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June 7, 1938. c. v. LlTTON Q 2,119,679 X-RAY TUBE Filed May 29., 1936 ~ _ 3 Sheets-Sheet 1 I ' l0 l1 ,. 33 FL‘ . <5’ / r-IIIlllllllllllllll'lillllm . 1/3 34 0149155 kl/rm/v 3 5] . ATTOE/VfK June 7, 1938. 2,119,679 C. V. LITTON ' X-RAY TUBE Filed May 29, 1936, , 3 Sheets-Sheet 2 K. f m 7 43 . . ': “llllllflllfH 47E l WW I I I I'I I'W % lmln 144 l'l'l'l'l'l'l'l' 40 + 4.5 + 2 Z TTOQAIEK June 7, 1938. c. v. LITTION 2,119,679 , X-RAY TUBE Filed May 29, 1936 r 3 Sheets-Sheet 3 a 0..E,\.,A \W \,H H\“._1IFI 2/’ .N$J. ¢lJ w w; 2 6/“ m 3sf/ p ..2 .6 49 - m.0w6w hlHlIJ N ‘ y .. . 5 z ar ‘ N /2:5./5: .7 20' 12 . z;v _ 477024145X ' ' . Patented June 7, 1938 * ' 2,119,679 UNITED STATES PATENT or'rlcs 2,119,010 x-nsr runs Charles V. Litton, San Mateo County, Calif. Application my 29, ms, Serial No. cam ‘ 15 Claims. (onto-s5) This invention relates to x-ray tubes and has to do more particularly with tubes designed for use in the making of x-ray pictures. For radiographic purposes it is desirable always 5 to use a tube with a very small focal spot be anode heat than one in which the anode is ro tatable. In order to achieve the above-stated objective it is essential that the cathode beam be move able laterally of its direction of propagation dur ing operation of the tube; and to eifect such a lateral movement of the beam I prefer to make cause by so doing the maximum de?nition is ob tainable‘. possible to use a very small spot where a_ consid erable thickness must be penetrated because the 10 target would not withstand the great tempera ture which would result from concentrating the necessarily high milliamperage on such a small area for the time required to e?ect a suiiicient exposure. Therefore it is necessary with ordinary use of what may be termed electrical de?ecting means-operating upon the beam either electro statically or electromagnetically. But I do not 10' consider that the scope of my invention is limited, in all of its aspects, to any particular mode or means by which the lateral movement of the 15 tubes to use larger focal-spots on heavy work“ beam is accomplished. and to accept as inevitable the concomitant sac ri?ce of de?nition. ‘ The hypothetically possible methods of meet ing the aforementioned de?ciency are: 20 (1) To discover a satisfactory target metal that will withstand much higher temperatures than any metal now known; (2) To discover much more e?'icient means than is now known for dissipating the generated heat and: (3) To eii'ect a continuous movement of the - focal-spot over the face of the target so that no one portion of the target is exposed to bombard ment for a suiiicient length of time to permit of 30 an excessive temperature rise. The present invention falls within the third mentioned classi?cation. - For radiographic purposes it is usually neces sary, or at least preferable, that the focal spot be 15 substantially stationary in space-that is, from the viewpoint of the object being radiographed and, likewise, from the viewpoint of the photo graphic ?lm or plate. In one of its principal aspects, my invention is characterized by the fact that the focal spot is caused to traverse (scan) the face of the target (during operation of the tube) while at the same time the tube as a whole is moved more or less bodily in directional opposition to the target 26 traversing movement of the focal spot-the focal spot being thereby maintained substantially ?xed in space. There are two known electrical methods by 80 which a cathode beam, 1. e: a beam of electrons, It has been proposed heretofore to provide ro tating or otherwise continuously moving targets 35 and it is believed that such tubes have been de~ veloped commercially; but there are inherent and seemingly unavoidable di?iculties standing in the way of commercial production and use of x-ray tubes of that character—which dimculties arise 40 out of the fact that there are moving parts inside the tube which cannot be lubricated, yet must be > closely ?tted in order to maintain a proper de gree of precision. One of the principal objects of the present in 45 vention is to devise an x-ray tube of the type wherein the focal spot continuously traverses the face of the target during operation of the tube, but in which the anode, including the target, is ?xed-that is, not rotatable or otherwise move able with respect to the envelope of the tube-the ultimate objective being an x-ray tube of the class referred to which is free from internal me and moving electrical contactsand which, in ad for the dissipation of A cathode beam traversing a magnetic field in space, more‘ or less normally to the magnetic lines of force, will be deflected laterally, crosswise of 45 the magnetic lines of force, just as a metallic conductor passing through a magnetic ?eld and carrying a'current (as in an electric motor) will be caused to move transversely of‘ the lines of force; and, if the magnetic ?eld is .al beam will be reciprocated ‘ ternating the cathode laterally. The two aforementioned methods of de?ecting the cathode beam may be employed individually 55 2,119,079 2 or jointly. That is to say, the beam may be os cillated and thus caused to scan the target in two directions simultaneously by means either‘of anode and wholly or to a large extent prevents the electrons of the cathode beam being in?u enced by the anode until they have passed beyond two sets of electrostatic de?ectors or two de?ect ing magnets or by means of one set of electro static de?ectors and one de?ecting magnet. The two scanning movements of the cathode beam are preferably approximately at right angles to each the point or points where they are laterally de ?ected. The electrons, instead of being accel erated initially by the anode ?eld, are,‘ instead, in?uenced wholly or mainly by the ?eld set up by the shield potential-the shield, itself, being, in other-one occurring preferably at a fairly high frequency such as sixty cycles per second while the other occurs at a relatively low frequency, say one to ?ve cycles per second. The low frequency a sense, a sort of intermediate anode. At the same time, the constricted portion of the shield 10 having the opening through which the beam passes is, in effect, a virtual cathode-that is, scanning of the target is in synchronism with the oscillatory physical movement of the tube as a whole and is in a plane such that, from the viewpoint of the object being radiographed, the focal-spot is substantially stationary. To bring about a predetermined lateral de ?ection of a cathode beam either electrostatically or electromagnetically, the required electrostatic deflecting potential or magnetic ?eld intensity, as from the viewpoint of the anode. It is contemplated that the cathode beam may be in the form of a pencil having a more or less circu 15 lar cross-section as in a conventional round-focus X-ray tube or that it may have a more or less rectangular cross-section as in a conventional line-focus tube. With a cathode beam of the last mentioned form the scanning of the target need 20 be only in one direction, that is laterally of the linear focal-spot. The scanning in that case the case may be, is more or less proportional to would be at a low frequency only, isochronously the anode potential. By this I mean that the with the reciprocatory movement of the tube. 25 electrical potential or magnetic force required to Referring to the drawings: de?ect the cathode beam in an ordinary X-ray Fig. 1 is a side elevational view of an X-ray tube to any given extent is more or less directly’ tube mounted on a support which is adapted to proportional to the voltage across the anode be reciprocated, together with the tube. This cathode terminals. With a tube operating at, view also depicts a driving motor and speed reduc let us say, one hundred k. v., the necessary de tion gear together with a low frequencyalter 30 ?ecting potential would be quite high. Similarly, nating current generator or magneto which serves a magnetic ?eld of very considerable strength to provide alternating de?ecting voltage in syn would be needed to e?ect a like de?ection of the chronism with the reciprocatory movement of beam. tube; It is very desirable to be able to bring about the theFig. 2 is an endwise view of the tube and other 35 requisite deflection of the beam without having to resort to excessively high potentials on the elec trostatic de?ecting electrodes and, similarly, to avoid the necessity for a very powerful magnetic ?eld where the de?ecting is accomplished mag-' netically. I have discovered a method and means whereby the de?ecting of the beam can be brought about with relatively small de?ecting potentials or a relatively weak magnetic ?eld, as the case may be. This I accomplish through an arrange parts shown in Fig. 1; Fig. 3 is a circuit diagram of an arrangement for providing low frequency alternating potential from a source of direct current. tube and also illustrating diagrammatically the electrical connections; 45 ment which operates to shield the cathode beam from the in?uence of the high anode potential until after the electrons which constitute the beam have traveled past the point or points in their space path at which they are laterally de electrons being caused to move at 50 ?ected-the relatively low velocity through the initial por tion of their space path (during which period they are laterally de?ected) and thereafter at a greatly increased velocity. The velocity of electrons in a highly evacuated 55 space path is a function of the space potential which in an ordinary x-ray tube is the potential difference across the anode-cathode terminals. If the space potential actually operating upon the 60 electrons emitted by the cathode can be made materially less than the anode-cathode potential difference, during an initial portion of the elec tron movement from cathode to anode, the ve locity of the electrons through such initial por tion of the space path becomes correspondingly less. - Fig. 4 is a view, mostly in longitudinal section, showing the interior construction of the X-ray - In the X-ray tubes illustrated in the accom Fig. 5 is a cross-sectional view of the tube .45 taken along the line 5-5 of Fig. 4; Fig. 6 is a cross-sectional view taken along the line 6—6 of Fig. 4; Fig. 7 is a face view of the target showing the focal-spot and illustrating the movement of the focal-spot back and forth across the face of the target; Fig. 8 is also a view of the face of the target with the path of the focal-spot depicted there on. This view illustrates the result of a pencil like cathode beam scanning the target in one di 66 rection (vertically) at a relatively high frequency, say sixty cycles per second, and in the other di rection at a relatively low frequency, say from one to ?ve cycles per second; Fig 9 is an external elevational view of an X-ray tube which is much the same as those il lustrated in the preceding figures but differing therefrom in that an external de?ecting magnet is employed to take the place of one of the two sets of electrostatic de?ector plates; 0 Fig. 10 is an elevational view of the de?ecting , magnet shown in Fig. 8 and a cross-sectional view through the tube illustrating more especially the space relation between the pole pieces of the there is included a shield on which is impressed magnet and the electrostatic de?ector plates in- '1 a suitable intermediate positive potential. The side the tube; shield has a somewhat constricted opening Fig. 11 is a view of the cathode end of an al through which the cathode beam passes to the ternative tube structure in which the projected target without physical obstruction; but, at the beam is of rectangular cross-section, that is to panying drawings and hereinafter described, same time, the shield operates as a barrier to the . say. a line-focus beam; and 7i electrostatic lines of force emanating from the 9,110,079 Fig. 12 is a cross-sectional view taken along the line l2-l2 of Fig. In Figures 1 and 2, reference numeral I des 11. - . ignates, as an entirety, an X-ray tube in accord ance with this invention comprising an evacu ated glass envelope of cylindrical form in which are enclosed all the usual elements including the anode with its target and a thermionic cathode‘ together with other parts shownin Fig. 4. At 10 the anode end of the tube is an air-cooling radi ator 2 of conventional form. The left hand or cathode end of the tube is provided ‘with a con ventional screw plug 3 which is shown inserted in a screw socket 4. Heating current is supplied 15 to the cathode of the tube through the screw plug 3 and socket 4. The whole tube together 3 desired low frequency alternating potential can be produced across the terminals 31 and 38. Figs. 4, 5 and 6 illustrate somewhat in detail an x-ray tube wherein‘ the cathode beam is in the form of a pencil of small diameter and more or less circular cross-section. The cathode beam 1 is reciprocated at a fairly high frequency, say sixty cycles per second, in directions toward and away from the object to be radiographed-thus producing, in effect, a linear focai-spot-and at the same time the cathode beam is reciprocated 10 slowly at right angles to the '- previously men tioned plane of reciprocation-thus, in‘ effect, causing the linear focal-spot to move laterally back and forth across the face of the target. Fig. with the radiator 2 and socket 4 are mounted on 7 illustrates, approximately, how the focal-spot 15 and supported by a pair of uprights 5 and 6, respectively, which, in turn, are mounted on and cillatory transverse movement of the target. Fig. would appear to an observer and depicts the os 20 carried by a cross member ‘I of insulating ma terial. Cross member 1 is provided with an 8 illustrates the path of the focal-spot when re ciprocating in one direction at say sixty cycles opening 3 through which X-rays are emitted. To per second and in the other direction at say one the lower side of cross member ‘I and at either end is attached a pair of channel-shaped mem 25 bers 9 and- HJ respectively. These latter are seat ed in guides II and I2 in which they are free to ray tube which is designated as a whole by ref erence numeral i comprises a glass envelope 20 slide reciprocably as indicated by the double headed arrow in Fig. 2. ' to ?ve cycles per second.v , Referring more particuarly to Fig. 4, the X of generally cylindrical form, the interior of which is‘ highly evacuated. Inside the ‘envelope are shown an anode 2i which is usually of cop per, a thermionic cathode 22, a "gun” or accel-i Guides II and I2 are secured to and carried .30 on the top of a table or base plate l3, of insu latin material, which would generally form a erator 23, a pair of electrostatic de?ector plates 24 and 25 and a second pair of similar electro 30 static de?ector plates 26 and 21. Inserted in the anode 2| is a circular tungsten button part %of or be carried by the adjustable arm of an X-ray machine. Mounted upon base plate I3 is an'electric mo 35 tor l4 having a speed reduction gear enclosed within a housing i 5. A drive-shaft projecting from the speed reduction gear housing has an o?-set crank pin it, to which is journaled a con necting rod I], one end of which is pivotally con nected at l8 to the cross member 'I. With the motor in operation the cross member ‘I to gether with the X-ray tube and other parts carried by the cross member are reciprocated In addition to the‘elements already mentioned it is desirable to provide a cylindrical shield 29 and a focusing coil 30. The thermionic cathode is provided‘ with a suitable focusing shield 3| having a circular opening 32 throughwhich a stream of electrons 40 known as the cathode ‘beam is 'emitted—this beam being projected toward the target 28 as in slow1y—-the length of the stroke being madeto all conventional X-ray tubes. The accelerator equal the distance spanned by the cathode beam or gun 23 is provided with a central opening large in its travel across the face of the target in the same direction as that in which the tube is re enough to permit passage of the cathode beam 45 ciprocated. The scanning of the target andv the physical reciprocatory movement of the tube are isochronized so that from the viewpoint of the upon it a suitable predetermined positive poten tial. The function of the gun is to form the object being X-rayed the focal-spot remains sta tionary. As a matter of fact the focal-spot is stationary in space but there is a relative movement between the focal-spot and the surface of 55 the target. Also shown mounted on the table I3 is an electric generator or magneto l9. This is driven through the speed reduction gear l5’ and it is designed to produce an alternating voltage of the same frequency as that at which the X-ray tube is physically oscillated. The voltage from this generator is isochronous with the oscillatory movement of the tube .and is of a magnitude such as to be suitable for application to the low 65 frequency electrostatic de?ector plates which will be described later. ' As an alternative to the low frequency gen erator l9 there may be provided an arrangement such as shown in Fig. 3 which comprises a direct 70 current source 33 across the terminals of which is connected a potentiometer 34 having two slid ing contacts 35 and 36. By moving these con tacts continuously, in opposite directions, at the desired low frequency and isochronously with the 75 oscillatory movement of the X-ray tube, the ' electronic discharge into a concentrated beam and propel the beam toward the target. The use of such guns in oscillograph machines is well known. . The electrostatic de?ectors 24, 25, 26 and 21 consist each of a small metal plate which may be 55 rectangular in form as shown. Across the de ?ector plates 24 and 25 is applied suitable magnitude. This low frequency poten tial is the one which may be supplied by the generator I 9 or the arrangement of Fig. 3. It must be isochronous with the reciprocatory 65 movement of the tube in order that the focal spot may remain stationary in space. The cylindrical shield 29 has a constricted neck portion at the end thereof adjacent the target, which neck portion de?nes an opening through which the cathode beam must pass to reach the Shield 29 operates as a barrier to the electrostatic lines of force emanating from the anode, wherefore the electrons forming the cath 2,119,079 4 ode beam are not in?uenced by the target until they have entered and at least partially passed through the opening in the shield-at which point the electrons are quickly accelerated by the high anode potential and thus caused to strike the target at a suitable velocity for the production of X-rays. A positive potential of some suitable intermediate value is impressed ?ected transversely of the magnetic lines of force passing between the pole pieces. 0n the con trary, the cathode beam is not de?ected trans versely of the electrostatic lines of force between the de?ector plates but, instead, it is de?ected toward the positive plate. This accounts for the space relationship between the de?ector plates 28, 21 and the pole pieces of magnet 41 as illus trated in Fig. 10. It is possible‘to use two sets of de?ecting mag nets and thus eliminate both sets of electrostatic de?ector plates, but it is thought that it would upon shield 29 and, as a consequence, the shield performs the function of an anode in that it im parts a propulsive force to the electrons, caus ing them to move toward the target-but at a lower velocity than that at which they would be be necessary to provide considerable separation between the two magnets in order to keep their space fields sumciently isolated. Figs. 11 and 12 illustrate the construction of the cathode end portion of a tube similar to that of Figs. 4, 5 and 6, except that a cathode beam of linear form (rectangular cross-section) is pro jected. In this case the thermionic cathode 4l instead of being in the form of a conical spiral is of linear form; the aperture 49 in the focusing shield and likewise the passageway 50 through propelled if under the in?uence of the high anode potential. Thus the electrons are caused to move at a relatively low velocity through that part of their space path in which they are acted upon by the de?ector plates and, resultantly, a relatively low potential on those plates will answer the purpose. Were it not for the shield 29, the de?ecting, potentials would necessarily be quite large in X-ray tubes operating at high anode voltages-a condition which it is highly desirable to avoid. What has been said with 95 the gun 23 are rectangular in form. Only one set of de?ector plates 26 and 21 is required be- _ cause the linear beam scans the target only in one plane, i. e. laterally of the linear focal-spot. respect to the effect of the shield upon the de ?ecting potentials applies also to its effect upon the requirements as to the intensity of the mag netic ?eld which may be employed to de?ect the beam as a substitute for electrostatic de?ection. The function of the focusing coil 30 is to con centrate or reconcentrate the cathode beam. It is well known that the effect of a magnetic ?eld upon a cathode beam passing axially’ there through is to concentrate the beam. Thus, if the beam shows any tendency to spread out this may be cured by means of a focusing coil Ill. The focusing coil should not be confused with the A de?ecting magnet may be used with the tube structure of Figs. 11 and 12 to take the place of the electrostatic de?ector plates 28 and 21. What is claimed is: 1. The combination in an X-ray tube compris ing a target, a cathode and focusing means, of means for cyclically de?ecting the cathode beam thereby causing the focal-spot cyclically to scan the target, and means for cyclically moving the target isochronously with the cyclical scanning movement of the focal-spot whereby to maintain the focal-spot substantially stationary in space. magnetic de?ecting coil which presently will be described. They perform entirely different func 2. The combination in an X-ray tube compris ing a target, a cathode and focusing means, of 40 tions. In addition to physical structure, Fig. 4 in means for cyclically de?ecting the cathode beam thereby causing the focal-spot cyclically to scan the target, and means for cyclically reciprocat ing the target isochronously with the cyclical cludes a diagrammatic showing of electrical con nections. There is depicted _a transformer 39 having a primary winding 40,, a secondary wind ing 4i, which supplies heating current to the 45 cathode and a secondary winding 42 which sup scanning movement of the focal-spot whereby‘ to maintain the focal-spot substantially station plies sixty cycle potential to the electrostatic ary in space. de?ector plates 24 and 25. The low frequency generator 19 shown in Fig. 1 is also illustrated diagrammatically in Fig. 4. A source of direct current 43 supplies biasing potential to the focus ing shield ll; another direct current source 44 supplies a positive potential to the gun 23 and the cylindrical shield 29 has impressed upon it a still higher positive potential by .virtue of the 55 inclusion in its circuit of the additional direct current source 45. The maximum positive poten tial is of course applied to the anode 2! as is indi cated by the inclusion of still another direct source 46. In practice the several D. C. poten tials would generally be derived from recti?ed and ?ltered alternating current. . _ In Figs. 9 and 10 are illustrated a combination which includes a de?ecting magnet 41 between the pole pieces of which the X-ray tube I is 85 mounted. The de?ecting magnet 41 takes the place of one of the two pairs of electrostatic de ?cctor plates. It may be substituted for either pair. If substituted for plates 24 and 25 the winding of magnet 41 would be supplied with 70 sixty cycle current; but if the magnet is used as a substitute for de?ector plates 26 and 21 its winding would be supplied with low frequency current. As previously stated, the cathode beam is de 3. The combination in an X-ray tube compris ing a target, a cathode and focusing means, of electrical means for cyc'lically de?ecting the cathode beam thereby causing the focal-spot cy clically to scan the target, and means for cycli cally reciprocating the tube together with said target isochronously with the cyclical scanning movement of the focal-spot whereby to maintain the focal-spot substantially stationary in space. 4. In combination, an X-ray tube comprising an evacuated envelope, a target and a cathode within said envelope, focusing means for con centrating electrons propagated by said cathode into a beam and directing said beam toward said target, two sets of electrical de?ecting means operable individually to de?ect said beam later ally in different directions respectively, one of 65 said sets of electrical de?ecting means being con nected to a source of relatively high frequency alternating potential, the other of said sets of electrical de?ecting means being connected to a source of relatively low frequency alternating potential whereby the focal-spot projected upon 70 said target is caused to scan said target cycli cally in two directions substantially at right angles and means for reciprocating said tube cyclically in the same plane as that in which the focal-spot scans the target at low frequency“ 2, 1 19,679 5 the reciprocatory movement of said tube being isochronous with the low frequency scanning ments of both the x-ray tube and the focal-spot movement of the focal- t. 5. The combination with an X-ray tube com prising a target and means for projecting a 'cath-' ode beam at said target, of means for causing the focal-spot produced thereby to scan said target reciprocably and means for reciprocating said 10 tube isochronously with the scanning movement of said focal-spot,‘ the reciprocatory movement of said tube and the reciprocatory movement of said focal spot being at all times in mutual directional opposition so that said focal spot remains sub 16 20 stantially stationary in space. 6. The combination in an X-ray tube compris ing an envelope, a target, a cathode and focusing means within said envelope; of means for de ?ecting the cathode beam whereby to cause the‘ occuring in the same plane, said plane of oscilla- - tion being such that the focal-spot is maintained substantially stationary relatively to the subject being radiographed. 10. The combination in an x-ray tube of -an evacuated envelope, an electronic-emissive cath ode and an anode in spaced relation within said envelope, means for concentrating the electronic emission from said cathode into a beam and di 10 recting said beam toward said anode, a shield forming a space within said envelope which is isolated to a substantial degree from the in?uence _of said anode so that the electrons emitted by said cathode are not greatly accelerated by the anode field,- at leastvuntil they have traversed‘ a substantial portion of the space path between' focal-spot to traverse the face of the target, and , said cathode and said anode, said cathode being mechanism for moving the x-ray tube bodily in situated within said isolated space, said shield having an opening to permit . passage there 20 unison with the aforementioned traversing move ment of the focal-spot but oppositely in direction through of the cathode beam, and electrical whereby to maintain the focal-spot substantially ?xed relatively to the subject being radiographed, 25 said last-mentioned means and said mechanism being so interassociated as to operate in timed relation one to the other. ‘ _ 7. The combination with, an X-ray. tube com 30 prising an envelope, a target, a cathode and fo cusing-means within said envelope, of means for means operative upon said beam within said iso lated space for de?ecting said beam laterally of its direction of propagation. - 11. The combination in‘an X-ray tube of an 25 evacuated envelope, an electronic-emissive cath ode and an anode in spaced relation within said envelope, means for concentrating the electronic emission from said cathode into a beam and di recting said beam toward said anode, a tubular 30 shield within said , a chamber which to maintain the focal-spot ‘substantially ?xed envelope, said shield forming is largely isolated, by virtue of the shield, from the in?uence of the anode elec trostatic ?eld, said cathode being situated in said chamber, said shield having an opening for the 35 passage therethrough of the cathode beam, means relatively to the subject being radiographed, said - for impressing a positive high potential on said last-mentioned means and said mechanism being 40 so interconnected as to operate in timed relation one to the other. ' ' lower than that of the anode, upon said shield, and electrical means operative within said cham 40 ber to deflect said beam laterally of its direction 8. The improved method of operating a radio-, of propagation. , graphic X-ray tube of thetype comprising a. tar 12. The combination in an X-ray tube of an get, a cathode and cathode-beam focusing means 45 within an envelope and wherein the cathode beam evacuated envelope, an electronic-emissive cath is caused to impinge upon the face of the target ode and an anode in spaced relation within said and produce thereon a focal-spot, said improved envelope, means for concentrating the electronic 45 method comprising: moving the cathode beam laterally of its direction of propagation so as to cause the focal-spot to traverse the face of the target and, at the same time, moving the X-ray tube bodily in a direction opposite to the lateral movement of the cathode beam at substantially 50 the same speed as that at which the focal-spot 55 traverses the face of the target so that the focal spot remains substantially stationary relatively to the subject being radlographed notwithstanding 55 its movement relatively to the face of the target. 9. The improved method of operating a radio graphic X-ray tube of the type comprising a tar get, a cathode and cathode-beam focusing means within an envelope and wherein the cathode beam is caused to impinge upon the face of the target and produce thereon a focal-spot, said improved 65 60 method comprising: oscillating the cathode beam laterally of its direction of propagation so as to that of the anode, upon said shield, and means cause the focal-spot oscillatorily to traverse the face of the target and, at the same time, oscil lating the X-ray tube bodily so that the face of 70 the target moves always in directional opposition to the movement of the focal-spot thereacross, the oscillatory movement of the face of the target for impressing potentials of opposing polarities upon said de?ecting electrodes. '13. The combination in an X-ray tube of an evacuated envelope, an electronic-emissive cath ode and an anode in spaced relation within said envelope, means for‘ concentrating the electronic 70 being maintained always at substantially the emission from said cathode into a beam and di same speed as that at which the focal-spot trav recting said beam toward said anode, shielding erses the face of the target, the oscillatory move means dividing the space path between said cath ode and anode into at least two successive parts, 75 8,110,079 at least one of said parts being electrically iso lated, at least to a substantial degree, from the in?uence oi’ said anode, said shielding means having an opening to permit passage of said beam to said anode, the arrangement being such that the electrons constituting said beam move toward said anode through an initial portion of the space path at a relatively low velocity and, thereafter, at a relatively high velocity, electri 10 cal beam de?ecting means adiacent a portion of the space path wherein the electrons move at rel atively low velocity, means for‘ impressing a rela tively high positive potential on said anode with respect to said cathode, and means for impress ing a lower positive potential on said shielding means with respect to said cathode. on said anode, means ior impressing a positive potential, lower than that of the anode, upon said shield, means for impressing a potential upon said gun and means for impressing a vary ing potential across said de?ecting electrodes. 15. The combination in an electrical discharge device of an evacuated envelope, an ion-emitting electrode and a second electrode in spaced rela tion within said envelope,'means for concentrat ing the ionic emission from said first-mentioned electrode into a beam and directing said beam toward said second electrode, a shield forming a space within said envelope which is isolated to a substantial degree from the in?uence of said sec ond electrode so that the ions emitted by said ll ?rst electrode are not greatly accelerated by the ileld or said second electrode, at least until they l4. Thecombination in an x-ray tube of an have traversed a substantial portion oi’ the space evacuated envelope, an electronic-emissive cath path between said electrodes, said ?rst electrode ode and an anode in spaced relation within said being situated within said isolated space, said envelope, a gun adjacent said cathode, an elon shield having an opening to permit passage~ there gated tubular shield enveloping said cathode and through of said beam, and electrical means oper gun, and at least one pair of electrostatic de ?ecting electrodes within said tubular shield, said electrodes being arranged in mutual opposition and operative to effect lateral de?ection of the beam of electrons propagated from said cathode, means for impressing a positive high potential ative upon said beam within said isolated space for de?ecting said beam laterally of its direction oi propagation. , CHARLES V. LI'I'I'ON.