US2499545A

US2499545A - Rotary x-ray tube

Info

Publication number: US2499545A
Application number: US662133A
Authority: US
Inventors: Tuuk Jacob Hermannus Van Der; Combee Bart
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1943-12-31
Filing date: 1946-04-15
Publication date: 1950-03-07
Anticipated expiration: 1967-03-07
Also published as: FR915221A; NL71102C; NL114571B; GB624030A; CH251524A; BE461891A

Description

Mardl 1950 J. H. VAN DER TUUK ETAL 2,499,545

ROTARY X-RAY TUBE Filed April 15, 1946 Z8 Z4 Z2 J6 g v/ M l JNVENTORS.

AITUKZVEX Patented Mar. 7, 1950 no'rAnYx-RAY TUBE Jacob Hermannus van der Tuuk, and Bart Combee, Eindhoven,

Netherlands, assignors,

mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 15, 1946, Serial No. 662,133 In the Netherlands Deeember31, 1943 Section L PubIicLaW 690, August s, 1946 Patentexpires December 31,1963

. '1 Claims. (01150 -145) With X-ray tubes having a rotary-anode the heat cannot be transmitted by conduction from the anode to a cooler located outside the tube as it is impossible or at least very diflicult to lead a rotating bar through the wall of the tube in an airtight manner. For the same reason it is impossible'to bring a circulating cooling liquid into contact with the anode. Though it has been achieved, by eflicient constructions of the rotary anode, to transmit a comparatively high power by radiation, the full exploitation of the advan tage of the rotary anode is made impossible by the difliculty of the transport of heat.

It becomes possible, indeed, to cool a rotating anode directly, if the whole of the X-ray tube rotates. An X-ray tube of this type is known, for example, from German patent specification No. 574,865. In this tube the cathode is arranged in the axis of rotation and, in order to deflect the electron beam, use is made of the' electric field between the anode and the cathode. Bymean's of a stationary directing body which is fastened to the anode this field is given the structure required for this purpose.

The invention likewise relates to a rotary!!- ray tube, wherein thecathode is located-in the axis of rotation. The electrons are also moved to the anode in an oblique direction without the use of cross fields. According to the invention, the stationary directingbody serving for this purpose is arranged in the proximity of the cathode. This form of construction is better suitable for obtaining a sharply defined'focal spot than the well-known constructions and-consequently it favours the sharpnessof definition of the image; Besides; it has the-advantage that rapid secondary electrons, which in X-ray tubes may have allsorts of detrimental effects occur to amuch smaller extent.

The directing body may be electrically-connected to the incandescent'cathode. Under determined conditions, for example if it is desired that the focal spot should be movable in a radial direction, it is advantageous to keep the directing body insulated from the incandescent cathode and to provide it with a separate current supply wire, so that between the directing body and the cathode a potential difierence can be maintained.

The directing body may serve at the same time as a. collecting device which concentrates the electrons in the focal spot. It is mounted so as to be rotatable about the incandescent cathode and it has an oblique front face which exhibits an aperture for the passa e of the beam 2 of electrons which is located eccentrically with respect to the axis of rotation.

In the Well-known rotary X-ray tubes comprising a cathode which is also rotatable the electrons, only after having reached a considerable velocity, experience a noticeable force which forces them in a lateral direction, since the electric field in the proximity of the cathode still extends in an axial direction. With the tube according to the invention, on the contrary, the electrons have already the desired direction when they enter the discharge path, owing to which the beam may beshorter and exhibits less disperson, which is beneficial to the sharp-'- wise the size and the'position of the focal spot would no longer be completely independent of the anode voltage. The voltage on thedirecting body may also be negative with respect to the cathode and proportional to the anode voltage.

In one particular form of construction of this X-ray apparatus a device for controlling the suction anode voltage iscoupled-with the selector of the anode voltage in such a manner that, independently of the voltage chosen, the suction anode always has the same percentage of the anode voltage.=

A directing body having a positive potential may be struck by electrons. -With the tube according to the invention the disadvantage caused by the impact of electrons on the directing body is much less than with the tube wherein the directingbody is fastened-to the anode, since these electrons have a much higher speed and consequently generate X-rays and secondary electrons. A loss of electrons ensues, indeed, due to the deflection towards the suction anode, but this drawback canbe obviated by the use of a directing body which comprises two diaphragms insulated from one another, of which the outer one is provided with a separate current supply wire and the inner one-is connected to the cathode or also has a separate current supply wire; The outer diaphragm can be given in this case such a positive. "voltage proportional to the anode voltage that it aotsljas a suction anode. The

inner diaphragm, which acquires the potential of the cathode or a more negative potential, acts as a screen. In front of the cathode there is obtained in this case an electron-optical lens which, in agreement with the object of the invention, concentrates the cathode rays on a very narrow focal spot.

With the tube according to the invention the retracting efiect of the field in the proximity of the anode is slight owing to-the high speed the electrons have in the place. This effect can, indeed, be suppressed by rotatably fastening to the anode a diaphragm whose front face is normal to the direction of the axis of the electron beam at the cathode. In this case the axis of the electric field in the acceleration space is a straight line and the space between the diaphragm and the anode is free from any field. The diaphram exhibits a narrowed portion and in this place the directing body is mounted so as to be rotatable about the wall of the tube, consequently outside the vacuum. This body should preferably have a rotation-symmetric shape and exhibit a longitudinal slit. It may have the shape of a funnel as well as that of a cylinder. The slit causes disturbance of the radial symmetry of the electric field in the proximity of the cathode, which makes the electrons travel in an oblique direction.

In order that the invention may be clearly understood and readily carried into effect, it will now be explained more fully with reference to the accompanying drawing, which represents in section by way of example, three forms of construction of an X-ray tube according to the invention.

Fig. 1 is a tube wherein the directing body has cathode potential.

Fig. 2 is a form of construction wherein the directing body consists of two parts.

Fig. '3 represents a tube wherein the directing body is located outside the vacuum.

Fig. 4 is an "axial projection of the directing body of the tube shown in Fig. 3.

In the first three "figures the glass wall o'f the tube, the anode and the incandescent cathode are. denoted by I, 2 and 3 respectively. The anode, which is shown in section only in Fig.1, exhibits a cavity 4 for the purpose of cooling by means of a circulating liquid supplied through a "tube 5.

Between the incandescent cathode 3 and the anode is located a directing body which, in the tubes according to Figs. 1 and 2, held in place by a magnetic yoke 6 when the X-ray tube rotatable about its axis 1 is set rotating.

In the form of construction according to Fig. 1 the directing body is constituted by a collecting device 8 which is mounted on a metal cylinder 9 so as to be easily rotatable, said cylinder carrying the incandescent cathode. It is provided with ferromagnetic poles It in order to be immobilised magnetically with the aid of the yoke 6 when the tube is rotating. In order to give the desired direction to the lines of force of the electric field in the place where the electrons leave the body '8 the directing body exhibits an oblique front'face. Owing to the eccentric position of the aperture "I "l destined for the passage of the electrons, the latter are drawn towards the anode 2 at an angle with respect to the axis 1 and they strike the anode outside the axis on the conical front face 12, on which the anode target is provided.

In the form of construction according to Fig. 2 the directing body consists of two metal caps l3 and 14 which are insulated from one another, each of them having on the front side an oblique diaphragm. They are fastened to the pole system It by bolts l5, but rings I6 of insulating material ensure that only the cap I4 is electrically connected to the anchor l U. The cap I3 is placed on a ball block l1 and thus it is connected with a current supply wire I8. The anchor I0 bears on a ball block l9 and is thus connected with a current supply wire 20. The wires I 8 and 20 are connected to bushes 2! and 22 which are secured to one another by means of an intermediate piece 23 of glass sealed thereto. The blocks I1 and [9 are mounted on the bushes 21. The bush 22 is clamped around a glass cylinder 24 which is sealed to the re-entrant portion 25 of the wall of the tube, which portion also carries a pinch 26.

Current supply wires

21 and 28 serve to'conduct the heating current of the cathode.

When using the tube the wire 18 and therefore the cap 13 may be given a negative potential,

for this rotation serves to render possible a higherspecificload on the anode and therefore to permit a smaller focal spot with a given power.

The diaphragms of the caps l3 and II have each an ecc'entrically arranged

aperture

28 and 30 respectively. The beam of electrons passes through these apertures to the outside in the direction designated by 3| at such an angle with respect to the axis 1 that the anode target [2 is hit at some distance from the axis.

With the tube shown in Fig. 3 the wall I exhibits in the proximity of the incandescent cathode 3 a narrowed part "32, so that between the wall and the cylinder 33 whose edge surrounds the filament there is at this place only a narrow space. A directing body 34 .is rotatably arranged around the part 32. This can be kept completely stationary when the tube rotates about its axis 1, owing'to which vacillation of the focal spot, which cannot always be avoided when the direct ing body is magnetically immobilised, is excluded.

The directing body 34 has the shape of a funnel and exhibits awidelongitudinal slit 35 (Fig. 4). The consequence thereof is that with a negative potential of the directing body the electrons are deflected towards the slit and move in the direction indicated by 36 in the plane of symmetry of the body 34 to the anode target 12.

By varying the potential or the locality of the directing body '34, it is possible to modify the locality of the focal spot. This is important, for example, with tubes designed for the testing of materials, in which case "it is required to generate X-rays of determined wavelengths. It may, in this case, be necessary to have at ones disposal anode targets of different materials, in order to be able to make a choice out of different spectra of the rays emitted. With a tube according to the invention these anode targets may be provided as concentric rings on the front face l2 of the anode. By regulating the potential -or. the,

locality of the directing body it is possible to modify the direction of the electrons and thus to place the focal spot on the desired ring.

If the directing body 34 is given a positive potential with respect to the cathode, it attracts the beam of electrons and it causes the focal spot to be produced on the opposite side. It is consequently possible to cause the X-rays to emerge at will from the tube on two opposite sides.

I What we claim is:

- 1. An X-ray tube comprising a tubular evacuated envelope, cathode and anode electrodes mounted in said envelope and having a given axis for rotation thereabout with said envelope, said cathode having an emitting surface the diameter of which is small relative to the diameter of the area of electron impact on the anode, an electrostatic focussing element having a focussing axis forming an oblique angle with respect to the axis of rotation for directing a stream of electrons from the cathode at said anode, and means to fixedly position said focussing member to thereby permit relative rotation between said focussing member and said cathode during rotation of said tube.

2. An X-ray tube comprising a tubular evacu ated envelope, cathode and anode electrodes mounted within said envelope and having a given axis for rotation thereabout with said envelope, said cathode having an emitting surface the diameter of which is small relative to the diameter of the area of electron impact on the anode, an electrostatic focussing member interposed between the cathode and the anode having a iocussing axis forming an oblique angle with the said axis of rotation, means to apply a potential to said focussing member to focus a beam of electrons emitted by said cathode at said anode along said focussing axis, and means to fixedly position the focussing member to thereby permit relative rotation between the cathode and the focussing member during rotation of the tube.

3. An X-ray tube comprising a tubular evacuated envelope having a givenaxis for rotation thercabout, cathode and anode electrodes mounted within said envelope for rotation therewith about the axis of rotation, said cathode having an emitting surface the diameter of which is small relative to the diameter of the area of electron impact on the anode, a tubular body having a curved end portion enclosing one end thereof surrounding said cathode, said curved end portion having an aperture eccentrically located with respect to the axis of rotat on of said tubular evacuated envelope for providing an electron beam focussing axis forming an oblique angle with respect to the axis of rotation for directing a stream of electrons from the cathode at the anode, means for applying an energizing potential to said tubular body, bearing means interposed between said tubular body and said cathode to permit said tube to rotate relative to said tubular body, and means to fixedly position said tubular body to thereby permit relative rotation between said tubular body and said cathode during rotation of said tube.

4. A rotary Xray tube comprising a tubular evacuated envelope having a given axis for rotation thereabout, cathode and anode electrodes mounted within said envelope for rotation therewith about the axis of rotation, said cathode having an emitting surface the diameter of which is small relative to the diameter of the area of electron impact on the anode, an electrostatic focussing member comprising a plurality of diaphragm members electricallyinsulated from one another and positioned in proximity to said cathode electrode, said diaphragm members having aligned apertures eccentrically positioned with respect to the axis of rotation of said tube to provide an electron beam focussing axis forming an oblique angle with respect to the axis of rotation for directing a stream of electrons from the cathodeat the anode, bearing means interposed between said focussing member and said cathode to permit said tube to rotate relative to said focussing member, and means to fixedly position said focussing member within said envelope to thereby permit relative rotation between said focussing member and said cathode during rotation of said tube.

5. A rotary X-ray tube comprising an evacuated tubular envelope having a given axis for rotation thereabout, cathode and anode electrodes mounted within said envelope for rotation therewith about the axis of rotation, said cathode having an emitting surface, the diameter of which is small relative to the diameter of the area of electron impact on the anode, an electrostatic focussing member comprising two diaphragm members spacedly positioned within said envelope and electrically insulated from each other, said diaphragm members positioned in proximity to said cathode and having aligned apertures eccentrically positioned with respect to the axis of rotation of said tube for providing an electron beam focussing axis forming an oblique angle with respect to the axis of rotation for directing a stream of electrons from the cathode at the anode, means for applying a negative potential to one of said diaphragm members, means for applying a positive potential to the other of said diaphragm members, bearing means interposed between said focussing member and said cathode to permit said tube to rotate relative to said focussing member, and means to fixedly position said iocussing member within said envelope to thereby permit relative rotation between said focussing member and cathode during rotation of said tube.

6. A rotary X-ray tube comprising an evacuated tubular envelope having a given axis for rotation thereabout, cathode and anode electrodes mounted within said envelope for rotation therewith about the axis of rotation, an electrostatic focussing member fixedly positioned external to said envelope and in proximity to said cathode for directing a stream of electrons emitted from said cathode at said anode in an oblique direction relative to said axis of rotation, and means for applying a negative potential to said focussing member.

'7. A rotary X-ray tube comprising a tubular evacuated envelope having a portion of reduced cross-section and. having a given axis for rotation thereabout, cathode and anode electrodes mounted within said reduced portion for rotation with the envelope about the axis of rotation, a funnel-shaped member adapted to fit said reduced portion external to said envelope, and means for applying a negative potential to said funnelshaped member to thereby direct a stream of electrons emitted from said cathode at said anode in an oblique direction relative to said axis of rotation while said tube rotates relative to said funnel-shaped member.

JACOB HERMANNUS VAN DER 'IU'UK. BART COMBEE.

(References on following page) 7 REFERENCES CITED The following references are of record in the me of this patent:

UNITED STATES PATENTS Number" Name Date Coolidge Oct. 31, 1916 Langmuir Mar. 20', 1917 Coolidge July 15, 1919 Mesick Aug. 17, 1937 Ung'eIe'nk Mar. 15, 1938 Litton June 7, 1938 Number Number