Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
  • H01J35/08—Anodes; Anti cathodes
  • H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
  • H01J35/105—Cooling of rotating anodes, e.g. heat emitting layers or structures
  • H01J35/106—Active cooling, e.g. fluid flow, heat pipes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/086—Target geometry
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/12—Cooling
  • H01J2235/1204—Cooling of the anode

Definitions

• the field of the invention is that of X-ray generating tubes.
• the invention relates more particularly to the arrangement of the emitting surfaces which are at the source of the X-ray.
• FIG. 1 The operating principle of an X-ray generator tube 10 is exposed in FIG. 1. It mainly comprises a vacuum enclosure 6 comprising at one of these ends a cathode block 4 carried by an insulator 3 and at the other end an anode block 2.
• the anode block 2 comprises a target holder assembly 1 comprising a flat metal surface said target 9 disposed opposite the cathode block.
• the electron beam 7 coming from the cathode is accelerated under the action of very high electric voltages greater than 10 kVolts and strikes the target 9 in a focusing zone O where the electrons lose their kinetic energy. There follows a significant release of heat and an emission 8 of X-rays (symbolized by the arrows in FIG. 1). X-rays pass through the wall of the anode block at privileged locations 5 called windows.
• the release of heat causes very intense localized heating at the target.
• the rise in the temperature of the target is such that it could lead to the destruction of the target by fusion.
• the release of heat is evacuated by a cooling circuit 60 passing through the target holder 1 under the target 9.
• the target 9 is inclined at an angle ⁇ relative to the mean direction of the electron beam 7.
• the production of a target holder assembly therefore has two main constraints. On the one hand, the angle of inclination a must be adapted to the use and on the other hand, the cooling circuit must allow sufficient removal of the calories due to the impact of the electron beam.
• the target holder assembly In known X-ray tubes, the target holder assembly generally has the shape of a shouldered cylinder as shown in FIGS. 2, 3 and 4. The axis of this cylinder is parallel to the direction of the electron beam .
• a cutaway of the cylinder inclined at an angle ⁇ constitutes the target subjected to the beam.
• the target holder assembly is connected to the anode block so that the calories are first transmitted to the periphery of the anode block by conduction through the various metal parts of the target holder assembly and of the anode block (internal white arrows in Figure 2) then evacuated to the outside by convection (external white arrows in Figure 2).
• FIG. 3 illustrates a first embodiment of the cooling duct arranged inside the target holder assembly. It comprises a single tube 60 passing under the surface of the target and which best matches said surface.
• FIG. 4 illustrates a second embodiment of a coaxial type conduit. It comprises an inlet tube 60 located in the axis of the cylinder of the target holder, an internal cavity 61 which conforms as best as possible to the interior of the target holder and an outlet tube 62 connected to the internal cavity. This arrangement optimizes the exchange surface between the cooling fluid and the target holder assembly.
• This indicator has a maximum for ⁇ zero and tends to 0 when 0 tends to 90 degrees. It is not possible to use all the X-ray emitted and only part is recovered through a transmission window which defines a limited solid angle of emission. This window is necessarily located outside the path of the electron beam. If it is desired to recover a large part of the radiation emitted, the angle of inclination ⁇ must then be sufficiently large.
• the angle of inclination also conditions the geometric resolution of the emission source X as illustrated in FIGS. 6 and 7.
• An electron beam 7 with a circular section of diameter, section also called finesse, falls on an inclined target of an angle ⁇ with respect to the direction of incidence. This beam will generate X-ray radiation.
• the X-ray radiation passing through a diaphragm 11 of very small diameter, then has a divergence ⁇ .
• This divergence ⁇ is proportional to the angle ⁇ as shown in FIGS. 6 and 7.
• This divergence ⁇ conditions the resolution of the X-ray generator tube and the sharpness of the images observed.
• the angle of inclination ⁇ is necessarily the result of a compromise between, on the one hand the energy of the X-ray radiation and on the other hand, the resolution of the tube.
• the tube designers are thus led to propose, for the same configuration of tubes, different versions of target-holder assemblies in which the inclinations of the target vary.
• the study, implementation and management of these different variants generate additional costs and additional delays which can be important, given the complexity of the room and the materials used.
• the invention proposes to replace these different variants by a single assembly making it possible to adjust the angle of inclination of the target.
• the arrangement of the part also makes it possible to improve the geometry of the cooling circuit in order to significantly increase its efficiency.
• the various mechanical parts do not involve complex machining.
• the subject of the invention is an X-ray generator tube comprising an electron gun emitting an electron beam, an anode block comprising a target holder assembly having a plane surface called the target on which the electron beam is focused in a spot.
• focusing characterized in that the target holder assembly has an axis of revolution substantially perpendicular to the mean direction of the electron beam and passing through the plane of the target.
• the target-holder assembly is of generally cylindrical shape with circular section, the target being located in a plane passing through the axis of revolution of the cylinder and the anode block comprises a housing of also generally cylindrical shape in which is housed said target holder assembly so that the axis of revolution of the target holder assembly passes through the focusing spot.
• the target holder assembly comprises at least one internal main coolant circulation duct passing through the target holder assembly in a direction substantially parallel to its axis of revolution and passing under the target to cool it.
• Figure 1 shows a sectional view of an X-ray generator tube comprising a target holder assembly according to the prior art.
• Figure 2 shows a sectional view of an anode block comprising a target holder assembly without cooling circuit according to the prior art.
• Figure 3 shows a sectional view of an anode block comprising a target holder assembly comprising a first type of cooling circuit according to the prior art.
• Figure 4 shows a sectional view of an anode block comprising a target holder assembly comprising a second type of cooling circuit according to the prior art.
• Figure 5 shows the X-ray emission indicator.
• Figures 6 and 7 represent [influence of the angle of inclination of the target on the resolution of the tube.
• Figure 8 shows a perspective view of the target holder assembly according to the invention.
• Figure 9 shows a front view and a side view of the target holder assembly according to the invention.
• Figure 10 shows a sectional view of a target holder assembly according to the invention comprising a coolant circulation duct.
• Figure 11 shows a perspective view of the part of the conduit located under the target.
• Figure 12 shows a perspective view of a set of cylindrical secondary conduits with circular section placed under the target.
• Figure 13 shows a sectional front view and a side view of the target holder assembly comprising cylindrical secondary conduits with circular section.
• Figure 14 shows a perspective view of a set of secondary cylindrical conduits of triangular section placed under the target.
• Figure 15 shows a perspective view of a set of cylindrical secondary conduits in the shape of an arch placed under the target.
• Figure 16 shows a sectional front view and a sectional side view of the target holder assembly comprising cylindrical secondary conduits of triangular section.
• the heart of the invention is to make the angle of inclination of the target adjustable on the mean direction of the electron beam while maintaining the focusing of the beam on the target.
• the target holder assembly 1 has the general shape shown in the perspective view of FIG. 8.
• This figure represents a target holder assembly 1 without a coolant circulation duct.
• the target holder assembly generally has the shape of a cylinder of revolution.
• the central part of this cylinder includes machining.
• half of the cylinder has been removed in order to define a planar surface 9 which constitutes the surface of the target.
• the target is in a plane passing through the axis 20 of the cylinder so that when the cylinder rotates about its axis, the center of the target always occupies a fixed position.
• FIG. 9 represents a front view and a sectional profile view of the target holder assembly 1 mounted in the anode block 2.
• This comprises a cylindrical recess of diameter substantially equal to that of the target holder assembly so that said assembly 1 can rotate without play in the anode block.
• the axis of revolution of this cylinder is substantially perpendicular to the mean direction of the electron beam and this axis passes through the focusing spot of the electron beam 7 as indicated in FIG. 8.
• This arrangement makes it possible to optimize the diameter of the focusing spot O. Under these conditions, when the target holder assembly is rotated in the anode block, the target surface tilts at a variable angle ⁇ and the focusing of the electron beam on the target is preserved .
• To position the target at a particular angle ⁇ there are different possible methods using, for example, a suitable tool which are not the subject of this invention and which are known to those skilled in the art.
• the target-holder assembly is brazed in the anode block in order on the one hand to maintain this inclination and on the other hand to ensure the vacuum tightness of the assembly, sealing necessary for the operation of the electron gun.
• This provision is very advantageous insofar as the machining operations of the various parts (target holder assembly and anode block) are simple and can be carried out with great precision.
• FIG. 10 represents a sectional view of a target-holder assembly of the type of that of FIGS. 8 and 9 comprising a coolant circulation pipe 60.
• This passes right through 'target carrier assembly along its axis of revolution and passes under the target 9.
• the exchange of calories is mainly in the area below the target called exchanger.
• This geometry which does not have mechanical bends ensures good transfer of the coolant through the target holder assembly, greater than that of the devices according to the prior art.
• Sleeves 63 arranged at the ends of the duct ensure its connection with the circuits for the arrival and discharge of the coolant.
• the exchanger conditions the efficiency of the coolant circulation duct. It results from a compromise between optimal efficiency and acceptable mechanical complexity.
• the exchanger mainly consists of two plane walls parallel to each other and separated by a thickness e.
• the first wall is located under the target and parallel to it. Consequently, the water circulates in the exchanger in the form of a sheet of thickness e (parallel arrows in FIG. 11).
• This exchanger has reduced performance given its limited exchange surface. It is possible to improve its efficiency by using it in two-phase mode, the quantities of heat absorbed by the phase changes, for example when the liquid water passes in the form of vapor, thus making it possible to improve the efficiency of the circuit of cooling.
• FIG. 12 shows a first embodiment of an exchanger with a large exchange surface.
• the exchange surface consists of a plurality of secondary conduits 64 of cylindrical shape and generator parallel to the axis of revolution of the target holder assembly.
• the conduits 64 are separated from a wall of thickness P and have a diameter d.
• the diameter d is between 0.8 millimeters and 3 millimeters and the thickness P must be less than d. This optimizes the exchange surface which is, in this case, much greater than that illustrated in Figure 1 1.
• Figure 13 shows two views of the target holder assembly comprising an exchanger according to the previous arrangement.
• the conduit 60 has at its ends two cylindrical bores 65 and in the area of the exchanger a plurality of secondary conduits 64 according to the arrangement of FIG. 12, each of these conduits opening into the cylindrical bores 65.
• the exchanger assembly follows the inclination of the target.
• the machining of the conduit can be done simply by drilling through one of the ends of the cylinder. However, drilling holes of small diameter, typically less than 1.5 millimeters in materials such as copper can be difficult over long lengths, typically greater than 10 times the diameter. In this case, it is possible to replace the process for producing the exchanger by conventional machining with the process comprising the following production steps:
• This second set can be of generally cylindrical shape.
• FIGS. 14 and 15 show two forms of grooves 103.
• FIG. 14 represents a front view in section and a profile view in section showing the arrangement of the target holder assembly 1 comprising the mechanical assembly 102 in the anode block 2.
• the ends of the conduit can also have adapter sleeves 63.

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• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• X-Ray Techniques (AREA)

Applications Claiming Priority (2)

Publications (2)

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• 2003
  • 2003-06-20 FR FR0307498A patent/FR2856513A1/fr not_active Withdrawn
• 2004
  • 2004-06-17 US US10/561,262 patent/US7302044B2/en not_active Expired - Fee Related
  • 2004-06-17 EP EP04741818A patent/EP1636818B1/de not_active Expired - Lifetime
  • 2004-06-17 WO PCT/EP2004/051143 patent/WO2004114353A1/fr active Application Filing

Non-Patent Citations (1)

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