WO2004042769A1 - X-ray generator with improved thermal dissipation and method for making same - Google Patents

X-ray generator with improved thermal dissipation and method for making same Download PDF

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Publication number
WO2004042769A1
WO2004042769A1 PCT/EP2003/050781 EP0350781W WO2004042769A1 WO 2004042769 A1 WO2004042769 A1 WO 2004042769A1 EP 0350781 W EP0350781 W EP 0350781W WO 2004042769 A1 WO2004042769 A1 WO 2004042769A1
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WIPO (PCT)
Prior art keywords
target
electron beam
evaporator
generator
heat pipe
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PCT/EP2003/050781
Other languages
French (fr)
Inventor
Philippe Fillion
Gérard MUFFAT
Christophe Malmejac
Original Assignee
Thales
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Priority to AU2003301780A priority Critical patent/AU2003301780A1/en
Publication of WO2004042769A1 publication Critical patent/WO2004042769A1/en

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/02Details
    • H01J35/04Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/08Anodes; Anti cathodes
    • H01J35/12Cooling non-rotary anodes
    • H01J35/13Active cooling, e.g. fluid flow, heat pipes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2235/00X-ray tubes
    • H01J2235/12Cooling
    • H01J2235/1225Cooling characterised by method
    • H01J2235/1262Circulating fluids
    • H01J2235/1287Heat pipes

Definitions

  • the invention relates to an X-ray generator and to a method for producing this generator.
  • X-rays are used in particular in the medical environment for imaging or radiotherapy and in the industrial environment for the control of mechanical parts or for local treatment by irradiation.
  • Known X-ray generators generally include, inside a closed enclosure or electronic tube, a cathode emitting an electron beam towards an anode or target. The beam is accelerated and focused by means of electrodes located between the cathode and the target. When the electron beam bombards the target, a small part of its energy generates X-rays and the rest of its energy is transformed into heat energy which it is necessary to dissipate outside the closed enclosure.
  • the bar is then fixed at one of its ends to the target and at another end to a radiator forming a wall of the tube.
  • the radiator may include fins located outside the tube depending on the amount of heat energy to be removed. One can circulate between these fins a coolant ensuring the cooling thereof by natural or forced convection.
  • the power of X-rays is mainly limited by the ability of the target to dissipate the heat energy generated there.
  • the invention finds particular use for X-ray tubes for microfocus. This type of tube is mainly used in imagery where one seeks to produce a source of X-ray as punctual as possible. Indeed, the sharpness of the image obtained by irradiation depends on the fineness of the X-ray source. The smaller the source, the more we can distinguish the details in the image produced. It is known, for example, to produce an X-ray source using a 10 W electron beam accelerated to an energy of 130 KeV and generating a spot of approximately 7 ⁇ m on a target made of tungsten. When the power is reduced for example to 0.5 W, the spot can be reduced to approximately 1 ⁇ m on the target. For the same spot size, the fact increasing the power of the electron beam would cause damage to the target due to excessive heating of the target.
  • the invention aims to improve the heat dissipation of the target, which in particular makes it possible either to increase the power for a given spot size, or to reduce the size of the spot for a given power.
  • the invention is not limited to X-ray generators with microfocus and it can be implemented in other types of generators for which it is sought to improve the heat dissipation of the target.
  • the subject of the invention is an X-ray generator comprising a closed enclosure inside which there is a vacuum sufficient to allow the displacement of an electron beam, the generator comprising inside the enclosure, a cathode intended to emit the electron beam, a target intended to receive the electron beam and to emit X-radiation and means for cooling the target, characterized in that the means for cooling the target comprise an evaporator.
  • the subject of the invention is also a method of producing an X-ray generator comprising a closed enclosure inside which there is a vacuum sufficient to allow the displacement of an electron beam, the generator comprising inside the enclosure, a cathode intended to emit the electron beam, a target intended to receive the electron beam and to emit X-radiation and means for cooling the target, characterized in that the means for cooling the target comprise an evaporator and a condenser forming with the evaporator a heat pipe inside which circulates a refrigerant fluid and in that the method consists in placing the heat pipe inside the closed enclosure, then in producing the vacuum at inside the enclosure and finally to introduce the coolant into the heat pipe.
  • FIG. 2 shows a second embodiment of an X-ray generator tube according to the invention.
  • the X-ray generator 1 shown in FIG. 1 comprises a tube 2 forming a closed enclosure inside which there is sufficient vacuum to allow the displacement of an electron beam.
  • a cathode 3 generates an electron beam 4 towards a target 5 which transforms the energy received by the electron beam 4 partly into X-ray radiation 6 leaving the tube 2 through a window 7 and partly into thermal energy that it is necessary to evacuate.
  • the generator 1 also includes means for focusing the electron beam 4. These means are not shown in FIG. 1. They can be formed from a winding in which an electric current flows generating a magnetic field inside the tube 2. This magnetic field is oriented so as to focus the electron beam 4 on a substantially point area of the surface of the target 5. It is also possible to focus the electron beam 4 by electrostatic means.
  • the X-ray generator 1 comprises means for cooling the target 5 and according to the invention, these means comprise an evaporator 8.
  • the evaporator is located in the immediate vicinity of an area 9 of the target 5, area 9 receiving the electron beam 4.
  • the target 5 is formed of a material deposited in a layer on the wall of the evaporator 8. More precisely, it is not necessary to produce a layer of thickness greater than the maximum penetration of the electron beam 4 in the material of the target anode 5.
  • tungsten As the material of the target 5, it has been found that, for an electron beam 5, whose energy is 130 KeV, the penetration of electron beam 5 into tungsten does not exceed hardly 20 to 30 ⁇ m.
  • the layer has, for example, a thickness of less than 50 ⁇ m.
  • the envelope of the evaporator 8 then serves as a support for the material of the target 5. It is for example made of copper for its good thermal conductivity.
  • the envelope of the evaporator 8 has the smallest possible thickness with regard to the mechanical strength of the envelope. At the level of the target 5 the thickness is for example of the order of 0.5 mm.
  • the materials usually used to make the target 5, such as for example tungsten have a thermal conductivity very much lower than that of the materials, such as for example copper, usually used to make an evaporator.
  • target 5 deposited in layer on the shell of the evaporator 8 the mechanical strength of the wall of the evaporator 8 and of the target 5 is ensured only by the wall of the evaporator 8 and the good thermal conductivity of the wall of the evaporator 8 and of the target 5 is ensured by the material of the envelope of the evaporator 8 and the small thickness of the target 5.
  • the X-ray generator 1 comprises a condenser 10 forming with the evaporator 8 a heat pipe 11 inside which a refrigerant fluid circulates.
  • the heat pipe 11 comprises a closed envelope 12 inside which a heat transfer fluid, such as for example water, is subjected to a cooling cycle implementing two phase changes of the fluid.
  • a first phase change is formed by the evaporation of the fluid in the evaporator 8 located at the level of a hot part of the heat pipe 11, in this case in the immediate vicinity of an area 9 of the target 5, area receiving the beam of electrons 4.
  • the fluid thus evaporated moves towards a cold part of the heat pipe 11, part where the condenser 10 is located.
  • the heat pipe also has means for bringing the heat transfer fluid back to the liquid state from the condenser to the evaporator 8. These means are, for example, formed by a capillary network 13 located in the vicinity of the closed casing 12 of the heat pipe 11. The heat thus transported from the hot part to the cold part of the heat pipe 11 is then discharged for example to an ambient fluid circulating outside the generator 1 of X-rays.
  • the generator X comprises means for cooling the condenser 10. More specifically, the transfer of heat from the cold part of the heat pipe 11 to the ambient fluid can be improved by means of fins 14 fixed on the closed casing 12 of the heat pipe 11 and between which the ambient fluid circulates. The ambient fluid can circulate between the fins by natural or forced convection.
  • Water is advantageously chosen as the coolant circulating inside the heat pipe 11.
  • this fluid is inexpensive and its latent heat of transformation is high, which allows it to convey a significant amount of heat from the evaporator. 8 to condenser 10.
  • a heat pipe 11 thus formed and filled with water does not allow it to withstand a temperature above 300 ° C.
  • the X-ray generator 1, for its part, requires, to reach a sufficient vacuum, a pumping operation which usually takes place at a temperature of the order of
  • the X-ray generator 20 shown in FIG. 2 comprises a tube 2 forming a closed enclosure inside which there is sufficient vacuum to allow the displacement of an electron beam.
  • a cathode 3 generates an electron beam 4 towards a target 21 which transforms the energy received by the electron beam 4 partly into X-ray radiation 6 leaving the tube 2 through a window 7 and partly into thermal energy that it is necessary to evacuate.
  • the target 21 is massive. It is made of a material capable of generating X-radiation under the effect of the electron beam 4.
  • the target 21 is for example made in tungsten.
  • the target 21 is formed of a plate a few millimeters thick.
  • the target 21 is assembled on a solid body 22 fixed to the enclosure 2.
  • the assembly of the target 21 on the a solid body 22 is for example carried out by molding. More specifically, a tungsten plate is placed in a mold into which the material of the solid body 22 is poured. This material is for example copper in order to better conduct the thermal energy produced at the target 21 during the bombardment by the electron beam 4.
  • the solid body 22 has a hole 23 which serves as a housing for the evaporator 8.
  • the heat pipe 11, used to cool the target 21 is located partly in the hole 23.
  • the condenser 10 is located in a tube 24, a first end 25 of which is closed.
  • a second end 26 of the tube 24 is open and is connected in leaktight manner to the bore 23.
  • the method for producing the generator 1 can of course be implemented to produce the generator 20.

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

Abstract

The invention concerns an X-ray generator and a method for making such a generator. The X-ray generator (1) comprises a closed chamber (2) wherein prevails a vacuum sufficient for the displacement of an electron beam (4). The generator (1) comprises inside the chamber (2), a cathode (3) for emitting the electron beam (4), a target (5; 21) for receiving the electron beam (4) and for emitting an X-radiation (6) and means for cooling the target (5). The means for cooling the target (5; 21) comprise a heat pipe (11). The method consists in arranging the heat pipe (11) inside the closed chamber (2), then in producing the vacuum inside the chamber (2) and finally in introducing a coolant into the heat pipe (11).

Description

GENERATEUR DE RAYONS X A DISSIPATION THERMIQUE AMELIOREE ET PROCEDE DE REALISATION DU GENERATEUR X-RAY GENERATOR WITH IMPROVED THERMAL DISSIPATION AND METHOD FOR PRODUCING THE GENERATOR
L'invention se rapporte à un générateur de rayons X et à un procédé de réalisation de ce générateur. Les rayons X sont notamment utilisés dans le milieu médical pour l'imagerie ou la radiothérapie et dans le milieu industriel pour le contrôle de pièces mécaniques ou pour le traitement local par irradiation.The invention relates to an X-ray generator and to a method for producing this generator. X-rays are used in particular in the medical environment for imaging or radiotherapy and in the industrial environment for the control of mechanical parts or for local treatment by irradiation.
Des générateurs de rayons X connus comportent généralement, à l'intérieur d'une enceinte fermée ou tube électronique, une cathode émettant un faisceau d'électrons en direction d'une anode ou cible. Le faisceau est accéléré et focalisé au moyen d'électrodes situées entre la cathode et la cible. Lorsque le faisceau d'électrons bombarde la cible, une petite partie de son énergie génère un rayonnement X et le reste de son énergie est transformé en énergie calorifique qu'il est nécessaire de dissiper hors de l'enceinte fermée.Known X-ray generators generally include, inside a closed enclosure or electronic tube, a cathode emitting an electron beam towards an anode or target. The beam is accelerated and focused by means of electrodes located between the cathode and the target. When the electron beam bombards the target, a small part of its energy generates X-rays and the rest of its energy is transformed into heat energy which it is necessary to dissipate outside the closed enclosure.
On peut réaliser la dissipation de cette énergie calorifique au moyen d'un barreau réalisé en cuivre. Le barreau est alors fixé à l'une de ses extrémités à la cible et à une autre extrémité à un radiateur formant une paroi du tube. Le radiateur peut comporter des ailettes situées à l'extérieur du tube en fonction de la quantité d'énergie calorifique à évacuer. On peut faire circuler entre ces ailettes un fluide colloporteur assurant le refroidissement de celle-ci par convection naturelle ou forcée.We can achieve the dissipation of this heat energy by means of a bar made of copper. The bar is then fixed at one of its ends to the target and at another end to a radiator forming a wall of the tube. The radiator may include fins located outside the tube depending on the amount of heat energy to be removed. One can circulate between these fins a coolant ensuring the cooling thereof by natural or forced convection.
La puissance du rayonnement X est principalement limitée par la capacité de la cible à dissiper l'énergie calorifique qui y est générée. L'invention trouve une utilité particulière pour les tubes générateurs de rayons X à microfoyer. Ce type de tube est principalement utilisé dans l'imagerie où on cherche à réaliser une source de rayonnement X la plus ponctuelle possible. En effet, la netteté de l'image obtenue par irradiation dépend de la finesse de la source de rayonnement X. Plus la source sera petite, plus on pourra distinguer les détails dans l'image réalisée. On sait par exemple réaliser une source de rayonnement X à l'aide d'un faisceau électronique de 10 W accéléré à une énergie de 130 KeV et générant une tache d'environ 7 μm sur une cible réalisée en tungstène. Lorsque la puissance est réduite par exemple à 0,5 W, la tache peut être réduite à environ 1 μm sur la cible. Pour une même dimension de tache, le fait d'augmenter la puissance du faisceau électronique entraînerait des dommages sur la cible dus à un échauffement trop important de celle-ci.The power of X-rays is mainly limited by the ability of the target to dissipate the heat energy generated there. The invention finds particular use for X-ray tubes for microfocus. This type of tube is mainly used in imagery where one seeks to produce a source of X-ray as punctual as possible. Indeed, the sharpness of the image obtained by irradiation depends on the fineness of the X-ray source. The smaller the source, the more we can distinguish the details in the image produced. It is known, for example, to produce an X-ray source using a 10 W electron beam accelerated to an energy of 130 KeV and generating a spot of approximately 7 μm on a target made of tungsten. When the power is reduced for example to 0.5 W, the spot can be reduced to approximately 1 μm on the target. For the same spot size, the fact increasing the power of the electron beam would cause damage to the target due to excessive heating of the target.
L'invention a pour but d'améliorer la dissipation thermique de la cible, ce qui permet notamment soit d'augmenter la puissance pour une dimension de tache donnée, soit de réduire la dimension de la tache pour une puissance donnée.The invention aims to improve the heat dissipation of the target, which in particular makes it possible either to increase the power for a given spot size, or to reduce the size of the spot for a given power.
Il est bien entendu que l'invention n'est pas limitée aux générateurs de rayons X à microfoyer et elle peut être mise en œuvre dans d'autres types de générateurs pour lesquels on cherche à améliorer la dissipation thermique de la cible.It is understood that the invention is not limited to X-ray generators with microfocus and it can be implemented in other types of generators for which it is sought to improve the heat dissipation of the target.
Pour atteindre ce but, l'invention a pour objet un générateur de rayons X comportant une enceinte fermée à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons, le générateur comportant à l'intérieur de l'enceinte, une cathode destinée à émettre le faisceau d'électrons, une cible destinée à recevoir le faisceau d'électrons et à émettre un rayonnement X et des moyens pour refroidir la cible, caractérisé en ce que les moyens pour refroidir la cible comportent un évaporateur.To achieve this object, the subject of the invention is an X-ray generator comprising a closed enclosure inside which there is a vacuum sufficient to allow the displacement of an electron beam, the generator comprising inside the enclosure, a cathode intended to emit the electron beam, a target intended to receive the electron beam and to emit X-radiation and means for cooling the target, characterized in that the means for cooling the target comprise an evaporator.
L'invention a également pour objet un procédé de réalisation d'un générateur de rayons X comportant une enceinte fermée à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons, le générateur comportant à l'intérieur de l'enceinte, une cathode destinée à émettre le faisceau d'électrons, une cible destinée à recevoir le faisceau d'électrons et à émettre un rayonnement X et des moyens pour refroidir la cible, caractérisé en ce que les moyens pour refroidir la cible comportent un évaporateur et un condenseur formant avec l'évaporateur un caloduc à l'intérieur duquel circule un fluide réfrigérant et en ce que le procédé consiste à disposer le caloduc à l'intérieur de l'enceinte fermée, puis à réaliser le vide à l'intérieur de l'enceinte et enfin à introduire le fluide réfrigérant dans le caloduc.The subject of the invention is also a method of producing an X-ray generator comprising a closed enclosure inside which there is a vacuum sufficient to allow the displacement of an electron beam, the generator comprising inside the enclosure, a cathode intended to emit the electron beam, a target intended to receive the electron beam and to emit X-radiation and means for cooling the target, characterized in that the means for cooling the target comprise an evaporator and a condenser forming with the evaporator a heat pipe inside which circulates a refrigerant fluid and in that the method consists in placing the heat pipe inside the closed enclosure, then in producing the vacuum at inside the enclosure and finally to introduce the coolant into the heat pipe.
L'invention sera mieux comprise et d'autres avantages apparaîtront à la lecture de la description détaillée d'un mode de réalisation donné à titre d'exemple, mode de réalisation donné à titre d'exemple, et illustré par le dessin joint dans lequel : - la figure 1 représente schématiquement un premier mode de réalisation d'un tube générateur de rayons X conforme à l'invention ;The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, embodiment given by way of example, and illustrated by the attached drawing in which : - Figure 1 schematically shows a first embodiment of an X-ray generator tube according to the invention;
- la figure 2 représente un second mode de réalisation d'un tube générateur de rayons X conforme à l'invention.- Figure 2 shows a second embodiment of an X-ray generator tube according to the invention.
Pour ne pas surcharger la description, les mêmes éléments porteront les mêmes repères dans les deux modes de réalisation.In order not to overload the description, the same elements will have the same references in the two embodiments.
Le générateur 1 de rayons X représenté sur la figure 1 comporte un tube 2 formant une enceinte fermée à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons. Une cathode 3 génère un faisceau d'électrons 4 en direction d'une cible 5 qui transforme l'énergie reçue par le faisceau d'électrons 4 en partie en rayonnement X 6 sortant du tube 2 par une fenêtre 7 et en partie en énergie thermique qu'il est nécessaire d'évacuer. Le générateur 1 comporte également des moyens de focalisation du faisceau d'électrons 4. Ces moyens ne sont pas représentés sur la figure 1. Ils peuvent être formés d'enroulement dans lesquels circule un courant électrique générant un champ magnétique à l'intérieur du tube 2. Ce champ magnétique est orienté de façon à focaliser le faisceau d'électrons 4 sur une zone sensiblement ponctuelle de la surface de la cible 5. On peut également focaliser le faisceau d'électrons 4 par des moyens électrostatiques.The X-ray generator 1 shown in FIG. 1 comprises a tube 2 forming a closed enclosure inside which there is sufficient vacuum to allow the displacement of an electron beam. A cathode 3 generates an electron beam 4 towards a target 5 which transforms the energy received by the electron beam 4 partly into X-ray radiation 6 leaving the tube 2 through a window 7 and partly into thermal energy that it is necessary to evacuate. The generator 1 also includes means for focusing the electron beam 4. These means are not shown in FIG. 1. They can be formed from a winding in which an electric current flows generating a magnetic field inside the tube 2. This magnetic field is oriented so as to focus the electron beam 4 on a substantially point area of the surface of the target 5. It is also possible to focus the electron beam 4 by electrostatic means.
Le générateur 1 de rayons X comporte des moyens pour refroidir la cible 5 et selon l'invention, ces moyens comportent un évaporateur 8. Avantageusement, l'évaporateur est situé à proximité immédiate d'une zone 9 de la cible 5, la zone 9 recevant le faisceau d'électrons 4. En effet, plus l'évaporateur 8 est proche de la zone 9, plus la résistance thermique s'opposant à la circulation d'un flux thermique de refroidissement de la cible 5 par conduction se réduit.The X-ray generator 1 comprises means for cooling the target 5 and according to the invention, these means comprise an evaporator 8. Advantageously, the evaporator is located in the immediate vicinity of an area 9 of the target 5, area 9 receiving the electron beam 4. In fact, the closer the evaporator 8 is to zone 9, the more the thermal resistance opposing the circulation of a thermal flux for cooling the target 5 by conduction decreases.
Avantageusement, la cible 5 est formée d'un matériau déposé en couche sur la paroi de l'évaporateur 8. Plus précisément, il n'est pas nécessaire de réaliser une couche d'épaisseur supérieure à la pénétration maximale du faisceau d'électrons 4 dans le matériau de l'anode cible 5. Par exemple, lorsqu'on souhaite utiliser le tungstène comme matériau de la cible 5, on a constaté que, pour un faisceau d'électrons 5, dont l'énergie est de 130 KeV, la pénétration du faisceau d'électrons 5 dans le tungstène n'excède guère 20 à 30 μm. La couche a par exemple une épaisseur inférieure à 50 μm.Advantageously, the target 5 is formed of a material deposited in a layer on the wall of the evaporator 8. More precisely, it is not necessary to produce a layer of thickness greater than the maximum penetration of the electron beam 4 in the material of the target anode 5. For example, when it is desired to use tungsten as the material of the target 5, it has been found that, for an electron beam 5, whose energy is 130 KeV, the penetration of electron beam 5 into tungsten does not exceed hardly 20 to 30 μm. The layer has, for example, a thickness of less than 50 μm.
L'enveloppe de l'évaporateur 8 sert alors de support au matériau de la cible 5. Elle est par exemple réalisée en cuivre pour sa bonne conductibilité thermique. L'enveloppe de l'évaporateur 8 a une épaisseur la plus faible possible au regard de la tenue mécanique de l'enveloppe. Au niveau de la cible 5 l'épaisseur est par exemple de l'ordre de 0,5 mm.The envelope of the evaporator 8 then serves as a support for the material of the target 5. It is for example made of copper for its good thermal conductivity. The envelope of the evaporator 8 has the smallest possible thickness with regard to the mechanical strength of the envelope. At the level of the target 5 the thickness is for example of the order of 0.5 mm.
On a constaté que les matériaux habituellement utilisés pour réaliser la cible 5, comme par exemple le tungstène, ont une conductibilité thermique très nettement inférieure à celle des matériaux, comme par exemple le cuivre, habituellement utilisés pour réaliser un évaporateur. Dans cette variante de l'invention, cible 5 déposée en couche sur l'enveloppe de l'évaporateur 8, la tenue mécanique de la paroi de l'évaporateur 8 et de la cible 5 est assurée uniquement par la paroi de l'évaporateur 8 et la bonne conductibilité thermique de la paroi de l'évaporateur 8 et de la cible 5 est assurée par le matériau de l'enveloppe de l'évaporateur 8 et la faible épaisseur de la cible 5.It has been found that the materials usually used to make the target 5, such as for example tungsten, have a thermal conductivity very much lower than that of the materials, such as for example copper, usually used to make an evaporator. In this variant of the invention, target 5 deposited in layer on the shell of the evaporator 8, the mechanical strength of the wall of the evaporator 8 and of the target 5 is ensured only by the wall of the evaporator 8 and the good thermal conductivity of the wall of the evaporator 8 and of the target 5 is ensured by the material of the envelope of the evaporator 8 and the small thickness of the target 5.
Avantageusement, le générateur 1 de rayons X comporte un condenseur 10 formant avec l'évaporateur 8 un caloduc 11 à l'intérieur duquel circule un fluide réfrigérant. Plus précisément, le caloduc 11 comporte une enveloppe fermée 12 à l'intérieur de laquelle un fluide caloporteur, comme par exemple de l'eau, est soumis à un cycle de refroidissement mettant en œuvre deux changements de phase du fluide. Un premier changement de phase est constitué par l'évaporation du fluide dans l'évaporateur 8 situé au niveau d'une partie chaude du caloduc 11 en l'occurrence à proximité immédiate d'une zone 9 de la cible 5, zone recevant le faisceau d'électrons 4. Le fluide ainsi évaporé se déplace vers une partie froide du caloduc 11, partie où le condenseur 10 est situé. C'est dans le condenseur 10 qu'intervient le second changement de phase du fluide : sa condensation. Le caloduc dispose, par ailleurs, de moyens pour ramener le fluide caloporteur à l'état liquide du condenseur vers l'évaporateur 8. Ces moyens sont, par exemple, formés par un réseau capillaire 13 situé au voisinage de l'enveloppe fermée 12 du caloduc 11. La chaleur ainsi transportée de la partie chaude vers la partie froide du caloduc 11 est ensuite évacuée par exemple vers un fluide ambiant circulant à l'extérieur du générateur 1 de rayons X.Advantageously, the X-ray generator 1 comprises a condenser 10 forming with the evaporator 8 a heat pipe 11 inside which a refrigerant fluid circulates. More specifically, the heat pipe 11 comprises a closed envelope 12 inside which a heat transfer fluid, such as for example water, is subjected to a cooling cycle implementing two phase changes of the fluid. A first phase change is formed by the evaporation of the fluid in the evaporator 8 located at the level of a hot part of the heat pipe 11, in this case in the immediate vicinity of an area 9 of the target 5, area receiving the beam of electrons 4. The fluid thus evaporated moves towards a cold part of the heat pipe 11, part where the condenser 10 is located. It is in the condenser 10 that the second phase change of the fluid occurs: its condensation. The heat pipe also has means for bringing the heat transfer fluid back to the liquid state from the condenser to the evaporator 8. These means are, for example, formed by a capillary network 13 located in the vicinity of the closed casing 12 of the heat pipe 11. The heat thus transported from the hot part to the cold part of the heat pipe 11 is then discharged for example to an ambient fluid circulating outside the generator 1 of X-rays.
Avantageusement, le générateur X comporte des moyens de refroidissement du condenseur 10. Plus précisément, le transfert de chaleur de la partie froide du caloduc 11 vers le fluide ambiant peut être amélioré au moyen d'ailettes 14 fixées sur l'enveloppe fermée 12 du caloduc 11 et entre lesquelles circule le fluide ambiant. Le fluide ambiant peut circuler entre les ailettes par convection naturelle ou forcée.Advantageously, the generator X comprises means for cooling the condenser 10. More specifically, the transfer of heat from the cold part of the heat pipe 11 to the ambient fluid can be improved by means of fins 14 fixed on the closed casing 12 of the heat pipe 11 and between which the ambient fluid circulates. The ambient fluid can circulate between the fins by natural or forced convection.
On choisit avantageusement l'eau comme fluide réfrigérant circulant à l'intérieur du caloduc 11. En effet, ce fluide est peu onéreux et sa chaleur latente de transformation est élevée, ce qui lui permet de véhiculer une quantité importante de chaleur de l'évaporateur 8 vers le condenseur 10.Water is advantageously chosen as the coolant circulating inside the heat pipe 11. In fact, this fluid is inexpensive and its latent heat of transformation is high, which allows it to convey a significant amount of heat from the evaporator. 8 to condenser 10.
En revanche, un caloduc 11 ainsi constitué et rempli d'eau ne permet pas de supporter une température supérieure à 300°C. Le générateur 1 de rayons X, quant à lui, nécessite, pour atteindre un vide suffisant, une opération de pompage qui se déroule habituellement à une température de l'ordre deOn the other hand, a heat pipe 11 thus formed and filled with water does not allow it to withstand a temperature above 300 ° C. The X-ray generator 1, for its part, requires, to reach a sufficient vacuum, a pumping operation which usually takes place at a temperature of the order of
400°C. On constate donc qu'un caloduc 11 , utilisant de l'eau comme fluide réfrigérant, ne supporterait pas l'opération de pompage.400 ° C. It is therefore found that a heat pipe 11, using water as a refrigerant, would not support the pumping operation.
Pour pallier ce problème, on propose de disposer le caloduc 11 à l'intérieur de l'enceinte fermée 2, puis à réaliser le vide à l'intérieur de l'enceinte 2 et enfin à introduire le fluide réfrigérant dans le caloduc 11.To overcome this problem, it is proposed to arrange the heat pipe 11 inside the closed enclosure 2, then to create a vacuum inside the enclosure 2 and finally to introduce the refrigerant fluid into the heat pipe 11.
Il est également possible d'utiliser d'autres types de fluides réfrigérant pouvant supporter les températures de pompage, comme par exemple le lithium. On note cependant que le lithium est moins efficace que l'eau pour transporter de l'énergie calorifique.It is also possible to use other types of refrigerant fluids which can withstand pumping temperatures, such as for example lithium. Note, however, that lithium is less efficient than water for transporting heat energy.
Le générateur 20 de rayons X représenté sur la figure 2 comporte un tube 2 formant une enceinte fermée à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons. Une cathode 3 génère un faisceau d'électrons 4 en direction d'une cible 21 qui transforme l'énergie reçue par le faisceau d'électrons 4 en partie en rayonnement X 6 sortant du tube 2 par une fenêtre 7 et en partie en énergie thermique qu'il est nécessaire d'évacuer.The X-ray generator 20 shown in FIG. 2 comprises a tube 2 forming a closed enclosure inside which there is sufficient vacuum to allow the displacement of an electron beam. A cathode 3 generates an electron beam 4 towards a target 21 which transforms the energy received by the electron beam 4 partly into X-ray radiation 6 leaving the tube 2 through a window 7 and partly into thermal energy that it is necessary to evacuate.
A la différence du premier mode de réalisation, la cible 21 est massive. Elle est réalisée dans un matériau apte à générer un rayonnement X sous l'effet du faisceau d'électrons 4. La cible 21 est par exemple réalisée en tungstène. La cible 21 est formée d'une plaque de quelques millimètres d'épaisseur. La cible 21 est assemblée sur un corps massif 22 fixé à l'enceinte 2. L'assemblage de la cible 21 sur le un corps massif 22 est par exemple réalisé par moulage. Plus précisément, on place une plaque de tungstène dans un moule dans lequel on coule le matériau du corps massif 22. Ce matériau est par exemple du cuivre afin de mieux conduire l'énergie thermique produite au niveau de la cible 21 lors du bombardement par le faisceau d 'électrons 4. Le corps massif 22 comporte un perçage 23 qui sert de logement à l'évaporateur 8. Le caloduc 11, utilisé pour refroidir la cible 21 est situé en partie dans le perçage 23. Le condenseur 10 est situé dans un tube 24 dont une première extrémité 25 est fermée. Une seconde extrémité 26 du tube 24 est ouverte et est raccordée de façon étanche au perçage 23. Ici aussi, il est avantageux de fixer des ailettes 14, sur les parois extérieures du tube 24, comme moyens de refroidissement du condenseur 10. Dans ce second mode de réalisation, il est bien entendu possible de remplir le caloduc 11 après avoir réaliser le vide à l'intérieur de l'enceinte 2.Unlike the first embodiment, the target 21 is massive. It is made of a material capable of generating X-radiation under the effect of the electron beam 4. The target 21 is for example made in tungsten. The target 21 is formed of a plate a few millimeters thick. The target 21 is assembled on a solid body 22 fixed to the enclosure 2. The assembly of the target 21 on the a solid body 22 is for example carried out by molding. More specifically, a tungsten plate is placed in a mold into which the material of the solid body 22 is poured. This material is for example copper in order to better conduct the thermal energy produced at the target 21 during the bombardment by the electron beam 4. The solid body 22 has a hole 23 which serves as a housing for the evaporator 8. The heat pipe 11, used to cool the target 21 is located partly in the hole 23. The condenser 10 is located in a tube 24, a first end 25 of which is closed. A second end 26 of the tube 24 is open and is connected in leaktight manner to the bore 23. Here too, it is advantageous to fix fins 14, on the external walls of the tube 24, as means for cooling the condenser 10. In this second embodiment, it is of course possible to fill the heat pipe 11 after having produced the vacuum inside the enclosure 2.
Le procédé de réalisation du générateur 1 peut bien entendu être mis en œuvre pour réaliser le générateur 20. The method for producing the generator 1 can of course be implemented to produce the generator 20.

Claims

REVENDICATIONS
1. Générateur (1 ; 20) de rayons X comportant une enceinte fermée (2) à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons (4), le générateur (1 ) comportant à l'intérieur de l'enceinte (2), une cathode (3) destinée à émettre le faisceau d'électrons (4), une cible (5 ; 21) destinée à recevoir le faisceau d'électrons (4) et à émettre un rayonnement X (6) et des moyens pour refroidir la cible (5), les moyens pour refroidir la cible (5 ; 21) comportant un évaporateur (8), caractérisé en ce que la cible (5) est formée d'un matériau déposé en couche sur une paroi de l'évaporateur (8).1. X-ray generator (1; 20) comprising a closed enclosure (2) inside which there is sufficient vacuum to allow the movement of an electron beam (4), the generator (1) comprising inside the enclosure (2), a cathode (3) intended to emit the electron beam (4), a target (5; 21) intended to receive the electron beam (4) and to emit a X-ray (6) and means for cooling the target (5), the means for cooling the target (5; 21) comprising an evaporator (8), characterized in that the target (5) is formed from a deposited material in a layer on a wall of the evaporator (8).
2. Générateur (1 ; 20) de rayons X selon la revendication 1 , caractérisé en ce que la cible (5 ; 21 ) comporte une zone (9) recevant le faisceau d'électrons (4) et en ce que l'évaporateur (8) est situé à proximité immédiate de la zone (9).2. X-ray generator (1; 20) according to claim 1, characterized in that the target (5; 21) comprises a zone (9) receiving the electron beam (4) and in that the evaporator ( 8) is located in the immediate vicinity of zone (9).
3. Générateur (1 ) de rayons X selon l'une des revendications précédentes, caractérisé en ce que la couche a une épaisseur inférieure à 50 μm.3. Generator (1) of X-rays according to one of the preceding claims, characterized in that the layer has a thickness of less than 50 μm.
4. Générateur (1 ; 20) de rayons X selon l'une des revendications précédentes, caractérisé en ce qu'il comporte un condenseur (10) formant avec l'évaporateur (8) un caloduc (11) à l'intérieur duquel circule un fluide réfrigérant4. X-ray generator (1; 20) according to one of the preceding claims, characterized in that it comprises a condenser (10) forming with the evaporator (8) a heat pipe (11) inside which circulates a refrigerant
5. Générateur (1 ; 20) de rayons X selon l'une des revendications précédentes, caractérisé en ce qu'il comporte des moyens (14) de refroidissement du condenseur (10).5. X-ray generator (1; 20) according to one of the preceding claims, characterized in that it comprises means (14) for cooling the condenser (10).
6. Procédé de réalisation d'un générateur (1 ; 20) de rayons X comportant une enceinte fermée (2) à l'intérieur de laquelle règne un vide suffisant pour permettre le déplacement d'un faisceau d'électrons (4), le générateur (1 ) comportant à l'intérieur de l'enceinte (2), une cathode (3) destinée à émettre le faisceau d'électrons (4), une cible (5 ; 21 ) destinée à recevoir le faisceau d'électrons (4) et à émettre un rayonnement X (6) et des moyens pour refroidir la cible (5), caractérisé en ce que les moyens pour refroidir la cible (5) comportent un évaporateur (8) et un condenseur (10) formant avec l'évaporateur (8) un caloduc (11 ) à l'intérieur duquel circule un fluide réfrigérant et en ce que le procédé consiste à disposer le caloduc (11) à l'intérieur de l'enceinte fermée (2), puis à réaliser le vide à l'intérieur de l'enceinte (2) et enfin à introduire le fluide réfrigérant dans le caloduc (11). 6. A method of producing an X-ray generator (1; 20) comprising a closed enclosure (2) inside which there is a vacuum sufficient to allow the displacement of an electron beam (4), the generator (1) comprising inside the enclosure (2), a cathode (3) intended to emit the electron beam (4), a target (5; 21) intended to receiving the electron beam (4) and emitting X-ray (6) and means for cooling the target (5), characterized in that the means for cooling the target (5) comprise an evaporator (8) and a condenser (10) forming with the evaporator (8) a heat pipe (11) inside which a coolant circulates and in that the method consists in placing the heat pipe (11) inside the closed enclosure ( 2), then to create a vacuum inside the enclosure (2) and finally to introduce the coolant into the heat pipe (11).
PCT/EP2003/050781 2002-11-08 2003-11-03 X-ray generator with improved thermal dissipation and method for making same WO2004042769A1 (en)

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US10901112B2 (en) 2003-04-25 2021-01-26 Rapiscan Systems, Inc. X-ray scanning system with stationary x-ray sources
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WO2021202707A1 (en) * 2020-03-31 2021-10-07 Empyrean Medical Systems, Inc Coupled ring anode with scanning electron beam bremsstrahlung photon flux intensifier apparatus
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FR2847074A1 (en) 2004-05-14

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