US2900543A - X-ray tube - Google Patents

Description

Aug. 18, 1959 o. LQ/HEUSE X-RAY TUBE Fild May 24, 1955 3 Sheets-Sheet 1 Attorneys Aug. 18, '1959 'X-RAY TUBE 3 Sheets-Sheet 2 Filed May 24, '1955 I m E171? OTTO L. HEUSE Attorneys:

Unii

2,900,543 X-RAy TUBE Otto L. Heuse, Kronberg (Taunus), Germany, assignor to Max-Planck-Institut fiir Biophysik, Frankfurt am Main, Germany Application May 24, 1955, Serial No. 510,790 Claims priority, application Germany May 24, 1954 3 Claims. (Cl. 313-60) it is well known that a considerable amount of heat is generated in the focal spot of an X-ray anode when rays are caused to emanate therefrom; and (2) The utilization within the smallest possible space of the largest possible portion of the X-rays produced by the electrons in the focal spot.

In order to solve the first problem, it has been suggested in the prior art, when a high dosage yield from the input is desired, to provide a displaceable, e.g., a rotatable anode, thereby causing the focal spot to scan the rotating target portion of the anode. It has also been suggested to cause a coolmt to circulate in the interior of the rotating anode (O. Heuse, Zeitschrift fiir Angewandte Physik,. vol. 5, pp. 361463, 1953).

An essential drawback of these and similar constructions lies in the fact that the work-space must be located a certain distance from the focal spot, which distance is at least equal to the distance from the focal spot to the X-ray tube window. Since the dosage yield; i.e., the intensity of radiation, decreases approximately with the square of that distance, the useful dosage yield available in the work space is relatively small.

It is true that this drawback is eliminated to a great extent in the so-called concave-anode tubes; i.e., tubes in which the X-rays pass through the anode. In these tubes, the electron beam is caused to impinge upon an anode which is given the form of a membrane and which simultaneously serves as the ray-transmissive window of the tube. Usually, the anode membrane is cooled by circulating a coolant between the aforesaid membrane and a second external window. In this arrangement,

almost the entire outwardly directed radiation is available for useful work within a relatively small work space, because the X-rays have a particularly high dosage in the vicinity of the external window, due to the short dis tance' of the work space from the focal spot. However, these tubes are limited to a low output, since the heat characteristics of the anode material and the thermal conductivity through the cooling surface limit the dissipation of heat from the focal spot into the coolant.

It-;is an object of the invention to provide an X-ray tube' having such improved sealing and cooling means as to permit a high capacity for loading over long periods of time.

It is another object of this invention to provide a source of X-rays having a high dosage yield and being adapted for continuous performance.

Other objects and advantages of my invention will become apparent as the description of the latter proceeds.

States atent The aforesaid objects are achieved according to my invention by providing an X-ray tube wherein the anode is arranged rotatably relative to the cathode, wherein the useful portion of the radiation passes through the focal spot of the anode into the work space, and wherein vacuum sealing means are provided between the cathode-carrying assembly and the body of the anode. I further provide an effective cooling of the anode while maintaining the work space at a short distance from the focal spot.

The normally high capacity for loading of the X-ray tube according to my invention can be further augmented if'the heating of the above-mentioned sealing means is avoided by providing direct cooling means therefor.

The sealing means according to my invention may comprise collars, packing boxes, ground-in joints and the like. v

The rotating anode may be surrounded by a mantle, and a coolant may be circulated through the chamber formed between the mantle and the external surface of the rotating anode. The mantle forms a part of the stationary casing or of the stationary cathode-carrying assembly of the X- ray tube and is provided with an external ray-transmissive window in the region of the focal spot. If a coolant is caused to flow between the two surfaces, a turbulance is caused therein by the relative movement of the mantle and rotating anode, which turbulance eliminates dead angles and persistent eddys in which the coolant would not be replaced. It is a special advantage of the arrangement according to my invention that a large portion of the coolant passing through the mantle is brought into direct contact with the surface to be cooled, owing to this turbulance. The turbulance can be further controlled by altering the distance of the mantle and rotating anode from one another and/or by changing the type of coolant and the velocity of flow thereof. The above-described flow of the coolant therefore provides for a very favorable transfer of heat from the surface to be cooled to the coolant.

In a preferred embodiment of the apparatus according to my invention, collars are used as the above-mentioned sealing means. The coolant is circulated through a chamber formed by two such collars in spaced relation to one another, by thewall of the cathode carrying member, and the body of the anode. It is advantageous to employ as a coolant a liquid having a low vapor pressure, such as mercury, or, in particular, an organic liquid such as diffusion pump oil or vacuum pump oil. Apart from the cooling effect, the use of such liquids offers the additional advantage of providing a low vapor pressure in the chamber adjacent the exhausted space.

In another preferred embodiment of the X-ray tube according to my invention, a vacuum resistance or vacuum trap is provided between the exhausted space and the aforesaid sealing means, and a separate outlet for connection to a high vacuum pump is provided in the chamber between the sealing means and the vacuum trap. This outlet may preferably be combined with an other outlet from the aforesaid trap in a common socket for connection to the high vacuum pump.

According to another feature of the invention, a membrane is used as the anode, which membrane is mounted on the rotating anode body by mechanically detachable fastening means, a vacuum sealing being arranged be tween the membrane and the anode body.

According to a further preferred embodiment, the anode membrane is mounted in a bisected straining ring which may be fastened, preferably by means of screws, to a flange on the anode body carrying the membrane. An annular groove is preferably provided in the anode body for receiving oneof the rings of said bisected straining ring therein. The outer ring of the bisectedstraining ring is advantageously of a trapeze-shaped cross section. It is also of advantage to devise the body carrying the anode membrane in such a manner that the anode membrane is mounted approximately in the plane of the bottom side of the last-named ring of the bisected straining ring.-

According to a further advantageous feature of the invention, the anode membrane is relieved from the pressure of the atmosphere by a supporting member. This supporting member may be fastened on the anode membrane, for instance by soldering, cementing, or preferably providing a circular opening in the center of the anode membrane for receiving therein a projecting portion of the supporting member. The supporting member consists, for instance, of a mushroom-shaped upper portion, a packing, and a lower portion, which latter part is pressed against the membrane so as to provide a vacuum-tight sealing between these two parts. The portion of the housing surrounding the anode membrane and the supporting member is given such geometrical shape that the flow of the coolant in the vicinity of the focal spot meets with no resistance.

The several objects and advantages referred to abovewill become more apparent upon reference to the accompanying drawings, wherein:

Figure l is a schematic view, partially in longitudinal section, of one form of the X-ray tube according to the invention;

Figure 2 is a schematic view partially in longitudinal section, of another embodiment of the Xray tube;

Fig. 3 shows in partial longitudinal section a schematic view of yet another embodiment of the invention provided with special coolant-circulating means;

Figure 4 shows a further embodiment of the invention represented schematically and partially in longitudinal section, in which the anode comprises a membrane;

Figure '5 is a detailed longitudinal section of the embodiment shown in Figure 4; and

Figure 6 is an exploded view of the membrane-carrying anode member as shown in Figure 5.

Referring now to the drawings more in detail and in particular to Figure 1, reference numeral 1 designates a rotating anode, part of which is formed as a hollow cylinder 2. The focal spot 3 is located on the wall of this cylinder 2, which is ray-transmissive in this region. The cathode 4 is carried by the member 5 and a sealing means consisting of collars 6 is arranged between the member 5 and the anode cylinder 2. A packing box or a ground-in joint may be used as a sealing means instead of collars 6. A high vacuum pump (not shown) is connected to the connecting pipe stud 7 for the purpose of exhausting the X-ray tube.

In the embodiment shown in Figure 2, like parts are designated by like reference numerals. In this embodiment, the rotating anode 11 comprises a bell-shaped portion 12, the base of which is covered by a ray-transmissive membrane 13 mounted on the rim of the anode portion 12. The focal spot 3 is formed on this membrane 13.

This arrangement has the advantage that the membrane 13 may be easily exchanged, if it is desired to use an anode of a different material, or if the membrane has been damaged or destroyed. The anode membrane 13 can be relieved from atmospheric pressure by supporting means arranged on the outside or inside surface of the membrane. For instance, a grid 14 consisting of narrow ribs may be positioned on the inside of the membrane.

In a particularly advantageous embodiment as shown in Figure 3, a stationary cylinder 15 having an external ray-transmissive window registering with the focal spot 3, is arranged substantially equidistant to the anode cylinder 2 on the outside thereof. The anode cylinder 2 rotates inside the external cylinder 15 which forms a cooling mantle around the rotating anode, the coolant 16 circulating through the space between the external cylinder 15' and the anode cylinder 2.

In a further improved arrangement for the flow of the coolant according to Figure 3, turbine-like blades 19 (or grooves) may be provided on an extension 17 at the free end of the rotating anode 2. When the anode cylinder 2 is rotated by a motor (not shown) by means of the shaft 18, the circulation of the coolant is. constantly maintained. In the arrangement of Figure 3, it would also be possible to rotate the anode cylinder 2 without using a motor, solely by the pressure exercised by the flow of the coolant 16 on the blades 19.

In the preferred embodiment shown in Figure 4, the anode arrangement is essentially the same as in Figure 2, except that a mantle 15 is provided around the rotating anode through which a coolant 16 is circulated in the same manner as in Figure 3. In this embodiment, the membrane 13 is centrally supported on the outside by the driving shaft 18, which rotates the anode member 11.

Yet another embodiment of the X-ray tube built according to the invention is shown in greater detail in Figure 5. A cylindrical anode body 111 is rotatably mounted by means of ball bearings 201, 202, 203 in the carrier member 105 which forms part of the cathodecarrying assembly. Roller hearings, or slide bearings, may also be used instead of ball bearings 201, 202, 203. Between the ball bearings 201 and 202 a pully 212 is mounted, for instance by means of screws 213, on the anode cylinder 111. This cylinder is rotated from a motor 210, for instance by way of a belt transmission 211 which rotates the pully 2.12. The arc-shaped portions 214 of the cathode carrying member 105 rigidly connect the ball bearings 201 and 202 and protect the sealing means, and in particular sealing 61, from being affected by mechanical stresses originating from the drive, by way of the pully 212.

The bell-shaped portion consisting of parts 121 and 122, which is attached concentrically to the free end of the rotating anode cylinder 111 is covered by a membrane 13 forming an annular ray-transmissive window on which the electron beam emanated from the cathode impinges at the focal spot 3.

Where the two parts which move relatively to one another; namely, the rotating anode cylinder 111 and the cathode-carrying member 105, come into contact, sealing means in the form of a collar 61 are provided in order to seal the interior of the anode hermetically against the surrounding atmosphere. A second collar 62 is provided around the rotating anode cylinder 111 in spaced relation to the first collar 61. An annular chamber 66 is formed by the two collars 61, 62, the outer surface of the anode cylinder 111 and the back wall of a recessed portion of the central bore 67 provided in the cathode-carrying member 105. A coolant having a low vapor pressure, such as a vacuum pump oil, is circulated through inlet and outlet condiuts 64, 65 in order to cool the sealing 61. The remaining parts of the coolant circulating system are not shown.

Apart from the carrier member the cathode-carrying assembly comprises in an overhead structure a T-joint member 74 provided with flanges 73, 77, 78 at its three openings. It is detachably fastened by means of flange 77 and bolt means 75 to a flange 68 provided around the outer end of the central bore 67 of the carrier member 105. In the interior of the T-joint member 74, a transverse annular shield 71 having a central sleeve portion is rigidly attached. The free end of the sleeve portion 70 projects into the open end of the rotating anode cylinder 111. Only a very narrow gap 79 exists between the stationary sleeve portion 70 and the end of the rotating anode cylinder 111. The annular shield 71 bears a shield extension 72 which divides the central branch of the T-joint member 74- into two chambers 171, 172, and forms a vacuum trap against the interior 100 of the X-ray tube. The shield extension 72 ends in the T-joint opening 7 to which a vacuum pump (not shown) is connected by means of flange 73.

. A leakage occurring in the seal 61 will not immediately aifect the remaining internal parts of the X-ray tube which are under high electrical tension, since the vacuum trap formed by chamber 172, shields 71 and 72, and the narrow gap 79 will provide time for interrupting the operation of the tube before damage is caused. Furthermore, a small quantity of gas leaking through the sealing 61 will be pumped off immediately and thus cause practically no disturbance in the high voltage field.

All mechanically detachable parts under high vacuum are sealed in a suitable manner by means of packing rings 76. As a further part of the cathode-carrying assembly, an oil-filled head 82 is mounted on flange 78 of the T-joint member 74. This head 82 encloses the lead-ins 81 for electrical power supplying high voltage and heating voltage for the tube from sources of electrical current (not shown).

The parts of the X-ray tube under high voltage are insulated as illustrated in Figure 5 by an insulating cone 83, an insulating cylinder 84 and three rods 85 of insulating material, one of which is visible in Figure 5. Each of the rods 85 is provided with an adjusting device 86, for instance of the turnbuckle type, connected by means of a toggle joint 89 with the end cover member 87 mounted in the insulating cylinder 84. This arrangement of parts 86 and 89 permits an exact centering of the cathode 4 in the tube. A bellows-shaped (or accordion-shaped) intermediary member 88 made, for instance, of tombac, imparts a certain amount of flexibility in longitudinal and transverse direction to the mounting of the cathode 4 and the cover member 87 relative to the remaining parts 84, 74, 105 of the cathode-carrying assembly.

The cathode 4 comprises two electrical conduits under high voltage, being electrically insulated against one another, which feed the heating voltage to the electrodeemanating part 90 of the cathode 4 from a source of current (not shown). This cathode part 90 is mounted in an arm 91 arranged on the cathode cylinder 104 at an angle to the longitudinal axis of the latter.

Parts 121 and 122 forming the bell-shaped portion of the rotating anode are connected by bolt means 140 with one another, and the membrane 13 is fastened to the flanged rim 92 of part 122 by means of screws 191. Packing rings 76 are arranged at all detachable joints mentioned above. I

The cathode carrying part 105 is also provided with a bell-shaped portion 180 which is connected by bolt means 143 to a cylindrical part 181 which, in turn, bears a cover plate 182 fastened to the free rim of part 181 by screw means 93. This cover plate 182 is so arranged as to leave a narrow interspace between the same and the outer surface of the membrane 13. Another membrane forms the external ray-transmissive window 115 in the cover plate 182, which window registers with the electron emanating part 90 of the cathode 4. This external ray transmissive window 115 is attached by means of a straining ring and screw arrangement 184 (not shown in detail) to the cover plate 182 in principally the same manner as is hereinafter described relative to the fastening of membrane 13 to part 122. A coolant 16 is circulated through the interspace between the membrane 13 and the cover plate 182, and the interior of the chamber formed by the parts 180 and 181 of the stationary cathode-carrying assembly and the parts 121 and 122 of the rotating anode by way of an inlet conduit 141 and an outlet conduit 142. The remaining coolant circulating system is not shown. Thereby the bell-shaped portion of the anode and, in particular, the membrane 13 are continuously cooled. The ball bearings 202 and 203 are protected against the coolant by pairs of sealing collars 94 and 95.

As will be understood from Figure 6, the membrane 13 is mounted in the following manner. The seating ring 194 and the packing ring 76 are first laid in corresponding recesses in the face of flange 92 of the cylindrical part 122. The membrane 13 interposed between rings 192 and 193 of the bisected straining ring is then mounted on the flange 92 and fastened thereon by means of screws 191. The flange 92 is of such shape that the tightened anode membrane is located approximately in the plane of the surface of the ring 193 away from flange 92. This is achieved by conical surfaces 96 and 97 on the flange 92 and the ring 193, respectively, which conical surfaces register with one another. By this arrangement of the membrane, undesirable resistance to the flow of the coolant 16 past'the membrane and the formation of dead angles are avoided.

The anode membrane 13- can be replaced by first detaching the cylindrical member and the screws 143 whereupon the cylindrical part 181 of the stationary cathode-carrying assembly can be dismounted. Thereby screws 191 become easily accessible. After removing them, it is easy to exchange the membrane 13 which is fixed between the rings 192 and 193 of a bisected straining ring. It is advisable to connect these straining rings by screw means. As can be seen in the exploded view of these parts in Figure 6, this connection is achieved by means of the screws 189. A packing ring 76 is also provided between the anode membrane 13 and the cylindrical part 122 of the bell-shaped anode portion.

A membrane-supporting assembly is arranged centrally in relation to the anode membrane 13 in order to relieve the same from the pressure of the atmosphere. The ex-.

ploded view of Figure 6 shows individual parts of this assembly.

The supporting assembly comprises a mushroomshaped supporting disk 195 which is threadedly connected to a stem part 98 which passes through a central opening in the membrane 13. A packing ring 76 mounted in an annular groove 99 in the-supporting disk 195 provides a vacuum-tight sealing of this part against the membrane 13, when the sleeve 199 which passes over the stem 98' the stem can be arranged by means of the nut 197 and a pair of lock nuts 198. This arrangement permits, together with the pairs of lock nuts 150, 151, and 152, 153 on the anode cylinder 111, in a simple manner an adjustment of the distance between the anode membrane 13 and the cover plate 182 bearing the external window 115, which adjustment is achieved by changing the position of lock nut pair 197, 198 on the sleeve 196 together with the positions of lock nut pair 150, 157 and 152, 153 on the anode cylinder 111 A special advantage of the embodiment shown in Figure 5 resides in the fact that the bell-shaped anode part 121 is fastened to the cylindrical anode part 122 by means of bolts 140 and the use of a packing 76. Upon removing screws 143 and the nut 197, which results in loosening the seat of the supporting assembly in the ball bearing 203, and upon then removing the supporting assembly, cover plate 182, and the cylindrical part 181, the cathode becomes freely accessible by detaching the screws 140 and removing the cylindrical anode part 122 and the membrane 13, which may be accomplished without altering the centering adjustment of the cathode-carrying assembly.

The part of the atmospheric pressure eifective in the direction of the axis of rotation of the membrane is taken up by the bearing 203.

X-ray tubes according to the invention may be used to particular advantage if a high intensity of radiation is desired Within a relatively short period of time, but where the radation time is nevertheless so long that an essentially continuous dissipation of the generated heat is necessary. These X-ray tubes may be used, for instance, for X-ray therapy and diagnosis in medicine, for the destruction and mutation of organisms in biology, and for the decomposition and alteration of substances in chemistry and related fields. These fields comprise the destruction of organisms causing fermentation and other detrimental eifects in food, medicants, objects of art, and the like; further the testing of materials used in roentgen radiology with regard to their resistance to radiation; tests of other materials; and the preparation of X-ray pictures.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of theappended claims.

What is claimed is:

1. An X-ray tube having an anode and a cathode being movable relative to one another, and wherein the useful portion of the X-rays is transmitted through the focal spot of the anode to the workspace outside the tube, comprising a cathode-carrying assembly having an axis, an anode mounted for rotation about an axis coincident with said first-mentioned axis, a ray-transmissive membrane forming a vacuum tight covering for the base of said anode, said focal spot being located on said membrane, and sealing means between said rotatable anode and said cathode-carrying assembly and permitting the continuous rotation of said anode with respect to said cathode-carrying assembly for maintaining a high vacuum in said anode under high loading of the tube during long periods of operation, a bisected straining ring having a first and second ring, said membrane being clamped between said first and second ring, supporting means for supporting said membrane against atmospheric pressure, first cooling means for cooling said rotating anode, said first cooling means comprising a mantle arranged substantially equidistant from that part of said membrane forming the Zone of said focal spot, second cooling means for cooling said sealing means and a vacuum trap arranged between said sealing means on the one hand and the interior of said anode and that part of the interior of that cathode carrying assembly being under high vacuum on the other hand.

2. An X-ray tube having an anode and a cathode being movable relative to one another, and wherein the useful portion of the X-ray is transmitted through the focal spot of the anode to the workspace outside the tube, comprising a cathode-carrying assembly having an axis, an anode mounted for rotation about an axis coincident with said first-mentioned axis, a ray-transmissive membrane forming a vacuum tight covering for the base of said anode, said focal spot being located on said membrane, and sealing means between said rotatable anode and said cathodecarrying assembly for maintaining a high vacuum in said anode under high loading of the .tube during long periods of operation, supporting means for supporting said membrane against atmospheric pressure, said membrane being provided with a central opening, said supporting means being mounted in said central opening and vacuum tight sealing means being provided between said membrane and said supporting means, said supporting means comprising a mushroom-shaped head part, a packing means between fastening means and said membrane, and a lower part to be attached to said head part, and bearing means being provided between said supporting means and said cathode-carrying assembly, said bearing means taking up the part of the atmospheric pressure effective in the direction of the axis of rotation of said membrane.

3. An X-ray tube having an anode and a cathode movable relative to one another, and wherein the useful portion of the X-rays is transmitted through the focal spot of-t he anode to the work spaceoutside the tube, comprising a cathode-carrying assembly having an axis; an anode mounted for rotation about an axis coincident with said first-mentioned axis; a ray-transmissive membrane covering the base of said anode, said focal spot being located on saidmembrane; detachable fastening means for fastening said membrane to said anode so as to make said membrane exchangeable, said fastening means comprising a bisecting straining ring having a first and second ring, said membrane being clamped therebetween, the membranecarrying member and said second ring of said bisected straining ring each being provided with conical surfaces registering with one another so as to hold said membrane substantially in the plane of the surface of said second ring away from said membrane-carrying member; and sealing means between said rotatable anode and said cathode-carrying assembly and permitting continuous rotation of said anode with respect to said cathode-carrying assembly for maintaining a high vacuum in said anode under high loading of the tube during long periods of operation.

References Cited in the file of this patent UNITEDSTATES PATENTS 1,621,926 Fujimoto Mar. 22, 1927 2,209,963 Du Mond Aug. 6, 1940 2,290,226 Du Mond July 21, 1942 2,430,800 Atlee Nov. 11, 1947 2,488,200 Juhlin et a1 Nov. 15, 1949 2,653,260 Taylor Sept. 22, 1953 2,718,605 Fenner et al Sept. 20, 1955 FOREIGN PATENTS 534,612 Great Britain Mar. 12, 1941

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