plate of a condenserthe other plate |31 of which is electrically connected with the transformer 21. By manipulating the handle I 33 outwardly of the casing, the transformer may be tuned to deliver operating potential of desired frequency to the X-ray generator. Y

It will be noted that, as shown in Figure 6 of the drawing, the anode, including the target 25,

is electrically connected to ground comprising the metallic portions of the generator as well as the casing in which the generator is mounted. The adjustable side of the condenser likewise is connected to ground. One end of the transformer likewise is grounded, ,as by connecting the same on the casing. The secondary windings of the transformer are 'electrically connected through the regulating means |29 to the lament conductors 51. Consequently the only electrical connection that need be made when mounting the generator in the casing is the connection of the filament conductors 51 to appropriate terminals of the regulating apparatus |29. The transformer |21 may be powered fromV a suitable external low voltage power source |39 through a grounded conductor |4| connected to a terminal |63 on and electrically connected to the casing |23 and aconductor |45 electrically connected with the transformer |21 by means of an insulated terminal |41 mounted in the walls of the casing |23.

The claims of the present application are directed to an X-ray tube and the transformer unit, while the claims to the cooling means for the X-ray tube are claimed in applicants application Serial No. 539,884, filed June 12, 1944. and assigned t0 the present assignee.

Itis thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made `X-ray tube having a metal mounting portion, a

closed casing in which said tube may be mounted by securing the mounting portion on said'casing, tube energizing means having high and low voltage portions and including a transformer enclosed in said casing and having windings adapted for electrical connection to said tube and a grounded winding electrically connected to and grounded on said casing, means to deliver electrical energy to the primary winding from a source of power disposed outwardly of the casing, and adjustable means for tuning the transformer for operation at a selected frequency, all high voltage carrying portions of the generating apparatus being enclosed within said casing.

2. X-ray generating apparatus comprising an X-ray tube having a metal mounting portion, a closed casing in which said tube may be mounted Aby securing its mounting portion on said casing,

tube energizing means having high and low voltage portions and including a transformer enclosed in said casing and having coils disposed in position encircling said tube, the transformer having windings adapted for electrical connection to said tube and a grounded winding one end of which is electrically connected to and grounded on said casing, a condenser having a condenser plate mounted on and electrically connected to the other end of the grounded winding of said transformer, and an adjustable condenser plate on and electrically connected to said casing to adjust the frequency of operation of said energizing means.

3. X-ray generating apparatus comprising an X-ray tube having a metal mounting portion, a closed casing in which said tube may be mounted by securing the mounting portion on said casing, tube energizing means having high and low voltage portions and including a transformer enclosed in said casing and having coils disposed in position encircling said tube, the transformer having windings adapted for electrical connection to said tube and a grounded winding one end of which is electrically connected to and grounded on said casing, a variable condenser comprising a condenser plate mounted and electrically connected to the other end of the grounded winding of said transformer, and an adjustable condenser plate within and electrically connected to said casing whereby the frequency of operation of said energizing means may be adjusted.

4. X-ray generating apparatus comprising an X-ray tube having a metal mounting portion, a t

closed casing in which said tube may be mounted by securing the mounting portion on said casing, tube energizing means having high and low voltage portions and including a transformer enclosed in said casing and having coils disposed in position encircling said tube, the transformer having windings adapted for electrical connection to said tube and a grounded winding onel end of which is electrically connected to and grounded on said casing, a variable condenser comprising a condenser plate mounted and electrically connected to the other end of the ,grounded winding of said transformer, an adjustable condenser within and electrically connected to saidcasing whereby the frequency of operation of said energizing means may be adjusted, and means without said casing in operative connection with said adjustable condenser plate for adjusting the same.

5. X-ray generating apparatus comprising an X-ray tube having a metal mounting portion, a closed casing in which said tube may be mounted by securing the mounting portion on said casina tube energizing means having high and low voltage portions and including a transformer enclosed in said casing and having coils disposed in position encircling said tube, the transformer having windings adapted for electrical connection to said tube and va grounded winding one end of which is electrically connected to and grounded on said casing, a variable condenser comprising la condenser plate mounted and electrically connected to the other end ofthe grounded winding of said transformer, an adjustable condenser within and electrically connected to said casing whereby the frequency of operation of said energizing means may be adjusted, and means Without said casing in operative connection with said adjustable condenser plate for adjusting the same, said last mentioned means being in axial alignment with the longitudinal axis Aof the transformer. i

ZED J. A'ILEE. HOWARD W. BRACKNEY.

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