US2121631A

US2121631A - X-ray tube

Info

Publication number: US2121631A
Application number: US78995A
Authority: US
Inventors: Malvern J Gross; Zed J Atlee
Original assignee: General Electric X Ray Corp
Current assignee: General Electric X Ray Corp
Priority date: 1936-05-11
Filing date: 1936-05-11
Publication date: 1938-06-21
Anticipated expiration: 1955-06-21
Also published as: GB495435A; DE708479C; GB495441A

Description

June 21, 19380 M. J. GROSS ET AL; 2,121,631

X-RAY TUBE Filed May 11, 1956 IIIIIIIIIJIIIIIIIII4O Inventors .Malver'n J. Gross;

Zed J. Atlee fr wajw w Their Attorney.

Patented June 21, 1938 x-RAY V 'Malvern J Gross and Zed J; Atlee,-: Chicago, 111;,

, assignors to General ElectridlXaRziy corpora-c.

tion, a corporation of-New..-Yorkr,-

Applicat onM 11; 193mmtime. 4 Claims. (01. '250-:.-;35)1

The present. invention relates tax-ray tubes, and ..mo,re particularly to. an improved. cathode structure. suitable. for-.use inan X-ray. tube. of. the .type in.,which.the anodeis rotatable toprovide. relative motionnbetweengthe. electron. beam andthetar-get surface. a

It..is.v a. primary object of. the invention to. provide, acathode capableof .producing two or more independently usable electron beams of substantially different. cross-sectional area which maybe. projected as substantially parallel elongated focal. spots. on closely. adjacent peripheral elements of .a. rotating target; o

The. noveLfeatures which we consider to be characteristicof. our inventionwill be pointed out with ,particularily in. the-appended. claims. The inventiontitself, however; togetherwith further objects ,and. advantages thereof, will best be un.-, derstood. by, reference tothe. following specificaf tiomtakenin. connection with the. drawing; in which, ,Eig. 11,shows; in elevation an X-ray tube suitably embodying the inventionp- Fig. 2 is an enlarged view. showing the cathode in'section and illustrating the relationship between the cath-.

ode and. the anti-cathode oritarget; Fig. 3 com-.

prisesv aseries of. schematic views illustrating a particular aspectof the. invention, and Fig. 4.1 comprisesa similar group of views illustrating. apreferred modification thereof. I e

.Gne applicationofthe..invention is illustrated in Fig. 1, in whichewe haveshown a rotatable anode X-raytubesuitable for'use in apparatus of the type disclosedand claimed in our copending. application, Serial No; 78,994, filed May-11, 1936, and assigned to. the same assignee as the present invention. The tube comprises an evacuated en-. velope: l v enclosing an anode or target 3, and a cathode l. The cathodeisaxiallyspaced and is offset with respect to the center of the anode and is supplied with heating current and with potential from an external-high voltage source (not shown) by means of the lead -in wires ll, l2, l3. and. I

The anode is mechanically connected to a rotata-ble structure 6 comprising an electromagnetic rotor l, for example, of these-called squirrel cage induction type. Thispreferably consists ofxa laminated magnetic core having longitudinal slots therein filled with a highly conductive metal as, for example, vacuum-cast'copper, The rotatablestruct-ure asa wholemay be supportedonan inwiardly projecting portion of, a shaft 9. by means of suitable antifriction bearings (not shown). Outside theenvelope and'in theregion of: the rotor 1, is arranged an electromagnetic staton. lll provided with energizing windings l5, for supplying a., rotati ng field effective tolinduce. a turning force in the rotor I. The details .of,,; construction. of ,theanode driving means aredisose i ndr m d i v r. neappl atiom. SerialNo. 78,9,96; filed May ,11, 1936, and assigned, tothe same assignee as the present invention.

The nature of the cathode and anode and of the co- .operative relationship between. ib-6H1:is well illustrated in Fig. 2. It will be.noted that, the rotata ble anode (Us providedwith a beveled, target face l8,-.,suitably.consisting-of. a refraQa. tory metalsuch a's tungsten, inclinedat ananglev shownas about '75 degrees-with respect to theaxis o f ,rot at ion,of, theanode. The cathode, which.v may be supported. byneans of. a glass-to-metal seal 2.0 from, a reentrant. envelope stem.- 2] cornprisesalaterally-projectingsleeve 23 and anelectrostatic focusing,cup,25supported at the extrem ity; of the -sleeve, Agskirt-like. shield 21, mounted at, ther'base. of the cathode, serves, tov intercept r'andoin X r'ay emanations. and. electrically charged particles corning from the direction. of the anode Thefocusing -cup is provided.-in- ,.its.

ersefacewith apair. ofrecesses or depression s of which onl y one, designated as,26,.is,-.1ap. parent in Fig 2, 1 Theserecesseseare,spaced from onesanother transverselyythat. is, in a" direction transverse to their .maj oraxes.-- At the bottom of each such-recess ..is. arranged at substantially. linearly} disp'psed' incandescible. filament, suitablyof turigstemj one .of such filaments being shown at Yr 2 inconnection with-the. recess 26.. As -previously indicated, theseare supplied with heating-current. by means of .the in.1ea d conductors, l2; IQ anciJA,sealed into theglass press 29; Inorderi to. permit ;the cathode-structure to; beplaced as ,.,far as p )ssib1e.=f1 -om.tl lewallv of--the envelope and-.therebygto. decrease thedanger of electrical breakdpwn, the. axis. of. each filament and of its associated focusing recess. is somewhat inclined withrespecttothe planelof rotation of the:anode so as ;to face towarc l.theiouter periphery-of the target face, I

When ahigh potential is impressed between thev anodeand cathode, the. electron beamemanating; from the heated filament..28 istdirected primarily by. the electrostatic .elfect of. the .walls of. the re-- cess ,2.,so as. toforrnan elongated .-focal spot" on the beveledfacef l8.of the.. anode 3,. the. extremitics of this; spot. being represented;- by. the. dotte d projectionilinesa, 1).. Due to the extreme angle of inclination of the target face the .corre sp nding X-ray pattern. formed on an external bject. 9; ill e resen a fo h d r is tion of the focal spot as indicated at .r. This mode of concentrating the X-rays emanating from an elongated focal spot obtains the effect of a small X-ray source of high energy content and is very desirable from the standpoint of producing a sharply defined radio-graphic image.

In the practical application of X-ray tubes, and more especially of rotatable anode tubes, it is of great importance that each tube have a wide range of operation in order to avoid the need for frequent substitution of units. While it is possible to vary the intensity of radiation of the X-rays and thereby the depth of their penetration by changing the heating current of a particular filament, the flexibility of an X-ray tube of given size may be still further increased by providing it with a plurality of independently usable filaments having different dimensions or which produce electron beams of different cross sectional dimensions. In Fig. 3 we have shown one example of a cathode construction which takes advantage of this latter possibility.

Here, the lowest view shows the frontal appearance of the cathode structure while the two center views show the cooperative relationship between the cathode and the target face I8 as seen from below. In the center views the cathode is shown as a section taken along the line A-A of the frontal view previously mentioned. As hereinbefore explained, the cathode structure comprises a focusing cup 25 having a pair of

elongated recesses

26 and 32 formed in the mu-' tually inclined faces thereof. These recesses may be described as being approximately radially directed with respect to the axis of rotation of the anode 3. However, when this mode of description is used herein and in the appended claims, it is to be understood as comprising an arrangement such as that shown in Fig. 3 in which either or both of the recesses may depart somewhat from a precisely radial orientation.

Within the recesses there are provided substantially linear

incandescible filaments

28 and 33 which are also approximately radially directed with respect to the axis of rotation of the anode. The position of each filament with respect to its corresponding recess is such that electrons emitted from it'during the operation of the tube will be projected toward the target face IS in the form of an elongated beam. Due to the fact that the two faces of the cathode cup 25 are mutually inwardly inclined to face a common region of the target l8, the two beams corresponding to the separate filaments will strike the target at adjacent focal spots which are substantially closer together than the filaments themselves. This is desirable in order tohave the central beams of X-rays from each of the two focal spots in approximately the same relation with respect to an external objective.

It will be noted, however, that with the parallel arrangement of filaments shown in Fig. 3, the individual focal spots will not be precisely parallel but will have central axes which if projected will intersect as shown in the two upper views of thefigure, which views, will be recognized as different aspects of the same target face. This intersection, which may be readily verified as a matter of projective geometry is due to the fact that the cathode filaments and the target surface are relatively inclined with respect to one another.

This means that if the axis of one focalspot is perfectly alined with respect to an external radiographic objective, so as to produce the maximum concentration of X-ray energy, as previously explained, the other focal spot will necessarily be somewhat out of alinement and will constitute a more diffused source of X-rays than is desirable. Consequently, in changing from one filament to another in the operation of the tube, the best possible radiographic results will not be attainable under all conditions of use.

This difiiculty may be overcome and parallelism' of the focal spots assured by arranging the individual filaments as shown in Fig. 4, in which the various views correspond to those already described in connection with Fig. 3. By inspection of these views, it will be seen that if the fo cusing recess 26' (corresponding to the similarly" numbered recess of Fig. 2) is arranged so that the axis of the focal spot produced by an electron beam emanating from the filament 28' assumes the position indicated by the line a, b, then the complementary filament 33 can be made to produce an electron beam whose focal spot has a parallel axis by disposing the filament itself in a non-parallel position as shown. Functionally expressed, the central planes of the two electron beams should intersect the target face in lines which are essentially parallel and which are substantially closer together than are the filaments themselves. Referred to the cathode structure this means that projections of the filaments 28' and 33 on a plane which is precisely normal to the path of the electron beams should be non-parallel and slightly convergent toward the axis of rotation of the anode or toward the portion of the cathode most nearly approached by the anode surface. The amount of this latter convergence will depend on the relative dimensions and spacing of the electrode parts and on the electrostatic efiect of the envelope and may be determined experimentally or by calculation 1 for a particular case so that the focal spots are actually parallel as indicated.

While we have shown particular embodiments of our invention, it will be understood by those skilled in the art that'modifications in the structure may be made without departing from our invention, and we aim in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

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

1. In an X-ray tube, a rotatable anode having a peripherally extending target surface thereon and a cathode structure axially spaced from the anode, said cathode structure including a plurality of transversely spaced linear filaments each relatively inclined with respect to the target surface and adapted during the operation of said tube to project an electron beam toward a common focal region on said surface, said filaments being arranged approximately radially with respect to the axis of rotation of said anode and being slightly convergent in the direction of said axis thereby to cause said'electron beams to form parallel elongated focal spots on said focal region of said target surface.

2. In an X-ray tube, a rotatable anode, a cathode structure axially spaced therefrom, a peripherally extending target surface on said anode angularly inclined away from said cathode structure, said cathode structure including a focusing body having a pair of mutually inwardly inclined surfaces thereon facing toward a common focal region on said target surface, each of said surfaces being provided with an elongated recess therein approximately radially directed with respect to the axis of rotation of said anode, and linear filaments respectively arranged in each of said recesses, said filaments being slightly convergent toward the axis of rotation of said anode.

3. In an X-ray tube, a rotatable anode having a peripherally extending target surface thereon, a cathode structure including a pair of transversely spaced linear filaments each arranged approximately radially with respect to the axis of rotation of said anode, means for connecting said filaments to an energy source, and electrostatic means for focusing the electrons emitted bysaid filaments into elongated beams the central planes of which intersect a common focal region of said target surface in approximately radially extending lines substantially closer together than said filaments, said filaments being usable independently and being adapted to produce electron beams of substantially different cross-sectional area.

4. In an X-ray tube, a rotatable anode having a peripherally extending target surface thereon and a cathode structure axially spaced from the anode, said cathode structure including a focusing body having a pair of spaced elongated recesses therein approximately radially directed with respect to the axis of rotation of the anode, and independently operable linear filaments respectively arranged in each of said recesses, said recesses being located in surfaces of said focusing body which are mutually inwardly inclined to face toward a common focal region on said target surface, whereby electron beams projected from the respective filaments during the operation of said X-ray tube produce on said common focal region of the target surface elongated focal spots which are substantially closer together than said filaments.

MALVERN J. GROSS. ZED J. ATLEE.