US2886724A - X-ray tubes - Google Patents

Description

G. W. STEEN May 12, 1959 X-RAY TUBES 2 Sheets-Sheet -1 Filed March 15, 1957 INVENTOR.

GOTTFRID W. STEEN FIG. I

G. W. STEEN X-RAY TUBES May 12, 1959 2 Sheets-Sheet 2 Filed March 15; 1957 FIG.2

INVENTOR.

GOTTFRID W. STEEN FIG. 3

AGENT X-RAY TUBES Gottfrid W. Steen, Stamford, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn, a coriteration of Connecticut Application March 15, 1957, Serial No. 646,360

Claims. (Cl. 313-62) This invention relates to X-ray tubes and has particular reference to cooling means for the anodes of X-ray tubes.

More particularly, the present invention is concerned with an improved cooling system for X-ray tubes of the types which are adapted to be cooled by the introduction into the interior of the anode of a suitable liquid coolant such as oil or water.

In the manufacture of certain X-ray tubes such as are used, for example, in the administration of therapeutic treatments or in radiography, an anode structure is axially mounted within a glass envelope and carries a target which is adapted to be bombarded by electrons from a suitable cathode for the production of X-radiation. Such bombardment causes the anode, particularly in the areas adjacent the target, to attain a temperature high enough to require means for dissipating the heat to prevent damage to or even destruction of the anode.

In X-ray tubes of the presently described type, the anode is provided with an integral tubular hood or shield which extends beyond the target toward the cathode and thus forms a restricted enclosure through which electrons flow as they pass from the cathode to the anode. The hood is for the purpose of providing an X-ray shield as well as a means of confining secondary or stray electrons within the hood and thereby reducing the number of such electrons which are enabled to bombard the glass envelope. Such a hood also prevents, to a great extent, bombardment of the outer surfaces of the anode by secondary electrons, which causes undesirable secondary X-radiation. An X-ray transparent window is mounted in one of the walls of the hood to permit restricted exit of X-radiation produced by electron bombardment of the target.

In the normal operation of conventional X-ray tubes, electron bombardment of the target generates heat which sometimes ruptures the targe-anode bond, resulting in shortened tube life.

Secondary electrons from the target impinge upon the walls of the hood and also contribute to the overall anode heat. Such electrons also impinge upon the window, which is generally formed of material such as beryllium, with resultant increase in the temperature of the window. Heat in the area of the window also sometimes causes the material of the windows to buckle or craze, at times even separating the windows from their supporting structures.

Known prior attempts to cool anodes have been concentrated upon reducing the temperature of the interior portions of the anodes immediately behind the targets. This has been done by providing chambers of various shapes, the surfaces of which were sometimes provided with channels for controlling the flow of a coolant through the chambers. Some chambers were provided with moving parts for the purpose of preventing the formation of deposits upon the walls of the chambers, which deposits supposedly acted as thermal barriers. Later structures employed one or more jets through which coolant *atent was forced under pressure against the walls of the chambers, the intention being to increase the velocity and turbulence of the coolant as it was urged through the chambers.

While most of the prior art was successful to some degree in lowering the anode temperatures, complete success was not achieved. In some cases the reduction in temperature was very insufiicient; in other cases the complicated structures involved considerable expense because of difficulty in fabrication; in still others: which involved moving parts the devices becameeasily damaged or inoperable and required considerable repair and replacement.

In all known prior art devices little or no attempt has been made to utilize, for cooling purposes, the areas of the anodes which are subjected to bombardment by secondary electrons.

, Accordingly, it is a primary object of this invention to provide X-ray tubes with improved, simple, and relatively inexpensive systems for efficiently cooling the anodes of the tubes.

Another object is to provide an X-ray tube anode with cooling means which functions efiiciently to lower the temperature of the anode in areas additional to the area immediately rearwardly of the target.

A further object is the provision, in an X-ray tube embodying a hooded anode having a window therein, of means for providing a large area of anode material, including the hood, in contact with coolant for reducing theoverall temperature of the anode.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, in which Fig. 1 is an axial sectional view of an X-ray tube embodying the invention;

Fig. 2 is an enlarged view of the anode partly in axial section and partly with only the outer casing removed, illustrating particularly the cooling means thereof; and

Fig. 3 is a horizontal sectional view taken substantially on line 33 of Fig. 2 looking in the direction of the arrows.

Referring more particularly to Fig. 1, there is shown an X-ray tube which embodies a cylindrical dielectric envelope 10 having integral end portions 11 and 12 of reduced diameter. End portion 12 has a reentrant part 13 which terminates in a stem press 14 carrying a conventional cathode structure 15. The cathode structure 15 embodies an electron emitting filament 16 and focusing means 17 of a suitable type for aiding in beaming electrons liberated by the filament 16 toward an anode 18.

The anode 18 is essentially a block 19 of copper which is supported on the inner end of a reentrant part 20 of the end portion 11 of the envelope by suitable means such as tubular structure 21. The anode 18 is provided in its end nearest the cathode with a recess 22 having at the base thereof a tungsten target 23 which is embedded in the material from which the anode is formed. The target 23 is disposed at a predetermined angular relation to the axis of the tube so as to aid in more efficiently directing X-radiation through a Window 24 formed of beryllium or other selected metal relatively transparent to X-rays. Such X-radiation is emitted in the conventional and well-known manner by the target 23 upon bombardment by the electrons from the cathode.

The provision of the recess 22 in the end of the anode facing the cathode forms a hood 25 about the target 23 extending a substantial distance in the direction of the cathode. This hood 25 partially encloses the target and thereby restricts emission from the tube of unused X-radiation, and also confines the major portion of secondary electron emission within the hood and thereby 3 reduces bombardment of the glass envelope and anode exterior by secondary electrons.

The window 24 is mounted within an opening 26 (Fig. 2) in the hood 25 by any suitable means.

In accordance with the present invention means is provided for cooling the interior of the anode block 19 as well as portions thereof nearer the surface, and the hood 25. An inlet pipe 28 is connected at one end, as by a nut 29, to a suitable source of coolant such as oil or water. The inlet pipe 28 extends coaxially within the reentrant part 20 of the envelope and the tubular anode-supporting structure 21, and is connected to the anode 18. The inner end of the pipe 28 carries a jetsupporting member 30 (Fig. 2) secured within one end of a sleeve 31 which is brazed or otherwise fixedly supported within a bore 32 in the adjacent end of the anode block 19.

The interior of inlet pipe 28 communicates with a conical-shaped chamber 33 in member 30 whereby it can expel coolant into the chamber. The inner wall of the member 30, which is nearest the target 28, carries a plurality of jets 34 which extend into a corresponding number of individual passages 35 provided in the anode block 19. Coolant which is urged under pressure through the inlet pipe 28 passes from the chamber 33 into the jets 3-4 and is forcibly ejected with considerable velocity onto the walls of the passageways 35. Since the passageways extend well into the anode block 19 and terminate near the target 23, the coolant will function to reduce the temperature of the interior portion of the anode.

In conventional tube structures embodying jet-type or other cooling systems, the coolant passes from the passageways, or other chamber rearwardly of the target, directly through suitable conduit means to the exterior of the tube structure.

In the presently described tube, the means for cooling additional portions of the anode, including those portions such as the hood which become heated by secondary electron bombardment, comprises two longitudinal channels or chambers 37 and 38 which are located near the surface of the anode block 19 and extend into the hood 25 (Figs. 2 and 3). The channels 37 and 38 are formed by providing longitudinal recesses in the surface of the anode block 19 and hood 25 and subsequently enclosing the block and hood within a casing 36. One side of each channel extends near a respective side of the window opening 26 in hood 25, and the adjacent sides of the channels are spaced by portions of the anode block and hood so that communication between the channels is prevented throughout their lengths. Both channels 37 and 38, however, terminate in an annular channel 39 (Figs. 1 and 2) which is provided within the end of the hood which is nearest the cathode.

One channel only is connected with the inlet means and the other is connected to the outlet means so that a one-way circulation system is provided. At the inlet end of the structure, channel 37 communicates with bore 32 by means of a plurality of openings 40 (Fig. 3) through which coolant is permitted to flow from bore 32 into channel 37. After passing lengthwise of the anode block 19 and hood 25 through channel 37, the coolant flows through annular channel 39 into channel 38, and then again lengthwise along the opposite side of the hood and anode block through channel 38.

At the end of the anode block 19, the coolant is blocked by a mounting ring 41 (Fig. 2) which seals the space between the sleeve 31 and inner end of the casing 36 and deflects the coolant through ports 42 in sleeve 31 into the space between the jet-supporting member 30 and adjacent end of a tubular member 43. The tubular member 43 is threaded into sleeve 31 and has fixed to it one end of an outlet pipe 44, the outlet pipe and tubular member 43 encircling the inlet pipe 28 in spaced relation therewith so that the coolant can exit by passing outwardly through member 43 and outlet pipe 44 exteriorly of the inlet pipe 28.

Any suitable means may be provided in the outlet pipe 44 outside the tube for ejecting the coolant therefrom.

In the operation of an X-ray tube of the character described, the portion of the anode immediately behind the target acquires exceptionally high temperatures, as has been described hereinbefore, which results in damage to the tube, such as impairment of the target-to-anode bond. The prior art shows that various attempts to cool this portion of the anode directly have not been completely successful. I discovered, however, that surprising results are obtained by directly cooling remote portions of the anode which are at a much lower temperature than the area adjacent the target. The table which follows sets forth the temperatures attained by an anode of standard or conventional construction and an anode embodying the present invention. Measurements were taken by locating a thermocouple at the bottom of the central hole in the jet structure, with no coolant flowing in that jet hole during measurement.

Conven- Present Coolant, Pints per Minute tional Invention,

Tube, F. F.

The above measurements were obtained using oil as a coolant, with the coil being introduced into the tube at a temperature of approximately 30 F. It is to be understood that the actual temperature values may vary portion as well as in the main body portion of the anode.

In an anode embodying the improved cooling structure described, more than three times as much surface of the anode is exposed to coolant than in an anode embodying only the jet-type cooling feature. Therefore, a considerably lower operating temperature is obtained.

In the manufacture of anode structures embodying this invention, it is to be understood that certain refinements may be incorporated such as, for example, the provision of resilient ring seals between the sleeve 31 and the respective members 43 and 30. It is also to be understood that a person skilled in the art may conceive of many changes and modifications in the construction shown and described which will come within the scope of this invention. All matter shown and described herein is, therefore, to be considered as illustrative.

I claim:

1. An X-ray tube comprising an evacuated envelope enclosing an anode and a cathode in spaced relation, the anode having a main body portion and a hood projecting therefrom in the direction of the cathode and encircling a portion of the anode-cathode interelectrode space, a target in the main body portion and within the hood, and cooling means for the anode comprising inlet and outlet conduits extending from the main body portion to the exterior of the envelope, longitudinal spaced channels within and adjacent the surface of the anode and extending through the main body portion and the hood, the channels being respectively connected to the inlet and outlet conduits at one end, and a connecting channel in the hood joining together the opposite ends.

of the longitudinal channels.

2. An X-ray tube comprising an evacuated envelope assayed enclosing an anode and a cathode in spaced relation, the anode having a main body portion and a hood extending in the direction of the cathode, the main body portion having a target encircled by the hood and facing the cathode, and a cooling system for the anode comprising inlet and outlet conduit means extending from the anode exteriorly of the envelope, inclosure means internally of the anode rearwardly of the target and connected with one of said conduit means, and channels within the main body portion of the anode adjacent the surface thereof having one end extending within the hood, the channels being in communication with the inclosure means and being connected with the other of said conduit means, the inclosure means being adapted to receive coolant for primarily cooling the interior portions of the anode, and the channels being adapted to receive coolant for cooling portions of the anode which are not effectively cooled by the coolant in the inclosure means.

3. An X-ray tube comprising an evacuated envelope enclosing an anode and a cathode in spaced relation, the anode having a main body portion with a target in the surface thereof facing the cathode and a tubular hood extending from the main body portion in the direction of the cathode and encircling the target and a portion of the anode-cathode interelectrode space, a window in the hood transparent to X-rays, and means for cooling the anode comprising, inlet and outlet conduit means extending from the main body portion of the anode exteriorly of the envelope, an inclosure internally of the anode rearwardly of the target and connected with one of said conduit means whereby upon introduction of coolant into the inclosure the adjacent interior portions of the anode will be substantially cooled thereby, a pair of spaced longitudinal channels within and adjacent the surface of the anode and extending through the main body portion and the hood on opposite sides of the window, a passage connecting one of the longitudinal channels with the inclosure and a second passage connecting the other channel at the same end with one of the conduit means, and a connecting channel in the hood joining together the opposite ends of the longitudinal channels and completing a circulatory system for coolant within the anode.

4. An X-ray tube comprising an evacuated envelope enclosing an anode and a cathode in spaced relation, the anode having a main body portion with a target in the surface thereof facing the cathode and a tubular hood extending from the main body portion toward the cathode and encircling the target and a portion of the anode-cathode interelectrode space, a window in the hood transparent to X-rays, inlet and outlet conduit means extending from the main body portion exteriorly of the envelope, means for cooling the interior portions of the anode rearwardly of the target comprising an inclosure in said interior portion of the anode connected with one of said conduit means whereby upon introduction of coolant into the inclosure during operation of the tube the temperatures of the adjacent interior portions of the anode will be lowered, and means for cooling surface portions of the anode comprising a pair of spaced longitudinal channels within and adjacent the surface of the anode and extending through the main body portion and the hood on opposite sides of the window, one of the longitudinal channels being connected at one end with the inclosure and the other channel being connected at the same end with one of the conduit means, and an annular channel in the end of the hood joining together the opposite ends of the longitudinal channels and completing a circulatory system for coolant within the anode.

5. An X-ray tube comprising an evacuated envelope enclosing an anode and a cathode in spaced relation, the anode having a target in the surface thereof facing the cathode, a tubular hood extending from the anode and encircling a portion of the anode-cathode interelectrode space, a window in the hood transparent to X-rays, a chamber within the interior of the anode rearwardly of the target, an inlet pipe carried by the anode and extending from the chamber therein exteriorly of the envelope, first and second spaced longitudinal channels within and adjacent the surface of the anode and extending into the hood on opposite sides of the window, the channels each being of a width greater than the width of the spaces therebetween, the first of the longitudinal channels being connected at one end with the chamber, for passage of coolant into said channel from the chamber, an annular channel within the hood in the end thereof nearest the cathode and connecting together the adjacent ends of the two longitudinal channels for passage of coolant between the channels, and an outlet pipe connected with the opposite end of the second channel for exit of coolant therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,655,455 Coolidge Jan. 10, 1928 2,480,198 Rogers Aug. 30, 1949 2,790,102 Atlee Apr. 23, 1957

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